MV Cable insulation testing 1

[parlitu]

What testing method for MV cable insulation do you thing is more reliable? A tan delta that gives a general quality of insulation for entire cable plus a pd test? Or tan delta plus VLF hipot test? I am looking to find the best way to do cable insulation testing, and I need a method that can tell me with some time before if a cable is near fail or not, and if is possible, where weak point are. Unfortunately, in my opinion, to do just a insulation resistance is not enough. And it will be better if testing method will not produce fail, or to make a bigger damage to the cable, which I can't tell for method I write above.

Thank you

 

[Zogzog]

You will hear some great arguments for both VLF and PD, but really it comes down to what type of testing will be done in the future? On line PD or off line Tan Delta? You are establishing some great baseline data with a new cable and will want to use that for your trending in the future.

 

[dpmac]

I never understood the "argument" part. They are different test methods that give different information. We don't perform Power Factor Tests on 100MVA transformers INSTEAD of a Turns Ratio Test. We don't perform Time and Motion tests INSTEAD of Contact Resistance tests on HV circuit breakers do we? We typically won't perform ANY of these tests on a 30KVA dry type transformers or 30A molded case breakers either.

To determine the health of MV cable insulation may require that different tests be performed. It depends on how important the cable is TO YOU and how much money YOU are willing to spend to find out.

Its not about the technology its about the money. Its always about he money.

If someone could tell you with absolute certainty the present condition and expected life expectancy of your cable run would you pay them $100,000? $50,000? $10,000?

Maybe. Maybe not. Thats your call

(My apologies to the OP, long day)

 

[VLFit]

There are three tests that are now perfromed on MV cable, which one or all used depends on the data you seek and what you are prepared to do with that data, as well as cost and convenience of each test.

A VLF Withstand test will stress the cable and intentionally cause failure where the insulation, or more likely, splices and terminations, are weak. It does not harm good insulation nor does it aggravate defects that do not start partial discharge under the test voltage. Simple pass/fail hipot, but VLF AC.

VLF Tangent Delta measures the overall degradation in the cable from one end to another. It is is best used when testing many cables and using the results to compare and prioritize for replacement and or silicon injection, or to determine what other tests may be valuable.

VLF Partial Discharge testing shows the location, severity, and the inception and extinction point of PD. It is a good test but not right for may situations. It is the most expensive and interpretive test of all. It is worthwhile in some instances. Don't let PD testing service companies try to tell you it is the only thing that works and everything else is no good. All three are effective but provide different info.

Know what you want from your tests and what repairs or replacements you are prepared to perfrom.

 

[parlitu]

As you all understood, I am interested in finding the best method on the market to evaluate expected life expectancy of cables. As I red into some papers on the internet, and also in a EPRI report, usualy they recommend tan delta that will give a average information about insulation (can't made difference between a sum of small imperfection and a big imperfection). Tan delta can be combine with VLF test, but this one can bring the cable to fail, and can make a defect to progress. Or tan delta can be combine with PD.
If you know other test with better results that can be perform to evaluate life expected of a cable (diferent tipes, diferent insulation- EPR, PVC, CSPE, XLPE), I'll appreciate your advice.

Thank you