Outer Sheath MV cable DC test

[mikelangel78]

Hello!

I'm performing DC test to verify the outer sheath integrity on a MV 36kV cable after laying, according to IEC 60840 & IEC 60229 standards. I'm using a BAUR testing equipment. According to the manufacter, the test equipment negative (-) terminal should be connected in the outer sheath and the positive (+) terminal in the earth (ground). Both cable ends should de disconnected from earth. My question is, if I connect the positive terminal (+) in the sheath and the negative terminal (-) in the earth the test will not work?

Thanks in advanced.

 

[mikelangel78]

I've been thinking about my own question. Perhaps if I connect the negative terminal (-) of the DC source in the earth and the positive terminal (+) in the cable sheath, and because the electrons flow from the (-) to (+), i'm not be able to detect a defect in the insulation of the cable. Am I correct?

Thanks

 

[Marmite]

For your own safety, please engage the services of someone experienced and competent in cable testing. It is very easy to receive a nasty and potentially fatal electric shock if you don't know what you are doing, which is inferred by the basic nature of your question.
Regards
Marmite

 

[mikelangel78]

Thank you for your wise advice.
Regards

 

[collies99]

Yeo, should work, look for high Mohm values.

 

[Supertester]

In dielectric testing insulation that is in an air environment we use a positive ground reference. Most DC test sets output a negative DC voltage at the HV test lead, so you really don't have a choice. What is important in cable sheath HV testing is the ampacity of the test set, a simple insulation resistance tester (Megger) is not really suitable for a cable sheath test. The BAUR Shirla is a good example of this type of set.

The only time I used a Negative output test voltage (200 kVdc) was in an oil filled two bushing reactor filter equipment, that was subject to shipping damage. It passed.