Overview

Partial Discharge - The Path to Failure

Partial Discharge (PD) is an electrical discharge that does not completely bridge the space between two conducting electrodes. The discharge may be in a gas filled void in a solid insulating material, in a gas bubble in a liquid insulator or around an electrode in a gas. When partial discharge occurs in a gas, it is usually known as corona.

Partial discharge is generally accepted as the predominate cause of long term degradation and eventual failure of electrical insulation. As a result, its measurement is standard as part of the factory testing of most types of high voltage equipment. In addition, partial discharge activity is very often monitored on in-service equipment to warn against pending insulation failure.

Test specifications set a maximum permissible level for partial discharges depending on the type of equipment being tested and the insulating material used. As insulation systems have increasingly moved towards polymers, acceptable discharge levels have lowered dramatically as they are less resistant to damage by discharge.

Partial Discharge is low energy electrical activity that can have very serious implications. Although each discharge is small, they are a very localised and can happen many times every second. Over time this can cause damage such that the insulation becomes so weak that it fails.

Resources and support

• Datasheets
• White papers
• Published papers & articles
• IPEC technical enquiry