Multi-lightning-stroke overvoltage protection method for overhead line-direct-current submarine cable conversion station

Abstract

The invention discloses a multi-lightning overvoltage protection method for an overhead line-direct current submarine cable conversion station, and belongs to the technical field of lightning overvoltage protection, and the method comprises the steps: building an electromagnetic transient simulation model of the overhead line-direct current submarine cable conversion station; building a lightning current source model; selecting the most stringent waveform and constructing a multi-lightning-stroke lightning current source; building a reactor broadband equivalent circuit model, simulating the working condition of a lightning shielding failure like-polarity line, and preliminarily determining the inductance value of the reactor; evaluating whether the reversed-polarity lightning impulse overvoltage of the direct-current submarine cable exceeds a tolerance range, and selecting an optimal inductance value which enables the reversed-polarity lightning impulse overvoltage of the direct-current submarine cable to meet requirements; and optimizing a lightning arrester configuration scheme, and selecting an optimal scheme with the best overvoltage suppression effect and the electrical stress of the lightning arrester meeting the requirement. By adopting the method, the problem that a conversion station and submarine cable lightning overvoltage protection scheme cannot be designed according to the direct-current submarine cable lightning impulse withstand voltage tolerance characteristic in the prior art is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of lightning overvoltage protection, and in particular to a method for protecting an overhead line-DC submarine cable conversion station from multiple lightning strikes and overvoltages. Background Art

[0002] The DC line of this first integrated land-sea ±500 kV flexible DC transmission project in China and abroad utilizes a hybrid structure of overhead lines and submarine cables, connected via a transfer station. While submarine cables are immune to direct lightning strikes, lightning overvoltages generated by lightning strikes on the DC overhead lines can be transmitted as intrusion waves to the transfer station and submarine cables, threatening the insulation safety of equipment within the transfer station and the connected submarine cables. Current manufacturing capabilities of DC submarine cables are limited, with a single-polarity lightning impulse withstand voltage of only 1175 kV and a reverse-polarity withstand voltage of 630 kV. This creates a relatively limited insulation margin, necessitating the design of a scientific and rational lightning overvoltage protection solution for this system.

[0003] Existing research on the effects of lightning overvoltage primarily focuses on single lightning strikes, using typical single lightning current waveforms such as 2.6 / 50μs, 2.0 / 50μs, and 1 / 70μs to simulate overvoltages and propose corresponding protection schemes. Long-term statistical data from a province's lightning location system indicates that multiple return strokes account for over 40% of total lightning-to-ground lightning strikes, and in recent years, there have been numerous incidents of multiple lightning strikes causing damage and failure of equipment such as lightning arresters within stations. Therefore, it is necessary to design effective protection against lightning intrusion waves in converter stations subjected to multiple lightning strikes. Furthermore, there are significant differences in the multiple lightning waveforms recommended by existing standards. For example, the IEEE recommends simulating the first and subsequent return strokes of negative polarity using 5.63 / 77.5μs and 0.75 / 30.2μs, respectively, while the IEC recommends 1 / 200μs and 0.25 / 100μs. Differences in lightning current waveform parameters will significantly affect the overvoltage level that the equipment is subjected to, resulting in large deviations in protection design. Waveform factors have not yet been fully considered in protection design.

[0004] Although relevant research has explored the propagation mechanism and protection strategies of lightning intrusion waves, the existing technology for overvoltage analysis and protection of DC overhead lines and submarine cables still has the following shortcomings: First, existing research on lightning intrusion waves is mostly limited to single lightning strike situations. The subsequent return stroke waveforms of multiple lightning strikes have a shorter wavefront time, which is quite different from a single lightning strike. In addition, multiple lightning strikes have a short-term energy accumulation effect, and the energy absorbed by the lightning arrester far exceeds that of a single lightning strike, resulting in a major safety hazard in the protection design.

[0005] Second, existing research lacks a systematic analysis of the impact of lightning current waveform parameters on inrush wave overvoltage levels and electrical stresses in protective devices. Typical protective designs often use standard waveforms, such as 2.6 / 50μs and 1 / 70μs, for simulation analysis. These analyses fail to incorporate the differences between first and subsequent return stroke waveforms recommended by standards such as IEEE or IEC. Consequently, a methodology for assessing the most stringent overvoltages and arrester electrical stresses based on different waveform characteristics has yet to be established.

[0006] Furthermore, existing technologies haven't fully considered the differences in insulation capacity of DC submarine cables to optimize protection strategies. When the DC overhead pole line at the incoming section of a converter station is struck by a reverse-polarity lightning current, the DC operating voltage superimposed on the reverse-polarity lightning impulse voltage can cause a polarity reversal of the overvoltage at the submarine cable access point. At this point, a high electric field exists between the space charge in the submarine cable and the electrodes, leading to strong electric field distortion in the cable insulation, significantly reducing the cable's insulation level. Existing protection schemes lack effective suppression measures for lightning intrusion wave overvoltages at the submarine cable, especially reverse-polarity lightning overvoltages.

