AC Electrical Machine MCQ Q1/ For all the following point, chose the right answer between a, b, c, and d. 1. One of the following points are not of transformer utilization in ac power
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system. a) Convert the ac power with different voltage, current, and frequency. b) Electric generation at the most economical generator voltage c) Power transfer at the most economical transmission voltage d) Power utilization at the most voltage for the particular utilization device The magnitude of flux that induced in primary winding of transformer depends on a) Primary voltage, current, and number of primary turns. b) Primary voltage, current, and the angle between them c) Primary voltage, frequency, and number ofprimary turns. d) Primary voltage, load, and number of primary turns The mutual flux in transformer will link the open circuit secondary winding and induced emf its magnitude depends on a) Number of secondary turns, magnitude of mutual flux, source voltage. b) Number of secondare and brimary turns, magnitude of flux, load. c) Number of secondary turns, magnitude of mutual flux and primary current. d) Number of secondary turns, magnitude of mutual flux, and frequency. The essence of transformer action requires only the existing of a) Two windings with one of them connected to a dc source b) Two winding, and iron core. c) Time-varying mutual flux linking two winding. d) Move a conductor in magnatic field. The magnetic circuit (Core) usually consists of a stack of thin laminations a) To reduce leakage flux. b) To can connect the two winding magnatically. c) To reduce iron loss in transformer. d) To reduce cu loss in transformer. One of the main disadvantages of induction motor is a) Its speed cannot be varied without sacrificing some of its efficiency. b) Its need to synchronies to start run. c) It has a low P.F d) Its effeciency is low because high loss. In a 3-ph induction motor, the relation between the number of poles and the speed is: a) Greater the number of poles, more the speed. b) Greater the number of poles, lesser the speed. c) The number of poles have no effect on speed. d) The number of poles = (120/f) NS. One of the reseans of slight skew in rotor slots in induction motors is: a) It reduce the cu losses in rotor windings b) It reduce the iron loss in rotor core.
AC Electrical Machine MCQ c) It increase the number of windings in rotor to increase the e.m.f induced in rotor. d) it helps to make the motor run quietly by reducing the magnetic hum 9. when 3-ph windings displaced in space by 120º, are fed by 3-ph currents, displaced in time by 120º, they produce a resultant magnetic flux a) a constant value=
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Фm, and rotating at synchronous speed Ns = 120
f/p. b) a constant value =
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Φm, and rotates at synchronous speed Ns = 120
f/P. c) a variable value of Фm, and rotate at synchronous speed Ns = 120f/p. d) a varible value of Фm, and with a constant pole mechnically. If the rotor speed N, and synchronous speed Ns become to be equal the machine a) Will be run at a constant speed, because there is no more accelration. b) Will be drawn a constant current from the source. c) Will be stopped, because there are no relative speed between N, and Ns. d) Will be more quite, and we get the maximum efficiency. In three phase transformer the connection is most economical for small, highvoltage transformers is a) Delta – delta connection b) Star – star connection. c) Star – delta connection. d) Delta- star connection. In the 3-ph transformer star-star connection a) There is a phase shift of 45o between the phase voltages and line voltages both on the primary and secondary sides b) There is no phase shift between the phase voltgae and line voltage both on the primary and secondary sides. c) There is a phase shift of 180o between the phase voltages and line voltages both on the primary and secondary sides d) There is a phase shift of 30° between the phase voltages and line voltages both on the primary and secondary sides. The connection of 3-ph transformers, that always used at the substation end of the transmission line is a) delta-delta connection. b) star – delta connection. c) delta – star connection. d) T-T connection. One of the main drawbaks of star-star connection is that a) Its works satisfactorily only if the load is balanced. b) There is a phase shift between phase and line voltage on both primary and secondary sides. c) Its should work with unity power factor only to avoid unbalance load share. d) The inside sorce impedance effect on the operation of transformer.
