Abstract:
The invention is based on the problem of creating an additional device to act as a “secondary emergency device” in the case that one or more standard emergency devices fail to adjust the blade angle of one or multiple rotor blades into a position of power limitation. The method of braking a wind turbine in an emergency by adjusting the rotor blades for wind turbines with power control via the principle of pitch control or active stall control and of holding the position of a rotor blade for each rotor blade with at least one actuator and at least one holding brake is a redundant measure for an emergency. This enables one or more holding brakes to open depending on the rotor-blade direction that is required and to close or to be kept closed when an adjustment of a rotor-blade direction is not desired.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of German Application No. DE 102012101484.1 filed on Feb. 4, 2012, and European Application No. EP 13156489.0 filed on Feb. 23, 2013; all applications are incorporated by reference herein in their entirety. 
       BACKGROUND 
       [0002]    The present invention relates to a wind turbine with a rotor hub and at least one rotor-blade connected to a pivot-bearing. By at least one electrical, pneumatic and/or hydraulic actuator, each rotor-blade can be rotated on its longitudinal axis and can be held in a defined position by means of a brake, whereat the brake is connected to the actuator. There is at least one gear box connected to the actuator, which rotates on a pivot-bearing. The pivot-bearing comprises an inner and outer ring, wherein one ring is screwed onto the hub and the other one connects the rotor blade. By rotating the ring, to which the blade is mounted on, the rotor blade can be rotated in its longitudinal axis. This ring may be the outer or the inner ring of the bearing. In order to limit the energy caused by the wind in case of an emergency, or to interrupt or reduce the energy generation, the rotor blade is turned into the position in which a lower amount of wind power is absorbed by the rotor. In order for each blade to be provided with a self-sufficient rotation about its longitudinal axis, even on failure of the mains supply, each drive has one or more independent energy storages, which in case of an emergency, provide one or more rotor blade drives (actuators) on each rotor blade, with energy and release one or more holding brakes. 
         [0003]    The rotor blade pitching of a wind turbine is used for speed control (power control) of the turbine at the range of nominal power, and also as an aerodynamic braking system. Therefore each rotor blade has one or more actuators. To achieve this with the pitch system, it is rotated to an angle between vane position and working position, and with the system using the principle of active-stall into the opposite direction to stall. 
         [0004]    In case of a failure it is advantageous to turn all rotor blades into the position with a low power generation if possible. A version of existing systems for rotor blade pitch comprises one or more electric drive-modules for each rotor blade, including one or more connected actuators, which are equipped with one or more holding brakes to keep the position. This allows for each blade to be pitched and held at position individually. However, nearly at all known actuators, the holding brakes of rotor blades are designed so that the disconnection of the brake control leads to the blocking of the actuator shaft and thus there is the risk that the blade-pitch cannot or can only be performed insufficiently, if, for example, a cable-connection to a brake has been interrupted. Especially in the case that an actuator does not deliver any torque, the corresponding rotor blade stays in its maximum working position. In a system working with active brakes, there is the disadvantage that they cannot keep the rotor blade from rotating into the direction in which a further rotation of the rotor takes place, in the event that the actuation of the brake-coils is not possible. 
         [0005]    Consequently a malfunction of the rotor blade pitch-drive can cause a critical situation for the entire wind turbine. In particular, exceeding the permissible rotor speed can cause danger to people or a substantial or total damage to the wind turbine. 
         [0006]    According to the state of the art technology, brakes used in the drive-train for pitch-drives are executed in such a way, that the brake-coil with friction lining is fixed, for example to the motor housing, and the brake-hub is rotating together with the motor shaft, and thus a closing of the brake consequently stops the motor shaft and the associated gear and rotor-blade. However, one or more brakes on an actuator system for the rotor-blades, may as well be, for example connected between the motor and gearbox or via geared-belt-drive to the rotor-blade. 
