# Multiple choice question for engineering

## Set 1

1. The speed torque characteristics of the dc motor is best described by following the equation

w=(Vt/k*flux)-Ra*T/((R*flux)^2)

a)

b)

c)

d)

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2. Mark the correct option which affects the terminal voltage of a dc shunt motor.

a) Armature reaction

b) Source voltage variations

c) Compensating winding

d) Any of the mentioned

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3. For a dc shunt motor of 5 kW, running at 1000 rpm, the induced torque will be

a) 47.76 N

b) 57.76 N

c) 35.76 N

d) 37.76 N

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4. The flux and the internally generated voltage of a dc machine is a ________ function of its magneto-motive force.

a) non-linear

b) linear

c) constant

d) inverse

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5. It is advised not to run dc series motor with no load. Why?

a) Because zero torque at no load will make speed infinite

b) Because zero torque as no load will not let machine start

c) Because infinite torque will be produced

d) None of the mentioned

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6. Identify the speed torque characteristics of a dc series motor.

a)

b)

c)

d)

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7. Choose the best option which identifies about the below characteristics.

a) (1)series motor (2) Cumulative compound motor (3) Shunt motor

b) (1)Cumulative compound motor (2) series motor (3) Shunt motor

c) (1)Cumulative compound motor (2) Shunt motor (3) series motor

d) (1)Shunt motor (2) series motor (3) Cumulative compound motor

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8. How will the speed torque characteristic of a dc shunt motor and cumulatively compound dc motor perform at no load?

a)

b)

c)

d)

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9. The speed torque of the differential compound dc motor is shown below. What conclusions can be made?

a) This is an unstable machine

b) There is regenerative increment in the speed

c) This is impractical to be used

d) All of the mentioned

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10. It is impossible to start a differential compounded dc motor.

a) True

b) False

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11. A student is given a differential compound motor and he has been asked to make it start. How will he try?

a) By shorting series field at start

b) To run as shunt motor at start

c) By making rated current at start

d) All of the mentioned

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12. For a 100 hp 250 V, compound dc motor with compensating winding has a field current of 5 A to produce a voltage of 250 V at 1200 rpm. What will be the shunt field current of this machine at no load?

a) 5 A

b) 5.6 A

c) 4 A

d) 0 A

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13. The torque characteristic is best described for a dc series motor with respect to armature current is

a)

b)

c)

d) None of the mentioned

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14. The torque vs armature current of a differential compound motor in the strong field is

a)

b)

c)

d)

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15. A dc shunt motor is connected to the source through 3-point starter. Suddenly if we starter handle is moved fastly from off to on position, then

a) motor will draw large current

b) motor will not start

c) motor will burn

d) all of the mentioned

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## Set 2

1. A 10 kW, 400 V, 3-phase, 4-pole, 50 Hz induction motor develops the rated output at rated voltage with its slip rings shorted.

The maximum torque equal to twice the full load torque occurs at the slip of 10% with zero external resistance in the rotor circuit.

The slip at the full load torque will be

a) 2.7%

b) 5%

c) 3.7%

d) 10%

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2. A 10 kW, 400 V, 3-phase, 4-pole, 50 Hz induction motor develops the rated output at rated voltage with its slip rings shorted.

The maximum torque is twice the full load torque occurs at the slip of 10% with zero external resistance in the rotor circuit.

The speed at the full load torque will be

a) 1460 rpm

b) 1400 rpm

c) 1360 rpm

d) 1470 rpm

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3. A 10 kW, 400 V, 3-phase, 4-pole, 50 Hz induction motor develops the rated output at rated voltage with its slip rings shorted.

The maximum torque is twice the full load torque occurs at the slip of 10% with zero external resistance in the rotor circuit.

An external resistance is now tripled in the rotor circuit. Then the slip at which maximum torque occur for the same load torque is

a) 0.3

b) 0.268

c) 0.03

d) 3

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4. A 10 kW, 400 V, 3-phase, 4-pole, 50 Hz induction motor develops the rated output at rated voltage with its slip rings shorted. The maximum torque is twice the full load torque occurs at the slip of 10% with zero external resistance in the rotor circuit. An external resistance is now tripled in the rotor circuit. Then the stator current will

a) remain constant

b) increase

c) decrease

d) any of the mentioned

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5. Introducing the external resistance increases

(i) speed

(ii) output power

(iii) starting torque

a) (iii)

b) (ii),(iii)

c) (ii)

d) (i), (ii), (iii)

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6. Introducing the external resistance decreases

(i) speed

(ii) output power

(iii) starting torque

a) (iii)

b) (ii),(iii)

c) (i),(ii)

d) (i), (ii), (iii)

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7. For a three phase induction motor, maximum torque is double the full load torque and starting torque is 1.6 times the full load torque.

