Question

Fractional pitch winding is used in DC machines to:

• A. Increase eddy current
• B. Decrease the generated voltage
• C. Increase distorting harmonics
• D. Reduce sparking and save copper

Hint:

Fractional pitch = shorter coils → less copper + reduced harmonics = better performance and durability.

Answer 1

The Correct Option is D

Fractional pitch winding is a technique used in the design of DC machines to address specific electrical and performance characteristics. Let's explore why it is employed:

1. Reduction of Sparking: One of the significant benefits of fractional pitch winding is its ability to reduce sparking at the commutator. Sparking is problematic as it can cause wear and tear on the commutator segments and brushes, leading to maintenance issues and reduced machine lifespan. By using fractional pitch windings, the coil sides do not span the full pole pitch, effectively reducing the circulating currents that often cause sparking.

2. Copper Savings: Fractional pitch windings use less copper as the end connections of the coils are shorter compared to full-pitch windings. This not only results in a significant reduction of the manufacturing costs but also decreases the weight of the winding, improving the machine's efficiency.

Combining these benefits, fractional pitch windings are preferred to increase the operational efficiency of DC machines. By decreasing sparking and saving copper, they enhance the machine's reliability and cost-effectiveness.