Thermal collapse risk assessment method for lightning arresters in offshore wind farms throughout their life cycle

Abstract

The present invention discloses a method for assessing the thermal collapse risk of lightning arresters in the entire life cycle of offshore wind farms, which belongs to the field of thermal collapse risk assessment of lightning arresters and includes the following steps: S1, statistically analyzing the lightning parameters in the area where the offshore wind farm is located; S2, analyzing the differences in energy absorption of lightning arresters of offshore wind turbines under single lightning strikes and multiple lightning strikes; S3, obtaining the energy absorbed by the lightning arrester during the first lightning strike through simulation, and obtaining the amplitude of the lightning current corresponding to subsequent lightning strikes; S4, calculating the interval probability of the thermal collapse risk of the lightning arrester under different intervals, different polarities and different return stroke times under ground lightning; S5, calculating the thermal collapse risk of the lightning arrester in the entire life cycle of the offshore wind farm. Using the above-mentioned method for assessing the thermal collapse risk of lightning arresters in the entire life cycle of offshore wind farms, based on the energy accumulation characteristics of offshore wind power under multiple lightning strikes, the method combines electromagnetic transient simulation with probability statistics to achieve the first accurate quantification of the thermal collapse risk of lightning arresters under multiple lightning strikes.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal collapse risk assessment of lightning arresters, and in particular to a method for assessing the thermal collapse risk of lightning arresters throughout the entire life cycle of an offshore wind farm. Background Art

[0002] Offshore wind farms are located in complex marine environments, where frequent lightning activity, often accompanied by multiple strikes, poses a significant threat to the safe operation of wind turbines. When an offshore wind turbine is struck by lightning, the lightning current is conducted along the blade down conductors to the nacelle and tower, ultimately grounding through seawater. During this process, electromagnetic induction creates a strong coupling effect between the wind turbine tower and adjacent internal equipment, generating high-amplitude lightning overvoltages that directly threaten the stable operation of the turbine's internal electrical systems.

[0003] As the core lightning protection device within wind turbines, lightning arresters are crucial for resisting these types of overvoltages and ensuring reliable operation in harsh environments such as severe thunderstorms and multiple lightning strikes. Especially with the widespread adoption of "box-mounted transformers on nacelles" in offshore wind turbines, lightning arresters have become even more prominent, becoming an indispensable core component for ensuring the safety of turbine electrical systems.

[0004] The current-carrying capacity of the arrester is determined by the size of its internal resistor. When the energy absorbed in a short period of time exceeds its own threshold, thermal collapse will occur and cause an explosion, resulting in the unit's electrical system being in a state without arrester protection and losing lightning overvoltage protection.

[0005] However, current lightning protection designs have significant limitations: First, research has mostly focused on the current-carrying capacity of arresters under single lightning strike scenarios, and lightning protection measures have been developed based on this, with insufficient consideration of the impact of multiple lightning strikes. Second, existing research focuses on transmission and distribution lines, while offshore wind turbines differ significantly from transmission and distribution lines in terms of structural characteristics and operating environments. This results in large deviations in the energy calculation results of arresters under single and multiple lightning strikes, making it difficult to directly apply existing conclusions. Third, while the preventive maintenance strategy currently used in offshore wind turbine operations can diagnose the progressive degradation of arresters through online monitoring, it cannot effectively assess the instantaneous risk of thermal breakdown. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for assessing the thermal collapse risk of lightning arresters in the entire life cycle of an offshore wind farm, so as to solve the above technical problems.

