D.C. Generators MCQ Questions & Answers

41

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

A) Magnetic flux, direction of current flow and resultant force B) Magnetic flux, direction of motion and the direction of e.m.f. induced C) Magnetic field strength, induced voltage and current D) Magnetic flux, direction of force and direction of motion of conductor

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Answer & Solution

Answer: Option B

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42

Compensating windings are used in D.C. generators

A) Mainly to reduce the eddy currents by providing local short-circuits B) To provide path for the circulation of cooling air C) To neutralize the cross-magnetizing effect of the armature reaction D) None of the above

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Answer & Solution

Answer: Option C

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43

Flashing the field of D.C. generator means

A) Neutralizing residual magnetism B) Creating residual magnetism by a D.C. source C) Making the magnetic losses of forces parallel D) Increasing flux density by adding extra turns of windings on poles

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Answer & Solution

Answer: Option B

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44

In a separately excited generator supplying rated load the armature reaction:

A) Is always present B) Is always absent C) May be sometimes present D) None of the above

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Answer & Solution

Answer: Option A

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45

If a D.C. generator fails to build up the probable cause could not be

A) Imperfect brush contact B) Field resistance less than the critical resistance C) No residual magnetism in the generator D) Faulty shunt connections tending to reduce the residual magnetism

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Answer & Solution

Answer: Option B

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46

D.C. generators are connected to the bus-bars or disconnected from them only under the floating condition

A) To avoid sudden loading of the prime mover B) To avoid mechanical jerk to the shaft C) To avoid burning of switch contacts D) All above

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Answer & Solution

Answer: Option D

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47

Two generators are running in parallel. One of the generators may run as motor for which of the following reasons?

A) The direction of that generator is reversed B) The speed of that generator is increased C) The field of that generator is weakened D) That generator takes large share of loads

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Answer & Solution

Answer: Option D

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48

The function of pole shoes in the case of D.C. machine is

A) To reduce the reluctance of the magnetic path B) To spread out the flux to achieve uniform flux density C) To support the field coil D) To discharge all the above functions

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Answer & Solution

Answer: Option D

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49

In case of a 4 pole D.C. generator provided with a two layer lap winding with sixteen coils, the pole pitch will be

A) 4 B) 8 C) 16 D) 32

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Answer & Solution

Answer: Option B

Solution:

Here's an explanation to help you understand the question:

First, let's define pole pitch. It is the distance between the center of two adjacent poles in a DC generator.

To calculate the pole pitch, we need to know the total number of slots or coil sides around the armature and the number of poles.

We are given:
* Number of poles (P) = 4
* Number of coils = 16
* Two layer winding means each coil has two coil sides.

Since it's a two-layer winding, the total number of coil sides is twice the number of coils: 16 coils * 2 coil sides/coil = 32 coil sides.

In a lap winding, the number of coil sides equals the number of armature conductors or slots. So, we have 32 slots.

The formula for pole pitch is:
Pole Pitch = (Total Number of Slots) / (Number of Poles)

So, Pole Pitch = 32 / 4 = 8

Therefore, the correct answer is Option B: 8.

50

For the parallel operation of two or more D.C. compound generators, we should ensure that

A) Voltage of the incoming generator should be same as that of bus bar B) Polarity of incoming generator should be same as that of bus bar C) All the series fields should be run in parallel by means of equalizer connection D) Series fields of all generators should be either on positive side or negative side of the armature

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Answer & Solution

Answer: Option D

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D.C. Generators MCQ Questions & Answers | Electrical Engineering