powerpoint presentation · 2020. 4. 17. · [uppcl (ae) 2016] a) 810 rpm b) 750 rpm c) 720 rpm d)...
TRANSCRIPT
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ashishsoniwifistudy
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1. The starting current of a 3-ϕ Induction motor is 5times the rated current, while the rated slip is 4%. The
ratio of starting torque to full-load torque is? [ESE 2001]
a) 0.6
b) 0.8
c) 1.0
d) 1.2
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2. The rotor power output of 3-phase induction motor is
15 KW. The rotor copper losses at slip of 4% will be?
[ESE 2001]
a) 600 W
b) 625 W
c) 650 W
d) 700 W
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3. Which one of the following statements is correct?
[ESE 2004]
a) as speed will reduce
b) its efficiency will improve
c) its power factor will reduce
d) its breakdown torque will reduce
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4. Which one of the following is the correct statement?
OR
In a 3-phase induction motor, the resultant flux is of a
constant nature and is? [ESE 2007]a) equal to 𝛟𝐦 where 𝛟𝐦 is maximum flux due to anyphase
b) 1.5 time maximum value of flux due to any
c)𝟑
𝟐times maximum value of flux due to any
d) 𝟑 𝛟𝐦
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5. When the applied rated voltage per phase is reduce
to one-half, the starting torque of a three-phase
squirrel cage induction motor becomes? [ESE 2006]
a) ½ of the initial value
b) ¼ of the initial value
c) Twice of the initial value
d) 4 times of the initial value
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6. If the full-load speed of a 3-phase, 50 Hz induction
motor is 950 rpm, what is its half-load speed nearly
equal to? [ESE 2007]
a) 1000 rpm
b) 450 rpm
c) 1900 rpm
d) 975 rpm
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7. Which one of the following statements is correct? A
smaller air gap in a polyphase induction motor helps
to? [ESE 2004]
a) reduce the chances of crawling
b) increase the starting torque
c) reduce the chance of cogging
d) reduce the magnetizing current
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8. The advantage of the double squirrel-cage
induction motor over single cage rotor is that its?
[ESE 2001]
a) efficiency is higher
b) power factor is higher
c) slip is larger
d) starting current is lower
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9. What is the frequency of rotor current of a 50 Hz
induction motor operating at 2% slip? [ESE 2007]
a) 1 Hz
b) 100 Hz
c) 2 Hz
d) 50 Hz
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10. A 6 pole, 50 Hz, 3 phase induction motor is running
at 950 r.p.m. It has rotor copper loss of 5 kW. The rotor
input will be: [UPRVUNL (AE) 2016]
a) 100 kW
b) 95 kW
c) 10 kW
d) 5.3 kW
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11. In AC rotating machines the generated or speed
EMF [RRB SSE 2015]a) leads ϕ by 90°b) lags ϕ by 90°c) is in phase with working fluxd) lags ϕ by 180°
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12. The crawling in an induction motor is caused by
[RRB SSE Secundrabad 2015]
a) Improper design of the machine
b) Low voltage supply
c) High loads
d) Harmonics developed in the motor
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13. Which of the following motors is represented by the
characteristic curve shown below?
[SSC JE Electrical 2017]
a) D.C. shunt motor
b) D.C. series motor
c) D.C. compound motor
d) Asynchronous motor
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14. Rotating magnetic field is produced in a ……..
[RRB SSE 2015]
a) Single-phase induction motor
b) Three-phase induction motor
c) D.C. series motor
d) A.C. series motor
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15. The output power of any electric motor is taken
from– [RRB JE 2015]
a) frame
b) commutator
c) coupling mounted on shaft
d) armature
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16. If the rotor circuit resistance of a 3 phase induction
motor is increased, then [UPPCL (AE) Electrical 2015]
a) The starting torque will increase but the maximum
torque will remain unchanged
b) Both the starting and the maximum torque will
decrease
c) The starting torque will decrease but the maximum
torque will remain unchanged
d) Both the starting and the maximum torque will
increase
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17. The following speed-torque characteristics are
obtained for a 3-phase induction motor. Pick up the
correct method of speed control from the option.
