Abstract:
The disclosure relates to checking a rotational speed relay of a wind turbine. The wind turbine comprises a rotational speed sensor for the rotational speed of a shaft. The rotational speed sensor outputs a rotational speed signal, which is fed to a signal input of the rotational speed relay. According to disclosure, the rotational speed signal fed to the rotational speed relay is first inactivated. Then a signal generator is activated, which produces a check signal equivalent to the rotational speed signal. The check signal is fed to the signal input of the rotational speed relay. The signal generator is operated with a check signal that is beyond a rotational speed limit, and a check is performed to determine if the rotational speed relay generates a switch-off command. This allows the functional capability of the rotational speed relay to be checked reliably and at low cost.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a national stage application under USC 371 of International Application No. PCT/EP2011/059193, filed Jun. 3, 2011, which claims the priority of German Application No. 102010023279.3, filed Jun. 10, 2010, and German Application No. 102010024566.6, filed Jun. 22, 2010, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to a method for testing a rotational speed relay of a wind energy installation. The wind energy installation comprises a rotational speed sensor for the rotational speed of a shaft. The rotational speed sensor outputs a rotational speed signal which is supplied to a signal input of the rotational speed relay. The rotational speed relay generates a switch-off command if the rotational speed of the shaft exceeds a predefined rotational speed limit value. The invention also relates to a wind energy installation for carrying out the method. 
       BACKGROUND OF THE INVENTION 
       [0003]    The rotational speed at which the rotor of a wind energy installation rotates is a safety-relevant parameter. If the rotational speed moves out of the intended rotational speed range, the wind energy installation may be damaged. The controller for the wind energy installation is set up such that the relevant rotational speed limits are not exceeded during normal operation. However, if faults occur in the wind energy installation, for example a defect in the controller or a faulty signal from a sensor, the situation may occur in which the wind energy installation no longer operates as intended and the rotational speed limits are exceeded. 
         [0004]    An additional safety mechanism is provided for this situation. The rotational speed is continuously monitored using a rotational speed relay and a switch-off command is generated if a rotational speed limit value is exceeded. The switch-off command which has priority over the normal controller commands causes the wind energy installation to be deactivated as quickly as possible. 
         [0005]    The rotational speed relay is checked for proper operation at regular maintenance intervals. Hitherto, the following method has been provided for this purpose. A service engineer travels to the wind energy installation and stops the latter. The rotational speed relay is reprogrammed to a new rotational speed limit value which can be exceeded during normal operation. The service engineer then starts the wind energy installation, with the result that the lower rotational speed limit value which has now been newly set is exceeded. The service engineer tests whether the rotational speed relay provides a switch-off command in the proper manner. If the test is positive, the wind energy installation is stopped again, the rotational speed relay is programmed back to the original rotational speed limit value and the wind energy installation is changed to normal operation again. This process is prone to errors. It is conceivable, inter alia, for the rotational speed relay to be programmed to an incorrect limit value, rather than the original limit value, at the end. 
       SUMMARY OF THE INVENTION 
       [0006]    On the basis of the prior art mentioned at the outset, the invention is based on the object of presenting a wind energy installation and a method which can be used to check the rotational speed relay in a cost-effective and reliable manner. The object is achieved by the features as broadly described herein. Advantageous developments are the subject matter of the detailed embodiments described below. 
         [0007]    A number of terms are first of all explained. In the sense of the invention, a shaft is any element of the mechanical drive train, the rotational speed of which is in a fixed relationship with respect to the rotational speed of the rotor. The term shaft comprises, for example, the rotor shaft as well as rotating components of the transmission and generator. The rotational speed of the rotor can be directly derived from the rotational speed of the shaft. The rotational speed signal represents the rotational speed of the shaft. 
         [0008]    The rotational speed limit value limits the rotational speed range within which the wind energy installation moves during normal operation. The rotational speed limit value may provide an upper or lower limit for the rotational speed range. Both the case in which the upper limit value is exceeded and the case in which the lower limit value is undershot are considered to be cases in which the rotational speed limit value is exceeded. 