[0007] To achieve the above objectives, the present invention provides a method for assessing the thermal collapse risk of lightning arresters in an offshore wind farm over its entire life cycle, comprising the following steps:

[0008] S1. Calculate the lightning parameters in the area where the offshore wind farm is located based on the lightning location system data;

[0009] S2. Based on the offshore wind turbine connection and the lightning down-conduction path, a lightning electromagnetic transient simulation model for the offshore wind turbine is constructed. Combined with the lightning parameters statistically calculated in step S1, the lightning arrester energy simulation calculations under single lightning strikes and multiple lightning strikes are performed respectively. Based on the simulation calculation results, the difference in energy absorption of the lightning arrester of the offshore wind turbine under single lightning strikes and multiple lightning strikes is analyzed;

[0010] S3. Considering the differences in energy absorption of the arrester under single and multiple lightning strikes, the lightning current amplitude is divided into multiple intervals. For each interval, in a multiple lightning strike scenario, the energy absorbed by the arrester during the first lightning strike is obtained through simulation. The maximum absorbed energy of subsequent lightning strikes is determined based on the arrester's absorption energy threshold, and the lightning current amplitude corresponding to the subsequent lightning strikes is further simulated.

[0011] S4. Using the lightning parameters calculated in step S1 and the simulation results in step S3, calculate the interval probability of thermal breakdown risk of the arrester under different intervals, different polarities, and different return stroke times of ground lightning;

[0012] S5. Considering the spatial characteristics and design life of the entire offshore wind farm, the lightning parameters calculated in step S1 and the calculation results in step S4 are used to calculate the thermal collapse risk of the lightning arrester over the entire life cycle of the offshore wind farm.

[0013] Preferably, the lightning parameters in step S1 include ground-to-ground lightning density , the number of return-to-ground lightning, the average frequency of multiple return-to-ground lightning, and the cumulative probability of lightning current amplitude ;

[0014] Among them, the number of return-to-ground lightning includes the number of positive polarity single return-to-ground lightning , Number of negative polarity single return ground flashes , Number of positive polarity multiple return ground lightning and the number of negative polarity multiple return ground lightning ;

[0015] Average multiple return ground flash frequency including positive polarity average multiple return ground flash frequency Average frequency of negative polarity multiple return ground flashes ,in, Indicates the number of return strikes of a multi-return ground flash. and Represents positive and negative polarity respectively The percentage of return ground lightning;

[0016] Cumulative probability of lightning current amplitude The expression is as follows:

[0017] (1);

[0018] Where, Indicates the amplitude of the actual lightning current; Indicates the set lightning current amplitude threshold; and They represent the scale parameter and shape parameter of lightning current amplitude distribution respectively;

[0019] Based on formula (1), the cumulative probability function of the positive first return stroke lightning current amplitude of multiple return strokes to ground lightning is obtained: , cumulative probability function of negative polarity first return stroke lightning current amplitude , cumulative probability function of positive polarity subsequent return stroke lightning current amplitude Cumulative probability function of the amplitude of subsequent negative polarity return stroke lightning current .

[0020] Preferably, step S2 specifically includes the following steps:

[0021] S21. Use PSCAD to model the wind turbine blade down conductor, moving contact part, tower, cable body, transformer, lightning arrester and surge protector, and tower bottom switchgear of the offshore wind turbine. The wind turbine blade down conductor, tower, and cable body are modeled using chain equivalent circuits, the moving contact part is modeled using typical parameters, the transformer is modeled using a high-frequency model, the lightning arrester and surge protector are modeled using nonlinear resistors, the tower bottom switchgear is modeled using ground capacitance, and the lightning current is modeled using Heidler function simulation.

[0022] S22. Use the finite element method to calculate the coupling capacitance between the tower wall, cable armor layer, cable shield layer, and cable core wire, quantify the effect of the coupling on transient energy transfer, and obtain a lightning electromagnetic transient simulation model for offshore wind turbines;

[0023] S23. Based on the electromagnetic transient simulation model of lightning strikes on offshore wind turbines, simulate single lightning strikes and multiple lightning strikes combined with the average frequency of multiple return ground lightning strikes, and calculate the energy absorbed by the lightning arrester;

[0024] S24. Compare the energy absorbed by the arrester calculated in step S23 with the energy threshold corresponding to thermal breakdown of the arrester, and analyze the difference in energy absorption of the arrester of the offshore wind turbine under single lightning strikes and multiple lightning strikes based on the comparison result.

