GIS fault analysis method based on multi-physics field coupling simulation

Abstract

A GIS fault analysis method based on multi-physics field coupling simulation belongs to the technical field of power equipment state monitoring, and comprises the following steps: step S1, sorting equipment data; s2, electromagnetic transient analysis software ATP constructs an overall model; s3, establishing a GIS grounding grid model; s4, performing characteristic analysis on the switch operation overvoltage; s5, analyzing the characteristics of the lightning stroke overvoltage; s6, analyzing the characteristics of the grounding fault; s7, performing safety evaluation on the equipment; s8, performing safety assessment on the personnel; and checking the contact voltage and the step voltage, and positioning a high-risk area. The scheme has the advantages of comprehensiveness, multi-physical field coupling capability, comprehensive analysis covering multiple fault scenes, strict safety evaluation, innovative dynamic simulation and efficient verification mechanism.

Description

Technical Field

[0001] This invention belongs to the field of power equipment condition monitoring technology, and in particular relates to a GIS fault analysis method based on multi-physics field coupling simulation. Background Technology

[0002] Gas-insulated switchgear (GIS), due to its compact structure, small footprint, high operational reliability, long maintenance cycle, and strong environmental adaptability, has become a core component of urban power grids. Compared to traditional switchyards, the main characteristic of GIS is that it replaces the traditionally independently installed circuit breakers, air breakers (ABS), and bay buses with a complete set of equipment. This complete set of equipment includes circuit breakers, disconnectors, busbars, voltage transformers, current transformers, and surge arresters, all enclosed in a metal housing and using SF6 as the insulation and arc-extinguishing medium. However, its fully enclosed structure also makes internal faults difficult to detect visually, and the fault propagation speed is fast, easily triggering chain reactions, resulting in more severe consequences than open switchyards.

[0003] Current GIS simulations largely rely on static mathematical models (such as circuit equivalent models), which have the following drawbacks: Spatial attributes are missing: spatial characteristics such as the three-dimensional layout of equipment and electromagnetic field distribution are not integrated. Traditional solutions are limited to discussions on transformers and lines. For example, they are limited to the characteristic analysis of lightning strikes in power systems and whether the ground potential rise (GPR) value meets the safety design value of the grounding system.

[0004] Traditional methods are limited to analyzing the transient electromagnetic activity of transformers and lines, lacking a comprehensive analysis of the electromagnetic characteristics of the grounding grid and whether related equipment in the field can withstand the transient and steady-state voltages generated by these faults and overvoltages.

[0005] To overcome the above limitations, it is urgent to develop a GIS multiphysics dynamic simulation method. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a GIS fault analysis method based on multiphysics field coupling simulation.

[0007] To achieve the above objectives, the present invention adopts the following technical solution.

[0008] The GIS fault analysis method based on multiphysics coupling simulation includes the following steps: Step S1, Organizing equipment data: The GIS system connects the power transmission system and the power plant; the GIS system includes main busbars, section busbars, gas-insulated switchgear, busbar voltage transformers and surge arresters; the power transmission system includes overhead transmission lines and power sources; the power plant includes generators, main transformers, starting transformers and starting transformer loads; Collect the electrical and geometric parameters of the above-mentioned equipment, and simultaneously integrate the data of the GIS grounding network; Step S2: Construct the overall model using the electromagnetic transient analysis software ATP: Step S21, GIS system model establishment: Sequentially establish the main busbar model, section busbar model, gas-insulated switchgear model, busbar voltage transformer model, and surge arrester model; Step S22, Modeling of Overhead Transmission Lines: Sequentially establish the overhead transmission line model and the power source model; Step S23, Establishment of the power plant model: Sequentially establish the generator model, main transformer model, starting transformer model, and starting transformer load model; Step S3, Establishment of GIS grounding grid model: Construct GIS grounding grid model using CDEGS grounding system electromagnetic characteristic analysis software; Step S4: Characteristic analysis of overvoltage during switch operation; simulate synchronous, asynchronous, opening and closing of the disconnecting switch, and extract the peak value and waveform of transient overvoltage; Step S5: Characteristic analysis of lightning overvoltage; inject 40kA lightning current to evaluate the equipment insulation withstand and surge arrester operation characteristics; Step S6, Characteristic analysis of grounding fault; Set a short circuit in phase A of the main busbar to verify the current shunting capacity of the grounding grid; Step S7, Safety assessment of the equipment; compare the overvoltage peak value with the equipment's BIL and BSL limits to verify that the insulation margin is ≥20%; Step S8: Safety assessment of personnel; verification of contact voltage and step voltage, and location of high-risk areas.

[0009] Further, step S21 includes: step S211, main bus model establishment and parameter setting: input the following parameters in ATP to establish the main bus model: inner conductor inner diameter, inner conductor outer diameter, outer shell inner diameter, outer shell outer diameter, inner conductor resistivity and outer shell resistivity; Step S212, Section busbar model establishment and parameter setting: The ultra-high voltage system adopts a one-and-a-half circuit breaker busbar architecture, with three sets of circuit breakers configured for each span; a set of disconnecting switches are connected in series upstream and downstream of each circuit breaker; input the following parameters into ATP to establish the section busbar model: inner conductor inner diameter, inner conductor outer diameter, cylinder shell inner diameter, cylinder shell outer diameter, inner conductor resistivity, and shell resistivity.

[0010] Step S213, Model establishment and parameter setting of gas-insulated switchgear: Input the following parameters into ATP to establish the model of gas-insulated switchgear: inner conductor inner diameter, inner conductor outer diameter, outer shell inner diameter, outer shell outer diameter, inner conductor resistivity and outer shell resistivity; Step S214, Bus voltage transformer model establishment and parameter setting: The bus voltage transformer is a three-phase, three-winding transformer, with the primary, secondary, and tertiary sides all using a Y connection; input the following parameters into ATP to establish the bus voltage transformer model: rated capacity, primary winding rated voltage, secondary winding rated voltage, tertiary winding rated voltage, primary winding impedance percentage, secondary and tertiary winding impedance percentage, reactance-resistance ratio, and load power factor; Step S215, Surge arrester model establishment and parameter setting: Input the following parameters into ATP to establish the surge arrester model: reference voltage, flashover voltage per unit, initial voltage, number of conductors in parallel and error tolerance.

[0011] Further, step S22 includes: Step S221, Establishment and parameters of the overhead transmission line model: Input the following parameters into ATP to establish the overhead transmission line model: voltage level, phase conductor specifications, conductor material, conductor diameter, conductor resistance, overhead ground wire type, ground wire diameter and ground wire resistance; Step S222, Power supply model establishment and parameters: Input the following parameters into ATP to establish the power supply model: rated voltage, peak phase voltage, short-circuit current, power supply frequency, voltage phase angle difference, reactance-resistance ratio, system equivalent impedance, equivalent resistance, equivalent inductive reactance, and equivalent inductance.

