Circuit-Breaker Field Testing at 87% of Line-To-Line Voltage

A 3-phase interrupting test on a circuit breaker is the most severe test to demonstrate the breaker's interrupting ability. To demonstrate the 3-phase interrupting capability on a single-pole test, the fundamental frequency recovery voltage must be equal to 87% of line-to-line voltage. Most power utilities find it difficult to obtain proper voltage for this type of field test. This paper describes the test equipment and method employed, and the principle involved, in obtaining a single-pole circuit-breaker test at 87% of line-to-line voltage of 34.5-kv circuit breakers, conducted by the Department of Water and Power (DW&P) of The City of Los Angeles.