UBC Theses and Dissertations

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UBC Theses and Dissertations

Power transmission harmonic current and its use in geophysical exploration McCollor, Douglas Clayton 1982

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c. POWER T R A N S M I S S I O N H A R M O N I C C U R R E N T A N D I T S U S E I N G E O P H Y S I C A L E X P L O R A T I O N b y D O U G L A S C L A Y T O N M c C O L L O R B . S c , T h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , 1 9 7 9 A T H E S I S S U B M I T T E D I N P A R T I A L F U L F I L L M E N T O F T H E R E Q U I R E M E N T S F O R T H E D E G R E E O F M A S T E R O F S C I E N C E i n T H E F A C U L T Y O F G R A D U A T E S T U D I E S ( D e p a r t m e n t o f G e o p h y s i c s a n d A s t r o n o m y ) We a c c e p t t h i s t h e s i s a s c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A M a r c h 1 9 8 2 © D o u g l a s C l a y t o n M c C o l l o r , 1 9 8 2 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of G)lffllwft€l$ 4^J^>^^U) ' f u ; ' The University of B r i t i s h Columbia 1956 Main Mall Van couve r, Canada V6T 1Y3 Date DE-6 (.3/81) i i ABSTRACT C o m m e r c i a l e l e c t r i c a l power t r a n s m i s s i o n l i n e s c a n be u s e d as an e c o n o m i c a l r e c o n n a i s s a n c e method o f g e o p h y s i c a l e x p l o r a t i o n . The a d v a n t a g e s o f t h e t e c h n i q u e i n c l u d e t h e remote s o u r c e a s p e c t of t h e method, p l u s t h e s t r o n g , m u l t i - f r e q u e n c y s i g n a l t h a t a r i s e s f r o m t h e e x i s t i n g c u r r e n t i n t h e t r a n s m i s s i o n l i n e . The main l i m i t a t i o n i s t h a t t h e a r e a must be i s o l a t e d f r o m e x t r a n e o u s s o u r c e s o f c o m m e r c i a l 60 Hz s i g n a l s . However, t h e p r o p o s e d t e c h n i q u e w o u l d be s u i t a b l e f o r d e v e l o p i n g a r e a s , i n w h i c h a power t r a n s m i s s i o n l i n e i s commonly b u i l t t h r o u g h an i s o l a t e d r e g i o n w e l l b e f o r e u r b a n i z a t i o n of t h e a r e a b e g i n s . A 500 KV B.C. H y d r o t r a n s m i s s i o n l i n e e x t e n d i n g i n an E a s t -West d i r e c t i o n f r o m N i c o l a t o l o c o , B.C. ( n e a r V a n c o u v e r ) was u t i l i z e d i n t h i s t h e s i s t o d e t e r m i n e t h e v i a b i l i t y o f t h e p r o p o s e d method o f e l e c t r o m a g n e t i c e x p l o r a t i o n . A c c e s s t o m o n i t o r t h e t r a n s m i s s i o n l i n e h a r m o n i c c u r r e n t was made t h r o u g h M e r i d i a n s u b s t a t i o n , n e a r l o c o , B.C. and y i e l d e d q u a n t i t a t i v e i n f o r m a t i o n on h a r m o n i c c u r r e n t s t r e n g t h . In a d d i t i o n , t h e c o r r e s p o n d e n c e between n a t u r a l g e o m a g n e t i c f i e l d a c t i v i t y and q u a s i - D C g e o m a g n e t i c a l l y i n d u c e d c u r r e n t (GIC) i n t h e t r a n s m i s s i o n l i n e was d e t e r m i n e d . A t h e o r e t i c a l d i s c u s s i o n of t h e r e l a t i o n between GIC a n d h a r m o n i c c u r r e n t g e n e r a t i o n i s g i v e n , a s w e l l as i l l u s t r a t i v e d a t a showing t h e e f f e c t o f GIC on h a r m o n i c c u r r e n t s . An e x t e n s i v e EM s u r v e y was u n d e r t a k e n i n an i s o l a t e d r e g i o n s i t u a t e d t o t h e n o r t h o f t h e N i c o l a - l o c o t r a n s m i s s i o n l i n e . The magnitude of the t o t a l v e r t i c a l magnetic f i e l d component, at f o u r s o u r c e f r e q u e n c i e s (60 Hz, 180 Hz, 300 Hz, and 420 Hz) was measured a t 66 s t a t i o n s w i t h i n a 120 km 2 a r e a . The r e s u l t s of the e x p e r i m e n t a l survey were q u a l i t a t i v e l y i n t e r p r e t e d i n terms of a u n i f o r m c o n d u c t i n g e a r t h model. One a s p e c t of t h e model i s t h a t the v e r t i c a l ambient f i e l d component e x h i b i t s an i n v e r s e r e l a t i o n w i t h d i s t a n c e near the s o u r c e , and b e g i n s t o f a l l o f f as 1 / r 3 a t g r e a t e r d i s t a n c e s from the s o u r c e , the d i s t a n c e of t h i s t r a n s i t i o n b e i n g dependant on s o u r c e f r e q u e n c y and h a l f -space c o n d u c t i v i t y . The d a t a s u p p o r t s t h i s model, and some t h e o r e t i c a l c a l c u l a t i o n s on the t r a n s i t i o n d i s t a n c e a r e g i v e n . In a d d i t i o n , d i f f e r e n t g e o l o g i c r e g i o n s were found t o c o r r e l a t e w i t h f e a t u r e s of the d a t a , i n d i c a t i n g c o n d u c t i v i t y c o n t r a s t s a s s o c i a t e d w i t h the g e o l o g i c r e g i o n s . Thus the proposed method of e l e c t r o m a g n e t i c e x p l o r a t i o n i s shown, by the r e s u l t s p r e s e n t e d i n t h i s t h e s i s , t o be a v i a b l e and p r a c t i c a b l e t e c h n i q u e f o r mapping g e o l o g i c c o n d u c t i v i t y c o n t r a s t s , and c o u l d be a s u c c e s s f u l , i n e x p e n s i v e method of r e c o n n a i s a n c e e x p l o r a t i o n f o r o r e b o d i e s . i v T able of Contents Page A b s t r a c t i i L i s t of Tables v L i s t of F i g u r e s v i Acknowledgments i x Chapter I: I n t r o d u c t i o n 1 Chapter I I : Power Systems 6 2.1 General 6 2.2 Harmonics 8 Chapter I I I : Experimental Procedure 17 3.1 Experimental O b j e c t i v e s 17 3.2 Instrumentation 22 3.3 C a l i b r a t i o n Procedure 25 Chapter IV: Experimental R e s u l t s 29 4.1 GIC's d e t e c t e d i n 5L82 at Meri d i a n S u b s t a t i o n 29 4.2 Harmonic Current Measurements i n M e r i d i a n 30 4.3 E f f e c t s of GIC on Harmonic Currents 34 Chapter V: EM Survey: Experiment and R e s u l t s 48 5.1 I n t r o d u c t i o n to EM Experiment 48 5.2 P r e l i m i n a r y Experiment and Apparatus 49 5.3 R e s u l t s of the 1981 Survey 60 5.4 A n a l y s i s and I n t e r p r e t a t i o n 61 Chapter VI: C o n c l u s i o n 82 References 90 Appendix A: Harmonic A n a l y s i s 93 Appendix B: Instrumentation and C a l i b r a t i o n 96 Appendix C: EM-Survey Data A n a l y s i s 113 V L i s t of T a b l e s Page T a b l e 2.1 Phase Sequence C u r r e n t s 11 T a b l e 4.1 Maximum Harmonic C u r r e n t Measurements on 5L82 a t M e r i d i a n S u b s t a t i o n .32 T a b l e 6.1 D e t e r m i n i n g 6 /c (minimum d i s t a n c e from l i n e source for which ay>6 and y>>h), which c o r r e s p o n d s to a t o t a l f i e l d - d i s t a n c e r e l a t i o n of 1 / r 3 85 T a b l e 6.2 Magnet ic F i e l d S t r e n g t h s at base s t a t i o n (15:50 L T , 22 /7 /81) 88 v i L i s t o f F i g u r e s P a g e F i g . 2 . 1 A g e n e r a t o r c o n n e c t e d t h r o u g h t r a n s f o r m e r s a n d a h i g h v o l t a g e l i n e t o a d i s t a n t l o a d 7 F i g . 2 . 2 A t h r e e - p h a s e t r a n s f o r m e r b a n k , t h e d i s c o n n e c t s w i t c h e s , a n d a t h r e e - p h a s e c i r c u i t b r e a k e r c o n n e c t i n g t o a t h r e e - p h a s e t r a n s m i s s i o n l i n e 7 F i g . 2 . 3 A t h r e e - p h a s e s y s t e m , 9 F i g . 2 . 4 T w o c o m m o n t h r e e - p h a s e i m p e d a n c e c o n n e c t i o n s 9 F i g . 2 . 5 T h r e e - p h a s e t r a n s f o r m e r s y s t e m i n Y - c o n n e c t i o n 10 F i g . 2 . 6 D i a g r a m o f a n i d e a l i z e d A C m a c h i n e 10 F i g . 2 . 7 G I C ( g e o m a g n e t i c a l l y i n d u c e d c u r r e n t ) f l o w i n g i n g r o u n d o f t r a n s f o r m e r b a n k 14 F i g . 3 . 1 L o c a t i o n o f s u r v e y a r e a f o r E M f i e l d w o r k 18 F i g . 3 . 2 T o p o g r a p h i c a l m a p o f s u r v e y a r e a 20 F i g . 3 . 3 S c h e m a t i c r e p r e s e n t a t i o n o f a p p a r a t u s 23 F i g . 3 . 4 H a r m o n i c c u r r e n t a n d G I C c a l i b r a t i o n c i r c u i t s . . . . 2 7 F i g . 4 . 1 E f f e c t o f g e o m a g n e t i c f i e l d o n G I C i n 5 L 8 2 (3 M a r c h 1 9 8 1 ) 36 F i g . 4 . 2 E f f e c t o f g e o m a g n e t i c f i e l d o n G I C i n 5 L 8 2 ( 4 A p r i l 1 9 8 1 ) 37 v i i Page F i g . 4 . 3 Harmonic c u r r e n t l e v e l s (3 March 1981) 38 F i g . 4 . 4 Harmonic c u r r e n t l e v e l s and g e o m a g n e t i c f i e l d (1 1 June 1981 ) 42 F i g . 4 . 5 C o r r e s p o n d e n c e of r e l a t i v e v a l u e s and c u r r e n t c a l i b r a t i o n 47 F i g . 5 . 1 L o c a t i o n of m o b i l e r e c e i v e r s t a t i o n s w i t h i n s u r v e y a r e a 51 F i g . 5 . 2 R e s u l t s of t h r e e s u r v e y s ( 1 9 7 9 , 8 0 , 81) t o show 1/r dependance of t o t a l f i e l d s t r e n g t h . . . . . . 5 2 F i g . 5 . 3 A F - m e a s u r e m e n t s a t base s t a t i o n (3 March 1981) 55 F i g . 5 . 4 A F - m e a s u r e m e n t s a t base s t a t i o n (11 June 1981) 57 F i g . 5 . 5 EM s u r v e y c o n t o u r e d d a t a 63 F i g . 5 . 6 R e f e r e n c e f i e l d 67 F i g . 5 . 7 P r o f i l e l o c a t i o n s 72 F i g . 5 . 8 P r o f i l e d a t a - S e c t i o n A - B 73 F i g . 5 . 9 P r o f i l e d a t a - S e c t i o n C -D 75 F i g . 5 . 1 0 G e o l o g i c map of s u r v e y a r e a 79 F i g . 5 . 1 1 G e o l o g i c c r o s s - s e c t i o n (E-W) t h r o u g h J a c o b s Lake r e g i o n 81 F i g . 6 . 1 V e r t i c a l I n d u c e d F i e l d ( H z ) c a l c u l a t i o n s 84 v i i i P a g e F i g . A . 1 G r a p h i c a l a n a l y s i s o f h a r m o n i c g e n e r a t i o n 94 F i g . A . 2 H y s t e r e s i s l o o p . . . 9 5 F i g . B . 1 S c h e m a t i c r e p r e s e n t a t i o n o f a p p a r a t u s 97 F i g . B . 2 C a l i b r a t i o n c i r c u i t s f o r h a r m o n i c c u r r e n t s a n d G I C d e t e c t o r 98 F i g . B . 3 C a l i b r a t i o n c h a r t s 103 F i g . B . 4 S c h e m a t i c d i a g r a m o f c a l i b r a t i o n c i r c u i t a n d c a l c u l a t i o n s f o r m o b i l e A F r e c e i v e r s y s t e m 111 F i g . B . 5 S e n s i t i v i t y ( m V / n T ) c a l i b r a t i o n c h a r t f o r m o b i l e A F r e c e i v e r s y s t e m 112 F i g . C l C o n t o u r e d d a t a 118 F i g . C . 2 T h e o r e t i c a l d a t a i n S C A T C N p r o g r a m 122 F i g . C . 3 G e o m a g n e t i c f i e l d d a t a ( 2 2 / 7 / 8 1 - 2 3 / 7 / 8 1 ) 123 F i g . C . 4 B a s e S t a t i o n A F S i g n a l ( 2 2 / 7 / 8 1 - 2 3 / 7 / 8 1 ) 125 ix Acknowledgments I would l i k e to acknowledge the cooperation and assistance of Mr. R.M. Shier and Mr. Ron Finnie, of B.C. Hydro Research and Development, Surrey, B.C., and as well the supervisory personnel and technicians of Meridian substation, loco, B.C. For their assistance in the design and construction of the receiver instrumentation systems I acknowledge Dr. K. Tsuruda of the Institute of Aeronautics and Space Science, University of Tokyo; Dr. K. Hayashi of the Geophysics Research Laboratory, University of Tokyo; and Mr. Brian E. Chapel of U.B.C. I would l i k e to thank Dr. Jules Lajoie of Cominco Ltd. for i n i t i a t i n g the geologic interpretation during one of his v i s i t s to U.B.C. I would l i k e to acknowledge the administration and st a f f of the U.B.C. Research Forest, where much of the work of this thesis was done. I would l i k e to take t h i s space to acknowledge those who have assisted me, either d i r e c t l y or i n d i r e c t l y , in preparing t h i s t h e s i s : The people who started out with me as fellow students and ended up as friends - Neil Bird, Rob Coenraads, Jim Horn, Tim Scheuer, and Kerry Stinson; with their presence, the time I spent in the Geophysics department here at U.B.C. was enjoyable and enlightening; Miss Kathryn Belevsky, for i n d i r e c t l y f i l l i n g my non-thesis hours and days. I would l i k e to thank my supervisor, Dr. Tomiya Watanabe, for h is invaluable help with every aspect of thi s X thesis; suggesting the topic, c o l l e c t i n g the f i e l d data, analyzing the re s u l t s , and proofreading the manuscript. I would l i k e to thank Dr. R.D. Russell and Dr. W.F. Slawson for their discussions and supervision throughout the period spent on t h i s t h e s i s . Fi n a n c i a l assistance was provided by G.R.E.A.T. Award #17(GC-1), co-sponsored by the Secretariat on Science, Research and Development, Government of B r i t i s h Columbia, and B.C. Hydro Corporation. The project was a d d i t i o n a l l y financed by U.B.C. Committee on Natural, Applied and Health Sciences no. (21-9602). 1 Chapter I INTRODUCTION Geoph y s i c a l e x p l o r a t i o n can be c o n s i d e r e d an " a p p l i c a t i o n of the p r i n c i p l e s of geophysics to g e o l o g i c e x p l o r a t i o n " ( H e i l a n d , 1940, p. 3). From the time of the 19th century, systematic e f f o r t s have been undertaken to y i e l d i n f o r m a t i o n about the e a r t h ' s i n t e r i o r . Magnetic and g r a v i t a t i o n a l o b s e r v a t i o n s were the f i r s t used to determine the shape and c o n s t i t u t i o n of the e a r t h . E a r l y s t u d i e s were concerned with expansive r e g i o n a l features;, present methods aim at the l o c a t i o n of l o c a l g e o l o g i c s t r u c t u r e s and m i n e r a l d e p o s i t s . The development of e x p l o r a t i o n geophysics arose from a s u b s t a n t i a l i n c r e a s e i n accuracy and r e l i a b i l i t y of f i e l d methods, c o i n c i d e n t with advances in p h y s i c s i n general and e l e c t r o n i c implementation i n p a r t i c u l a r . The enhanced m o t i v a t i o n f o r e x p l o r a t i o n came from the need f o r raw m a t e r i a l s as economies expanded duri n g and a f t e r each of the World Wars. T h i s t h e s i s * d e a l s with the form of g e o p h y s i c a l e x p l o r a t i o n known as an "electromagnetic (EM) method." The method i s c h a r a c t e r i z e d by the measurement of induced e l e c t r o m a g n e t i c f i e l d s i n a c i r c u i t ( g e n e r a l l y a c o i l of l o w - r e s i s t a n c e i n s u l a t e d w i r e ) . The measuring c i r c u i t (or c o i l ) does not come in c o n t a c t with the ground, as opposed to p o t e n t i a l methods, i n which p o t e n t i a l s and c u r r e n t s are measured u s i n g e l e c t r o d e s i n 2 c o n t a c t with the c o n d u c t i v e ground. The EM method of e x p l o r a t i o n , then, c o n s i s t s of an a l t e r n a t i n g c u r r e n t source s u p p l y i n g the primary f i e l d , and a c o i l measuring the t o t a l induced f i e l d i n the d i r e c t i o n of the a x i s of the c o i l . The t o t a l f i e l d r e p r e s e n t s the v e c t o r sum of the f i e l d o r i g i n a t i n g d i r e c t l y from the source (primary f i e l d ) and any secondary e f f e c t s due to c u r r e n t s induced i n conductive bodies i n the l o c a l i z e d region of the r e c e i v i n g c o i l (secondary, or anomalous, f i e l d ) . Consider a s i m p l i f i e d v e r s i o n of EM e x p l o r a t i o n which c o n s i s t s of t r a n s m i t t e r , r e c e i v e r , and b u r i e d conductor, and can be represented by a t r i o of e l e c t r i c a l c i r c u i t s coupled by e l e c t r o m a g n e t i c i n d u c t i o n . The source ( t r a n s m i t t e r ) i s u s u a l l y i n d u c t i v e (that i s , the source may be an EM f i e l d , o r i g i n a t i n g from a c u r r e n t c a r r y i n g wire or a r a d i a t i n g antenna), though i t may be i n d i r e c t c o n t a c t with the ground. The d e t e c t o r i n v a r i a b l y r e c e i v e s i t s s i g n a l by i n d u c t i o n . The method responds best to good e l e c t r i c a l conductors at shallow depth ( T e l f o r d et a l . , 1976, p. 500). R e c e i v i n g d e v i c e s are d i v e r s i f i e d and can be extremely complex. T h e i r fundamental c o n s t r u c t i o n c o n s i s t s of an a m p l i f i e r connected to a c o i l of wire on an i n s u l a t i n g frame. A r e c e i v e r may have more than one c o i l , o r i e n t e d so that i t measures d i f f e r e n t components of the t o t a l f i e l d s i m u l t a n e o u s l y , and a s t a t i o n a r y r e f e r e n c e c o i l may a l s o be employed. The a m p l i f i e r can be designed to measure both amplitude and phase components (the secondary f i e l d i s s h i f t e d i n phase, r e l a t i v e to the primary f i e l d , i n the v i c i n i t y of a good c o n d u c t o r ) . Other 3 p o s s i b l e a m p l i f i e r designs r e s u l t i n measured r a t i o s of v a r i o u s components, or in' e l i m i n a t i o n of the primary f i e l d ' s e f f e c t . T r a n s m i t t e r s c o n s i s t of c u r r e n t - c a r r y i n g wires i n the form of long c a b l e s , r e c t a n g u l a r loops, or c i r c u l a r c o i l s ; the c u r r e n t most o f t e n s u p p l i e d by a g a s o l i n e - f u e l e d a l t e r n a t o r or b a t t e r y powered o s c i l l a t o r - p o w e r a m p l i f i e r . The frequency of the source f i e l d depends on the technique used, and the depth of p e n e t r a t i o n d e s i r e d . The t r a n s m i t t e r output i s g e n e r a l l y s i n u s o i d a l and i n the lower audio range, from 100 Hz to 5 KHz ( T e l f o r d et a l . , 1976, p. 520). Lower f r e q u e n c i e s make energy t r a n s m i s s i o n too i n e f f i c i e n t , and higher f r e q u e n c i e s lack depth p e n e t r a t i o n and produce too much i n t e r f e r e n c e (Heiland, 1940, p. 763). Some systems c o o r d i n a t e two f r e q u e n c i e s to d i s c r i m i n a t e between shallow and deep conductors or to i n d i c a t e the c o n d u c t i v i t y of a s t r u c t u r e ( T e l f o r d et a l . , 1976, p. 520). In g e n e r a l , the d i s t a n c e between source and r e c e i v e r i s of the order of a kilometer or l e s s ; f o r f r e q u e n c i e s s m a l l e r than 5 KHz t h i s i s only a very small f r a c t i o n of a free-space wavelength. T h i s means that i n the regions w i t h i n which o b s e r v a t i o n s are made, the e f f e c t s of propagation can be wholly d i s r e g a r d e d (Grant and West, 1965, p. 445). There are disadvantages a s s o c i a t e d with p r o v i d i n g a source t r a n s m i t t e r f o r EM e x p l o r a t i o n ; l a y i n g out long t r a n s m i s s i o n wires i s tedious and may be d i f f i c u l t i n rough t e r r a i n , the a l t e r n a t o r can be cumbersome and d i f f i c u l t to t r a n s p o r t , and the e x t r a c o s t i n v o l v e d i n machinery and p e r s o n n e l . T h e r e f o r e the use of a l t e r n a t i v e sources has been s t u d i e d . Two such methods are VLF and AFMAG, which make use of remote EM sources and 4 consequently do not need a t r a n s m i t t e r . The main o r i g i n of the primary f i e l d i n the AFMAG (audio-frequency magnetic f i e l d s ) method i s l i g h t n i n g d i s c h a r g e s a s s o c i a t e d w i t h worldwide thunderstorm a c t i v i t y . The r e s u l t i s a random s i g n a l i n the ELF range, from 1 to 1000 Hz ( T e l f o r d et a l . , 1976, p. 534). N a t u r a l e l e c t r o m a g n e t i c s i g n a l s with a frequency g r e a t e r than about 1 Hz are denoted s f e r i c s ; those l e s s than 5 Hz f a l l i n the category of m i c r o p u l s a t i o n s . The VLF method uses s i g n a l s broadcast by c e r t a i n n a v i g a t i o n systems as sources f o r EM e x p l o r a t i o n , in the frequency range 5-25 KHz. The VLF and AFMAG methods share s i m i l a r d e t e c t i o n systems, g e n e r a l l y a set of p e r p e n d i c u l a r c o i l s (one used to provide a r e f e r e n c e s i g n a l ) , and one or two narrow-band f i l t e r s i n the a m p l i f i e r . T h i s t h e s i s p r e s e n t s an experimental method of EM e x p l o r a t i o n which uses the c u r r e n t i n h i g h - v o l t a g e t r a n s m i s s i o n l i n e s as a remote e l e c t r o m a g n e t i c source. T h i s method i n c o r p o r a t e s the advantages of other remote source schemes, and, in a d d i t i o n : the source c o n s i s t s of a number of s e l e c t f r e q u e n c i e s i n the lower audio range, namely 60 Hz and i t s harmonics; the s i g n a l i s r e l a t i v e l y s t rong, subsequently a r e l a t i v e l y low s e n s i t i v i t y d e t e c t o r i s needed. Areas once c o n s i d e r e d i n a c c e s s i b l e , due to s i g n a l i n t e r f e r e n c e from a hi g h - v o l t a g e t r a n s m i s s i o n l i n e , can be surveyed, using the t r a n s m i s s i o n l i n e as a source. S e v e r a l r e s t r i c t i o n s with the proposed method immediately come to mind: the source i s immobile, and the area to be surveyed must be i s o l a t e d from power l i n e s other than the primary source. 