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Transformers Multiple-Choice Worksheet

Total questions: 161

Worksheet time: 1hrs 21mins

Name
Class
Date
1.

A certain transformer has 400 turns in the primary winding and 2,000 turns in the secondary winding. The turns ratio is:

a)

0.2

b)

0.4

c)

5

d)

25

2.

The primary winding of a transformer has 110 V ac. What is the secondary voltage if the turns ratio is 1/5?

a)

550V

b)

10V

c)

220V

d)

110V

3.

A transformer

a)

Changes AC to DC

b)

Changes DC to AC

c)

Steps up or down DC voltage.

d)

Steps up or down AC voltage

4.

Which of the following does not change when a transformer is working?

a)

Current.

b)

Voltage.

c)

Frequency.

d)

All of the above.

5.

What is the working principle of a single phase transformer?

a)

Faraday’s law.

b)

Lenz’s law.

c)

Archimedes's law.

d)

Einstein’s law.

6.

What does EMF stand for?

a)

Electro-motive force.

b)

Engine-motor frequency.

c)

Electro-motor force.

d)

Engine-motive force.

7.

The unit of measurement of transformer capacity is

a)

VA or KVA

b)

W OR KW

c)

both a and b right

d)

both a and b wrong

8.

Material used for construction of transformer core is:

a)

Wood.

b)

Copper.

c)

Aluminium.

d)

Silicon steel

9.

In transformer the energy is conveyed from primary to secondary

a)

Through to secondary.

b)

Through air.

c)

By the flux

d)

None of the above.

10.

An ideal transformer has 750 turns on the primary coil and 50 turns on the secondary coil. The current in the secondary coil is 3 A and the primary voltage is 30 V. The secondary voltage is

a)

2V

b)

3V

c)

20V

d)

15V

11.

An ideal transformer has 750 turns on the primary coil and 50 turns on the secondary coil. The current in the secondary coil is 3 A and the primary voltage is 30 V. The current flowing through the primary coil

a)

0.1A

b)

0.2A

c)

0.4A

d)

0.3A

12.

The voltage transformation ratio of a transformer is equal to the ratio of

a)

primary turns to secondary turns

b)

secondary current to primary current

c)

secondary induced e.m.f. to primary induced e.m.f.

d)

secondary terminal voltage to primary applied voltage

13.

The maximum load that a power transformer can carry is limited by its

a)

temperature rise

b)

dielectric strength of oil

c)

voltage ratio

d)

copper loss

14.

If a transformer is continuously operated the maximum temperature rise will occur in

a)

core

b)

windings

c)

tank

d)

any of the above

15.

Losses which occur in rotating electric machines and do not occur in transformers are

a)

friction and windage losses

b)

magnetic losses

c)

hysteresis and eddy current losses

d)

copper losses

16.

For given applied voltage, with the increase in frequency of the applied voltage

a)

eddy current loss will decrease

b)

eddy current loss will increase

c)

eddy current loss will remain unchanged

d)

none of the above

17.

The size of a transformer core will depend on

a)

frequency

b)

area of the core

c)

flux density of the core material

d)

(A) and (B) both

18.

The transformer oil should have _____ volatility and _____ viscosity.

a)

low, low

b)

high, high

c)

low, high

d)

high, low

19.

For the parallel operation of single phase transformers it is necessary that they should have

a)

same efficiency

b)

same polarity

c)

same kVA rating

d)

same number of turns on the secondary side

20.

If the supply frequency to the transformer is increased, the iron loss will

a)

not change

b)

decrease

c)

increase

d)

any of the above

21.

The magnetising current of a transformer is usually small because it has

a)

small air gap

b)

large leakage flux

c)

laminated silicon steel core

d)

fewer rotating parts

22.

Delta/star transformer works satisfactorily when

a)

load is balanced only

b)

load is unbalanced only

c)

on balanced as well as unbalanced loads

d)

none of the above

23.

