Electrical Machines - Special Purpose Machines

Special Purpose Machines - IAS previous year questions......

1.  which one of the following can be obtained by the equivalent circuit of an electrical machine?
[IAS-1993]
a. Temperature rise of the machine.
b. Type of protection used in the machine
c.  Design parameters of the windings
d. Type of protection used in the machine.

2.  the voltage across the open -circuited field terminals of a synchronous machine under slip test is [IAS-1994]
a. DC
b. Ac of slip frequency
c. a modulated supply frequency ac voltage with slip frequency envelope
d. Ac of supply frequency

3.  In a line printer used to print the output of a computer the paper is required to be advanced by a line spacing as soon as printing of the line is over. which one of the following motors is best suited for this application ?
[IAS-1995]
a. Dc motor
b. Synchronous motor
c. Induction motor
d. Steper motor

4.  Consider the following statements about single phase reluctance motor:
1. The starting torque is a function of rotor position.
2. The torque developed at sub synchronous speeds varies sinusoidally.
3. Starting is asynchronous but running is synchronous.
4. It pulls synchronism on switching on dc excitation.
Of these statements correct : [IAS-1996]
a.1,2&3
b.2,3&4
c.1,3&4
d. 1&4

5. For proper synchronisation of a large synchronous machine to a bus, the frequency of the-incoming machine [IAS-1997]
a. Should be equal to
b. Should be higher than
c. Should be lower than
d. Any value

6. In the slew range of a stepper motor, it [IAS-2001]
a. can start, stop and reverse as desired
b. cannot start but can stop and reverse on command
c. cannot start, stop and reverse on command
d. cannot start and synchronize but can reverse or command

Electrical Machines - Special Purpose Machines

Special Purpose Machines - IES Previous year questions.....

1. Hysteresis motors are used for Hi-Q record players because of their [IAS-1998]
a. Constant synchronous speed
b. insensitivity to supply voltage fluctuations
c. Extreamly study torque
d. non-dependence on centrifugal switch requirement

2. A two-phase servomotor develops maximum torque at [IAS-1999]
a.  Forward speed  half of the synchronous speed
b. Reverse speed  half of the synchronous speed
c. Synchronous speed
d. Twice the synchronous speed

3. In a shaded-pole induction motor, the rotor runs from the [IAS-2000]
a. shaded portion to the unshaded portion of the pole while the flux in the former leads that of the latter
b. shaded portion to the unshaded portion of the pole while the flux in the former lags that of the latter
c. unshaded portion to the shaded portion of the pole while the flux in the former leads that of the latter
d. Unshaded portion to the shaded portion of the pole while the flux in the former lags that of the latter

4.  Stepper motor are widely used because of [IAS-2001]
a. Wide speed range
b. no need for field control
c. Compatibility with digital system
d. large rating

5. Consider the following types of single phase motors:
1. Capacitor starts induction motor 2. Capacitor start and run induction motor
3. Permanent split capacitor motor 4. Shaded pole motor
The correct sequence of these in the ascending order of magnitude of starting torque is [IAS-2003]
a. 4,3,2,1
b. 2,3,4,1
c. 3,4,2,1
d. 1,2,3,4

6. For a reluctance type motor, if the stator magnetic field angular velocity is 'W' and the actual rotor angular velocity is 'Wr' then which one of the following equation is satisfied if the average electromagnetic torque is NOT zero? [IAS-2004]
a. W=Wr/2
b. W= Wr
c. W=2*Wr
d. W=4*Wr

7. In hand tool applications, which one of the following single phase motor is used? [IAS-2005]
a. Shaded pole motor
b. Capacitor run motor
c. Capacitor start motor
d. Ac series motor

8. In which one of the following is reluctance power developed? [IAS-2006]
a. Salient pole motor
b. Non-sailent pole motor
c. Squirrel cage induction motor
d. Transformer.

