220KV CABLE SEALING END FAILURE

[smnellore]

Dear Friends,
Two weeks back we had a failure in one of our Gen-Transformer (166MVA) 220kv cable sealing end due to the cable insulation failure.. It causes a lot of fire and damage to the radiators and other two phases cables (400 sqmm XLPE). As a precautionary measure we did the PD measurements at the cable sealing ends of other transformers. These measurements revealed higher PD values (>100pc)from two other cable sealing ends of different transformers. Immediately we shutdown the GT and inspected one of the cable sealing end of the transformer. These cable sealing ends are from Brugg type TT1.245-11. These are located inside HV cable box. Cable sealing end is filled with silicone oil. After dismantling the cable sealing end for inspection we found some strange jelly type material (photo attached) inside the cable sealing end in addition to the silicon oil. So far we could not able to find out what it is. Siemens expert called for the investigation. I will update the information once we complete the inspection. Any feedbacks /comments on above ?

 

[DanDel]

This is interesting, but there is no attached photo.

 

[HSKabel]

Provided that the PD measurement did pick up PD from the termination and not from other sources (bus, transformer, bushings, etc), high level PD activity inside the termination would leave traces of PD, i.e. discharge marks on cable insulation or insulator surfaces or at interfaces such as between the stress cone and the cable surface. The Brugg TT245 should have a silicone rubber stress cone and it would have to be cut and removed to look for these marks and, obviously, it cannot be reused.
Did not see a picture but gels forming in the fluid are a specialty that depends on the fluid supplier. By themselves they do not mean much.
Hope this helps. Obviously you are sitting on a bigger problem. Have you contacted Brugg and/or contacted an independent expert (depends on where you are).