This paper analyzes the action behavior of protective relay after an actual event of internal 10 kV electrical cable joint failure in a hydropower plant. It reports methods of observing the problems such as sampling errors of grounding ze-ro-sequence current of protective relays,protective action dead zone,etc. It also proposes effective countermeasures inclu-ding adjusting cable zero-sequence CT installation position,optimizing installation position of 10 kV bus incoming circuit breaker,and adding live display devices.
cable failureprotective actionaction dead zoneinstrument transformercircuit breaker