9. ) Match List -I with List -II and select the correct answer using the code given below the lists :
List - I
A. General purpose split phase FHP(Fractional HP) motor
B. General purpose capacitor start FHP motor
C. Permanent split capacitor start FHP motor
D. Shaded pole FHP motor
List-II
1. Refrigerator
2. Hair dryers
3. Unit Heaters
4. Fans, Blowers [IAS-2007]
a. A-1, B-2, C-4, D-3
b. A-4, B-1, C-2, D-3
c. A-4, B-1, C-3, D-2
d. A-4, B-3, C-2, D-1

10. The emf induced in a conductor of machine driven at 600 rpm, the peak value of flux density is 1.0 Wb/m 2 ., diameter of machine 2.0 meter and length of machine 0.30 m is [IAS-2010]
a. 41.83
b. 29.58
c. 9.42
d. 18.84

1. Statement (I) : The rotor of a servomotor is built with resistance so that its X/R ratio becomes small. Statement (II): The servomotor has good accelerating characteristics. [IAS-2012]
a. Both are true and Statement (II) correct explanation for Statement(I)
b. Both are true and Statement (II) not  correct explanation for Statement(I)
c. Statement(I) is correct and Statement (II) is false
d. Statement(I) is false and Statement (II) is true

Electrical Machines - Special purpose machines

Special purpose machines - GATE previous year questions....

1. The developed electromagnetic force and/or torque in electro-mechanical energy conversion systems act in a direction that tends [GATE-1992]
a. to increase the stored energy at constant mmf
b. to decrease the co-energy at constant mmf
c. to increase the co-energy at constant mmf
d. to decrease the stored energy at constant mmf

2. Which material is used in controlling chain reaction in a nuclear reactor? [GATE-1996]
a. Thorium
b. Boron
c. Heavy water
d. Beryllium

3. Ratio of the rotor reluctance X to the rotor resistance R for a two-phase servomotor [GATE-2000]
a. Equal to the induction motor
b. Less than to the induction motor
c. More than to the induction motor
d. More than or Less than to the induction motor

4. List-I lists different applications and List-II lists the motors for these applications . Match the application with the most suitable motor and choose the right combination among the choices given these after
List - I 
A. Food mixer 
B.Cassette tape recorder
C.Domestic water pump
D.Escalator
List - II
1 . Permanent magnet dc motor
2. Single -phase induction on motor
3. Universal motor
4.Three-phase induction motor
5.Dc series motor
6.
[GATE-2003]
a.  A-3,B-6,C-4,D-5
b. A-1,B-3,C-2,D-4
c.  A-3,B-1,C-2,D-4
d. A-3,B-2,C-1,D-4

5. The type of single –phase induction motor having the highest power factor at full load is [GATE-2004]
a. Shaded pole
b. Split phase
c. Capacitor run
d Capacitor start

6. In a single phase induction motor driving a fan load , the reason for having a high resistance rotor is to achieve  [GATE-2005]
a. low starting torque
b. High efficiency
c. Quick acceleration
d. Reduced size

7. For a single phase capacitor start induction motor which of the following statements is valid ? [GATE-2006]
a. the direction of rotation can be changed by interchanging the supply terminals
b. Direction of rotation can not be changed
c. Capacitor is used for Power factor improvment
d.  the direction of rotation can be changed by interchanging the supply terminals

8.  A 3-φ, 3 stack ,variable reluctance step motor has 20 poles on each rotor andstator stack .The step angle of this step motor is  [GATE-2007]
a. 3 degrees
b. 6 degrees
c. 9 degrees
d. 12 degrees

9. Distributed winding and short chording employed in AC machines will result in  [GATE-2008]
a. Increase in EMF and reduction in harmonics
b. Decrease in EMF and induction in harmonics
c. Decrase in EMF and harmonics
d. Increase in EMF and harmonics

Electrical Machines - Synchronous Machines

Synchronous Machines - IAS previous year questions.....

1. A synchronous machine working in the motor mode, 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 [IAS-1994]
a. Absorbs active power and reactive power from the bus.
b. Delivers active power and reactive power to the bus
c. Absorbs active power from the bus and delivers reactive power to the bus
d. Absorbs reactive power from the bus and delivers active power to the bus

2. In a synchronous generator operating at zero pf lagging, the effect of armature reaction is
[IAS-1995]
a. Magnetising
b. Demagnetising
c. Cross magnetising
d. Both magnetising and demagnetising

3. Consider the following statements about a three phase synchronous generator synchronized to an infinite bus when its mechanical input is increased gradually with field current held constant:
1. The power factor of the current supplied becomes more lagging.
2. The power factor of the current supplied improves.
3. The power factor remains unity. 4. The load angle is increased Of these statements [IAS-1996]
a. 1 alone is correct
b. 2 alone is correct
c. 2 and 4 is correct
d. 3 and 4 is correct

4. A 3-phase alternator delivers power to a balanced 3-phase load of power factor 0.707 lagging. It is observed that the open-circuit emf phasor leads the corresponding terminal voltage phasor by Neglecting the effect of harmonics, the angle between the axis of the main field mmf and the axis of the armature mmf will be [IAS-1997]
a. 30 degrees electrical
b. 60 degrees electrical
c. 90 degrees electrical
d. 150 degrees electrical

