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# Sizing Step Down Transformers

## Sizing Step Down Transformers

(OP)
I am planning to replace a 5KV step down transformer to accommodate an additional load of approximately 800Amps @ 208V. I am confused by the term Volt Amperes and also input and output specifications. I have IEEE 57.12.26.1992 but it assumes an understanding of the terms. I would appreciate any information or direction.

### RE: Sizing Step Down Transformers

From the basic three phase power calculation, KVA = VOLTS X AMPERES X SQRT(3)/2.  Your 800 ampere, 208 volt additional load is 288 KVA.  The input and output voltages are to be found on the nameplate of the existing transformer.  I suggest that you engage a profewssional engineer to assist you in determining the available parameters of your electrical distribution system to determine if you can add the load to the existing distribution system.

### RE: Sizing Step Down Transformers

I apologize for the incorrect formula.  The correct formula is VA = VOLTS X AMPERES X SQRT(3)/1000.

### RE: Sizing Step Down Transformers

The easy non-technical answer is to think of kVA as essentially the same as kilowatts (kW), and roughly the same as horsepower.

JohnHamburger is right, hire yourself a PE, this is not rocket science but it's not a Home Depot project either.

### RE: Sizing Step Down Transformers

Slight mistake in the formula:
VA = VOLTS X AMPERES X SQRT(3)/1000

actually, it is:

VA = VOLTS X AMPERES X SQRT(3)

or:

kVA = VOLTS X AMPERES X SQRT(3)/1000

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