[0012] Further, step S23 includes: Step S231, Generator Model Establishment and Parameter Setting: Input the following parameters into ATP to establish the generator model: rated voltage, rated capacity, power factor, subtransient reactance, power supply frequency, and voltage source phase difference; Step S232, Main transformer model establishment and parameter setting: The main transformer model is established by raising the generator output voltage to the transmission level. Its low-voltage side voltage must be consistent with the generator output voltage, and its high-voltage side is matched to the grid level. The simulated main transformer model is an ideal transformer, without considering iron loss and excitation current. The following parameters are input into ATP to establish the main transformer model: main transformer capacity, primary side rated line voltage, secondary side rated line voltage, and equivalent impedance at 75°C. Step S233, Start transformer model establishment and parameter setting: Input the following parameters in ATP to establish the transformer model: capacity, primary line voltage, secondary line voltage, tertiary line voltage and impedance percentage; Step S234, Start the transformer load model establishment and parameter setting: Start the load connected to the secondary and tertiary sides of the transformer; input the following parameters in ATP to establish the transformer load model: Secondary-side load 1: system capacity, voltage level, and power factor; Third-side load 2: system capacity, voltage level, and power factor.

[0013] Furthermore, in step S3, the parameters of the GIS grounding grid model are: coverage area, cross-sectional area of ​​a single bare copper wire, grid cell size, number of horizontal conductors, number of vertical conductors, and burial depth.

[0014] Grounding down conductors include forced grounding points and potential balancing reinforcement points for equipment. Forced grounding points for equipment include auxiliary grounding wires for main busbars, neutral points of voltage transformers, segment connection points, grounding of surge arresters, and grounding of GIS shells. Potential balancing reinforcement points include the four corners of the grounding grid boundary and the central area of ​​the grid. The verification criteria are as follows: Potential gradient limit: The surface potential difference between adjacent injection points ≤ 10V / m; Current distribution error: The error between the measured current at the equipment grounding point and the ATP simulation value < 5%; Grid density verification: If the potential gradient at the center of a 5m×5m grid is > 15V / m, it needs to be densified to 3m×3m; The transient current amplitude and phase data of the grounding down conductor are obtained by simulation using the electromagnetic transient analysis software ATP, and then input into the grounding system electromagnetic characteristic analysis software CDEGS to complete the three-dimensional grounding grid electromagnetic field calculation. Establish a coordinate mapping database between GIS equipment grounding points and grounding grids to achieve accurate tracing of fault current paths.

[0015] Furthermore, in step S4, with the circuit breaker open, the transient voltage generated by the switching operation of the disconnecting switches connected before and after the circuit breaker is simulated using the electromagnetic transient analysis software ATP. Operating conditions: 1. When operating the upper disconnect switch, all disconnect switches and circuit breakers in the middle and lower sections should remain closed and energized. 2. When operating the lower disconnect switch, all disconnect switches and circuit breakers in the middle and upper sections should remain closed and energized. 3. When not in the operating position, all disconnect switches and circuit breakers remain in the closed state, and the system is loaded with rated voltage; Settings for the electromagnetic transient analysis software ATP: For equipment in non-operational sections, the status of circuit breakers and disconnectors is as follows: closing time = -1 second, opening time = 1 second; at this time, the equipment remains in a closed and energized state. For the circuit breaker status corresponding to the operating section, the closing time = 1 second, and the opening time = -1 second; When closing synchronously, the closing time is 0.01667 seconds and the opening time is 1 second.

[0016] During synchronous tripping, the closing time is -1 second and the tripping time is 0.01667 seconds. The operating mode of switch operation overvoltage is used to summarize the transient voltage peaks generated by the switchgear and find the maximum value of the transient voltage peak. Record the current data of each grounding point injected into the switchyard grounding network, obtain the data of each grounding down conductor through the electromagnetic transient analysis software ATP, obtain the current data of each grounding point injected into the GIS grounding network, and input them into the grounding system electromagnetic characteristic analysis software CDEGS to perform electromagnetic characteristic analysis of the switchyard grounding system; the electromagnetic characteristic items include: ground potential rise, ground surface potential, step voltage, contact voltage, conductor current and magnetic field distribution.

[0017] Furthermore, in step S5, all circuit breakers and disconnectors are operated in the closed state, that is, the main busbar and section busbar are in the energized operating state. A 40kA lightning current is injected into the phase conductors, overhead ground wires and GIS grounding grid of the transmission tower of circuit one, and the lightning overvoltage generated by each device is observed. The current data of each grounding point injected into the switchyard grounding grid is recorded. The current data of each grounding down conductor obtained by ATP is used to obtain the current data of each grounding point injected into the GIS grounding grid. The data is then input into CDEGS for electromagnetic characteristic analysis of the switchyard grounding system. The electromagnetic characteristic items include: ground potential rise, ground surface potential, step voltage, contact voltage, conductor current and magnetic field distribution.

[0018] Furthermore, it is characterized in that, In step S6, the fault mode is: the main busbar has an LCC line module, and the A phase conductor of the LCC line module is short-circuited with the auxiliary grounding wire; Fault timing: A single-phase ground fault is triggered at 0.1 seconds and cleared at 0.2 seconds; Analysis objective: To monitor the voltage and current transient characteristics of critical equipment during a fault. Record the current data of each grounding point injected into the switchyard grounding network, obtain the data of each grounding down conductor obtained through ATP, obtain the current data of each grounding point injected into the GIS grounding network, and input them into CDEGS for electromagnetic characteristic analysis of the switchyard grounding system; the electromagnetic characteristic items include: ground potential rise, ground surface potential, step voltage, contact voltage, conductor current and magnetic field distribution.

[0019] Furthermore, in step S7, the data of lightning impulse withstand voltage (BIL) and switching impulse withstand voltage (BSL) of each device are summarized. Combined with the ATP simulation results, the device withstand capability for lightning strikes, switching overvoltages and grounding faults is evaluated. The actual peak overvoltage experienced by the device is compared with the insulation withstand voltage limit to verify whether the insulation margin is ≥20%.

[0020] Furthermore, in step S8, the ground potential rise, step voltage, contact voltage, and transfer voltage are examined, and personnel safety limits are set. For switch operation overvoltage and grounding fault, it is determined that the resulting ground potential rise, contact voltage and step voltage are all less than the personnel safety limit. For lightning overvoltage, examine the ground potential rise and step voltage when the lightning strikes the phase conductor and grounding grid of the transmission tower to see if they exceed the personnel safety limits.

[0021] This solution addresses the impact of switching operation overvoltages, lightning currents, lightning strikes, and single-phase grounding faults on ultra-high voltage GIS and its grounding system. It uses the electromagnetic transient analysis program ATP to construct an electromagnetic transient model of the ultra-high voltage GIS and its grounding system. Since the electromagnetic transient analysis program ATP is based on spatial geometric parameters, it fully considers various electrical parameters and conductor distribution parameters, including distributed inductance, mutual inductance, and capacitance, as well as the magnetic permeability and dielectric properties of the materials.

