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What is the reactive power?

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    What is the 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?

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  3. cecil6108@yahoo.com is offline Junior Member Pro Subscriber
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    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.

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    Quote Originally Posted by cecil6108@yahoo.com View Post
    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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    Trigonometry Help for Level 3 Exam

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

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    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/tri...ight-triangles

    Hope this helps, and good luck!

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  11. MDTannen is offline Junior Member
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    Quote Originally Posted by McDaniel8402 View Post
    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.

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    Quote Originally Posted by MDTannen View Post
    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

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  15. JoshQ86 is offline Junior Member Pro Subscriber
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    Quote Originally Posted by SecondGen View Post
    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.

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    Quote Originally Posted by JoshQ86 View Post
    Calculator is not set in degrees.
    Ah, yes. SIN(20) in radians will give you 0.9129

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    Quote Originally Posted by trhea@saberpower.com View Post
    • 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

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