3-phase transformers example problems (20 - Electricity Distribution)

Wild leg (high leg delta) connection analysis, calculation of power rating changes when a single transformer in a bank of three fails, and wiring up a pole transformer in the U.S.
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Aaron Danner is a professor in the Department of Electrical and Computer Engineering at the National University of Singapore.
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Video filmed and edited by Cheryl Lim.
@randomcheryl

[@Sparky-ww5re]

I some installations, there are two transformers feeding a three phase service, typically on farms where a farmer is running mostly your typical 120/240v split phase, but needs the ability to run a couple of three phase motors, in this situation the capacity of a closed delta is not needed, so the power company assuming three phase is available in the area, will install a second transformer instead of all three. This greatly reduces costs. This situation can be easily identified if you see two transformers, one larger than the other, this is what was done.

[@Sparky-ww5re]

In extremely rare installations, there is a wild leg system at 480 V. 240V line to neutral, 415V wild leg to neutral. (Essentially the 120/240V three phase delta, but double the voltage ) This service is practically nonexistent, nonetheless it never hurts to be aware of it.

[@Sparky-ww5re]

Wild leg delta systems although seldom used in new installations, nonetheless can be very useful in very specific applications. For instance they work great in a small commercial building, like say an auto repair shop or woodworking shop that has a lot of three phase motors, but also has some 120 volt loads, although typically nowadays you'd have a 120/208Y. The major disadvantage is it's more difficult to balance loads especially if there is a lot of 120 volt equipment. Also, it's a very common (and costly) mistake to accidentally hook up a single pole breaker where 120 volts is desired, to the wild leg, and smoke up the equipment, because you will be getting 208v.

[@alisaeedi7620]

Hi can I connect neutral of two transformer