         [0009]    The switch-off command may be transmitted, in the form of an electrical signal, to a component of the wind energy installation which switches off the wind energy installation. The transmission of the switch-off command may also involve opening the safety chain of the wind energy installation. The safety chain denotes a line via which a plurality of safety-relevant elements of the wind energy installation are coupled to one another. If a fault occurs in one of the elements, the safety chain is opened, which results in the wind energy installation being stopped. 
         [0010]    In the method according to the invention, the rotational speed signal is first of all deactivated, with the result that the rotational speed relay no longer receives a signal from the rotational speed sensor. This may be effected, for example, by interrupting a corresponding cable connection. It is also possible to stop the wind energy installation, with the result that the rotational speed sensor no longer provides a signal for this reason. A signal generator which generates a test signal equivalent to the rotational speed signal is also activated. A test signal is equivalent to a rotational speed signal when the rotational speed relay can gather an item of rotational speed information from the test signal. The signal generator is operated in such a manner that it generates a test signal beyond the rotational speed limit value. The rotational speed relay thus gathers the information that the rotational speed limit value has been exceeded from the test signal. When the limit value has been exceeded, a rotational speed relay operating properly must provide a switch-off command. A test is carried out in order to determine whether this switch-off command is actually provided. 
         [0011]    Using a synthetic test signal to feign particular rotational speeds to the rotational speed relay makes it possible to test the response of the rotational speed relay without the shaft actually having this rotational speed. In particular, this makes it possible to carry out checks outside the normal rotational speed range. There is no need for the error-prone reprogramming of the rotational speed relay, which is otherwise required in order to be able to simulate situations in which the limit value is exceeded in the normal rotational speed range. 
         [0012]    The method can be advantageously carried out in such a manner that the signal generator is first of all operated with a test signal which is within the normal rotational speed range, that is to say with which no rotational speed limit value is exceeded. The test signal can then be changed such that the rotational speed limit value is exceeded. This makes it possible to reliably check whether the rotational speed relay is triggered at the correct time. 
         [0013]    As explained, the method can be carried out in such a manner that a service engineer stops the wind energy installation in situ and connects a signal generator to the rotational speed relay instead of the rotational speed sensor. Alternatively, provision may also be made for an automatic changeover between the rotational speed signal from the rotational speed sensor and the test signal from the signal generator. This makes it possible to check the rotational speed relay during remote maintenance. If necessary, the wind energy installation may remain in operation during the check if it is possible to resort to alternative sensors in the wind energy installation. 
         [0014]    A wind energy installation often comprises a plurality of rotational speed sensors which are used to detect the rotational speed of the rotor shaft and/or of shafts coupled to the rotor shaft. For example, two redundant rotational speed sensors may be arranged on the rotor shaft which is simultaneously the input shaft of the transmission. A further rotational speed sensor may be situated on the generator shaft as the output shaft of the transmission. The rotational speed relay may be designed in such a manner that it receives the rotational speed signals from a plurality of rotational speed sensors via a plurality of signal inputs. A switch-off command is preferably already generated when only one of the rotational speed sensors reports that the rotational speed limit value has been exceeded. Applying the test signal from the signal generator to the different signal inputs in succession makes it possible to check the proper operation of a plurality of signal inputs. A plurality of rotational speed relays may alternatively be provided, one rotational speed relay preferably being assigned to each rotational speed sensor. The plurality of rotational speed relays may be tested in succession or in a parallel manner. 
         [0015]    If a plurality of rotational speed sensors are present, the proper method of operation of these sensors may also be checked within the scope of the method according to the invention. For this purpose, the rotational speed signals from the different rotational speed sensors are compared with one another as the shaft rotates. With proper operation, all rotational speed signals would have to provide the same rotational speed information; a discrepancy between the items of rotational speed information indicates a fault. If one rotational speed sensor is on a fast shaft and one rotational speed sensor is on a slow shaft, the rotational speeds of the shafts being in a fixed relationship, the rotational speed signals must be accordingly converted before a comparison is possible. This applies, for example, to rotational speed sensors on the slow rotor shaft and on the fast generator shaft, which are coupled to one another in a fixed relationship via the transmission. If necessary, it is additionally possible to check whether identical rotational speed signals are interpreted as the same rotational speed by different components. The different components may be, for example, two rotational speed relays or one rotational speed relay and the controller for the wind energy installation. This check makes it possible to discover further possible faults in the wind energy installation. Alternatively, it is possible to test whether rotational speed signals which are in a known relationship with respect to one another are correctly interpreted by the components. 
