An analysis method, device and medium for impedance mismatch and imbalance characteristics of a hybrid operation system based on XLPE cable aging

Abstract

The present invention provides a method, device, and medium for analyzing the impedance mismatch and imbalance characteristics of a hybrid operating system based on XLPE cable aging. This method, which belongs to the technical field of cable aging analysis, involves performing equivalent simplification on the power grid in a simulation system, retaining switchyards and substations, and constructing a cable structure model. The method then obtains cable structure parameters, sets three-phase unbalanced current-carrying simulation conditions, obtains operating parameters, constructs a cable finite element thermal field analysis model, inputs cable thermal field analysis data, and sets the cable burial depth and surrounding parameters. The method then compares and analyzes temperature distribution differences, obtains temperature data on the inner and outer surfaces of the insulation layer, and calculates the average temperature difference of the insulation layer under the two operating conditions. Based on the average temperature difference, the method quantifies the impact of a single-phase energized operating condition on the cable insulation life compared to a symmetrical operating condition. Based on the evaluation results, a more reasonable cable maintenance plan and replacement cycle can be formulated to prevent failures caused by insulation aging in advance and ensure the safe and reliable operation of the power system.

Description

Technical Field

[0001] The present invention belongs to the technical field of cable aging analysis, and in particular relates to an analysis method, device and medium for impedance mismatch and unbalance characteristics of a hybrid operation system based on XLPE cable aging. Background Art

[0002] As the construction of the Energy Internet deepens, cross-sea interconnection projects, as key infrastructure for optimizing energy resource allocation and improving regional power supply reliability, are attracting widespread attention for their technological evolution and safe operation. Demand for submarine cables, a crucial component of offshore wind power transmission, remote island power supply, and regional power grid interconnection, continues to expand. In submarine cable projects, lines often span tens or even hundreds of kilometers, requiring enormous resource and capital investments. Construction and operation and maintenance costs significantly impact the project's lifecycle profitability. Cross-linked polyethylene (XLPE) insulated cables, due to their environmental performance and superior electrical properties, are gradually replacing traditional oil-filled cables in new submarine transmission projects. However, in actual projects, there is often a transition period where new and old technologies coexist, and the impact of heterogeneous mixed operating conditions on system stability has yet to be effectively analyzed.

[0003] Current research exhibits a significant disciplinary divide: the materials science field focuses on the aging mechanisms and lifespan prediction of XLPE cables, while the power system field focuses on the impact of three-phase imbalance on system stability. However, research on the coupling effect between the two is relatively scarce. Under mixed operating conditions, impedance mismatch and length mismatch contribute to the system's unbalanced characteristics, and the dynamic modulation of the system's impedance parameters by the aging process further complicates the problem. Currently, there is a lack of in-depth analysis of the interaction mechanism between cable aging and system imbalance under mixed operating conditions, making it impossible to quantify the impact of unbalanced operating conditions on cable insulation life. This results in operations and maintenance personnel being unable to understand the aging status of cable insulation and ensure the safe and reliable operation of the power system. Summary of the Invention

[0004] The present invention provides a method for analyzing the impedance mismatch and imbalance characteristics of a hybrid operation system based on XLPE cable aging. Based on the evaluation results, the method formulates a more reasonable cable maintenance plan and replacement cycle, prevents failures caused by insulation aging in advance, and ensures the safe and reliable operation of the power system.

[0005] The method includes: S101: performing equivalent simplification on the power grid in the simulation system, retaining the switch station and the substation, and simplifies the remaining power grid to the retained stations, and constructing a structural model of a three-core cross-linked polyethylene cable and an oil-filled cable;

[0006] S102: Obtain structural parameters of the three-core cross-linked polyethylene cable and the oil-filled cable, including the nominal thickness, outer diameter, and electrical characteristics of each layer of material, and form an electrical parameter table of the cable;

[0007] S103: Set the simulation conditions for three-phase unbalanced current carrying. Configure phase A to use a three-core cross-linked polyethylene cable and phases BC to use an oil-filled cable. Set the power transmitted by any phase under full load conditions. Obtain the operating parameters for a single-phase current in the three-core cable to reach a preset current value. Compare the current differences between the phases under symmetrical conditions.

[0008] S104: Constructing a finite element thermal field analysis model for the cable. A three-dimensional thermal field analysis model of the three-core cross-linked polyethylene cable is established based on current parameters obtained through real-time simulation. The cable thermal field analysis data is input, and the cable burial depth and the thermal conductivity parameters of the surrounding seabed saturated sediment and seawater are set.

[0009] S105: Comparing and analyzing temperature distribution differences, simulating single-phase power-on and three-phase symmetrical operating conditions in the thermal field model, obtaining temperature data of the inner and outer surfaces of the insulation layer, and calculating the average temperature difference of the insulation layer under the two conditions;

[0010] S106: Based on the average temperature difference, the Arrhenius equation is used to analyze the change in the aging rate of the insulation material and quantify the impact of single-phase power-on conditions on the cable insulation life compared to symmetrical operating conditions.

[0011] It should be further explained that step S101 specifically includes: constructing a mixed operation power grid model including 500kV cable lines, overhead lines and substations on the real-time digital simulation system platform, by retaining the 500kV W switch station, A substation, X substation on the left and the 500kV F substation, Z switch station, H substation on the right and treating the remaining power grid parts as equivalent, setting equivalent additional lines between the W switch station and the A substation, and between the Z switch station and the H substation, and at the same time inputting the conductor structure, insulation layer configuration and sheath component parameters of the three-core cross-linked polyethylene cable and the oil-filled cable to establish a three-dimensional cable structure model.

[0012] It should be further explained that step S102 specifically includes: obtaining the structural parameters of the three-core cross-linked polyethylene cable and the oil-filled cable, including the nominal thickness, outer diameter and electrical characteristics of each layer of material, establishing a geometric dimension and material property parameter table including the conductor shielding layer, insulation layer, sheath layer and armor layer based on the cable structure layering data, and generating a comparison table of positive-sequence, negative-sequence and zero-sequence electrical parameters of different cable types.

[0013] It should be further explained that step S103 specifically includes:

[0014] In the simulation system, the rated voltage and copper core cross-section parameters of the A-phase three-core cross-linked polyethylene cable and the rated voltage of the BC-phase oil-filled cable were configured. The rated transmission power of any phase was set under full load conditions. The current in the three-core cross-linked polyethylene cable during mixed operation was obtained, and the difference in current amplitude of each phase was compared when only the three-core cross-linked polyethylene cable was normally energized and under symmetrical operating conditions.

[0015] It should be further explained that step S103 also includes:

[0016] Based on the three-phase voltage and current data obtained in real-time simulation, the positive sequence, negative sequence and zero sequence components are obtained through Clarke and Fortescue sequence component transformation;

[0017] Calculate the negative sequence voltage and zero sequence voltage unbalance based on formula (1);

[0018] (1)

[0019] In the above formula, 、 are the RMS values ​​of the positive and negative sequence voltages, respectively;

[0020] Calculate the negative sequence current and zero sequence current imbalance based on formula (2);

[0021] (2)

[0022] In the above formula, 、 are the RMS values ​​of the positive and negative sequence voltages, respectively.