AC Electrical Machine MCQ 15. In star-delta connection of 3-ph transformer, the ratio between the secondary
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and primary line voltage is a) Depends on the transformation ratio of each transformer b) √3 times the transformation ratio of each transformer. c) 1⁄√3 times the transformation ratio of each transformer. d) 2⁄√3 times the transformation ratio of each transformer. We can avoide the effect of unblance load on the star-star 3-ph transformers by a) Use V- connection to aviode eddy current in side transformer b) Connecting the primary neutral back to the generator. c) Conncting the both primary and secondary neutrals to the earth. d) Open one of the phases in the secondary side and connect it to ground. In 3-ph transformers, the connection is economical for large, low-voltage transformers is a) Star – star connection. b) Open delta or V- connection c) Delta-delta connection. d) T-T connection. In delta –delta connection of a 3-ph transformers a) There is no phase shifit between phase voltages and line voltages of both primary and secondary sides. b) There is a phase shift of 30o between phase and line voltages of both primary and secondary sides. c) There is a phase shift of -30o between phase and line voltages of both primary and secondary sides. d) There is a phase shift of 45o between phase and line voltages of both primary and secondary sides One of the following points are not one of the reasens to use V-V connection a) When the three-phase load is too small to warrant the installation of full three-phase transformer bank. b) When one of the transformers in a Δ − Δ bank is disabled. c) When the load was unbalance on the three phases of transformer. d) When the load cycle is down. The total load that can be carried by a V − V bank is a) 2/3 of the capacity of a Δ – Δ connection. b) 1/√3 of the capacity of a Δ – Δ connection. c) √3 of the capacity of a Δ – Δ connection. d) 1/3 of the capacity of a Δ – Δ connection. The capacity to rating ratio in a T–T. connection is A. Equal to 57.7%. B. Equal to 75%. C. Equal to 33.3%. D. Equal to 86.6%. A Transformer is designed to be operated on both 50 & 60 Hz frequency.For the Same rating, which one will give more out put; when, A. Operates on 50 Hz
AC Electrical Machine MCQ B. Operates on 60 Hz 23. In a Transformer , The primary flux is always _________ the secondary ( flux). A. Greater then B. Smaller then C. Equal D. Equal in both step up and Step down Transformer 24. What would happen if we operate a 60 Hz Transformer on 50 Hz Source of Supply.(and how can we do that? A. Current will decrease (so increase the current) B. Current will increase ( so decrease the current) C. Current will be same in both cases. D. No Effect ( We can do that without changing anything) E. We can’t perform such an operation. 25. A Step-Up Transformer which has 110/220 turns.What would happen if we replace it with 10/20 turns? (because Turns ratio would be same in both cases) A. induced E.M.F wold be same B. Induced E.M.F would be decreased 26. The rating of transformer may be expressed in ____________. A. kW B. kVAR C. kVA D. Horse power. 27. What will happen if the primary of a transformer is connected to D.C supply? A. Transformer will operate with low efficiency B. Transformer will operate with high efficiency C. No effect D. Transformer may start to smoke and burn 28. What would happen if a power transformer designed for operation on 50 Hz (frequency) were connected to a 500 Hz (frequency) source of the same voltage? A. Current will be too much high B. Transformer may start to smoke and burn C. Eddy Current and Hysteresis loss will be excessive D. No effect 29. What would happen if a power transformer designed for operation on 50 Hz (frequency) were connected to a 5 Hz (frequency) source of the same voltage? A. Current will be too much low B. Transformer may start to smoke C. Eddy Current and Hysteresis loss will be excessive D. No effect 30. A Step Up transformer _____________. A. Step Up the level of Voltage B. Step down the level of current C. Step up level the power D. Step up the level of Frequency E. 1 and 2 only 31. Under what condition is D.C supply applied safely to the primary of a transformer?