         [0016]    The invention also relates to a wind energy installation which is designed to automatically carry out the method. The wind energy installation comprises a rotational speed sensor which can be used to detect the rotational speed of a shaft. The wind energy installation also comprises a rotational speed relay with a signal input to which a rotational speed signal from the rotational speed sensor can be applied. The rotational speed relay is designed to generate a switch-off command as soon as the rotational speed signal exceeds a predefined rotational speed limit value. A signal generator is also provided in order to generate a test signal equivalent to the rotational speed signal. A changeover module can be used to change over between the rotational speed signal and the test signal at the signal input of the rotational speed relay. Finally, the wind energy installation comprises a control module which controls the signal generator and the changeover module. The control module instructs the changeover module to apply the test signal to the signal input and gives the signal generator the command to generate a test signal beyond the rotational speed limit value. The control module then tests whether the rotational speed relay generates a switch-off command. 
         [0017]    The rotational speed relay may have a plurality of signal inputs, and the changeover module may be designed to change over between the rotational speed signal and the test signal at each of the signal inputs. As a result, the method according to the invention can also be carried out automatically when the wind energy installation has a plurality of rotational speed sensors, the rotational speed signals from which are supplied to the rotational speed relay. The wind energy installation may also have a comparison module for comparing the rotational speed signals from the plurality of rotational speed sensors. If a transmission is located between two rotational speed sensors, the rotational speed signal must be accordingly converted so that a comparison becomes possible. 
         [0018]    The wind energy installation may be combined with further features described above with reference to the method according to the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The invention is described by way of example below using an advantageous embodiment and with reference to the accompanying drawings, in which: 
           [0020]      FIG. 1 : shows a schematic illustration of a wind energy installation; 
           [0021]      FIG. 2 : shows an enlarged illustration of components of the wind energy installation from  FIG. 1 ; 
           [0022]      FIG. 3 : shows a schematic illustration of a rotational speed signal; 
           [0023]      FIG. 4 : shows a schematic illustration of a rotational speed relay with a signal generator connected to the latter; 
           [0024]      FIG. 5 : shows a schematic view of a wind energy installation according to the invention; and 
           [0025]      FIG. 6 : shows a flowchart of the method according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    In the case of a wind energy installation  10  shown in  FIG. 1 , a rotor  11  drives a generator  12 . The generator is used to convert the rotational energy into electrical energy. The electrical energy is fed into a power supply system (not illustrated). A controller  14  for the wind energy installation  10  controls the interaction between the components of the wind energy installation  10 . The controller  14  ensures, inter alia, that a particular predefined rotational speed limit value n limit  is not exceeded during normal operation of the wind energy installation  10 . 
         [0027]    The wind energy installation  10  comprises a transmission  13  with which the slow rotation of a rotor shaft  15  is converted to a higher rotational speed and is delivered to a generator shaft  16  again. The generator shaft  16  is used to drive the generator  12 . Although the wind energy installation  10  is designed in such a manner that a rotational speed range limited by rotational speed limit values n limit  is not left during normal operation, it is not excluded that one of the rotational speed limit values n limit  may be exceeded in extraordinary situations, for example a fault in the controller  14 . The wind energy installation  10  therefore comprises a rotational speed relay  17  which intervenes if the rotational speed limit value n limit  is exceeded and ensures that the wind energy installation  10  is stopped in a controlled manner. As soon as the rotational speed relay  17  determines that the rotational speed has been exceeded, it passes a switch-off command to a switch-off module  18 . The switch-off module  18  carries out emergency switch-off of the wind energy installation  10 , which is used to quickly stop the wind energy installation  10 . For this purpose, the rotor blades of the rotor  11  are set in such a manner that they no longer receive any critical energy from the wind but rather brake the rotor  11 . In order to completely stop the wind energy installation  10 , a brake acting on the rotor  11  can additionally be pulled (for example in the case of an excessively low rotational speed). 