[0025] Preferably, step S3 specifically includes the following steps:

[0026] S31. Divide the lightning current amplitude into interval, set The first interval, in Heavy lightning strike, first lightning strike The energy absorbed by the lower arrester is , calculate the subsequent Maximum absorbed energy of a lightning strike :

[0027] (2);

[0028] Where, Indicates the energy absorption threshold of the arrester;

[0029] S32. Assume that the amplitude of the subsequent lightning current is smaller than that of the first lightning current, and assume that all subsequent lightning currents are smaller than that of the first lightning current. The amplitude of the lightning current of the secondary lightning strike is equal. At this time, simulation calculation is performed to determine whether the The corresponding lightning current amplitude .

[0030] Preferably, the calculation formula of the interval probability of the thermal breakdown risk of the lightning arrester in step S4 is as follows:

[0031] (3);

[0032] Where, Indicates the interval, positive or negative polarity The probability of thermal collapse risk interval of lightning arrester under heavy lightning strike, , Indicates positive polarity, Indicates negative polarity, when for hour, and Select separately and ,when for hour, and Select separately and , thus obtaining the positive polarity Probability of thermal collapse risk interval of lightning arrester under heavy lightning strike and negative polarity Probability of thermal collapse risk interval of lightning arrester under heavy lightning strike , For the The lower limit of lightning current amplitude in each interval, For the The upper limit of lightning current amplitude in each interval.

[0033] Preferably, step S5 specifically includes the following steps:

[0034] S51. Calculate the number of positive polarity multiple lightning strikes suffered by offshore wind farm wind turbines each year and negative polarity multiple lightning strikes :

[0035] (3);

[0036] (4);

[0037] Where, represents the annual average density of ground-to-ground flashes; Indicates the lightning-inducing area of ​​the offshore wind farm;

[0038] S52, combined with positive polarity The proportion of return ground lightning , under negative polarity The proportion of return ground lightning , under positive polarity Probability of thermal collapse risk interval of lightning arrester under heavy lightning strike and negative polarity Probability of thermal collapse risk interval of lightning arrester under heavy lightning strike , and consider the design life of offshore wind farms , assessing the risk of thermal collapse over the entire life cycle of the offshore wind farm :

[0039] (5).

[0040] Therefore, the present invention adopts the above-mentioned method for assessing the thermal collapse risk of lightning arresters in the entire life cycle of offshore wind farms, which has the following beneficial effects:

[0041] 1. The finite element method is used to calculate the coupling capacitance between the tower and the cable, restoring the energy transfer law in a complex electromagnetic environment. This significantly reduces the error in lightning current energy calculation and lays an accurate data foundation for subsequent risk assessment.

[0042] 2. Based on the formula for multiple return-to-ground lightning frequency (weighted calculation for positive and negative polarity respectively), the "number of return strokes - energy accumulation" law of multiple lightning strikes is quantified. The energy absorption difference of lightning arresters under single and multiple lightning strikes is also compared, revealing the core risk of "multiple lightning strikes triggering thermal collapse due to energy accumulation," thus filling the gap in risk assessment in complex lightning environments.

[0043] 3. Through simulation, the correlation between the energy of the first lightning strike and the allowable amplitude of subsequent lightning strikes is clarified, and the probability of thermal collapse risk intervals under different scenarios is finally calculated, so that abstract risks can be converted into quantifiable probability indicators, improving the scientific nature of the assessment.

