Abstract:
A wind turbine having a generator for generating electrical energy and a transformer is disclosed. The transformer is designed to receive electrical energy from the generator on a secondary side and to discharge said electrical energy again on a primary side at a higher voltage. The wind turbine also comprises a temperature monitoring means for the transformer. The voltage supply to the temperature monitoring means is fed from the primary side of the transformer. The temperature monitoring means is thereby independent of the control system of the wind turbine. The temperature monitoring means reduces the risk of the transformer overheating. A method for operating such a wind turbine is also disclosed.

Description:
[0001]    REFERENCE TO RELATED APPLICATIONS 
         [0002]    This application is a national stage application under 35 USC 371 of International Application No. PCT/EP2011/070153, filed Nov. 15, 2011, which claims the priority of German Application No. 10 2010 051 675.9, filed Nov. 17, 2010, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0003]    The invention relates to a wind energy installation having a generator for generating electrical energy and having a transformer. The transformer receives electrical energy from the generator on a secondary side and outputs said electrical energy again at a higher voltage on a primary side. The wind energy installation further comprises a temperature-monitoring means for the transformer. The invention also relates to a method for operating a wind energy installation of this type. 
       BACKGROUND OF THE INVENTION 
       [0004]    Conventionally, the control system for the wind energy installation is responsible for monitoring the temperature of the transformer. Information about the temperature of the transformer is processed in the control system. If the temperature exceeds predefined limit values, the control system initiates suitable countermeasures. For example, a cooling means may be put into operation or the transformer may be isolated from the mains. This temperature monitoring is dependent on the control system of the wind energy installation being in operation. 
       SUMMARY OF THE INVENTION 
       [0005]    The problem addressed by the invention is that of providing a wind energy installation and a method for operating a wind energy installation in which the risk of damage to the transformer is reduced. Proceeding from the prior art mentioned at the outset, the problem is solved by means of the features as broadly described herein. Advantageous embodiments are found in the detailed embodiments described below. In the case of the wind energy installation, the invention provides that the voltage supply for the temperature-monitoring means is fed from the primary side of the transformer. 
         [0006]    The invention has identified that there are phases during the operation of a wind energy installation in which the control system of the wind energy installation is not in operation but in which the primary side of the transformer is nevertheless connected to the mains without transferring appreciable power into the mains. In particular, this state regularly arises before a wind energy installation is first put into operation. The transformer already has the primary side connected to the medium-voltage network while the wind energy installation is not yet in operation. All of the no-load power of the transformer is then converted into heat. There is the danger of overheating since no protective measures can be initiated by the control system. The transformer can be destroyed within a few hours. 
         [0007]    In the case of the wind energy installation according to the invention, the temperature-monitoring means is independent of the control system of the wind energy installation and has its own power supply, which is permanently connected to the transformer. As soon as the primary side of the transformer is connected to the mains, the voltage supply is also available for the temperature-monitoring means. It is ensured that the temperature of the transformer cannot increase unnoticed and the transformer cannot suffer damage as a result. 
         [0008]    The voltage on the primary side of the transformer is regularly higher than 10 kV and lies in the range between 10 kV and 33 kV, for example. The operating voltage of the temperature-monitoring means is substantially lower, for example in the order of 100 V. Preferably, a voltage transformer, which is used to convert the voltage present on the primary side of the transformer into a suitable auxiliary operating voltage for the temperature-monitoring means, is provided. The auxiliary operating voltage is preferably lower than 500 V, more preferably lower than 200 V. In many cases, the auxiliary operating voltage is a different voltage than the voltage on the secondary side of the transformer. 
         [0009]    Temperature sensors are regularly configured such that they have an electrical resistance for which the value changes as a function of the measured temperature. The temperature sensor is preferably a PTC thermistor for which the electrical resistance increases with temperature. There is normally a continuous relationship between the temperature and the electrical resistance. In order to be able to determine when a predefined temperature limit value has been exceeded, the PTC thermistor can be combined with a PTC thermistor triggering device. If the electrical resistance of the PTC thermistor exceeds a predefined limit value, the PTC thermistor triggering device outputs a signal and countermeasures can be triggered. 
         [0010]    If the transformer has a power breaker which can be used to isolate the primary side of the transformer from the mains, the countermeasures can consist in opening the power breaker. Preferably, an energy store is provided for the power breaker, which energy store can be used to open the power breaker without additional power having to be supplied from outside. For this purpose, the voltage transformer can be designed to charge said energy store too. 
