In an ac servometer, the control winding is supplied with input voltage of

same frequency as the reference windings voltage and also having same phase.

same frequency as the reference winding voltage but with 90 phase difference.

same frequency as the reference windings voltage and also having same phase.

any frequency compared to t he reference winding but with 90 phase difference.

any frequency compared to the reference winding but of the same phase.

An ac servomotor exhibits

two time constants which depend upon rotor inertia and mechanical friction

two time constants which depend upon rotor inertia, the slope of its torque speed characteristic and mechanical friction.

a dominant time constant which depends upon rotor inertia and mechanical friction

a dominant time constant which depends upon rotor inertia, the slope of its torque-speed characteristic and mechanical friction.

If an a.c. servomotor has one of its winding excited by a.c., t hen voltage measured at the other winding with rotor running will be

proportional to the square of the rotor speed

A two-phase servomotor develops maximum torque at

backward speed of one-half of the synchronous speed

forward speed of one-half of the synchronous speed

backward speed of one-half of the synchronous speed

a speed of twice the synchronous speed

Driving power from the prime mover driving the alternator is lost but the alternator remains connected to the supply network and the field supply also remains on. The alternator will

behave as a synchronous motor but will rotate in a reverse direction to that corresponding to generator action.

behave as an induction motor but will rotate in the opposite direction

behave as a synchronous motor and will rotate in the same direction

behave as a synchronous motor but will rotate in a reverse direction to that corresponding to generator action.

In a phase of synchronous converter the position of minimum copper loss

is the tapping point whatever may be the power factor.

varies with the power factor and this position is displaced from the taping point by the power factor angle.

is middle of the phase whatever may be the power factor.

varies with the power factor and this position is displaced from the middle of the phase by the power factor angle.

Damping winding in a synchronous motor is generally used to

prevent hunting and provide the starting torque

Voltage across the open-circuited field terminals of a synchronous machine under slip test is

a modulated supply frequency ac voltage with slip frequency envelope

A synchronous machine working in the motor made, is fed from an infinite bus and is delivering half full-load. If an increase in field current causes an increase in the armature current, then the motor will

deliver reactive power and active power to the bus

absorb reactive power and active power from the bus

absorb reactive power from the bus and deliver active power to the bus

deliver reactive power to the bus and absorb active power from the bus.

The torque angle at a synchronous machine operating from a constant voltage bus is usually defined as the space angle between

rotor mmf wave and resultant flux density

rotor mmf wave and startor mmf wave

rotor mmf wave and resultant flux density

startor mmf wave and resultant flux density wave

A synchronous generator connected to an infinite bus is supplying electrical power at unity p.f. to the bus. If its field current is now increased, then

active power supplied will increase and the machine will draw leading reactive power

both active and reactive power output of the generator will remain unchanged

active power supplied will remain unchanged but the machine will also supply lagging reactive power

active power supplied will increase and the machine will draw leading reactive power

active power supplied will decrease and the machine will supply leading reactive power.

The subtransient reactance of a synchronous generator is much less than its synchronous reactance in the initial phase of short circuit from no load as

demagnetizing ampere-turns appear because of induced filed and damper winding currents as the air -gap flux cannot change instantaneously from its no-load value.

magnetizing ampere-turns appear because of induced field and damper winding current as the air-gap flux cannot change instantaneously from its no load value.

demagnetizing ampere-turns appear because of induced filed and damper winding currents as the air -gap flux cannot change instantaneously from its no-load value.

magnetizing ampere-turns, appear because of induced field and damper winding currents as the air-gap flux must reduce instantaneously from its no-load value.

demagnetizing ampere-turns appear because of induced field and damper winding currents as the air-gap flux must reduce instantaneously from its no-load value.

In a cylindrical rotor synchronous machine, the phasor addition of startor and rotor mmf is possible because

one mmf is stationary and the other mmf is rotating

two mmfs are rotating in opposite direction

two mmfs are rotating in same direction at different speeds

two mmfs are stationary with respect to each other

one mmf is stationary and the other mmf is rotating

309 + Mcqs in Electrical machines miscellaneous in Electrical Machines Page 6 McqOptions

251.	A 4 pole generator with 16 coil has a two layer lap winding. The pole pitch is _______
A.	1
B.	2
C.	3
D.	4
Answer» E.

