EX-801 Electrical Drives - May 2022 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. 7 Marks
   aWhat is the requirement of Electric Drives?
   How to answer

   • Definition of electric drive and its major parts
   • Need for controllable electrical energy to mechanical energy conversion
   • Requirements: speed-torque control, efficiency, reliability, braking
2. 7 Marks
   bDiscuss about constant power and constant torque drives.
   How to answer

   • Define constant torque vs constant power load characteristics
   • Speed-torque and power relations $P = T\omega$
   • Examples of each type of drive
   • Control implications
3. 7 Marks
   aWhat do you understand by rating of drives and how should be the selection of drives be done?
   How to answer

   • Meaning of drive rating: continuous, short-time, intermittent
   • Thermal and load considerations in rating
   • Factors for selection: load torque, speed range, duty cycle
   • Environmental and economic selection criteria
4. 7 Marks
   bGive a brief review of AC and DC motors.
   How to answer

   • Construction and principle of DC motors
   • Types of AC motors: induction and synchronous
   • Comparison of performance and control
   • Suitability for drive applications
5. 7 Marks
   aDiscuss about the mechanical systems stability of electric drives.
   How to answer

   • Mechanical system dynamics: torque balance equation
   • Condition for steady-state stability $dT/dN$ criterion
   • Transient stability concept
   • Role of inertia and load characteristics
6. 7 Marks
   bDiscuss about the referred moment of inertia and torque of motor load combination.
   How to answer

   • Concept of referring load inertia and torque to motor shaft
   • Gear ratio and efficiency effects
   • Formulas for equivalent $J$ and $T_L$
   • Significance for motor selection
7. 7 Marks
   aDiscuss about phase, controlled and chopper controlled drives.
   How to answer

   • Principle of phase-controlled converter fed drives
   • Principle of chopper-controlled DC drives
   • Comparison of performance and harmonics
   • Applications of each scheme
8. 7 Marks
   bDiscuss about Energy Recovery System.
   How to answer

   • Need for energy recovery / regeneration
   • Scheme and working of energy recovery system
   • Power flow during braking
   • Advantages and limitations
9. 7 Marks
   aDiscuss about conventional method of starting braking and speed control.
   How to answer

   • Conventional starting methods for AC and DC motors
   • Conventional braking: plugging, rheostatic, regenerative
   • Conventional speed control methods
   • Limitations of conventional methods
10. 7 Marks
    bDiscuss about current sources fed 1M drives.
    How to answer

    • Principle of current source inverter fed induction motor
    • Control characteristics and torque-speed control
    • Advantages: regeneration, short-circuit protection
    • Applications and limitations
11. 7 Marks
    aExplain about VSI and CSI fed synchronous motor drives.
    How to answer

    • VSI fed synchronous motor: circuit and control
    • CSI fed synchronous motor: circuit and control
    • Comparison of VSI vs CSI operation
    • Performance characteristics
12. 7 Marks
    bExplain about Self-Controlled-Brush less and commutator less DC and AC motor drives.
    How to answer

    • Concept of self-controlled brushless operation
    • Commutatorless DC and AC motor drive schemes
    • Rotor position sensing and inverter control
    • Applications in high-speed drives
13. 7 Marks
    aExplain the fundamentals of switched reluctance motors.
    How to answer

    • Construction and working principle of SRM
    • Torque production by variable reluctance
    • Converter and control requirements
    • Characteristics and applications
14. 7 Marks
    bDiscuss about the digital control of drives.
    How to answer

    • Need for digital control in drives
    • Block diagram of microprocessor-based control
    • Advantages: precision, programmability
    • Examples of digital control functions
15. 14 Marks
    Write short notes on any two of the followings.

    1. i)Slip controlled 1M drives
    2. ii)Crammers and Scherbius drives
    3. iii)CNC
    How to answer

    • Select any two topics with principle and diagram
    • Explain slip-controlled IM drive / Kramer / Scherbius / CNC
    • Control scheme and power flow
    • Applications and merits-limitations