Lightning stroke overvoltage analysis method and system for wind power plant in mountainous area

Abstract

The lightning stroke overvoltage analysis method comprises the following steps: establishing a wind power plant current collection system equivalent model comprising a current collection circuit, a box-type transformer and a wind turbine generator; under the equivalent model of the wind power plant current collection system, respectively obtaining phase voltage waveforms of high and low voltage sides of a box-type transformer under a lightning shielding failure path, voltage waveforms of two sides of an insulator of a hit tower and a terminal tower of the wind power plant current collection system under a lightning direct stroke path, and voltage waveforms of high and low voltage side phases of the box-type transformer under a lightning grounding grid counterattack path; and comparing the high-voltage and low-voltage waveform characteristic differences of the box-type transformer under the lightning shielding failure path, the direct stroke path and the grounding grid counterattack path to obtain a lightning protection analysis result of the box-type transformer of the wind power plant.

Description

Technical Field

[0001] The invention belongs to the field of lightning protection of wind farm collection systems, and in particular relates to a lightning overvoltage analysis method and system for wind farms in mountainous areas. Background Art

[0002] With the rapid development of global wind power technology, wind farms are expanding rapidly as a key part of clean energy. my country's onshore wind farms are relatively mature, such as Inner Mongolia Mengdong, Xinjiang Hami, Gansu Jiuquan and Hebei Zhangbei are all important bases. They are mostly located in high-altitude mountainous areas to obtain good wind power, but the corridor of the collector line increases the risk of lightning strikes. The collector system, but its complex topological structure makes it more difficult to study the propagation of lightning voltage under lightning conditions. Different topological structures have a great impact on the amplitude and propagation of lightning overvoltage. The existing technology mainly focuses on the impact of lightning strikes on the wind turbine blades on the wind turbine body, and the current protection focuses on the selection and installation location of the surge protector of the wind turbine blade material and the communication system, and there is relatively little research on the intrusion overvoltage of the collector system. These technologies have never considered the impact of the grounding grid on electrical equipment. This problem is particularly evident in wind farms with complex grounding grid layouts. At the same time, with the increasing demand for intelligent operation and maintenance, it has become critical to quickly analyze the problems of lightning strikes on the collector system, which can improve the wind farm's ability to resist lightning strikes, ensure power stability and economy, and support the development of clean energy. Summary of the invention

[0003] The object of the present invention is to provide a method and system for analyzing lightning overvoltage in a wind farm in a mountainous area to solve the above-mentioned problem.

[0004] To achieve the above object, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a method for analyzing lightning overvoltage in a mountainous wind farm, comprising: Establish an equivalent model of the wind farm collection system including collection lines, box transformers and wind turbines; Under the equivalent model of the wind farm collection system, the voltage waveforms of the high and low voltage sides of the box-type transformer under the lightning shielding path, the voltage waveforms on both sides of the insulators of the struck tower and terminal tower of the wind farm collection system under the lightning direct stroke path, and the voltage waveforms of the high and low voltage sides of the box-type transformer under the lightning grounding grid counter-strike path are obtained respectively; By comparing the differences in high and low voltage waveform characteristics of box-type transformers under three paths: lightning shielding path, direct stroke path, and grounding grid counter-strike path, the lightning protection analysis results of wind farm box-type transformers were obtained.

[0005] Furthermore, an equivalent model of the wind farm collection system including the collection line, box transformer and wind turbine is established, including: The Heidler module is used to establish a lightning current model in parallel with the wave impedance to equalize the lightning channel. The lightning current is used to characterize the discharge characteristics of lightning, and the parallel resistance is used to characterize the impedance parameters of the lightning discharge channel:

[0006] in: I is the amplitude of lightning current, τ 1 and τ 2 are the rise and decay time constants of lightning current, n is the steepness coefficient of the lightning current front, which is 3. η is the lightning current amplitude correction factor:

[0007] Establish a suitable tower model for transient calculation of wind farm collection lines, using a multi-wave impedance model, including two types of single-circuit towers and double-circuit towers: Among them, the wave impedance calculation formula of the main part of each layer of vertical tower is:

[0008]

[0009] The wave impedance of each layer of the tower Z LK is the main wave impedance Z TK 9 times, so:

[0010] The wave impedance of the cross arm of the tower is:

[0011] in: h k Represents the main height of the tower; r Tk Represents the radius of the vertical support between towers; r B Represents the radius of the bottom support of the tower; R Tk Represents the distance between the horizontal supports of the tower body; R B Represents the distance between the bottom supports of the tower; r Ak Half of the cross-sectional radius of the connection between the tower cross arm and the tower column; Based on the winding-to-ground capacitance and inter-winding capacitance in the transient process, a high-frequency model of the box-type transformer is established; Establish overhead line and lightning arrester models, using J. Marti frequency-dependent line model; An insulator equivalent model is established. The intersection method is used to identify the moment when the voltage at both ends is greater than the insulator volt-second characteristic. A switch is used to simulate the flashover situation. When the switch is turned on, the insulator maintains insulation performance and is insulated from the tower. When the switch is closed, the insulator flashes over and the insulation performance is destroyed. The insulator volt-second characteristic is fitted by the following formula:

[0012] in, U inf It is the 50% impulse flashover voltage of the insulator; The overvoltage protector model is established and a highly nonlinear device is used to simulate it. When it operates, it introduces lightning transient surges into the earth. According to the working characteristics of the overvoltage protector, its volt-ampere characteristic function is expressed as:

[0013] Where: C is a constant that depends on the material; α is the nonlinear coefficient.