[0044] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1This is a flow chart of the method for assessing the thermal collapse risk of lightning arresters in the entire life cycle of an offshore wind farm according to the present invention;

[0046] Figure 2 Schematic diagram of the coupling calculation of the simulation experiment of the present invention, wherein (a) is the finite element calculation diagram between the core wire and the shielding layer, (b) is the finite element calculation diagram between the shielding layer and the armor layer, (c) is the finite element calculation diagram between the shielding layer and the shielding layer, and (d) is the finite element calculation diagram between the armor layer and the tower;

[0047] Figure 3 This is a wiring diagram of a lightning electromagnetic transient simulation model for an offshore wind turbine generator system used in a simulation experiment of the present invention;

[0048] Figure 4 This is a simulation result diagram of the energy absorbed by the arrester under a single lightning strike in the simulation experiment of the present invention;

[0049] Figure 5 This is a diagram showing the simulation results of the energy absorbed by the arrester under multiple lightning strikes in the simulation experiment of the present invention;

[0050] Figure 6 This is a schematic diagram of the topology of an offshore wind farm and its lightning induction surface in the simulation experiment of the present invention. DETAILED DESCRIPTION

[0051] In order to make the purposes, technical solutions and advantages disclosed in the embodiments of the present invention clearer, the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the embodiments of the present invention and are not intended to limit the embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. Examples of the embodiments are shown in the accompanying drawings, where the same or similar numbers throughout represent the same or similar elements or elements with the same or similar functions.

[0052] It should be noted that the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or server that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or are inherent to these processes, methods, products or devices.

[0053] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0054] like Figure 1 As shown in FIG, the thermal collapse risk assessment method of lightning arresters in the entire life cycle of an offshore wind farm includes the following steps:

[0055] S1. Calculate the lightning parameters in the area where the offshore wind farm is located based on the lightning location system data;

[0056] The lightning parameters in step S1 include ground-to-ground lightning density , the number of return-to-ground lightning, the average frequency of multiple return-to-ground lightning, and the cumulative probability of lightning current amplitude ;

[0057] Among them, the number of return-to-ground lightning includes the number of positive polarity single return-to-ground lightning , Number of negative polarity single return ground flashes , Number of positive polarity multiple return ground lightning and the number of negative polarity multiple return ground lightning ;

[0058] Average multiple return ground flash frequency including positive polarity average multiple return ground flash frequency Average frequency of negative polarity multiple return ground flashes ,in, Indicates the number of return strikes of a multi-return ground flash. and Represents positive and negative polarity respectively The percentage of return ground lightning;

[0059] Cumulative probability of lightning current amplitude The expression is as follows:

[0060] (1);

[0061] Where, Indicates the amplitude of the actual lightning current; Indicates the set lightning current amplitude threshold; and They represent the scale parameter and shape parameter of lightning current amplitude distribution respectively;

[0062] Based on formula (1), the cumulative probability function of the positive first return stroke lightning current amplitude of multiple return strokes to ground lightning is obtained: , cumulative probability function of negative polarity first return stroke lightning current amplitude , cumulative probability function of positive polarity subsequent return stroke lightning current amplitude Cumulative probability function of the amplitude of subsequent negative polarity return stroke lightning current .

[0063] S2. Based on the offshore wind turbine connection and the lightning down-conduction path, a lightning electromagnetic transient simulation model for the offshore wind turbine is constructed. Combined with the lightning parameters statistically calculated in step S1, the lightning arrester energy simulation calculations under single lightning strikes and multiple lightning strikes are performed respectively. Based on the simulation calculation results, the difference in energy absorption of the lightning arrester of the offshore wind turbine under single lightning strikes and multiple lightning strikes is analyzed;

[0064] Step S2 specifically includes the following steps:

[0065] S21. Use PSCAD to model the wind turbine blade down conductor, moving contact part, tower, cable body, transformer, lightning arrester and surge protector, and tower bottom switchgear of the offshore wind turbine. The wind turbine blade down conductor, tower, and cable body are modeled using chain equivalent circuits, the moving contact part is modeled using typical parameters, the transformer is modeled using a high-frequency model, the lightning arrester and surge protector are modeled using nonlinear resistors, the tower bottom switchgear is modeled using ground capacitance, and the lightning current is modeled using Heidler function simulation.

