“Method for warning about lightning activity in wind farms”

TECHNICAL FIELD

The present invention relates to methods for warning about lightning activity in wind farms, and more specifically about upward lightning activity

PRIOR ART

Wind-driven power generators are exposed to lightning strikes due to their height and location. There are two types of lightning strikes: downward lightning strikes and upward lightning strikes (upward lightnings). Downward lightning strikes are the most common, but upward lightning strikes often occur in tall structures. Upward lightning strike activity is known to be greater than 30% in structures over 150 meters high. This percentage increases in tall structures located on mountain tops or in places where the phenomenon known as “thundersnow” takes place. The “thundersnow” phenomenon consists of winter storms characterized by storm clouds with a low charge and with the center of the negative charge being at lower heights (1 to 3 km compared to 6 to 9 km for the summer or convective storms) Storm warning systems that aim to detect summer storms (relating to high downward lightning activity) are known, such as the one disclosed in US20160291204A1 , for example, which is based on magnetic field meters and/or electromagnetic sensors.

International standards cover storm warning systems, such as IEC 62793:2016, for example. Again, this standard describes practices and systems for detecting convective storms (summer storms), but not winter storms in which upward lightning activity can make up 100% of all lightning events. In some wind farms, more than ten upward events occur in a wind-driven power generator during a single winter storm. Winter storms are hard to detect because all upward events originate from tall structures (wind-driven power generators), and there is no downward lightning activity. In other words, there is no prior lightning activity before upward lightnings originate from the wind-driven power generators.

DISCLOSURE OF THE INVENTION

The object of the invention is to provide a method for warning about lightning activity in wind farms, as defined in the claims.

The method is suitable for predicting the generation of upward lightnings in wind farms, where upward lightnings are the lightnings that are generated in the actual wind-driven power generators and not in the clouds, and for warning about said possible generation.

To that end, in the method the presence or absence of a storm cell in the wind farm and/or in the vicinity thereof, preferably within a radius of less than 400 km, is detected, the local electric field is measured, at least one atmospheric condition is identified or measured under given premises, and the probabilities of the generation of upward lightnings originating from the wind-driven power generators of the wind farm are determined depending on the result of said measurements, identifications and detections, a warning signal being transmitted in the event that the determined probability exceeds a given threshold value.

Determining the presence of a storm cell in a given location is already known. In the method said presence in the wind farm or in the vicinity (preferably within a radius of less than 400 km) is detected, and to reinforce and assure the presence of a storm in the actual wind farm, the presence of a storm in the wind farm is furthermore determined depending on the local electric field present in said wind farm. However, with these determinations it is not possible to determine the risk of upward lightnings occurring, so the method takes other added factors into account.

It has surprisingly been found that if a given relationship between different atmospheric conditions (or between an atmospheric condition and a given premise linked to another atmospheric condition), combined with the detection of the presence of a storm by means of the electric field and the detection of a storm cell, is satisfied, a winter storm, and therefore a risk of the generation of upward lightnings, can be successfully forecast or anticipated. For this reason, the identification or measurement of at least one atmospheric condition are furthermore added to the previously considered factors.

As it has been found that satisfying a given relationship between different atmospheric conditions (or an atmospheric condition and a given premise linked to another atmospheric condition), combined with the detection of the presence of a storm by means of the electric field and the detection of a storm cell, is enough to detect a risk of the generation of upward lightnings, measuring just one atmospheric condition under the atmospheric conditions or given premises of at least one other atmospheric condition is enough to successfully predict or anticipate a winter storm. So, for example, by using an atmospheric pressure value as a given atmospheric condition (or height with respect to sea level as a given premise linked to another atmospheric condition) as a reference, the temperature existing at said pressure (or at said height) can be measured or identified, where it is determined that a risk exists if a given relationship is satisfied.

Depending on the location of the wind farm, the value of the atmospheric conditions, under the given premises, may vary, as may said conditions (the value of those conditions to be considered), i.e., the relationship between the atmospheric condition and the given conditions may vary from one location to another. Therefore, by establishing the suitable relationship corresponding to the location of the wind farm, the method allows knowing the risk of upward lightnings being generated in said wind farm, and this detection has not been disclosed in the prior art.

Therefore, the probabilities of the generation of upward lightnings originating from the wind-driven power generators of the wind farm are determined with the method depending on the result of the aforementioned measurements, identifications and detections, and a warning signal announcing this fact is transmitted in the event that the determined probability exceeds a given threshold value. The warning signal can be sent wherever required in order to act as deemed necessary.

These and other advantages and features of the invention will become evident in view of the drawings and the detailed description of the invention.

DESCRIPTION OF THE DRAWINGS

Figure 1 shows a wind farm.

