Ies electrical engineering - electrical machines

IES Electrical Engineering Topic wise QuestionsElectrical Machines

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YEAR 2008

MCQ 1

Consider the following statements:

Skewing of rotors slots in a 3-phase induction motor (cage rotor) may

1. introduce additional leakage reactance

2. eliminate slot harmonics

Which of the statements given above is/are correct ?

(A) 1 only

(B) 2 only

(C) Both 1 and 2

(D) Neither 1 nor 2

MCQ 2

In the equivalent circuit of a double-cage induction motor, the two rotor cages can be considered

(A) to be in parallel

(B) to be in series-parallel

(C) to be in series

(D) to be in parallel with stator

MCQ 3

A 3-phase squirrel-cage induction motor is started by means of a

IES EE Topic wise 2001-2008 Electrical Machines

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star/delta switch. What is the starting current of the motor ?

(A) 3 times the current with direct on line starting

(B) 1/3 times the current with direct on line starting

(C) /1 3 times the current with direct on line starting

(D) 3 times the current with direct on line starting

MCQ 4

Sludge formation in transformer oil is due to which one of the following ?

(A) Ingress of duct particles and moisture in the oil

(B) Appearance of small fragments of paper, varnish, cotton and other organic materials in the oil

(C) Chemical reaction of transformer oil with the insulating materials

(D) Oxidation of transformer oil

MCQ 5

A single-phase transformer rated for 220/440 V, 50 Hz operates at no load at 220 V, 40 Hz. This frequency operation at rated voltage results in which one of the following ?

(A) Increase of both eddy-current and hysteresis losses

(B) Reduction of both eddy-current and hysteresis losses

(C) Reduction of hysteresis loss and increase in eddy-current loss

(D) Increase of hysteresis loss and no change in the eddy-current loss

MCQ 6

What is the load at which maximum efficiency occurs in case of a 100 kVA transformer with iron loss of 1 kW and full-load copper loss of 2 kW ?

(A) 100 kVA

(B) 70.7 kVA

(C) 50.5 kVA

(D) 25.2 kVA

MCQ 7

Cores of large power transformers are made from which one of the


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following ?

(A) Hot-rolled steel

(B) Cold-rolled non-grain oriented steel

(C) Cold-rolled grain oriented steel

(D) Ferrite

MCQ 8

A transformer has a percentage resistance of 2% and percentage reactance of 4%. What are its regulations at power factor 0.8 lagging and 0.8 leading, respectively ?

(A) 4% and 0.8%−

(B) 3.2% and 1.6%−

(C) 1.6% and 3.2%−

(D) 4.8% and 0.6%−

MCQ 9

The full-load copper loss and iron loss of a transformer are 6400 W and 5000 W, respectively. What are the above copper loss and iron loss, respectively at half-load ?

(A) 3200 W, 2500 W

(B) 3200 W, 5000 W

(C) 1600 W, 1250 W

(D) 1600 W, 5000 W

MCQ 10

Assertion (A) : A d.c motor draws high current at the time of starting.

Reason (R) : While starting a d.c. motor, it takes some time to develop a non-zero value of back e.m.f.

(A) Both A and R are true and R is the correct explanation of A

(B) Both A and R are true but R is not the correct explanation of A

(C) A is true but R is false

(D) A is false but R is true

MCQ 11

Assertion (A) : For a 3-phase alternator operating on leading p.f. at

phaneendra

Cross-Out


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full load, the terminal voltage may be more than the no-load induced e.m.f.

Reason (R) : At leading power factor, the effect of armature reaction is demagnetizing.





MCQ 12

Assertion (A) : AC armature windings are short chorded by selecting value of coil span more than the pole pitch.

Reason (R) : Short chording is done to eliminate harmonics in the induced e.m.f.





MCQ 13

Assertion (A) : The leakage reactance of a 3-phase induction motor should be small.

Reason (R) : A small value of leakage reactance will increase the maximum power output of motor.





MCQ 14

Assertion (A) : Both the efficiency and regulation of a 3-winding ideal transformer are 100%.

Reason (R) : The flux leakage and the magnetic reluctance of the magnetic core in an ideal transformer are zero. Moreover, losses are absent in ideal transformers.


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MCQ 15

The graph shown below represents which characteristic of a d.c. shunt generator ?

(A) Internal characteristic

(B) External characteristic

(C) Open-circuit characteristic

(D) Magnetic characteristic

MCQ 16

When is the mechanical power developed by a d.c. motor maximum ?

(A) Back e.m.f. is equal to applied voltage

(B) Back e.m.f. is equal to zero

(C) Back e.m.f. is equal to half the applied voltage

(D) None of the above

MCQ 17

Match List I (DC machine quantity) with List II (Relation) and select the correct answer using the code given below the lists :

List I List II

A. Developed power 1. Nα φ

B. Torque 2. E Ib aα


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C. Generated e.m.f. 3. /Ebα φ

D. Speed 4. Iaα φ

Codes :

A B C D

(A) 2 4 1 3

(B) 3 1 4 2

(C) 2 1 4 3

(D) 3 4 1 2

MCQ 18

A shunt generator has a critical field resistance of 200 Ω at a speed of 800 r.p.m. If the speed of the generator is increased to 1000 r.p.m., what is the change in the critical field resistance of the generator ?

(A) Decrease to 160 Ω

(B) Remains the same of 200 Ω

(C) Increases to 250 Ω

(D) Increases to .312 5 Ω

MCQ 19

Which one of the following curves represents the speed-torque characteristic of a d.c. series motor ?


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MCQ 20

Match List I (Machine characteristic) with List II (Quantity) and select the correct answer using the code given below the lists :

List I List II

A. Open-circuit characteristic 1. . . .p f vs If

B. V curve 2. .E vs Ia a

C. Internal characteristic 3. .E vs Ig f

D. Inverted V-curve 4. .I vs Ia f


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Codes :

A B C D

(A) 3 1 2 4

(B) 2 4 3 1

(C) 3 4 2 1

(D) 2 1 3 4

MCQ 21

Which of the following conditions are to be satisfied for proper synchronization of alternators ?

1. Equal terminal voltage

2. Same frequency

3. Same phase sequence

4. Same kVA rating

5. Same phase displacement

Select the correct answer using the code given below :

(A) 1, 3 and 4

(B) 1, 2, 4 and 5

(C) 2, 3, 4 and 5

(D) 1, 2, 3 and 5

MCQ 22

If the excitation of a 3-phase alternator operating on infinite bus bars is changed, which one of the following shall alter ?

(A) Active power of machine

(B) Reactive power of machine

(C) Terminal voltage of machine

(D) Frequency of machine

MCQ 23

The stator of a 3-phase, 6-pole a.c. machine has 45 slots. The stator winding has 45 coils with a coil span of 6 slots. What type of winding will be selected for this machine ?

(A) Double-layer, fractional slot, short-pitched winding


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(B) Single-layer, fractional slot, short-pitched winding

(C) Single-layer, integral slot, full-pitch winding

(D) Double-layer, fractional slot, full-pitch winding

MCQ 24

When are eddy-current losses in a transformer reduced ?

(A) If laminations are thick

(B) If the number of turns in primary winding is reduced

(C) If the number of turns in secondary winding is reduced

(D) If laminations are thin

MCQ 25

Why is a centrifugal switch used in a single-phase induction motor ?

(A) To protect the motor from overloading

(B) To improve the starting performance of the motor

(C) To cut off the starting winding at an appropriate instant

(D) To cut in the capacitor during running conditions

MCQ 26

What is the operating slip of a 400 V, 50 Hz, 6-pole, 3-phase induction motor, while the speed is 936 r.p.m. with a 400 V, 48 Hz, 3-phase supply ?

(A) 0.036

(B) 0.064

(C) 0.025

(D) 0.075

MCQ 27

A 3-phase slip-ring induction motor having negligible stator impedance drives a constant torque load. If an additional resistance is included in the rotor circuit, what does the motor experience ?

(A) Increase in both the stator current and the slip

(B) No change in the stator current and increase in the slip

(C) Increase in the stator current and no change in the slip

(D) Decrease in the stator current and increase in the slip


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MCQ 28

Breakdown torque in a 3-phase induction motor of negligible stator impedance is

(A) directly proportional to rotor resistance

(B) inversely proportional to rotor resistance

(C) directly proportional to rotor leakage reactance

(D) inversely proportional to rotor leakage reactance

MCQ 29

A balanced 3-phase induction motor runs at slip S . If sω is its synchronous speed, what is the relative speed between the stator m.m.f. and rotor m.m.f. ?

(A) S sω

(B) ( )S1 sω−

(C) sω

(D) zero

MCQ 30

Match List I (Method of speed control of 3-phase wound-type induction motor) with List II (Performance achieved) and select the correct answer using the code given below the lists :

List I List II

A. Stator voltage control 1. Both speed and p.f. can be controlled

B. Rotor resistance control 2. Maximum torque remains constant

C. Constant volts/Hz control 3. Starting torque increases

D. Injection of voltage in rotor circuit

4. Starting torque decreases

Codes :

A B C D

(A) 2 1 4 3

(B) 4 3 2 1

(C) 2 3 4 1


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(D) 4 1 2 3

YEAR 2007

MCQ 31

Assertion (A) : Large synchronous machines are constructed with armature winding on stator.

