DC Hipot test voltages for new cable
DC Hipot test voltages for new cable
(OP)
I am required to do a hipot acceptance test of newly installed 15KV EPR copper cable. I have heard that a standard rule would be to Hipot at 3 times the rated cable voltage or 45KV DC. Is this a good rule to follow?






RE: DC Hipot test voltages for new cable
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Rafiq Bulsara
http://www.srengineersct.com
RE: DC Hipot test voltages for new cable
I would hope someone doing acceptance testing of MV cables would know what the test voltages should be. I also recommend you read this thread.
http://www.eng-tips.com/viewthread.cfm?qid=248906
RE: DC Hipot test voltages for new cable
RE: DC Hipot test voltages for new cable
RE: DC Hipot test voltages for new cable
No mention of VLF, TD, or PD testing at all. I think this has to be an out of date document or the folks at southwire need to get it updated to current standards they are referencing.
RE: DC Hipot test voltages for new cable
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RE: DC Hipot test voltages for new cable
RE: DC Hipot test voltages for new cable
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RE: DC Hipot test voltages for new cable
There are many discussion threads in this forum on the subject that you may want to research but a very brief, incomplete summary of field tests is as follows:
1. For extruded insulation (XLPE, EPR) cables, DC withstand testing on NEW CABLE ONLY (on the reel)may not hurt but it also is known not to detect much.
2. For older (aged) cables and cables installed with accessories (splices, terminations) DC withstand testing is not recommended due to the risk of damage to the insulation (older cables) or the accessories.
3. For MV cables rated 5-46kV, a VLF test (very low frequency) using an AC test voltage is the way to go. This test combines to some extent combines the economic advantages of DC testing with the relevance of AC testing.
4. For HV cables rated 69kV and higher, if a simple soak test of the installed system is not acceptable or considered insufficient, an AC resonant voltage withstand test, preferably combined with a PD test, is to be recommended.
RE: DC Hipot test voltages for new cable
In the years that I've tested cables, one thing that is a common find on DC tests of new cables is NOT a "bad" cable, but rather a poorly executed termination (stress cone) or splice.
old field guy
RE: DC Hipot test voltages for new cable
RE: DC Hipot test voltages for new cable
per what standard?
NETA/ANSI Acceptance test voltages are max of 56kVDC for 100% insulation rating and 64kVDC for 133% insulation.
Maintenence test values are max of 18kVDC and 20kVDC. These are for up to 5 year old cable, after 5 years no values are given.
THe ICEA has the same values.
RE: DC Hipot test voltages for new cable
RE: DC Hipot test voltages for new cable
At present there are a lot of somewhat conflicting opinions, recommendations and even standards related to cable applied voltage testing. But very few of these sources of "knowledge" have any financial stake or liability in YOUR cable.
"Theory is when you know all and nothing works. Practice is when all works and nobody knows why. In this case we have put together theory and practice: nothing works... and nobody knows why! (Albert Einstein)
RE: DC Hipot test voltages for new cable
RDVETT:
One of the reasons you may not have determined the cable was "bad" was probably due to the current meter range on the thumper. Typically a thumper is defaulted to the highest current range. A unit with a 50kV hipot would most likely have a 100mA high range. If you had the opportunity to test all three phases with a basic hipot (lower current meter ranges) you may very well have been able to determine which phase was faulted.
I have seen ice in a riser pole cut the same type of cable so clean it can withstand 30kVdc hipot prior to flashing over. This same cable was then re-energized for weeks even though it was cut in two.
RE: DC Hipot test voltages for new cable
RE: DC Hipot test voltages for new cable
RE: DC Hipot test voltages for new cable
RE: DC Hipot test voltages for new cable
The test voltages would be 55kVdc/65kVdc for 175mil or 220mil respectively per IECA/AEIC/NETA. These specifications also may make mention not to exceed test ratings for installed equipment. This would include elbows and terminations. Do keep in mind 15kV load break elbows may or may not be able to withstand the higher DC field test voltage depending on manufacturer and style (test point).
I believe ANSI/IEEE 386 requires a 200A elbow to be able to withstand a factory test of 53kVdc for 15 min and 34kVAC, 60Hz for 1 min. Field Testing 15kV cables with elbows at these levels will of course require proper preparation of the elbow by using a proper parking stand in good clean condition. Most terminations seem to hold up well with DC testing if installed properly, kept clean and tested with proper corona suppression.
RE: DC Hipot test voltages for new cable
RE: DC Hipot test voltages for new cable
RE: DC Hipot test voltages for new cable
I always enjoy asking asking the VLF Hipot sales rep that question after a half hour "DC is bad lecture".
One VLF hipot mfg did produce a small (low joule) VLF thumper for a year or two. It simply charged + DC and thumped then charged - DC and thumped.
In reality the thumper voltages and duration in which it is actually applied are certainly less then the DC maintenance test voltages that began the "DC Bad" movement in the first place.