Commissioning of an old 11kV unused cable

[krisys]

I have an 11kV cable of about three (3) kilometer length installed between two facilities. Both facilities have their own power generation system and they are operating in island mode. This 11kV cable was originally intended to supply and standby power source for the black start of one facility from the other facility power supply. However, each facility has its own black start DG sets from the beginning. Hence this 11kV interconnection was never used. Not even energized/commissioned! The cable is lying un-used for the last 20 years.

Now we are intending to energise this cable. But people are not sure what are the tests required to establish the healthiness of the cable. If anyone can share your experience in similar set up, is highly appreciated. For your information, this is a offshore facility and it is a subsea (submarine) cable.

 

[krisys]

Can any one tell the following?

a) Advantages of VLF test compared to the DC high voltage test for the cables?
b) Partial discharge test is for the cable termination or for the cable itself?
c) Is tan (δ) test applicable for the medium voltage cables?

Thanks in advance

 

[ScottyUK]

What cable type? VLF AC tests are generally considered less damaging to XLPE insulation than equivalent DC tests. PD tests generally find weakness at the terminations because that is where there are more likely to be imperfections and discontinuities in the insulation system. If there are imperfections elsewhere in the bulk cable then a PD test will likely find them. The tan delta test is worthwhile, perhaps more so on PILC cable than XLPE although others will disagree with that opinion.

 

[krisys]

Thanks ScottyUK!
Your inputs are very useful.

Actually the cables were installed sometimes during 1981. The cable data sheet and test reports are not available. It could be either first generation XLPE or PILC, but not sure. The cable length is about 3 km.