[Meadow]

When was the last time an electrician hooked up a wye ungrounded delt transformer? When was the last time a line man had a primary wye ungrounded delta can?

 

[Meadow]

Thanks. Why are neutrals not used on these? I have only ever done doorbell transformers.

Because what they are teaching students isn't exactly real world. Wye ungrounded delta transformers are rare in the real world both for NEC electricians and poco linemen. Any engineer would discourage their use. A functioning connection yes, but rare.

However, an ungrounded delta secondary is often used to feed factories especially old ones. Often the 3 phases X1, X2, X3 are not grounded at any point. This system has no neutral since all the loads are connected between phases. Of curse the loads must be for the higher phase to phase voltage. Most of these run at a voltage of 240, 480 or 600. The electrical system has no neutral. Of course you still have ground wires and ground busses, but no neutral wire. Just phase 1 2 and 3 plus a ground wire. A device called a ground detector makes sure none of the 3 phases are faulted to ground or a metal frame somewhere in the system. This again is called an ungrounded system.

Another system is a corner grounded system. One phase, usually the X2 is grounded down (connected to the ground buss at the service). All loads are connected phase to phase, but one of those phases just like a neutral remains close to ground potential.


Hope this helps.

 

[brian john]

When was the last time an electrician hooked up a wye ungrounded delt transformer? When was the last time a line man had a primary wye ungrounded delta can?

But you can have a grounded wye feeding the above original post, just no neutral.

And I know you know that just for the OP.

 

[Big John]

Because what they are teaching students isn't exactly real world....

That's why I shot my mouth off when I saw the apparently odd-ball IDs on those terminals, because in my experience this schooling often has a bunch of hypotheticals that will never, ever be applied, and as far as I'm concerned it's a waste of the student's brain-power.

But in fairness, if they're actually letting guys build their own ganged transformers out of little single phase versions, that's actually a really neat way to teach the theory, even if the configurations are unusual.

I've run into and installed more than one ungrounded wye. It would definitely be rare in new construction, but for retrofits and old gear, they're out there.

 

[owl]

What are the most common transformer configurations used?

 

[brian john]

In commercial distribution, 3 phase Delta Wye.

 

[brian john]

But in fairness, if they're actually letting guys build their own ganged transformers out of little single phase versions, that's actually a really neat way to teach the theory, even if the configurations are unusual.

With a few small single phase transformers I'd say that is a great teaching method.