Field Tests on a 138-Kv High-Speed Oil Circuit Breaker at Philip Sporn Power Plant [includes discussion]

The continuing and rapid expansion of the 138-kv transmission system of the American Gas and Electric (AG&E) Company and of its superimposed 330-kv system in terms of installed capacity and interconnections has created a demand for 138-kv circuit breakers rated considerably in excess of 5,000 megavolt-amperes (mva). At key points of the system 10,000-mva breakers are being installed in large numbers, and existing breakers are relocated to positions remote from large concentrations of power. The new breakers were purchased on the strength of single-pole factory tests made at full voltage and reduced interrupting current, and at full current and reduced voltage up to the limit of available testing facilities. Though this kind of 2-part test is never a complete substitute for full-capacity tests, it was felt that satisfactory performance under field conditions could reasonably be predicted on the basis of such tests. Some of the 5,000-mva breakers recently installed are from a manufacturer who lacks facilities for factory testing. The field tests described in this paper were made to prove this breaker up to its full rating, and then to increase the short-circuit duty until the limit of either the breaker or the system was reached. The limitation proved to be the available system short-circuit capacity, which resulted in a maximum breaker duty of 6,900 mva. It is believed that this is the heaviest fault interruption ever made at the 138-kv breaker rating.