220-Kv. transmission transients and flashovers

The conclusion has been reached that birds are the cause of flashovers on the Southern California Edison line. The frequency and location of flashovers is given for nine years of operation at 150 kv. and two years at 220 kv. The increase in the number of flashovers when first going to 220 kv. has been reduced so that now there is no greater number than there was at 150 kv. This has been done by installing bird guards which are, however, not yet completely bird proof. Other possible causes of flashovers are considered, including corona, standing and traveling waves of high voltage, harmonic resonance, sustained high-frequency effects, lightning, and highly ionized air. Investigations to discover the presence of such disturbances are described; they included the use of a homemade photographic surge recorder, the klydonograph, and oscillograph. The amplitude of voltage surges caused by various switching operations and the quantity of tertiary and residual current at the different stations on the system are tabulated. The conclusions reached are that there are not any voltage disturbances of greater magnitude than those produced by normal switching, and that such voltage rises as do occur are totally inadequate to cause flashovers or cause any damage to connected apparatus. The evidence is all against the existence of sustained high-frequency currents or voltages and it may be stated confidently that they do not exist.