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This is a follow-up question to an answer to How does a wind farm prevent the fastest spinning turbine from driving the slowest one?

Spinning a DC motor will generate electricity on it's terminals. When the direction of the spin is reversed, I expect the polarity at the terminals will reverse too.

So when a wind turbine is run, how is it the battery/bank it is connected to is not damaged when the direction of spin is reversed?

a. Does the charge controller OC when the polarity is reversed?

b. Is the wind turbine geared so it will only spin in one direction?

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    when operating as intended, they actually rotate the machine to face into the wind, so it does only spin in one direction. – JustJeff Sep 18 '11 at 01:51

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Generally speaking, wind turbines are not connected to generators that operate like a DC motor.

Their shafts are connected to generators. (see https://en.wikipedia.org/wiki/Electric_generator) that are normally linked through complex gearbox systems, sometimes many generators at once.

Like in most power stations that convert mechanical energy into electric power through generators, some wind turbines have generators that are in-phase with the AC grid. The generator excitation fields and turbine blade pitch are used to control how much energy is fed into the grid. In theory, if the wind stopped suddenly, the turbine would actually drain current from the grid as if it were an AC motor in a fan, until pitch/gearbox/excitation is adjusted.

Because they are in-phase and normally have many poles, it is impossible to rotate these in the opposite direction. If you were to force the blades to suddenly drive the generator out of phase, the current on the generator would raise dramatically and trip-open a protection circuit, effectively disconnecting it from the grid (or setting everything on fire)

Not all wind turbines run in sync with the grid. Some modern wind turbines use rectifiers to convert the generated electricity to DC, and then massive inverters to generate AC in-phase with the grid. Though these could in theory rotate the other way around, in practice that does not happen. If you were to reverse the direction of the wind fast enough, the turbine controller would adjust the blade pitch and/or bring the whole thing to a halt until it can re-orientate the whole turbine again.

istepaniuk
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There is no such thing as "polarity" in AC power generation. There is only "phase" - and as with all power generators wind turbines are phase-matched before being linked to the grid.

Also, wind turbines only spin one way. They pivot so that they face into the wind, and the wind can only turn the blades in one direction. The blades work on the same principle as aeroplane wings. If they could be blown in either directions then aeroplanes couldn't fly.

Majenko
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    Your analogy to airplane wings is incorrect. Airplanes can fly upside-down. – markrages Sep 17 '11 at 16:46
  • @markrages: To maintain aloft, airplanes must have the leading edge of the wing higher than the trailing edge. If an airplane is configured so that the wings would have a suitable angle when the fuselage is horizontal, flying upside-down will require the front of the fuselage be angled substantially upward. Otherwise, the plane will fly very rapidly into the ground. – supercat Sep 17 '11 at 17:14
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    Certainly the turbines are designed to rotate only one direction. Do you know if some/all have adjustable blade pitch? Winds can sometimes change direction unexpectedly; if the blades don't have adjustable pitch, I would think that a sudden change in wind direction could make it necessary to dynamic-brake the blades and dump energy from them between the time the wind changed and the time the windmill could be re-oriented. If the blade pitch could be changed dynamically, one could minimize the pitch and drive the blades (with mininal friction) to keep them at proper speed and phase. – supercat Sep 17 '11 at 17:17
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    @supercat you forget momemtum. The blades are spinning - very very fast (they don't look it, but the tips travel at hundreds of miles per hour). If the wind changes it takes a long time for that change to be reflected in a change in the spinning of the blades. Plenty of time for the turbine to be re-orientated. – Majenko Sep 17 '11 at 19:53
  • The large ones certainly do have blade pitch control. If the weather is producing too much wind, or significant winds that change direction too dramatically, the machine is put in a safe mode with the blades feathered and the brakes on. – JustJeff Sep 18 '11 at 01:57
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    Not all wind turbines generate AC current in-phase with the grid. Modern ones certainly don't as this requires complex gearboxes and control systems to keep the generator speed constant. – istepaniuk May 12 '15 at 23:16