A few months back, Windstuff Ed ran an experiment where he rectified the voltage from the star point of a two-phase generator. Zubbly identified this configuration as a "Scott T" connection and Ed called it "Pseudo-delta". Unfortunately the thread drifted off in to the relative merits of two-phase generation, and the significance of the experiment was lost. After analyzing the current flows, I realized Ed had shown us a simple and elegant way to provide a star - delta switch from a single set of stator windings.
In a star configuration, current flows through all three-phases when a voltage is induced in any one phase - full current in the induced phase and half current in each of the other two adjacent phases. This is why the resistance in a star wired stator is 2x the resistance of any single phase.
In a delta configuration, the three phases are in parallel so the current will flow through the two end points of the phase and the phase resistance is equal to the resistance of any single phase. Since the phase resistance is half that of star, the current flow is theoretically twice that of star. (Not entirely true in practice, I am ignoring the effects of parasitic current flow in the adjacent phases for the sake of simplicity.) Delta provides more current, and the induced voltage is virtually identical in each.
Now let's wire our stator in star, but bring a forth wire down the tower from the star point to our rectifiers. In this line, insert either a mechanical or electrical switch between the star point and the rectifier. When this switch is open, the generator performs as a star wired stator. However when the switch is closed, the three phases are now paralleled and the generator performs as a delta wired stator. This may be a simple way to extend the range of the system in varying wind conditions using a single set of windings. There are of course implications for stator losses, heating, and prop performance, which I shall leave to others to explain.
Regards,
Kevin