field windings are on rotor and instead of armature windings, commutator windings exist

field windings are on rotor and armature windings are on stator

field windings are on stator and armature windings are on rotor

field windings are on rotor and instead of armature windings, commutator windings exist

distributed field windings are on rotor

For a DC welding Motor-Generator set, which type of DC generator is used?

Differential compound DC generator

Cumulative compound DC generator

Two generators are running in parallel. One of the generators may run as motor for which of the following reasons?

he direction of that generator is reversed

he speed of that generator is increased

he field of that generator is weakened

hat generator takes large share of loads

Commutator of electrical machines is made up of:

Iron lamination and copper segments

Directions: It consists of two statements, one labeled as the ‘Statement (I)’ and the other as ‘Statement (II)’. Examine these two statements carefully and select the answer using the codes given below:Statement (I): When the armature-iron of a dc machine rotates, it goes through the influence of the north and the south poles, thus causing cyclic variations of the linked magnetic flux and resulting in the occurrence of hysteresis loss in the armature core.Statement (II): The laminated armature construction limits the hysteresis loss to a lower value.

Statement (I) is false but statement (II) is true

Statement (I) and Statement (II) are individually true and statement (II) is the correct explanation of statement (II)

Statement (I) and Statement (II) are individually true but statement (II) is not the correct explanation of statement (I)

Statement (I) is true but statement (II) is false

Statement (I) is false but statement (II) is true

Let T be the net torque developed by the rotor runs at ω rad/s. What is the mechanical power developed?

\({P_{mech}} = \frac{{2\pi \omega }}{{60}}T\)

\({P_{mech}} = \frac{\omega }{{60}}T\)

Direct on-line starters are not suitable for starting large DC motors because:

the starting torque becomes very low

large voltage drop may occur in the supply main

the starting torque becomes very low

Assuming a uniform distribution of current over the armature surface conductors, the shape of the resultant armature m.m.f. in space of a loaded dc machine is a symmetrical

Triangular wave with its peak along the pole axis

Triangular wave with its peak along the inter-polar axis

Triangular wave with its peak along the pole axis

Rectangular wave with its central axis coinciding with the inter-polar axis

Rectangular wave with its central axis coinciding with the pole axis

In DC machines, the magnetisation curve is the relationship between:

air gap flux and armature voltage

air gap flux and field winding current

air gap flux and armature voltage

In a DC generator, whenever the rotating armature coil is parallel to the lines of flux:

the flux linked with the coil is maximum

the rate of change of flux linkage is minimum

the flux linked with the coil is minimum and rate of change of flux linkage is maximum

the flux linked with the coil is maximum

the flux linked with the coil is maximum and rate of change of flux linkage is minimum

Directions: It consists of two statements, one labelled as the ‘Statement (I)’ and the other as ‘Statement (II). Examine these two statements carefully and select the answer using the codes given below:Statement (I): In a dc shunt generator the ‘build-up’ induced voltage, at its terminals, is given by the intersection point of the Field Resistance Line (FRL) with the No-Load Characteristics (NLC) of the machine.Statement (II): The generator fails to build up any voltage at its terminals, when the slope of the FRL is higher than that of the straight line portion of the NLC.

Both Statement (I) and Statement (II) are individually true but Statement (II) is not the correct explanation of Statement (I)

Both Statement (I) and Statement (II) are individually true and Statement (II) is the correct explanation of Statement (I)

Both Statement (I) and Statement (II) are individually true but Statement (II) is not the correct explanation of Statement (I)

Statement (I) is true but Statement (II) is false

Statement (I) is false but Statement (II) is true

378 + Mcqs in D.C. Generators in Electrical Engineering Page 3 McqOptions

101.	For a simplex wave wound generator, emf generated path is given by _______.Φ: Flux / pole in WeberZ: Total number of armature conductorsP: Number of generator polesN: Armature rotation in revolution per minute (rpm)
A.	(ΦPN) / 120
B.	(ΦZPN) / 120
C.	(ΦZPN) / 180
D.	(ΦZP) / N60
Answer» C. (ΦZPN) / 180

Discussion

102.	How many parallel paths are there in a 6-pole simplex lap-wound DC machine?
A.	3
B.	2
C.	12
D.	6
Answer» E.

Discussion

103.	In DC generators, current to the external circuit from the armature is given through
A.	Commutator
B.	slip rings
C.	Solid connections
D.	Yoke
Answer» B. slip rings

Discussion

104.	For which operation of a DC motor is generally preferred over an AC motor
A.	Low speed operation
B.	High speed operation
C.	Fixed speed operation
D.	Variable speed operation
Answer» E.

