To obtain a partial-discharge monitoring apparatus in which an external noise is removed so as to obtain an accurate measured value by a method wherein a partial-discharge current which is generated across a conductor and a ground potential is converted into a voltage signal by a detecting impedance so as to be divided into two signals, the phase of the signal on one side is delayed and a partial discharge is detected on the basis of the difference signal between the signal on one side and the signal on the other side.
A partial-discharge current which is generated across a conductor 1 and a ground potential 2 is converted into a voltage signal. The voltage signal as the output signal of a detecting impedance 3 is attenuated by an attenuator 5, it is amplified by an amplifier 6, and a level is adjusted. The voltage signal is divided into two signals by a branching filter 10. The phase of the divided signal on one side is delayed by a delaying device 11. The difference between the divided signal on the other side and the signal which is delayed by the delaying device 11 is found by a computing unit 12. An amplifier 13 amplifies the voltage difference signal of the computing unit 12. A detection circuit 7 detects a generation frequency on the basis of the signal of the amplifier 13. A signal processing part 8 judges whether an abnormality exists in the output signal of the detection circuit 7. An output part 9 outputs a result to the outside.
KAWABATA OSAMU
KAMIYAMA YOSHIHIRO
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