[0022] The advantages of this solution lie in its comprehensiveness, multi-physics coupling capability, integrated analysis covering multiple fault scenarios, rigorous safety assessment, innovative dynamic simulation, and efficient verification mechanism. By combining ATP and CDEGS software, it not only solves the problem of missing spatial attributes in traditional GIS simulation, but also provides quantitative basis for equipment insulation design and personnel safety protection, significantly improving the reliability and safety of the power system.

[0023] 1. Comprehensive and High-Precision Modeling Capabilities. This method covers all core components of the GIS system (such as main busbars, section busbars, gas-insulated switchgear, etc.), power transmission systems, and power plant equipment, and constructs accurate models through detailed parameter inputs (such as geometric dimensions and electrical characteristics). For example, in step S21, parameters such as the inner conductor diameter and shell resistivity are input to ensure that the model accurately reflects the physical structure. In steps S22 and S23, the overhead transmission line and power plant models are based on data such as voltage levels and material specifications, improving the realism of the simulation.

[0024] 2. Multiphysics Dynamic Coupling Simulation. The scheme integrates transient electromagnetic analysis (ATP) and grounding system electromagnetic field analysis (CDEGS) to achieve multiphysics collaborative simulation: In step S3, transient current data of the grounding down conductor is obtained through ATP and input into CDEGS to calculate the three-dimensional grounding network electromagnetic field (such as potential gradient and current distribution), breaking through the limitations of traditional single-circuit equivalent models. In steps S4-S6, for switch operation overvoltage, lightning strike overvoltage, and grounding fault, the transient response of the equipment and the characteristics of the grounding network (such as ground potential rise and conductor current) are analyzed simultaneously.

[0025] 3. Comprehensive analysis covering multiple fault scenarios. The solution systematically covers three key fault scenarios and quantifies their impact: Switch operation overvoltage (step S4): Simulates synchronous / asynchronous operation of disconnecting switches (e.g., 16 operation cases), extracts transient overvoltage peak values, and records grounding grid current data. Lightning overvoltage: Injects 40kA lightning current into the transmission tower or grounding grid to assess the arrester's operating characteristics and equipment insulation withstand capabilities (e.g., maximum overvoltage). Grounding fault (step S6): Sets a short circuit in phase A of the main busbar and monitors the voltage / current transient characteristics during the fault (e.g., steady-state peak analysis). Comprehensive diagnosis of GIS system vulnerabilities (e.g., the rise in ground potential during lightning strikes) provides targeted risk warnings.

[0026] 4. A rigorous safety assessment mechanism. The method combines equipment insulation margin and personnel safety limits to achieve dual protection: Equipment safety assessment (step S7): Compare the overvoltage peak value with the equipment's BIL / BSL limit (e.g., circuit breaker BSL limit), verify that the insulation margin is ≥20% (actual margin 39%-74%), and ensure the equipment's withstand capability. Personnel safety assessment (step S8): Check the contact voltage, step voltage, and ground potential rise, and locate high-risk areas (e.g., step voltage reaching 902V during a lightning strike). Advantages: Quantify safety thresholds (e.g., a standard for a 50kg person under wet cement conditions), assist in designing insulation and grounding protection measures, and reduce accident risks.

[0027] 5. Innovation and Practicality. This solution breaks through traditional limitations by introducing dynamic simulation technology. Traditional methods only focus on the electromagnetic analysis of transformers or lines, while this solution uses the distributed parameter model of ATP (such as distributed inductance and capacitance) to simulate the impact of GIS coaxial bus wave impedance (step S2). A coordinate mapping database between equipment grounding points and the grounding grid is established (step S3), enabling precise fault path tracing. Advantages: Improves the reliability of the GIS system, supports efficient maintenance and design optimization of urban power grids, and reduces maintenance costs. Attached Figure Description

[0028] Figure 1 This is the main electrical wiring diagram for a 500kV GIS system. Figure 2This is a location diagram of the 46 grounding down conductors in the GIS grounding network model, where the symbol X represents a grounding down conductor. Detailed Implementation

[0029] The present invention will now be described in further detail with reference to the accompanying drawings.

[0030] In ultra-high voltage systems, the reliability and safety of GIS equipment are paramount. The main types of accidents that can lead to equipment damage include: Switching operation overvoltage: Disconnecting switch operation generates ultra-fast transient overvoltage (amplitude ≤ 2 times system phase voltage, wavefront steepness 73.69 MV / μs). The GIS coaxial bus impedance (60–100Ω) is significantly lower than that of the overhead line, resulting in amplification of the intrusion wave and triggering inter-turn resonance breakdown in the transformer winding.

[0031] Lightning overvoltage: The peak value of lightning intrusion wave can reach several kilovolts, and a steep wavefront (wavefront time 1.2μs) can easily cause flashover of the internal insulation of GIS.

[0032] Grounding faults: Single-phase grounding faults cause the neutral point zero-sequence voltage to rise. When the zero-sequence / positive-sequence reactance ratio is greater than 3, the neutral point zero-sequence voltage can reach 35% of the line voltage, leading to thermal collapse of the zinc oxide surge arrester. Grounding system defects (such as high-resistance grounding) can exacerbate ground potential rise (GPR), causing excessive touch voltage.

[0033] Given the aforementioned major accident types that may exist in ultra-high voltage systems, traditional static models are insufficient to accurately quantify these transient effects. Therefore, this solution employs a GIS-based fault analysis method based on multiphysics coupled simulation. By dynamically simulating the impact of grounding system defects, it achieves fault path tracing and risk closed-loop control.

[0034] The GIS fault analysis method based on multiphysics coupling simulation includes the following steps: Step S1: Organizing equipment data.

[0035] The GIS system connects the power transmission system and power plants; The GIS system includes main busbars, section busbars, gas-insulated switchgear, busbar transformers, and surge arresters; The power transmission system includes overhead power lines and power sources; The power plant includes a generator, a main transformer, a starting transformer, and a starting transformer load; Collect the electrical parameters (e.g., rated voltage, short-circuit capacity, and impedance) and geometric parameters (e.g., conductor outer diameter, cylinder diameter) of the above-mentioned equipment, and simultaneously integrate the data of the GIS grounding network (e.g., grounding network grid).

[0036] Step S2: Construct the overall model using the electromagnetic transient analysis software ATP.

[0037] The Alternative Transients Program Draw (ATP) is a simulation program widely used for analyzing electromagnetic transient phenomena in power systems. Its technological origins can be traced back to the Electromagnetic Transient Analysis Program (EMTP) developed by the Bonneville Power Administration (BPA) in the United States in 1984. In 1991, the Norwegian Institute of Technology developed the ATP program based on the core algorithm of EMTP. This software can accurately simulate complex power systems and circuit topologies. In addition to transient calculations, it integrates multiple functional extension modules (such as harmonic analysis and frequency scanning), extending its application scope far beyond transient analysis. This solution uses ATP Windows Version 5.6. Its core modeling modules include Probe & 3-phase, Branch Linear, Switches, Sources, Line & Cables, and Transformers. These core modeling modules together constitute the core components for electromagnetic transient modeling and overvoltage and ground fault analysis of gas-insulated switchgear (GIS).

