Overvoltage suppression method based on lightning overvoltage characteristics of 220kV overhead-cable line

Abstract

The invention belongs to the technical field of power systems, and particularly relates to an overvoltage suppression method based on 220kV overhead-cable line lightning overvoltage characteristics. The method comprises the steps that a 220kV overhead-cable mixed line lightning overvoltage simulation model is constructed, the model comprises a mixed line model and a lightning current model, the mixed line model is divided into an overhead line section and a cable line section, and the overhead line model is a JMarti model; the lightning current model adopts a Hardler model, and the lightning current waveform is a double-exponential wave; based on the simulation model, multiple measuring points are arranged on a cable section to collect overvoltage data of a cable core and a sheath, and an overvoltage transmission rule under a lightning stroke working condition is analyzed; aiming at rules, optimizing suppression measures, namely adjusting parameters of a cable terminal lightning arrester, optimizing a sheath protector, and adopting low-resistance grounding to reduce the grounding resistance of a tower; and verifying the effectiveness of the scheme, ensuring that conventional lightning stroke overvoltage control indexes are met, and if not, analyzing and optimizing again until reaching the standard.

Description

Technical Field

[0001] This disclosure belongs to the field of power system technology, specifically relating to an overvoltage suppression method based on the lightning overvoltage characteristics of 220kV overhead-cable lines. Background Technology

[0002] With the growth of urban power grid load and the optimization of its layout, 220kV transmission lines are gradually evolving from a single overhead form to "overhead-cable hybrid lines"—overhead lines are suitable for long-distance, open-area transmission, with low cost and convenient maintenance; cable lines, due to their small footprint and strong resistance to external interference, have become the preferred choice for urban core areas. The combination of the two forms a hybrid line to adapt to different scenario requirements.

[0003] Lightning overvoltage is a major cause of insulation breakdown and equipment damage in 220kV lines. In mixed lines, the impedance difference between overhead and cable sections is extremely large (approximately 300-400Ω for overhead lines and approximately 30-50Ω for cable lines). Lightning surges are prone to severe reflection and refraction at the junctions, leading to a sudden increase in overvoltage at cable terminals, joints, and other parts, far exceeding the insulation withstand limit of the equipment. Furthermore, cable insulation has poor self-healing properties and irreversible failure. Accumulated partial discharge can cause electrical treeing aging in the insulation layer, further exacerbating the risk of breakdown. Therefore, lightning overvoltage protection for mixed lines is of paramount importance.

[0004] Existing suppression methods suffer from core problems such as oversimplified models and limited effectiveness of single protective measures. On the one hand, some schemes rely on field test data to optimize suppression measures, lacking system analysis based on accurate simulation models. Oversimplification of models makes it difficult for operators to quickly identify the area with the most severe overvoltage in the mixed line after a lightning strike. On the other hand, existing methods mostly adopt "single-point" designs, such as simply installing surge arresters at cable terminals or reducing tower grounding resistance without considering the impedance characteristics of the mixed line and the overvoltage transmission law, resulting in weak collaborative protection capabilities. Summary of the Invention

[0005] This disclosure proposes an overvoltage suppression scheme based on the lightning overvoltage characteristics of 220kV overhead-cable lines, in order to solve the problems of oversimplification of the model and limited suppression effect of single protection measures in existing schemes.

[0006] The first aspect of this disclosure provides an overvoltage suppression method based on the lightning overvoltage characteristics of 220kV overhead-cable lines, comprising:

[0007] A simulation model of lightning overvoltage for a 220kV overhead-cable hybrid line was constructed. The simulation model includes a 220kV overhead-cable hybrid line model and a lightning current model. The 220kV overhead-cable hybrid line model is divided into overhead line segments and cable line segments. The cables in the cable line segments are cross-interconnected and the metal sheath is grounded through a sheath protector. The overhead line model includes a line model reflecting frequency characteristics. The lightning current model adopts the Heidelberg model, and the lightning current waveform is a double exponential wave.

[0008] Based on the simulation model, multiple measurement points are set at preset intervals in the cable section. By collecting overvoltage data of the cable core and sheath at each measurement point, the transmission law of overvoltage in the hybrid line under lightning strike conditions is analyzed.

[0009] In response to the aforementioned overvoltage transmission pattern, overvoltage suppression measures are optimized, including adjusting the flashover voltage and volt-ampere characteristics of the cable terminal surge arrester, optimizing the operating time and impedance of the sheath protector, and adopting a low-resistance grounding structure to reduce the tower grounding resistance.

[0010] Integrate the aforementioned overvoltage suppression measures to form a synergistic suppression scheme;

[0011] Verify the effectiveness of applying the synergistic suppression scheme to the 220kV overhead-cable hybrid line, ensuring that the overvoltage control index under normal lightning strike conditions is met. If it is not met, reanalyze the voltage transmission law and optimize the overvoltage suppression measures until the effectiveness requirements are met.

[0012] In some embodiments of this disclosure, the overhead line segment consists of three towers and four line segments, each line segment being 0.5 km long, and each line segment includes a tower, a conductor, and a lightning protection wire, with two lightning protection wires arranged above the conductor;

[0013] The cable line segment consists of three interconnected 450m long cable sections.

[0014] In some embodiments of this disclosure, the cable model is YJLW02-Z127 / 220k-1×2500.

[0015] In some embodiments of this disclosure, both the conductor and the lightning protection wire are made of JL / G1A-630 / 45 steel-cored aluminum stranded wire.

[0016] In some embodiments of this disclosure, the tower uses a multi-wave impedance model.

[0017] In some embodiments of this disclosure, the line model reflecting frequency characteristics is the JMarti model.

[0018] In some embodiments of this disclosure, the preset interval is 150m.

[0019] In some embodiments of this disclosure, the low-resistance grounding structure includes: a deep well grounding electrode, a copper-clad steel grounding grid, a bentonite-based resistance-reducing agent, or a three-dimensional grounding structure.

[0020] In some embodiments of this disclosure, optimizing the impedance of the sheath protector includes:

[0021] The impedance value of the sheath protector is reduced from the initial 10Ω to 1Ω, while the model structure of the sheath protector remains that a three-phase voltage-controlled switch is connected in series with the impedance and grounded; wherein, the operating threshold of the three-phase voltage-controlled switch is set to close and ground when the voltage between the cross-interconnection and ground exceeds 100V.

[0022] In some embodiments of this disclosure, the overvoltage control parameters under conventional lightning strike conditions include:

[0023] The overvoltage drop of the cable joint shall not be less than 55%, and the overvoltage amplitude shall meet the requirements of GB / T18890-2015 and DL / T5221-2016 standards.

[0024] In summary, the overvoltage suppression method based on the lightning overvoltage characteristics of 220kV overhead-cable lines provided in the embodiments of this disclosure establishes a hybrid line lightning overvoltage simulation model composed of a 220kV overhead-cable hybrid line model and a Heidler lightning current model. Based on this model, multiple measurement points are set according to preset rules in the cable section to collect overvoltage data of the cable core and sheath. This provides sufficient data to analyze the transmission law of overvoltage in the hybrid line under lightning strike conditions, avoiding the problem of difficulty in locating the most severely overvoltage area due to oversimplification of the model in existing technologies. At the same time, by adopting the collaborative optimization measures of "surge arrester adjustment + sheath protection device optimization + low-resistance grounding", the problem of weak collaborative protection capability of existing "single-point" designs is solved. In addition, by establishing an index verification and iteration mechanism, re-analysis and optimization are performed when the standards are not met, thereby ensuring that the suppression effect meets the standards. Attached Figure Description

[0025] The features and advantages of this disclosure will be more clearly understood by referring to the accompanying drawings, which are schematic and should not be construed as limiting the scope of this disclosure in any way.

[0026] Figure 1 This is a framework diagram of the collaborative suppression model and method for lightning overvoltage in 220kV overhead-cable hybrid lines as disclosed in this publication;

[0027] Figure 2 This is a flowchart illustrating an overvoltage suppression method based on the lightning overvoltage characteristics of a 220kV overhead-cable line, according to some embodiments of this disclosure.

[0028] Figure 3 This is the overhead-cable hybrid line topology on which the 220kV overhead-cable hybrid line model described in this disclosure is based;

[0029] Figure 4 This is the cable laying diagram upon which the model of the 220kV cross-linked polyethylene insulated cable was constructed in this disclosure;

[0030] Figure 5 This is the schematic diagram of cross-interconnection grounding of the cable sheath, which was used as the basis for constructing the model of the 220kV cross-linked polyethylene insulated cable in this publication;

[0031] Figure 6 It is the cable core overvoltage amplitude transmission characteristic of a 220kV overhead-cable hybrid line under lightning strike conditions;

[0032] Figure 7 It is the overvoltage amplitude transmission characteristic of the cable sheath in a 220kV overhead-cable hybrid line under lightning strike conditions;

[0033] Figure 8 This is a simulation verification of the cable core voltage amplitude transfer characteristics of a cooperative suppression scheme according to an embodiment of this disclosure;

[0034] Figure 9 One embodiment of this disclosure demonstrates the sheath voltage amplitude transfer characteristics through simulation verification of a collaborative suppression scheme. Detailed Implementation

[0035] In the following detailed description, numerous specific details of this disclosure are set forth by way of example in order to provide a thorough understanding of the relevant disclosure. However, it will be apparent to those skilled in the art that this disclosure may be practiced without these details. It should be understood that the terms “system,” “apparatus,” “unit,” and / or “module” used in this disclosure are a method of distinguishing different parts, elements, sections, or components at different levels in a sequential arrangement. However, these terms may be replaced by other expressions if they can achieve the same purpose.

[0036] It should be understood that when a device, unit, or module is referred to as being "on," "connected to," or "coupled to" another device, unit, or module, it may be directly connected to or coupled to, or communicate with, other devices, units, or modules, or there may be intermediate devices, units, or modules present, unless the context explicitly indicates otherwise. For example, the term "and / or" as used in this disclosure includes any one and all combinations of one or more of the associated listed items.

[0037] The terminology used in this disclosure is for the purpose of describing particular embodiments only and is not intended to limit the scope of this disclosure. As shown in this specification and claims, unless the context clearly indicates otherwise, words such as "a," "an," "an," and / or "the" do not specifically refer to the singular and may include the plural. Generally speaking, the terms "comprising" and "including" only indicate the inclusion of explicitly identified features, integrals, steps, operations, elements, and / or components, and such expressions do not constitute an exclusive list, in which other features, integrals, steps, operations, elements, and / or components may also be included.

[0038] Referring to the following description and accompanying drawings, these and other features and characteristics, operating methods, functions of related structural elements, combinations of parts, and economics of manufacture of this disclosure can be better understood, wherein the description and drawings form part of the specification. However, it is clearly understood that the drawings are for illustrative and descriptive purposes only and are not intended to limit the scope of protection of this disclosure. It is understood that the drawings are not drawn to scale.

[0039] Various structural diagrams are used in this disclosure to illustrate various variations of embodiments according to this disclosure. It should be understood that the preceding or following structures are not intended to limit this disclosure. The scope of protection of this disclosure is defined by the claims.

[0040] With the acceleration of new urbanization and the transformation of energy structure, modern power systems are gradually transforming from single overhead lines to hybrid overhead-cable lines. Statistics show that in 2023, the cable coverage rate of urban distribution networks exceeded 65%, and hybrid lines accounted for over 40% of ultra-high voltage transmission projects. However, due to the abrupt change in wave impedance between the overhead and cable sections, hybrid lines significantly exacerbate the risk of lightning overvoltage. The CIGRE TB856 report points out that the overvoltage accident rate of hybrid lines is 3-5 times that of single lines, becoming a key bottleneck restricting grid stability. Lightning surges at the overhead-cable connection cause multiple reflections due to wave impedance mismatch, and the overvoltage amplitude in a 220kV system can reach 4.2-6.8 times the nominal voltage, far exceeding the cable insulation withstand level. Furthermore, cable insulation has poor self-healing properties and irreversible failure; accumulated partial discharge can cause electrical treeing aging in the insulation layer, ultimately leading to breakdown accidents.

[0041] Current research on the suppression of lightning overvoltage in overhead-cable hybrid lines, both domestically and internationally, suffers from problems such as oversimplification of propagation models and insufficient adaptability of protective measures. On the one hand, model simplification leads to a lack of effective data, making it difficult for operators to quickly locate the most severely overvoltage area in the hybrid line after a lightning strike. On the other hand, existing suppression methods are mostly single protective measures, which have limited effectiveness in suppressing overvoltage in hybrid lines and make it difficult to ensure the reliability of power grid operation.

[0042] To address the aforementioned issues, this disclosure proposes an overvoltage suppression method based on the lightning overvoltage characteristics of 220kV overhead-cable lines. The implementation of this method relies on a simulation foundation built from multiple models, including a 220kV overhead-cable hybrid line model and a lightning current model. The framework relating the models and the method is as follows: Figure 1 As shown in the figure. This solution addresses the shortcomings of existing technologies by achieving a breakthrough through two core design steps: First, it constructs an accurate simulation model of lightning overvoltage in a 220kV overhead-cable hybrid line and analyzes the propagation law of lightning overvoltage in the hybrid line based on the model; second, based on the obtained overvoltage transmission characteristics, it first proposes a single suppression method with optimized configuration of terminal surge arresters, sheath protectors, and grounding resistance, and then further integrates them to form a synergistic lightning overvoltage suppression method for 220kV overhead-cable hybrid lines involving "terminal surge arresters, sheath protectors, and tower grounding resistance".

[0043] In some embodiments, a flowchart of the overvoltage suppression method based on the lightning overvoltage characteristics of 220kV overhead-cable lines is shown below. Figure 2 As shown, the specific steps include:

[0044] S210, Construct a simulation model of lightning overvoltage for a 220kV overhead-cable hybrid line. The simulation model includes a 220kV overhead-cable hybrid line model and a lightning current model. The 220kV overhead-cable hybrid line model is divided into overhead line segments and cable line segments. The cables in the cable line segments are cross-connected and the metal sheath is grounded through a sheath protector. The overhead line model includes a line model reflecting frequency characteristics. The lightning current model adopts the Heidelberg model and the lightning current waveform is a double exponential wave.

[0045] First, based on the technical requirements of the "Design Manual for High-Voltage Transmission Lines in Power Engineering" and DL / T2209-2021 "Guidelines for Lightning Protection of Overhead Transmission Lines", a simulation model of lightning overvoltage for a 220kV overhead-cable hybrid line was established. The simulation model includes a 220kV overhead-cable hybrid line model and a lightning current model.

[0046] in, Figure 3 This refers to establishing the overhead-cable hybrid line topology of the 220kV overhead-cable hybrid line model. For example... Figure 3 As shown, the hybrid line model is divided into overhead line sections and cable line sections: the overhead line section consists of three towers and four line segments, each line segment being 0.5km long; the cable line section consists of three 450m long cable segments interconnected.

[0047] Cable line segment model construction:

[0048] This disclosure refers to the "Design Manual for High-Voltage Transmission Lines in Power Engineering" and uses the general-purpose YJLW02-Z127 / 220k-1×2500 cable for modeling. The cable parameters are shown in Table 1. The cable laying method is as follows: Figure 4 As shown. The high-voltage cable's metallic sheath uses a cross-interconnection grounding method. Figure 5 This is a schematic diagram of the cross-interconnection grounding of cable sheaths. In the model, the cross-interconnection cabinet between each cable segment is grounded through a sheath protector. When establishing the simulation model, the sheath protector is simplified to a voltage-controlled switch connected in series with a 10Ω resistor and grounded. When the voltage between the cross-interconnection point and ground exceeds the insulation threshold of 100V, the voltage-controlled switch closes and grounds.

[0049] surface YJLW02-Z127 / 220k-1×2500 power cable parameters

[0050]

[0051] Overhead line model construction:

[0052] This invention discloses a multi-wave impedance model for tower simulation. The multi-wave impedance model considers the wave propagation on the tower crossarm, support, and diagonal members, as well as the changes in stray capacitance to the ground at different heights of the tower. The calculated results are more consistent with the wave process of high towers.

[0053] This disclosure refers to the "Design Manual for High-Voltage Transmission Lines in Power Engineering" and uses steel-cored aluminum stranded wire of type JL / G1A-630 / 45.

[0054] In this disclosure, the line model selected is the JMarti model, which reflects the frequency characteristics, and double lightning protection wires are arranged above the transmission line.

[0055] Lightning current model:

[0056] Referring to DL / T2209-2021 "Guidelines for Lightning Protection of Overhead Transmission Lines", the lightning current simulation waveform in this disclosure adopts a 2.6 / 50μs double exponential wave. The lightning current model uses the Heidler model, and the lightning current expression is as follows:

[0057]

[0058] Where α, β, and A are the wavefront coefficient, wave tail coefficient, and waveform correction coefficient, respectively. This represents the amplitude of the lightning current.

[0059] S220, based on the simulation model, multiple measurement points are set at preset intervals in the cable section. By collecting overvoltage data of the cable core and sheath at each measurement point, the transmission law of overvoltage in the hybrid line under lightning strike conditions is analyzed.

[0060] A 220kV overhead-cable hybrid transmission line model was simulated using the ATP-EMTP simulation software. The parameters were set as follows: the total cable length was 1350m; the heights of the three phases A, B, and C were 47.3m, 39.8m, and 33m, respectively; and the height of the double lightning protection wires above the transmission line was 51.3m. Ten measurement points (numbered 1 to 10) were set every 150m along the cable segment, from the incoming end to the load end. The overvoltage waveforms and amplitudes of the cable core and sheath were measured. A common initial lightning strike current of 16kA was used. By changing the lightning strike measurement points and the lightning current amplitude, the lightning overvoltage characteristics of the overhead-cable hybrid transmission line were analyzed based on the simulation data.

[0061] Voltage and current characteristics under normal operating conditions

[0062] Under normal operating conditions of the power system, the cable core voltage and current exhibit sinusoidal waveform characteristics at the power frequency, with a voltage amplitude of approximately ±179.32V per phase. Due to the balanced three-phase load, the waveforms of phases A, B, and C have a phase difference of 120°, exhibiting good waveform symmetry and a total harmonic distortion rate of less than 3%.

[0063] When the cable sheath is directly grounded at both ends, the sheath voltage and sheath current exhibit a saddle-shaped distribution characteristic of "high in the middle and low at both ends" along the line. During normal operation, the metal sheath is interconnected through cross-connection and forms a closed loop through grounding at both ends, effectively suppressing the induced electromotive force.

[0064] Overvoltage transmission law under lightning strike conditions

[0065] A simulated 16kA lightning current strikes an overhead conductor. The overvoltage amplitude of the cable core shows a slow upward trend along the cable. At the two cable joint locations (measuring points 4 and 7), the increase slows down or even slightly decreases. The overvoltage amplitude transmission characteristics (lightning phase) of the cable core are as follows: Figure 6 As shown in the diagram, analysis reveals that the electromagnetic coupling effect between the cable's metallic sheath and the cable core continuously accumulates induced voltage along long lines. The potential gradient formed by the sheath's own resistance and inductive reactance gradually raises the cable core voltage through coupling. High-frequency components decay rapidly due to the skin effect and dielectric loss, while low-frequency energy gradually accumulates along the cable line. Coupled with the superposition of reflected waves caused by grounding impedance mismatch, this further exacerbates the increase in overvoltage amplitude along the line. The protective grounding of the sheath disperses the current path, causing the overvoltage amplitude to slow down significantly or even slightly decrease at the cable joints.

[0066] Under the same simulation conditions, the overvoltage amplitude of the cable sheath shows a significant attenuation trend along the line, and the overvoltage amplitude rebounds at the two joints (measurement points 4 and 7). The overvoltage amplitude transfer characteristics of the cable sheath are as follows: Figure 7As shown in the diagram. Analysis reveals that the physical disconnection and high impedance state of the sheath at the cross-connection joint constitute an impedance barrier to high-frequency lightning waves. The lightning waves undergo strong forward reflection at this point (the voltage wave reflection coefficient is close to +1). The reflected wave superimposes with the incident wave, causing a significant instantaneous increase in the sheath-to-ground voltage at the joint location. This effect is particularly pronounced under the influence of the high-frequency components of the lightning wave. Due to the cross-connection, the phase of the maximum sheath overvoltage occurs once at each cross-connection point.

[0067] The location of the lightning strike point was further varied, set to 0.5km, 1km, and 1.5km from the beginning of the cable line. The simulation results of overvoltage amplitude at different lightning strike locations are shown in Table 2. The analysis shows that as the distance of the lightning strike point from the beginning of the cable increases, the overvoltage amplitude of both the cable core and the sheath decreases.

[0068] surface Overvoltage amplitude at different lightning strike locations

[0069]

[0070] The lightning current amplitude in the simulation model was further varied, set to 16kA, 25kA, 35kA, 45kA, and 200kA (extreme lightning strike conditions). Table 3 shows a comparison of the simulation results for the overvoltage amplitude at the cable sheath's beginning and end points under different lightning current amplitudes. Analysis reveals that the lightning current amplitude significantly affects the overvoltage amplitude of the cable sheath; the larger the lightning current, the higher the overvoltage amplitude, posing a significant threat under extreme lightning strike conditions.

[0071] surface Overvoltage amplitude at the beginning and end of the cable sheath when the lightning current amplitude is different

[0072]

[0073] In summary, the characteristics of lightning overvoltage in 220kV overhead-cable hybrid lines are as follows: After a lightning strike on the overhead conductor, the voltage amplitude of the cable core increases significantly, showing an upward trend along the cable line. The increase slows down or even slightly decreases at the two cable joint locations. The location of the lightning strike and the magnitude of the lightning current on the overhead line have a significant impact on its amplitude. The voltage amplitude of the cable sheath attenuates along the line, and its phase changes with cross-interconnection transposition. Its value is also affected by the location of the lightning strike and the magnitude of the lightning current on the overhead line. The lightning current amplitude has a significant impact on the overvoltage amplitude of the cable sheath; the larger the lightning current, the higher the overvoltage amplitude of the sheath, posing a great threat under extreme lightning strike conditions.

[0074] S230, In response to the overvoltage transmission law, optimize overvoltage suppression measures, including adjusting the flashover voltage and volt-ampere characteristics of the cable terminal surge arrester, optimizing the operating time and impedance of the sheath protector, and adopting a low-resistance grounding structure to reduce the tower grounding resistance.

[0075] Based on the lightning overvoltage characteristic analysis of a 220kV overhead-cable hybrid line, a simulation of the 220kV overhead-cable hybrid line model was performed in the ATP-EMTP simulation software. A lightning strike current of 16kA was still used. First, the optimization and verification of a single suppression measure were conducted:

[0076] Optimize the parameters of the cable terminal surge arrester

[0077] In the original simulation model, the cable terminal arrester was a three-phase voltage-controlled resistor. Optimization was achieved by reducing its flashover voltage and adjusting its volt-ampere characteristic curve. Specifically, the flashover voltage of the cable terminal arrester was reduced from 204kV to 193kV, and its volt-ampere characteristic curve was adjusted.

[0078] Simulation results show that at cable joint 1 (measurement point 4), the core voltage amplitude decreased from 523.21kV to 278.25kV, and the sheath voltage amplitude decreased from 33.44kV to 16.75kV; at joint 2 (measurement point 7), the voltage decreased from 532.88kV to 284.98kV, and the sheath voltage amplitude decreased from 26.21kV to 12.46kV. This measure has a significant effect on suppressing overvoltage in the cable core.

[0079] Optimize the parameters of the sheath protector

[0080] In the original simulation model, the sheath protector model structure consisted of a three-phase voltage-controlled switch connected in series with a fixed-resistance impedance and grounded. Optimization was achieved by appropriately shortening the voltage-controlled switch's operating time and reducing its impedance value, specifically reducing the impedance value from 10Ω to 1Ω.

[0081] Simulation results show that at cable joint 1 (measurement point 4), the core voltage amplitude decreased from 523.21kV to 483.56kV, and the sheath voltage amplitude decreased from 33.44kV to 9.89kV; at joint 2 (measurement point 7), the voltage decreased from 532.88kV to 492.81kV, and the sheath voltage amplitude decreased from 26.21kV to 8.44kV. This measure has a significant effect on suppressing cable sheath overvoltage, but a weak effect on suppressing core overvoltage.

[0082] Reduce tower grounding resistance

[0083] By adopting deep-well grounding electrodes, laying copper-clad steel grounding grids, adding bentonite-based resistance-reducing agents, and constructing a three-dimensional grounding structure that combines vertical grounding bodies with horizontal radial lines, the grounding resistance is effectively reduced and the lightning current discharge capacity is improved. Specifically, the tower grounding resistance value is reduced from 15Ω to 5Ω.

[0084] Simulation results show that at joint 1 (measurement point 4), the core voltage amplitude decreased from 523.21kV to 510.39kV, and the sheath voltage amplitude decreased from 33.44kV to 30.16kV; at joint 2 (measurement point 7), the voltage decreased from 532.88kV to 516.77kV, and the sheath voltage amplitude decreased from 26.21kV to 25.50kV. This measure reduces the overall overvoltage of the cable to a small extent, but does not meet the suppression standard of the national standard GB / T18890-2015 "Cross-linked polyethylene insulated power cables and their accessories with rated voltage of 220kV (Um=252kV)".

[0085] S240, integrate the overvoltage suppression measures to form a synergistic suppression scheme.

[0086] The aforementioned overvoltage suppression measures are then integrated to form a synergistic suppression scheme. Specifically, this includes comprehensively considering the installation of cable terminal surge arresters, optimization of cable sheath protector parameters, and reduction of tower grounding resistance values, proposing a synergistic "terminal surge arrester-shelter protector-tower grounding resistance" method for suppressing lightning overvoltages in 220kV overhead-cable hybrid lines.

[0087] S250, verify the effectiveness of applying the synergistic suppression scheme to the 220kV overhead-cable hybrid line, ensuring that the overvoltage control index under normal lightning strike conditions is met. If it is not met, re-analyze the voltage transmission law and optimize the overvoltage suppression measures until the effectiveness requirements are met.

[0088] Finally, the suppression scheme involving the coordinated operation of the "terminal surge arrester-shelter protector-tower grounding resistance" was simulated and verified. In one embodiment of this disclosure, the suppressed cable core voltage amplitude transfer characteristics are as follows: Figure 8 As shown, the voltage amplitude transfer characteristics of the sheath are as follows: Figure 9 As shown in the figure. Simulation results show that: at cable joint 1, the core voltage amplitude decreased from 523.21kV before suppression to 233.14kV, and the sheath voltage amplitude decreased from 33.44kV before suppression to 4.69kV; at cable joint 2, the core voltage amplitude decreased from 532.88kV before suppression to 236.56kV, and the sheath voltage amplitude decreased from 26.21kV before suppression to 6.51kV.

[0089] As can be seen, in this embodiment, the synergistic suppression scheme is effective, with the overvoltage reduction at the joint exceeding 55% under conventional lightning strikes. The overvoltage amplitude meets the requirements of GB / T18890-2015 "Rated Voltage 220kV (Um=252kV) Cross-linked Polyethylene Insulated Power Cables and Their Accessories" and DL / T5221-2016 "Design Code for Urban Power Cable Lines". This provides a feasible solution and reference for suppressing lightning overvoltage in overhead-cable hybrid lines.

[0090] If the simulation results do not meet the validity requirements, the voltage transfer law should be re-analyzed and the overvoltage suppression measures optimized until the overvoltage control indicators under normal lightning strike conditions are met.

[0091] In summary, the overvoltage suppression method based on the lightning overvoltage characteristics of 220kV overhead-cable lines provided in the embodiments of this disclosure establishes a hybrid line lightning overvoltage simulation model composed of a 220kV overhead-cable hybrid line model and a Heidler lightning current model. Based on this model, multiple measurement points are set according to preset rules in the cable section to collect overvoltage data of the cable core and sheath. This provides sufficient data to analyze the transmission law of overvoltage in the hybrid line under lightning strike conditions, avoiding the problem of difficulty in locating the most severely overvoltage area due to oversimplification of the model in existing technologies. At the same time, by adopting the collaborative optimization measures of "surge arrester adjustment + sheath protection device optimization + low-resistance grounding", the problem of weak collaborative protection capability of existing "single-point" designs is solved. In addition, by establishing an index verification and iteration mechanism, re-analysis and optimization are performed when the standards are not met, thereby ensuring that the suppression effect meets the standards.

