For a single phase capacitor start induction motor which of the following statements is valid ?

The direction of rotation cannot be changed

The capacitor is used for power factor improvement

The direction of rotation can be changed by reversing the main winding terminals

The direction of rotation cannot be changed

The direction of rotation can be changed by interchanging the supply terminals

In a DC machine, which of the following statements is true ?

Compensating winding is used for improving commutation while interpole winding is used for neutralizing armature reaction

Compensating winding is used for neutralizing armature reaction while interpole winding is used for producing residual flux

Compensating winding is used for neutralizing armature reaction while interpole winding is used for improving commutation

Compensating winding is used for improving commutation while interpole winding is used for neutralizing armature reaction

Compensating winding is used for improving commutation while interpole winding is used for producing residual flux

In transformers, which of the following statements is valid ?

In an open circuit test, copper losses are obtained while in short circuit test, core losses are obtained

In an open circuit test, current is drawn at high power factor

In a short circuit test, current is drawn at zero power factor

In an open circuit test, current is drawn at low power factor

A three-phase synchronous motor connected to ac mains is running at full load and unity power factor. If its shaft load is reduced by half, with field current held constant, its new power factor will be

dependent on machine parameters

In a transformer. zero voltage regulation at full load is

possible at lagging power factor load

possible at unity power factor load

possible at leading power factor load

possible at lagging power factor load

In a stepper motor, the detent torque means

maximum of the static torque with the phase winding unexcited.

minimum of the static torque with the phase winding excited.

maximum of the static torque with the phase winding excited.

minimum of the static torque with the phase winding unexcited.

maximum of the static torque with the phase winding unexcited.

Distributed winding and short chording employed in AC machines will result in

increase in emf and reduction in harmonics

reduction in emf and increase in harmonics

increase in both emf and harmonics

reduction in both emf and harmonics

The angle in the swing equation of a synchronous generator is the

angle between stator voltage and current.

angular displacement of the rotor with respect to the stator.

angular displacement of the stator mmf with respect to a synchronously rotating axis.

angular displacement of an axis fixed to the rotor with respect to a synchronously rotating axis.

A three-phase, salient pole synchronous motor is connected to an infinite bus. It is operated at no load at normal excitation. The field excitation of the motor is first reduced to zero and then increased in the reverse direction gradually. Then the armature current

first decreases and then increases steeply

first increases and then decreases steeply

first decreases and then increases steeply

309 + Mcqs in Electrical machines miscellaneous in Electrical Machines Page 5 McqOptions

201.	For a single phase capacitor start induction motor which of the following statements is valid ?
A.	The capacitor is used for power factor improvement
B.	The direction of rotation can be changed by reversing the main winding terminals
C.	The direction of rotation cannot be changed
D.	The direction of rotation can be changed by interchanging the supply terminals
Answer» C. The direction of rotation cannot be changed

Discussion

202.	A synchronous generator is feeding a zero power factor (lagging) load at rated current.
A.	magnetizing
B.	demagnetizing
C.	cross-magnetizing
D.	ineffective
Answer» C. cross-magnetizing

Discussion

203.	A 400 V, 50 Hz, three phase balanced source supplies power to a star connected load whose rating is 12
A.	28.78
B.	21.60
C.	16.60
D.	12.47
Answer» E.

Discussion

204.	In a DC machine, which of the following statements is true ?
A.	Compensating winding is used for neutralizing armature reaction while interpole winding is used for producing residual flux
B.	Compensating winding is used for neutralizing armature reaction while interpole winding is used for improving commutation
C.	Compensating winding is used for improving commutation while interpole winding is used for neutralizing armature reaction
D.	Compensating winding is used for improving commutation while interpole winding is used for producing residual flux
Answer» C. Compensating winding is used for improving commutation while interpole winding is used for neutralizing armature reaction

Discussion

205.	In transformers, which of the following statements is valid ?
A.	In an open circuit test, copper losses are obtained while in short circuit test, core losses are obtained
B.	In an open circuit test, current is drawn at high power factor
C.	In a short circuit test, current is drawn at zero power factor
D.	In an open circuit test, current is drawn at low power factor
Answer» E.

