Method for operating a wind farm

ES 2 634 838 T3

DESCRIPTION

Procedure for the operation of a wind farm.

The invention relates to a method for operating a wind farm, as well as to a wind farm as such.

Wind power plants were always initially installed as individual units and it is only in recent years that wind power plants have started to be installed on a frequent basis in wind farms, also as a result of administrative and construction regulations. A wind farm is at its smallest unit an arrangement of at least two wind power plants, although often the number is clearly higher. As an example, mention could be made of the wind farm in Holtriem (East Friesland), in which more than 50 interconnected wind power plants are installed. It is expected that both the number and installed capacity of wind power plants will also increase significantly in future years. In most cases, the wind potential is highest in areas of the electricity supply networks with low short-circuit power and low population density. It is precisely in these areas that the technical connection limits of wind power plants are quickly reached, which means that no other wind power plants can be installed on such sites.

Therefore, a conventional wind farm, which is connected, for example, to a 50 MW electrical substation, can have at most only a total power of 50 MW, that is, for example, 50 wind power plants with a nominal power of 1 MW respectively.

Taking into account the fact that wind power plants are not operated continuously in the nominal operating mode and therefore the entire wind farm also does not continuously reach its maximum power (nominal power), it can be determined that the wind farm it is not used optimally, if the nominal power of the wind farm corresponds to the maximum possible total power to be supplied.

In document WO 01/25630 it has already been proposed to provide a wind farm with a total power, greater than the maximum possible grid power supply. If this applies to the example mentioned above, the power can be increased to a value higher than 50 MW, for example 53 MW. As soon as the wind speeds are high enough to produce the limit power of 50 MW, the regulation system of the wind farm, according to the invention, is activated and regulates the individual installations or all the installations, when the total maximum power is exceeded, in such a way that it is fulfilled at all times. This means that in the presence of wind speeds above the nominal wind (wind speed, at which a wind power plant reaches its nominal power), at least one installation or all installations are operated with a reduced power (slightly) (for example, with a power of 940 kW, instead of 1 MW).

The advantages of the present solution are obvious. In general, the network components of the supply network (the network components are, for example, the transformer and the lines) can be used optimally or used to the maximum (use up to the thermal limit is also possible). Consequently, existing wind farm areas can be better utilized by installing a maximum possible number of wind power plants. The amount is no longer going to be limited (so strongly) by existing network capacity.

For the control / regulation of a wind power plant, it is convenient that it has a data input that allows the electrical power to be adjusted in a range from 0 to 100% (with respect to the nominal power). If, for example, a nominal value of 350 kW is entered in this data entry, the maximum power of this wind power plant will not exceed the nominal value of 350 kW. Every value from 0 to nominal power (eg 0 to 1 MW) is possible as nominal value.

This data entry can be used directly to limit power.

However, it is also possible to regulate the generator power with the help of a regulating device depending on the grid voltage (in the wind farm grid or in the power grid).

Another important function is explained below by means of a wind farm regulation. For example, it is assumed that a wind farm is made up of 10 wind power plants each having a nominal power of 600 kW. Based on the capabilities of the network components (capabilities of

ES 2 634 838 T3 line) or the limited capacities in the electrical substation, it is also assumed that the maximum power (limit power), to be delivered, is limited to 5200 kW.

It is then possible to limit all wind power plants to a maximum power of 520 kW with the aid of the nominal value (data entry). In this way, the requirement to limit the power to be delivered is always fulfilled.

Another possibility consists in not allowing the maximum power to be exceeded as the sum of all the installations and in producing, however, at the same time a maximum of energy (kW hours (work)).

