paralleling transformers in a secondary circuit

[mikekuta]

Recently our utility had an in-service training day dealing with paralleling transformers into a live existing secondary circuit. If my memory serves me correctly, I learned to, among other things, close the new tub, find the zero or near-zero between phases with a meter, then open the new tub to make connections. In our pole yard, we were told we had a choice as to whether we opened the new tub or not. Any thoughts out there??????

[Special ED]

When parralleling transformers which was in rare occasionions such as not being able to have an outage or such. We would hang a can on the next pole down hook it up to the same phase feeding the can already in service and then between the legs of the new can and the secondaries we would check voltage and zeros matched up. You would open the can make your connections then close it back in to tie. Then you would go open the pre existing can and remove it or whatever so you could do your work.

Not too sure what exactly your askin here though.

[copperpenny]

The procedure we follow is the same , same phase , close the new tank, find the same secondary phases . Here's where we differ , we leave the tank closed to make the connections . On the old tank ( or one being removed ) we cut the secondary leads clear first , then we open the cut out . We've found that there's a bit of difference , when you pick up , or drop the windings . It barley barks at all if the tank is energized .
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easy vape
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XTZ 750

[topgroove]

its no big deal with a 25kva transformer but try that stunt with a 75 or hundred and you'll get a surprise. its always better to keep the windings hot so your not picking them up or dropping the windings. sounds like a good way to ruin a pair of bolt cutters.

[Pootnaigle]

Copperpenny is correct Picking up the new transformer thru the secondary windings will most definately draw a purdy good arc when ya slap the connections together. Wayyyyyyyyyyy safer to energize the pot thru the primary winding first and then phase in the secondary side.

[Phoenix-7]

its no big deal with a 25kva transformer but try that stunt with a 75 or hundred and you'll get a surprise. its always better to keep the windings hot so your not picking them up or dropping the windings. sounds like a good way to ruin a pair of bolt cutters.

Not only that, when using ampact connectors or any connectors with 75 kva and up, they will create a pretty good splash of metal when you are picking up the windings. Not bad with copper, but Al. secondaries usually melt down.

[Meat]

The other reason is you are backfeeding the new can anyway. Someone not thinking might shape the cutout jumper or put his hand where it shouldn't be. Don't do it that way ever! Meat.

[markwho]

We Energize new pot, check for zero or near , if o.k. we make secondary connections and then cut taps of secondaries on old pot and then open cutout of the pot being replaced. I watched a fellow on my crew who worked for another utility previous to ours do the opposite, It works,but like mentioned will pick up some fire on larger pots. We don't like the fact that you will have back feed at the bottom of the cutout.

Do any of you have xfmr banks that you leave paralleled to feed customers? We have two, three pot banks paralleled together. They are 100kva pots. I checked secondary amperage one day and had close to 900 amps. Made the meter vibrate! Secondary conductors are paralleled 477 al.

[topgroove]

I've seen that a couple times with two banks of 167's I guess they didn't feal like going with a platform and using 333's

[THE KID]

We have several banks that the secondary sides are tied together. Usually the banks that we tie together are 6 500 KVA transformers with three 556 jumpers. Have pictures if you would like to see. Have pictures of 6 500 KVA transformers on FIRE pretty impressive.