Analysis of some problems on 220 kV transformers in bypassing transformer's breaker

In substations with double busbar and bypass system,the operation using bypass circuit breaker to substitute a line circuit breaker is often needed.For the 220 kV transformers,when the higher voltage breaker is replaced by bypass breaker,how to eliminate the protection′s deadzone when by-pass circuit breaker replaces the CB of 220 kV main transformer,is presented.The breaker failure protection may startup incorrectly if the startup circuit of higher voltage breaker failure protection is not switched on.This paper brings forward a modified scheme to the startup circuit of failure protection for 220 kV transformers.In bypassing transformer's breaker,attention should be paid to the current switching and operation of the differential protection.