[0007] In summary, existing technologies still lack a complete and effective modeling analysis and protection design system when faced with practical factors such as multiple lightning strikes, differences in current waveforms, and limited lightning impulse insulation levels of DC submarine cables. This makes it difficult to adapt to the high-reliability operation requirements of integrated land-sea DC transmission projects in complex lightning environments. Summary of the Invention

[0008] The purpose of the present invention is to provide a method for protecting an overhead line-DC submarine cable conversion station from multiple lightning strikes to overvoltages, so as to solve the problems mentioned in the background art.

[0009] To achieve the above object, the present invention provides a method for protecting an overhead line-DC submarine cable converter station from multiple lightning strikes and overvoltages, comprising the following steps: S1. Establish an electromagnetic transient simulation model of the overhead line-DC submarine cable conversion station based on the electrical wiring diagram of the conversion station, the incoming line section tower, and the relevant parameters of the equipment in the conversion station; S2. Based on the statistical results of artificial lightning induction and lightning location systems, as well as relevant standards, a lightning current waveform parameter model is proposed and a lightning current source model is constructed; S3. Study the impact of lightning current waveform parameters on the overvoltage amplitude of station equipment, reverse polarity voltage of DC submarine cables, and electrical stress of lightning arresters. Select the most stringent waveform and build multiple lightning current sources. S4. Build a broadband equivalent circuit model of the reactor to simulate the working conditions of a lightning shielding failure on a line with the same polarity. Study the impact of the reactor inductance on the overvoltage of various equipment points within the station and the DC submarine cable, and preliminarily determine the reactor inductance value. S5. Based on the most severe lightning current waveform and the reactor selected in step S4, simulate the reverse polarity line working condition of the lightning current shielding strike to evaluate whether the reverse polarity lightning impulse overvoltage of the DC submarine cable exceeds the tolerance range. If it does not meet the requirements, return to S4 to increase the inductance value of the reactor until the optimal inductance value is selected so that the reverse polarity lightning impulse voltage of the DC submarine cable meets the requirements; S6. Optimize the lightning arrester configuration plan based on the overvoltage distribution characteristics of the equipment after adding the inductor, and check whether the lightning arrester electrical stress meets the requirements. If the lightning arrester electrical stress exceeds its tolerance range, consider increasing the number of parallel lightning arrester columns and select the optimal solution with the best overvoltage suppression effect and the lightning arrester electrical stress meeting the requirements.

[0010] Preferably, step S1 specifically includes: S11. According to the electrical wiring diagram of the conversion station, some equipment of the conversion station is simulated with impact inlet capacitors; S12. Setting the scatter points of the nonlinear resistor volt-ampere characteristics in the simulation according to the arrester technical parameters and volt-ampere characteristics; S13. Build a tower multi-wave impedance model based on the incoming line segment tower diagram.

[0011] Preferably, step S2 includes the following steps: S21. Based on the lightning current waveform parameters under different return strokes obtained by artificial lightning induction, the average time of the lightning current wave front and the average time of the wave tail under subsequent return strokes are calculated, and a lightning current parameter model of actual lightning stroke is proposed. At the same time, the Heidler lightning current waveform function is used to fit it. S22. Propose multiple lightning current parameter models based on the statistical parameters in step S21; S23. Combined with the statistical data of the lightning location system, calculate the time interval between two adjacent return strokes and the proportion of different return stroke times, determine the number of return strokes and the time interval between two adjacent return strokes; determine the lightning current amplitude by comparing the lightning resistance level of the tower and the maximum shielding current; establish a lightning current source model in the simulation software.

[0012] Preferably, in step S21, the actual lightning current source model is fitted using the Heidler function, and the obtained formula is as follows: ; Where: Indicates lightning current, is the peak base current, is the wavefront attenuation coefficient, is the wave tail attenuation coefficient, is a parameter describing the steepness of the lightning base current, and η is the current peak correction coefficient.

[0013] Preferably, step S23 is specifically as follows: combining the statistical data of the lightning location system, calculating the corresponding time intervals of two adjacent return strokes and the proportions of different return stroke times, and determining the time intervals and return stroke times of multiple lightning strikes; determining the lightning current amplitude by comparing the tower shielding failure lightning resistance level and the maximum shielding failure current, using the electrical geometry model to calculate the maximum shielding failure current of the tower, and then simulating the tower shielding conditions of lightning currents of different amplitudes through software to obtain the maximum lightning current amplitude that will not cause flashover of the insulator string, as the tower shielding failure lightning resistance level, and taking the smaller value of the two as the lightning current amplitude of single lightning strikes and multiple lightning strikes; establishing a single lightning strike lightning current source model by connecting a controlled current source in parallel with the lightning channel wave impedance.

