Method and device for calculating transient electromagnetic environment of transformer substation

Abstract

The invention provides a substation transient electromagnetic environment calculation method and device, and belongs to the field of substations. The method comprises the following steps: establishing a transient electromagnetic field calculation model; based on the model, determining the contribution of a current element electric dipole to an electromagnetic field of an observation point and integrating along the length of a bus to obtain a single-point transient electromagnetic field intensity; carrying out boundary processing by adopting an FDTD method and combining a Mur absorption boundary condition, and iteratively expanding the single-point transient electromagnetic field intensity to the whole space of the transformer substation to obtain initial space transient electromagnetic field distribution; considering ground influence, performing reflection and attenuation correction on the initial spatial transient electromagnetic field distribution to obtain corrected spatial transient electromagnetic field distribution; and integrating the corrected spatial transient electromagnetic field distribution to obtain a calculation result of the transient electromagnetic environment of the transformer substation. According to the method, transient electromagnetic environment calculation considering calculation efficiency and spatial distribution details is realized, and reliable theoretical support is provided for transient electromagnetic interference protection design of the transformer substation.

Description

Technical Field

[0001] This invention belongs to the field of substation technology, specifically relating to a method and apparatus for calculating the transient electromagnetic environment of a substation. Background Technology

[0002] With the development of power systems, substations play a crucial role in power transmission and distribution. However, under abnormal operating conditions such as short-circuit faults and lightning strikes, substations generate transient electromagnetic environments with high amplitude, wide bandwidth, and rapid changes. These transient electromagnetic signals can interfere with secondary equipment, such as relay protection, automation devices, and 5G communication equipment, through spatial radiation or conduction coupling, seriously threatening the safe and stable operation of the power grid. Therefore, accurately calculating the transient electromagnetic environment of substations is of great significance for ensuring the reliable operation of the power system.

[0003] Currently, methods for calculating transient electromagnetic environments mainly include the Finite-Difference Time-Domain (FDTD) method and electromagnetic transient simulation software. The FDTD method analyzes the electromagnetic field distribution across space using discrete Maxwell's equations, but it requires sophisticated mesh generation and boundary treatment. Electromagnetic transient simulation software focuses on circuit-level transient analysis, such as short-circuit current, but it is insufficient in characterizing the spatial electromagnetic field distribution. These methods have some application in single scenarios, such as short-circuit faults under ideal conditions.

[0004] Existing methods for calculating the transient electromagnetic environment of substations have several shortcomings. Firstly, their applicability is limited; a single method struggles to balance efficiency at a single point with detailed spatial distribution, failing to provide comprehensive and accurate theoretical support for the design of transient electromagnetic interference protection in substations. Secondly, transient electromagnetic field calculations often neglect key environmental factors, particularly the impact of ground reflection and scattering on the electromagnetic field. They assume the electromagnetic field propagates in infinite free space, which contradicts the actual ground-based influences experienced by substations. Furthermore, they fail to consider electromagnetic scattering from metal equipment within the substation, leading to significant deviations in local field strength calculations. Additionally, the use of ideal current sources does not match the complex current waveforms generated by actual short-circuit faults, resulting in the omission of high-frequency components in the calculation. Summary of the Invention

[0005] In view of this, the present invention provides a method and apparatus for calculating the transient electromagnetic environment of a substation that fits the actual environment of the substation and takes into account both accuracy and completeness. It aims to fully consider the influence of ground factors (reflection and scattering) on ​​the electromagnetic field distribution, establish a calculation model of the transient electromagnetic field in the switch operation space that includes ground factors, and improve the accuracy of transient electromagnetic field calculation.

[0006] To achieve the above objectives, the technical solution provided by the present invention is as follows:

[0007] In a first aspect, the present invention provides a method for calculating the transient electromagnetic environment of a substation, comprising the following steps:

[0008] A transient electromagnetic field calculation model is established; in the transient electromagnetic field calculation model, the transient current of the substation bus is subdivided into uniformly distributed current element electric dipoles;

[0009] Based on the transient electromagnetic field calculation model, the electromagnetic field contribution of the current element electric dipole to the observation point is determined and integrated along the length of the generatrix to obtain the transient electromagnetic field intensity at a single point.

[0010] Using the FDTD method and combining Mur absorption boundary conditions for boundary treatment, the single-point transient electromagnetic field intensity is iteratively extended to the entire space of the substation to obtain the preliminary spatial transient electromagnetic field distribution.

[0011] Considering the influence of the ground, the initial spatial transient electromagnetic field distribution is corrected by reflection and attenuation to obtain the corrected spatial transient electromagnetic field distribution;

[0012] By integrating and correcting the spatial transient electromagnetic field distribution, the calculation results of the transient electromagnetic environment of the substation are obtained.

[0013] Furthermore, a transient electromagnetic field calculation model is established, including:

[0014] The substation busbar is subdivided into several small segments along its length. Each segment is used as a current element electric dipole with uniform current distribution, and the current of the current element electric dipole is characterized by transmission line waveform.

[0015] Define the distance from the current element electric dipole to the observation point, and determine the basic physical parameters of the transient electromagnetic field calculation model.

[0016] Furthermore, the contribution of the current element electric dipole to the electromagnetic field at the observation point is determined and integrated along the length of the generatrix to obtain the transient electromagnetic field intensity at a single point, including:

[0017] The time partial derivative of the current in the electric dipole of the current element is approximated by the difference quotient formula, and the time integral of the current is approximated by the composite trapezoidal rule.

[0018] Substituting the results of the time partial derivative and time integral into the calculation formula of the electromagnetic field of the electric dipole, we obtain the horizontal electric field, radial electric field and magnetic field components generated by the current element electric dipole at the observation point.

[0019] The horizontal electric field, radial electric field, and magnetic field components are integrated along the length of the substation busbar, and the single-point transient electromagnetic field intensity at the observation point is obtained based on the integration results.

[0020] Furthermore, using the FDTD method combined with Mur absorption boundary conditions for boundary treatment, the single-point transient electromagnetic field intensity is iteratively extended to the entire space of the substation, yielding a preliminary spatial transient electromagnetic field distribution, including:

[0021] Based on Maxwell's equations for two-dimensional TE waves in cylindrical coordinates, the FDTD iterative formulas for the electric and magnetic field components are obtained.

[0022] The Mur absorption boundary condition is used to process the boundary in the plane below the busbar, and the FDTD iterative formula of the magnetic field component at the boundary is obtained. According to the active region and the passive region where the busbar is located, the FDTD iterative formula of the electric field component in the active region and the passive region is obtained.

[0023] Using the single-point transient electromagnetic field intensity as the initial input, the data is discretized and extended to the entire space of the substation through all FDTD iterative formulas to obtain the preliminary spatial transient electromagnetic field distribution.

