Polyphase system

The chief advantage of these was that the winding configuration was the same as for a single-phase capacitor-start motor and, by using a four-wire system, conceptually the phases were independent and easy to analyse with mathematical tools available at the time.

This is less important in modern machines that create a nearly ideal rotating field using sinusoidally distributed windings, but three-phase systems retain other advantages.

Induction motors using a rotating magnetic field were independently invented by Galileo Ferraris and Nikola Tesla and developed in a three-phase form by Mikhail Dolivo-Dobrovolsky in 1889.

[3] Previously all commercial motors were DC, with expensive commutators, high-maintenance brushes and characteristics unsuitable for operation on an alternating current network.

[5] Six-phase operation thus lets an existing double-circuit transmission line carry more power without requiring additional conductor cable.

However, it requires the capital expense and impedance losses of new phase-converting transformers to interface with the conventional three-phase grid.

[6]: xvii–xviii Three-phase power lines rely on transposition to equalize across all phases transmission losses due to slight deviations from ideal geometry.

Since the rotation speed of a wind turbine may be too slow for a substantial portion of its operation to generate single-phase or even three-phase AC power, higher phase orders allow the system to capture a larger portion of the rotational energy as electric power.