[0023] It should be further noted that step S104 also includes: establishing a three-dimensional thermal field analysis model of the three-core cross-linked polyethylene cable, obtaining the temperature distribution characteristics of the insulation layer during unbalanced operation, and quantifying the temperature difference between the insulation layer and the insulation layer during three-phase symmetrical operation;

[0024] The copper conductor of the three-core XLPE cable is set to linear resistivity, and the resistivity is calculated using formula (3);

[0025] (3)

[0026] In the formula is the reference temperature T ref The resistivity under is the temperature coefficient of resistivity.

[0027] It should be further explained that step S105 also includes:

[0028] The current parameters obtained by the simulation system are input as boundary conditions into the established three-core cross-linked polyethylene cable three-dimensional thermal field analysis model. The single-core energized condition and the three-phase symmetrical operation condition are simulated in the thermal field model.

[0029] Obtain temperature data inside the insulation layer close to the conductor side and outside under two working conditions;

[0030] The logarithmic mean temperature calculation method of cylindrical insulators is used to calculate the average temperature of the insulation layer under the two operating conditions, and the difference in the average temperature of the insulation layer under the single-core operating condition and the three-phase symmetrical operating condition is obtained.

[0031] It should be further explained that the calculation formula for the logarithmic mean temperature of a cylindrical insulator is:

[0032]

[0033] in, is the temperature inside the insulation layer, is the external temperature of the insulation layer;

[0034] According to the Arrhenius equation:

[0035]

[0036] in, is the insulation life, is the activation energy, k is the Boltzmann constant, T is the absolute temperature.

[0037] According to another embodiment of the present application, an electronic device is provided, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, the steps of the method for analyzing the impedance mismatch and imbalance characteristics of a hybrid operating system based on XLPE cable aging are implemented.

[0038] According to another embodiment of the present application, a storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, the steps of the method for analyzing the impedance mismatch and imbalance characteristics of a hybrid operation system based on XLPE cable aging are implemented.

[0039] It can be seen from the above technical solutions that the present invention has the following advantages:

[0040] The analysis method of the impedance mismatch and unbalance characteristics of the hybrid operation system based on XLPE cable aging provided in this application reduces the system complexity, reduces the consumption of simulation computing resources, and improves modeling efficiency by simplifying the power grid equivalent while retaining the electrical characteristics of key nodes; constructs a model of the actual engineering cable structure to make the simulation close to the real scene. The structural parameters and electrical characteristics of each layer of the cable are obtained to form a standardized electrical parameter table, which provides a quantitative basis for the electrical performance analysis of the hybrid cable system and ensures that the simulation results can reflect the conductivity, insulation and other characteristics of the actual cable. Setting a three-phase unbalanced current-carrying condition and comparing it with the symmetrical condition can quantify the difference in cable current under different operating modes and reveal the current distribution law of the hybrid cable system under unbalanced conditions. A three-dimensional thermal field analysis model is established and multi-physics field parameters are input to convert the current parameters into thermal boundary conditions, realize the coupled analysis of the electromagnetic field and thermal field, and intuitively present the cable temperature distribution characteristics. By comparing the temperature difference between the single-core and symmetrical conditions, the impact of unbalanced operation on the temperature of the cable insulation layer is quantified, the risk of local overheating is discovered, and key indicators are provided for cable heat dissipation design and operation monitoring. Using the Arrhenius equation to convert temperature differences into a quantitative analysis of insulation aging rates, a "temperature-aging-lifespan" correlation model is established to scientifically assess the impact of unbalanced operating conditions on cable life. This quantitative analysis correlates current differences, temperature distribution, and the impact on insulation life, avoiding the ambiguity of traditional qualitative analysis and enhancing the scientific nature and credibility of the assessment results. Risks such as current concentration, localized overheating, and accelerated insulation aging caused by unbalanced operation can be identified in advance. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solution of the present invention, the following is a brief introduction to the drawings required for the description. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0042] Figure 1 This is a flow chart of the analysis method for impedance mismatch and unbalance characteristics of mixed operation systems based on XLPE cable aging;

[0043] Figure 2 This is the simplified system wiring diagram after equalization;

[0044] Figure 3 It is a structural diagram of a three-core cable;

[0045] Figure 4 This is a schematic diagram of the oil-filled cable structure;

[0046] Figure 5 This is a schematic diagram of the imbalance of the hybrid operation system before aging;

[0047] Figure 6 Schematic diagram of temperature distribution for mixed operation and symmetrical operation, where Figure 6 Figure a is a schematic diagram of a three-core cable in symmetrical operation, and figure b is a schematic diagram of a three-core cable in mixed operation with only one core connected.

[0048] Figure 7 Schematic diagram of the change of dielectric properties of XLPE after thermal aging, where: Figure 7 (a) is a schematic diagram of the change of dielectric constant with frequency, and (b) is a schematic diagram of the change of dielectric loss with frequency;

[0049] Figure 8 Schematic diagram of the evolution trend of negative sequence imbalance at each measurement point in the system;

[0050] Figure 9 It is a schematic diagram of the relationship between the negative sequence imbalance growth rate characteristic and the distance;

[0051] Figure 10 Schematic diagram of the three-dimensional mutual feedback relationship model of aging-impedance mismatch-imbalance;

[0052] Figure 11 Schematic diagram of an electronic device. DETAILED DESCRIPTION

[0053] The analysis method of the impedance mismatch and unbalance characteristics of the hybrid operation system based on XLPE cable aging in this application constructs an electric field-thermal field-aging analysis framework to explore the influence mechanism of aging on imbalance in the hybrid operation system. An accurate simulation model of the hybrid operation system is established based on actual engineering parameters, and high-precision calculation of power grid currents and transient characteristics is achieved through a real-time digital simulation system platform. Finite element software is then used to construct a cable thermal field distribution model to analyze the temperature gradient characteristics under different working conditions. Targeted accelerated aging experiments are designed to obtain the degradation laws of key parameters of XLPE materials under unbalanced electrical stress, and to establish an aging-parameter relationship mathematical model. This application proposes the indicator of hybrid operation impedance mismatch coefficient, which reveals the influence mechanism of XLPE cable aging on imbalance.

[0054] The following describes in detail the specific steps of the method for analyzing the impedance mismatch and imbalance characteristics of a hybrid operation system based on XLPE cable aging, as described in this application. Specific details, such as specific system structures and technologies, are provided for illustration, not limitation, to facilitate a thorough understanding of the embodiments of this application. However, it should be apparent to those skilled in the art that this application may also be implemented in other embodiments without these specific details.

[0055] It should be understood that when used in this specification, the term "comprising" indicates the presence of the described features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or their collections. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized.

[0056] The phrases "one embodiment" or "some embodiments" described in this application mean that the specific features, structures, or characteristics described in the embodiment are included in one or more embodiments of the application. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in other embodiments," etc. that appear in different places in this application do not necessarily refer to the same embodiment, but rather mean "one or more but not all embodiments," unless otherwise specifically emphasized.