         [0011]    Alternatively or in addition, the countermeasures can also consist in starting up a cooling means for the transformer. For this purpose, the voltage transformer can be designed to supply the cooling means too with electrical energy. In one advantageous embodiment, a cooling means is started up in the event that a first temperature limit value is exceeded, and the power breaker is opened in the event that a second, higher temperature limit value is exceeded. 
         [0012]    The temperature is preferably measured in a region of the transformer in which the voltage is lower than on the primary side of the transformer. The lower the voltage, the higher the current intensity and therefore the larger the amount of heat introduced into the transformer. The temperature measurement can, for example, take place on the secondary side of the transformer. If the transformer is operated under no-load conditions, the temperature increases in the core of the transformer rather than in the windings. For this reason, the temperature measurement preferably relates to the core of the transformer. The temperature limit value at which the transformer must be isolated from the mains can be 150° C., for example. 
         [0013]    The voltage transformer responsible for the voltage supply for the temperature-monitoring means can also be used to supply other functions on the primary side of the transformer with voltage. For example, these functions can be a voltage measurement or a power measurement on the primary side of the transformer. 
         [0014]    In addition to the first temperature-monitoring means according to the invention, which is supplied with voltage from the primary side of the transformer, a second temperature-monitoring means can be provided which is independent of the primary side of the transformer. The second temperature-monitoring means can, for example, be connected to the control system of the wind energy installation. 
         [0015]    During normal operation of the wind energy installation, the first temperature-monitoring means and the second temperature-monitoring means can be active in parallel with one another. A higher temperature limit value is preferably assigned to the first temperature-monitoring means than to the second temperature-monitoring means. Suitable measures for cooling the transformer can be taken by means of the control system of the wind energy installation if the lower temperature limit value of the second temperature-monitoring means is exceeded. Such measures can include switching on a cooling means or reducing the output power, for example. The higher temperature limit value of the first temperature-monitoring means is only exceeded when said measures are not effective. This provides additional safety against overheating of the transformer. 
         [0016]    The invention also relates to a method for operating a wind energy installation of this type. The method involves tapping off the voltage on the primary side of the transformer and converting said voltage into a lower auxiliary operating voltage. The transformer is the main transformer of the wind energy installation, and receives electrical energy from the generator on the secondary side and outputs said electrical energy again at a higher voltage on the primary side. A temperature-monitoring means for the transformer is operated using the auxiliary operating voltage tapped off on the primary side. The auxiliary operating voltage can be a different voltage than the voltage present on the secondary side of the transformer. If it is detected that a temperature limit value has been exceeded, a countermeasure can be taken in order to avoid a further increase in temperature. For example, the countermeasure can consist in isolating the primary side the transformer from the mains. The temperature measurement for the temperature-monitoring means is preferably performed on the secondary side of the transformer. The method can be combined with further features which have been described above with respect to the wind energy installation according to the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The invention will be described by way of example in the following text on the basis of an advantageous embodiment and with reference to the appended drawings, in which: 
           [0018]      FIG. 1  shows a schematic illustration of a wind energy installation; 
           [0019]      FIG. 2  shows an enlarged illustration of components of the wind energy installation from  FIG. 1 ; 
           [0020]      FIG. 3  shows an enlarged illustration of the transformer from  FIG. 2 ; and 
           [0021]      FIG. 4  shows the view from  FIG. 3  in the case of another embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    A wind energy installation  10  in  FIG. 1  comprises a machine housing  12  arranged on a tower  11 . A rotor  13  having three rotor blades  16  is mounted in the machine housing  12 , said rotor being connected to a generator  18  via a gear mechanism  17  which is shown in  FIG. 2 . The electrical energy which is generated by the generator is output via an inverter  19  and a transformer  20  to a medium-voltage network  22 . The electrical energy is directed to a transfer point  14  via the medium-voltage network  21  and is transferred from said transfer point to a power distribution network  15 . The wind energy installation  10  is usually combined with a plurality of further wind energy installations to form a wind farm, wherein the electrical energy from the wind energy installations is brought together at the transfer point  14 . A control system  21  controls the interaction of the components of the wind energy installation. 
         [0023]    The electrical energy at a voltage of, for example, 660 V is routed from the inverter  19  to the secondary side of the transformer  20 . A conversion to a higher voltage of, for example, 30 kV takes place in the transformer  20 . At this voltage, the electrical energy is transferred from the primary side of the transformer  20  to the medium-voltage network  22 . A power breaker  23 , which can be used to interrupt the flow of current, is arranged on the primary side of the transformer  20 . If the wind energy installation is in operation and is feeding electrical energy into the mains, both switches  23 ,  24  are closed. 
