Induction Motor Slip decrease with frequency decrease for same load.

  1. Hi,

    Does anyone know or could help me understand the reasoning for the amount of slip within an induction motor decreasing with frequency under the same load conditions? I.e. For no external load, the slip is higher at 50Hz than at 20Hz etc? Thanks
  2. jcsd
  3. jim hardy

    jim hardy 5,450
    Science Advisor
    Gold Member
    2014 Award

    What about internal load, ie bearing friction and windage loss?

    Is windage proportional to speed2 or to speed3 ?
  4. “No-load” it does not mean “no load at all”. There are no-load losses –iron losses, ventilation and friction-bearing losses and copper losses. The no-load current-mainly reactive-is about 30% of rated and copper [winding] losses could be elevated. As jim hardy already said, ventilation and friction are proportional with square of rpm, so less frequency less rpm [rpm=60*freq/p where p= no.of pole pairs] less slip. The iron losses decrease with the frequency and so the no-load current and in turn no-load copper losses. The mechanical power requested in order to maintain the rotor in rotation will decrease even if the torque remains constant P=T*(2*PI()*Freq:
    [itex] P=T\omega=2\pi_fT [/itex]
    Less power less slip.
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