Lightning detection device

Abstract

This invention provides a lightning detection device that can accurately detect lightning strikes using a bar antenna. [Solution] The lightning strike detection device 1 comprises a bar antenna 10, a detection signal generation circuit that processes the output signal of the bar antenna 10 to generate a detection signal corresponding to the magnetic field detected by the bar antenna 10, and a microcontroller 50 (determination circuit) that calculates the amount of charge Q over a predetermined time T by integrating the values ​​of the detection signals, and compares the amount of charge Q with a predetermined set value QT to determine whether or not lightning has struck the wind turbine 100 (structure).

Description

Technical Field

[0001] The present invention relates to a lightning strike detection device.

Background Art

[0002] As a representative example of the existing technology of the lightning strike detection method, as shown in FIG. 11, a method using a Rogowski coil is known. Since the Rogowski coil is a magnetic closed circuit, it can accurately detect current, but it is necessary to change the diameter according to the size of the detection target. Further, in order to ensure the detection accuracy in the observation system using the Rogowski coil, it is necessary to change the circuit constants according to the diameter of the Rogowski coil. For example, since the output from the Rogowski coil is a differential waveform, as shown in FIG. 12, it is necessary to convert it into a current waveform using an integrating circuit using a resistor and a capacitor. However, since the magnitude of the differential waveform changes due to the change in the diameter of the Rogowski coil, it is necessary to change the resistance value and the capacitance value according to the diameter. On the other hand, when using a bar antenna, the output of the bar antenna changes depending on the size of the detection target, but unlike the Rogowski coil, it is not necessary to change the resistance value and the capacitance value, and it can be dealt with by volume resistance. For example, Patent Document 1 discloses a system that issues an alarm when a current equal to or higher than a preset threshold value is detected using a single bar antenna. Further, Patent Document 2 discloses a system that determines that a lightning strike has occurred on the detection target when the currents detected using a plurality of bar antennas have the same polarity.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, if a noise source is present near the bar antenna, the noise may cause the detection of a current with a peak value equivalent to that of a lightning strike. In such cases, methods that compare the detected current with a threshold, as described in Patent Documents 1 and 2, may misinterpret the noise generated by the noise source as a lightning strike on the target. [Means for solving the problem]

[0005] The present invention has been made to solve at least some of the aforementioned problems and can be realized in the following embodiments or applications.

[0006] [Application Example 1] The lightning strike detection device according to this application example is characterized by comprising: a bar antenna; a detection signal generation circuit that processes the output signal of the bar antenna to generate a detection signal corresponding to the magnetic field detected by the bar antenna; and a determination circuit that calculates the amount of charge over a predetermined time by integrating the values ​​of the detection signal and compares the amount of charge with a predetermined set value to determine whether or not lightning has struck a structure. In the lightning detection device according to this application example, the bar antenna is an open circuit and therefore picks up ambient noise and outputs a signal corresponding to that noise. However, even if the maximum value of the detection signal when noise occurs is about the same as the maximum value of the detection signal when lightning strikes, the amount of charge obtained by integrating the detection signals over a predetermined time differs greatly between the two. Therefore, the lightning detection device according to this application example can accurately detect lightning strikes on structures by comparing the amount of charge over a predetermined time with a set value. Furthermore, while a Rogowski coil requires changing its diameter and the resistance and capacitance values ​​of the integrating circuit according to the size of the structure, a bar antenna is... Since there is no need to change the size depending on the size of the structure, and the amplification factor of the output signal only needs to be changed according to the size of the structure, the lightning detection device in this application example is also advantageous in terms of cost reduction.

[0007] [Application Example 2] In the lightning detection device according to the above example, upper and lower frequency limits are defined for detecting the current flowing through the structure due to the lightning strike, and the detection signal generation circuit may amplify the signal component of the lower frequency limit included in the output signal of the bar antenna with a gain higher than the signal component of the upper frequency limit. According to the lightning detection device in this application example, since the bar antenna exhibits the characteristic of outputting signal components with lower gain for lower frequencies, by amplifying the signal component at the lower limit frequency of the current detection frequency band with a higher gain than the signal component at the upper limit frequency of the bar antenna's output signal, a current waveform close to that of a lightning current can be reproduced, improving the accuracy of the charge amount calculation.

