14 March 2018

Rotating Magnetic Field produced by the Two Phase Supply in the Induction Motor

Rotating magnetic Field by the Two Phase Winding

  • Let us consider that the two windings P and Q are placed at 90o with respect to each other. 
  • We assume that when the two phase supply is given to the winding, flux produces in each winding is purely sinusoidal. 
  • The waveform of the flux is shown in the figure A. 
  • The direction of the flux is assumed as positive whereas its opposite sides indicates negative values. The instantaneous value of flux can be given by
       FP = Fm Sin θ
       FQ = Fm Sin ( θ – 90o )

flux produced by the two phase winding

Point 1
  • FP = 0 and
  • FQ = –  Fm
  • Resultant flux F = √ P2 + Q2 – 2PQCos θ
                                 = √ 0 + ( –  Fm )2 – 0
                                 =  Fm 
Point 2
  • FP = Fm / √ 2 and
  • FQ = –  Fm / √ 2
  • Resultant flux F = √ P2 + Q2 – 2PQCos θ
                                 = √ ( Fm2 / 2 ) + ( Fm2 / 2 ) + 0
                                 =  Fm
Point 3
  • FPFm and
  • FQ = 0
  • Resultant flux F = √ P2 + Q2 – 2PQCos θ
                                 = √ ( Fm )2 + 0
                                 =  Fm 
Point 4
  • FP = – Fm / √ 2 and
  • FQ = Fm / √ 2
  • Resultant flux F = √ P2 + Q2 – 2PQCos θ
                                 = √ ( Fm2 / 2 ) + ( Fm2 / 2 ) + 0
                                 =  Fm

direction of magnetic field due to two phase supply

Conclusion

  • We can conclude that the rotating magnetic field produced by two phase winding is constant in magnitude. 
  • It rotates at constant synchronous speed in the clockwise direction.
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