Abstract: This paper investigates a case in an extra-high-voltage (EHV) power grid in which the manual reset of a 500 kV circuit breaker pole-discrepancy relay caused the unexpected operation of the circuit breaker autoreclosure, resulting in erroneous three-phase closing of the circuit breaker. The pole-discrepancy circuit of the circuit breaker mechanism, the closing circuit, and the protection autoreclosure principle are studied in depth, and the causes of the operation and the entire operation sequence are analyzed. Finally, three countermeasures are proposed to address this problem, and their respective advantages and disadvantages are analyzed. These measures are expected to play a positive role in reducing the number of fault-induced impacts on the power system, improving system transient stability, and extending the service life of circuit breakers.