How does this autotransforer work?

[rockman7892]

I recently came across that attached wiring diagram for an autotransformer and am trying to understand how this transformer operates. I am familiar with how autotransformers operate but am a bit confused with some of the additional circuitry with how the various windings of the autotransformer are configured as well as the additional single winding transformers connected in series on the output of each phase?

From what I can tell there appear to be several Variacs wired in parallel on the input of each phase. What is the point of having multiple variacs in series like this aside from possibly just dividing the current amongst several variacs?

Autotransformer is being used to vary a 480V input to a range of 0 to 480V output.

 

[waross]

First, it is common for auto-transformers to be energized at a tap so that the output voltage may be higher than the input voltage.
That is how you get 560 Volts output from a 480 volt input.
The series transformers. These don't add any voltage. they are used as current transformers.
The effect is two fold.
With the secondaries in series, the same current is forced through each primary and so the auto-transformers will share the load equally.
Secondly, they will even out and compensate any slight unintentional inequalities in the voltage output of the auto-transformers.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[rockman7892]

Thanks waross

I’m curious why several smaller variacs are used in parallel here as opposed to one larger variance on each phase? Most autotransformer I have seen in the past have been a larger single core and winding on each phase instead of multiple ones in parallel.

 

[BlackWhite24]

The autotransformer serves a role similar to that of the normal transformer to increase or lower voltage. It consists of a single continuous twisting using a tap brought out in some intermediate stage as shown in Fig.1. Since the primary and secondary windings of the autotransformer are physically connected, the output and supply voltage aren't insulated from one another.