QUESTION BANK SPECIAL ELECTRICAL MACHINES

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1 SEVENTH SEMESTER EEE QUESTION BANK SPECIAL ELECTRICAL MACHINES TWO MARK QUESTIONS 1. What is a synchronous reluctance 2. What are the types of rotor in synchronous reluctance 3. Mention some applications of synchronous reluctance 4. What are the advantages of increasing L d / L q ratio in synchronous reluctance 5. Compare Synchronous reluctance motor with induction 6. Write down the torque equation of synchronous reluctance 7. Draw the torque-angle characteristics of synchronous reluctance 8. Draw the speed-torque characteristics of synchronous reluctance 9. Draw the steady state phasor diagram of synchronous reluctance 10. What is a vernier 11. What is the application of vernier 12. Mention some advantages and disadvantages of synchronous reluctance 13. List out any two properties of synchronous reluctance 14. What do you mean by reluctance torque in synchronous reluctance 15. Highlight the design considerations in synchronous reluctance 16. Comment on stepper 17. Define the term step angle. 18. Define slewing. 19. Mention the formula for motor speed of stepper 20. Define Resolution. 21. State some applications of stepper 22. Enumerate the advantages and disadvantages of stepper 23. What are different types of stepper 24. What are the different modes of excitation in a stepper 25. What is meant by full-step operation? 26. What is meant by half-step configuration? 27. Sketch the diagram of a VR stepper

2 28. What is meant by micro stepping in stepper 29. What are the main applications of micro stepping VR stepper 30. What is a multi-stack VR stepper 31. What are advantages and disadvantages of VR stepper 32. What are the advantages and disadvantages of permanent magnet stepper 33. What is a hybrid stepper 34. What are the advantages and disadvantages of hybrid stepper 35. Draw the typical static characteristics of a stepper 36. Distinguish between VR, PM, and hybrid stepper 37. Define holding and detente torque. 38. Define torque constant. 39. Draw the typical dynamic characteristics of a stepper 40. Differentiate pull-in torque from pull-out torque. 41. Differentiate pull-in rate from pull-out rate. 42. What is a response range? 43. What do you mean by slewing range? 44. What do you mean by synchronism in stepper 45. What do you mean by mid-frequency resonance in stepper 46. Draw the block diagram of the drive system of a stepper 47. What is a logic sequencer? 48. What is meant by power drive circuit in stepper 49. What is the use of current suppression circuit? 50. What are the different types of current suppression circuit? 51. Draw any two drive-circuits for stepper 52. How is step of permanent magnet stepper motor controlled? 53. Mention the types of power controllers used for switched reluctance 54. Why rotor position sensor is essential for the operation of switched reluctance 55. List out the drawbacks of switched reluctance 56. Mention the merits of switched reluctance 57. Draw the general speed-torque characteristics of switched reluctance 58. What are the applications of SRM? 59. What do you mean by switched reluctance 60. Draw the λ-i curve for SRM. 61. What are the two types of current control techniques? 62. What do you mean by energy ratio? 63. Draw the simple block diagram of SRM.

3 64. Draw the circuit of PWM type current control. 65. What do you understand by phase windings? 66. Highlight the essential difference between SRM and stepper 67. Write down the torque equation for a switched reluctance motor drive. 68. Sketch the C-dump converter circuit for switched reluctance 69. What do you mean by hysteresis current control? 70. Define chopping and single pulse mode of operation of SRM. 71. List down the advantages and disadvantages of brushless dc motor drives. 72. List the various permanent magnet materials. 73. Draw the magnetic circuit of 2 pole permanent magnet brushless dc 74. Bring down the differences between mechanical and electronic commutators? 75. Write the torque and emf equation of square wave brushless dc motor drive. 76. Mention some applications of PMBLDC 77. Compare conventional dc motor with PMBLDC 78. Why the PMBLDC is motor called as the electronically commutated 79. What are the classifications of BLPM dc 80. What are two types of BLPM SQW DC 81. Name the position sensors that are used for PMBLDC 82. What are materials that are used for making Hall IC pallet? 83. What are the relative merits of the brushless dc motor drives? 84. Draw the circuit diagram of electronic commutator. 85. Compare PMBLDC motor and switched reluctance 86. Differentiate Hall sensor from optical sensor. 87. What are the types of permanent magnet DC 88. What is permanent magnet DC commutator 89. What are features of permanent magnet synchronous 90. Highlight the advantages of load commutation. 91. Write down the expressions for power input and torque of permanent magnet synchronous 92. List the applications of permanent magnet synchronous 93. What are features of closed-loop speed control of load commutated inverter fed synchronous motor drive? 94. What are merits and demerits of permanent magnet synchronous

4 95. Write the emf equation of permanent magnet synchronous 96. What are the assumptions made in derivation of emf equation for permanent magnet synchronous 97. Why PMSM operating in self controlled mode is known commutatorless dc 98. What do you mean by pulsed mode of operation of permanent magnet synchronous 99. Clearly explain the differences between synchronous reluctance motor and permanent magnet synchronous 100. Write down the expressions for self and synchronous reactance of permanent magnet synchronous 101. What do you mean by self control of permanent magnet synchronous 102. What is meant by field oriented control of permanent magnet synchronous 103. How are PMBLDC and PMSM different? 104. Draw the phasor diagram of a permanent magnet synchronous 105. State any two classifications of permanent magnet synchronous motor and its types Distinguish between self control and vector control of permanent magnet synchronous 107. What is meant by slotless 16 MARKS QUESTION 1. Explain the principle of operation and constructional features of synchronous reluctance 2. Explain circle diagram and torque-speed characteristics of synchronous reluctance 3. Explain the working of vernier motor with neat diagram. 4. Compare the constructional features of axial and radial gap synchronous reluctance 5. Describe the construction and principle of operation of synchronous reluctance motor with neat diagrams. 6. Draw and explain the steady sate phasor diagram of synchronous reluctance What changes will be made if a permanent magnet is placed on the rotor of same? 7. Explain the different modes of excitation used in variable reluctance stepper