Discussion

206.	A three-phase squirrel cage induction motor has a starting torque of 150% and a maximum torque of 300% with respect to rated torque at rated voltage and rated frequency. Neglect the stator resistance and rotational losses. The value of slip for maximum torque is
A.	13.48%
B.	16.24%
C.	18.92%
D.	26.79%
Answer» E.

Discussion

207.	A three-phase synchronous motor connected to ac mains is running at full load and unity power factor. If its shaft load is reduced by half, with field current held constant, its new power factor will be
A.	unity
B.	leading
C.	lagging
D.	dependent on machine parameters
Answer» C. lagging

Discussion

208.	A 100 k VA. 415 V (line). star -connect ed synchronous machine generates rated open circuit voltage of 415 V at a field current of 15 A. The short circuit armature current at a field current of 10 A is equal to the rated armature current. The per unit saturated synchronous reactance is
A.	1.731
B.	1.5
C.	0.666
D.	0.577
Answer» B. 1.5

Discussion

209.	A single - phase 50 kVA, 250V/ 500 V two winding transformer has an efficiency of 95% at full load, unity power factor. If it is reconfigured as a 500 V/ 750 V auto-transformer, its efficiency at its new rated load at unity power factor will be
A.	95.752%
B.	97.851%
C.	98.276%
D.	99.241%
Answer» D. 99.241%

Discussion

210.	A three-phase, three-stack, variable reluctance step motor has 20 poles on each rotor and stator stack. The step angle of this step motor is
A.	3
B.	6
C.	9
D.	18
Answer» C. 9

Discussion

211.	The dc motor, which can provide zero speed regulation at full load without any controller, is
A.	series
B.	shunt
C.	cumulative compound
D.	differential compound
Answer» C. cumulative compound

Discussion

212.	In a transformer. zero voltage regulation at full load is
A.	not possible
B.	possible at unity power factor load
C.	possible at leading power factor load
D.	possible at lagging power factor load
Answer» D. possible at lagging power factor load

Discussion

213.	A 400 V, 50 Hz, 4 pole, 1400 rpm, star connected squirrel cage induction motor has the following parameters referred to the stator
A.	20.6 V, 2.7 Hz
B.	133.3 V, 16.7 Hz
C.	266.6 V, 33.3 Hz
D.	323.3 V, 40.3 Hz
Answer» C. 266.6 V, 33.3 Hz

Discussion

214.	A 400 V, 50 Hz, 30 hp,three-phase induction motor is drawing 50 A current at 0.8 power factor lagging. The stator and rotor copper losses are 1200 W. The air-gap power of the motor will be
A.	23.06 kW
B.	24.11 kW
C.	25.01 kW
D.	26.21 kW
Answer» D. 26.21 kW

Discussion

215.	A 230 V, 50 Hz, 4-pole, single-phase induction motor is rotating in the clockwise (forward) direction at a speed of 1425 -rpm. If the rotor resistance at standstill is 7.8 Ω. then the effective rotor resistance in the backward branch of the equivalent circuit will be
A.	2 &ohm;
B.	4 &ohm;
C.	78 &ohm;
D.	156 &ohm;
Answer» C. 78 &ohm;

Discussion

216.	In a stepper motor, the detent torque means
A.	minimum of the static torque with the phase winding excited.
B.	maximum of the static torque with the phase winding excited.
C.	minimum of the static torque with the phase winding unexcited.
D.	maximum of the static torque with the phase winding unexcited.
Answer» D. maximum of the static torque with the phase winding unexcited.

Discussion

217.	Distributed winding and short chording employed in AC machines will result in
A.	increase in emf and reduction in harmonics
B.	reduction in emf and increase in harmonics
C.	increase in both emf and harmonics
D.	reduction in both emf and harmonics
Answer» E.