         [0007]    The WO 99/23384 describes an apparatus for adjusting of rotor-blades at a rotor-hub of a wind turbine, which has a drive for rotating the rotor-blades. The rotor-blade adjustment can also be used as a braking system for shutdown of the wind turbine by turning the rotor-blades towards vane position, and so reducing the power, respectively speed, of the wind turbine. In order to ensure the slow-down of the wind turbine by the pitch-system, even in the event of a power loss, a switchable return stop is connected to the rotor blades, to block the motor-shaft which prevents the rotor blades to turn from vane position into working-position. The return stop is deactivated during failure-free operation and is automatically activated at failure of power supply, which causes the blades to only be able to turn into vane position and be kept there. 
         [0008]    In the document EP 1 763 126 B1 a device for controlling the blade angle of a rotor-blade of a wind turbine is described, wherein the device contains the following components: a pitch control system with a power converter, a DC voltage circuit with capacitor for power supply to the pitch control system, an AC power source for energy supply to the DC voltage circuit and an alternative buffer battery for power supply to the control system in case of AC power failure. 
         [0009]    The different versions of these suggestions have significant negative impacts, such as e.g. the system with switchable freewheel has the disadvantage that the full motor-torque has to be blocked, causing a rigorous blocking in one direction and that it requires an additional coupling for activation, or an auxiliary power supply. The systems using a passive brake do not feature a redundant emergency method respectively do not describe a truly redundant emergency apparatus, in case of an error at the actuator system, e.g. damaged actuator, or when a brake fails to release. 
         [0010]    The object of this invention is to provide an additional device, means a “redundant emergency apparatus for each rotor blade”, in the event that one or more standard emergency devices because of a failure, do not adjust the pitch-angle of one or more rotor-blades into a position of power limitation. 
         [0011]    These problems shall be solved in the way that each available brake is opened or is kept open, as soon as a torque on the rotor-blades longitudinal axis attempts to rotate the rotor-blade in the direction of a decreasing driving torque for the rotor, and in the case of a torque trying to move the rotor-blade into the maximum working position, this rotary movement shall be stopped already at the beginning, anyhow an adjustment to the aerodynamic braking position (vane position) is carried out for the corresponding rotor-blade. 
       SUMMARY 
       [0012]    Method and apparatus for braking of a wind turbine in case of emergency. The underlying purpose of the invention is to create an additional apparatus as a “second emergency apparatus”, in the case that one or multiple standard emergency devices are, because of an error, failing to adjust the rotor-blade angle of one or multiple rotor blades, into a position of power limitation. The method to decelerate a wind turbine in case of an emergency by adjusting the rotor blades for wind turbines with power control by the concept of pitch control or active stall control, and for each rotor blade with at least one actuator and at least one holding brake to secure the position of one rotor blade, includes a redundancy for emergency, in order to open one or multiple holding brakes ( 10 ), which fixate the rotor blade ( 29 ) against pitching, depending on the required rotor blade direction of turning, the brake resp. the brakes opens resp. open, and in case of a unwanted direction of rotation, the holding brake resp. the holding brakes ( 10 ) closes resp. are closing or kept closed. 
         [0013]    The inventive devices contain at least one actuator ( 13 ), once with at least one active holding brake ( 10 ), and once with at least one passive holding brake ( 10 ), and each with corresponding parts for fulfilling the function of the apparatus. 
       DETAILED DESCRIPTION 
       [0014]    When the actuator is used for active-stall system, the rotation of each rotor blade for aerodynamic braking of the rotor is done in the direction of stall. In normal operation the auxiliary device shall have no influence on the operation and the costs of the system shall be affected only marginally. 
         [0015]    The function is achieved by the inventive method and the inventive mechanism, which in case of disturbed emergency adjustment of one or more rotor-blades, the necessary aerodynamic braking by turning the blades is obtained nevertheless by a controlled opening or closing of the holding brakes, depending from which direction of the rotor-blade longitudinal axis a torque is originated. 
