Question Bank Of Asynchronous Machines
Question Bank of Asynchronous Machines1.At zero slip in an induction motora) Motor runs as a generatorb) Motor does not runc) The motor runs an at synchronous speedd) Slip produced is zeroAns: (b)2. In an induction motor, rotor slots are usually not quite parallel to the shaft but are given aslight skewa) To reduce the magnetic humb) To reduce the locking tendency of the rotorc) Both (a) and (b) aboved) To increase the speed of the motorAns: (c)3. The field of an induction motor rotor rotates relative to the stator ata) Rotor speedb) Synchronous speedc) Slip speedd) Very low speedAns: (b)4. In an induction motor, rotor runs at a speeda) Equal to the speed of stator fieldb) Lower than the speed of stator fieldc) Higher than the speed of stator fieldd) Having no relation with the speed of stator fieldAns: (b)5. Starters are used in induction motor becausea) Its starting torque is highb) It is run against heavy loadc) It can not run in reverse directiond) Its starting current is five times or more than its rated currentAns: (d)6. When an induction motor runs at rated load and speed, the iron losses are
a) Negligibleb) Very heavyc) Independent of supply frequencyd) Independent of supply voltageAns: (a)7. By synchronous wattage of an induction motor is meanta) Stator input in wattsb) Rotor output in wattsc) Rotor input in wattsd) Shaft output in wattsAns: (c)8. The emf induced in the rotor of an induction motor is proportional toa) Voltage applied to statorb) Relative velocity between flux and rotor conductorsc) Both (a) and (b) aboved) SlipAns: (c)9. The synchronous speed of an induction motor is defined asa) Natural speed at which a magnetic field rotatesb) The speed of a synchronous motorc) The speed of an induction motor at no loadd) None of theseAns: (a)10. The starting torque of an indication motor is maximum whena) Rotor resistance equals rotor reactanceb) Rotor resistance is twice the rotor reactancec) Rotor resistance is half the rotor reactanced) Rotor resistance is R2 times the rotor reactanceAns: (a)11. Three-phase induction motor is mainly suitable for which of the following applicationa) For running different machine tools where several speeds are requiredb) For running paper machine requiring exact speed controlc) For running electric vehiclesd) For running rolling mills needing exact speed control
Ans: (a)12. Wattmeter reading in no-load test of induction motor givesa) Copper losses in the statorb) Friction and winding lossesc) Sum of (a) and (b) aboved) Total losses in the rotor on no loadAns: (d)13. The slip frequency of an induction motor isa) The frequency of rotor currentsb) The frequency of stator currentsc) Difference of the frequencies of the stator and rotor currentsd) Sum of the frequencies of the stator and rotor currentsAns: (a)14. The field winding of a three phase synchronous machine is excited bya) Single-phase ac supplyb) Three- phase ac supplyc) Dc supplyd) Supply obtained from an inverterAns: (c)15. With increase of load, the speed of induction motor operating in the stable regiona) Increasesb) Decreasesc) Remains constantd) Increases and then becomes constantAns: (b)16. When a polyphase induction motor is loadeda) Increases and its frequency decreasesb) Increases and its frequency increasesc) Decreases and its frequency increasesd) Decreases and its frequency decreasesAns: (a)17. In the following motor, external resistance can be added to start the motor
a) Slip ring induction motorb) Squirrel cage induction motorc) Salient pole synchronous motord) Wound rotor synchronous motorAns: (a)18. If in a 3-phase induction motor, two phases open accidently, the motor willa) Run at dangerously high speedb) Stopc) Continue to run depending on loadd) None of theseAns: (c)19. An induction motor is running at its rated torque and rated applied voltage of 440 volts.The effect of reducing the applied voltage to say 350 volts isa) That the motor stopsb) Current decreases slightlyc) Speed reduces slightlyd) Motor heats up with passage of timeAns: (d)20. A three-phase synchronous machine is aa) Single excited machineb) Double excited machinec) Machine in which three-phase supply is fed to both stator and rotor windingd) None of theseAns: (c)21. The disadvantage of starting an induction motor with a star-delta starter is thata) The starting torque is one-third of the torque in case of delta connectionb) During starting high losses resultc) The starting torque increases and the motor runs with jerksd) None of theseAns: (a)22. Squirrel cage induction motor hasa) Zero starting torqueb) Very small starting torquec) Medium starting torqued) Very high starting torque
