The typical secondary circuit of three-phase inconsistent protection for a circuit breaker is described along with its influence on the safe operation of the power grid. Also

the action reliability of the protection circuit is analyzed. Based on the performance test results of the time relay for the three-phase inconsistent protection

the action time and the action voltage are thoroughly investigated. Then an improved secondary circuit of three-phase inconsistent protection is proposed to solve the incorrect operation problems of relay protection

which are caused by the relay failure

contactor failure

or action time migration of the time relay. Finally

several measures have also been proposed to enhance the maintenance of three-phase inconsistent protection.