Formation Of Partial Discharges Research Articles

Influence of overvoltage waves on the development of partial discharges

A theoretical study of the development dynamics of partial discharges in defects in cable insulation of medium voltage networks in the presence of an overvoltage wave has been carried out. Simulation modeling of the development of partial discharges was performed on the basis of a model with three capacitors, supplemented by a model for the appearance of a seed electron. A single-phase short circuit to earth with several breaks in the electric arc was the source of the overvoltage wave. Simulation modeling showed that the number and power of partial discharges significantly increased over the period of the fundamental harmonic. The amplitude of the periodic component of the transient process was already enough to recharge the defect for large insulation defect and it is the highest harmonic that becomes decisive in the formation of partial discharges. This fact may be one of the explanations for a possible trend in medium voltage cable networks, where a failure on one cable is followed by a group of subsequent failures in nearby cable lines within a few days.

Investigations of Accelerated Aged Polymeric Insulators Using Partial Discharge Signal Measurement and Analysis

Reduction in pollution performance of polymeric insulators, aged due to water absorption stress and thermal stress, is a major threat to the reliable operation of power transmission and distribution system. Formation of partial discharges on the surface of wet polluted insulator plays a major role in determining the life time and pollution performance of outdoor polymeric insulators. However, reports on partial discharge characteristics of water absorption stress aged and thermal aged polymeric insulators are scanty. This paper discusses the pollution performance characteristics of accelerated aged polymeric insulators using the advanced ultra wide band PD signal measurement and analysis. Laboratory experiments on accelerated aged polymeric insulators were carried out as per IEC 60507 under AC voltage, at different humidity and contamination levels using NaCl as a contaminant. PRPD pattern and Time-Frequency map analysis of PD signals were carried out. From the results, it can be speculated that PD analysis is a well suited technique to understand the pollution performance of aged polymeric insulators.

Partial discharge behavior in switching-surge-aged oil-paper capacitor bushing insulation

Partial discharge (PD) diagnostics are utilised to examine the aging process of mineral oil-impregnated-high density kraft paper capacitor bushing models, subjected to repetitive voltage switching surges. It is demonstrated that the PD measurements of cumulative apparent charge transfer and discharge inception stress constitute an effective means for assessing aging and its reversibility due to gas evolution and re-absorption or solubility of a mineral oil-impregnated-paper insulation system in the presence and absence of switching surges. While the experimental results indicate that electrically overstressed solid-liquid insulation can recover in part its initial electrical properties following an electrical stress-free period, long term stability is only effectively achieved by a reduction in the switching surge overstress through an increase in the overall insulation thickness. The electrical stress levels, employed in the experiments, are found to be not sufficiently elevated to lead to any detectable partial discharge formation within the oil phase itself; the observed discharge behavior is rather characteristic of the type that is normally associated with macroscopic cavities occluded within the oil-paper insulation systems.

Initiation and formation of partial discharges in mineral-based insulating oil

This paper reports the results of fundamental investigations concerning the behavior of partial discharges (PD) in mineral-based oil with the aim of characterizing the physical mechanisms that lead to the initiation and formation of PD pulses. First the influence of the parameters temperature, moisture, pressure and oil condition on the PD inception voltage, the apparent charge and the number of PD pulses are introduced. Furthermore some results achieved by investigating the shape of PD pulses and the behavior of visible PD channels using the Schlieren technique are explained. The paper ends with a discussion of the obtained results.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>