[0024] Furthermore, the initial spatial transient electromagnetic field distribution is corrected for reflection and attenuation to obtain the corrected spatial transient electromagnetic field distribution, including:

[0025] Obtain ground medium parameters and air parameters; ground medium parameters include at least the relative permittivity and conductivity of the ground; air parameters include at least the permittivity and conductivity of the air.

[0026] Ground medium parameters and air parameters are incorporated into the calculation model of the preliminary space transient electromagnetic field distribution to correct the preliminary space transient electromagnetic field distribution.

[0027] By correcting the calculations, the spatial transient electromagnetic field distribution after considering ground reflection and attenuation is obtained, which is the corrected spatial transient electromagnetic field distribution.

[0028] Secondly, the present invention provides a substation transient electromagnetic environment calculation device, comprising:

[0029] The model building module is used to establish a transient electromagnetic field calculation model. In the transient electromagnetic field calculation model, the transient current of the substation bus is subdivided into uniformly distributed current element electric dipoles.

[0030] The first calculation module is used to determine the electromagnetic field contribution of the current element electric dipole to the observation point based on the transient electromagnetic field calculation model and integrate it along the length of the generatrix to obtain the transient electromagnetic field intensity at a single point.

[0031] The second calculation module is used to perform boundary processing using the FDTD method combined with Mur absorption boundary conditions, and iteratively extend the single-point transient electromagnetic field intensity to the entire space of the substation to obtain the preliminary spatial transient electromagnetic field distribution.

[0032] The correction module is used to take into account the influence of the ground and perform reflection and attenuation correction on the initial space transient electromagnetic field distribution to obtain the corrected space transient electromagnetic field distribution.

[0033] The results output module is used to integrate the corrected spatial transient electromagnetic field distribution to obtain the calculation results of the transient electromagnetic environment of the substation.

[0034] Furthermore, in the model building module, a transient electromagnetic field calculation model is established, including:

[0035] The substation busbar is subdivided into several small segments along its length. Each segment is used as a current element electric dipole with uniform current distribution, and the current of the current element electric dipole is characterized by transmission line waveform.

[0036] Define the distance from the current element electric dipole to the observation point, and determine the basic physical parameters of the transient electromagnetic field calculation model.

[0037] Furthermore, in the first calculation module, the electromagnetic field contribution of the current element electric dipole to the observation point is determined and integrated along the length of the generatrix to obtain the transient electromagnetic field intensity at a single point, including:

[0038] The time partial derivative of the current in the electric dipole of the current element is approximated by the difference quotient formula, and the time integral of the current is approximated by the composite trapezoidal rule.

[0039] Substituting the results of the time partial derivative and time integral into the calculation formula of the electromagnetic field of the electric dipole, we obtain the horizontal electric field, radial electric field and magnetic field components generated by the current element electric dipole at the observation point.

[0040] The horizontal electric field, radial electric field, and magnetic field components are integrated along the length of the substation busbar, and the single-point transient electromagnetic field intensity at the observation point is obtained based on the integration results.

[0041] Furthermore, in the second calculation module, the FDTD method is used, combined with Mur absorption boundary conditions, to perform boundary processing. The single-point transient electromagnetic field intensity is iteratively extended to the entire space of the substation, resulting in a preliminary spatial transient electromagnetic field distribution, including:

[0042] Based on Maxwell's equations for two-dimensional TE waves in cylindrical coordinates, the FDTD iterative formulas for the electric and magnetic field components are obtained.

[0043] The Mur absorption boundary condition is used to process the boundary in the plane below the busbar, and the FDTD iterative formula of the magnetic field component at the boundary is obtained. According to the active region and the passive region where the busbar is located, the FDTD iterative formula of the electric field component in the active region and the passive region is obtained.

[0044] Using the single-point transient electromagnetic field intensity as the initial input, the data is discretized and extended to the entire space of the substation through all FDTD iterative formulas to obtain the preliminary spatial transient electromagnetic field distribution.

[0045] Furthermore, in the correction module, the initial spatial transient electromagnetic field distribution is corrected for reflection and attenuation to obtain the corrected spatial transient electromagnetic field distribution, including:

[0046] Obtain ground medium parameters and air parameters; ground medium parameters include at least the relative permittivity and conductivity of the ground; air parameters include at least the permittivity and conductivity of the air.

[0047] Ground medium parameters and air parameters are incorporated into the calculation model of the preliminary space transient electromagnetic field distribution to correct the preliminary space transient electromagnetic field distribution.

[0048] By correcting the calculations, the spatial transient electromagnetic field distribution after considering ground reflection and attenuation is obtained, which is the corrected spatial transient electromagnetic field distribution.

[0049] Thirdly, the present invention provides a computer device, the device including a processor and a memory:

[0050] The memory is used to store computer programs and send the instructions of the computer programs to the processor;

[0051] The processor executes instructions from a computer program, such as the method for calculating the transient electromagnetic environment of a substation as described in the first aspect.

[0052] Fourthly, the present invention provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements a method for calculating the transient electromagnetic environment of a substation as described in the first aspect.

[0053] In summary, this invention provides a method and apparatus for calculating the transient electromagnetic environment of a substation, including establishing a transient electromagnetic field calculation model; in the transient electromagnetic field calculation model, the transient current of the substation bus is subdivided into uniformly distributed current element electric dipoles; based on the transient electromagnetic field calculation model, the electromagnetic field contribution of the current element electric dipoles to the observation point is determined and integrated along the length of the bus to obtain the single-point transient electromagnetic field intensity; using the FDTD method, combined with Mur absorption boundary conditions for boundary processing, the single-point transient electromagnetic field intensity is iteratively extended to the entire space of the substation to obtain a preliminary spatial transient electromagnetic field distribution; considering the ground influence, the preliminary spatial transient electromagnetic field distribution is corrected by reflection and attenuation to obtain a corrected spatial transient electromagnetic field distribution; integrating the corrected spatial transient electromagnetic field distribution, the calculation result of the transient electromagnetic environment of the substation is obtained. This invention solves for the transient electromagnetic field intensity at a single point by subdividing the transient current of the substation bus into uniformly distributed current element electric dipoles. Then, it iteratively extends the calculation to the entire space using the FDTD method combined with Mur absorption boundary conditions, while also considering ground influence factors. This achieves accurate calculation of the transient electromagnetic environment that balances computational efficiency and spatial distribution details, effectively improving the fit between the calculation results and the actual scenario, and providing reliable theoretical support for the design of transient electromagnetic interference protection in substations. Attached Figure Description

[0054] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0055] Figure 1 A flowchart of a method for calculating the transient electromagnetic environment of a substation, provided as an embodiment of the present invention;

[0056] Figure 2 A diagram illustrating the electromagnetic field model of a pole on an ideal conductor, provided as an embodiment of the present invention.

