14/03/2018

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 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 indicate negative values. The instantaneous value of flux can be given by

FP = Fm Sin θ

FQ = Fm Sin ( θ – 90o )

  • 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.



flux produced by the two phase winding


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.

FP = 0 and

FQ = –  Fm

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

                           = √ 0 + ( –  Fm )2 – 0

                           =  Fm 

Rotating Magnetic Field: Point 2

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

FP = Fm / √ 2 and

FQ = –  Fm / √ 2

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

                           = √ Fm2 / 2 + Fm2 / 2 + 0

                           =  Fm

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.

FPFm and

FQ = 0

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

                           = √ ( Fm )2 + 0

                           =  Fm 

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.

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

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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