1) Iron losses are considered to be the constant losses. It depends ona. Voltageb. Frequencyc. Both (a) and (b)d. None of these

ANSWER: Both (a) and (b)

2) Copper losses in a rotating machine area. Variable lossesb. Constant lossesc. Both (a) or (b)d. None of these

ANSWER: Variable losses

3) Stray losses are the losses which vary with the load but their relationship with load current cannot beidentified. Stay losses is maximum ina. Synchronous machinesb. D.C. machinesc. Induction machinesd. Equal in all types of machines

ANSWER: D.C. machines

4) The brush contact losses in a d.c. Machine isa. Inversely proportional to the square of currentb. Directly proportional to the square of currentc. Inversely proportional to the currentd. Directly proportional to the current

ANSWER: Directly proportional to the current

5) Electrical power output in a d.c. generator is equal to1/10

a. Electrical power developed in armature – copper lossesb. Mechanical power input – iron and friction lossesc. Electrical power developed in armature – iron and copper lossesd. Mechanical power input – iron and friction losses – copper losses

ANSWER: Mechanical power input – iron and friction losses – copper losses

6) Mechanical power developed in armature of a d.c. motor is given bya. Electrical power input to motor – copper lossesb. Motor output + iron and friction lossesc. Both (a) & (b)d. None of these

ANSWER: Both (a) & (b)

7) Out of electrical, mechanical and magnetic losses, the losses which is minimum isa. All are equalb. Electrical lossesc. Magnetic lossesd. Mechanical losses

ANSWER: Mechanical losses

8) The hysteresis motor are mainly used in tape recorders becausea. Of its extremely steady torqueb. Constant speedc. Reduced initial currentd. None of these

ANSWER: Of its extremely steady torque

9) If % ηm is the mechanical efficiency of a DC machine and % η e is the electrical efficiency. Then theoverall efficiency of DC machine is given by

a. % η m + % η eb. % η m X % η ec. (% η m + % η e) / % η md. (% η m + % η e) / % η e

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ANSWER: % η m X % η e

10) The current flowing through the armature of a d.c. shunt machine at maximum efficiency is given bya. √(P / Ra)b. √(Ra / P )

c. √(P / R2a)

d. √(Ra / P2 )

ANSWER: √(Pi / Ra)

11) A 120 V shunt generator running at 850 rpm has its armature and shunt field resistance of 0.15 ohm and50 ohm respectively. It supplies 200 lamps each rated at 60 W, 100 V. The friction and windage and core lossof the machine is 400 W. its armature copper loss on full load and shunt field loss isa. 2156.7 W, 200 Wb. 2232.6 W, 200 Wc. 2156.7 W, 240 Wd. 2232.6 W, 240 W

ANSWER: 2232.6 W, 200 W

12) A d.c. shunt generator delivers 190 A at a terminal voltage of 220 V. The copper losses and stray lossesare 2000 W and 1000 W respectively. The efficiency of the generator isa. 91.35 %b. 92.60 %c. 93.30 %d. 94.23 %

ANSWER: 93.30 %

13) A 4 pole d.c. shunt generator having a wave winding supplies 45 lamps, each of 50 W at 100 V. Thearmature and field resistance are 0.15 ohm and 50 ohm respectively. The current in armature conductor isa. 11.25 Ab. 11.50 Ac. 12.25 Ad. 13.50 A

ANSWER: 12.25 A

14) A 120 V d.c. shunt motor runs at speed of 1200 rpm. When the motor is operated unloaded but an3/10

additional resistance of 4 ohm is connected in series with the shunt field, then the speed increases andreaches to 1370 rpm with the same terminal voltage. The value of series resistance isa. 28.23 ohmb. 32.48 ohmc. 35.72 ohmd. 36.82 ohm

ANSWER: 28.23 ohm

15) A 240 V, 17 kW d.c. shunt motor draws an armature current of 80 A at full load. The armature and shuntfield resistances are 0.2 ohm and 195 ohm respectively. The rotational losses and efficiency of motor at fullload isa. 87.20 %b. 89.32 %c. 89.67 %d. 90.03 %

ANSWER: 87.20 %

16) Out of different methods available for testing of d. c. motors, Swinburne’s test and Hopkinson’s testare commonly used in practice ona. Shunt generatorsb. Series motorsc. Shunt motorsd. All of these

ANSWER: Shunt motors

17) Swinburne’s test and brake testsa. Both are direct method of testingb. Direct method of testing, indirect method of testingc. Indirect method of testing, direct method of testingd. Both are indirect method of testing