Discussion

105.	In a d.c machine iron losses occurs in
A.	the yoke
B.	the pole shoe
C.	the armature
D.	the field
Answer» D. the field

Discussion

106.	A dc shunt motor runs at 1000 rpm at no load from 250 V dc supply and takes 9 A. The motor resistances are Rsh = 250 Ω and Ra = 0.5 Ω. Calculate the speed when loaded and taking 41 A.
A.	123000/115 rpm
B.	12300/115 rpm
C.	115000/123 rpm
D.	11500/123 rpm
Answer» D. 11500/123 rpm

Discussion

107.	A 220-V DC machine has an armature resistance of 1 Ω. If the full-load current is 20 A, the difference between the induced voltage when the machine runs as motor and as a generator is:
A.	20 V
B.	10 V
C.	40 V
D.	0 V
Answer» D. 0 V

Discussion

108.	In case of a simple lap wound generator, the number of parallel path is equal to the:
A.	flux per pole
B.	number of poles
C.	emf induced
D.	speed of the machine
Answer» C. emf induced

Discussion

109.	In case of DC generators, the critical resistance is equal to the resistance of the:
A.	load
B.	armature
C.	field
D.	brushes
Answer» D. brushes

Discussion

110.	In a DC machine, the current in the armature winding is:
A.	Alternating
B.	Unidirectional
C.	Less than the field current
D.	Zero
Answer» B. Unidirectional

Discussion

111.	At 1200 rpm the induced emf of a dc machine is 200 V. For an armature current of 15 A the electromagnetic torque produced would be:
A.	23.8 N-m
B.	238 N-m
C.	2000 N-m
D.	3000 N-m
Answer» B. 238 N-m

Discussion

112.	A differentially compound DC generator has its series and shunt field providing 20% and 80% flux respectively. The series field is suddenly short circuited without changing the load. Then the terminal voltage ignoring all the resistances
A.	Remains same
B.	Reduce by 20%
C.	Increases by 33.33%
D.	Reduces by 80%
Answer» D. Reduces by 80%

Discussion

113.	Consider the following factors for a dc machine:1. Interpole2. Armature resistance3. Reduction in field currentWhich of the above factors are responsible for decrease in terminal voltage of a shunt generator?
A.	1 and 2 only
B.	2 and 3 only
C.	1 and 3 only
D.	1, 2 and 3
Answer» C. 1 and 3 only

Discussion

114.	In electrical machines, the process of electromechanical energy conversion is
A.	a reversible one
B.	not reversible
C.	lossless
D.	without mechanical motion
Answer» B. not reversible

Discussion

115.	Calculate the force experienced by the conductor, with L = 0.5 m and B = 4 Wb/m2, when the armature current is 5 Amp?
A.	5 N
B.	10 N
C.	15 N
D.	20 N
Answer» C. 15 N

Discussion

116.	In a d.c. machine,
A.	field windings are on rotor and armature windings are on stator
B.	field windings are on stator and armature windings are on rotor
C.	field windings are on rotor and instead of armature windings, commutator windings exist
D.	distributed field windings are on rotor
Answer» C. field windings are on rotor and instead of armature windings, commutator windings exist

Discussion

117.	A four-pole generator, having lap wound armature winding, has 51 slots, each slot containing 20 conductors. What will be the voltage generated in the machine when driven at 1500 rpm, assuming the flux per pole to be 7.0 mWb?
A.	278.5 V
B.	188.5 V
C.	168.5 V
D.	178.5 V
Answer» E.