[0008] [Application Example 3] In the lightning strike detection device according to the above application example, the determination circuit may calculate the amount of charge for the predetermined time when the value of the detection signal becomes equal to or greater than a first threshold. According to the lightning strike detection device in this application example, the maximum value of the detection signal will be equal to or greater than the first threshold when lightning strikes, so there is no risk of missing a lightning strike. Furthermore, since there is no need to perform the process of calculating the amount of charge until the maximum value of the detection signal is equal to or greater than the first threshold, the processing load is reduced.

[0009] [Application Example 4] In the lightning strike detection device according to the above application example, the determination circuit may calculate the average value of the detection signal during the period when the value of the detection signal is less than the first threshold, calculate a correction value to correct the value of the detection signal based on the average value, and when the value of the detection signal becomes equal to or greater than the first threshold, calculate the charge amount for the predetermined time by accumulating the value of the detection signal corrected by the correction value. In the lightning detection device according to this application example, the output signal of the bar antenna 10 is minute and therefore needs to be greatly amplified by signal processing. This amplification results in a DC offset being included in the value of the detected signal. Therefore, if the values ​​of the detected signal are accumulated without removing the DC offset, the amount of charge will be very large, which may reduce the accuracy of lightning detection. In contrast, the lightning detection device according to this application example calculates the amount of charge by accumulating the values ​​of the detected signal corrected by a correction value based on the average value of the detected signal (a value equivalent to the DC offset), thus enabling accurate detection of lightning strikes on structures.

[0010] [Application Example 5] In the lightning strike detection device according to the above application example, the determination circuit may calculate the charge amount for the predetermined time by setting it to zero if the value of the detection signal is less than or equal to the second threshold. According to the lightning strike detection device in this application example, if the value of the detection signal is below the second threshold, it is set to zero. This prevents the accumulation of noise components that are constantly included in the detection signal, thus enabling accurate detection of lightning strikes on structures. [Brief explanation of the drawing]

[0011] [Figure 1] This is an external view of the lightning strike detection device according to this embodiment. [Figure 2] This diagram shows the lightning strike detection device according to this embodiment attached to a wind turbine. [Figure 3] (A) is a front view of the lightning detection device attached to the wind turbine, and (B) is a side view of the lightning detection device 1 attached to the wind turbine. [Figure 4] This is a functional block diagram of the lightning strike detection device according to this embodiment. [Figure 5] This is a diagram showing the configuration of a filter circuit. [Figure 6] This figure shows the detection signal for lightning current waveforms. [Figure 7] This figure shows the detection signal for the noise waveform. [Figure 8] This diagram shows an example of how to install an external sensor. [Figure 9] This is a flowchart showing the procedure of the lightning strike detection device according to this embodiment. [Figure 10] This is a flowchart showing the procedure for calculating the correction value. [Figure 11] This is an explanatory diagram of the lightning strike detection method using a Rogowski coil. [Figure 12] This is a diagram showing the integrating circuit connected to the Rogowski coil.

Mode for Carrying Out the Invention

[0012] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. The drawings used in this description are for convenience of explanation. Note that the embodiments described below do not unduly limit the content of the present invention described in the claims. Also, not all of the configurations described below are essential constituent elements of the present invention.

