Circuit Breaker Shock Testing - Individual Component Tests and Apparatus Mounted Tests

Abstract

The integrity of circuit breakers in a shock environment is essential to the survivability of naval combatant ships. A momentary disruption of power due to the opening of circuit breakers can disable essential combat systems equipment for a substantial period of time relative to the required response time of these systems. Even with the ongoing effort to provide shock hardened circuit breakers, the record indicates that shock integrity has been a continuing area of concern during ship shock trials. An historical review is provided of the efforts which have been undertaken to improve the shock resistance characteristics of circuit breakers and of the circuit breaker mounting structures (i.e., in switchboards or panelboards). Circuit breakers have exhibited varying shock resistance characteristics when tested individually versus when tested as an integral member of a switchboard or panelboard, therefore, a comparison is provided of the shock testing specification requirements of circuit breakers tested as components and of the assemblies into which they are commonly mounted. The differences are analyzed to postulate possible causes for the inconsistency of shock qualified circuit breakers when shock tested in their operating environment. An analysis is provided of the similarities and differences of shock impacts on circuit breakers when tested as components and when tested in a switchgear or panelboard assembly. Two series of tests were conducted, one involving circuit breakers in a panelboard and the other involving circuit breakers in a switchboard. The analysis compares the acceleration-time histories, velocity, displacements, and the shock spectrum derived therefrom. Of particular interest is the mounting structure of circuit breakers when shock tested as components and the interaction of the switchboard structure with the circuit breakers under shock impacts. Recommendations are provided for improvements in specifications, for improvements in the design of the assemblies which house the circuit breakers, for improvements in circuit breakers and for more stringent requirements regarding first article testing of assemblies.