252.	The startor of a 6-pole, 3-phase induction motor is fed from a 3-phase, 50 Hz supply which contains a pronounced fifth time harmonic. The speed of the fifth space harmonic field produced by the fifth time harmonic in the startor supply will be _______ rmp .
A.	500 rpm
B.	1500 rpm
C.	100 rpm
D.	2000 rpm
Answer» C. 100 rpm

253.	At a slip of 4%, maximum possible speed of a 3 phase squirrel-case induction motor is _______ rpm .
A.	920 rpm
B.	1380 rpm
C.	2880 rpm
D.	None of the above
Answer» D. None of the above

254.	If starting current of a 3 Ω induction motor is 5 times the rated current, while rated slip is 4%, then ratio of starting torque to full-load torque is _______ .
A.	0
B.	1
C.	2
D.	3
Answer» C. 2

255.	A 3-phase slip-ring induction motor is wound for 4 poles on startor and 6 poles on rotor. When 3- phase balanced voltage source at 50 Hz is applied to motor, it will run at _______ rpm .
A.	750 rpm
B.	150 rpm
C.	450 rpm
D.	765 rpm
Answer» B. 150 rpm

256.	A 3-phase motor is driving at constant torque load of 1 pu at 5% slip. It has a maximum torque of 2 pu at 10% slip. Torque-speed variation in stable zone is assumed to be linear. For the stable operation of the motor, the minimum pu supply voltage is approximately _______ .
A.	1.72
B.	3.707
C.	0.707
D.	7.07
Answer» D. 7.07

257.	In an induct ion motor, the ratio of starting current to full load current is 12.65 and the ratio of starting torque to full load torque is 1.6. Then percentage slip at full load will be _______ % .
A.	0.01 %
B.	0.1 %
C.	1 %
D.	10 %
Answer» B. 0.1 %

258.	The energy stored in the magnetic field of solenoid 30 cm long and 3 cm diameter wound with 1000 turns of wire carrying a current of 10 A is _____ J.
A.	5 joule
B.	0.15 joule
C.	15 joule
D.	All of the above
Answer» C. 15 joule

259.	A dc shunt generator delivers 395 A at 250 V and resistance of the shunt field and armature are 50 Ω and 0.05 Ω , respectively. The generated emf will be _______ V .
A.	270 V
B.	70 V
C.	20 V
D.	135 V
Answer» B. 70 V

260.	If hysteresis loop of a magnetic material has an area of 5 cm
A.	2.5 W
B.	5 W
C.	15 W
D.	25 W
Answer» E.

261.	A 6-pole, 50 Hz wound rotor induction motor when supplied at the rated voltage and frequency with slip-ring open-circuited, developed a voltage of 100 V between any two rings. If the rotor is driven by an external means at 1000 rpm opposite to the direction of stator field, the frequency of voltage across slip-rings will be _______ Hz .
A.	50 Hz
B.	100 Hz
C.	300 Hz
D.	None of the above
Answer» C. 300 Hz

263.	An auto-transformer having a transformation ratio of 0.8 supplies a load of 10 kW. The power transferred inductively from the primary to the secondary is _______ kW .
A.	1 kW
B.	2 kW
C.	3 kW
D.	4 kW
Answer» C. 3 kW

266.	Given the maximum efficiency of a transformer of a 500 kVA, 3300/500V, 50 Hz single-phase transformer is 97% and occurs at 3/4 of full-load, unity power factor. If the impedance is 10%, the regulation at full-load, power factor 0.8 lagging will be _____ % .
A.	8.25%
B.	17.52%
C.	7.52%
D.	10.52%
Answer» D. 10.52%

268.	A single-phase transformer when supplied from 220V, 50 Hz has eddy current loss of 50 W. If transformer is connected to a voltage of 330 V, 50 Hz, then eddy current loss will be _______ W .
A.	11.25 W
B.	112.5 W
C.	21.05 W
D.	1125 W
Answer» C. 21.05 W