         [0016]    These functions are achieved after shut-off of an solenoid, which has connection to one or more brakes which are available at one or more devices of each rotor-blade actuator, that in the version “passive braking” has a manual release-lever for forced opening and in the version “active braking” has a brake lever for a forced close of the brake when necessary. To achieve this, the passive brake is mounted in such a way that its housing can be rotated at a small angle, and after the lack of application of force at the manual release lever, after the shut-off of the solenoid, a rotation of the brake housing can be executed. This connection allows an adjustment of the manual release lever on the passive brake by spring or by bar and detection of the rotational direction, or automatically when the friction pad is closed, to the direction of lever position “brake mechanically released”, and operates the mechanically actuated releasing of the brake pad when required. 
         [0017]    With an active brake, a switch-off of the solenoid also causes the release of the rotation of the brake housing by the release of a lock lever, and in dependence of the rotary direction of the actuator, the activation or release of the brake is effected by adjusting of at least one brake lever as a brake-closing lever, by spring force and the detection of rotational direction. In the event that with the passive brake, a torque arises from the rotor-blade in the direction of maximum working position, the rotatable mounted brake-housing, including a respective end-stop on the right and left, by a rocker lever, which is turned by the rotation of a carrier on the drive-shaft, is turned away from the end-stop, so that the manual release lever, which is connected to the rotation, is set back into neutral position, and consequently the brake pads close. As long as the torque for the rotor blade rotation in the direction of work-position is available, the manual release lever is held in position “neutral” by the closed friction pad of the brake, because of the torque having turned the brake housing in the direction, which brings the manual release lever into neutral position, using the rotation of the brake housing. 
         [0018]    In the case that an actuator does not generate a torque, the torque which is generated by gravitational force, as well as cyclic with the rotor rotation originating from the rotor blade longitudinal axis is used, at the pitch system to adjust the rotation of the rotor-blade to the direction of vane position, and with the active-stall system it is turned in direction of increasing stall. When using an active brake, the shutdown of the solenoid causes no rotational movement of the brake housing, or respectively the brake housing not being pulled into the position without activation of the brake lever, when the rotor-blade is turning in the direction of reduced wind energy generation. When changing the direction of rotation, the spring force that held the hand brake lever, is eliminated immediately by a rocker lever, and turning the brake housing, together with the pushing or pulling of the hand brake lever into the position “brake closed” and is held there as long as the direction of the available torque on the drive or the rotor-blade has not been changed, the brake housing and thus the brake lever associated with the rotational movement of the brake housing is held in position “brake closed”. 
         [0019]    The operation of the invention of the described system of a wind turbine comprises the following cases: 
         [0020]    a) During each automatic start of the wind turbine a functional test of the redundant mechanical brake-release is executed. This is performed in dependence of the rotor position and carries out a service request, if test fails. 
         [0021]    b) When using a passive brake, as soon as the mechanical release of the brake has turned the rotor-blade, towards the direction of reduced torque generation by the rotor, an end-stop sensor will set back the hand-lever of the brake to the neutral position, so that the angular motion of the rotor-blade is stopped. A functional check of the redundant and direction-dependent release of the rotation, can be done by the controller for activation and deactivation of the solenoid and thus of the manual release. 
         [0022]    c) When a active brake is used, at reaching a position of the rotor blade in that a low torque at the rotor is occurring, the brake hub is moved by a mechanical probe in such a way that the brake doses and the rotor blade rotation stops. 
         [0023]    d) Shutting off the solenoid at one drive in a situation of failure in the emergency system releases the mechanical brake control, i.e. the opening and dosing is dependent on the rotational direction of the motor shaft and the release of the direction of rotation is depending on the selected version of the pitch-system, and the driving direction, so that the adjustment decelerates the rotor. 
         [0024]    e) In case of using an electric drive system, each converter (for controlling a pitch motor) continuously performs a torque-check, which is used to detect an activated brake (fixing the position), or also to detect an increase in torque, required to rotate a rotor-blade, and for example as a result bringing the wind turbine to a safe operating condition. Thereby also a possibly increased torque is detected during the angle adjustment. If the actuator is working against the not opened brake, the controller independently deactivates the locking (turns off the solenoid) to initiate the redundant mechanical release of the brake depending on the rotational direction. When using an active brake (means not fixing position at power-off) an identified drive-blocking is corrected by a second deactivation function of the brake supply voltage, and thus likewise the brake is dosed or opened, as a function of the torque direction. 