[0014] Furthermore, when obtaining the high and low voltage waveforms of the box-type transformer under the three paths of lightning shielding path, direct stroke path, and grounding grid counterattack path, the constraints of the influence of lightning current waveform, lightning strike position, and grounding resistance factors on lightning intrusion waves are constructed: Key observation quantities of overvoltage: the time when the voltage starts to rise, the moment when the first oscillation peak is generated, the maximum overvoltage and the moment when the maximum overvoltage occurs; Given a uniform lightning current amplitude of 100 kA, the wavefront time and half-peak time are 0.25 / 100 μs, 2.6 / 50 μs, 1 / 200 μs and 10 / 350 μs respectively; If the gap between the ground wire and the phase wire does not break down when the lightning strikes the center of the span, the overvoltage will propagate from the lightning strike point to both sides, forming a negative reflection at the tower grounding resistance. For wind farms in mountainous areas, the grounding resistance value shall not exceed 10Ω.

[0015] Furthermore, under the equivalent model of the wind farm collection system, the phase voltage waveforms of the high and low voltage sides of the box-type transformer under the lightning shielding path are obtained, including: The formation of the strike path, the electrical geometric model uses the strike distance to describe the distance between the last jump of the lightning leader and the struck object, that is, the lightning will hit the object if it falls within the corresponding strike distance. The relevant strike distance expression recommended by IEEE is:

[0016]

[0017] In the formula,r c is the striking distance between the lightning rod and the conductor, m; r g is the striking distance of the earth, m; y c is the height of the overhead line, m; I is the lightning current, kA; The larger the lightning current, the greater the strike distance. r c The bigger, D c The smaller the distance, the lightning will first hit the lightning conductor or the ground; when the lightning current is small, the strike distance is r c Reduced, wire exposure distance D c It becomes larger and is more likely to hit the conductor, forming a lightning strike path of "phase line-underground cable-overvoltage protector-box transformer".

[0018] Furthermore, the voltage waveforms on both sides of the struck tower and terminal tower insulators of the wind farm collection system under the direct lightning path are obtained, including: The formation of a direct strike path. When lightning strikes a lightning conductor or the top of a power tower, the lightning current usually flows through the tower into the grounding device at the bottom of the tower, and then flows into the earth through the grounding grid or grounding resistor. When a large lightning current flows through the tower and its grounding resistor, a large voltage drop will be generated, and a strong overvoltage will be generated at the tower connection end of the insulator. When the insulator cannot withstand it, the tower will discharge back to the phase line, forming a direct lightning strike path from "tower / lightning conductor-insulator-underground cable-overvoltage protector-box transformer".

[0019] Furthermore, the voltage waveforms of the high and low voltage side phases of the box-type transformer under the lightning grounding grid counterattack path are obtained, including: The formation of the grounding grid counter-attack path. When lightning strikes the wind turbine blades, the lightning current cannot be discharged in time, causing the grounding grid to generate a high potential, forming a grounding grid counter-attack path of "wind turbine blades-tower-common grounding grid-box transformer".

[0020] Furthermore, a comparative analysis is conducted on the specific responses of the box-type transformer when lightning overvoltages from three different paths invade the box-type transformer.

[0021] In a second aspect, the present invention provides a method system for analyzing lightning overvoltage in a mountainous wind farm, comprising: Model building module, used to build an equivalent model of wind farm collection system including collection lines, box transformers and wind turbines; The waveform collection module is used to obtain the phase voltage waveforms of the high and low voltage sides of the box-type transformer under the lightning shielding path, the voltage waveforms on both sides of the insulators of the struck tower and the terminal tower of the wind farm collection system under the lightning direct stroke path, and the voltage waveforms of the high and low voltage sides of the box-type transformer under the lightning grounding grid counter-strike path. The analysis output module is used to compare the differences in high and low voltage waveform characteristics of box-type transformers under three paths: lightning shielding path, direct stroke path, and grounding grid counter-strike path, and obtain the lightning protection analysis results of wind farm box-type transformers.

[0022] In a third aspect, the present invention provides a computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of a method for analyzing lightning overvoltage in a mountainous wind farm when executing the computer program.

[0023] In a fourth aspect, the present invention provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of the method for analyzing lightning overvoltage in a wind farm in a mountainous area.

[0024] Compared with the prior art, the present invention has the following technical effects: The present invention establishes an electrical model of the wind farm power collection system, studies the influence of the changes of different parameters in the power collection system on the electrical performance of the system, analyzes the overvoltage propagation characteristics under overhead line shielding and direct strikes, studies the impact effect of grounding grid counterattack on system voltage fluctuations, and obtains the overvoltage waveform characteristics of the high and low voltage sides of the box-type transformer under different external propagation paths. This provides a theoretical basis and technical support for improving the lightning protection level of wind farms.

[0025] The invention proposes a lightning overvoltage analysis strategy for wind farm box-type transformers in mountainous areas under multiple paths. Through in-depth analysis of the lightning overvoltage propagation characteristics of different paths, it is concluded that different transmission paths of lightning overvoltage, soil grounding resistance, etc. have different effects on the box-type transformer. Based on these results, the strategy can effectively distinguish lightning overvoltages under different paths, providing important data support and theoretical basis for the design of electrical protection systems for wind farms, significantly improving the lightning resistance of wind farm box-type transformers, reducing equipment damage and shutdown risks, and further ensuring the safe and stable operation of wind farms.

[0026] The present invention analyzes the overvoltage that invades the transformer through the overhead line path, studies the transient overvoltage behavior under lightning shielding and analyzes the mechanism and impact of direct flashover. This process not only reveals the propagation characteristics of shielding lightning and how it causes voltage fluctuations on the box transformer, but also analyzes the occurrence mechanism and direct impact on the box transformer for direct flashover events, and explores the impact degree and consequences of transient overvoltage caused by direct flashover on the transformer. Through a comprehensive study of these two paths, the analysis strategy proposed in the present invention provides theoretical support for the optimization of protective measures and the formulation of equipment protection strategies, greatly enhancing the stability and reliability of the box transformer under lightning strike conditions.