5 The use of a power l i n e as a source f i e l d , as suggested i n t h i s t h e s i s , w i l l only prove p r a c t i c a l i f the a c t u a l c u r r e n t s and c o n f i g u r a t i o n s of the power system are known. To use power harmonics as sources of d i f f e r i n g f r e q u e n c i e s , the g e n e r a t i o n and i n t e n s i t i e s of the harmonics ( r e l a t i v e to the fundamental) must be s t u d i e d . A d d i t i o n a l l y , the v a r i a t i o n of harmonic c u r r e n t s with time must be known; that i s , how do v a r y i n g loads on the power system a f f e c t harmonic l e v e l s , and how can t h i s be d e a l t with when using the method? A l s o , what i s the e f f e c t of geomagnetic a c t i v i t y on the system? These are e s s e n t i a l l y the o b j e c t i v e s of t h i s t h e s i s ; or, more c o n c i s e l y , are power t r a n s m i s s i o n l i n e s a v i a b l e and p r a c t i c a l source f o r use i n EM e x p l o r a t i o n ? The bulk of t h i s t h e s i s d e t a i l s r e s e a r c h d i r e c t e d towards answering the above q u e s t i o n s . An a f f i r m a t i v e c o n c l u s i o n i s drawn from the study and experimental r e s u l t s . The next chapter d e a l s with the o p e r a t i o n of power systems and t r a n s m i s s i o n l i n e s as r e l a t e s to t h i s study. Chapter three d e s c r i b e s the experimental method of o b t a i n i n g measurements, and i n c l u d e s i n s t r u m e n t a t i o n and c a l i b r a t i o n procedures. The f o u r t h chapter d e t a i l s the r e s u l t s of the experimental work i n v o l v i n g harmonic c u r r e n t s i n a p a r t i c u l a r t r a n s m i s s i o n l i n e . The r e s u l t s of EM survey work, to show the p r a c t i c a b i l i t y of the method of using a t r a n s m i s s i o n l i n e as a source, are given i n chapter f i v e . A l s o , an i n t e r p r e t a t i o n of the EM survey r e s u l t s i s suggested i n chapter f i v e , and the c o n c l u s i o n of the t h e s i s i s presented i n chapter s i x . 'Three appendices to the tex t are i n c l u d e d t o g i v e d e t a i l e d i n f o r m a t i o n of p a r t i c u l a r s u b j e c t s of i n t e r e s t . 6 Chapter II POWER SYSTEMS 2.1 General The most general form of power t r a n s m i s s i o n system ( f i g u r e 2.1) c o n s i s t s of the prime mover, a generator, transformer banks, a h i g h - v o l t a g e l i n e , and the l o a d . The prime mover i s a d e v i c e , such as a steam d r i v e n t u r b i n e or h y d r a u l i c t u r b i n e , which converts some form of a v a i l a b l e energy ( f o r example heat, f a l l i n g water, or f u e l ) i n t o r o t a t i o n of a s h a f t , which i n turn d r i v e s the generator. The generator i s u s u a l l y an AC machine (or a l t e r n a t o r ) . P r a c t i c a l power systems c o n s i s t of three conductors, with a s s o c i a t e d c i r c u i t breakers and di s c o n n e c t s f o r each conductor ( f i g u r e 2.2). A three-phase system of v o l t a g e s i s i l l u s t r a t e d i n f i g u r e 2.3. The set of c o i l s i n f i g u r e 2.3(a) r e p r e s e n t s three windings (ab,cd,ef) of a transformer bank which generate v o l t a g e s Vab,Vcd,Vef, r e s p e c t i v e l y . The v o l t a g e s are presented as a f u n c t i o n of time i n f i g u r e 2.3(b) and as a phasor diagram i n f i g u r e 2.3(c). The system i s s a i d to be "balanced" i f the three v o l t a g e s have equal magnitude and the time displacement between any two i s o n e - t h i r d c y c l e (120 d e g r e e s ) . That i s , the balanced v o l t a g e s Vab,Vcd,Vef can be rep r e s e n t e d as three 7 Prime Mover Transformer Generator o—o : High-voltage line Transformer Load F i g . 2.1 A generator connected through transformers and a high voltage l i n e to a distant load (Eaton, 1972, p. 8). O Of O Of - P O l — Ho-Or— Ho_Oj— Ho-Or— Transformer Bank "^=" Disconnects o o o Circuit Breaker Disconnects Transmission Line F i g . 2.2 A three-phase transformer bank, the disconnect switches, and a three-phase c i r c u i t breaker connecting to a three-phase transmission l i n e (Eaton, 1972, p. 19). 8 equal-magnitude s i n u s o i d s , with r e s p e c t i v e phases 0 , 2 i r / 3 , and 4 i r / 3 . The c o i l s i n f i g u r e 2 . 3 ( a ) are independant of each other and may be connected as d e s i r e d . Two common c o n f i g u r a t i o n s are shown i n f i g u r e 2 . 4 . In f i g u r e 2 . 4 ( a ) the c o i l s are connected i n d e l t a to form a three-phase system with l i n e conductors X , Y , Z . The c o n f i g u r a t i o n i n f i g u r e 2 . 4 ( b ) i s the Y- (or s t a r ) c o n n e c t i o n . The common p o i n t of a Y-connection i s termed the n e u t r a l and i s designated by the l e t t e r N. The secondary windings of a three-phase system i n a Y-connection are shown s c h e m a t i c a l l y i n f i g u r e 2 . 5 . 2 . 2 Harmonics The power system shown s c h e m a t i c a l l y i n f i g u r e 2 . 1 i s designed to generate an AC v o l t a g e from the prime mover at a s p e c i f i c frequency. The frequency i s governed by the angular speed of the r o t o r with res p e c t to the s t a t o r ( f i g u r e 2 . 6 ) and i s 60 Hz i n North America. The three l i n e v o l t a g e s Vab,Vcd,Vef (mentioned here simply as phases A,B,C) are then arranged i n a c o n f i g u r a t i o n such as shown i n f i g u r e 2 . 4 . Due to the arrangement of the c o i l s i n f i g u r e 2 . 6 , each of the three v o l t a g e s induced (V A ,VB ,VC ) w i l l be of equal magnitude and ± 1 2 0 degrees from the other two (as expressed i n f i g u r e 2 . 3 ( b ) , 2 . 3 ( c ) ) . With the Y-connection of f i g u r e 2 . 4 ( b ) i n mind, i t can be determined that i n a balanced three-phase c i r c u i t , only m u l t i p l e s of t h i r d harmonic v o l t a g e s and c u r r e n t s e x i s t at the n e u t r a l p o s i t i o n . The t r i p l e - f r e q u e n c y q u a n t i t i e s 9 F i g . 2.3 A three-phase system, (a) C o i l s i n which voltages are generated, (b) The sine wave voltages produced i n the three c o i l s , (c) Phasor r e p r e s e n t a t i o n of the three voltages (Eaton, 1972, p. 53). (a) (b) F i g . 2.4 Two common three-phase impedance connections, (a) Delta-connected impedances. (b) Y-connected impedances (Eaton, 1972, p. 52). 10 3-PHASE TRANSMISSION LINE B TRANSFORMER BANK -ww-F i g . 2.5 T h r e e - p h a s e t r a n s f o r m e r s y s t e m i n Y - c o n n e c t i o n , F i g . 2.6 D i a g r a m o f a n i d e a l i z e d A C m a c h i n e ( A d k i n s a n d H a r l e y , 1975, p . 6). i 11 a r e c a l l e d " z e r o p h a s e - s e q u e n c e " q u a n t i t i e s ( o r s i m p l y " z e r o - s e q u e n c e " ) . T h a t i s , a l l b u t t r i p l e h a r m o n i c s w i l l t e n d t o c a n c e l a t t h e n e u t r a l , d u e t o t h e v e c t o r i a l a d d i t i o n o f c o m p o n e n t s a t t h i s p o i n t , w h i l e t r i p l e h a r m o n i c s w i l l a d d . N o n - t r i p l e h a r m o n i c s a r e t e r m e d t h r e e - p h a s e q u a n t i t i e s , a n d w i l l b e e i t h e r p o s i t i v e - s e q u e n c e o r n e g a t i v e - s e q u e n c e , a s s e e n i n t a b l e 2 . 1 ( B l u m e , 1 9 3 8 , p . 3 9 ) . T A B L E 2 . 1 P H A S E A N G L E P H A S E H A R M O N I C B E T W E E N A , B , C S E Q U E N C E 1 s t o, 1 2 0 , 2 4 0 P o s i t i v e 2 n d o, 2 4 0 , 4 8 0 N e g a t i v e ( - 1 2 0 ) ( - 2 4 0 ) 3 r d o, 3 6 0 , 7 2 0 Z e r o ( 0 ) ( 0 ) 4 t h o, 4 8 0 , 9 6 0 P o s i t i v e ( + 1 2 0 ) ( + 2 4 0 ) 5 t h o, 6 0 0 , 1 2 0 0 N e g a t i v e ( - 1 2 0 ) ( - 2 4 0 ) 6 t h o, 7 2 0 , 1 4 8 0 Z e r o ( 0 ) ( 0 ) 7 t h o, 8 4 0 , 1 6 8 0 P o s i t i v e ( + 1 2 0 ) ( + 2 4 0 ) 9 t h o, 1 0 8 0 , 21 60 Z e r o ( 0 ) ( 0 ) e t c . T a b l e 2.1 P h a s e S e q u e n c e C u r r e n t s ( f r o m B l u m e , 1938, p . 3 9 ) . A d i s t i n c t i o n i s m a d e , b a s e d o n t h e a b o v e d i s c u s s i o n , b e t w e e n t r i p l e a n d n o n - t r i p l e h a r m o n i c s . T h i s i s d u e t o t h e f a c t t h a t , o n a Y - c o n n e c t e d , b a l a n c e d s y s t e m , t h i r d h a r m o n i c v o l t a g e s a n d c u r r e n t s e x i s t a t t h e n e u t r a l p o i n t , w h i l e n o n - t r i p l e h a r m o n i c s a r e s u p p r e s s e d . T h e e x i s t e n c e o f n o n - t r i p l e h a r m o n i c 1 2 q u a n t i t i e s a t t h e n e u t r a l i s g e n e r a l l y c o n s i d e r e d a n i n d i c a t i o n o f t h e i m b a l a n c e o f t h e t h r e e - p h a s e s y s t e m ( i n w h i c h V a b , V c d , V e f a r e n o t o f e q u a l m a g n i t u d e ) . T h e d i s c u s s i o n t o t h i s p o i n t h a s i n d i c a t e d t h e a s p e c t o f z e r o - p h a s e q u a n t i t i e s w h i c h g i v e r i s e t o t r i p l e h a r m o n i c s ( 3 r d , 6 t h , 9 t h , e t c . ) a t t h e n e u t r a l p o s i t i o n d u e t o s u p e r p o s i t i o n . T h e f o l l o w i n g d i s c u s s i o n r e g r e s s e s a s t e p a n d ( p o i n t s t o t h e o r i g i n o f a l l h a r m o n i c s w i t h r e g a r d t o a s i n g l e l i n e o f a t h r e e - p h a s e s y s t e m . T h e o r i g i n o f h a r m o n i c s i n a l i n e i s t r a c e d t o t h e p o w e r t r a n s f o r m e r . T h e u s e o f h i g h i n d u c t i o n d e n s i t i e s i n t h e c o r e s o f p o w e r t r a n s f o r m e r s i s i m p o s e d b y t h e r e q u i r e m e n t o f a n e c o n o m i c a l d e s i g n a n d r e d u c t i o n o f w e i g h t ( S a y , 1 9 6 5 , p . 9 4 ) . U n f o r t u n a t e l y f o r p o w e r s y s t e m d e s i g n e r s , t h i s p r a c t i c e r e s u l t s i n s a t u r a t i o n o f t h e m a g n e t i c c i r c u i t a n d t h e r e s u l t a n t n o n - l i n e a r i t y o f t h e f l u x / m a g n e t i c f o r c e r e l a t i o n ( h y s t e r e s i s ) . T h e e f f e c t c a n b e s t a t e d : d u e t o s a t u r a t i o n o f t h e t r a n s f o r m e r c o r e m a t e r i a l , a s i n u s o i d a l m a g n e t i z i n g f o r c e r e s u l t s i n a n o n - s i n u s o i d a l f l u x d e n s i t y . I n a p o w e r s y s t e m , t h e m a g n e t i c f o r c e r e p r e s e n t s t h e m a g n e t i z i n g c u r r e n t o f t h e t r a n s f o r m e r p r i m a r y s u p p l i e d b y o n e l i n e o f t h e g e n e r a t o r , a n d t h e r e s u l t i n g m a g n e t i c f l u x d r i v e s t h e t r a n s f o r m e r s e c o n d a r y c u r r e n t . F o r t h e m o s t c o m m o n f o r m o f h y s t e r e s i s c u r v e ( o n e w i t h p o i n t s y m m e t r y ) , t h e i n d u c e d s e c o n d a r y c u r r e n t c o n s i s t s o f o d d h a r m o n i c s o n l y , w i t h d e c r e a s i n g m a g n i t u d e a s t h e o r d e r i s i n c r e a s e d ( s e e A p p e n d i x A f o r a g r a p h i c a l a n a l y s i s o f h a r m o n i c c o n t e n t ) . H o w e v e r , i f a D C m a g n e t i c f i e l d e x i s t s i n t h e t r a n s f o r m e r c o r e ( u n t i l now i t w a s a s s u m e d o n l y A C f i e l d s , d u e t o t h e p r i m a r y 13 c u r r e n t , e x i s t ) , the h y s t e r e s i s curve e x h i b i t s no p o i n t symmetry. In the l a t t e r case, a l l m u l t i p l e s of the fundamental v e x i s t , and the s p e c i f i c harmonic magnitudes depend on the p a r t i c u l a r h y s t e r e s i s curve (Hayashi et a l . , 1979). T h e r e f o r e , due to n o n - l i n e a r i t i e s i n magnetization of ferromagnetic core m a t e r i a l s , odd c u r r e n t harmonic components are expected to e x i s t i n the secondary c i r c u i t of the power transformer. If a DC magnetic f i e l d e x i s t s i n the core, a l l harmonics may e x i s t i n the secondary c i r c u i t . Harmonic c u r r e n t s are disadvantageous to the power system designer, due to e f f e c t s such as a d d i t i o n a l power l o s s and i n t e r f e r e n c e with communication c i r c u i t s and p r o t e c t i o n equipment. The harmonic content i n three-phase systems i s dependant on the connection p a t t e r n of the three phases: t r i p l e harmonics are suppressed i n d e l t a - c o n n e c t e d transformer windings, but are enhanced i n Y-connected windings. T h e o r e t i c a l l y , the occurrence of even harmonics has been t r a c e d to a DC l e v e l magnetic f i e l d w i t h i n the high-** metal core of a transformer (Hayashi et a l . , 1979). P r a c t i c a l l y , t h i s magnetic f i e l d i s caused by a DC l e v e l c u r r e n t f l o w i n g i n the ground connection of a transformer bank ( f i g u r e 2.7). Under normal o p e r a t i n g c o n d i t i o n s , the 60 Hz s i g n a l i s grounded through a transformer at each end of the t r a n s m i s s i o n l i n e , which can be s e v e r a l hundred k i l o m e t e r s i n l e n g t h . The e x i s t e n c e of n a t u r a l l a r g e - s c a l e e a r t h c u r r e n t s i s w e l l known ( f i r s t e s t a b l i s h e d by Barlow i n 1847 i n the course of s t u d y i n g the f i r s t B r i t i s h t e l e g r a p h system ( T e l f o r d et a l . , 1976, p. 468)). The e a r t h c u r r e n t s ( t e l l u r i c c u r r e n t s ) are 14 TRANSMISSION LINE GIC J TRANSFORMER BANKS POTENTIAL DIFFERENCE F i g . 2.7 GIC (geomagnetically induced c u r r e n t ) flowing i n ground of transformer bank. 15 i n d u c e d b y l a r g e s c a l e , g e n e r a l l y l o w f r e q u e n c y m a g n e t o t e l l u r i c f i e l d s ( i n t h e r a n g e o f m i c r o p u l s a t i o n s a n d s f e r i c s ) . D u e t o t h e s e t i m e - v a r y i n g , l a r g e s c a l e c u r r e n t s a n d t h e g r e a t d i s t a n c e s i n v o l v e d i n t r a n s m i s s i o n l i n e s , t h e p o t e n t i a l o f t h e t w o g r o u n d s a t e a c h e n d o f t h e l i n e m a y b e d i f f e r e n t . T h i s , o f c o u r s e , l e a d s t o a c u r r e n t i n t h e g r o u n d c o n n e c t i o n o f t h e t r a n s f o r m e r . T h e c u r r e n t s i n t h e t r a n s f o r m e r ' s g r o u n d c o n n e c t i o n a r e t e r m e d " q u a s i - D C " s i n c e t h e i r f r e q u e n c y i s m u c h l o w e r t h a n t h e 60 H z s i g n a l i n h e r e n t i n t h e s y s t e m . T h e m a g n e t o t e l l u r i c f i e l d s a r e k n o w n t o o r i g i n a t e o u t s i d e t h e e a r t h ; p e r i o d i c a n d t r a n s i e n t f l u c t u a t i o n s c a n b e c o r r e l a t e d w i t h p h e n o m e n a s u c h a s d i u r n a l v a r i a t i o n s i n t h e e a r t h ' s m a g n e t i c f i e l d , s o l a r e r u p t i o n s , a n d a u r o r a l a c t i v i t y . S u c h m a g n e t i c a c t i v i t y h a s a d i r e c t i n f l u e n c e o n i o n o s p h e r i c c u r r e n t s ; i t i s g e n e r a l l y t h o u g h t t h a t t e l l u r i c c u r r e n t s a r e i n d u c e d i n t h e e a r t h b y i o n o s p h e r i c c u r r e n t s . A s p r e v i o u s l y s t a t e d , t h e q u a s i - D C c u r r e n t s i n t h e t r a n s f o r m e r g r o u n d c o n n e c t i o n a r e c a u s e d b y t e l l u r i c c u r r e n t s a n d a r e r e s p o n s i b l e f o r q u a s i - D C m a g n e t i c f i e l d s i n t h e t r a n s f o r m e r c o r e . T h e q u a s i - D C m a g n e t i c f i e l d s i n t h e c o r e t h e n g i v e r i s e t o c h a n g e s i n h a r m o n i c c u r r e n t l e v e l . T h e s t r e n g t h o f e a c h h a r m o n i c h a s b e e n f o u n d t o c h a n g e c o n c u r r e n t l y w i t h g e o m a g n e t i c a c t i v i t y ( H a y a s h i e t ' a l . , 1979). I t i s a t t h i s s t a g e t h a t t h e p o w e r s y s t e m p r o t e c t i o n d e s i g n e r b e c o m e s i n t e r e s t e d i n q u a s i - D C t r a n s f o r m e r c u r r e n t s ( d e n o t e d G I C : g e o m a g n e t i c a l l y i n d u c e d c u r r e n t s ) . T h e a s s o c i a t i o n o f G I C l e v e l w i t h g e o m a g n e t i c f i e l d a c t i v i t y h a s b e e n s t u d i e d a n d r e p o r t e d b y B o t e l e r ( 1 9 7 9 ; t o b e p u b l i s h e d ) . 16 E v e n t h o u g h g e o m a g n e t i c e f f e c t s o c c u r m o s t s t r o n g l y a n d f r e q u e n t l y i n t h e h i g h e r l a t i t u d e s , p r o t e c t i o n e n g i n e e r s a s s o c i a t e d w i t h p o w e r s y s t e m s i n t h e m o r e p o p u l a t e d m i d d l e l a t i t u d e s h a v e e x p e r i e n c e d s o l a r a c t i v i t y r e l a t e d p r o b l e m s s u c h a s t r i p p e d s a f e t y r e l a y s a n d c i r c u i t b r e a k e r s , a n d e v e n o v e r l o a d s w h i c h h a v e b l o w n o p e n t r a n s f o r m e r s ( F i s h e r , 1 9 8 1 ) . 17 Chapter I I I Experimental Procedure 3.1 Experimental O b j e c t i v e s The t r a n s m i s s i o n l i n e used as an EM e x p l o r a t i o n source i n t h i s work i s B.C. Hydro power l i n e 5L82, which c a r r i e s power from the Mica Creek g e n e r a t i n g s t a t i o n , through N i c o l a t e r m i n a l s t a t i o n , t o M e r i d i a n s u b s t a t i o n , near l o c o , B.C. F i g u r e s 3.1 and 3.2 show the survey area, which i n c l u d e s most of the U.B.C. Research F o r e s t and the southwestern s e c t i o n of Golden Ears P r o v i n c i a l Park. The 500 KV t r a n s m i s s i o n l i n e i s s i t u a t e d in a g e n e r a l l y East-West d i r e c t i o n , j u s t below the U.B.C. Research F o r e s t southern boundary. The survey area was chosen because i t i s near a h i g h - v o l t a g e t r a n s m i s s i o n l i n e (5L82), yet otherwise i s f a i r l y remote and i s o l a t e d from other sources of commercial elecromagnetic s i g n a l s . Access to a c t u a l harmonic c u r r e n t l e v e l s on 5L82 and GIC i n the transformer ground connection are made, with the c o o p e r a t i o n of B.C. Hydro personnel, at M e r i d i a n (MDN) s u b s t a t i o n . Experimental measurements can be d i v i d e d i n t o three groups, based on l o c a t i o n : 18 F i g . 3.1 Location of survey area for EM f i e l d work (from Boteler et a l . , to be published). INSET F i g . 3.1 Continued F i g . 