Transients Due to Short Circuits A Study of Tests Made on the Southern California Edison 220-Kv. System

The paper deals with records which have been obtained during short circuits upon the Southern California Edison's 220-kv. system. The main features of the system are outlined, and such operating data as are necessary to afford an understanding of the various conditions which have to be met are included. The general scheme of relays is described, and the causes of flashovers and their times of occurrence are tabulated, together with the percentages which cause interruptions to service. Whether or not interruption is caused is found to depend, among other things, upon the load being carried at the time. With load below 150,000 kw., there are no interruptions unless relays are inoperative. A number of typical records of short circuits are shown and analyzed. It is shown that large amounts of power are consumed in short circuits, but that this is dependent upon the ground resistance. Practically all short circuits are single-phase to ground. The advantage of low-reactance machines is discussed and the various factors that prevent loss of synchronism pointed out. The records show that there is but little if any tendency for synchronous machines at either end of the line to fall out of step among themselves as a group, but that the sending end under certain conditions will get out of step with the receiving end.