[0013] 1. Outline of Lightning Strike Detection Device The lightning strike detection device 1 according to this embodiment detects a lightning strike on a structure by capturing the magnetic flux generated by the lightning strike on the structure. FIG. 1 is an external view of the lightning strike detection device 1. Also, FIG. 2 is a diagram showing an example of the method of attaching the lightning strike detection device 1 to a structure. In the example of FIG. 2, the structure to be detected for lightning strikes is the windmill 100 for wind power generation As shown in Figure 1, the lightning detection device 1 comprises a rectangular parallelepiped housing 3, which houses a rectangular parallelepiped housing 2, a bar antenna 10, and a GPS antenna 60. For example, housing 3 is made of resin, and housing 2 is made of metal such as stainless steel. A display unit 80 is provided on the front of housing 2, and two mounting brackets 4, an optical terminal 70, a GPS terminal 90 to which the GPS antenna 60 is connected, and a connection part 92 to which the bar antenna 10 is connected are provided on the side of housing 2. The bar antenna 10 has a configuration in which a wire forming a coil 11 is wound around one or more rod-shaped ferrite cores 12. When the magnetic flux generated by lightning striking a structure passes inside the coil 11, an electromotive force is generated by electromagnetic induction, and a current flows through the coil 11. The lightning detection device 1 detects lightning based on the current flowing through the coil 11 of the bar antenna 10. The performance requirements for Class I as defined in JIS C 1400-24 are: current detection frequency bandwidth: 0.1 Hz to 100 kHz, maximum measurable current value: 100 kA or more, minimum detectable current value (trigger current value): 1% of the maximum measurable current value or 2 kA or less, maximum measurable charge value: 600 C or more, minimum detectable charge value: 1 C or less, and observation time: 0.5 s or more. Therefore, the lightning detection device 1 detects lightning strikes in a manner that satisfies these performance requirements.

[0014] As shown in Figure 2, the wind turbine 100 to be inspected comprises a tower 101, a nacelle 102 connected to the tower 101, and a wind turbine rotor 103 connected to the nacelle 102. The wind turbine rotor 103 is supported by the tower 101 via the nacelle 102. The wind turbine rotor 103 comprises a rotor head (hub) 104 and blades 105 attached to the rotor head 104. The wind turbine rotor 103 may be provided with one blade 105 or with multiple blades 105. The blades 105 contain a lightning receiver 106, which is a conductor for capturing lightning, and a lightning conductor 110. The tip of the lightning conductor 110 is connected to the receptor 106. The tower 101 houses a ladder 107 for access and a grounding wire 120. The base of the lightning conductor 110 is connected to one end of the grounding wire 120. The other end of the grounding wire 120 is connected to the support column of the access ladder 107. The access ladder 107 is at the same potential (0V) as the ground G, and the grounding wire 120 is grounded via the access ladder 107. Therefore, lightning captured by the receptor 106 is discharged to the ground G via the lightning conductor 110, the grounding wire 120, and the access ladder 107. The lightning strike detection device 1 is attached to the stainless steel band 5 (5a, 5b) by the mounting bracket 4 (Figure 1), and the stainless steel band 5 (5a, 5b) is wrapped around the tower 101, thereby fixing the lightning strike detection device 1 to the tower 101. The lightning strike detection device 1 is The built-in bar antenna 10 detects lightning strikes on the wind turbine 100 by capturing the magnetic flux generated by the lightning current flowing through the grounding wire 120. Since this magnetic flux is generated in concentric circles with the grounding wire 120 as the center, it is preferable that the lightning detection device 1 be fixed so that the central axis of the coil 11 of the bar antenna 10 is perpendicular to the grounding wire 120 in order to maximize the magnetic flux passing through the inside of the coil 11 of the bar antenna 10.

[0015] Figures 3(A) and 3(B) are enlarged views of the area in Figure 2 where the lightning detection device 1 is installed. In Figure 3(A), the front of the lightning detection device 1 is visible, and in Figure 3(B), the side of the lightning detection device 1 is visible. Note that the housing 2 and bar antenna 10 are actually built into the lightning detection device 1 and are not visible from the outside, but for the sake of explanation, the housing 2 and bar antenna 10 are shown in Figures 3(A) and 3(B). Similarly, the grounding wire 120 is actually housed inside the tower 101 and is not visible from the outside, but for the sake of explanation, the grounding wire 120 is shown in Figures 3(A) and 3(B). As shown in Figures 3(A) and 3(B), the grounding wire 120 is provided along the Z direction, so the lightning detection device 1 is fixed to the tower 101 using stainless steel bands 5 (5a, 5b) such that the central axis 11a of the coil 11 is aligned along the X direction, which is perpendicular to the Z direction. For example, if the Z direction is vertical, then the X direction is horizontal. Therefore, the installer of the lightning detection device 1 uses a spirit level to fix the lightning detection device 1 (bar antenna 10) so that it is horizontal. Note that the method of fixing the lightning detection device 1 to the structure to be inspected does not have to be the method using the stainless steel band 5. For example, the lightning detection device 1 may be fixed to the structure by a magnet.