3.2 21 (a) Harmonic c u r r e n t l e v e l s on 5L82, and GIC measurements, made at MDN s u b s t a t i o n ; (b) Magnetic f i e l d s i g n a l s , induced from AC c u r r e n t l e v e l s i n 5L82, made at a "base s t a t i o n " l o c a t e d i n the U.B.C. Research F o r e s t , approximately 350 m (p e r p e n d i c u l a r ) from 5L82 (these s i g n a l s are denoted "AF s i g n a l s " , as they l i e w i t h i n the audio frequency range); a l s o geomagnetic f i e l d components, measured at the base s t a t i o n ; (c) Magnetic f i e l d measurements (using 5L82 as source) on an a r r a y of 66 " s t a t i o n s " to complete an EM survey. The s t a t i o n s are l o c a t e d throughout the survey area ( f i g u r e 3.2). Consider the o b j e c t i v e s of the experimental work of t h i s t h e s i s : (a) The f i r s t o b j e c t i v e i s to determine the magnetic f i e l d s t r e n g t h as a f u n c t i o n of the d i s t a n c e from the t r a n s m i s s i o n l i n e . For the proposed e x p l o r a t i o n method to be e f f e c t i v e , the magnetic f i e l d s t r e n g t h must f a l l o f f as 1/r (r i s the p e r p e n d i c u l a r d i s t a n c e to the tr a n s m i s s i o n l i n e ) . The we l l known B i o t - S a v a r t law s t a t e s that the magnetic f i e l d due to an i n f i n i t e l i n e c u r r e n t in non-conducting space f o l l o w s a 1/r r e l a t i o n . However i n c o n s i d e r i n g the r e a l , s i t u a t i o n , t h i s r e l a t i o n cannot be assumed, f o r i n f a c t the t r a n s m i s s i o n l i n e c o n s i s t s of three e q u a l l y - s p a c e d conductors over a conducting e a r t h . T h e r e f o r e experimental v e r i f i c a t i o n of the 1/r r e l a t i o n i s necessary before proceeding. I t should be noted that a survey which monitored a s i n g l e harmonic component (180 Hz) at v a r i o u s d i s t a n c e s from the t r a n s m i s s i o n l i n e (5L82) was undertaken i n 1979 (Watanabe e t . a l . , 1981). The success of t h i s survey i n e x p e r i m e n t a l l y determining a 1/r r e l a t i o n warranted f u r t h e r work, and a s i m i l a r survey, i n c o r p o r a t i n g more source f r e q u e n c i e s and s l i g h t l y d i f f e r e n t methods, was done in 1980. An a d d i t i o n a l o b j e c t i v e of the 1980 survey was to determine l i m i t s on the d i s t a n c e one c o u l d range from the t r a n s m i s s i o n l i n e and s t i l l r e c e i v e a u s e f u l s i g n a l ; (b) Another primary o b j e c t i v e i n the experimental work i s to ensure that the c u r r e n t i n 5L82 i s in f a c t the source of the s i g n a l d e t e c t e d by the r e c e i v i n g u n i t ( l o c a t e d at the base s t a t i o n ) . As seen from f i g u r e 3.1, there are a d d i t i o n a l power l i n e s i n the re g i o n , though 5L82 i s by f a r the nearest to the survey a r e a . Simultaneous measurements of harmonic c u r r e n t l e v e l s i n 5L82 and AF s i g n a l s are needed to show that 22 t r a n s m i s s i o n l i n e c u r r e n t h a r m o n i c s i n 5 L 8 2 a r e s o l e l y r e s p o n s i b l e f o r t h e p r i m a r y m a g n e t i c s i g n a l r e c e i v e d a t t h e U . B . C . R e s e a r c h F o r e s t b a s e s t a t i o n . I n a d d i t i o n , i t s h o u l d b e v e r i f i e d e x p e r i m e n t a l l y t h a t t h e A F s i g n a l r e c e i v e d a t t h e b a s e s t a t i o n i s r e p r e s e n t e d b y t h e v e c t o r i a l s u m o f t h e c u r r e n t s i n t h e t h r e e c o n d u c t o r s o f 5 L 8 2 . C o m p a r i s o n o f A F s i g n a l h a r m o n i c c o n t e n t w i t h n e u t r a l c u r r e n t h a r m o n i c c o n t e n t s h o u l d s h o w t h i s t o b e t h e c a s e ; ( c ) A t h i r d e x p e r i m e n t a l o b j e c t i v e i s t o s h o w q u a l i t a t i v e m e a s u r e m e n t s o f G I C a t MDN s u b s t a t i o n a n d s i m u l t a n e o u s m a g n e t o m e t e r d a t a t a k e n a t t h e b a s e s t a t i o n . I f p o s s i b l e , e f f e c t s o f G I C o n h a r m o n i c c u r r e n t a r e t o b e m e a s u r e d a t M D N ; ( d ) F i n a l l y , i t i s t o b e s h o w n t h a t t h e t r a n s m i s s i o n l i n e i s a n e f f e c t i v e s o u r c e f o r E M e x p l o r a t i o n . F r o m t h e r e s u l t s o f t h e e x p e r i m e n t c o m p l e t e d i n 1 9 8 0 ( p r e v i o u s l y m e n t i o n e d i n 3 . 1 ( a ) ) , a n e x t e n s i v e s u r v e y w a s p l a n n e d f o r 1981 ( f o r t h e r e s u l t s o f e a c h o f t h e s e s u r v e y s , s e e C h a p t e r 5 ) . 3 . 2 I n s t r u m e n t a t i o n T o o b t a i n s i m u l t a n e o u s d a t a ( a t t w o l o c a t i o n s : MDN a n d t h e U . B . C . R e s e a r c h F o r e s t ) c o n c e r n i n g h a r m o n i c c u r r e n t l e v e l s , G I C , A F s i g n a l s , a n d g e o m a g n e t i c a c t i v i t y , a n u m b e r o f d i f f e r e n t i n s t r u m e n t s w e r e e m p l o y e d . C u r r e n t l e v e l s a n d G I C m e a s u r e m e n t s w e r e o b t a i n e d a t M e r i d i a n s u b s t a t i o n , u s i n g t h e f o l l o w i n g e q u i p m e n t ( s e e f i g u r e 3 . 3 f o r a s c h e m a t i c r e p r e s e n t a t i o n o f a p p a r a t u s ) : ( a ) A f o u r - c h a n n e l a u d i o - f r e q u e n c y d i r e c t r e c o r d i n g d e v i c e w a s u s e d t o r e c o r d c u r r e n t l e v e l s . O n e c h a n n e l e a c h w a s r e s e r v e d f o r ( i ) n e u t r a l c u r r e n t ; ( i i ) A - p h a s e c u r r e n t ; ( i i i ) A - p h a s e h a r m o n i c c u r r e n t ( t h a t i s , A - p h a s e c u r r e n t w i t h t h e 6 0 H z f u n d a m e n t a l r e m o v e d ) ; a n d ( i v ) t i m e c o d e i n f o r m a t i o n ; ( b ) A m u l t i - c h a n n e l F M r e c o r d i n g s y s t e m w a s u s e d t o r e c o r d G I C l e v e l a n d t i m e c o d e i n f o r m a t i o n . 23 SL82 AUDIO FREQUENCY TAPE (O) FM TAPE (b) A F ANTENNA N-S E-W Z ~L o—t> TIME CODE HI-* 3 COMPONENT MAGNETOMETER V/F CONVERTER AUDIO FREQUENCY TAPE FM TAPE (0 (d) AF ANTENNA o—\t> • o WWV AUDIO RECEIVER PICKUP AUDIO FREQUENCY TAPE (e) F i g . 3.3 Schematic r e p r e s e n t a t i o n of apparatus. 24 Instruments used f o r AF measurements and geomagnetic f i e l d a c t i v i t y , p l a c e d i n the U.B.C. Research F o r e s t , are l i s t e d below: (c) An AF a n t e n n a - r e c e i v e r u n i t was used to d e t e c t the magnetic f i e l d due to harmonic c u r r e n t i n the t r a n s m i s s i o n l i n e . The s i g n a l from the antenna was recorded on one channel of an audio-frequency d i r e c t r e c o r d i n g machine, with time code on another channel; (d) A three-component magnetometer, set up at the base s t a t i o n , was used to measure the geomagnetic f i e l d v a r i a t i o n . The i n f o r m a t i o n was recorded on three channels of an FM tape system, with another channel used f o r time code. The t o t a l harmonic c u r r e n t l e v e l and the AF s i g n a l are s i m u l t a n e o u s l y recorded on audio-frequency tapes, and can then be analyzed f o r s p e c t r a l content i n the l a b using an analog-input spectrum a n a l y z e r . Comparing the p a r t i c u l a r harmonic l e v e l s of the two s i g n a l s , over a p e r i o d of time, w i l l i n d i c a t e that the AF s i g n a l d e t e c t e d at the base s t a t i o n i s induced by the harmonic c u r r e n t s i n 5L82. A l s o , GIC measurements at MDN should show a d i r e c t c o r r e l a t i o n to magnetometer measurements, i n p a r t i c u l a r the North-South component of the geomagnetic f i e l d , s i n c e the l i n e l i e s East-West. The next stage of experimental work i n c l u d e d an EM survey using harmonic c u r r e n t l e v e l s i n 5L82 as the primary inducing source. The equipment used i n t h i s survey f o l l o w s : (e) A mobile AF r e c e i v e r , u s ing a battery-powered, l i g h t - w e i g h t c a s s e t t e r e c o r d e r (channel one f o r the AF s i g n a l , channel two f o r r e c o r d i n g time i n f o r m a t i o n ) ; 25 ( f ) A s t a t i o n a r y AF r e c e i v i n g u n i t , l o c a t e d at the base s t a t i o n , t o use as a r e f e r e n c e s i g n a l f o r harmonic amplitudes ( l i s t e d p r e v i o u s l y i n s e c t i o n 3 . 2 ( c ) ) ; (g) A three-component magnetometer, to measure geomagnetic f i e l d a c t i v i t y ( l i s t e d p r e v i o u s l y i n s e c t i o n 3.2(d)), a good p r a c t i c e i n e l e c t r i c a l e x p l o r a t i o n methods. 3.3 C a l i b r a t i o n Procedure Accurate c a l i b r a t i o n procedures are e s s e n t i a l f o r the q u a n t i t a t i v e measurements i n v o l v e d . Determing q u a n t i t a t i v e harmonic c u r r e n t l e v e l s was done at MDN by c a l i b r a t i n g the d e t e c t i n g , a m p l i f y i n g , and r e c o r d i n g system as a complete u n i t . F i g u r e 3.3 shows the access to 5L82 i s through the secondary windings of a set of three 400:1 c u r r e n t transformers ( l a b e l l e d CT i n f i g u r e 3.3). A device known as a c u r r e n t probe i s u t i l i z e d , , which i n d u c t i v e l y c o n v e r t s an AC c u r r e n t to an AC v o l t a g e . During data r e c o r d i n g p e r i o d s , one c u r r e n t probe i s a t t a c h e d to a l i n e from the A-phase c u r r e n t transformer, and another probe i s a t t a c h e d to a l i n e from the n e u t r a l p o s i t i o n . For c a l i b r a t i o n purposes, the probes were att a c h e d to a t e s t c i r c u i t i n which the c u r r e n t i s a c c u r a t e l y known ( f i g u r e 3.4>. The t e s t c i r c u i t i n c l u d e s a s i g n a l generator which al l o w s c a l i b r a t i o n i n c u r r e n t l e v e l at each harmonic frequency. Using the same method of data a n a l y s i s f o r both r e a l data and t e s t data ( s p e c t r a l a n a l y s i s of recorded s i g n a l ) , a r e l i a b l e r e l a t i o n i s known between the s i g n a l on tape at a p a r t i c u l a r frequency and the c o r r e s p o n d i n g c u r r e n t i n 5L82. Two important f a c t s must be noted, however: 26 ( i ) Each c u r r e n t transformer i s c a l i b r a t e d at 400:1 only at the 60 Hz fundamental; i t must be assumed that the same r a t i o h olds f o r harmonic c u r r e n t s as w e l l (that i s , i n the frequency range 60 Hz-1 KHz). T h i s assumption can be s u b s t a n t i a t e d , however, by s p e c t r a l comparison of the n e u t r a l c u r r e n t and the AF s i g n a l ; s i m i l a r s i g n a l s would i n d i c a t e the r e l i a b i l i t y of the assumption, s i n c e the AF s i g n a l i s an i n d i c a t i o n of a c t u a l harmonic c u r r e n t s i n 5L82; ( i i ) The n e u t r a l c u r r e n t d i s c u s s e d i n t h i s s e c t i o n does not e x i s t , per se, i n 5L82, s i n c e 5L82 c o n s i s t s of three separate conductors A, B, and C. The n e u t r a l c u r r e n t represents the v e c t o r i a l sum of the c u r r e n t i n the three conductors. I t e x i s t s i n the c u r r e n t transformer c i r c u i t , s i n c e the secondary windings of the three c u r r e n t transformers on 5L82 are Y-connected (as i n f i g u r e 3.3). The a d d i t i o n of the three magnetic f i e l d s (generated by c u r r e n t s i n conductors A, B, and C) at the AF antenna w i l l appear to o r i g i n a t e from a " n e u t r a l c u r r e n t " i n 5L82. The GIC measuring system i s c a l i b r a t e d i n the same manner as the harmonic c u r r e n t d e t e c t i o n system. The GIC d e t e c t o r i s a H a l l - e f f e c t transducer d e v i c e ( d i s c u s s e d i n Appendix B) which i s connected to the transformer ground connection of 5L82. A t e s t c i r c u i t i s again used to c a l i b r a t e the e n t i r e d e t e c t i o n - a m p l i f i c a t i o n - r e c o r d i n g system at once, in which a known DC c u r r e n t i s passed through the d e t e c t o r ( f i g u r e 3.4). I t i s thought that "on s i t e " c a l i b r a t i o n of an e n t i r e system, as d i s c u s s e d i n t h i s s e c t i o n , i s s u p e r i o r to r e l y i n g on " i n the lab", c a l i b r a t i o n of i n d i v i d u a l components. The apparatus used f o r the EM e x p l o r a t i o n survey c o n s i s t e d of an antenna, a m p l i f i e r , and DR ( d i r e c t r e c o r d i n g ) tape re c o r d e r to record the t o t a l f i e l d s i g n a l at each mobile s t a t i o n . The c a l i b r a t i o n of t h i s system was accomplished by p l a c i n g the antenna i n a s i n u s o i d a l l y - v a r y i n g magnetic f i e l d of known s t r e n g t h and frequency and r e c o r d i n g the subsequent s i g n a l on tape. The c a l i b r a t i o n of the EM mobile system and base CURRENT HARMONICS CALIBRATION CIRCUIT SIGNAL GENERATOR CURRENT PROBE D (AMPLIFYING & RECORDING SYSTEM DC SOURCE GIC CALIBRATION CIRCUIT 0 HALL-EFFECT TRANSDUCER 5 ° I AMPLIFYING & RECORDING SYSTEM . 3.4 Harmonic current and GIC c a l i b r a t i o n c i r c u i t s . 28 s t a t i o n s y s t e m i s f u r t h e r d i s c u s s e d i n s e c t i o n 5 . 2 , a n d a d e t a i l e d d i s c u s s i o n i n c l u d i n g g r a p h i c a l r e s u l t s o f c a l i b r a t i o n i s f o u n d i n A p p e n d i x B . 29 C h a p t e r I V E X P E R I M E N T A L R E S U L T S 4 . 1 G I C s d e t e c t e d i n 5 L 8 2 a t M e r i d i a n S u b s t a t i o n S e c t i o n 3 . 2 d e s c r i b e d a s y s t e m t o m e a s u r e a n d r e c o r d G I C d a t a a n d h a r m o n i c c u r r e n t d a t a . T h e s y s t e m w a s s e t u p a t MDN s u b s t a t i o n t o d e t e c t a n d r e c o r d G I C a n d h a r m o n i c c u r r e n t s a s s o c i a t e d w i t h B . C . H y d r o t r a n s m i s s i o n l i n e 5 L 8 2 . I n t h i s c h a p t e r s p e c i f i c d a t a w i l l b e p r e s e n t e d a n d d i s c u s s e d i n t h e t e x t . T h e t h e o r y f o r t h e o r i g i n o f G I C i n t r a n s m i s s i o n l i n e s w a s p r e s e n t e d i n t h e p r e v i o u s c h a p t e r . T h e e x i s t e n c e o f G I C i n 5 L 8 2 i s s h o w n e x p l i c i t l y i n f i g u r e s 4 . 1 a n d 4 . 2 , w i t h s i m u l t a n e o u s m e a s u r e m e n t s o f t h e c h a n g i n g g e o m a g n e t i c f i e l d i n t h e v i c i n i t y o f 5 L 8 2 . I n f i g u r e 4 . 1 , a m o d e r a t e g e o m a g n e t i c e v e n t ( a b o u t 0 . l 5 y a t a p e r i o d o f 1 5 0 s ) i s r e s p o n s i b l e f o r a G I C l e v e l o f ± 1 A m p . I t i s a l s o c l e a r t h a t i t i s t h e N - S c o m p o n e n t o f t h e g e o m a g n e t i c f i e l d w h i c h i n f l u e n c e s t h e G I C m e a s u r e d i n t h e E - W t r a n s m i s s i o n l i n e . F i g u r e 4 . 2 i s a n o t h e r r e c o r d o f G I C a n d g e o m a g n e t i c f i e l d , t h o u g h t h e g e o m a g n e t i c f i e l d i s r e l a t i v e l y q u i e t d u r i n g t h e t i m e o f m e a s u r e m e n t . N e v e r t h e l e s s , a c u r r e n t o f ± 1 / 8 A m p e x i s t s i n t h e t r a n s m i s s i o n l i n e , d u e t o s m a l l g e o m a g n e t i c f i e l d v a r i a t i o n s . I t i s r e a s o n a b l e t o e x p e c t t h a t a 30 q u a s i - D C c u r r e n t o f a t l e a s t ± 1 t o ± 2 A m p s c o u l d e x i s t i n 5 L 8 2 d u r i n g a g e o m a g n e t i c a l l y a c t i v e p e r i o d , w i t h p o s s i b l e f l u c t u a t i o n s o f s e v e r a l A m p s . 4 . 2 H a r m o n i c C u r r e n t M e a s u r e m e n t s i n M e r i d i a n H a r m o n i c c u r r e n t l e v e l s a s s o c i a t e d w i t h t r a n s m i s s i o n l i n e 5 L 8 2 a r e p r e s e n t e d i n t h i s s e c t i o n . F i g u r e s 4 . 3 ( a ) a n d 4 . 4 ( a ) i n d i c a t e c u r r e n t l e v e l s u p t o t h e 1 1 t h h a r m o n i c i n o n e p h a s e ( A - p h a s e ) o f 5 L 8 2 . F i g u r e s 4 . 3 ( b ) a n d 4 . 4 ( b ) d e p i c t h a r m o n i c c u r r e n t s ( a l s o u p t o t h e 1 1 t h h a r m o n i c ) a t t h e n e u t r a l p o i n t . T h e d a t a i s s h o w n i n t e r m s o f h a r m o n i c s p e c t r a i n f i g u r e s 4 . 3 ( c ) , 4 . 3 ( d ) , 4 . 4 ( c ) , a n d 4 . 4 ( d ) . T o f u l l y u n d e r s t a n d t h e w a y i n w h i c h t h e d a t a i s p r e s e n t e d , t h e f o l l o w i n g i t e m s s h o u l d b e n o t e d : ' ( a ) E a c h t r a c e r e p r e s e n t s t h e c u r r e n t l e v e l ( i n RMS A m p s ) m e a s u r e d a t a p a r t i c u l a r h a r m o n i c f r e q u e n c y , a s a f u n c t i o n o f t i m e ( t h e l a s t t r a c e g i v e s t i m e c o d e i n f o r m a t i o n ) . ( b ) T h e c u r r e n t s t a t e d f o r e a c h h a r m o n i c r e p r e s e n t s t h e c u r r e n t i n 5 L 8 2 . T h a t i s , t h e a c t u a l c u r r e n t m e a s u r e d , w h i c h i s f r o m t h e c u r r e n t t r a n s f o r m e r s , h a s b e e n m u l t i p l i e d b y t h e c o n s t a n t c u r r e n t t r a n s f o r m e r f a c t o r ( 4 0 0 ) . ( c ) E a c h t r a c e i s r e c o r d e d o n a l o g a r i t h m i c a m p l i t u d e s c a l e f o r r e l a t i v e c a l i b r a t i o n . T h e m a j o r d i v i s i o n s c o r r e s p o n d t o a 10 d B c h a n g e i n c u r r e n t , w i t h t h e - 2 0 d B m a r k o n e a c h t r a c e l a b e l l e d o n t h e r i g h t s i d e w i t h t h e c a l i b r a t e d c u r r e n t m e a s u r e m e n t . A n a c c e p t a b l e S / N r a t i o i s i n t h e r a n g e f r o m 0 d B t o - 5 0 d B f o r t h e A - p h a s e s y s t e m ( - 1 0 d B t o - 6 0 d B f o r t h e n e u t r a l c u r r e n t s y s t e m ) . N o t e t h a t a r e l a t i v e d i f f e r e n c e o f 2 0 d B c o r r e s p o n d s t o a f a c t o r t e n i n c u r r e n t ; t h a t i s , a l e v e l o f - 4 0 d B i s 1 / 1 0 t h t h e c u r r e n t o f - 2 0 d B , a n d - 6 0 d B i n d i c a t e s 1 / 1 0 0 t h t h e c u r r e n t o f - 2 0 d B . T h e b a s i s o f t h i s c o n v e n t i o n i s t h a t t h e s i g n a l g i v e n i n d B 31 i s i n f a c t the RMS amplitude of the v o l t a g e s i g n a l recorded on tape, u s i n g the d e f i n i t i o n : dB=201og(V/Vref), where the r e f e r e n c e v o l t a g e Vref=1.0 Vrms. Due to l a c k of space a f u l l c u r r e n t s c a l e on each harmonic i s not i n c l u d e d , however f u l l i n f o r m a t i o n i s a v a i l a b l e with use of the c a l i b r a t i o n c h a r t s (Appendix B). To ensure c l a r i t y i n r e a d i n g the data, r e f e r to f i g u r e 4.5. The convention adopted here i s constant throughout t h i s r e p o r t . (d) The data i s a l s o presented i n the form of harmonic s p e c t r a to give an o v e r a l l view of the r e l a t i o n among harmonic c u r r e n t s . In a d d i t i o n , the f o l l o w i n g i n f o r m a t i o n should be noted i n regard to f i g u r e s 4.3(a), 4.3(b), 4.4(a), and 4.4(b): (f) To save time in p r o c e s s i n g the data, each t r a c e was analyzed i n d i v i d u a l l y at four times r e a l time. T h e r e f o r e the s i g n a l was sampled at 1/4 the r a t e of a c o r r e s p o n d i n g r e a l time s i g n a l , which proved to be s t i l l a l a r g e enough sampling r a t e to a v o i d any l o s s of i n f o r m a t i o n . The data shown i n f i g u r e s 4.4(a) and 4.4(b) cover, a s h o r t e r time segment, however, and thus were analyzed i n r e a l time. (g) Flaws i n the data of f i g u r e s 4.4(a) and 4.4(b), caused by a f a u l t y connector, are designated by markers on the time t r a c e , and do not represent any changes in harmonic c u r r e n t l e v e l . With the preceeding comments in mind, one can look at the data i n terms of harmonic c u r r e n t s t r e n g t h . As d i s c u s s e d i n general terms in s e c t i o n 2.2, only c u r r e n t s t r e n g t h s at odd harmonics ( i n a p a r t i c u l a r phase) should e x i s t , due to n o n - l i n e a r i t i e s i n the h y s t e r e s i s r e l a t i o n s h i p . The data e s t a b l i s h e s the f a c t that odd c u r r e n t harmonics are g e n e r a l l y an order of magnitude stronger than even c u r r e n t harmonics. The r e l a t i v e s t r e n g t h s of odd harmonic c u r r e n t s do not n e c e s s a r i l y decrease with order', as the data shows that the f i f t h or seventh harmonic can be the s t r o n g e s t A-phase harmonic c u r r e n t . 