Reason (R) : Stationary armature winding would have reduced armature reactance.





MCQ 32

If the armature current is increased to double its previous value, and the time of commutation is halved, how will the reactance voltage vary ?

(A) It will be halved

(B) It will remain the same

(C) It will be doubled

(D) It will become four times

MCQ 33

Neglecting all loses, how is the developed torque T̂ h of a dc separately excited motor, operating under constant terminal voltage, related to its output power P^ h ?

(A) T P\

(B) T P\

(C) T P2 3\

(D) T is independent of P

MCQ 34

A dc shunt generator is supplying a load of 1.8 kW at 200 V. Its armature and field resistances are .0 4 Ω and 200 Ω respectively. What


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is the generated emf ?

(A) 190 V

(B) 196 V

(C) 204 V

(D) 210 V

MCQ 35

The field flux method of speed control of dc shunt motor is generally used for which one of the following ?

(A) Constant hp drive below the base speed

(B) Constant torque drive above the base speed

(C) Constant torque drive below the base speed

(D) Constant hp drive above the base speed

MCQ 36

A 5 kW, 200 V dc shunt motor has armature resistance of 1 ohm and shunt field resistance of 100 ohm. At no load, the motor draws 6 A from 200 V supply and runs at 1000 rpm. What is the total copper loss of the machine ?

(A) 400 W

(B) 16 W

(C) 36 W

(D) 416 W

MCQ 37

When does a synchronous motor operate with leading power factor current ?

(A) While it is under-excited

(B) While it is critically excited

(C) While it is over-excited

(D) While it is heavily loaded

MCQ 38

A 10 pole, 25 Hz alternator is directly coupled to and is driven by 60 Hz synchronous motor. What is the number of poles for the


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synchronous motor ?

(A) 48

(B) 12

(C) 24

(D) 16

MCQ 39

What is the angle between the induced voltage and supply voltage of a synchronous motor under running condition ?

(A) zero

(B) Greater than zero but 90c#

(C) Between 90c and 180c

(D) 180> c

MCQ 40

What does the SCR (short circuit ratio) of a synchronous machine yield ?

(A) X

1(unsaturated) pus

(B) X

1(unsaturated) in Ohms

(C) X

1(adjusted) pus

(D) X

1(adjusted) in Ohms

MCQ 41

How can the reactive power delivered by a synchronous generator be controlled ?

(A) By changing the prime mover input

(B) By changing the excitation

(C) By changing the direction of rotation

(D) By changing the prime mover speed

MCQ 42

Which one of the following is the correct statement ?


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(A) The armature current upon symmetrical 3-phase short circuit of a synchronous machine (armature resistance is negligible) constitutes q-axis current only

(B) The armature current upon symmetrical 3-phase short circuit of a synchronous machine (armature resistance is negligible) constitutes d-axis current only

(C) The armature current upon symmetrical 3-phase short circuit of a synchronous machine (armature resistance is negligible) has both d-axis and q-axis current only

(D) Short circuit current can be divided into d-axis and q-axis components

MCQ 43

If the full-load speed of a 3-speed, 50 Hz induction motor is 950 rpm, what is its half-load speed nearly equal to ?

(A) 1000 rpm

(B) 450 rpm

(C) 1900 rpm

(D) 975 rpm

MCQ 44


In a 3-phase induction motor, the resultant flux is of a constant nature and is

(A) equal to mφ , where mφ is maximum flux due to any phase

(B) 1.5 time maximum value of flux due to any phase

(C) /3 2 times maximum value of flux due to any phase

(D) 3 mφ

MCQ 45

In an induction motor, what is the ratio of rotor copper loss and rotor input ?

(A) /s1

(B) s

(C) s1 −^ h


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(D) /s s1 −^ h

MCQ 46

In an induction motor, air gap power is 10 kW and mechanically developed power is 8 kW. What are the rotor ohmic losses ?

(A) 1 kW

(B) 3 kW

(C) 2 kW

(D) 0.5 kW

MCQ 47


The output line in an induction motor circle diagram is the line joining the tip of the

(A) no load current phasor to the point corresponding to slip 0=

(B) no load current phasor to the point corresponding to slip 1=

(C) short circuit current phasor to the point corresponding to slip 1=

(D) short circuit current phasor to the point corresponding to slip 0=

MCQ 48

Match List I with List II and select the correct answer using the code given below the lists :

List I List II

A. General purpose split phase FHP motor

1. Refrigerators

B. General purpose capacitor start FHP motor

2. Hair dryers

C. Permanent split capacitor start FHP motor

3. Unit heaters

D. Shaded pole FHP motor 4. Fans, blowers

Codes :

A B C D

(A) 1 2 4 3

(B) 1 2 3 4


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(C) 4 1 2 3

(D) 4 1 3 2

MCQ 49

In a large power transformer, a “conservator” drum is provided above the completely oil filled transformer tank and connected to it by a short pipe. The conservator drum is linked to external air through a breather. What is the purpose of providing the conservator ?

(A) To store reserve oil to make up oil losses due to leakage

(B) To prevent explosion due to rise in oil pressure inside the tank during a fault

(C) To accommodate change in oil-level during the “load-cycle” of the transformer load

(D) To exert additional pressure by the conservator-oil on the oil inside the main tank to prevent disintegration of oil at high temperature

MCQ 50

A 500 kVA transformer has constant losses of 500 W and copper losses at full load are 2000 W. Then at what load, is the efficiency maximum ?

(A) 250 kVA

(B) 500 kVA

(C) 1000 kVA

(D) 125 kVA

MCQ 51

On which of the following factors does hysteresis loss depend ?

1. Flux density

2. Frequency

3. Thickness of lamination

4. Time


(A) 2 and 3

(B) 1 and 2


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(C) 3 and 4

(D) 1 and 4

MCQ 52

Consider the following statements regarding transformers :

1. The function of the magnetizing component of no load current is to sustain the alternating flux in the core.

2. Short circuit test is performed to find core losses only.

3. The function of the breather in transformer is to arrest flow of moisture when outside air enters the transformer.

Which of the statements given above are correct ?

(A) 1 and 2

(B) 1 and 3

(C) 2 and 3

(D) 1, 2 and 3

MCQ 53

Two transformers when operating in parallel will share the load depending upon which of the following ?

(A) Magnetizing current

(B) Leakage reactance

(C) Per unit impedance

(D) Efficiency

MCQ 54

What is the frequency of rotor current of a 50 Hz induction motor operating at 2% slip ?

(A) 1 Hz

(B) 100 Hz

(C) 2 Hz

(D) 50 Hz

MCQ 55

Torque developed by the armature of a dc motor is proportional to which one of the following ?


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(A) (Back emf)#(Armature current)

(B) (Magnetic flux per pole)#(Armature current)

(C) (Back emf)#(Magnetic flux per pole)

(D) (Back emf)/(Magnetic flux per pole)

MCQ 56

Which of the following are the variable losses in a rotating machine ?

(A) Core loss and mechanical loss

(B) Core loss and stray load loss

(C) Copper loss and core loss

(D) Copper loss and stray load loss

MCQ 57

Which of the following are true is respect of interpoles in dc machines ?

1. Reduce armature reaction effects in interpolar region.

2. Windings are connected in series with armature.

3. Have the same dimensions as main poles.


(A) 1 and 2

(B) 2 and 3

(C) 1 and 3

(D) 1, 2 and 3

MCQ 58

What are slot wedges in a dc machine, made of ?

(A) Mild steel

(B) Silicon steel

(C) Fibre

(D) Cast iron

MCQ 59

An 8-pole single phase induction motor is running at 690 rpm. What is its slip with respect to forward and backward fields, respectively ?


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(A) 0.08,2.0

(B) 0.08,1.92

(C) 1.92,0.08

(D) 2.0,0.08

YEAR 2006

MCQ 60

What is the value of the load angle when the power output of a salient pole sychronous generator is maximum ?

(A) 0c

(B) 45c

(C) 90c

(D) None of the above

MCQ 61

Which one of the following statements is not correct in respect of synchronous machines ?

(A) In a salient pole machines, the direct-axis synchronous reactance is greater than the quadrature axis synchronous reactance

(B) The damper bars help the motor to self-start

(C) Short circuit ratio is the ratio of field current required to produce the rated voltage on open circuit to the rated armature current

(D) The V-curve of a synchronous motor represents the variation in the armature current with field excitation at a given output power

MCQ 62

In which one of the following is reluctance power developed ?

(A) Salient pole alternator

(B) Non-salient pole alternator

(C) Squirrel cage induction motor

(D) Transformer

MCQ 63


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When the applied rated voltage per phase is reduced to one-half, the starting torque of a three-phase squirrel cage induction motor becomes

(A) 1/2 of the initial value

(B) 1/4 of the initial value

(C) Twice of the initial value

(D) 4 times of the initial value

MCQ 64

The required load torque line intersects the resultant torque-speed characteristic of a 3-phase squirrel cage induction motor at points P, Q and R as shown in the figure below. Which is/are the stable operating point(s) ?

