Movements of Overhead Line Conductors During Short Circuits

Abstract
When overhead lines carry large short-circuit currents, the resulting magnetic forces on the conductors are such as to cause the cables to be repelled to greater distances than the usual spacings. The elementary principles involved are stated. A single-phase short circuit is shown to be the one producing the greatest movements. A theoretical calculation of the forces and actual experience showed the necessity of making tests to study the problem. A description of the tests indicates how photographic records of the movements of relatively large cables were obtained. The results of over 330 tests are shown by pictures and curves. The effects of a variation in each of the five principal variables, cable size, span length, spacing, tension, and current are discussed. A mathematical expression is derived by means of which the maximum movement of conductors in a horizontal plane can be approximately determined. It has been found possible to set up a miniature test with small wire that very closely duplicates to a small scale the movements of a larger conductor. The results indicate that it is necessary for moderately large systems to take account of these short-circuit forces in the design of their overhead systems. There is a large field for research on this subject and more work should be done.

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