[0014] Preferably, step S3 is specifically as follows: S31. Based on the lightning current source model constructed in step S2, simulate and analyze the overvoltage distribution characteristics of the equipment in the station when the lightning current waveform parameters are different; S32. Compare the stresses generated on the arrester by different lightning current parameters, and select the strict waveform based on the analysis results of S31.

[0015] Preferably, step S31 is specifically as follows: based on the lightning current source model constructed in step S2, simulation and analysis are performed on the overvoltage distribution characteristics of the equipment in the station when the lightning current waveform parameters are different, and further consideration is given to the working conditions of lightning shielding with different polarities, specifically including two working conditions: negative polarity lightning shielding strikes the positive line and positive polarity lightning shielding strikes the negative line. At this time, the submarine cable will be subjected to reverse polarity voltage.

[0016] Preferably, step S4 includes the following steps: S41. Build a broadband equivalent circuit for the reactor and set the reactor inductance, parallel capacitance at both ends, and capacitance to ground parameters. S42. Simulate the working conditions of the same polarity line caused by lightning shielding and study the inhibitory effect of the inductance value of the reactor on overvoltage.

[0017] Preferably, step S5 is specifically as follows: based on the most severe lightning current waveform selected in step S3 and the reactor selected in step S4, simulate the lightning current shielding reverse polarity line working condition, evaluate whether the reverse polarity lightning impulse overvoltage of the DC submarine cable exceeds the tolerance range, if the reverse polarity overvoltage has exceeded the tolerance level of the DC submarine cable, return to step S4 and select a larger inductance value for re-verification until the optimal inductance value is selected so that the reverse polarity lightning impulse withstand voltage of the DC submarine cable meets the requirements.

[0018] Preferably, step S6 includes the following steps: S61. Optimize the lightning arrester configuration plan based on the overvoltage distribution of the equipment in the station after adding the reactor; S62. Simulate and analyze the overvoltage characteristics of the station equipment under different lightning arrester configuration schemes, verify the insulation margin of the station equipment, the same-polarity lightning impulse withstand voltage of the DC submarine cable, and the electrical stress of each lightning arrester, and select the best scheme.

[0019] Therefore, the present invention adopts the above-mentioned method for protecting overhead line-DC submarine cable converter station from multiple lightning strikes and has the following beneficial effects: (1) The present invention proposes a lightning protection design method for overhead line-DC submarine cable conversion station. Combining the lightning location system and artificial lightning induction data, a variety of lightning current waveform parameter models are proposed. The lightning current source model and the conversion station model are constructed using PSCAD software. The electrical stress of the equipment under different lightning current waveform parameters is simulated and analyzed. The most stringent waveform for lightning protection design is proposed, and a multiple lightning current source is constructed. This solves the problem that the existing technology only considers a single lightning strike, ignores the influence of lightning current waveform parameters, and designs protection schemes in a one-sided manner.

[0020] (2) Design lightning protection methods for DC submarine cables and conversion station equipment by configuring reactors and lightning arresters. At the same time, consider the situation of lightning current striking the reverse polarity line and evaluate the reverse polarity lightning impulse tolerance of DC submarine cables. This solves the problem that existing technologies cannot design lightning overvoltage protection schemes for conversion stations and submarine cables based on the lightning impulse tolerance voltage tolerance characteristics of DC submarine cables.

[0021] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a flow chart of a method for protecting an overhead line-DC submarine cable conversion station from multiple lightning strikes to overvoltages according to an embodiment of the present invention; Figure 2 1 is a schematic diagram of a broadband equivalent circuit of a reactor after adding a lightning arrester according to an embodiment of the present invention; Figure 3 is a wiring diagram of a conversion station according to an embodiment of the present invention; Figure 4 is a diagram showing the distribution of overvoltage amplitudes of equipment according to an embodiment of the present invention; Figure 5 The influence of the inductance value of the reactor of the embodiment of the present invention on the overvoltage amplitude; Figure 6 is a schematic diagram of solution 1 of an embodiment of the present invention; Figure 7 Schematic diagram of solution 2 of an embodiment of the present invention; Figure 8 Schematic diagram of solution three of an embodiment of the present invention. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0024] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0025] Example like Figure 1 As shown, the present invention provides a method for protecting an overhead line-DC submarine cable conversion station from multiple lightning strikes and overvoltages, comprising the following steps: S1. Based on the electrical wiring diagram of the conversion station, the incoming line section towers, and the relevant parameters of the equipment in the conversion station, an electromagnetic transient simulation model of the overhead line-DC submarine cable conversion station is established.

[0026] S2. Based on the statistical results of artificial lightning induction and lightning location systems, as well as relevant standards, a lightning current waveform parameter model is proposed and a lightning current source model is constructed.

[0027] S3. Study the impact of lightning current waveform parameters on the overvoltage amplitude of station equipment, the reverse polarity voltage of DC submarine cables, and the electrical stress of lightning arresters, select the most stringent waveform, and build multiple lightning current sources.