[0066] S22. Use the finite element method to calculate the coupling capacitance between the tower wall, cable armor layer, cable shield layer, and cable core wire, quantify the effect of the coupling on transient energy transfer, and obtain a lightning electromagnetic transient simulation model for offshore wind turbines;

[0067] S23. Based on the electromagnetic transient simulation model of lightning strikes on offshore wind turbines, simulate single lightning strikes and multiple lightning strikes combined with the average frequency of multiple return ground lightning strikes, and calculate the energy absorbed by the lightning arrester;

[0068] S24. Compare the energy absorbed by the arrester calculated in step S23 with the energy threshold corresponding to thermal breakdown of the arrester, and analyze the difference in energy absorption of the arrester of the offshore wind turbine under single lightning strikes and multiple lightning strikes based on the comparison result.

[0069] S3. Considering the differences in energy absorption of the arrester under single and multiple lightning strikes, the lightning current amplitude is divided into multiple intervals. For each interval, in a multiple lightning strike scenario, the energy absorbed by the arrester during the first lightning strike is obtained through simulation. The maximum absorbed energy of subsequent lightning strikes is determined based on the arrester's absorption energy threshold, and the lightning current amplitude corresponding to the subsequent lightning strikes is further simulated.

[0070] Step S3 specifically includes the following steps:

[0071] S31. Divide the lightning current amplitude into interval, set The first interval, in Heavy lightning strike, first lightning strike The energy absorbed by the lower arrester is , calculate the subsequent Maximum absorbed energy of a lightning strike :

[0072] (2);

[0073] Where, Indicates the energy absorption threshold of the arrester;

[0074] S32. Assume that the amplitude of the subsequent lightning current is smaller than that of the first lightning current, and assume that all subsequent lightning currents are smaller than that of the first lightning current. The amplitude of the lightning current of the secondary lightning strike is equal. At this time, simulation calculation is performed to determine whether the The corresponding lightning current amplitude .

[0075] S4. Using the lightning parameters calculated in step S1 and the simulation results in step S3, calculate the interval probability of thermal breakdown risk of the arrester under different intervals, different polarities, and different return stroke times of ground lightning;

[0076] The calculation formula for the interval probability of the thermal breakdown risk of the lightning arrester in step S4 is as follows:

[0077] (3);

[0078] Where, Indicates the interval, positive or negative polarity The probability of thermal collapse risk interval of lightning arrester under heavy lightning strike, , Indicates positive polarity, Indicates negative polarity, when for hour, and Select separately and ,when for hour, and Select separately and , thus obtaining the positive polarity Probability of thermal collapse risk interval of lightning arrester under heavy lightning strike and negative polarity Probability of thermal collapse risk interval of lightning arrester under heavy lightning strike , For the The lower limit of lightning current amplitude in each interval, For the The upper limit of lightning current amplitude in each interval.

[0079] S5. Considering the spatial characteristics and design life of the entire offshore wind farm, the lightning parameters calculated in step S1 and the calculation results in step S4 are used to calculate the thermal collapse risk of the lightning arrester over the entire life cycle of the offshore wind farm.

[0080] Step S5 specifically includes the following steps:

[0081] S51. Calculate the number of positive polarity multiple lightning strikes suffered by offshore wind farm wind turbines each year and negative polarity multiple lightning strikes :

[0082] (3);

[0083] (4);

[0084] Where, represents the annual average density of ground-to-ground flashes; Indicates the lightning-inducing area of ​​the offshore wind farm;

[0085] S52, combined with positive polarity The proportion of return ground lightning , under negative polarity The proportion of return ground lightning , under positive polarity Probability of thermal collapse risk interval of lightning arrester under heavy lightning strike and negative polarity Probability of thermal collapse risk interval of lightning arrester under heavy lightning strike , and consider the design life of offshore wind farms , assessing the risk of thermal collapse over the entire life cycle of the offshore wind farm :

[0086] (5).

[0087] Simulation experiment

[0088] This simulation experiment selected a total of ten years of data from 2014 to 2023 from a certain province's lightning location system, and took all offshore lightning data 65 km from the shore. When counting the number and frequency of return strokes to ground lightning, the number of positioning stations must be greater than or equal to 2; for the statistics of the probability of return stroke current amplitude, the number of positioning stations must be greater than or equal to 3. The following statistical data was obtained: Based on the location of a certain offshore wind farm, the ground lightning density in the area was statistically obtained. 6.67 times / (km 2 a).

