Improved Reliability from Statistical Redundancy of Three Phase Operation of High Voltage Circuit Breakers

Experimental and statistical evidence is given which concludes that the great majority of practical circuit breakers derive considerable benefit from redundancy of three pole operation on a three phase system. The value of the standard deviation can be much more important than that of the voltage interrupted by the first phase to clear. For the same probability of failure, the poles in a "good" three phase circuit breaker can function reliably at more than 60% higher voltage than they can when acting alone (see Table XI).