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Homework Help: Phase Power Calculation

  1. Jan 15, 2016 #1
    1. The problem statement, all variables and given/known data
    I need to calculate the power for phase A, B, and C so that I can determine the total power into the system.

    I have measured the following data:
    VA magnitude = 117.7 [v]
    VA angle = 0°
    IA magnitude = 7.5 [A]
    IA angle = -25.5°
    VB magnitude = 117.7 [v]
    VB angle = -124.1°
    IB magnitude = 7.7 [A]
    IB angle = -145.7°
    VC magnitude = 117.2 [v]
    VC angle = 117.5°
    IC magnitude = 7.3 [A]
    IC angle = 94.8°

    2. Relevant equations

    3. The attempt at a solution
    Does this mean?:
    Phase A power = 882.75 [w]
    Phase B power = 906.29 [w]
    Phase C power = 855.56 [w]

    Total power into system = 2644.6 [w]
  2. jcsd
  3. Jan 15, 2016 #2


    User Avatar

    Staff: Mentor

    Hi TurboST2 :welcome:

    So you didn't take phase angle into account? That means you've calculated volt-amps for each phase, not watts.

    Does your textbook show a formula for AC power?
  4. Jan 15, 2016 #3
    Thank you for the helpful reply. No I did not take the phase angle into account. I wasn't sure if this was necessary for calculating power in this way.

    Taking the angle into account would I use this equation instead? P=VIcos(θv-θi) giving the following results:

    Pa = 796.75 [w]
    Pb = 842.64 [w]
    Pc = 789.28 [w]

    Ptotal = 2428.67 [w]
  5. Jan 15, 2016 #4


    User Avatar

    Staff: Mentor

    If you showed the data you used in arriving at those new numbers, it would be easy to judge whether you are on the right track.

    What is the nature of your load here?
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