In this sense, it should be known that in the presence of low to moderate wind speeds within the wind farm it often happens that wind power plants receive a lot of wind in favorable (good) locations (which are the locations, in which the wind occurs first within the wind farm). If all wind power plants are now simultaneously regulated to their reduced value (eg 520 kW respectively), this generated power is achieved in some wind power plants that are located in good locations. Some other wind power plants, however located in the “wind shadow” of well-located wind power plants (in the second and third row), receive less wind and operate, for example, only with a power of 460 kW and do not reach the value of the reduced maximum power of 520 kW. Consequently, the total power produced from the wind farm is essentially below the permitted power limit of 5,200 kW.

The power regulation system of the wind farm in this case regulates the individual installations in such a way that the maximum possible energy yield is set. This means in particular that, for example, the installations in the first row (that is, in good locations) are regulated at a higher power, for example, than the nominal power (that is, without reduction). Therefore, the total electrical power increases in the wind farm. The park's regulation system, however, regulates each individual installation in such a way that the maximum permitted electrical connection power is not exceeded, while the work produced (kWh) reaches a maximum value at the same time.

The wind farm management system can be easily adapted to the respective situations that arise. Thus, for example, a further reduction of the power of individual installations can be carried out very easily, if a single installation or several installations of a wind farm are separated (or have to be separated) from the grid and if for maintenance reasons or for other reasons, a single installation or several installations have to be temporarily stopped.

To control / regulate the wind farm or the individual installations, a data processing / control device can be used which is connected to the data inputs of the installations and which from the data on the wind speed, which are determined ( for each installation), calculates the most favorable reduced power value in each case for an individual installation or for the entire wind farm.

Figure 1 known from document WO 01/25630 shows in a block diagram the control of a wind power plant by means of a microprocessor μΡ that is connected to an inverter (PWR) and allows supplying multiphase alternating current to an electrical supply network . The microprocessor has a power input P, ​​an input to enter a power factor (cos phi), as well as an input to enter the power gradient (dP / dt).

The inverter, made up of a rectifier, a direct current intermediate circuit and a converter, is connected to the generator of a wind power plant and obtains from it the energy produced by the generator in a variable manner with respect to the rotation speed, that is that is, regardless of the rotational speed of the rotor of the wind power plant.

The design depicted in the figure serves to explain how the power value, delivered by a wind power plant, can be limited to a maximum possible grid power value.

Figure 2 shows the schematic representation of a wind farm, composed of, for example, three wind power plants 1, 2 and 3, of which two are located next to each other and the third is located behind the two. first, seen from the direction of the wind. Since each of the individual wind power plants has a power input to adjust the power of the respective installation (figure 1), by means of a data processing device, which controls the entire wind farm, it can be adjusted in each case the

ES 2 634 838 T3 powers of an individual wind power plant to a desired value. In figure 1, the favorable locations of wind power plants are those, in which the wind affects first, that is, installation 1 and

2.

In the case of weak (isolated) electrical networks, the frequency of the network increases very quickly (sharply), if a larger consumer is separated from the electrical network. Drive machines, eg diesel engines, hydraulic wheels, etc., need some time to reduce their power (mechanical and electrical). During this time, such generators produce more energy than the energy taken by the electrical grid. This energy is then consumed during the acceleration of the generators. This increases the speed of rotation and therefore also the frequency of the network.

Since many electrical appliances, for example computers, electric motors and the like, which are connected to the mains, however, are not designed for fluctuating mains frequencies or their sudden changes, this can cause damage to electrical machines and even the breakage of these machines.

The invention aims to eliminate the problems described above, if wind power plants (a wind farm) are connected to the electricity grid.

According to the invention, this solution is achieved by a process with the features of claim 1, as well as by a wind power plant with the features of claim 10. Advantageous variants are correspondingly described in the sub-claims.

It is proposed, if wind power plants are operated with such weak networks, to control their electrical (and mechanical) power depending on the frequency of the network that is increasing. In this way, a further increase in the network frequency or a reduction in the network frequency must be prevented.

This aspect of the invention is explained in detail below by means of an exemplary embodiment.