[0016] 2. Functional configuration of a lightning strike detection device Figure 4 is a functional block diagram of the lightning strike detection device 1. As shown in Figure 4, the lightning strike detection device 1 includes a bar antenna 10, an integrating circuit 20, a filter circuit 30, an A / D conversion circuit 40, a microcontroller 50, a GPS antenna 60, a GPS module 62, an optical terminal 70, an optical receiver 72, a display unit 80, a voltage-free contact 82, a LAN port 84, and a recording medium 86. The integrating circuit 20 converts the current output from the bar antenna 10 into a voltage and outputs a signal obtained by integrating that voltage. As shown in Figure 5, the output signal of the bar antenna 10 exhibits a characteristic where the gain is higher for signal components with higher frequencies, and the output signal of the integrating circuit 20 exhibits a characteristic where signal components with frequencies lower than 0.1 Hz, which is the lower limit frequency of the current detection frequency band specified in JIS C 1400-24, are cut off, and signal components around 0.1 Hz are boosted.

[0017] The filter circuit 30 performs various filtering operations on the output signal of the integrating circuit 20. As shown in Figure 5, the filter circuit 30 includes a low-pass filter 31, an amplification circuit 32, a high-pass filter 33, a low-pass filter 34, and an output circuit 35. The low-pass filter 31 outputs a signal from the output signal of the integrating circuit 20 that has signal components (noise components) with frequencies higher than 100 kHz, which is the upper limit frequency of the current detection frequency band specified in JIS C 1400-24. The output signal of the low-pass filter 31 shows characteristics in which signal components outside the current detection frequency band (0.1 Hz to 100 kHz) are cut, and signal components around 0.1 Hz and around 100 kHz are boosted. The amplification circuit 32 outputs a signal in which the output signal of the low-pass filter 31 is amplified over the entire frequency range. The high-pass filter 33 outputs a signal from the output signal of the amplification circuit 32 that has the signal components around 0.1 Hz boosted by the integrating circuit 20 attenuated. The low-pass filter 34 outputs a signal from the output signal of the high-pass filter 33 with the signal component around 100kHz, which was boosted by the low-pass filter 31, attenuated. The output circuit 35 buffers and outputs the output signal of the low-pass filter 34. The output signal of the output circuit 35 has the signal component within the current detection frequency band (0.1Hz to 100kHz) amplified with a constant gain, and the signal component outside the current detection frequency band (noise component) is... This shows the characteristics that have been cut. Thus, the lightning detection device 1 has defined upper and lower frequency limits (100 kHz and 0.1 Hz) for detecting the current flowing through the wind turbine 100 (structure) due to a lightning strike. The integrating circuit 20 and the filter circuit 30 amplify the signal component at the lower frequency limit (0.1 Hz) included in the output signal of the bar antenna 10 with a higher gain than the signal component at the upper frequency limit (100 kHz). As a result, the integrating circuit 20 and the filter circuit 30 correct the frequency characteristics of the current detected by the bar antenna 10 and output a signal that amplifies the lightning current in the current detection frequency band (0.1 Hz to 100 kHz) flowing through the grounding wire 120 with a constant gain.