(A) P and Q

(B) Q and R

(C) P and R

(D) Only R

MCQ 65

Which of the points on the torque-speed curve of the induction motor represents operation at a slip greater than 1 ?


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(A) W

(B) X

(C) Y

(D) Z

MCQ 66

If the load on an induction motor is increased from no load to full load, its slip and the power factor will, respectively

(A) decrease, decrease

(B) decrease, increase

(C) increase, decrease

(D) increase, increase

MCQ 67

The voltage actually used for setting up of the useful flux in the air gap of a 3-phase induction motor is

(A) = Applied voltage

(B) > Applied voltage

(C) < Applied voltage

(D) = Rotor induced emf

MCQ 68

Which one of the following is the type of single phase induction motor having the highest power factor at full load ?

(A) Shaded pole type


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(B) Split-phase type

(C) Capacitor-start type

(D) Capacitor-run type

MCQ 69

A single phase induction motor is running at N r.p.m. Its synchronous speed is Ns . If its slip with respect of forward field is s , what is the slip with respect to the backward field ?

(A) s

(B) s−

(C) s1 −^ h

(D) s2 −^ h

MCQ 70

Which one among the following has the highest numerical value in a stepper motor ?

(A) Detent torque

(B) Holding torque

(C) Dynamic torque

(D) Ripple torque

MCQ 71

Which of the following parameters in an induction motor influences the magnetizing reactance to the maximum extent ?

(A) Axial length of the rotor stack

(B) Axial length of the stator stack

(C) Radial length of air gap

(D) Number of slots on the stator

Direction : The following item consist of two statements, one labelled as Assertion ‘A’ and the other labelled as Reason ‘R’. You are to examine these two statement carefully and decide if the Assertion A and the Reason R are individually true and if so, whether the Reason is a correct explanation of the Assertion. Select your answers to these items using the codes given below :

Codes :


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(B) Both A and R are true but R is NOT the correct explanation of A



MCQ 72

Assertion (A) : Under V/f control of induction motor, the maximum value of the developed torque remains constant over a wide range of speed in the sub-synchronous region.

Reason (R) : The magnetic flux is maintained almost constant at the rated value by keeping the ratio V/f constant over the considered speed range.

MCQ 73

A loss-less cylindrical rotor synchronous generator is floating on the system bus-bar after being properly synchronised and is running at no-load. Now, if the prime mover is acting as a mechanical load on the machine, then

(A) the torque developed by the machine will act in the same direction as the prime-mover torque

(B) the torque developed by the machine will act in the opposite direction to that of the prime-mover torque

(C) the machine rotor would fall-back and the induced emf would lag behind the terminal voltage

(D) the machine rotor would over-speed and the induced emf would lead the terminal voltage

MCQ 74

The resultant flux density in the air gap of a synchronous generator is the lowest during

(A) Open circuit

(B) Solid short circuit

(C) Full load

(D) Half load


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MCQ 75

A 50 kW d.c. shunt motor is loaded to draw rated armature current at any given speed. When driven (i) at half the rated speed by armature voltage control and (ii) at 1.5 times the rated speed by field control, what are the approximate output powers delivered by the motor ?

(A) 25 kW in (i) and 75 kW in (ii)

(B) 25 kW in (i) and 50 kW in (ii)

(C) 50 kW in (i) and 75 kW in (ii)

(D) 50 kW in (i) and 50 kW in (ii)

MCQ 76

For a constant supply voltage, what are the effects of inserting a series resistance in the field circuit of a d.c. shunt motor, on its speed and torque ?

(A) Speed will decrease and the torque will decrease

(B) Speed will increase and the torque will increase

(C) Speed will increase and the torque will decrease

(D) Speed will decrease and the torque will increase

MCQ 77

Consider the following statements in respect of d.c. generators :

1. Compensating windings are located in teeth cut out in main poles

2. Compensating windings are series connected so that the armature reaction is aided at any load

3. Compensating windings are series connected for cancellation of the armature reaction at any load

4. Compensating windings are shunt connected to aid the main poles at any load


(A) 1 and 2

(B) 1, 2 and 3

(C) 1 and 3

(D) 2, 3 and 4


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MCQ 78

A self-excited d.c. shunt generator, driven by its prime-mover at the rated speed fails to build up voltage across its terminals at no-load. What reason can be assigned for this ?

(A) The field circuit resistance is higher than the critical resistance

(B) The initial shunt field mmf does not assist the residual magnetism

(C) One of the inter-pole connections is reversed

(D) The brush-axis shifts slightly from the geometrical neutral axis of the machine

MCQ 79

Wave winding is employed in a d.c. machine of

(A) high current and low voltage rating

(B) low current and high voltage rating

(C) high current and high voltage rating

(D) low current and low voltage rating

MCQ 80


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An elementary cylindrical machine has one full-pitch coil in the stator, but the rotor may have (i) two poles or (ii) four poles of permanent magnets.

The time-varying voltage that could be induced in the stator coil for one rotation of the rotor, while the rotor is revolving at a constant speed are shown in the figures A, B, C and D above. Select the correct combination from the code given below :

2-Pole 4-Pole

(A) A D

(B) A B

(C) C D

(D) B C

MCQ 81

What is the form of an air gap flux density waveform of an uncompensated 2-pole d.c. shunt motor at full-load ?


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MCQ 82

Which three-phase connection can be used in a transformer to introduce a phase difference of 30c between its output and corresponding input line voltages ?

(A) Star-delta

(B) Star-star

(C) Delta-delta

(D) Delta-zigzag

MCQ 83

What is the efficiency of an auto-transformer in comparison to that of a two-winding transformer of the same rating ?

(A) Slightly less than that of a two-winding transformer

(B) Same as that of a two-winding transformer

(C) More than that of a two-winding transformer

(D) As low as 1/5th of the efficiency of a two-winding transformer

MCQ 84

A two-winding transformer is converted into an auto-transformer. If we apply additive polarity and subtractive polarity for the connections, then the secondary voltage is 2640 V and 2160 V, respectively. What


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is the ratio of primary to secondary voltage of the original transformer ?

(A) 66 : 54

(B) 54 : 66

(C) 10 : 1

(D) 1 : 10

MCQ 85

Percentage resistance and percentage reactance of a transformer are 1% and 4%, respectively. What is voltage regulation at power factor 0.8 lagging and 0.8 leading ?

(A) 2.4% and 0.8%− , respectively

(B) 3.2% and 1.6%− , respectively

(C) 3.2% and 3.2%− , respectively

(D) 4.8% and 1.6%, respectively

MCQ 86

If P1 and P2 be the iron and copper losses of a transformer at full load, and the maximum efficiency of the transformer is at 75% of the full load, then what is the ratio of P1 and P2 ?

(A) 9/16

(B) 10/16

(C) 3/4

(D) 3/16

MCQ 87

If the iron core of a transformer is replaced by an air core, then the hysteresis losses in the transformer will

(A) increase

(B) decrease

(C) remain unchanged

(D) become zero

MCQ 88

The equivalent circuit of a transformer has the leakage reactances


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, 'X X1 2 and the magnetising reactance Xm . What is the relationship between their magnitudes ?

(A) 'X X X>> >> m1 2

(B) 'X X X<< << m1 2

(C) 'X X X>> m1 2.

(D) 'X X X<< m1 2.

MCQ 89

If the voltage applied to a transformer primary is increased by keeping the V/f ratio fixed, then the magnetizing current and the core loss will, respectively,

(A) decrease and remain the same

(B) increase and decrease

(C) remain the same and remain the same

(D) remain the same and increase

MCQ 90

Which among the following magnetic materials has the highest energy-product to make it a permanent magnet ?

(A) Alnico

(B) Ferrite

(C) Samarium Cobalt

(D) Cobalt-Iron alloy

YEAR 2005

MCQ 91

A coil of 1000 turns is wound on a core. A current of 1 A flowing through the coil creates a core flux of 1 mWb. What is the energy stored in the magnetic field ?

(A) 41 J

(B) 21 J

(C) 1 J

(D) 2 J


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MCQ 92

Match List I (Type of Coil) with List II (Use of Coil) and select the correct answer using the codes given below the lists :

List I List II

A. Sandwitch coils 1. Low voltage coils for currents above 100 A

B. Disc coils 2. High voltage windings of small transformers

C. Cross-over coils 3. Cooling oil is in contact with each turn of the winding

D. Spiral type 4. Shell-type transformer core

Codes :

A B C D

(A) 2 3 4 1

(B) 4 1 2 3

(C) 2 1 4 3

(D) 4 3 2 1

MCQ 93

Match List I (Test) with List II (Quantities) and select the correct answer using the code given below the lists :

List I List II

A. OC Test 1. Copper loss and iron loss

B. SC Test 2. Total losses

C. Sumpner’s Test 3. Iron loss

D. Load Test 4. Copper loss

Codes :

A B C D

(A) 3 4 1 2

(B) 2 1 4 3

(C) 3 1 4 2

(D) 2 4 1 3


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MCQ 94

The exact equivalent circuit of a two-winding transformer is given in the figure above. For affecting simplification, the parallel magnetising branch, consisting of RC and XQ is shifted to the left of the primary leakage impedance ( )r jx1 1+ . This simplification introduces the inaccuracy, in the neglect of :

(A) Voltage-drop in the primary impedance due to the secondary current

(B) Voltage-drop in the primary impedance due to the exciting current

(C) Voltage-drop in the secondary impedance due to the exciting current

(D) Reduction in values of RC and XQ of the exciting circuit

MCQ 95

A single-phase, 10 kVA, 2000/200 V, 50 Hz transformer is connected to form an auto transformer as shown in the figure given above. What are the values of V1 and I2, respectively ?