[0057] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0058] See also Figure 1 FIG. 1 is a flow chart of a method for analyzing impedance mismatch and imbalance characteristics of a hybrid operation system based on XLPE cable aging in a specific embodiment. The method includes:

[0059] Step S101: In the simulation system, the power grid is simplified and equivalent, the switch station and substation are retained, the remaining power grid is equivalent to the retained stations, and the structural models of the three-core cross-linked polyethylene cable and the oil-filled cable are constructed.

[0060] In some embodiments, as Figure 2As shown in the figure, in the simulation system, the grid architecture is simplified based on actual data. On the left side of the grid, the 500kV W switchyard, 500kV A substation, and 500kV X substation are retained intact, while the remaining power system is simplified and equivalent to the W switchyard and A substation. On the right side of the grid, the 500kV F substation, 500kV Z switchyard, and 500kV H substation are retained, while the remaining 500kV grid is equivalent to the Z switchyard and H substation, and the 220kV grid is uniformly equivalent to the F substation. Simultaneously, a three-core cross-linked polyethylene cable structure model with a rated voltage of 500kV and a copper core cross-section of 3×1000 + 2×48 (steel armor) is constructed for phase A, and an oil-filled cable structure model with a rated voltage of 500kV is constructed for phase BC.

[0061] This embodiment simplifies complex power grids based on the principle of circuit equivalent transformation, while preserving the electrical characteristics of key nodes. By analyzing the impact of various grid components on power, voltage, and other aspects of key sites, the simplified components are replaced with equivalent power supplies, impedances, and other components, transforming the complex system into a model that facilitates analysis and calculation. The cable structure model is constructed based on the physical structure and material properties of the cable, transforming it into a digital model that can be recognized and processed by the simulation system.

[0062] Step S102: Obtain structural parameters of the three-core cross-linked polyethylene cable and the oil-filled cable, including the nominal thickness, outer diameter and electrical characteristics of each layer of material, to form an electrical parameter table of the cable.

[0063] In some embodiments, for the constructed three-core cross-linked polyethylene cable and oil-filled cable structural models, the detailed structural parameters of each layer of material are comprehensively obtained. For example, the three-core cross-linked polyethylene cable includes the combined outer diameter of the copper conductor and the water-blocking tape, the thickness and outer diameter of the semi-conductive double-sided water-blocking binding tape and the inner shield, etc.; the oil-filled cable includes the oil channel diameter, conductor size, etc. With reference to national standards, international standards and actual engineering data, the electrical characteristics of the two cables, such as resistance, reactance, capacitance and other parameters, are determined, and finally an electrical parameter table including cable structure, length, positive sequence, negative sequence and zero sequence parameters is formed. It can accurately reflect the electrical behavior of the cable in actual operation, provide a reliable basis for studying the power flow distribution, voltage and current characteristics of the power grid, and improve the accuracy and credibility of the simulation results.

[0064] Step S103: Set the three-phase unbalanced current simulation conditions, configure phase A to use a three-core cross-linked polyethylene cable, configure phase BC to use an oil-filled cable, set the transmission power of any phase under full load conditions, obtain the operating parameters when the single-phase current in the three-core cable reaches the preset current value, and compare the current differences of each phase under symmetrical conditions.

[0065] In some embodiments, in the simulation system, simulation conditions for three-phase unbalanced current carrying are set based on the actual engineering topology and equipment parameters. Specifically, phase A is configured as a three-core cross-linked polyethylene cable, phase BC is an oil-filled cable, and the rated transmission power of any phase under full load conditions is set to 200MW. After running the simulation, the operating parameters of the single-phase current in the three-core cross-linked polyethylene cable reaching 858.4A during hybrid operation are obtained. At the same time, the symmetrical operating condition of normal power supply using only the three-core cross-linked polyethylene cable is simulated, and data with a current amplitude of 866.7A for each phase is obtained. The current conditions under the two operating conditions are compared and analyzed. In this way, by setting different operating conditions and obtaining current parameters, the current characteristics of the hybrid cable system under unbalanced operation can be studied, and the impact of unbalanced operation on the cable current can be clearly understood by comparing the symmetrical operating conditions.

[0066] Step S104: Construct a cable finite element thermal field analysis model, establish a three-dimensional thermal field analysis model of the three-core cross-linked polyethylene cable based on the current parameters obtained by real-time simulation, input the cable thermal field analysis data, and set the cable burial depth and the thermal conduction parameters of the surrounding seabed saturated sediment and seawater.

[0067] In some embodiments, the cable thermal field analysis data includes but is not limited to conductor conductivity, dielectric constant of the insulation layer, thermal conductivity of each material, and constant-pressure heat capacity parameters.

[0068] Using the current parameters obtained from real-time simulation as boundary conditions, a three-dimensional thermal field analysis model of a three-core cross-linked polyethylene cable was built on the finite element simulation platform. The thermal field analysis data of each part of the cable were input into the model in sequence, such as the copper conductor conductivity of 6×10 7 S / m, XLPE insulation relative dielectric constant 2.3, etc.; at the same time, the cable burial depth is set to 1.0m, and the thermal conductivity of the seabed saturated sedimentary soil is 1.0W / (m·K), the thermal conductivity of seawater is 0.6W / (m·K), and other surrounding thermal conduction parameters are set.

[0069] This embodiment establishes a three-dimensional thermal field analysis model of the cable and accurately sets parameters, which can simulate the temperature changes of the cable in the actual operating environment, and provide an intuitive and accurate analysis method for studying the temperature characteristics of the cable insulation layer and evaluating the thermal stability and life of the cable.

[0070] Step S105: Comparing and analyzing the temperature distribution differences, simulating single-phase power-on and three-phase symmetrical operation conditions in the thermal field model, obtaining the temperature data of the inner and outer surfaces of the insulation layer, and calculating the average temperature difference of the insulation layer under the two conditions.

[0071] In some embodiments, the current parameters output by the real-time digital simulation system are imported into the established three-dimensional thermal field analysis model of the three-core cross-linked polyethylene cable to simulate the single-core energized condition and the three-phase symmetrical operating condition, respectively. The temperature data of the inner side of the cable insulation layer near the conductor and the outer side are obtained under the two operating conditions. The inner temperature of the insulation layer under the three-phase symmetrical operating condition is 84.9°C and the outer temperature is 79.1°C. The inner temperature of the insulation layer under the single-core operating condition is 87.8°C and the outer temperature is 80.5°C. Using the logarithmic mean temperature calculation method of cylindrical insulators, the average temperature of the insulation layer under the two operating conditions is calculated, and it is found that the average temperature of the insulation layer under the single-core operating condition is about 2.3°C higher than that under the three-phase symmetrical operating condition. By comparing and analyzing the differences in the temperature distribution of the cable insulation layer under different operating conditions, the impact of unbalanced operation on the cable temperature can be intuitively understood.

[0072] Step S106: Based on the average temperature difference, the Arrhenius equation is used to analyze the change in the aging rate of the insulation material, and to quantify the impact of the single-phase power-on condition on the cable insulation life compared with the symmetrical operating condition.

