Method and device for diagnosing failure state of circuit breaker

The invention provides a method and device for diagnosing the failure state of a circuit breaker. The method comprises the following steps of obtaining a current signal characteristic value f0 (t10, i10 and S0) of an opening and closing coil in a circuit breaker predelivery test; obtaining a current signal, in the power-on process, of the opening and closing coil of a circuit breaker to be tested; performing morphological filtering processing on the current signal to obtain the de-noised current signal of the opening and closing coil of the circuit breaker to be tested; calculating a corresponding characteristic value f1(t11, i11 and S1) of the de-noised current signal; judging whether the value meets the formula shown in the specification; if the value meets the formula shown in the specification, further judging whether the value meets a formula shown in the specification; if the value does not meet the formula shown in the specification, judging that an iron core of the circuit breaker is normal and a power supply of the opening and closing coil fails; if the value does not meet the formula shown in the specification, further judging whether the value meets the formula that (S1-S0)/S0 is larger than theta; if the value meets the formula that (S1-S0)/S0 is larger than theta, judging that starting lagging failures happen to the iron core of the circuit breaker. According to the technical scheme, the diagnosing efficiency can be improved, and the diagnosing precision can be obviously improved. The requirement that the circuit breaker is diagnosed online on site can be well met.