[0057] Figure 3 A diagram illustrating the calculation model of the switching electromagnetic field provided in an embodiment of the present invention;

[0058] Figure 4 The bus current waveform diagram provided in the embodiment of the present invention;

[0059] Figure 5 The waveform diagram for single-point electric field calculation provided in the embodiment of the present invention;

[0060] Figure 6 The waveform diagram for single-point magnetic field calculation provided in the embodiment of the present invention;

[0061] Figure 7 This is a schematic diagram of the spatial distribution of electric and magnetic fields in cylindrical coordinates provided in an embodiment of the present invention;

[0062] Figure 8 A boundary map showing the boundary processing of the Mur absorption boundary provided in this embodiment of the invention;

[0063] Figure 9 This is a diagram showing the electromagnetic field distribution above the ground after the disconnecting switch is closed, provided in an embodiment of the present invention.

[0064] Figure 10 This is a diagram showing the spatial electromagnetic field distribution after the disconnecting switch is closed, taking into account ground influence, provided in an embodiment of the present invention.

[0065] Figure 11 A diagram showing the magnitude of the electric field on the ground provided for an embodiment of the present invention;

[0066] Figure 12 A block diagram of a substation transient electromagnetic environment calculation device provided in an embodiment of the present invention;

[0067] Figure 13 This is a block diagram of a computer device provided in an embodiment of the present invention. Detailed Implementation

[0068] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0069] In high-voltage substations, switching operations are required for operation, maintenance, or fault protection activation, generating switching overvoltages on the conductors. Furthermore, during switching operations, dozens or even hundreds of repeated arcing and extinguishing occur between the contacts, creating a series of complex transient processes within the oscillating circuit formed by the inductance and capacitance of the system, resulting in an electrical fast transient pulse (EFT) cluster. These EFTs, radiating from the transmission conductors like antennas, create transient electromagnetic fields in the surrounding space, interfering with the substation's secondary control equipment. Therefore, this invention proposes a method and apparatus for calculating the transient electromagnetic environment of substations that balances single-point accuracy with global distribution and considers ground-level influences.

[0070] Please see Figure 1 This embodiment provides a method for calculating the transient electromagnetic environment of a substation, including the following steps:

[0071] S11: Establish a transient electromagnetic field calculation model; in the transient electromagnetic field calculation model, the transient current of the substation bus is subdivided into uniformly distributed current element electric dipoles.

[0072] It should be noted that transient electromagnetic fields refer to electromagnetic fields generated during substation switching operations (such as arc ignition and arc extinguishing) that change rapidly over time. They are characterized by their instantaneous, high-frequency, and pulsed nature, and are the main source of electromagnetic interference affecting the normal operation of secondary equipment.

[0073] Transient current is a rapidly changing current (containing high-frequency components) generated by the oscillation of circuit inductance and capacitance during switching operations.

[0074] Current-element electric dipole: A busbar is decomposed along its length into countless infinitesimally small segments, each with a uniformly distributed current. The combination of this small current segment and the segment itself constitutes a current-element electric dipole.

[0075] The transient current of a substation busbar is a complex spatiotemporal variable, making direct calculation of the electromagnetic field it generates extremely difficult. This step utilizes a discretization approach, decomposing the busbar transient current into countless uniformly distributed current element electric dipoles. The magnitude and direction of the current in each current element can be approximated as constant, simplifying the calculation of the electromagnetic field of a single unit. Simultaneously, a computational model framework is constructed that includes current element parameters, busbar geometry, and fundamental physical parameters (such as the vacuum permittivity).

[0076] S12: Based on the transient electromagnetic field calculation model, the electromagnetic field contribution of the current element electric dipole to the observation point is determined and integrated along the length of the busbar to obtain the transient electromagnetic field intensity at a single point.

[0077] It should be noted that the observation point refers to any point in space where the electromagnetic field strength needs to be calculated (such as the installation location of secondary equipment or the cable laying path), which is the target location for electromagnetic field calculation.

[0078] The electromagnetic field contribution is the tiny electromagnetic field (including electric and magnetic field components) generated by a single current element electric dipole at the observation point.

[0079] Based on the superposition principle of electromagnetics, the electromagnetic field (i.e., the electromagnetic field contribution) generated by a single current element electric dipole at the observation point can be solved using classical electromagnetic theory. The total field strength of the entire busbar at the observation point is the vector sum of the contributions of all current element electric dipoles. This step, through integration along the length of the busbar, summarizes the minute contributions of countless current elements, ultimately obtaining the single-point transient electromagnetic field strength at the observation point.

[0080] S13: Using the FDTD method and combining Mur absorption boundary conditions for boundary treatment, the single-point transient electromagnetic field intensity is iteratively extended to the entire space of the substation to obtain the preliminary spatial transient electromagnetic field distribution.

[0081] It should be noted that FDTD (Finite-Difference Time-Domain) is a numerical computation method that discretizes space into a grid and time into step sizes, and solves Maxwell's equations iteratively.

[0082] Mur absorbing boundary conditions are a boundary processing technique used in FDTD calculations. By absorbing electromagnetic waves at the boundary through a differential scheme, it reduces the interference of boundary reflections on the calculation results and simulates the propagation effect of electromagnetic fields in infinite space.

[0083] Iterative expansion uses the transient electromagnetic field intensity at a single point as the initial input. Through time-step iteration and spatial grid update using the FDTD method, the electromagnetic field data of all grid points in the entire space of the substation are calculated step by step, realizing the expansion from a single point to the entire domain.

[0084] The preliminary spatial transient electromagnetic field distribution is the magnitude and spatiotemporal variation law of the transient electromagnetic field at various points in the entire space without considering the influence of the ground.

[0085] The core of the FDTD method is to divide the space into a uniform grid and the time into fixed step sizes. By discretizing Maxwell's equations, the electromagnetic field components at each grid point are iteratively updated. Combined with Mur absorbing boundary conditions, the reflection interference of electromagnetic waves by the grid boundaries can be avoided, simulating the propagation effect in infinite space. This step uses the transient electromagnetic field intensity at a single point as the initial input, and through FDTD iterative calculation, gradually updates the electromagnetic field data of all grid points in the entire space, ultimately obtaining a preliminary spatial transient electromagnetic field distribution.

[0086] S14: Considering the influence of the ground, the initial spatial transient electromagnetic field distribution is corrected by reflection and attenuation to obtain the corrected spatial transient electromagnetic field distribution.

[0087] It should be noted that reflection and attenuation correction refers to compensating for the changes in field strength caused by electromagnetic wave reflection at ground level and soil attenuation by introducing ground medium parameters and air parameters, thereby correcting the deviation in the initial distribution.

[0088] This step corrects the initial spatial distribution by taking into account ground influences, compensating for the field strength superposition caused by ground reflection and the field strength attenuation caused by soil conduction, so that the calculation results fit the actual environment of the substation (air-earth binary medium).

