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Test: Methods Of Excitation


10 Questions MCQ Test Electrical Machines | Test: Methods Of Excitation


Description
Attempt Test: Methods Of Excitation | 10 questions in 10 minutes | Mock test for Electrical Engineering (EE) preparation | Free important questions MCQ to study Electrical Machines for Electrical Engineering (EE) Exam | Download free PDF with solutions
QUESTION: 1

Consider a DC generator running at the rated speed of 2000 rpm, suddenly there is an insulator falls on the field circuit and breaks it. Then

Solution:

As the field circuit gets broken there is interruption in the flux to the dc machine, and as a result the motor stops in few seconds.

QUESTION: 2

 If a self excited DC generator is failed to run, this refers to

Solution:

Any of the reasons are valid for no build up of an emf.

QUESTION: 3

The self-excited dc generator with gradual build up of residual voltage and EMF corresponds to

Solution:

It responds to a positive feedback because the gain is always more than one in the linear region.

QUESTION: 4

The critical resistance refers to
Solution:

After taking a glance at the magnetization curve, it can be concluded that the emf will not build up if the resistance is greater than critical resistance.

QUESTION: 5

 If a DC shunt generator fails to start, the most primitive action would be
Solution:

The first measure is to check if the field winding as properly connected with additive polarity so that the flux is aiding in nature.

QUESTION: 6

Flashing is used to
Solution:

It is a method to give a kick start to dc machine when its residual magnetism is vanished.

QUESTION: 7

A series generator, having external characteristics which is a straight line through 0 to 50 V at 200 A is connected as a booster, between a station bus-bar and feeders of 0.5 ohm resistors. The voltage at the far end of feeder at current of 50 A is
Solution:

V = voltage drop-voltage added up by boosters
= (0.3*50 – 50*50/200)
= 15-12.50
= 2.5 V

QUESTION: 8

 The number of parallel paths in the armature is increased by
Solution:

 It is increased by increasing magnetic poles which give parallel path to the magnetic circuit.

QUESTION: 9

 A dc series generator as armature and field connections are reversed, the generator
Solution:

It happens due to non build up voltage.

QUESTION: 10

 ____ is responsible for mechanical power output of a DC motor
Solution:

Primarily it is the electrical input power which starts the motoring action.

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