PARTIAL DISCHARGE TESTING OF POWER CABLE

Partial Discharge (PD) in Electrical Power Cable:


Why PD?
No matter way where you are an engineer or a technician for electrical power cable, you need a pretty good knowledge about Partial Discharge or shortly PD to understand your cable life or the possibility of unwanted cable fault. You may gather knowledge about PD by watching video clips in YouTube or reading a blog or article about PD.

Introduction of Partial Discharge (PD):  
Partial discharge (PD) is one of the most important factors for power cable system. The partial discharge measurement methods of assessing the quality of the insulation of power cable systems especially for extruded insulation materials.

Where Partial Discharge Occur:
We can think partial discharge for cable system from two major points view:

01. Partial Discharge within the whole cable
02. Partial Discharge in an individual location


Partial Discharge Measurement:
Normally major factory test carried out on the insulation of whole drum of extruded cable is the partial discharge test. This is usually done at power frequency, but can also be carried out at very low frequency and at some voltage significantly higher than normal working voltage to ground. PD test is very sensitive methods to find out very minor failing such as little void or skip of insulation layer during manufacturing time.

But this factory test is not sufficient for end user for cable system, during cable shipping, cable installation, cable jointing and termination; cable insulation may damage or crack. Minor damage or crack is not possible to find out during commissioning or energizing time. After a little longer time this defect increase slowly and finally cracked. By statistic from cable system most of the cable fault occur in cable jointing and termination point.

For Better Result:
So it is better to observing the magnitude and phase of the partial discharge signals and how they vary with increasing and then decreasing test voltage, results will disclose information on the type and position of the defects and their probable effect on cable life.


Finally in conclusion we can say, if the cable system can be tested in the field to show that its partial discharge level is comparable with that obtained in the factory tests on the cable and accessories, it is the most convincing evidence that the cable system is in excellent condition.


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