[0089] S15: Integrate the corrected spatial transient electromagnetic field distribution to obtain the calculation results of the transient electromagnetic environment of the substation.

[0090] This embodiment provides a method for calculating the transient electromagnetic environment of a substation. This method solves for the transient electromagnetic field intensity at a single point by subdividing the transient current of the substation bus into uniformly distributed current element electric dipoles. Then, iteratively extends the calculation to the entire space using the FDTD method combined with Mur absorption boundary conditions, while also considering ground influences. This achieves accurate calculation of the transient electromagnetic environment that balances computational efficiency and spatial distribution details, effectively improving the fit between the calculation results and the actual scenario, and providing reliable theoretical support for the design of transient electromagnetic interference protection in substations.

[0091] In one embodiment of the present invention, a transient electromagnetic field calculation model is established, including:

[0092] S21: The substation busbar is subdivided into several small segments along its length. Each segment is used as a current element electric dipole with uniform current distribution, and the current of the current element electric dipole is characterized by the transmission line waveform.

[0093] S22: Define the distance from the current element electric dipole to the observation point and determine the basic physical parameters of the transient electromagnetic field calculation model.

[0094] Please see Figure 2 , Figure 2 A model of the electromagnetic field of a dipole on an ideal conductor is shown. During the propagation of the transient electromagnetic wave generated by the switching operation, the busbar can be considered as a linear antenna, and the electromagnetic field generated by the transient current in the busbar can be regarded as the superposition of fields generated by the motion of dipoles in the conductor channel. Assuming the current propagates at a uniform velocity *c* along the *z* direction, a transmission line waveform is adopted for this current, i.e.:

[0095] (1)

[0096] Given the pulse current on the transmission line, such as Figure 2 As shown, the conductor is subdivided into many small segments, each of which is considered a current source. It is assumed that the current in each segment is uniformly distributed, and the length of the segment is used as the reference value. Approximate equivalence The field generated at point P by the current in the entire conductor is the vector summation of the field quantities generated at point P by the current in each small segment. That is, the current element... Treating it as a dipole, the electromagnetic field of each current element is calculated, and then the electromagnetic field around the conductor can be obtained by integrating along the line. Figure 2 middle, The observation point to be calculated is shown below. The electric field formula for a single electric dipole is as follows:

[0097] (2)

[0098] (3)

[0099] (4)

[0100] In the formula, , , They represent Electric field intensity element in the direction, Electric field intensity element in the direction, The magnetic field strength element in the direction; This represents the distance difference between the observation point and the current element along the axial direction (z-direction). For a single current dipole, the length of the infinitesimal element is... Let R be the vacuum conductivity, and R be the distance from the current dipole to the observation point. c is the speed of light.

[0101] Let the length of the conductor be L, then the electromagnetic field strength at the observation point is:

[0102] (5)

[0103] In the formula, , , They represent the observation points respectively. electric field strength in the direction, electric field strength in the direction, The magnetic field strength in the direction.

[0104] It should be noted that, since Equation 5 cannot be solved analytically, a small segment of the conductor is discretized in both time and space. The discretization of the bounded domain in time and space is strictly performed according to the FDTD stability condition. Spatial point coordinates. Can be recorded as , where Δr and Δz represent the grid step size in the r and z coordinate directions, respectively. The time step is taken as... According to the stability conditions of FDTD, the following should be satisfied:

[0105] (6)

[0106] Where C max Let be the maximum propagation speed of electromagnetic waves in the computation medium. Furthermore, to minimize the impact of numerical dispersion errors on accuracy, the spatial step size and the minimum wavelength of the electromagnetic problem under consideration must satisfy the following constraint: ,in, The maximum value of the spatial step size. It is the minimum wavelength.

[0107] In one embodiment of the present invention, determining the electromagnetic field contribution of the current element electric dipole to the observation point and integrating it along the length of the generatrix to obtain the transient electromagnetic field intensity at a single point includes:

[0108] S31: The time partial derivative of the current in the electric dipole of the current element is approximated by the difference quotient formula, and the time integral of the current is approximated by the complex trapezoidal formula.

[0109] For example, the time partial derivatives of the current in equations 2 to 4 can be approximated using difference quotients as follows:

[0110] (7)

[0111] The time integral of the current in equations 2 to 4 can be approximated using the composite trapezoidal rule:

[0112] (8)

[0113] Where R j is the spatial distance from the j-th current element to the observation point, n is the index number of the time step, and N is the total number of time steps.

[0114] S32: Substitute the results of the time partial derivative and time integral into the calculation formula of the electromagnetic field of the electric dipole to obtain the horizontal electric field, radial electric field and magnetic field components generated by the current element electric dipole at the observation point.

[0115] Substituting equations 7 and 8 into equations 2 to 4, we can obtain the horizontal electric field generated by the current element electric dipole at the observation point. Direction), radial electric field ( Direction) and magnetic field components ( direction).

[0116] S33: Integrate the horizontal electric field, radial electric field, and magnetic field components along the length of the substation busbar, and obtain the single-point transient electromagnetic field intensity based on the integration results.

[0117] Combining equations 2 to 4, and summing the integrals of equation 5, we can obtain the electromagnetic field generated by the transient current at various points in space. The single-point electromagnetic field is represented as follows:

[0118] (9)

[0119] In the formula, E and H represent the electric and magnetic fields generated by the transient current at a point in space.

[0120] by Figure 3 Taking the switching electromagnetic field calculation model shown as an example, this paper introduces the calculation of transient electromagnetic field intensity at different single points in space. Figure 3 As shown, the busbar height is 8m and the busbar length is 200m. The current is taken as: The switching current waveform is as follows Figure 4 As shown. Let A be the distance from the busbar. The four points along the busbar are A(1,10), B(1,100), C(6.5,10), and D(6.5,100).

[0121] Figure 5 The waveforms of the single-point electric field at points A, B, C, and D are calculated. Figure 5 (a) shows the calculated waveform of the electric field in the horizontal direction, (b) shows the calculated waveform of the electric field in the radial direction, and (c) shows the calculated waveform of the total electric field. From (a), it can be seen that the horizontal electric field is largest at point A(1,10) (near field). =70kV / m; while the horizontal electric field is smallest at point D(6.5,100) (far field). =7kV / m. Furthermore, the greater the horizontal distance from the off-operation point, the smaller the electric field fluctuation. Therefore, the horizontal electric field waveforms at points A and C have a larger fluctuation range than those at points B and D. From (b), it can be seen that the radial electric field is largest at point B(1,100) (near field). =85kV / m; while the radial electric field at point D(6.5,100) (far field) is the smallest, E rmax =15kV / m. Furthermore, the radial electric field waveforms at points A and B are larger than those at points C and D. Therefore, the magnitude of the radial electric field is inversely proportional to the perpendicular distance from the busbar. This is because the electric field is directly proportional to the charge on the busbar, that is, the time integral of the busbar current. When the charge equals the peak voltage to ground (408kV for a 500kV system) multiplied by the transmission line's capacitance to ground, the radial electric field on the busbar during switching operations can be expressed as:

[0122] (10)

[0123] In the formula, It is the voltage relative to ground. It is wave impedance. It is the vertical height of the busbar above the electric field sensor. From Figure 5 As can be seen from (c), the electric field did not decay to 0 in the end. This is because the electric field is proportional to the charge on the busbar, and the charge on the busbar will not decay to 0 over time. After a period of time, the charge on the busbar will remain unchanged.