[0028] S4. Build a broadband equivalent circuit model of the reactor to simulate the working conditions of the same-polarity line caused by lightning shielding failure, study the impact of the reactor inductance on the overvoltage of various equipment points in the station and the DC submarine cable, and preliminarily determine the reactor inductance value.

[0029] S5. Based on the most severe lightning current waveform and the reactor selected in step S4, simulate the reverse polarity line working condition of the lightning current shielding strike and evaluate whether the reverse polarity lightning impulse overvoltage of the DC submarine cable exceeds the tolerance range. If the requirement is not met, return to S4 to increase the inductance value of the reactor until the optimal inductance value is selected so that the reverse polarity lightning impulse voltage of the DC submarine cable meets the requirement.

[0030] S6. Optimize the lightning arrester configuration plan based on the overvoltage distribution characteristics of the equipment after adding the inductor, and check whether the lightning arrester electrical stress meets the requirements. If the lightning arrester electrical stress exceeds its tolerance range, consider increasing the number of parallel lightning arrester columns and select the optimal solution with the best overvoltage suppression effect and the lightning arrester electrical stress meeting the requirements.

[0031] In this embodiment, step S1 specifically includes: S11. According to the electrical wiring diagram of the conversion station, some equipment of the conversion station is simulated by using the impact inlet capacitor. In this embodiment, the electrical wiring diagram of the conversion station is as follows: Figure 3 The device inlet capacitance is shown in Table 1.

[0032] Specifically: using PSCAD / EMTDC electromagnetic transient simulation software and a segmented modeling method, the conversion station is mostly composed of switchgear. Under the action of lightning waves, the disconnectors, circuit breakers, transformers and other equipment in the conversion station can be equivalent to impact entrance capacitance. The volt-ampere characteristics of the lightning arrester in the station are simulated using nonlinear resistors, and the Bergeron model is used to simulate the connecting lines of the equipment in the station.

[0033] Table 1 Inlet capacitance of different devices ;

[0034] S12. Set the scatter points of the nonlinear resistor's volt-ampere characteristic in the simulation based on the arrester's technical parameters and volt-ampere characteristics. In this embodiment, the station arrester has a coordinated current of 20 kA, a residual voltage of 1050 kV, and a maximum allowable absorbed energy of 5000 kJ. The arrester's volt-ampere characteristics are shown in Table 2: Table 2 Arrester volt-ampere characteristics ;

[0035] S13. Build a multi-wave impedance model of the tower according to the incoming line segment tower diagram. In this embodiment, the tower models are JG372 and ZC375. The wave impedance values ​​at different positions of the tower are calculated as shown in Table 3.

[0036] Table 3 Tower and cross-arm wave impedance (unit: kV) ;

[0037] In this embodiment, step S13 specifically includes: simulating the overhead line using a frequency-dependent model, calculating the wave impedance of the main frame, bracket, and tower crossarm based on the tower model, height, crossarm length, span, conductor height and splitting, and ground wire height and splitting, and building a tower multi-wave impedance model. The specific formula is as follows: Wave impedance of each part of the main frame The calculation formula is as follows: ; in, Indicates the tower The equivalent radius of the segment is calculated as follows: ; in, For the tower Partial strut radius; is the radius of the bottom support of the tower; For the tower The distance between two adjacent pillars; It is the distance between two adjacent pillars at the bottom of the tower.

[0038] Wave impedance of each part of the bracket Calculated by the following formula: ; The tower crossarm is also simulated by a distributed parameter line segment, and its wave impedance is The calculation formula is as follows: ; in, For the tower Part of the cross arm equivalent radius, Indicates the Partial cross-arm height. The DC submarine cable simulation uses a frequency-dependent model; the insulator flashover criterion model considers the physical mechanism of insulator flashover and adopts the pilot development model recommended by CIGRE (International Conference on Large Electric Systems), as shown in the following formula: ; in, t For time; U ( t ) is the impulse voltage across the insulator; is the leader length; d is the insulator dry arc distance; E 0 is the minimum field strength to maintain streamer development; is the leading development speed coefficient. Take 0.8, E 0 out of 600.

[0039] In this embodiment, step S2 includes the following steps: S21. According to the different lightning current waveform parameters under artificial lightning induction, the average time of the lightning current wave front and the average time of the wave tail under subsequent return stroke are calculated, and the actual lightning current parameter model is proposed. At the same time, the Heidler lightning current waveform function is used to fit it and the Heidler lightning current waveform is obtained. The value of the parameter, is the wavefront attenuation coefficient, is the wave tail attenuation coefficient, is a parameter describing the steepness of lightning base current. is the current peak correction factor.

[0040] Step S21 is specifically as follows: according to the results of the artificial lightning induction experiment, including the number of return strokes under different lightning induction times, the lightning current amplitude, wavefront time, wavetail time and time interval parameters corresponding to each return stroke, the average value of the wavefront and wavetail time is calculated to obtain the actual subsequent return stroke waveform parameter model.

