The present invention relates to a device for locking a turbine blade of a wind power plant at a predetermined pitch angle which wind power plant comprises a rotor hub and at least one turbine blade where the blade root of the at least one blade is connected to the rotor hub through a pitch bearing so that the pitch angle of the at least one blade is adjustable by turning of the at least one blade about its longitudinal axis relative to the rotor hub.
Adjusting the pitch angle of turbine blades is a way of controlling the rotational speed (rpm) of a wind turbine. In order to reduce the load or completely stop rotation the blades are directed to a feathered position where the wind will not engage with the blade and the blades are urged to stall and rotation of the turbine will decrease and/or stop. Once turbine is stopped and the blades have been put into a parked position it is important that the pitch angle of the blades does not accidentally change since this would cause the blades to catch the air starting an uncontrolled rotation of the turbine. For this reason, some sort of locking mechanism for the blades is needed, and is especially important during maintenance work where events of accidental rotation may cause substantial damages to components and indeed to personnel performing such maintenance on the wind turbine. Another reason to shut down the turbine is extreme wind conditions where the design of a wind power plant is unable to cope. In such a case blades are put into a no-power, feathered position for protecting the wind power plant.
Heretofore, turbine blades have been kept in place by hydraulic pressure systems or preventing means in the form of disc brakes or pneumatic means applied onto the blades ensuring that aerodynamic forces acting on the blades will not cause the pitch to alter and the turbine to start turning. A disadvantage with many like conventional systems is that they depend on an external force in order to function properly, which adds a certain risk of failure for instance in case of a power outage. Also, many adjustment mechanisms and lockouts depend on electrical control systems which are complicated and expensive both to set up and to maintain.
An example of preventing mean comprising disc brake is disclosed in U.S. Pat. No. 6,428,274 where an activatable lockout is connected to each rotor blade and prevents turning of the rotor blades into operating position, but allows turning into feathered position. Further, GB2191823 discloses adjustment means for ram air turbine rotor blades including lockout which, when activated, turns the blades to a feathered pitch and locks it in that position.
It is an object of the present invention to provide an improved locking device for locking a turbine blade in a predetermined pitch angle, preferably where the predetermined pitch angle corresponds to a feathered position of the turbine blade.
According to embodiments of the invention, a system for a wind power plant is provided that will increase security and reliability and that is able to keep the blades of a wind power plant locked in a predetermined position independently of any control system or electrical system. This, and further objects of the invention, is achieved by a locking device for a wind power plant, which wind power plant comprises a rotor hub and at least one turbine blade where the blade root of the at least one blade is connected to the rotor hub through a pitch bearing so that the pitch angle of the at least one blade is adjustable by turning of the at least one blade about its longitudinal axis relative to the rotor hub and wherein the locking device comprises a mechanical snap-in mechanism which in a locked position prevents the at least one turbine blade from turning about its longitudinal axis thus fixating the blade in the predetermined pitch angle.
The locking device according to the invention leads to a number of advantages, whereof the most beneficial are the following:
A locking device according to the present invention is arranged to lock a turbine blade in one predetermined pitch angle. The invention is specifically advantageous for locking turbine blades into a feathered pitch, for instance during maintenance work, but it may also be used for locking blades into other pitch angles. The position where a blade is locked by a device according to the invention depends on where onto the pitch bearing the locking device has been mounted. As an example, in order to lock a turbine blade into a feathered pitch the device is mounted onto pitch bearing in such a position that when the blade has turned relative to the hub into the feathered angle the snap-in mechanism of the locking device is activated, fixating the blade relative to the hub.
It is understood that general operation of the wind power plant is known in the art and therefore will not be described in detail. For instance, the wind power plant includes a blade pitch system whereby the pitch angle of the turbine blades may be changed and locked into different angles in a continuous manner with respect to a wind direction. Blade pitch system further includes one or more actuators coupled to hub and blades for changing the pitch angle of blade by turning about its longitudinal axis relative to the rotor hub. Actuators may be driven by any suitable means such as, but not limited to, hydraulic fluid, electrical power, and/or mechanical power. Blade pitch system further includes means for continuously fixating the blades in any desired pitch angle, as is known in the art, for instance by means of a gear system and/or with the aid of disc brakes. A blade lock device according to the invention, however, is used for mechanically locking the blade into one specific pitch angle selected for a certain purpose. One such purpose would be to lock the blade in a feathered position for instance during maintenance work, or due to extreme wind conditions.
