High leg Delta transformer - Contractor Talk - Professional Construction and Remodeling Forum

pudge565 · 01-23-2009, 09:24 PM

Ok I have a question about a high leg delta transformer. I know that phases A and C to neutral you get 120 and that phase B to neutral you get 208. I also know that between any two phases you get 240. My question is why don't you get 328 volts from phase B to either phase A or C? I believe it has to do with the was the sine waves are off from each other but am not totally sure. Does any one have a good explaination? Or maybe a diagram of the sine waves?

InPhase277 · 01-23-2009, 11:00 PM

Quote:

Originally Posted by pudge565

Ok I have a question about a high leg delta transformer. I know that phases A and C to neutral you get 120 and that phase B to neutral you get 208. I also know that between any two phases you get 240. My question is why don't you get 328 volts from phase B to either phase A or C? I believe it has to do with the was the sine waves are off from each other but am not totally sure. Does any one have a good explaination? Or maybe a diagram of the sine waves?

Draw the pic of a delta setup. You will see that between each phase is 240 V. With the high leg setup, all we've done is tap the center of the coil between A and C, giving us a neutral. We have not changed the relationship between each phase.

In other words, between any two phases, is one full transformer coil. Between B and N, there is a coil and a half. And the phase relation between the two sine waves is such that we get 208 V.

Magnettica · 01-24-2009, 02:08 AM

What would you need 328 volts for?

Like 277 said, an open delta is just a regular single-phase set up with an additional transformer that's not center tapped. The 208 volts is a math equation. It's just a cheap way for the power company to deliver 3-phase power to it's customer but they are slowly but surely doing away with this set up.

pudge565 · 01-24-2009, 12:55 PM

Quote:

Originally Posted by Magnettica

What would you need 328 volts for?

Like 277 said, an open delta is just a regular single-phase set up with an additional transformer that's not center tapped. The 208 volts is a math equation. It's just a cheap way for the power company to deliver 3-phase power to it's customer but they are slowly but surely doing away with this set up.

I don't know what you would need 328 volts for but I was just curious as to why you don't get it.