What is the relation between coil span and harmonics?

In electric motors and generators, the coil span (also known as the coil pitch) is the physical distance between the two sides of a coil wound around the stator. The coil span significantly influences the generation of harmonics in the machine’s operation. Harmonics are sine waves that have frequencies that are integer multiples of the fundamental frequency of operation. Here’s how coil span relates to harmonics:

– Short-Pitched or Chorded Coils: When the coil span is less than the full pitch (the distance equal to one complete wavelength of the fundamental frequency), it is called short-pitching or chording. This design intentionally reduces certain higher-order harmonics. By reducing the coil span, the winding cuts the higher odd harmonics (5th, 7th, 11th, etc.), which improves the waveform of the generated or utilized electrical current and reduces losses and heating in the machine. Short-pitching is effective because it exploits the phase difference between the voltages induced in the two sides of the coil, which, due to their physical placement, naturally opposes higher-order harmonics.

– Full-Pitch Coils: When the coil span is equal to the full pitch, it means each coil spans exactly one pole pitch (the center-to-center distance between two adjacent magnetic poles). This configuration can generate a more significant amount of certain harmonics compared to a short-pitched coil because there’s no inherent cancellation of harmonics through the coil design. However, full-p