According to one aspect of the invention the locking device comprises one hub part which is permanently connected to the hub and one blade part which is permanently connected to the turbine blade. Each part comprises a mounting plate which is permanently attached to the hub and the blade respectively. When locking a blade in a certain pitch the blade is turned by actuators relative to the hub until the blade mounting plate is brought adjacent to the hub mounting plate. In this position the snap-in mechanism of the locking device is activated causing the hub—and blade parts to connect to one another by means of form-fitting thus preventing further turning of the turbine blade.
According to another aspect of the invention the blade part comprises at least a first and a second locking block mounted at a certain distance from each other thus defining an open space in between the two blocks. Further, the hub part comprises a protruding element which is designed to essentially match the open space as defined by the locking blocks. Preferably, but not necessarily, the protruding element is a protruding pivot element but it is equally possible that the protruding element may be in the form of a movable locking pin. The pivot element is preferably pressed continually in the direction towards the pitch bearing of the turbine blade. When locking an unlocked turbine blade, the blade is rotated around its longitudinal axis relative to the hub, and the blade part of the locking device rotates therewith. The hub part of the locking device is fixed relative to the rotor blade. When the blade has turned to a position where hub part and the blade part meet the protruding pivot element will snap into the open space between the two locking blocks thus connecting the two parts to one another locking the blade.
A person skilled in the art will understand that the hub part and blade part respectively are interchangeable, meaning they may switch positions with each other so that the blade part may equally be connected to the rotor hub and vice versa, without affecting the locking function of the invention.
According to yet another aspect of the invention the pivot element is pressed continually towards the turbine blade by the force of a spring element. In a locked mode, the spring element will ensure that the pivot element remains in place within the open space between the locking blocks.
According to yet another aspect of the invention the locking device comprises means for disconnecting the hub part the blade part from one another thus unlocking the device so that the blade may rotate again. Preferably, but not exclusively, the means for disconnecting the pivot element from the open space between the locking blocks comprises an electromagnet which when activated withdraws the spring element so that the pivot element is released from the open space between the two locking blocks. The part which is connected to the rotor blade is thus disconnecting from the part which is connected to the rotor hub, and the rotor blade is free to rotate.
The following detailed description, and the examples contained therein, are provided for the purpose of describing and illustrating certain embodiments of the invention only and are not intended to limit the scope of the invention in any way.
As is seen in
Finally,
Once in a locked position the turbine blade is prevented from further turning in at least three ways. First the spring force will keep the pivot element 210 pressed downward relative to the flange 22. Second, the tip portion of the pivot element 210 lies adjacent to the rear vertical edge of locking block 310 which stops turning in one direction, and third the holding block 211 is adjacent to the second locking block 311 of the locking device 1 which stops turning in the other direction.
The pivot element 210 and the holding block 211 together essentially matches the space between the two locking blocks 310, 311. Once the plates 21, 31 which are connected to the flange 22 and the bearing ring 41 respectively are brought adjacently to one another and are interconnected as in
In order to unlock the device 1 according to the invention, the pivot element 210 is retracted from the space between the locking blocks 310, 311 by pivoting upwards relative to the bearing ring 41. Such a retraction may be achieved for instance by integrating an electromagnet with the spring element 213. The electromagnet may be activated so that the spring is retracted and lifts the pivot element 210 from a locked position in between the locking blocks 310, 311.
The invention is not to be seen as limited by the embodiments described above, but can be varied within the scope of the appended claims. For instance, the pivot element 210 may be differently shaped than herein described, and one wind power plant may comprise more than one installed blade lock devices 1. Many other variations are also possible, as will be readily understood by the person skilled in the art.
Number | Date | Country | Kind |
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0950591-8 | Aug 2009 | SE | national |