[0018] Returning to the explanation of Figure 4, the A / D conversion circuit 40 converts the output signal (analog signal) of the filter circuit 30 into a digital signal and outputs it to the microcontroller 50. The integrating circuit 20, filter circuit 30, and A / D conversion circuit 40 function as detection signal generation circuits that process the output signal of the bar antenna 10 to generate a detection signal corresponding to the magnetic field detected by the bar antenna 10. The GPS antenna 60 receives satellite signals transmitted from each GPS (Global Positioning System) satellite. The GPS module 62 demodulates the navigation messages contained in each satellite signal received by the GPS antenna 60, generates a PPS (Pulse Per Second) signal based on the navigation messages, and outputs it to the microcontroller 50. The microcontroller 50 performs various processes according to a program stored in memory (not shown). Specifically, the microcontroller 50 generates time information based on the PPS signal output from the GPS antenna 60. The microcontroller 50 also determines whether or not lightning has struck the wind turbine 100 (structure) based on the digital signal (detection signal) output from the A / D conversion circuit 40. In other words, the microcontroller 50 functions as a determination circuit to determine whether or not lightning has struck the structure. When lightning strikes the wind turbine 100, as shown in Figure 6, the value of the detection signal increases sharply to a peak and then decreases. Therefore, when the value (absolute value) of the detection signal becomes greater than or equal to the first threshold TH1, the microcontroller 50 (determination circuit) calculates the charge amount Q for a predetermined time T by accumulating the values ​​(absolute values) of the detection signal, and compares the charge amount Q with a predetermined set value QT to determine whether or not lightning has struck the wind turbine 100 (structure). In Figure 6, the first threshold TH1 is 1kA and the predetermined time T is 0.5s, but these may be set to other values ​​as appropriate. Note that 1kA is defined as JIS The upper limit of the trigger current value specified in JIS C 1400-24 (the upper limit when the maximum measurement current value is 100kA or more) and 0.5s is the lower limit of the observation time specified in JIS C 1400-24. In addition, the set value QT is set to a value lower than 1C in order to satisfy the minimum detectable charge amount value specified in JIS C 1400-24.

[0019] However, since the bar antenna 10 is an open circuit, even if no lightning current flows through the ground wire 120, it will pick up ambient noise and output a current corresponding to that noise. For example, when a maintenance worker on the wind turbine 100 uses a power tool to perform maintenance, the bar antenna 10 may detect the magnetic field generated by the power tool and output a current. When the bar antenna 10 picks up noise, the value of the detection signal fluctuates temporarily, as shown in Figure 7. When the peak value of the detection signal exceeds the first threshold TH1, the microcontroller 50 will calculate the charge amount Q for the noise over a predetermined time T. Therefore, in order to avoid misjudging the presence or absence of lightning, it is required that the charge amount Q calculated for the noise over a predetermined time T be less than the set value QT. On the other hand, the current output from the bar antenna 10 is minute, and this current is greatly amplified by the integrating circuit 20 and the filter circuit 30, so the value of the detected signal will include a DC offset. Therefore, if the value of the detected signal is integrated without removing this DC offset, the charge amount Q will become a very large value, and the charge amount Q calculated for the noise may exceed the set value QT. Therefore, the microcontroller 50 (decision circuit) constantly monitors the detected signal, calculates the average value of the detected signal (DC offset) during the period when the value of the detected signal (absolute value) is less than the first threshold TH1, and corrects the value of the detected signal based on this average value. A correction value α is calculated. Then, when the value (absolute value) of the detected signal becomes greater than or equal to the first threshold TH1, the microcontroller 50 calculates the charge amount Q for a predetermined time T by integrating the value of the detected signal corrected by the correction value α (the value obtained by subtracting the correction value α from the value of the detected signal). Figures 6 and 7 show the waveform of the detected signal corrected by the correction value α.

[0020] However, as shown in Figures 6 and 7, the detection signal contains noise components with minute amplitudes, and if these noise components are accumulated, the charge amount Q may exceed the set value QT. Therefore, the microcontroller 50 (decision circuit) calculates the charge amount Q for a predetermined time T by setting it to zero if the value (absolute value) of the detection signal is less than or equal to the second threshold TH2. The second threshold TH2 is, for example, a value lower than the first threshold TH1, and is set to an appropriate value in advance based on the measured value of the noise waveform. For example, if the second threshold TH2 is set to 0.5kA, the charge amount Q calculated when the detection signal is the lightning current waveform shown in Figure 6 will be approximately 28C. On the other hand, the charge amount Q calculated when the detection signal is the noise waveform shown in Figure 7 will be approximately 0.02C. Therefore, by setting the set value QT to, for example, any value within the range of 0.5C ± 20%, it will be correctly determined that there was a lightning strike on the wind turbine 100 when the detected signal is the lightning current waveform shown in Figure 6, and correctly determined that there was no lightning strike on the wind turbine 100 when the detected signal is a noise waveform. If the microcontroller 50 determines that lightning has struck the wind turbine 100, it displays the calculated charge amount Q, the maximum value of the lightning current (maximum positive and negative values), the time of the lightning strike, and other information (lightning strike information) on the display unit 80 and records it on a recording medium 86 such as an SD card. In addition, if the microcontroller 50 determines that lightning has struck the wind turbine 100, it outputs an alarm via a dry contact 82 and transmits the lightning strike information to other devices connected to the network via the LAN port 84.