[0041] The results of the artificial lightning induction experiment in this embodiment are shown in Table 4. The subsequent return stroke lightning current waveform parameters are 0.36 / 18μs, and the subsequent return stroke current waveform parameters are obtained by fitting. 、 、 .

[0042] Table 4 Results of artificial lightning induction experiments ;

[0043] S22. According to the provisions of IEC 62305-1, IEEE Std 1410-2010, and GB / T 50064-2014, and in combination with the statistical parameters in step S21, a plurality of lightning current parameter models are proposed.

[0044] In this embodiment, according to the subsequent return stroke lightning current waveform parameters obtained in step S21 and relevant standards, lightning current parameter models are established as 2.6 / 50μs, 5.72 / 77μs, 0.36 / 18μs, 1 / 200μs and 0.25 / 100μs.

[0045] Lightning current waveform parameter models were supplemented based on relevant standards. Specifically, the IEC 62305-1 standard specifies waveform parameters of 1 / 200 μs for the first negative short-duration lightning stroke and 0.25 / 100 μs for subsequent short-duration lightning strokes. The IEEE Std 1410-2010 standard specifies waveform parameters of 5.63 / 77.5 μs for the first negative return stroke. Furthermore, GB / T 50064-2014 specifies the use of 2.6 / 50 μs as the single-stroke lightning current waveform parameters. Based on these lightning current waveforms, various lightning current parameter models were proposed. The lightning current source model was fitted using the Heidler function, as shown in the following equation. The fitting results are shown in Table 5.

[0046] ; Where: Indicates lightning current, is the peak base current, is the wavefront attenuation coefficient, is the wave tail attenuation coefficient, is a parameter describing the steepness of lightning base current. is the current peak correction factor.

[0047] Table 5 Heidler function fitting table ;

[0048] S23. Combine statistical data from the lightning location system to calculate the time interval between two consecutive return strokes and the proportion of different return strokes. Determine the number of return strokes and the time interval between two consecutive return strokes. Determine the lightning current amplitude by comparing the tower's lightning resistance level with the maximum shielding failure current. Build a lightning current source model in PSCAD / EMTDC software.

[0049] Step S23 specifically involves: combining statistical data from the lightning location system, calculating the corresponding time intervals between two adjacent return strokes and the proportions of different return stroke times, and determining the time intervals and number of return strokes for multiple lightning strikes; determining the lightning current amplitude by comparing the tower's shielding failure withstand level and the maximum shielding failure current; calculating the tower's maximum shielding failure current using the Electrical Geometry Model (EGM); then simulating tower shielding current conditions with different amplitudes using PSCAD / EMTDC software to determine the maximum lightning current amplitude that does not cause insulator string flashover, which is used as the tower's shielding failure withstand level. The smaller of the two values ​​is used as the lightning current amplitude for single and multiple lightning strikes. A single lightning current source model is established by connecting a controlled current source in parallel with the lightning channel wave impedance.

[0050] In this example, the average time interval between multiple lightning strikes was statistically determined to be 35-80 ms. Among multiple return-to-ground lightning strikes, 2-5 return strikes accounted for 79.83%. Therefore, the number of return strikes was set to 5, and the interval was set to 10 ms without affecting the simulation results. The maximum shielding failure current of the tower was calculated using the electrical geometry model to be 20 kA. Simulation showed that the tower's shielding failure withstand level was greater than 20 kA, so 20 kA was selected as the lightning current amplitude, and Tower 1, closest to the conversion station, was chosen as the lightning strike point. Lightning currents were simulated in PSCAD / EMTDC software using a controlled current source in parallel with a lightning wave impedance. Components from the CSMF library were used to simulate the Heidler function, and the lightning wave impedance was set to 800 Ω.

[0051] Step S3 is specifically as follows: S31. Based on the lightning current source model constructed in step S2, simulate and analyze the overvoltage distribution characteristics of the equipment in the station, considering the working conditions of lightning strikes of different polarities. That is, when negative polarity lightning strikes the positive line, the cable on the positive line will be subjected to negative polarity voltage. Similarly, when positive polarity lightning strikes the negative line, the cable on the negative line will generate positive polarity overvoltage.

[0052] In this embodiment, the overvoltage distribution in the station is as follows: Figure 4 As shown in the figure, it can be seen that for equipment closer to the lightning strike point, the shorter the wavefront time of the lightning current, the higher the overvoltage generated on the equipment in the station under the same lightning current amplitude. Therefore, the overvoltage generated by 0.25 / 100 μs is higher; but since the submarine cable is far away from the lightning strike point, there is wave attenuation and refraction and reflection, and its overvoltage amplitude appears in the middle and late stages of the lightning current propagation oscillation. The 0.36 / 18 μs wave tail is short and the lightning current energy duration is limited. The overvoltage at the submarine cable access point is less than 1 / 200 μs; and the reverse polarity voltages caused by 1 / 200 μs and 0.25 / 100 μs are relatively high, at 177 kV and 151 kV, respectively.