Discussion

118.	For a DC welding Motor-Generator set, which type of DC generator is used?
A.	Differential compound DC generator
B.	DC Series generator
C.	DC Shunt generator
D.	Cumulative compound DC generator
Answer» B. DC Series generator

Discussion

119.	_______is used as a coolant in electrical machines to increase their efficiency.
A.	H2
B.	CO2
C.	SF6
D.	N2
Answer» B. CO2

Discussion

120.	In a dc machine, for the same number of slots and same current in the armature conductor, which one of the following will induce higher emf?
A.	Lap winding
B.	Wave winding
C.	Compensating winding
D.	Pole winding
Answer» C. Compensating winding

Discussion

121.	A separately excited DC generator has an armature resistance of 0.1Ω and negligible armature inductance. At rated field current and rated rotor speed, its open-circuit voltage is 200 V. When this generator is operated at half the rated speed, with half the rated field current, an uncharged 1000 μF capacitor is suddenly connected across the armature terminals. Assume that the speed remains unchanged during the transient. At what time (in microsecond) after the capacitor is connected will the voltage across it reach 25V?
A.	62.25
B.	69.3
C.	73.25
D.	77.3
Answer» C. 73.25

Discussion

122.	In a D.C. generator in order to reduce sparking at brushes, the self-induced e.m.f. in the coil is neutralized by all of the following except
A.	nterpoles
B.	ummy coils
C.	ompensating winding
D.	hifting of axis of brushes
Answer» C. ompensating winding

Discussion

123.	The terminal voltage of a series generator is 150 V when the load current is 5 A. If the load current is increased to 10 A, the terminal voltage will be
A.	50 V
B.	ess than 150 V
C.	reater than 150 V
D.	one of the above
Answer» D. one of the above

Discussion

124.	Two generators A and B have 6 poles each. Generator A has wave wound armature while generator B has lap wound armature. The ratio of the induced e.m.f. is generator A and B will be
A.	: 3
B.	: 1
C.	: 2
D.	: 3
Answer» C. : 2

Discussion

125.	Following energized winding of a D.C. machine should not be opened as it would produce high inductive voltage which may be dangerous to personnel and may cause its own insulation failure.
A.	eries field
B.	ompensating field
C.	nter pole field
D.	hunt field
Answer» E.

Discussion

126.	In any rotating machine that part which houses the conductors and in which e.m.f. induced is to be utilised is called
A.	otor
B.	tator
C.	ield
D.	rmature
Answer» E.

Discussion

127.	Two generators are running in parallel. One of the generators may run as motor for which of the following reasons?
A.	he direction of that generator is reversed
B.	he speed of that generator is increased
C.	he field of that generator is weakened
D.	hat generator takes large share of loads
Answer» E.

Discussion

128.	Two D.C. shunt generators, each with armature resistance of 0.02 ohm and field resistance of 50 ohm run in parallel and supply a total current of 1000 amperes to the load circuit. If their e.m.fs. are 270 V and 265 V, their bus bar voltage will be
A.	70 V
B.	67.5 V
C.	65 V
D.	57.4 V
Answer» C. 65 V

Discussion

129.	Commutator of electrical machines is made up of:
A.	Copper segments
B.	Iron laminations
C.	Iron lamination and copper segments
D.	None of these
Answer» B. Iron laminations

Discussion

130.	Directions: It consists of two statements, one labeled as the ‘Statement (I)’ and the other as ‘Statement (II)’. Examine these two statements carefully and select the answer using the codes given below:Statement (I): When the armature-iron of a dc machine rotates, it goes through the influence of the north and the south poles, thus causing cyclic variations of the linked magnetic flux and resulting in the occurrence of hysteresis loss in the armature core.Statement (II): The laminated armature construction limits the hysteresis loss to a lower value.
A.	Statement (I) and Statement (II) are individually true and statement (II) is the correct explanation of statement (II)
B.	Statement (I) and Statement (II) are individually true but statement (II) is not the correct explanation of statement (I)
C.	Statement (I) is true but statement (II) is false
D.	Statement (I) is false but statement (II) is true
Answer» D. Statement (I) is false but statement (II) is true

Discussion

131.	Let T be the net torque developed by the rotor runs at ω rad/s. What is the mechanical power developed?
A.	Pmech = 2πωT
B.	\({P_{mech}} = \frac{{2\pi \omega }}{{60}}T\)
C.	\({P_{mech}} = \frac{\omega }{{60}}T\)
D.	Pmech = ωT
Answer» E.

