Hi friends, this post is about induction motor objectives. These are some of the questions asked in previous question papers of Gate, IES and other competitive exams. check out and comment if you have any doubts....
1) An increase in number of poles of an induction motor results in
A) decrease in maximum pf
B) increase in maximum pf
C) no change in maximum pf
D) cannot be predicted
Ans:A
2) An induction motor with larger number of slots has................... overload capacity
A) low
B) large
C) no effect on
D) none of these
Ans:B
3) Increase in length of air-gap in an induction motor causes
A) decrease in power factor
B) decrease in pulsation losses
C) increase in ampere-turns required to produce same flux density in the air-gap
D) all of the above
Ans:D
4) The stator of a small(upto 5hp) induction motor is provided with
A) open slots with parallel teeth
B) open slots with tapered teeth
C) semi-closed slots with parallel teeth
D) totally closed slots with parallel teeth
Ans:C
5) In a 3-phase induction motor, the stator slots are
A) equal to rotor slots
B) exact multiple of rotor slots
C) not exact multiple of rotor slots
D) none of the above
Ans:C
6) The 3-phase induction motor provided with open slots has
A) reduced leakage reactance
B) increased starting current, starting torque and breakdown torque
C) better pf
D) improved efficiency
E) both (a) and (b)
Ans:E
7) Semi-closed or totally closed slots are used in induction motors essentially to
A) improve pull-out torque
B) increase pull-out torque
C) increase efficiency
D) reduce magnetizing current and improve power factor
Ans:D
8) Cogging in induction motor occurs when
A) number of stator teeth - number of rotor teeth = odd number
B) number of stator teeth - number of rotor teeth = even number
C) number of stator teeth - number of rotor teeth = 0
D) number of stator teeth - number of rotor teeth = negative number
Ans:C
9) To avoid cogging in a squirrel cage induction motor the following stator slots (Z1) and rotor slot (Z2) combination must be avoided
A) Z1 = Z2
B) Z1 - Z2 = 2 P + 1
C) Z1 - Z2 = 3 P + 1
D) Z1 - Z2 = 3 P - 1
Ans:A
10) skew of rotor bar eliminates
A) the effect of space harmonics
B) the entire effect of crawling
C) magnetic noise
D) vibration due to unequal force developed on rotor
Ans:A
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1) An increase in number of poles of an induction motor results in
A) decrease in maximum pf
B) increase in maximum pf
C) no change in maximum pf
D) cannot be predicted
Ans:A
2) An induction motor with larger number of slots has................... overload capacity
A) low
B) large
C) no effect on
D) none of these
Ans:B
3) Increase in length of air-gap in an induction motor causes
A) decrease in power factor
B) decrease in pulsation losses
C) increase in ampere-turns required to produce same flux density in the air-gap
D) all of the above
Ans:D
4) The stator of a small(upto 5hp) induction motor is provided with
A) open slots with parallel teeth
B) open slots with tapered teeth
C) semi-closed slots with parallel teeth
D) totally closed slots with parallel teeth
Ans:C
5) In a 3-phase induction motor, the stator slots are
A) equal to rotor slots
B) exact multiple of rotor slots
C) not exact multiple of rotor slots
D) none of the above
Ans:C
6) The 3-phase induction motor provided with open slots has
A) reduced leakage reactance
B) increased starting current, starting torque and breakdown torque
C) better pf
D) improved efficiency
E) both (a) and (b)
Ans:E
7) Semi-closed or totally closed slots are used in induction motors essentially to
A) improve pull-out torque
B) increase pull-out torque
C) increase efficiency
D) reduce magnetizing current and improve power factor
Ans:D
8) Cogging in induction motor occurs when
A) number of stator teeth - number of rotor teeth = odd number
B) number of stator teeth - number of rotor teeth = even number
C) number of stator teeth - number of rotor teeth = 0
D) number of stator teeth - number of rotor teeth = negative number
Ans:C
9) To avoid cogging in a squirrel cage induction motor the following stator slots (Z1) and rotor slot (Z2) combination must be avoided
A) Z1 = Z2
B) Z1 - Z2 = 2 P + 1
C) Z1 - Z2 = 3 P + 1
D) Z1 - Z2 = 3 P - 1
Ans:A
10) skew of rotor bar eliminates
A) the effect of space harmonics
B) the entire effect of crawling
C) magnetic noise
D) vibration due to unequal force developed on rotor
Ans:A
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