Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This Question of the Day, concerning the method of converting kW rating to kVA, and power factor, is answered by the ECA, the NICEIC and SELECT:
So what is the applicable formula for converting kW to kVA for transformers and general applications?
Answer by the ECA: The following equation is used: kW = kVA x Power Factor (PF).
It is better to work out loadings for transformers etc in kVA rather than kW - otherwise you could end up under-sizing if the power factor is lower than you thought.
Answer by the NICEIC: Please refer to the attached document published previously in our 'Connections Magazine' - this should help you to calculate kVA.
Please click on the link below to download the attachment (PDF doc - 2.25MB file size).
Answer by SELECT: The kVA figure will always be equal to or higher than the kW figure, i.e. kVA = kW/PF.
The only difference between kW and kVA is the power factor, so the conversion of kVA to kW is governed by the equation kVA = kW/PF). For example, if the PF is 0.6, then: 120 kVA X 0.6 = 72kW.
Alternatively, again, the only difference between kW and kVA is the PF, but the PF (unless known) is an approximation. If you do not know the PF, you may need to make an estimate. Therefore, for the purposes of our calculations, we use a PF of 0.85. The kVA value is always higher than the value for kW:
kW to kVA: kW/0.85 = same value expressed in kVA
kVA TO kW: kVA X 0.85 = same value expressed in kW
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