32 The c u r r e n t s t r e n g t h s r e p r e s e n t i n g the n e u t r a l p o s i t i o n are given i n f i g u r e s 4.3(b) and 4.4(b). The l a r g e 60 Hz component i s a measure of the imbalance of the system, s i n c e i t would be zero i f the three phases (A, B, and C) were of equal magnitude. Since only A-phase c u r r e n t was monitored i n a d d i t i o n to the n e u t r a l c u r r e n t , some in f o r m a t i o n on the imbalance i s l o s t . Due to the imbalance of 60 Hz c u r r e n t among the three phases, the n e u t r a l waveform does not c o n s i s t s o l e l y of zero-phase sequence c u r r e n t s . The str o n g e s t n e u t r a l c u r r e n t s occur at f r e q u e n c i e s of 60 Hz, 180 Hz, 300 Hz, and 420 Hz, of which only 180 Hz i s a zero-phase sequence q u a n t i t y . However, s i n c e the n e u t r a l c u r r e n t i s the sum of the c u r r e n t i n the three phases, i t i s e s s e n t i a l l y only zero-phase c u r r e n t s that are stronger i n the n e u t r a l than i n a s i n g l e phase (see t a b l e 4.1). Harmonic A-Phase N e u t r a l A-Phase N e u t r a l Frequency A(rms) A(rms) A(rms) A(rms) 13:39-14:17 LT 13:50-14:15 LT 3/3/81 -11/6/81 60 Hz 800 34.0 880 42.0 1 20 Hz 0.40 1.6 0.40 1 .7 180 Hz 2.2 7.0 4.5 9.8 240 Hz 0.50 0.42 0.32 0.90 300 Hz 7.0 1 .9 3.5 1 .9 360 Hz 0.38 0.6 0.22 0.72 420 Hz 4.6 1 .9 4.6 3.6 480 Hz 0.36 0.42 0.10 0.35 540 Hz 0.45 0.24 0.35 1 . 1 600 Hz 0.45 0.24 0.54 0.20 660 Hz 0.35 0.35 0.22 0.70 Table 4.1 Maximum Harmonic Me r i d i a n S u b s t a t i o n . Current Measurements on 5L82 at 33 The 180 Hz n e u t r a l c u r r e n t s t r e n g t h i s of the order of three times the A-phase 180 Hz c u r r e n t s t r e n g t h , while at 300 Hz and 420 Hz (as w e l l as the fundamental 60 Hz), the n e u t r a l c u r r e n t s t r e n g t h i s l e s s than the A-phase c u r r e n t s t r e n g t h . Other examples of zero-phase c u r r e n t s are 360 Hz and 540 Hz (see f i g u r e s 4.4(a) and 4.4(b) - 11/6/81). The 360 Hz component i n A-phase i s about 0.22 Amps and about 0.72 Amps i n the n e u t r a l . S i m i l a r r e s u l t s f o r 540 Hz show c u r r e n t s of about 0.35 Amps and 1.1 Amps i n A-phase and the n e u t r a l , r e s p e c t i v e l y , i n d i c a t i n g that zero-phase c u r r e n t s tend to i n c r e a s e a f a c t o r of three when summed at the n e u t r a l . However, i t must be noted that c o n s i s t e n t r e s u l t s only occur f o r p a r t i c u l a r harmonic c u r r e n t s whose s t r e n g t h i s g r e a t e r that about 1.0 Amp i n the examples given, or about 0.1 per cent of the s t r e n g t h of the fundamental. The i n c o n s i s t e n t r e s u l t s are most l i k e l y due to i n n a c c u r a c i e s i n d e t e c t i n g and r e c o r d i n g very small c u r r e n t s (a c u r r e n t of 1.0 Amp i n the t r a n s m i s s i o n l i n e i s d e t e c t e d as 2.5 mA due to the 400:1 r a t i o of each c u r r e n t t r a n s f o r m e r ) . The 120 Hz cu r r e n t component appears to be 0.40 Amps i n A-phase and about 1.6 Amps in the n e u t r a l ( f o r both data p e r i o d s ) , though i t i s an even, non-zero phase' c u r r e n t and t h e r e f o r e should be small ( l e s s than 1.0 Amps, f o r example) i n each. The accuracy of the 120 Hz n e u t r a l c u r r e n t values i s q u e s t i o n a b l e f o r t h i s reason, p l u s the f a c t that the values do not c o r r e l a t e with simultaneous AF antenna o b s e r v a t i o n s (see s e c t i o n 5.2). 34 4.3 E f f e c t s of GIC on Harmonic Currents I t was shown i n s e c t i o n 2.2 that the e f f e c t of GIC i n t r a n s m i s s i o n l i n e t r a n s f o r m e r s i s a deformation of the h y s t e r e s i s curve of the trans f o r m e r ' s c o r e . The change to a non-symmetric h y s t e r e s i s curve was shown t o be the source of f l u c t u a t i o n s i n harmonic q u a n t i t i e s , i n p a r t i c u l a r c r e a t i n g even harmonic c u r r e n t s . The data supports the theory that odd harmonics would e x i s t i n sing l e - p h a s e c u r r e n t s . However the data a l s o i n d i c a t e s the e x i s t e n c e of very s m a l l even harmonic c u r r e n t s i r r e s p e c t i v e of GIC a c t i v i t y . P a r t i c u l a r A-phase even harmonic c u r r e n t s are shown i n the the data to be of the order of 0.05% of the 60 Hz c u r r e n t l e v e l . Compared with the content of p a r t i c u l a r odd harmonic c u r r e n t s (up to n e a r l y one per cent of the 60 Hz cu r r e n t l e v e l ) , the even harmonic c u r r e n t s are shown to be exceedingly s m a l l . I t i s only even harmonic c u r r e n t s t h a t are a f f e c t e d by GIC a c t i v i t y , however. A moderate i n c r e a s e in GIC a c t i v i t y (see f i g u r e s 4.1 and 4.3(a)) measured c o n c u r r e n t l y with harmonic c u r r e n t data (13:43 LT, 3 / 3 / 8 1 ) , i s accompanied by f l u c t u a t i o n s i n c e r t a i n even harmonic c u r r e n t s . Note the A-phase 240 Hz harmonic, which i n i t i a l l y r i s e s to about 0.50 Amps, then drops to 0.10 Amps, and subsequently resumes i t s pr e v i o u s l e v e l of about 0.40 Amps as the GIC event passes. Odd harmonic c u r r e n t l e v e l s are u n a f f e c t e d by the GIC event. N e u t r a l c u r r e n t f l u c t u a t i o n s , i n t e r e s t i n g l y enough, were observed to f o l l o w a s l i g h t l y d i f f e r e n t p a t t e r n than harmonic c u r r e n t s i n the A-phase conductor. Odd harmonic c u r r e n t s are not a f f e c t e d , but the f l u c t u a t i o n s i n even harmonic c u r r e n t s due to GIC a c t i v i t y d i f f e r from the A-phase even harmonic components. 35 In the case of the n e u t r a l c u r r e n t , the harmonic most a f f e c t e d i s the 360 Hz component (see f i g u r e 4.3(b)), which f o l l o w s a p a t t e r n of a small i n c r e a s e (to 0.80 Amps) fo l l o w e d by a decrease (to about 0.2 Amps), and a resumption to i t s pre v i o u s l e v e l (0.60 Amps) at the end of the GIC event. The 240 Hz component i n the n e u t r a l c u r r e n t , however, shows no e f f e c t of the GIC event. The apparent i n c o n s i s t e n c y i n these r e s u l t s i s a t t r i b u t a b l e to the low st r e n g t h s of the harmonic c u r r e n t s i n v o l v e d . T h e r e f o r e the zero-phase 360 Hz component i n the n e u t r a l shows an e f f e c t of the GIC event s i n c e i t i s the sum of three s m a l l e r c u r r e n t s ; the 240 Hz n e u t r a l component shows no e f f e c t of the GIC event because, not being a zero-phase c u r r e n t , i t i s very s m a l l i n the n e u t r a l . To conclude t h i s s e c t i o n , i t must be s a i d t h a t , s i n c e only one GIC event, of moderate magnitude, was recorded s i m u l t a n e o u s l y with harmonic c u r r e n t l e v e l s , only a ra t h e r incomplete p i c t u r e can be presented (note that f i g u r e s 4.4(a) and 4.4(b) are harmonic c u r r e n t data recorded d u r i n g a geomagnetically q u i e t time - see f i g u r e 4.4(e)). Obviously much more data of t h i s type would be needed to complete the p i c t u r e and determine the general e f f e c t of GIC's on harmonic c u r r e n t i n a l l three phases of a t r a n s m i s s i o n l i n e . 14=00 L' 3381 F i g . 4.1 E f f e c t o f g e o m a g n e t i c f i e l d o n GIC i n 5L82 (3 M a r c h 1981). B o t t o m t r a c e i s t i m e c o d e . \y at 0.1 UUiiilliJiHiitillkll •^i-i..ii.niii:i)iii WIRIII W l l l l l l 11 If I • M { J f I!!linilTI 'Vaflo ui 5:00 l l F i g . 4.2 Effect of geomagnetic f i e l d on GIC in 5L82 (4 A p r i l 1981). The magnetic f i e l d and GIC scales are the same as in figure 4.1 C O (rms) 60 Hz 120 Hz 180 Hz 240 Hz 300 Hz 360 Hz 420 Hz 480 Hz 540 Hz i i l i . , i u i l . l u u u m ffiltifiJMjjiiD Hii l i i l l iH ; ! ! ! ; ! imi ! i ! i ! ! | ^ ! ! : ! ; ! ! j : H J i ! ! l ! -300 - 9.0 5.5 m m WW-WW !!!!! iiillMliifli ' 1 • • _js4-*+T"f: * •' ' • ill — k f n i . u i f f l t i } H i « miu j in 'H i l i 600 Hz • " " " " j — * 660 Hz m |;!it.il;i:::::::!;:i:!n!rn:m:ffit M. • i a. .2:00 UI 14:00 L1 3-3-81 F i g . 4.3(a) A-phase harmonic c u r r e n t l e v e l s (3 March 1981). On the v e r t i c a l s c a l e , two d i v i s i o n s c o r r e s p o n d t o a f a c t o r ten i n c u r r e n t . Bottom t r a c e i s time code. 60 Hz 120 Hz 180 Hz 540 Hz 600 Hz 660 Hz mm ifitii i iBtlii l i B iiiiii;iiiiiii$iiiiiui«af£«ii>iiaiii« • 14:(in L I 3-3-81 Fig. 4.3(b) N e u t r a l h a r m o n i c c u r r e n t l e v e l s (3 M a r c h 1981). O n t h e v e r t i c a l s c a l e , t w o d i v i s i o n s c o r r e s p o n d t o a f a c t o r t e n i n c u r r e n t . B o t t o m t r a c e i s t i m e c o d e . CO JV1 JV) TV) X X X o o o o CO oo « — « CM JVI JVI X X X X X o o o o o o CO CM CO 00 sr m HARMONIC FREQUENCY X X O O O CO CO CO F i g . 4.3(c) S p e c t r a l r e p r e s e n t a t i o n of data of 4.3(a). 41 F i g . 4.3 (d) S p e c t r a l r e p r e s e n t a t i o n o f d a t a o f 4.3 ( b ) . 60 Hz 120 Hz 180 Hz • i , , , , , , 1 ; ^ ^ ^ ^ " ^ ' ^ ^ W I M W M M M I M f ^ ^ M M J ^ ^ M M | | I H M M ^ ^ 240 Hz fe (rms) -300 -ao -5.5 -4,7 480 Hz 540 Hz 600 Hz 660 Hz 14:00 LT 11-6-81 F i g . 4.4 (a ) A - p h a s e h a r m o n i c c u r r e n t l e v e l s (11 J u n e 1981) O n t h e v e r t i c a l s c a l e , t w o d i v i s i o n s c o r r e s p o n d ' t o a t a c t o r t e n xn c u r r e n t . B o t t o m t r a c e i s t i m e c o d e 1 0 1 (rms) 60 Hz 120 Hz 180 Hz 240 Hz 300 Hz 360 Hz 420 Hz 480 Hz 540 Hz 600 Hz 660 Hz i 111 ij weak 21:00 UT| 14:00 LT n-G-81 F i g . 4.4 (b) N e u t r a l h a r m o n i c c u r r e n t l e v e l s (11 J u n e 1 9 8 1 ) . O n t h e v e r t i c a l s c a l e , t w o d i v i s i o n s c o r r e s p o n d t o a f a c t o r t e n i n c u r r e n t . B o t t o m t r a c e i s t i m e c o d e . 44 F i g . 4.4(c) S p e c t r a l r e p r e s e n t a t i o n of data of 4.4(a) 45 F i g . 4.4(d) Spectral representation of data of 4.4(b). F i g . 4.4(e) Geomagnetic f i e l d d u r i n g c u r r e n t harmonic measurements of 4.4(a) and 4.4(b), (11 June 1981). CTl HARMONIC FREQUENCY H—I—I—I—l-H—r—i —i—I—I—h I I I I I I I I I I I I I I I I I I I J . : : I. H I 1 TTTT-!:|iH= . . . . . . . . i::: i n : rff! TTTT|TTTT - I T T ' m$ ^ H l ! iijipnjHiilili! : : i : TTTT :HI : :i r m TTTT iiiuirmi :fnf:TT! ;;;;):•: I-" " ; -Iii! !: J: ::;T:::I LfiAC • - frr . : : i : : : : : - i i :n ITTTT i i m$ I i i i i l i i r l ; i : • iii; wvU " T " " i . ] ] " : : • : t : III! i i l i i i i : : 1 ! " •; ] :;: : :i • • ' : ........ -i —t • • • : • • : : . . : : : ; [ : ' : : I - 20 dB - 30 dB - 4 0 dB - 50 dB - 60dB - 70dB REFER TO CALIBRATION CHARTS (APPENDIX B) FOR dB - Amps CONVERSION F i g . 4.5 C o r r e s p o n d e n c e o f r e l a t i v e v a l u e s a n d c u r r e n t c a l i b r a t i o n . 48 Chapter V EM SURVEY: EXPERIMENT AND RESULTS 5.1 I n t r o d u c t i o n to EM Experiment The p r o p e r t i e s of a g e n e r a l method of EM e x p l o r a t i o n can be s t u d i e d i n terms of a set of mutually i n d u c t i v e c o i l s , denoted primary c o i l , r e c e i v e r c o i l , and secondary c o i l (as d i s c u s s e d i n Chapter 1). The c u r r e n t chapter d e s c r i b e s the experimental methods and r e s u l t s of an EM reconnaissance survey i n which a h i g h - v o l t a g e t r a n s m i s s i o n l i n e i s used as the source of the primary f i e l d . Suggestions f o r f u r t h e r work to improve the experimental method w i l l be d i s c u s s e d w i t h i n the chapter, which concludes by suggesting a g e o l o g i c i n t e r p r e t a t i o n of the r e s u l t s of the EM survey. The prime o b j e c t i v e of any EM technique i s to determine s p a t i a l changes i n the secondary f i e l d through measurements of the t o t a l f i e l d . O b v iously something must be known about the primary f i e l d , g e n e r a l l y a f u n c t i o n of both space and time. Most EM methods f a l l i n t o two c a t e g o r i e s : f o r remote source methods such as AFMAG and VLF, the primary f i e l d i s c o n s i d e r e d s p a t i a l l y uniform, and time v a r i a t i o n s are monitored as a r e f e r e n c e s i g n a l . For c o n t r o l l e d source methods such as h o r i z o n t a l loop, v e r t i c a l antenna, and long wire, the source of the primary f i e l d 49 i s w e l l c o n t r o l l e d a t t h e t r a n s m i t t e r . T h e p r i m a r y f i e l d c a n t h e n b e c a l c u l a t e d a s a f u n c t i o n o f s p a t i a l c o o r d i n a t e s o n l y . T h e m e t h o d s m e n t i o n e d h e r e s u c c e e d i n m a k i n g t h e p r i m a r y f i e l d a f u n c t i o n o f t i m e o r s p a t i a l c o o r d i n a t e s o n l y , w h i c h s i m p l i f i e s a n a l y s i s o f t h e d a t a . T h e u s e o f a c o m m e r c i a l h i g h - v o l t a g e t r a n s m i s s i o n l i n e a s a n E M s o u r c e h a s t h e a d v a n t a g e o f a r e m o t e s o u r c e t e c h n i q u e , b e i n g a f a s t , i n e x p e n s i v e r e c o n n a i s s a n c e m e t h o d . I n a d d i t i o n t h e s o u r c e c o n s i s t s o f a n u m b e r o f d i s c r e t e f r e q u e n c i e s i n t h e l o w e r A F r a n g e ( 6 0 H z - 1 K H z ) . H o w e v e r , a d i s a d v a n t a g e l i e s i n t h e f a c t t h a t t h e p r i m a r y f i e l d o f t h i s s o u r c e i s b o t h s p a t i a l l y a n d t i m e d e p e n d a n t , m a k i n g d a t a a n a l y s i s m o r e d i f f i c u l t . F o r t h i s i n t r o d u c t o r y s t u d y , m u c h o f t h e q u a n t i t a t i v e a n a l y s i s w i l l b e s p e n t i n a d e t e r m i n a t i o n o f t h e p r i m a r y f i e l d . E x p e r i m e n t a l r e s u l t s s h o w i n g t h e e f f e c t s o f t h e s e c o n d a r y f i e l d w i l l b e p r e s e n t e d , a s w e l l a s s u g g e s t i o n s f o r f u r t h e r w o r k t o i m p r o v e t h e m e t h o d . 5 . 2 P r e l i m i n a r y E x p e r i m e n t a n d A p p a r a t u s P r i o r t o t h e m a j o r s u r v e y o f 66 m o b i l e s t a t i o n s i n 1 9 8 1 , m u c h w o r k w a s d o n e t o f i e l d t e s t t h e a p p a r a t u s a n d e n s u r e t h a t t r a n s m i s s i o n l i n e 5 L 8 2 w a s t h e s o u r c e o f t h e p r i m a r y f i e l d d e t e c t e d b y t h e r e c e i v e r ( s e e f i g u r e 5 . 1 f o r t h e l o c a t i o n o f r e c e i v e r s t a t i o n s w i t h i n t h e s u r v e y a r e a ) . T h e f i r s t e x p e r i m e n t w a s d o n e i n 1 9 7 9 i n w h i c h t h e a m p l i t u d e o f t h e 180 H z v e r t i c a l c o m p o n e n t w a s m e a s u r e d a t n i n e s t a t i o n s t h r o u g h o u t t h e s u r v e y a r e a ( W a t a n a b e e t a l . , 1 9 8 1 ) . T h e r e s u l t s o f t h i s w o r k i n d i c a t e d a t o t a l f i e l d s t r e n g t h - d i s t a n c e r e l a t i o n o f l / r u p t o a d i s t a n c e 50 o f a b o u t e i g h t km f r o m 5 L 8 2 . T h e e n c o u r a g i n g r e s u l t s o f t h e 1 9 7 9 w o r k s p u r r e d i n t e r e s t i n t h e s u b j e c t o f t r a n s m i s s i o n l i n e s a s a n E M s o u r c e , a n d s e r v e d a s a n i m p e t u s f o r f u r t h e r w o r k e x p r e s s e d b y t h i s t h e s i s . A s u r v e y d o n e i n 1 9 8 0 a s p a r t o f t h i s t h e s i s e x p a n d e d o n t h e w o r k d o n e t h e y e a r b e f o r e . T h e e x p e r i m e n t a l t e c h n i q u e w a s i m p r o v e d b y r e c o r d i n g t h e s i g n a l o n t a p e t o m o n i t o r a l l h a r m o n i c f r e q u e n c i e s p r o v i d e d b y t h e s o u r c e . M o b i l e r e c e i v e r m e a s u r e m e n t s w e r e m a d e a t 13 s t a t i o n s w i t h i n t h e s u r v e y a r e a , i n c l u d i n g t h e n i n e s t a t i o n s o f t h e 1 9 7 9 s u r v e y . F u r t h e r i m p r o v e m e n t s i n t h e 1981 s u r v e y i n c l u d e d s i m u l t a n e o u s m e a s u r e m e n t s o f t h e A F b a s e s t a t i o n s i g n a l a n d c u r r e n t l e v e l s i n 5 L 8 2 , a n d a n e x t e n s i v e s u r v e y o f 66 m o b i l e s t a t i o n s ( i n c l u d i n g t h e 13 s t a t i o n s o f t h e 1 9 8 0 s u r v e y ) . F r o m t h e d a t a s h o w n i n f i g u r e 5 . 2 ( r e s u l t s o f t h r e e s u r v e y s , u s i n g 180 H z , i n 1 9 7 9 , 1 9 8 0 , a n d 1 9 8 1 ) , t h e f o l l o w i n g p o i n t s s h o u l d b e n o t e d : ( i ) t h e g e n e r a l 1 / r t r e n d o f t h e d a t a ( t h r e e t y p e c u r v e s a r e g i v e n ; 1 / r , 1 / r 2 , 1 / r 3 ; ( i i ) t h e g o o d r e p r o d u c i b i l i t y o f t h e d a t a o v e r t h e t h r e e y e a r p e r i o d ; a n d ( i i i ) t h e m e a s u r e m e n t s i n t h e A l o u e t t e L a k e r e g i o n ( n u m b e r s 10 a n d 1 1 ) , d o n o t f i t t h e g e n e r a l 1 / r t r e n d ( f o r t w o y e a r s o f d a t a a v a i l a b l e , 1 9 8 0 a n d 1981). I n a d d i t i o n , t h e ' b a s e s t a t i o n d a t a p l a y e d a m o r e i m p o r t a n t r o l e i n t h e 1981 s u r v e y . I n t h e t w o p r e v i o u s y e a r s , b a s e s t a t i o n d a t a w a s u s e d t o s h o w t h a t t h e s o u r c e s t r e n g t h v a r i e d b y l e s s t h a t ± 1 0 % o v e r t h e d u r a t i o n o f t h e s u r v e y , a n d t h e m o b i l e s t a t i o n d a t a w a s p l o t t e d d i r e c t l y . T h e 1981 s u r v e y - w a s m u c h m o r e e x t e n s i v e , t h e r e f o r e t h e m e a s u r e m e n t a t e a c h m o b i l e s t a t i o n w a s w e i g h t e d w i t h t h e b a s e s t a t i o n r e a d i n g f o r t h e s a m e t i m e f o r e a c h p a r t i c u l a r f r e q u e n c y , 51 Fig. 5.1 Location of mobile receiver stations within survey area. i 52 F i g . 5.2 R e s u l t s of three surveys (1979, 80, 81) to show 1/r dependance of t o t a l f i e l d s t r e n g t h and r e p r o d u c i b i l i t y of r e s u l t s . 