"Applied Science, Faculty of"@en . "Mechanical Engineering, Department of"@en . "DSpace"@en . "UBCV"@en . "Tsou, Shang-Jen"@en . "2012-03-20T20:42:57Z"@en . "1948"@en . "Master of Applied Science - MASc"@en . "University of British Columbia"@en . "In the conventional joints for aluminum core steel reinforced (A.C.S.R.) conductors the path of the electric current in the outer strands passes through two mechanical contacts, while for the inner strands the number of contacts is considerably more. It is recognized that the present techniques of making compression Joints is considered by many to be satisfactory. However, it is obvious that a continuous metal Joint would be superior. Recent advances in welding make the construction of such a Joint possible.\r\nIn the Joints constructed for experimental purposes each strand of a 397,500 C M conductor was brought out between two aluminium sleeves and Heliarc welded. In the finished Joint the weld bonds the inner and outer sleeves and the Individual conductors. The ends of the joint are compressed to prevent ingress of moisture which may be injurious to the conventional steel compression sleeve which connects the steel cores together.\r\nTests of the Individual strand resistance as measured between the central part of the Joint and the strands showed the strand resistances to be uniform and equal to an equivalent length of strand. This shows that each strand was satisfactorily connected at the weld. Overall resistance, heat and mechanical tests indicate that the welded-compression joint should be satisfactory in the field.\r\nIn addition to the welded-compression joint two cast-aluminium Joints were also investigated. These, however, due to poor bonding were found unsatisfactory."@en . "https://circle.library.ubc.ca/rest/handle/2429/41593?expand=metadata"@en . "AN INVESTIGATION OF WELDED AND CAST JOINTS FOR A.C.S.R. CONDUCTORS by Shang-Jen Tsou A Thesis Submitted in Partial Fulfilment of The Requirements for the Degree of MASTER 'OF APPLIED SCIENCE In the Department of MECHANICAL AND ELECTRICAL ENGINEERING 3 7 Cap I Approved: In Charge of Major Work H^d of --Department'. THE UNIVERSITY OF BRITISH COLUMBIA September, AN INVESTIGATION OF WELDED AND CAST JOINTS . FOR A.C.S.R. CONDUCTORS In the conventional Joint9 for aluminum core steel reinforced (A.C.S.R.) conductors the path of the electric current in the outer strands passes through two mechanical contacts, while for the inner strands the number of contacts i s considerably more. It i s recog-nized that the present techniques of making compression Joints i s considered by many to be satisfactory. However, i t i s obvious that a continuous metal Joint would be superior. Recent advances in welding make the con-struction of such a Joint possible. In the Joints constructed for experimental purposes each strand of a 3 9 7 , 5 0 0 c M conductor wasi brought out between two aluminium sleeves and Heliarc welded. In the finished Joint the weld bonds the inner and outer sleeves and the Individual conductors. The ends of the Joint are compressed to prevent ingress of mol3ture which may be injurious to the conventional steel compression sleeve which connects the steel cores to-gether. Tests of the Individual strand resistance as measured between the central part of the Joint and the s t r a n d s showed the s t r a n d r e s i s t a n c e s to be u n i f o r m and equal to an e q u i v a l e n t l e n g t h o f s t r a n d . T h i s shows t h a t each s t r a n d was s a t i s f a c t o r i l y connected a t the w e l d . O v e r a l l r e s i s t a n c e , heat and mechanical t e s t s i n d i c a t e t h a t the welded-compress ion j o i n t should be s a t i s f a c t o r y i n the f i e l d . I n a d d i t i o n to the welded-compress lon j o i n t two c a s t - a l u m i n i u m J o i n t s were a l s o i n v e s t i g a t e d . These, however, due to poor bonding were found u n -s a t i s f a c t o r y . Shang-Jen Tsou U n i v e r s i t y o f B r i t i s h Columbia September, 13k&. 2 TABLE OP CONTENTS PAGE 1 . Introduction 3 II. Investigation 8 A. Welded-compression joint for A.C.S.R. conductors & 1 . Procedure & 2 . Electrical conductivity tests ... . * 1 1 3 . Heating test .... 