5. A 3-phase alternator delivers power to a balanced 3-phase load of power factor 0.707 lagging. It is observed that the open-circuit emf phasor leads the corresponding terminal voltage phasor by Neglecting the effect of harmonics, the angle between the axis of the main field mmf and the axis of the armature mmf will be  [IAS-1998]
a. 240 V  b. 220 V  c. 200 V  d. 180 V

6. In a synchronous machine, the electric circuits are armature circuit, field circuit and damper circuit and X is d-axis synchronous reactance; X' is d-axis transient synchronous reactance and X" is d-axis sub-transient synchronous reactance. If there is no damper winding, then [IAS-1999]
a. X = X'
b. X' = X"
c. X = X"
d. X = X' = X"

7. A 3-phase 20-pole,synchronous generator has 180 stator slots with single-layer full pitch coils.There are 6 conductors per slot and all coils per phase are committed in have series. The rotor is driven at 300 rpm and the flux per pole (sinusoidally distributed) is 25 mWb. The voltage induced per phase is nearest to
[ IAS-2000]
a. 1000   b. 500   c. 1500   d. 2000

8. An alternator is operating on infinite bus. It will develop maximum synchronizing power when it is operating at [ IAS-2001]
a. No load
b. Full load
c. Steady state stability limit
d. Any load

9. Which of the following information is obtained, by Potier's method using open circuit characteristic and zero power factor characteristics ? [ IAS-2003]
a.field current equivalent to armature reactance.
b. Synchronous reactance
c. Leakage reactance
d. Both a and b

10. A 3-phase cylindrical rotor alternator is delivering rated power to a grid at its rated power factor On account of some fault, steam supply to the turbine of the alternator is cut-off. The alternator would [ IAS-2004]
a. Stop
b. continue running as an alternator at synchronous speed Ns and deliver active power to the grid
c. continue running as a synchronous motor at Ns and deliver reactive power to the grid.
d. continue running as a synchronous motor at and absorbs reactive power from the grid.

11. Consider the following statements for a single -phase hysteresis motor :
1.Torque is constant from standstill up to synchronous speed .
2.Rotor is provided with narrow slots embedded with bars.
3. Torque at starting is somewhat more than that at synchronous speed
4. As the name suggests. only hysteresis torque is produced from zero speed right up to
5. Rotor material possesses very wide hysteresis loop
which of the statements given above [ IAS-2005]
a. 1,2 and 5 correct.
b. 3 and 5 correct.
c. 1 and 4 correct.
d. 2,3 and 4 correct.

12. An under-excited synchronous motor is operating at no load on an infinite bus of voltage 7.o p.u and drawing a current of 0.8 p.i. Its synchronous reactance is 0.5 p.u. What is the p.u. value of its excitation emf ? [ IAS-2006]
a. 1.4       b. 1.0      c. 0.6      d 0.4

Electrical Machines - Synchronous Machines

Synchronous Machines - IES Previous year wise questions......

1. If the dimensions of all the parts of a synchronous generator, and the number of field and armature turns are doubled, then the generated voltage will change by a factor of  [IES-1997]
a. 1         b. 2        c. 4       d. 8

2. The phasor diagram of a synchronous machine connected to an infinite bus is shown i above figure The machine is acting as a (on graph x-axis terminal voltage 'v' and at some angle induced voltage 'E' & angle is approxmatly at 45) [IES-1998]
a. Generator and operating at leading power factor
b. Generator and operating at lagging power factor
c. Motor and operating at leading power factor
d. Motor and operating at lagging power factor

3. 1) Match List I (Power factor) with list II (Armature reaction of an alternator) and select the correct answer :
List I
A. UPF
B. ZPF lagging
C. ZPF leading
D. Intermediate Lagging
List II
1. Fully demagnetising
2. Fully magnetising
3. Cross - magnetising
4. Partly cross-magnetising and
5. partly demagnetising [IES-2000]

        A.       B.        C.       D
a.     3.        1.        4.       2
b.     3.        1.        2.       4
c.     1.        3.        2.       4
d.     1.        3.        4.       2