[0073] This embodiment uses the average insulation layer temperature difference obtained in step S105 as a basis and employs the Arrhenius equation to establish a quantitative relationship between temperature and insulation material aging rate. By substituting relevant parameters, the aging rate of the cable insulation material under single-phase power supply conditions compared to symmetrical operating conditions is calculated, thereby quantifying the impact of this unbalanced operating condition on the cable insulation lifespan.

[0074] The Arrhenius equation describes the exponential relationship between the aging rate and temperature in cable insulation aging, which can be compared to the aging process itself. Increasing temperature accelerates the aging reaction of the insulation material. By substituting temperature data under different operating conditions into the equation, the change in aging rate is calculated, thereby assessing the impact on insulation life.

[0075] As can be seen, quantifying the impact of unbalanced operating conditions on cable insulation life can provide a scientific basis for power system operation and maintenance. Based on the assessment results, operators can formulate more reasonable cable maintenance plans and replacement cycles, proactively preventing failures caused by insulation aging, ensuring the safe and reliable operation of the power system, and reducing operation and maintenance costs and the risk of power outages.

[0076] Furthermore, as a refinement and extension of the specific implementation of the above embodiment, in order to fully illustrate the specific implementation process in this embodiment, the analysis method of the impedance mismatch and imbalance characteristics of the hybrid operation system based on XLPE cable aging further includes the following steps:

[0077] Combine Figure 2Based on actual project data, a detailed model of the relevant cable lines, overhead lines, and substations in the Hainan interconnection project was constructed on a real-time digital simulation system platform. To facilitate simulation and calculation research, the actual power grid in the project was simplified and equivalent. On the left side, the 500kV W switch station, 500kV A substation, and 500kV X substation were retained, and the remaining systems were equivalent to the W switch station and A substation. On the right side, the 500kV F substation, 500kV Z switch station, and 500kV H substation were retained, and the remaining 500kV power grid was equivalent to the Z switch station and H substation, and the 220kV power grid was equivalent to the F substation. The lines between the W switch station and the A substation, and between the Z switch station and the H substation, are all equivalent additional lines.

[0078] In the simulation system, phase A is selected as a three-core cross-linked polyethylene cable with a rated voltage of 500 kV and a copper core cross-sectional parameter of 3×1000+2×48 (steel armor). Figure 3 The basic structure diagram of the three-core cable is shown in Table 1. The three-core integrated structure parameters of the 500kV AC cross-linked polyethylene cable are given in Table 1.

[0079] Figure 3 The three-core XLPE cable described in the specification has three cores, each consisting of a copper conductor + water-blocking tape 1, a semi-conductive double-sided water-blocking binding tape + an inner shield 2, XLPE insulation 3, an outer shield 4, a semi-conductive water-blocking tape 5, an alloy lead sheath 6, and an MDPE jacket 7. The three-core XLPE cable also has filler material 8 and an optical fiber unit 12. The three-core XLPE cable also has an inner lining 9, an armor layer 10, and an outer sheath 11.

[0080] Table 1

[0081]

[0082] In the simulation system, the BC phase is selected as an oil-filled cable with a rated voltage of 500 kV. The oil-filled cable adopts an oil-filled insulation structure and is suitable for complex marine environmental conditions of high voltage and large capacity AC transmission. Figure 4 The diagram shows the basic structure of an oil-filled cable. From the inside out, the cable comprises: oil channel 1, conductor 2, insulation layer 3, lead alloy 4, inner lining 5, polyethylene sheath 6, outer lining 7, armor 8, and outer sheath 9. Table 2 lists the structural parameters of a 500kV oil-filled cable.

[0083] Table 2

[0084]

[0085] After inputting the above structural parameters into the simulation model, the electrical parameter comparison of the two cables is shown in Table 3.

[0086] Table 3

[0087]

[0088] To meet the modeling requirements for transformers, high-voltage reactors, and overhead lines in engineering systems, this example constructs an electrical model consistent with on-site operating scenarios based on the topology and equipment parameter characteristics of the actual project. The resulting current in a three-core cross-linked polyethylene cable during full hybrid operation, when any phase reaches its rated transmission power of 200 MW, is 858.4 A.

[0089] If the system does not use oil-filled cables and only uses a three-core cross-linked polyethylene cable for normal power supply, the current amplitude of each phase is 866.7A when operating under this symmetrical working condition.

[0090] The three-phase voltage and current data obtained from real-time simulation can be used to obtain their positive sequence, negative sequence and zero sequence components through Clarke and Fortescue sequence component transformation.

[0091] The unbalance of negative-sequence voltage and zero-sequence voltage is defined as the ratio of negative-sequence to zero-sequence components divided by the positive-sequence component, and is expressed in percentage form, as shown in formula (1).

[0092] (1)

[0093] In formula (1), 、 The negative-sequence and zero-sequence voltage imbalances are calculated and analyzed for transformer substations X, F, N, and L, respectively, where is the RMS value of the positive-sequence and negative-sequence voltages. Similarly, the negative-sequence and zero-sequence current imbalances are defined as the ratio of the negative-sequence to zero-sequence components to the positive-sequence components, as shown in Equation (2).

[0094] (2)

[0095] In the above formula, 、 The negative sequence and zero sequence unbalance of the current flowing through the cable are calculated and the results are plotted against the voltage unbalance of the transformer station and terminal station. Figure 5 middle.

[0096] As for the construction method of the cable finite element model in this embodiment, the three-phase unbalanced current-carrying condition obtained by system simulation can be used as the boundary condition, and a three-dimensional thermal field analysis model of the three-core XLPE cable can be established through the finite element simulation platform to obtain the temperature distribution characteristics of the insulation layer during unbalanced operation, and quantify the temperature difference between the insulation layer and the insulation layer during three-phase symmetrical operation.

[0097] The input parameters of different parts of the cable are shown in Table 4.

[0098] Table 4

[0099]

[0100] Among them, the copper conductor is set to linear resistivity, and its resistivity is calculated using formula (3).

[0101] (3)

[0102] In the formula is the reference temperature T ref The resistivity under the condition of 1.72×10 -8 Ω·m, is the temperature coefficient of resistivity, set to 0.0039.

[0103] Based on the actual project, the cable was buried at a depth of 1.0 m. The surrounding environment was primarily saturated seabed sediment and seawater. The thermal conductivity of saturated sandy soil was assumed to be 1.0 W / (m·K), and the thermal conductivity of seawater was 0.6 W / (m·K). The seabed ambient temperature is relatively stable, with the average seawater temperature in the area measured at 12°C, and the soil temperature is close to this value. These parameters were used in the simulation to accurately reflect the thermal conductivity characteristics of the cable during operation, providing reliable input for temperature field calculations.

[0104] The current parameters obtained in the real-time digital simulation system are used as boundary conditions to input the temperature distribution of the three-core cable under mixed operation conditions. The temperature distribution under mixed operation conditions is compared with that under normal symmetrical operation. Figure 6 shown. Figure 6 Figure a is a schematic diagram of a three-core cable in symmetrical operation, and figure b is a schematic diagram of a three-core cable in mixed operation with only one core passing through.

