Diagnosis of insulation conditions : Interpretation of partial discharges from φ-q-n pattern, pulse-sequence and pulse waveform
ABSTRACT Appearance of electrical discharges in high voltage apparatuses with reasonable magnitude and frequency can be interpreted as abnormal condition. The discharge may take place in several types. Firstly, corona discharges which represents abnormal electric stress on a conductor. Secondly, void discharge which represents discharge take place in a gas filled void in solid or liquid insulation. Thirdly, treeing discharge which takes place in tree channels inside a solid insulation. This paper reports experimental results on the three kinds of discharges. The analysis was focused on the phi-q-n pattern, the time sequence between consecutive pulses and the waveform of a discharge pulses. The difference among them maybe useful to diagnose of insulation condition.
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ABSTRACT: Partial discharge pulse phase analysis carried out on a mineral oil and a perfluoropolyether with point-to-plane electrodes provided further and additional evidence that discharge epochs tend to be concentrated in the vicinity of the alternating voltage peaks at discharge inception in lieu of the voltage zeros characteristic of normal cavities occluded in solid and liquid-impregnated solid insulating systems. Relatively large positive polarity discharge pulses, having an associated charge transfer of ⩾15 pC with a recurrence rate of at least one per every ten consecutive cycles, appear initially on the positive half-cycle; with further increases in applied voltage both their number and magnitude continue to exceed those of negative polarity over the negative half-cycle. This behavior is to be distinguished from that commonly observed with high sensitivity measurements, which clearly indicate that early discharge onset in liquids is characterized by the occurrence of minute highly intermittent negative polarity pulses. The increase in charge transfer of the discharge pulses with applied voltage is suggestive of the development of longer more intense streamers in the dielectric liquids at the more elevated electrical fields. Also the results infer that discharges or streamers form and propagate more readily in the mineral oil than in the electronegative perfluoropolyetherIEEE Transactions on Dielectrics and Electrical Insulation 03/2000; · 1.36 Impact Factor