Effect of Skewing the Rotor Slots in Squirrel cage Motor

Effect of Skewing the Rotor Slots in Squirrel cage Motor:



Skewing

Skewing:


  • Many problems in induction motor like noise, vibrations, cogging etc can be reduced or eliminated by skewing either the stator or rotor. Generally the rotor bars are skewed by an angle just sufficient to cause induction of two equal and opposite harmonic emf in each bar.The bars must be skewed such that they should lie under alternate hamonic poles of same polarity so they are skewed through 2 pole pitches.

     Angle of skew  =  2 × 360°/np

     Where, 
     n = Number of harmonic (I. e. 3, 5, 7 etc.)
     P = Number of poles

    QsK = 720°/np  (mechanical) 

    and
    
    Qsk = 720°/np × p/2 = 360°/n  (Electrical) 

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