Voltage secondary of power transformer

[Jed057]

Plase help me
There is Transformer 2000 kVA, 11kV/420kV, and Tap changer in primary 5 step +/- 5%.
So now we having a overvoltage 418 Vac at MCC now (operation voltage 400 V)
please advise how I can make a reducing voltage to 400 Vac at MCC.
Thanks
Junior Engineer

 

[dpc]

Raising the primary tap to a higher turns ratio will lower the secondary voltage. Make sure this is done with the transformer de-energized.

But 418 V on a 400 V is not really a cause for major concern, especially when measured at the MCC bus.

David Castor

http://www.cvoes.com

 

[racobb]

First it appears you mean 11kV/420V....not kV. Most likely your steps are 2.5% each and you are 4.5% above 400 volts. That would equate to 1 or 2 steps on the tap changer depending on the actual voltage you need to end up with.

The second question is the existing position of the tap changer. Sounds like you have a center position with 2 steps above and 2 steps below. I am assuming for this example the tap changer is on the high side (typical in US). If it is not already in the highest "high side" voltage position, then you can adjust to lower the secondary voltage.

Please note that it will be a de-energized tap changer so the transformer MUST be taken out of service and the high side disconnected to change the taps!

Since the voltage is only 4.5% high you may just need to reset your overvoltage alarm level if possible. Otherwise depending on the supply voltage swing, if you drop the voltage by 5%, you may get unacceptable low voltage at times when the supply voltage drops.

You may only want to adjust the tap by one 2.5% step and see if you can live with it.

Also note that to lower the secondary voltage, you must go to a higher primary voltage tap setting....again assuming high side tap changer.

Hope it helps!

Alan

 

[racobb]

OOPS....missed the fact that the OP said it was on the primary.

Alan