Background of the Invention Up-to-date wind turbines having a tower of 100 m height or more and a rotor rotatably supported at the top of said tower and having a diameter of 80 m or more can have a rated output of more than 3 megawatts. This rated outputs are achieved when the efficiency is optimized by adjusting the individual elements of the wind turbine depending on the prevailing wind conditions. To this end, the rotor as a whole can be adjusted depending on the wind conditions by rotating it about a rotation axis substantially extending in the direction of gravitation. Furthermore, in up-to-date wind turbines the individual rotor blades of the rotor rotatable about a substantially horizontally extending rotor axis are pivoted about lateral pivot axes preferably extending normal to the rotor axis to achieve an optimal approaching flow of the rotor blades. For this purpose, respective actuators are usually housed in the rotor hub connecting the rotor blades with the rotor shaft extending substantially in horizontal direction.

To avoid damage of such wind turbines, it must be provided for that the rotor blades are automatically adjusted to a particularly low load condition on the occurrence of predetermined operating conditions like a power failure jeopardizing the operation of the actuators. This is normally the so-called feathered pitch in which the main surfaces of the rotor blades extend approximately parallel to the rotor axis so that they present a specifically low resistance to the wind flowing against them and the wind flowing against them does not lead to an excessive lift. Usually, the automatic adjustment of the rotor blades is accomplished by a locking device comprising a switch arrangement operable on occurrence of at least one predetermined operating condition of the wind turbine like an

interrupt of the power supply of the actuators, and an actuator operable in response to the operation of said switch arrangement. Normally, the actuator is operated with the aid of batteries connected to the actuator as to be responsive to an operation of the switch arrangement to thereby allow an adjustment of the individual elements of the wind turbine even when the power supply via the normally used power grid is interrupted. Therein, the switch arrangement can have a plurality of switch elements for sensing critical operating conditions of the wind turbine. These switch elements are usually serially connected in a safety chain so that the operation of a switch element leads to the actuator is operated for adjusting at least one element of the wind turbine independent of the operation of other switch elements.

To carry out repair and maintenance work, the rotor of wind turbines must be stopped and locked. When the rotor is locked, the condition of lowest load for the rotor lock is achieved when the rotor blades are pivoted about 90° in the plane of the rotor blades with respect to the so-called feathered pitch. However, an intentional or unintentional operation of the switch arrangement can occur during repair and maintenance work. In this case it must be prevented that the condition of lowest load for the locked rotor is left by adjusting the rotor blades in the feathered pitch. Therefore, the switch elements connected to a safety chain of known wind turbines are bridged during repair and maintenance work so that no adjustment of the rotor blades occurs even when the switch arrangement is operated.

However, it may occur during the course of repair and maintenance work that the locking of the rotor is suspended or the rotor lock breaks and the rotor resumes its rotation.

Then, it must be provided that the rotor blades are again adjusted to the lowest load feathered pitch for a rotating rotor to prevent damage on the wind turbine and injuries of the maintenance crew. For this purpose, a condition is usually precipitated which also leads to an adjustment of the rotor blades to the feathered pitch also when the safety chain is bridged. However, precise knowledge of the plant logic and plant management are necessary therefor. For this reason, specifically well trained experts must be used even for carrying out low-level repair and maintenance work to prevent damage on the wind turbine on the occurrence of critical conditions during the repair or maintenance work.

In view of these problems of the prior art, it is an object of the present invention to provide a wind turbine of the initially described type which allows for the accomplishment of repair and maintenance work without jeopardizing the wind turbine even in a case where staff is used that does not have precise knowledge of plant logic and plant management.

Summary of the Invention This object is solved by a further development of a known wind turbine which is substantially characterized in that the locking device comprises a switch arrangement that has at least one switching device operable by the rotation of the rotor.

With a locking device comprising such a switch arrangement, suspension or damage of the rotor lock and the rotation of the rotor caused thereby can be immediately sensed and the actuator for adjusting the elements of the wind turbine can be operated in the condition of lowest load for a rotating rotor in response thereof without the necessity of precise knowledge of plant logic and plant management even when the safety chain used in operation with rotating rotor of the wind turbine is bridged for repair and maintenance work. Thereby, it was discovered within the framework of this invention that the additional expenses caused by the provision of an additional switching device operable by the rotation of the rotor is acceptable in view of the increase of operating safety achieved thereby even if additional measures have to be provided for that no adjustment of the individual elements of the wind turbine is triggered by an operation of the switching device caused by the rotation of the rotor during use.