4. Match List - I (equivalent circuit parameter) with List -II(Values) for a 50 MVA three phase alternator and select the correct answer
List - I
A. Armature resistance
B. Synchronous reactance
C. Leakage reactance
List - II
1. 1pu
2. 0.1 pu
3. 0.01 pu [IES-2001]
a. A-1,B-2,C-3
b. A-3,B-1,C-2
c. A-3,B-2,C-1
d. A-1,B-3,C-2

5. When the excitation of normally operating unloaded salient-pole synchronous motor suddenly gets disconnected. it continues to run as a [IES-2002]
a. S charge motor
b. Spherical motor
c switched reluctance motor
d variable reluctance motor

6. If the field of a synchronous motor is under-excited, the power factor will be [IES-2003]
a. Leading
b. Lagging
c. Unity
d. More than unity

7.  Which one of the following is the primary reason for placing field on rotor in an alternator? [IES-2004]
a. Low current in field circuits
b. Insulation of high voltage is made easy on stator than on rotor
c. Large power in stator
d. Large current in stator

8. A synchronous motor is operated from a bus zero power factor lading current. Its synchronous reactance is 0.5u. What is the excitation emf of the motor? [IES-2005]
a. 2.0    b. 1.5.    c. 1.0    d. 0.5

9. A loss-less cylindrical rotor synchronous generator is floating on the system bus bar after being properly synchronized and is running at no-load. Now, if the prime mover is acting as a mechanical load on the machine, then [IES-2006]
a. the torque developed by the machine will act in the same direction as the prime-mover torque
b. the torque developed by the machine will act in the opposite direction to that of the prime mover torque
c. the machine rotor would fall-back and the induced emf would lag behind the terminal voltage
d.  the machine rotor would fall-back and the induced emf would lead the terminal voltage

10. A 10 pole, 25 Hz alternator is directly coupled to and is driven by 60Hz synchronous motor. What is the number of poles for the synchronous motor [IES-2007]
a. 48     b. 12       c. 24      d. 16

11.  Assertion (A) : AC armature winding are short chorded by selecting value of coil span more than the pole pitch.
Reason (R) : Short chording is done to eliminate harmonics in the induced e.m.f  [IES-2008]
a. Both are true and reason is correct explanation for assertion
b. Both are true and reason is not correct explanation for assertion
c. Assertion is correct and reason is false
d. Assertion is false and  reason is true

12. The resultant flux density in the air gap of a synchronous generator is the lowest during
a. Open circuit
b. Solid Short circuit
c. At half-load
d. At full-load

13. A three phase 50 Hz, 11KV and 37.5 MW at 0.9 p.f. capacity synchronous generator has its stator bore diameter of 765 cm and an axial core length of 80 cm. For which power plants this generator is suitable? [IES-2009]
a. Thermal coal fired plant
b. Hydroelectric power plant
c. Nuclear power plant
d. pumped Storage power plant

14. Consider the following :
1.EMF
2. Reversal
3. MMF
4.Direct
which method among these are for the determination of voltage regulation of an alternator?  [IES-2010]
a. 1,2,3 and 4
b. 1 and 3
c.  1 and 2
d.  2 and 3

15. Assertion (A) : While running on light load a salient pole synchronous machine can continue to operate on infinite bus - bars even if its excitation fails.
Reason (R) : A Salient pole machine develops reluctance power due to the variable reluctance offered by the salient poles  [IES-2011]
a. Both are true and reason is correct explanation for assertion
b. Both are true and reason is not correct explanation for assertion
c. Assertion is correct and reason is false
d. Assertion is false and  reason is true

16.  A synchronous generator has its effective internal impedance Zs = 10 ohm and resistance Ra = 1.0 ohm . Its generated voltage Ef and terminal voltage Vt are both 500 V. The maximum power out put is [IES-2012]
a. 5000w
b. 4550W
c. 3000 W
d. 2250 W

17. The maximum power delivered by 1500 kW, 3-phase, star-connected, 4 kV, 48 pole 50 Hz synchronous motor, with synchronous reactance of 4n/phase and unity power factor [IES-2013]
a. 4271.2 kw
b. 35.5 kw
c. 120.61 kw
d. 2078 kw

Electrical Machines - Synchronous Machines

Synchronous Machines - GATE previous year questions......