         [0025]    f) The mechanical opening of the passive brake can be mechanically locked during transport, assembly, installation and service work. For service work, a non-positive locking of the rotation is available at the second shaft of the motor. When using active brakes, a closing of the brake can be realized by mechanical device, by the locking of the brake-lever, at cases where there is no power supply for the brake or in case of a dysfunction of power supply. 
         [0026]    g) An increase in the emerging drive torque for the pitching of the rotor-blade, resulting from the force of gravity and perhaps by aerodynamics, is effected by the generator-load of the wind turbine. Therefore, in case of a disturbance of the pitch system, the braking of the rotor is assisted by the generator load in accordance with the characteristic curve, and in the case that no power can be fed into the grid, it is assisted by a damp-load or an energy storage, which are connected to the generator-converter system. This equipment can be placed directly on the link of the converter or between the converter and the generator, or on the grid side. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    Design examples of the invention as a pitch system are shown in the drawings and will be described in detail below. 
           [0028]    Shown in drawings: 
           [0029]      FIG. 1  is a combined view of the side- and sectional view of the device for deceleration of a wind turbine in case of an emergency situation in status, manual release set to neutral, via an end-stop at the rotor-blade in vane position, and correlating the position with energized solenoid, 
           [0030]      FIG. 2  shows the side- and sectional view of the device for deceleration of a wind turbine in case of emergency in status, manual release activated, after switch-off of the solenoid. 
           [0031]      FIG. 3  combines the side- and sectional view of the device for deceleration of a wind turbine in case of emergency in status, rocker lever activated, the resetting of the manual release lever to “neutral” begins, when the shaft is rotating into the direction of operating position and 
           [0032]      FIG. 4  is a combined view of the side- and sectional view of the device for deceleration of a wind turbine in case of emergency with an active brake. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0033]    An additional emergency regulation of the rotatable mounted rotor blade  29  on the hub is achieved by switching off a solenoid  14 . Therefore the end of the shaft of an actuator  13  has a holding brake  10  with a friction-lining  17 , which is fixed by screws  10 . 1  to a flange  12 . Furthermore, the brake  10  includes a manual release lever  11  with a small spring  19 , as shown in  FIG. 1 , pulling with a low force to neutral position. 
         [0034]    The flange  12  is rotatable connected to the housing of the actuator  13 , using a fixed connection  24 . By rotation of the flange plate  12 , a small rotation angle on the housing of the holding brake  10  is released. 
         [0035]    On malfunction of the emergency system, the solenoid  14 , which blocks the rotation of the housing of the holding brake  10 , is switched off and pulls, via the strong spring  25  and the connection  21 , the manual release lever  11  to position “active” ( FIG. 2 ), provided a turn to vane position is needed and in case the electrical opening of the holding brake  10  fails and the holding brake  10  blocks the motor shaft  16 , or one or more actuators  13  don&#39;t generate a torque. During a rotary movement of the motor shaft  16  into vane direction, and the closed braking pad  17  of the holding brake  10 , the housing of the holding brake  10  is rotated at a small angle by the motor shaft  16 . This rotation angle is used to hold a rocker lever  23  in position “neutral” by means of a cable pull  22  and to flip by spring tension, while pulling the manual release lever  11  of the holding brake  10  in position “released” by an additional cable. At failure-free operation the rocker lever  23  is held out of reach of the carrier  30  by means of an auxiliary spring  26 . Provided that the direction of the counter-clockwise rotating carrier  30  doesn&#39;t change, this position is maintained until a mechanical end position probe  28  detects the vane position of the rotor blade  29  via end-stop  31  on the rotor blade  29  and the manual release lever  11  is pulled into neutral position against the spring force with the cable  27 . Thus the redundant release of the holding brake  10  is deactivated making the holding brake  10  electrically controllable only. 