1 3 k-. Tensile strength test 1 5 5 . Microscopic examination , 1 J 6. Heliarc welding technique 21. B. Aluminum cast joint for A.C.S.R. conductors 2k-1 . Procedure . 2 ^ 2 . Electrical conductivity tests 2 6 3 . Heating test 2 6 Tensile strength test 2& 5 . Microscopic examination 29 III. Discussion and Prospectus 3 1 IV. References 3 3 V. Acknowledgements \u00E2\u0080\u00A2\u00E2\u0080\u00A2 3 5 VI. Drawings \u00E2\u0080\u00A2 3*> 3 AN INVESTIGATION OF WELDED AND CAST JOINTS FOR A.C.S.R. CONDUCTORS 1. INTRODUCTION An important consideration in the installation of power transmission lines i s the making of conductor Joints which w i l l retain throughout the useful l i f e of the conductor both high electrical conductivity and mechanical strength. During service conductors are exposed to extreme variations in temperature and tension, vibration stresses, short-circuit currents and atmospheric corrosion for a period of 5\u00C2\u00B0 years or more. The main d i f f i c u l t y in making a satisfactory joint in Aluminum-Core-Steel Reinforced (A.C.S.R.) conductors i s due to the formation of aluminum oxide on the surface of the strands. Several types of joints have been developed and. among them are the bolted and clamped joints, twisted sleeve joints, threaded compression joints, core joints and compression sleeve joints. Most of .these, with the exception of the compression sleeve joint have been found unsatisfactory for large size A.C.S.R. conductors. x According to Gordon B. Tebors (7) investigations deterioration of twisted sleeve joints i s indicated f i r s t by increase of resistance and heating. This i s followed in x A l l numbered references given i n References. extreme cases by the appearance of holes in the sleeve, pro-duced by internal arcing, and f i n a l l y the conductor f a i l s mechanically at or near one end of the sleeve. \u00E2\u0080\u00A2The threaded compression joints have a very bad operating record. After 20 years in service on a 110 kv line, several hundred such joints i n 312,000 cm A.C.S.R. conductors were tested, and more than ^>0% had a resistance greater than 10 time normal. In most cases the high resistance was i n the threaded connection. According to the Report made by W.J. Nichols (6) on a l l 132 kv lines, prior to 1933, the A.C.S.R. conductors were jointed i n midspan by cone-type joints gripping the steel and aluminum strands separately by means of steel and aluminum cones respectively. These joints were thoroughly tested before adoption, both for mechanical strength, 95$ \u00C2\u00B0f the breaking strength of the conductor being required, and for conductivity, the resistance having to be less than that of an equivalent length of conductor. In 193^, the compression joint was introduced on new lines and for the maintenance of existing lines. The reason for this change x^ ras the increasing number of failures of cone-type joints. The cone-joint failures began to take a general form of break in the conductor, usually some 12 - IS* inches from one end of the joint. There was evidence of heating at the break and also in the Joint, the steel strands showing signs of heating over the length between the joint and the break. This evidence pointed to 5 high resistance in the. aluminum portion of the joint, with the resultant transfer of current to the steel core i n the joint and back to the aluminum strands a short distance out-side i t . This high resistance was checked and i t was found that the resistance of many joints had increased seriously in service. Experience with compression sleeve joints (7) has been generally satisfactory. Occasionally, hoi^ever, an aluminum conductor burns off at or near a compression sleeve. Examination usually discloses improper cleaning of strands of the conductor and the sleeve. The resultant high resistance causes heating, arcing, annealing, and f i n a l l y rupture of the conductor. The location of this rupture i s usually just at the entry to the sleeve, but i s sometimes a foot or more away from the sleeve. Investigation i n such cases has shown high inter-strand resistance in the joint with consequent uneven current distribution. The few high-conductivity but over-loaded strands become red-hot i n the vicini t y of the joint. Besides the above-mentioned methods of jointing A.C.S.R. conductors, the A.I.A.G-. in Switzerland has developed so-called Alutherm procedure for welded conductor joints. The original strength of the cable being somewhat diminished in the weld3, joints i n the spans were mechanically reinforced by aluminum sleeves which were pressed onto the cable. Unfortunately there i s very l i t t l e data available on a welded joint by this method. 