Cable Testing
Cable Testing
(OP)
A question about the testing of medium voltage copper cables: what should be the minimum megger test volatge for a 30kV cable? Can a 30kV cable be tested by a 2.5kV megger?
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RE: Cable Testing
RE: Cable Testing
collies99
RE: Cable Testing
RE: Cable Testing
RE: Cable Testing
You might also want to investigate low frequency AC cable testing as an alternative type of test for polymeric cables.
RE: Cable Testing
If the standards say that use 5kV Megger for insulation resistance of 11 -33kV cables, we will do it that is not a problem. I just want to understand the theory that how will a Megger test voltage of only 5kV measure the insulation resistance of 11-33kV cable. Please let me know comments!
RE: Cable Testing
RE: Cable Testing
RE: Cable Testing
Bill
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"Why not the best?"
Jimmy Carter
RE: Cable Testing
DC cable testing is now frown upon as it can accelerate insulation defects which leads to earlier failure of cables both new and service aged.
RE: Cable Testing
Don't dismiss an I.R test on a cable as useless. A P.I. test carried out using a Megger, followed by a little careful analysis of the results can give you a fair bit of confidence (albeit a go/no go decision) as to whether or not to energise a circuit, although I agree that 2.5kV on a 30kV cable seems low. Insulation resistance is the same value whether you test at 2.5kV or 5kV, it's just the stress that you put the cable under that is different. Personally I would probably be looking for a 10kV I.R. test on that voltage, but I'm not a cable testing expert. I personally am more comfortable making decisions about energisation when I have a P.I. and resistance reading, rather than a leakage current value from the HiPot set, but that's just me.
The situtations I am usually involved in (with respect to cabling) are testing of new cables prior to first energisation and testing cables after a trip. For new cables we use I.R. (P.I. test) and HiPot, after trips obviously just I.R. I have never been involved with VLF testing for condition assessment.
I would also say that you are almost always testing a cable connected to a piece of equipment (usually via the circuit spouts) and regardless of what any standard tells you, you have to observe the equipment manufacturer's recommendation. For example, some old 11kV switchgear that I regularly come across has a manufacturer's recommended maximum DC test voltage of 18kV, so that's what we HiPot the cables at (even new polymeric cables). That value then set the cable DC test voltage standard of 18kV across the site for 11kV cables, even on new switchgear.
Sorry I can't give you an absolute value to use for your cable, but the standard that Scotty posted might give you a better clue.
RE: Cable Testing
5kV Megger is used for the insulation testing of low voltage cables as mentioned at the following link: http://www.nexans.us/eservice/US-en_US/fileLibrary...
There are several cable tests but most of them (like tan δ test and partial impulse test) are done during the manufacturing of cable. But I am basically only concerned about the after-installation Megger test of medium voltage cable.
RE: Cable Testing