269.	In a single-phase transformer, magnitude of leakage reactance is twice that of resistance of both primary and secondary. With secondary short-circuited, the input power factor is _______ .
A.	<table><tr><td rowspan="2"></td><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>2</center></td></tr><tr><td style="text-align: center;"> <span style=" text-decoration: overline;">5</span></td></tr></table>
B.	<table><tr><td rowspan="2"></td><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>1</center></td></tr><tr><td style="text-align: center;"> <span style=" text-decoration: overline;">3</span></td></tr></table>
C.	<table><tr><td rowspan="2"></td><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>5</center></td></tr><tr><td style="text-align: center;"> <span style=" text-decoration: overline;">2</span></td></tr></table>
D.	<table><tr><td rowspan="2"></td><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>3</center></td></tr><tr><td style="text-align: center;"> <span style=" text-decoration: overline;">4</span></td></tr></table>
Answer» B. <table><tr><td rowspan="2"></td><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>1</center></td></tr><tr><td style="text-align: center;"> <span style=" text-decoration: overline;">3</span></td></tr></table>

262.	For a three-phase induction motor input power on no load is W
A.	183 W
B.	81 W
C.	123 W
D.	18 W
Answer» B. 81 W

264.	A 3 phase delta/star transformer is supplied at 6000 V on the delta-connected side. The terminal voltage on the secondary side when supplying full load at 0.8 lagging power-factor is 415 V. The equivalent resistance and reactance drops for the transformer are 1% and 5% respectively. The turns ratio of the transformer is _______ .
A.	4
B.	24
C.	12
D.	All of the above
Answer» C. 12

265.	A 100 k VA, 2400 / 240V, 50 Hz single phase transformer has an exciting current of 0.64 A and a core loss of 700 watts, when its high-voltage side is energised at rated voltage and frequency. If load current is 40 A at 0.8 power factor of on the LV side then the primary current will be _______ A .
A.	4.58 A
B.	45 A
C.	45.8 A
D.	None of these
Answer» B. 45 A

267.	A 10 kVA, 400 V/ 200 V, single phase transformer with a percentage resistance of 3% and percentage reactance of 6% is supplying a current of 50 A to a resistive load. The value of the load voltage is _______ V .
A.	57 V
B.	131 V
C.	194 V
D.	105 V
Answer» D. 105 V

270.	A 2 kVA transformer has iron loss of 150 Watts and full - load copper loss of 250 Watts. The maximum efficiency of the transformer would occur when the total loss is _______ W .
A.	3 W
B.	100 W
C.	30 W
D.	300 W
Answer» E.

271.	The voltage regulation of a transformer at full load and 0.8 power factor lagging is 2.5%. The voltage regulation at full load, 0.8 power factor leading will be _______ % .
A.	0.1 %
B.	1 %
C.	2 %
D.	10 %
Answer» C. 2 %

272.	An auto transformer having a transformation ratio of 0.8 supplies a load of 3 kW. The power transferred conductively from primary to secondary is _______ kW .
A.	24 kW
B.	12 kW
C.	2.4 kW
D.	None of the above
Answer» D. None of the above

273.	For a 1.15 kVA, 460/230 V transformer connected to a standard single phase 50 Hz supply, the no load current is likely to be _______ A .
A.	0.1 A
B.	0.01 A
C.	1 A
D.	10 A
Answer» B. 0.01 A

274.	A three phase transformer has rating at 20 MVA, 220 kV (star), 33 kV (delta) with leakage reactance at 12%. The transformer reactance (in ohms) referred to each phase of the L.V delta connected side is _______ .
A.	10.96
B.	19.6
C.	1.6
D.	196
Answer» C. 1.6

275.	The percentage resistance and percentage reactance of a 10 kVA, 400 V / 200 V, 3-phase transformer are 2% and 10% respectively. If the constant losses in the machine are 1%, the maximum possible percentage efficiency of the transformer is _______ .
A.	97.25
B.	57.25
C.	67.75
D.	None of the above
Answer» B. 57.25

Explore topic-wise MCQs in Electrical Machines.

A 4 pole generator with 16 coil has a two layer lap winding. The pole pitch is _______

The startor of a 6-pole, 3-phase induction motor is fed from a 3-phase, 50 Hz supply which contains a pronounced fifth time harmonic. The speed of the fifth space harmonic field produced by the fifth time harmonic in the startor supply will be _______ rmp .

At a slip of 4%, maximum possible speed of a 3 phase squirrel-case induction motor is _______ rpm .

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

A 3-phase slip-ring induction motor is wound for 4 poles on startor and 6 poles on rotor. When 3- phase balanced voltage source at 50 Hz is applied to motor, it will run at _______ rpm .

A 3-phase motor is driving at constant torque load of 1 pu at 5% slip. It has a maximum torque of 2 pu at 10% slip. Torque-speed variation in stable zone is assumed to be linear. For the stable operation of the motor, the minimum pu supply voltage is approximately _______ .