They show:

Fig. 11 a frequency / power versus time diagram of a wind power plant;

Fig. 12 side view of a wind power plant;

Fig. 13 a block diagram of a microprocessor controlled inverter of a wind power plant;

Fig. 14 representation of a regulating device of a wind power plant;

Fig. 15 representation of a coupling of a wind power plant to an electrical network;

Fig. 16 alternative representation of figure 13.

Figure 11 shows the requirement for a wind energy installation (a wind farm) to reduce its output power P depending on the electrical frequency f of the network. The value of 100% here represents the nominal frequency (50 Hz, 60 Hz) of the electrical network. The values ​​100.6% or 102% are correspondingly higher values ​​of the grid frequency f.

The electrical power of the wind power plant (of the wind farm) is not yet down-regulated, for example, by increasing the grid frequency by 0.6% (that is, to 100.6%). If the grid frequency continues to increase then the electrical power of the wind power plant is regulated downward. In the example shown, the electrical power of the wind power plant is regulated to zero power by increasing the grid frequency to 102%.

Figure 13 shows an exemplary embodiment of a wind power plant that meets this requirement. The wind power plant features adjustable rotor blades (pitch angle regulation of the rotor blades) to be able to regulate the mechanical power of the wind power plant. If, for example, the angle of attack of the rotor blades is adjusted with respect to the wind, the force on the rotor blades can also be reduced to a desired value. The alternating electric current of the generator (not shown), connected to the rotor that supports the blades of

ES 2 634 838 T3 rotor, it is rectified by means of a rectifier 2 and smoothed by a capacitor 3. The converter 4 then transforms the direct voltage into an alternating current which is supplied to the network L1, L2, L3. The frequency of this output current is predefined by the network. The regulation device 5, made up of a microprocessor, measures the grid frequency and controls the power switches of the converter in such a way that the output frequency corresponds to the grid voltage (grid frequency). If the frequency of the network increases, as described above, the electrical power is regulated downwards, according to the representation of figure 11.

Figure 14 shows the regulating device. The rotor 4 of the wind power plant, represented schematically, is coupled to a generator G that supplies an electrical power, dependent on the wind speed and, therefore, on the power of the wind. The alternating voltage, produced by the generator G, is first rectified by the converter and then transformed into an alternating voltage having a frequency that corresponds to the frequency of the network. Using the mains frequency recording device, the mains voltage is determined at the mains supply point. As soon as the grid frequency exceeds a predetermined value, see figure 11, the supplied electrical power is reduced to counteract a further increase in the grid frequency. With the aid of the regulating device, the grid frequency is regulated to a desired grid frequency value, at least it is prevented from increasing further.

By means of a supply, regulated in this way, of the power supplied by the wind power plant, fluctuations in the frequency of the grid can be avoided or considerably reduced.

Figure 15 shows the coupling of a wind power plant to an electrical network, supplying the electrical power, produced by the wind power plant, to the network at the power point of the network, Several consumers are connected to the electrical network which are drawn as houses in the depicted example.

Figure 24 shows essential components of the control and regulation device in a somewhat different representation than in figure 13. The control and regulation arrangement has a rectifier, in which the alternating voltage produced in the generator is rectified. A frequency converter, connected to the rectifier, transforms the direct voltage, first rectified in the intermediate circuit, into an alternating voltage that is fed as a three-phase alternating voltage to the network through the line L1, L2 and L3. The frequency converter is controlled with the help of the microcomputer which is part of the entire regulation device. For this purpose, the microprocessor is coupled to the frequency converter. As input variables for the regulation of the voltage, with which the electrical power, made available by the wind power plant 2, is supplied to the grid, are the current grid voltage, the grid frequency f, the electric power P of the generator, the reactive power factor cos _, as well as the power gradient dP / dt. According to the invention, the microprocessor regulates the voltage to be supplied with its desired mains frequency.

