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Test: MMF & Flux Density Waveforms in DC Machines - Electrical Engineering (EE) MCQ


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

Test: MMF & Flux Density Waveforms in DC Machines for Electrical Engineering (EE) 2024 is part of Electrical Machines preparation. The Test: MMF & Flux Density Waveforms in DC Machines questions and answers have been prepared according to the Electrical Engineering (EE) exam syllabus.The Test: MMF & Flux Density Waveforms in DC Machines MCQs are made for Electrical Engineering (EE) 2024 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests for Test: MMF & Flux Density Waveforms in DC Machines below.
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Test: MMF & Flux Density Waveforms in DC Machines - Question 1

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

Detailed Solution for Test: MMF & Flux Density Waveforms in DC Machines - Question 1

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

Test: MMF & Flux Density Waveforms in DC Machines - Question 2

Armature reaction in a dc machine is

Detailed Solution for Test: MMF & Flux Density Waveforms in DC Machines - Question 2

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

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Test: MMF & Flux Density Waveforms in DC Machines - Question 3

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

Detailed Solution for Test: MMF & Flux Density Waveforms in DC Machines - Question 3

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

Test: MMF & Flux Density Waveforms in DC Machines - Question 4

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

Detailed Solution for Test: MMF & Flux Density Waveforms in DC Machines - Question 4

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

Test: MMF & Flux Density Waveforms in DC Machines - Question 5

The method needed to limit cross-magnetizing effect is

Detailed Solution for Test: MMF & Flux Density Waveforms in DC Machines - Question 5

Correct Answer :- a

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

Test: MMF & Flux Density Waveforms in DC Machines - Question 6

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

Detailed Solution for Test: MMF & Flux Density Waveforms in DC Machines - Question 6

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

Test: MMF & Flux Density Waveforms in DC Machines - 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.

Detailed Solution for Test: MMF & Flux Density Waveforms in DC Machines - Question 7

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

Test: MMF & Flux Density Waveforms in DC Machines - Question 8

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

Detailed Solution for Test: MMF & Flux Density Waveforms in DC Machines - Question 8

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

Test: MMF & Flux Density Waveforms in DC Machines - Question 9

 Compensating winding has advantage of

Detailed Solution for Test: MMF & Flux Density Waveforms in DC Machines - Question 9

Correct Answer :- a

Explanation : A compensation winding in a DC shunt motor is a winding in the field pole face plate that carries armature current to reduce stator field distortion. Its purpose is to reduce brush arcing and erosion in DC motors that are operated with weak fields, variable heavy loads or reversing operation such as steel-mill motors. When flux from the armature current is about equal to the flux from the field current, the flux at the field pole plate is shifted.

Test: MMF & Flux Density Waveforms in DC Machines - Question 10

A dc shunt motor is connected to the source through 3-point starter. If the field id kept open and starter handle is moved from off to on position, then

Detailed Solution for Test: MMF & Flux Density Waveforms in DC Machines - Question 10

Leaving the field winding open, the machine will not start as the exciting flux is zero.

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