Discussion

218.	A D.C shunt motor is running at 1200 rpm, when excited with 220 V D.C. neglecting losses and saturation, speed of the motor when connected 175V D.C. supply will be _______ rmp.
A.	1134 rpm
B.	650 rpm
C.	550 rpm
D.	1650 rpm
Answer» E.

Discussion

219.	In a properly designed d.c generator of 10 kW capacity, total losses may be of the order of _______ W .
A.	500 W
B.	690 W
C.	100 W
D.	1000 W
Answer» B. 690 W

Discussion

220.	A single phase 440 V, 60 Hz induction motor is to be operated at 25 Hz. Voltage that should be applied to the machine if air gap flux density is to be maintained at its normal value, is _______ V
A.	13 V
B.	83 V
C.	113 V
D.	183 V
Answer» E.

Discussion

221.	A 240 V, d.c shunt motor with an armature resistance of 05 Ω has a full load current of 40 A. The ratio stalling torque to the full load torque when a resistance of 1 Ω is connected in series with the armature, will be _______ .
A.	21
B.	6
C.	22
D.	83
Answer» C. 22

Discussion

222.	A dc shunt motor having unsaturated magnetic circuit runs at 1000 rpm with rated voltage. If applied voltage is half of the rated voltage, then motor will run at _______ rmp.
A.	500 rpm
B.	1000 rpm
C.	200 rpm
D.	1250 rpm
Answer» C. 200 rpm

Discussion

223.	A DC shunt motor is running at 1200 rpm, when excited with 220 V DC. Neglecting the losses and saturation, the speed of the motor when connected to a 175 V DC supply is _______ rmp .
A.	1200 rpm
B.	600 rpm
C.	1800 rpm
D.	2400 rpm
Answer» B. 600 rpm

Discussion

224.	If rotor power output of 3-phase induction motor is 15 kW, then rotor copper losses at a slip of 4% will be _______ W .
A.	300 W
B.	340 W
C.	600 W
D.	1000 W
Answer» D. 1000 W

Discussion

225.	The rotor of a three phase, 5 kW, 400 V, 50Hz, slip ring induction motor is wound for 6 poles while its startor is wound for 4 poles. The approximate average no load steady state speed when this motor is connected to 400 V, 50 Hz supply is _______ rpm .
A.	100 rpm
B.	1000 rpm
C.	2000 rpm
D.	500 rpm
Answer» C. 2000 rpm

Discussion

226.	The area of the hysteresis loop of a given magnetic material is 50 cm
A.	2.5 kW
B.	25 kW
C.	5 kW
D.	0.25 kW
Answer» B. 25 kW

Discussion

227.	An induction motor having full load torque at 60 Nm, when delta connected develops a starting torque of 120 Nm. For the same supply voltage, if the motor is change to star connection, the starting torque developed will be _______ NM .
A.	10 Nm
B.	20 Nm
C.	30 Nm
D.	40 Nm
Answer» E.

Discussion

228.	A 4-pole, separately excited, wave wound DC machine with negligible armature resistance is rated for 230 V and 5 kW at a speed of 1200 rpm. If the same armature coils are reconnected to forms a lap winding, what is the rated voltage (in volt s) and power (in kW) respectively at 1200 rpm of the reconnected machine if the field circuit is left unchanged ?
A.	230 and 5
B.	115 and 5
C.	115 and 2.5
D.	230 and 2.5
Answer» C. 115 and 2.5

Discussion

229.	A single-phase transformer has no-load loss of 64 W, as obtained from an open-circuit test. When a short-circuit test is performed on it with 90% of the rated currents flowing in its both LV and HV windings, the measured loss is 81 W. The transformer has maximum efficiency when operated at
A.	50.0% of the rated current.
B.	64.0% of the rated current.
C.	80.0% of the rated current.
D.	88.8% of the rated current.
Answer» D. 88.8% of the rated current.