In wind power plants known to produce electrical energy from wind energy, the generator is operated in parallel mode with an electrical consumer, often an electrical network. During the operation of the wind power plant, the active electrical power, supplied by the generator, can vary depending on the current wind speed. As a result of the above, the grid voltage (magnitude and / or phase), for example at the power point, can also vary depending on the current wind speed. This is also valid for the current to be supplied.

If the electrical power produced is fed into an electrical network, for example, a public power network, fluctuations in the voltage of the network may arise. However, such fluctuations are permissible only within very narrow limits in the interest of safe operation of the connected consumers.

By actuating, for example, switching devices, such as tap transformers, larger differences with respect to the nominal value of the mains voltage in the power supply network, in particular in the medium voltage level, can be compensated if predetermined limit values ​​are exceeded or not reached. In this way, the grid voltage is kept essentially constant within predefined tolerance limits.

The aim is to specify a procedure for the operation of a wind power plant, as well as a wind power plant or a wind farm that are capable, also in case of a fluctuating supply of active power, of reducing or at least increasing unwanted voltage fluctuations at a predefined point in the grid not significantly compared to the situation without wind power plant (s).

This objective is achieved in the case of a procedure of the type mentioned at the beginning by varying the phase angle φ

ES 2 634 838 T3 of the electrical power, supplied by the wind power plant / plants, depending on at least one voltage detected in the network.

In the case of a wind farm of the type mentioned at the beginning, the objective is achieved by at least one device respectively, capable of executing the method according to the invention, and a voltage detecting device respectively for each part of the separately adjustable wind farm.

Unwanted fluctuations in the voltage applied to the consumer, in particular in the electrical voltage existing in a network, are avoided by varying the phase angle of the power supplied depending on the voltage of the consumer or the network. This compensates for unwanted voltage fluctuations that originate as a result of changes in the active power, supplied by the wind power plant / plants, or in the power taken from the grid by the consumers.

With particular preference, the phase angle is varied in such a way that the voltage remains essentially constant at at least one predefined point in the network. In this regard, the voltage has to be detected at at least one point in the network to obtain the necessary control magnitude.

In particular, this point may be different from the feed point. This detection of the magnitude of the voltage and a suitable variation of the phase angle of the electrical power, supplied by the wind power plant / plants, allow a timely and effective regulation.

In a particularly preferred embodiment, the values ​​to be adjusted for the phase angle are derived from predefined characteristic values. These characteristic values ​​can be made available in the form of a table, in which a predetermined family of characteristic curves is represented in the form of discrete values, which makes it possible to deduce the phase angle to be adjusted.

In a preferred variant of the invention, regulation can directly or indirectly cause the voltage to be brought back into the tolerance range by actuating a switching device in the network, for example a tap-changer, if voltage fluctuations have exceeded the predefined limit values. At the same time or additionally, the phase angle is adjusted to a constant value, preferably a mean value, for example zero, for a predetermined time interval in order to be able to compensate for the resulting voltage fluctuations by means of a suitable variation of the phase angle.

In a particularly preferred variant of the invention, voltage detection and a corresponding adjustment of the phase angle can also be carried out separately in electrically separated sub-areas of the network, in order to regulate each sub-area so that the voltage is maintained. essentially constant in each of the partial zones.

The wind power plant is advantageously improved by a control device having a microprocessor, since digital control can be implemented in this way.

The wind farm, mentioned at the beginning, is preferably improved by having respectively a device capable of executing the method according to the invention and respectively a voltage detecting device for each part of the wind farm that can be regulated separately, therefore also partial areas of the The electrically separated network can be regulated separately in such a way that the voltage remains essentially constant in each part of the network.

In the following, a method for operating a wind power plant is explained by means of an exemplary embodiment with reference to the drawings. They show:

Figure 21 a wind power plant, which is to feed a network, in a simplified representation;

Figure 22 a regulation device for the operation of a wind power plant;

Figure 23 a representation that explains the relationship between the network voltage and the phase angle;

Figure 24 essential components of the regulating device shown in figure 22; Y

Figure 25 a simplified representation of a common or separate regulation of several wind power plants

ES 2 634 838 T3 depending on the network situation.

