Method and system for measuring partial discharge
In the measurement of partial discharge, a voltage detected by an antenna is input to a spectrum analyzer and a phase difference between an operating voltage and a power supply of the spectrum analyzer is obtained by phase domain analysis using the spectrum analyzer. Based on the phase difference and the voltage phase shift associated with the input impedance of a signal converter circuit, the time axis displayed on the screen of the spectrum analyzer is compensated. After the compensation has been carried out, the voltage detected by the antenna is input into the spectrum analyzer and the partial discharge pattern which synchronizes with the operating voltage is measured by phase domain analysis using the spectrum analyzer.
1. A method of measuring partial discharge, comprising the steps of:
detecting a voltage of a conductor encased in a container together with an insulation material by a voltage sensor;
detecting an operating voltage supplied to said conductor based on said detected voltage of said conductor;
transmitting the operation voltage detected by said voltage sensor to a measuring instrument through a signal converter circuit;
compensating an original phase difference θ between the power supply voltage of said measuring instrument and said detected operating voltage which is transmitted into said measuring instrument through said signal converter circuit, and a phase shift Φ caused by said signal converter circuit;
determining the phase of the time axis to be displayed on a screen of said measuring instrument based on said compensated operating voltage;
displaying said determined phase of the time axis in the screen of said measuring instrument;
displaying said detected partial discharge on said phase of the time axis in the screen of said measuring instrument;
detecting said partial discharge through an electric cable which bypasses said signal converter circuit and reaches said measuring instrument; and
displaying said partial discharge transmitted through said electric cable to said measuring instrument on said time axis on the screen of said measuring instrument which is compensated by said phase difference θ and said phase shift Φ.
2. The method of measuring partial discharge according to claim 1 , wherein: said phase shift Φ is caused by an input impedance in said signal converter circuit.
3. The method of measuring partial discharge according to claim 1 , wherein: said phase shift Φ is caused by an input impedance of a comparator in said signal converter circuit.
4. A partial discharge measuring system comprising; a conductor encased in a container together with an insulation material;
a voltage sensor which detects the voltage of said conductor;
an operating voltage detecting means for detecting an operating voltage of said conductor in which an operating voltage in the output voltage of said voltage sensor passes through a signal converter circuit and reaches a measuring instrument;
a display means with a screen in said measuring instrument;
a phase compensating means for compensating an original phase difference θ between the power supply voltage of said measuring instrument and said operating voltage which is transmitted into said measuring instrument through said signal converter circuit, and a phase shift Φ caused by said signal converter circuit;
a time axis displaying means for displaying the phase of the time axis based on said compensated operating voltage on said screen;
a partial discharge detecting means for detecting the partial discharge of said conductor based on said detected voltage of said conductor;
an electric cable for bypassing said signal converter circuit and connecting said voltage sensor and said measuring instrument; and
a partial discharge displaying means for displaying said detected partial discharge on the phase of said time axis on said screen of said measuring instrument.
5. The partial discharge measuring system according to claim 4 , wherein: said phase shift Φ is caused by an input impedance in said signal converter circuit.
6. The partial discharge measuring system according to claim 4 , wherein: said phase shift Φ is caused by an input impedance of a comparator in said signal converter circuit.
7. The partial discharge measuring system according to claim 4 , wherein said signal converter circuit further comprises:
a comparator which responds to said operating voltage detected by said voltage sensor and converts the waveform of said operating voltage to a square-wave,
a half-wave rectification circuit which half-wave rectifies the square-wave outputted by said comparator, and
an oscillation circuit which converts an output voltage of said half-wave rectification circuit into a voltage of higher frequency than that of said operating voltage.
8. The partial discharge measuring system according to claim 4 , wherein:
said measuring instrument comprises a spectrum analyzer.
9. The partial discharge measuring system according to claim 4 , wherein:
said measuring instrument comprises an oscilloscope.
10. The partial discharge measuring system according to claim 4 , wherein:
said container is connected to a switchgear encasing container which encases a gas insulated switchgear, and
said conductor is connected to an electrode of said gas insulated switchgear.