Star/star transformers work satisfactorily when

a)

load is unbalanced only

b)

load is balanced only

c)

on balanced as well as unbalanced loads

d)

none of the above

24.

In a transformer the resistance between its primary and secondary is

a)

zero

b)

1 ohm

c)

1000 ohms

d)

infinite

25.

The thickness of laminations used in a transformer is usually

a)

0.4 mm to 0.5 mm

b)

4 mm to 5 mm

c)

14 mm to 15 mm

d)

25 mm to 40 mm

26.

The purpose of providing iron core in a step-up transformer is

a)

to provide coupling between primary and secondary

b)

to increase the magnitude of mutual flux

c)

to decrease the magnitude of magnetizing current

d)

to provide all above features

27.

The maximum efficiency of a distribution transformer is

a)

at no load

b)

at 50% full load

c)

at 80% full load

d)

at full load

28.

Power transformers are designed to have maximum efficiency at

a)

nearly full load

b)

70% full load

c)

50% full load

d)

no load

29.

The primary winding of a transformer has a 120 V ac supply. What is the value of secondary voltage if the turn ratio is 10?

a)

120 V

b)

12 V

c)

12000 V

d)

1200 V

30.

If the supply frequency (f) of a transformer decreases, the effect of frequency on the transformer's secondary output voltage?

a)

Remain the same

b)

Decreases

c)

Increases

d)

All of these

31.

Transformer core are laminated in order to

a)

Reduce copper loss

b)

Minimize eddy current loss

c)

Reduce eddy current and hysteresis loss

d)

Reduce hysteresis loss

32.

The short circuit test in the transformer is performed on

a)

High voltage side

b)

light voltage side

c)

Both

d)

Either option A or B.

33.

The secondary voltage is 440 Volt, and primary voltage is 220 Volt, then a comparison of the secondary coil and primary coil is

a)

4/1

b)

5/2

c)

2/1

d)

7/5

34.

The transformer ratings are expressed in terms of

a)

KW (Kilo-Watt)

b)

Volts

c)

KVAR (Kilo-Volt-Ampere-Reactive)

d)

KVA (Kilo-Volt-Ampere)

35.

Oil is provided in an oil-filled transformer for

a)

Lubrication

b)

Cooling

c)

Insulation

d)

Both cooling and Insulation

36.

The efficiency of a transformer is maximum when

a)

Eddy current loss = iron loss

b)

Hysteresis loss = copper loss

c)

Eddy current loss = hysteresis loss

d)

Iron loss = copper loss

37.

Which winding in a transformer has a greater number of turns

a)

Constant voltage winding

b)

Low voltage winding

c)

Secondary winding

d)

High voltage winding

38.

The necessary condition for the parallel operation of two single-phase transformers is that they must have the same

a)

Turn ratio

b)

Polarity

c)

KVA rating

d)

Both option A & B

39.

In an autotransformer, the primary and secondary are ....... coupled.

a)

Magnetically coupled

b)

Electrically coupled

c)

Both magnetically and electrically coupled

d)

None of these

40.

The maximum load that a power transformer can carry is limited by its

a)

Voltage ratio

b)

Dielectric strength of the coil

c)

Copper loss

d)

Temperature rise

41.

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

42.

An induction motor works with

a)

DC only

b)

AC only

c)

Both AC & DC

d)

None of these

43.

The stator frame in an induction motor is used to

a)

Hold the armature stampings in position

b)

Ventilate the armature

c)

Protect the whole machine

d)

Provide return path for the flux

44.

The stator core of a 3-phase induction motor is laminated in order to reduce the

a)

Eddy current loss

b)

Hysteresis loss

c)

Both eddy current and hysteresis loss

d)

Weight of the stator

45.

If all the stator coils of an induction motor are connected for the same magnetic polarity, there will be formed an equal number of

a)

Rotor poles with same polarity

b)

Rotor poles with opposite polarity

c)

Consequent poles with opposite polarity

d)

Consequent poles with same polarity

46.