5 8. Describe the construction and working principle of hybrid stepping 9. Write detail about mini step drive. 10. Describe the working of a 3 stack stepper motor having 12 poles in stator and in rotor. 11. Analyze the mechanism of torque production in VR stepper motors. 12. State and explain static and dynamic characteristics of a stepper 13. Discuss in detail the different types of power drive circuits for stepper 14. Draw the bi-directional two phase logic sequencer for four phase stepper motor and draw the truth table and explain its operation. 15. Explain dual voltage drives for a two phase on drive of a four phase motor with necessary circuit diagrams. 16. Explain the different types of current suppression circuits. 17. A stepper motor driven by a bipolar drive circuit has the following parameters: winding inductance = 30 mh, rated current = 3A, DC supply = 45V, total resistance in each phase = 15Ω. When the transistors are turned off, determine (i) the time taken by the phase current to decay to zero and (ii) the proportion of the stored inductive energy returned to the supply. 18. A stepper motor has a step angle of 3. Determine (a) resolution (b) number of steps required for the shaft to make 25 revolutions and (c) shaft speed, if the stepping frequency is 3600 pps. 19. A stepper motor has a step angle of 1.8. What number should be loaded into the encoder of its drive system if it is desired to turn on the shaft ten complete revolutions? 20. What is the motor torque T m required to accelerate an initial load of 3*10-4 kg m 2 from f 1 = 1000 Hz to f 2 = 2000 Hz during 100 ms. The frictional torque T f is 0.05 N-m and the step angle is Explain the construction and working principle of SRM. 22. Explain why rotor position sensor is essential for the operation of SRM. 23. Describe the various power controller circuits applicable to switched reluctance motor and also explain any one scheme operation with neat diagrams. 24. Draw the schematic diagram and explain the operation of a C dump converter used for the control of SRM. 25. Discuss the various converter topologies for a 3 phase SR motor with merits and demerits of each. Explain any two of them.

6 26. Sketch the general speed-torque curve of SR motor and discuss the type of control strategy used for different regions of the curve. Sketch the typical phase current waveforms of low speed operation. 27. Describe the hysterisis type and PWM type current regulator for one phase of a SRM. 28. Explain the various duty cycle schemes for a phase of three SR motor and its operation with phase current waveforms. 29. Discuss in detail about microprocessor based control of SRM. 30. Discuss in detail about computer control of SRM. 31. What is the step angle of a 5 phases SRM and commutation frequency in each phase for the speed of 6000 rpm. SRM is having 10 stator poles and 4 rotor poles. 32. A SRM with 6 stator poles and 4 rotor poles has a stator pole arc of 30 degree and rotor pole arc of 32 degree. The aligned inductance is 10.7 mh and unaligned inductance is 1.5 mh. Saturation can be neglected. Calculate the instantaneous torque when the rotor is 30 degree before the aligned position and phase current is 7A. What is the maximum energy conversion one stoke, if the current is limited to 7A? Determine the average torque corresponding to this energy conversion. 33. Sketch the structure of controller for PMBLDC motor and explain the functions of various blocks. 34. Explain the closed loop control scheme of a permanent magnet brushless DC motor drive with suitable schematic diagram. 35. Derive the expressions for emf and torque of a PM brushless dc 36. Discuss in detail about the operation of an electronic commutator. 37. Discuss the use of Hall sensors for position sensing in PMBLDC motors. 38. Compare PMBLDC motor with switched reluctance motor and bring out its features. 39. A PMBLDC motor has torque constant 0.12 Nm/A referred to DC supply. Find no load speed when connected to 48V DC supply. Find stall current and stall torque if armature resistance is 0.15Ω / phase and drop in controller transistors is 2V. 40. A PMBLDC motor has a no-load speed of 6000 rpm when connected to a 120 V supply. The armature resistance is 2.5Ω and rotational and iron losses may be neglected. Determine the speed when the supply voltage is 60V and the torque is 0.5 Nm. 41. Explain the construction and operation of PMSM. 42. Compare electromagnetic excitation with permanent magnet of a PMSM.

7 43. Clearly in detail explain the differences between synchronous reluctance motor and PMSM. 44. Explain the principle of operation of a sine wave PMSM in detail by drawing the phasor diagram and also derive the torque equation. 45. Derive the emf equation of PMSM. 46. Derive the expressions for power input and torque of a PMSM. Explain how its torque-speed characteristics is obtained. 47. Explain in detail the vector control of PMSM. 48. Explain the microprocessor based control of PMSM. 49. A three phase, four pole, brushless PM rotor has 36 stator slots. Each phase winding is made up of three coils per pole with 20 turns per coil. The coil span is seven slots. If the fundamental component of magnetic flux is 1.8 Mwb, Calculate the open circuit phase emf at 3000 rpm. 50. A three phase, 16 poles synchronous motor has a star connected winding with 144 slots and 10 conductors per slot. The flux per pole is 0.03 wb, sinusoidally distributed and the speed is 375 rpm. Find the frequency and the phase and line emf. Assume full pitched coil.

COLLEGE OF ENGINEERING DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING QUESTION BANK SUBJECT CODE & NAME : EE 1001 SPECIAL ELECTRICAL MACHINES

KINGS COLLEGE OF ENGINEERING DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING QUESTION BANK SUBJECT CODE & NAME : EE 1001 SPECIAL ELECTRICAL MACHINES YEAR / SEM : IV / VII UNIT I SYNCHRONOUS RELUCTANCE