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You are here: Experts > Computing/Technology > Job Searching: Technical > Electrical Engineering > Power Factor
Expert: cleggsan - 11/7/2009
Question
Hello Sir,
I am conducting an experiment in which I have an auto transformer connected to a 35 ohm load. I have a Yokogawa digital meter that provides me with input voltage, current, wattage, and VARs.
Now to my question- for several of my measurements, I am trying to calculate power factor with the equation Pf = P in / S in. Where P is my input power in watts from my Yokogawa meter, and S is apparent power and is input voltage * input current (both as measured by Yokogawa meter).
For a certain instance, my measurements are as follows:
P = 478 | E = 114.2 | I = 4.16
Assuming my calculations are correct, this gives me a power factor of 1.0062??
I have taken several measurements like this on this system where my power factor has been above 1.0. This isn't possible, is it? Surely I am doing something wrong...
Thank you for your time!
Answer
Yes, you are doing something wrong. It is very difficult for it to be greater than one unless you have some energy being generated within the load. Power factor is much easier measured using a scope and simple comparing the phase angle between the input voltage and the current. You can measure it quite accurately on the screen of the scope. Do you have an oscilloscope to check it with?
I think your problem is the voltage times the current in determining the S value is where you are in error because these are complex numbers with angles associated with them and the multiplication must be done in the polar or complex domain.
Depending on what your load is it may be more simple to measure the heating wattage at the load and compare it with the total power going in. That ratio will also give you the PF.
Good Luck.
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