The induction motor shaft should be

a)

Hollow

b)

Stiff

c)

Flexible

d)

Any of these

47.

The induction motor is made of

a)

Mild steel

b)

Cast iron

c)

High speed steel

d)

Stainless steel

48.

In a 3-phase squirrel cage induction motor

a)

Rotor conductors are short circuited through end rings

b)

Rotor conductor ends are short circuited through slip rings

c)

Rotor conductors are kept open

d)

None of the above

49.

The squirrel cage rotor of a 6-pole induction motor can be used for ____ induction motor

a)

Only 6-pole

b)

6 or 12 poles

c)

Any number of poles in an induction motor

d)

None of the above

50.

The squirrel cage induction motors are provided with blades in order to

a)

Facilitate cooling of rotor

b)

Balance the rotor dynamically

c)

Eliminate noise

d)

None of these

51.

The rotor of a 3-phase wound rotor induction motor is provided with

a)

Single phase winding

b)

Three phase winding

c)

Heavy copper or aluminum bars placed in rotor slots

d)

Heavy short-circuited end rings

52.

In a 3-phase slip ring induction motor, the rotor winding terminals are brought out through slip rings to

a)

Connect extra resistance across them during starting

b)

Connect them either in star or in delta as per need

c)

Connect to 3-phase AC supply

d)

Close the rotor circuit externally

53.

The rotor winding for a 3-phase slip ring induction motor having delta connected stator must be connected in

a)

Delta

b)

Star

c)

Delta or star according to need

d)

None of the above

54.

In a 3-phase slip ring induction motor, brushes are connected to

a)

External star connected resistors

b)

DC supply

c)

3-phase AC supply

d)

Equalizing coils

55.

At s=0s = 0 the torque of an induction motor is

a)

0

b)

Equal to full load

c)

Very high

d)

Nearly zero

56.

A 3 phase slip ring induction motor has

a)

Short circuit rotor

b)

Wound rotor

c)

Double cage rotor

d)

All of the above

57.

Copper loss in rotor of a induction motor

a)

Is lost in friction

b)

Is lost in windage

c)

Appears as noise

d)

Appears as heat

58.

The difference between the synchronous speed and the actual speed of an induction motor is known as

a)

Lag

b)

Slip

c)

Back lash

d)

Regulation

59.

An induction motor works with

a)

DC only

b)

AC only

c)

Both AC and DC

d)

None of them

60.

As the load on an induction motor increases

a)

Its power factor goes on increasing up to full load then it falls again

b)

Its power factor goes on increasing

c)

Its power factor goes on decreasing

d)

Its power factor remains unchanged

61.

In a squirrel cage induction motor, the starting current is

a)

Half the rated current

b)

Equal to the rated current

c)

2 to 3 times the rated current

d)

5 to 7 times the rated current

62.

A 3 phase induction motor takes a line current of 30 A30\,\text{A} when started by direct switching. If a star-delta starter is used, the line current would be

a)

10 A

b)

5 A

c)

30 A

d)

17.32 A

63.

Direct on line starting current as compared with star-delta starting current is approximately

a)

5 times

b)

4 times

c)

3 times

d)

2 times

64.

For induction motors, normally

a)

The stator winding is connected to supply and the rotor winding is open circuited

b)

Both the stator and the rotor winding are connected to supply

c)

The stator winding is connected to supply and the rotor winding is short circuited

d)

The rotor winding is connected to supply and the stator winding is short circuited

65.

A wound rotor induction motor can be distinguished from squirrel cage induction motor by

a)

Presence of slip rings

b)

Diameter of shaft

c)

Direction of rotation

d)

Size of frame

66.

As the load on induction motor goes on increasing

a)

Power factor remains practically unchanged

b)

Power factor goes on increasing up to rated load then it starts falling

c)

Power factor goes on increasing even beyond full load

d)

Power factor goes on decreasing

67.

