Power Cable Resistance Unbalance

Cable damage springs to mind, have you done an inspection of the cable run?

Why are you using 11KV cable for 433V? Or have I misread something? 2off 630mm seems way undersized for 1.6MVA.

It will be prudent to replace the cable now, to prevent another shut down in near future.

I don't understand why do you need 11 kV cable for outgoing feeder of 0.433 kV [for a transformer of 1600 kVA 6.6/0.433 kV].Even for an old cable 12 megohms it is low. It could be wet at the ends. Try to dry it exposing it to a low voltage with no load[the far end open] for 10-12 hours.

"Try to dry it exposing it to a low voltage with no load[the far end open] for 10-12 hours."

How does that help?

The capacitive current [400 V it is enough] will heat the insulation and the water vapors will leave the cable through the conductor.

It is true I did it on a 3 cores cable PVC insulated of a few hundreds meter 48 hours and it succeeded!

Got some math and numbers to back that up particularly input wattage levels achived?

I think it is difficult to calculate the dielectric losses due to lack of some data.

First of all we don't know what kind of cable it is really: -11 KV then has to be shielded ,

- are they 2 cables in parallel and both present low insulation resistance?

-if they are low voltage cables in what configuration are they?

Second: if the water penetrated along the conductor the capacity between conductor and the ground will be elevated since water permittivity is about 80

but of HEPR could be 3 [and tandeltha 0.02] so at wet end the dielectric losses could be elevated.

Unbalanced resistance in not an issue. Check the IEE and the BS for the least required phase insulation value. Its been a while for me but I think you are ok with the value advised above.

I think, it is important to change the cable, since the plant is now down. You not changing the cable can led to imbalnces in the system and that can also led to the transformer exploding due to unbalance phase.

Inadequate protection arrangements cause transformers to explode. Mere phase imbalance doesn't.

The problem is already clear, and perform the following work step :-

1. Open both end of the cable.

2. Cut the insulation 1/2 ins below the cable lug.

3. Megger the cable and obtain the megger result is infinity.

4. Tag the cable with high tension tag.

3. Reconnect back both end cable, remove the VT and megger test the complete, the megger result is back to normal.

During to the cable termination process, the cable jointer have condamenate the suaface between the cable and cable scan.