1. Partial Discharge
Partial discharge refers to discharge occurring in localized positions of insulation, which does not constitute a complete breakdown of the entire insulation. It includes three forms of discharge: internal discharge (within the dielectric), surface discharge (on the dielectric surface), and corona discharge (at electrode tips).
2. Charge Quantity q
When a certain amount of charge is instantaneously injected at both ends of the test object, causing the change in terminal voltage of the test object to be the same as that 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 charge generator. Before the test, it outputs a fixed charge to both ends of the test object, simulating the response of the partial discharge tester when the test object discharges at this charge level. At this time, the scale factor is adjusted to determine the range of the partial discharge detector, so that during the test, the apparent discharge of the test object at rated voltage can be measured. Since this discharge is indirectly measured by comparison with the standard charge generator, rather than directly measured, it is called "apparent discharge."
The calibration charge generator is an essential instrument for measuring partial discharge, and its performance parameters directly affect the accuracy of test results.
The apparent discharge calibrator consists of a calibration pulse voltage generator and a calibration capacitor connected in series. Its main parameters include: pulse waveform rise time, decay time, internal resistance, pulse peak value, calibration capacitance value, etc.
The rise time of the calibration pulse voltage generator's voltage waveform is the time from 0.1U0 to 0.9U0, and the decay time is defined as the time from the peak value dropping to 0.1U0.
4. Detection Impedance
Detection impedance is a device for picking up detection signals. In use, appropriate detection impedance should be selected according to different test purposes and types of test objects 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. Since in actual tests, especially in field tests, some interference is inevitably introduced, the use of the time window becomes even more important.
The working principle of the time window is to divide the elliptical scanning time base into two parts: conduction (brightened area) and cutoff (non-brightened area). By changing the position and width of the time window, the discharge pulse is placed in the conduction (brightened area), and the interference pulse is placed in the cutoff (non-brightened area). At this time, the meter reading is the value of the discharge pulse, and interference, regardless of its magnitude, will not affect the discharge pulse value. If both time windows are closed simultaneously, the meter reading is the peak value of the pulses on the entire ellipse.