AC Electrical Machine MCQ A. We can connect directly to DC. No condition required B. We can’t connect to DC Supply C. A High resistance should be connect in series with primary, but circuit will be useless. D. The above statement is wrong 32. An Auto-transformer (which has only one winding) may be used as a ______? A. Step-Up Transformer B. Step-Down Transformer C. Both Step-Up and Step-Down transformer D. None of the above 33. E.M.F Equation of the Transformer is _________. A. E1 = 4.44 f N1 Øm , E2=4.44 f N2 Øm B. E1= 4.44 f N1 Bm A , E2 = 4.44 f N2 BmA C. E1= 4.44 N1 Øm/T , E2=4.44 N2 Øm/T D. All of the above E. None of the above 34. The friction losses in Real Transformers are _________? A. 0% B. 5% C. 25% D. 50% 35. In Three Phase Transformer, The load Current is 139.1A, and Secondary Voltage is 415V. The Rating of the Transformer would be ___________. A. 50kVA B. 57.72kVA C. 100kVA D. 173kVA 36. In Single Phase Transformer, The Primary Current and Primary Voltage is 4.55 and 11kV respectively. The Rating of the transformer would be________? A. 50kVA B. 86kVA C. 100kVA D. 150kVA 37. An Isolation Transformer Has Primary to Secondary turns ratio of __________. A. 1 : 2 B. 2 : 1 C. 1 : 1 D. Can be any ratio 38. In an Auto Transformer, The Primary and Secondary are__________Coupled. A. Only Magnetically B. Only Electrically C. Magnetically as well as Electrically D. None of the above 39. A Transformer______________. A. Changes ac to DC
AC Electrical Machine MCQ B. Changes dc to AC C. Steps up or down DC Voltages & Current D. Steps up or down AC Voltages & Current 40. Transformer is a device which:________________. A. Transfer Electrical power from one electrical circuit to another Electrical circuit B. It’s working without changing the frequency C. Work through on electric induction. D. When, both circuits take effect of mutual induction E. Can step up or step down the level of voltage. F. Its Working without changing the Power. G. All of the above 41. For a transformer with number of secondary windings more than the number of primary windings, the secondary current will be _____________ ? A. More than the primary current B. Less than the primary current C. Equal to the primary current D. Zero 42. DC power is never applied to transformer A. True B. False 43. Impedance Ratio of a transformer is equal to _____________. A. Square of turns ratio B. Turns ratio C. 1 D. Infinite 44. For a single-phase transformer with 250 primary turns and 50 secondary turns, connected across a 1500 Volts, 50Hz supply, the maximum value of flux is—– A. 1 Wb B. 027Wb C. 04Wb D. 5Wb 45. For a single phase, 230/2300 Volts, 50Hz core type transformer of cross section 25 cm, if the maximum flux density is 1.12 wb/m2, the number of primary and secondary turns is———– A. 8, 148 B. 16, 160 C. 23, 230 D. 14, 140 46. For a 300KVA, 11000 Volts/440 Volts, 50Hz single phase transformer, the values of primary and secondary currents are ————– A. 30 Amperes, 750 Amperes B. 2 Amperes, 681.8 Amperes
AC Electrical Machine MCQ C. 1 Amperes, 752.5 Amperes D. 5 Amperes, 637.5 Amperes 47. For a practical transformer at no-load, the input power is equal to the iron losses A. True B. False 48. For actual transformers with higher load, leakage flux is prominent A. True B. False
Three phase induction motor 1-Slip ring induction motor has A. Low starting torque B. Medium starting torque C. High starting torque D. None of these 2) The frequency of the induced emf in an induction motor is a. Greater than the supply frequency b. Lesser than the supply frequency c. Same as the supply frequency d. None of these 3) The frequency of rotor current in an induction motor is a. slip times the frequency of stator current b. slip times the frequency of supply c. One by slip times the frequency of stator current d. One by slip times the frequency of supply Answer Explanation 4) Slip of an induction motor increases with a. increase in current and decrease in torque b. increase in current and torque c. decrease in current and torque d. decrease in current and increase in torque Answer Explanation 5) In an induction motor, rotor speed is always a. Less than the stator speed
AC Electrical Machine MCQ
b. More than the stator speed c. Equal to the stator speed d. None of these 6) The resultant flux in an induction motor is equal to the a. Maximum value of flux due to any phase b. Twice of the maximum value of flux due to any phase c. 0.5 times the maximum value of flux due to any phase d. 1.5 times the maximum value of flux due to any phase 7) Slip ring induction motor are employed only for a. Speed control b. High starting torque c. Both (a) and (b) d. None of these 8) The advantage of skewing in induction motor is / are a. Motor runs smoothly as the magnetic hum is reduced