Discussion

230.	A separately excited DC generator has an armature resist ance of 0.1 Ω and negligible armature inductance. At rated field current and rated rotor speed its open-circuit voltage is 200V. When this generator is operated at half the rated speed, with half the rated field current, an un-charged 1000 F 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

231.	For a specified input voltage and frequency, if the equivalent radius of the core of a transformer is reduced by half, the factor by which the number of turns in the primary should change to maintain the same no load current is
A.	<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;">4</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;">2</td></tr></table>
C.	2
D.	4
Answer» D. 4

Discussion

232.	A single phase induction motor is provided with capacitor and centrifugal switch in series with auxiliary winding. The switch is expected to operate at a speed of 0.7 N s, but due t o malfunctioning the switch fails to operate. The torque-speed characteristic of the motor is represented by
A.	<img src="http://images.interviewmania.com/wp-content/uploads/2019/12/as-146.jpg">
B.	<img src="http://images.interviewmania.com/wp-content/uploads/2019/12/as-147.jpg">
C.	<img src="http://images.interviewmania.com/wp-content/uploads/2019/12/as-148.jpg">
D.	<img src="http://images.interviewmania.com/wp-content/uploads/2019/12/as-149.jpg">
Answer» D. <img src="http://images.interviewmania.com/wp-content/uploads/2019/12/as-149.jpg">

Discussion

233.	The parameters measured for a 220V/110V, 50 Hz, single-phase transformer are :
A.	5mH, 20mH and 40mH
B.	5mH, 80mH and 40mH
C.	25mH, 10mH and 20mH
D.	45mH, 30mH and 20mH
Answer» C. 25mH, 10mH and 20mH

Discussion

234.	In a synchronous machine, hunting predominantly damped by
A.	mechanical losses in the rotor
B.	iron losses in the rotor
C.	copper losses in the stator
D.	copper losses in the rotor
Answer» E.

Discussion

235.	The angle in the swing equation of a synchronous generator is the
A.	angle between stator voltage and current.
B.	angular displacement of the rotor with respect to the stator.
C.	angular displacement of the stator mmf with respect to a synchronously rotating axis.
D.	angular displacement of an axis fixed to the rotor with respect to a synchronously rotating axis.
Answer» E.

Discussion

236.	A cylindrical rotor generator delivers 0.5 pu power in the steady-state to an infinite bus through a transmission line of reactance 0.5 pu. The generator no-load voltage is 1.5 pu and the infinite bus voltage is 1 pu. The inertia constant of the generator is 5 MW-s/MVA and the generator reactance is 1 pu. The critical clearing angle, in degrees, for a three-phase dead short circuit fault at the generator terminal is
A.	53.5
B.	60.2
C.	70.8
D.	79.6
Answer» D. 79.6

Discussion

237.	A 4-pole induction motor, supplied by a slightly unbalanced three-phase 50 Hz source, is rotating at 1440 rpm. The electrical frequency in Hz of the induced negative sequence current in the rotor is
A.	100
B.	98
C.	52
D.	48
Answer» C. 52

Discussion

238.	A 220 V, DC shunt motor is operating at a speed of 1440 rpm. The armature resistance is 1.0 Ω and armature current is 10 A. If the excitation of the machine is reduced by 10%, the extra resistance to be put in the armature circuit to maintain the same speed and torque will be
A.	1.79 &ohm;
B.	2.1 &ohm;
C.	3.1 &ohm;
D.	18.9 &ohm;
Answer» B. 2.1 &ohm;

Discussion

239.	A single-phase air core transformer, fed from a rated sinusoidal supply, is operating at no load. The steady state magnetizing current drawn by the transformer from the supply will have the waveform
A.	<img src="http://images.interviewmania.com/wp-content/uploads/2019/12/as-154.jpg">
B.	<img src="http://images.interviewmania.com/wp-content/uploads/2019/12/as-155.jpg">
C.	<img src="http://images.interviewmania.com/wp-content/uploads/2019/12/as-156.jpg">
D.	<img src="http://images.interviewmania.com/wp-content/uploads/2019/12/as-157.jpg">
Answer» D. <img src="http://images.interviewmania.com/wp-content/uploads/2019/12/as-157.jpg">

