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Figure 4-2.Two-phase motor stator
THREE-PHASE ROTATING FIELDS

Neets Module 05-Introduction to Generators and Motors
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4-5 Figure 4-3.—Two-phase rotating field. The waveforms in figure 4-3 are of the two input phases, displaced 90º because of the way they were generated in a two-phase alternator. The waveforms are numbered to match their associated phase. Although not shown in this figure, the windings for the poles 1-1A and 2-2A would be as shown in the previous figure. At position 1, the current flow and magnetic field in winding 1-1A is at maximum (because the phase voltage is maximum). The current flow and magnetic field in winding 2-2A is zero (because the phase voltage is zero). The resultant magnetic field is therefore in the direction of the 1-1A axis. At the 45-degree point (position 2), the resultant magnetic field lies midway between windings 1-1A and 2-2A. The coil currents and magnetic fields are equal in strength. At 90º (position 3), the magnetic field in winding 1-1A is zero. The magnetic field in winding 2-2A is at maximum. Now the resultant magnetic field lies along the axis of the 2-2A winding as shown. The resultant magnetic field has rotated clockwise through 90º to get from position 1 to position 3. When the two-phase voltages have completed one full cycle (position 9), the resultant magnetic field has rotated through 360º . Thus, by placing two windings at right angles to each other and exciting these windings with voltages 90º out of phase, a rotating magnetic field results. Two-phase motors are rarely used except in special-purpose equipment. They are discussed here to aid in understanding rotating fields. You will, however, encounter many single-phase and three-phase motors. Q5. What is the angular displacement between field poles in a two-phase motor stator?






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