How does a wind turbine protect the bank from a reversal in polarity when spin direction is reversed?

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.

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.