Discussion

240.	A three-phase, salient pole synchronous motor is connected to an infinite bus. It is operated at no load at normal excitation. The field excitation of the motor is first reduced to zero and then increased in the reverse direction gradually. Then the armature current
A.	increases continuously
B.	first increases and then decreases steeply
C.	first decreases and then increases steeply
D.	remains constant
Answer» C. first decreases and then increases steeply

Discussion

241.	The locked rotor current in a 3-phase, st ar connected 15 kW, 4-pole, 230 V, 50 Hz induction motor at rated conditions is 50 A. Neglecting losses and magnetizing current, the approximate locked rotor line current drawn when the motor is connected to a 236 V, 57 Hz supply is
A.	58.5 A
B.	45.0 A
C.	42.7 A
D.	55.6 A
Answer» C. 42.7 A

Discussion

242.	A field excitation of 20 A in a certain alternator results in an armature current of 400 A in short circuit and a terminal voltage of 2000 V on open circuit. The magnitude of the internal voltage drop within the machine at a load current of 200 A is
A.	1 V
B.	10 V
C.	100 V
D.	1000 V
Answer» E.

Discussion

243.	The flux density at a point in space is given by B = 4xa
A.	2
B.	0.5
C.	+0.5
D.	+2
Answer» B. 0.5

Discussion

244.	The direct axis and quadrature axis reactances of a salient pole alternator are 1.2 p.u. and 1.0 p.u. respectively. The armature resistance is negligible. If this alternator is delivering rated KVA at upf and at rated voltage then its power angle is
A.	30
B.	45
C.	60
D.	90
Answer» C. 60

Discussion

245.	A three-phase 440 V, 6 pole, 50Hz, squirrel cage induction motor is running at a slip of 5%. The speed of stator magnetic field with respect to rotor magnetic field and speed of rotor with respect to stator magnetic field are
A.	zero, 5 rpm
B.	zero, 955 rpm
C.	1000 rpm, 5 rpm
D.	1000 rpm, 955 rpm
E.	None of the above
Answer» F.

Discussion

246.	A 3 phase, 50 Hz, six pole induction motor has a rotor resistance of 0.1 Ω and reactance of 0.92 Ω. Neglect the voltage drop in stator and assume that the rotor resistance is constant. Given that the full load slip is 3%, the ratio of maximum torque to full load torque is
A.	1.567
B.	1.712
C.	1.948
D.	2.134
Answer» D. 2.134

Discussion

247.	The core loss of a single phase, 230/115 V, 50Hz power transformer is measured from 230 V side by feeding t he pr imar y (230 V side) fr om a variable voltage variable frequency source while keeping the secondary open circuited. The core loss is measured to be 1050 W for 230 V, 50 Hz input. The core loss is again measured to be 500 W for 138 V, 30 Hz input. The hysteresis and eddy current losses of the transformer for 230 V, 50Hz input are respectively.
A.	508 W and 542 W
B.	468 W and 582 W
C.	498 W and 552 W
D.	488 W and 562 W
Answer» B. 468 W and 582 W

Discussion

248.	A 20-pole alternator is having 180 identical stator slots with 6 conductors in each slot. All the coils of a phase are in series. If the coils are connected to realize single-phase winding, the generated voltage is V
A.	<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>
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;">2</td></tr></table>
C.
D.	<span style=" text-decoration: overline;">3</span>
E.	2
Answer» E. 2

Discussion

249.	A permanent magnet dc commutator motor has a no load speed of 6000 rpm when connected to a 120 V dc supply. The armature resistance is 2.5 ohms and other losses may be neglected. The speed of the motor with supply voltage of 60 V developing a torque 0.5 Nm, is _______ rpm .
A.	1337 rpm
B.	2673 rpm
C.	1671 rpm
D.	773 rpm
Answer» C. 1671 rpm

Discussion

250.	A 240 V dc series motor takes 40 A when giving its rated output at 1500 rpm. Its resistance is 0.3 ohms. The value of resistance which must be added to obtain rated torque at 1000 rpm is _______ ohms
A.	1.9 ohms
B.	19 ohms
C.	4.2 ohms
D.	None of the above
Answer» B. 19 ohms

Discussion

Explore topic-wise MCQs in Electrical Machines.

