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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,

Solution:

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

QUESTION: 2

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

Solution:

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

QUESTION: 3

Retardation test on DC shunt motor is used for finding _______

Solution:

Retardation test is used for finding the stray losses.

QUESTION: 4

The quantities needed to complete retardation test are/is

Solution:

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

QUESTION: 5

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

Solution:

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

QUESTION: 6

If the field current and armature current are reversed, then

Solution:

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

QUESTION: 7

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

Solution:

All the factors can cause the overheating of commutator.

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?

Solution:

Ea/Eb = 1.4/1.3

Ea= 1.077 Eb > Eb

So, the machine will act as motor.

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?

Solution:

Ea/Eb = 1.4/1.3

Ea= 1.077 Eb > Eb

So, the machine will act as generator.

QUESTION: 10

Hopkinson’s test is also called regenerative test due to

Solution:

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

QUESTION: 11

The most appropriate relation to find efficiency of the generator

Solution:

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

QUESTION: 12

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

Solution:

Because the constant losses are known.

QUESTION: 13

The possible assumption is/are made while doing swineburne’s test

(i) mechanical loss constant

(ii) Armature reaction neglected

(iii) Increase

Solution:

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

QUESTION: 14

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

Solution:

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

QUESTION: 15

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

Solution:

The machines have to be mechanically coupled together.

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