Discussion

132.	Direct on-line starters are not suitable for starting large DC motors because:
A.	the motor may not start
B.	large voltage drop may occur in the supply main
C.	the starting torque becomes very low
D.	the motor my runaway
Answer» C. the starting torque becomes very low

Discussion

133.	If an electrical machine converts mechanical energy into electrical energy, it is called ______.
A.	Generator
B.	Transformer
C.	DC Motor
D.	AC Motor
Answer» B. Transformer

Discussion

134.	A 4 pole lap wound DC generator has a developed power of P watts and a voltage of E volts. Two adjacent brushes of the machines are removed as they are worn out. If the machine operates with the remaining brushes, the developed voltage and the power obtained in the machines are
A.	E,P
B.	E/2,P/2
C.	E,P/4
D.	E,P/2
Answer» D. E,P/2

Discussion

135.	Assuming a uniform distribution of current over the armature surface conductors, the shape of the resultant armature m.m.f. in space of a loaded dc machine is a symmetrical
A.	Triangular wave with its peak along the inter-polar axis
B.	Triangular wave with its peak along the pole axis
C.	Rectangular wave with its central axis coinciding with the inter-polar axis
D.	Rectangular wave with its central axis coinciding with the pole axis
Answer» B. Triangular wave with its peak along the pole axis

Discussion

136.	A DC short-shunt compound generator has the following specifications: Ra = 0.05Ω, Rsf = 0.3Ω, Rshf = 200Ω and voltage drop per brush is 1 V. Find the generated EMF when the generator deliver a load of 30 A at 220 V.
A.	240.62 V
B.	232.56 V
C.	220 V
D.	230 V
Answer» C. 220 V

Discussion

137.	If shunt generator delivers 100 A at 200 V, and the resistance of the shunt field and armature are 100 ohm and 0.01 ohm respectively, the generated e.m.f. will be
A.	212 V
B.	205 V
C.	210 V
D.	201.02 V
Answer» E.

Discussion

138.	In DC machines, the magnetisation curve is the relationship between:
A.	torque and speed
B.	armature voltage and speed
C.	air gap flux and field winding current
D.	air gap flux and armature voltage
Answer» D. air gap flux and armature voltage

Discussion

139.	For C coils and P poles, the commutator pitch for simplex wave winding is:
A.	\(\frac{{2C \pm 1}}{{P/2}}\)
B.	\(\frac{{2C + 1}}{{P/2}}\)
C.	\(\frac{{2C - 2}}{{P/2}}\)
D.	\(\frac{{C \pm 1}}{{P/2}}\)
Answer» E.

Discussion

140.	Armature reaction of an unsaturated DC machine results in _______ effect.
A.	Cross-Magnetising
B.	Demagnetising
C.	Axial Magnetising
D.	Two-Pole Magnetising
Answer» B. Demagnetising

Discussion

141.	Determine the flux per pole for 6-pole dc machine having 240 wave connected conductors, which generates an open circuit voltage of 500 volt, which is running at 1000 rpm.
A.	0.129 Wb
B.	0.021 Wb
C.	0.042 Wb
D.	7 mWb
Answer» D. 7 mWb

Discussion

142.	Armature coil of a DC machine is usually made up of
A.	Mica
B.	Copper
C.	Brass
D.	Graphite
Answer» C. Brass

Discussion

143.	“A time–varying flux causes an induced electromotive force”. What law does this statement represent?
A.	Ampere’s law
B.	Faraday’s law
C.	Lenz’s law
D.	Field form of Ohm’s law
Answer» C. Lenz’s law