[0027] The present invention analyzes the high potential impact caused by the shared grounding grid of wind turbines and box-type transformers, and conducts a propagation mechanism and hazard assessment of the grounding grid counterattack. During the analysis, the present invention reveals how the high potential impact is transmitted to the box-type transformer through the shared grounding grid, thereby causing local overvoltage and potential faults. Through this series of studies, a scientific basis is provided for the design of the grounding system of wind farms, and guidance is provided for optimizing the grounding protection measures of the power system.

[0028] The present invention reveals the propagation characteristics of lightning overvoltage of box-type transformers under different paths, and provides theoretical support for lightning strike tracing and fault analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the power collection system model of a wind farm in a mountainous area; Figure 2 It is the lightning current equivalent circuit diagram; Figure 3 (a) and Figure 3 (b) are schematic diagrams of impedance equivalent models; Figure 4 It is the equivalent model diagram of high frequency transformer; Figure 5 This is a schematic diagram of an insulator flashover; Figure 6 It is a schematic diagram of multi-path intrusion box transformer; Figure 7 There are several important factors of overvoltage waveform; Figure 8 are different lightning current waveforms; Fig. 9 It is the voltage on the high-voltage side of the rear box transformer (different grounding resistance); Fig.10 It is the electrical geometry model; Figure 11(a) is the voltage waveform on the high-voltage side of the box-type transformer after the shielding failure; Figure 11(b) is the voltage waveform on the low-voltage side of the box-type transformer after the shielding failure; Figure 12(a) is the voltage waveform at both ends of the struck tower insulator; Figure 12(b) is the voltage waveform across the terminal tower insulator; Figure 13(a) is the voltage waveform on the high-voltage side of the box-type transformer after the direct impact; Figure 13(b) is the voltage waveform on the low-voltage side of the box-type transformer after the direct impact; Figure 13(c) is the voltage waveform on the high-voltage side of the box-type transformer at the instant of direct impact; Figure 13(d) is the voltage waveform on the low-voltage side of the box-type transformer at the moment of direct impact; Figure 14(a) is the voltage waveform on the high-voltage side of the box-type transformer after the grounding grid is reversed; Figure 14(b) is the voltage waveform on the low-voltage side of the box-type transformer after the grounding grid is reversed.

[0030] Fig.15 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0031] The present invention is further described below in conjunction with the accompanying drawings: Example 1, please refer to Fig.15 The present invention provides a method for analyzing lightning overvoltage in a mountainous wind farm, comprising: Establish an equivalent model of the wind farm collection system including collection lines, box transformers and wind turbines; Under the equivalent model of the wind farm collection system, the voltage waveforms of the high and low voltage sides of the box-type transformer under the lightning shielding path, the voltage waveforms on both sides of the insulators of the struck tower and terminal tower of the wind farm collection system under the lightning direct stroke path, and the voltage waveforms of the high and low voltage sides of the box-type transformer under the lightning grounding grid counter-strike path are obtained respectively; By comparing the differences in high and low voltage waveform characteristics of box-type transformers under three paths: lightning shielding path, direct stroke path, and grounding grid counter-strike path, the lightning protection analysis results of wind farm box-type transformers were obtained.

[0032] Embodiment 2, the present invention provides a method for analyzing lightning overvoltage in a wind farm in a mountainous area, specifically comprising: The present invention considers the wind farm box-type transformer lightning overvoltage analysis strategy under multiple paths, comprehensively considers the external propagation characteristics of overvoltage, and provides a theoretical basis for improving the lightning protection level of wind farm box-type transformers. Specifically, by establishing an electrical model of the wind farm collection system, studying the impact of changes in different parameters in the collection system on the electrical performance of the system, analyzing the overvoltage propagation characteristics under overhead line shielding and direct strikes, studying the impact effect of grounding grid counterattack on system voltage fluctuations, and obtaining the overvoltage waveform characteristics of the high and low voltage sides of the box-type transformer under different external propagation paths. It provides a theoretical basis and technical support for improving the lightning protection level of wind farms.

[0033] Follow the steps below to implement it: Step 1: Establish an equivalent model of the wind farm collection system including collection lines, box transformers and wind turbines.

[0034] In step 1, an electrical model of the wind farm power collection system was established based on ATP-EMTP. The simplified schematic diagram of the power collection system is shown in Figure 1 As shown in the figure, it mainly considers the linear connection with a higher application ratio and more complex topological structure in actual overhead lines. This connection scheme means that each wind turbine is connected to the overhead line through an underground cable and a box-type step-up transformer, and the cables and overhead lines are arranged alternately in sequence. The specific modeling process is: Step 1.1: Use the Heidler module to establish a lightning current model in parallel with the wave impedance to obtain the equivalent lightning channel. Figure 2 The lightning current equivalent circuit diagram shown uses lightning current to characterize the discharge characteristics of lightning, and the parallel resistor characterizes the impedance parameters of the lightning discharge channel.