b. The tendency of the rotor teeth to remain under the stator teeth due to direct magnetic attraction is redu c. More uniform torque is obtained while running d. All of these 9) In induction motor, greater the number of poles a. Lesser the speed b. Greater the speed c. Lesser the frequency d. All of these 10) For induction motors, a. Should be essentially a constant speed motor b. Its speed reduces to some extent with increase in load c. Does not need to be synchronized d. All of these 11- Which of the following component is usually fabricated out of silicon steel ? (a) Bearings (b) Shaft
AC Electrical Machine MCQ (c) Stator core (d) None of the above
2. The shaft of an induction motor is made of (a) stiff (b) flexible (c) hollow (d) any of the above
3. The shaft of an induction motor is made of (a) high speed steel (b) stainless steel (c) carbon steel (d) cast iron
4. In an induction motor, no-load the slip is generally (a) less than 1% (b) 1.5% (c) 2% (d) 4%
5. In medium sized induction motors, the slip is generally around (a) 0.04% (b) 0.4% (c) 4% (d) 14%
6. In squirrel cage induction motors, the rotor slots are usually given slight skew in order to (a) reduce windage losses (b) reduce eddy currents (c) reduce accumulation of dirt and dust (d) reduce magnetic hum
7. Slip rings are usually made of (a) copper (b) carbon (c) phosphor bronze (d) aluminum
8. The number of slip rings on a squirrel cage induction motor is usually (a) two (b) three
AC Electrical Machine MCQ (c) four (d) none
9. A double squirrel-cage induction motor has (a) two rotors moving in oppsite direction (b) two parallel windings in stator (c) two parallel windings in rotor (d) two series windings in stator
10. Star-delta starting of motors is not possible in case of (a) single phase motors (b) variable speed motors (c) low horse power motors (d) high speed motors
11. In case of the induction motors the torque is (a) inversely proportional to (Vslip) (b) directly proportional to (slip)2 (c) inversely proportional to slip (d) directly proportional to slip
12. The injected e.m.f. in the rotor of induction motor must have (a) zero frequency (b) the same frequency as the slip frequency (c) the same phase as the rotor e.m.f. (d) high value for the satisfactory speed control
13. Which of the following methods is easily applicable to control the speed of the squirrel-cage induction motor ? (a) By changing the number of stator poles (b) Rotor rheostat control (c) By operating two motors in cascade (d) By injecting e.m.f. in the rotor circuit
14. The speed of a squirrel-cage induction motor can be controlled by all of the following except (a) changing supply frequency (b) changing number of poles (c) changing winding resistance (d) reducing supply voltage
15. The power factor of an induction motor under no-load conditions will be closer to (a) 0.2 lagging
AC Electrical Machine MCQ (b) 0.2 leading (c) 0.5 leading (d) unity
16. In an induction motor the relationship between stator slots and rotor slots is that (a) stator slots are equal to rotor slots (b) stator slots are exact multiple of rotor slots (c) stator slots are not exact multiple of rotor slots (d) none of the above
17. If a 3-phase supply is given to the stator and rotor is short circuited rotor will move (a) in the opposite direction as the direction of the rotating field (b) in the same direction as the direction of the field (c) in any direction depending upon phase squence of supply
18. Which type of bearing is provided in small induction motors to support the rotor shaft ? (a) Ball bearings (b) Cast iron bearings (c) Bush bearings (d) None of the above
19. A 3-phase slip ring motor has (a) double cage rotor (b) wound rotor (c) short-circuited rotor (d) any of the above 20. In a three-phase induction motor (a) iron losses in stator will be negligible as compared to that in rotor (b) iron losses in motor will be neg¬ligible as compared to that in rotor (c) iron losses in stator will be less than that in rotor (d) iron losses in stator will be more than that in rotor
21. The shape of the torque/slip curve of induction motor is (a) parabola (b) hyperbola (c) rectangular parabola (d) straigth line
22. The stating torque of the slip ring induction motor can be increased by adding (a) external inductance to the rotor (b) external resistance to the rotor
AC Electrical Machine MCQ (c) external capacitance to the rotor (d) both resistance and inductance to rotor