53 i n c r e a s i n g the accuracy of the measurements. I t i s t h i s method of a n a l y s i s i n which the mobile r e c e i v e r measurement of the v e r t i c a l component at a p a r t i c u l a r frequency i s d i v i d e d by the simultaneous base s t a t i o n measurement (at the same frequency) that h e l p s e l i m i n a t e the time dependance of the primary f i e l d . The f a c t that a 1/r curve c l o s e l y f i t s the data ( i n which the b a s e l i n e c o i n c i d e s with the t r a n s m i s s i o n l i n e ) s t r o n g l y suggests t h a t the s p a t i a l v a r i a t i o n s of the primary f i e l d are caused by 5L82. A f u r t h e r t e s t was done to ensure time v a r i a t i o n s i n the t o t a l f i e l d are caused by time v a r i a t i o n s of the c u r r e n t i n 5L82. To accomplish t h i s , measurements of the n e u t r a l c u r r e n t a t MDN were made si m u l t a n e o u s l y with measurements of the AF s i g n a l at the base s t a t i o n . F i g u r e 5.3(a) i s base s t a t i o n AF data recorded simultaneously with M e r i d i a n n e u t r a l c u r r e n t data ( f i g u r e 4.3(b)), and f i g u r e 5.4(a) i s a l s o AF data recorded s i m u l t a n e o u s l y with n e u t r a l c u r r e n t data ( f i g u r e 4 .4(b)). For comparison purposes, r e l a t i v e s p e c t r a l r e p r e s e n t a t i o n s of the data are presented i n f i g u r e s 5.3(b) and 5.4(b). The n e u t r a l c u r r e n t data has been normalized so that the 180 Hz n e u t r a l c u r r e n t component i s 1.0. S i m i l a r l y , the AF s i g n a l recorded on tape has been normalized r e l a t i v e to a 180 Hz component value of 1.0. In t h i s way a r e l a t i v e comparison of the magnitudes of the harmonics of the two s i g n a l s can be made, which c l e a r l y shows that the AF s i g n a l r e c e i v e d at the base s t a t i o n i s p r i m a r i l y the induced e f f e c t of the " n e u t r a l " c u r r e n t in 5L82. The r e l a t i v e amplitudes of the stronger .components (60 Hz, 180 Hz, 300 Hz, and 420 Hz) of the two se t s of data show a d i s t i n c t c o r r e l a t i o n . The other f r e q u e n c i e s , much smal l e r i n 54 a m p l i t u d e , a r e m o r e a f f e c t e d b y n o i s e , h e n c e s h o w l e s s c o r r e l a t i o n . A s f i r s t s t a t e d i n s e c t i o n 4 . 2 , t h e 120 H z c o m p o n e n t d o e s n o t c o r r e l a t e w e l l b e t w e e n t h e t w o s i g n a l s . T h e 120 H z A F c o m p o n e n t i s m u c h s m a l l e r t h a n w o u l d b e e x p e c t e d f r o m l o o k i n g a t t h e 120 H z n e u t r a l c o m p o n e n t . T h i s , i n a d d i t i o n t o t h e f a c t t h a t t h e 120 H z c o m p o n e n t i s a n o n - z e r o p h a s e c u r r e n t a n d w a s m e a s u r e d t o b e s m a l l i n A - p h a s e , s h e d s s o m e d o u b t o n t h e v a l i d i t y o f t h e m e a s u r e m e n t s o f t h e 120 H z n e u t r a l c u r r e n t c o m p o n e n t . H o w e v e r , i n a d d i t i o n t o t h e g e n e r a l s i m i l a r i t i e s b e t w e e n t h e s p e c t r a o f t h e t w o s i g n a l s , n o t e t h e c h a n g e i n t h e 3 6 0 H z n e u t r a l c u r r e n t c o m p o n e n t a t MDN ( d u e t o a G I C e v e n t - f i g u r e 4 . 3 ( b ) ) . T h e s a m e e f f e c t i s s e e n i n t h e A F s i g n a l ( f i g u r e 5 . 3 ( a ) ) , w h i c h i s s t r o n g s u p p o r t f o r s a y i n g t h e o r i g i n o f t h e A F s i g n a l a t t h e b a s e s t a t i o n i s t h e s u m o f t h e t h r e e p h a s e s ( n e u t r a l c u r r e n t ) i n 5 L 8 2 . T h e c o r r e l a t i o n b e t w e e n t h e n e u t r a l c u r r e n t s i g n a l a t MDN a n d t h e A F s i g n a l a t t h e b a s e s t a t i o n d o e s n o t e n s u r e t h a t a n y A F s i g n a l m e a s u r e d t h r o u g h o u t t h e s u r v e y a r e a w o u l d s h o w t h e s a m e c o r r e l a t i o n o f d a t a , h o w e v e r . I t w o u l d b e h i g h l y i m p r a c t i c a l t o t r y t o e x p e r i m e n t a l l y s h o w c o r r e l a t i o n o f t h e t w o s i g n a l s t h r o u g h o u t t h e s u r v e y a r e a ; h o w e v e r t h e t w o t e s t s d i s c u s s e d h e r e ( d e t e r m i n a t i o n o f 1 / r r e l a t i o n a n d t i m e c o r r e l a t i o n o f n e u t r a l c u r r e n t a n d A F s i g n a l ) a r e s t r o n g l y s u p p o r t i v e o f t h e h y p o t h e s i s t h a t t h e c u r r e n t i n 5L82 i s t h e o n l y s o u r c e o f t h e p r i m a r y A F m a g n e t i c f i e l d i n t h e s u r v e y a r e a ( o b v i o u s l y i g n o r i n g n a t u r a l A F e m m i s s i o n s ; p r e s u m a b l y t h e s e w o u l d b e n e g l i g i b l e a n d , i f n o t , w o u l d b e s e e n i n t h e b a s e s t a t i o n d a t a ) . 6C Hz ~ 120 Hz 180 Hz 240 Hz 300 Hz 360 Hz 420 Hz 480 Hz 540 Hz 600 Hz 660 Hz 1|!f!; ::,ti:\:::±';ir^ ~ -50 - 13 Ii T| i im ] i ' i " ' :n : ' i I i :n - u' i n i r n' J n n n 11 r mjn i' i in — " I ' m w i tmm m mmm mmm w <j 5 5 - i i I !• i. ; ! ; ? 2 : 0 0 UT : ! • ;: 14:00 Lf 3-381 F i g . 5.3(a) AF-measurements at base s t a t i o n (3 March 1981). Compare with f i g u r e 4.3(b). On the v e r t i c a l s c a l e , two d i v i s i o n s correspond to a f a c t o r ten i n magnetic f i e l d . oi 56 X X X X X X X X X X X o o o o o o o o g o o — » N . n n « ^ in to io HARMONIC FREQUENCY F i g . 5.3(b) S p e c t r a l r e p r e s e n t a t i o n of simultaneous n e u t r a l c u r r e n t s i g n a l (top) and base s t a t i o n AF s i g n a l (bottom) (3/3/81). a) AF-measurements at base s t a t i o n (11 June 1981) Compare with f i g u r e 4.4(b). On the v e r t i c a l s c a l e * two d i v i s i o n s c orrespond to a f a c t o r ten i n magnetic f i e l d . The o r i g i n of the i n c r e a s e d n o i s e i n these t r a c e s i s unknown. OB to X X X X X X X X X X r o CO o fM O CO 9 rsi o o ro o to ro o fM o i 3 in o o CO a (O CO HARMONIC FREQUENCY 10 HARMONIC FREQUENCY F i g . 5.4(b) Spectral representation of current signal (top) and (bottom) (11/6/81). simultaneous base sta t i o n neutral AF signal 59 The base station for the EM survey i s the same as that used in the study of harmonic currents and GIC in transmission l i n e 5L82 (chapters 3 and 4), located 350 m from 5L82. The designs of the base station receiver and mobile station receiver are sim i l a r , consisting of a loop antenna followed by an amplifier which i s connected to a DR tape recorder. Time information (radio station WWV) i s recorded audibly on the mobile station tape recorder, and through FM pulses on the base station tape recorder (from radio station WWVB). In addition, as in most EM surveys, a magnetometer was used to monitor geomagnetic f i e l d condit ions. As discussed previously (in section 3.3), the mobile receiver system was c a l i b r a t e d by placing the antenna in a sinu s o i d a l l y varying magnetic f i e l d of known magnitude and frequency, and recording the subsequent amplified signal on tape (see Appendix B for a schematic diagram of the apparatus and a detailed discussion of c a l i b r a t i o n procedures). The recorded c a l i b r a t i o n signal i s then played back through the spectrum analyzer in the same manner the f i e l d data i s analyzed. Thus the recorded signal strength/magnetic f i e l d magnitude rel a t i o n i s known as a function of frequency over the band of interest (60 Hz - 1 KHz). Spectral analysis of both the mobile and base station data consists of feeding the signal into an analog-input spectrum analyzer, on which the controls are set to sample the signal 64 times, which takes the spectrum analyzer 18 seconds. Therefore each sample i s 0.281 seconds, or about 16 cycles of the fundamental frequency, and the spectrum of 64 consecutive samples i s averaged to give the f i n a l output. This analysis i s 60 a p p l i e d to both mobile s t a t i o n data and base s t a t i o n data f o r  the same 18 second p e r i o d to give a time-averaged value f o r each mobile s t a t i o n , t a k i n g i n t o account time v a r i a t i o n of the primary f i e l d . 5.3 R e s u l t s of the 1981 Survey On the b a s i s of the r e s u l t s of the surveys done in 1979 and 1980, a more e x t e n s i v e survey u s i n g 5L82 as a source was completed i n 1981. As s t a t e d i n the p r e v i o u s s e c t i o n , the s i g n a l recorded at each s t a t i o n was played back i n the l a b through a spectrum a n a l y z e r . The four s t r o n g e s t frequency components, co r r e s p o n d i n g to the four s t r o n g e s t harmonic c u r r e n t components i n the n e u t r a l of 5L82, were used i n the i n t e r p r e t a t i o n . The three harmonics (180 Hz, 300 Hz, 420 Hz) p l u s the fundamental (60 Hz) have been shown in p r e v i o u s chapters to be the s t r o n g e s t and most s t a b l e to use. For each frequency, the data r e p r e s e n t s the r a t i o of the v e r t i c a l component at each s t a t i o n to the simultaneous v e r t i c a l component at the base s t a t i o n . The data i s normalized so the measurement at the base s t a t i o n equals 1.0 (note the base s t a t i o n a l s o served as one of the mobile r e c e i v e r s t a t i o n s ) . The r e s u l t a n t data i s shown in f i g u r e s 5 . 5 ( a ) , ( b ) , ( c ) , and ( d ) . Concerning the data presented i n f i g u r e 5.5, the f o l l o w i n g should be noted: 61 (a) The area represented by each f i g u r e i s the same as that i n f i g u r e 5.1, and has been r e f e r r e d t o i n t h i s work as the "survey a r e a . " (b) The l o c a t i o n of mobile r e c e i v e r s t a t i o n s i s l a r g e l y due to a c c e s s i b i l i t y i n the mountainous t e r r a i n of the survey area. Regions with few or no measurements i n d i c a t e an i n a c c e s s i b l e a r e a . Based on the r e s u l t s of the smaller s c a l e survey done i n 1980, the d e n s i t y of s t a t i o n s was i n c r e a s e d i n the Jacobs Lake area and i n the region near A l o u e t t e Lake. (c) A n t i c i p a t i n g the 1/r r e l a t i o n shown i n the 1979 and 1980 data, the contours are spaced at i n t e r v a l s of 1/n, n an i n t e g e r from 2 to 50. A d e t a i l e d d e s c r i p t i o n of the manner in which the data was determined and contoured i s given i n Appendix C. 5.4 A n a l y s i s and I n t e r p r e t a t i o n The b a s i s of an i n t e r p r e t i v e a n a l y s i s of the data c o n s i s t s of determining the c o n f i d e n c e of the r e s u l t s , d e s c r i b i n g known e f f e c t s , and i n v e s t i g a t i n g f u r t h e r any unexplained r e s u l t s . To study known e f f e c t s on the data, f i g u r e 5.6 i s presented as a " r e f e r e n c e f i e l d . " The r e f e r e n c e f i e l d i s the c a l c u l a t e d v e r t i c a l f i e l d component due to the c u r r e n t source alone. The t h e o r e t i c a l approach to o b t a i n i n g the r e f e r e n c e f i e l d c o n s i s t s of u s i ng the B i o t - S a v a r t law f o r summing f i n i t e - l e n g t h c u r r e n t elements i n f r e e space. The geometry of the f i n i t e - l e n g t h c u r r e n t elements simulates the l a y o u t of t r a n s m i s s i o n l i n e 5L82 (from M e r i d i a n s u b s t a t i o n i n the west to about 30 km east of the base s t a t i o n ) , and f i g u r e 5.6 r e p r e s e n t s the survey area used i n the experimental work. The contours are s e t to values of 1/n (n an i n t e g e r ) , with the value of the p o i n t corresponding to 62 the base station normalized to 1.0 (that i s , the reference f i e l d i s presented in the same manner as the data to aid int e r p r e t a t i o n ) . Thus the reference f i e l d presented here represents the normalized primary f i e l d in the survey area due to transmission l i n e 5L82. From the data presented in figure 5.5, i t i s clear that the general trend of the contours i s similar to that of the reference f i e l d . However, aspects of the data which cannot be attributed to the geomenty of 5L82 are seen as i r r e g u l a r i t i e s in the contours of the data, and exist in three regions in the survey area: (a) The Alouette Lake region; (b) The Jacobs Lake region; (c) The northwestern part of the survey area. 63 F i g . 5.5(a) EM survey contoured data - 60 Hz. 64 65 F ig . 5.5(c) EM survey contoured data - 300 Hz. F i g . 5.5(d) EM survey contoured data - 420 Hz. 67 68 T h e d a t a c l e a r l y s h o w s t h a t t h e e x p e r i m e n t a l l y m e a s u r e d t o t a l f i e l d d i f f e r s f r o m t h e r e f e r e n c e f i e l d i n t h e t h r e e r e g i o n s j u s t m e n t i o n e d , f o r a l l f o u r f r e q u e n c i e s u s e d i n t h e s u r v e y . T h e e f f e c t s s h o w n i n t h e d a t a a r e t h e r e s u l t o f a c o m b i n a t i o n o f t h e f o l l o w i n g : ( a ) p o s s i b l e s y s t e m a t i c e f f e c t s o n t h e d a t a w h i c h h a v e n o t b e e n d e t e r m i n e d ; ( b ) r a n d o m e r r o r i n m e a s u r i n g a n d d e t e r m i n i n g t h e o b s e r v e d t o t a l f i e l d ; ( c ) s e c o n d a r y f i e l d e f f e c t s d u e t o t h e c o n d u c t i v e s t r u c t u r e s o f t h e e a r t h . T h e e f f e c t o f t h e g e o m e t r y o f 5 L 8 2 h a s b e e n s h o w n t o p r o d u c e t h e g e n e r a l t r e n d o f t h e c o n t o u r s o f t h e d a t a , f o l l o w i n g t h e c o n f i g u r a t i o n o f t h e t r a n s m i s s i o n l i n e , a s w o u l d b e e x p e c t e d . H o w e v e r t h e p o s s i b i l i t y o f o t h e r p o w e r l i n e s i n t h e r e g i o n s y s t e m a t i c a l l y i n f l u e n c i n g t h e t o t a l f i e l d m e a s u r e m e n t s m u s t b e e x a m i n e d . T h e s u r v e y a r e a w a s c h o s e n b e c a u s e o f i t s i s o l a t i o n f r o m s o u r c e s o t h e r t h a n 5 L 8 2 , b u t f i g u r e 3 . 1 s h o w s o t h e r p o w e r l i n e s d o e x i s t i n t h e r e g i o n . A s e t o f t h r e e 60 K V l i n e s r u n i n a n E a s t - W e s t d i r e c t i o n a b o u t 3 km t o t h e s o u t h o f 5 L 8 2 ; a l i n e r u n s n o r t h w a r d f r o m M e r i d i a n S u b s t a t i o n , p e r p e n d i c u l a r t o 5 L 8 2 , a b o u t 16 km f r o m t h e w e s t e r n e d g e o f t h e s u r v e y a r e a ; a n o t h e r N o r t h - S o u t h l i n e e x i s t s a b o u t 10 km f r o m t h e e a s t e r n e d g e o f t h e s u r v e y a r e a ; a n d f i n a l l y t h e o n l y p o w e r l i n e w i t h i n t h e s u r v e y a r e a i s a l o n g t h e s o u t h w e s t e r n e d g e , a n d i s a s m a l l l o c a l l i n e s u p p l y i n g p o w e r t o a c a m p n e a r L o o n L a k e . E x p e r i m e n t a l w o r k f o u n d t h a t t h e s i g n a l f r o m t h e l o c a l l i n e w i t h i n t h e s u r v e y a r e a w a s o n l y d i s t i n g u i s h a b l e f r o m t h e 5 L 8 2 s i g n a l t o a p e r p e n d i c u l a r d i s t a n c e o f 2 0 0 m . A m o b i l e r e c e i v e r 69 s t a t i o n was employed at a p o i n t 200 m from the l o c a l power l i n e , but the data from t h i s s t a t i o n was d i s c a r d e d i n any case. The c l o s e s t r e c e i v e r s t a t i o n from which data was o b t a i n e d i s about 750 m from the l o c a l l i n e , and the data from t h i s s t a t i o n f i t s w e l l w i t h i n the general t r e n d and i s not w i t h i n one of the three r e g i o n s of i n t e r e s t d i s c u s s e d p r e v i o u s l y . In r e f e r e n c e to the other power l i n e s i n the r e g i o n , i t i s not known what power or c u r r e n t i s c a r r i e d , hence the e f f e c t on the primary f i e l d w i t h i n the survey area cannot be c a l c u l a t e d . However i t i s most u n l i k e l y that the l o c a l i z e d r e g i o n s of i n t e r e s t i n the data of the survey area are due to f i e l d s produced by other power l i n e s i n the r e g i o n . That i s , the f a c t that the g e n e r a l t r e n d of the data f o l l o w s that shown by the r e f e r e n c e f i e l d s t r o n g l y i m p l i e s that 5L82 i s the s o l e source of the primary f i e l d w i t h i n the survey area. Another source of systematic e r r o r i n the data i s e x h i b i t e d by the f a c t that the h o r i z o n t a l l y - p l a c e d r e c e i v e r antenna may not be i n the plane of the t r a n s m i s s i o n l i n e . T h i s i s e s s e n t i a l l y an e l e v a t i o n , or c o s i n e e r r o r . That i s , i f the e l e v a t i o n of the r e c e i v i n g s t a t i o n d i f f e r s from the e l e v a t i o n of 5L82, an e r r o r i n determining the magnitude of the v e r t i c a l component i s i n t r o d u c e d . The e r r o r f a c t o r i s determined by the c o s i n e of the angle between the h o r i z o n t a l and the d i r e c t i o n of 5L82. For example, i f a s t a t i o n i s 1 km from 5L82, and the d i f f e r e n c e i n e l e v a t i o n between 5L82 and the mobile s t a t i o n i s 100 m, then the c o s i n e f a c t o r would be 0.995. In a d d i t i o n , 5L82 does not l i e i n a h o r i z o n t a l plane, but f o l l o w s the r e l i e f of the t e r r a i n upon which i t was b u i l t . As s t a t e d p r e v i o u s l y , the 70 data suggests that the systematic e f f e c t s on the data presented here are e s s e n t i a l l y n e g l i g i b l e to w i t h i n the accuracy of the experiment. To r e f i n e the proposed method, i t i s c l e a r l y p o s s i b l e to e x p e r i m e n t a l l y determine the e f f e c t of other power l i n e s (by measuring the c u r r e n t i n the l i n e i t s e l f , or the t o t a l f i e l d c l o s e to the other l i n e ) . A l s o , the other systematic procedures c o u l d be taken i n t o account by i n c l u d i n g the c o s i n e f a c t o r i n mobile s t a t i o n measurements, and by determining a r e f e r e n c e f i e l d i n which the t h r e e - d i m e n s i o n a l c o n f i g u r a t i o n of the source i s taken i n t o account i n the f i n i t e c u r r e n t element technique. The p r e v i o u s d i s c u s s i o n i s meant to show that the v a r i a t i o n s i n the data i n the three regions of i n t e r e s t are not due to a systematic e r r o r i n v o l v e d i n the i n t e r p r e t a t i o n . The f o l l o w i n g d i s c u s s i o n w i l l p o i n t out sources of random e r r o r , and i n d i c a t e the magnitude of these e r r o r s . The main source of random e r r o r i n t h i s experiment l i e s i n the apparatus used to r e c o r d and analyze the data. Both mobile r e c e i v e r s i g n a l s and base s t a t i o n s i g n a l s were recorded on audio-frequency tape. The main problems with d i r e c t r e c o r d i n g are a l i m i t e d v o l t a g e range and imperfect amplitude r e p r o d u c t i o n . The four f r e q u e n c i e s used here f a l l w i t h i n an a c c e p t a b l e range of about 33 dB (60 Hz l a r g e s t , 300 Hz s m a l l e s t ) . However amplitude r e p r o d u c t i o n i s l i m i t e d , determined e x p e r i m e n t a l l y , to l e s s than ± 0 . 5 dB, or about ±5% of the s i g n a l . Since each data p o i n t c o n s i s t s of the mobile r e c e i v e r reading d i v i d e d by the base s t a t i o n reading (each with ±5% random e r r o r ) , a maximum random e r r o r of ±10% i s a s s i g n e d to each data p o i n t , u s i n g the method of Topping (1966, p. 17) f o r 71 e r r o r e s t i m a t i o n : e =mobile r e c e i v e r e r r o r m €. =base s t a t i o n e r r o r D € =maximum random e r r o r 1 f o r each data p o i n t = le I + le I = 10% The e r r o r i s a l s o shown g r a p h i c a l l y i n the c a l i b r a t i o n of the mobile r e c e i v e r system, i n Appendix B. For f u r t h e r work, i t i s t h i s method of r e c o r d i n g the data that c o u l d be g r e a t l y improved. An FM r e c o r d i n g d e v ice would improve the accuracy of the amplitude measurements. A l s o , a system which d e t e c t s the amplitude of the s p e c i f i c f r e q u e n c i e s and g i v e s a d i g i t a l readout would i n c r e a s e the c o n f i d e n c e of the r e s u l t s by d e c r e a s i n g a s s o c i a t e d random e r r o r . In a d d i t i o n , i t would be most f e a s i b l e to repeat some f i e l d measurements du r i n g the same survey; that i s , c e r t a i n survey l i n e s arranged in a g r i d p a t t e r n c o u l d be t r a v e r s e d once in each d i r e c t i o n ( p e r p e n d i c u l a r to the l i n e s o u r c e ) , again to i n c r e a s e the c o n f i d e n c e of the r e s u l t s . T h i s i s , i n f a c t , common in some commercial g e o p h y s i c a l surveys. To g r a p h i c a l l y show the random e r r o r i n v o l v e d i n the data, a set of two p r o f i l e s were taken, in which the data i s p l o t t e d a g a i n s t the d i s t a n c e from the source. The two p r o f i l e l o c a t i o n s are shown i n f i g u r e 5.7. The a m p l i t u d e - d i s t a n c e r e l a t i o n s are p l o t t e d l i n e a r l y i n f i g u r e s 5.8(a) and 5.9(a), and on a l o g - l o g s c a l e i n f i g u r e s 5.8(b) and 5.9(b) (with e r r o r bars i n d i c a t i n g the ±10% e r r o r a s s o c i a t e d with the data p o i n t s ) . 