In an induct ion motor, the ratio of starting current to full load current is 12.65 and the ratio of starting torque to full load torque is 1.6. Then percentage slip at full load will be _______ % .

The energy stored in the magnetic field of solenoid 30 cm long and 3 cm diameter wound with 1000 turns of wire carrying a current of 10 A is _____ J.

A dc shunt generator delivers 395 A at 250 V and resistance of the shunt field and armature are 50 Ω and 0.05 Ω , respectively. The generated emf will be _______ V .

If hysteresis loop of a magnetic material has an area of 5 cm

For a three-phase induction motor input power on no load is W

An auto-transformer having a transformation ratio of 0.8 supplies a load of 10 kW. The power transferred inductively from the primary to the secondary is _______ kW .

A 100 k VA, 2400 / 240V, 50 Hz single phase transformer has an exciting current of 0.64 A and a core loss of 700 watts, when its high-voltage side is energised at rated voltage and frequency. If load current is 40 A at 0.8 power factor of on the LV side then the primary current will be _______ A .

Given the maximum efficiency of a transformer of a 500 kVA, 3300/500V, 50 Hz single-phase transformer is 97% and occurs at 3/4 of full-load, unity power factor. If the impedance is 10%, the regulation at full-load, power factor 0.8 lagging will be _____ % .

A 10 kVA, 400 V/ 200 V, single phase transformer with a percentage resistance of 3% and percentage reactance of 6% is supplying a current of 50 A to a resistive load. The value of the load voltage is _______ V .

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

In a single-phase transformer, magnitude of leakage reactance is twice that of resistance of both primary and secondary. With secondary short-circuited, the input power factor is _______ .

A 2 kVA transformer has iron loss of 150 Watts and full - load copper loss of 250 Watts. The maximum efficiency of the transformer would occur when the total loss is _______ W .

The voltage regulation of a transformer at full load and 0.8 power factor lagging is 2.5%. The voltage regulation at full load, 0.8 power factor leading will be _______ % .

An auto transformer having a transformation ratio of 0.8 supplies a load of 3 kW. The power transferred conductively from primary to secondary is _______ kW .

For a 1.15 kVA, 460/230 V transformer connected to a standard single phase 50 Hz supply, the no load current is likely to be _______ A .

A three phase transformer has rating at 20 MVA, 220 kV (star), 33 kV (delta) with leakage reactance at 12%. The transformer reactance (in ohms) referred to each phase of the L.V delta connected side is _______ .

The percentage resistance and percentage reactance of a 10 kVA, 400 V / 200 V, 3-phase transformer are 2% and 10% respectively. If the constant losses in the machine are 1%, the maximum possible percentage efficiency of the transformer is _______ .

The low voltage winding of a 400 / 230V, 1 phase, 50 Hz transformer is to be connected to a 25 Hz, the supply voltage should be _______ V .

The startor of a 415 V, 50 Hz, 6-pole, 970 rpm, 3-phase slip-ring induction motor is fed with normal voltage. The rotor with slip rings opencircuited is rotated at 500 rpm along the normal direction of it s rotation. The frequency of the voltage across slip rings will be _______ HZ.

A 200/100 V, 50 Hz transformer is to be excited at 40 Hz from the 100 V side. For the exciting current to remain the same, the applied voltage should be _______ V.

A single-phase transformer when supplied from 220V, 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_______ W.

If 1.8 step, 4-phase stepper motor has a total of 40 teeth on 8 poles of startor, then number of rotor teeth for this motor will be

In an ac servometer, the control winding is supplied with input voltage of

An ac servomotor exhibits

If an a.c. servomotor has one of its winding excited by a.c., t hen voltage measured at the other winding with rotor running will be

A two-phase servomotor develops maximum torque at

Driving power from the prime mover driving the alternator is lost but the alternator remains connected to the supply network and the field supply also remains on. The alternator will

In a phase of synchronous converter the position of minimum copper loss

Damping winding in a synchronous motor is generally used to

Voltage across the open-circuited field terminals of a synchronous machine under slip test is

A synchronous machine working in the motor made, is fed from an infinite bus and is delivering half full-load. If an increase in field current causes an increase in the armature current, then the motor will

The torque angle at a synchronous machine operating from a constant voltage bus is usually defined as the space angle between

