1. The power factor of an induction motor under no-load conditions will be closer to
(a) 0.2 lagging
(b) 0.2 leading
(c) 0.5 leading
(d) unity
Ans: a
2. The 'cogging' of an induction motor can be avoided by
(a) proper ventilation
(b) using DOL starter
(c) auto-transformer starter
(d) having number of rotor slots more or less than the number of stator slots (not equal
Ans: d
3. If an induction motor with certain ratio of rotor to stator slots, runs at 1/7 of the normal speed, the phenomenon will be termed as
(a) humming
(b) hunting
(c) crawling
(d) cogging
Ans: c
4. Slip of an induction motor is negative when
(a) magnetic field and rotor rotate in opposite direction
(b) rotor speed is less than the syn-chronous speed of the field and are in the same direction
(c) rotor speed is more than the syn-chronous speed of the field and are in the same direction
(d) none of the above
Ans: c
5. Size of a high speed motor as compared to low speed motorfor the same H.P. will be
(a) bigger
(b) smaller
(c) same
(d) any of the abov
Ans: b
6. A 3-phase induction motor stator delta connected, is carrying full load and one of its fuses blows out. Then the motor
(a) will continue running burning its one phase
(b) will continue running burning its two phases
(c) will stop and carry heavy current causing permanent damage to its winding
(d) will continue running without any harm to the winding
Ans: a
7. A 3-phase induction motor delta connected is carrying too heavy load and one of its fuses blows out. Then the
motor
(a) will continue running burning its one phase
(b) will continue running burning its two phase
(c) will stop and carry heavy current causing permanent damage to its winding
(d) will continue running without any harm to the winding
Ans: c
8. Low voltage at motor terminals is due to
(a) inadequate motor wiring
(b) poorely regulated power supply
(c) any one of the above
(d) none of the above
Ans: c
9. In an induction motor the relationship between stator slots and rotor slots is that
(a) stator slots are equal to rotor slots
(b) stator slots are exact multiple of rotor slots
(c) stator slots are not exact multiple of rotor slots
(d) none of the above
Ans: c
10. Slip ring motor is recommended where
(a) speed control is required
(6) frequent starting, stopping and reversing is required
(c) high starting torque is needed
(d) all above features are required
Ans: d
11. As load on an induction motor goes on increasing
(a) its power factor goes on decreasing
(b) its power factor remains constant
(c) its power factor goes on increasing even after full load
(d) its power factor goes on increasing upto full load and then it falls again
Ans: d
12. If a 3-phase supply is given to the stator and rotor is short circuited rotor will move
(a) in the opposite direction as the direction of the rotating field
(b) in the same direction as the direction of the field
(c) in any direction depending upon phase squence of supply
Ans: b
13. It is advisable to avoid line starting of induction motor and use starter because
(a) it will run in reverse direction
(b) it will pick up very high speed and may go out of step
(c) motor takes five to seven times its fullload current
(d) starting torque is very hig
Ans: c
14. The speed characteristics of an induction motor closely resemble the speedload characteristics of which of the
following machines
(a) D.C. series motor
(b) D.C. shunt motor
(c) universal motor
(d) none of the above
Ans: b
15. Which type of bearing is provided in small induction motors to support the rotor shaft
?
(a) Ball bearings
(b) Cast iron bearings
(c) Bush bearings
(d) None of the above
Ans: a
16. A pump induction motor is switched on to a supply 30% lower than its rated voltage.
The pump runs. What will eventually happen ? It will
(a) stall after sometime
(b) stall immediately
(c) continue to run at lower speed without damage
(d) get heated and subsequently get damaged
Ans: d
17. 5 H.P., 50-Hz, 3-phase, 440 V, induction motors are available for the following r.p.m.
Which motor will be the costliest ?
(a) 730 r.p.m.
(b) 960 r.p.m. (c) 1440 r.p.m. (d) 2880 r.p.m
. Ans: a
18. A 3-phase slip ring motor has
(a) double cage rotor
(6) wound rotor
(c) short-circuited rotor
(d) any of the above
Ans: b
19. The starting torque of a 3-phase squirrel cage induction motor is
(a) twice the full load torque
(b) 1.5 times the full load torque
(c) equal to full load torque
Ans: b
20. Short-circuit test on an induction motor cannot be used to determine
(a) windage losses
(b) copper losses
(c) transformation ratio
(d) power scale of circle diagram
Ans: a
No comments:
Post a Comment