[0089] Table 1 Statistics of ground-to-ground lightning

[0090] ;

[0091] Table 2 Statistics of multiple return-to-ground lightning frequency

[0092] ;

[0093] Taking 10kA as a node, the number of lightning current amplitudes was counted and fitted according to formula (1), and the results are shown in Table 3.

[0094] Table 3

[0095] ;

[0096] Based on the above parameters, PSCAD is used to model the down conductor of offshore wind turbine blades, moving contact parts, tower, cable body, transformer, lightning arrester and SPD, tower bottom switchgear, and lightning current function. The coupling between tower wall, cable armor layer, cable shield layer, and cable core wire is carried out as follows. Figure 2 The finite element electric field calculation shown in the figure obtains the coupling capacitance, which is then obtained as follows: Figure 3 The electromagnetic transient simulation model of an offshore wind turbine generator system struck by lightning is shown (SA1 and SA2 are lightning arresters of the wind turbine generator system).

[0097] The energy simulation of SA1 and SA2 under a single lightning strike was carried out, and the lightning current waveform used in the simulation under a single lightning strike was 1 / 200μs. The results are as follows Figure 4 At the same time, combined with the statistical results in Tables 1 to 3, it can be seen that the average frequency of multiple return ground lightning is 4. Under quadruple lightning strikes, the energy simulation of SA1 and SA2 is carried out. At this time, the first positive lightning current waveform is 10 / 350μs, the first negative lightning current waveform is 1 / 200μs, and the subsequent positive and negative lightning current waveforms are both 0.25 / 100μs. The results are as follows Figure 5 shown.

[0098] At the same time, since the energy threshold corresponding to the thermal collapse of the arrester is related to the size of the resistor, currently, 35kV arresters mainly use the current carrying capacity corresponding to the nominal discharge current of 5kA. At the same time, there are also 35kV arresters with the current carrying capacity corresponding to the nominal discharge current of 10kA. In this embodiment, the absorbed energy density of the resistor is 170J / cm 3 , then use the 35kV energy threshold of different size resistors into Table 4.

[0099] Table 4 35kV arrester energy threshold

[0100] ;

[0101] It can be seen that for a commonly used 35kV arrester with a nominal discharge current of 5kA, under a single lightning strike, there is theoretically no risk of thermal breakdown of SA1 and SA2 due to exceeding the energy threshold. However, under multiple lightning strikes, the risk of thermal breakdown of SA1 and SA2 exceeding the energy threshold is higher, especially for SA1. Therefore, based on these results, it is believed that the risk of thermal breakdown of arresters in offshore wind farms mainly comes from multiple lightning strikes on offshore wind turbines.

[0102] Therefore, the lightning current amplitude range is set to 0-250kA, with each 5kA as an interval, and the average value of the interval is used as the simulation calculation input of the interval. A total of 50 intervals are taken to simulate and calculate the first intervals, The first lightning strike under heavy lightning The lower arrester absorbs energy .

[0103] This example shows that for the [245kA, 250kA] range, under the negative polarity five-fold lightning strike, the first lightning strike SA1 absorbs 38.04kJ of energy, and SA2 absorbs 19.27kJ of energy. Combined with the arrester absorption energy threshold (The arrester energy absorption threshold in Table 4 is 54.96kJ), according to formula (2), the subsequent Maximum absorbed energy of a lightning strike SA1 16.92kJ, SA2 is 35.69kJ, which corresponds to the subsequent lightning amplitude 82.5kA and 167.5kA respectively. The calculated results are 1.90287E-05 and 1.75044E-06 respectively.

