Terminology commonly used in partial discharge measuring instruments

1. Partial discharge
Partial discharge refers to the discharge at a local location of the insulation, which does not constitute a penetrating breakdown of the entire insulation. It contains three discharge forms: internal discharge (inside the medium), creeping discharge (on the surface of the medium), and corona discharge (at the tip of the electrode).
2. Charge quantity q
Instantaneously inject a certain amount of charge at both ends of the test object, so that the change of the terminal voltage of the test object is the same as the change of the terminal voltage caused by the partial discharge itself. This injected amount is the apparent charge of the partial discharge.
3. Apparent discharge calibrator
The apparent discharge calibrator is a standard electricity generator. Before the test, it outputs a fixed amount of electricity and adds it to both ends of the sample to simulate the response of the partial discharge tester when the sample is discharged under this amount of electricity. At this time, adjust the scale coefficient. Determine the range of the partial discharge detector so as to measure the apparent discharge of the sample under rated voltage during the test. Because the discharge capacity is indirectly measured by comparison with a standard power generator, rather than directly measured, the discharge capacity is called "apparent discharge capacity".
Calibration power generator is an essential instrument when measuring partial discharge, and its performance parameters are directly related to the accuracy of test results.
The apparent discharge calibrator is composed of a calibration pulse voltage generator and a calibration capacitor in series, and its parameters mainly include: pulse waveform rise time, decay time, internal resistance, pulse peak value, calibration capacitor value, etc.
The rise time of the voltage waveform of the calibration pulse voltage generator is the time from 0.1U0 to 0.9U0, and the decay time is defined as the time from the peak value to 0.1U0.
4. Detection impedance
The detection impedance is a device for picking up the detection signal. In use, the appropriate detection impedance should be selected according to different test purposes and the type of the test object, so as to improve the sensitivity, resolution, waveform characteristics and signal-to-noise ratio of partial discharge measurement.
5. Time window (gate unit)
The time window is a circuit device designed to prevent interference signals larger than partial discharge from entering the peak detection circuit. Because some interference will inevitably be introduced in the actual test, especially in the field test, so the use of time window is more important.
The working principle of the time window is to divide the elliptical scanning time base into two parts: conduction (highlighted area) and cut-off (non-highlighted area), and the discharge pulse is placed in conduction (highlighted area) by changing the position and width of the time window. , the interference pulse is set to the cut-off (unhighlighted area), at this time the meter reading is the value of the discharge pulse, and the interference will not affect the value of the discharge pulse regardless of its size. If the two time windows are closed at the same time, the meter reading is the peak value of the pulse on the entire ellipse.