Patent ID: 7285961

Claim:
An insulation degradation diagnostic device comprising: a current detector configured to have a filtering function with an amount of attenuation of −60 dB or less and a slope characteristic of −5 dB/oct or less at a commercial frequency, and detect a current flowing through a line to be measured; a first high-pass filter configured to remove a low frequency component from a current signal based on a current detected by the current detector; a low-pass filter configured to remove a high frequency component from a current signal from the first high-pass filter; an amplifier configured to amplify a current signal from the low-pass filter to a predetermined level; a second high-pass filter configured to extract a signal corresponding to a discharge current caused by a partial discharge that has occurred in the line to be measured, from a current signal amplified by the amplifier; and a discharge judgment section configured to judge whether or not a partial discharge has occurred in the line to be measured based on a signal extracted by the second high-pass filter.