Surf Wiki
Save to docs
general/electrical-generators

From Surf Wiki (app.surf) — the open knowledge base

Winding factor

In power engineering, winding factor k_w provides a way to compare of the effectiveness of different designs of stators for alternators. Winding factor is the ratio of electromotive force (EMF) produced by a stator having a short-pitch, distributed, or skewed winding, with a stator having full-pitch, concentrated, and non-skewed, windings.

For most alternators, the stator acts as the armature. Winding factor also applies to other electric machines, but this article focuses on winding factor as it applies to alternators.

Practical alternators have a short-pitched and distributed windings to reduce harmonics and maintain constant torque. Also, either the stator or rotor may be slightly skewed from the rotor's axis to reduce cogging torque. The armature winding of each phase may be distributed in a number of pole slots. Since the EMF induced in different slots are not in phase, their phasor sum is less than their numerical sum. This reduction factor is called distribution factor k_d. The other factors that can reduce the winding factor are pitch factor k_p and skew factor k_s.

Pitch

In alternator design, pitch means angle. The shaft makes a complete rotation in 360 degrees, and is called mechanical degrees. However, the current in a conductors makes a complete cycle in 360 electrical degrees. Electrical degrees and mechanical degrees are related as follows:

:\text{electrical degrees} = \frac{P }{2}\cdot \text{mechanical degrees}

where P is the number of poles.

No matter how many poles, each pole always spans exactly 180 electrical degrees, and it is called pole pitch. Coil pitch is the number of electrical degrees spanned by the coil.

Short pitch factor

A full-pitched coil is 180 electrical degrees, meaning it spans the entire pole. A short-pitched coil is less than 180 electrical degrees, meaning it does not spans the entire pole. The amount the coil is short-pitched is given by the variable a in electrical degrees:

a = \text{pole pitch} - \text{coil pitch}, and the pitch factor is:

k_p = \cos(\frac{a}{2}).

A short pitched coil is also called chorded, in reference to the chord of a circle.

Calculating winding factor

The winding factor can be calculated as

k_w = k_d k_p k_s

where

k_d is the distribution factor.

k_p is the pole factor.

k_s is the skew factor resulting from the winding being skewed from the axis of the rotor.

Example

For a 3-phase 6 slot 4 pole non-overlapping winding alternator:

\text{coil pitch} = \frac{2 \pi}{6} = \frac{\pi}{3} (\text{mech}) = \frac{2 \pi}{3} (\text{elec})

\text{pole pitch} = \frac{2 \pi}{4} = \frac{\pi}{2} (\text{mech}) = \pi (\text{elec})

Most of 3-phase motors have winding factor values between 0.85 and 0.95.

The winding factor (along with some other factors like winding skew) can help to improve the harmonic content in the generated EMF of the machine.

References

References

  1. Suad Ibrahim Shahl. "Introduction to AC Machines".
  2. (5 January 2016). "Armature Winding". Circuit Globe.
  3. Mustafa Al-Refai. (2018). "Synchronous generator". Electrical and Communications Consulting Office (ECCO).
Info: Wikipedia Source

This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page.

electrical-generators
Want to explore this topic further?

Ask Mako anything about Winding factor — get instant answers, deeper analysis, and related topics.

Research with Mako

Free with your Surf account

Content sourced from Wikipedia, available under CC BY-SA 4.0.

This content may have been generated or modified by AI. CloudSurf Software LLC is not responsible for the accuracy, completeness, or reliability of AI-generated content. Always verify important information from primary sources.

Report