(Output constant) [APGenco-12]
a)𝐕
𝐟control
b)𝐄
𝐟control
c) pole changing with f constant
d) stator voltage control, f constant
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18. A 3-phase cage rotor induction motor has its stator
wound for 8 poles. The rotor of this motor can be used
in any other induction motor of the same size and
having [EPDCL-10]
a) 4 poles
b) 8 poles
c) 2 poles
d) any number of poles
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19. A 4-pole 3-phase induction motor which has a
rotor current of frequency 3Hz gets supply from a 6-
pole 3-phase alternator running at 600 rpm. At what
speed does the motor operates? [UPPCL (AE) 2016]
a) 810 rpm
b) 750 rpm
c) 720 rpm
d) 1060 rpm
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20. maximum internal torque generated in a
Polyphase induction motor cannot be referred as:-
[UPPCL (AE) 2016]
a) Stalling torque
b) Pull-out torque
c) Breakdown torque
d) total torque
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21. If rotor speed of an induction motor is 480 rpm and
rotor gross output is 2000W, the magnitude of shaft
torque developed is:- [UPPCL (AE) 2016]
a) 31.14 N-m
b) 39.80 N-m
c) 38.67 N-m
d) 41.89 N-m
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22. Sometimes, in a 3-phase induction motor, in order
to improve starting torque– [UPPCL 2016]
a) piece of wood are placed deep inside the rotor
b) copper bars are removed from the rotor
c) Cast Iron bearings are used to support rotor
d) copper bars are placed deep inside the rotor
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23. 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. [DMRC 2016]
a) (2s)
b) (1-s)
c) (2-s)
d) Zero
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24. A 3 phase, 50 Hz induction motor draws 50 kW from
the mains. If the stator losses are 2 kW and rotor emf
oscillates at 100 oscillations per minute the rotor
copper losses will be: [LMRC SC/TO 2015]
a) 1.8 kW
b) 1.2 kW
c) 1.9 kW
d) 1.6 kW
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25. A star/delta starter of a 3 phase induction motor is
equivalent to an auto transformer starter having a
tapping of: [LMRC SC/TO 2015]
a)𝟏
𝟑
b)𝟑
𝟐
c)𝟏
𝟐
d) 𝟑
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26. The rotor reactance per phase, in an induction
motor is– [UPPCL 2016]
a) directly proportional to the square of slip
b) directly proportional to slip
c) inversely proportional to the square of slip
d) inversely proportional to slip
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27. A 3-phase delta connected squirrel cage induction
motor when started with a DOL starter has a starting
torque of 600NM. Its starting torque when star delta
starter is used: [DMRC 2016 & Uttarakhand AE Electrical
2013]
a) 600Nm
b) 200Nm
c) 300Nm
d) 1200Nm
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28. The main reason for low power factor is the
installation of: [LMRC SC/TO 2015]
a) synchronous motors
b) single phase motor
c) induction motors
d) rectifiers
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29. The major disadvantage of DOL starting of
Induction motors is that its application is restricted to–
[UPPCL 2016]
a) low horsepower motors
b) high speed motors
c) high horsepower motors
d) variable speed motors
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30. Slip ring motor is preferred over Squirrel Cage
motor when– [UPPCL 2016]
1. high starting torque is required
2. load torque is heavy
3. heavy pull out torque is required
a) Only 3
b) Only 1
c) Only 1 and 2
d) Only 2 and 3
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31. Which of the following does not increase/improve
when load on Squirrel Cage induction motor is
increased from No-load to Full-load? [UPPCL 2016]
a) Stator power factor
b) Torque developed by the motor (up to the
magnitude of applied torque)
c) Slip
d) Magnetising component of stator exciting current
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32. The torque of an induction motor in synchronous
watt is equal to [MP JE 2016]
a) rotor input
b) stator output
c) stator input
d) watts at rotor speeds
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33. The low power factor of induction motor is due to
[UPSSC 2015]
a) rotor leakage reactance
b) stator reactance
c) the reactive lagging magnetizing current necessary
to generate the magnetic flux
d) all of the above
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34. In a three phase Induction motor normally
[UPSSC 2015]
a) the rotor rotates in the direction of the rotating
magnetic field
b) The rotor rotates against the direction of the rotating
magnetic field
c) the rotor rotates depending upon the supply given
to it
d) The direction of rotor rotation does not depend
upon the phase sequence of the stator supply
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35. The stator of 5 H.P. induction motors is provided with
[IOF 2014]
a) Open slots with tapered teeth
b) Open slots with parallel teeth
c) Closed slots with parallel teeth
d) Semi closed slots with parallel teeth
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36. 3-phase, 50 Hz, 500 V induction motor develops 20
HP at slip of 5%. Mechanical losses are 1 HP, and stator
loss is 1 kW. The efficiency will be [Uttrakhand 2013]
a) 95.3%
b) 90.5%
c) 91.3%
d) 85.3%
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(28) In a steam power plant…………heats the feed water on its way to the boiler by
delivering heat from the flue gases: -
(A) Superheater (B) Economizer
(B) Preheater (D) Turbine
(29) Power generation of thermal power plants is based on: -
(A) Rankine cycle
(B) Otto cycle
(C) Diesel cycle
(D) Carnot cycle