Discussion

144.	In a DC generator, whenever the rotating armature coil is parallel to the lines of flux:
A.	the rate of change of flux linkage is minimum
B.	the flux linked with the coil is minimum and rate of change of flux linkage is maximum
C.	the flux linked with the coil is maximum
D.	the flux linked with the coil is maximum and rate of change of flux linkage is minimum
Answer» C. the flux linked with the coil is maximum

Discussion

145.	Let V be the terminal voltage, Ia be the armature current and Ish be the shunt current. The power delivered to a load of a self-exited dc shunt generator is:
A.	V × Ish W
B.	V × Ia W
C.	V × (Ia - Ish) W
D.	V × (Ia + Ish) W
Answer» D. V × (Ia + Ish) W

Discussion

146.	Directions: It consists of two statements, one labelled as the ‘Statement (I)’ and the other as ‘Statement (II). Examine these two statements carefully and select the answer using the codes given below:Statement (I): In a dc shunt generator the ‘build-up’ induced voltage, at its terminals, is given by the intersection point of the Field Resistance Line (FRL) with the No-Load Characteristics (NLC) of the machine.Statement (II): The generator fails to build up any voltage at its terminals, when the slope of the FRL is higher than that of the straight line portion of the NLC.
A.	Both Statement (I) and Statement (II) are individually true and Statement (II) is the correct explanation of Statement (I)
B.	Both Statement (I) and Statement (II) are individually true but Statement (II) is not the correct explanation of Statement (I)
C.	Statement (I) is true but Statement (II) is false
D.	Statement (I) is false but Statement (II) is true
Answer» B. Both Statement (I) and Statement (II) are individually true but Statement (II) is not the correct explanation of Statement (I)

Discussion

147.	A DC generator works on the principle of:
A.	Faraday’s law
B.	Steinmetz’s law
C.	Lenz’s law
D.	Ampere’s law
Answer» B. Steinmetz’s law

Discussion

148.	In an unloaded shunt generator, when switch is closed, a small field current is produced which leads to generation of still larger voltages due to addition of.
A.	Armature voltage
B.	Residual flux voltage
C.	Generated voltage
D.	Voltage drop
Answer» C. Generated voltage

Discussion

149.	A 220 V DC shunt motor takes 3A at no-load. It draws 25 A when running at full-load at 1500 rpm. The armature and shunt resistances are 0.5 Ω and 220 Ω, respectively. The no-load speed in rpm.
A.	1549.57 rpm
B.	1497.23 rpm
C.	1579.32 rpm
D.	1500 rpm
Answer» D. 1500 rpm

Discussion

150.	In lap winding of a P pole dc machine, the number of brushes are equal to
A.	2
B.	4
C.	P
D.	2P
Answer» D. 2P

Discussion

Explore topic-wise MCQs in Electrical Engineering.

For a simplex wave wound generator, emf generated path is given by _______.Φ: Flux / pole in WeberZ: Total number of armature conductorsP: Number of generator polesN: Armature rotation in revolution per minute (rpm)

How many parallel paths are there in a 6-pole simplex lap-wound DC machine?

In DC generators, current to the external circuit from the armature is given through

For which operation of a DC motor is generally preferred over an AC motor

In a d.c machine iron losses occurs in

A dc shunt motor runs at 1000 rpm at no load from 250 V dc supply and takes 9 A. The motor resistances are Rsh = 250 Ω and Ra = 0.5 Ω. Calculate the speed when loaded and taking 41 A.

A 220-V DC machine has an armature resistance of 1 Ω. If the full-load current is 20 A, the difference between the induced voltage when the machine runs as motor and as a generator is:

In case of a simple lap wound generator, the number of parallel path is equal to the:

In case of DC generators, the critical resistance is equal to the resistance of the:

In a DC machine, the current in the armature winding is:

At 1200 rpm the induced emf of a dc machine is 200 V. For an armature current of 15 A the electromagnetic torque produced would be:

A differentially compound DC generator has its series and shunt field providing 20% and 80% flux respectively. The series field is suddenly short circuited without changing the load. Then the terminal voltage ignoring all the resistances

Consider the following factors for a dc machine:1. Interpole2. Armature resistance3. Reduction in field currentWhich of the above factors are responsible for decrease in terminal voltage of a shunt generator?

