In a 3-phase voltage source inverter used for speed control of induction motor, anti-parallel diodes are used across each switching device. The main purpose of diodes is to:

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In a 3-phase voltage source inverter used for speed control of induction motor, anti-parallel diodes are used across each switching device. The main purpose of diodes is to: Allow the motor to return energy during regeneration

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Description : A 3-phase induction motor is driving a constant torque load at rated voltage and frequency. If both voltage and frequency are halved, following statements relate to the new condition if stator resistance, leakage reactance and core loss are ... (A) All (B) 1, 2 and 3 (C) 2, 3 and 4 (D) 1 and 4

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Description : No-load test on a 3-phase induction motor was conducted at different supply voltage and a plot of input power versus voltage was drawn. This curve was extrapolated to intersect the y-axis. The intersection point ... ) Core loss (B) Stator copper loss (C) Stray load loss (D) Friction and windage loss

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Description : A three-phase cage induction motor is started by direct-on-line (DOL) switching at the rated voltage. If the starting current drawn is 6 times the full load current, and the full load slip is 4%, then ratio of the ... load torque is approximately equal to (A) 0.24 (B) 1.44 (C) 2.40 (D) 6.00

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Description : 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

Last Answer : 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 98 

Description : If a 3-phase, 400V, 50Hz, 4 pole induction motor is running at a slip of 5% then the relative speed of rotor field with respect to stator filed is:

Last Answer : If a 3-phase, 400V, 50Hz, 4 pole induction motor is running at a slip of 5% then the relative speed of rotor field with respect to stator filed is: zero

Description : in a three-phase induction motor, the rotor field runs at the following speed with respect to the stator structure: 

Last Answer : in a three-phase induction motor, the rotor field runs at the following speed with respect to the stator structure: At synchronous speed in the direction of stator field

Description : The stator mmf and rotor mmf of a 3-phase induction motor (A) are equal (B) rotate with slip speed (C) are opposite but rotate with synchronous speed (D) rotate with the same rotor speed 

Last Answer : a

Description : The rotor frequency for a 3-phase 6-pole, 1000 r.p.m. induction motor with a slip of 0.04 is (a) 2 Hz (b) 4 Hz (c) 6 Hz (d) 8 Hz  

Last Answer : 2hz is rotor frequency

Description : A 3-phase delta connected squirrel cage induction motor when started with a DOL starter has a starting torque of 600 NM. Its starting torque when star delta starter is used:

Last Answer : A 3-phase delta connected squirrel cage induction motor when started with a DOL starter has a starting torque of 600 NM. Its starting torque when star delta starter is used: 200 NM

Description : A 3-phase induction motor is running at slip ‘s’. If its two supply leads are interchanged, then the operating slip at that instant will be:

Last Answer : A 3-phase induction motor is running at slip ‘s’. If its two supply leads are interchanged, then the operating slip at that instant will be: (2-s)

Description : A three phase slip ring induction motor is fed from the rotor side with stator winding short circuited stator is: (1) Slip frequency (2) Supply frequency (3) Frequency corresponding to rotor speed (4) Zero

Last Answer : A three phase slip ring induction motor is fed from the rotor side with stator winding short circuited stator is: Slip frequency

Description : A single-phase induction motor with only the main winding excited would exhibit the following response at synchronous speed  (A) Rotor current is zero (B) Rotor current is non-zero and is ... and backward rotating fields are equal (D) Forward rotating field is more than the backward rotating field

Last Answer : A single-phase induction motor with only the main winding excited would exhibit the following response at synchronous speed  (A) Rotor current is zero (B) Rotor current is non-zero and is ... backward rotating fields are equal (D) Forward rotating field is more than the backward rotating field

Description : The direction of rotation of a 3-phase induction motor is clockwise when it is supplied with 3-phase sinusoidal voltage having phase sequence A-B-C. For counter clockwise rotation of the motor, the phase sequence of the power supply should be  (A) B-C-A (B) C-A-B (C) A-C-B (D) B-C-A or C-A-B