[0053] S32. Compare the stresses generated on the arrester by different lightning current parameters, and select the most demanding waveform based on the analysis results of S31. Specifically, study the effects of different lightning current waveform parameters on the overvoltage in the station and the reverse polarity voltage of the DC submarine cable, compare the electrical stress of the arrester when the lightning current parameters are different, and select the waveform with the highest overvoltage of the station equipment and the highest reverse polarity voltage of the submarine cable and the maximum energy absorbed by the arrester as the most demanding waveform for lightning protection design. Combine the calculated data in S2 to build a multiple lightning current source.

[0054] In this embodiment, among the above-mentioned single lightning strike waveforms, the arrester absorbs the largest energy, reaching 148 kJ, during the 1 / 200 μs shielding strike. Due to the same lightning current amplitude, the current amplitude difference flowing through the arrester is small. Considering the electrical stress and overvoltage amplitude of the arrester, the first return stroke of 1 / 200 μs and the subsequent return stroke of 0.25 / 100 μs are selected as the most stringent waveform design protection scheme.

[0055] Step S4 includes the following steps: S41. Build a broadband equivalent circuit for the reactor and set the parameters for the reactor inductance, parallel capacitance at both ends, and capacitance to ground at both ends. In actual projects, a lightning arrester needs to be connected in parallel at both ends of the reactor to protect the reactor. After adding the lightning arrester, the broadband equivalent circuit of the reactor is as follows: Figure 2 shown.

[0056] In this embodiment, the capacitances before and after the reactor to ground are both 300 pF, and the parallel capacitance at both ends of the reactor is 400 pF.

[0057] S42, the working condition of the simulation lightning shielding same polarity line is simulated, and the suppression effect of the reactor inductance value on the overvoltage is researched, specifically: when the selected severe waveform in S3 is used to simulate the shielding line, the suppression effect of the series reactor on the overvoltage of the equipment after the reactor is analyzed, and the change of the overvoltage of the equipment before the reactor is also needed to be concerned; the overvoltage of the equipment in the station under different inductance values is simulated, and the suppression effect of the different reactor inductance values on the overvoltage of the equipment after the reactor and the influence on the amplitude of the overvoltage of the equipment before the reactor are researched; the influence of the reactor on the overvoltage distribution in the station and the economy are comprehensively considered to preliminarily determine the inductance value of the configured reactor.

[0058] As shown in the simulation results of the reactor with an inductance value of 2, 4, 6 and 8 mH in the embodiment, Figure 5 it can be seen from the figure that when the inductance value is 4 mH, the overvoltage of the equipment after the reactor is reduced by 294 kV, and the suppression of the reactor on the overvoltage has a saturation effect, but the overvoltage of the equipment before the reactor increases significantly after the reactor is increased, and with the increase of the inductance value of the reactor, the overvoltage of the equipment before the reactor increases slightly, so a 4 mH reactor is preliminarily analyzed to suppress the overvoltage.

[0059] Step S5 is specifically: based on the most severe lightning current waveform selected in step S3 and the reactor selected in step S4, the lightning current shielding opposite polarity line working condition is simulated, and whether the opposite polarity lightning impulse overvoltage of the DC submarine cable exceeds the withstand range is evaluated, if the opposite polarity overvoltage has exceeded the withstand level of the DC submarine cable, return to step S4 to select a larger inductance value to re-verify until the best inductance value is selected to make the opposite polarity lightning impulse withstand voltage of the DC submarine cable meet the requirements.

[0060] In this embodiment, when the 4 mH reactor is added, the opposite polarity voltage is lower than 630 kV when the most severe waveform is used, which meets the requirements, and the 4 mH reactor selected in step S4 is comprehensively considered to suppress the overvoltage.

[0061] Step S6 includes the following steps: S61, according to the overvoltage distribution of the equipment in the station after the reactor is added, the configuration scheme of the surge arrester is optimized, specifically: according to the overvoltage distribution characteristics of the equipment in the station obtained in step S4, by increasing the surge arrester, adjusting the position of the surge arrester and setting the line surge arrester and the like, a variety of configuration schemes of the surge arrester of the converter station are proposed under the premise of considering the reactor surge arrester, so as to optimize the configuration scheme of the surge arrester.

[0062] As shown in Figure 6 , in this embodiment, the overvoltage at L1 point is high after the reactor is added, so the following three configuration schemes are considered: scheme 1, moving DL2 surge arrester to L1; scheme 2, adding a column surge arrester at L1 based on the original configuration scheme; scheme 3, moving DL2 surge arrester to L1 and adding a column line surge arrester at the tower closest to the converter station.