In electrical machines, the process of electromechanical energy conversion is

Calculate the force experienced by the conductor, with L = 0.5 m and B = 4 Wb/m2, when the armature current is 5 Amp?

In a d.c. machine,

A four-pole generator, having lap wound armature winding, has 51 slots, each slot containing 20 conductors. What will be the voltage generated in the machine when driven at 1500 rpm, assuming the flux per pole to be 7.0 mWb?

For a DC welding Motor-Generator set, which type of DC generator is used?

_______is used as a coolant in electrical machines to increase their efficiency.

In a dc machine, for the same number of slots and same current in the armature conductor, which one of the following will induce higher emf?

In a D.C. generator in order to reduce sparking at brushes, the self-induced e.m.f. in the coil is neutralized by all of the following except

The terminal voltage of a series generator is 150 V when the load current is 5 A. If the load current is increased to 10 A, the terminal voltage will be

Two generators A and B have 6 poles each. Generator A has wave wound armature while generator B has lap wound armature. The ratio of the induced e.m.f. is generator A and B will be

Following energized winding of a D.C. machine should not be opened as it would produce high inductive voltage which may be dangerous to personnel and may cause its own insulation failure.

In any rotating machine that part which houses the conductors and in which e.m.f. induced is to be utilised is called

Two generators are running in parallel. One of the generators may run as motor for which of the following reasons?

Two D.C. shunt generators, each with armature resistance of 0.02 ohm and field resistance of 50 ohm run in parallel and supply a total current of 1000 amperes to the load circuit. If their e.m.fs. are 270 V and 265 V, their bus bar voltage will be

Commutator of electrical machines is made up of:

Let T be the net torque developed by the rotor runs at ω rad/s. What is the mechanical power developed?

Direct on-line starters are not suitable for starting large DC motors because:

If an electrical machine converts mechanical energy into electrical energy, it is called ______.

A 4 pole lap wound DC generator has a developed power of P watts and a voltage of E volts. Two adjacent brushes of the machines are removed as they are worn out. If the machine operates with the remaining brushes, the developed voltage and the power obtained in the machines are

Assuming a uniform distribution of current over the armature surface conductors, the shape of the resultant armature m.m.f. in space of a loaded dc machine is a symmetrical

A DC short-shunt compound generator has the following specifications: Ra = 0.05Ω, Rsf = 0.3Ω, Rshf = 200Ω and voltage drop per brush is 1 V. Find the generated EMF when the generator deliver a load of 30 A at 220 V.

If shunt generator delivers 100 A at 200 V, and the resistance of the shunt field and armature are 100 ohm and 0.01 ohm respectively, the generated e.m.f. will be

In DC machines, the magnetisation curve is the relationship between:

For C coils and P poles, the commutator pitch for simplex wave winding is:

Armature reaction of an unsaturated DC machine results in _______ effect.

Determine the flux per pole for 6-pole dc machine having 240 wave connected conductors, which generates an open circuit voltage of 500 volt, which is running at 1000 rpm.

Armature coil of a DC machine is usually made up of

“A time–varying flux causes an induced electromotive force”. What law does this statement represent?

In a DC generator, whenever the rotating armature coil is parallel to the lines of flux:

Let V be the terminal voltage, Ia be the armature current and Ish be the shunt current. The power delivered to a load of a self-exited dc shunt generator is:

A DC generator works on the principle of:

In an unloaded shunt generator, when switch is closed, a small field current is produced which leads to generation of still larger voltages due to addition of.

A 220 V DC shunt motor takes 3A at no-load. It draws 25 A when running at full-load at 1500 rpm. The armature and shunt resistances are 0.5 Ω and 220 Ω, respectively. The no-load speed in rpm.

In lap winding of a P pole dc machine, the number of brushes are equal to