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Thread: electrical

  1. #1
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    May 2008
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    electrical

    in a single phase induction motor if the number of poles is 4 frequency is 50hz then what is the speed (RPM) of the motor?


  2. #2
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    May 2008
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    1

    Re: electrical

    speed= 120f/p
    =120X50/4=1500 rpm


  3. #3
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    Re: electrical

    n=120f/p simple.......


  4. #4
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    Nov 2008
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    Re: electrical

    practically i feed 50 hz frequency, for 4 pole induction machine, but i not get 1500 instead i get 1440 RPM, can you please tell, why the droping of rpm


  5. #5
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    Lightbulb Re: electrical

    Becasue of slip. if it runs on 1500 rpm it will become syn. motor . It is the property of induction motor.


  6. #6
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    Nov 2008
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    Re: electrical

    well,n=120*f/p gives the speed of the rotating mmf or the synchronous speed.An induction moor will develop zero torque at this speed and hence will always run at a lower speed(s*n)where s is called the slip.(s is usually in the range .02 to .08 and depends on the load)


  7. #7
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    Wink Re: electrical

    f=PNs/120
    NS=120f/P
    =120*50/4
    =1500 rpm

    Nr= Rotor Speed will depend on slip.

    Nr= Ns(1-s)


  8. #8

    Re: electrical

    how can i select the cable for amps rating


  9. #9
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    Jun 2009
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    7

    Re: electrical

    that u can calculate simply by the formulas:

    Ns=120*f/p where Ns=speed of the stator ,f =frequency of supply,
    and p=no of poles

    slip(S)=(Ns-Nr)/Ns

    nd rotor frequency fr=S*supply frequency

    with the help o fthese formulas you can get wat u want....


  10. #10
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    Jun 2009
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    7

    Re: electrical

    cable size primarily depends on its voltage rating or kW
    rating of load. From the kW rating, we can calculate the
    current that should be carried by cable and the number of
    runs required. we also have to calculate voltage drop
    during starting and running in case of a motor load.


  11. #11
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    Jul 2009
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    3

    Re: electrical

    Quote Originally Posted by zabeer View Post
    practically i feed 50 hz frequency, for 4 pole induction machine, but i not get 1500 instead i get 1440 RPM, can you please tell, why the droping of rpm
    all things in practice is not ideal,though F=50 Hz. I.M doesnot rotate at 1500RPM by120F/P formula b'use if speed is 1500RPM r,rotor speed =1500RPM,Synchronous flux rotate at 1500RPM ,and EMF induced in the Rotor is zero due to SAME speed hence no induced emf.,no force and Motor will not run.hence slip=Syn.speed-Actual speed =Somthing value Must for rotating motor.


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