[0063] S62. Simulate and analyze the overvoltage characteristics of station equipment under different lightning arrester configurations. Verify the insulation margin of station equipment, the same-polarity lightning impulse withstand voltage of the DC submarine cable, and the electrical stress of each lightning arrester to select the optimal solution. Verify that the lightning arrester electrical stress meets the requirements. If the lightning arrester electrical stress exceeds its tolerance range, consider increasing the number of parallel lightning arrester columns. Select the optimal solution that provides the best overvoltage suppression and meets the lightning arrester electrical stress requirements.

[0064] In this embodiment, the simulation results obtained using the most stringent waveform are shown in Table 6. When Scheme 1 is used, the maximum overvoltage at the coupling capacitor C1 is 1303 kV; when Scheme 2 is used, the maximum overvoltage at the insulating bushing is 1101 kV; when Scheme 3 is used, the maximum overvoltage at the insulating bushing is 1003 kV, and the submarine cable overvoltage is 767 kV. When Scheme 3 is used, the stress of each lightning arrester is within the tolerance range, and there is no need to optimize the number of parallel lightning arrester columns. At the same time, the equipment insulation margin is high, so Scheme 3 is selected as the best scheme.

[0065] Table 6 Overvoltage amplitude of equipment under different lightning arrester configuration schemes (unit: kV) ;

[0066] On the one hand, the present invention takes into account the characteristic of the short subsequent return stroke wavefront time of multiple lightning strikes, studies the influence of different lightning current waveform parameters on the overvoltage of equipment in the station, proposes a method for identifying the most severe overvoltage conditions, and takes into account the short-time energy accumulation effect of multiple lightning strikes, and proposes an evaluation method for the electrical stress of multiple lightning arresters.

[0067] On the other hand, the present invention takes into account the limited lightning impulse withstand voltage of the DC submarine cable, and designs an overvoltage protection scheme by integrating two methods: series inductor and optimized lightning arrester configuration scheme, while taking into account the verification of the reverse polarity lightning impulse withstand voltage of the DC submarine cable, providing a reference and reference for the multiple lightning protection design and simulation analysis of the overhead line-DC submarine cable conversion station.

[0068] Therefore, the present invention adopts the above-mentioned overhead line-DC submarine cable conversion station multiple lightning overvoltage protection method to solve the problem that the existing technology cannot design the conversion station and submarine cable lightning overvoltage protection scheme based on the DC submarine cable lightning impulse withstand voltage tolerance characteristics.

[0069] 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 protecting overhead line-DC submarine cable conversion stations from multiple lightning strikes and overvoltages, characterized in that: The following steps are involved: S1. Establish an electromagnetic transient simulation model of the overhead line-DC submarine cable conversion station based on the electrical wiring diagram of the conversion station, the incoming line section tower, and the relevant parameters of the equipment in the conversion station; S2. Based on the statistical results of artificial lightning induction and lightning location systems, as well as relevant standards, a lightning current waveform parameter model is proposed and a lightning current source model is constructed; S3. Study the impact of lightning current waveform parameters on the overvoltage amplitude of station equipment, reverse polarity voltage of DC submarine cables, and electrical stress of lightning arresters. Select the most stringent waveform and build multiple lightning current sources. S4. Build a broadband equivalent circuit model of the reactor to simulate the working conditions of a lightning shielding failure on a line with the same polarity. Study the impact of the reactor inductance on the overvoltage of various equipment points within the station and the DC submarine cable, and preliminarily determine the reactor inductance value. S5. Based on the most severe lightning current waveform and the reactor selected in step S4, simulate the reverse polarity line working condition of the lightning current shielding strike to evaluate whether the reverse polarity lightning impulse overvoltage of the DC submarine cable exceeds the tolerance range. If it does not meet the requirements, return to S4 to increase the inductance value of the reactor until the optimal inductance value is selected so that the reverse polarity lightning impulse voltage of the DC submarine cable meets the requirements; S6. Optimize the lightning arrester configuration plan based on the overvoltage distribution characteristics of the equipment after adding the inductor, and check whether the lightning arrester electrical stress meets the requirements. If the lightning arrester electrical stress exceeds its tolerance range, consider increasing the number of parallel lightning arrester columns and select the optimal solution with the best overvoltage suppression effect and the lightning arrester electrical stress meeting the requirements.

2. The method for protecting an overhead line-DC submarine cable converter station from multiple lightning strikes and overvoltages according to claim 1, wherein: Step S1 specifically includes: S11. According to the electrical wiring diagram of the conversion station, some equipment of the conversion station is simulated with impact inlet capacitors; S12. Setting the scatter points of the nonlinear resistor volt-ampere characteristics in the simulation according to the arrester technical parameters and volt-ampere characteristics; S13. Build a tower multi-wave impedance model based on the incoming line segment tower diagram.

