# How to calculate transformer size from total load

#### elec.engnr

Joined Feb 3, 2014
1
Hi,

Recently when I've visited an electrical panel room, I've noticed that the current readings in the Digi Ammeter were around 160A in each phase. Now for a voltage of 415V and current as mentioned above i.e. Ir = 160A, Iy = 158A, Ib = 145A what would be the transformer capacity (11 / 0.415kV) in kVA and what is the calculation procedure?

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#### Kermit2

Joined Feb 5, 2010
4,162
Not sure what the 11 divided by .415 is about. 415 volts (V) times 160 amps (A) is 66,400 VA. This is the power per leg of the AC circuit you speak of. Leading or lagging current caused by the power factor would modify this power level giving you the required min. Power rating.

#### inwo

Joined Nov 7, 2013
2,419
I come up with 115 KVA

Using 160 amps.

I'll let someone else give you the formula when phase currents differ.
I'd use the average current. Then closer to 110 KVA

Power factor should not enter the equation as all measurements are VA not watts.

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#### crutschow

Joined Mar 14, 2008
29,466
Sounds like a cleverly worded homework problem.

#### GetDeviceInfo

Joined Jun 7, 2009
2,080
I'd calculate based on the highest current, so 115KVA. If however you are supplying motors, I'd provide extra for load dynamics.