
Help with question on calculating reactive power
• A given 120VAC 60Hz circuit has a load of 10A with a 20° lagging power factor for 30 minutes. What is the reactive power?
Someone help with this one?

You have to use the trigonometry principles. Remember SOH,CAH,TOA. You will need to calculate for the apparent power which is volts times amps and they give you the angle for theta. VA=1200. So the solution would be cos. 20 times 1200.

Originally Posted by
cecil6108@yahoo.com
You have to use the trigonometry principles. Remember SOH,CAH,TOA. You will need to calculate for the apparent power which is volts times amps and they give you the angle for theta. VA=1200. So the solution would be cos. 20 times 1200.
I'm afraid you've got your trig functions mixed up. Reactive power will be sine(theta), where (theta) is the power factor angle. Be careful to first compute the apparent power (V*I) as was done here, then multiply by sine(theta).
cos(theta) would compute the power factor, which would yield active (real) power when multiplied by the apparent power.
In this case, the reactive power would be 410.4 VAR. If the question were to ask anything about inductive or capacitive, the fact that the load angle is lagging tells you that the reactive power is inductive.
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