Full load current of a 20 kW20\,\text{kW} , 3 phase, 50 Hz50\,\text{Hz} , 440 V440\,\text{V} induction motor is

a)

78 A

b)

48 A

c)

38 A

d)

10 A

68.

A two-pole induction motor has a synchronous speed of 3600 rpm3600\,\text{rpm} . The frequency of supply to the stator is

a)

60 Hz

b)

50 Hz

c)

40 Hz

d)

36 Hz

69.

Two induction motors A and B have no load operating power factor of 0.150.15 and 0.250.25 respectively. It can be concluded that

a)

Motor B will have more windage losses as compared to motor A

b)

Motor A will have more windage losses as compared to motor B

c)

Motor B will be bigger in size as compared to motor A

d)

Motor A will be bigger in size as compared to motor B

70.

If a squirrel cage induction motor runs hot the possible cause could be

a)

Over load

b)

Uneven airgap

c)

Low supply frequency

d)

Any of the above

71.

In case of slip ring induction motors, the starting torque can be increased by

a)

adding external resistance and inductance to the rotor

b)

adding external resistance to the rotor

c)

adding external inductance to the rotor

d)

adding external capacitance to the motor

72.

In case the air gap in an induction motor is increased

a)

power factor will increase

b)

the magnetizing current of the rotor will decrease

c)

the magnetizing current of the rotor will increase

d)

noise will increase

73.

Various methods for starting a 3-phase induction motor are given. Which method will require six stator terminals?

a)

DOL

b)

Auto transformer

c)

Rheostat

d)

Star-delta

74.

If an induction machine is run at above synchronous speed, it acts as

a)

a synchronous motor

b)

an induction generator

c)

an induction motor

d)

none of the above

75.

A 60 HP, 440 V, 50 Hz, 3-phase 6 pole, induction motor runs at 960 rpm at full load. The slip s and frequency of rotor f are

a)

s = 2.5, f = 125

b)

s = 4.0, f = 2.0

c)

s = 4.0, f = 2.5

d)

s = 4.0, f = 20

76.

A 4-pole, 3-phase, 400 V, induction motor runs at 480 rpm when the slip is 4%. Supply frequency must be

a)

100 Hz

b)

50 Hz

c)

25 Hz

d)

16 2/3 Hz

77.

When the supply to an induction motor is switched on, in the beginning, the induced emf in the rotor will be

a)

zero

b)

minimum

c)

maximum

d)

same as during running

78.

A 3-phase induction motor has a copper loss of 80 watts and slips of 4%. The rotor input must be

a)

8 kW

b)

4 kW

c)

2 kW

d)

0.2 kW

79.

A slip ring induction motor is preferred to squirrel cage induction motor when

a)

fluctuating loads are anticipated

b)

frequent starting is necessary

c)

low starting torque is desired

d)

high starting torque is desired

80.

For a squirrel cage induction motor running on no load

a)

rotor induced emf is very small

b)

slip is very large

c)

rotor current is large

d)

power factor is large

81.

Generally, in alternator divided winding rotor is preferred to a conventional winding rotor, because it gives

a)

Better damping

b)

Less harmonics

c)

More efficiency

d)

None of these

82.

For a two pole, 50 Hz, 3 phase synchronous motor the speed of rotating magnetic field is

a)

1000 rpm

b)

2000 rpm

c)

3000 rpm

d)

3500 rpm

83.

The open circuit voltage and short circuit current of a 3 phase, star connected alternator are 1050 V and 250 A respectively. Its field current is 12 A. Then the synchronous impedance of alternator will be

a)

1.34 ohm

b)

1.69 ohm

c)

2.42 ohm

d)

2.85 ohm

84.

Which type of rotor is generally used for high speed alternators or turbo alternators?

a)

Salient pole type

b)

Projected pole type

c)

Smooth cylindrical type

d)

Both (A) & (B)

85.

If the field of the synchronous motor is overexcited then its power factor will be

a)

Lagging

b)

Leading

c)

Unity

d)

Zero

86.

