Technical Information

Calculating kVA Single Phase

The calculating for single phase loads is slightly more complex due to the fact that a three phase generator has to be de-rated by a third when used on a single phase supply. This is because the current for an equivalent kVA, single phase is much higher than for a three phase.


V = Voltage generated
I = Amps available
kVA = Kilo Volt Amps
0.66 = Derating factor 1/3

Example 1

The current which can be supplied by a three phase 50kVA generator when connected 240 volt single phase is determined as follows:

Derate by 1/3 eg. 50kVA x .66 = 33 kVA

For single phase I = kVA x 1000 = 33 x 1000 = 137.5 Amps
  Volts 240  

Example 2

A customer requires 30 Amps single phase 240 volt.

What size set does he require?

1 Phase kVA VXI = 240 x 30 = 7.2 kVA
  1000 1000  

If you have a three phase machine then the derating factor must be used.

kVA = 7.2 = 10.9kVA

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