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.

Formulae

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
0.66

Technical Info