how to do HIPOT or VLF HV test on non armored cables?

[mehul0211]

hi
here in metro rail project we are using non-armored cable
how we can do HIPOT test or VLF HV test on non armored cables
regards
mehul0211

 

[7anoter4]

Medium Voltage cables are shielded and the insulation of conductors is inserted between conductor and shield. The test voltage is applied between conductor and shield then.
For low voltage single-core cable see IEC 60502-1:
15.3.2 Test procedure for single-core cables
For single-core screened cables, the test voltage shall be applied for 5 min between the conductor and the metallic screen. Single-core unscreened cables shall be immersed in water at room temperature for 1 h and the test voltage then applied for 5 min between the conductor and the water. It is only a routine test.
There are tests made by the manufacturer on each manufactured length of cable to check that each length meets the specified requirements.

 

[VLFit]

You say non-armored cable. I assume your cable has a concentric or taped neutral ground shield over the insulation around the conductor. If this is the case, it is not unlike every other cable that is hipoted: apply the test voltage between grounded shield and the disconnected conductor. The previous answer cited the test spec for IEC testing standards - 5 minutes. That is assuming the use of power frequency 50/60 Hz AC voltage is used. If VLF 0.1 Hz. AC voltage is the source, the the IEEE400.2 or IEC guidelines should be followed. The test will be for 30 - 60 minutes.

If your cables are non-shielded low voltage cables, say 600 volt rating, then there is little that can be done to field test the using an AC withstand method except for hipoting phase to phase and all three to any possible grounded raceway or conduit they may be in. More info is needed to provide a better answer int his case.

 

[mehul0211]

thanks 7anoter4 & VLFit
these cables are non armored and non shield for ground
Cable specification- Cu/XLPE/HFFR 1.5kV 1C x 300sqmm
in service voltage - 750VDC
Laid on Cable Tray, some are through non metallic conduit

We are now conducting
IR measurement @1kV for 1min. and
VLF withstand test @4.4kV, 0.1Hz for 15min.
*for IR & VLF test we are taking reference of Cable tray

can you advise is this right practice to do measurement of non-armored cables.

 

[Supertester]

You have chosen the cable tray as your ground reference, which is about all you physically can do.