[0038] Figure 1 This is the main electrical wiring diagram for a 500kV GIS system. Figure 1 For example, the GIS system uses four longitudinal section busbars (Circuit 1, Circuit 2, Circuit 3, and Circuit 4) and two sets of transverse main busbars (NO.1 and NO.2) to form the backbone network. Both the section busbars and the main busbars use gas-insulated switchgear (GIS), and the GIS is filled with sulfur hexafluoride (SF6) as the insulating medium.

[0039] The four longitudinal busbars are three-phase separated structures. Each longitudinal busbar is equipped with current transformers (CT1~CT6, for measurement and protection), grounding switches (ES, such as ES 3690LE and ES 3690BE in circuit one, for safety grounding during equipment maintenance), disconnecting switches (DS, such as DS 3691 and DS 3692 in circuit one, for maintenance isolation), and circuit breakers (CB, such as CB3690 in circuit one, to interrupt fault current). Line transformers (LPTs) are installed in the middle section of the busbars to detect line undervoltage.

[0040] The main bus is equipped with a bus current transformer (BPT) (used for system synchronization, bus voltage monitoring and protection).

[0041] The connection between the section busbar and the main busbar adopts a T-type connection point, and electrical segmentation is achieved through the disconnecting switch DS and the grounding switch ES.

[0042] Figure 1 The LA at the bottom center is a surge arrester, an overvoltage protection device responsible for conducting overvoltages to the ground and automatically discharging abnormal voltages such as lightning strikes and switching operation overvoltages to prevent insulation damage to system equipment.

[0043] The following is based on Figure 1 For example, we will build a model.

[0044] Step S21, GIS system model establishment, including: Step S211, Main busbar model establishment and parameter setting: ATP's Line & Cables module is specifically designed for electromagnetic transient modeling of long-distance overhead transmission lines and power cables. Its core components include the Single Core Cable, the Overhead Line, and the Enclosing Pipe. This module uses a set of parametric units to represent the full length of a single cable segment, serving as an electrical connection bridge between equipment within the field.

[0045] Enter the following parameters into ATP to establish the main bus model: Inner conductor inner diameter: 150mm. Inner conductor outer diameter: 180mm. Outer shell inner diameter: 498mm. Outer shell outer diameter: 508mm. Inner conductor resistivity: 1.7×10⁻⁶. -8 Ω·m. Resistivity of the outer shell: 5.7 × 10⁻⁶ -8 Ω·m.

[0046] Step S212, Section busbar model establishment and parameter setting: The ultra-high voltage system adopts a one-and-a-half circuit breaker (1½CB) busbar structure, with three circuit breakers configured for each span. A disconnecting switch (DS) is connected in series upstream and downstream of each circuit breaker.

[0047] Enter the following parameters into ATP to establish the segment busbar model: Inner conductor inner diameter: 85mm. Inner conductor outer diameter: 120mm. Cylinder outer shell inner diameter: 498mm. Cylinder outer shell outer diameter: 508mm. Inner conductor resistivity: 3.13510 -8 Ω·m. Shell resistivity: 5.710 -7 Ω·m.

[0048] Step S213, Model establishment and parameter setting of gas-insulated switchgear: Referring to the manufacturer's technical manual, enter the following parameters in ATP to create a model of the gas-insulated switchgear: Inner conductor inner diameter: 228mm; Inner conductor outer diameter: 240mm; Outer shell inner diameter: 920mm; Outer shell outer diameter: 960mm; Inner conductor resistivity: 3.135×10⁻⁶ -8 Ω·m; Resistivity of outer shell: 5.7×10 -7 Ω·m.

[0049] Step S214, Bus voltage transformer model establishment and parameter setting: The bus voltage transformer is a three-phase, three-winding transformer, with the primary, secondary, and tertiary sides all using a Y-connection.

[0050] Enter the following parameters into ATP to establish the bus voltage transformer model: Rated capacity: 1500VA; primary winding rated voltage: 500kV; secondary winding rated voltage: 115V; tertiary winding rated voltage: 115V; primary winding impedance percentage: 0.8%; secondary and tertiary winding impedance percentage: 4%; reactance-resistance ratio: 6; load power factor: 0.85.

[0051] Step S215, Lightning arrester model establishment and parameter setting: Enter the following parameters into ATP to build a model of the surge arrester: Reference voltage: 950kV; Flashover voltage per unit: -2p.u; Initial voltage: 0; Number of conductors in parallel: 1 (single surge arrester structure); Error tolerance: 0.03pu.

[0052] Step S22: Model of overhead transmission line established.

[0053] Each overhead transmission line consists of ten ATP-EMTP line and cable assemblies, with each assembly corresponding to one transmission tower. Each module is 0.35 km long, and the ten assemblies are connected in series to form a line with a total length of 3.5 km. Each tower carries a double-circuit, six-phase conductor system.

[0054] Step S221, Establishment and parameters of the overhead transmission line model: An overhead transmission line model is used to define the characteristics of power transmission and quantify the loss, delay, and distortion in the electromagnetic energy propagation process through line parameters (resistance, inductance, and capacitance).

[0055] Enter the following parameters into ATP to establish the model of the overhead transmission line: Voltage rating: 500kV; Phase conductor specification: 1520MCM; Conductor material: 54 / 7ACSR; Conductor diameter: 38.2mm; Conductor resistance: 30.0372Ω / km; Overhead ground wire type: Fiber optic composite ground wire (OPGW-24B1-150); Ground wire diameter: 16.8mm; Ground wire resistance: 0.212Ω / km.

[0056] Step S222, Establishment of the power supply model and parameters: The power supply model defines the power input characteristics, including rated voltage (500kV), short-circuit current (50kA), frequency (60Hz), and phase symmetry (120°).

[0057] Enter the following parameters into ATP to establish the power source model: Rated voltage: 500kV; Peak phase voltage: 408kV; Short-circuit current: 50kA; Power supply frequency: 60Hz; Voltage phase angle difference: 120°; Reactance-resistance ratio |X / R|: 20; System equivalent impedance: 5.773Ω; Equivalent resistance: 0.2886Ω; Equivalent inductive reactance: 5.772Ω; Equivalent inductance: 15.31mH.

[0058] Step S23: Establishment of the power plant model.

[0059] Step S231, Generator model establishment and parameter setting: The generator model is a characteristic constraint that converts mechanical energy (driven by a steam turbine) into three-phase alternating current and outputs rated voltage, etc.

[0060] This plan involves two generators with identical parameters. Based on the manufacturer's information, their technical characteristics have been compiled.