6 It Is quite clear, that i f the conductors are jointed together by any of these methods, the interface i s essentially a discontinuous region, and there i s a more or less abrupt change in the conditions of current flow from one conductor to the other. If the conductors are welded together, the joint i s mechanically and electrically con-tinuous, and there i s in general less disturbance i n the current flow, provided that the weld i s homogeneous and of uniform conductivity. The art of welding, necessitated by the demands of industry i n wartime, has progressed considerably. A method known as the \"HELLIARC\" process (l) has been developed which can be used i n the welding of corrosion-resistant metals. The question therefore, arose as to whether this technique could be; applied in making satisfactory A.C.S.R. conductor joints. The idea of a welded-compression joint was dis-cussed with Mr. Laird of the Vancouver Office of the Aluminum Company of Canada, and also with Mr. Underwood of the Van-couver office of the Dominion Oxygen Company. As a result of these discussions these two companies supplied the necessary materials and' some equipment for the construction of two experimental joints. During the investigation certain d i f f i c u l t i e s arose which suggested the idea of making cast aluminum joints containing 12% silicon. Two experimental joints were con-structed and tested. The results of the tests were not as hoped for. 7 However, recent developments in aluminum solders may make this technique feasible and plans are now under way to make up experimental joints employing aluminum solder. The details are discussed in a later section of this thesis. 11. INVESTIGATION A. Welded-compression J o i n t f o r A.C.S.R. Conductors Procedure Two experimental j o i n t s were constructed f o r the i n v e s t i g a t i o n . These are shown i n photographs #1, 2 and 3.. Photograph #4- shows the 1 0 0 -ton model E h y d r a u l i c press used i n making the j o i n t s . I n the development of the welded-compression j o i n t f o r A.C.S.R. conductors, an endeavour was made to use standard p a r t s and equipment i n so f a r as p o s s i b l e . Care was taken to ensure that the e l e c t r i c a l c o n d u c t i v i t y of the j o i n t and the t e n s i l e s t r e n g t h were not impaired by damage to aluminum strands and s t e e l core during assembly or by heating d u r i n g the welding operation. The con-s t r u c t i o n a l d e t a i l s of the experimental j o i n t s are shown i n drawings F i g . 1, 2, and 3\u00C2\u00BB The f o l l o w i n g procedure was employed i n assembling the j o i n t s j F i r s t the aluminum end or outer sleeves were placed on each of two conductors to be j o i n t e d . Then approximately 1$ inches of the aluminum strands of one conductor were unwound and fanned out. Care was taken not to unduly bend, the strands d u r i n g t h i s o p e r a t i o n . The i n n e r sleeve was then p l a c e d over the s t e e l core o f t h i s conductor. Next, the strands of the.other conductor 9 Photograph #1 showing the component p a r t s of the welded-compression j o i n t (A) standard s t e e l sleeve (B) Inner aluminum sleeve (C) End or outer sleeves. Photograph #2 showing welded-aluminum compression j o i n t p r i o r to welding. Photograph #3 shoving ( l & 2 ) welded-aluminum compression j o i n t s and (3 & *0 cast aluminum j o i n t s p r i o r to t e s t i n g . Photograph #K, Hydraulic compressor 100 ton cap a c i t y Model E. 11 were fanned out back to about k- inches. The steel sleeve was then put i n place and the steel compress-ion Joint made in the conventional manner. Following this the inner aluminum sleeve was placed centrally over the steel sleeve