What are full pitch and short pitch (chorded) windings? When the coil span is equal to pole pitch (180° electrical) the winding is called full pitched winding. When the coil span is less than the pole pitch (180° electrical) the winding is called short pitched or chorded winding.
The correct answer and explanation is :
Full Pitch and Short Pitch (Chorded) Windings in Electrical Machines
Definition:
- Full Pitch Winding: A winding in which the coil span (distance between the two sides of the coil) is equal to the pole pitch, i.e., 180° electrical. In this case, the coil sides lie under the centers of adjacent poles of opposite polarity, ensuring maximum induced electromotive force (EMF) in the coil.
- Short Pitch (Chorded) Winding: A winding in which the coil span is less than the pole pitch (i.e., less than 180° electrical). The coil is “chorded” or “short-pitched” by a certain angle to reduce specific harmonics in the EMF.
Explanation (Approximately 300 words):
In rotating electrical machines like alternators and motors, windings are placed in slots on the stator or rotor. The configuration of these windings affects the performance of the machine significantly.
In full pitch windings, each coil spans exactly 180° electrical, which means the two sides of the coil are placed under opposite poles (e.g., one under a north pole and the other under a south pole). This arrangement produces the maximum possible EMF, as the induced voltages in the two coil sides are in phase and add up directly. However, full pitch windings also retain higher-order harmonics in the generated EMF, which can lead to waveform distortion and increased core losses.
To address this issue, short pitch or chorded windings are used. In this configuration, the coil span is deliberately made shorter than 180° electrical (typically 150° to 160°). This results in a slight reduction in the total EMF per coil, as the two sides of the coil are not perfectly aligned with opposite poles. However, the advantage is that certain harmonics, particularly the 5th and 7th, are significantly reduced or even eliminated. This improves the waveform quality and reduces associated losses such as eddy currents and acoustic noise.
Short pitch windings also reduce the amount of copper needed due to shorter end connections, leading to better material efficiency and compact winding design. Therefore, although short pitch windings have a slightly lower fundamental EMF compared to full pitch windings, they are often preferred in practical machine design due to their overall performance benefits.