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 piece of pretty good knowledge about Partial Discharge or shortly PD to understand your cable life or the possibility of unwanted cable faults. You may gather knowledge about PD by watching video clips on 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 a 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 of partial discharge for cable systems from two major points of 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 the 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 a very sensitive method to find out very minor failures such as little void or skip of insulation layer during manufacturing time.

But this factory test is not sufficient for the end users of the cable systems, 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 increased slowly and finally cracked. By statistics from the cable systems, most of the cable faults occur in cable jointing and termination point.

For Better Results:

So it is better to observe 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.