1. Which of the following loss in a D.C. generator is dissipated in the form of heat?
(a) Mechanical loss
(b) Core loss
(c) Copper loss
(d) All of the above
Ans: d
2. Which of the following losses are significantly reduced by laminating the core of a
D.C. generator ?
(a) Hysteresis losses
(b) Eddy current losses
(c) Copper losses
(d) Windage losses
Ans: b
3. The total losses in a well designed D.C. generator of 10 kW will be nearly
(a) 100 W
(b) 500 W
(c) 1000 W
(d) 1500 W
Ans: b
4. The condition for maximum efficiency for a D.C. generator is
(a) eddy current losses = stray losses
(b) hysteresis losses = eddy current losses
(c) copper losses = 0
(d) variable losses = constant losses
Ans: d
5. D.C. generators are normally designed for maximum efficiency around
(a) full-load
(b) rated r.p.m.
(c) rated voltage
(d) all of the above
Ans: a
6. In a D.C. generator, the iron losses mainly take place in
(a) yoke
(b) commutator
(c) armature conductors
(d) armature rotor
Ans: d
7. D.C. generators are installed near the load centres to reduce
(a) iron losses
(b) line losses
(c) sparking
(d) corona losses
Ans: b
8. The purpose of retardation test on D.C. shunt machines is to find out
(a) stray losses
(b) eddy current losses
(c) field copper losses
(d) windage losses
Ans: a
9. Which of the following tests will be suitable for testing two similar D.C. series motors of large capacity ?
(a) Swinburne's test
(b) Hopkinson's test
(c) Field test
(d) Brake test
Ans: c
10. Hopkinson's test on D.C. machines is conducted at
(a) no-load
(b) part load
(c) full-load
(d) overload
Ans: c
11. During rheostat braking of D.C. series motors
(a) motor is run as a generator
(b) motor is reversed in direction
(c) motor is run at reduced speed
Ans: a
12. For which types of D.C. motor, dynamic braking is generally used ?
(a) Shunt motors
(b) Series motors
(c) Compound motors
(d) All of the above
Ans: d
13. Which method of braking is generally used in elevators ?
(a) Plugging
(b) Regenerative braking
(c) Rheostatic braking
(d) None of the above
Ans: a
14. In variable speed motor
(a) a stronger commutating field is needed at low speed than at high speed
(b) a weaker commutating field is needed at low speed than at high speed
(c) same commutating field is needed at low speed than at high speed
(d) none of the above is correct
Ans: b
15. When the armature of a D.C. motor rotates, e.m.f. induced is
(a) self-induced e.m.f.
(b) mutually induced e.m.f.
(c) back e.m.f.
(d) none of the above
Ans: c
16. Where D.C. motor of H.P. 12 or more requires frequent starting, stopping, reversing and speed control
(a) drum type controller is used
(b) three point starter is used
(c) four point starter is used
(d) all above can be used
Ans: a
17. If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens
(a) this will make armature to take heavy current, possibly burning it
(6) this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses
(c) nothing will happen to motor
(d) motor will come to stop
Ans: a
18. D.C. motor is to drive a load which has certain minimum value for most of the time and some peak value for short duration. We will select the
(a) series motor
(b) shunt motor
(c) compound motor
(d) any of the above
Ans: a
19. D.C. motor is to a drive a load which is almost nil for certain part of the load cycle and peak value for short duration. We will select this
(a) series motor
(b) shunt motor
(c) compound motor
(d) any of the above
Ans: c
20. Which D.C. motor has got maximum self relieving property ?
(a) Series motor
(6) Shunt motor
(c) Cumulatively compounded motor
(d) Differentially compounded motor
Ans: a
21. In the D.C. motor the iron losses occur in
(a) the field
(b) the armature
(c) the brushes
(d) the commutator
Ans: b
22. The speed of a D.C. shunt motor is required to be more than full load speed. This is possible by
(a) reducing the field current
(b) decreasing the armature current
(c) increasing the armature current
(d) increasing the excitation current
(e) none of the above methods
Ans: a
23. One D.C. motor drives another D.C. motor. The second D.C. motor when excited and
driven
(a) runs as a generator
(b) does not run as a generator
(c) also runs as a motor comes to stop after sometime
Ans: a
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