A Conserved-Pressure Air-Blast Circuit Breaker For High-Voltage Service

This paper describes the design and construction of a 138-kv, 1,500,000-kva air-blast circuit breaker. The construction is made possible by the use of a new interrupting device which utilizes the axial blast nozzle together with a ``conserved pressure'' chamber. The chamber receives the exhaust from the interrupting nozzle and contains the movable contact of the breaker in its open position. By means of a spring-loaded relief valve the pressure and dielectric strength of the air in the chamber are maintained at a high level. The pressure in the chamber is at the same time less than 50 per cent of the pressure above the nozzle restriction so that the air flow through the interrupting nozzle is unimpaired, being the same as through the same nozzle discharging to atmospheric pressure. As a consequence, the conserved pressure breaker is found to have the same ability to interrupt current as a conventional axial nozzle but to be capable of interrupting circuits of much higher voltage. The 138-kv three-phase breaker consists of two interrupting units in series per pole with a disconnecting device included as part of the breaker. Operation of the breaker is entirely pneumatic, opening and closing being performed by energizing the electrically operated valve.