Insulation testing for cables

[BoomerSooner7]

Hello all,

I have a question concerning the best method/approach to testing the integrity of both our low voltage (480v) and medium voltage (cables). I have read that DC hi-pot testing is destructive for aged cables, which is what we have. I have also read the PD testing is a good alternative to medium voltage cables, however I guess this does not apply to 480v. Anyone have any recommendations on sound test for testing for insulation damage on both 480v and 4160v?

Thanks in advance

 

[cuky2000]

For LV cable, PD may not be practical.

See the link below for details.

http://www.eaton.com/ecm/idcplg?IdcService=GET_FILE&dID=167378

 

[EricAXEWC]

You may want to look into getting a copy IEEE 400: Guide for Field Testing and Evaluation of the Insulation of SHIELDED Power Cable Systems.

You can also find some reports on the EPRI website about aged cable testing as well, do a search on epri.com for 1003663.

For obvious reasons there is a lot of information out there on cable aging, hi-pot is the very tip of the iceberg. Hi-pot isn't going to provide great metrics for comparison unless you have historical data and you're right that it can actually shorten the life of the cable being tested. I personally view it as a go/no-go test on new installations only, but I'm interested to hear others opinions.

 

[VLFit]

There is so much to say on this subject that it is difficult to start. Regarding MV cable, there are presently 2 well known and established methods of testing and a third that is just now starting to be adopted.

VLF AC Withstand Testing
VLF Tan Delta Diagnostic Testing
VLF Partial Discharge Testing

With VLF AC hipots so commonplace now after 15 years of transition, DC testing on aged, solid diectric insulation is not in favor, banned in most places. AC field cable testing is now possible with the many VLF hipots from the 4 - 5 major vendors producing them.

VLF Withstand testing your cable is a go/no-go test, just like we do on many other loads. It is an excellent method of verifying the integrity of a cable and exposing defects.

Instead of Withstand testing, many wish to perform diagnostic testsing to learn something about the cables insulation without risking failure during the test. The VLF instrument becomes the voltage generator for these off-line tests perfomed at elevated voltages.

VLF Tan Delta measures the quality of the insuation from point A to B. Compare many cables by degradation and prioritze your replacement or injection action, or other testing.

VLF Partial Discharage attempts to pinpiont the locations of PD and their severity.

All three methods work well and are usefull, which ones depend on your appication.

For more info check out the Presentations Offered on

http://www.gatech.neetrac.edu.

or Google VLF Testing cable

For LV cable there is little and we do not get into it.

good luck