The correct answer is: A. The brushes of opposite polarity should track each other.
The brushes of a DC machine are two or more conducting blocks that make contact with the commutator. The commutator is a cylindrical metal ring that is divided into segments. The brushes are held in place by brush holders and are pressed against the commutator by springs.
The brushes conduct current from the external circuit to the rotor windings. The current flows through the rotor windings and creates a magnetic field. The magnetic field interacts with the stator field to produce torque.
The brushes must track each other to ensure that the current flows evenly to the rotor windings. If the brushes do not track each other, the commutator will groove.
Grooving of the commutator can cause a number of problems, including:
- Increased resistance in the rotor windings
- Decreased efficiency of the machine
- Increased sparking at the brushes
- Damage to the commutator
To avoid grooving of the commutator, the brushes must be kept clean and free of debris. The brush holders should be adjusted so that the brushes are in good contact with the commutator. The commutator should be inspected regularly and resurfaced if necessary.
The following are the incorrect answers and their explanations:
B. The brushes of same polarity should track each other.
This is incorrect because the brushes of opposite polarity should track each other. The brushes of same polarity will repel each other and will not track properly.
C. Brush position has no effect on the commutator grooving.
This is incorrect because the brush position has a significant effect on the commutator grooving. If the brushes are not in good contact with the commutator, the commutator will groove.
D. All of the above.
This is incorrect because only option A is correct.