[0035]

[0036] in: I is the amplitude of lightning current, τ 1 and τ 2 are the rise and decay time constants of lightning current, n is the steepness coefficient of the lightning current front, which is 3. η is the lightning current amplitude correction factor:

[0037] Step 1.2: In order to accurately analyze the overvoltage and overcurrent of the collector line, a suitable transient calculation tower model must be established. The propagation process of lightning current on the tower is extremely complex. The collector line generally adopts a 35kV transmission line, and the tower types are single-circuit towers and double-circuit towers. The model in the present invention adopts a multi-wave impedance model, and the "up"-shaped tower and the "Wang"-shaped tower are used to replace the above two towers respectively. Taking the single-circuit tower Figure 3 (a) ("up" shape) as an example, its structure and its corresponding multi-wave impedance equivalent model are shown in Figure 3 (b).

[0038] Among them, the wave impedance calculation formula of the main part of each layer of vertical tower is:

[0039]

[0040] According to the measured data, the wave impedance of each layer of the tower support is Z LK is the main wave impedance Z TK 9 times, so:

[0041] The wave impedance of the cross arm of the tower is:

[0042] in: h k Represents the main height of the tower; r Tk Represents the radius of the vertical support between towers; r B Represents the radius of the bottom support of the tower; R Tk Represents the distance between the horizontal supports of the tower body; R B Represents the distance between the bottom supports of the tower; r Ak Half of the cross-sectional radius of the connection between the tower crossarm and the tower column.

[0043] Step 1.3, as a key device connecting the collector line and the wind turbine, the box-type transformer is susceptible to lightning current intrusion from multiple paths. In the transient analysis process, it is usually necessary to consider the ground capacitance of the winding and the capacitance between the windings. The existence of these stray capacitances is an important factor affecting the transmission of overvoltage. High-frequency impact does not transmit overvoltage through the transformation ratio like the electromagnetic coupling of the power frequency, but is quickly transmitted through the coupling capacitance between the high and low voltage windings. The propagation of the intrusion wave between the primary and secondary sides of the transformer includes two components, namely the electrostatic induction component and the electromagnetic induction component. Both exist at the same time, but the former generally plays a dominant role. Figure 4 Schematic diagram of the high-frequency model of the transformer.

[0044] Step 1.4, the lightning impulse wave front time is short, the equivalent frequency is high, and the line skin effect is obvious. The present invention adopts the J.Marti frequency-dependent line model, which uses the Foster-I type RC network to approximate the amplitude-frequency characteristics and phase-frequency characteristics of the discrete wave impedance and the propagation coefficient (weight function), and the wave impedance Z c And the weight function e -λl The accurate Bode diagram of is replaced by a line Bode diagram, which is approximated as a rational function. The transient process is solved in the frequency domain by Fourier transform.

[0045] Step 1.5: When the overhead line is struck by direct lightning, the flashover of the insulator needs to be considered. The 35kV insulator uses the intersection method to identify the flashover, and the flashover is simulated by the switch. When the switch is open, the insulator maintains insulation performance and insulation between the tower and the pole; when the switch is closed, the insulator flashes and the insulation performance is destroyed.

[0046] like Figure 5 As shown in the figure, the intersection method is to identify the moment when the voltage at both ends is greater than the volt-second characteristic of the insulator. tFlashover occurs at time 0. The volt-second characteristic of 35kV insulator can be fitted by the following formula:

[0047] in, U inf It is the 50% impulse flashover voltage of the insulator.

[0048] Step 1.6: In order to protect the safe operation of electrical equipment, overvoltage protectors are installed on both the high and low voltage sides of the box-type transformer to prevent the intrusion of lightning overvoltage. A highly nonlinear device is used for simulation, which can introduce lightning transient surges into the earth when it operates. According to the working characteristics of the overvoltage protector, its volt-ampere characteristic function can be expressed as:

[0049] Where: C is a constant that depends on the material; α is the nonlinear coefficient ( α The smaller it is, the higher the nonlinearity of the valve plate and the better the performance).

[0050] Step 2: Study the overvoltage analysis elements and analyze the influence of lightning current waveform, lightning strike location, grounding resistance and other factors on lightning intrusion wave. When lightning strikes the lightning arrester or the top of the power tower, the lightning current usually flows through the tower into the grounding device at the bottom of the tower, and then flows into the earth through the grounding grid or grounding resistance. Figure 6 It is a schematic diagram of the lightning intrusion wave invading the electrical system of a wind farm. Figure 7 The key observable quantities of statistical overvoltage are given, namely the time when the voltage starts to rise, the moment when the first oscillation peak is generated, the maximum overvoltage and the moment when the maximum overvoltage occurs. The moment when the voltage starts to rise represents the time required for the overvoltage to propagate to the device, the moment when the first peak is generated is the transient response of the intrusion wave, and the maximum overvoltage and its moment are important bases for studying the insulation level.

[0051] Influence of lightning current waveform. In order to control the variables, a uniform lightning current amplitude of 100kA is given, and the wavefront time and half-peak time are 0.25 / 100μs, 2.6 / 50μs, 1 / 200μs and 10 / 350μs respectively. Influence of lightning strike position, Figure 8 These are different lightning current waveforms.

[0052] Consider the influence of lightning on the tower top, remote lightning conductor and winding conductor on the intrusion wave overvoltage. The overvoltage generated by lightning on the tower top is different from the intrusion wave overvoltage generated by lightning in the middle of the ground wire span. If the gap between the ground wire and the phase wire is not broken down when lightning strikes the middle of the span, the overvoltage will propagate from the lightning strike point to both sides, forming a negative reflection at the tower grounding resistance, and the oscillation process is more complicated than that of lightning on the tower top.

