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

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

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

Retardation test is used for finding the stray losses.

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

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

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

All the factors can cause the overheating of commutator.

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

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

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

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

Because the constant losses are known.

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

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

The machines have to be mechanically coupled together.