[0021] Incidentally, if another wind turbine 100A is located near wind turbine 100, depending on the arrangement of wind turbine 100 and wind turbine 100A, a lightning strike on wind turbine 100A may be mistakenly identified as a lightning strike on wind turbine 100. For example, as shown in Figure 8, if the lightning detection device 1 is mounted on wind turbine 100 on the opposite side from wind turbine 100A, the lightning detection device 1 will detect the magnetic field generated by a lightning strike on wind turbine 100, as well as the magnetic field generated by a lightning strike on wind turbine 100A, which may lead to a misidentification. As a countermeasure, it is effective to determine whether or not wind turbine 100 has been struck by lightning by detecting the lightning current using an external sensor 200 together with the lightning detection device 1. For this reason, the lightning detection device 1 has an optical terminal 70 (see Figures 1 and 4) that can be connected to the external sensor 200, as shown in Figure 1. The external sensor 200 is a sensor capable of detecting the magnetic field generated by a lightning strike on wind turbine 100A, and may be, for example, a bar antenna. The external sensor 200 is mounted on the tower 101 of the wind turbine 100 so that its magnetic field detection direction differs from that of the lightning detection device 1, in order to avoid detecting the same noise as the lightning detection device 1. For example, as shown in Figure 8, it is desirable that the magnetic field detection direction of the external sensor 200 is offset by 90° from the magnetic field detection direction of the external sensor 200. With this arrangement, the magnetic field detection direction of the external sensor 200 coincides with the direction of the magnetic field generated by a lightning strike on the wind turbine 100, and is perpendicular to the direction of the magnetic field generated by a lightning strike on the wind turbine 100A. As a result, there is a large difference in the peak value of the output signal of the external sensor 200 between the time of a lightning strike on the wind turbine 100 and the time of a lightning strike on the wind turbine 100A, so the lightning detection device 1 can determine whether or not there has been a lightning strike on the wind turbine 100 based on the peak value of the output signal of the external sensor 200. Specifically, when an external sensor 200 is connected to the optical terminal 70, the optical receiver 72 (see Figure 4) receives the signal input from the optical terminal 70 (the output signal of the external sensor 200) and outputs it to the microcontroller 50. The microcontroller 50 can determine that lightning has struck the wind turbine 100 if the calculated charge amount Q over a predetermined time T is greater than or equal to a set value QT, and the peak value of the output signal of the optical receiver 72 (the output signal of the external sensor 200) is greater than or equal to a predetermined threshold. As shown in Figure 8, the lightning detection device 1 and the external sensor 200 can also be installed on the wind turbine 100A in the same position as the wind turbine 100. It can also detect lightning strikes. In the lightning detection device 1 shown in Figure 1, the bar antenna 10 and the subsequent circuit section are housed in a single enclosure 2, but they may be housed in two separate enclosures. In this case, the first enclosure housing the bar antenna 10 may be fixed to the tower 101, and the second enclosure housing the subsequent circuit section may be installed, for example, inside the tower 101.