[0061] Enter the following parameters into ATP to establish the generator model: Rated voltage: 500kVrms; Rated capacity: 1095MVA; Power factor: 0.9; Subtransient reactance: 28.3%; Power supply frequency: 60Hz; Voltage source phase difference: 120°.

[0062] Step S232, Main transformer model establishment and parameter setting: The main transformer model raises the generator output voltage to the transmission level, enabling long-distance and efficient transmission. Its low-voltage side voltage must be consistent with the generator output voltage, and its high-voltage side must match the grid level.

[0063] The simulated main transformer model is an ideal transformer, and iron loss and excitation current are not considered.

[0064] Enter the following parameters into ATP to establish the main transformer model: Main transformer capacity: 350MVA; primary side rated line voltage: 21kVrms (Δ connection); secondary side rated line voltage: 500kVrms (Y connection); equivalent impedance at 75℃: (0.2309+j34.49)% (per unit).

[0065] Step S233: Start the transformer model creation and parameter setting: The start-up transformer model draws power from the grid and steps it down to the plant's auxiliary power level during unit startup or failure. The low-voltage side phase must be consistent with the plant's auxiliary system and parallel switching is supported.

[0066] The two starting transformers are identical.

[0067] Enter the following parameters into ATP to establish the start-up transformer model: Capacity: 38.6MVA; Primary line voltage: 500kVrms (Y-connected); Secondary line voltage: 13.8kVrms (Y-connected); Tertiary line voltage: 4.16kVrms; Impedance percentages: Zn is (6.6+j168.4)% (per unit), Zs is (0.0134+j0.567)% (per unit), Zt is (0.00099+j0.00329)% (per unit).

[0068] Step S234: Start the transformer load model establishment and parameter setting: A model of the starting transformer load is used to simulate real working conditions, characterize the operating characteristics of auxiliary equipment, and verify the voltage sag withstand capability and voltage regulation strategy of the starting transformer.

[0069] Start the load connected to the secondary and tertiary sides of the transformer; input the following parameters into ATP to establish the load model of the starting transformer: Load 1 (secondary side): System capacity: 19.7MVA; Voltage level: 13.8kVrms; Power factor: 0.8 (lagging). Load 2 (third side): System capacity: 19.7MVA; Voltage level: 4.16kVrms; Power factor: 0.8 (lagging).

[0070] Step S3: Establishment of the GIS grounding grid model.

[0071] A GIS grounding grid model was constructed using CDEGS, a software for analyzing the electromagnetic characteristics of grounding systems.

[0072] The parameters of the GIS grounding grid model are as follows: the coverage area is 130 meters × 110 meters, the single cross-sectional area of ​​the bare copper wire is 100 square millimeters, the grid unit size is 5 meters × 5 meters, there are 23 horizontal conductors and 27 vertical conductors, and the burial depth is 1 meter below the ground surface.

[0073] There are a total of 46 grounding leads, including 32 forced grounding points for equipment and 14 potential equalization reinforcement points.

[0074] The equipment's forced grounding point includes: Main busbar auxiliary grounding wires: at both ends of each main busbar, 2 groups × 2 ends = 4 points; Neutral point of voltage transformer (PT): Each PT is independently grounded, 2 units × 1 point = 2 points; Segment connection points: Upper-middle / middle-lower gear shift points, 4 corners × 2 segments = 8 points; Surge arrester grounding: upper / lower lead surge arrester base, longitudinal 4 positions × 2 ends = 8 points; GIS enclosure grounding: disconnector switch / circuit breaker operating mechanism box, 1 point at each interval, for a total of 10 points.

[0075] Potential equalization reinforcement points include: Four points at the four corners of the grounding grid boundary; The central area of ​​the grid contains 10 points.

[0076] The verification criteria are as follows: Potential gradient limit: The surface potential difference between adjacent injection points ≤ 10V / m; Current distribution error: The error between the measured current at the equipment grounding point and the ATP simulation value is < 5%; Grid density verification: If the potential gradient at the center of a 5m×5m grid is > 15V / m, it needs to be densified to 3m×3m.

[0077] The transient current amplitude and phase data of 46 grounding down conductors were obtained by simulation using the electromagnetic transient analysis software ATP, and then input into the grounding system electromagnetic characteristic analysis software CDEGS to complete the three-dimensional grounding grid electromagnetic field calculation. Establish a coordinate mapping database between GIS equipment grounding points and grounding grids to achieve accurate tracing of fault current paths.

[0078] Figure 2 This is a location diagram of the 46 grounding down conductors in the GIS grounding network model, where the symbol X represents a grounding down conductor.

[0079] Step S4, Analysis of the characteristics of overvoltage during switch operation.

[0080] With the circuit breaker (CB) in the open state, the electromagnetic transient analysis software ATP is used to simulate the switching operation overvoltage generated by the switching operation (opening or closing) of the disconnecting switches (DS) connected before and after the circuit breaker (CB).

[0081] The system adopts both three-phase synchronous and three-phase asynchronous (with a time difference of 4.2ms) operating modes to match actual switching operations.

[0082] The specific settings are as follows: The operated objects are: the upper disconnect switches (DS3692, DS3691) and the lower disconnect switches (DS3672, DS3671) of the first position of the section bus. The circuit breakers CB (upper CB3690, lower CB3670) corresponding to the operated positions are forced into the open state to simulate the no-current interruption condition of the disconnect switches DS.

[0083] System operating conditions: 1. When operating the upper disconnect switch, all disconnect switches (DS) and circuit breakers (CB) in the middle and lower sections should remain closed and energized. 2. When operating the lower disconnect switch, all disconnect switches (DS) and circuit breakers (CB) in the middle and upper sections should remain closed and energized. 3. In non-operational positions (second to fourth positions), all disconnecting switches and circuit breakers remain in the closed state, and the system is loaded with rated voltage.

[0084] Settings for the electromagnetic transient analysis software ATP: For equipment in non-operational sections (second to fourth positions), the circuit breaker and disconnector status is as follows: closing time (Tclose) = -1 second, opening time (Topen) = 1 second. During this time, the equipment remains in a closed, energized state.

[0085] For the corresponding circuit breaker (CB) status of the operating section (upper section CB3690 and lower section CB3670), the closing time (Tclose) = 1 second and the opening time (Topen) = -1 second.

[0086] During synchronous closing, the closing time (Tclose) = 0.01667 seconds and the opening time (Topen) = 1 second.

[0087] During synchronous opening, the closing time (Tclose) is -1 second, and the opening time (Topen) is 0.01667 seconds.

[0088] There are 16 operating modes, which are composed of three types of variables: operating object (upper disconnector DS3692, upper disconnector DS3691, lower disconnector DS3672 or lower disconnector DS3671) × operating type (closing or opening) × operating mode (synchronous or asynchronous).

[0089] Table 1 is a summary table of operating methods for switching operations with overvoltage.

