(Electrical Circuits) What is the pf?

A capacitor,an electric resistance heater and an impedance are connected in parallel to a 120V 60 hertz system. The capacitor draws 50 var, the heater draws 100W and the impedance coil draws 269VA at a p.f. 0.74 lag. Determine the system p.f.?

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  • 10 years ago
    Best Answer

    Cos of the phase angle in the impedance coil circuit = .74

    Phase angle of impedance coil circuit = arc cos .74 = 42.27 degrees

    Inductive vars = (sin 42.27 degrees) x 269 VA = 180.93 var

    Watts of impedance coil = p.f. x VA = .74 x 269 = 199 Watts

    net circuit var = Inductive var - capacitive var = (180.93 - 50)var = 130.93var

    net circuit Watts = heater Watts + impedance coil Watts = (100 +199)W = 299 Watts

    System phase angle = arc tan [(net circuit var) / (net circuit Watts)] = arc tan (130.93 var / 299W) = 23.65 degrees

    System power factor = cos (system phase angle) = cos 23.65 degrees = .92

    Add on: You must be taking the same course as joel. I answered this same question for him 4 days ago.

  • Angela
    Lv 4
    4 years ago

    Mykra, be careful when calculating between the differences between rotating eqpt and xforms. It certainly appears your referring to a generator. The phase impedance is not a constant; it depends on the generator manufacturer.

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