(A) 2200 V, 55 A

(B) 2200 V, 45 A

(C) 2000 V, 45 A

(D) 1800 V, 45 A


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MCQ 96

Three single phase 1100/220 V transformers are connected to form 3-phase transformer bank. High voltage side is connected in star, and low voltage side is in delta. What are the voltage ratings and turn ratio of 3-phase transformer ?

(A) 19052/220 V, 50

(B) 19052/220 V, 50 3

(C) 11000/381 V, 50 3

(D) 11000/220 V, 50

MCQ 97

If the wave form of the voltage impressed on the primary of a Y-Δ bank contains 5th harmonics, what are the wave forms of the resultant voltages of the primary and the secondary ?

Primary Secondary

(A) Peaked Peaked

(B) Peaked Flat-topped

(C) Flat-topped Peaked

(D) Flat-topped Flat-topped

MCQ 98

Match List I (Machine) with List II (Test) and select the correct answer using the codes given below the lists :

List I List II

A. DC motors 1. Slip test

B. Single phase transformers 2. Blocked rotor test

C. 3-phase induction motrors 3. Swinburne’s test

D. Salient pole alternators 4. Sumpner’s test

Codes :

A B C D

(A) 1 2 4 3

(B) 3 4 2 1

(C) 1 4 2 3


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(D) 3 2 4 1

MCQ 99

Two single phase transformers A and B are connected in parallel, observing all requirements of a parallel operation, except that the induced voltage Ea is slightly greater than Eb ; Zea and Zeb being the equivalent impedances of A and B, both referred to the secondary side.

Under this operating condition with the primary bus-bars being energised, a circulating current will flow :

(A) Only in the secondary windings of A and B

(B) In both the primary and the secondary windings of A and B

(C) In both the primary and the secondary windings of A and B, as well as in the primary side network

(D) In the primary and the secondary windings of A and B and boost the voltages on the secondary side of both A and B

MCQ 100

The armature resistance of a 6-pole lap wound d.c. machine is .0 05 Ω. If the armature is rewound as a wave-winding, what is the armature resistance ?

(A) .0 45 Ω

(B) .0 30 Ω

(C) .0 15 Ω

(D) .0 10 Ω


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MCQ 101

In a d.c. compound generator, “flat-compound” characteristic, required for certain applications, may be obtained by connecting a variable resistance :

(A) A cross the series field

(B) In series with the series field

(C) In parallel with the shunt field

(D) In series with the shunt field

MCQ 102

A 6-pole lap wound d.c. machine armature has 720 conductors and it draws 50 A from supply mains. What is the flux distribution produced by the armature reaction per pole ?

(A) Rectangular in wave shape with a peak of 500AT

(B) Rectangular in wave shape with a peak of 100AT

(C) Triangular in wave shape with a peak of 500AT

(D) Triangular in wave shape with a peak of 1000AT

MCQ 103

Match List I (DC motor) with List II (Characteristic) and select the correct answer using the code given below the lists :

List I List II

A. Comulatively compound motor

1. Fairly constant speed irrespective of the load

B. Differentially compound motor

2. It may start in reverse direction

C. Series motor 3. Definite no-load speed

D. Shunt motor 4. Is never started without load

Codes :

A B C D

(A) 4 1 3 2

(B) 3 2 4 1

(C) 4 2 3 1

(D) 3 1 4 2


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MCQ 104

A synchronous motor is operated from a bus voltage of 1.0 pu and is drawing 1.0 pu zero power factor leading current. Its synchronous reactance is 0.5 pu. What is the excitation emf of the motor ?

(A) 2.0

(B) 1.5

(C) 1.0

(D) 0.5

MCQ 105

In the measurement of ,X Xd q (in ohms), following data are obtained by the slip test on a salient pole machine :

maxId 10 A= minId 6.5 A= maxVd 30 V= minVd 25 V=

Which one of the following is correct ?

(A) , .X X3 3 86d q= =

(B) . , .X X4 615 2 5d q= =

(C) , .X X3 2 5d q= =

(D) . , .X X4 61 3 86d q= =

MCQ 106

What are the conditions to be satisfied for alternator to be synchronised with an incoming supply ?

1. Equal voltage

2. Equal frequency

3. Same power rating

4. Same phase sequence


(A) 2, 3 and 4

(B) 3 and 4

(C) 1, 2 and 3

(D) 1, 2 and 4


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MCQ 107

The stator and the rotor of a 3-phase, 4-pole wound rotor induction motor are excited, respectively, from a 50 Hz and a 30 Hz source of appropriate voltage. Neglecting all losses, what is/are the possible no-load speed/speeds at which the motor would run ?

(A) 1500 rpm and 900 rpm

(B) 2400 rpm and 600 rpm

(C) 2400 rpm only

(D) 600 rpm only

MCQ 108

A starting torque of 80 Nm is developed in an induction motor by an auto-transformer starter with a tapping of 30%. If the tapping of auto-transformer starter is 60%, then what is the starting torque ?

(A) 40 Nm

(B) 160 Nm

(C) 240 Nm

(D) 320 Nm

MCQ 109

Which of the following methods are suitable for the speed control of squirrel cage induction motors ?

1. Voltage control

2. Rotor resistance control

3. Frequency control

4. Pole changing method

Select the correct answer using the codes given below :

(A) 2, 3 and 4

(B) 1, 3 and 4

(C) 1, 2 and 3

(D) 2 and 4

MCQ 110

A capacitor-start single-phase induction motor is used for :

(A) Easy to start loads


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(B) Medium start loads

(C) Hard to start loads

(D) Any type of start loads

MCQ 111

In hand-tool applications, which one of the following single-phase motors is used ?

(A) Shaded pole motor

(B) Capacitor start motor

(C) Capacitor run motor

(D) AC series motor

MCQ 112

What is the phase displacement between primary and secondary voltages for a star-delta, 3-phase transformer connection shown above ?

(A) 30c lagging

(B) 30c leading

(C) 0c

(D) 180c

MCQ 113

What is the shunt resistance component in equivalent circuit obtained by no load test of an induction motor representative of ?

(A) windage and frictional losses only

(B) core losses only

(C) core, windage and frictional losses

(D) copper losses


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MCQ 114

A 400 V D.C. shunt motor takes 5 A at no-load. . ,R R0 5 200a fΩ Ω= =. What is the ratio of speed from full load to no-load, when the D.C. shunt motor takes 50 A on full load ?

(A) 0.94

(B) 0.8

(C) 0.6

(D) 0.4

MCQ 115

A linear ac servomotor must have :

(A) High rotor resistance

(B) High rotor reactance

(C) A large air gap

(D) Both high rotor resistance and reactance

MCQ 116

A wound rotor induction motor runs with a slip of 0.03 when developing full load torque. Its rotor resistance is 0.25 ohm per phase. If an external resistance of 0.50 ohm per phase is connected across the slip rings. What is the slip for full torque ?

(A) 0.03

(B) 0.06

(C) 0.09

(D) 0.1

MCQ 117

Match List I (Characteristics) with List II (Relation) and select the correct answer using the code given below the lists :

List I List II

A. Open circuit characteristics 1. .V v If

B. Internal characteristics 2. .E v If0

C. External characteristics 3. .E v Ia

D. Load saturation curve 4. .V v I


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Codes :

A B C D

(A) 4 3 2 1

(B) 2 1 4 3

(C) 4 1 2 3

(D) 2 3 4 1

MCQ 118

In the block diagram of a separately excited dc motor, how does the armature indeed emf appear as ?

(A) Positive feedback

(B) Negative feedback

(C) Disturbance input

(D) Output

Direction : The following two items consist of two statements, one labelled as Assertion ‘A’ and the other labelled as Reason ‘R’. You are to examine these two statements carefully and decide if the Assertion A and the Reason R are individually true and if so, whether the Reason is a correct explanation of the Assertion. Select your answers to these items using the codes given below :

Codes :(A) Both A and R are true and R is the correct explanation of A




MCQ 119

Assertion (A) : For obtaining improved magnetic properties, the transformer magnetic core is assembled using cold-rolled silicon-steel sheets.

Reason (R) : The laminations for the core could be cut out of the cold-rolled silicon steel sheets, cutting either in the direction of rolling or transverse there of, without affective the magnetic properties in any way.


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MCQ 120

Assertion (A) : In a d.c. generator, even though the armature magnetic field is in quadrature with the main magnetic field, each considered alone, the resultant magnetic field due to interaction of both the fields is shifted backwards by certain angle from the geometrical neutral axis depending upon the load.

Reason (R) : In a d.c. generator, the trailing pole-tips get magnetically saturated as the load reaches its rated value.

