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 90^o 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

       F_P = F_m Sin θ

       F_Q = F_m Sin ( θ – 90^o )

Point 1

• F_P = 0 and
• F_Q = –  F_m
• Resultant flux F = √ P² + Q² – 2PQCos θ

                                 = √ 0 + ( –  F_m )² – 0

                                 =  F_m 

Point 2

• F_P = F_m / √ 2 and
• F_Q = –  F_m / √ 2
• Resultant flux F = √ P² + Q² – 2PQCos θ

                                 = √ ( F_m² / 2 ) + ( F_m² / 2 ) + 0

                                 =  F_m

Point 3

• F_P =  F_m and
• F_Q = 0
• Resultant flux F = √ P² + Q² – 2PQCos θ

                                 = √ ( F_m )² + 0
                                 =  F_m 

Point 4

• F_P = – F_m / √ 2 and
• F_Q = F_m / √ 2
• Resultant flux F = √ P² + Q² – 2PQCos θ

                                 = √ ( F_m² / 2 ) + ( F_m² / 2 ) + 0

                                 =  F_m

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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