Power factor problem

Discussion in 'Homework Help' started by NyanLin Steve, Nov 11, 2015.

  1. NyanLin Steve

    Thread Starter New Member

    Sep 7, 2015
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    0
    Two loads connected in parallel draw a total of 2.4 kW at 0.8 lagging pf from a 120 V rms , 60 Hz line . One load absorbs 1.5 kW at a 0.707 lagging pf . Determine : (a) the pf of the second load , (b) the parallel element required to correct the pf to 0.9 lagging for the two loads.

    Attempt :

    Firstly , I used (2.4 kW - 1.5 kW) to find the power that the second load draws . Secondly I used the formula : P = V rms I rms pf in order to find the I rms current supplied from the source and then the second load , which is around 7.32 Amps . However , when i used the same formula to find the pf i.e

    900 / (120 * 7.32 ) , I realised that the power factor exceeds 1 . May I know what I have done wrongly ?

    Thanks in advance.
     
  2. WBahn

    Moderator

    Mar 31, 2012
    17,743
    4,795
    You are only showing a fraction of your work. Where did you get 7.32 A for the rms current in the second load?

    Let me guess. You found the rms current for the source and the rms current for the first load and you subtracted them, forgetting everything that they have been trying to teach you about how things that are not in phase add (and how they don't add).
     
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