YEAR 2004

MCQ 121

The diagram given below shows the connection of a four-wire delta bank for obtaining a 3-phase 4-wire distribution system. The secondary voltages between the terminals are as indicated.

What is the voltage between the terminals b and d in the above system when the primary side is energized from an appropriate symmetrical 3-phase system ?

(A) 230/ 2 V

(B) 230/ 3 V

(C) 115 3 V#

(D) 115 2 V#

MCQ 122

If per unit impedance of two transformers connected in parallel are not equal, then which one of the following statements is correct ?

(A) The power factor of the two transformers will be different from that of the connected load

(B) Transformers will get overloaded


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(C) Dead short circuit occurs

(D) The transformer with higher per unit impedance will share more load.

MCQ 123

Match List I (Machine) with List II (Performance) and select the correct answer using the codes given below :

List I List II

A. Three phase induction motor

1. Adjustable speed

B. Synchronous motor 2. High starting torque

C. D.C. series motor 3. Not self-starting

D. D.C. shunt motor 4. Self-starting

Codes :

A B C D

(A) 3 4 1 2

(B) 4 3 1 2

(C) 3 4 2 1

(D) 4 3 2 1

MCQ 124

In a d.c. machine, for the same value of ,Zφ and N ; which one of the following statements is correct ?

(A) Armature e.m.f. is more with wave winding than with lap winding

(B) Armature e.m.f. is less with wave winding than with lap winding

(C) Armature e.m.f. depends on whether the machine is running as a motor or a generator

(D) Armature e.m.f. is the same as long as the flux density in the air gap remains the same

MCQ 125

Match List I (Constructional Components) with List II (Machines) and select the correct answer using the codes given below :


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List I List II

A. Damper bars 1. Cylindrical-rotor synchronous generator

B. Equalizer rings 2. Salient pole synchronous motor

C. Skewed slots 3. Squirrel-cage induction motor

D. Water-cooling ducts 4. Direct current generator

Codes :

A B C D

(A) 2 4 3 1

(B) 1 3 4 2

(C) 1 4 3 2

(D) 2 3 4 1

MCQ 126

A d.c. shunt motor is excited from an alternating power frequency voltage source. Its brush-axis is rotated by an angle α from the geometrical neutral axis. The torque developed will be proportional to which one of the following ?

(A) sinα

(B) cosα

(C) tanα

(D) cos2α

MCQ 127

Four types of d.c. generators of constant speed are considered (List I). Their external characteristics at constant speed are given in List II. Match List I (Type of d.c. generator) with List II (External characteristics) and select the correct answer using the codes given below :


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Codes :

A B C D

(A) 2 3 1 4

(B) 1 4 2 3

(C) 1 3 2 4

(D) 2 4 1 3

MCQ 128

Consider the following statements : The speed of a d.c. motor can be controlled by the variation of

1. armature voltage

2. field current

3. armature circuit resistance

4. angle of brush shift


(A) 1, 2 and 3

(B) 2, 3 and 4

(C) 1, 3 and 4

(D) 1, 2 and 4

MCQ 129

What is the increase in the torque expressed as percentage of initial torque, if the current drawn by a d.c. series motor is increased from 10 A to 12 A (Neglect saturation) ?


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(A) 21%

(B) 25%

(C) 41%

(D) 44%

MCQ 130

Consider the following statements :

In a d.c. machine, iron loss occurs in

1. armature core

2. yoke

3. pole cores

4. pole shoes


(A) 1 and 4

(B) 1 and 2

(C) 1 and 3

(D) 2 and 3

MCQ 131

Four important parameters of alternators have comparatively larger or smaller values. In comparison to a steam turbine driven alternator, a hydraulically driven machine will have which one of the following combinations ?

Number of armature conductors

Axial length of armature

Number of poles

Operating speed

(A) smaller larger smaller higher

(B) larger smaller larger lower

(C) larger larger smaller lower

(D) smaller smaller larger higher

MCQ 132

Which one of the following is the primary reason for placing field on rotor in an alternator ?


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(A) Smaller power in field circuit

(B) Insulation of high voltage is made easy on stator than on rotor

(C) Large power in stator

(D) Large current in the stator

MCQ 133

Consider the following :

1. Supply voltage

2. Excitation current

3. Maximum value of load angle

The maximum power developed by a synchronous motor is a function of which of the above ?

(A) 1 and 2

(B) 1 and 3

(C) 2 and 3

(D) 1, 2 and 3

MCQ 134

When a 3-phase alternator is suddenly short-circuited at its terminals, the initial value of the short-circuit current is limited by which one of the following ?

(A) Subtransient reactance ''x d

(B) Transient reactance 'x d

(C) Synchronous reactance xs

(D) Sum of '' , 'x xd d and xs

MCQ 135

Which one of the following methods gives more accurate results for determination of voltage regulation of an alternator ?

(A) m.m.f method

(B) Synchronous impedance method

(C) Potier triangle method

(D) American Institution Standard method

MCQ 136


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Which one of the following statements is correct ?

In a salient pole synchronous machine the air gap is

(A) uniform under the whole pole shoe

(B) least under the middle of the pole shoe and increases outwards

(C) largest under the middle of the pole shoe and decreases outwards

(D) least at one end of the pole shoe and increases to the maximum value at the other end.

MCQ 137

Which one of the following is not a necessary condition to be satisfied for synchronizing an incoming alternator to an already operating alternator ?

(A) Same voltage magnitude

(B) Same frequency

(C) Same prime mover speed

(D) Same phase sequence

MCQ 138

Which one of the following statements is correct ? A smaller air gap in a polyphase induction motor helps to

(A) reduce the changes of crawling

(B) increase the starting torque

(C) reduce the chance of cogging

(D) reduce the magnetizing current

MCQ 139


In an induction motor, if the air gap is increased,

(A) its speed will reduce

(B) its efficiency will improve

(C) its power factor will reduce

(D) its breakdown torque will reduce

MCQ 140


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In a 3-phase induction motor, the torque developed is maximum when the rotor circuit resistance per phase is equal to

(A) rotor leakage reactance per phase at standstill

(B) slip times the rotor leakage reactance per phase at standstill

(C) stator resistance per phase

(D) stator leakage reactance per phase

MCQ 141

The supply voltage to an induction motor is reduced by 10%. By what percentage, approximately, will the maximum torque decrease ?

(A) 5%

(B) 10%

(C) 20%

(D) 40%

MCQ 142

Consider the following curve

Which of the following characteristics of the induction motor are represented by the above curve ?

x-axis y-axis

A. Output p.f.

B. Speed p.f.

C. Load efficiency

D. Speed torque


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MCQ 143

A squirrel-cage induction motor having a rated slip of 4% on full load has a starting torque same as the full load torque. Which one of the following statements is correct ?

The starting current is

(A) equal to the full load current

(B) twice the full load current

(C) four times the full load current

(D) five times the full load current

MCQ 144

Which one of the following types of motors is most suitable for a computer printer drive ?

(A) Reluctance motor

(B) Hysteresis motor

(C) Shaded pole motor

(D) Steppzer motor

MCQ 145

For a reluctance type motor, if the stator magnetic field angular velocity is ω and the actual rotor angular velocity is rω , then which one of the following equations is satisfied if the average electromagnetic torque is not zero ?

(A) /2rω ω=

(B) rω ω=

(C) 2 rω ω=

(D) 4 rω ω=

MCQ 146


When a single phase induction motor is excited with single phase a.c. voltage, the magnetic field set up is equivalent to

(A) two fields, rotating in opposite directions with different speeds

(B) two fields, rotating at synchronous speed in opposite directions

(C) two fields, rotating at synchronous speed


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(D) two fields rotating in the same direction but at different speeds

Direction : The following six items consist of two statements, one labelled as Assertion ‘A’ and the other labelled as Reason ‘R’. You are to examine these two statements carefully and decide if the Assertion A and the Reason R are individually true and if so, whether the Reason is a correct explanation of the Assertion. Select your answers to these items using the codes given below :





MCQ 147

Assertion (A) : A single-phase induction motor is not self-starting as such.

Reason (R) : A single-phase induction motor develops only pulsating magnetic field which provides zero torque at standstill.

MCQ 148

Assertion (A) : In the “3-point” type of starter of a d.c. series motor, the “holding coil” for holding the starter handle in the “ON” stud is connected in such a manner that it is short-circuited when the “over load” relay picks up.

Reason (R) : In a d.c. series motor starter, to guard against “racing” due to sudden large reduction of shaft-load, the “holding coil” is connected in series with the armature circuit and the series field winding.

MCQ 149

Assertion (A) : A synchronous motor operating from constant voltage and constant frequency source has a substantially constant resultant air-gap flux.

Reason (R) : If the d.c. field current in this motor can set up the required resultant air-gap flux, the lagging reactive volt-amperes


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drawn from a.c. source is zero.

MCQ 150

Assertion (A) : Transformer is not used in a d.c. line.

Reason (R) : Losses in the d.c. circuit are not negligible.

MCQ 151

Assertion (A) : 3-connected tertiary windings tend to act as an automatic feedback control system.