72 F i g . 5.7 P r o f i l e l o c a t i o n s . Distances are determined from the p r o f i l e - b a s e l i n e i n t e r s e c t i o n and are marked along the r e s p e c t i v e p r o f i l e i n 1 km i n t e r v a l s . The b a s e l i n e i s e q u i v a l e n t to the t r a n s m i s s i o n l i n e (5L82) source. 74 0 01 4 1 1 1 1 1 1 T ' I 1 1 . 1 1 I.I.—l - -• t , i ,— 0 1 10 10 ' ;i io DISTANCE FROM SOURCE (km) Ol STANCE FROM SOURCE (km) F i g , 5.8 (b) P r o f i l e d d a t a - S e c t i o n A-B. 76 DISTANCE FROM SOURCE (km) DISTANCE FROM SOURCE (km) DISTANCE FROM SOURCE (km) ' DISTANCE FROM SOURCE (km) F i g . 5.9(b) P r o f i l e d data - Section C-D. 77 T h e i n t e n t o f p r e s e n t i n g t h e d a t a i n p r o f i l e i s t o b e t t e r s h o w t h e e f f e c t o f t h e s e c o n d a r y f i e l d i n t h e m e a s u r e d v e r t i c a l t o t a l f i e l d . I n a r e c o n n a i s s a n c e i n t e r p r e t a t i o n , t h e d a t a s h o w s t h r e e r e g i o n s o f i n t e r e s t , a s s e e n i n t h e c o n t o u r e d d a t a m a p s a n d s t a t e d p r e v i o u s l y i n t h i s s e c t i o n . T h e p r o f i l e d a t a , o f c o u r s e , s h o w t h e s a m e e f f e c t s . P r o f i l e A - B e x t e n d s f r o m t h e b a s e l i n e ( 5 L 8 2 ) n o r t h w a r d t o t h e e d g e o f t h e s u r v e y a r e a . F i g u r e 5 . 8 ( b ) s h o w s s l i g h t d e v i a t i o n f r o m t h e t h e o r e t i c a l 1 / r r e l a t i o n i n t h e J a c o b s L a k e r e g i o n , t h o u g h t h i s d e v i a t i o n i s n e a r l y a c c o u n t e d f o r b y r a n d o m e r r o r ( a s s h o w n b y t h e e r r o r b a r s ) . N o t e t h a t a n i n v e r s e r e l a t i o n i s g r a p h e d o n a l o g - l o g p l o t a s a s t r a i g h t l i n e w i t h s l o p e - 1 . T h e h i g h e r f r e q u e n c i e s ( 3 0 0 H z a n d 4 2 0 H z ) s h o w g r e a t e r d e v i a t i o n f r o m a n i n v e r s e r e l a t i o n i n t h e n o r t h w e s t e r n p a r t o f t h e s u r v e y a r e a ( a t d i s t a n c e s g r e a t e r t h a n 6 km f r o m t h e s o u r c e ) . P r o f i l e C - D ( f i g u r e s 5 . 9 ( a ) a n d 5 . 9 ( b ) ) i s i n t h e A l o u e t t e L a k e r e g i o n , a n d s h o w s a s i g n i f i c a n t d e v i a t i o n f r o m t h e g i v e n t h e o r e t i c a l 1 / r r e l a t i o n , w e l l b e y o n d t h e a s s o c i a t e d r a n d o m e r r o r o f t h e a p p a r a t u s . T h e r e m a i n d e r o f t h i s c h a p t e r w i l l g i v e a p o s s i b l e g e o l o g i c i n t e r p r e t a t i o n o f t h e g i v e n d a t a . H o w e v e r a n y d e t a i l e d i n f o r m a t i o n o r d e f i n i t i o n s o f g e o p h y s i c a l a n o m a l i e s w o u l d o n l y c o m e a b o u t w i t h a w e l l - d e f i n e d d e t a i l e d s u r v e y o f t h e r e g i o n s o f i n t e r e s t f o u n d w i t h t h e p r o p o s e d E M m e t h o d o f r e c o n n a i s s a n c e e x p l o r a t i o n . G e o l o g i c i n f o r m a t i o n o f t h e s u r v e y a r e a a n d s u r r o u n d i n g r e g i o n i s g i v e n i n f i g u r e 5 . 1 0 . G r a n i t e , g r a n o d i o r i t e , q u a r t z d i o r i t e a n d d i o r i t e a r e t h e m a i n g e o l o g i c c o n s t i t u e n t s o f t h e s u r v e y a r e a . H o w e v e r , l a t e ( Q u a t e r n a r y p e r i o d ) g l a c i a l d e p o s i t s 78 a r e a l s o s h o w n , a n d c o r r e l a t e w i t h t h e r e g i o n s o f i n t e r e s t a s d i s c u s s e d p r e v i o u s l y . T h e A l o u e t t e L a k e a r e a i s w i t h i n a n e x t e n s i v e r e g i o n o f g l a c i a l d e p o s i t s . T h e n o r t h e r n s e c t i o n o f t h e s u r v e y a r e a a l s o s h o w s t h i s f e a t u r e , w i t h a d e p o s i t e x t e n d i n g i n a n a r r o w b a n d s o u t h w a r d , e n d i n g j u s t s o u t h o f J a c o b s L a k e . F i g u r e 5 . 1 1 i s a g e o l o g i c c r o s s - s e c t i o n i n a n E a s t - W e s t d i r e c t i o n t h r o u g h J a c o b s L a k e . W i t h n o f u r t h e r k n o w l e d g e o f t h e r e g i o n , i t c a n o n l y b e h y p o t h e s i z e d t h a t a s i g n i f i c a n t c o n t r a s t i n e l e c t r i c a l c o n d u c t i v i t y e x i s t s b e t w e e n t h e b a c k g r o u n d i g n e o u s r o c k s a n d t h e g l a c i a l d e p o s i t s . S i n c e t h e a m p l i t u d e o f t h e s i g n a l w a s d e t e r m i n e d t o b e s m a l l e r w i t h i n t h e A l o u e t t e L a k e r e g i o n , t h e d a t a s u g g e s t s t h e g l a c i a l d e p o s i t s a r e m u c h h i g h e r i n e l e c t r i c a l c o n d u c t i v i t y t h a n t h e b a c k g r o u n d r o c k s . T h i s i s a v e r y p l a u s i b l e r e s u l t , k n o w i n g t h e f a c t t h a t g r a n i t i c r o c k s a r e e x t r e m e l y p o o r e l e c t r i c a l c o n d u c t o r s , h o w e v e r a d d i t i o n a l i n f o r m a t i o n w o u l d b e n e e d e d t o d e t e r m i n e q u a n t i t a t i v e c o n d u c t i v i t y v a l u e s . T h e r e s u l t s o f t h i s t h e s i s w o u l d s i t w e l l w i t h i n a p a c k a g e o f i n f o r m a t i o n i n c l u d i n g p e r h a p s o t h e r g e o p h y s i c a l s u r v e y s a n d g e o l o g i c s a m p l i n g a n d t e s t i n g o f t h e g l a c i a l d e p o s i t m a t e r i a l . H o w e v e r , t h e s c o p e a n d o b j e c t i v e o f t h i s t h e s i s i s t o s h o w t h e f e a s i b i l i t y o f t h e u s e o f t r a n s m i s s i o n l i n e s a s a n E M s o u r c e ; t h e d e t a i l e d g e o l o g i c s t u d y o f t h e U . B . C . R e s e a r c h F o r e s t a n d A l o u e t t e L a k e a r e a w i l l b e l e f t f o r a f u t u r e p r o j e c t . 79 QUATCKNAaV GARIBALDI GROUP i a conyian—tf. mm. nj» «nrf co* C K C T A C I O O S I ~ 1 MRM FORMATION: JUMASCIC «N0 C N C T M I O U S L O W M c i t m c i a u * GAMBIfR CROUP' mil meat, J ^ D I W M LT3: JURASSIC HARRISON LAKE fORMATION: rai-JUMtSMC ISLANO GROUP: COAST PLUTONIC ROCKS 1-A jg§3 •,bi ,t>2 b 3 i;1 • 1 I E l ELI S 3 E£l F i g . 5.10 Ge o l o g i c map of survey a r e a . F i g . 5.10 Continued (from G e o l o g i c a l Survey of Canada Map 1153A) . F i g . 5 . 1 1 G e o l o g i c c r o s s - s e c t i o n (E-W) through Jacobs Lake r e g i o n . 82 Chapter VI CONCLUSION The c o n c l u s i o n of t h i s t h e s i s must begin with i t s o b j e c t i v e s . Obviously, the nature of the source of the EM e x p l o r a t i o n method had to be w e l l s t u d i e d . Secondly, the p r a c t i c a b i l i t y of the method, i n ' terms of the c a p a b i l i t y to c a r r y out the experiment and o b t a i n meaningful measurements, had to be known. In a d d i t i o n , the dimension of a r e g i o n which c o u l d reasonably be surveyed was important, because i t would have an e f f e c t on the e f f i c i e n c y of the method. F i n a l l y , the method had to be t e s t e d to prove i t to be u s e f u l as an economical reconnaissance method of g e o p h y s i c a l e x p l o r a t i o n . Chapter Two d e s c r i b e d i n d e t a i l the o p e r a t i o n of power systems and t r a n s m i s s i o n l i n e s as r e l a t e s to t h i s work. The experimental method of o b t a i n i n g measurements was d e s c r i b e d i n Chapter Three, i n c l u d i n g i n s t r u m e n t a t i o n and c a l i b r a t i o n . The f o u r t h chapter d e t a i l e d the r e s u l t s of t e s t s and experiments d e a l i n g with the c u r r e n t s in t r a n s m i s s i o n l i n e 5L82 and systems i n M e r i d i a n s u b s t a t i o n . The r e s u l t s of two t e s t surveys, to show the p r a c t i c a b i l i t y of the method, and an e x t e n s i v e survey, to t e s t the u s e f u l n e s s of the method, were given i n Chapter F i v e . The r e s u l t s c l e a r l y i n d i c a t e t h a t the method of an EM survey 83 u s i n g a h i g h - v o l t a g e t r a n s m i s s i o n l i n e a s a s o u r c e c a n b e b o t h p r a c t i c a l a n d u s e f u l , i f i t s l i m i t a t i o n s a r e u n d e r s t o o d a n d p r o p e r c o n d i t i o n s ( m o s t n o t a b l y t h e s u i t a b i l i t y o f t h e l o c a t i o n o f t h e a r e a t o b e s u r v e y e d ) a r e m e t . I n t e r m s o f e f f i c i e n c y , a 120 k m 2 a r e a o f m o u n t a i n o u s t e r r a i n w a s s u r v e y e d ( w i t h n o n - u n i f o r m c o v e r a g e , h o w e v e r ) i n t h r e e p e r s o n n e l - d a y s , u s i n g a m i n i m a l a m o u n t o f e q u i p m e n t . T o c o n t i n u e c o n c l u d i n g r e m a r k s , t h e r e m a i n d e r o f t h i s c h a p t e r w i l l d e a l w i t h o t h e r r e l a t e d w o r k s a n d i d e a s o f i n t e r e s t . A n i m p r o v e m e n t i n t h e m e t h o d o f e x p l o r a t i o n a s p r o p o s e d w o u l d b e t o i n c r e a s e t h e t h e o r e t i c a l u n d e r s t a n d i n g o f t h e p r o c e s s a s w e l l a s i m p r o v i n g e x p e r i m e n t a l d e s i g n . T h e s t u d y o f e l e c t r o m a g n e t i c f i e l d s a n d t h e i r i n t e r a c t i o n w i t h t h e e a r t h i s e x t e n s i v e i n g e o p h y s i c s , a n d h a s p e r t i n e n t a p p l i c a t i o n i n e x p l o r a t i o n w o r k . D u e t o t h e e x p e r i m e n t a l d i r e c t i o n o f t h i s t h e s i s , t h e t h e o r e t i c a l m o d e l , a s e x p r e s s e d b y t h e f r e e - s p a c e B i o t - S a v a r t c a l c u l a t i o n s , w a s s i m p l i f i e d a n d d i d n o t e n c o m p a s s s e c o n d a r y e f f e c t s o f a c o n d u c t i v e e a r t h . O n e o f t h e e a r l i e r a n d b e t t e r k n o w n w o r k s o n t h e s u b j e c t ( P r i c e , 1 9 5 0 ) d e a l s w i t h e l e c t r o m a g n e t i c f i e l d s o v e r a u n i f o r m e a r t h , a n d i n c l u d e s i n p a r t i c u l a r a l i n e c u r r e n t s o u r c e n e a r t h e s p a c e - e a r t h b o u n d a r y . A v e r y i m p o r t a n t c o n s e q u e n c e o f o n e o f t h e r e s u l t s o f t h a t p a p e r , w i t h r e s p e c t t o E M e x p l o r a t i o n , i s t h a t t h e t o t a l f i e l d f a l l s o f f a s 1 / r 3 f a r f r o m t h e s o u r c e , w h i l e a 1 / r f a l l o f f i s e x p e c t e d n e a r e r t h e s o u r c e . T h e 1 / r 3 r e l a t i o n d e p e n d s o n t h e c o n d u c t i v i t y o f t h e g r o u n d a n d t h e f r e q u e n c y o f t h e s o u r c e , a s s e e n i n f i g u r e 6 .1 a n d t a b l e 6 . 1 : CONSIDER A PERIODIC LINE CURRENT cccos ut IN THE x- DIRECTION ALONG THE LINE y=0,z = h (Price's notation): z •line current cccosut (§1^ ) free space semi-infinite conductor THE DIRECT FIELD OF THE LINEAR CURRENT CAN BE EXPRESSED IN THE FORM: HyiH I = 2=*£PSHt , 0 f Z = Q h-iy SIMILAR IN FORM. THE COMPONENTS OF THE INDUCED FIELD ARE GIVEN IN THE FOLLOWING EXPANSION: Hy .iH, = 2c.acosut (f'-jStC2- 3C4.15C6. 315C S . )} • • 2c.asinut (4C3-£(C2 .3C4 .15C6 - 315C8 ... )) Q) [equation 10.7 in Price (1950)] VALID TO THREE SIGNIFICANT FIGURES IF K|S6 WHERE: C s ah • iay o2= 4 n a y 0= conductivity (sec1) ^magnetic permeability (assumed to beD NOTE THAT WHEN a (AND THEREFORE a) TENDS TO INFINITY, Hy • iHj T E N D S T O 2c.cpsnt S O T H A T T H E I N D U C E D F I E L D IS T H A T O F A n • iy CURRENT. EQUAL AND OPPOSITE TO THE INDUCING CURRENT, ALONG THE LINE y*O.Z=-h. IN AGREEMENT WITH IMAGE THEORY. IF y IS SUFFICIENTLY LARGE. THEN THE ASSUMPTIONS |C| 5 6 and y » h ARE BOTH VALID. IN THIS CASE. r. J iay and the induced field (in the vertical direction) becomes; iH = 2c. a cos wt [,—J • 2c, asinuit[C-—; 3 ] (3) 1 day) day) THE TOTAL FIELD IN THE z - DIRECTION IS THE SUM OF THE DIRECT FIELD [from equation (1)1 AND THE INDUCED FIELD [equation (3) ], IN WHICH THE COSINE TERMS CANCEL: H z (total field) = 2c.sinut • - U <4> a* y J EQUATION (4) SHOWS EXPLICITLY THE "1/r3" NATURE OF THE TOTAL FIELD FOR SUFFICIENTLY LARGE " r " F i g . 6.1 V e r t i c a l Induced F i e l d (H z) c a l c u l a t i o n s , 85 Rock Type G r a n i t e S o i l Waters N a t u r a l Waters TABLE 6.1 R e s i s t i v i t y (nm) f (Hz) o (cm - 1) 6/c (km) 10 s 60 2 . 1 8 X 1 0 ' 7 270 180 3 . 7 8 X 1 0 " 7 160 300 4 . 8 7 X 1 0 " 7 120 420 5.76x10" 7 100 TO4 60 2.18x10* 6 28 180 3.77x10" 6 1 6 300 4.87x10" 6 12 420 5 . 7 6 X 1 0 ' 6 10 3X10 2 60 1.26xl0' 5 4.8 180 2.18x10- 5 2.7 300 2 . 8 1 X 1 0 " 5 2.1 420 3 . 3 2 X 1 0 " 5 1 .8 10 60 2.18X10" 5 2.8 180 3.77x10- 5 1 .6 300 4.87xl0" 5 1 .2 420 5 . 7 6 X 1 0 " 5 1 .0 900 60 7 . 2 6 X 1 0 " 5 0.83 180 1.26x10" * 0.48 300 1.62x10' 4 0.37 420 1.92X10- 4 0.31 300 60 1.26xl0* 4 0.48 . 180 2.18x10" 4 0.28 300 2.81x10-" 0.21 420 3.32x10" 4 0.18 o 2 = 8 r r 2 c r w f / c 2 (cnT 2) c r=conductivity ( s e c ' 1 ) » i=magnetic p e r m e a b i l i t y (assumed to be 1) f=frequency (Hz) h<20 m Table 6.1 Determining 6/o (minimum d i s t a n c e from l i n e source for which oy>6 and y>>h), which corresponds to a t o t a l f i e l d - d i s t a n c e r e l a t i o n of 1/r 3 (see f i g u r e 6.1). Rock type r e s i s t i v i t y range from T e l f o r d (1976, p. 4 5 2 - 4 5 4 ) . The d i s t a n c e from the l i n e source to the ground, h, i s l e s s than 20 m. From the r e s u l t s of the preceeding d i s c u s s i o n i t i s p o s s i b l e to e x p l a i n c e r t a i n a s p e c t s of the data obtained from the f i e l d experiment. In the northern region of the survey area, 8 6 t h e d a t a s h o w s t h e v e r t i c a l t o t a l f i e l d s i g n a l f a l l s o f f a t a g r e a t e r r a t e t h a n 1 / r ( a s s e e n i n b o t h t h e c o n t o u r e d d a t a a n d p r o f i l e d a t a ) . O n e p o s s i b l e e x p l a n a t i o n i s t h e f a c t t h a t t h e s o u r c e i s o f f i n i t e l e n g t h , w h i c h w o u l d h a v e g r e a t e r e f f e c t o n t h e s i g n a l f u r t h e r a w a y f r o m t h e s o u r c e . H o w e v e r t h e r e f e r e n c e f i e l d ( f i g u r e 5 . 6 ) i s b a s e d o n t h e f i n i t e l e n g t h s o u r c e m o d e l , a n d d o e s n o t e x h i b i t t h e p a t t e r n s a s s e e n i n t h e d a t a . I n a d d i t i o n , i t i s i m p o r t a n t t o n o t e t h a t t h e i n c r e a s e d f a l l o f f i s m o r e a p p a r e n t i n t h e h i g h e r f r e q u e n c i e s u s e d ( 3 0 0 H z a n d 4 2 0 H z ) t h a n t h e l o w e r f r e q u e n c i e s ( 6 0 H z a n d 180 H z ) , w h i c h i s n o t a n e f f e c t o f t h e f i n i t e l e n g t h o f t h e p r i m a r y s o u r c e . H o w e v e r , t h e f r e q u e n c y u s e d d o e s a f f e c t t h e d i s t a n c e a t w h i c h t h e 1 / r 3 r e l a t i o n c o m e s i n t o e f f e c t ( i n w h i c h h i g h e r f r e q u e n c i e s a r e a f f e c t e d n e a r e r t h e s o u r c e ) . T a b l e 6 . 1 i s i n t e n d e d a s a n e x a m p l e o f t h e e f f e c t o f t h e s e c o n d a r y f i e l d o n t h e v e r t i c a l t o t a l f i e l d s t r e n g t h , riot a s a g e o l o g i c i n t e r p r e t a t i o n o f t h e d a t a . H o w e v e r i t d o e s s h o w t h a t t h e 1 / r 3 t o t a l f i e l d f a l l o f f i s d e p e n d a n t u p o n b o t h t h e s o u r c e f r e q u e n c y a n d t h e c o n d u c t i v i t y o f t h e u n d e r l y i n g m a t e r i a l s . T h e d i s t a n c e a t w h i c h i t c o m e s i n t o e f f e c t ( l a s t c o l u m n o f t a b l e 6 . 1 ) m a y v a r y w i d e l y w i t h i n d i s t a n c e s t y p i c a l t o t h o s e p r e s e n t e d i n t h e d a t a . T h u s i t s e e m s c l e a r t h a t p a t t e r n s s e e n i n t h e d a t a ( d i s c u s s e d a t l e n g t h p r e v i o u s l y ) a r e q u a l i t a t i v e l y e x p l a i n e d b y s e c o n d a r y f i e l d e f f e c t s , a n d t h a t t h e g e o l o g i c d i f f e r e n c e s w i t h i n t h e s u r v e y a r e a a r e r e p r e s e n t e d b y t h e p a t t e r n s s e e n i n t h e d a t a . T h e e x p e r i m e n t a l m e t h o d u t i l i z e d i n t h i s t h e s i s c o u l d b e v a r i e d t o m a k e i t m o r e e f f e c t i v e . T h e a m p l i t u d e o f t h e v e r t i c a l c o m p o n e n t w a s m e a s u r e d i n t h e p r e s e n t e x p e r i m e n t ; h o w e v e r , 87 h o r i z o n t a l components c o u l d e a s i l y be measured by proper o r i e n t a t i o n of the r e c e i v e r c o i l . H o r i z o n t a l components are much sm a l l e r i n magnitude than v e r t i c a l components (with r e s p e c t to a h o r i z o n t a l l i n e c u r r e n t source) and would be expected to be more s u s c e p t i b l e to n a t u r a l s i g n a l n o i s e . However, the h o r i z o n t a l component of the magnetic i n d u c t i o n i s t o t a l l y i s o l a t e d from the d i r e c t source c o n t r i b u t i o n , which i s a c e r t a i n advantage o ( A b o u l - A t t a et a l . , 1981). I t should be noted that EM e x p l o r a t i o n , i n c l u d i n g the proposed method, i s v a l u a b l e i n s e a r c h i n g f o r geothermal l o c a t i o n s as w e l l as c o n d u c t i v e ore d e p o s i t s , due to the i n c r e a s e in c o n d u c t i v i t y of m i n e r a l - l a d e n geothermal waters. The system as i t stands can a l s o be used f o r absolute magnetic f i e l d measurements, s i n c e the mobile r e c e i v e r was c a l i b r a t e d with respect to magnetic f i e l d s t r e n g t h (Appendix C). With a more advanced t h e o r e t i c a l b a s i s , and knowledge of n e u t r a l c u r r e n t s t r e n g t h s at the time of survey measurements, a q u a n t i t a t i v e measure of c o n d u c t i v i t y s t r u c t u r e s c o u l d be determined. In the present survey, i t was not f e a s i b l e to measure l i n e c u r r e n t s c o n c u r r e n t l y with mobile r e c e i v e r measurements. However, the a b s o l u t e values (as measured at the base s t a t i o n ) of the magnetic f i e l d f o r the four f r e q u e n c i e s u t i l i z e d are given here f o r completeness, though simultaneous n e u t r a l c u r r e n t i n f o r m a t i o n i s not known (see t a b l e 6.2): 88 TABLE 6.2 Frequency 60 Hz 180 Hz 300 Hz 420 Hz Amplitude of Magnetic F i e l d (nT(rms)) 50 nT 3.6 nT 0.16 nT 0.67 nT • Table 6.2 Magnetic f i e l d s t r e n g t h s at base s t a t i o n (15:50 LT, 22/7/81). Note: 1r=1 nT. The r e c e i v e r system used i n the experiment would have to be m o d i f i e d to o b t a i n phase i n f o r m a t i o n from the s i g n a l . Phase i n f o r m a t i o n i s important data used i n many EM i n t e r p r e t a t i o n systems to study conductive f e a t u r e s . C u r r e n t l y underway i n Dr. R.D. R u s s e l l ' s i n s t r u m e n t a t i o n group (U.B.C.) i s a study using a r e c e i v e r which