[0124] Figure 6 Calculate the waveforms of the single-point magnetic field at points A, B, C, and D. Figure 6 It can be seen that the transient current waveform and the magnetic field waveform of the busbar are basically the same. This is because the magnetic field component is directly proportional to the current I on the busbar, expressed as:

[0125] (11)

[0126] When the radial distance from the busbar is the same, the changes in the magnetic field waveform are basically the same, except that there is a certain time delay at points farther away due to the propagation of the current on the busbar. When the radial distance increases, the attenuation of the magnetic field is more obvious, and the magnetic field at point A is much stronger than that at point C.

[0127] In the study of the characteristics of electromagnetic fields in substations, measurement studies can only obtain data at a certain point in space. To further study the changes and propagation of electromagnetic field waveforms over time, it is also necessary to know the changes in electric and magnetic fields throughout the entire substation space. The finite-difference time-domain method can be used to discretize the data from a single point in space to the entire space to calculate the spatial electromagnetic field.

[0128] In one embodiment of the present invention, the FDTD method is used, combined with Mur absorption boundary conditions for boundary treatment, to iteratively extend the single-point transient electromagnetic field intensity to the entire space of the substation, thereby obtaining a preliminary spatial transient electromagnetic field distribution, including:

[0129] S41: Based on Maxwell's equations for two-dimensional TE waves in cylindrical coordinates, the FDTD iterative formulas for the electric and magnetic field components are obtained.

[0130] In a three-dimensional cylindrical coordinate system, the coordinate variable is r. When the medium is rotationally symmetric about the Z-axis, Maxwell's equations in three-dimensional cylindrical coordinates can be transformed into partial differential equations in two-dimensional cylindrical coordinates, including TE and TM waves. Studying two-dimensional TE waves in cylindrical coordinates, in anisotropic or nondispersive medium spaces, Maxwell's formulas state:

[0131] (12)

[0132] (13)

[0133] Where E is the electric field vector and H is the magnetic field vector. It is the permeability. It is the dielectric constant. It is electrical conductivity.

[0134] The curl F of any vector can be known as:

[0135] (14)

[0136] Applying the formula to the two equations above, and performing difference discretization in time and space, the following formula can be derived in cylindrical coordinates:

[0137] (15)

[0138] (16)

[0139] (17)

[0140] in, It is a time increment. It is the vertical length of the rectangular unit. It is the side length. Electric field in 2-D cylindrical coordinates. , and magnetic field Spatial distribution such as Figure 7 As shown. During the calculation process, , , The numerical computation stability requirement, i.e., the Courant stability condition, should be met:

[0141] (18)

[0142] Where v is the propagation speed of electromagnetic waves in the medium.

[0143] S42: The Mur absorption boundary condition is used to process the boundary in the plane below the busbar, and the FDTD iterative formula of the magnetic field component at the boundary is obtained. According to the active region and the passive region where the busbar is located, the FDTD iterative formula of the electric field component in the active region and the passive region is obtained.

[0144] Currently, Mur absorbing boundary conditions are widely used, and in recent years, perfectly matched layer PML absorbing boundary conditions have also seen widespread development and application. Because the amount of computational space data in substations is very large, although the accuracy of Mur absorbing boundary conditions is not as high as that of perfectly matched layer PML absorbing boundary conditions, the amount of data is small, and the accuracy is sufficient. Therefore, this embodiment uses Mur absorbing boundary conditions.

[0145] like Figure 8 As shown, utilizing the symmetry of cylindrical coordinates, only the boundary in the plane below the generatrix needs to be considered. In the generatrix system, three boundaries need to be considered: the ground plane, the left boundary, and the right boundary. After considering the boundary conditions, a discretized analysis is performed. The first-order connected boundary conditions for the magnetic field components are as follows:

[0146] 1) Along the z-direction

[0147] Left boundary (j=0-1 / 2, i+1 / 2):

[0148] (19)

[0149] Right boundary ( ):

[0150] (20)

[0151] 2) Along the r direction

[0152] lower boundary ( ):

[0153] (twenty one)

[0154] in: ;

[0155] c represents the propagation speed of electromagnetic waves in the air. For cylindrical coordinate systems, the active and passive regions within a conductor must be treated differently. For example, regarding the active and passive regions within a conductor:

[0156] Passive region:

[0157] (twenty two)

[0158] Active region:

[0159] (twenty three)

[0160] in, Indicates the busbar is Current unit.

[0161] S43: Using the single-point transient electromagnetic field intensity as the initial input, the single-point data is discretized and extended to the entire space of the substation through all FDTD iterative formulas to obtain the preliminary spatial transient electromagnetic field distribution.

[0162] Based on the FDTD iterative formulas for the electric and magnetic fields of two-dimensional TE waves in cylindrical coordinates, as well as the Mur absorption boundary conditions and the iterative rules for the active region (bus current unit region) and the passive region, the previously calculated single-point transient electromagnetic field intensity is used as the initial input data for FDTD iteration. Under the time and space step size that satisfies the Courant stability condition, the electric and magnetic field components of the discrete grid points in the substation space are updated one by one in the time domain (while the electromagnetic wave absorption at the edge of the space is handled by the boundary conditions to avoid reflection errors). Finally, the electromagnetic field data that only reflects a single point is discretized and extended to all grid points in the entire substation space to obtain the preliminary spatial transient electromagnetic field distribution containing different locations and times.

[0163] In one embodiment of the present invention, the preliminary spatial transient electromagnetic field distribution is corrected by reflection and attenuation to obtain a corrected spatial transient electromagnetic field distribution, including:

[0164] S51: Obtain ground medium parameters and air parameters; ground medium parameters include at least the relative permittivity and conductivity of the ground; air parameters include at least the permittivity and conductivity of the air.

[0165] S52: Introduce ground medium parameters and air parameters into the calculation model of the preliminary space transient electromagnetic field distribution to correct the preliminary space transient electromagnetic field distribution.