[0105] from Figure 6 It can be seen that when only one core of a three-core cross-linked polyethylene cable is energized and the other two cores are unloaded, the temperature of the insulation layer around the energized core is significantly higher than that under the three-phase symmetrical operation condition. This phenomenon can be attributed to two factors: the electromagnetic thermal coupling effect and the change in the heat conduction path. At the electromagnetic thermal coupling level, although the current passing through the conductor (858.4A) under the single-phase energization condition is slightly smaller than the current per phase (866.7A) under symmetrical operation, the current density is concentrated on a single conductor, resulting in an increase in the local heat source density. More importantly, when the three phases are symmetrically energized, the currents of each phase have a spatial phase difference of 120°, and the magnetic fields generated tend to cancel each other out in the core area of ​​the cable, significantly reducing the induced eddy currents in the metal sheath; while in the single-phase energization condition, the lack of the magnetic field cancellation effect of the other phase currents results in the generation of larger eddy currents in the cable metal sheath. This eddy current loss is converted into an additional heat source, further increasing the temperature of the insulation layer. This additional loss can be expressed by the eddy current density formula:

[0106] (5)

[0107] in, is the material conductivity, is the magnetic induction intensity, is the position vector. According to the thermoelectric coupling control equation:

[0108] (6)

[0109] in, represents Joule heat, Represents eddy current loss. The total heat source intensity under single-core energized conditions increases significantly, causing the temperature of the insulation layer to rise.

[0110] In terms of heat conduction mechanism, when a single core is powered, the unloaded state of the other two cores causes a significant change in the originally balanced heat conduction path. The three-core symmetrical design is originally based on the principle of equal distribution of thermal resistance and follows Fourier's law of heat conduction:

[0111] (7)

[0112] Among them, the heat flux q With temperature gradient Proportional to thermal conductivity k When only one core is energized, the heat flow is forced to propagate along a non-optimal path, and the effective thermal resistance increases, which can be expressed as:

[0113] (8)

[0114] in, is the thermal path correction factor, when a single core is powered on The value increases significantly. In addition, the skin effect and proximity effect lead to more uneven current distribution under single-core energization conditions, increasing the heat source density gradient inside the conductor. When operating under normal symmetrical conditions, the innermost temperature of the insulation layer is 84.9°C and the outermost temperature is 79.1°C. The logarithmic mean temperature formula for cylindrical insulators is:

[0115] (9)

[0116] in, is the temperature inside the insulation layer (close to the conductor side), is the external temperature of the insulation layer. The calculated average temperature is approximately 81.9°C. When only a single core is in operation, the internal temperature of the insulation layer is 87.8°C and the external temperature is 80.5°C. According to formula (8), the average temperature is approximately 84.2°C, which is approximately 2.3°C higher than the symmetrical operation state. This temperature difference will significantly affect the aging rate of the insulation material in long-term operation. According to the Arrhenius equation:

[0117] (10)

[0118] in is the insulation life, is the activation energy, k is the Boltzmann constant, T is the absolute temperature.

[0119] This embodiment verifies the aging state of the cable. The following uses a specific experiment as an example to establish the corresponding relationship between the actual operating temperature and the accelerated aging temperature. Based on the Arrhenius equation, the acceleration factor (AF) calculation formula can be derived:

[0120] (11)

[0121] The activation energy of XLPE insulation material is generally in the range of 1.1-1.3 eV [20-21]. This example uses the activation energy of 1.24 eV measured for 500kV XLPE cable insulation material. By modifying equation (11), the required experimental time at different accelerated aging temperatures can be obtained:

[0122] (12)

[0123] At an aging temperature of 130°C, the acceleration factor reached 124, meaning that one hour of aging at 130°C in the experiment is equivalent to 124 hours under actual operating conditions. Based on this, the critical aging time nodes were determined to be 360 ​​hours, 720 hours, 1080 hours, and 1440 hours, corresponding to approximately 5.1 years, 10.2 years, 15.3 years, and 20.4 years of actual operation, respectively. These cover the critical first half of the 40-year design life of XLPE cables.

[0124] The choice of a temperature parameter of 130°C was based on dual theoretical considerations: on the one hand, this temperature is within the active range of thermal oxidative aging (110°C-140°C), which reasonably shortens the experimental period and avoids non-Arrhenius behavior induced by high temperature; on the other hand, Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) characterizations confirm that the microscopic mechanisms of molecular chain breakage and cross-linking network relaxation in XLPE materials at this temperature are consistent with the aging process under actual operating conditions.

[0125] The four time points are based on the key kinetic stages of cable insulation aging: 360 hours corresponds to the critical point of antioxidant consumption, during which the dielectric loss factor increases linearly; 720 hours captures the inflection point of the dielectric constant change rate, corresponding to the accelerated period of molecular chain oxidation and breakage; 1080 hours represents the stable stage of the free radical chain reaction; and 1440 hours reflects the quasi-equilibrium state of aging, with the microstructural adjustments of the insulation material stabilizing. This experimental plan meets the requirements of the IEC 60216 standard for thermal life assessment of insulation materials and covers the critical 50% of the safe operating life of typical XLPE cable insulation.

[0126] Taking the 500kV three-core cable products of a certain cable manufacturer as the reference object, the XLPE insulation specimens used in the experiment were pressed from the same raw materials as the main insulation of the cable. The raw material components include a cross-linking agent (diisopropylbenzene peroxide), polyethylene particles, and an antioxidant. The materials were mixed by extrusion using a flat-plate vulcanizer, and the insulation material was placed in a drying oven for drying. Secondly, the insulation material was preheated without pressure at 130°C in a flat-plate vulcanizer for 4 minutes; then pressurized at 130°C for 6 minutes; again, pressurized at 180°C for 15 minutes, and finally pressurized and cooled at room temperature for 8 minutes to produce an insulation layer specimen with a thickness of about 0.3 mm.

[0127] The experimental results are analyzed below. The pressed samples were placed in a vacuum oven at 130°C for aging. After aging for 360h, 720h, 1080h and 1440h, they were taken out and their dielectric properties were tested using a broadband dielectric spectrometer. The change patterns of the XLPE dielectric constant and dielectric loss at different aging time nodes are shown in the figure below. Figure 7 shown. Figure 7 (a) is a schematic diagram of the change of dielectric constant with frequency. Figure 7 (b) is a schematic diagram showing the variation of dielectric loss with frequency.

[0128] The dielectric constant shows a gradual increase with aging time. At 50 Hz, the dielectric constant increases from 2.283 before aging to 2.587 after 360 hours, 2.739 after 720 hours, 2.769 after 1080 hours, and 2.816 after 1440 hours, with increases of 13.32%, 20.02%, 21.29%, and 23.37%, respectively. This indicates that the polarization ability of XLPE material significantly increases with aging time. This is because, under the influence of thermal oxidative aging, the XLPE molecular chains break, generating polar groups such as carbonyl and ether groups. Under the action of an applied electric field, these polar groups participate in polarization, enhancing the material's polarization properties and, in turn, causing an increase in the dielectric constant. Longer aging time indicates more severe molecular degradation and more polar groups are generated, leading to a trend of increasing dielectric constant with aging time.

