Patent ID: 7463036

Claim:
A method to determine a deviation in a time characteristic of a circuit breaker coil within a power system which comprises a coil signature element, the method comprising: measuring an analog coil voltage and a coil current of the circuit breaker coil to determine a time characteristic baseline solely for the voltage across the circuit breaker coil and solely for the current flowing through the circuit breaker coil; measuring an analog coil voltage and a coil current of the circuit breaker coil over time to determine an ongoing time characteristic solely for the voltage across the circuit breaker coil and solely for the current flowing through the circuit breaker coil and wherein each measuring of the analog coil voltage and the coil current comprises measuring the maximum circuit breaker coil current, the duration of the current flowing through the circuit breaker coil, and the minimum voltage during each coil operation; comparing the ongoing time characteristic with the time characteristic baseline to identify any changes from the time characteristic baseline that exceed a predetermined threshold; and outputting a signal where the changes exceed the predetermined threshold.