Field Tests at Grand Coulee Dam on 10,000-Mva 230-Kv Low-Oil-Content Impulse Circuit Breaker

This paper describes field acceptance tests made on the 230-kv 10,000- mva (megavolt-ampere) impulse circuit breaker switching units furnished for the new Right Switchyard at the Grand Coulee Dam power plant. Details of the circuit breaker design are followed by a description of a successful series of line dropping and fault tests made on a single pole circuit breaker unit to observe its performance up to rating and to determine the capabilities of the circuit breaker for higher short circuit duties which will be available at this location in the near future. Line dropping tests were made up to a maximum of 300 lines-miles without restrikes and, therefore, without abnormal overvoltages. Seven fault tests were made at full station capacity with short circuit duties up to 12,000 mva, with interrupting times ranging from 1.75 to 3.0 cycles, and with reclosing times of 9 cycles. The condition of the contacts and oil at the end of the test indicated that a substantial number of additional tests could have been made without replacement. There was no distress on any test and no trouble developed with any mechanical operations or breaker parts. These tests together with factory laboratory tests indicate the suitability of the 10,000 mva interrupting rating for this design of low-oil-content impulse circuit breaker and the possibility of building similar circuit breakers for higher ratings when the requirement arises.