AC MotorsAC MOTOR TYPESSummaryThe important information in this chapter is summarized below.AC Motor Types SummaryIn a split-phase motor, a starting winding is utilized. This winding has a higherresistance and lower reactance than the main winding. When the same voltage(VT) is applied to the starting and main windings, the current in the mainwinding lags behind the current of the starting winding. The angle between thetwo windings is enough phase difference to provide a rotating magnetic field toproduce a starting torque.A synchronous motor is not a self-starting motor because torque is onlydeveloped when running at synchronous speed.A synchronous motor may be started by a DC motor on a common shaft or bya squirrel-cage winding imbedded in the face of the rotor poles.Keeping the same load, when the field excitation is increased on a synchronousmotor, the motor operates at a leading power factor. If we reduce field excitation,the motor will operate at a lagging power factor.The induction motor is the most commonly used AC motor in industrialapplications because of its simplicity, rugged construction, and relatively lowmanufacturing costs.Single-phase motors are used for very small commercial applications such ashousehold appliances and buffers.Synchronous motors are used to accommodate large loads and to improve thepower factor of transformers in large industrial complexes.Rev. 0 Page 15 ES-12
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