i n c o r p o r a t e s an adap t i v e f i l t e r technique (Frydecky,1980) to measure s i g n a l harmonic l e v e l s . The 60 Hz component d e t e c t e d i n the f i e l d i s used as a r e f e r e n c e f o r which subsequent harmonics are notched with the extremely high-Q c a p a b i l i t i e s of the a d a p t i v e f i l t e r . Each harmonic i s represented by a s i n e and c o s i n e term, so that r e l a t i v e phase i n f o r m a t i o n among the harmonics i s a v a i l a b l e . It was noted p r e v i o u s l y i n s e c t i o n 3.2(g) that the geomagnetic f i e l d was monitored dur i n g the EM survey measurements (see Appendix C f o r t h i s d a t a ) . With the r e c o r d of the geomagnetic f i e l d , the survey data can be checked f o r i n d i c a t i o n s of geomagnetic a c t i v i t y a f f e c t i n g the measurements. T h i s i s accomplished by r e c o r d i n g the time of measurement at each mobile r e c e i v e r s t a t i o n . In the present work, i t was found t h a t the geomagnetic f i e l d was q u i e t t o moderate i n a c t i v i t y d u r i n g the measurements, and was not a f a c t o r i n a n a l y z i n g the 89 d a t a . O f c o u r s e t h e m o s t i m p o r t a n t c r i t e r i a i n t h i s a s p e c t o f t h e a n a l y s i s i s t h e c o n t i n o u s m o n i t o r i n g o f t h e A F s i g n a l a t t h e b a s e s t a t i o n . T h i s c h a p t e r c o n c l u d e s b y m e n t i o n i n g r e l a t e d w o r k s o f i n t e r e s t t o t h e r e a d e r . A c o n t r o l l e d - s o u r c e e x p e r i m e n t w h i c h u t i l i z e d a h i g h - v o l t a g e D C t r a n s m i s s i o n l i n e w a s u s e d i n a l o w - f r e q u e n c y E M s u r v e y ( L i e n e r t , 1 9 7 9 ) . T h e r e g i o n c o v e r e d b y t h e s u r v e y w a s e x t e n s i v e , a n d o n e - d i m e n s i o n a l e l e c t r i c a l c o n d u c t i v i t y m o d e l s o f t h e l o w e r a n d u p p e r c r u s t w e r e o b t a i n e d . T h e o r e t i c a l w o r k p e r t a i n i n g g e n e r a l l y t o e l e c t r o m a g n e t i c i n d u c t i o n i n a s e m i - i n f i n i t e c o n d u c t o r i s p r e v a l e n t ( P r i c e , 1 9 5 0 ; G o r d o n , 1 9 5 1 ; W e a v e r , 1 9 7 1 ; W e a v e r , 1 9 7 3 ) . M u c h w o r k h a s b e e n d o n e p e r t a i n i n g , i n p a r t i c u l a r , t o f i e l d s o f a l i n e c u r r e n t s o u r c e a b o v e t h e e a r t h ( P r i c e , 1 9 5 0 ; W a i t a n d S p i e s , 1 9 6 9 ) , a n d e x p l i c i t l y f o r t h e p u r p o s e o f e l e c t r o m a g n e t i c s o u n d i n g ( A b o u l - A t t a e t a l . , 1 9 8 1 ) . T h e e f f e c t o f g e o m a g n e t i c a c t i v i t y ( a n d G I C ) o n p o w e r s y s t e m s h a s b e e n s t u d i e d ( H a y a s h i e t a l . , 1 9 7 8 b ; H a y a s h i e t a l . , 1 9 7 9 ; B o t e l e r e t a l . , t o b e p u b l i s h e d ) . A l s o , t h e i n t e r a c t i o n o f t r a n s m i s s i o n l i n e p o w e r h a r m o n i c r a d i a t i o n w i t h s t i m u l a t e d V L F e m i s s i o n s i n t h e m a g n e t o s p h e r e i s w e l l r e p r e s e n t e d i n t h e l i t e r a t u r e ( H e l l i w e l l , 1 9 7 5 ; L u e t t e , 1 9 7 7 ; P a r k , 1 9 7 7 ) . 90 REFERENCES Aboul-Atta, 0., S h a f a i , L., Vohra, D.R., ' A p p l i c a b i l i t y of the Theory of I n f i n i t e L i n e Current Above Layered E a r t h f o r E l e c t r o m a g n e t i c Sounding', paper g i v e n a t CGU Conference, Calgary, A l b e r t a , May, 1981. Adkins, B., and Harley, R.G., The General Theory of A l t e r n a t i n g  Current Machines, Chapman and H a l l , L t d . , London, U.K., 1975. Blume, L.F., C a m i l l i , G., B o y a j i a n , A., Montsinger, V.M., Transformer E n g i n e e r i n g , John Wiley and Sons, Inc., New York, N.Y.,1938. B o t e l e r , D.H., ' H a l l - E f f e c t Current Transducers', U.B.C./B.C. Hydro GIC Study I n t e r n a l Report, 1979. B o t e l e r , D.H., 'The Problem of S o l a r Induced C u r r e n t s ' , S o l a r -T e r r e s t r i a l P r e d i c t i o n s Proceedings, R.F. Donnelly, ed., Boulder, C o l o . , V o l . 2, A p r i l 1979, pp. 149-161. B o t e l e r , D.H., Watanabe, T., S h i e r , R.M., and H o r i t a , R.E., ' C h a r a c t e r i s t i c s of Geomagnetically Induced Currents i n the B.C. Hydro 500 KV System 1, accepted f o r p u b l i c a t i o n i n IEEE,  Power Apparatus and Systems. Eaton, J.R., E l e c t r i c Power Transmission Systems, P r e n t i c e - H a l l , Inc., Englewood C l i f f s , New J e r s e y , 1972. F i s h e r , A r t h u r , 'Science Newsfront - From the Sun: Power Outages', Popular Science, V o l . 218, No. 6, 1981. Frydecky, Ivan Igor, 'The Induced P o l a r i z a t i o n R e c e i v e r ' , M.Sc. t h e s i s , U n i v e r s i t y of B r i t i s h Columbia, 1980. Gordon, A.N., 'Electromagnetic Induction i n a Uniform Semi-I n f i n i t e Conductor', Quart. J . Mech. Appl. Math., V o l . 4, Pt. 1, 1951, pp. 116-128. 91 G r a n t , F . S . A n d W e s t , G . F . , I n t e r p r e t a t i o n T h e o r y i n A p p l i e d  G e o p h y s i c s , M c G r a w - H i l l B o o k C o m p a n y , New Y o r k , N . Y . , 1 9 6 5 . H a y a s h i , K . , O g u t i , T . , W a t a n a b e , T . , a n d Z a m b r e s k y , L . F . , -' A b s o l u t e S e n s i t i v i t y o f a High-»i M e t a l C o r e S o l e n o i d a s a M a g n e t i c S e n s o r ' , J . G e o m a g . G e o e l e c t r . , 3 0 , 1 9 7 8 a , p p . 6 1 9 -6 3 0 . H a y a s h i , K . , O g u t i , T . , W a t a n a b e , T . , T s u r u d a , K . , K o k u b u n , S . , a n d H o r i t a , R . E . , ' P o w e r H a r m o n i c R a d i a t i o n E n h a n c e m e n t D u r i n g t h e S u d d e n C o m m e n c e m e n t o f a M a g n e t i c S t o r m ' , N a t u r e , V o l . 2 7 5 , 1 9 7 8 b , p p . 6 2 7 - 6 2 9 . H a y a s h i , K . , O g u t i , T . , W a t a n a b e , T . , T s u r u d a , K . , K o k u b u n , S . , a n d H o r i t a , R . E . , ' H a r m o n i c s o f 60 H z i n P o w e r S y s t e m s C a u s e d b y G e o m a g n e t i c D i s t u r b a n c e s ' , S o l a r - T e r r e s t r i a l P r e d i c t i o n s P r o c e e d i n g s , R . F . D o n n e l l y , e d . , B o u l d e r , C o l o . , V o l . 2 , A p r i l 1 9 7 9 , p p . 1 7 2 - 1 8 1 . H e i l a n d , C . A . , G e o p h y s i c a l E x p l o r a t i o n , P r e n t i c e - H a l l , I n c . , New Y o r k , N . Y . , 1 9 4 0 . H e l l i w e l l , R . A . , K a t s u f r a k i s , J . P . , B e l l , T . F . , a n d R a g h r a m , R . J . , ' V L F L i n e R a d i a t i o n i n t h e E a r t h ' s M a g n e t o s p h e r e a n d I t s A s s o c i a t i o n W i t h P o w e r S y s t e m R a d i a t i o n ' , J . G e o p h y s . R e s . , V o l . 8 0 , N o . 3 1 , 1 9 7 5 , p p . 4 2 4 9 - 4 2 5 8 . J a c k s o n , J . D . , C l a s s i c a l E l e c t r o d y n a m i c s , J o h n W i l e y a n d S o n s , I n c . , New Y o r k , N . Y . , 1 9 7 5 . L i e n e r t , B a r r y R . , ' C r u s t a l E l e c t r i c a l C o n d u c t i v i t i e s A l o n g t h e E a s t e r n F l a n k o f t h e S i e r r a N e v a d a s ' , G e o p h y s i c s , V o l . 4 4 , N o . 1 1 , 1 9 7 9 , p p . 1 8 3 0 - 1 8 4 5 . L u e t t e , ' J . P . , P a r k , C . G . , a n d H e l l i w e l l , R . A . , ' L o n g i t u d i n a l V a r i a t i o n s o f V L F C h o r u s A c t i v i t y i n t h e M a g n e t o s p h e r e : E v i d e n c e o f E x c i t a t i o n b y E l e c t r i c a l P o w e r T r a n s m i s s i o n L i n e s ' , G e o p h y s . R e s . L e t t . , V o l . 4 , N o . 7 , 1 9 7 7 , p p . 2 7 5 - 2 7 8 . 92 Park, C , 'VLF Wave A c t i v i t y During A Magnetic Storm: A Case Study of the Role of Power Line R a d i a t i o n ' , J . Geophys.  Res., V o l . 82, No. 22, 1977, pp. 3251-3260. P r i c e , A.T., 'Electromagnetic Induction i n a S e m i - I n f i n i t e Conductor with a Plane Boundary', Quart. J . Mech. Appl.  Math., V o l . 3, Pt. 4, 1950, pp. 385-410. Say, M.G., The Performance and Design of A l t e r n a t i n g Current Machines, S i r Isaac Pitman and Sons L t d . , London, U.K., 1965. T e l f o r d , W.M., G e l d a r t , L.P., S h e r i f f , R.E., Keys, D.A., A p p l i e d  Geophys i e s , Cambridge U n i v e r s i t y - Press, Cambridge, U.K., 1 976. Topping, J . , E r r o r s of O b s e r v a t i o n and T h e i r Treatment, Chapman and H a l l L i m i t e d , London, 1966. Wait, J.R., and S p i e s , K.P., 'On the Image Repres e n t a t i o n of the Q u a s i - S t a t i c F i e l d s of a L i n e Current Source Above the Ground', Canadian J . P h y s i c s , V o l . 47, 1969, pp. 2731-2733. Watanabe, T., Slawson, W.F., and Chapel, B., 'Power Harmonic R a d i a t i o n as an E.M. P r o s p e c t i n g Source', U.B.C. Dept. of Geophysics and Astronomy (Aeronomy group) I n t e r n a l Report, 1981. Weaver, J.T., 'The General Theory of E l e c t r o m a g n e t i c Induction in a Conducting Half-Space' , Geophys. J . R. A s t r . S o c , V o l . 22, 1971, pp. 83-100. Weaver, J.T., 'Induction i n a Layered Plane E a r t h by Uniform and Non-Uniform Source F i e l d s ' , P h y s i c s of the E a r t h and  P l a n e t a r y I n t e r i o r s , V o l . 7, 1973, pp. 266-281. 93 A P P E N D I X A H A R M O N I C A N A L Y S I S T h e u s e o f h i g h i n d u c t i o n d e n s i t i e s i n t h e c o r e s o f p o w e r t r a n s f o r m e r s i s i m p o s e d b y t h e r e q u i r e m e n t s o f a n e c o n o m i c a l d e s i g n a n d t h e r e d u c t i o n o f w e i g h t ( S a y , 1 9 6 5 , p . 9 4 ) . H o w e v e r t h i s p r a c t i c e i n t r o d u c e s p r o b l e m s d u e t o t h e s a t u r a t i o n o f t h e m a g n e t i c c i r c u i t a n d t h e d e p a r t u r e f r o m r e c t i l i n e a r i t y o f t h e f l u x / c u r r e n t r e l a t i o n , a n e f f e c t o f h y s t e r e s i s i n t h e c o r e . F i g u r e A . 1 i l l u s t r a t e s a g r a p h i c a l m e t h o d o f p l o t t i n g t h e m a g n e t i z i n g c u r r e n t a s a f u n c t i o n o f t i m e , a s s u m i n g a s i n u s o i d a l f l u x d e n s i t y ( c o r r e s p o n d i n g t o a s i n u s o i d a l e . m . f . ) , a n d a c o r r e s p o n d i n g h y s t e r e s i s c u r v e f o r t h e m a t e r i a l . I n t h e e x a m p l e s h o w n ( S a y , 1 9 6 5 , p . 9 4 ) , a f l u x - d e n s i t y c o r r e s p o n d i n g t o P o n t h e h y s t e r e s i s l o o p a n d t o Q o n t h e s i n u s o i d a l w a v e f o r m r e q u i r e s 8 u n i t s o f m a g n e t i z i n g c u r r e n t . T h e f o r m o f t h e c u r r e n t c u r v e , p l o t t e d i n t h i s m a n n e r t h r o ' u g h o n e p e r i o d , T , i s s e e n t o b e f a r f r o m s i n u s o i d a l ; i t c o n s i s t s o f a f u n d a m e n t a l t e r m a n d a s e r i e s o f o d d h a r m o n i c s , m a i n l y t h e t h i r d a n d f i f t h . H o w e v e r , t h e f i f t h a n d s e v e n t h m a y b e m o r e i m p o r t a n t t h a n t h e t h i r d h a r m o n i c ( S a y , 1 9 6 5 , p . 9 4 ) . T h u s a s i n u s o i d a l f l u x ( r e q u i r e d b y a s i n u s o i d a l a p p l i e d v o l t a g e ) d e m a n d s a m a g n e t i z i n g c u r r e n t w i t h h a r m o n i c c o n t e n t . T h e s i t u a t i o n p r e s e n t e d h e r e i s s y m m e t r i c ; a s i n u s o i d a l m a g n e t i z i n g c u r r e n t c o u p l e d w i t h a n o n - s i n u s o i d a l 94 i 95 f l u x (that i s , one c o n t a i n i n g harmonics) can a l s o r e s u l t from the same h y s t e r e s i s curve. A mathematical procedure has been developed (Hayashi et a l . , 1979) to determine the stren g t h of each harmonic based on the h y s t e r e s i s loop of a transformer core m a t e r i a l . E s s e n t i a l l y , the magnetic f l u x i s represented as a F o u r i e r s e r i e s , i n which the F o u r i e r c o e f f i c i e n t s can be expressed i n summation form, and depends on the shape of the h y s t e r e s i s curve. When the h y s t e r e s i s curve i s of a f a m i l i a r shape and point-symmetric ( f i g u r e A.2(a)), a l l even harmonics v a n i s h . The loop f o r a D.C. biased case l a c k s point-symmetry ( f o r example, f i g u r e A.2(b)), and the r e s u l t a n t waveform co n t a i n s harmonics of a l l orders. F i g . A.2 H y s t e r e s i s loop (a) poi n t symmetry; (b) no poi n t symmetry (Hayashi et a l . , 1979). 96 A P P E N D I X B I N S T R U M E N T A T I O N A N D C A L I B R A T I O N T h e i n s t r u m e n t a t i o n d e s c r i b e d i n s e c t i o n 3 . 2 i s s u m m a r i z e d a s f o l l o w s : ( a ) H a r m o n i c c u r r e n t m e a s u r e m e n t s o n t r a n s m i s s i o n l i n e 5 L 8 2 a t M e r i d i a n S u b s t a t i o n ; ( b ) G I C m e a s u r e m e n t s o n 5 L 8 2 ; ( c ) A F s i g n a l s ( s o u r c e b e i n g t h e c u r r e n t i n 5 L 8 2 ) m e a s u r e d a t t h e b a s e s t a t i o n w i t h i n t h e " s u r v e y a r e a . " ; ( d ) G e o m a g n e t i c f i e l d m o n i t o r i n g a t t h e b a s e s t a t i o n ; ( e ) E M s u r v e y m e a s u r e m e n t s u s i n g m o b i l e r e c e i v e r s y s t e m . T h e h a r m o n i c c u r r e n t m e a s u r e m e n t s a r e s e p a r a t e d i n t o t w o s y s t e m s , o n e t o m e a s u r e s i n g l e - p h a s e c u r r e n t h a r m o n i c s ( A - p h a s e ) a n d o n e t o m e a s u r e n e u t r a l c u r r e n t h a r m o n i c s . E a c h s y s t e m u s e s i t s own d e t e c t i o n ( c u r r e n t p r o b e ) a n d a m p l i f i c a t i o n d e v i c e s , a n d t h e s i g n a l s a r e r e c o r d e d o n d i f f e r e n t c h a n n e l s o f t h e s a m e a u d i o - f r e q u e n c y t a p e r e c o r d e r ( t h e a p p a r a t u s i s d i a g r a m m e d s c h e m a t i c a l l y i n f i g u r e B . 1 ) . F o r c a l i b r a t i o n p u r p o s e s , t h e c u r r e n t p r o b e s w e r e c o n n e c t e d t o a t e s t c i r c u i t c o n s i s t i n g o f a s i g n a l g e n e r a t o r a n d a k n o w n r e s i s t i v e l o a d ( f i g u r e B . 2 ) . F r o m a s u g g e s t i o n o f M r . R . M . S h i e r , o f B . C . H y d r o , t h e r e s u l t a n t s i g n a l w a s r e c o r d e d o n t a p e i n t h e s a m e m a n n e r a s t h e a c t u a l 97 5L82 AUDIO FREQUENCY TAPE (a) FM TAPE (b) N-S E-W Z AF ANTENNA O — L > 1 0 TIME CODE 3 COMPONENT MAGNETOMETER V/F CONVERTER AUDIO FREQUENCY TAPE FM TAPE (0 (d) AF ANTENNA OHt> • o-WWV AUDIO RECEIVER PICKUP AUDIO FREQUENCY TAPE (e) Fig. B .1 Schematic representation of apparatus (previously presented as figure 3.3). CURRENT HARMONICS CALIBRATION CIRCUIT SIGNAL GENERATOR L-vv -<§>-CURRENT PROBE > AMPLIFYING & RECORDING SYSTEM DC SOURCE GIC CALIBRATION CIRCUIT 0 HALL-EFFECT TRANSDUCER J AMPLIFYING & RECORDING SYSTEM F i g . B.2 C a l i b r a t i o n c i r c u i t s f o r harmonic c u r r e n t s and GIC detector ( p r e v i o u s l y presented as f i g u r e 3.4). 9 9 l i n e c u r r e n t d a t a , o n s i t e a t M e r i d i a n S u b s t a t i o n . I t w a s t h o u g h t t h a t t h i s ' o n s i t e ' c a l i b r a t i o n o f a n e n t i r e s y s t e m w o u l d b e m o r e a c c u r a t e t h a n a n ' i n t h e l a b ' c a l i b r a t i o n o f t h e d e t e c t i n g a n d r e c o r d i n g d e v i c e s u s e d i n M e r i d i a n . T h u s a t e a c h h a r m o n i c f r e q u e n c y , t h e a m p l i t u d e o f t h e s i g n a l o n t a p e i s c a l i b r a t e d t o a k n o w n c u r r e n t i n p u t . T h e s i g n a l w a s p r o c e s s e d b y s p e c t r a l a n a l y s i s o n a n a n a l o g i n p u t m a c h i n e , i n t h e s a m e w a y t h e d a t a w a s a n a l y z e d . T h e r e s u l t s o f t h e t e s t i n g a r e g i v e n i n t h e c a l i b r a t i o n c h a r t s f o r t h e A - p h a s e c u r r e n t d e t e c t i o n s y s t e m a n d t h e n e u t r a l c u r r e n t d e t e c t i o n s y s t e m , f i g u r e s B . 3 ( a ) - B . 3 ( h ) . T h e G I C d e t e c t i o n a n d r e c o r d i n g s y s t e m e m p l o y s a H a l l -e f f e c t t r a n s d u c e r t o d e t e c t q u a s i - D C c u r r e n t i n t h e g r o u n d c o n n e c t i o n o f t h e t r a n s f o r m e r s o f 5 L 8 2 a t M e r i d i a n S u b s t a t i o n . T h e b a s i s o f t h e t r a n s d u c e r i s a H a l l - e f f e c t d e v i c e w h i c h i s p l a c e d w i t h i n a h i g h - M m e t a l r i n g . I f t h i s r i n g e n c i r c l e s a c u r r e n t - c a r r y i n g c o n d u c t o r , t h e m a g n e t i c f i e l d i n t h e r i n g i s p r o p o r t i o n a l t o t h e c u r r e n t i n t h e c o n d u c t o r . A n a d j u s t a b l e c u r r e n t s o u r c e i s c o n n e c t e d t o t h e t r a n s d u c e r o u t p u t t o r e m o v e a n y z e r o c u r r e n t - l e v e l o f f s e t . T h e f r e q u e n c y r e s p o n s e o f t h e G I C m e a s u r i n g s y s t e m i s f l a t f r o m D C t o 1 H z , w i t h a l o w p a s s c o r n e r f r e q u e n c y o f 3 H z ( B o t e l e r , 1 9 7 9 ) . T h e G I C s y s t e m w a s c a l i b r a t e d b y p a s s i n g a k n o w n D C c u r r e n t t h r o u g h t h e H a l l - e f f e c t t r a n s d u c e r o n s i t e a t M e r i d i a n ( s e e f i g u r e B . 2 ) . T h e r e s u l t a n t s i g n a l w a s a m p l i f i e d a n d r e c o r d e d o n F M t a p e , a n d w a s f o u n d t o b e p r o p o r t i o n a l t o t h e m a g n i t u d e o f t h e c u r r e n t . I n a d d i t i o n , t h e p o l a r i t y o f t h e G I C s y s t e m w a s n o t e d d u r i n g c a l i b r a t i o n , s o t h a t t h e d i r e c t i o n o f c u r r e n t f l o w f r o m t h e t r a n s m i s s i o n l i n e i n t o t h e t r a n s f o r m e r g r o u n d i s s h o w n 100 in the data in terms of conventional current (positive to negative charge flow). The c a l i b r a t i o n was incorporated into the presentation of the data (figures 4.1 and 4.2). A low-pass f i l t e r (corner frequency=2.5 Hz) was used on the playback of the GIC measurements to eliminate 60 Hz noise on the signal trace. The AF receiver at the base station consisted of an antenna, amplifier, a length of low-resistance cable, and an audio-frequency DR tape recorder. The signal from the base station receiver was used with simultaneous monitoring of transmission l i n e harmonic currents, and as a reference in the EM survey work. Thus only information regarding r e l a t i v e changes in magnetic f i e l d strength was required from base station data. For t h i s reason no absolute c a l i b r a t i o n procedure was performed. However simultaneous readings of base station AF signals with both the base station system and the mobile receiver system yielded a scale which i s used in the data showing base station magnetic f i e l d strengths at p a r t i c u l a r frequencies (figures 5.3(a), 5.4(a), C.4(a), and C.4(b)). The induction magnetometer used at the base station consists of two mutually orthogonal air-core c o i l s (N-S and E-W orientation) and one high-^ metal core v e r t i c a l c o i l (Z component). The amplified natural signals are recorded on a slow speed FM tape recorder. The s e n s i t i v i t y of the air-core c o i l for the N-S component has been calculated t h e o r e t i c a l l y and checked experimentally. It is convenient to express the s e n s i t i v i t y (V a) in terms of Caner, that i s as an electro-motive force induced by a sinusoidal magnetic f i e l d v a r i a t i o n of 1 Hz in frequency and 1 mr n n in amplitude (note that a sensor of 1 Caner in 101 s e n s i t i v i t y , p l a c e d w i t h i n a u n i f o r m e x t e r n a l m a g n e t i c f i e l d w i t h a f r e q u e n c y o f 1 H z a n d w i t h a n a m p l i t u d e o f 1 my ( 1 0 ~ 1 2 T e s l a ) , g i v e s r i s e t o a n e l e c t r o m o t i v e f o r c e o f 1 m i c r o v o l t ( H a y a s h i e t a l . , 1 9 7 8 a ) ) : V a = 0 . 