Reason (R) : In the event of unbalanced secondary load currents, both secondary and primary load voltages are restored to their normal phase magnitude and angle.

MCQ 152

Assertion (A) : If the load requirement of a synchronous motor exceeds the pull-out torque, the synchronous motor action is lost.

Reason (R) : Rotor and stator fields are no longer stationary with respect to each other.

YEAR 2003

MCQ 153

The direction of rotation of a d.c. series motor can be reversed

(A) By interchanging supply terminals

(B) By interchanging field terminals

(C) Either by interchanging supply terminals or by interchanging field terminals

(D) By interchanging supply terminals as well as field terminals

MCQ 154

Match List I (Machine) with List II (Graph) and select the correct answer :

List I List II

A. DC motor 1. Circle diagram


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B. DC generator 2. V-curve

C. Alternator 3. Open circuit characteristics

D. Induction Motor 4. Speed-Torque characteristics

Codes :

A B C D

(A) 4 3 1 2

(B) 3 4 2 1

(C) 4 3 2 1

(D) 3 4 1 2

MCQ 155

The current drawn by a 120 V d.c. motor with back emf of 110 V and armature resistance of 0.4 ohm is

(A) 4 A

(B) 25 A

(C) 274 A

(D) 300 A

MCQ 156

Armature torque of a d.c. motor is function of which of the following factors ?

1. Speed

2. Field Flux

3. Armature Current

4. Residual Magnetism


(A) 2 and 3

(B) 1 and 4

(C) 3 and 4

(D) 1 and 2

MCQ 157


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The dummy coils in d.c. machines are useful to

A. Increase the efficiency

B. Improve the commutation

C. Reduce the cost of the machine

D. Maintain mechanical balance of armature

MCQ 158

The speed of a d.c. shunt motor may be varied by varying

1. Field current

2. Supply voltage

3. Armature circuit


(A) 1, 2 and 3

(B) 1 and 2

(C) 1 and 3

(D) 2 and 3

MCQ 159

If the field of a synchronous motor is under-excited, the power factor will be

(A) Lagging

(B) Leading

(C) Unity

(D) More than unity

MCQ 160

Which of the following graphs represents the speed-torque characteristic of a synchronous motor ?


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MCQ 161

Match List I (Machine components) with List II (Functions) and select the correct answer :

List I List II

A. Damper winding 1. Used in synchronous motor to provide starting torque

B. Interpole winding 2. Used in d.c. generator to neutralize the reactance voltage and cross-magnetizing effect of armature reaction

C. End ring 3. Used to short circuit rotor bars of cage type induction motor


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D. Conservator 4. Used to protect transformers from damage when oil expands due to rise in temperature

Codes :

A B C D

(A) 2 1 3 4

(B) 1 2 4 3

(C) 2 1 4 3

(D) 1 2 3 4

MCQ 162

An induction motor having 8 poles runs at 727.5 rpm. If the supply frequency is 50 Hz, the emf in the rotor will have a frequency of

(A) 1.5 Hz

(B) 48.5 Hz

(C) 51.5 Hz

(D) 75 Hz

MCQ 163

The synchronous reactance is the

(A) Reactance due to armature reaction of the machine

(B) Reactance due to leakage flux

(C) Combined reactance due to leakage flux and armature reaction

(D) Reactance either due to armature reaction or leakage flux.

MCQ 164

Match List I (Type of AC Winding) with List II (Feature of AC Windings) and select the correct answer :

List I List II

A. Single Layer 1. Coil span and pole pitch are equal

B. Double Layer 2. Coil span is shorter than pole pitch


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C. Full pitch 3. Number of slots is equal to number of coils

D. Chorded 4. Number of slots is twice the number of coils

Codes :

A B C D

(A) 4 3 1 2

(B) 3 4 2 1

(C) 4 3 2 1

(D) 3 4 1 2

MCQ 165

Match List I (Machines) with List II (Tests) and select the correct answer :

List I List II

A. Transformer 1. Slip test

B. DC motor 2. Blocked Rotor test

C. Alternator 3. Sumpner’s test

D. Induction motor 4. Swinburne’s test

Codes :

A B C D

(A) 3 4 1 2

(B) 4 3 2 1

(C) 3 4 2 1

(D) 4 3 1 2

MCQ 166

The leakage reactance of a three-phase alternator determined by performing

(A) Open circuit and zero power factor tests

(B) Zero power factor and slip tests

(C) Open-circuit and short-circuit tests


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(D) Short-circuit and slip tests

MCQ 167

Consider the following types of single-phase motors :

1. Capacitor start induction motor

2. Capacitor start and run induction motor

3. Permanent split capacitor motor

4. Shaded pole motor

The correct sequence of these in the ascending order of magnitude of starting torque is

(A) 1, 2, 3, 4

(B) 2, 3, 4, 1

(C) 3, 4, 2, 1

(D) 4, 3, 2, 1

MCQ 168

Which one of the following statements is correct in respect of an induction motor ?

(A) The maximum torque will depend on rotor resistance

(B) Although the maximum torque does not depend on rotor resistance, yet the speed at which maximum torque is produced depends on rotor resistance

(C) The maximum torque will not depend on standstill rotor reactance

(D) The slip of induction motor decreases as torque increases

MCQ 169

The crawling in the induction motor is caused by

(A) Improper design of stator laminations

(B) Low voltages supply

(C) High loads

(D) Harmonics developed in motor

MCQ 170

The rotor slots are slightly skewed in squirrel-cage induction motor to

(A) increase the strengths of rotor bars


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(B) Reduce the magnetic hum and locking tendency of rotor

(C) Economise on the copper to be used

(D) Provide ease of fabrication

MCQ 171

The injected e.m.f. in the rotor of induction motor must have

(A) The same frequency as the slip frequency

(B) The same phase as the rotor emf

(C) A high value for satisfactory speed control

(D) The same phase as the rotor e.m.f. and a high value for satisfactory speed control

MCQ 172

In an induction motor, when the number of stator slots is equal to an integral multiple of rotor slots

(A) There may be a discontinuity in torque-slip characteristics

(B) A high starting torque will be available

(C) The maximum torque will be high

(D) The machine may fail to start

MCQ 173

The use of higher flux density in the transformer design

(A) Reduces the weight per kVA

(B) Increases the weight per kVA

(C) Has no relation with the weight of transformer

(D) Increases the weight per kW

MCQ 174

The function of oil in a transformer is to provide

(A) Insulation and cooling

(B) Protection against lightning

(C) Protection against short circuit

(D) Lubrication


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MCQ 175

A coil of 1000 turns is wound on a core. A current of 1 A flowing through the coil creates a core flux of 1 mWb. The energy stored in the magnetic field is

(A) 0.25 J

(B) 0.5 J

(C) 1 J

(D) 2 J

MCQ 176

Consider the following statements relating to the constructional features of a large power transformer :

1. The conservator is used to maintain the level of oil in the transformer tank

2. The bushing is using to protect transformer insulation against lightning over-voltages

3. The Buchholz relay is an over current relay

4. Silica gel is used to absorb moisture

Which of these statements are correct ?

(A) 1, 2, 3 and 4

(B) 2 and 3

(C) 1 and 4

(D) 1, 2 and 4

MCQ 177

Two transformers operating in parallel will share the load depending upon their

(A) Ratings

(B) Leakage reactance

(C) Efficiency

(D) Per unit impedance

MCQ 178

A 1 kVA, 200/100 V, 50 Hz, single-phase transformer gave the following test results on 50 Hz.


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OC (LV side) : 100 V, 20 watts SC (HV side) : 5 A, 25 watts

It is assumed that no-load loss components are equally divided. The above test were then conducted on the same transformer at 40 Hz.

Test results were :

OC (HV) : 160 V, W watts1

SC (LV) 10 A, W watts2

Neglecting skin effect, W1 and W2 will be(A) 16 25W Wwatts, watts1 2= =

(B) 25 , 31.25W Wwatts watts1 2= =

(C) 20 , 20W Wwatts watts1 2= =

(D) 14.4 , 25W Wwatts watts1 2= =

Direction : The following four items consists of two statements, one labelled as Assertion ‘A’ and the other labelled as Reason ‘R’. You are to examine these two statements carefully and decide if the Assertion A and the Reason R are individually true and if so, whether the Reason is a correct explanation of the Assertion. Select your answers to these items using the codes given below.

Codes :



(C) A is true and R is false


MCQ 179

Assertion (A) : DC series motors are suitable for cranes.

Reason (R) : DC series motors provide high starting torque

MCQ 180

Assertion (A) : The short circuit ratio (SCR) of a three-phase alternator should be high.

Reason (R) : A high value of SCR will decrease the value of voltage regulation and will increase the maximum power output.


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MCQ 181

Assertion (A) : Single-phase induction motor is not self-starting.

Reason (R) : No rotating magnetic field is set up in the air gap of a single-phase induction motor.

MCQ 182

Assertion (A) : A double-cage induction motor has good starting characteristics.

Reason (R) : At starting, a large portion of starting current flows in the bottom cage.