ANSWER: Indirect method of testing, direct method of testing

18) Swinburne’s test can be performed ata. Any loadb. Only no loadc. Only full loadd. Only half load

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ANSWER: Only no load

19) While performing Swinburne’s test, the iron losses are assumed to bea. Constantb. Absentc. Variabled. None of these

ANSWER: Constant

20) The speed in d.c. machine can be measured by usinga. Anemometerb. Tachometerc. Voltmeterd. Ammeter

ANSWER: Tachometer

21) While carrying out brake tests if the belt snaps, then the motor willa. Rotate at reduced speed but in forward directionb. Rotate at increased speed but in forward directionc. Rotate at reduced speed but in backward directiond. Rotate at increased speed but in backward direction

ANSWER: Rotate at increased speed but in forward direction

22) While performing retardation tests, the machine whose test is to be taken is run at a speed which isa. Slightly less than its rated speedb. Equal to its rated speedc. Slightly greater than its rated speedd. All of these

ANSWER: Slightly greater than its rated speed

23) The rotational or stray losses includesa. Iron losses onlyb. Iron losses, friction and windage lossesc. Iron losses, copper losses, friction and windage lossesd. None of these

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ANSWER: Iron losses, copper losses, friction and windage losses

24) The rotational losses in d.c. machines is equal to thea. Kinetic energy of armatureb. Half of the kinetic energy of armaturec. Square of the kinetic energy of armatured. Rate of change of kinetic energy

ANSWER: Rate of change of kinetic energy

25) In regenerative test, the supply is given to the motora. To account for lossesb. To drive generatorc. Both (a) and (b)d. None of these

ANSWER: To account for losses

26) The back to back test is best suited fora. Small machinesb. Medium size machinesc. Large machinesd. All of these

ANSWER: Large machines

27) For performing Hopkinson’s test two identical machines are required which are mechanically coupled.The iron losses in the two machinesa. Can be obtained separatelyb. Cannot be separatedc. Both d.None of these

ANSWER: Cannot be separated

28) The test which can be performed on the d.c. series motor isa. Brake testb. Hokinson’s testc. Swinburne’s test

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d. Field test

ANSWER: Field test

29) To perform field test on d.c. machines two motors are required. The motors used area. Series motorsb. One will be series motor and other will be shunt motorsc. Shunt motorsd. None of these

ANSWER: Series motors

30) The difference between field test and regenerative test is thata. Field test requires two identical machines while regenerative test requires only one machineb. In field test iron losses can be separated while in regenerative test it cannotc. In field test generator output is not fed back to the motor while in regenerative test generator output is fed back tothe motord. All of these

ANSWER: In field test generator output is not fed back to the motor while in regenerative test generatoroutput is fed back to the motor

31) The most common method used to check for shorted windings is to performa. Field testb. Drop testc. Regenerative testd. Brake test

ANSWER: Drop test

32) To have an induced emf in the d.c. generator, there should be relative motion between the conductorand flux. The plane of rotation and plane of fluxa. Should be parallel to each otherb. Should not be parallel to each otherc. Both (a) & (b)d. None of these

ANSWER: Should not be parallel to each other

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33) To have d.c. voltage, a device is used in a d.c. generator to convert alternating emf to unidirectionalemf. This device is calleda. Armatureb. Commutatorc. Brushesd. All of these

ANSWER: Commutator

34) Yoke in d.c. machine serves the outermost cover. For magnetic flux it providesa. A low reluctance pathb. A high reluctance pathc. Both (a) & (b)d. Does not provide path for magnetic flux

ANSWER: A low reluctance path

35) Functions of commutator in d.c. machines area. To facilitate the collection of current from armature conductorsb. To convert internally developed induced emf to unidirectional emfc. To produce unidirectional torque in case of motorsd. All of thesee. None of these

ANSWER: All of these

36) Brushes in d.c. machines are made up ofa. Cast ironb. Mild steelc. Copperd. Carbon

ANSWER: Carbon

37) If A is the number of parallel paths and P is the number of poles, then the number of parallel path in lapwinding and in wave winding isa. A = P, A = 2b. A = 2P, A = Pc. A = 2, A = Pd. A = P, A = 2P

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ANSWER: A = P, A = 2

38) A 4 pole, d.c. generator has a wave wound armature with 812 conductors. The flux per pole is 0.014Wb. The speed at which it should be run to generate 240 V on no load isa. 623.23 rpmb. 633.35 rpmc. 643.36 rpmd. 645.53 rpm

