DC Generator Question and Answer with Solution

1. Consider the following statements

1. In a dc series generator, full-load voltage is more than the no-load voltage.
2. In a separately excited de generator full-load voltage is more than the no-load voltage.
3. In a dc shunt generator, full-load voltage is less than the no-load voltage.

Of these statements.
(a) 1, 2 and 3 are correct.
(b) 1 and 2 are correct.
(c) 2 and 3 are correct.
(d) 1 and 3 are correct.

2. The terminal voltage of an over-compounded dc generator

(a) decreases with the increase in load current.
(b) increases with the increase in load current.
(c) remains constant at all load currents.
(d) none of the above.

3. Consider the following statements:

For a level compounded dc generator to run at constant speed, the series field mmf must effectively compensate

1. armature reaction mmf.
2. armature resistance voltage drop.
3. brush contact voltage drop.

Which of these statements is/are correct?
(a) 2 and alone.
(b) 1 and 2.
(c) 1 and 3.
(d) 1, 2 and 3.

4. In a dc compound generator, “flat compound” characteristic, required for certain applications, may be obtained by connecting a variable resistance:

(a) across the series field.
(b) in series with the series field.
(c) in parallel with the shunt field.
(d) in series with the shunt field.

5. A self excited dc shunt generator driven by its prime mover at the rated speed fails to build up voltage across its terminals at no load. What reason can be assigned for this?

(a) The field circuit resistance is higher than the critical resistance.
(b) The initial shunt field mmf does not assist the residual magnetism.
(c) One of the interpole connection is reversed.
(d) The brush-axis shifts slightly from the geometrical neutral axis of the machine.

6. A cumulatively compounded dc generator is supplying 20 A at 200 V. Now if the series field winding is short circuited, the terminal voltage

(a) will remain unaltered at 200 V.
(b) will rise to 220 V.
(c) will shoot up to a very high value.
(d) will become less than 200 V.

7. A dc generator will be flat compounded if

(a) its terminal voltage remains constant irrespective of the load current supplied by the generator.
(b) generated voltage is in proportion to load current.
(c) the generator is capable of producing higher voltage at light load.
(d) terminal voltage increases slightly with the load.

8. Over or under compounding of a dc generator is achieved by

(a) shunting more or less current from the shunt field.
(b) shunting more or less current from the series field.
(c) connecting it as long shunt.
(d) connecting it as short-shunt.

9. Which of the following dc generators will be in a position to build up without any residual magnetism in the field?

(a) Series
(b) Shunt
(c) Separately excited
(d) Compound

10. Which of the following dc generators has rising V – I characteristics?

(a) Series
(b) Shunt
(c) Compound
(d) None.

11. Which of the following dc generators will have negligible terminal voltage on no load?

(a) Shunt
(b) Series
(c) Compound
(d) None

12. An exciter for turbo-generator is a …………dc generator.

(a) shunt
(b) series
(c) compound
(d) separately excited

13. For a specific open-circuit voltage of a dc generator, the short-circuit current will be maximum when it is

(a) separately excited.
(b) shunt connected.
(c) cumulatively compounded.
(d) differentially compounded.

14. The voltage regulation of a dc generator at full load being zero implies that the generator is

(a) shunt-connected.
(b) differentially compounded.
(c) cumulatively compounded.
(d) series-connected

15. The ………… generator has the poorest voltage regulation.

(a) shunt
(b) over compounded
(c) under compounded
(d) differential compounded

16. The voltmeter connected across a generator reads voltage same at no load and at full load (rated). The generator is of the type:

(a) shunt generator.
(b) series generator.
(c) level compound.
(d) short-shunt compound.

17. A dc shunt generator when driven without connecting field winding shows an open-circuit terminal voltage of 12 V. When field winding is connected and excited the terminal voltage drops to zero because

(a) field resistance is higher than critical resistance.
(b) there is no residual magnetism in the field circuit.
(c) field winding has got wrongly connected.
(d) there is a fault in armature circuit.

18. A dc shunt generator, when driven at its rated speed, is found to be not generating any voltage. Which of the following would account for this?

1. There is no residual magnetism.
2. The connection of the field winding is not proper with respect to armature terminals.
3. The resistance of the field circuit is greater than the critical field resistance.
4. The load resistance is less than the critical armature resistance.

Select the correct answer using the codes given below:
(a) 3 and 4.
(b) 1, 3 and 4.
(c) 1, 2 and 3.
(d) 1, 2, 3 and 4.

19. The residual magnetism of a dc shunt generator can be regained by

(a) connecting the shunt field to a battery.
(b) running the generator on no load for some time.
(c) grounding the shunt field.
(d) reversing the direction of rotation of the generator.

20. Flashing of field of dc generator means

(a) neutralization of residual magnetism.
(b) creation of residual magnetism by a dc source.
(c) increasing flux density by providing extra ampere-turns in field.
(d) none of the above.

21. A dc series generator is employed

(a) as a booster to maintain constant voltage at the load end of the feeder.
(b) for supplying traction load.
(c) for supplying industrial load at constant voltage.
(d) for battery charging.

22. The type of dc generator used for arc welding purposes is a

(a) series generator.
(b) shunt generator.
(c) cumulatively compounded generator.
(d) differentially compounded generator.

23. The essential condition for satisfactory parallel operation of two dc generators is that they should have same

(a) kW output rating.
(b) drooping voltage characteristics.
(c) percentage regulation.
(d) speed of operation.

24. When two dc series generators are operating in parallel, an equalizer bar is used

(a) to reduce armature reaction.
(b) to increase emf.
(c) to increase the speed.
(d) to reduce the flux.
(e) so that the two similar machines take approximately equal load current.

25. The simplest way of shifting load from one shunt generator to the other operating in parallel is by

(a) adjustment of speeds.
(b) adjustment of armature resistances.
(c) adjustment of field rheostats.
(d) using equalizer connections.

26. Two dc shunt generators having equal open-circuit emfs but slight different load characteristics are operating in parallel, then

(a) the machines will share load equally.
(b) the machine with more drooping characteristic will supply less load.
(c) the machine with more drooping characteristic will supply more load.

27. If field of one of two generators operating in parallel is made very weak, then it will

(a) not take any load.
(b) take major share of load.
(c) operate as a motor and run in the same direction.
(d) operate as a motor and run in the opposite direction.

28. DC generators are connected to or disconnected from the bus-bar only under the floating condition. This is done to avoid

(a) burning of switch contacts.
(b) sudden loading of the prime mover.
(c) mechanical jerk to the shaft.
(d) all of the above.

29. The main factor that leads to unstable parallel operation of flat or over compounded dc generators is

(a) their rising voltage characteristics.
(b) unequal series field resistances.
(c) unequal speed regulation of their prime movers.
(d) their drooping voltage characteristics.

30. In the case of parallel operation of dc compound wound generators, for proper division of load from no load to full load it is essential that they should have the same

(a) KW output rating.
(b) percentage regulation.
(c) series field resistance.
(d) speed of operation.

 

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