Aurotransfomrer

[petersonra]

So I am looking at a diagram for wiring up an auto transformer to convert 115 volts to 100 volts. I don't really think much about it but the qa guy He's having a cow about the fact that the winding wires are number 14 and he's wondering how we can get 100 amps through that. I'm sort of wondering myself. Am I overthinking this? I never really thought about this before.

 

[curt swartz]

What size transformer?

 

[wwhitney]

If you have a single phase transformer with ratio 20:3, and you connect H1 to X0, and apply 115V to H0 and X1, you will get 100V between H0 and H1. If you then connect a 23A load to H0 and H1, you will see 20A on the supply to H0 and X1.

If we consider this 20A as originating into X1, it all flows through the "secondary" coil to X0/H1. There it meets up with 3A flowing through the "primary" coil from H0 to H1/X0. The currents add to become 23A going to the load and returning to H0. There the current splits, with 3A flowing through the primary coil to H1/X0, and 20A flowing back to the source.

So the currents in the transformer coils are in ratio 20:3, as expected. That means that with a 100A 100V load, the high voltage coil will only see 13A of current, which is fine for #14.

Cheers, Wayne