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Test: Efficiency & Testing of DC Machines - Electrical Engineering (EE) MCQ


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15 Questions MCQ Test Electrical Machines - Test: Efficiency & Testing of DC Machines

Test: Efficiency & Testing of DC Machines for Electrical Engineering (EE) 2024 is part of Electrical Machines preparation. The Test: Efficiency & Testing of DC Machines questions and answers have been prepared according to the Electrical Engineering (EE) exam syllabus.The Test: Efficiency & Testing of 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: Efficiency & Testing of DC Machines below.
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Test: Efficiency & Testing of DC Machines - Question 1

A dc motor is connected in the short-shunt configuration, but the series and the shunt windings get interchanged by mistake and the motor is connected to the rated voltage,

Detailed Solution for Test: Efficiency & Testing of DC Machines - Question 1

In the short shunt configuration, the winding interchanging does not change the configuration of the set up so none of the winding get affected.

Test: Efficiency & Testing of DC Machines - Question 2

 The main concern before doing hopkinson’s test for finding efficiency is

Detailed Solution for Test: Efficiency & Testing of DC Machines - Question 2

It is must that both the machines are identical as required by the calculations.

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Test: Efficiency & Testing of DC Machines - Question 3

 Retardation test on DC shunt motor is used for finding _______

Detailed Solution for Test: Efficiency & Testing of DC Machines - Question 3

Retardation test is used for finding the stray losses.

Test: Efficiency & Testing of DC Machines - Question 4

The quantities needed to complete retardation test are/is

Detailed Solution for Test: Efficiency & Testing of DC Machines - Question 4

We need the angular acceleration and the moment of inertia of the machine.

Test: Efficiency & Testing of DC Machines - Question 5

 ______ test is used for determining the efficiency of a traction motor

Detailed Solution for Test: Efficiency & Testing of DC Machines - Question 5

Field test is used for finding efficiency of a traction motor.

Test: Efficiency & Testing of DC Machines - Question 6

 If the field current and armature current are reversed, then

Detailed Solution for Test: Efficiency & Testing of DC Machines - Question 6

Explanation: When both field current and armature current are reversed then the direction will not change.

Test: Efficiency & Testing of DC Machines - Question 7

 Mark the possible causes of overheating of commutator in a DC machine.

Detailed Solution for Test: Efficiency & Testing of DC Machines - Question 7

All the factors can cause the overheating of commutator.

Test: Efficiency & Testing of DC Machines - Question 8

In the hopkinson’s test on two DC machines. Machine A has field current of 1.4A and B has field current of 1.3A. Which machine acts as motor?

Detailed Solution for Test: Efficiency & Testing of DC Machines - Question 8

Correct answer is option A.
Ea/Eb = 1.4/1.3
Ea= 1.077 Eb > Eb
So, the machine will act as motor.

Test: Efficiency & Testing of DC Machines - Question 9

In the Hopkinson’s test on two DC machines. Machine A has field current of 1.4A and B has field current of 1.3A. Which machine acts as generator?

Detailed Solution for Test: Efficiency & Testing of DC Machines - Question 9

Ea/Eb = 1.4/1.3
Ea= 1.077 Eb > Eb
So, the machine will act as generator.

Test: Efficiency & Testing of DC Machines - Question 10

 Hopkinson’s test is also called regenerative test due to

Detailed Solution for Test: Efficiency & Testing of DC Machines - Question 10

Regenerative phenomena utilizes the energy of the running machine to tap the dynamically produced energy and use it to charge the battery.

Test: Efficiency & Testing of DC Machines - Question 11

The most appropriate relation to find efficiency of the generator

Detailed Solution for Test: Efficiency & Testing of DC Machines - Question 11

For a generator the output can be measured and so this expression is used

Test: Efficiency & Testing of DC Machines - Question 12

The efficiency in the swineburne’s test can be found.

Detailed Solution for Test: Efficiency & Testing of DC Machines - Question 12

Because the constant losses are known.

Test: Efficiency & Testing of DC Machines - Question 13

The possible assumption is/are made while doing swineburne’s test
(i) mechanical loss constant
(ii) Armature reaction neglected
(iii) Increase

Detailed Solution for Test: Efficiency & Testing of DC Machines - Question 13

There is decrease in flux due to positive temperature coefficient of resistance in shunt machine.

Test: Efficiency & Testing of DC Machines - Question 14

Swineburne’s test is applicable to those machines in which flux is practically _______

Detailed Solution for Test: Efficiency & Testing of DC Machines - Question 14

Because the constant losses are known in advance of the test is conducted.

Test: Efficiency & Testing of DC Machines - Question 15

Similarity between Hopkinonson’s and field’s test is that

Detailed Solution for Test: Efficiency & Testing of DC Machines - Question 15

The machines have to be mechanically coupled together.

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