Development of a Circuit Breaker for Large Generators. Final Report

摘要

This report deals with the evaluation of design concepts for the development of Circuit Breakers for large generators and attempts to define a rating structure for a generator circuit breaker. It includes studies on the influence of the system upon the performance of the circuit breaker. This study covers: The harmonic content in the fault current, the absence of current zeros, the influence of the dynamics of the generator shaft upon the current, and the magnitude and characteristics of the inherent transient recovery voltage produced by the system. Design requirements such as storage volumes, operating pressures and size of nozzle's orifice are identified for SF sub 6 synchronous and non synchronous interrupters of the axial flow type. The concept of a current limiting generator circuit breaker is introduced and two variations of a current limiting element are evaluated. One of the concepts uses liquid metal (NaK 78) as the current limiting element, and the other considers the use of a frangible conductor. The preliminary results obtained with an experimental model of a NaK device shows that a magnetic pinching effect reduces the time required for the initiation of the liquid metal vaporization which determines the onset of current limitation and shows that the NaK device appears to offer promise for the development of a current limiting generator breaker. (ERA citation 07:046627)