Circuit breakers for Boulder Dam line

Because of its length, 270 miles, the 275 kv transmission line from Boulder Dam to Los Angeles, Calif., requires extremely high speed switching for stability. To meet the requirements, a high voltage impulse circuit breaker, extending the oil blast theory to cover a multibreak construction with double cross-blast ports, has been built. It provides over-all switching times consistently less than 3 cycles (3/60 second). Approximately 10 per cent as much oil is used as in a comparable breaker of conventional design, and only 1/10 of this is exposed to arcing. Large factors of safety are provided over and above the interrupting rating of 5,000 amperes, 287 kv, or 2,500,000 kva.