A wind power plant 2, schematically represented in figure 21, with a rotor 4 is connected to an electrical network 6 which can be, for example, a public network. Several electrical consumers 8 are connected to the network. The electric generator, not shown in figure 21, of the wind power plant 2 is coupled to an electric control and regulation device 10 that first rectifies the alternating current produced in the generator and then transforms it into an alternating current with a frequency that corresponds to the frequency of the network. The control and regulation device 10 has a regulation device according to the invention.

At any point 22 in the network 6, a voltage detection device 22 can be provided which (in addition to the phase) measures in particular the magnitude of the network voltage and sends the measured value as a corresponding control variable to the control device. regulation 10.

Figure 22 shows the regulating device. The rotor 4, represented schematically, is coupled to a generator 12 that supplies an electrical power that can depend on the wind speed. The alternating voltage, produced in the generator 12, can be rectified first and then transformed into an alternating voltage having the frequency that corresponds to the frequency of the network.

With the aid of a voltage recording device (not shown), the mains voltage is measured at a location 22 in the mains 6. Depending on the determined mains voltage, it is calculated, if necessary, by means of a microprocessor shown in Fig. Figure 4, an optimal phase angle φ. The regulating device then regulates the mains voltage U to the desired value Unominal. By varying the phase angle, the electrical power supplied by the generator 12 to the network 6 is regulated.

The representation of figure 23 shows the relationship between the voltage in the network and the phase angle. If the voltage differs from its nominal value Unominal, located between the voltage value Umin, and Umax., The phase angle φ is varied in correspondence with the characteristic curve in the diagram in such a way that depending on the sign of the difference inductive or capacitive reactive power is supplied to thereby stabilize the voltage at the voltage detection point (22 in figure 21).

Figure 24 shows essential components of the control and regulation device 10 of figure 21. The control and regulation device 10 has a rectifier 16, in which the alternating current produced in the generator is rectified. A frequency converter 18, connected to the rectifier 16, transforms the direct current, rectified first, into an alternating current that is fed as three-phase alternating current to the network 6 through the lines L1, L2 and L3.

The frequency converter 18 is controlled with the aid of a microcomputer 20 which is part of the entire regulation device. To this end, the microprocessor 20 is coupled to the frequency converter 18. As input quantities of the microp processor 20 are the current mains voltage U, the electrical power P of the generator, the nominal value of the mains voltage Unominal, as well as as the power gradient dP / dt. In the microprocessor 20 the regulation, according to the invention, of the power to be supplied is carried out.

In FIG. 25, two wind power plants 2 are shown as an example of a wind farm. A regulating device 10 is assigned to each of these wind power plants 2 which can of course be symbolically present also for a plurality of wind power plants. The regulation device 10 detects the voltage at predefined points 22, 27 of the network 6, 7 and transmits it to the regulation device 10, assigned respectively, through lines 25, 26.

The sub-zones 6, 7 of the network can be connected or disconnected to each other by means of a switching device 23. In parallel to this switching device 23, a switching device 24 is provided which allows the two regulation devices to be connected or disconnected from each other 10 in correspondence with the connection status of the switching device 23.

If the two partial zones 6, 7 of the network are connected to each other, the two regulating devices 10 are also connected to each other, so that the entire network is considered one unit and is powered as one unit by the entire wind farm, in turn regulating the wind farm in a unified way depending on the voltage at the detection point 22, 27.

If the two subzones 6, 7 are switched off by the switching device 23, then both of them

ES 2 634 838 T3 regulation devices 10 are also disconnected from each other in such a way that a part of the wind farm is monitored by the regulation device 10 from a detection point 22 through a line 25 and the assigned part of the wind farm can be adjusted accordingly, while the other partial zone of the network 7 is monitored from a detection point 27 through a line 26 by means of the regulation device 10 that regulates in a corresponding manner the other part of the wind farm to stabilize the voltage in the partial zone of network 7.

