A Three-Cycle 3,500-Megavolt-Ampere Air-Blast Circuit Breaker for 138,000-Volt Service

Early investigation of the air-blast principle of arc interruption clearly indicated that this principle was based on sound fundamentals and that continued research and development would lead to an economical and practical design. Preliminary studies indicated that the axial-flow interrupter was admirably suited to the high-voltage breakers with their lower current ratings, while the high current of the low-voltage equipments could be handled best by an interrupter comprising a cross-blast principle. Outdoor axial-blast breakers having interrupting ratings as high as 1,500 megavolt-amperes for service up to 138 kv have been in service for the past few years. Circuit-breaker designers and operating engineers have expended many years of diligent effort in the development of high-voltage oil circuit breakers to their present high degree of dependability and performance. Although the development of high-voltage air-blast breakers is of much more recent origin, the rate of progress has been relatively so rapid that the air-blast breaker described in this paper has exhibited performance characteristics so outstanding as to merit careful attention.