[0090] The operating mode of switch operation overvoltage is used to summarize the transient voltage peaks generated by the switchgear equipment, and the maximum value of the transient voltage peak (at 408kV) is found.

[0091] Table 2 is a summary table of grounding grid current data.

[0092] Record the current data at each grounding point injected into the switchyard grounding grid. Obtain the data for each grounding down conductor using the electromagnetic transient analysis software ATP. Input the current data at each grounding point injected into the GIS grounding grid into the grounding system electromagnetic characteristic analysis software CDEGS for electromagnetic characteristic analysis of the switchyard grounding system. Electromagnetic characteristic items include: ground potential rise, ground surface potential, step voltage, contact voltage, conductor current, and magnetic field distribution.

[0093] Step S5, Characteristic analysis of lightning overvoltage.

[0094] The instantaneous characteristics of lightning strike current generated by simulating natural lightning phenomena entering the system and injected into different locations of the internal grounding system and transmission lines were observed and recorded. The relevant equipment data when the system experienced lightning overvoltage were also recorded. Similarly, the current data of each grounding point injected into the switchyard grounding network in the ATP lightning overvoltage case were recorded.

[0095] All circuit breakers and disconnectors were operated in the closed state, meaning the main busbar and section busbars were energized. A 40kA lightning current was injected into the phase conductors, overhead ground wires, and GIS grounding grid of the transmission tower in circuit one, and the lightning overvoltage generated by each device was observed. The simulated equipment included surge arresters connected to circuit one, DS3691, DS3692, CB3690, the main transformer, the starting transformer, and the grounding grid.

[0096] When struck by lightning, the maximum overvoltage of the phase conductors of the transmission tower is 666.33kV, the maximum overvoltage of the overhead ground wire is 303.59kV, and the GIS grounding grid is 282.45kV.

[0097] Record the current data of each grounding point injected into the switchyard grounding network. Obtain the current data of each grounding down conductor through ATP, and input the data of each grounding point injected into the GIS grounding network into CDEGS for electromagnetic characteristic analysis of the switchyard grounding system. Electromagnetic characteristic items include: ground potential rise, ground surface potential, step voltage, contact voltage, conductor current, and magnetic field distribution.

[0098] The maximum values ​​of magnetic field distribution, conductor current, and step voltage occur when the phase conductor of the transmission tower is struck by lightning, while the maximum values ​​of ground potential rise, ground surface potential, and contact voltage occur when lightning is injected into the grounding grid.

[0099] Step S6, Characteristic analysis of grounding faults.

[0100] A single-phase ground fault occurs when the auxiliary grounding wire of the main busbar is short-circuited to one of the three phases (A, B, C) of the cable. Since there are a total of eight LCC line modules in the two main busbars, and each main busbar is constructed from four LCC line modules, there are a total of eight single-phase ground fault cases.

[0101] Based on the main busbar structure: The first main busbar connects two main transformers and two starting transformers, therefore it has four LCC line modules. Corresponding equipment: high-voltage side of the main transformers and high-voltage side of the starting transformers.

[0102] The second main busbar connects four 500kV transmission lines, therefore it has four LCC line modules. Corresponding equipment: line inlet terminal.

[0103] Fault mode: The A-phase conductor of each LCC line module is short-circuited with the auxiliary grounding wire.

[0104] Fault timing: A single-phase ground fault is triggered at 0.1 seconds and cleared at 0.2 seconds (duration 0.1 seconds).

[0105] Analysis objectives: To monitor the instantaneous and steady-state peak values ​​of core equipment during a fault, as well as the current waveform of the grounding down conductor and the potential distribution of the grounding grid.

[0106] Instantaneous peak value refers to the peak value at the instant of a ground fault (0.1 seconds). Steady-state peak value refers to the peak value measured after the fault waveform has stabilized after approximately two cycles following a ground fault.

[0107] Core equipment: surge arresters, disconnecting switches (DS3691 / DS3692), circuit breakers (CB3690), main transformers, and starting transformers; The ATP simulation results show that the steady-state peak value of the grounding grid (including steady-state current and steady-state voltage) occurs at the second terminal cable of the second main bus circuit.

[0108] Record the current data of each grounding point injected into the switchyard grounding network, obtain the data of each grounding down conductor obtained through ATP, obtain the current data of each grounding point injected into the GIS grounding network, and input them into CDEGS for electromagnetic characteristic analysis of the switchyard grounding system; the electromagnetic characteristic items include: ground potential rise, ground surface potential, step voltage, contact voltage, conductor current and magnetic field distribution.

[0109] Step S7, Safety assessment of the equipment.

[0110] Equipment insulation withstand voltage standards and data: Lightning Impulse Withstand Voltage (BIL): Measures the ability of equipment to withstand a lightning impulse (1.2 × 50 μs full-wave pulse).

[0111] Operating shock withstand voltage (BSL): measures the ability of equipment to withstand operating shocks (250 × 2500 μs full-wave pulses).

[0112] Table 3 is a summary table of the pressure resistance data of each device.

[0113] Since the Breaking Voltage Suppression (BSL) is the operating impulse withstand voltage, and both switching operation overvoltages and single-phase ground faults involve the closing and opening of disconnecting switches, they must be included in the assessment. However, lightning strikes are a natural phenomenon and do not involve switching operations; therefore, lightning overvoltages do not require assessment of the BSL of the relevant system equipment.

[0114] The data of lightning impulse withstand voltage (BIL) and switching impulse withstand voltage (BSL) of each device are summarized. Combined with the ATP simulation results, the device withstand capability of lightning strikes, switching overvoltages and grounding faults is evaluated. The actual peak overvoltage experienced by the device is compared with the insulation withstand voltage limit (BIL / BSL) to verify whether the margin is ≥20%.

[0115] Margin = (1-V) 限值 / V 实际 )×100%. Where, V 限值 It is the highest permissible voltage value set to ensure personal or equipment safety, V 实际 It is the voltage value measured during actual operation or testing.

[0116] Switch operation overvoltage and grounding fault: Circuit breaker: Maximum transient voltage 580kV (<950kV BSL, margin 39%); Main transformer: Maximum fault voltage 245kV (<950kV BSL, margin 74%); Surge arrester: Maximum withstand voltage 666kV (<1300kV BIL, margin 49%).

[0117] Conclusion: The equipment has sufficient insulation margin and the equipment risk is controllable.

[0118] Lightning overvoltage (BIL assessment only): Busbar voltage transformer: Lightning voltage 673kV (<1300kV BIL, margin 48%) Other equipment: all meet the requirement of V lightning strike ≤ 0.8 × BIL (e.g., the limit for 1040kV circuit breakers). Conclusion: No limits exceeded. All equipment is safe.

[0119] Step S8, personnel safety assessment.

[0120] Standards and data for personnel safety assessment: 1. Ground potential rise (GPR): The voltage difference between the highest potential of the grounding grid and the distant zero potential reference point, reflecting the overall energization level of the grounding system during a fault or lightning strike.

