Patent ID: 8749100

Claim:
A system comprising: a power source side voltage detector operable to measure a waveform of a power source side voltage that is a voltage to ground at a power system side of a circuit breaker; a transmission line side voltage detector operable to measure a waveform of a transmission line side voltage that is a voltage to ground at the transmission line side of the circuit breaker; a waveform calculating device in communication with the power source side voltage detector and transmission line side voltage detector operable to: calculate an added waveform of the waveform of the power source side voltage that is measured by the power source side voltage detector and the waveform of the transmission line side voltage that is measured by the transmission line side voltage detector; calculate a waveform of an absolute value of the added waveform; extract a waveform of a component in a frequency band which is lower than a frequency of the power source side voltage and higher than a frequency of a DC component, from the waveform of the absolute value; and detect a cycle of the extracted waveform; and a switch operable to close the circuit breaker based on the detected cycle.