Last Answer : The direction of rotation of a 3-phase induction motor is clockwise when it is supplied with 3-phase sinusoidal voltage having phase sequence A-B-C. For counter clockwise rotation of the motor, the phase sequence of the power supply should be  A-C-B 

Description : The type of single-phase induction motor having the highest power factor at full load is (A) shaded pole type (B) split-phase type (C) capacitor-start type (D) capacitor-run type

Last Answer : The type of single-phase induction motor having the highest power factor at full load is capacitor-run type

Description : In a single phase induction motor driving a fan load, the reason for having a high resistance rotor is to achieve (A) low starting torque (B) quick acceleration (C) high efficiency (D) reduced size

Last Answer : In a single phase induction motor driving a fan load, the reason for having a high resistance rotor is to achieve quick acceleration

Description : 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 ... maximum torque is  (A) 13.48% (B) 16.42% (C) 18.92% (D) 26.79%

Last Answer : 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 26.79%

Description : 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 ... rotation cannot be changed D) The direction of rotation can be changed by interchanging the supply terminals

Last Answer : 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 ... cannot be changed D) The direction of rotation can be changed by interchanging the supply terminals

Description : Consider the following statements: Star delta starter is used in 3-phase induction motor because it  1. Prevents heating of the motor winding  2. Ensures permissible minimum starting current  3. Is regulated by electricity ... and 4 are correct (c) 1, 3 and 4 are correct (d) 1 and 2 are correct 

Last Answer : Consider the following statements: Star delta starter is used in 3-phase induction motor because it  1. Prevents heating of the motor winding  2. Ensures permissible minimum starting current  3. Is regulated by ... and 4 are correct (c) 1, 3 and 4 are correct (d) 1 and 2 are correct 

Description : A three phase slip ring induction motor with chopper controlled resistance has its torque proportional to   (a) Rotor current (b) Stator resistance (c) Square of rotor current (d) Square root of rotor current 

Last Answer : A three phase slip ring induction motor with chopper controlled resistance has its torque proportional to Square of rotor current

Description : The number of poles in a phase induction motor at 50 Hz and running at 1500 rpm will be?

Last Answer : The number of poles in a phase induction motor at 50 Hz and running at 1500 rpm will be 4.

Last Answer : Single phase induction motor usually operates on 0.6 power factor lagging.

Last Answer : A single-phase induction motor is inherently non-self-starting with low torque.

Last Answer : The power factor of a single-phase induction motor is usually lagging.

Description : A capacitor-start single phase induction motor is switched on to supply with its capacitor replaced by an inductor of equivalent reactance value. It will?

Last Answer : A capacitor-start single phase induction motor is switched on to supply with its capacitor replaced by an inductor of equivalent reactance value. It will not start at all.

Description : When the supply voltage to an induction motor is reduced by 10%, the maximum torque will decrease by about  A) 5% B) 10% C) 20% D) 40%

Last Answer : When the supply voltage to an induction motor is reduced by 10%, the maximum torque will decrease by about 20%

Description : The variable resistance placed in the rotor circuit of a wound-rotor induction motor provides for __________. A. speed control B. frequency control C. voltage control D. use as a split-phase motor

Last Answer : Answer: A

Description : Explain speed control method of 3 phase induction motor by the following methods: (1) Pole changing (2) Rotor resistance control (3) Stator voltage

Last Answer : 1) Pole Changing Method:  Synchronous speed is given by, From the above equation of synchronous speed, it can be seen that synchronous speed (and hence, running speed) can ... in voltage and consequently the speed decreases and vice versa. Ultimately speed depends on the supply voltage.

