1 Answer

Things You'll Need
Power factor of 3-phase motor or device (listed on nameplate)
3-Phase power formulas:
KVA = 1.73 * volts * amperes/1000
KW = KVA * power factor
KW=1.73 * Volts * amperes * power factor/1000

Instructions
1
Understand the above-listed formulas. Essentially, the KVA equation is for the potential of the electrical circuit. This means the electrical circuit can provide this much power to the motor or device. The KW equation will give the actual power used by the device or motor since the power factor of the motor is multiplied into the formula. The power factor is generally listed on the identification nameplate of most larger electrical motors that use a 3-phase power.

2
Calculate the KVA of an electrical circuit that has the potential of 480 volts at 50 amperes. Multiply 1.73 times 480 times 50 will equal 41,520 VA. Note that the answer is in VA (volt amperes) and not KVA. We must divide 1000 by the final answer in order to change the VA into KVA. To find KVA from 41,520 VA divide this number by 1000, this will equal 41.52 KVA.

3
Find the KW rating or consumption of the 3-phase circuit if the power factor of the device is 1.15 as identified on the nameplate. Use the formula, (KW = KVA * power factor) to find the result. KW is equal to 41.52 KVA times 1.15, which results in 47.748 KW.

4
Find the KW consumption of the following 3-phase motor circuit that has a voltage of 230 VAC, a current draw of 75 amperes and a power factor rating of .95. Using the formula (KW = 1.73 * volts * amperes * power factor/1000) we can plug in the numbers so the equation looks like, KW = 1.73 * 230 * 75 * .95/1000. This will equal 28.350 KW.

Read more: http://www.ehow.com/how_5017317_convert-kva-kw-phase.html#ixzz2XXYN8hxb