YEAR 2002

MCQ 183

A d.c. series motor is accidentally connected to single-phase a.c. supply. The torque produced will be

(A) of zero average value

(B) oscillating

(C) steady and unidirectional

(D) pulsating and unidirectional

MCQ 184

The ‘synchronous-impedance method’ of finding the voltage regulation by a cylindrical rotor alternator is generally considered as

(A) a pessimistic method because saturation is not considered

(B) an optimistic method because saturation is not considered

(C) a fairly accurate method even if power factor is not taken into account while determining synchronous impedance

(D) a fairly accurate method when power factor is taken into account while determining synchronous impedance.

MCQ 185

Generally the no-load losses of an electrical machine is represented in its equivalent circuit by a

(A) parallel resistance with a low value


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(B) series resistance with a low value

(C) parallel resistance with a high value

(D) series resistance with a high value

MCQ 186

The power factor of a synchronous motor

(A) improves with increase in excitation and may even become leading at high excitations

(B) decreases with increase in excitation

(C) is independent of its excitation

(D) increases with loading for a given excitation

MCQ 187

When the excitation of normally operating unloaded salient-pole synchronous motor suddenly gets disconnected, it continues to run as a

(A) Schrage motor

(B) Spherical motor

(C) Switched-reluctance motor

(D) Variable-reluctance motor

MCQ 188

A 6-pole, 3-phase alternator running at 1000 rpm supplies to an 8-pole, 3-phase induction motor which has a rotor current of frequency 2 Hz. The speed at which the motor operates is

(A) 1000 rpm

(B) 960 rpm

(C) 750 rpm

(D) 720 rpm

MCQ 189

For maximum current during ‘Slip Test’ on a synchronous machine, the armature mmf aligns along

(A) d-axis

(B) q-axis


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(C) 45c to d-axis

(D) 45c to q-axis

MCQ 190

Match List I (Name of test) with List II (Result) and select the correct answer :

List I List II

A. Open circuit and short circuit tests

1. Leakage reactance

B. Open circuit and zero power factor tests

2. Direct axis synchronous reactance

C. Slip test 3. Quadrature axis synchronous reactance

D. Maximum lagging current test

4. Ratio of direct axis synchronous reactance to quadrature axis synchronous reactance

Codes :

A B C D

(A) 1 2 4 3

(B) 1 2 3 4

(C) 2 1 4 3

(D) 2 1 3 4

MCQ 191

A 3-phase 50 MVA,10 kV generator has a reactance of 0.2 ohm per phase. Hence the per-unit value of the reactance on a base of 100 MVA, 25 kV will be

(A) 1.25

(B) 0.625

(C) 0.032

(D) 0.32

MCQ 192


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The results of a ‘Slip Test’ for determining direct-axis ( )Xd and quadrature-axis ( )Xq reactance of a star-connected, salient-pole alternator are given below :

Phase values : 108 96 12 10V V IV; V, A,I Amax min max min= = = = . Hence the two reactances will be

(A) 10.8X ohmsd = and 8X ohmsq =

(B) 9X ohmsd = and 9.6X ohmsq =

(C) 9.6X ohmsd = and 9X ohmsq =

(D) 8X ohmsd = and 10.8X ohmsq =

MCQ 193

Stepper motors are widely used because of

(A) wide speed range

(B) large rating

(C) no need for field control

(D) compatibility with digital systems

MCQ 194

A 2-phase servomotor in control system uses

(A) drag-cup rotor

(B) solid cylindrical rotor without slots or windings

(C) ordinary squirrel-cage rotor

(D) slip-ring rotor with inherent low rotor resistance

MCQ 195

Capacitance in a single-phase induction motor is used for

(A) improving the power factor

(B) improving the starting torque

(C) starting the motor

(D) reducing the harmonics

MCQ 196

Match List I (Transformer) with List II (Voltage ratio) and select the correct answer :


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List I List II

A. Power transformer 1. 230 V/230 V

B. Auto transformer 2. 220 V/240 V

C. Welding transformer 3. 400 V/100 V

D. Isolation transformer 4. 132 kV/11 kV

Codes :

A B C D

(A) 4 2 3 1

(B) 4 2 1 3

(C) 2 4 1 3

(D) 2 4 3 1

MCQ 197

A two-winding transformer is used as an auto-transformer. The kVA rating of the auto-transformer compared to the two-winding transformer will be

(A) 3 times

(B) 2 times

(C) 1.5 times

(D) same

MCQ 198

A 20 kVA, 2000/200 V, 1-phase transformer has name-plate leakage impedance of 8%. Voltage required to be applied on the high-voltage side to circulate full-load current with the low-voltage winding short-circuited will be

(A) 16 V

(B) 56.56 V

(C) 160 V

(D) 568.68 V

MCQ 199

The full-load copper-loss and iron-loss of a transformer are 6400 W and 5000 W respectively. The copper-loss and iron-loss at half load


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will be, respectively

(A) 3200 W and 2500 W

(B) 3200 W and 5200 W

(C) 1600 W and 1250 W

(D) 1600 W and 5000 W

MCQ 200

In a 100 kVA , 1100/220 V, 50 Hz single-phase transformer with 2000 turns on the high-voltage side, the open-circuit test result give 200 V, 91 A, 5 kW on low-voltage side. The core-loss component of current is, approximately

(A) 9.1 A

(B) 22.7 A

(C) 45.0 A

(D) 91 A

MCQ 201

Match List I (Types of electrical loads) with List-II (Torque-speed characteristics) and select the correct answer :

List I List II

A. Hoist 1. Torque speed 2\ ^ h

B. Fans 2. Torque speed\ ^ h

C. Machine Tools (Lathe, Milling machine etc.)

3. Constant Torque

D. Loads with fluid friction 4. /1Torque speed\ ^ h

Codes :

A B C D

(A) 1 3 2 4

(B) 1 3 4 2

(C) 4 1 3 2

(D) 3 1 2 4

MCQ 202

phaneendra

Cross-Out


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For a given torque, reducing the diverter-resistance of a d.c. series motor

(A) increases its speed but armature current remains the same

(B) increases its speed demanding more armature current

(C) decreases its speed demanding less armature current

(D) decreases its speed but armature current remains the same

MCQ 203

Match List I (Types of motors) with List II (Characteristics) and select the correct answer :

List I List II

A. d.c. series motor 1. Constant speed

B. d.c. shunt motor 2. High starting torque

C. 3-phase induction motor 3. Low starting torque

D. Synchronous motor 4. Poor stability

Codes :

A B C D

(A) 2 4 3 1

(B) 3 1 2 4

(C) 2 1 3 4

(D) 3 4 2 1

MCQ 204

Match List I with List II and select the correct answer :

List I List II

A. Commutation 1. Inductive load

B. V-curves 2. Capacitive load

C. Free wheeling diode 3. Interpole

D. Overlap 4. Source inductance

5. Synchronous motor

Codes :

A B C D


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(A) 3 5 1 4

(B) 2 4 3 5

(C) 3 4 1 5

(D) 2 5 3 4

MCQ 205

Possible three-to-three phase transformer connection for parallel operation is

(A) Y YtoΔ Δ− −

(B) YtoΔ Δ Δ− −

(C) Y Y Yto Δ− −

(D) Y YtoΔ Δ− −

MCQ 206

Match List I with List II and select the correct answer :

List I List II

A. Silica gel 1. Bushing

B. Porcelain 2. Buccholz relay

C. Mercury 3. Tank

D. Fins 4. Breather

Codes :

A B C D

(A) 2 1 4 3

(B) 4 3 2 1

(C) 2 3 4 1

(D) 4 1 2 3

MCQ 207

A 4 kVA, 400/200 V single-phase transformer has resistance of 0.02 p.u. and reactance of 0.06 p.u. Its actual resistance and reactance referred to h.v. side, are respectively

(A) 0.2 ohm and 0.6 ohm

(B) 0.8 ohm and 2.4 ohm


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(C) 0.08 ohm and 0.24 ohm

(D) 2 ohm and 6 ohm

MCQ 208

A certain R-L series combination is connected across a 50 Hz single-phase ac supply. If the instantaneous power drawn was found to be negative for 2 milliseconds in one cycle, the ‘power factor angle’ of the current must be

(A) 9c

(B) 18c

(C) 36c

(D) 45c

MCQ 209

Stepper motors are mostly used for

(A) high power requirements

(B) control system applications

(C) very high speed of operation

(D) very low speed of operation

MCQ 210

A delta/star transformer has a phase-to-phase voltage transformation ratio of K

K star phase voltagedelta phase voltage=c m

The line-to-line voltage ratio of star/delta connection is given by

(A) /K 3

(B) K

(C) K 3

(D) /K3

MCQ 211

Two 10 kV/440 V, 1-phase transformers of ratings 600 kVA and 350 kVA are connected in parallel to share a load of 800 kVA. The reactances of the transformers, referred to the secondary side are0.0198 Ω and .0 0304 Ω respectively (resistances negligible). The load


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shared by the two transformer will be, respectively

(A) 484.5 kVA and 315.5 kVA

(B) 315.5 kVA and 484.5 kVA

(C) 533 kVA and 267 kVA

(D) 267 kVA and 533 kVA

MCQ 212

Two transformers, with equal voltage ratio and negligible excitation current, connected in parallel, share load in the ratio of their kVA rating only, if their p.u. impedances (based on their own kVA) are

(A) equal

(B) in the inverse ratio of their ratings

(C) in the direct ratio of their ratings

(D) purely reactive

Direction : The following three items consist of two statements, one labelled as Assertion ‘A’ and the other labelled as Reason ‘R’. You are to examine these two statements carefully and decide if the Assertion A and the Reason R are individually true and if so, whether the Reason is a correct explanation of the Assertion. Select your answers to these items using the codes given below :





MCQ 213

Assertion (A) : Even at no load a large three-phase squirrel-cage induction motor is started at reduced voltage.