To have effective synchronization without any interruption, the necessary conditions which must be satisfied are

a)

The terminal voltage and frequency of the incoming machine must be same as that of bus bar voltage and frequency

b)

With respect to the external load, the phase of alternator voltage must be identical with that of the bus bar voltage

c)

Both (A) and (B)

d)

None of these

87.

Back emf in case of synchronous motor depends on the

a)

Excitation given to the field winding

b)

Speed

c)

Both (A) and (B)

d)

None of the above

88.

If two mechanically coupled alternators deliver power at 50 Hz and 60 Hz respectively, then the highest speed of alternators will be

a)

1200 rpm

b)

1500 rpm

c)

600 rpm

d)

300 rpm

89.

The synchronous motor as a synchronous condenser is used to

a)

Improve power factor

b)

Reduce hunting

c)

Both (A) and (B)

d)

None of these

90.

An over excited synchronous motor operating on no load condition is called as

a)

Synchronous capacitor

b)

Synchronous condenser

c)

Both (A) and (B)

d)

None of these

91.

When the excitation of a synchronous motor is changed keeping the load constant then the

a)

Power factor will change

b)

I, cos φ remains constant

c)

Both (a) and (b)

d)

None of these

92.

In a synchronous motor the torque produced will be maximum when load angle is equal to

a)

0° electrical

b)

90° electrical

c)

180° electrical

d)

360° electrical

93.

If the load on a synchronous motor increases then its

a)

Current drawn by motor increases and load angle decreases

b)

Current drawn by motor decreases and load angle remains constant

c)

Current drawn by motor remains constant and load angle increases

d)

Current drawn by motor increases and load angle also increases

94.

With increase in load, the speed of synchronous motor

a)

Increases

b)

Decreases

c)

Remains constant

d)

None of the above

95.

A synchronous motor is started by using damper winding. When the motor runs at synchronous speed then the induced emf in the damper winding will be

a)

Zero

b)

Maximum

c)

Half of the terminal voltage

d)

None of these

96.

The method used for starting synchronous motor is/are

a)

Using pony motors

b)

Using damper windings

c)

As a slip ring induction motor

d)

All of the above

97.

Synchronous motors are

a)

Self starting

b)

Not self starting

c)

Both (A) and (B)

d)

None of these

98.

Synchronous motor works on the principle of

a)

Mutual induction

b)

Electromagnetic induction

c)

Magnetic locking

d)

None of these

99.

A synchronous motor draws 2 MVA at a power factor of 0.8 leading. If the efficiency developed in the motor is 90% then the power developed is equal to

a)

1212 kW

b)

1440 kW

c)

1676 kW

d)

1767 kW

100.

The increase in mechanical torque in case of alternator will

a)

Increase the armature current and reduce the power factor

b)

Increase the armature current and improve the power factor

c)

Decrease the armature current and improve the power factor

d)

Decrease the armature current and reduce the power factor

101.

The change in excitation of the two alternators operating in parallel causes

a)

Only the kVAR sharing of two alternators without disturbing kW sharing of the two machines

b)

Only the kW sharing of two alternators without disturbing kVAR sharing of the two machines

c)

Both the kVAR sharing and kW sharing of two alternators

d)

None of the above

102.

If a 3 phase alternator is short circuited at its terminal, then the initial value of short circuit current will be limited by

a)

Synchronous reactance

b)

Transient reactance

c)

Sub transient reactance

d)

All of the above

103.

In a salient pole synchronous generator direct axis reactance is

a)

Greater than quadrature axis reactance

b)

Less than quadrature axis reactance

c)

Equal to quadrature axis reactance

d)

None of the above

104.

The direct axis reactance XdX_d and quadrature axis reactance XqX_q obtained from slip test are

a)

XdX_d = minimum voltage/minimum current, XqX_q = maximum voltage/maximum current

b)

XdX_d = minimum voltage/maximum current, XqX_q = maximum voltage/maximum current

c)

XdX_d = maximum voltage/minimum current, XqX_q = minimum voltage/maximum current

d)

XdX_d = maximum voltage/maximum current, XqX_q = minimum voltage/minimum current

105.

