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The location of flashovers on Transmission lines Evans, Donald John

Abstract

The object of this thesis is to find a method for locating transient as well as permanent faults on transmission lines. Transient faults are those lasting for a fraction of a second or so which do not cause serious enough damage to necessitate immediate repairs before the line may be reenergized. However, transient faults such as insulator flashovers may cause enough damage to be a potential permanent outage. It is thus desirable to be able to locate the position of the fault, and to inspect the line and insulators so that they may be repaired if necessary when the line can be conveniently removed from service. The method that seemed most desirable was based on the echo-ranging principle such as is used in radar. This method has the advantages of accuracy and ease of interpretation. A damped sine wave pulse is generated at short intervals and fed onto the transmission line by means of a coupling capacitor. This pulse travels along the line and is partially reflected from any discontinuity such as a flashover to ground. The transmitted pulse, and pulses reflected from the end of the line and the fault are shown on a viewing tube; the distance to the fault being found by proportion. The line is pulsed only on the occurrence of a fault; thus any interference with radio is eliminated. The pulse generator is tripped by zero-sequence current or from the surge created by the fault itself. The pulses were to be recorded on a skiatron or memory tube which holds the trace on the tube until it is erased at will by the operator. This eliminates the necessity of photographic equipment and the disadvantages of delay and inconvenience of developing the film. The work accomplished on the project included the theory of wave propagation along transmission lines and the reflection to be expected for arcing ground faults. A pulse generator was built to produce either a damped sine wave or a sharp-fronted wave with exponential decay. Experiments were -carried out on coaxial cable with carbon and oil arcs as the fault, but no experiments were carried out on actual transmission lines as no line was available. The results of these experiments and the theory indicate that the method should be satisfactory on transmission lines.

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