Transformer wiring

[ES09]

I had a question about the wiring in the uploaded circuit. the 3 phase power is 480V. I understand the voltage between 2 phases is going to be sqrt(3)*line voltage which would supply the transform, which would normally step it up or down. I came across a schematic with the primary and secondary windings jumpered as shown. My question is what would happen? I realize that the transformer would no longer be isolated but what voltage would it output? My initial inclination is that it would increase or decrease the output voltage based on its phase angle but I could be mistaken. I also realize that that is most certainly not a normal way to wire a transformer. Could any of you point me in the right direction, or explain what would happen? Thank you in advance.

 

[waross]

I understand the voltage between 2 phases is going to be sqrt(3)*line voltage
NO
The voltage between two phases IS line voltage.
The voltage will be Primary voltage PLUS secondary voltage.
OR
The voltage will be Primary voltage MINUS secondary voltage.
It depends on whether the transformer is additive or subtractive polarity.
output voltage based on its phase angle
Phase angle is the difference between two voltages at different phase angles.
A single phase circuit it not much different from itself.
This circuit is used to check polarity and is used whenever an auto transformer is needed. One of the most common uses is for voltage adjustments.
eg: 480V to 600V, 600V to 480V, 120V to 108V (Used for incandescent accent lighting in department stores to increase lamp life.)
Used to correct low voltage conditions (or high voltage conditions)
Used for motor starting.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[DaveMeharg]

yes I agree with waross. The voltage between two phases will be 480 volts. the diagram that you have looks like an autotransformer connection. I have used autotransformers to increase the voltage form 208 volts to 220 volts to run equipment that has a 220 volt rating and is too sensitive to run at 208 volt. You can google autotransfomrer to get more information on how they work.

 

[Masbibe]

This bridge between primary and secondary winding will not efect secondary voltage value.

Secondary voltage will be Us = 460 * Ns / Np.

Ns - number of turns on secondary winding
Np - number of turns on primary winding

Why connection like this is used I don't know.

This is not typical autotransformer connection.

Milovan Milosevic

 

[waross]

MM. Please do a little study on auto-transformers.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[davidbeach]

The drawing leaves a bit to be desired, but would be a perfectly good autotransformer if modified slightly. The load would be connected between 2 and the terminal on the "secondary" opposite the line from 2. As Bill said, the resulting voltage will either be Primary + Secondary or Primary - Secondary; depends on whether or not the transformer has additive or subtractive polarity.

 

[Masbibe]

If you connect load like davidbeach said yes it will be autotransformer.
But as I understood original question was what will be with output voltage (two terminals bellow). My answer was in this direction that this bridge will not change anything with output voltage.

Milovan Milosevic

 

[waross]

Most of us understood the voltage question to be the combined voltage. For voltage adjustment this connection (called a "buck" connection) will give a slightly different voltage than a step down auto-transformer.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ES09]

I'm sorry, I should have been more clear. I was curious as to whether or not the connection would effect the output voltage of the transformer. I asked around a bit at work and the answer seems to have been no it will not change the voltage on the secondary side of the transformer, however it does make it un-isolated. As to how the load is hooked up, I believe that it is hooked up on the secondary sides of the transformer, not as Davidbeach said. I am almost certain that the drawing is wrong and that it is supposed to be a regular transformer and the grounding is drawn wrong, I just wanted to understand where and why it is wrong, and the effects of actually wiring it like that. By the way I do appreciate all of your input so far.