Naturally, this division does not have to be limited to two subzones. This division can be eliminated until an individual installation is assigned to a partial zone of the network.

The central regulation according to the invention, according to the present application, of a wind farm essentially takes into account that the wind farm not only feeds electrical energy to a public electricity supply network, but is also controlled at the same time to support the network , preferably by the public network operator (ESE, electricity supply company). Whenever a wind farm is referred to in the present application, this also means an individual wind power plant and not just a plurality of wind power plants in all cases, preferably a plurality of wind power plants always forming a wind farm. .

For the central control, according to the invention, according to claim 1, of the wind farm, the operator of the public electricity supply network not only has a control access to the wind farm / to the wind power plant through a control line corresponding (bus system), but also receives data from the wind farm / wind power plant, such as measured wind data, data on the status of the wind farm and also, for example, data on the available power (current power (active power)) of the wind farm.

Such central control may also mean, for example, that the wind farm is completely separated from the grid in certain cases, for example, if the wind farm cannot comply with the grid connection regulations set by the operator of the public supply grid. electric.

If, for example, the grid voltage falls below a certain predefined value, for example to a value of 70 to 90% of the grid voltage, the wind farm has to be separated from the grid within a preset time, for example, two to six seconds.

Finally, it is necessary to bear in mind that the change in power (dP) of the wind farm is not only predefined by the wind, but can also be varied in determined complete time intervals. Therefore, this power quantity is also called the power gradient and indicates by what percentage the respective available power can be varied within a predetermined time (eg per minute). Thus, for example, it can be envisaged that the power gradient of the wind farm is a maximum of 5 to 15%, preferably 10% of the connection capacity of the network per minute.

Such regulation of the wind farm can be carried out, for example, by simultaneously or uniformly increasing all wind power plants in a park their power supply in the predetermined power gradient. As an alternative, it is of course also possible for one or two installations (in the respective order of magnitude of the power gradient) to initially supply full power and then for other installations to be switched on, depending on the predefined power gradient, within a certain time. default, until it is possible to supply all the available power of the wind farm, in the case of a wind farm with, for example, 10 to 20 installations.

Another aspect of the regulation of the wind farm, according to the invention, is the provision of the reserve power with a percentage level, for example, 10% of the current available power of the wind farm, or with a fixed magnitude, for example , 500 kW to 1 MW or more per wind farm. This reserve power must not be confused with a farm power that exceeds the connection power of the wind farm network. The reserve power is mainly a reserve power (this includes both active power and reactive power) that is not exceeded in the range of the grid connection power. This reserve power can be set by the operator of the public electricity supply network. That is, if there is enough wind to feed the connection power of the wind farm network to the grid, the electricity supply company can guarantee, on the basis of the control action, described above, in the wind farm, that this power, theoretically possible, is not supplied in its entirety and that a part of this power remains available as reserve power. A particular aspect of this standby power is that in the event of an unexpected power plant power failure (in other grid feed areas), the grid can be stabilized by requesting the corresponding standby power.

ES 2 634 838 T3

Consequently, in the case of the central control of the wind farm mentioned above, the power supplied is lower under normal conditions than the power, which the wind farm will make available (maximum available power), depending on the respective power demand. In the net.

To be able to carry out this power control described above, the network operator also needs the data described above, such as wind speed, the status of the wind farm installation (the number of installations in operation, out of operation or damaged ) and preferably also the maximum possible supply of active power. In this connection, as the maximum possible supply of active power, the limitation that this has to be made available in the form of data can be applied only if it is not possible to determine it from the wind speed and the state of the installation.

A normal bus system is used, for example also a standardized bus system, for the control of the wind farm as well as for the supply of data to the utility company. For such standardized bus systems, eg a profibus system, standardized interfaces already exist, so that by means of correspondingly standardized control instructions the central control of the wind farm can also be realized.

