Verifying circuit-breaker interrupting capacity

TWELVE high-speed 230-kv oil circuit breakers rated 10,000,000 kva interrupting capacity are installed now in transmission-line and bus-tie positions of the left switchyard at the Grand Coulee Power Plant. The development of these important pieces of protective equipment has required extensive short-circuit testing both in a manufacturer´s high-power laboratory and at Grand Coulee Dam. This article covers the final stages of that development and describes in particular the field tests which were made in August 1950 in order to verify the circuit-breaker interrupting capacity rating of 10,000,000 kva and also to determine any possible margin above this figure.