Partial discharge (PD) occurs in voids, along surfaces or at sharp edges where local electric stress exceeds the breakdown strength of a small region without bridging the whole gap. Each event is tiny, measured in picocoulombs, but repeated discharges erode insulation and lead to failures of cables, switchgear and machine windings. It is picked up with coupling capacitors, high-frequency CTs, TEV sensors and ultrasonic probes, and trended to catch trouble before breakdown.
TEV readings on panel 6 jumped to 35 dB, that's active partial discharge, book an outage before it lets go.
Also heard as
- PD
- discharge activity
Related terms
Corona
Faint glowing discharge around high-voltage conductors where the air is overstressed, causing noise and loss.
Tracking
Conductive carbon trail that leakage arcs through dirt and moisture gradually burn across an insulating surface.
Hipot
High-potential test: applying a voltage well above working level to prove insulation will not break down.
Insulation resistance test
DC test that applies a high voltage between conductors and earth and reads leakage resistance in megohms.