[0129] The dielectric loss factor also increases significantly with aging, particularly in the low-frequency range. At 50 Hz, the dielectric loss factor increases from 0.0038 before aging to 0.0043 after 360 hours, 0.0049 after 720 hours, 0.0054 after 1080 hours, and 0.0057 after 1440 hours, representing increases of 13.16%, 28.95%, 42.11%, and 50.00%, respectively. This change in the dielectric loss factor indicates that the material's loss characteristics continue to deteriorate during aging. This phenomenon is primarily attributed to the combined effects of high temperature and oxygen, which cause the XLPE molecular chains to break and generate a large number of polar groups. These polar groups not only increase polarization losses but also increase dielectric conductivity losses, leading to an increase in the dielectric loss factor.

[0130] Regarding the impact of insulation aging on the unbalanced characteristics of hybrid systems, the following analysis examines the factors influencing unbalance under hybrid operation. In a hybrid system consisting of cross-linked polyethylene (XLPE) cables and oil-filled cables, the mismatch in electrical parameters between the cables is the root cause of system unbalance. Especially under conditions where power flow distribution and insulation aging are coupled, the unbalance exhibits a complex evolution over operating time. Based on simulation results and experimental data, this analysis analyzes the key drivers of the hybrid system's unbalanced characteristics to reveal its changing mechanisms under different operating conditions.

[0131] In the hybrid system power distribution model established based on simulation, the impedance difference between XLPE cables and oil-filled cables directly leads to asymmetry of three-phase current and voltage, which in turn triggers the continuous accumulation of negative sequence current. The equivalent impedance per unit length of XLPE cables is significantly higher than that of oil-filled cables. Through simulation and evaluation of the operating parameters of the actual system, it can be found that under normal operating conditions, the impedance of the oil-filled cables is , and the impedance of XLPE cable is due to its material properties and structural differences. The power carried by XLPE cables with larger impedance is significantly lower than that of oil-filled cables, which leads to a tilt in the overall power distribution and eventually causes system imbalance. In order to quantify this phenomenon more accurately, the “hybrid operation impedance mismatch coefficient” is defined. ", used to measure the impedance difference between XLPE cable and oil-filled cable:

[0132] (12)

[0133] The calculation results of the impedance mismatch coefficient show that although the impedance per unit length of XLPE cable is higher than that of oil-filled cable, the difference is low under normal operating conditions. However, in actual operation, due to the difference in cable length, this impedance mismatch effect will accumulate with the length, further exacerbating the impact on power distribution. In order to quantify the amplification effect of length difference on system imbalance, the "hybrid operation length mismatch coefficient" is defined. ”:

[0134] (13)

[0135] Calculations show that the length mismatch coefficient of the hybrid system increases as the length difference between the XLPE cable and the oil-filled cable increases. The coefficient indicates that the impedance mismatch between the two cables in the hybrid system is more pronounced when the length difference is large. When the length mismatch coefficient is low, the system imbalance is mild, and the current distribution remains relatively balanced. However, when the length mismatch coefficient exceeds a certain threshold, the negative sequence current increases significantly, and the system imbalance exhibits a nonlinear growth trend. This result indicates that the length mismatch has an amplifying effect on the imbalance of the hybrid system. In actual operation, the impedance per unit length of the XLPE cable determines the system's sensitivity to length differences. As the mismatch coefficient increases, the oil-filled cable side bears less actual current, while the XLPE cable bears a correspondingly greater burden. This uneven distribution directly affects the overall stability of the hybrid system. Calculating the length mismatch coefficient provides a theoretical basis for system design and operation, guiding the optimal matching of cable run lengths and thus minimizing imbalance.

[0136] In a mixed operation environment, the aging process of XLPE cables will have a complex impact on the imbalance characteristics of the system. This embodiment reveals how insulation aging modulates the imbalance behavior of a mixed operation system and establishes a mathematical correlation between cable aging parameters and system imbalance.

[0137] The imbalance at all measurement points increased with aging time. The imbalance at the L terminal increased from an initial 0.38% to 0.56% after 1440 hours, a total increase of 47.4%. The imbalance at the X substation increased from 0.28% to 0.36%, a 28.6% increase. The Z switch station and the F substation increased from 0.22% and 0.18% to 0.26% and 0.21%, respectively, with increases of 18.2% and 16.7%. The change in the slope of the curve reflects the material's kinetic transformation during aging. The growth rate in the initial stage (0-720 hours) was significantly higher than that in the later stages (720-1440 hours). This phased nature is consistent with the aging mechanism of XLPE materials: antioxidant consumption and oxidative chain scission reactions dominate in the initial stage, followed by a relatively stable structural reorganization phase in the later stages.

[0138] Figure 8 and Figure 9 A spatial analysis reveals the distribution characteristics of negative sequence imbalance at each measurement point in the system and its evolution over time. Histograms compare negative sequence imbalance at four measurement points across five aging stages, quantifying the spatial distribution characteristic of "high near-end, low far-end." Figure 8 Schematic diagram of the evolution trend of negative sequence imbalance at each measurement point in the system. Figure 9 This is a schematic diagram showing the relationship between the negative sequence imbalance growth rate and distance. Stacked bar charts quantitatively analyze the growth rate changes at each measurement point during different aging stages, revealing the cumulative effect of the growth rate over time. An exponential decay curve quantifies the spatial decay pattern. The exponential decay curve accurately describes the relationship between the imbalance growth rate and the measurement point location:

[0139] (14)

[0140] in, x Represents the electrical distance (km) between the measurement point and the XLPE cable segment. This curve quantifies the spatial attenuation of imbalance growth with high fitting accuracy. The physical meaning corresponds to a 9.5% decrease in the growth rate of imbalance for every 10km increase in electrical distance.

[0141] The imbalance growth characteristics caused by aging can be explained by coupling the evolution of material parameters with changes in electrical properties. Experimental tests show that after 1440 hours of aging, the dielectric constant of XLPE material increased from 2.283 to 2.816, an increase of 23.37%, and the dielectric loss factor increased from 0.0038 to 0.0057, an increase of 50.00%. Changes in these key parameters directly lead to adjustments in the cable impedance parameters, which in turn cause the system imbalance to increase. Analysis of the correlation between the increase in imbalance at the L terminal and changes in material parameters revealed a nonlinear relationship between the two, which can be characterized by a modified exponential function:

[0142] (15)

[0143] in, is the saturation amplification coefficient, is the time scale parameter, n is a nonlinear exponent. The experimental data are fitted to obtain n =0.68, indicating that the imbalance growth caused by aging is sublinear, which is consistent with the diffusion-controlled mechanism of insulation material aging.

[0144] From a theoretical perspective, the increase in negative sequence imbalance is mainly due to the change in impedance parameters caused by the aging of XLPE insulation materials. In a three-phase system, the relationship between negative sequence voltage and current can be expressed as:

[0145] (16)

[0146] in, is the negative sequence self-impedance, The polar groups formed during the thermal oxidation aging process of XLPE insulation material change the dielectric polarization characteristics, resulting in Drift occurs, which in turn affects the negative sequence current distribution.