The synchronous generator supplies leading power factor and lagging power factor respectively when it is

a)

Over excited, under excited

b)

Over excited, over excited

c)

Under excited, under excited

d)

Under excited, over excited

106.

The electrical power output of an alternator will be maximum, if the power angle is equal to

a)

0∘0^{\circ}

b)

45∘45^{\circ}

c)

90∘90^{\circ}

d)

180∘180^{\circ}

107.

The synchronous generator is loaded for obtaining zero power factor characteristics by using

a)

D.C. motor

b)

Lamp load

c)

Synchronous motor

d)

All of these

108.

An ideal synchronous motor has no starting torque because the

a)

Rotor is made up of salient poles

b)

Relative velocity between the stator and the rotor mmfs is zero

c)

Relative velocity between the stator and rotor mmfs is not zero

d)

Rotor winding is highly reactive

109.

In a synchronous motor

a)

The rotor mmf and stator mmf are stationary with respect to each other

b)

Rotor mmf rotates slightly faster in comparison to stator mmf

c)

Stator mmf rotates slightly faster than rotor mmf

d)

None of the above

110.

A synchronous machine is of revolving armature and stationary field type. Under steady running condition the air-gap field

a)

Rotates at synchronous speed with respect to stator

b)

Rotates at synchronous speed in the direction of rotation of rotor

c)

Remains stationary with respect to stator

d)

Remains stationary with respect to rotor

111.

In a synchronous machine, if the armature field axis is ahead of the field flux axis in the direction of rotation, the machine is operating as a

a)

Synchronous motor

b)

Synchronous generator

c)

Asynchronous motor

d)

Asynchronous generator

112.

In a 3‑phase synchronous motor

a)

Remains constant at all loads

b)

Varies with load

c)

Varies with speed

d)

Varies with power factor

113.

In a 3‑phase synchronous motor, the armature mmf leads the air‑gap flux and the air‑gap flux leads the field mmf

a)

The filed mmf leads the air gap flux leads the armature mmf

b)

The armature mmf leads the air gpap flux and air gap flux leads the field mmf

c)

The armature mmf leads the air gap flux and air gap flux lags behind the field mmf

d)

None of the above

114.

The relative speed between the magnetic fields of stator and rotor under steady‑state operation is zero for

a)

A d.c. machine

b)

An induction machine

c)

A synchronous machine

d)

All of the above

115.

A 3‑phase synchronous motor has

a)

High starting torque

b)

No starting torque

c)

Low starting current

d)

Low starting torque

116.

A 1010 ‑pole, 25 Hz25\,\text{Hz} alternator is directly coupled to and is driven by a 60 Hz60\,\text{Hz} synchronous motor. What is the number of poles for the synchronous motor?

a)

4848

b)

1212

c)

2424

d)

1616

117.

A 3‑phase synchronous motor needs dc supply for excitation

a)

Continuously

b)

At the starting instant only

c)

Of stator

d)

None of these

118.

The armature current of a synchronous motor on no load

a)

Leads the applied voltage by 90∘90^{\circ}

b)

Lags behind the applied voltage by 90∘90^{\circ}

c)

Is in phase with the applied voltage

d)

Is zero

119.

As the load is increased on a synchronous motor, its speed

a)

Decreases

b)

Increases

c)

Remains constant and additional load is supplied by shift in relative position of the rotor with respect to the stator rotating magnetic field

d)

Remains constant for some time and then falls abruptly

120.

The synchronous motor meets an increase in load by taking more armature current because

a)

The rotor pole falls back relative to the stator pole causing an increase in motor current

b)

The back emf decreases causing an increase in motor current

c)

The rotating field is strengthened causing an increase in motor current

d)

None of the above

121.

In a d.c. machine, the form of armature reaction mmf is

a)

Triangular

b)

Sinusoidal

c)

Saw‑tooth

d)

Rectangular

122.