[0022] 3. Processing Procedure for Lightning Strike Detection Device Finally, Figure 9 shows a flowchart illustrating the processing procedure of the lightning strike detection device 1 described above. For example, the microcontroller 50 executes the process shown in Figure 9 by running a program stored in a memory not shown. As shown in Figure 9, when measurement starts (step S10), the microcontroller 50 first acquires current values ​​(output signals of the A / D conversion circuit 40) until it has saved N or more current values ​​(N in step S30), and saves the current values ​​obtained by subtracting the correction value α (step S20). After saving N or more current values ​​(Y in step S30), the microcontroller 50 acquires current values ​​until the absolute value of the current value is equal to or greater than the first threshold TH1 (N in step S60), calculates the current value obtained by subtracting the correction value α (step S40), deletes the first current value, and saves the current value (step S50). When the absolute value of the current value of the microcontroller 50 exceeds the first threshold TH1 (Y in step S60), it acquires the current value and stores the current value after subtracting the correction value α until a predetermined time T has elapsed (N in step S80) (step S70). Then, when the predetermined time T has elapsed (Y in step S80), it calculates the charge amount Q by integrating the current values ​​for the predetermined time T (step S90). In step S90, if the absolute value of the current value of the microcontroller 50 is less than or equal to the second threshold TH2, it treats this current value as zero and integrates it. If the charge amount Q is greater than or equal to the set value QT (Y in step S100), the microcontroller 50 determines that it is a lightning strike, records the lightning strike information on the recording medium 86, displays the lightning strike information on the display unit 80 (step S110), and then repeats the processing from step S10 onwards. If the charge amount Q is less than the set value QT (N in step S100), the microcontroller 50 determines that it is not a lightning strike (step S120), and then repeats the processing from step S10 onwards.

[0023] As mentioned above, if an external sensor 200 is connected to the optical terminal 70, the microcontroller 50 only needs to determine that lightning has struck the wind turbine 100 if the calculated charge amount Q over a predetermined time T is equal to or greater than the set value QT, and the peak value of the output signal of the optical receiver 72 (output signal of the external sensor 200) is equal to or greater than a predetermined threshold. The microcontroller 50 performs a process to calculate a correction value α in parallel with the process shown in Figure 9 during the period when the absolute value of the current value is less than the first threshold TH1. A flowchart showing the procedure for calculating the correction value α is shown in Figure 10. As shown in Figure 10, the microcontroller 50 calculates the average value of N current values ​​(current values ​​before correction) (step S210), and if the average value is outside the error range of the reference value (N in step S220), it calculates the difference between the average value and the reference value as the correction value α (step S230), and if the average value is within the error range of the reference value (Y in step S220), it resets the correction value α to zero.

[0024] 4. Effects As described above, in the lightning detection device 1 according to this embodiment, the detection signal generation circuit (integrating circuit 20 and filter circuit 30) performs various filtering and amplification processes on the output signal of the bar antenna 10 according to the characteristics of the bar antenna 10. In particular, since the bar antenna 10 exhibits the characteristic of outputting signal components with lower gain for lower frequencies, the signal components outside the current detection frequency band are attenuated from the output signal of the bar antenna 10, and the signal components at the lower limit frequency (0.1 Hz) of the current detection frequency band are amplified with a higher gain than the signal components at the upper limit frequency (100 kHz), thereby reproducing a current waveform close to that of a lightning current for detection. A signal is obtained. The output signal of the bar antenna 10 is minute and therefore needs to be greatly amplified by signal processing. This amplification causes a DC offset to be included in the value of the detected signal. However, the microcontroller 50 can calculate the charge amount Q at a predetermined time T with high accuracy by integrating the values ​​of the detected signal corrected by a correction value α based on the average value of the detected signal (a value corresponding to the DC offset). Furthermore, the detected signal contains noise components with a constant small amplitude. The microcontroller 50 integrates the detected signal by treating it as zero when the value is below the second threshold TH2, thereby preventing the integration of these noise components and enabling the calculation of the charge amount Q at a predetermined time T with high accuracy.

