Transformer HV terminal box breathers

[allan789]

Hello all,

On my site we are looking at installing silica breathers at the bottom of our transformer HV terminal boxes. We have had a few failures where water has ingresed into the terminal box and caused a flashover.

The concept is that the breather at the bottom will let any water/moisture ingress leave the terminal box as well as giving an indication that there is significant moisture present (via coulour change of the silica).

Just wondering if anyone has gone through the same process and whether they have had any pro's or cons to this.

cheers

 

[Marmite]

I don't think you are going to solve water ingress using a silica breather. It sounds like an issue with the cable box design. Are the boxes designed for indoor or outdoor use? Normal practice where I'm from with dry boxes is to leave a 10mm gap in the cork gasket on the bottom edge of the gasket as a breather hole/drain, or preferably a breather hole with an insect screen. I've never come across a silica gel breather on a cable box, though it will be interesting to hear what others say.
Regards
Marmite

 

[ScottyUK]

I've seen them on generator isolated phase bus termination cubicles. They are a waste of time. Either design the housing to inherently self-drain, or to not let water in in the first place).

Is the water definitely coming in from outside? PD activity produces water as polymer insulation breaks down.


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If we learn from our mistakes I'm getting a great education!

 

[allan789]

They are outdoor transformers but degradation over time has lead to the water ingress. Its definately water ingress as we can see the water trails.
Regular maintenance of our transformers is whats letting us down most, we are on a mite site and our HV maintenance is only reciently starting to come up to scratch.

 

[stevenal]

Suggest a pair of screened vents, top and bottom; and a heater inside the box. Water always finds its way in; this method helps it find a way back out.