23. Blocked rotor test on induction motors is used to find out (a) leakage reactance (b) power factor on short circuit (c) short-circuit current under rated voltage (d) all of the above
24. An induction motor can run at synchronous speed when (a) it is run on load (b) it is run in reverse direction (c) it is run on voltage higher than the rated voltage (d) e.m.f. is injected in the rotor circuit
25. Which motor is preferred for use in mines where explosive gases exist ? (a) Air motor (b) Induction motor (c) D.C. shunt motor (d) Synchronous motor
26. The torque developed by a 3-phase induction motor least depends on (a) rotor current (b) rotor power factor (c) rotor e.m.f. (d) shaft diameter
27. When R2 is the rotor resistance, X2 the rotor reactance at supply frequency and s the slip, then the condition for maximum torque under running conditions will be (a) sR2X2 = 1 (b) sR2 = X2 (c) R2 = sX2 (d) R2 = s2X2
28. The purpose of using short-circuit gear is (a) to short circuit the rotor at slip rings (b) to short circuit the starting resistances in the starter (c) to short circuit the stator phase of motor to form star (d) none of the above
29. A squirrel cage induction motor is not selected when (a) initial cost is the main consideration (b) maintenance cost is to be kept low
AC Electrical Machine MCQ (c) higher starting torque is the main consideration (d) all above considerations are involved
30. Slip ring motor is preferred over squirrel cage induction motor where (a) high starting torque is required (b) load torque is heavy (c) heavy pull out torque is required (d) all of the above
31. In a star-delta starter of an induction motor (a) resistance is inserted in the stator (b) reduced voltage is applied to the stator (c) resistance is inserted in the rotor (d) applied voltage per stator phase is 57.7% of the line voltage
32. The starting torque of a three-phase induction motor can be increased by (a) increasing slip (b) increasing current (c) both (a) and (b) (d) none of the above
AC Electrical Machine MCQ
Single phase induction motor Q1.The spit phase induction motor has a. Low starting current and high starting torque b. Moderate starting current and moderate starting torque c. Low starting current and moderate starting torque d. Moderate starting current and low starting torque
Q2. In washing machines, most commonly used motors are a. Split phase induction motors b. Slip ring induction motors c. Capacitor start induction motors d. Shaded pole induction motors
Q3. Split phase induction motors are available in the range of a. 1/2 to 1/10 kW b. 1/20 to 1/2 kW c. 1/10 to 1/20 kW d. None of these
Q4. In capacitor start capacitor run induction motor, the capacitor a. Only at start b. Only during running condition c. At start as well as during running condition d. None of these Q5. The capacitor connected permanently in capacitor run motor a. Improves power factor b. Lowers power factor c. Does not affect power factor d. None of these Q6. In refrigerators the commonly used motors are a. Split phase induction motors b. Capacitor induction motors c. Shaded pole induction motors d. None of these Q7. In shaded pole induction motor, the direction of rotation of magnetic field is from a. Shaded pole to nonshaded pole
AC Electrical Machine MCQ b. Nonshaded pole to shaded pole c. Doesn't depend on the poles d. None of these Q8. The starting torque and power factor of shaded pole induction motor a. High, low b. Low, high c. Low, low d. High, high Q9. In a single phase induction motor, the motor speed on no load is a. Almost equal to its synchronous speed b. Less than its synchronous speed c. Greater than synchronous speed d. None of these
Q10. The torque equation of single phase induction motor contains a constant term superimposed over by a pulsating torque. The pulsating frequency is a. Equal to the supply frequency b. Twice of the supply frequency c. Half of the supply frequency d. None of these
Q11. The stator of split phase induction motor has two windings, main winding and auxiliary winding. These windings are displaced in space by a. 30 electrical degrees b. 90 electrical degrees c. 120 electrical degrees d. 180 electrical degrees
Q12. The flux under the unshaded pole of shaded pole induction motor a. Is in equal phase of flux under the shaded pole b. Lags the flux under the shaded pole c. Leads the flux under the shaded pole d. None of these
Q13. A two phase servomotor is commonly used in feedback control system to drive the loads and as sensors to measure a. Speed of controlled element
AC Electrical Machine MCQ b. Position of controlled element c. Both (a) & (b) d. None of these