The switching device of an embodiment of the present invention operable through rotation of the rotor practically has a switch element and an operation mechanism, wherein it has been proven advantageous with respect to design that the switch element is movable by the rotation of the rotor, especially when it is mounted to a rotor shaft supporting the rotor and the operation mechanism is mounted to a non-rotating component of the wind turbine, e. g. the base frame of the machine nacelle disposed at the top of the tower of the wind turbine.

The at least one switch element of the switching device of a wind turbine according to an embodiment of the present invention and operable through rotation of the rotor can be optically, mechanically and/or magnetically operable with aid of the operation mechanism. In view of the fact that optically and/or magnetically operable switch elements normally require their own power supply, it turned out to be especially advantageous when the switch element is mechanically movable. In this case, the switch element can be formed in a known manner as a rotatable actuation lever, wherein said actuation lever can be practically rotated about a transverse rotation axis, preferably extending approximately perpendicularly and/or parallel to the axis of the rotor shaft.

Thereby, the arrangement of the actuation lever and the operation mechanism is preferably formed so that the actuation lever is rotatable in a predetermined direction by the operation mechanism independent of the direction of rotation of the rotor since such switch elements can be provided offhand. The operation mechanism for such a switching device can be simply formed when it comprises at least two actuation levers offset in the direction of the rotor shaft axis, wherein the rotation axis of the actuation lever of the switch element is disposed between them. When the actuation lever has two flanges extending from the rotation axis in opposite directions, an operation of the switch element through rotation in a predetermined direction of rotation can be caused by the cooperation of one of the actuation toggles with a respective flange of the actuation lever. Thereby, an interference of the operation of the actuation lever can be prevented by the respective other actuation toggle when the actuation toggles are offset to each other in a direction normal to the plane spanned by the rotor shaft axis and the rotation axis of the actuation lever.

Additionally or alternatively, the actuation toggles can be rotatable in opposite directions with respect to a pivot axis extending parallel to the rotation axis of the actuation lever. In this case, two actuation toggles pivotable in same direction can be provided on each side of the actuation lever, respectively, the toggles being offset to each other in a direction normal to a plane spanned by the rotor shaft axis and the rotation axis of the actuation lever.

Thereby, the pivot axes of the individual actuation toggles can be disposed at the angles of a square having its sides extending parallel to the rotor shaft axis.

It was mentioned before that a undesirable adjustment of individual elements of the wind turbine in response to an operation of the switch arrangement during operation must be prevented by additional measures. In this context, it has been proven constructively particularly simple when the at least one switching device operable by rotation of the rotor can be switched between an idle condition in which it is operable by rotation of the rotor, and an operation condition in which it is not operable by rotation of the rotor.

As is explained above, the rotor of a wind turbine according to an embodiment of the present invention has at least one rotor blade being pivotable about a transverse pivot axis preferably extending approximately perpendicular with respect to the rotor shaft axis and, in response to an operation of the switch arrangement, being adjustable to a feathered pitch in which it is oriented approximately parallel to the rotor shaft axis. If the rotor in usual design comprises a plurality of rotor blades pivotable about transverse pivot axes preferably extending approximately perpendicular with respect to the rotor shaft axis, during repair or maintenance work, it has been proven advantageous with respect to an increase in operation safety that the switching device operable through rotation of the rotor has at least two switch elements, preferably disposed after another in a circumferential

direction of the rotor axis, each being assigned to a pivotable rotor blade, wherein an actuator for adjusting a rotor blade is assigned to each switch element corresponding to the respective rotor blade. Thereby, it can be achieved that, even when a switch element and/or an actuator is damaged, an adjustment of at least one rotor blade to the feathered pitch can be effected by the remaining switch elements and actuators. This results in a considerable reduction of mechanical load on the wind turbine when the rotor is rotating.

To ensure operation safety of wind turbines according to an embodiment of the present invention during operation, the switch arrangement has at least one further switch arrangement operable independent of the rotation of the rotor. This switch arrangement is operated, e. g. , when the power supply of the actuators is interrupted. As is initially explained, it is particularly useful for conducting failure-free repair and maintenance work when the at least one further switching device can be switched between an idle condition preventing the operation of the at least one actuator responsive to an operation of the further switch arrangement, and an operation condition allowing the operation of the at least one actuator responsive to an operation of the further switch arrangement.