[0166] Conductivity of free space The dielectric constants are 0 and 0, respectively. Regarding equations 22 and 23, the dielectric constant of air... electrical conductivity magnetic permeability The relative permittivity of the earth is electrical conductivity At the air-ground interface, the dielectric constant and conductivity can be taken as the average of the two. Due to the abrupt changes in the electromagnetic parameters of air and ground (air has low dielectric and low conductivity; ground has high dielectric and high conductivity), in order to adapt to the calculation logic of FDTD continuous grid cells, this embodiment takes the average of the dielectric constant and conductivity of the two at the air-ground interface (to smooth out parameter abrupt changes and avoid numerical oscillations); then these ground medium parameters are substituted into the FDTD iterative formula (i.e., the preliminary spatial transient electromagnetic field distribution) of the aforementioned embodiment.

[0167] S53: By correcting the calculation, the spatial transient electromagnetic field distribution after considering the effects of ground reflection and attenuation is obtained, that is, the corrected spatial transient electromagnetic field distribution.

[0168] By combining the reflection and attenuation laws of electromagnetic waves at the interface of the medium, and using the iterative formula after substituting the ground parameters, the electromagnetic field components of the grid points in the whole space are updated, and finally the corrected distribution is obtained.

[0169] Many studies have neglected the influence of ground factors when calculating transient electromagnetic fields induced within substations. However, ground reflection and scattering of waves necessitate consideration of these factors to prevent significant errors in calculations. The following is a calculation and comparative analysis of the spatial field caused by switch operations, considering whether or not ground influences are taken into account:

[0170] Using the established mathematical model, the spatial electromagnetic field distribution of the physical model is calculated. The conductor is placed along the Z-axis, and its length is taken. The conductor's height above the ground is tentatively set to 8m, i.e., r = 8m. Applying the Finite-Difference Time-Domain (FDTD) method, the spatial and temporal mesh generation is performed while strictly considering the FDTD stability conditions and specific application requirements. The spatial step size for mesh generation is determined accordingly. Time step ,in Let be the spatial step size, and c be the propagation speed of the electromagnetic wave in space. The excitation source is a damped oscillating current source. ,in =1000A, , .

[0171] Without considering ground influences, the variation of the transient electromagnetic field generated by the switching operation in space on the ground plane is as follows: Figure 9 As shown, (a) and (b) are the spatial magnetic field distributions at time t=500*dt and t=1000*dt, respectively; (c) and (d) are the radial electric field distributions at time t=500*dt and t=1000*dt, respectively; (e) and (f) are the horizontal electric field distributions at time t=500*dt and t=1000*dt, respectively.

[0172] Figure 9 The electric and magnetic field distributions at times t=500*dt and t=1000*dt were calculated, showing the decay of the electric and magnetic fields over time. In (a), the maximum magnetic field value at t=500*dt exceeds 20 A / m, while in (b), the maximum magnetic field value at t=1000*dt does not exceed 14 A / m, and the magnetic field has almost decayed to zero near the switch. In (c), the radial electric field at the near-field end begins to increase at t=500*dt, with a maximum value not exceeding 8 kV / m, but at t=1000*dt (e.g., ... Figure 9 In (d), the maximum electric field does not exceed 5 kV / m. At the far-field end, the electric field begins to increase as the current propagates and eventually decays to a stable value. In (e) and (f), the horizontal electric field first increases and then decays at the near end. As zl increases, the horizontal electric field at the far end also begins to increase and eventually decays to a stable value.

[0173] Taking the influence of the ground surface into account, the relative permittivity of the earth is: electrical conductivity At the air-ground interface, the dielectric constant and conductivity are taken as the average of the two. The variation of the spatial electromagnetic field after considering the influence of ground factors is as follows: Figure 10 As shown, (a) and (b) are the spatial magnetic field distributions at time t=500*dt and t=1000*dt, respectively; (c) and (d) are the radial electric field distributions at time t=500*dt and t=1000*dt, respectively; (e) and (f) are the horizontal electric field distributions at time t=500*dt and t=1000*dt, respectively.

[0174] Figure 10 From (e) and (f), it can be seen that the horizontal electric field is very small, almost zero, in most regions; the influence of the radial electric field is mainly considered. From Figure 9 and Figure 10Comparison shows that the spatial electromagnetic field considering the ground's influence is smaller than that without considering it, due to the attenuation and reflection effects of the ground. At the interface between the ground and air (r=8m), both the electric and magnetic fields decay rapidly. In the land area below the ground plane (r>8m), the electric and magnetic fields change with the spatial electromagnetic field and decay first. The calculations indicate that the horizontal and radial electric fields below the ground (r≥8m) are not very large. Therefore, for cables buried underground, although the spatial electromagnetic field generated by switching operations within the substation will cause coupling interference, the amplitude of this coupling interference will be relatively small, and the interference to secondary cables will primarily be conducted interference.

[0175] At the ground-air interface (r≥8m), the radial electric field and the horizontal electric field are as follows: Figure 11 As shown, (a) represents the radial electric field at the ground (r≥8m), and (b) represents the horizontal electric field at the ground (r≥8m). Figure 11 It can be seen that the radial electric field at ground level is almost zero, while the horizontal electric field does not exceed 8V / m, and the electric field below ground level is even smaller; and when the relative permittivity is... electrical conductivity and relative permittivity are electrical conductivity At this time, the effect on the calculation results of the electric field is not significant.

[0176] In summary, the above comparative analysis shows that the dielectric constant, conductivity, and air-ground interface characteristics of the ground medium significantly alter the spatial distribution and amplitude of the transient electromagnetic field in the substation through reflection and attenuation. Ignoring the ground influence leads to overestimation of the field strength and deviation from the actual distribution pattern. Therefore, incorporating the ground influence into the correction process is irreplaceable in this invention. After considering the ground influence, the electromagnetic field attenuates rapidly at the air-ground interface, and the field strength below the ground is significantly reduced. Furthermore, the dielectric constant and conductivity of the soil have limited impact on the calculation results within the range of conventional engineering applications.

[0177] Based on the same inventive concept, this application also provides a substation transient electromagnetic environment calculation device for implementing the above-mentioned substation transient electromagnetic environment calculation method. The solution provided by this device is similar to the solution described in the above-described method. Therefore, the specific limitations in the substation transient electromagnetic environment calculation device embodiments provided below can be found in the limitations of the substation transient electromagnetic environment calculation method described above, and will not be repeated here.

[0178] Please see Figure 12 This invention also provides a substation transient electromagnetic environment calculation device, comprising:

[0179] The model building module is used to establish a transient electromagnetic field calculation model. In the transient electromagnetic field calculation model, the transient current of the substation bus is subdivided into uniformly distributed current element electric dipoles.

[0180] The first calculation module is used to determine the electromagnetic field contribution of the current element electric dipole to the observation point based on the transient electromagnetic field calculation model and integrate it along the length of the generatrix to obtain the transient electromagnetic field intensity at a single point.