and compressed in place. The aluminum strands were then returned more or less to their original position i n such a manner that the ends of the strands lay along the outer ends of the inner sleeve. The end or outer sleeves were then driven in place so that the ends of the strands were held firmly as shown in photograph #2. The two ends of each outer sleeve were then compressed ; and the ends of the strands were welded together and to the sleeves by Heliarc welding. Elec t r i c a l Conductivity Test. In general i t may be stated that a joint which has a low resistance i n i t i a l l y may be expected to give satisfactory service. For reference the resistance of a joint i s compared with that of the equivalent length of conductor. In this particular case the specifications on 3 9 7 , 5 0 0 C.M. A.C.S.R. conductors are as follows: Number of aluminum strands 26 Number of layers . 2 Diameter of aluminum strand ... O . I 2 3 6 \" 12 Number of s t e e l strands 7 Diameter of s t e e l strand O.O96I Outside diameter of the conductor .... 0.7^3 Ultimate strength, pounds l6l90# Weight, pounds per mile 2&S5# Approximate current c a p a c i t y 59\u00C2\u00B0 amp. Resistance at 50\u00C2\u00B0C fo.r 60 c y c l e , ohms per conductor per mile 0.259 ohms o , Resistance at 25 C f o r 50 c y c l e , ohms per conductor per mile .............. 0.235 ohms. The f o l l o w i n g r e s i s t a n c e s were obtained w i t h an Evershed and Vignoles \"Ductor\": The r e s u l t was as f o l l o w s : (Room temperature 20 C) Resistance of \u00C2\u00A397,500 C.M. A.C.S.R. 44 microhms per f o o t . Resistance of welded aluminum compression j o i n t No. 1, 23\" l o n g . .. 34 microhms Resistance of welded aluminum compression J o i n t No. 2, 25\" l o n g .... 40 microhms. From these data i t i s seen that the r e s i s t a n c e . Of.'Joint No. 1 i n terms of the r e s i s t a n c e of an equivalent l e n g t h of the 397,500 A.C.S.R. cable i s 34 x 12 - koM 23 x 44 and that the r e s i s t a n c e of j o i n t No. 2 i s 40 x 12 = 4 3 . 0 % 25 x 44 13 These results are in very close agreement with the figures given by Mr. R. Lemire (5) of the Hydro-Electric Power Commission of Ontario,, which states that a well-made Joint i s about K0% of the resistance of the same length of cable. The welded-compression Joint No. 2 ha3 a .higher resistance than the No. 1. This might explain the fact that the No. 2 joint was welded f i r s t , with a current at 100 amp. which was not high enough. The No. 1 joint was welded at a higher current - 120 amp. which gave a better result. It was found, following a suggestion in Mr. Tebo's paper, that the individual strand resistance as measured between the central part of the joint and strands was uniform and equal to that of an equivalent length of strand. This shows that each strand was satisfactorily connected at the weld. Heating Test. For the heating test an 18* kw, 6 0 0 A , 30 v Hawthorn D.C. generator was used, t'tiis being the only big current source available. A l l the samples of conductor joints were connected in series. The current 'was kept constant by adjusting.the f i e l d current of the generator. During the tests the room temperature was almost constant at 1&|-0C. After two hours time an approximate steady state was reached. 14 The Heating Test was repeated six times, the longest one being continued for ten hours. The results of these tests were almost the same. The temperatures obtained in s t i l l a i r at current loading 7 5 \u00C2\u00B0 amp. for the cable and the welded aluminum compression joints are l i s t e d in Table 1 and plotted in Pig. 4. Taking the average steady state temperature rise for cable and for the joints, the following results are obtained: Temperature rise for the cable 118\u00C2\u00B0 _ 1 2 L 5 0 . 9 9 . 5 \u00C2\u00B0 c . Temperature rise for Joint No. 1 SO0 - 18 .5\u00C2\u00B0 =: 6 l . 5\u00C2\u00B0C. Temperature rise for joint No. 2 84\u00C2\u00B0 - 13 .5\u00C2\u00B0 \u00C2\u00BB 65.5\u00C2\u00B0C. The temperature rise of the joints In percent-age with respect to the cable: For welded-compression joint No. 1 i s For welded-compressicm joint No. 2 \u00C2\u00A75J5 9 66% 9 9 . 