Q14. For moment of inertia to be small in two phase servomotor, the ratio of rotor diameter to its length should be a. Equal to 1 b. small c. large d. All of these
Q15. In a split phase motor (a) the starting winding is connected through a centrifugal switch (b) the running winding is connected through a centrifugal switch (c) both starting and running windings are connected through a centrifugal switch (d) centrifugal switch is used to control supply voltage
Q16. Which of the following motor will give relatively high starting torque ? (a) Capacitor start motor (b) Capacitor run motor (c) Split phase motor (d) Shaded pole motor
Q17. Which of the following motor will have relatively higher power factor ? (a) Capacitor run motor (b) Shaded pole motor (c) Capacitor start motor (d) Split phase motor
Q18. In a shaded pole motor, the shading coil usually consist of (a) a single turn of heavy wire which is in parallel with running winding (b) a single turn of heavy copper wire which is short-circuited and carries only induced current (c) a multilayer fine gauge copper wire in parallel with running winding (d) none of the above
Q19. If a particular application needs high speed and high starting torque, then which of the following motor will be preferred ? (a) Universal motor (b) Shaded pole type motor (c) Capacitor start motor (d) Capacitor start and run motor
AC Electrical Machine MCQ Q20. The value of starting capacitor of a fractional horse power motor will be (a) 100 uF (b) 200 uF (c) 300 uF (d) 400 uF
Q21. In repulsion motor direction of rotation of motor (a) is opposite to that of brush shift (b) is the same as that of brush shift (c) is independent of brush shift
Q22. In a single phase motor the centrifugal switch (a) disconnects auxiliary winding of the motor (b) disconnects main winding of the motor (c) reconnects the main winding the motor (d) reconnects the auxiliary winding of the motor
Q23. The running winding of a single phase motor on testing with meggar is found to be ground. Most probable location of the ground will be (a) at the end connections (b) at the end terminals (c) anywhere on the winding inside a slot (d) at the slot edge where coil enters or comes out of the slot
Q24. Which of the following motors is used in mixies ? (a) Repulsion motor (b) Reluctance motor (c) Hysteresis motor (d) Universal motor
Q25. Which of the following motors is inherently self starting ? (a) Split motor (b) Shaded-pole motor (c) Reluctance motor (d) None of these
Q26. The direction of rotation of an hysteresis motor is determined by (a) interchanging the supply leads (b) position of shaded pole with respect to main pole (c) retentivity of the rotor material (d) none of these Q27. Short-circuiter is used in (a) repulsion induction motor
AC Electrical Machine MCQ (b) repulsion motor (c) repulsion start induction run motor (d) none of the above
Q28. The range of efficiency for shaded pole motors is (a) 95% to 99% (b) 80% to 90% (c) 50% to 75% (d) 5% to 35%
Q29. For which of the applications a reluctance motor is preferred ? (a) Electric shavers (b) Refrigerators (c) Signalling and timing devices (d) Lifts and hoists
Q30. The motor used on small lathes is usually (a) universal motor (b) D.C. shunt motor (c) single-phase capacitor run motor (d) 3-phase synchronous motor
Q31. Which of the following motors is preferred for tape-recorders ? (a) Shaded pole motor (b) Hysteresis motor (c) Two value capacitor motor (d) Universal motor
Q32. A schrage motor can run on (a) zero slip (b) negative slip (c) positive slip (d) all of the above
Q33. Single phase induction motor usually operates on (a) 0.6 power factor lagging (b) 0.8 power factor lagging (c) 0.8 power factor leading (d) unity power factor Q34. In a two value capacitor motor, the capacitor used for running purposes is (a) air capacitor (b) paper spaced oil filled type (c) ceramic type
AC Electrical Machine MCQ (d) a.c. electrolytic type
Q35. In A.C. series motor compensating winding is employed to (a) reduce the effects of armature reaction (b) increase the torque (c) reduce sparking at the brushes (d) none of the above
Q36. In case of a shaded pole motor the direction of rotation of the motor is (a) from main pole to shaded pole (b) from shaded pole to main pole (c) either of the above depending on voltage (d) either of the above depending on power factor
Q37. The speed of a universal motor is generally reduced by using (a) gear trains (b) V-belts (c) brakes (d) chains
Q38. When a D.C. series motor is connected to A.C. supply, the power factor will be low because of (a) high inductance of field and armature circuits (b) induced current in rotor due to variations of flux (c) fine copper wire winding (d) none of the above
