# In a loaded DC generator, If the brushes are given a shift from the interpolar axis in the direction of rotation, then the commutation will

Electrical Engineering XYZ MCQs

In a loaded DC generator, If the brushes are given a shift from the interpolar axis in the direction of rotation, then the commutation will:

1. Improve with rise in Vt
2. Improve with fall of terminal voltage Vt
3. Deteriorate with rise in vt
4. Deteriorate with fall of Vt

Correct answer: 2. Improve with fall of terminal voltage Vt

Explanation: In case of a loaded DC generator, commutation refers to the process of transferring current from one commutator segment to the next without any interruption in the circuit. The ideal scenario is to achieve perfect commutation, where the brushes shift at exactly the right moment to maintain a constant output voltage.

Now, let’s analyze the given options:

1. Improve with rise in Vt: This option suggests that if the terminal voltage (Vt) increases, commutation will improve. This is incorrect because an increase in terminal voltage might lead to increased arcing between the brushes and the commutator segments, which can degrade commutation rather than improving it.
2. Improve with fall of terminal voltage Vt: This option proposes that as the terminal voltage decreases, commutation will improve. This is a plausible statement. A decrease in terminal voltage often implies less voltage stress on the commutator segments, leading to smoother commutation.
3. Deteriorate with rise in Vt: This option suggests that an increase in terminal voltage will deteriorate commutation. As mentioned earlier, higher terminal voltage can lead to increased arcing and sparking at the brushes, worsening commutation.
4. Deteriorate with fall of Vt: This option implies that as the terminal voltage falls, commutation will worsen. This is contrary to the usual behavior observed in DC generators. A decrease in terminal voltage generally helps in reducing arcing and hence can improve commutation.

So, based on the analysis, the correct answer is:

Improve with fall of terminal voltage Vt.

Explanation: As the terminal voltage decreases, the likelihood of arcing between the brushes and the commutator segments decreases, leading to smoother and better commutation.