D.C. Generators

21. D.C. generators are connected to the busbars or disconnected from them only under the floating condition

1. to avoid sudden loading of the primemover
2. to avoid mechanicaljerk to the shaft
3. to avoid burning of switch contacts
4. all above

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22. D.C. series generator is used

1. to supply traction load
2. to supply industrial load at constant voltage
3. voltage at the toad end of the feeder
4. for none of the above purpose

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23. Eddy currents are induced in the pole shoes of a D.C. machine due to

1. oscillating magnetic field
2. pulsating magnetic flux
3. relative rotation between field and armature
4. all above

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24. Equilizer rings are required in case armature is

1. wave wound
2. lap wound
3. delta wound
4. duplex wound

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25. Flashing the field of D.C. generator means

1. neutralising residual magnetism
2. creating residual magnetism by a D.C. source
3. making the magnetic losses of forces parallel
4. increasing flux density by adding extra turns of windings on poles

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26. Fleming's right-hand rule regarding direction of induced e.m.f., correlates

1. magnetic flux, direction of current flow and resultant force
2. magnetic flux, direction of motion and the direction of e.m.f. induced
3. magnetic field strength, induced voltage and current
4. magnetic flux, direction of force and direction of motion of conductor

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27. Following D.C. generator will be in a position to build up without any residual magnetism in the poles

1. series generator
2. shunt generator
3. compound generator
4. self-excited generator

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28. For a D.C. generator when the number of poles and the number of armature conductors is fixed, then which winding will give the higher e.m.f. ?

1. Lap winding
2. Wave winding
3. Either of (a) and (b) above
4. Depends on other features of design

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29. For a D.C. machines laboratory following type of D.C. supply will be suitable

1. rotary converter
2. mercury are rectifier
3. induction motor D.C. generator set
4. synchronous motor D.C. generator set

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30. For both lap and wave windings, there are as many commutator bars as the number of

1. slots
2. armature conductors
3. winding elements
4. poles

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