[0181] The second calculation module is used to perform boundary processing using the FDTD method combined with Mur absorption boundary conditions, and iteratively extend the single-point transient electromagnetic field intensity to the entire space of the substation to obtain the preliminary spatial transient electromagnetic field distribution.

[0182] The correction module is used to take into account the influence of the ground and perform reflection and attenuation correction on the initial space transient electromagnetic field distribution to obtain the corrected space transient electromagnetic field distribution.

[0183] The results output module is used to integrate the corrected spatial transient electromagnetic field distribution to obtain the calculation results of the transient electromagnetic environment of the substation.

[0184] Furthermore, in the model building module, a transient electromagnetic field calculation model is established, including:

[0185] The substation busbar is subdivided into several small segments along its length. Each segment is used as a current element electric dipole with uniform current distribution, and the current of the current element electric dipole is characterized by transmission line waveform.

[0186] Define the distance from the current element electric dipole to the observation point, and determine the basic physical parameters of the transient electromagnetic field calculation model.

[0187] Furthermore, in the first calculation module, the electromagnetic field contribution of the current element electric dipole to the observation point is determined and integrated along the length of the generatrix to obtain the transient electromagnetic field intensity at a single point, including:

[0188] The time partial derivative of the current in the electric dipole of the current element is approximated by the difference quotient formula, and the time integral of the current is approximated by the composite trapezoidal rule.

[0189] Substituting the results of the time partial derivative and time integral into the calculation formula of the electromagnetic field of the electric dipole, we obtain the horizontal electric field, radial electric field and magnetic field components generated by the current element electric dipole at the observation point.

[0190] The horizontal electric field, radial electric field, and magnetic field components are integrated along the length of the substation busbar, and the single-point transient electromagnetic field intensity at the observation point is obtained based on the integration results.

[0191] Furthermore, in the second calculation module, the FDTD method is used, combined with Mur absorption boundary conditions, to perform boundary processing. The single-point transient electromagnetic field intensity is iteratively extended to the entire space of the substation, resulting in a preliminary spatial transient electromagnetic field distribution, including:

[0192] Based on Maxwell's equations for two-dimensional TE waves in cylindrical coordinates, the FDTD iterative formulas for the electric and magnetic field components are obtained.

[0193] The Mur absorption boundary condition is used to process the boundary in the plane below the busbar, and the FDTD iterative formula of the magnetic field component at the boundary is obtained. According to the active region and the passive region where the busbar is located, the FDTD iterative formula of the electric field component in the active region and the passive region is obtained.

[0194] Using the single-point transient electromagnetic field intensity as the initial input, the data is discretized and extended to the entire space of the substation through all FDTD iterative formulas to obtain the preliminary spatial transient electromagnetic field distribution.

[0195] Furthermore, in the correction module, the initial spatial transient electromagnetic field distribution is corrected for reflection and attenuation to obtain the corrected spatial transient electromagnetic field distribution, including:

[0196] Obtain ground medium parameters and air parameters; ground medium parameters include at least the relative permittivity and conductivity of the ground; air parameters include at least the permittivity and conductivity of the air.

[0197] Ground medium parameters and air parameters are incorporated into the calculation model of the preliminary space transient electromagnetic field distribution to correct the preliminary space transient electromagnetic field distribution.

[0198] By correcting the calculations, the spatial transient electromagnetic field distribution after considering ground reflection and attenuation is obtained, which is the corrected spatial transient electromagnetic field distribution.

[0199] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the system can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0200] Reference Figure 13 The present invention also provides a computer device, including: a memory and a processor, and a computer program stored in the memory. When the computer program is executed on the processor, it implements the substation transient electromagnetic environment calculation method as described in any of the above methods.

[0201] The computer device may be a desktop computer, laptop, handheld computer, or cloud server, etc. This computer device may include, but is not limited to, a processor and memory. Those skilled in the art will understand that... Figure 13 The examples of computer devices are merely examples and do not constitute a limitation on computer devices. They may include more or fewer components than shown in the illustration, or combinations of certain components, or different components. For example, they may also include input / output devices, network access devices, etc.

[0202] The processor referred to can be a Central Processing Unit (CPU), but it can also be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor can be a microprocessor or any conventional processor.

[0203] In some embodiments, the memory may be an internal storage unit of the computer device, such as a hard drive or RAM. In other embodiments, the memory may be an external storage device of the computer device, such as a plug-in hard drive, Smart Media Card (SMC), Secure Digital (SD) card, or Flash Card. Furthermore, the memory may include both internal and external storage units of the computer device. The memory is used to store the operating system, applications, boot loader, data, and other programs, such as the program code of the computer program. The memory can also be used to temporarily store data that has been output or will be output.

[0204] This invention also provides a computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the substation transient electromagnetic environment calculation method as described in any of the above methods.

[0205] In this embodiment, if the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include at least: any entity or device capable of carrying computer program code to a photographing device / terminal device, a recording medium, a computer memory, a read-only memory (ROM), a random access memory (RAM), an electrical carrier signal, a telecommunication signal, and a software distribution medium. Examples include USB flash drives, portable hard drives, magnetic disks, or optical disks. In some jurisdictions, according to legislation and patent practice, computer-readable media cannot be electrical carrier signals or telecommunication signals.

[0206] This invention provides a computer program product, including a computer program that, when executed by a processor, implements the substation transient electromagnetic environment calculation method as described in any of the above methods.

[0207] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0208] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0209] In the embodiments disclosed in this application, it should be understood that the disclosed devices / terminal equipment and methods can be implemented in other ways. For example, the device / terminal equipment embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the displayed or discussed mutual coupling or direct coupling or communication connection may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0210] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for calculating the transient electromagnetic environment of a substation, characterized in that, Includes the following steps: A transient electromagnetic field calculation model is established; in the transient electromagnetic field calculation model, the transient current of the substation bus is subdivided into uniformly distributed current element electric dipoles; Based on the transient electromagnetic field calculation model, the electromagnetic field contribution of the current element electric dipole to the observation point is determined and integrated along the length of the generatrix to obtain the transient electromagnetic field intensity at a single point. Using the FDTD method and combining Mur absorption boundary conditions for boundary treatment, the single-point transient electromagnetic field intensity is iteratively extended to the entire space of the substation to obtain the preliminary spatial transient electromagnetic field distribution. Taking into account the influence of the ground, the preliminary spatial transient electromagnetic field distribution is corrected by reflection and attenuation to obtain the corrected spatial transient electromagnetic field distribution; By integrating and correcting the spatial transient electromagnetic field distribution, the calculation results of the transient electromagnetic environment of the substation are obtained.