Q39. In a hysteresis motor, the rotor must have (a) retentivity (b) resistivity (c) susceptibility (d) none of the above
Q40. The rotor of a hysteresis motor is made of (a) aluminium (b) cast iron (c) chrome steel (d) copper Ans: c 27. The electric motor used in portable drills is (a) capacitor run motor (b) hysteresis motor
AC Electrical Machine MCQ (c) universal motor (d) repulsion motor
Q41. Which of the following applications always have some load whenever switched on ? (a) Vacuum cleaners (b) Fan motors (c) Pistol drills (d) All of the above
Q42. In repulsion motor, maximum torque is developed when (a) brush axis is at 45° electrical to the field axis (b) brush axis coincides with the field axis (c) brush axis is at 90° electrical to the field axis (d) none of the above
Q43. Speed torque characteristic of a repulsion induction motor is similar to that of a D.C. (a) shunt motor (b) series motor (c) compound motor (d) separately excited motor
Q44. The shaded pole motor is used for (a) high starting torque (b) low starting torque (c) medium starting torque (d) very high starting torque
Q45. The motor used for the compressors is (a) d.c. series motor (b) shaded pole motor (c) capacitor-start capacitor-run motor (d) reluctance motor
Q46. Which of the following motors is used in a situation where load increases with speed ? (a) Induction motor (b) Three-phase series motor (c) Schrage motor (d) Hysteresis motor
Q47. In repulsion motor, zero torque is developed when
AC Electrical Machine MCQ (a) brush axis is 45° electrical to field axis (b) brush axis coincides with the field axis (c) brush axis is 90° electrical to field axis (d) both (b) and (c)
Q48. If a single phase induction motor runs slower than normal, the most likely defect is (a) worn bearings (b) short-circuit in the winding (c) open-circuit in the winding (d) none of the above Q49. Which of the following motors is used in tape-recorders ? (a) Hysteresis motor (b) Reluctance motor (c) Capacitor-run motor (d) Universal motor Q50. In a universal motor, the most common cause of brush sparking is (a) open armature winding (b) shorted armature winding (c) shorted field winding (d) high commutator mica (e) all of the above Q51. Most of the fractional horsepower motors have either (a) hard and annealed bearings (b) ball or roller bearings (c) soft and porous bearings (d) plain or sleeve bearings Q52. Which of the following motors has two separate windings on the motor ? (a) Repulsion motor (b) Repulsion induction motor (c) Repulsion start induction run motor (d) None of the above Q53. A shaded pole motor does not possess (a) centrifugal switch (b) capacitor (c) commutator (d) all of the above Q54. In a A.C. series motor armature coils are usually connected to commutator (a) through resistance (b) through reactances (c) through capacitors (d) solidly
AC Electrical Machine MCQ
Synchronous Machines 1. In an alternator, voltage drops occurs in (A) armature resistance only (B) armature resistance and leakage reactance (C) armature resistance, leakage reactance and armature reaction (D) armature resistance, leakage reactance, armature reaction and earth connections.
2. The magnitude of various voltage drops that occur in an alternator, depends on (A) power factor of the load (B) load current (C) power factor x load current (D) power factor x (load current)2.
3. In an alternator, at lagging power factor, the generated voltage per phase, as compared to that at unity power factor (A) must be same as terminal voltage (B) must be less than the terminal voltage (C) must be more than the terminal voltage (D) must be 1.41 time the terminal voltage.
4. The power factor of an alternator depends on (A) Load (B) Speed of rotor (C) Core losses (D) Armature losses.
5. Which kind of rotor is most suitable for turbo alternators which arc designed to run at high speed ? (A) Salient pole type (B) Non-salient pole type (C) Both (A) and (B) above (D) None of the above.
6. Salient poles are generally used on
AC Electrical Machine MCQ (A) high speed prime movers only (B) medium speed prime movers only (C) low speed prime movers only ( D) low and medium speed prime movers.
7. The frequency of voltage generated in an alternator depends on (A) number of poles (B) rotative speed (C) number of poles and rotative speed (D) number of poles, rotative speed and type of winding.
8. The frequency of voltage generated by an alternator having 8 poles and rotating at 250 rpm is (A) 60 Hz (B) 50 Hz (C) 25 Hz (D) 16 2/3 Hz.