[0121] 2. Step voltage Vs: The voltage difference (between feet) caused by the difference in ground potential when a person's feet are 1 meter apart. Risk scenario: People walking near the grounding grid during lightning / faults.

[0122] Safety limit ≤ 697V peak value (wet cement floor, 50kg person).

[0123] 3. Contact voltage Vt: The potential difference between the person's standing point and the casing of the grounded equipment being touched (between hand and foot). Risk scenario: Personnel touching the casing of energized equipment.

[0124] Safety limit ≤ 563V peak value (wet cement floor, 50kg person).

[0125] 4. Transfer Voltage Vtrf: The potential difference between the high potential of the grounding grid (GPR) conducted to the external area through a metallic conductor (such as cable shielding or a conduit) and the distant ground. Transfer voltage creates metal-to-metal contact voltage: The potential difference between two metal objects (such as a fence and a lamppost) when a person's hands simultaneously touch them. Transfer voltage creating metal-to-metal contact voltage is the most dangerous situation. The peak value of transferred voltage forming metal-to-metal contact voltage is ≤519V.

[0126] The limits are calculated based on wet cement ground (ρ_s=21Ω·m), 50kg personnel, and a failure time of 0.1 seconds.

[0127] The ground potential rise (GPR), contact voltage, and step voltage generated by switch operation overvoltage and grounding fault are all less than the personnel safety limits (GPR < 563V, step voltage < 697V). Therefore, the risk of harm to personnel is relatively small. Lightning overvoltage occurs because after a lightning strike to the phase conductors of a transmission tower, the lightning current flows into the busbar of the section, resulting in a substantial current flowing through all equipment. This current eventually reaches the grounding grid and enters the earth. Therefore, when lightning strikes the phase conductors of the tower and the grounding grid itself, they experience considerable lightning current. This causes the ground potential rise (GPR) and step voltage at these locations to exceed the permissible values ​​for personnel safety, reaching as high as 2408V and 902V respectively, posing an extremely high risk of harm to personnel. If a lightning strike actually occurs, it will cause immense damage. The solution is to strengthen overvoltage protection on low-voltage equipment and zinc oxide surge arresters, and ensure proper insulation and grounding to prevent disasters.

[0128] It is understood that those skilled in the art can make equivalent substitutions or modifications to the technical solution and inventive concept of the present invention, and all such substitutions or modifications should fall within the protection scope of the appended claims.

Claims

1. A GIS fault analysis method based on multiphysics coupling simulation, characterized in that, Includes the following steps: Step S1, Organizing equipment data: The GIS system connects the power transmission system and the power plant; the GIS system includes main busbars, section busbars, gas-insulated switchgear, busbar voltage transformers and surge arresters; the power transmission system includes overhead transmission lines and power sources; the power plant includes generators, main transformers, starting transformers and starting transformer loads; Collect the electrical and geometric parameters of the above-mentioned equipment, and simultaneously integrate the data of the GIS grounding network; Step S2: Construct the overall model using the electromagnetic transient analysis software ATP: Step S21, GIS system model establishment: Sequentially establish the main busbar model, section busbar model, gas-insulated switchgear model, busbar voltage transformer model, and surge arrester model; Step S22, Modeling of Overhead Transmission Lines: Sequentially establish the overhead transmission line model and the power source model; Step S23, Establishment of the power plant model: Sequentially establish the generator model, main transformer model, starting transformer model, and starting transformer load model; Step S3, Establishment of GIS grounding grid model: Construct GIS grounding grid model using CDEGS grounding system electromagnetic characteristic analysis software; Step S4: Characteristic analysis of overvoltage during switch operation; simulate synchronous, asynchronous, opening and closing of the disconnecting switch, and extract the peak value and waveform of transient overvoltage; Step S5: Characteristic analysis of lightning overvoltage; inject 40kA lightning current to evaluate the equipment insulation withstand and surge arrester operation characteristics; Step S6, Characteristic analysis of grounding fault; Set a short circuit in phase A of the main busbar to verify the current shunting capacity of the grounding grid; Step S7, Safety assessment of the equipment; compare the overvoltage peak value with the equipment's electrical impulse withstand voltage and switching impulse withstand voltage limit to verify that the insulation margin is ≥20%; Step S8: Safety assessment of personnel; verification of contact voltage and step voltage, and location of high-risk areas.

2. The GIS fault analysis method based on multiphysics coupling simulation according to claim 1, characterized in that, Step S21 includes: Step S211, Main busbar model establishment and parameter setting: Input the following parameters into ATP to establish the main busbar model: inner conductor inner diameter, inner conductor outer diameter, outer shell inner diameter, outer shell outer diameter, inner conductor resistivity and outer shell resistivity; Step S212, Section busbar model establishment and parameter setting: The ultra-high voltage system adopts a one-and-a-half circuit breaker busbar architecture, with three sets of circuit breakers configured for each span; a set of disconnecting switches is connected in series upstream and downstream of each circuit breaker; input the following parameters into ATP to establish the section busbar model: inner conductor inner diameter, inner conductor outer diameter, cylinder shell inner diameter, cylinder shell outer diameter, inner conductor resistivity, and shell resistivity; Step S213, Model establishment and parameter setting of gas-insulated switchgear: Input the following parameters into ATP to establish the model of gas-insulated switchgear: inner conductor inner diameter, inner conductor outer diameter, outer shell inner diameter, outer shell outer diameter, inner conductor resistivity and outer shell resistivity; Step S214, Bus voltage transformer model establishment and parameter setting: The bus voltage transformer is a three-phase, three-winding transformer, with the primary, secondary, and tertiary sides all using a Y connection; input the following parameters into ATP to establish the bus voltage transformer model: rated capacity, primary winding rated voltage, secondary winding rated voltage, tertiary winding rated voltage, primary winding impedance percentage, secondary and tertiary winding impedance percentage, reactance-resistance ratio, and load power factor; Step S215, Surge arrester model establishment and parameter setting: Input the following parameters into ATP to establish the surge arrester model: reference voltage, flashover voltage per unit, initial voltage, number of conductors in parallel and error tolerance.

3. The GIS fault analysis method based on multiphysics coupling simulation according to claim 2, characterized in that, Step S22 includes: Step S221, Establishment and parameters of the overhead transmission line model: Input the following parameters into ATP to establish the overhead transmission line model: voltage level, phase conductor specifications, conductor material, conductor diameter, conductor resistance, overhead ground wire type, ground wire diameter and ground wire resistance; Step S222, Power supply model establishment and parameters: Input the following parameters into ATP to establish the power supply model: rated voltage, peak phase voltage, short-circuit current, power supply frequency, voltage phase angle difference, reactance-resistance ratio, system equivalent impedance, equivalent resistance, equivalent inductive reactance, and equivalent inductance.