[0053] The influence of grounding resistance. Due to the complexity of soil and geological conditions in mountainous wind farms, the influence of grounding resistance on overvoltage is very significant. There are various types of soil in mountainous areas, such as rocks, sand, clay, etc., and their conductivity varies greatly, which in turn affects the performance of the wind farm grounding system. Referring to the relevant specifications of IEC (International Electrotechnical Commission) and IEEE (Institute of Electrical and Electronics Engineers), for mountainous wind farms, the grounding resistance value may be appropriately relaxed, but it should still be controlled within a reasonable range as much as possible (usually not exceeding 10Ω). When the grounding resistance is large, it will hinder the discharge of lightning current, and a large overvoltage will appear on the tower. After the line is directly hit, the waveform on the high-voltage side of the box transformer is as follows: Fig. 9 shown.

[0054] Step 3: Formation of the shielding failure path. Although the towers of the 35kV collector lines are equipped with lightning arresters, when the lightning current is small and the strike distance is not large, a shielding failure interval between the lightning arrester and the earth will be formed, resulting in a shielding failure phenomenon in which lightning directly hits the phase line. The electrical geometry model uses the strike distance to describe the distance between the last jump of the lightning leader and the object being struck, that is, lightning will strike the object if it falls within the corresponding strike distance. The relevant strike distance expression recommended by IEEE is:

[0055]

[0056] In the formula, r c is the striking distance between the lightning rod and the conductor, m; r g is the striking distance of the earth, m; y c is the height of the overhead line, m; I is the lightning current, kA.

[0057] The larger the lightning current, the greater the strike distance. r c The bigger, D c The smaller, Fig.10 It can be seen that lightning will first strike the lightning conductor or the ground, and the lightning conductor can provide a relatively ideal protection effect; when the lightning current is small, the strike distance is r c Reduced, wire exposure distance D c It becomes larger and is easier to hit the wire, thus forming a lightning strike path of "phase line-underground cable-overvoltage protector-box transformer".

[0058] The specific process of step 4 is as follows: The formation of a direct strike path. When lightning strikes a lightning arrester or the top of a power tower, the lightning current usually flows through the tower into the grounding device at the bottom of the tower, and then flows into the earth through the grounding grid or grounding resistor. When a large lightning current flows through the tower and its grounding resistor, a large voltage drop will be generated, thereby generating a strong overvoltage at the tower connection end of the insulator. When the insulator cannot withstand it, it will be broken down and flashed, and the tower will discharge back to the phase line, thus forming a direct lightning strike path from "tower / lightning arrester-insulator-underground cable-overvoltage protector-box transformer".

[0059] The specific process of step 5 is as follows: The formation of the grounding grid strikeback path. When lightning strikes the blades of a wind turbine, the lightning current cannot be discharged in time, resulting in a higher potential in the grounding grid, considering the high soil resistivity and large grounding resistance of wind farms in mountainous areas. This potential increase will cause a strikeback voltage in the grounding grid, which in turn affects the box-type transformers connected to the same grounding system, forming a grounding grid strikeback path of "wind turbine blades-tower-common grounding grid-box transformer".

[0060] The specific process of step 6 is as follows: By comparing and analyzing the specific responses of the box-type transformer when lightning overvoltages from three different paths intrude into the box-type transformer, these characteristics provide a basic basis for studying the performance of the box-type transformer under lightning current impact and reveal the impact of different lightning currents on the box-type transformer.

[0061] Example The present invention builds a system-wide simulation model on the ATP-EMTP platform. The main parameters of the simulation model of the box-type transformer and the overhead line are shown in Table 1 and Table 2. The main object is the box-type transformer, that is, the lightning current intrusion into the box-type transformer through the lightning path, the direct lightning path and the grounding grid counterattack path is analyzed.

[0062] Table 1

[0063] Table 2

[0064] (1) Study on transient overvoltage behavior under lightning strike Figure 11(a) shows the three-phase voltage waveform after lightning strikes phase A. When the shielding strike occurs (at about 0ms), a significant transient voltage spike appears on phase A, with an amplitude of nearly 40kV. This phenomenon indicates that when the shielding strike occurs, the lightning current is conducted through phase A, resulting in a transient overvoltage on phase A on the high-voltage side.

[0065] Compared with phase A, the voltage fluctuations of phases B and C are smaller, showing an indirect coupling effect. After the lightning current hits phase A, it affects phases B and C through electromagnetic coupling. Although they do not have significant voltage spikes, there are still some fluctuations. After the voltage spike of phase A appears, the voltage rapidly decays to near zero after 0.5ms, indicating that the system can quickly absorb the energy caused by the strike. After that, phase A enters a stable state, showing no obvious long-term high-frequency oscillation. However, phases B and C also show certain fluctuations after the strike, especially phase B has a slight rebound near 0ms, and then enters a gradual recovery process. Phase C also experienced similar slight oscillations after the strike. After 1ms, the voltages of phases A, B, and C tend to be stable, indicating that the voltage fluctuations of the high-voltage side system decay rapidly after the strike. Even in the case of a large strike, the three-phase voltages on the high-voltage side do not show long-term high-frequency oscillations.

[0066] Phase A on the low-voltage side also shows large voltage fluctuations. At 0ms, a significant voltage spike appeared on phase A, with an amplitude of about 1.5kV. Although the voltage spike amplitude on the low-voltage side is much smaller than that on the high-voltage side (the high-voltage side reaches 40kV), it still shows the impact of the lightning current on the low-voltage side equipment after the A-phase winding strike. Phases B and C on the low-voltage side are also affected by the coupling of the winding strike, but their voltage spike amplitudes are relatively small. The fluctuation amplitudes of phases B and C are both around 0.5kV, indicating that the low-voltage side responds relatively gently to the lightning current impact. After the voltage spike, phase A experienced multiple oscillations, and the amplitude gradually decreased. These oscillations are transient phenomena caused by the lightning current impact, with an oscillation amplitude of about 0.5-1kV and a very short duration. As can be seen from Figure 11(b), the oscillations gradually disappeared after 0.5ms, and the system returned to a stable state. Phases B and C also showed small oscillations, but the amplitude and frequency were relatively low, indicating that they were much less affected by the winding strike than phase A.

