Cable Integrity Testing

[Shells]

Good Day

We had a cable that has been exposed to a fire. Visibly the jacket seems to be scorched but the damage does not seem to be that bad. Of course we need to test to be sure or we can replace also because it was a FIRE. We did do an IR test at 5kV and the results are as follows:


Generator 12kV Cable L1-G 3.78Gohm
L2-G 4.16Gohm
L3-G 4.36Gohm
2 min test L1-L2 92.9Gohm
2 min test L1-L3 54.3Gohm
2 min test L2-L3 39.4Gohm

I know that Gohm is typically ok but NETA recommends at 2.5kV the min resistance should be 5Gohm. Also I was concerned about the variances between phases >50%. Was considering to do a HIPOT since we do not have a VLF tester but not sure voltage to test - waiting on feedback from manufacturer. Any guiudance on the results thus far? Do you recommend a HIPOT on such an old cable?

Regards

 

[zog]

Every cable testing standard will recommend against a DC hipot test on service aged cables. I recommend a VLF or Tan Delta test to be performed, a testing company won't charge much to come do it for you.

 

[Shells]

Every cable testing standard will recommend against a DC hipot test on service aged cables. I recommend a VLF or Tan Delta test to be performed, a testing company won't charge much to come do it for you.

Just to be clear I am on the same page, what info will I get from the tan delta that the IR won't? I mean I am all for more diagnostic info to validate the IR test but I guess based on the IR test results the cable seems ok?

 

[zog]

Tan delta is similar to a Power Factor test, it will tell you the actual condition of the insulation. A DC Megger (IR) test will only find gross installation errors or severe failures. This has all been discussed at length here many times, just do a forum search on the topic.