[0104] In such Figure 6 Under the spatial distribution of offshore wind farms shown in the figure, the above calculation results and the lightning area of ​​offshore wind farms are combined Substituting into formulas (3) and (4), we get , In this example, the design life of the offshore wind farm is taken as 25 years. Using formula (5), the thermal collapse risk calculation results of SA1 and SA2 under different arrester current carrying capacity selections are obtained.

[0105] Table 4 Calculation results of thermal collapse risk of lightning arresters over the entire life cycle of offshore wind farms

[0106] ;

[0107] According to the calculation results in Table 4, SA1 has a high risk of thermal collapse throughout the life cycle of the wind farm. Due to the inability to conduct timely maintenance, it poses a direct threat to the safe operation of wind turbines in the complex offshore lightning environment. SA2, on the other hand, is located at the bottom of the tower and is less affected by overvoltage. Its risk of instantaneous failure is 94.2% lower than that of SA1. Therefore, SA1 should use a large through-current arrester with a nominal current of 10kA, which can reduce its risk of instantaneous failure by 69.4%. However, in this case, the thermal collapse risk of 10kA SA1 is still more than 5 times that of 5kA SA2. It is possible to further consider selecting larger-sized resistors or parallel multi-column arresters to reduce the risk of instantaneous failure, which proves the application prospects of the present invention in the direction of selection guidance.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for assessing the thermal collapse risk of lightning arresters in the entire life cycle of an offshore wind farm, characterized by: The following steps are involved: S1. Calculate the lightning parameters in the area where the offshore wind farm is located based on the lightning location system data; S2. Based on the offshore wind turbine connection and the lightning down-conduction path, a lightning electromagnetic transient simulation model for the offshore wind turbine is constructed. Combined with the lightning parameters statistically calculated in step S1, the lightning arrester energy simulation calculations under single lightning strikes and multiple lightning strikes are performed respectively. Based on the simulation calculation results, the difference in energy absorption of the lightning arrester of the offshore wind turbine under single lightning strikes and multiple lightning strikes is analyzed; S3. Considering the differences in energy absorption of the arrester under single and multiple lightning strikes, the lightning current amplitude is divided into multiple intervals. For each interval, in a multiple lightning strike scenario, the energy absorbed by the arrester during the first lightning strike is obtained through simulation. The maximum absorbed energy of subsequent lightning strikes is determined based on the arrester's absorption energy threshold, and the lightning current amplitude corresponding to the subsequent lightning strikes is further simulated. S4. Using the lightning parameters calculated in step S1 and the simulation results in step S3, calculate the interval probability of thermal breakdown risk of the arrester under different intervals, different polarities, and different return stroke times of ground lightning; The calculation formula for the interval probability of the thermal breakdown risk of the lightning arrester in step S4 is as follows: （3）； Where, Indicates the interval, positive or negative polarity The probability of thermal collapse risk interval of lightning arrester under heavy lightning strike, , Indicates positive polarity, Indicates negative polarity, when for hour, and Select separately and ,when for hour, and Select separately and , thus obtaining the positive polarity Probability of thermal collapse risk interval of lightning arrester under heavy lightning strike and negative polarity Probability of thermal collapse risk interval of lightning arrester under heavy lightning strike , For the The lower limit of lightning current amplitude in each interval, For the Upper limit of lightning current amplitude in each interval; S5. Considering the spatial characteristics and design life of the entire offshore wind farm, the lightning parameters calculated in step S1 and the calculation results in step S4 are used to calculate the thermal collapse risk of the lightning arrester over the entire life cycle of the offshore wind farm.