1. The torque angle of a synchronous machine operating from a constant voltage bus, is usually defined as the space angle between [GATE- 1992]
a. Rotor mmf wave and stator mmf wave
b. Rotor mmf wave and resultant flux density wave
c.  Stator mmf wave and resultant flux density wave
d. Stator mmf wave and resultant wave

2. A synchronous motor operates at 0.8 p.f lagging. If the field current of the motor is continuously increased [GATE-1993]
a. the power factor decreases upto a certain value of field current and there after it increases
b. the armature current increases upto a certain value of field current and thereafter it decreases
c. the power factor increases upto a certain value of field current and there after it decreases
d. the armature current decreases upto a certain value of field current and thereafter it increases

3. A synchronous motor on load draws a current at a leading power factor angle 'x'.If the internal power factor angle – which is the phase angle between the excitation e.m.f. and the current in the time phasor diagram is 'y', then the air gap excitation m.m.f lags the armature m.m.f by [GATE- 1995]
a. A
b. Pi/2 + A
c. Pi/2 - A
d. Pi/2+x
( where A is )

4. A cylindrical rotor synchronous motor is switched on the supply with its field windings shorted on themselves. It will [GATE- 1996]
a. It will not start
b. Start but not run at synchronous speed
c. Start as induction motor and run as synchronous motor
d. Start and run as synchronous motor

5. The armature of a single phase alternator is completely wound with T single turn coils distributed uniformly. The induced voltage in each turn is 2V (rms). The emf of the whole winding is [GATE- 1998]
a. 2 T volts
b. 1.11 T volts
c. 1.414 T volts
d. 1.273 T volts

6. A three phase alternator is wound with a 60 degree phase-spread armature windings and develops 300 kVA. If the armature is reconnected utilizing all the coils for single phase operation with a phase spread of 180 degrees, the new rating of the machine is
[GATE- 1999]
a. 100 kva             b. 200 kva
c. 250 kva              d. 300 kva

7. It is desirable to eliminate harmonic voltage from the phase voltage of an alternator. The coils should be short-pitched by an electrical angle of [GATE-2000]
a. 30 degrees        b. 36 degrees
c. 72 degrees        d. 18 degrees

8. X,X',X"are steady state d-axis synchronous reactance, transient d-axis reactance and sub-transient d-axis reactance of a synchronous machine respectively. Which of the following statements is true? [GATE-2001]
a.  X>X'>X"
b. X">X'>X
c.  X'>X">X
d. X>X">X

9. The flux per pole in a synchronous motor with the field circuit ON and the stator disconnected from the supply is found to be 25 mWb. When the stator is connected to the rated supply with the field excitation unchanged, the flux per pole in the machine is found to be 20 mWb while the motor is running on no load. Assuming no load losses to be zero, the no load current down by the motor from the supply [GATE-2002]
a. Lags the supply voltage
b. Leads the supply voltage
c. In phase with the supply voltage
d.is Zeo

10. A 400 V, 50 kVA, 0.8 pf leading ∆-connected ,50 Hz synchronous machine has asynchronous reactance of 2 Ω and negligible armature resistance . The friction and windage losses are 2 kW and the core loss is 0.8 kW. The shaft is supplying9 kW load at a power factor of 0.8 leading . The line current drawn is  [GATE-2004]
a. 12.29A                b.16.24 A
c. 21.29 A                d. 36.88A

11.  A 3-phase ,400 V, 5 kW, star connected synchronous motor having an internal reactance of 10 Ω is operating at 50 % load, unity power factor . Now, the excitation is increased by 1%. What will be the new load in percent ,if the power factor is to be kept same ? Neglect all losses and consider linear magnetic circuit [GATE-2006]
a. 67.9 %                  b. 56.9 %
c. 51 %                      d. 50 %

12. A 100 kVA, 415(line) ,star-connected 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 10A is equal to the rated armature current . The per unit saturated synchronous reactance is [GATE-2007]
a. 1.731 b. 1.5   c. 0.666  d. 0.577

13. A synchronous motor is connected to an infinite bus at 1.0 pu voltage and draws 0.6 pu current at unity power factor . Its synchronous reactance is 1.0 pu and resistance is negligible
The excitation voltage (E) and load angle (δ) will respectively be  [GATE-2008]
a. 0.8 pu and 36.86 degrees lead
b. 0.8 pu and 36.86 degrees lag
c. 1.76 pu and 30.96 degrees lag
d. 1.76 pu and 30.96 degrees lead

14. A 500MW, 21kV,, 50Hz, 3-phase, 2-pole synchronous generator having a rated p.f=0.9, has a moment of inertia of
27.5* 10^3 kg-m^2 . The inertia constant (H) will be  [GATE-2009]
a. 2.44 s.                    b. 2.71 s
c. 4.88 s.                     d. 5.42 s

15. The direct axis and quadrature axis reactance’s of a salient pole alternator are 1.2p.u and 1.0p.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 [GATE-2011]
a. 30 degrees
b. 45 degrees
c. 60 degrees
d. 90 degrees

Electrical Machines - Induction Machines

Induction Machine -IAS previous year questions.....

