The diagram shows the turbine yawed to the position where its power cables are completely untwisted. In this case, the cable that untwists the yaw system attaches to its topmost pulley wheel in such a way that it is not wrapped around that topmost pulley wheel at all. (The topmost pulley wheel is the one with the axis of rotation that is coincident with the turbine’s yaw axis). Now as the turbine yaws, it doesn’t matter which direction the turbine yaws in. Whichever way the turbine yaws, it wraps the untwist cable around the topmost pulley wheel, and in so doing it draws the twist sensing component that is attached to the untwist cable (colored purple) up to a higher elevation. When this part of the sensor passes close by the topmost twist sensor component (colored red), the control system knows that the power cables are twisted up. To untwist the turbine, the controller simply turns on the small electric motor at the base of the tower until the cable mounted twist sensor component passes by the lowest red colored twist sensor component, then turns the motor back off. If the system fails for some reason, the result is that the small untwist motor will burn up or blow a fuse – a minor repair indeed. The controller might wait until the wind isn’t blowing before untwisting the power cables.
In this variation, the controller merely untwists the turbine every time the wind speed drops to zero (rotor blades not turning). Some kind of slip clutch mechanism might be provided to keep the untwist motor from burning up if it runs too long. Alternatively, the motor could be turned off whenever the power it draws jumps up by a large value (indicating the turbine has been completely untwisted). Or a simple mechanical switch could be tripped whenever the turbine is completely untwisted.
A manual version of this device might also work well. In this case, the controller might issue some kind of mechanical or telecommunications signal to let someone know that the turbine needs untwisting.