         [0028]    In  FIG. 2 , the wind energy installation  10  comprises three rotational speed relays  171 ,  172 ,  173  which are supplied with information relating to the rotational speed of the rotor shaft  15  and of the generator shaft  16  via three signal inputs  25 ,  26 ,  27 . In order to generate the rotational speed signal, two rotational speed sensors  20 ,  21  are formed on the rotor shaft and one rotational speed sensor  22  is formed on the generator shaft. The duplicate design of the rotational speed sensors  20 ,  21  on the rotor shaft  15  is used for redundancy and to detect the direction of rotation. Each of the rotational speed sensors  20 ,  21 ,  22  comprises a toothed disk  23  and an inductive or optical measuring sensor  24 . The toothed disks  23  rotate with the rotor shaft  15  and the generator shaft  16 , with the result that a tooth or a tooth gap is alternately present at the measuring sensors  24 . The measuring sensors  24  pick up this information and use it to generate a square-wave signal, as is illustrated in  FIG. 3  by way of example. The square-wave signals are supplied to the signal inputs  25 ,  26 ,  27  of the rotational speed relays  171 ,  172 ,  173 . The square-wave signal is evaluated in the rotational speed relays  171 ,  172 ,  173  and the frequency of the square-wave signal is used to determine how fast the associated shaft is rotating. 
         [0029]    The rotational speed determined from the square-wave signals is continuously compared with the rotational speed limit value n limit , a correspondingly higher rotational speed limit value applying to the square-wave signal from the rapidly rotating rotor shaft  16  than for the slowly rotating rotor shaft  15 . If it is determined that the rotational speed limit value n limit  has been exceeded at one of the signal inputs  25 ,  26 ,  27 , the associated rotational speed relay  171 ,  172 ,  173  transmits a switch-off command to a switch-off module  18 . The switch-off module  18  assumes control of the wind energy installation  10  and rapidly switches off the wind energy installation  10 . The switch-off module  18  is preferably arranged in the hub of the wind energy installation  10 . Commands from the switch-off module  18  then have priority over commands from the controller  14 . 
         [0030]    The proper operation of the rotational speed relays  171 ,  172 ,  173  is checked at particular maintenance intervals. In the case of an embodiment illustrated in  FIG. 4 , the method according to the invention is carried out by a service engineer in situ. The service engineer disconnects a connecting line between one of the rotational speed sensors  20 ,  21 ,  22  and the associated signal input  25 ,  26 ,  27  and thus deactivates the rotational speed signal supplied to the rotational speed relay  171 ,  172 ,  173 . This is illustrated in  FIG. 4  using the example of the signal input  25 . Instead of the rotational speed sensor  20 , a signal generator  28  is connected to the signal input  25 , which signal generator generates a square-wave signal and thus a test signal equivalent to the rotational speed signal. The signal generator  28  is first of all operated in such a manner that the test signal corresponds to a rotational speed which is lower than an upper rotational speed limit value n limit.  The service engineer increases the frequency of the rotational speed signal until the test signal finally corresponds to a rotational speed which is above the rotational speed limit value n limit . In order to test a lower rotational speed limit value, the method is accordingly used with a reduction of the frequency. When the rotational speed limit value n limit  has been exceeded, a rotational speed relay  171 ,  172 ,  173  operating properly generates a switch-off command. The service engineer uses a measuring device  29  to check whether the switch-off command is correctly generated. If necessary, the switch-off command can also be checked using a corresponding monitoring light on the rotational speed relay  171 ,  172 ,  173  or using a fault message which is received in the controller  14 . If the switch-off command is correctly generated, the signal generator  28  is disconnected from the signal input  25  and the rotational speed sensor  20  is connected again instead. If the service engineer detects a fault in one of the rotational speed relays  171 ,  172 ,  173 , the corresponding rotational speed relay must be repaired or replaced. In simple cases, it may suffice to reparameterize the rotational speed relay. 