Within the framework of the present invention, not only the manufacturing of com- plete wind turbines comprising a locking device according to an embodiment of the invention is addressed. Moreover, also the upgrading of already existing wind turbines is an issue within the framework of the present invention. A locking device for this purpose comprises a switch arrangement with at least one switching device operable through rotation of the rotor and an actuator operable responsively to an operation of the switch arrangement for adjusting at least one element of the wind turbine to a predetermined condition. Therein, the switch arrangement of a locking device according to an embodiment of the present invention can have a switch element mounted to a rotor shaft and/or a rotor hub. A switch arrangement suitable for the creation of such a locking device comprises at least one switching device operable through rotation of the rotor, which can have a switch element fixed to the rotor shaft and/or the rotor hub.

As can be seen from the above explanations of wind turbines according to embodi- ments of the present invention, a method according to the invention for operating a wind turbine in which the rotor is stopped and locked for maintenance and/or repair work is substantially characterized in that the switching device operable through rotation of the rotor is switched to idle condition after stopping and locking the rotor. Thereby, the switch elements movable together with the rotor and assigned to the individual rotor blades can be switched to idle condition one after another, wherein the individual rotor blades are pivoted

to an idle condition one after another and subsequently the corresponding switch elements are switched.

Description of the Drawings In the following, the present invention will be described with reference to the draw- ings, which are referred to regarding essential details which are not emphasized in the de- scription. In the drawings Fig. 1 shows a schematic illustration of a wind turbine according to an embodiment of the present invention, and Fig. 2 shows a schematic illustration of a switching device according to an embodiment of the present invention.

Detailed Description Fig. 1 shows a rotor shaft 10 formed as a hollow shaft with a total of three switch elements 20,22, and 24 fixed thereto. Each of the switch elements 20,22, and 24 fixed to rotor shaft 10 is assigned to a rotor blade fixed to the rotor shaft 10 via a rotor hub (not shown). When one of the switch elements 20,22 and 24 is switched during a rotation of the rotor shaft 10 from the"off"to the"on"position by means of an actuation mechanism formed as a switch cam, a pivoting of the rotor blade associated with this switch element to the feathered pitch is effected by a corresponding actuator. The actuation cam 30 is mounted to a non-rotating component of the wind turbine, e. g. a base frame of the machine nacelle.

Being comprised by a locking device, the switching device 100 shown in Fig. 2 comprises a switch element fixable to the rotor shaft and denoted in total by 120, and an actuation mechanism designated in total by 130, which is mounted to a non-rotating component of the wind turbine.

The switch element 120 comprises an actuation lever 122 rotatable about a rotation axis 124 extending perpendicularly to the rotor shaft axis 12, said actuation lever 122 having two flanges extending in opposite directions from the rotation axis 124. The rotation axis 122 is rotatable in the direction indicated by arrow PI.

The actuation mechanism comprises a total of four actuation toggles 132,134, 136 and 138, two of which, namely actuation toggles 132 and 134, are disposed on one side of the rotation axis 124 in the direction of the rotor shaft axis 12, and the other two, namely actuation toggles 136 and 138 are disposed on the other side of the rotation axis 124 in the direction of the rotor shaft axis 12. The actuation toggles 134 and 136 are offset with respect to the actuation toggles 132 and 138 in a direction normal to the plane spanned by the rotor shaft axis 12 and the rotation axis 124. The actuation toggles 132,136, 136, and 138 are pivotable with respect to the pivot axes 133,135, 137, and 139, respectively.

Starting out from the position depicted in Fig. 2, actuation toggles 132 and 134 are pivotable in the direction indicated by arrows P3, while actuation toggles 136 and 138 are pivotable in the opposite direction as indicated by arrows P2. It is achieved by this arrangement of the actuation mechanism that, starting out from the idle condition depicted in Fig. 2, the actuation lever 122 is rotated through a rotation of the rotor shaft 10 in the direction indicated by arrow PI independent of the direction of rotation of the rotor shaft 10. This rotation of actuation lever 122 is allowed by pivotal evasion of a respective one of the actuation toggles 132,134, 136, and 138. A wind turbine according to an embodiment of the present invention can have two or more switch elements of the type depicted in Fig.

2 and two or more actuation mechanisms of the type depicted in Fig. 2, wherein the switch elements and/or the actuation mechanisms can be disposed one after another in a circumferential direction of the rotor shaft.

The present invention is not limited to the embodiments explained with reference to the drawings. Rather, also the use of switching devices is intended having the switch elements fixedly disposed and the actuation mechanisms fixed to the rotor shaft.

Furthermore, the switch elements and/or the actuation mechanisms can also be disposed at the drive shaft of a gear box coupled to the rotor shaft. Also, the use of optical and/or electrical switch elements is intended. In this case, a permanent magnet can be used instead of a cam and a conducting loop or coil can be used instead of the switch element shown in the figure. All of the aforementioned embodiments can also be used as parts of locking devices for wind turbines.