In a complementary way to the above, it can also be envisaged that the wind farm is treated from a pre-designed power, for example, a total power greater than 50 MW, such as a large-scale power plant and also has to meet the conditions of large-scale power plants.

Finally, it can also be envisaged that the wind farm is regulated in such a way that the network connection value (the connection capacity of the network) is not exceeded.

Finally, at the time of connection / start-up of the wind farm, it must be ensured that no unwanted repercussions are generated on the network. For example, the current during the connection / start-up of a wind farm cannot be greater than a predetermined value of the nominal current that corresponds to the connection capacity. Such a value can be situated, for example, in the range of 1.0 to 1.4.

If the frequency in the public electricity supply network increases, it must be ensured in this case, as already described, that from a certain frequency value, for example, from 50.25 Hz (with a nominal frequency of 50 Hz), the active power supplied from the wind farm is automatically reduced until the grid frequency stabilizes again at a value described above.

Therefore, the wind farm must also always be able to operate with a reduced power supply in order to meet the requirements of the network. This regulation of the park also means that the supplied power (in particular the active power) can be reduced to any value in each operating state and from each operating point.

Thus, for example, the supply power can be limited to below the available supply power, if there are dangers to safe operation of the system, if bottlenecks are feared or the danger of overloading in upstream networks, if there is a problem. danger of the formation of an isolated network, if the static or dynamic stability of the network is in danger, if the increase in frequency can put the entire system of the network in danger and if it is necessary to carry out also, for example, repair work or other shutdown operations, conditioned by operation, in the electricity supply company.

In addition to the active power supply, which has been described and which must be adjusted if necessary, a certain reactive power must also be made available, being able to adjust it also at the request of the electricity supply company, specifically both in the inductive and capacitive range, that is, under and over-excited. For this purpose, the electricity supply company may predetermine the respective values.

The nominal value of the reactive power, made available, can be adjusted in a variable way, the nominal value being predefined at the network connection node for the power factor (cos phi) or a voltage magnitude. A fixed nominal value can also be predefined.

As described above, the power supply is reduced and / or the wind farm is completely separated from the grid, if determined frequency values ​​are exceeded or not reached in the grid. Thus, for example, it may be

ES 2 634 838 T3 planned to disconnect the wind farm from the grid when a grid frequency of approximately 48 Hz is not reached (with a grid frequency of 50 Hz) or in the case of 51 to 52 Hz. In the presence of values ​​below the Predicted range may also be provided within the limits of the range that only a part of the current available power is supplied, for example about 80 to 95% of the current available power.

If the grid voltage also falls below a predetermined value, the same applies as in the case of the grid frequency difference. In other words, when a predetermined grid voltage is not reached or exceeded by the determined value, a reduced power supply is first carried out and when certain limit values ​​of the grid voltage are not reached or exceeded, the installations are completely separated from the power supply. network or at least the supplied power is brought to zero.

Lastly, provision can also be made for a reliable disconnection of the wind farm on reaching certain grid voltage and / or grid frequency values, without previously carrying out a reduced power supply.

This also means at the same time that in the event of certain frequency differences / voltage differences within a predetermined range around the grid frequency / grid voltage, automatic separation of the wind farm from the grid is not allowed.

Finally, it can also be foreseen to protect the network that the disconnection time when the voltage value is exceeded is clearly shorter (for example, 50 to 200 milliseconds) than in the case of the voltage reduction protection (disconnection time greater than 1 second, preferably about 2 to 6 seconds). The switch-off time when the still permissible predetermined limit value of the upper frequency or lower frequency is exceeded or not reached is here approximately in the range of the switch-off time when the voltage is exceeded (above a voltage value predetermined).

Finally, when a grid failure occurs, for example a short circuit, an automatic separation of the wind farm from the grid should not always be carried out immediately, but the wind farm can also be controlled so that depending on the the network connection, this will continue to feed the network to contribute to the short-circuit power as apparent power and thus be able to continue supporting the network in a certain way. This means that the wind farm has to supply at least within a certain short-circuit duration, at most only a few seconds, the maximum possible apparent current (apparent power) corresponding, for example, to once or up to 1, 5 times the current equivalent to the network connection capacity.

