132kV Cable HVAC Testing after Installation 2

[RRaghunath]

The IEC60840 allows the 132kV cable to be tested by applying rated voltage (Uo of 76kV) for 24hrs. This is as an alternative to applying 132kV Phase-Earth for 1hr.

I would like to know
* How common is the 24hr testing practiced.
* Is the test performed by connecting the cable to the grid, in somewhat similar to Transformer Soak test.

Thanks in anticipation.

 

[ANGIBEW25]

THIS TEST IS IDENTICAL TO A TRANSFORMER SOAK TEST AND MANY UTILITIES REFER TO THIS TEST AS A CABLE SOAK TEST.
PRIOR TO A SOAK TEST SOME UTILITIES ALSO PERFORM A JACKET LEAKAGE TEST. THE JACKET LEAKAGE TEST WILL VERIFY IF THE OUTSIDE JACKET OF THE CABLE HAS BEEN COMPROMISED DURING INSTALLATION, SPLICING OR TERMINATING. THIS TEST CAN ONLY BE PERFORMED ON CABLES WHOSE OUTSIDE JACKET IS SEMI-CON BASED.

GOOD LUCK.

 

[RRaghunath]

ANGIBEW25,
Thanks for the insight.
Do you think once the jacket leakage test is done the cable can be connected to the grid without hesitation as the test establishes the integrity of the cable outersheath.

 

[ausphil]

raghun,

be aware that the cable sheath test gives some confidence that the cable was installed correctly and jointed correctly with respect to the sheath. so it gives some confidence on the laid "cable" condition, but not necessarily on the joint or termination condition - which is where most of the failures are going to occur.

we recently had a 132kV cable fail on soak after 16 seconds. it had passed all the sheath tests.

it really comes down to the risk that the company wants to take, and then money that they want to spend on test equipment.

phil

 

[ANGIBEW25]

raghun:
Sorry for the delayed reply, I was occupied on a project. with regards to when the cable should placed into service:
I personally would prefer that the cable pass a jacket test and then at the very least a Hi-potential test prior to the soak test. If you now the parameters (length, charging current, megohms per ft) of your cable you can estimate the expected leakage before the hipot test. If the expected result matches the emperical result then you can soak away.

Good Luck.

 

[RRaghunath]

ANGIBEW25 & ausphil,

Thanks for your mails.

The update is that the owner has energised the 132kV cable and soaked it without any event.
The cable has not been tested with HV (I am not aware of the reasons completely, though the difficulty in getting the AC HV test equipment could be one reason).

Thanks once again, I agree that the terminations / joints could not have been proven by Outersheath test alone and the best thing would be to go through the HiPot.

Looking back, the cable is 700metre long and I guess the test equipment for AC HV test would be quite a bulky one and not easy to obtain.