Transformers and power factor

Thread Starter


Joined Jan 24, 2012
I have an inductive load (HID ballast) whose power factor I wish to measure. There are two options for powering the ballast - a 480V switching power supply, and a 240V switching power supply with a 2:1 transformer on the output to provide 480V.

My question is - will the presence of an intermediate transformer between the supply and ballast have any impact on the measured power factor of the ballast?

Also, would having the intermediate transformer between the source and ballast effect the ballast's open circuit voltage?

Sorry if these are silly questions, I'm a mechanical guy that has gotten thrown in the deep end! Any help greatly appreciated.


Joined Oct 26, 2011
Generally speaking, the transformer should not affect the power factor of the load. However, with heavily loaded or lightly loaded transformers there may be significant errors introduced. Also, if the current waveform contains many harmonics as in a distorted waveform, the transformer will tend to attenuate the higher frequencies.