[0025] Since the bar antenna 10 is an open circuit, it picks up ambient noise and outputs a signal corresponding to that noise. However, even if the maximum value of the detection signal when noise occurs is about the same as the maximum value of the detection signal when lightning strikes, the amount of charge Q obtained by integrating the detection signals over a predetermined time T will be significantly different in the two cases. Therefore, according to the lightning detection device 1 of this embodiment, the microcontroller 50 can accurately determine whether the wind turbine 100 (structure) is struck by lightning or is just noise by comparing the amount of charge Q with a set value QT. Furthermore, according to the lightning detection device 1 of this embodiment, when lightning strikes, the maximum value of the detection signal will be equal to or greater than the first threshold TH1, so there is no risk of missing the lightning strike. Moreover, since there is no need to calculate the amount of charge Q until the maximum value of the detection signal is equal to or greater than the first threshold TH1, the processing load on the microcontroller 50 is reduced. Furthermore, while the Rogowski coil requires changing its diameter to match the size of the wind turbine 100 (structure) and altering the resistance and capacitance values ​​of the integrating circuit, the bar antenna 10 does not need to be resized according to the size of the wind turbine 100 (structure). Therefore, the resistance and capacitance values ​​of the integrating circuit 20 do not need to be changed, and only the amplification factor of the amplification circuit 32 needs to be changed according to the size of the wind turbine 100 (structure). Thus, the lightning detection device 1 according to this embodiment is also advantageous in terms of cost reduction.

[0026] The present invention is not limited to the embodiments described above, and various further modifications are possible. For example, the present invention includes configurations that are substantially identical to the configurations described in the embodiments (for example, configurations with the same function, method, and result, or configurations with the same purpose and effect). The present invention also includes configurations in which non-essential parts of the configurations described in the embodiments are replaced. The present invention also includes configurations that produce the same effects or achieve the same purpose as the configurations described in the embodiments. Furthermore, the present invention includes configurations that add known technology to the configurations described in the embodiments. [Explanation of symbols]

[0027] 1...Lightning strike detection device, 2...Housing, 3...Housing, 4...Mounting bracket, 5, 5a, 5b...Stainless steel band, 10...Bar antenna, 11...Coil, 11a...Central axis, 12...Ferrite core, 20...Integrating circuit, 30...Filter circuit, 31...Low-pass filter, 32...Amplifying circuit, 33...High-pass filter, 34...Low-pass filter, 35...Output circuit, 40...A / D conversion circuit, 50...Microcontroller, 60...GPS antenna Na, 62...GPS module, 70...Optical terminal, 72...Optical receiver, 80...Display unit, 82...Voltage-free contact, 84...LAN port, 86...Recording medium, 90...GPS terminal, 92...Connection unit, 100, 100A...Wind turbine, 101...Tower, 102...Nacell, 103...Wind turbine rotor, 104...Rotor head, 105...Blade, 106...Receptor, 107...Ladder for access, 110...Lightning conductor, 120...Grounding wire, 200...External sensor

Claims

1. Bar antenna and A detection signal generation circuit that processes the output signal of the bar antenna to generate a detection signal corresponding to the magnetic field detected by the bar antenna, A lightning strike detection device comprising a determination circuit that calculates the amount of charge over a predetermined period of time by integrating the values ​​of the detection signal, and compares the amount of charge with a predetermined set value to determine whether or not lightning has struck a structure.

2. In the lightning detection device according to claim 1, The upper and lower frequency limits for detecting the current flowing through the structure due to the lightning strike are defined. The lightning detection device is characterized in that the detection signal generation circuit amplifies the signal component of the lower limit frequency included in the output signal of the bar antenna with a gain higher than the signal component of the upper limit frequency.

3. In the lightning detection device according to claim 1, The lightning strike detection device is characterized in that the determination circuit calculates the amount of charge for a predetermined time when the value of the detection signal becomes equal to or greater than a first threshold.

4. In the lightning detection device according to claim 3, The lightning strike detection device is characterized in that the determination circuit calculates the average value of the detection signal during the period when the value of the detection signal is less than a first threshold, calculates a correction value to correct the value of the detection signal based on the average value, and calculates the charge amount for the predetermined time by accumulating the value of the detection signal corrected by the correction value when the value of the detection signal becomes equal to or greater than the first threshold.

5. In the lightning detection device according to any one of claims 1 to 4, The lightning strike detection device is characterized in that the determination circuit calculates the charge amount for the predetermined time by setting the value of the detection signal to zero if it is less than or equal to a second threshold.

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