hi

we have 13.8 KV Medium voltage cables directly burried, since there was no waterproofing in the cables ducts, so sea water penetrated there, cables were submerced for 4 few months in the water. though the cables are energized and working, but we are worried about the health of it. kindly assist me which type of tests we require to know the health conditions of the cables.

Note: these are new cables but sea water seepage occurred.

 

What type of cables? What is the present sheathing?
Max.

 

What type of cables? What is the present sheathing?
Max.

The cable type is CU/XLPE/STA/PVC
Insulation material: XLPE
Insulatioin screen: strippable semiconductor material
Metalic screen: copper tape
Bedding: PVC compound
Armoring: Galvanized steel taps
Jacketing: PVC Compound

 

Although I imagine that great suggestions can be found here, I wonder if it would be advisable to instead contact a professional service that could do this evaluation for you - after all, regulations may change depending on where you live and your work. An example of the different requirements can be found at:
https://www.southwire.com/support/DCFieldTestforMedVoltageCbls.htm

Given the dielectric is solid, my biggest suspicion is that the dielectric degradation is not heavily significant and it probably suffered only a reduced lifespan - still, I would test it for dielectric losses in both 50/60 or VLF (is this an AC or DC link?).

The major issue in your case is, as you mentioned, water ingress that will cause the metal to increase its resistance over a shorter time - reduced lifespan again. However, in this case I think the degradation is much worse. The comments section of the reference below talks about some suggestions to test for water ingress.
https://electrical-engineering-portal.com/the-good-bad-ugly-cable-insulation

My experience is with dielectric degradation in medium voltage but very low power systems.

 

If rsjsouza advice is not what You waited for, another advice would be to organize the Cocrofr-Walton circuit improvizated, with some microamps max current and voltage about 15 kV. Switch it on the cable piece and keep some 20 minutes. If infrared cam sees no a hotspots in darkness, be sure, cable is in good condition. If defects are seen, then know where them are. P.S. current monitoring will help to judge well, too.