ECN Forum Forums Technical Discussion Electrical Theory and Applications Pot Transformers

quote
"Oh yeah and DON'T drop any tools,washers, or other foreign matter in the pot, it makes for a long day. Not that I know anybody that has done that or anything..."

I remember when I was working for GE and one of the techs tied off all of his tools and stuff before opening the cover. He tied off his flashlight so he could use it to inspect the interior. As soon as he flipped the flashlight on, the lens fell off, followed by the batteries and the rest of the guts of the flashlight.

Dang!! I wish I had been on site that day...I could have used a good laugh!!

Dnk:

It would probably be wisest to contact the local POCO, thier linemen/troublemen have a lot of experience in dealing with those things.

Even if the tubs are privately owned, they may be willing to take care of the tap change at no charge or maybe a modest fee.

There are a lot of factors involved, such as safely de-energizing them, ensuring no backfeed of any kind, dealing with the warm (or hot) oil, which may be PCB contaminated, not introducing any dirt, water or other foreign objects into the tank, how to actually operate the tap changer (Does it just turn, do you push it in and turn, pull it out and turn, does it take a special tool, is there a setscrew device or other locking device, etc.)

And are you prepared to deal with the possible violent failure of one or more of these if the tap changer or windings are bad? The POCO guys I know have told me horror stories from doing what they thought was to be a simple tap change.

If I were in your shoes, I wouldn't touch 'em. I don't have the necessary experience. I've read a lot about them, but I don't consider myself anywhere near qualified to deal with them!!

Good luck!!

Dnkldorf
Although it isn't impossible that the tapchanger control knob is inside the tank, it's very highly unlikely. It should be somewhere on the outside. It is usually a composite (plastic) knob or lever and should be held in its present position by a set screw or similar. Completely DE-ENERGIZE the transformers before doing anything! ( I know you already know that, but others who happen along to your post may not read everything. I would hate for someone to end up dead, or worse) Previous posts gave the correct instructions. If your present input voltage is 5% lower than the nameplate rated volts, move the tapchanger to the 95% position. Oh, by the way, make really sure you re-tighten the set screw, you would be some surprised what a medium sized curious raccoon can do with that tap handle! Always re-energize from a safe distance whenever possible.
Regards