9. An alternator is generating power at 210 V per phase while running at 1500 rpm. If the need of the alternator drops to 1000 rpm, the generated voltage per phase will be (A) 180 V (B) 150 V (C) 140 V (D) 105 V.
10. A 10 pole AC generator rotates at 1200 rpm. The frequency of AC voltage in cycles per second will be (A)120 (B) 110 (C) 100 (D) 50.
11. The number of electrical degrees passed through in one revolution of a six pole synchronous alternator is
AC Electrical Machine MCQ (A)360: (B)720 (C) 1080 (D)2160 .
12. Fleming's left hand rule may be applied to an electric generator to find out (A) direction of rotor rotation (B) polarity of induced emf (C) direction of induced emf (D) direction of magnetic field.
13. If the input to the prime mover of an alternator is kept constant but the excitation is changed, then the (A) reactive component of the output is changed (B) active component of the output is changed (C) power factor of the load remains constant (D) power factor of the load reduces. 14. An alternator is said to be over excited when it is operating at (A) unity power factor (B) leading power factor (C) lagging power factor (D) lagging to leading power factor. 15. When an alternator is running on no load the power supplied by the prime mover is mainly consumed (A) to meet iron losses (B) to meet copper losses (C) to meet all no load losses (D) to produce induced emf in armature winding. 16. As the speed of an alternator increases (A) the frequency increases (B) the frequency decreases (C) the frequency remains constant but power factor decreases (D) none of the above.
AC Electrical Machine MCQ 17. For an alternator when the power factor of the load is unity (A) the armature flux will have square waveform (B) the armature flux will be demagnetising (C) the armature flux will be cross-magnetising (D) the armature flux will reduce to zero. 18. The driving power from the prime mover driving the alternator is lost but the alternator remains connected to the supply network and the field supply also remains on. The alternator will (A) get burnt (B) behave as an induction motor but will rotate in the opposite direction (C) behave as a synchronous motor and will rotate in the same direction (D) behave as a synchronous motor but will rotate in a reverse direction to that corresponding to generator action. 19. If the input of the prime mover of an alternator is kept constant but the excitation is changed, then (A) the active component of the output is changed (B) the reactive component of the output is changed (C) power factor of the load remains constant (D) power factor of the load changes from lagging to leading. 20. For 50 Hz system the maximum speed of an alternator can be (A) approximately 3600 rpm (B) approximately 3000 rpm (C) 3600 rpm (D) 3000 rpm. 21. Voltage characteristic of an alternator is shown in figure. Which curve represents the characteristics for leading power factor ?
(A) A (B) B
AC Electrical Machine MCQ (C) C (D) D.
Get Answer 22. In the above figure, the characteristic for unity power factor is represented by the curve maked (A) A (B) B (C)C (D )D. In a 50 kVA, star connected 440 V, 4-phase 50 Hz alternator, the effective armature resistance is 0.25 ohm per phase. The synchronous reactance is 3.2 ohm per phase and leakage reactance is 0.5 ohm per phase. 23. Full load output current at unity power factor will be (A) 65.6 A (B) 55.4 A (C) 45.6 A (D) 35.4 A. 24. Full load line voltage will be (A) 500 V (B) 471 V (C) 450 V (D) 435 V. 25. No load line voltage will be (A) 600 V (B) 599 V (C)592V (D) 580 V. 26. Percentage regulation of the alternator is approximately (A) 55% (B) 45% (C) 35% (D) 25%.
AC Electrical Machine MCQ
27. In order that two alternators be put in parallel, which of the following factors should be identical for both ? (A) Voltage (B) Frequency (C) Phase sequence (D) All of the above. 28. When two alternators are running in parallel, their RKVA load share is changed by changing their ................ while their kW load share is changed by changing their .............. (A) excitation, driving torque (B) driving torque, excitation (C) excitation, excitation (D) driving torque, driving torque. 29. Two-alternators are running in parallel. If the driving force of both the alternators is changed, this will result in change is (A) frequency (B) back emf (C) generated voltage (D) all of the above. 30. A three phase alternator has a phase sequence of RYB for its three output voltages. In case the field current is reversed, the phase sequence will become (A) RBY (B) RYB (C) YRB (D) none of the above.