To get a full load slip of 5%, percentage reduction in the rotor resistance should be

a) 62.7%

b) 75%

c) 60%

d) 35%

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8. The speed-power output characteristic of a 3-phase induction motor is

a)

b)

c)

d)

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9. The power factor variation of the 3-phase induction motor is given by

a)

b)

c)

d)

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10. Four students had been conducting conducting experiments on the same induction motor for its efficiency characteristics. Which student has taken the best results?

a)

b)

c)

d)

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11. The stator current of the induction motor is given by which of the below?

a)

b)

c)

d)

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12. Slip vs the torque developed in an induction motor is given as

a)

b)

c)

d)

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13. The stable point in the operation of the induction motor is

a) C

b) D

c) B

d) A

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14. At which point shall the induction machine be operated to attain a stable operation?

a) The machine will not start

b) A

c) B

d) Both A as well as B.

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15. The stable point to use the induction motor possesing the below characteristic.

a) C

b) D

c) C and D

d) Machine will not start

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16. Mark the stable operating point when the load torque shifts from Tl1 to Tl2.

a) A

b) A,B

c) B,C

d) A,C

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17. A 3-phase, 50 Hz, 6-pole induction motor has a shaft output of 10kW at 930 rpm. Friction and windage losses is 1% of the output.Total stator losses is 600W.

The rotor input is

a) 10860 W

b) 10100 W

c) 11460 W

d) 11000 W

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18. A 3-phase, 50 Hz, 6-pole induction motor has a shaft output of 10kW at 930 rpm. Friction and windage losses is 1% of the output.Total stator losses is 600W.

The rotor input is

a) 10860 W

b) 10100 W

c) 11460 W

d) 11000 W

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## Set 3

1. The qualities aspired to obtain a good permanent magnet is/are

a) high residual flux

b) low coercivity

c) high coercivity

d) high residual flux and high coercivity

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2. The type of field winding required in PMMDC is

a) series winding

b) shunt winding

c) cumulative winding

d) None of the mentioned

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3. PMMDC are smaller in size due to

a) ansence of field winding

b) presence of smaller field winding

c) present of magnets

d) Any of the mentioned

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4. PMMDC offers ______ characteristics.

a) shunt

b) series

c) armature

d) cumulative

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5. Select the possible dc magnetization characteristics of permanent magnetic materials.

a)

b)

c)

d)

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6. Mark the speed torque characteristic of the PMDC.

a)

b)

c)

d) None of the mentioned

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7. PMDC had no ________ excited machine.

a) electrically

b) magnetically

c) none of the mentioned

d) least

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8. How to manage run-away issue for dc shunt motor in industry?

a) By using PMDC motor

b) By using constant field motors

c) This can not be avoided

d) None of the mentioned

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9. A PMMDC motor has as armature resistance of 4.2 ohms. When 6 V supply is applied to motor it runs at 1215 rpm drawing 14.5 mA on no-load. The rotational losses is

a) 86.1 mW

b) 86.1 W

c) 8.6 W

d) 8.6 mW

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10. PMMDC can only be armature controlled.

a) True

b) False

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## Set 4

1. Floating of synchronous machine on infinite bus means

a) Fa = 0 and machine neither generator nor motor

b) Fa is not zero and machine neither generator nor motor

c) Fa = 0 and machine is not excited

d) frequency is zero

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2. If the field poles are ahead of resultant mmf, then the 3-phase synchronous machine is operating as

a) generator

b) motor

c) reluctance motor

d) any of the mentioned

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3. At steady state operation in a 3-phase synchronous generator

a) Tem = Tpm

b) Tem > Tpm

c) Tem < Tpm

d) can not be coupled

where Tem is developed electromagnetic torque developed in the machine and Tpm is the prime mover torque.

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4. Active power in synchronous machine is proportional to

a) torque

b) excitation

c) sinϕ

d) all of the mentioned

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5. The reactive power in synchronous machine is proportional to

a) torque

b) excitation

c) sinϕ

d) all of the mentioned

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6. If the synchronous machine is loaded from floating conditions, the alternator begins to operate at

a) leading p.f

b) lagging p.f

c) unity p.f

d) zero p.f

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7. If the synchronous machine is loaded from floating conditions, the synchronous motor begins to operate at

a) leading p.f

b) lagging p.f

c) unity p.f

d) zero p.f

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8. Reactive power flow in synchronous machine can be controlled by

a) varying field excitation

b) varying field current

c) varying field flux

d) any of the mentioned

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9. If the 3-phase alternator has 4 poles and has synchronous speed of 120 rad/s.