4. The GIS fault analysis method based on multiphysics coupling simulation according to claim 3, characterized in that, Step S23 includes: Step S231, Generator Model Establishment and Parameter Setting: Input the following parameters into ATP to establish the generator model: rated voltage, rated capacity, power factor, subtransient reactance, power supply frequency, and voltage source phase difference; Step S232, Main transformer model establishment and parameter setting: The main transformer model is established by raising the generator output voltage to the transmission level. Its low-voltage side voltage must be consistent with the generator output voltage, and its high-voltage side is matched to the grid level. The simulated main transformer model is an ideal transformer, without considering iron loss and excitation current. The following parameters are input into ATP to establish the main transformer model: main transformer capacity, primary side rated line voltage, secondary side rated line voltage, and equivalent impedance at 75°C. Step S233, Start transformer model establishment and parameter setting: Input the following parameters in ATP to establish the transformer model: capacity, primary line voltage, secondary line voltage, tertiary line voltage and impedance percentage; Step S234, Start the transformer load model establishment and parameter setting: Start the load connected to the secondary and tertiary sides of the transformer; input the following parameters in ATP to establish the transformer load model: Secondary-side load 1: system capacity, voltage level, and power factor; Third-side load 2: system capacity, voltage level, and power factor.

5. The GIS fault analysis method based on multiphysics coupling simulation according to claim 4, characterized in that, In step S3, the parameters of the GIS grounding grid model are: coverage area, cross-sectional area of ​​a single bare copper wire, grid cell size, number of horizontal conductors, number of vertical conductors, and burial depth. Grounding down conductors include forced grounding points and potential balancing reinforcement points for equipment. Forced grounding points for equipment include auxiliary grounding wires for main busbars, neutral points of voltage transformers, segment connection points, grounding of surge arresters, and grounding of GIS shells. Potential balancing reinforcement points include the four corners of the grounding grid boundary and the central area of ​​the grid. The verification criteria are as follows: Potential gradient limit: The surface potential difference between adjacent injection points ≤ 10V / m; Current distribution error: The error between the measured current at the equipment grounding point and the ATP simulation value < 5%; Grid density verification: If the potential gradient at the center of a 5m×5m grid is > 15V / m, it needs to be densified to 3m×3m; The transient current amplitude and phase data of the grounding down conductor are obtained by simulation using the electromagnetic transient analysis software ATP, and then input into the grounding system electromagnetic characteristic analysis software CDEGS to complete the three-dimensional grounding grid electromagnetic field calculation. Establish a coordinate mapping database between GIS equipment grounding points and grounding grids to achieve accurate tracing of fault current paths.

6. The GIS fault analysis method based on multiphysics coupling simulation according to claim 5, characterized in that, In step S4, with the circuit breaker open, the transient voltage generated by the switching operation of the disconnecting switches connected before and after the circuit breaker is simulated using the electromagnetic transient analysis software ATP. Operating conditions:

1. When operating the upper disconnect switch, all disconnect switches and circuit breakers in the middle and lower sections should remain closed and energized.

2. When operating the lower disconnect switch, all disconnect switches and circuit breakers in the middle and upper sections should remain closed and energized.

3. When not in the operating position, all disconnect switches and circuit breakers remain in the closed state, and the system is loaded with rated voltage; Settings for the electromagnetic transient analysis software ATP: For equipment in non-operational sections, the status of circuit breakers and disconnectors is as follows: closing time = -1 second, opening time = 1 second; at this time, the equipment remains in a closed and energized state. For the circuit breaker status corresponding to the operating section, the closing time = 1 second, and the opening time = -1 second; During synchronous closing, the closing time is 0.01667 seconds and the opening time is 1 second. During synchronous tripping, the closing time is -1 second and the tripping time is 0.01667 seconds. The operating mode of switch operation overvoltage is used to summarize the transient voltage peaks generated by the switchgear and find the maximum value of the transient voltage peak. Record the current data of each grounding point injected into the switchyard grounding network, obtain the data of each grounding down conductor through the electromagnetic transient analysis software ATP, obtain the current data of each grounding point injected into the GIS grounding network, and input them into the grounding system electromagnetic characteristic analysis software CDEGS to perform electromagnetic characteristic analysis of the switchyard grounding system; the electromagnetic characteristic items include: ground potential rise, ground surface potential, step voltage, contact voltage, conductor current and magnetic field distribution.

7. The GIS fault analysis method based on multiphysics coupling simulation according to claim 6, characterized in that, In step S5, all circuit breakers and disconnectors are operated in the closed state, meaning the main busbar and section busbar are energized. A 40kA lightning current is injected into the phase conductors, overhead ground wires, and GIS grounding grid of the transmission tower in circuit 1, and the lightning overvoltage generated by each device is observed. The current data of each grounding point injected into the switchyard grounding grid are recorded. The current data of each grounding down conductor obtained through ATP are used to obtain the current data of each grounding point injected into the GIS grounding grid. The data are then input into CDEGS for electromagnetic characteristic analysis of the switchyard grounding system. The electromagnetic characteristic items include: ground potential rise, ground surface potential, step voltage, contact voltage, conductor current, and magnetic field distribution.

8. The GIS fault analysis method based on multiphysics coupling simulation according to claim 7, characterized in that, In step S6, the fault mode is: the main busbar has an LCC line module, and the A phase conductor of the LCC line module is short-circuited with the auxiliary grounding wire; Fault timing: A single-phase ground fault is triggered at 0.1 seconds and cleared at 0.2 seconds; Analysis objective: To monitor the voltage and current transient characteristics of critical equipment during a fault. Record the current data of each grounding point injected into the switchyard grounding network, obtain the data of each grounding down conductor obtained through ATP, obtain the current data of each grounding point injected into the GIS grounding network, and input them into CDEGS for electromagnetic characteristic analysis of the switchyard grounding system; the electromagnetic characteristic items include: ground potential rise, ground surface potential, step voltage, contact voltage, conductor current and magnetic field distribution.

9. The GIS fault analysis method based on multiphysics coupling simulation according to claim 8, characterized in that, In step S7, the data of lightning impulse withstand voltage (BIL) and switching impulse withstand voltage (BSL) of each device are summarized. Combined with the ATP simulation results, the device withstand capability for lightning strikes, switching overvoltages and grounding faults is evaluated. The actual overvoltage peak value borne by the device is compared with the insulation withstand voltage limit to verify whether the insulation margin is ≥20%.

10. The GIS fault analysis method based on multiphysics coupling simulation according to claim 9, characterized in that, In step S8, the ground potential rise, step voltage, contact voltage, and transfer voltage are examined, and personnel safety limits are set. For switch operation overvoltage and grounding fault, it is determined that the resulting ground potential rise, contact voltage and step voltage are all less than the personnel safety limit. For lightning overvoltage, examine the ground potential rise and step voltage when the lightning strikes the phase conductor and grounding grid of the transmission tower to see if they exceed the personnel safety limits.

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