Electrical Engineering XYZ MCQs
In a loaded dc motor, if brushes are given a shift from the interpolar axis in the direction of Rotation, then commutation will:
- Deteriorate and the speed falls
- Improve and the speed rises
- Improve and the speed falls
- Deteriorate and the speed rises
Correct answer: 1. Deteriorate and the speed falls
Explanation: In a loaded DC motor, commutation is the process of reversing the current in the coil or armature winding as the rotor turns, ensuring a continuous and smooth rotation. Commutation is crucial for maintaining a constant direction of the current flow in the armature coil, which helps in sustaining a constant torque and preventing speed fluctuations.
When brushes are shifted from the interpolar axis (the neutral plane), it can lead to problems with commutation. The neutral plane is the position where the coil sides are neither under the influence of the north nor the south pole, ensuring a smooth transition of current during commutation.
If the brushes are shifted in the direction of rotation, it can cause the following issues:
- Deterioration of Commutation: Shifting the brushes in the direction of rotation may cause a delay in the reversal of current in the coil, leading to poor commutation. This results in sparking at the brushes and an uneven current distribution in the coil.
- Reduction in Speed: Poor commutation leads to an increase in electrical losses and a decrease in motor efficiency. As a result, the overall performance of the motor deteriorates, leading to a reduction in speed.
So, the correct choice is “Deteriorate and the speed falls.”