Partial Discharge Testing for Cables

A partial discharge is an electrical discharge that only partly bridges the insulation between conductors. The purpose of the partial discharge test is to verify that the cable insulation is free from partial discharges above a specified magnitude at a specified voltage. This partial discharge may or may not take place adjacent to the conductor.

To conduct the partial discharge test requires equipment including a high voltage power supply with a kilovolt-ampere capacity adequate for the length of cable under test, a voltmeter suitable for high voltages, a partial discharge measuring device, and a discharge calibrator.

The partial discharge measuring device includes a circuit with the following components: An oscilloscope coupled with indicating equipment, a voltmeter connected to the high voltage supply, and an amplifier coupled to the oscilloscope to detect existence of partial discharge and individual discharge pulses.

The test procedure for testing partial discharge involves applying a test voltage between the conductors and the screen. The voltages are determined by the relevant cable standard.