induction motor

Discussion in 'Homework Help' started by mary_owen, Apr 30, 2008.

  1. mary_owen

    Thread Starter New Member

    Apr 30, 2008
    5
    0
    hi guys, ive just joined the froum so helpfully you dont mind helping me. im totally lost with this question

    a 3.3kw single-phase induction motor. The power factor is 0.8 lagging

    Determine:

    A)Current drawn from the 230V supply.
    B)The output power if the overall motor efficiency is 85%
    C)The active and reactive components of the input current.
    D) The apparent power and reactive power consumed.
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    A) current drawn =power/voltage=3300/230=14.35 amps

    B) input power is Vrms*Irms*cosφ , where cosφ is the power factor=0.8
    thus input power Pin=230*14.35*0.8=2640.4 watts
    the efficiency is 85% thus the motor outputs 85% of its input power
    so output power Pout=Pin*85%=2640.4*85/100=2244.34 watts

    C) i am not sure what do you want

    D) apparent power S=Vrms*Irms=230*14.35=3300 VA
    reactive power Q=Vrms*Irms*sinφ

    φ=arccos(0.8)=36.86 degrees

    therefore Q=230*14.35*sin(36.86)=1979.84 VAR
     
  3. mary_owen

    Thread Starter New Member

    Apr 30, 2008
    5
    0
    thats great mike. very much apreciated. just ne lastquestion. where abouts did the 36.86 degress come from?:)
     
  4. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    power factor=cos(φ)=0.8

    thus φ=arccos(0.8)=36.86
     
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