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4. Partial discharge test with frequency higher than 50 Hz
When partial discharge test higher than 50 Hz is required, press the "working frequency"
button to select the corresponding frequency range, and take 10v-250v test voltage from
high frequency test power supply and send it to socket 4.
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3
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Supplementary Provisions
1. Identification of discharge type and discharge source
Firstly, the ellipse track on the oscillograph screen is introduced. It rotates clockwise. The
positive zero mark pulse indicates that the test voltage begins to change from negative to
positive; on the contrary, the midpoint between the two zero standards is the positive and
negative peak positions of the test voltage.
It is a highly technical and practical knowledge to identify discharge types and various
interferences from discharge patterns on ellipses (it is better to combine with other
methods to confirm). CIGRE (International Conference on large power grid) has also
compiled a pamphlet for recognizing the discharge pattern. It is judged according to the
discharge position and movement in the discharge pattern, the consistent degree of
discharge amplitude in positive and negative half cycle, and the variation characteristics
of discharge amplitude with test voltage and pressurization time, which can only be
roughly introduced here.
Generally speaking, the main characteristic of partial discharge, which is regarded as the
formation of real internal bubble, is that most of the partial discharge occurs within two
and a half weeks near the rising position of the test voltage peak.
(1) Typical internal bubble partial discharge (see Figure 5), waveform characteristics: a
discharge is mainly shown in the test voltage from zero to peak within two elliptical phase
limits. B when the initial voltage UI, the discharge usually occurs near the peak value.
When the test voltage exceeds UI, the discharge extends to the zero position. C the
discharge times and amplitudes of the two opposite half cycles are approximately the
same (the maximum difference is 3:1). The discharge waveform can be distinguished.
There are several situations: 1) if the discharge amplitude increases with the increase of
