Unbalanced winding

An unbalanced winding has a combination of number of poles and number of slots that does not allow to arrange the coils in such a way that they produce a symmetrical system of equally time-phase displaced emf's of identical magnitude, frequency, and waveform.

In the Emetor winding calculator, black cells indicate unbalanced windings.

If a winding is feasible, i.e. balanced, depends solely on the number of slots $Q_s$ and the number of poles $p$. A winding layout will yield unsymmetrical phase coils, whenever the number of slots per phase per machine periodicity is not an integer.

The greatest common divisor (GCD) between the number of slots and the number of pole pairs indicates the number of winding symmetries, respectively the machine periodicity.

Examples: A look at the Emetor winding calculator shows that unbalanced windings only appear when the number of pole pairs is a multiple of 3, i.e., $p=$6, 12, 18, ...
A 6-pole 9-slot winding has 3 winding symmetries and is balanced, since: $\frac{Q_s}{3\cdot GCD\left( Q_s, \frac{p}{2} \right)} = \frac{9}{3\cdot 3} = 1$.

A 6-pole 12-slot winding has also 3 winding symmetries but is unbalanced, since: $\frac{Q_s}{3\cdot GCD\left( Q_s, \frac{p}{2} \right)} = \frac{12}{3\cdot 3} = 1.33$.

Read about another glossary term