# Kwh Calculations for a balanced 3 Phase circuit

Discussion in 'General Electronics Chat' started by Houdini, Sep 22, 2008.

1. ### Houdini Thread Starter Member

Dec 13, 2007
10
0
Quick question,

I'm trying to find the Kwh of a 3 phase machine. It is a balanced 3 phase resistive load. To find the Kwh that the machine draws do I multiply the line to line voltage and the current then divide by 1.73? Then multiply that by how many hours it has ran?

eg: Voltage = 480 Volts
Current = 57 Amps
Run 15 Hours
balanced

= ((480 x 57) /1000) / 1.73) * 15
= 237 Kwh

Is this right?

2. ### theamber AAC Fanatic!

Jun 13, 2008
321
0
Check on this calculator.
http://www.dieselserviceandsupply.com/Power_Calculator.aspx

If the 57A current is per leg and to be more accurate if you know the PF rating should multiply it too.
KW=VOLTS X AMPS X PF X 1.73 /1000
37.86624*15= 568Kwh. I think it this.

3. ### Houdini Thread Starter Member

Dec 13, 2007
10
0
Looks like I messed up in my calculations a bit. Looks like I was dividing by 1.73 when I should have been multiplying.

So.....

For 3 phases, then, the total power is 3 times the power in any phase. 3 x the line to line voltage x the line current divided by the square root of 3. AND since 3 divided by the Sq root of 3 simplifies to just the Sq root of 3. Multiplying that , as you noted , would give me the watts of a 3 phase circuit (assuming the power factor is 1).

Sound right?

Thanks!