         [0031]    After the method has been concluded for the signal input  25  and the rotational speed relay  171 , it is then carried out in the same manner for the signal inputs  26 ,  27  and the rotational speed relays  172 ,  173 . In the case of the signal input  27  which is responsible for the fast generator shaft  16 , the test signal must have a correspondingly higher frequency in order to simulate the case in which the rotational speed limit value n limit  is exceeded. If the check for all three signal inputs  25 ,  26 ,  27  and all rotational speed relays  171 ,  172 ,  173  leads to the result that the switch-off command is correctly generated, the test is successfully concluded and the wind energy installation  10  can be started up normally again. 
         [0032]    In an alternative embodiment shown in  FIG. 5 , the wind energy installation  10  comprises an individual rotational speed relay  17  with three signal inputs  25 ,  26 ,  27 . In this example, the wind energy installation  10  is set up in such a manner that the method can be automatically carried out. For this purpose, the signal generator  28  is permanently installed in the wind energy installation  10  and a changeover module  30  is provided in order to apply a test signal from the signal generator  28  to the signal inputs  25 ,  26 ,  27  instead of the rotational speed signal. The method is carried out in the same manner as that described with reference to  FIG. 4 , a control module  31  controlling the signal generator  28  and the changeover module  30  in such a manner that they carry out the steps of the method according to the invention. The control module  31  also checks whether a switch-off command is generated by the rotational speed relay  17  at the correct time in each case. 
         [0033]    According to  FIG. 5 , the wind energy installation  10  also comprises a comparison module  32 . The comparison module  32  taps off the rotational speed signals from the rotational speed sensors  20 ,  21 ,  22  at the signal inputs  25 ,  26 ,  27  of the rotational speed relay  17  and compares the signals with one another. The rotational speed signal from the fast generator shaft  16 , which is applied to the signal input  27 , is converted according to the transmission ratio of the transmission  13 , with the result that a direct comparison with the rotational speed signals from the rotor shaft  15  is possible. If the comparison leads to the result that the same rotational speed information arrives at all three signal inputs  25 ,  26 ,  27 , this indicates that the rotational speed sensors  20 ,  21 ,  22  are operating properly. 
         [0034]      FIG. 6  illustrates the method according to the invention in the form of a flowchart. After the method has been started at  100 , the connection to the associated rotational speed sensor  20 ,  21 ,  22  is disconnected at one of the signal inputs  25 ,  26 ,  27  in step  110  and the rotational speed signal is thus deactivated for this signal input. After the signal generator  28  has been connected to the relevant signal input in step  120 , the test signal is increased by a value on this side of the rotational speed limit value n limit  in step  130  until the rotational speed limit value n limit  is exceeded. If the check in step  140  leads to the result that the rotational speed relay has not generated a proper switch-off command, it is determined at  150  that the rotational speed relay  17  is faulty and the method is concluded with step  160 . 
         [0035]    If the inquiry in step  140  leads to the result that the switch-off command is correctly generated, the signal generator is disconnected from the signal input at  170  and a connection to the associated rotational speed sensor is established again. The method is then carried out in the same manner for the other signal inputs. 
         [0036]    In step  180 , the rotational speed signal is tapped off at the signal inputs  25 ,  26 ,  27  as the rotor  11  rotates. The rotational speed signal at the signal input  27  is converted according to the transmission ratio of the transmission  13 , with the result that a direct comparison with the rotational speed signal at the signal inputs  25 ,  26  is possible. If the inquiry in step  200  leads to the result that the rotational speed signals match, the check has been successful and the method is concluded at  210 . If a discrepancy between the rotational speed signals is determined in step  200 , a fault message is output in step  220  and the rotational speed sensors  20 ,  21 ,  22  must be checked.