Cable VLF testing - How does it withstand
Cable VLF testing - How does it withstand
(OP)
Hi all,
I a trying to understand how it is that the HV cable can withstand the VLF hipot testing.
I thought that when a cable insulation is rated for a voltage, say 6.35/11kV, then the cable cannot be subject to voltages above 6.35kV ph-E and subjecting it to higher voltages would result in insulation damage.
However, I understand that VLF testing is performed by placing the cable up to 3 x Ph-E voltage for a period of time, say 15-30 minutes to check the integrity of the cable insulation.
How does this test not damage the insulation? Is it because it is done at a very low frequency (0.01 Hz)? Even if it is low frequency, I calculate that the peak voltage of 3 x Ph-E voltage will be applied to the cable for as many as 180 times over a 30 minute period. I thought the frequency was lowered purely so that the test kit could actually supply such a high voltage without pumping too much current.
Am I missing a fundamental point here??
I a trying to understand how it is that the HV cable can withstand the VLF hipot testing.
I thought that when a cable insulation is rated for a voltage, say 6.35/11kV, then the cable cannot be subject to voltages above 6.35kV ph-E and subjecting it to higher voltages would result in insulation damage.
However, I understand that VLF testing is performed by placing the cable up to 3 x Ph-E voltage for a period of time, say 15-30 minutes to check the integrity of the cable insulation.
How does this test not damage the insulation? Is it because it is done at a very low frequency (0.01 Hz)? Even if it is low frequency, I calculate that the peak voltage of 3 x Ph-E voltage will be applied to the cable for as many as 180 times over a 30 minute period. I thought the frequency was lowered purely so that the test kit could actually supply such a high voltage without pumping too much current.
Am I missing a fundamental point here??






RE: Cable VLF testing - How does it withstand
RE: Cable VLF testing - How does it withstand
RE: Cable VLF testing - How does it withstand
Of course was was in the days when dinosaurs roamed the earth.
In a demonstration for electrical students I put over 50 kVDC on a length of THHN 600 volt cable before insulation failure.
old field guy
RE: Cable VLF testing - How does it withstand
RE: Cable VLF testing - How does it withstand
In a nut shell, if I am going to energize an 11 kV cable with a line to ground voltage of 8.9 kV peak stress forever, it had better be able to hold off 2 - 3 times that for a 30 minute test.
Hope this helps
RE: Cable VLF testing - How does it withstand