Description : The speed of a three-phase induction motor is controlled by variable voltage variable frequency control (i.e. keeping V/f constant). As the frequency is reduced, the slip at maximum torque  (1) Decreases (2) Increases (3) Remains constant (4) None of the above

Last Answer : The speed of a three-phase induction motor is controlled by variable voltage variable frequency control (i.e. keeping V/f constant). As the frequency is reduced, the slip at maximum torque Increases 

Description : The speed of a 4-pole induction motor is controlled by varying the supply frequency while maintaining the ratio of supply voltage to supply frequency (V/f ) constant. At rated frequency of 50 Hz and rated voltage of 400 V ... load torque is constant  (A) 882 rpm (B) 864 rpm (C) 840 rpm (D) 828 rpm

Last Answer : The speed of a 4-pole induction motor is controlled by varying the supply frequency while maintaining the ratio of supply voltage to supply frequency (V/f ) constant. At rated frequency of 50 Hz and rated voltage of 400 ... torque is constant  (A) 882 rpm (B) 864 rpm (C) 840 rpm (D) 828 rpm

Description : The actual speed of an induction motor is always • Less than synchronous speed • More than synchronous speed • Equal to synchronous speed • None of the above.

Last Answer : Less than the syncronous speed

Description : The synchronous speed for the seventh space harmonic mmf wave of a 3-phase, 8-pole, 50 Hz induction machine is  (A) 107.14 rpm in forward direction (B) 107.14 rpm in reverse direction (C) 5250 rpm in forward direction (D) 5250 rpm in reverse direction

Last Answer : The synchronous speed for the seventh space harmonic mmf wave of a 3-phase, 8-pole, 50 Hz induction machine is 107.14 rpm in forward direction 

Description : A 3-phase voltage source inverter is operated in 180o conduction mode. Which one of the following statements is true ?  (A) Both pole-voltage and line-voltage will have 3rd harmonic components ... from 3rd harmonic (D) Both pole-voltage and line-voltage will be free from 3rd harmonic components

Last Answer : A 3-phase voltage source inverter is operated in 180o conduction mode. Which one of the following statements is true ?  (A) Both pole-voltage and line-voltage will have 3rd harmonic components ... from 3rd harmonic (D) Both pole-voltage and line-voltage will be free from 3rd harmonic components

Description : A 3-phase voltage source inverter operates in 180° conduction mode with a star connected resistive load. If input dc voltage is 100 V, then the peak to peak output line voltage is :

Last Answer : A 3-phase voltage source inverter operates in 180° conduction mode with a star connected resistive load. If input dc voltage is 100 V, then the peak to peak output line voltage is : 200 V

Description : A single-phase voltage source square -wave inverter feeds pure inductive load. The waveform of the load current will be

Last Answer : A single-phase voltage source square -wave inverter feeds pure inductive load. The waveform of the load current will be triangular

Description : Why diodes should be connected in antiparallel with the thyristors in inverter circuits?

Last Answer : For RL loads, load current will not be in phase with load voltage and the diodes connected in antiparallel will allow the current to flow when the main thyristors are turned off. These diodes are called feedback diodes.

Description : A split-phase induction squirrel-cage motor will not come up to speed, even though the rated voltage, rated frequency, and rated load are applied. The suspected trouble could be due to _____________. A. a faulty centrifugal switch B. broken rotor bars C. worn bearings D. all of the above

Last Answer : Answer: D

Description : The speed of a multi-speed, squirrel-cage, induction motor operating in a fixed frequency system can be changed by _____________. A. reconnecting stator windings for different numbers of poles B. ... sequence of the applied voltage D. reconnecting the stator so that no poles have the same polarity

Last Answer : Answer: A

Description : A balanced three-phase, 50 Hz voltage is applied to a 3 phase, 4 pole, induction motor. When the motor is delivering rated output, the slip is found to be 0.05. The speed of the rotor m.m.f. relative to the rotor structure is (A) 1500 r.p.m. (B) 1425 r.p.m. (C) 25 r.p.m. (D) 75 r.p.m.

Last Answer : (D) 75 r.p.m.