2. The method for calculating the transient electromagnetic environment of a substation according to claim 1, characterized in that, Establish a transient electromagnetic field calculation model, including: The substation busbar is subdivided into several small segments along its length. Each segment is used as a current element electric dipole with uniform current distribution, and the current of the current element electric dipole is characterized by transmission line waveform. Define the distance from the current element electric dipole to the observation point, and determine the basic physical parameters of the transient electromagnetic field calculation model.

3. The method for calculating the transient electromagnetic environment of a substation according to claim 1 or 2, characterized in that, The electromagnetic field contribution of the current element electric dipole to the observation point is determined and integrated along the length of the generatrix to obtain the transient electromagnetic field intensity at a single point, including: The time partial derivative of the current in the electric dipole of the current element is approximated by the difference quotient formula, and the time integral of the current is approximated by the complex trapezoidal rule. Substituting the results of the time partial derivative and time integral into the calculation formula of the electromagnetic field of the electric dipole, we obtain the horizontal electric field, radial electric field and magnetic field components generated by the current element electric dipole at the observation point. The horizontal electric field, radial electric field, and magnetic field components are integrated along the length of the substation busbar, and the single-point transient electromagnetic field intensity at the observation point is obtained based on the integration results.

4. The method for calculating the transient electromagnetic environment of a substation according to claim 1, characterized in that, Using the FDTD method, combined with Mur absorption boundary conditions for boundary treatment, the single-point transient electromagnetic field intensity is iteratively extended to the entire space of the substation, resulting in a preliminary spatial transient electromagnetic field distribution, including: Based on Maxwell's equations for two-dimensional TE waves in cylindrical coordinates, the FDTD iterative formulas for the electric and magnetic field components are obtained. The Mur absorption boundary condition is used to process the boundary in the plane below the busbar, and the FDTD iterative formula of the magnetic field component at the boundary is obtained. According to the active region and the passive region where the busbar is located, the FDTD iterative formula of the electric field component in the active region and the passive region is obtained. Using the single-point transient electromagnetic field intensity as the initial input, the data is discretized and extended to the entire space of the substation through all the FDTD iterative formulas to obtain the preliminary spatial transient electromagnetic field distribution.

5. The method for calculating the transient electromagnetic environment of a substation according to claim 1, characterized in that, Considering ground influences, the preliminary transient electromagnetic field distribution in space is corrected for reflection and attenuation to obtain the corrected transient electromagnetic field distribution in space, including: Obtain ground medium parameters and air parameters; the ground medium parameters include at least the relative permittivity and conductivity of the ground; the air parameters include at least the permittivity and conductivity of the air. The ground medium parameters and air parameters are incorporated into the calculation model of the preliminary spatial transient electromagnetic field distribution to correct the preliminary spatial transient electromagnetic field distribution. By correcting the calculations, the spatial transient electromagnetic field distribution after considering ground reflection and attenuation is obtained, which is the corrected spatial transient electromagnetic field distribution.

6. A device for calculating the transient electromagnetic environment of a substation, characterized in that, include: The model building module is used to build a transient electromagnetic field calculation model; In the transient electromagnetic field calculation model, the transient current of the substation bus is subdivided into uniformly distributed current element electric dipoles. The first calculation module is used to determine the electromagnetic field contribution of the current element electric dipole to the observation point based on the transient electromagnetic field calculation model and integrate it along the length of the generatrix to obtain the transient electromagnetic field intensity at a single point. The second calculation module is used to perform boundary processing by using the FDTD method and combining Mur absorption boundary conditions to iteratively extend the single-point transient electromagnetic field intensity to the entire space of the substation, and obtain the preliminary spatial transient electromagnetic field distribution. The correction module is used to take into account the influence of the ground and perform reflection and attenuation correction on the preliminary spatial transient electromagnetic field distribution to obtain the corrected spatial transient electromagnetic field distribution. The results output module is used to integrate the corrected spatial transient electromagnetic field distribution to obtain the calculation results of the transient electromagnetic environment of the substation.

7. The substation transient electromagnetic environment calculation device according to claim 6, characterized in that, In the model building module, a transient electromagnetic field calculation model is established, including: The substation busbar is subdivided into several small segments along its length. Each segment is used as a current element electric dipole with uniform current distribution, and the current of the current element electric dipole is characterized by transmission line waveform. Define the distance from the current element electric dipole to the observation point, and determine the basic physical parameters of the transient electromagnetic field calculation model.

8. The substation transient electromagnetic environment calculation device according to claim 6 or 7, characterized in that, In the first calculation module, the electromagnetic field contribution of the current element electric dipole to the observation point is determined and integrated along the length of the generatrix to obtain the transient electromagnetic field intensity at a single point, including: The time partial derivative of the current in the electric dipole of the current element is approximated by the difference quotient formula, and the time integral of the current is approximated by the complex trapezoidal rule. Substituting the results of the time partial derivative and time integral into the calculation formula of the electromagnetic field of the electric dipole, we obtain the horizontal electric field, radial electric field and magnetic field components generated by the current element electric dipole at the observation point. The horizontal electric field, radial electric field, and magnetic field components are integrated along the length of the substation busbar, and the single-point transient electromagnetic field intensity at the observation point is obtained based on the integration results.

9. The substation transient electromagnetic environment calculation device according to claim 6, characterized in that, In the second calculation module, the FDTD method is used, combined with Mur absorption boundary conditions for boundary processing, to iteratively extend the single-point transient electromagnetic field intensity to the entire space of the substation, obtaining a preliminary spatial transient electromagnetic field distribution, including: Based on Maxwell's equations for two-dimensional TE waves in cylindrical coordinates, the FDTD iterative formulas for the electric and magnetic field components are obtained. The Mur absorption boundary condition is used to process the boundary in the plane below the busbar, and the FDTD iterative formula of the magnetic field component at the boundary is obtained. According to the active region and the passive region where the busbar is located, the FDTD iterative formula of the electric field component in the active region and the passive region is obtained. Using the single-point transient electromagnetic field intensity as the initial input, the data is discretized and extended to the entire space of the substation through all the FDTD iterative formulas to obtain the preliminary spatial transient electromagnetic field distribution.

10. The substation transient electromagnetic environment calculation device according to claim 6, characterized in that, In the correction module, the initial spatial transient electromagnetic field distribution is corrected for reflection and attenuation to obtain the corrected spatial transient electromagnetic field distribution, including: Obtain ground medium parameters and air parameters; the ground medium parameters include at least the relative permittivity and conductivity of the ground; the air parameters include at least the permittivity and conductivity of the air. The ground medium parameters and air parameters are incorporated into the calculation model of the preliminary spatial transient electromagnetic field distribution to correct the preliminary spatial transient electromagnetic field distribution. By correcting the calculations, the spatial transient electromagnetic field distribution after considering ground reflection and attenuation is obtained, which is the corrected spatial transient electromagnetic field distribution.

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