AC Hi pot Test

[zaza123]

we are doing AC hiPot test for Medium voltsge cables,the volateg level is 4.16 kV & 13.8 KV .for 4.16 KV , the isulation withstand level for 4.16 Kv is 6/10 Kv ,so we can inject 3 times Uo (ie 18kv) FOR 1 hOUR. I am under the impression that this is as per VDE standard , can somebody confirm this

 

[dpc]

You need to follow manufacturer's recommendations. IEEE no longer recommends hi-pot testing for MV cables, IIRC.

Search this forum. This has been discussed previously.

 

[electricpete]

I remember IEEE has reduced discussion of dc hi-pot of cables (if memory serves me right, it's still listed in but not necessarily recommended)

I didn't realize the same applied to ac hi-pot. Does it?

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[Zogzog]

AC hipot is still OK, but a 60Hz an AC hipot needs a ton of power to charge a MV cable of any signifigant lengh, thats why VLF is used instead of power frequency for AC cable hipotting.

I will need to double check your testing specs Monday but sounds right to me. (Not sure an hour is necessary, you dont mean 1 hour per phase do you?)

 

[dpc]

My bad - I missed the ac reference.

 

[zaza123]

We insert 0.1hz frequency, all the Phases are joined together & for 4.16 KV cable (insulation level 6/10 KV)we give 3Uo ie 18KV for 1 hour, the leakage current in one sample we got 3.1mA.This particular method was advised by the Testing company.so the voltage which we are giving is given to three phases simultaneoulsy.

 

[zaza123]

i forgot to add the reference CENELEC HD 620 S1 part 5 Sction C (indent with the German Norm VDE 0276-620)

 

[Zogzog]

So you are using VLF, should be good. Cant help you with the spec (In the USA) we follow ANSI/NETA, IEC, and IEEE specs, dont have the VDE. Even so, an hour sounds like a long time to test 1 phase.

 

[zaza123]

While doing this test we are connecting all the three phases of the cable ie L1, L2 & L3 together ,is it right or it should be done seperately for each phase.

 

[Zogzog]

Seperate, you will want to compare the results between the 3 phases, unless you are a testing company that does this for a living and have a large database of test results comparing phases is all you really have to go on for condition assesment.