What is the reactive power?

[trhea@saberpower.com]

• 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?

[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.

[McDaniel8402]

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.

[ghernandez]

Studying for this level 3 exam..... having some set backs with the trigonometry part of it... any suggestions...

[fljubichich]

When I was doing my degree, these two sites had saved me a thousand times when trying to get through complex math. Try:

https://www.mathsisfun.com/algebra/trigonometry.html

https://www.khanacademy.org/math/trigonometry/trigonometry-right-triangles

Hope this helps, and good luck!

[MDTannen]

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.

im getting 0.9129..... for sine 20. The product of that and 1200 is 1095.5. Am I missing something? It's late and I'm a little burnt out.

[SecondGen]

im getting 0.9129..... for sine 20. The product of that and 1200 is 1095.5. Am I missing something? It's late and I'm a little burnt out.

How did you get 0.9129? This is how i punch it in my calc:

SIN(20) = 0.342
1200 * SIN(20) = 410.42

[JoshQ86]

How did you get 0.9129? This is how i punch it in my calc:

SIN(20) = 0.342
1200 * SIN(20) = 410.42

Calculator is not set in degrees.

[SecondGen]

Calculator is not set in degrees.

Ah, yes. SIN(20) in radians will give you 0.9129

[codycody103]

• 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?

to help remember what the powre triangle is, i use the word ART ( APPARENT, RACTIVE AND TRUE) just remember how the triangle looks and ur good to go

[MDTannen]

Calculator is not set in degrees.

Thanks