[0147] Electromagnetic field analysis shows that after 1440 hours of aging, the maximum electric field strength in the cable insulation layer increases by approximately 9.1%, and the field strength enhancement coefficient rises from 1.18 to 1.29. The field strength distribution becomes more uneven, accelerating the accumulation of space charge. The temporal evolution of the imbalance exhibits a distinct segmented nature—the growth rate is generally higher in the early stages (0-720 hours) than in the later stages (720-1440 hours). Within the latter stages, the growth rate rebounds between 1080 and 1440 hours. This non-monotonic trend reflects the complex nonlinear nature of the material aging process and is associated with the accelerated free radical chain reaction formed in the XLPE insulation during the later stages of aging.

[0148] Aging-induced unbalanced growth with defined hybrid run length mismatch coefficient Closely related. Experimental data analysis shows that and the imbalance growth rate There is a linear relationship between:

[0149] (17)

[0150] The goodness of fit R² = 0.962. This relationship reveals the role of length mismatch in the unbalanced growth caused by aging and provides a quantitative basis for the optimal design of hybrid operation systems.

[0151] Figure 10 The negative sequence imbalance degree increases nonlinearly with the aging time and the increase of impedance mismatch coefficient. When it is 9.4%, the corresponding imbalance is 0.28%; as the aging process progresses, at t=1440h It rose to 15.6%, and the imbalance increased to 0.36%, an increase of 28.6%. Figure 9 The inhomogeneity of the surface gradient distribution reveals a critical feature of the system behavior - when After exceeding the critical threshold of 15%, the imbalance growth rate increases significantly, indicating that the system has entered an unstable range.

[0152] During the aging process of XLPE cables, the evolution of sequence impedance parameters shows significant differences. Experimental measurements show that after 1440 hours of aging, the positive, negative, and zero sequence impedances increase by 7.3%, 9.1%, and 13.6%, respectively. However, due to the continuous replenishment and self-healing properties of the insulating oil, the impedance parameters of the oil-filled submarine cable remain basically stable. This differential evolution of impedance parameters directly leads to the From the initial 9.4% to 15.6%, Figure 10 The growth trajectory of medium-unbalanced economies is consistent.

[0153] Zero-sequence unbalance is more sensitive to aging conditions than negative-sequence current. Over the same aging cycle, the cable's zero-sequence current unbalance increases from 2.54% to 3.27%, a 28.7% increase. This increase accelerates in the later stages of aging (1080h-1440h). This sequence-selective response stems from the structural characteristics of different sequence circuits. The sensitivity coefficient of zero-sequence impedance to insulation parameter changes is:

[0154] (17)

[0155] Calculations show that SZ 0 >SZ 2 , confirming the high sensitivity of zero-sequence impedance to changes in dielectric parameters. The zero-sequence circuit involves a ground loop and a metal shield, and the relationship between its loop impedance and insulation parameters is more complex:

[0156] (18)

[0157] Dielectric constant and loss factor Through influence and The effect of changing the zero-sequence impedance is amplified by nonlinear mapping, resulting in a higher sensitivity of zero-sequence unbalance to aging.

[0158] From the perspective of energy conversion, the increase in imbalance leads to an 11.6% increase in cable AC loss, and the measured temperature rise is 2.3°C higher than that under symmetrical operating conditions. The relationship between dielectric loss power density, electric field strength and loss factor is:

[0159] (19)

[0160] This additional loss accelerates the insulation thermal aging process, forming a typical positive feedback mechanism. Eigenvalue analysis shows that the damping ratio of the system's most unstable mode decreases with increasing aging, decreasing by 8.3% after 1440 hours of aging, confirming the progressive decline in the system's stability margin.

[0161] Based on the close relationship between aging and imbalance, a comprehensive evaluation index is constructed:

[0162] (twenty one)

[0163] in, α 2 and α 0 is the weight coefficient, which reflects the relative importance of negative sequence and zero sequence imbalance in system evaluation. Based on experimental data, α 2 =0.6, α 0 =0.4. This indicator can be used for comprehensive evaluation of the aging status of mixed-operation cable systems.

[0164] The degree of imbalance is exponentially correlated with the degree of aging, forming a state assessment function:

[0165] (twenty two)

[0166] Where, is the system imbalance indicator, is the initial value, λ is the sensitivity coefficient, is the time-varying sequential impedance mismatch. This function reflects the cumulative effect of the aging process on the unbalanced characteristics and provides a theoretical basis for the status assessment of mixed-operation cable systems.

[0167] Comprehensive analysis shows that the impact of XLPE cable aging on the system imbalance characteristics presents three characteristics: in the time dimension, it manifests as a phased growth, reflecting the dynamic characteristics of the evolution of the material microstructure; in the parameter dimension, there is a critical threshold effect, revealing the nonlinear transition of the system stability; in the sequence component dimension, it manifests as a differentiated sensitivity characteristic of zero sequence being higher than negative sequence.

[0168] This example constructs an electric field-thermal field-aging multi-physics field coupling analysis framework for a mixed XLPE / oil-filled cable system. Through theoretical analysis and experimental verification, the mechanism of how XLPE cable aging affects the system's unbalanced characteristics is obtained. Specifically:

[0169] 1) The negative-sequence and zero-sequence imbalances caused by XLPE cable aging exhibit differentiated nonlinear growth characteristics. Experiments have shown that after 1440 hours of cable aging, the system's negative-sequence imbalance increases by 24.4%, and the zero-sequence imbalance increases by 28.7%. Zero-sequence imbalance is more sensitive to material aging than negative-sequence imbalance and exhibits a distinct segmented growth characteristic, with the growth rate significantly accelerating during the deep aging stage (aging time > 1080 hours). During the aging process, the mixed operation impedance mismatch coefficient It gradually increases from 9.4% in the initial state to 15.3%, resulting in a rapid accumulation of unbalanced components.

[0170] 2) Under mixed operating conditions, the decay of negative-sequence imbalance over electrical distance follows an exponential distribution, and the decay parameter is significantly affected by the aging of the XLPE cable. Measurement results show that the imbalance detected at measurement points closer to the XLPE cable is significantly higher than at further distances, with an imbalance decay coefficient of approximately 0.008 / km. As aging progresses, the system imbalance distribution exhibits a gradient characteristic, with "high near the end and low far the end," and this gradient becomes more pronounced with increasing aging. After 1440 hours of aging, the maximum electric field strength within the cable insulation increases by approximately 9.1%, and the field strength distribution becomes more uneven.

[0171] 3) There is a critical impedance mismatch threshold in the hybrid operation system. When the hybrid operation impedance mismatch coefficient or length mismatch coefficient When the critical value is exceeded, the system imbalance shifts from a linear growth to a nonlinear, accelerating trend. The combined thermal and vibration effects of negative-sequence current cause the dielectric constant of the XLPE cable to increase by 23.37% and the dielectric loss factor to increase by 50.34% during aging, leading to a continuous deterioration in the system's imbalance characteristics. Eigenvalue analysis shows that the damping ratio of the system's most unstable mode decreases with increasing aging, reaching a reduction of approximately 8.3% after 1440 hours of aging.

[0172] like Figure 11 As shown, the present application also provides an electronic device, including a display module 103, a memory 102, a processor 101, and a computer program stored in the memory and executable on the processor 101. When the processor 101 executes the program, the steps of the method for analyzing the impedance mismatch and unbalance characteristics of a hybrid operating system based on XLPE cable aging are implemented.

