Partial discharges occur when minor defects are present in electrical insulation systems. When partial discharges occur repetitively in solid insulation material, the destructive energy released deteriorates the insulation material at that site. Over time, this deterioration spreads and can completely penetrate the insulation material creating a total insulation breakdown.
Premature failures of insulation systems have been attributed to the action of partial discharges. For this reason, testing for partial discharges in an insulation system has been adopted as a quality control measure for applications where high reliability is a concern.
The requirement for partial-discharge testing is found in power delivery products such as power cable, terminations and joints; generators and motors; bushings; circuit breakers and switchgear; instrument transformers (CTs and PTs); capacitors; transformers (power and epoxy cast coil); lightning arresters and fuses.
In addition, electronic devices found in aerospace and defense applications have thin insulation systems that are subject to high stress and the harsh operating environments.
Partial-discharge testing helps ensure components such as the following operate reliably: rectifiers, connectors, wiring harnesses, test capacitors, diodes, transformers and dc power supplies.