1 27 C a n e r T h e D . C . r e s i s t a n c e o f t h e c o i l i s 5 . 4 5 kfl a n d t h e i n p u t i m p e d a n c e o f t h e a m p l i f i e r i s 7 . 5 0 kn. T h e r e f o r e , t h e i n p u t v o l t a g e f o r t h e a m p l i f i e r , c r e a t e d b y a s i n u s o i d a l m a g n e t i c f i e l d v a r i a t i o n o f 1 H z a n d 1 my , w i l l b e o b t a i n e d b y PP m u l t i p l y i n g t h e e . m . f . i n d u c e d i n t h e c o i l b y t h e r a t i o o f t h e i n p u t i m p e d a n c e t o t h e s u m o f t h e i n p u t i m p e d a n c e a n d c o i l r e s i s t a n c e : I n p u t v o l t a g e : 0 . 1 2 7 „ V X 7 . 5 0 P P 7 . 5 0 + 5 . 4 5 T h e t o t a l g a i n o f t h e a m p l i f i e r , G , i s 2 X 1 0 5 : G = 2 X 1 0 5 T h e r e f o r e , t h e o u t p u t v o l t a g e o f t h e e . m . f . w i l l b e : 0 . 1 2 7 „V_ X 7 . 5 0 X 2 X 1 0 5 = 1 4 . 7 mV P P 7 . 5 0 + 5 . 4 5 P P I n a c t u a l i t y , a l o w - p a s s f i l t e r i s c o n n e c t e d b e t w e e n t h e a m p l i f i e r a n d t h e t a p e r e c o r d e r t o r e j e c t c o m p o n e n t s h i g h e r t h a n 0 . 2 H z i n f r e q u e n c y . H o w e v e r , t h e f r e q u e n c y r e s p o n s e o f t h e w h o l e s y s t e m f o r t h e e . m . f . i n d u c e d i n t h e c o i l i s f l a t f o r f r e q u e n c i e s l e s s t h a n 0 . 1 H z . T h e r e f o r e , t h e o u t p u t o f t h e m a g n e t o m e t e r f o r t h e N - S c o m p o n e n t i s c a l i b r a t e d t o b e : 1 . 4 7 m V p p f o r 1 m y p p a t 0 . 1 H z T h e o u t p u t f o r f r e q u e n c i e s l e s s t h a n 0 . 1 H z i s p r o p o r t i o n a l t o f r e q u e n c y . 1 02 The AF m o b i l e s y s t e m c o n s i s t s of a p o r t a b l e a i r - c o r e a n t e n n a , a m p l i f i e r , and p o r t a b l e t a p e r e c o r d e r . The c a l i b r a t i o n o f t h e s y s t e m was done by p l a c i n g t h e a n t e n n a i n a m a g n e t i c f i e l d c r e a t e d by a s o l e n o i d c o n n e c t e d t o a s i g n a l g e n e r a t o r . The s o l e n o i d i s f a r enough f r o m t h e a n t e n n a t o be t r e a t e d a s a m a g n e t i c d i p o l e s o u r c e . The m a g n e t i c f i e l d o f t h i s s o u r c e i s c a l c u l a t e d a t t h e p o s i t i o n o f t h e a n t e n n a . The r e s u l t a n t emf i n d u c e d i n t h e a n t e n n a i s a m p l i f i e d and r e c o r d e d on t h e DR t a p e r e c o r d e r . S p e c t r a l a n a l y s i s o f t h e s i g n a l ( i n t h e same manner as a n a l y s i s o f t h e s u r v e y d a t a ) , r e s u l t s i n t h e c a l i b r a t i o n o f t h e s y s t e m as a f u n c t i o n o f f r e q u e n c y and s o u r c e f i e l d s t r e n g t h . The t a p e r e c o r d e r u s e d t o r e c o r d t h e m o b i l e r e c e i v e r AF s i g n a l s i n c o r p o r a t e s a manual g a i n c o n t r o l i n t o i t s d e s i g n . In a d d i t i o n , t h e a m p l i f i e r has two g a i n s e t t i n g s . The s y s t e m was c a l i b r a t e d w i t h t h e a m p l i f i e r i n t h e l o w e r g a i n p o s i t i o n and t h e t h r e e d i f f e r e n t g a i n s e t t i n g s o f t h e t a p e r e c o r d e r u s e d i n t h e f i e l d s u r v e y . The h i g h e r g a i n p o s i t i o n o f t h e a m p l i f i e r i s d e s i g n e d t o i n c r e a s e t h e o v e r a l l g a i n o f t h e s y s t e m by 22 dB. The c a l i b r a t i o n t e s t c i r c u i t and c a l c u l a t i o n s a r e g i v e n i n f i g u r e B.4, and t h e g r a p h i c a l c a l i b r a t i o n r e s u l t s , showing t h e t h r e e s e p a r a t e g a i n s e t t i n g s , a r e g i v e n i n f i g u r e B.5. -10 -20 A-PHASE CURRENT CALIBRATION (60 Hz) -30 -to dB -50 -60 -70 100 500 Amps (rms) 1000 F i g . B.3(a) C a l i b r a t i o n c h a r t : A-phase - 60 Hz. o A-PHASE CURRENT CALIBRATION (120 Hz) dB . . :. • T 1 — I - • i I I — • 1 .VM. \ \ : : | • • : : : : : : : : .". i •* 1 . 1 1.. . 1 . . . . I . • — T T H — 1 —T— 1 :• ir r :: I." ~ - • T . 1 | : i — i : ; ; - 1 • : >.. j : : j .— '•I i i : : ; •-:!:. . . . . i . . : : : j • •; . ..(.. T'~7." ... i. : ; •; ::::!::: : : : : I •| i i ; ; ; ; : i . i. " i -i" • !: " • i T . . 1 . . . I I • . .1 - — 1. ! i. r • ...1.. ••: 1. . . i . . . !. - — - .1. _^ 1 - -: • : . 1-• i 1. .. — 1 as io SJO \OJQ sao Amps (rms) B.3(b) C a l i b r a t i o n c h a r t : A-phase - 120 Hz. A-PHASE CURRENT CALIBRATION (180 Hz) •U -10 -20 -30 -40 dB -50 -60 -70 as LO 5.0 10-0 sao Amps (rms) F i g . B.3(c) C a l i b r a t i o n c h a r t : A-phase - 180 Hz. o A-PHASE CURRENT CALIBRATION (240 Hz) dB i -ijii: 1 i : . - - ' - ... i . . : . - | . .vi:- • • • f • • • J •- ' i r i 1 J i _ ' : ir- 1 _ _ : • I- : - - ~ l - ::::|r.. : .: _ : 'j - 1 i. ::•{:•: — - - 1 1.: • ' z . - i - r . i .. —1— I ."..I : .1 - - T[: - _••_ :• : - i - : — l . , 1 .1 : . j : I" • i : L:.: : rl • .::-;.;-:.-fz •-. : : Lift i:"i" _ 'Z -.1. • ::! . . . . . . . - ::K *f ; : ~T~ ': r:- : ... : -.-.:.. ; : ' ii: rr:": 1 r- : : 1 " - i . : : ... |:r t' — - . h ::)-: -r-~ 1 1 1 — r - : 1. L.ZL ... 1 _• - - - — ? - -J. • I . . . • \ 1 :-r-~-- r.:— ; 7—: TT-: _ i ~-r-r. - .-. :-: :•: — - ni: - 1 : ::r: -' '' ' ' ' I 1 I I I 1 I I I I I I as LO SXJ lao Amps (rms) F i g . B.3(d) C a l i b r a t i o n c h a r t : A-phase - 240 Hz. o CTl A-PHASE CURRENT CALIBRATION (300 Hz) dB : ,:.r.:: -rirr rri::: 1 ;-• r-i | :i-. i ;i i 1' • :::•!::. -: .7 iiii : ••• i . : . : . : : ::.:• .: !ii . _-rr ; ! ii;'-!:.:. r r r r r:: : -i:: :..-|- '""' ; :;;:!:-......... iiiiiii'. ;-'-_ ::::;:::. i I TIrufr|iii'-Liir r :: : ....I. • ':•}' : : :. : : : r ;;: . . 1 ::::):::: .. j.. ; • I =.-; iri •••• '•; :-:-T'i-L . i i . .. u.: . -•)-::::j:::: " r r : :.- rrr: ... (.. ::: ' | : : :- rrrr • . • ^ ! : ; ; . . r : . : ;;;.-i:r. r:r L r r r r i ~ r ? ; ;;::i;;..:; ;:i:iiii: -iiiiir ••: ' ........ ::::;::.. : r r £ rHlr:: -_ : .... [:;•: : . :| . : : . — - --::::r:::: 7T" • -r3rrr _rfr: ; r ; i ; - i : -• -I. .r.:::.: - \Z'.'. •: - ; rf : ' ::r :. 7 :r: ;.: r. :* *; :••;•: r.r:r; : .1.. ri-"' r. i: .:-: rrr:r: h-;:: - ::•• : : : r r : r r r r r : rr: :. 1 . :•:.!:. Irrr I•" rrrr:.: rr r: - -:; — :T: rrj;::: -rrrrr: :::•]::. i ; : ' ; : rrrr :~; — l. :;:.|:, irLfK • ' • :::i:r: -— T-T— -::::: .- : :•: _..p_ m • ^ : . : r . - ; : : —-• _. —r- .... ; r i-i •:•;•;? rrrrf. ::;; -:r - ; rr rtrr • T-as io 5.0 loo sao Amps (rms) F i g . B.3(e) C a l i b r a t i o n c h a r t : A-phase - 300 Hz. o A-PHASE CURRENT CALIBRATION (360 Hz) dB : , . .zr: ,: .4 - ..v.:.: : .z : z':l • . i... — L rrr ~z:r: t _ : :r : : -iii ; • :._-:: : |-::::l. ir ir . . :::r-: -iii- -i ~: : - -ii iiLL z=\ •• j: T~ Tfzrr' ii=r i :V ii .. :1 ._: - : Hi..!.: .I.~"z: ZZ i -\-z '.' .[:'. zrz-: i i " :\- [rz - '-. l-izizi rr • : 1 •:::-r.-; rrrl : :].:• : i | . rz.- i i ; zrrr rri:-' ::> • \± ii iii-i i: • : i -"i irf .:  : i. ^: :: VT .: :::. ::..! . ....j . r: "' !!• •'-.\:~r "iz :::: •rr ::•!;;; :. -^z\: rff f :: - ; ; 'il:: LT*. T: :i r::r rrr '-'"}"•• :r; •zzz^Br. r. zz: zzz: Hi!:-r • '- 'zz'--J \\rz- fiii ii - 1: .:: :r iii'" rrTi rr_- ::r|.:.. :.:.!. . 1 zr.: -zz- - zr :zz. •:::!'•* : : - :'zz: :: :; .. ; •-: -ir:. '-: ~-r: •••rr: ZZ ::i: '1 ' ;...f--- T=_ • :' ! ' " - iii- : .|.: : l . z :..-.- ™ T~T' ~ T:.:: -.\ H— - : : - rr ::.- ::- ... _. :; Vzzl i i ; . i i i". i . : : : :. zzl— :- r .-" :  :zz :ji: -'- -\ rr-:: z::z :: ••'4:; z'z---z- 1 r.-r-ff 1:1: r: : : T " ~ ' rzz rrr ;:;: ;- -r~r- •!:' i Hi: I r -r -. : : :i#*:i= UTT: i i i i •zr.l |::r :.!;: rrr: r L --: " H " :\ z l'z\ .... ... r :|: -: tr _ ~ . ; : : .: i i : i :.: i 10 SO 100 5O0 Amps (rms) Fig. B.3(f) Calibration chart: A-phase - 360 Hz. o oo dB -10 -20 -30 -40 -50 -60 -70 A-PHASE CURRENT CALIBRATION (420 Hz - 660 Hz) 500 Amps (rms) F i g . B.3(g) C a l i b r a t i o n c h a r t : A-phase - 420 Hz-660 Hz. o to NEUTRAL CURRENT CALIBRATION (60 Hz-660 Hz) dB i . i i' • • i --H-V-: - . :. 1 F l " ' I I 1 ! • 1 " :• • :•• | ' .. ! -••---1-! • 1 • •. • ]• ! • ' i I - — — j - r • • - - -—\- - .. j , • L:. : .J: : • j I . I : i - ! : - j ' ! • • i i • i • T i - . j . "!' ' . J . . 1 . | \ . " •"!'."'" i " " j 1 i. i 1:.:. .... .... . . . 1 . ' I . 1 . . . . i ' : . : i • • ; ! • : . . • : : : [ : • • "T" ] ; • ; : • 1 : : . : l : . : ; : ; | : . • _l_ J 1. . . . . . . . . . - - - • ; ! • 1 1 • - • i -r-j--• j • : : ! : ; -i 0.5 1.0 5D 10.0 SOJO Amps (rms) F i g . B.3(h) C a l i b r a t i o n c h a r t : Neutral - 60 Hz-660 Hz. 111 lP(x.y) Magnetic dipole Coil area Ac = ( 2a f a=0.25 m d=3.50 m turn number Nc=40 Total flux through c o i l : •=NC- //B(x,y)dxdy A c Magnetic Field at P(x,y): 4 i r r 3 M=dipole moment r=J(x+d)2 +y2 Magnetic Flux Density at P(x,y): B= UH i n 4ir ^(x+d)2 +y2 Therefore: * - £ n A M/dx/ y 2 ] 3, 2 dy Upon evaluation of integral: -2P.NCM f(d2i2a2_i2da)1'2 (d2 • 2a 2 - 2da>'2| , - U .NcMa 2 * " 4 l r a I d «a d-a J n c j3 Since the assumption d>>a holds, we can assume the fiel d of the solenoid at o is equivalent to that of a dipole, therefore: M=IAS I=current in solenoid A s"total area enclosed by current I To f ind area A s: Let n=winding per unit length of radius (assumed constant) Total turn number N,"25,000 v v Ns « /n(r)dr • n /dr • n(v-u) u u A, =/irr 2n(r)dr « un/ r 2 d r u u A, - l n ( v 3 - u 3 ) = intv-uX^+uv+u 2) 2u=38.2 mm 2v=95.3 mm A, =2NS (v2+uv+u2 ) Cross-Section of Solenoid Thus the magnitude of the flux through the co i l (ignoring sign): • ' W.NCNS I (v2+uv+u2 )^3-Then if we define B n g as the average magnetic flux density at o: ZTZ." Iivi±uv+uil (Tesla) 1 ? r t 3 It is in this manner that calibrated, as the E M F induced amplified and recorded on tape in the field survey. the mobile receiver system is by B (which is calculated) is the same way the data is recorded F i g . B.4 Schematic diagram of c a l i b r a t i o n c i r c u i t and c a l c u l a t i o n s f o r mobile AF r e c e i v e r system. 1 12 FREQUENCY (Hz) Fig. B.5 Sensitivity (mV/nT) calibration chart for mobile AF receiver system (least squares f i t to data; dashed lines indicate ±5% bounds attributable to scatter). APPENDIX C 113 EM-SURVEY DATA ANALYSIS The f i r s t stage i n a n a l y z i n g the data from the EM survey was to a s s i g n values to each mobile r e c e i v e r s t a t i o n . The magnitude of the t o t a l magnetic f i e l d at each s t a t i o n , at each of the four f r e q u e n c i e s (60 Hz, 180 Hz, 300 Hz, 420 Hz), was determined from the raw data by u s i n g the proper c a l i b r a t i o n graph. As d i s c u s s e d i n s e c t i o n 5.2 of the t e x t , the base s t a t i o n r e c e i v e r was a l s o used to e l i m i n a t e time dependancy of the s i g n a l . By d i v i d i n g the mobile r e c e i v e r s i g n a l by the base s t a t i o n s i g n a l , the a b s o l u t e value of the magnetic f i e l d i s l o s t , and the measurements at a l l the mobile r e c e i v e r s t a t i o n s become r e l a t i v e measurements. The data i s then normalized to a value of 1.0 at the base s t a t i o n to make a n a l y s i s e a s i e r ( n o t i n g t h a t , s i n c e the base s t a t i o n i s • the c l o s e s t s t a t i o n to the source, a l l mobile s t a t i o n v a l u e s w i l l be between 0 and 1.0). To a r r i v e at the contoured data, the U.B.C. Computing Centre L i b r a r y program SCATCN was used, which contours a set of s c a t t e r e d data p o i n t s u s i n g p r e - d e f i n e d contour v a l u e s . In a l l cases i n t h i s work, the contour v a l u e s are 1, 1/2, 1/3, 1/4, 1/50, such that data f i t t i n g a 1/r f a l l o f f w i l l e x h i b i t e q u a l l y - s p a c e d contour l i n e s . The program SCATCN contours the s c a t t e r e d data p o i n t s i n a 1 14 t w o - s t a g e p r o c e s s . F i r s t , t h e p r o g r a m g e n e r a t e s a g r i d o f a r t i f i c i a l v a l u e s , b a s e d o n t h e a c t u a l d a t a v a l u e s . T h e g r i d o f a r t i f i c i a l v a l u e s i s t h e n s e n t t o t h e L i b r a r y p r o g r a m C N T R , w h i c h c a n o n l y c o n t o u r d a t a p o i n t s w h i c h a r e c o n t a i n e d i n a r e g u l a r g r i d p a t t e r n . T h e i n p u t t o S C A T C N c o n s i s t s o f a t h r e e -d i m e n s i o n a l a r r a y , i n w h i c h t h e f i r s t t w o d i m e n s i o n s c o n t a i n t h e l o c a t i o n s o f t h e s c a t t e r e d d a t a p o i n t s , a n d t h e t h i r d c o n t a i n s t h e i r v a l u e s . S C A T C N t h e n g e n e r a t e s a g r i d , a n d t h e r e g i o n s u r r o u n d i n g e a c h g r i d - p o i n t ( o r i n t e r s e c t i o n ) i s d i v i d e d i n t o o c t a n t s . T h e a r t i f i c i a l v a l u e o f t h e g r i d - p o i n t i s s e t e q u a l t o t h e w e i g h t e d a v e r a g e o f t h e c l o s e s t d a t a p o i n t i n e a c h o c t a n t ( t h e w e i g h t i n g f a c t o r i s 1 / d 2 , w h e r e d i s t h e d i s t a n c e f r o m t h e d a t a p o i n t t o t h e g r i d i n t e r s e c t i o n b e i n g e v a l u a t e d ) . T h e g r i d o f a r t i f i c i a l v a l u e s i s t h e n u s e d a s t h e i n p u t t o C N T R . I n a r r i v i n g a t t h e a c t u a l c o n t o u r e d d a t a m a p s p r e s e n t e d i n t h i s w o r k , t h e p r o g r a m S C A T C N p r o d u c e d a g r i d m e a s u r i n g 44 X 5 0 , f o r a t o t a l o f 2 2 0 0 a r t i f i c i a l l y g e n e r a t e d g r i d p o i n t s . T h e p r o c e s s d e s c r i b e d h e r e w a s u s e d t o c o n t o u r t h e d a t a t a k e n i n t h e s u r v e y a r e a f o r e a c h o f t h e f o u r f r e q u e n c i e s . O b v i o u s l y a n a r e a o f f e w o r n o d a t a p o i n t s r e s u l t s i n a n i n a c c u r a t e r e p r e s e n t a t i o n o f t h e d a t a b y t h e a r t i f i c i a l g r i d . T h u s t h e c o n t o u r s a r e v e r y e r r a t i c i n a r e a s o f f e w o r n o d a t a p o i n t s , a s i s c l e a r l y i n d i c a t e d i n t h e a c t u a l o u t p u t s o f t h e r o u t i n e , f i g u r e s C . 1 ( a ) - C . l ( d ) . T h e s e e r r a t i c c o n t o u r s , d u e t o i n s u f f i c i e n t d a t a p o i n t s , w e r e i g n o r e d i n t h e p r e s e n t a t i o n o f t h e d a t a ( f i g u r e 5 . 5 ) i n s e c t i o n 5 . 4 . T h e " r e f e r e n c e f i e l d " p r e s e n t e d i n s e c t i o n 5 . 4 w a s i n c l u d e d t o i n d i c a t e t h e t h e o r e t i c a l e f f e c t o f t h e g e o m e t r y o f t h e p o w e r 115 l i n e , assuming a 1/r Biot-Savart r e l a t i o n . This was accomplished by mapping the configuration of transmission l i n e 5L82 in a series of connected l i n e segments. The region of the "survey area" was properly represented in r e l a t i o n to 5L82. A program was developed which calculated the theore t i c a l magnetic f i e l d , at a s p e c i f i c point within the "survey area", by summing the e f f e c t s of the f i n i t e l i n e segments, using the Biot-Savart equation for a l i n e segment: The "survey area" can be represented by a f i n e l y spaced g r i d , the value of the magnetic f i e l d B then calculated at each gr i d point, and the resultant g r i d of magnetic f i e l d B values contoured d i r e c t l y by CNTR. The result of this method was given in figure 5.6, l a b e l l e d the "reference f i e l d " since i t assumes the t h e o r e t i c a l c a l c u l a t i o n of the primary f i e l d within the survey area, independant of the location of the mobile receiver stations (the locations of the mobile receiver stations were included in figure 5.6 for purposes of comparison with the actual data). To show the innaccuracies inherent in the SCATCN program, figure C.2 was compiled. The same program which 1 16 generated the f i e l d data contour p l o t s was used to generate a t h e o r e t i c a l r e f e r e n c e f i e l d . The input to the program was the t h e o r e t i c a l v alue (normalized to 1.0 a t the base s t a t i o n ) of the free-space magnetic f i e l d at each of the 66 mobile r e c e i v e r s t a t i o n s . Thus f i g u r e 5.6 and f i g u r e C.2 only d i f f e r by the s i z e and coverage of the data s e t . Obviously SCATCN f a i l s to f a i r l y represent such h i g h l y s c a t t e r e d data i n regions of low coverage. The data presented i n p r o f i l e form ( s e c t i o n 5.4) was intended to show the secondary f i e l d e f f e c t s and that they are g r e a t e r than the a s s o c i a t e d random e r r o r of the data. The p r o f i l e s were compiled by simply p l o t t i n g the o r i g i n a l data ( r e f e r e n c e d and normalized to the base s t a t i o n measurements) in g r a p h i c a l form. The l i n e a r p l o t s are f o r an o v e r a l l view of the data, while the l o g - l o g p l o t s tend to show d e v i a t i o n s from a 1/r r e l a t i o n much more c l e a r l y (note t h a t an i n v e r s e p l o t on a l o g -log s c a l e g i v e s r i s e to a s t r a i g h t l i n e of slope - 1 ) . E r r o r bars i n d i c a t i n g ±10% random e r r o r are given f o r each data p o i n t , and the p l o t s are f i t t e d to the data, c o n s t r a i n i n g to a slope of -1 where p o s s i b l e . One p o i n t of i n t e r e s t i s t h a t the p r o f i l e s do not l i e p e r p e n d i c u l a r to the source, and are not p a r a l l e l . T h e i r l o c a t i o n s are a r e s u l t of a v a i l a b l e data p o i n t s , which were c o n s t r a i n e d by v e h i c u l a r a c c e s s i b i l i t y w i t h i n the r e g i o n . However, i t i s easy to show that the i n v e r s e r e l a t i o n of the data s t i l l h o l d s , and i n f a c t the o n l y change i s a v e r t i c a l s h i f t of the e n t i r e p l o t , which does not a f f e c t the a n a l y s i s presented i n t h i s t h e s i s : l e t y(d)=^ w ( l ) = i _ = _ L _ = constant d d I s i n G 1 log y=-log d log w=-log 1 + log (constant) The geomagnetic f i e l d was monitored during the EM survey, so that times of increased a c t i v i t y could be recorded. As stated in chapter s i x , the geomagnetic f i e l d was quiet to moderate in a c t i v i t y during the EM survey measurements, and was not taken into consideration in the interpretation of the r e s u l t s . For completeness, the magnetometer record i s included here in f u l l (figure C.3). Also., a spectral sample of the base station AF signal recorded on tape was taken every f i v e minutes, in addition to concurrent mobile receiver station readings. The res u l t s are plotted as a function of time, and are given in figure C.4(a)-C.4(b). 118 F i g . C.I(a) Contoured data - 60 Hz. 119 F i g . C.1(b) Contoured data - 180 Hz. 120 F i g . C.1(c) Contoured data - 300 Hz. F ig . C.1(d) Contoured data - 420 Hz. 1 2 2 F i g . C . 2 T h e o r e t i c a l data i n SCATCN program 123 124 0 -20 dB-40 -60 -80 B f l S E - 6 0 Hz 22 J U L Y 1981 L O C A L TIME 23 J U L Y 1981 BASE-180 Hz 22 JULY 1981 L O C A L TIME 23 JULY 1981 (rms) M 7 F i 9 ' C*4(a) JS'S. anf TSS°S» ^ ^ 2 / 7 / 8 1 - 2 3 / 7 / 8 i ) : BflSE-3.00 Hz H 1G 18 2 2 JULY 1981 I 2 0 LOCAL TIME "T" 10 12 ~1 16 18 23 JULY 1981 2 0 nT (rms) M O BflSE-420 Hz 22 JULY 1981 LOCAL TIME 23 JULY 1981 (rms) F i g . C.4(b) Base s t a t i o n AF s i g n a l (22/7/81-23/7/81): 300 Hz and 420 Hz. 

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