14 March 2018

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

Rotating magnetic Field due to two phase winding
  • Let us consider that the two winding 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 B. 
  • 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
  • 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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