         [0024]    The state can arise where the switch  23  is closed and, as a result, a connection exists from the medium-voltage network  22  to the transformer  20  while little or no power is transferred via the transformer. The transformer  20  is then operating under no-load conditions, which is associated with a power loss of approximately 10 kW. This power loss is converted into heat and causes the transformer  20  to heat up. If the switch  24  is open, the wind energy installation  10  as a whole is often also out of operation. This state regularly arises, for example, before the wind energy installation  10  is first put into operation. If the wind energy installation  10  is out of operation, the transformer  20  is not subject to any control by the control system  21 . 
         [0025]    The invention introduces a temperature-monitoring means for the transformer  20 , which means prevents the transformer  20  from overheating in this operating state. 
         [0026]    As shown in  FIG. 3 , a voltage transformer  25  is arranged on the primary side  28  of the transformer  20 . The voltage transformer  25  converts the medium voltage of 30 kV to an auxiliary operating voltage of, for example, 230 V. The temperature-monitoring means for the transformer  20  is operated using this auxiliary operating voltage. The temperature-monitoring means comprises a temperature sensor  26  in the form of a PTC thermistor and a PTC thermistor triggering device  27 . The temperature sensor  26  measures the temperature of the core of the transformer  20  on the secondary side  29 , because the danger of overheating while the transformer  20  is operating under no-load conditions is greatest there. The PTC thermistor comprises an electrical resistance for which the value changes depending on the measured temperature. The higher the temperature, the greater the electrical resistance of the PTC thermistor. 
         [0027]    The electrical resistance of the PTC thermistor is monitored by means of the PTC thermistor triggering device  27 . If the electrical resistance exceeds a predefined limit value, the PTC thermistor triggering device  27  outputs a signal to the power breaker  23 , with the result that the power breaker  23  is opened. If appropriate, an energy store, from which the actuation of the power breaker  23  is powered, can be provided. The predefined limit value can, for example, be chosen such that it is exceeded when the temperature in the core of the transformer  20  is 150° C. After the power breaker  23  has been opened, no further energy is supplied to the transformer  20  and there is no risk of further heating. Alternatively or in addition to opening the power breaker  23 , a cooling means for the transformer  20  can also be started up. 
         [0028]    In an alternative embodiment, which is shown in  FIG. 4 , the transformer  20  comprises, in addition to the 660 V on the secondary side  29  and the 30 kV on the primary side  28 , a third voltage level of 950 V or 6600 V. The voltage transformer  25  is again used to tap off the medium voltage on the primary side  28  of the transformer  20  and to convert it into an auxiliary operating voltage of 100 V. A temperature-monitoring means comprising a PTC thermistor triggering device  27  and two temperature sensors  26  is operated using the auxiliary operating voltage. The temperature sensors  26  measure the temperature of the core of the transformer  20 . One of the temperature sensors is arranged at the 660 V level and the other at the 950 V level. If the electrical resistance in one of the temperature sensors  26  exceeds a predefined limit value, the PTC thermistor triggering device  27  triggers and the power breaker  23  is opened. 
         [0029]    In addition, a measuring device  30  can also be operated using the auxiliary operating voltage. For this purpose, the measuring device  30  is configured to perform voltage and power measurements on the primary side  28  of the transformer  20 . 
         [0030]    Moreover, a plurality of further temperature sensors  31  is arranged on the transformer  20 , said sensors being connected to the control system  21  of the wind energy installation  10  via a PTC thermistor triggering device  32 . The temperature of the transformer  20  is monitored by means of said temperature sensors  31  during normal operation of the wind energy installation. The temperature sensors  31  measure both the temperature in the core of the transformer  20  and that in the windings. 
         [0031]    During normal operation of the wind energy installation  10 , the temperature-monitoring means having the temperature sensors  31  and the PTC thermistor triggering device  32  can operate in parallel with the temperature-monitoring  means having the temperature sensors  26  and the PTC thermistor triggering device  27 . The temperature signals from the temperature sensors  31  are processed in the control system  21  of the wind energy installation  10 . If one of the temperatures exceeds a predefined limit value, the control system  21  takes suitable measures to lower the temperature in the transformer  20  again. The control system  21  will primarily initiate active cooling measures, for example will switch on a ventilation means. If this is not sufficient, the power output of the wind energy installation  10  can be adapted. As a final measure, which can be triggered by the PTC thermistor triggering device  32 , for example, the wind energy installation  10  is switched off. The temperature limit values at which these countermeasures are taken in the control system  21  are lower than the temperature limit value at which the PTC thermistor triggering device  27  triggers and the power breaker  23  is opened. The temperature-monitoring means with the temperature sensor  26  and the PTC thermistor triggering device  27  therefore provides a second level of safety if the temperature in the transformer  20  increases further despite the countermeasures of the control system  21 .