Single Phase Induction Motor

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SINGLE PHASE INDUCTION MOTOR OBJECTIVES To investigate speed variation with torque of a single phase induction motor for capacitor start/run, capacitor run modes. To familiarize with the various ways of making a single phase induction motor self-starting. APPARATUS A resistor/capacitor board Centrifugal switch 12-slot wound stator Squirrel cage rotor 0-135V single phase Ac supply 0-200V AC voltmeter 0-5A AC ammeter Hand tachogenerator:0-3000rpm Band break or other dynamometer 0-1Nm THEORY When a single phase stator winding is connected to a source of single phase alternating voltage, the magnetic field produced is not of rotating nature. A single phase field is stationary in space but pulsating with time. The field changes in strength from positive maximum to negative maximum at the supply frequency but has no circular rotation. Such field cannot produce rotating torque in a stationary rotor, it can produce only pulsating torque hence the motor cannot start rotating in either direction. However, when the motor starts rotating, it picks up speed and continues rotating. Thus the rotor has no starting torque but it has running torque, as thus, various starting methods have been deviced, which which results in various types of motors: 1) Split phase induction motor 2) Capacitor induction motor 3) Shaded pole induction motor 4) Reluctance start induction motor Capacitor induction motors include 1) Capacitor Start 2) Permanent Capacitor 3) Capacitor Start-Capacitor run 1. CAPACITOR MOTOR The rotor has a squirrel cage construction. The stator has two windings, a main winding and a starting winding. In a capacitor motor, a capacitor is connected in series with the starting winding. In this way the current in starting winding becomes leading the voltage vector and large angle is developed between the currents in two windings A capacitor motor develops 3 to 4

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