Understanding Coil Span and Reduction

The coil span in an electrical machine winding is the distance between the two sides of a coil, usually measured in terms of electrical degrees.

A full-pitch coil has a coil span equal to the pole pitch, which is 180 electrical degrees. This means the two sides of the coil are under opposite poles (North and South).

When the span of the coil is reduced, it means the coil is made "short-pitched" or "fractional-pitched". This is done by making the coil span less than 180 electrical degrees. The reduction is measured from the full-pitch span.

Calculating the Reduced Coil Span

If the original span is that of a full-pitch coil (180 electrical degrees) and it is reduced by a certain amount, say $\alpha$ electrical degrees, the new span will be:

New Coil Span = Original Full-Pitch Span - Reduction

Substituting the values:

New Coil Span = $180^{\circ}$ electrical - $\alpha^{\circ}$ electrical

So, the coil span would be $(180 - \alpha)$ electrical degrees.

Comparing with Options

Let's look at the given options:

• Option 1: $90 + \alpha$ electrical degrees
• Option 2: $180 - \alpha$ electrical degrees
• Option 3: $90 - \alpha$ electrical degrees
• Option 4: $180 + \alpha$ electrical degrees

Our calculation shows the new coil span is $(180 - \alpha)$ electrical degrees, which matches Option 2.

Conclusion

Reducing the coil span of a full-pitch winding by $\alpha$ electrical degrees results in a new coil span equal to $180^{\circ} - \alpha^{\circ}$.