A New Air Circuit Breaker With 250,000-Kva Interrupting Capacity

Heretofore it has not been commercially feasible to apply air-type breakers of the 5,000-volt class to circuits capable of producing short-circuit currents equivalent to 250,000 kva. However the continued demand for air circuit breakers of higher interrupting ratings has stimulated the development of a new breaker suitable for these applications. This achievement has been accomplished through magnetically enhanced diffusion of ionized particles, establishing dielectric strength in a gaseous region which was previously highly conducting. The interrupter consists essentially of an arc chamber of laterally spaced refractory plates embodying V-shaped slots and a magnetic circuit which imposes an intense magnetic field transverse to the slotted plates during the arcing period. The theory of arc interruption by this new air breaker is considered. Design details are described and illustrated. Complete sets of test results are given, with representative oscillograms. The test results are discussed, and it is demonstrated that the new breaker is applicable to modern metal-clad switchgear.