Electric leakage detecting device

An electric leakage detecting device for shutting off an AC electric circuit by detecting a ground-fault current occurring in the AC electric circuit by a zero-phase current transformer, the electric leakage detecting device including:

• an A/D converter which analog-to-digital-converts a difference signal between positive and negative output signals of the zero-phase current transformer;
• a digital filter which extracts low-frequency components of a digital signal that is output from the A/D converter;
• a digital comparator which generates a detection signal by comparing an output signal of the digital filter with the positive threshold and the negative threshold;
• a trip control signal generator which generates a positive trip control signal or a negative trip control signal based on the detection signal output from the digital comparator;
• an electric leakage judging device which judges whether the AC electric circuit is in an electric leakage state based on the positive trip control signal and the negative trip control signal, and generates an electric leakage judgment signal if judging that the AC electric circuit is in the electric leakage state;
• a delay counter which generates a final trip control signal if the electric leakage judgment signal has been received continuously from the electric leakage judging device more than a first prescribed time;
• a reset signal generation counter which is reset every time the positive trip control signal or the negative trip control signal is received from the trip control signal generator, and resets the electric leakage judging device and the delay counter it neither the positive trip control signal nor the negative trip control signal is received in a second prescribed time after being reset;
• and
• a switch driving circuit which shuts off the AC electric circuit when the final trip control signal is received from the delay counter.