ANSWER: 633.35 rpm

39) A 4 pole, lap wound d.c. generators has 40 coils with 8 turns per coils. It is driven at 1200 rpm. If theflux per pole is 0.022 Wb, then the generated emf isa. 265.8 Vb. 276.3 Vc. 281.6 Vd. 287.9 V

ANSWER: 281.6 V

40) In a d.c. machine, the current rating and voltage rating of wave winding isa. Low, highb. High, lowc. High, highd. Low, low

ANSWER: Low, high

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1) The starting torque developed in the d.c. series motor and in d.c. shunt motor isa. High, lowb. High, moderatec. Moderate, lowd. Moderate, high

ANSWER: High, moderate

2) The speed of a d.c. series motor isa. Directly proportional to the both armature current and torque developedb. Inversely proportional to the armature current and square root of torque developedc. Directly proportional to the square of the armature current and square root of torque developedd. Inversely proportional to the square of the armature current and square of torque developed

ANSWER: Inversely proportional to the armature current and square root of torque developed

3) The speed armature current characteristics of a d.c. series motor isa. Rectangular hyperbolab. Linearc. Parabolicd. Parabolic till saturation and then linear

ANSWER: Rectangular hyperbola

4) If a d.c. series motor is started on very light load or on no load thena. It will run at dangerously high speed which may damage the motor mechanicallyb. It will run at very low speedc. Load does not effect the speed of d.c. series motord. None of these

ANSWER: It will run at dangerously high speed which may damage the motor mechanically

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5) Can a d.c. series motor be used for applications in belt drives?a. Yesb. No

ANSWER: No

6) D.C. series motors are used in electric traction. What happens to the speed and current of d.c motor ifthere is sudden slight drop in the mains voltage?a. Speed decreases and current also decreasesb. Speed decreases and current increasesc. Speed increases and current decreasesd. Speed decreases and current remains same

ANSWER: Speed decreases and current remains same

7) A long shunt compound motor and a short shunt compound motor can bea. Cumulative type, differential typeb. Differential type, cumulative typec. Both can be either cumulative or differential typed. None of these

ANSWER: Both can be either cumulative or differential type

8) Cumulative compound motor is capable of developing large amount of torque at low speeds just likeseries motor. Can cumulative compound motor be run on light load or no load?a. Yesb. No

ANSWER: Yes

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9) The speed current characteristics are shown in thegiven figure. Identify the different curves.a. 1 – series, 2 – shunt, 3 – cumulative compound, 4 –differential compoundb. 1 – cumulative compound, 2 – differential compound, 3– series, 4 – shuntc. 1 – cumulative compound, 2 – differential compound, 3– shunt, 4 – seriesd. 1 – differential compound, 2 – shunt, 3 – cumulativecompound 4 – series

ANSWER: 1 – differential compound, 2 – shunt, 3 –cumulative compound 4 – series

10) In a differential compound d.c. motor, with increase in load, speeda. Increasesb. Decreasesc. Remains samed. None of these

ANSWER: Increases

11) In electric traction, which type of motor is generally used?a. Shunt motorb. Series motorc. Cumulative compound motord. Differential compound motor

ANSWER: Series motor

12) Differential compound motors are mainly used ina. Drilling machinesb. Elevatorsc. Electric tractiond. Not suitable for any practical application

ANSWER: Not suitable for any practical application

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13) Which motor is not suitable for the application of centrifugal pumps?a. Shunt motorb. Series motorc. Cumulative compound motord. Differential compound motor

ANSWER: Series motor

14) Due to armature reaction magnetic neutral axis gets shifted by some angle. In case of motors thebrushes are shifted

a. Forwards same as the direction of rotationb. Backwards opposite to the direction of rotationc. Either (a) or (b)d. Does not get shifted

ANSWER: Backwards opposite to the direction of rotation

15) Speed of d.c. shunt motors are controlled bya. Flux control methodb. Rheostatic control methodc. Voltage control methodd. All of these

ANSWER: All of these

16) With the increase in temperature, the speed of series and shunt motor willa. Increase, decreaseb. Decrease, increasec. Increase, increased. Decrease, decrease

ANSWER: Decrease, increase

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Electrical Machine Objective TypeQuestions With Answer

Publisher : Faculty Notes Author : Panel Of Experts

Type the URL : http://www.kopykitab.com/product/11115

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