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# Test: MMF & Flux Density Waveforms in DC Machines

## 10 Questions MCQ Test Electrical Machines | Test: MMF & Flux Density Waveforms in DC Machines

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This mock test of Test: MMF & Flux Density Waveforms in DC Machines for Electrical Engineering (EE) helps you for every Electrical Engineering (EE) entrance exam. This contains 10 Multiple Choice Questions for Electrical Engineering (EE) Test: MMF & Flux Density Waveforms in DC Machines (mcq) to study with solutions a complete question bank. The solved questions answers in this Test: MMF & Flux Density Waveforms in DC Machines quiz give you a good mix of easy questions and tough questions. Electrical Engineering (EE) students definitely take this Test: MMF & Flux Density Waveforms in DC Machines exercise for a better result in the exam. You can find other Test: MMF & Flux Density Waveforms in DC Machines extra questions, long questions & short questions for Electrical Engineering (EE) on EduRev as well by searching above.
QUESTION: 1

### The flux distortion caused by cross magnetizing armature reaction is more pronounced in a

Solution:

Since field excitation remains substantially constant, while aarmature mmf reaches higher values at loading.

QUESTION: 2

### Armature reaction in a dc machine is

Solution:

It is cross magnetizing in nature which happens due to interaction between stator and field mmf.

QUESTION: 3

### The air-gap flux density waveform, has decreased flux under one pole tip and measured under the other is due to

Solution:

The flux density increases under one pole tip while it decreases under the other due to the saturation of iron magnetic circuit.

QUESTION: 4

The flux distortion caused by cross magnetizing armature reaction is more pronounced in a

Solution:

Since field excitation remains substantially constant, while aarmature mmf reaches higher values at loading.

QUESTION: 5

The method needed to limit cross-magnetizing effect is

Solution:

Explanation : By ultimately increasing the reluctance of the magnetic circuit at the pole tips so that the armature reaction effect is neutralized.

QUESTION: 6

The brushes of a dc motor, are shifted by 5′, from the main field axis, then

Solution:

When the brushes are shifted from GNA, there will either be magnetizing or demagnetizing effect will be observed.

QUESTION: 7

A 100KW, 250 V, 400 A, a long shunt compound generator has an armature resistance of 0.025 ohms. There are 1000 shunt fields turns per pole and 3 series field turns per pole. The series field is connected in a such a fashion that positive armature current produces direct-axis MMF which adds to that of the shunt field. Compute the gross MMF at the rated terminal current when shunt field current is 4.7A and speed is 1150 rpm.

Solution:

Series field current = Is = I(l)+I(f)
= 400+4.7
= 405 A(approx)
Main field mmf = I(f)+(Ns/Nf)*I(s)
= 4.7+(3/1000)*405
= 5.9 AT

QUESTION: 8

Compensating windings are embedded in pole faces and having the same polarity as that of adjoining armature winding.

Solution:

Compensating windings are embedded in pole faces and having an opposite polarity as that of adjoining armature winding.

QUESTION: 9

Solution: