Method for evaluating EMF of DC converter station and application thereof

Abstract

The application provides an EMF evaluation method and application of a direct current converter station, modeling a complex converter station electrical system, metal structure, auxiliary system and engineering environment in a three-dimensional interval, using a moment method to solve a numerical solution of current distribution (longitudinal and leakage current distribution) on the ground and buried conductors under power base frequency and each harmonic, thereby obtaining a scalar potential and an electromagnetic field. By comparing the calculation results with international / local standards, areas and index values that do not meet the standards are found out, and input parameters are modified and iterative calculation is performed, and finally an electromagnetic field safety distribution block diagram is formed. The application can pre-evaluate the electromagnetic field intensity of the converter station under various operation modes without implementing the project, identify possible problem areas, and provide guidance for safety production, occupational health evaluation and the like of engineering operation.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic compatibility technology of power systems, and in particular relates to an EMF (Electromagnetic Field) evaluation method and application for DC converter stations. Background Technology

[0002] Electromagnetic field (EMF) analysis is a crucial task in the design and maintenance of HVDC systems. This is because the electromagnetic environment within an HVDC converter station is highly complex, containing numerous sources of electromagnetic interference and intricate coupling pathways. This electromagnetic environment not only affects the normal operation of various sensitive devices within the station but also has direct or indirect impacts on human health.

[0003] Depending on the frequency of the electromagnetic field, these effects may include: (1) stimulating the central nervous system in the low-frequency range; (2) producing a thermal effect on the human body in the high-frequency range; (3) generating limb current in the high-frequency reactive near field; and (4) potentially causing inaccurate measurement systems or even triggering malfunctions in protection systems.

[0004] In China, existing research on EMF / EMC mainly focuses on ultra-high voltage AC / DC engineering and equipment research, while there is relatively little research on the overall safety assessment of applications in flexible DC engineering. Moreover, most studies are based on steady-state rated input conditions and do not calculate or evaluate the harmonic effects.

[0005] In fact, regardless of whether it's a LCC or VSC technology high-voltage direct current converter station, harmonics are particularly important and have a seriously detrimental effect on the converter station system. This is because, under steady-state conditions, the sum of the currents in a three-phase balanced system is essentially negligible. However, if harmonics are present in the system, harmonic currents will superimpose in the three-phase conductors, thereby generating significant harmonic currents and electromagnetic field strengths on the neutral conductor and in the spatial electromagnetic field under unfavorable conditions.

[0006] Furthermore, the increasingly compact design of offshore / onshore DC converter station areas, especially the proximity of sensitive equipment, personnel living and working areas, and high-voltage power distribution equipment areas in offshore converter stations without the need for prior assessment methods, may pose long-term health risks to operators. Summary of the Invention

[0007] The first objective of this invention is to address the gap in EMF (Electromagnetic Field) assessment for domestic DC converter stations, and the problem of increasingly compact designs of offshore / onshore converter station areas leading to the proximity of sensitive equipment, personnel living and working areas, and high-voltage power distribution equipment areas, yet lacking pre-assessment methods. This invention proposes a calculation method for assessing the electromagnetic field strength of DC system converter stations, providing guidance for the design of converter stations and for safety production and occupational health assessments during operation.

[0008] Therefore, the above-mentioned objective of the present invention is achieved through the following technical solution:

[0009] Using the extended antenna theory method of moments, Maxwell's electromagnetic field equations are solved based on electric field point matching. By solving the numerical solutions of the current distribution (longitudinal and leakage current distribution) on the ground and in buried conductors, scalar potentials and electromagnetic fields are obtained. At the same time, the effects of resistivity, dielectric constant and permeability of multi-layered soil are considered using full Sommerfeld integration.

[0010] Using frequency domain research tools, a script-like method is employed to automatically set the frequencies of various harmonics or interharmonics to be studied for a complex 3D model of a DC converter station system. This allows for analysis of all technically compatible scenarios and ranges within a feasible timeframe, considering various AC / DC system operating modes or conditions (e.g., different DC power levels, bipolar or unipolar operation, AC system conditions, etc.). Specifically, regarding harmonics, both AC-side and DC-side harmonics of the converter station can be considered.

[0011] Specifically, the EMF assessment method for the DC converter station calculates the EMF and harmonic effects of the converter station during steady-state operation. It involves three-dimensional modeling of the complex electrical system, metal structure, auxiliary systems, and engineering environment of the converter station. Automated settings for the frequencies and amplitudes of each harmonic or interharmonic are employed. The method of moments is used to calculate the electromagnetic field strength under various AC / DC system operating modes or different operating conditions. The method includes the following steps:

[0012] (1) Input conditions include:

[0013] Converter station design scheme, converter station environmental parameters, and voltage amplitude and direction of fundamental and harmonic waves, and current amplitude and direction of each harmonic under different operating conditions of the converter station;

[0014] (2) Simulate the components and spatial locations within the converter station, including transformers, converter valves, reactors, tubular cables, GIS, solid / hollow conductors or combinations of wires and split conductors, bare conductors and insulated conductors, converter valves, bridge arm reactors, overhead and buried conductors, etc.; and a multi-layered marine soil model, including seawater, sea mud and seabed rocks;

[0015] (3) Input steady-state fundamental current and voltage, as well as harmonic expansion calculations from the AC and DC sides of the converter station, and apply the method of moments to solve for the required physical quantities: AC power frequency electric field, AC power frequency magnetic field, DC magnetic field, AC side harmonic electromagnetic field, DC side harmonic electromagnetic field, etc.

[0016] (4) Compare the physical quantities obtained from the calculation results with internationally / locally recognized safety standards. If they are lower than the safety standards, the evaluation ends. If they are higher than the safety standards, the input conditions need to be changed, for example, necessary mitigation design or local input adjustment. Repeat steps (1) to (3) until the safety requirements are met.

[0017] While adopting the above technical solutions, the present invention may also adopt or combine the following technical solutions:

[0018] As a preferred embodiment of the present invention, the EMF evaluation method for the DC converter station further includes:

[0019] After completing all iterative calculations and meeting international / local standards, an electromagnetic field safety distribution block map is created based on the final calculation results to provide guidance for safe production and occupational health assessments during engineering operations.

[0020] As a preferred technical solution of the present invention: the converter station design scheme includes the dimensions and positioning of the converter station equipment and conductors, as well as the dimensions and materials of the main steel structure of the converter station.

[0021] As a preferred technical solution of the present invention: the environmental parameters of the converter station include the layer thickness and resistivity of soil, seawater, marine mud, and seabed rocks, as well as their position relative to the converter station.

[0022] As a preferred technical solution of the present invention: the evaluation target of the EMF evaluation method of the DC converter station is the power frequency electric field and power frequency magnetic field in the AC area of ​​the station, the electrostatic field in the DC field area, and the electromagnetic field generated by harmonics and interharmonics in each area.

[0023] For exposed high-voltage equipment such as valve halls and indoor DC fields, and areas with concentrated sensitive equipment such as secondary equipment rooms, the method of moments is applied to solve Maxwell's electromagnetic field equations based on electric field point matching. That is, by solving the numerical solutions of the current distribution (longitudinal and leakage current distribution) on the ground and buried conductors, scalar potential and electromagnetic field are obtained. At the same time, the full Sommerfeld integral is used to consider the influence of resistivity, dielectric constant and permeability of multi-layer soil.

[0024] As a preferred technical solution of the present invention: changing the input conditions can mainly change the equipment positioning, the size and relative relationship of the power distribution room, and secondly, the converter station system / equipment parameters can be changed. The operating mode and environmental parameters of the converter station are generally not changed.

[0025] As a preferred technical solution of the present invention, the frequency of the input calculation is set, including DC 0Hz, AC 50Hz, and the frequencies and amplitudes of harmonics and interharmonics from the AC side and DC side, and the harmonic order can be 0 to 2000Hz.

[0026] As a preferred technical solution of the present invention, the operating conditions include at least: bipolar full-power operation mode without metal return line, symmetrical bipolar full-power operation mode with metal return line, and asymmetrical unipolar full-power operation mode.

[0027] The second objective of this invention is to address the shortcomings of the prior art by providing an application of the EMF evaluation method for DC converter stations described above in DC LCC converter stations or in flexible DC VSC converter stations.

[0028] Another objective of this invention is to address the shortcomings of the prior art by providing an application of the EMF evaluation method for DC converter stations described above in onshore converter stations or in offshore converter stations.

[0029] This invention addresses the gap in EMF assessment for domestic DC converter stations and the problem of increasingly compact designs in offshore / onshore converter stations, leading to proximity of sensitive equipment, personnel living and working areas, and high-voltage power distribution equipment areas, yet lacking pre-assessment methods. It provides a method and application for EMF assessment of DC converter stations. This invention is applicable not only to steady-state rated operating conditions but also considers the potential impact of harmonics on field strength. The invention models the complex electrical system, metal structure, auxiliary systems, and engineering environment of the converter station in a three-dimensional space. It uses the method of moments (MoM) to solve for the numerical solutions of the current distribution (longitudinal and leakage current distribution) on the ground and in buried conductors under the fundamental frequency and various harmonics, thereby obtaining scalar potential and electromagnetic field. By comparing the calculation results with international / local standards, areas and index values ​​that do not meet the standards are identified. Input parameters are modified and iterative calculations are performed to ultimately generate an electromagnetic field safety distribution block map. This invention can pre-assess the electromagnetic field strength of converter stations under various operating modes without implementing the project, identify potential problem areas, and provide guidance for safety production and occupational health assessments during project operation.

[0030] This invention provides a relatively accurate calculation method for electromagnetic compatibility assessment of DC converter stations, thereby providing a calculation basis for the electromagnetic compatibility and safety zoning pre-assessment of converter stations. Specifically, it has the following beneficial effects:

[0031] (1) This invention is applicable to both conventional DC LCC converter stations and flexible DC VSC converter stations; it is applicable to both onshore and offshore converter stations.

[0032] (2) This invention can be used to evaluate the power frequency electromagnetic field generated by AC field, the electrostatic field generated by DC field, and the harmonic and interharmonic interference generated by power fluctuation, switching and converter valve operation, thereby realizing a multi-dimensional evaluation of the electromagnetic compatibility of converter station.

[0033] (3) According to the calculation results of this invention, an electromagnetic field safety distribution block map can be made, which can provide guidance for safe production and occupational health assessment in engineering operation. Attached Figure Description

[0034] Figure 1 The flowchart shows the calculation process of the EMF evaluation method for DC converter stations provided by this invention.

[0035] Figure 2 The three-dimensional calculation model of the offshore converter station provided in the embodiments of the present invention;

[0036] Figure 3 This is a color block diagram of the power frequency electric field generated in the AC field of the converter station in the embodiments provided by the present invention;

[0037] Figure 4 This is a color block diagram of the power frequency magnetic field generated by the AC field of the converter station in the embodiments provided by the present invention;

[0038] Figure 5 This is a color block diagram of the DC magnetic field distribution in steady state at the converter station, provided in the embodiments of the present invention.

[0039] Figure 6 This document provides a safety zoning diagram for the converter station and safety guidelines for each zone. Detailed Implementation

[0040] To describe the invention in more detail below, in conjunction with... Figures 1-6 The technical solution of the present invention will be described in detail through a typical case.

[0041] Based on the parameters of the flexible DC transmission system, the frequency and amplitude of the harmonics of the flexible DC system are calculated.

[0042]

[0043] In the formula: Iva, Ivb, and Ivc are the output current values ​​on the transformer valve side, respectively; Ivm is the amplitude of the transformer valve side current; γ va γ vb γ vc This represents the initial phase of the three-phase sinusoidal modulated wave; The phase angle difference is γ; Lac is the equivalent inductance between the AC output of the converter and the equivalent potential of the AC system; L0 is the inductive reactance of the bridge arm reactor; γ h =hγ va h is the harmonic multiple; k = 1, 2, 3... are positive integers.

[0044] Based on the above formulas, the amplitude and frequency of the fundamental wave (power frequency) and harmonics are obtained and used as one of the main inputs for the calculation. The above calculation conclusions are based on the calculation results of the DC system, which are not within the scope of this invention, and therefore will not be elaborated on in detail.

[0045] The steady-state input excitation and harmonic excitation of typical cases are shown in Tables 1 and 2, respectively. Table 1 is the steady-state operating parameter table of the converter station, and Table 2 is the maximum allowable level of harmonics and interharmonics: Typical values ​​of AC harmonics:

[0046] Table 1 Steady-state operating parameters of the converter station

[0047] Serial Number content unit parameter 1 Rated DC voltage kV ±525 2 Rated DC current A 1905 3 Maximum DC current A 1952 4 Rated AC voltage kV 66 / 280 5 Maximum AC current (280kV valve side) A 2100 6 Maximum AC current (66kV grid side) A 5170

[0048] Table 2 Maximum Permissible Levels of Harmonics and Interharmonics: Typical Values ​​of AC Harmonics

[0049] Frequency (Hz) Amplitude percentage (%) 100 0.686 125 0.0205 1000 0.025 1025 0.0157

[0050] The design conditions of the converter station (the size and positioning of the converter station equipment and conductors; the size and material of the main steel structure of the converter station) need to be based on the engineering design results; the environmental parameters of the converter station (the thickness and resistivity of seawater, sea mud and seabed rocks; the position relative to the converter station) are based on the on-site measurement results; the operation mode of the converter station can be carried out according to the specifications and the operation requirements of different projects. The above conditions are not within the scope of this invention, so they will not be elaborated on in detail.

[0051] Applying the method of moments in antenna theory, the main theoretical formulas involved are as follows: The electromagnetic field in a horizontally layered medium m can be represented by the Hertzian vector Π as:

[0052]

[0053]

[0054] γ 2 = jωμ m (4)

[0055] θ m = σ m + jωε m (5)

[0056] In the formula, E m H mLet σ represent the electric and magnetic field strengths in the horizontally layered dielectric m-layer. m μ represents the conductivity of the layer at the observation point. m Let ε be the conductivity at the observation point. m θ is the dielectric constant at the observation point; θm is the complex conductivity; Π m The Hertzian vector potential in layer m;

[0057] Since this method involves the evaluation of large converter stations, multiple devices, complex environments, and complex electric fields, and since the above theories are all relatively mature, software based on the above principles (method of moments) can be used to perform calculations for the entire station.

[0058] like Figure 1 As shown, the calculation process of this invention is as follows: First, software modeling based on the method of moments is applied; then, the fundamental and harmonic amplitudes and frequencies calculated based on the flexible DC system are input, along with environmental parameters; next, the physical quantity calculation results under each harmonic are calculated according to the set location and physical quantity calculation requirements. Finally, the calculation results are compared with the allowable values ​​of international / domestic standards. If they are not satisfied, the input conditions are changed until they are satisfied, and an electromagnetic field safety distribution block map is generated based on the final calculation results.

[0059] like Figure 2 As shown, this software simulates the components and spatial locations within a converter station, including transformers, converter valves, reactors, tubular cables, GIS, solid / hollow conductors or combinations of wires and split conductors, bare conductors and insulated conductors, converter valves, bridge arm reactors, overhead and buried conductors, etc.

[0060] like Figure 3 The image shows the AC power frequency electric field strength calculated using a typical case study; as shown... Figure 4 The image shows the calculated results of the AC power frequency magnetic field strength; as shown. Figure 5 The image shows the calculated DC magnetic field strength. The results need to be compared with international / local standards to identify areas that do not meet the standards and values ​​that exceed them.

[0061] Table 3 shows the calculated electromagnetic field strength generated by AC-side harmonics (full-power operation mode of AC-side symmetrical bipolar line with metallic return in the converter station), and Table 4 shows the calculated electromagnetic field strength generated by DC-side harmonics (full-power operation mode of DC-side bipolar line with metallic return in the converter station). The calculation results need to be compared with international / local standards to identify areas that do not meet the standards and values ​​that exceed the standards.

[0062] Table 3. Calculation results of harmonic and interharmonic electromagnetic fields on the AC side (full power operation mode of symmetrical bipolar band metallic loop at offshore station).

[0063]

[0064] Table 4. Calculation results of harmonic and interharmonic electromagnetic fields: DC side (full power operation mode of symmetrical bipolar band metallic loop at offshore station).

[0065]

[0066] like Figure 6 As shown, after multiple iterations and all electromagnetic field indicators meeting international / local standards, the converter station is divided into safety zones based on international / local standards for safety / health and other indicators.

[0067] The above specific embodiments are used to explain and illustrate the present invention, and are only preferred embodiments of the present invention, not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A method for EMF evaluation of a DC converter station, characterized in that: The EMF assessment method for DC converter stations calculates the EMF and harmonic effects of steady-state operation. It involves three-dimensional modeling of the complex electrical system, metal structure, auxiliary systems, and engineering environment of the converter station. Automated settings for the frequencies and amplitudes of each harmonic or interharmonic are employed. The method of moments (MoM) is used to calculate the electromagnetic field strength under various AC / DC system operating modes or different operating conditions. Specifically, the method includes the following steps: (1) Input conditions include: Converter station design scheme, converter station environmental parameters, and voltage amplitude and direction of fundamental and harmonic waves, and current amplitude and direction of each harmonic under different operating conditions of the converter station; (2) Simulate the components and spatial locations within the converter station, including transformers, converter valves, reactors, tubular cables, GIS, combinations of solid / hollow conductors or wires, bare conductors and insulated conductors, bridge arm reactors, overhead and buried conductors; and a multi-layered marine soil model, including seawater, sea mud and seabed rocks; (3) Input steady-state fundamental current and voltage, as well as harmonic expansion calculations from the AC and DC sides of the converter station, and apply the method of moments to solve for the required physical quantities: AC power frequency electric field, AC power frequency magnetic field, DC magnetic field, AC side harmonic electromagnetic field, and DC side harmonic electromagnetic field. (4) Compare the physical quantities obtained from the calculation results with internationally / locally recognized safety standards. If they are lower than the safety standards, the evaluation ends. If they are higher than the safety standards, the input conditions need to be changed and steps (1) to (3) are repeated until the safety requirements are met.

2. The EMF evaluation method for DC converter stations according to claim 1, characterized in that: The EMF assessment method for the DC converter station also includes: After completing all iterative calculations and meeting international / local standards, an electromagnetic field safety distribution block diagram is generated based on the final calculation results to provide guidance for safety production and occupational health assessments during project operation.

3. The EMF evaluation method for DC converter stations according to claim 1, characterized in that: The converter station design scheme includes the dimensions and positioning of the converter station equipment and conductors, as well as the dimensions and materials of the main steel structure of the converter station.

4. The EMF evaluation method for DC converter stations according to claim 1, characterized in that: The environmental parameters of the converter station include the layer thickness and resistivity of soil, seawater, marine mud, and seabed rocks, as well as their location relative to the converter station.

5. The EMF evaluation method for DC converter stations according to claim 1, characterized in that: The evaluation target of the EMF evaluation method for the DC converter station is the power frequency electric field and power frequency magnetic field in the AC area, the electrostatic field in the DC area, and the electromagnetic field generated by harmonics and interharmonics in each area.

6. The EMF evaluation method for DC converter stations according to claim 1, characterized in that: Changing the input conditions mainly involves altering the equipment location, the size and relative relationship of the power distribution room, and secondly, changing the converter station system / equipment parameters. The converter station's operating mode and environmental parameters remain unchanged.

7. The EMF evaluation method for DC converter stations according to claim 1, characterized in that: The input frequency for calculation includes 0 Hz DC, 50 Hz AC power frequency, and the frequencies and amplitudes of harmonics and interharmonics from the AC and DC sides, with harmonic frequencies ranging from 0 to 2000 Hz.

8. The EMF evaluation method for DC converter stations according to claim 1, characterized in that: The operating conditions are: full power operation mode of bipolar without metallic return, full power operation mode of symmetrical bipolar with metallic return, and full power operation mode of asymmetrical unipolar.

9. The application of the EMF evaluation method for DC converter stations according to claim 1, characterized in that: The application of the EMF evaluation method for DC converter stations includes its application in DC LCC converter stations or flexible DC VSC converter stations.

10. The application of the EMF evaluation method for DC converter stations according to claim 1, characterized in that: The application of the EMF evaluation method for DC converter stations includes applications on land-based converter stations or applications on offshore converter stations.

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