Figure 2 shows a storm cell in the vicinity of the wind farm Figure 3 shows the development of the local electric field in a wind farm, whereby the presence of a storm is determined

DETAILED DISCLOSURE OF THE INVENTION

The method is suitable for predicting the generation of upward lightnings in a wind farm 100 like the one shown in Figure 1 by way of example, where said lightnings are the lightnings that are generated in the actual wind-driven power generators 101 of the wind farm 100 and not in the clouds, and for warning about said possible generation

To that end, in the method the presence or absence of a storm cell 200 in the wind farm 100 and/or in the vicinity thereof (cell 200 depicted in Figure 2 by way of example) is detected. The detection is carried out in the actual wind farm 100, or within a radius of less than 400 km, because if such detection is performed in a geographical area located farther away, the possibility of said cell 200 not affecting the wind farm 100 considerably increases. The detection of the presence or absence of a storm cell 200 in the wind farm 100 and/or in the vicinity thereof is preferably performed, in an already known manner, by means of radar and/or by means of satellite. Furthermore, in the method the local electric field in the wind farm 100, which is a common way to detect a summer storm, is measured. The presence of a storm in the wind farm 100 can therefore be reinforced and assured with this measurement. In particular, and as is already known, if the electric field in the measurement area is positive with respect to a predetermined threshold value, said threshold value corresponding to the value of the electric field in good weather conditions, or if it suddenly changes with respect to said predetermined threshold value, as shown in the example of Figure 3, the presence of a storm in the location where the measurement of the electric field has been performed is determined. The value of the local electric field in good weather conditions is conventionally close to -100 V/m The predetermined threshold value is therefore preferably close to -100 V/m, said value being previously established with prior measurements and/or experiences. In the example of Figure 3, for example, the presence of a storm can be identified in area 300 (sudden change).

However, the presence or the risk of the presence of a storm in the wind farm 100 would be reinforced with this additional factor, but it would not be enough to enable determining the risk of upward lightnings occurring (it is not enough to determine that the storm is a winter storm).

As discussed above, it has been found that if a given relationship between different atmospheric conditions (or an atmospheric condition and a given premise linked to another atmospheric condition), combined with the detection of the presence of a storm by means of the electric field and the detection of a storm cell 200, is satisfied, a winter storm, and therefore a risk of the generation of upward lightnings, can be successfully forecast or anticipated. For this reason, the identification or measurement of at least one atmospheric condition are furthermore added to the previously considered factors.

As has also been discussed, measuring just one atmospheric condition under the given conditions or premises of at least one other atmospheric condition is enough. So, for example, by using an atmospheric pressure value as a given atmospheric condition (or height with respect to sea level as a given premise linked to another atmospheric condition) as a reference, the temperature existing at said pressure (or at said height) can be measured or identified, where it is determined that a risk exists if a given relationship is satisfied.

Depending on the location of the wind farm 100, the value of the atmospheric conditions, under the given premises, may vary, as may said conditions (the value of those conditions to be considered), i.e , the relationship between the atmospheric condition and the given conditions may vary from one site to another. Therefore, by establishing the suitable relationship corresponding to the location of the wind farm 100, the method allows knowing the risk of upward lightnings being generated in said wind farm 100, and the prior art is not able to perform this detection.

Therefore, the probabilities of the generation of upward lightnings originating from the wind-driven power generators of the wind farm 100 are determined with the method depending on the result of the aforementioned measurements, identifications and detections, and a warning signal announcing this fact is transmitted in the event that the determined probability exceeds a given threshold value. The warning signal can be sent wherever required in order to act as deemed necessary.

In summary, it is determined that the determined probability exceeds the given threshold value and a warning signal is sent if the presence of a storm cell 200 is detected (see Figure 2), a sudden growth of the local electric field or a positive local electric field with respect to the predetermined threshold value is detected (see Figure 3), and it is detected that the relationship between the atmospheric condition and the given premises comply with predetermined requirements.

The atmospheric condition to be taken into account is preferably the temperature, which is measured or identified, and the predetermined premise is a given pressure and/or a given height with respect to the sea. So the requirements that have to be satisfied in order for the probabilities to exceed the given threshold correspond to a given temperature at a given pressure and/or height.

The temperature is identified or measured preferably by means of one criterion or several criteria selected from

radio sounding performed in the vicinity of the wind farm 100, preferably within a radius of less than 400 km,

reanalysis data, preferably IRA-interim data, and

estimation of the temperature, under the given conditions, based on an estimation performed using the measured ground temperature of the wind farm 100

It has been found that in the presence of a storm and a storm cell 200, if the temperature is less than -10°C at a pressure of 700 hPa and/or at a height of about 3 km with respect to sea level, there is a high risk of upward lightnings being generated. This relationship can thereby be predetermined as a requirement to be satisfied by the relationship between the atmospheric condition (temperature in this case) and the given premises (pressure and/or height with respect to sea level): a temperature less than -10°C at a pressure of 700 hPa and/or at a height of about 3 km with respect to sea level.

However, as has also been discussed above, these requirements may vary depending on the location of the wind farm 100, so the method allows adjusting or adapting these requirements as needed.

In some embodiments of the method, the severity of the upward lightnings can furthermore be determined in the event that the risk of this upward lightnings being generated has been detected. To that end, in said embodiments the speed and force of the wind in the wind farm 100 is identified, the height with respect to the sea at which the wind farm 100 is located is considered and/or the orography of the site where the wind farm 100 is located is considered, where greater severity is determined the greater the speed and the force of the wind, the higher the site where the wind farm 100 is located, and the less homogenous the orography of said site is.

The electric field measurements and the measurements taken by means of radar must preferably be taken in the actual wind farm 100, since measurements of the actual conditions of the wind farm 100 are thereby obtained, unlike what occurs with radio sounding (for which there are various options, as discussed above).

The results of the measurements of the variables taken can be sent to remote equipment, for example, equipment which would be in charge of collecting said measurements and performing the necessary actions (such as an alarm algorithm, for example, to generate the warning signal).

The method can be implemented continuously and in real time, or it can be implemented in a discrete manner (at previously established time intervals), for example, to consume less energy.