         [0036]    If the rotor blade  29 , and with that the motor shaft  16 , rotate in the direction of working position, the carrier  30  rotates in a clockwise direction, the carrier  30  activates the resetting of the rocker lever  23 , and by pulling the cable  22  the strong spring  25  is tensioned again, and the small spring  19  pulls the manual release lever  11  into neutral position, as shown in  FIG. 1 . An inclined position of this function is shown in  FIG. 3 . At the same time the housing of the holding brake  10  is rotated (clockwise) again into the position in which the active solenoid  14  can block it from rotating. The rocker lever  23 , pulled by the auxiliary spring  26 , is again located outside of the engaging area of the spinning carrier  30  rotating with the motor shaft  16 . Consequently the holding brake  10  can be opened redundantly by the torque of the drive  13  with the motor shaft  16  or by torque from the force of gravity and in addition, if applicable, by the aerodynamics at the blade axis of rotor-blade  29 . 
         [0037]    For friction-prevented rotation of the rotor blade, with the passive brake system, the manual release lever  11  is locked in the neutral position, e.g. for maintenance or transport, in the version with the active brake  10 , the position of the pressed anchor-plate  33  is lockable. This prevents an accidental release of the motor shaft  16 . 
         [0038]    For releasing of the holding brake the following additional options are provided: 
         [0039]    a) The manual release lever  11  is moved in such a way that only about 90% braking torque is being reduced. Thus the twist of the holding brake  10  is maintained, as long as the rotational direction of the motor shaft  16  does not change. When setting the overall mechanics of the holding brake  10 , it is necessary that the friction lining  17  does not fully release, and thus a small torque on the housing of the holding brake  10  remains, which holds the manual release lever  11  in the released position. 
         [0040]    b) As a variation an additional spring-brake (auxiliary brake) is used, whose torque is set to a small value and whose housing is connected to the holding brake  10  as main brake  10 . The auxiliary brake is not mechanically opened when a failure occurs. Thus, upon rotation of the motor shaft  16  in the direction of vane position, the housing of the main brake  10  is held in position “manual release lever activated”. When changing the rotational direction, the housing of the brake  10  is turned to the direction “brake lever neutral position” whereby the main brake  10  closes, unless the electrical excitation is switched on. This enables the rotation of the motor shaft  16  into the direction of vane position. A rotation of the closed brake towards working position keeps the brake closed and holds the current position. 
         [0041]    c) By using an active brake, a forcibly function to open and close of the holding brake  10 , can also be achieved. This type closes the brake-pad  17  on activation and opens at power-off. For this purpose, closing the friction linings  17  is carried out by spring force when a rotation into working position is executed, and as soon as arrived at vane position. The detection and triggering of mode “arrest rotor blade rotation into direction working position” or “hold in vane position” is also realized by a solenoid, and achieved depending on direction of the rotational movement of the holding brake housing  10 , and by the release of rocker lever  23 . The pitch system that regulates the input power of the rotor by a stall at the rotor blades  29 , uses the same mode of operation, and then holds the rotor blades  29  in the control range with the least wind energy on the rotor blades  29  and rotor rotation affecting them. 
         [0042]    Using an active or a passive holding brake  10  results in a similar operation of the device, but with the difference that for a passive holding brake  10  a manual release lever  11  is needed, that releases the braking, and using an active holding brake  10  requires the closing of the friction lining  17  to the brake hub  33  by an additional device. 
         [0043]    When adjusting the rotor blades  29  it will be utilized, that during one revolution of the rotor an emerging torque, through wind and gravity of the rotor blade  29 , is detected on each rotor blade  29 , which occurs alternately once towards working position and back in the direction of vane position, while the rotor-blades  29  are designed accordingly, that its centre of inertia is outside of the rotor-blade centre. 
         [0044]    The present invention shall be seen as a complement to known safety devices, where in case of failure, in which one or more actuators  13  don&#39;t deliver a torque, anyhow let the correspondingly affected rotor-blade  29  gradually turn towards vane position and thus the risk of damaging the wind turbine due to use of emergency equipment is considerably reduced compared to state of the art technology. 
         [0045]    The design, construction and function of a version using one or more active holding brakes  10  in the drive-train for a rotor-blade  29  is described below. 
