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Hermetically sealed voltage & current transformers - CT VT

Hermetically sealed voltage & current transformers - CT VT

Hermetically sealed voltage & current transformers - CT VT

Good day,

In our network we have several Hermetically sealed voltage and current transformers ranging from 33 - 220kV.

There are several which have developed oil leaks.

Can these be repaired as they are Hermetically sealed units?

We would preferably repair them in-house / on site as we are a remote Sub Africa utility.

Thank you

RE: Hermetically sealed voltage & current transformers - CT VT

Sure, you can or rather should repair. A leaking CT/VT is dangerous to keep in system. Hermetic sealing can be of different types- just sealing with nitrogen or dry air over oil at a slight positive pressure, a metallic or rubber bellow over the oil. While repairing and fixing oil level, please remember these simple rules of science -air will dissolve in to oil by 8 % by volume, oil volume will expand by approx. 0.8 % for every 10C rise in temperature.

RE: Hermetically sealed voltage & current transformers - CT VT

It depends a lot on the type of design. Care has to be taken not to trap air in the unit.

If it uses a metallic bellows expansion system, I would recommend discussing it with the manufacturer.

Often times it's not as easy as it looks to repair a leaking instrument transformer.

RE: Hermetically sealed voltage & current transformers - CT VT

Thank you for the good insight. I think we will first try and strip down a out of service faulty unit and see how it goes. I will try post feedback here on the progress and findings. I will definitely contact the manufacturer.

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