3. The method for protecting an overhead line-DC submarine cable conversion station from multiple lightning strikes to overvoltage according to claim 1, characterized in that: Step S2 includes the following steps: S21. Based on the lightning current waveform parameters under different return strokes obtained by artificial lightning induction, the average time of the lightning current wave front and the average time of the wave tail under subsequent return strokes are calculated, and a lightning current parameter model of actual lightning stroke is proposed. At the same time, the Heidler lightning current waveform function is used to fit it. S22. Propose multiple lightning current parameter models based on the statistical parameters in step S21; S23. Combined with the statistical data of the lightning location system, calculate the time interval between two adjacent return strokes and the proportion of different return stroke times, determine the number of return strokes and the time interval between two adjacent return strokes; determine the lightning current amplitude by comparing the lightning resistance level of the tower and the maximum shielding current; establish a lightning current source model in the simulation software.

4. The method for protecting an overhead line-DC submarine cable converter station from multiple lightning strikes and overvoltages according to claim 3, wherein: In step S21, the actual lightning current source model is fitted using the Heidler function, and the resulting formula is as follows: ； Where: Indicates lightning current, is the peak base current, is the wavefront attenuation coefficient, is the wave tail attenuation coefficient, is a parameter describing the steepness of the lightning base current, and η is the current peak correction coefficient.

5. The method for protecting an overhead line-DC submarine cable conversion station from multiple lightning strikes to overvoltage according to claim 4, characterized in that: Step S23 is specifically as follows: combining the statistical data of the lightning location system, calculating the corresponding time intervals of two adjacent return strokes and the proportion of different return stroke times, and determining the time intervals and return stroke times of multiple lightning strikes; determining the lightning current amplitude by comparing the tower shielding failure lightning withstand level and the maximum shielding failure current, and using the electrical geometry model to calculate the maximum shielding failure current of the tower, and then using software to simulate the tower shielding failure conditions of lightning currents of different amplitudes to obtain the maximum lightning current amplitude that will not cause flashover of the insulator string, as the tower shielding failure lightning withstand level, and taking the smaller value of the two as the lightning current amplitude of single lightning strike and multiple lightning strikes; and establishing a single lightning strike lightning current source model by connecting a controlled current source in parallel with the lightning channel wave impedance.

6. The method for protecting an overhead line-DC submarine cable converter station from multiple lightning strikes and overvoltages according to claim 1, wherein: Step S3 is specifically as follows: S31. Based on the lightning current source model constructed in step S2, simulate and analyze the overvoltage distribution characteristics of the equipment in the station when the lightning current waveform parameters are different; S32. Compare the stresses generated on the arrester by different lightning current parameters, and select the strict waveform based on the analysis results of S31.

7. The method for protecting an overhead line-DC submarine cable conversion station from multiple lightning strikes to overvoltage according to claim 6, characterized in that: Step S31 is specifically as follows: based on the lightning current source model constructed in step S2, simulation and analysis are performed on the overvoltage distribution characteristics of the equipment in the station when the lightning current waveform parameters are different, and further consideration is given to the working conditions of lightning shielding with different polarities, specifically including two working conditions: negative polarity lightning shielding strikes the positive line and positive polarity lightning shielding strikes the negative line. At this time, the submarine cable will be subjected to reverse polarity voltage.

8. The method for protecting an overhead line-DC submarine cable converter station from multiple lightning strikes and overvoltages according to claim 1, characterized in that: Step S4 includes the following steps: S41. Build a broadband equivalent circuit for the reactor and set the reactor inductance, parallel capacitance at both ends, and capacitance to ground parameters. S42. Simulate the working conditions of the same polarity line caused by lightning shielding and study the inhibitory effect of the inductance value of the reactor on overvoltage.

9. The method for protecting an overhead line-DC submarine cable conversion station from multiple lightning strikes to overvoltage according to claim 1, characterized in that: Step S5 is specifically as follows: based on the most severe lightning current waveform selected in step S3 and the reactor selected in step S4, simulate the reverse polarity line working condition of the lightning current shielding, and evaluate whether the reverse polarity lightning impulse overvoltage of the DC submarine cable exceeds the tolerance range. If the reverse polarity overvoltage has exceeded the tolerance level of the DC submarine cable, return to step S4 and select a larger inductance value for re-verification until the optimal inductance value is selected so that the reverse polarity lightning impulse withstand voltage of the DC submarine cable meets the requirements.

10. The method for protecting an overhead line-DC submarine cable conversion station from multiple lightning strikes to overvoltage according to claim 1, characterized in that: Step S6 includes the following steps: S61. Optimize the lightning arrester configuration plan based on the overvoltage distribution of the equipment in the station after adding the reactor; S62. Simulate and analyze the overvoltage characteristics of the station equipment under different lightning arrester configuration schemes, verify the insulation margin of the station equipment, the same-polarity lightning impulse withstand voltage of the DC submarine cable, and the electrical stress of each lightning arrester, and select the best scheme.

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