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3 phase induction motor

  1. Mar 15, 2013 #1
    3 PHASE INDUCTION MOTOR

    A 15 hp/230V, three phase induction motor has a full load current of 42A per terminal.
    15HP= 11kW

    find:
    a) Full load kVA input
    b) If the full load power factor is lagging 0.85, what is the kW input.

    My question: How do I know whether its connected Wye or Delta?


    a) kVA= 1.732 X ELine X ILine

    ELine= 230V ILine=IPhase (Wye) and ILine=IPhase X 1.732 (Delta)

    b) P= 1.732 X Eline X ILineX PF
     
    Last edited: Mar 15, 2013
  2. jcsd
  3. Mar 15, 2013 #2
    A)

    Wye: kVA= 1.732 X 230V X 40A

    kVA= 16kVA

    Delta: kVA= 1.732 X 230V X 69A

    kVA= 27kVA

    B)

    Wye: P= 1.732 X 230V X 40A X 0.85

    P= 13.5kW

    Delta: P= 1.732 X 230V X 69A X 0.85

    P= 23.4kW


    How do these look?
     
  4. Mar 15, 2013 #3

    gneill

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    Staff: Mentor

    The problem stated the motor current as 42A per terminal. So that would be the line current. The motor is said to be 230V, so I think you can take that as the line-to-line voltage.
     
  5. Mar 15, 2013 #4
    Ok, so "per terminal" refers to "Line-to-Line"?
    so Id go with these:

    kVA= 1.732 X 230V X 40A
    kVA= 16kVA

    P= 1.732 X 230V X 40A X 0.85
    P= 13.5kW

    Also, the 15HP (11kW) stated in the original question. Would that be the motors rated power, while the 13.5kW calculated would be its input power?
     
  6. Mar 15, 2013 #5

    gneill

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    Staff: Mentor

    Well, at the very least it refers to the line current since the motor's terminals are where the lines connect. I'm less certain about the interpretation of the wording for the "230V, three phase...". It could refer to the "three phase voltage", making the individual line voltages about 133V. Or it could be the line-to-line voltage. [I hate these ambiguities due to topic-specific "common-knowledge" jargon!]
    Yeah, looks good as far as I can tell.
    That would be my interpretation.
     
  7. Mar 15, 2013 #6
    Yeah my prof likes to throw us off with his wording heh.
    Thanks again for your help.
    I have 3 more questions to go. Ill post them in this thread If im stuck.
     
  8. Mar 15, 2013 #7

    gneill

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    Staff: Mentor

  9. Mar 15, 2013 #8
    Nice! Good find :smile:
     
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