5 4 These results indicate that the welded aluminum compression joint has a lower temperature rise and better conductivity than the cable i t s e l f which meets the essential requirement for conductor-15 joints i n transmission lines. TABLE 1 Cable and Welded-compres3ion joint Temperatures obtained i n s t i l l air with a current of 75\u00C2\u00B0 Amperes DC. Time Joint No.. 1 Joint No. 2 Cable 0-00 0-05 0-10 0-15 0-20 0-25 0-30 0-40 0-45 0-50 0- 55 1- 00 1-10 1-20 1-30 1-40 1- 50 2- 00 125.5\u00C2\u00B0 22.0 29.0 34.5 46.0 51.0 55.0 59.0 62.0 65.0 67.5 72.0 74.5 77.4 79.5 s o . o 77.5 i3,5\u00C2\u00B0c 22 30.0 J 5 55 ,0 59.0 63.0 65 .0 69.0 72.0 75.0 32.6 84.5 34.4 34 .0 79.0 13.5 40 .0 62.0 lh5 34.0 92.0 97.5 101.5 105.0 IO5.5 110.0 112.0 114.0 116.3 119.0 122.5 113.0 116.0 107.0 4. Tensile Strength Test. The tensile strength test was made in the Federal Forest Products Laboratory at the University of Br i t i s h Columbia. In order to provide adequate gripping by the stamps of the testing machine, standard steel compression sleeves, and short pieces of 16 Photograph #5 showing the r e s u l t s o f t e n s i l e t e s t on experimental J o i n t #1. The break o c c u r r e d i n the s p e c i a l g r i p shown at the l e f t . 17 aluminum sleeving were compressed on the ends of the experimental cables. The overall length of each joint plus two cables ends was approximately 76 inches. Only one sample joint (#l) was tested. It was found to break at 15,200 pounds ultimate in the special grip as shown in photograph #5. The welded-compression joint was unaffected and there was no measurable permanent elongation. The elongation of the cable i t s e l f was 77 1/3\" - 76\" x 100 - 2.1# 76\" - 23\" As was mentioned previously the ultimate strength of 397,500 A.C.S.R. conductor i s 16,190 pounds. It i s therefore seen that the test-load applied was approximately Sk-% of maximum for the cable. This i s quite satisfactory as the safety factor of the joint i s at least 1.9 since the break occurred in the cable grip. Normally a safety factor of 2 to 2.2 i s used. The effect of compressing the inner end of the outer sleeve i s shown in photographs #6 and 7. While the damage to the strands in this case was not detrimental excessive flattening could cause over-heating. Microscopic Examination In order to ascertain the effect of heating due IS to the welding operation the folloxtfing mlcro3copic examinations were made of the steel core and the aluminum strands and sleeves. (I) Steel Cores. Two specimens of the steel core were examined; one from the welded compression joint and the other from unheated piece of conductor. Examination of the micro-photographs (photographs #3-9) shows that no there is^apparent difference in the micro-structure of the steel cores. (II) Welded Aluminum. An examination of the welded aluminum was made by microphotographlng a longitudinal section of the welded joint. A longitudinal section was used instead of a cross-section because i t was impossible to determine the actual position of the ends of the welded strands inside the Joint. The microstructure of the longitudinal section i s shown in photograph #10. Photograph #6. Showing damage to strands due to compression of the outer sleeve. Photograph #7. Showing the Junction of the inner and outer sleeves, strands and steel core. 20 F T % * - ^ r Photograph #&*. M i c r o s t r u c t u r e o f unheated s t e e l s t r a n d and p o r t i o n o f s t e e l s l e e v e . 4\u00E2\u0080\u0094 S t e e l s leeve 4 \u00E2\u0080\u0094 Z i n c c o a t i n g on s t e e l s t r a n d 4 \u00E2\u0080\u0094 S t e e l s t r a n d . JESB Photograph #9. M i c r o s t r u c t u r e o f heated s t e e l s t r a n d and p o r t i o n of s t e e l s l e e v e . *./ 4\u00E2\u0080\u0094 S t e e l s leeve 4\u00E2\u0080\u0094 Z i n c c o a t i n g on s t e e l s t r a n d . "Thesis/Dissertation"@en . "10.14288/1.0106655"@en . "eng"@en . "Mechanical Engineering"@en . "Vancouver : University of British Columbia Library"@en . "University of British Columbia"@en . "For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use."@en . "Graduate"@en . "An investigation of welded and cast joints for A.C.S.R. conductors"@en . "Text"@en . "http://hdl.handle.net/2429/41593"@en .