[0067] (2) Analysis of the mechanism and impact of direct flashover Figure 12 shows the voltage waveforms on both sides of the insulators of the struck tower and the terminal tower when the top of the tower is struck by lightning. At the moment when the lightning current directly hits the tower (0μs), the three-phase voltages all show significant transient voltage spikes. Due to the influence of the tower structure, the A-phase conductor is struck by lightning first. Its voltage rises rapidly, forming an overvoltage spike of about 900kV.

[0068] As the lightning current is conducted through the tower and the conductor, the voltage of phase A begins to decay gradually, especially within 10μs, the voltage spike drops rapidly. The overvoltage energy is gradually released by the system's grounding network and line conduction, causing the voltage to decay rapidly. When struck, the potential difference of the insulator of phase B exceeds the withstand voltage of the insulator, and flashover occurs (insulator breakdown, discharge path formed).

[0069] At the moment of flashover on phase B, the voltage difference dropped rapidly to 0. The voltage spike on phase C was similar to that on phase B, also close to 800 kV, but the oscillation amplitude and attenuation process were relatively stable, and the insulator maintained its isolation capability. The voltage on phase C dropped steadily over time, and eventually the system gradually dissipated the lightning energy through grounding. As for the terminal tower, the lightning current had been transmitted to the far end of the system, and the voltage spikes on phases A and C were significantly reduced, with a maximum of about 600 kV. This indicates that the lightning energy was partially dissipated during the transmission process. The voltages on phases A and C of the terminal tower showed an overvoltage phenomenon and gradually decayed. Since the insulator on phase B of the struck pole tower had been broken down, the lightning current was transmitted to the terminal tower along the discharge path, causing the insulator on phase B of the terminal tower to flash over again.

[0070] The overvoltage waveforms on the high-voltage side of the box-type transformer are shown in Figure 13 (a) and (c). It can be seen from the figure that on the high-voltage side, the voltage fluctuation amplitude of phase A and phase C is relatively stable, showing a typical AC voltage waveform, with fluctuation amplitudes of about plus or minus 40 kV. This shows that although phase A and phase C on the high-voltage side were affected by lightning, they did not suffer insulation failure, and the voltage fluctuation gradually returned to normal. Phase B showed a high-amplitude spike in the early stage (near 0 ms), after which the voltage dropped rapidly and approached 0, indicating that the current was discharged through the flashover path, and the insulator completely lost its isolation ability after failure, forming a short-circuit path between the phase B conductor and the grounding point. On the low-voltage side, the fluctuation amplitude of the three-phase voltage is significantly smaller than that on the high-voltage side, with a maximum voltage of about 6 kV. The voltage fluctuations of phase A and phase C are small, showing a normal overvoltage response. After the initial transient fluctuations, they gradually return to a relatively stable state, with a voltage fluctuation amplitude of about plus or minus 1 kV. Since phase B has flashed over, the voltage fluctuation of phase B on the low-voltage side is also relatively abnormal. Although the voltage of phase B did not return to zero completely, it fluctuated slightly and showed unstable oscillations. This shows that after the flashover of phase B, the current continued to conduct through the low-voltage side, causing its voltage to be unable to return to normal levels. After about 0.5ms, the oscillation gradually decayed and the system began to return to a stable state.

[0071] (3) Propagation mechanism and hazard assessment of grounding grid backlash Figure 14 shows the back-strike phenomenon caused by the lightning current being conducted to the neutral point of the box-type transformer through the grounding grid shared with the box-type transformer after the lightning strikes the wind turbine. The lightning current reaches the neutral point at 5ms, directly impacting the neutral point grounding of the system, causing a sharp change in the neutral point voltage and causing overvoltage fluctuations on the high and low voltage sides of the box-type transformer.

[0072] Before the lightning strike, the three-phase voltage showed a typical sine waveform, and the voltage waveforms of phases A, B, and C were normal. At 5ms, a significant voltage spike appeared on the three-phase voltage on the high-voltage side at the same time. This is because the lightning current instantly passed through the grounding grid, causing the potential of the system to rise, resulting in a sharp rise in the transient voltage on the high-voltage side.

[0073] As can be seen from Figure 14(a), the amplitude of the voltage spike is around 40-60kV, and the peak amplitudes of each phase are very close, indicating that the three phases were simultaneously impacted by the lightning current, and the impact amplitudes were comparable. This transient overvoltage spike phenomenon is a typical lightning transient response. After the voltage spike, the three-phase voltage quickly dropped and recovered to a near-original sinusoidal waveform. The enlarged image further demonstrates this phenomenon. The oscillation after the spike is not significant, and the voltage returned to a stable state in less than 0.1ms. This rapid recovery indicates that the system did not produce long-term high-frequency oscillations after the lightning impact, indicating that the system has good transient recovery capabilities.

[0074] Similar to the high-voltage side, before 5ms, the three-phase voltage on the low-voltage side also maintained a normal sine wave, without any signs of overvoltage. At the moment when the lightning current reached the neutral point, a short voltage spike also occurred on the low-voltage side, but its amplitude was significantly lower than that on the high-voltage side. The voltage spike on the low-voltage side was about 20-30kV, much lower than the voltage spike on the high-voltage side. The local enlarged image shows that the voltage spike on the low-voltage side is also instantaneous, and the oscillation also decays rapidly, without generating long-term overvoltage fluctuations.