Description : A three phase induction motor is driving full -load torque which is independent of speed. If the line voltage drops to 90% of the rated value, % increase in motor copper losses  (a) 23% (b) -18% (c) 123% (d) None of these

Last Answer : A three phase induction motor is driving full -load torque which is independent of speed. If the line voltage drops to 90% of the rated value, % increase in motor copper losses (a) 23% (b) -18% (c) 123% (d) None of these

Description : Stator Voltage Control of three phase induction motor

Last Answer : Stator Voltage Control of three phase induction motor

Description : Which statement out of the following is a wrong statement with regard to Induction motor? A) Auto-transformer starter is costlier to direct on line (DOL) starter B) DOL starter is used for ... Star delta starter connects the motor first in delta at the time of starting then in star for running

Last Answer : Which statement out of the following is a wrong statement with regard to Induction motor? A) Auto-transformer starter is costlier to direct on line (DOL) starter B) DOL starter is used for ... delta starter connects the motor first in delta at the time of starting then in star for running

Description : The stator of a 415V, 50 Hz, 4-pole slip ring Induction Motor is excited by rated frequency with slip rings open circuited. The rotor is made to rotate at a speed of 600 rpm in the opposite direction to the ... frequency of induced voltage across slip ring is A) 30 Hz B) 70 Hz C) 20 Hz D) 35 Hz

Last Answer : The stator of a 415V, 50 Hz, 4-pole slip ring Induction Motor is excited by rated frequency with slip rings open circuited. The rotor is made to rotate at a speed of 600 rpm in the opposite direction to the normal direction, The frequency of induced voltage across slip ring is 70 Hz

Description : Synchronous wattage of induction motor means: A) rotor input in watts B) stator input in watts C) combined stator and rotor input in watts D) shaft output in watts

Last Answer : Synchronous wattage of induction motor means: rotor input in watts 

Description :  Full load current of an Induction motor is 20 Ampere. The no-load current may be expected to be: A) 25 Ampere to 28 Ampere B) 15 Ampere to 18 Ampere C) 11 Ampere to 14 Ampere D) 6 Ampere to 10 Ampere

Last Answer : D

Description : An 8 pole wound rotor induction motor operating on 60 Hz supply is driven at 1800 r.p.m. by a prime mover in the opposite direction of revolving magnetic field. The frequency of the rotor current is (a) 30 Hz (b) 60 Hz (c) 120 Hz (d) 180 Hz 

Last Answer : 30 Hz As the frequency of the rotor is given by  F= N*P/120 so from the above equation the frequency of the rotor current can be easily calculated  i.e. 1800×8/120=30 Hence the required value of rotor frequency is 30 Hz

Description : A 6-pole, 50Hz, 3-φ induction motor is running at 950 r.p.m. and has Cu loss of 5kW. The rotor input is (a) 10 kW (b) 95 kW (c) 100 kW (d) 9.5 kW 

Last Answer : s=(Ns-N)/Ns =(1000-950)/1000=0.05.rotor cu.loss= s*rotor inputwe have rotor cu loss=5kWtherefore, rotor input= rotor cu.loss/s                              =5kW/0.05                              =100 kW

Description : The ratio of rotor output to rotor input in an induction motor is 0.96. The slip of the motor is (a) 0.04% (b) 4% (c) 6% (d) 12%

Last Answer : The ratio of rotor output to rotor input in an induction motor is 0.96. The slip of the motor is 4%

Description : A 400 V, 15 kW, 4-pole, 50 Hz, Y-connected induction motor has full load slip of 4%. The output torque of the machine at full load is  (A) 1.66 Nm (B) 95.50 Nm (C) 99.47 Nm (D) 624.73 Nm

Last Answer : A 400 V, 15 kW, 4-pole, 50 Hz, Y-connected induction motor has full load slip of 4%. The output torque of the machine at full load is 99.47 Nm

Description : The slip of an induction motor normally does not depend on  (A) rotor speed (B) synchronous speed (C) shaft torque (D) core-loss component

Last Answer : The slip of an induction motor normally does not depend on core-loss component

Description : Leakage flux in an induction motor is  (A) flux that leaks through the machine (B) flux that links both stator and rotor windings (C) flux that links none of the windings (D) flux that links the stator winding or the rotor winding but not both

Last Answer : Leakage flux in an induction motor is  flux that links the stator winding or the rotor winding but not both