[0092] Although the subject matter described herein is provided in the general context of execution on a computer system in conjunction with an operating system and applications, those skilled in the art will recognize that other implementations can also be executed in conjunction with other types of program modules. Generally, program modules include routines, programs, components, data structures, and other types of structures that perform specific tasks or implement specific abstract data types. Those skilled in the art will understand that the subject matter described herein can be practiced using other computer system configurations, including handheld devices, multiprocessor systems, microprocessor-based or programmable consumer electronics, minicomputers, mainframes, etc., and can also be used in distributed computing environments where tasks are performed by remote processing devices connected via a communication network. In a distributed computing environment, program modules may reside on both local and remote memory storage devices.

[0093] Those skilled in the art will recognize that the units and method 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 disclosure.

[0094] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of this disclosure and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of this disclosure should be included within the protection scope of this disclosure. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A method of overvoltage suppression based on the characteristics of lightning overvoltage of 220 kV overhead-cable line, characterized in that, The method comprises the following steps: a simulation model of lightning overvoltage of a 220kV overhead-cable hybrid line is constructed, the simulation model comprising a 220kV overhead-cable hybrid line model and a lightning current model; the 220kV overhead-cable hybrid line model is divided into an overhead line section and a cable line section, the cable of the cable line section adopts a cross-interconnection mode and the metal sheath is grounded through a sheath protector, and the overhead line model comprises a line model reflecting frequency characteristics; the lightning current model adopts a Heidler model and the lightning current waveform is a double-exponential waveform; based on the simulation model, a plurality of measurement points are arranged at preset intervals on the cable section, overvoltage data of the cable core and the sheath at each measurement point are collected, and the transmission law of overvoltage in the hybrid line under lightning working conditions is analyzed; for the overvoltage transmission law, overvoltage suppression measures are optimized, including adjusting the flashover voltage and volt-ampere characteristic of the cable terminal arrester, optimizing the action time and impedance of the sheath protector, and adopting a low-resistance grounding structure to reduce the tower grounding resistance; the overvoltage suppression measures are integrated to form a synergistic suppression scheme; the effectiveness of the synergistic suppression scheme applied to the 220kV overhead-cable hybrid line is verified to ensure that the overvoltage control index under the conventional lightning condition is met, and if not, the overvoltage transmission law is reanalyzed and the overvoltage suppression measures are optimized until the effectiveness requirement is met.

2. The method of claim 1, wherein: the overhead line section is composed of three towers and four line sections, each line section being 0.5km long and comprising a tower, a conductor and a ground wire, and two ground wires being arranged above the conductor; the cable line section is composed of three 450m-long cross-interconnected cables.

3. The method of claim 2, wherein, The cable model is YJLW02-Z127 / 220k-1×2500.

4. The method of claim 2, wherein, The conductor and the ground wire both adopt JL / G1A-630 / 45 type steel-cored aluminum stranded wire.

5. The method of claim 2, wherein, The tower uses a multi-wave impedance model.

6. The method of claim 1, wherein, The line model reflecting frequency characteristics is a JMarti model.

7. The method of claim 1, wherein, The preset interval is 150m.

8. The method of claim 1, wherein, The low-resistance grounding structure comprises a deep-well grounding electrode, a copper-coated steel grounding net, a bentonite-based resistance-reducing agent or a three-dimensional grounding structure.

9. The method of claim 1, wherein, Optimizing the impedance of the sheath protector comprises: reducing the impedance value of the sheath protector from an initial 10Ω to 1Ω, and maintaining the model structure of the sheath protector as a three-phase voltage-controlled switch connected in series with the impedance; wherein the action threshold of the three-phase voltage-controlled switch is set to close the ground when the voltage between the cross-interconnection point and the ground exceeds 100V.

10. The method of claim 1, wherein, The overvoltage control index under the conventional lightning condition comprises: the overvoltage drop at the cable joint is not less than 55%, and the overvoltage amplitude meets the requirements of GB / T18890-2015 and DL / T5221-2016 standards.

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