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60-HP 230 volt shunt motor problem

  1. Aug 23, 2008 #1
    I need some help!!!

    Can you help with these problems?

    1. A 60-HP 230 volt shunt motor has a shunt field resistance of 38.3 ohms and an armature resistance of 0.04 ohm. If the resistance in the starter is 0.66 ohm, calculate the current input to the motor at the instant it is started. (Assume a 3 volt brush drop)

    2. A 220 volt shunt motor has an armature resistance of 0.32 ohm and a field resistance of 110 ohms. at no load the armature current is 6 amp and the speed 1800 rpm. Assume that the flux does not vary with load and calculate; a.) the speed of the motor when the rated line current is 62 amp (assume a 2 volt brush drop) b.) the speed regulation of the motor.

    3. a 240 volt series motor has an armature resistance of 0.42 ohm and a series-field resistance of 0.18 ohm. If the speed is 500 rpm when the current is 36 amp, what will be the motor speed when the load reduces the line current to 21 amp? (assume a 3 volt brush drop and that the flux is proportional to the current.)

    4. A 25hp 230 volt 1200 rpm shunt motor has an armature resistance, including brushes, of 0.2 ohm, and the armature current is 92 amp when the machine is operating at rated load and speed. To reduce the speed, a 6.8 ohm resistance is shunted across the armature and a resistance of 1.6 ohms is connected in series with the parallel combination of armature and shunted resistor. If, under the latter conditions, the armature current is 20 amp, calculate the speed of the motor. assume that there is no flux change.

    5. A 550 volt long shunt compound motor has an armature resistance of 0.815 ohm and a series field resistance of 0.15 ohm. The full load speed is 1900 rpm when the armature current is 22 amp. a.) At what speed will the motor operate at no load if the armature current drops to 3 amp with a corresponding drop in flux to 88 per cent of the full-load value? (Assume a brush drop of 5 volts at full load and 2 volts at no load.) b.) Calculate the per cent speed regulation of the motor.


    I HOPE YOU COULD HELP ME?
     
  2. jcsd
  3. Aug 24, 2008 #2

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    Hi detski! :smile:

    Show us what you've tried, and where you're stuck, and then we'll know how to help you. :wink:

    Start with No. 1. :smile:
     
  4. Aug 25, 2008 #3
    Re: I need some help!!!

    I tried solving it and the answer i got was 330.29 amps.... is it correct?
     
  5. Aug 25, 2008 #4
    Re: I need some help!!!

    here was my solution here:
    k=constant
    Q=flux
    @ no load

    1800=[(220-2)-6(.32)]/kQ

    @ rated load

    speed=[(220-2)-62(.32)]/kQ

    [1800/speed]={[(220-2)-6(.32)]/kQ}/{[(220-2)-62(.32)]/kQ}

    speed= 1650 rpm


    pls. check
     
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