1. Consider the following statements regarding the equivalent circuit parameters of an induction motor :
1. Leakage reactance is dependent on supply current
2. Magnetising reactance is dependent on the air-gap flux
3. Core loss is dependent on the input voltage and frequency.
4. Rotor resistance is dependent on the speed Of these statements [IAS-1993]
a. 2 & 4 correct
b. 1,3 & 4 correct
c. 1,2,3 & 4 correct
d. 1,2 & 4 correct

2. A 3-phase induction machine operates on 3-phase fixed frequency ac mains at a per unit slip of 1.5 Consider the following statements regarding the operating condition of the machine.
1. It draws electric power from the mains
2. It draws mechanical power through the shaft
3. It delivers electrical power to the mains
4. It delivers mechanical power through the shaft . Of these statements : [IAS-1995]
a. 1 and 2 correct
b. 1 and 4 correct
c. 2 and 3 correct
d. 3 and 4 correct

3.  A 3-phase induction motor draws 1000 kVA at a pf of 0.8 lag. A synchronous condenser is connected in parallel to draw an additional 750 kVA ot 0.6 pf lead" The pf of the total load supplied by the mains is [IAS-1996]
a. unity                    b. 0.707 lead
b. 0.707 lag             d. Zero

4. Consider the following statements about the operation of a three-phase induction motor running at full load : If one of the supply line fuse blows off, the motor will
1. stall
2. continue to run with increased slip,
3. continue to run with normal supply current
4. continue to run with excessive supply current
Of these statements [IAS-1997]
a. 1 alone correct
b. 3 alone correct
c. 2 and 3 correct
d. 2 and 4 correct

5.  Consider the following statements: As a 3-phase induction motor is loaded from no load to rated load,
1.there is an improvement in the power factor.
2. the torque increases almost in proportion to slip.
3. the air-gap flux falls sharply. Of these statements [IAS-1998]
a. 1, 2 and 3 correct
b. 1 and 3 correct
c. 1 and 2 correct
d. 2 and 3 correct

6.  A 3-phase induction motor has a full-load slip of 3 per cent at normal voltage. Which one of the following will be the value of the slip of the motor if it develops the same torque theoretically while operating at 110 per cent of its normal voltage? [IAS-1999]
a. 2.48 %               b. 0.248%
c. 0.483%               d. 4.83%

7. Two separate induction motors having 6 poles and 4 poles are cascaded 3-phase, 400 V, 60Hz is the supply to the motors. The synchronous speeds (in rpm) of cascaded set will be [IAS-1999]
a. 720, 1200, 1800 and 2400
b. 600, 1000, 1500 and 3000
c. 720, 1200, 1800 and 3600
d. 600, 1200, 1800 and 2400

8. In a 3-phase induction motor,the rotor impedance angle at standstill is e. The load angle will be [IAS-2001]
a. Pi + thita
b. Pi - thita
c. Pi/2 + thita
d. Pi/2

9. The power input to an induction motor is 50 kW when it is running at 4% slip. If the stator resistance and core losses are neglected, the rotor copper loss is equal to [IAS-2002]
a. 38Kw    b. 20 Kw    c. 4Kw   d. 2Kw

10. Under variable frequency operation of 3-phase induction motor air gap flux is kept constant by adjusting the motor voltage.For constant air gap flux machine develops the same torque when the [IAS-2003]
a. Slip is kept constant
b. Slip speed is kept constant
c. power flow across the air gap is kept constant
d. Power input to stator is kept constant

11. 1) Match List -I (Motor) with List -II (Application) and select the correct answer using the code given below the Lists :
List-I (Motor)    
A. Hysteresis motor                                 B. Shaded-pole motor                                C. Reluctance motor 
D. Universal motor    
List-II (Application)
1. Photocopying machine
2. Phonograph turntable
3. Electric Shaver
4. Record player  [IAS-2006]

CODES.     A           B          C         D
          a.    4          3            2         1
          b.    2          1            4         3
          c.     4          1            2         3
          d.     2          3           4         1

12. In an induction motor, what will happen if air-gap is increased ?
[IAS-2008]
a. Speed will reduces
b. Efficiency will improves
c. Power factor will lowered
d break-down torque will reduces