Ans: (b)23. Improvement of the power factor in an induction motor results ina) Decreased torqueb) Increased torquec) Increased torque currentd) Increased torque and decreased current due to increased impedanceAns: (d)24. The purpose of blades in a squirrel cage induction motor isa) To reduce the magnetic resistance of the rotorb) To cool the rotorc) To reduce the electrical resistance of rotor caged) None of theseAns: (b)25. Which of the following function is served by the resistance placed in parallel with onephase of three-phase induction motor?a) Smooth startingb) Higher starting torquec) Higher maximum torqued) Higher reduced starting torqueAns: (a)26. Which of the following is the advantage of double squirrel cage rotor as compared to theround bar cage rotor?a) Large slipb) Lower starting torquec) Higher power factord) Higher efficiencyAns: (b)27. The rotor output of an induction motor is 15 kW and the slip is 4%. Then the rotor copperloss isa) 600 wattsb) 300 wattsc) 700 wattsd) 1200 wattsAns: (a)
28. On open circuiting the rotor of a squirrel cage induction motor, the rotora) Makes noiseb) Does not runc) Does not rund) Runs at dangerously high speedAns: (c)29. Number of different speed that can be obtained from two induction motors in cascade isa) 6b) 4c) 3d) 2Ans: (b)30. The drawback of speed control of a slip ring induction motor with the help of resistancein the circuit is thata) It is applicable only to motors having power of more than 100 kWb) It results in high lossesc) With reduction in speed, the torque decreases significantlyd) The speed can be controlled only very broadlyAns: (b)31. Advantage of slip ring induction motor over squirrel cage induction motor isa) Suitability of high speedsb) Higher efficiencyc) Higher power factord) That it can be started using factor resistanceAns: (d)32. In an induction motor, the rotor input is 600 W and slip is 4%. The rotor copper loss isa) 700 Wb) 625 Wc) 600 Wd) 650 WAns: (b)33. The starting torque of a cage rotor induction motor can be increased by using rotor havinga) Low inductance and low resistanceb) Low inductance and high resistance
c) High inductance and high resistanced) High inductance and low resistanceAns: (c)34. For smooth starting of three-phase squirrel cage induction motor, the starting methodpreferred isa) Rotor resistanceb) Star-deltac) Auto-transformerd) Stator resistanceAns: (c)35. Large air gap in an induction motor results ina) Reduced noiseb) Reduced pulsation lossesc) Better coolingd) Increased overload capacityAns: (b)36. The power factor of star connected induction motor is 0.5. On being connected in delta,the power factor will?a) Increaseb) Reducec) Remain the samed) Become zeroAns: (b)37. Simplest method of eliminating the harmonic induction torque isa) Integral slot windingb) Chordingc) Skewingd) None of theseAns: (b)38. Any odd harmonic in the current of an induction motor will result in magnetic field whicha) Is stationary relative to the field of the fundamentalb) Rotates in forward direction at the harmonic speedc) Rotates in backward directiond) Oscillates at harmonic frequency
Ans: (c)39. The drive generally used for lathe machines area) Dc shunt motorsb) Slip ring induction motorsc) Synchronous motorsd) Squirrel cage induction motorsAns: (d)40. Cogging of motor implies that motora) Refuses to start at loadb) Refuses to start at no loadc) Runs at low speed and then stopsd) Runs at very low speedAns: (b)41. Motor commonly used for traction purpose isa) Induction motorb) Dc series motorc) Dc shunt motord) Synchronous motorAns: (b)42. In a double cage induction motor, the inner cage hasa) Low R and low Xb) Low R and high Xc) High R and high Xd) High R and low XAns: (b)43. Maximum power developed in a synchronous motor occurs at a coupling angle ofa) 0 b) 60 c) 90 d) 120 Ans: (c)44. The back emf set up in the stator of synchro-nous motor depends on
a) Speed of the rotorb) Input to prime moverc) Rotor excitationd) Coupling angleAns: (c)45. The speed of a three-phase cage-rotor induction motor depends ona) Number of pole aloneb) Frequency of the supply alonec) Input voltaged) Number of poles and frequency of supplyAns: (d)46. Synchronous induction motors are mostly used for drivinga) Rotary compressorsb) Cranesc) Lathe machinesd) None of theseAns: (a)47.Dispersion coefficient o is the ratio ofa) Magnetizing current to ideal short circuit currentb) Magnetizing current to supply voltagec) Open circuit voltage to short circuit current for the same excitationd) None of theseAns: (a)48. The noise and tooth pulsation losses may be reduced by usinga) Large number of open slots in statorb) Large number of narrow slots in statorc) small number of open slots in statord) Small number of narrow slots in statorAns: (b)49. The faction slip of an induction motor is to ratioa) Rotor Cu loss/rotor inputb) Rotor Cu loss/rotor outputc) stator Cu loss/stator inputd) Rotor Cu loss/stator Cu loss
