Power Factor Calculation : Need help!

Discussion in 'Homework Help' started by schicco, Dec 31, 2013.

  1. schicco

    Thread Starter New Member

    Dec 31, 2013
    1
    0
    I need help with this problem.

    A balanced 3 phase, 60 Hz load consists of machinery of 500 kva at 0.5 PF lagging, and a 3 phase resistive load 300 Kw. The two loads are supplied by a 4160 volts feeder.

    a. What is the magnitude of the feeder current?
    b. Specify the number and ratings of capacitors required if it is desired to improve the feeder power factor to 0.8. Assume caps will be connected in Y.

    Here is what I tried to do:
    First to determine the current of each load. For the resistive load kW = kVA. The formula is I = kVA ÷ E ÷ sqrt(3). The resistive load has a power factor of 1.0, so it neither leads nor lags, so assign it an angle of 0° (Line 1 or A). For the machinery load, current angle is directly related to power factor: theta = arccos(PF).
    Where do I go from here?

    Thank you.
     
    Last edited: Dec 31, 2013
  2. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
    230
    Add the two, then solve for your reactive component.
     
  3. WBahn

    Moderator

    Mar 31, 2012
    17,715
    4,788
    Is that 4160V line-to-line? line-to-neutral? Is it amplitude or RMS? If you need to, rely on convention, but it's important to know what convention you are using.

    The formula that you are grabbing out of thin air for the current, does that give you the line current? The phase current? Is the E in that equation the line voltage? The phase voltage?

    What is the power factor to start with?

    What is the reactive power to start with?

    What is the real power to start with?

    How much compensating reactive power must the capacitors provide to achieve the desired power factor?
     
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