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ENEE202

Electrical Machine I

Syllabus

  1. Magnetism and Magnetic Circuits (4 hours)
    1. Review of magnetic field and electromagnet
    2. Magnetic hysteresis: B-H curve and B-H loop with DC excitation
    3. Magnetic hysteresis with AC excitation
    4. Magnetic circuit: Series and parallel circuit with air gaps
    5. Faraday's laws of electromagnetic induction: Statically induced EMF and dynamically induced EMF
    6. Force on current carrying conductor
  2. Transformer (14 hours)
    1. Transformer parts and their functions
    2. Transformer types: Core and shell types
    3. Working principle and EMF equation
    4. Ideal and practical transformer
    5. Mutual inductance and coupled circuit model
    6. No load and load operation, equivalent circuits and phasor diagrams
    7. Transformation of impedances, voltage regulation
    8. Capacity of transformers
    9. Exciting current harmonics
    10. Transformer inrush current
    11. Losses and efficiency of 1-phase transformer, all day efficiency
    12. Tests: Polarity test, open circuit test, short circuit test, Sumpner's test
    13. Instrument transformers: Potential transformer (PT) and current transformer (CT) and their applications
    14. Auto transformer: Construction, working principle and Cu saving
    15. Three phase transformers: Introduction, types of connections, Scott-T connection
    16. Introduction of three winding transformer
    17. Parallel operation of transformer: 1-phase and 3-phase
  3. DC Generator (8 hours)
    1. Introduction of DC machine and its construction
    2. Armature windings (lap and wave winding)
    3. Working principle, commutator action, EMF equation
    4. Method of excitation: Separately and self-excited, types of DC generator
    5. Characteristics of series, shunt and compound generator, and applications
    6. Voltage build up process
    7. Armature reaction
    8. Commutation: Interpoles and compensating windings
    9. Losses, efficiency and voltage regulation
  4. DC Motors (7 hours)
    1. Working principle, back EMF and torque equation
    2. Types of DC motor, characteristics of DC motors and their applications
    3. Losses and efficiency
    4. Starting of DC motors: 3 point and 4 point starters for shunt motor
    5. Speed control of DC motor: Series, shunt, and reversing the direction of rotation
    6. Testing of DC machine: Retardation test and Swinburne's test for shunt motor
  5. Three-Phase Induction Machines (12 hours)
    1. Three phase induction motor: introduction, constructional details, rotor types (squirrel cage and phase wound)
    2. Operating principle: Rotating magnetic field, synchronous speed, slip
    3. Analysis of standstill condition: Equivalent circuit, starting torque equation
    4. Analysis of running condition: Equivalent circuit, running torque equation
    5. Torque-slip characteristics and effect of rotor resistance
    6. Power stages in three phase induction motor, losses and efficiency
    7. Testing of three phase induction motor: No-load test and Block rotor test
    8. Methods of starting: Direct on-line method, primary resistor method, auto-transformer starter, star-delta starter, rotor rheostat starter
    9. Speed control methods: Primary voltage control, frequency control, cascade connection and rotor rheostat method
    10. Three phase induction generator: operating principle, T-S characteristic for generating mode, requirements of excitation capacitor, voltage build-up process
    11. Induction generator operation: Isolated and grid connected

Practicals

  1. Magnetic circuits: Draw B-H curve for two different samples of iron core and compare their relative permeabilities
  2. Two winding transformers: Perform turn ratio test, open circuit and short circuit test, determine regulation and efficiency at full load and examine exciting current waveform and harmonics
  3. DC generator: Draw open circuit characteristic of a DC shunt generator and calculate maximum voltage built up, critical resistance, critical speed and load characteristic of shunt generator
  4. DC motor: Perform speed control of DC shunt motor by armature control method and field control method and draw Torque-Speed characteristic curve
  5. Three phase induction motor: Perform the no-load test and blocked rotor test, draw torque-slip characteristics and observe the effect of rotor resistance on torque-speed characteristics