[0075] The voltage fluctuation on the high-voltage side comes from the electromagnetic coupling of the lightning current on the low-voltage side through the transformer. The lightning current first affects the low-voltage side through the grounding system, and then conducts to the high-voltage side through the inductive effect. Therefore, a larger voltage spike appears on the high-voltage side, which is because the high-voltage side cannot discharge the lightning current as quickly as the low-voltage side. The voltage spike on the high-voltage side reflects the transient overvoltage caused by the lightning current through coupling conduction. The duration is very short, and the voltage fluctuation quickly returns to stability. The lightning current first enters the system through the grounding point on the low-voltage side. Although the low-voltage side is the main conduction path of the lightning current, the voltage spike on the low-voltage side is relatively small because the grounding system can quickly disperse the energy.

[0076] (4) Overvoltage waveform characteristics under different paths Table 3

[0077] From the above analysis, it can be seen that the shielding phase usually has a large voltage fluctuation under the shielding lightning path, while the flashover phase is similar to this when the direct lightning causes a single-phase flashover, and the difference can be reflected in the insulator flashover situation. At the same time, the three-phase overvoltage fluctuations under the grounding grid counterattack path are relatively consistent, the transient overvoltage is significant, and the oscillation frequency is high. By analyzing the propagation characteristics of lightning overvoltage under different paths, theoretical support can be provided for lightning source tracing.

[0078] In yet another embodiment of the present invention, a system for analyzing lightning overvoltage in a wind farm in a mountainous area is provided, which can be used to implement the above-mentioned method for analyzing lightning overvoltage in a wind farm in a mountainous area. Specifically, the system includes: Model building module, used to build an equivalent model of wind farm collection system including collection lines, box transformers and wind turbines; The waveform collection module is used to obtain the phase voltage waveforms of the high and low voltage sides of the box-type transformer under the lightning shielding path, the voltage waveforms on both sides of the insulators of the struck tower and the terminal tower of the wind farm collection system under the lightning direct stroke path, and the voltage waveforms of the high and low voltage sides of the box-type transformer under the lightning grounding grid counter-strike path. The analysis output module is used to compare the differences in high and low voltage waveform characteristics of box-type transformers under three paths: lightning shielding path, direct stroke path, and grounding grid counter-strike path, and obtain the lightning protection analysis results of wind farm box-type transformers.

[0079] The division of modules in the embodiments of the present invention is schematic and is only a logical function division. There may be other division methods in actual implementation. In addition, each functional module in each embodiment of the present invention may be integrated into one processor, or may exist physically separately, or two or more modules may be integrated into one module. The above-mentioned integrated modules may be implemented in the form of hardware or in the form of software functional modules.

[0080] In another embodiment of the present invention, a computer device is provided, the computer device comprising a processor and a memory, the memory being used to store a computer program, the computer program comprising program instructions, and the processor being used to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or may be other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc., which are the computing core and control core of the terminal, which are suitable for implementing one or more instructions, and are specifically suitable for loading and executing one or more instructions in the computer storage medium to implement the corresponding method flow or corresponding function; the processor described in the embodiment of the present invention can be used for the operation of a method for analyzing lightning overvoltage in a mountainous wind farm.

[0081] In another embodiment of the present invention, the present invention further provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a computer device for storing programs and data. It is understandable that the computer-readable storage medium here can include both built-in storage media in the computer device and, of course, extended storage media supported by the computer device. The computer-readable storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by the processor are also stored in the storage space, and these instructions can be one or more computer programs (including program codes). It should be noted that the computer-readable storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. The processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the corresponding steps of the above-mentioned embodiment of a method for analyzing lightning overvoltage in a mountainous wind farm.

[0082] It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0083] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0084] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0085] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0086] 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 it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for analyzing lightning overvoltage in a mountainous wind farm, characterized in that: include: Establish an equivalent model of the wind farm collection system including collection lines, box transformers and wind turbines; Under the equivalent model of the wind farm collection system, the voltage waveforms of the high and low voltage sides of the box-type transformer under the lightning shielding path, the voltage waveforms on both sides of the insulators of the struck tower and terminal tower of the wind farm collection system under the lightning direct stroke path, and the voltage waveforms of the high and low voltage sides of the box-type transformer under the lightning grounding grid counter-strike path are obtained respectively; By comparing the differences in high and low voltage waveform characteristics of box-type transformers under three paths: lightning shielding path, direct stroke path, and grounding grid counter-strike path, the lightning protection analysis results of wind farm box-type transformers were obtained.

2. A method for analyzing lightning overvoltage in a mountainous wind farm according to claim 1, characterized in that: Establish an equivalent model of the wind farm collection system including collection lines, box transformers and wind turbines, including: The Heidler module is used to establish a lightning current model in parallel with the wave impedance to equalize the lightning channel. The lightning current is used to characterize the discharge characteristics of lightning, and the parallel resistance is used to characterize the impedance parameters of the lightning discharge channel: in: I is the amplitude of lightning current, τ 1 and τ 2 are the rise and decay time constants of lightning current, n is the steepness coefficient of the lightning current front, which is 3. η is the lightning current amplitude correction factor: Establish a suitable tower model for transient calculation of wind farm collection lines, using a multi-wave impedance model, including two types of single-circuit towers and double-circuit towers: Among them, the wave impedance calculation formula of the main part of each layer of vertical tower is: The wave impedance of each layer of the tower Z LK is the main wave impedance Z TK 9 times, so: The wave impedance of the cross arm of the tower is: in: h k Represents the main height of the tower; r Tk Represents the radius of the vertical support between towers; r B Represents the radius of the bottom support of the tower; R Tk Represents the distance between the horizontal supports of the tower body; R B Represents the distance between the bottom supports of the tower; r Ak Half of the cross-sectional radius of the connection between the tower cross arm and the tower column; Based on the winding-to-ground capacitance and inter-winding capacitance in the transient process, a high-frequency model of the box-type transformer is established; Establish overhead line and lightning arrester models, using J. Marti frequency-dependent line model; An insulator equivalent model is established. The intersection method is used to identify the moment when the voltage at both ends is greater than the insulator volt-second characteristic. A switch is used to simulate the flashover situation. When the switch is turned on, the insulator maintains insulation performance and is insulated from the tower. When the switch is closed, the insulator flashes over and the insulation performance is destroyed. The insulator volt-second characteristic is fitted by the following formula: in, U inf It is the 50% impulse flashover voltage of the insulator; The overvoltage protector model is established and a highly nonlinear device is used to simulate it. When it operates, it introduces lightning transient surges into the earth. According to the working characteristics of the overvoltage protector, its volt-ampere characteristic function is expressed as: Where: C is a constant that depends on the material; α is the nonlinear coefficient.

