Partial discharge

About: Partial discharge is a research topic. Over the lifetime, 13997 publications have been published within this topic receiving 102058 citations. The topic is also known as: PD.

Existence of partial discharges in low-voltage induction machines supplied by PWM drives

Abstract: When standard low voltage induction motors are supplied by pulse-width modulated (PWM) adjustable speed drives, some of the traditional sinusoidal system concepts cannot be applied. This paper reports the results of an investigation of the effect of PWM drives on the insulation of the stator winding. The characteristics of the employed dielectric material and the magnitude of the applied voltages led to the hypothesis of the possible existence of partial discharges within the insulation. Practical experiments were carried out and high frequency signals which could be associated with such a phenomenon were observed. These measurements also showed that the interturn insulation undergoes some high electrical stresses and that the nominal rotation speed (50 Hz) appears to be a point of high disturbance in the working of the motor. Further work is required, since most of the points identified here need to be understood fully.

Statistical pattern analysis methods of partial discharge measurments in high voltage insulation

Abstract: Statistical methods of partial discharge analysis utilizing histogram similarity measures are provided by quality assessment and condition monitoring methods of evaluating high voltage electrical insulation. The quality assessment method is utilized to evaluate the quality of insulation within the electrical equipment. The condition monitoring method is utilized during normal operation of the equipment to identify degradation in the insulation and to predict catastrophic insulation failures.

Evolution of partial discharges during early tree propagation in epoxy resin

Abstract: Electrical tree growth is a precursor to dielectric breakdown in high voltage polymeric insulation. Partial discharge (PD) has a close relationship with electrical tree propagation and can be both used to understand the aging process, and as a diagnostic tool for asset management. In this paper it is shown that PD patterns change through the early stages of tree growth, and consideration of these changes gives insight into the processes of tree growth. Here, trees have been grown in epoxy resin in needle-plane geometries with 2 mm gaps, at 15 kV peak AC. The PD phase-resolved pattern can be regarded as a combination of the well-known turtle-like and wing-like PD patterns. As a tree extends its length, a wing-like pattern is seen and the maximum discharge magnitude has an almost linear relationship with the maximum length of the growing branch. Comparison of the energy released by discharges and the vaporization energy needed for tree growth supports the proposal that the wing-like pattern corresponds to PDs responsible for growth in length of the trees. Implications for mechanisms for tree growth are considered. Results suggest that asset managers may be able to use partial discharge analysis to distinguish different stages of tree growth, providing a valuable prognostic tool for optimising high voltage plant management and replacement.

Observations of partial discharges in hexane under high magnification

Abstract: Partial discharges are observed in hexane by shadow photography under the application of DC voltages. A nonuniform field geometry is used and the growth of cavities associated with partial discharges at a point cathode was photographed at 200* magnification. The use of an image-preserving optical delay allows a record of the conditions which exist in the liquid prior to the initiation of the low-density streamer to be obtained. The cavity growth at a point cathode is anisotropic, which suggests that electrostatic forces are of primary importance in driving its expansion. The onset of instabilities in the cavity wall is suggested. The initial partial discharge current pulse precedes or is concurrent with the growth of the cavity. An upper bound of 60 ns between first current pulse and the growth of the cavity is obtained. >

Experimental study on conduction current of positive nanosecond-pulse diffuse discharge at atmospheric pressure

Abstract: Nanosecond pulsed discharges have various discharge modes, such as corona, diffuse discharge, spark or arc. A dense diffuse discharge is particularly desirable for various applications at atmospheric pressure. In this paper, a magnetic-compression pulse generator was used to produce repetitive positive nanosecond pulses for excitation of a diffuse discharge. The output pulse of the generator had a rise time of about 25 ns and a full width at half maximum of 40 ns. Electrical characteristics of the diffuse discharge were studied by measuring its voltage and current waveforms, as well as images of the discharge. The conduction current was calculated by the measured voltage and current, which was a true discharge current. The experimental results show that a stable diffuse discharge could be obtained at atmospheric pressure, and the conduction current was unipolar and had similar amplitude of several amperes under our experimental condition, which has the similar amplitude with the displacement current. Furthermore, the air gap spacing and pulse repetition frequency (PRF) affected the intensity and mode transition of the diffuse discharge. The conduction current increased with the PRF but decreased with the air gap spacing. Therefore, the diffuse discharge was likely available under some conditions of proper air gap, high PRF with positive pulse.