For a single phase capacitor start induction motor which of the following statements is valid ?

A synchronous generator is feeding a zero power factor (lagging) load at rated current.

A 400 V, 50 Hz, three phase balanced source supplies power to a star connected load whose rating is 12

In a DC machine, which of the following statements is true ?

In transformers, which of the following statements is valid ?

A three-phase squirrel cage induction motor has a starting torque of 150% and a maximum torque of 300% with respect to rated torque at rated voltage and rated frequency. Neglect the stator resistance and rotational losses. The value of slip for maximum torque is

A three-phase synchronous motor connected to ac mains is running at full load and unity power factor. If its shaft load is reduced by half, with field current held constant, its new power factor will be

A 100 k VA. 415 V (line). star -connect ed synchronous machine generates rated open circuit voltage of 415 V at a field current of 15 A. The short circuit armature current at a field current of 10 A is equal to the rated armature current. The per unit saturated synchronous reactance is

A single - phase 50 kVA, 250V/ 500 V two winding transformer has an efficiency of 95% at full load, unity power factor. If it is reconfigured as a 500 V/ 750 V auto-transformer, its efficiency at its new rated load at unity power factor will be

A three-phase, three-stack, variable reluctance step motor has 20 poles on each rotor and stator stack. The step angle of this step motor is

The dc motor, which can provide zero speed regulation at full load without any controller, is

In a transformer. zero voltage regulation at full load is

A 400 V, 50 Hz, 4 pole, 1400 rpm, star connected squirrel cage induction motor has the following parameters referred to the stator

A 400 V, 50 Hz, 30 hp,three-phase induction motor is drawing 50 A current at 0.8 power factor lagging. The stator and rotor copper losses are 1200 W. The air-gap power of the motor will be

A 230 V, 50 Hz, 4-pole, single-phase induction motor is rotating in the clockwise (forward) direction at a speed of 1425 -rpm. If the rotor resistance at standstill is 7.8 Ω. then the effective rotor resistance in the backward branch of the equivalent circuit will be

In a stepper motor, the detent torque means

Distributed winding and short chording employed in AC machines will result in

A D.C shunt motor is running at 1200 rpm, when excited with 220 V D.C. neglecting losses and saturation, speed of the motor when connected 175V D.C. supply will be _______ rmp.

In a properly designed d.c generator of 10 kW capacity, total losses may be of the order of _______ W .

A single phase 440 V, 60 Hz induction motor is to be operated at 25 Hz. Voltage that should be applied to the machine if air gap flux density is to be maintained at its normal value, is _______ V

A 240 V, d.c shunt motor with an armature resistance of 05 Ω has a full load current of 40 A. The ratio stalling torque to the full load torque when a resistance of 1 Ω is connected in series with the armature, will be _______ .

A dc shunt motor having unsaturated magnetic circuit runs at 1000 rpm with rated voltage. If applied voltage is half of the rated voltage, then motor will run at _______ rmp.

A DC shunt motor is running at 1200 rpm, when excited with 220 V DC. Neglecting the losses and saturation, the speed of the motor when connected to a 175 V DC supply is _______ rmp .

If rotor power output of 3-phase induction motor is 15 kW, then rotor copper losses at a slip of 4% will be _______ W .

