Moth balling 12 MVA oil filled transformer

[DaveMeharg]

Does anyone have any suggestions or experience with moth balling two 12 MVA oil filled transformer? We would like to leave them denergized for a year or so and only renergized in an emergency situation. Not sure if its simply a mater of turning off and placing a slight nitrogen purge on top. One transformer is over 40 years and the other about 10 years. Not sure if I need to be concerned about water migrating back into the paper insulation and accelerating the deteriation.

 

[ScottyUK]

I would be more concerned about water content when you come to re-instate it. Normally a medium-sized or large transformer would be connected to an vacuum oil processor which applies high vacuum and heat to the oil to draw water out of the oil and core. It can be a lengthy process, especially if the transformer is old or the oil is in poor condition! If you have time and money then it would be a nice-to-have before mothballing too, and would probably reduce you reinstatement period.

Some facilities short one winding and energise the other from a low voltage supply, just to keep some warmth in the core. The power required is fairly modest and one or other winding is often suited to direct connection to the LV supply system so it is not a big job.

 

[DaveMeharg]

ScottyUK Thanks for the help