| 摘要 |
PROBLEM TO BE SOLVED: To provide a protective relay which does not necessarily require a three-phase input and is always capable of deciding normality/abnormality of a filter circuit even with only a single phase. SOLUTION: This protective relay comprises a filter circuit 2, which takes in alternating-current waveform from an alternating-current system to be protected and removes noise from the alternating-current waveform, an inversion circuit 3 which inverts the alternating-current waveform from the filter circuit 2, a half-wave rectifying circuit 4, which is fed directly with an output waveform from the inverting circuit 3 and output waveform from the filter circuit 2 without intervening the inversion circuit 3 and half-wave-rectifies the waveform from both, and a CPU circuit 6 which is for issuing a command for opening the circuit to be protected, when a quantity of electricity based on the output waveform of the half-wave rectifying circuit 4 exceeds a specified value, and is provided with a function of detecting two direct-current components for a prescribed period, based on output waveform from the half-wave rectifying circuit 4, and when the difference between the two direct-current components exceeds a prescribed range, decides that the filter circuit 2 to be anomalous. |
