The coil span should be 8.33 percent of pole pitch to obtain the maximum reduction of harmonics.

The statement that the coil span should be 8.33 percent of the pole pitch to obtain the maximum reduction of harmonics is incorrect. In electrical engineering, specifically in the design of AC machines like alternators and induction motors, the coil span or coil pitch is an important factor in reducing harmonics. However, the optimum coil span to achieve the maximum reduction of harmonics is not 8.33 percent of the pole pitch; rather, it is generally advisable that the coil span be equal to one pole pitch.

The pole pitch is defined as the peripheral distance between the centers of two adjacent poles in an electrical machine, and it is directly related to the number of poles and the circumference of the armature. A pole pitch corresponds to 180 electrical degrees.

To minimize the effect of harmonics, especially the 5th and 7th harmonics which are the most detrimental, the coil span is often designed to be close to or exactly equal to one pole pitch. This equates to spanning the coil 180 electrical degrees.

When the coil span is equal to the pole pitch, it effectively means that when winding the coils, you place the two sides of the coil under two adjacent poles. This arrangement helps in achieving what’s known as “short pitching” or “chording,” which can significantly reduce the amplitude of certain harmonics produced by the machine, leading to a smoother and more efficient operation.

In specific configurations, adjusting the coil span slightly less than a full pole pitch might