Switching Overvoltage Hazard Eliminated in High-Voltage Oil Circuit Breakers

High-voltage transmission lines, when de-energized by conventional oil circuit breakers, are often subjected to high-voltage surges which present a real hazard to terminal equipment. The mechanism of surge generation is initiated by circuit-breaker restriking phenomena which are encouraged by the interruption of the large leading currents required to charge moderate and high-voltage lines. By interposing suitable resistors across the interrupting elements during the opening stroke of the breaker, the switching overvoltages may be either eliminated by preventing restriking or so reduced in magnitude in the event of restriking that the system is relieved of their hazard. The development of this achievement is presented chronologically: 1. Theoretical considerations 2. Transient-analyzer studies 3. Power-laboratory switching tests 4. Actual field tests on the 220-kv lines of Southern California Edison Company Ltd. at Boulder power plant