Unusual Performance of Standard 230-Kv Impulse and Tank-Type Oil Circuit Breakers on Field Tests

The requirements of the United States Bureau of Reclamation for 230-kv circuit breakers at Grand Coulee Dam which would far exceed present-day standard circuit-breaker ratings, required field tests to check the performance of standard circuit breakers in order to predict the required designs for higher ratings. Standard 3,500 megavlt-amperes (mva) low oil content impulse- and tank-type oil circuit breakers were tested on the meximum capacity available of over 7,000 mva. Usually satisfactory performance was observed under all test conditions indicating that standard circuit breakers of these types incorporatting modern methods of arc interruption, will require but little change to adapt them to the Grand Coulee Dam requirements for ratings of 10,000 mva.