Reason (R) : If a large three-phase squirrel-cage induction motor with no load is started at full voltage, it is damaged.

MCQ 214

Assertion (A) : A single-phase induction motor is not self-starting.


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Reason (R) : A three-phase induction motor is self-starting.

MCQ 215

Assertion (A) : The distribution transformers are designed for minimum core losses.

Reason (R) : Primary windings of distribution transformers are energized throughout the day.

YEAR 2001

MCQ 216

In an electromechanical energy conversion device, the developed torque depends upon

(A) stator field strength and torque angle

(B) stator field and rotor field strengths

(C) stator field and rotor field strengths and the torque angle

(D) stator field strength only

MCQ 217

Consider the following statements :

The use of interpoles in dc machines is to counteract the

1. reactance voltage

2. demagnetizing effect of armature mmf in the commutating zone

3. cross-magnetizing effects of armature mmf in the commutating zone

Which of these statement(s) is/are correct ?

(A) 1 and 2

(B) 2 and 3

(C) 1 and 3

(D) 3 alone

MCQ 218

In an alternator, if m is the number of slots per pole per phase and γ is the slot pitch angle, then the breadth or the distribution factor for the armature winding is


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(A) sin

sin

m m2

2γ

γ

(B) sin

sin

m

m

2

2γ

γ

a

a

k

k

(C) sin

sinm

m

2

2γ

γ

(D) sin

sin m

2

2γ

γ

a

a

k

k

MCQ 219

The current drawn by a 220 V dc motor of armature resistance .0 5 Ω and back emf 200 V is

(A) 40 A

(B) 44 A

(C) 400 A

(D) 440 A

MCQ 220

Match List I (Type of machine) with List II (Characteristics/application) and select the correct answer :

List I List II

A. dc shunt generator 1. Electric traction

B. dc series motor regulation 2. Has good voltage

C. Level compounded dc generator

3. Must have residual flux

D. dc series generator 4. Used as boosters

Codes :

A B C D

(A) 4 1 2 3

(B) 3 2 1 4

(C) 4 2 1 3


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(D) 3 1 2 4

MCQ 221

A dc shunt generator when driven without connecting field winding shows an open circuit terminal voltage of 12 V. When field winding is connected and excited, the terminal voltage drops to zero because

(A) field resistance is higher than critical resistance

(B) there is no residual magnetism in the field circuit

(C) field winding has got wrongly connected

(D) there is a fault in armature circuit

MCQ 222

Match List I (dc motors) with List II (Characteristics) labelled (1, 2, 3 and 4) and select the correct answer :

List I

A. Shunt motor

B. Series motor

C. Cumulative compound motor

D. Differential compound motor

List II

Codes :

A B C D

(A) 3 2 1 4

(B) 4 1 2 3

(C) 3 1 2 4


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(D) 4 2 1 3

MCQ 223

In the ‘V’ curve shown in the above figure for a synchronous motor, the parameter of y and x coordinates are, respectively

(A) armature current and field current

(B) power factor and field current

(C) armature current and torque

(D) torque and field current

MCQ 224

The advantage of the double squirrel-cage induction motor over single cage rotor is that its

(A) efficiency is higher

(B) power factor is higher

(C) slip is larger

(D) starting current is lower

MCQ 225

An induction motor when started on load does not accelerate up to full speed but runs at 1/7 th of the rated speed. The motor is said to be

(A) locking

(B) plugging

(C) crawling

(D) cogging


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MCQ 226

Match List I (Equivalent circuit parameter) with List II (Values) for a 50 MVA three phase alternator and select the correct answer :

List I List II

A. Armature resistance 1. 1 pu

B. Synchronous reactance 2. 0.1 pu

C. Leakage reactance 3. 0.01 pu

Codes :

A B C

(A) 1 2 3

(B) 3 1 2

(C) 3 2 1

(D) 1 3 2

MCQ 227

Synchronous condenser means

(A) a synchronous motor with capacitor connected across stator terminals to improve pf

(B) a synchronous motor operating at full load with leading pf

(C) an over-excited synchronous motor partially supplying mechanical load, and also improving pf of the system to which it is connected

(D) an over-excited synchronous motor operating at no-load with leading pf used in large power stations for improvement of pf

MCQ 228

Match List I (Tests) with List II (Machines) and select the correct answer :

List I List II

A. No-load and blocked rotor test

1. Transformer

B. Sumpner’s test 2. Induction motor

C. Swinburne’s test 3. Synchronous motor

4. dc motor


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Codes :

A B C

(A) 1 4 2

(B) 2 1 4

(C) 3 4 2

(D) 3 1 4

MCQ 229

Match List I (Regulation method) with List II (Relevant phasor) and select the correct answer :

List I List II

A. Synchronous impedance method

1. emf phasor

B. mmf mehtod 2. Predominantly mmf phasor

C. Zero power factor (ZPF) method

3. Both emf and mmf phasors

D. American Standard Association method

4. emf and mmf phasors including saturation

Codes :

A B C D

(A) 1 2 3 4

(B) 1 2 4 3

(C) 2 1 3 4

(D) 2 1 4 3

MCQ 230

In a cylindrical rotor synchronous machine, the phasor addition of stator and rotor mmfs is possible because

(A) two mmfs are rotating in opposite direction

(B) two mmfs are rotating in same direction at different speed

(C) two mmfs are stationary with respect to each other

(D) one mmfs is stationary and the other mmf is rotating


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MCQ 231

The rotor power output of 3-phase induction motor is 15 kW. The rotor copper losses at a slip of 4% will be

(A) 600 W

(B) 625 W

(C) 650 W

(D) 700 W

MCQ 232

Skewing of the rotor in a three-phase squirrel-cage induction motor reduces

(A) noise, parasitic torque, starting torque and pullout torque

(B) noise and parasitic torque, but increases starting torque and pullout torque

(C) noise and pullout torque, but increases parasitic torque and starting torque

(D) noise, parasitic torque and starting torque, but increases pullout torque

MCQ 233

In a shaded-pole induction motor, the rotor runs from the

(A) shaded portion to the unshaded portion of the pole while the flux in the former leads that of the latter

(B) shaded portion to the unshaded portion of the pole while the flux in the former lags that in the latter

(C) unshaded portion to the shaded portion while the flux in the former leads that in the latter

(D) unshaded portion to the shaded portion while the flux in the former lags that in the latter

MCQ 234

The torque of a reluctance motor can be effectively increased by

(A) increasing reluctance of the magnetic circuit along the direct axis

(B) decreasing the reluctance of the magnetic circuit along the quadrature axis

(C) increasing the ratio of the quadrature axis reluctance to direct


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axis reluctance

(D) decreasing the ratio of quadrature axis reluctance to direct axis reluctance

MCQ 235

The starting current of a 3φ induction motor is 5 times the rated current, while the rated slip is 4%. The ratio of starting torque to full-load torque is

(A) 0.6

(B) 0.8

(C) 1.0

(D) 1.2

MCQ 236

A single-phase transformer when supplied from 220 V, 50 Hz has eddy current loss of 50 W. If the transformer is connected to a voltage of 330 V, 50 Hz, the eddy current loss will be

(A) 168.75 W

(B) 112.5 W

(C) 75 W

(D) 50 W

MCQ 237

In case of auto-transformers, which of the following statements are correct ?

1. An auto-transformer requires less copper as compared to a conventional, 2-winding transformer of the same capacity.

2. An auto-transformer provides isolation between the primary and secondary windings

3. An auto-transformer has less leakage reactance as compared to the conventional, 2-winding transformer of the same capacity.


(A) 1, 2 and 3

(B) 1 and 2

(C) 1 and 3


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(D) 2 and 3

MCQ 238

If Pc and Psc represent core and full-load ohmic losses respectively, the maximum kVA delivered to load corresponding to maximum efficiency is equal to rated kVA multiplied by

(A) /P Pc sc

(B) /P Pc sc

(C) /P Pc sc2

^ h

(D) /P Psc c2

^ h

MCQ 239

Match List I (Motors) with List II (Applications) and select the correct answer :

List I List II

A. dc series motor 1. Shearing and pressing

B. Squirrel-cage induction motor

2. Haulage and hoisting

C. dc shunt motor 3. Rolling mill

Codes :

A B C

(A) 1 2 3

(B) 2 3 1

(C) 3 1 2

(D) 3 2 1

MCQ 240

Switched reluctance motor means

(A) salient pole synchronous motor without excitation winding

(B) a stepper motor with salient poles

(C) synchronous motor with salient poles on stator and rotor

(D) a stepper motor with closed loop control and with rotor position sensor