What is Partial Discharge?
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 predominant cause of long term degradation and eventual failure of electrical insulation. As a result, its measurement is standard procedure in the factory testing of many types of high voltage equipment. In addition, partial discharge activity can be tested for or monitored on in-service equipment to warn against pending insulation failure.