         [0046]    In case of malfunction, which does not allow giving torque by one or more actuators  13  on the drive train to a rotor blade  29 , the brake/s  10  will no longer be controllable, and therefore blade  29  will swing back and forth between aerodynamic deceleration and aerodynamic acceleration at each revolution of the rotor. Consequently there wouldn&#39;t be a rotor-blade pitching for continuous reduction of the rotor speed (no more aerodynamic deceleration of the rotor). To resolve this, each of the existing actuators  13  has a flange  13  and on the rotating shaft  16  there is arranged either a gear  34  or a friction wheel  34 , in or on which another outer wheel  35  can dip or can be pressed on radial, and thus a rotational movement can be absorbed. During normal operation, the displaceable outer wheel  35  is held out of contact with wheel  34 , by means of a lifting or pushing magnet  37 , which is connected to the rotation of the rotor blade  29 . The contacting of the movable gear  35  by spring force of spring  40  happens as soon as it is no longer held by magnet  37 . A detected error also causes the housing of the holding brake  10  to be released at a slight angle by the release of the locking lever  38 , via spring  46 , this can be carried out with the same electro-magnet  37 , which sets the movable gear  35  free and thus leading to a frictional engagement of wheel  35  to wheel  34 . If there is no error in the pitch system, the locking lever  38  is kept by cable  45  which is tensioned by the pulling solenoid  37 , and thus preventing rotation of the brake housing  10 , and leading to default behaviour of the electromagnetic brake. Therefore the disconnection of electromagnet  37  causes, that a force-fit or form-fit connection is done to motor shaft  16 , and a possible rotation of the brake housing  10  with a defined angle of rotation is enabled, which can be mechanically detected from the torque direction of the rotor blade, hence brake  10  is mechanically controlled. In addition to the mechanical detection, a technical measurement detection is possible with the disadvantage that electronics are required. 
         [0047]    The modes of operation are: 
         [0048]    a) Rotating the rotor blade  29  towards working position and 
         [0049]    b) rotating the rotor blade  29  towards vane position, resp. in the direction causing a reduction of wind power generation. 
         [0050]    In case a) a possibly originated rotation of motor shaft  16  in the direction of working position results in a pulling of brake-hub  33 , which is caused via lever  49  connected by cable  36  with displacing wheel  35 , and thus the brake hub  33 , which is form-fit slidable at gearing  39 , is pulled against friction pad  17  which is associated with brake housing  10 , and consequently spring  41  is tensioned. With the closing of the brake pad  17  a small rotation of the brake housing  10  to end stop DBz happens, and then motor shaft  16  is slowed down. Therefore the cable  36  has an sliding connection  47 , as sliding contact  47  with the shaft  16  of the rotating brake hub  33 , and the sliding contact is released again, by means of the spring  48  after the manual brake-lever  49  is no longer pulling the cable  36 , and thus brake hub  33  is no longer pressed against friction lining  17 . 
         [0051]    In order that the rotation of the brake housing  10  can happen, the housing of holding brake  10  is released simultaneously with the disconnection of magnet  37  from a position that is locked against rotation. In an error-free system, this locking is provided by means of a locking lever  38 , which puts tension on spring  46 , by pulling the solenoid  37  via cable  45 , and it engages the locking lever  38  at the brake flange  32  resp. brake housing  10  and thus, with energized solenoid  37  and deactivated connection of wheel  34  and  35 , no rotation of the brake housing is possible. Now the rotor blade  29  cannot rotate in the direction in which an increase torque would act on the rotor by the wind. During operation without interference the brake operates according to state of the art technology. 
