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220kv outdoor sealing end porcelaing abd cable failure

220kv outdoor sealing end porcelaing abd cable failure

220kv outdoor sealing end porcelaing abd cable failure

(OP)
thread238-236574: 220KV CABLE SEALING END FAILURE
We have 220KV cable ODSE supplied by Brugg AG and installed in 2007 at our power plant. Recently we found cracks and oil leak from porcelain in two ODSE. Upon opening sealing ends we discovered jelly formation and cable puncture. Based on the finding we open other odse and found the cable is puncture but no cracks on the porcelain. The jelly formation was found in all 3 phases and cable puncture at same height in the cable ( apprx. 91cm from top of seal end , total length of cable is 4.1m in ODSE). The ODSE is filled with silicone oil up to 85% of bushing and rest 15% is air. We have not measured PD so far for other ODSE.
I have read thread from Smnellore on this topic and fortunately the cable ODSE is from Brugg, type: TE 1.245-01SP, 220KV, 1200SQMM. Mr. Smnellore please let me know what root cause of jelly formation was and what action taken to mitigate it.

If someone has some suggestion/ idea, please share with me.
I am unable to load picture, please let me know if you need pictures.
Regards

RE: 220kv outdoor sealing end porcelaing abd cable failure

We had a porcelain sealing end failure on a 132 kV cable a number of years back. the sealing end was only 7 years old at the time.

There was a number of issues that were linked:

- similar to your issue, the sealing ends were silicon oil filled.
- the oil leaked out from the sealing end down into the metallic screen wires of the cable, lowering the height of insulating fluid in the sealing end, which eventually led to a flashover along the XLPE surface of the insulation inside the sealing end. as the fluid was contained between the insulation screen and the cable sheath, there was no visible method of detecting the problem.
- we pulled down a number of similar units, and found similarly low states of fluid levels. through a fair bit of work, we were able to determine the fluid height in the sealing end via IR thermography (at night time) to within a few sheds, which was sufficient to be happy with an external indication of the fluid height.
- a clamp, making the seal at the bottom of the sealing end, worked its way loose, which then allowed the fluid to leak out the bottom.
- the cable conductor was aluminium.

The root cause was that the conductor, being aluminium was expanding and contracting, which put pressure on the internals of the sealing end, which led to the clamp becoming dislodged.
The cable, as it approached the sealing end, was not snaked sufficiently in order to clamp the conductor to the screen and sheath, which allowed the conductor to move more freely.

We didn't experience the jellying that you describe, but I would assume that is either due to the oil being subjected to partial arcing within the sealing end or possibly to moisture ingress.


Has the sealing end failed explosively in service, or have you found this during maintenance?

Ausphil

RE: 220kv outdoor sealing end porcelaing abd cable failure

(OP)
Hi Ausphil,
Thanks for valuable information.
In our case we found craks and leak during routine inspection. There were no oil leak from clamp and our cable has copper conductor.The oil level has not drop down and as per design it is filled at certian level corresponding to ambient temperature and other portion is left for thermal expansion.The stress cone looks good and there is no issue with it. The partial discharge and jelly formation is evident near the cable fault point.Our case is very much similar to Mr. Smnellore problem as mentioned in thread238-236574: 220KV CABLE SEALING END FAILURE. Please let me know how to attach picture so that i can share it.
Regards,
GTPT

RE: 220kv outdoor sealing end porcelaing abd cable failure

Have a look below the large white box you wrote your reply in. There are a couple of ways to upload pictures: you can upload them to engineering.com and copy the link into the text box, or you can post a link to an external filehost if you have already uploaded them on Picasa or similar. Works for any kind of file, not just pictures.

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