Then the mechanical speed in rad/sec is

a) 60

b) 240

c) 120

d) 30

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10. The power load angle characteristic as maximum for a load angle of

a) 90°

b) 45°

c) more than 90°

d) 180°

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11. For running a 750 kW compressor, a synchronous motor is preferred because of

(i) lower noise

(ii) faster build up of pressure

(iii) better power factor

(iv) low starting torque

a) (ii),(iii)

b) (i),(ii),(iv)

c) (i),(ii),(iii),(iv)

d) (iii),(iv)

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12. A poly phase synchronous motor will be used for the load of ______ over poly phase induction motor.

a) 600 kW 500 rpm

b) 600 kW 1500 rpm

c) 600 kW 3500 rpm

d) 600 kW 1200 rpm

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13. During the starting of the 3-phase synchronous motor by damper bars, the field winding is usually short circuited so that starting torque is equal to

a) induction motor torque plus an additional torque produced by short circuited field winding

b) induction motor torque

c) electromagnetic torque

d) reluctance torque due to rotor saliency

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14. To start the synchronous motor, its field winding should be

a) short circuited

b) kept open

c) connected to dc excitation source

d) any of the mentioned

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15. Squirrel cage bars placed in the rotor pole faces of a 3-phase alternator help in reducing hunting

I. above synchronous speed

II. below synchronous speed

III. at synchronous speed

a) I,II

b) III

c) I,II,III

d) none of the mentioned

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## Set 5

1. Choose the correct power angle characteristics for the synchronous motor and generator

a)

b)

c)

d) None of the mentioned

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2. For a 3 phase 400V alternator having 0.5pu of synchronous reactance and its excitation voltage of 1.2pu and Vt of 1pu. Then the power delivered to the infinite bus is

a) 2.4pu

b) 4.8pu

c) 1.44pu

d) 1pu

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3. For a 3 phase 400V alternator supplying a load of 0.8 pf lagging at an armature current of 1.1pu. The power delivered to load is

a) 0.88pu

b) 0.8pu

c) 0.66pu

d) 1.375pu

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4. The power-angle characteristic for a three phase salient pole alternator is most correctly shown by

a)

b)

c)

d)

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5. A 3 phase 400V salient pole alternator is running at no-load. Suddenly the excitation is removed then the net power in the machine is proportional to

a) sin 2d

b) sin d

c) cos 2d

d) 0

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6. A 3 phase 400V cylindrical rotor is running at 1500rpm. Suddenly the field excitation zero. Then the net reluctance power is

a) 0

b) sin 2d

c) cos d

d) cos 2d

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7. A cylindrical rotor alternator can also run as reluctance motor

a) True

b) False

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8. If the synchronous machine is connected to an infinite bus of constant voltage Vt, through a transformed, a transmission line of reactance ‘X’. then power for a cylindrical machine is

a) P = (Ef*Vt sinδ)/(Xs + X)

b) P = (Ef*Ef sin2δ)/(Xs + X)

c) P = (Ef*Vt sinδ)/(Xs – X)

d) P = (Vt*Vt sinδ)/(Xs + X)

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9. Maximum power in cylinder rotor alternator occurs at load angle of

a) 90 degree

b) 45 degree

c) less than 90 degree

d) 180 degree

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10. A synchronous generator is operating with a Ef=1.40pu. This machine having Xs of 1.2pu, is delivering a synchronous power of 0.5pu to the bus. If the prime-mover torque is increased by 1%, by how much will the synchronous power P change?

a) 1%

b) 10%

c) -1%

d) 4%

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11. A synchronous generator is running over excited with a Ef=1.40pu. This machine, with a synchronous reactance of 1.2pu, is delivering a synchronous power of 0.5pu to the bus. If the prime-mover torque is increased by 1%, by how much will the reactive power, Q change?

a) -0.475 %

b) 0.475%

c) 4.75%

d) -4.75%

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12. A synchronous machine which is synchronized with an infinite bus. If it is desired to obtain a condition when the machine delivers the real power to the IBB without changing the field excitation, then

a) reactive power will be consumed by the machine

b) reactive power will be delivered by the machine

c) no reactive power flow will take place

d) none of the mentioned

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13. The phasor addition of stator and rotor mmfs in a cylindrical rotor synchronous machine, is possible because

a) mmfs are rotating in opposite direction

b) mmfs are rotating in same direction at different speeds

c) mmfs are stationary with respect to each other

d) one mmf is stationary and the other mmf is rotating

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14. For the effective electromechanical energy conversion in the device, the developed torque depends upon

a) stator field and torque angle

b) stator field and rotor field

c) stator field and rotor field and the torque angle

d) stator field only

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15. In a synchronous machine, hunting is predominantly damped by

a) mechanical losses in the rotor

b) iron losses in rotor

c) copper losses of stator

d) copper losses of rotor