Ans: (a)50. When a 3-phase synchronous motor is switched on, three exists a rotating magnetic field.The magnitude of this field fluxa) Varies with power factorb) Varies with loadc) Is constant at all loadsd) None of theseAns: (c)51. The complete circuit diagram of a 3-phase induction motor can be drawn with the help ofa) Block rotor test alone.b) Running-light and blocked-rotor and stator-resistance testsc) Both running-light and blocked-rotor testsd) Running-light test aloneAns: (b)52. Which of the following motors is most suitable for best speed control?a) Dc shunt motorb) Dc series motorc) Induction motord) Synchronous motorAns: (a)53. A SCIM runs at constant speed only so long asa) Stator flux remains constantb) Its torque exactly equals the mechanical loadc) Its supply voltage remains constantd) Torque developed by it remains constantAns: (b)54. If the frequency of input power to an induction motor increases, the rotor copper lossa) Decreasesb) Increasesc) Remains the samed) None of theseAns: (b)55. The synchronous speed of a linear induction motor does NOT depend on
a) Width of pole pitchb) Number of polesc) Supply frequencyd) Any of the aboveAns: (a)56. The stator frame in an induction motor is useda) To provide ventilation to the armatureb) To protect the whole machinec) To hole the armature stampings/statord) As a return path for the fluxAns: (d)57.If the stator voltage and frequency of an induction motor are reduced proportionately, itsa) Locked rotor current is reducedb) Torque developed is increasedc) Magnetizing current is decreasedd) Both (a) and (b)Ans: (d)58. Motor A has deeper and narrow slots, whereas motor B. It has shallow and wide slots.Induction motor A, as compared to motor B, hasa) More operating slipb) Lass starting torquec) More pull-out torqued) More starting torqueAns: (b)59. If a single phase motor runs hot. The probable cause may bea) Overloadb) Low voltagec) High voltaged) Amu pf the aboveAns: (d)60. Which of the following single phase motors is relatively free from mechanical andmagnetic vibration?a) Reluctance motorb) Hysteresis motorc) Universal motor
d) Shaded pole motorAns: (b)61. Single phase induction motor can be made self-starting bya) Adding series combination of capacitor and auxiliary winding in parallel with the mainwindingb) Adding an auxiliary winding in parallel with the main windingc) Adding an auxiliary winding in series with a capacitor and the main windingd) None of theseAns: (a)62. Which of the following single phase motors does not have constant speed characteristic?a) Reluctance motorb) Hysteresis motorc) Universal motord) All of the aboveAns: (c)63. For the same rating which of the following motors has the highest starting torque?a) Universal motorb) Split phase motorc) Synchronous motord) All have identical starting torqueAns: (a)64. All single phase motors havea) Large starting torqueb) Zero starting torquec) Medium starting torqued) Very small starting torqueAns: (b)65. If a single phase motor fails to start, the probable cause may bea) Open circuit in auxiliary windingb) Open circuit in many windingc) Blown fusesd) Any of the aboveAns: (d)
66. Single phase motors generally get overheated due toa) Overloadingb) Short windingc) Bearing troublesd) Any of aboveAns: (d)67. The speed of the split phase induction motor can be reversed by reversing the leads ofa) Auxiliary windingb) Mani windingc) Either (a) or (b)d) Speed can not be reversedAns: (c)68. If a single phase motor runs slow, it may be due toa) Overloadb) Low frequencyc) Low voltaged) Any of theseAns: (d)69. A capacitor start single phase induction motor will usually have power factor ofa) Unitsb) 0.6 leadingc) 0.8 leadingd) 0.6 laggingAns: (d)70. Which of the following single phase motors is cheapest?a) Capacitor run motorb) Capacitor start motorc) Reluctance motord) All have almost the same costAns: (b)
14. The field winding of a three phase synchronous machine is excited by a) Single-phase ac supply b) Three- phase ac supply c) Dc supply d) Supply obtained from an inverter Ans: (c) 15. With increase of load, the speed of induction motor operating in the stable region a) Increases b) Decreases c) Remains constant
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2005 SystemVerilog standard[3], making SVA a little tricky to use for describing asynchronous behaviors. Asynchronous behaviors usually fall into two categories: (1) asynchronous control, and (2) asynchronous communication. SystemVerilog assertions can be used for either, but each presents its own set of challenges.
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