Question Bank for Industrial Drives and Control.

  1. A single-phase bidirectional ac voltage controller delivers a load power of 50 kW with an efficiency and power factor of 0.9 and 0.85, respectively. The input voltage is 230V, 50Hz. Determine the maximum possible ratings of average and rms thyristor currents and repetitive voltage of thyristors.
  2. Explain steady state and transient stability of electrical drives. Support your answer with relevant mathematics and diagrams, as applicable.
  3. List Limitations and Applications of phase controlled line commutates, converters.
  4. Describe the working of a two-stage sequence control of voltage controllers for R load. What is the advantage of this controller over single-phase full- wave voltage controller ?
  5. Explain Principle of Operation of 3-phase Induction Motor.
  6. A 3-phase, 400V, 50Hz, 4-pole, star-connected reluctance motor, with negligible armature resistance, has Xd = 8 Ohms and Xq = 2 Ohms. For a load torque of 80 N-m, calculate the load angle, the line current and the input power factor. Neglect rotational losses.
  7. Describe 3-phase to 3-phase cycloconverter with relevant circuit arrangements using 18 SCR’s and 36 SCR’s.
  8. A single-phase full-bridge inverter is fed from a DC source such that fundamental component of output voltage is 230 V. Find the rms value of thyristor and diode currents for 2 Ohms resistive load.
  9. Discuss N-T characteristics of different industrial systems.
  10. Explain four quadrant operation of drive systems.
  11. A six-pulse cycloconverter, fed from a 3-phase, 400V, 50Hz source, is delivering a load current of 40A to a 1-phase resistive load. The source has an inductance of 1.2mH per phase. Calculate the rms value of load voltage for firing angle delays of 0 degrees and 30 degrees.
  12. Give the general circuit layout for single-phase de drives. Give their Applications and Limitations.
  13. A separately excited de motor is fed from two single-phase semi converters, one in the armature circuit, and other in the field circuit. Field current is constant at 2 A. Motor armature resistance is 0.8 Ohms and motor constant is 0.5 V-s/A-rad. AC voltage is 230V, 50 Hz. For a ripple-free armature current and speed of 1500 rpm, find the input supply factor.
  14. What are Chopper Drives ? Give their Applications.
  15. Discuss two methods of speed control normally employed for de motors. Sketch their characteristics.
  16. How three-phase semi converter is used for speed control of a DC series motor ? Explain.
  17. The speed of a 50 Kw, 500 V, 120 A, 1500 rpm separately excited de motor is controlled by a three-phase full converter fed from 400 V, 50 Hz supply. Motor armature resistance 0.1 Ohm. Find the range of firing angle required to obtain the speeds between 1000 rpm and -1000 rpm at rated torque.
  18. A single-phase semi converter feeds a separately-excited de motor. If armature current is ripple free, from the basics, mathematically derive the expression of input supply power factor.
  19. A 220 V, 60 A DC series motor, having combined resistance of armature and field of 0.15 Ohms, is controlled in regenerative braking mode. The DC source voltage is 220 V. Motor constant is 0.05 V-s/Arad. The average motor armature current is rated, and also, ripple free. For a duty cycle of 50%, find the speed during regenerative braking.
  20. Describe closed loop control of synchronous motors.
  21. What is Voltage and frequency control ? Explain it.
  22. Describe closed-loop control of DC motor. What are its schemes ? Give its Limitations.
  23. For fan-type loads, find the value of slip, when the rotor current in a 3- phase induction motor is maximum. State the assumptions made.
  24. What are different frictional systems ?
  25. What are the parameters for the selection of the motors for the electric drives ?
  26. List disadvantages of phase controlled line commutated converters.
  27. What are methods of cooling of drive motors ?
  28. List different power supply systems for motor drive.
  29. Give advantages and applications of 1-phase converter drives.
  30. Give advantages and disadvantages of 3-phase converter drives.
  31. Differentiate between AC Drives and DC Drives.
  32. List all methods of 3-phase Induction Motor control.
  33. How frequency control is done in the case of AC drives ?
  34. Starting from fundamental torque equation derive expression for time and energy loss in transient operations.
  35. Calculate the starting time of a drive with following parameters: J=10 kg-m², T=15+0.5 ωm and T1=5+0.60 ωm
  36. What do you understand by steady-state stability of a drive system ?
  37. Explain. What is the condition for steady-state stability ? Derive it.
  38. Explain the equivalent current, torque and power methods for determination of motor rating for fluctuating and intermittent loads.
  39. A constant speed drive has the following duty cycle:
    • i) load rising from 0 to 300 kw: 5 minutes
    • ii) Uniform load of 600 kw: 5 minutes.
    • iii) Regenerative power of 300 kw returned to the supply: 4 min
    • iv) Remains idle for: 2 minutes
      • Estimate power rating of the motor. Assume losses to be proportional to (power)2.
  40. Explain different speed control methods for de motors.
  41. Write short notes on
    • a) Classification of load torques.
    • b) Multiquadrant operation of drives
    • c) Closed loop speed control of multimotor drives
    • d) Thermal model of motor for heating and cooling
    • e) Regenerative braking in DC motor