If power input to the d.c. field at a 15 kVA (input) synchronous motor is 6 per cent of the rates a.c. input, then direct current that excites the field at 120 volt, is

If a 10 pole 25 Hz alternator is directly coupled to and is driven by a 60 Hz synchronous motor, then number of poles in a synchronous motor are

A salient pole synchronous machine can stay synchronized to the man when excitation is reduced to zero provided the load is

An unexcited single phase synchronous motor is

A synchronous generator connected to an infinite bus is supplying electrical power at unity p.f. to the bus. If its field current is now increased, then

During a disturbance of a synchronous machine, the rotor swings from A to B before finally setting down to a steady state at point C on the power angle curve. The speed of the machine during oscillation is synchronous at point (s)

If a synchronous condenser is installed to current the 2400 kVA, 0.65 power factor load in a plant to unity, then kilovolt ampere rating of condenser is

The subtransient reactance of a synchronous generator is much less than its synchronous reactance in the initial phase of short circuit from no load as

In a cylindrical rotor synchronous machine, the phasor addition of startor and rotor mmf is possible because

The startor of a salient pole synchronous generator is excited from a low voltage 50 Hz supply while the rotor is made to run at a slip of 0.05. The reluctance presented to the rotating startor mmf is

276.	The low voltage winding of a 400 / 230V, 1 phase, 50 Hz transformer is to be connected to a 25 Hz, the supply voltage should be _______ V .
A.	75 V
B.	315 V
C.	115 V
D.	65 V
Answer» D. 65 V

277.	The startor of a 415 V, 50 Hz, 6-pole, 970 rpm, 3-phase slip-ring induction motor is fed with normal voltage. The rotor with slip rings opencircuited is rotated at 500 rpm along the normal direction of it s rotation. The frequency of the voltage across slip rings will be _______ HZ.
A.	5 Hz
B.	25 Hz
C.	21 Hz
D.	45 Hz
Answer» C. 21 Hz

278.	A 200/100 V, 50 Hz transformer is to be excited at 40 Hz from the 100 V side. For the exciting current to remain the same, the applied voltage should be _______ V.
A.	10 V
B.	30 V
C.	40 V
D.	80 V
Answer» E.

279.	A single-phase transformer when supplied from 220V, 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_______ W.
A.	112.5 W
B.	12 W
C.	515 W
D.	None of the above
Answer» B. 12 W

280.	If 1.8 step, 4-phase stepper motor has a total of 40 teeth on 8 poles of startor, then number of rotor teeth for this motor will be
A.	40
B.	50
C.	100
D.	80
Answer» D. 80

281.	In an ac servometer, the control winding is supplied with input voltage of
A.	same frequency as the reference winding voltage but with 90 phase difference.
B.	same frequency as the reference windings voltage and also having same phase.
C.	any frequency compared to t he reference winding but with 90 phase difference.
D.	any frequency compared to the reference winding but of the same phase.
Answer» B. same frequency as the reference windings voltage and also having same phase.

282.	An ac servomotor exhibits
A.	two time constants which depend upon rotor inertia and mechanical friction
B.	two time constants which depend upon rotor inertia, the slope of its torque speed characteristic and mechanical friction.
C.	a dominant time constant which depends upon rotor inertia and mechanical friction
D.	a dominant time constant which depends upon rotor inertia, the slope of its torque-speed characteristic and mechanical friction.
Answer» E.

283.	If an a.c. servomotor has one of its winding excited by a.c., t hen voltage measured at the other winding with rotor running will be
A.	zero
B.	proportional to rotor speed
C.	proportional to the square of the rotor speed
D.	constant independent of speed.
Answer» C. proportional to the square of the rotor speed

284.	A two-phase servomotor develops maximum torque at
A.	forward speed of one-half of the synchronous speed
B.	backward speed of one-half of the synchronous speed
C.	synchronous speed
D.	a speed of twice the synchronous speed
Answer» B. backward speed of one-half of the synchronous speed

285.	Driving power from the prime mover driving the alternator is lost but the alternator remains connected to the supply network and the field supply also remains on. The alternator will
A.	get burnt
B.	behave as an induction motor but will rotate in the opposite direction
C.	behave as a synchronous motor and will rotate in the same direction
D.	behave as a synchronous motor but will rotate in a reverse direction to that corresponding to generator action.
Answer» D. behave as a synchronous motor but will rotate in a reverse direction to that corresponding to generator action.