For a low‑reluctance path for the flux in an armature, the permeability of the material should be

a)

High

b)

Low

c)

Both (A) and (B)

d)

None of these

123.

In a D.C. machine, the form of armature reaction mmf is

a)

Triangular

b)

Sinusoidal

c)

Saw‑tooth

d)

Rectangular

124.

If AA is the number of parallel paths and PP is the number of poles, then the number of parallel paths in lap winding and in wave winding is

a)

A=PA=P , A=2PA=2P

b)

A=2PA=2P , A=PA=P

c)

A=2A=2 , A=PA=P

d)

A=PA=P , A=2A=2

125.

In a self‑excited generator, if the series field opposes the shunt field, then the generator is

a)

Cumulatively compounded

b)

Differentially compounded

c)

Series generator

d)

None of these

126.

Laminations or stampings are used to reduce eddy‑current losses. The orientation of laminations should be such that

a)

They are perpendicular to the paths of eddy current and flux both

b)

They are parallel to the paths of eddy current and flux both

c)

They are perpendicular to the paths of eddy current and parallel to the flux

d)

They are parallel to the path of eddy current and perpendicular to the flux

127.

With the increase in temperature, the speed of series and shunt motor will respectively

a)

Increase, decrease

b)

Decrease, increase

c)

Increase, increase

d)

Decrease, decrease

128.

If EbE_b is the back emf of a d.c. motor and VV is the terminal voltage, then the condition for maximum power is

a)

Eb=VE_b=V

b)

Eb=2VE_b=2V

c)

Eb=V2E_b=\dfrac{V}{2}

d)

Eb=V2E_b=V\sqrt{2}

129.

The armature reaction in a d.c. machine causes distortion in the main field flux. This effect of armature reaction can be reduced by

a)

Increasing the length of air‑gap

b)

Decreasing the length of air‑gap

c)

Increasing the number of poles

d)

Decreasing the number of poles

130.

D.C. shunt motors are commonly used in

a)

Cranes

b)

Electric traction

c)

Elevators

d)

Lathe machines

131.

The brush contact losses in a d.c. machine are

a)

Inversely proportional to the square of current

b)

Directly proportional to the square of current

c)

Inversely proportional to the current

d)

Directly proportional to the current

132.

When a d.c. motor runs on no load, then

a)

Back emf is almost equal to applied voltage

b)

Back emf will be greater than applied voltage

c)

Back emf will be less than applied voltage

d)

None of these

133.

If the number of conductors and the speed of a lap‑wound generator are both doubled, then the generated emf will be

a)

Remain the same

b)

Twice the former

c)

Four times the former

d)

Half of the former

134.

If a shunt motor is started with its field winding open, then

a)

It will rotate at the same speed as with its field winding closed

b)

It will rotate at less speed than with its field winding closed

c)

It will rotate at dangerously high speed

d)

None of these

135.

Electrical power output in a d.c. generator is equal to

a)

Electrical power developed in armature - copper losses

b)

Mechanical power input - iron and friction losses

c)

Electrical power developed in armature - iron and copper losses

d)

Mechanical power input -iron and friction losses - copper losses

136.

Differential compound motors are mainly used in

a)

Drilling machines

b)

Elevators

c)

Electric traction

d)

Not suitable for any practical application

137.

Which motor is not suitable for the application of centrifugal pumps?

a)

series motor

b)

shunt motor

c)

Cumulatively compounded motor

d)

Differential compound motor

138.

The speed of permanent magnet d.c. motor cannot be controlled by

a)

Flux control method

b)

Rheostatic control method

c)

Electronic circuits

d)

None of these

139.

If a resistance is added in series with the field winding of a d.c. shunt motor, then its

a)

Both speed and torque decreases

b)

Both speed and torque increases

c)

Speed decreases, torque increases

d)

Speed increases, torque decreases

140.

