What is Partial Discharge (PD)?
Partial discharge (PD) is a critical factor in a power line system. Partial discharge measuring methods are used to assess the quality of power cable insulation, particularly for extruded insulation materials.
Partial discharge in cable networks can be considered from two perspectives:
1). Partial discharge within the entire cable.
2). Partial discharge at a single location.
Partial Discharge Testing of Power Cable
The partial discharge test is often the most extensive factory test performed on the insulation of an entire drum of extruded cable.
This is often done at power frequency, but it can also be done at very low frequency and with a voltage substantially higher than the normal working voltage to ground.
The PD test is an extremely sensitive method for detecting very slight faults, such as a small void or a skip of an insulation layer during manufacture.
However, this factory test is insufficient for end users of cable systems since cable insulation can be damaged or cracked during cable transportation, installation, jointing, and termination.
Minor damage or cracks cannot be detected during the commissioning or energizing process. After a little more time, this fault gradually developed and eventually cracked.
Cable system statistics show that the majority of cable problems occur at the cable jointing and terminating points.
For better results:
As a result, it is preferable to watch the size & phase of partial discharge signals as they vary with increasing and then lowering test voltage; the results will reveal information about the nature and location of the flaws, as well as their likely impact on cable life.
Finally, if the cable system can be evaluated in the field to demonstrate that its partial discharge level is comparable to that obtained in factory tests on the cable and accessories, this is the most convincing proof that the cable system is in great condition.