         [0052]    When, according to case b), rotor blade  29  rotates into direction of vane position resp. in the direction where lower wind power is generated, the clamping or adjusting mechanism for activating holding brake  10  is released again and the brake hub  33  is, by at least one spring  41 , no longer pressed against the brake pad  17 . This is done by reversing the direction of rotation of the connected wheel  35  by rotating the position of brake housing  10  via the closed friction pad  17 , enabling a rotary motion of wheels  34  and  35 , thus eliminating the tension of cable  36  and brake hub  33  disengages again from brake pad  17  via spring  41 . A tension spring  48  may revoke the sliding motion of the point of action, thus let brake hub  33  rotate freely. As long as wheel  34  rotates with wheel  35  and with the, via the freewheel  42 , associated winding device for the traction cable  36  in this direction, cable  36  remains in a position in which the manual brake lever  49  is not actuated by free wheel  42  and free wheel  42  allows further rotation of sliding wheel  35  after release of brake hub  33 . Thus the rotor blade  29  is released for a rotation, in the direction of position for aerodynamic deceleration of the rotor. Brake lever  33  remains in neutral position until a new cycle begins. Even in the event of failure of all rotor-blade pitch systems at a wind turbine of the present invention, the rotor is still slowed down to a lower rotational speed. 
         [0053]    So that there is no hard impact of a freely rotating rotor blade  29  in the vane position, a rotor blade end position spring  43  is proposed, in order to perform a mechanical closing of the brake as soon as the blade  29  has reached a predefined area. A mechanical sensor identifying this section, actively pulls or pushes the brake lever  33  and rotor-blade  29  will be stopped. The stop takes place, for example by shortening rope  36  for brake activation. Advantageously a damper is used that, for example, after one second, and after rotor blade  29  has been slowed down, releases cable  36  again. 
         [0054]    Until the restart of the pitch-system to normal mode without an error, a turning of each rotor-blade  29  in the direction of working position is prevented by the brake torque. 
         [0055]    This function of the blocking of an active brake  10  can also be used advantageously, to secure rotor blade  29  for transport, maintenance and service without a power source, by pressing the brake hub  33  against friction lining  17  by mechanical force. 
         [0056]    As soon as the pitch-system is in an undisturbed state again, solenoid  37  is activated which brings the shifting wheel out of contact. Simultaneously, locking lever  38  is actuated for fixing brake housing  10  by cable  45  against spring  46 . Holding brake  10  is activated electrically, so that the brake housing  10  can fully rotate into neutral position and locking mechanism  38  is able to lock, and with a short time of actuator torque, the normal position of the brake housing  10  is reached, in which the locking-device  38  can engage. A tension spring  44  on brake housing  10  assists the movement of brake housing  10  into neutral position. The actuator  13  can return to normal operation. The neutral position of brake adjustment and/or of the displacement wheel  35  is advantageously monitored by a sensor within the pitch- or control system. 
         [0057]    It is self-evident that cables  36 ,  45  are replaceable by rods. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           10 —holding brake, main-brake, brake-housing 
           10 . 1 —screws 
           11 —hand-lever 
           12 —flange 
           13 —actuator-motor, drive, motor-flange, servo-motor, rotor blade drives (seite 1 ) 
           14 —solenoid 
           15 —sliding device 
           16 —motor-shaft 
           17 —friction lining, 
           19 —light spring 
           20 —rope 
           21 —connection 
           22 —control-cable, cable 
           23 —rocker-arm, rocker-lever 
           24 —connection 
           25 —strong spring 
           26 —assistance-spring 
           27 —cable 
           28 —end-position sensor, end-position probe 
           29 —rotor-blade 
           30 —cam, carrier 
           31 —blocking device, end stop 
           32 —brake-flange 
           33 —brake-hub with toothing, brake-lever 
           34 —toothed wheel/friction drive on motor-shaft 
           35 —outer relocatable wheel 
           36 —rope 
           37 —solenoid, lifting-magnet 
           38 —lock-pin lever 
           39 —toothing 
           40 —spring 
           41 —spring 
           42 —freewheel 
           43 —spring at rotor-blade vane-position 
           44 —spring at brake housing 
           45 —rope, 
           46 —spring 
           47 —sliding contact, 
           48 —spring 
           49 —brake lever 
         VR—outer relocatable wheel 
         DR—rotor-blade rotation 
         DB—brake rotation 
         DBa—rotation “brake free” 
         DBz—rotation “brake closed”