Which method is suitable for the speed control below and above the normal rated speed of a d.c. shunt motor?

a)

Flux control method

b)

Rheostatic control method

c)

Voltage control method

d)

All of these

141.

In armature voltage control (rheostatic control) for speed control in a d.c. shunt motor, a variable resistance is

a)

Added in series with the armature

b)

Added in series with the field

c)

Connected across armature

d)

Both in series with armature and field

142.

In the flux control method for controlling the speed of a d.c. shunt motor, the speed control is not possible

a)

Below normal rated speed

b)

Above normal rated speed

c)

Both (A) and (B)

d)

None of these

143.

A series-wound motor is also called a universal motor because

a)

It will run equally well using either an ac or a dc voltage source

b)

It will run well below and above rated speed

c)

It can be used in all kinds of applications

d)

None of these

144.

Speed of d.c. shunt motors are controlled by

a)

Flux control method

b)

Rheostatic control method

c)

Voltage control method

d)

All of these

145.

In electric traction, which type of motor is generally used?

a)

Shunt motor

b)

Series motor

c)

Cumulative compound motor

d)

Differential compound motor

146.

In a differential compound d.c. motor, with increase in load, speed

a)

Increases

b)

Decreases

c)

Remains same

d)

None of these

147.

The speed–current characteristics are shown in the figure. Identify the different curves: 1, 2, 3, and 4.

a)

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

b)

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

c)

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

d)

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

148.

If a d.c. series motor is started on very light load or on no load then

a)

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

b)

It will run at very low speed

c)

Load does not affect the speed of a d.c. series motor

d)

None of these

149.

The speed–armature current characteristics of a d.c. series motor is

a)

Rectangular hyperbola

b)

Linear

c)

Parabolic

d)

Parabolic till saturation and then linear

150.

The speed of a d.c. series motor is

a)

Directly proportional to both armature current and torque developed

b)

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

c)

Directly proportional to the square of the armature current and square root of torque developed

d)

Inversely proportional to the square of the armature current and square of torque developed

151.

The starting torque developed in the d.c. series motor and in d.c. shunt motor is

a)

High, low

b)

High, moderate

c)

Moderate, low

d)

Moderate, high

152.

 Keeping the field excitation constant, the constant of proportionality between back emf and armature speed of d.c. motor is

a)

Twice of the proportionality constant between developed torque and armature current

b)

 Half of the proportionality constant between developed torque and armature current

c)

Same as that of proportionality constant between developed torque and armature current

d)

 None of these

153.

   As the load on d.c. motor increases, the current drawn by motor

a)

Increases

b)

Decreases

c)

Remains same

d)

None of these

154.

   A 220 V, d.c. motor draws an armature current of 20 A. Its armature resistance is 0.6 ohm. Then the induced emf in the motor will be

a)

 195 V

b)

202 V

c)

208 V

d)

215 V

155.

The compensating windings are used to neutralize the armature reaction in d.c. machines. These windings are connected

a)

Across armature

b)

In series with armature

c)

Both (A) and (B)

d)

 None of these

156.

In a D.C. machine, the commutator provides

a)

Half wave rectification

b)

Full wave rectification

c)

Semi controlled rectification

d)

Uncontrolled rectification

157.

The armature in d.c. machines are always placed on rotor

a)

 Otherwise commutation will not be possible

b)

Otherwise there will not be any induced emf

c)

Otherwise current will not flow

d)

 All of these

158.

In a d.c. machine, the eddy current losses mainly occurs in

a)

Armature

b)

windings

c)

Yoke

d)

At brush contact

159.

For the construction of the armature of a d.c. machine, the best suited material is

a)

cast iron

b)

Silicon steel

c)

Carbon

d)

All of these

160.

For the construction of the armature of a d.c. machine, the best suited material is

a)

 cast iron

b)

Silicon steel

c)

Carbon

d)

All of these

161.

If the armature current of dc series motor has become twice then the torque will become

a)

 Twice of the former

b)

Four times of the former

c)

One fourth of the former

d)

Remains same

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