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electric motors

Semester :  IV

Course Code : 18EE44

CIE Marks : 40                       SEE Marks : 60





DC Motors: Classification, Back emf, Torque equation, and significance of back emf, Characteristics of shunt, series & compound motors. Speed control of shunt, series and compound motors. Application of motors. DC motor starters – 3 points and 4 points.
Losses and Efficiency- Losses in DC motors, power flow diagram, efficiency, condition for maximum efficiency. 


Testing of DC Motors: Direct & indirect methods of testing of DC motors-Brake test, Swinburne’s test, Retardation test, Hopkinson’s test, Field’s test, merits and demerits of tests.
Three Phase Induction Motors: Review of concept and generation of rotating magnetic field, Principle of operation, construction, classification and types; squirrel-cage, slip-ring (No question shall be set from the review portion). Slip, Torque equation, torque-slip characteristic covering motoring, generating and braking regions of operation, Maximum torque, the significance of slip.


Module-3 Performance of Three-Phase Induction Motor: Phasor diagram of induction motor on no-load and on load, equivalent circuit, losses, efficiency, No-load and blocked rotor tests. Performance of the motor from the circle diagram and equivalent circuit. Cogging and crawling. High torque rotors-double cage and deep rotor bars. Equivalent circuit and performance evaluation of double cage induction motor. Induction motor working as an induction generator. 


Starting and Speed Control of Three-Phase Induction Motors: Need for a starter. Direct on line, Star-Delta and autotransformer starting. Rotor resistance starting. Speed control by voltage, frequency, and rotor resistance methods
Single-Phase Induction Motor: Double revolving field theory and the principle of operation. Construction and operation of split-phase, capacitor start, capacitor run, and shaded pole motors. Comparison of single-phase motors and applications.


Synchronous Motor: Principle of operation, phasor diagrams, torque and torque angle, Blondel diagram, the effect of change in load, the effect of change in excitation, V and inverted V curves. Synchronous condenser, hunting and damping. Methods of starting synchronous motors.
Other Motors: Construction and operation of Universal motor, AC servomotor, Linear induction motor and stepper motors