2. The method for assessing thermal collapse risk of lightning arresters in the entire life cycle of an offshore wind farm according to claim 1 is characterized by: The lightning parameters in step S1 include ground-to-ground lightning density , the number of return-to-ground lightning, the average frequency of multiple return-to-ground lightning, and the cumulative probability of lightning current amplitude ; Among them, the number of return-to-ground lightning includes the number of positive polarity single return-to-ground lightning , Number of negative polarity single return ground flashes , Number of positive polarity multiple return ground lightning and the number of negative polarity multiple return ground lightning ; Average multiple return ground flash frequency including positive polarity average multiple return ground flash frequency Average frequency of negative polarity multiple return ground flashes ,in, Indicates the number of return strikes of a multi-return ground flash. and Represents positive and negative polarity respectively The percentage of return ground lightning; Cumulative probability of lightning current amplitude The expression is as follows: （1）； Where, Indicates the amplitude of the actual lightning current; Indicates the set lightning current amplitude threshold; and They represent the scale parameter and shape parameter of lightning current amplitude distribution respectively; Based on formula (1), the cumulative probability function of the positive first return stroke lightning current amplitude of multiple return strokes to ground lightning is obtained: , cumulative probability function of negative polarity first return stroke lightning current amplitude , cumulative probability function of positive polarity subsequent return stroke lightning current amplitude Cumulative probability function of the amplitude of subsequent negative polarity return stroke lightning current .

3. The method for assessing thermal collapse risk of lightning arresters in the entire life cycle of an offshore wind farm according to claim 2, characterized in that: Step S2 specifically includes the following steps: S21. Use PSCAD to model the wind turbine blade down conductor, moving contact part, tower, cable body, transformer, lightning arrester and surge protector, and tower bottom switchgear of the offshore wind turbine. The wind turbine blade down conductor, tower, and cable body are modeled using chain equivalent circuits, the moving contact part is modeled using typical parameters, the transformer is modeled using a high-frequency model, the lightning arrester and surge protector are modeled using nonlinear resistors, the tower bottom switchgear is modeled using ground capacitance, and the lightning current is modeled using Heidler function simulation. S22. Use the finite element method to calculate the coupling capacitance between the tower wall, cable armor layer, cable shield layer, and cable core wire, quantify the effect of the coupling on transient energy transfer, and obtain a lightning electromagnetic transient simulation model for offshore wind turbines; S23. Based on the electromagnetic transient simulation model of lightning strikes on offshore wind turbines, simulate single lightning strikes and multiple lightning strikes combined with the average frequency of multiple return ground lightning strikes, and calculate the energy absorbed by the lightning arrester; S24. Compare the energy absorbed by the arrester calculated in step S23 with the energy threshold corresponding to thermal breakdown of the arrester, and analyze the difference in energy absorption of the arrester of the offshore wind turbine under single lightning strikes and multiple lightning strikes based on the comparison result.

4. The method for assessing thermal collapse risk of lightning arresters in the entire life cycle of an offshore wind farm according to claim 3 is characterized by: Step S3 specifically includes the following steps: S31. Divide the lightning current amplitude into interval, set The first interval, in Heavy lightning strike, first lightning strike The energy absorbed by the lower arrester is , calculate the subsequent Maximum absorbed energy of a lightning strike : （2）； Where, Indicates the energy absorption threshold of the arrester; S32. Assume that the amplitude of the subsequent lightning current is smaller than that of the first lightning current, and assume that all subsequent lightning currents are smaller than that of the first lightning current. The amplitude of the lightning current of the secondary lightning strike is equal. At this time, simulation calculation is performed to determine whether the The corresponding lightning current amplitude .

5. The method for assessing thermal collapse risk of lightning arresters in the entire life cycle of an offshore wind farm according to claim 4, characterized in that: Step S5 specifically includes the following steps: S51. Calculate the number of positive polarity multiple lightning strikes suffered by offshore wind farm wind turbines each year and negative polarity multiple lightning strikes : （3）； （4）； Where, represents the annual average density of ground-to-ground flashes; Indicates the lightning-inducing area of ​​offshore wind farm; S52, combined with positive polarity The proportion of return ground lightning , under negative polarity The proportion of return ground lightning , under positive polarity Probability of thermal collapse risk interval of lightning arrester under heavy lightning strike and negative polarity Probability of thermal collapse risk interval of lightning arrester under heavy lightning strike , and consider the design life of offshore wind farms , assessing the risk of thermal collapse over the entire life cycle of the offshore wind farm : （5）。

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