Empirical reliability models for generator circuit-breakers

The objective of this paper is to present an empirical reliability model for air-blast and SF₆ generator circuit-breakers (GenCBs) which can be used to perform availability studies of different power station layouts. The main achievement of this work is an analytical formula which allows to model the reliability of air-blast GenCBs with an hazard rate that depends on the age of equipment. For SF₆ GenCBs the hazard rate can be reasonably considered as constant. The investigation shows that SF₆ GenCBs with hydro-mechanical spring operating mechanism is the most reliable technology for GenCB application. Specifically the average failure frequency of air-blast GenCBs is 2.7 times higher than that of SF₆ GenCBs with pneumatic drive and even 5.6 times higher compared to SF₆ GenCBs with hydro-mechanical spring operating mechanism. The average failure frequency of HVCBs is 2.5 times higher than that of SF₆ GenCBs with hydro-mechanical spring operating mechanism according to the results of a failure survey conducted by a CIGRE working group on SF₆ HVCBs. The reliability of different types of operating mechanism has been compared too. The results of the analysis show that a hydro-mechanical spring operating mechanism surveyed for GenCB applications is more reliable than spring, hydraulic or pneumatic operating mechanisms installed on HVCBs.