3. A method for analyzing lightning overvoltage in a mountainous wind farm according to claim 2, characterized in that: When obtaining the high and low voltage waveforms of the box-type transformer under the three paths of lightning shielding path, direct strike path, and grounding grid counterattack path, the constraints of the influence of lightning current waveform, lightning strike position, and grounding resistance factors on the lightning intrusion wave are constructed: Key observation quantities of overvoltage: the time when the voltage starts to rise, the moment when the first oscillation peak is generated, the maximum overvoltage and the moment when the maximum overvoltage occurs; Given a uniform lightning current amplitude of 100 kA, the wavefront time and half-peak time are 0.25 / 100 μs, 2.6 / 50 μs, 1 / 200 μs and 10 / 350 μs respectively; If the gap between the ground wire and the phase wire does not break down when the lightning strikes the center of the span, the overvoltage will propagate from the lightning strike point to both sides, forming a negative reflection at the tower grounding resistance. For wind farms in mountainous areas, the grounding resistance value shall not exceed 10Ω.

4. The method for analyzing lightning overvoltage in a mountainous wind farm according to claim 1, characterized in that: Under the equivalent model of the wind farm collection system, the phase voltage waveforms of the high and low voltage sides of the box-type transformer under the lightning shielding path are obtained, including: The formation of the strike path, the electrical geometric model uses the strike distance to describe the distance between the last jump of the lightning leader and the struck object, that is, the lightning will hit the object if it falls within the corresponding strike distance. The relevant strike distance expression recommended by IEEE is: In the formula, r c is the striking distance between the lightning rod and the conductor, m; r g is the striking distance of the earth, m; y c is the height of the overhead line, m; I is the lightning current, kA; The larger the lightning current, the greater the strike distance. r c The bigger, D c The smaller the distance, the lightning will first hit the lightning conductor or the ground; when the lightning current is small, the strike distance is r c Reduced, wire exposure distance D c It becomes larger and is more likely to hit the wire, forming a lightning strike path of "phase line-underground cable-overvoltage protector-box transformer".

5. The method for analyzing lightning overvoltage in a mountainous wind farm according to claim 1, characterized in that: Obtain the voltage waveforms on both sides of the struck tower and terminal tower insulators of the wind farm collection system under the direct lightning path, including: The formation of a direct strike path. When lightning strikes a lightning arrester or the top of a power tower, the lightning current usually flows through the tower into the grounding device at the bottom of the tower, and then flows into the earth through the grounding grid or grounding resistor. When a large lightning current flows through the tower and its grounding resistor, a large voltage drop will be generated, and a strong overvoltage will be generated at the tower connection end of the insulator. When the insulator cannot withstand it, the tower will discharge back to the phase line, forming a direct lightning strike path from "tower / lightning arrester-insulator-underground cable-overvoltage protector-box transformer".

6. The method for analyzing lightning overvoltage in a mountainous wind farm according to claim 1, characterized in that: Obtain the voltage waveforms of the high and low voltage side phases of the box-type transformer under the lightning grounding grid counterattack path, including: The formation of the grounding grid counter-attack path. When lightning strikes the wind turbine blades, the lightning current cannot be discharged in time, causing the grounding grid to generate a high potential, forming a grounding grid counter-attack path of "wind turbine blades-tower-common grounding grid-box transformer".

7. The method for analyzing lightning overvoltage in a mountainous wind farm according to claim 1, characterized in that: By comparing and analyzing the voltages on both sides of the box-type transformer when lightning overvoltages from three different paths invade the box-type transformer: The time when the voltage starts to rise, the moment when the first oscillation peak is generated, the maximum overvoltage amplitude and the moment when the maximum overvoltage occurs are compared and analyzed.

8. A lightning overvoltage analysis method system for a mountainous wind farm, characterized in that: include: Model building module, used to build an equivalent model of wind farm collection system including collection lines, box transformers and wind turbines; The waveform collection module is used to obtain the phase voltage waveforms of the high and low voltage sides of the box-type transformer under the lightning shielding path, the voltage waveforms on both sides of the insulators of the struck tower and the terminal tower of the wind farm collection system under the lightning direct stroke path, and the voltage waveforms of the high and low voltage sides of the box-type transformer under the lightning grounding grid counter-strike path. The analysis output module is used to compare the differences in high and low voltage waveform characteristics of box-type transformers under three paths: lightning shielding path, direct stroke path, and grounding grid counter-strike path, and obtain the lightning protection analysis results of wind farm box-type transformers.

9. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the method for analyzing lightning overvoltage in a mountainous wind farm as claimed in any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the method for analyzing lightning overvoltage in a mountainous wind farm as claimed in any one of claims 1 to 7 are implemented.

Images