Transformer Bushing and Oil Replacement methods

[shawnroberts]

Hello,

Just curious to see if anyone has a best practice method for bushing replacement on a smaller distribution transformer. The oil will have to be drained, primary bushings replaced and new oil put back in for a 3MVA transformer and are looking for best practices with regards to keeping moisture out of the main tank while replacing the bushings. The bushings are inside the cable termination enclosure and are mounted horizontal. Any advice would be appreciated.

[backpack96]

Hello,

Just curious to see if anyone has a best practice method for bushing replacement on a smaller distribution transformer. The oil will have to be drained, primary bushings replaced and new oil put back in for a 3MVA transformer and are looking for best practices with regards to keeping moisture out of the main tank while replacing the bushings. The bushings are inside the cable termination enclosure and are mounted horizontal. Any advice would be appreciated.

Do not open the manhole if not required to limit the exposure to open air. If these are bolted in bushings and not welded then you should be to lower the oil level a little below the bushings. This will limit the exposure of the windings to open air. One thing that often helps is to have everything prepared to perform the bushing replacement so that the amount of time is as short as possible. I always liked to keep exposure time of the windings to a minimum.

I would advise performing as found tests and as left tests to make sure that this work does not cause issues. I reviewed some data in which the technician forgot to connect the 3 low side bushings. The power factor was off and as you know the TTR and winding resistance failed. The sad thing is the the company who replaced the bushings was not the same company who came in behind them to test.