High-voltage oil circuit breakers

ONLY a few years ago, 3,500,000 kva was the maximum standard rated interrupting capacity for high-voltage circuit breakers, and the interrupting-time ratings were mostly five and eight cycles. This article describes recent developments in interrupting devices that have made available standard circuit breakers for 5,000,000-kva interrupting capacity and 3-cycle interrupting time for 138-, 161-, and 230-kv voltage classes. Particular attention is directed to the circuit breakers recently shipped to the 230-kv switchyard at Grand Coulee Dam which carry a 10,000,-000-kva interrupting capacity rating on a 20-cycle reclosing duty cycle.