The behavior, described above, can also be made dependent on the level of the nominal voltage, for example, if it exceeds a predetermined value, for example, greater than 50 kV.

In order to be able to carry out the disconnections described above in a timely manner, for example, a protection relay (distance protection relay) must be installed for its implementation in the network connection node.

Finally, means must be provided to synchronize the voltage in the grid and in the wind farm during the start-up of the wind farm, because asynchronous voltages can considerably damage the grid and cause it to be disconnected when the wind farm is started up again.

Provided that, according to the present application, the power is regulated below a value of the power, which is currently to be made available by a wind farm, this can be implemented with the help of various measures.

Thus, for example, the power can be reduced in total for each individual installation so that the entire wind farm assumes the desired reduced power value. However, it may also alternatively be provided to reduce the value of the power supplied only to individual installations, whereby the entire value of the power supplied to the wind farm returns to the desired value.

Finally, it can also be envisaged that, for example, a certain power, made available by the wind farm, is temporarily stored in so-called dumploads (resistors) or in other energy storage devices or is transformed into heat or other form of energy so that the power value of the wind farm assumes the desired value.

The power reduction can also be carried out when a plant or certain wind power plants are completely disconnected from the grid, so that all the power of the wind farm (in particular the power

ES 2 634 838 T3 active) can in turn be set to the desired value and / or falls below the desired value.

To transmit the wind farm data (wind data, status data, power data, etc.) or to control the wind farm, a wireless communication device can also be provided, so that it is possible to transmit and process wirelessly. control data or information data.

In the case of the regulation of the wind farm, mentioned above, it must also be foreseen that within the wind farm the value is also determined, which can be made available as maximum energy, and that the amount of energy is also determined later. fed to the grid, so that from the difference, which is essentially due to the control of the wind farm by the electricity supply company, An amount of feed compensation can be calculated and reimbursed, if required.

As already described, it is not only possible that the electricity supply company, which operates the electricity supply network, can limit or restrict the power of the wind farm or individual wind power plants with access through a control line for different reasons (network protection, servo power), but it is also possible that the operator of the public electricity supply network simultaneously receives data on the status of the wind farm, for example, data on maximum available power, wind speed, etc. Since a power limitation below the current available power does not allow optimal use of the wind farm or wind power plants in a wind farm, this causes power losses for wind power plant operators. Therefore, according to the invention it is also proposed here to provide a virtual current meter that detects the difference with respect to what is not taken due to the participation of the electricity supply company in the regulation and, therefore, in the limitation of the power of the wind farm or wind power plant. Such a "virtual current meter" can determine, on the one hand, on the basis of the wind speed, the power to be made available, and if the electricity supply company or any other entity regulates the power of power plants. individual wind farms or an entire wind farm below the power that can be made available, the amount of energy that is not fed into the grid can be determined (counted) by an integration operation. The virtual current meter allows the operator of the wind power plant to receive remuneration also for the “virtual current”, that is, the current that is not fed due to participation in the regulation of the electricity supply. The “virtual current meter” can be installed both on the operator's side of the wind power plant, in the wind power plants themselves within the wind farm, in the electricity supply company or also on the side of the manufacturer of the wind power plants.

Whenever the term wind power plant is used in the present application, it is synonymous with the term wind farm. Provided that different aspects of the invention are described in the present application, these can be implemented in combination with wind power plants or their control. However, it is also possible to implement and claim the different approaches according to the invention individually, without the other aspects of the invention, although various aspects of the invention are regularly described together in the present application. In any case, it will be clear to the person skilled in the art that different aspects of the invention can also be implemented and claimed differently and that their joint description does not mean that they always have to be implemented and claimed all together.