| 摘要 |
An insulation degradation diagnostic device ( 1 a) comprises a current transformer ( 7 a), a first amplifier ( 15 ), a first high-pass filter ( 17 ), a low-pass filter ( 19 ), a second amplifier ( 20 ), a second high-pass filter ( 21 ), and a discharge determining part ( 30 ). The current transformer ( 7 a) has a filtering function, which has an attenuation amount of -60 dB or less and a slope characteristic of -5 dB/oct or less for commercial frequencies, and detects a current flowing through a grounding wire ( 5 ). The first amplifier ( 15 ) amplifies a current signal from the current transformer ( 7 a). The first high-pass filter ( 17 ) eliminates low frequency component from the amplified current signal. The low-pass filter ( 19 ) eliminates high frequency components from the current signal from which the low frequency components have been eliminated. The second amplifier ( 20 ) amplifies the current signal from the low-pass filter ( 19 ) up to a predetermined level. The second high-pass filter ( 21 ) extracts, from the current signal as amplified by the second amplifier ( 20 ), a signal corresponding to a discharge current caused by a partial discharge. The discharge determining part ( 30 ) determines, based on the signal as extracted by the second high pass filter ( 21 ), whether the partial discharge has occurred in a cable ( 2 ).
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