The rotor of a three phase, 5 kW, 400 V, 50Hz, slip ring induction motor is wound for 6 poles while its startor is wound for 4 poles. The approximate average no load steady state speed when this motor is connected to 400 V, 50 Hz supply is _______ rpm .

The area of the hysteresis loop of a given magnetic material is 50 cm

An induction motor having full load torque at 60 Nm, when delta connected develops a starting torque of 120 Nm. For the same supply voltage, if the motor is change to star connection, the starting torque developed will be _______ NM .

A single-phase transformer has no-load loss of 64 W, as obtained from an open-circuit test. When a short-circuit test is performed on it with 90% of the rated currents flowing in its both LV and HV windings, the measured loss is 81 W. The transformer has maximum efficiency when operated at

For a specified input voltage and frequency, if the equivalent radius of the core of a transformer is reduced by half, the factor by which the number of turns in the primary should change to maintain the same no load current is

A single phase induction motor is provided with capacitor and centrifugal switch in series with auxiliary winding. The switch is expected to operate at a speed of 0.7 N s, but due t o malfunctioning the switch fails to operate. The torque-speed characteristic of the motor is represented by

The parameters measured for a 220V/110V, 50 Hz, single-phase transformer are :

In a synchronous machine, hunting predominantly damped by

The angle in the swing equation of a synchronous generator is the

A 4-pole induction motor, supplied by a slightly unbalanced three-phase 50 Hz source, is rotating at 1440 rpm. The electrical frequency in Hz of the induced negative sequence current in the rotor is

A 220 V, DC shunt motor is operating at a speed of 1440 rpm. The armature resistance is 1.0 Ω and armature current is 10 A. If the excitation of the machine is reduced by 10%, the extra resistance to be put in the armature circuit to maintain the same speed and torque will be

A single-phase air core transformer, fed from a rated sinusoidal supply, is operating at no load. The steady state magnetizing current drawn by the transformer from the supply will have the waveform

A three-phase, salient pole synchronous motor is connected to an infinite bus. It is operated at no load at normal excitation. The field excitation of the motor is first reduced to zero and then increased in the reverse direction gradually. Then the armature current

The locked rotor current in a 3-phase, st ar connected 15 kW, 4-pole, 230 V, 50 Hz induction motor at rated conditions is 50 A. Neglecting losses and magnetizing current, the approximate locked rotor line current drawn when the motor is connected to a 236 V, 57 Hz supply is

A field excitation of 20 A in a certain alternator results in an armature current of 400 A in short circuit and a terminal voltage of 2000 V on open circuit. The magnitude of the internal voltage drop within the machine at a load current of 200 A is

The flux density at a point in space is given by B = 4xa

The direct axis and quadrature axis reactances of a salient pole alternator are 1.2 p.u. and 1.0 p.u. respectively. The armature resistance is negligible. If this alternator is delivering rated KVA at upf and at rated voltage then its power angle is

A three-phase 440 V, 6 pole, 50Hz, squirrel cage induction motor is running at a slip of 5%. The speed of stator magnetic field with respect to rotor magnetic field and speed of rotor with respect to stator magnetic field are

A 3 phase, 50 Hz, six pole induction motor has a rotor resistance of 0.1 Ω and reactance of 0.92 Ω. Neglect the voltage drop in stator and assume that the rotor resistance is constant. Given that the full load slip is 3%, the ratio of maximum torque to full load torque is

A 20-pole alternator is having 180 identical stator slots with 6 conductors in each slot. All the coils of a phase are in series. If the coils are connected to realize single-phase winding, the generated voltage is V

A permanent magnet dc commutator motor has a no load speed of 6000 rpm when connected to a 120 V dc supply. The armature resistance is 2.5 ohms and other losses may be neglected. The speed of the motor with supply voltage of 60 V developing a torque 0.5 Nm, is _______ rpm .

A 240 V dc series motor takes 40 A when giving its rated output at 1500 rpm. Its resistance is 0.3 ohms. The value of resistance which must be added to obtain rated torque at 1000 rpm is _______ ohms