Rotating Magnetic Filed by Two Phase Winding

Rotating Magnetic Field

• When three phase supply is given to three phase winding, it produces rotating magnetic field which rotates and synchronous speed. 
• Similarly, when two phase supply is given to the two-phase winding, the rotating magnetic field produced by the winding is given here.

Rotating Magnetic Field: 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 B. 
• The direction of the flux is assumed as positive whereas its opposite sides indicate 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 )

• The voltage of the winding P is taken as reference or zero degree and winding Q is taken at 90 degree with respect to winding P.

Rotating Magnetic Field: Point 1

The voltage of winding P is zero whereas winding Q is negative as shown in the figure. The voltage of the winding Q negative sign is taken because we assume that the direction of voltage for winding P and winding Q is positive in the first quadrant.

F_P = 0 and

F_Q = –  F_m

Resultant flux F = √ P² + Q² – 2PQCos θ

                           = √ 0 + ( –  F_m )² – 0

                           =  F_m 

Rotating Magnetic Field: Point 2

The voltage of the winding P and winding Q is 45 degrees but both are in the opposite direction.

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

Rotating Magnetic Field: Point 3

The voltage of the winding P is at 90 degree but voltage of the winding Q is at and winding Q is 180 degree.

F_P =  F_m and

F_Q = 0

Resultant flux F = √ P² + Q² – 2PQCos θ

                           = √ ( F_m )² + 0

                           =  F_m 

Rotating Magnetic Field: Point 4

The voltage of the winding P is at 135 degree but voltage of the winding Q is at and winding Q is 45 degree but both are in the opposite direction.

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

Position of winding	Voltage of winding P	Voltage of winding Q	Phase Difference between two winding
Point 1	0 degree	– 90 degree	90 degree
Point 2	45 degree	–  45 degree	90 degree
Point 3	90 degree	0 degree	90 degree
Point 4	135 degree	45 degree	90 degree
Point 5	180 degree	90 degree	90 degree
Point 6	–  225 degree	135 degree	90 degree

 

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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