partialdischarge

Partial discharge refers to a localized electrical discharge that occurs in an insulating medium without fully bridging the space between conductors. It typically takes place within gas-filled voids, microcracks, or inclusions inside solid insulation, or at interfaces in high-voltage equipment. PD is initiated by strong electric fields and can emit electrical pulses, acoustic energy, and light, depending on the local conditions.

PD is important because, although each discharge is small, repetitive activity can erode insulation, generate chemical byproducts, cause heating, and progressively reduce dielectric strength. Over time, a sufficient buildup of partial discharges can lead to insulation breakdown, equipment malfunction, or unexpected outages. PD activity often indicates manufacturing defects, aging insulation, moisture ingress, contamination, or mechanical and thermal stress.

Common locations of partial discharge include high-voltage cables, transformers, switchgear, bushings, and stator windings. Causes range from voids in epoxy or polymer insulations, mismanufacturing, and improper impregnation to aging, vibration, moisture, and particulate contamination. PD behavior is characterized by parameters such as discharge magnitude, number of pulses, phase angle, and PD inception and extinction voltages.

Detection and assessment are performed with electrical methods (pulse-by-pulse PD measurement and phase-resolved PD analysis) and, in some cases, acoustic or ultrasonic sensing. Standards such as IEC 60270 define methods for measuring partial discharge in high-voltage insulation systems. On-line monitoring and offline testing are used to evaluate insulation condition, track trends, and guide maintenance. Mitigation focuses on improved design, manufacturing quality, moisture and contaminant control, proper drying and impregnation, and reducing electrical stress within insulation.