[0173] In the embodiments of the present invention, electronic devices include, but are not limited to, laptop computers, desktop computers, workstations, personal digital assistants, servers, blade servers, mainframe computers, and other suitable computers. Electronic devices may also represent various forms of mobile devices, such as personal digital assistants, cellular phones, smart phones, wearable devices, and other similar computing devices. The components shown in this embodiment, their connections and relationships, and their functions are merely examples and are not intended to limit the implementation of the embodiments of the present application described and / or required in this embodiment.

[0174] In the embodiment of the present application, the processor 101 can be implemented by using at least one of an application-specific integrated circuit (ASIC), a programmable logic device (PLD), a field programmable gate array (FPGA), a processor, a controller, a microcontroller, a microprocessor, and an electronic unit designed to perform the functions described herein. In some cases, such an embodiment can be implemented in a controller. For software implementation, an embodiment such as a process or function can be implemented with a separate software module that allows the execution of at least one function or operation. The software code can be implemented by a software application (or program) written in any appropriate programming language, and the software code can be stored in a memory and executed by a controller.

[0175] The display module 103 is used to display information input by the user or information provided to the user. The display module 103 may include a display panel, which may be configured in the form of a liquid crystal display (LCD), an organic light-emitting diode (OLED), etc.

[0176] The memory 102 can be used to store software programs and various data. The memory 102 can include high-speed random access memory and non-volatile memory, such as at least one disk storage device, flash memory device, or other volatile solid-state storage device.

[0177] The present application also provides a storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method for analyzing the impedance mismatch and unbalance characteristics of a hybrid operation system based on XLPE cable aging.

[0178] The storage medium can be any combination of one or more readable media. The readable medium can be a readable signal medium or a readable storage medium. The readable storage medium can be, for example, but not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, device or component, or any combination thereof. More specific examples (non-exhaustive list) of readable storage media include: an electrical connection with one or more wires, a portable disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination thereof.

[0179] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined in this embodiment may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown in this embodiment, but is intended to conform to the widest scope consistent with the principles and novel features disclosed in this embodiment.

Claims

1. A method for analyzing impedance mismatch and imbalance characteristics of a hybrid operation system based on XLPE cable aging, characterized in that: Methods include: S101: In the simulation system, the power grid is simplified and equivalent, retaining the switch station and substation, and the remaining power grid is equivalent to the retained stations. The structural models of the three-core cross-linked polyethylene cable and the oil-filled cable are constructed. S102: Obtain structural parameters of the three-core cross-linked polyethylene cable and the oil-filled cable, including the nominal thickness, outer diameter, and electrical characteristics of each layer of material, and form an electrical parameter table of the cable; S103: Set the simulation conditions for three-phase unbalanced current carrying. Configure phase A to use a three-core cross-linked polyethylene cable and phases BC to use an oil-filled cable. Set the power transmitted by any phase under full load conditions. Obtain the operating parameters for a single-phase current in the three-core cable to reach a preset current value. Compare the current differences between the phases under symmetrical conditions. S104: Constructing a finite element thermal field analysis model for the cable. A three-dimensional thermal field analysis model of the three-core cross-linked polyethylene cable is established based on current parameters obtained through real-time simulation. The cable thermal field analysis data is input, and the cable burial depth and the thermal conductivity parameters of the surrounding seabed saturated sediment and seawater are set. S105: Comparing and analyzing temperature distribution differences, simulating single-phase power-on and three-phase symmetrical operating conditions in the thermal field model, obtaining temperature data of the inner and outer surfaces of the insulation layer, and calculating the average temperature difference of the insulation layer under the two conditions; S106: Based on the average temperature difference, the Arrhenius equation is used to analyze the change in the aging rate of the insulation material and quantify the impact of single-phase power-on conditions on the cable insulation life compared to symmetrical operating conditions.

2. The method for analyzing impedance mismatch and imbalance characteristics of a hybrid operation system based on XLPE cable aging according to claim 1, characterized in that: Step S101 specifically includes: constructing a mixed operation power grid model including 500kV cable lines, overhead lines and substations on a real-time digital simulation system platform, by retaining the 500kV W switch station, A substation, X substation on the left and the 500kV F substation, Z switch station, H substation on the right and treating the remaining power grid parts as equivalent, setting equivalent additional lines between the W switch station and the A substation, and between the Z switch station and the H substation, and at the same time inputting the conductor structure, insulation layer configuration and sheath component parameters of the three-core cross-linked polyethylene cable and the oil-filled cable to establish a three-dimensional cable structure model.

3. The method for analyzing impedance mismatch and imbalance characteristics of a hybrid operation system based on XLPE cable aging according to claim 1, characterized in that: Step S102 specifically includes: obtaining the structural parameters of the three-core cross-linked polyethylene cable and the oil-filled cable, including the nominal thickness, outer diameter and electrical characteristics of each layer of material, establishing a geometric dimension and material property parameter table including the conductor shielding layer, insulation layer, sheath layer and armor layer based on the cable structure layering data, and generating a comparison table of positive-sequence, negative-sequence and zero-sequence electrical parameters of different cable types.

4. The method for analyzing impedance mismatch and imbalance characteristics of a hybrid operation system based on XLPE cable aging according to claim 1, characterized in that: Step S103 specifically includes: In the simulation system, the rated voltage and copper core cross-section parameters of the A-phase three-core cross-linked polyethylene cable and the rated voltage of the BC-phase oil-filled cable were configured. The rated transmission power of any phase was set under full load conditions. The current in the three-core cross-linked polyethylene cable during mixed operation was obtained, and the difference in current amplitude of each phase was compared when only the three-core cross-linked polyethylene cable was normally energized and under symmetrical operating conditions.

5. The method for analyzing impedance mismatch and imbalance characteristics of a hybrid operation system based on XLPE cable aging according to claim 1, characterized in that: Step S103 further includes: Based on the three-phase voltage and current data obtained in real-time simulation, the positive sequence, negative sequence and zero sequence components are obtained through Clarke and Fortescue sequence component transformation; Calculate the negative sequence voltage and zero sequence voltage unbalance based on formula (1); （1） In the above formula, 、 are the RMS values ​​of the positive and negative sequence voltages, respectively; Calculate the negative sequence current and zero sequence current imbalance based on formula (2); （2） In the above formula, 、 are the RMS values ​​of the positive and negative sequence voltages, respectively.

6. The method for analyzing impedance mismatch and imbalance characteristics of a hybrid operation system based on XLPE cable aging according to claim 1, characterized in that: Step S104 also includes: establishing a three-dimensional thermal field analysis model of the three-core cross-linked polyethylene cable, obtaining the temperature distribution characteristics of the insulation layer during unbalanced operation, and quantifying the temperature difference between the insulation layer and the insulation layer during three-phase symmetrical operation; The copper conductor of the three-core XLPE cable is set to linear resistivity, and the resistivity is calculated using formula (3); （3） In the formula is the reference temperature T ref The resistivity under is the temperature coefficient of resistivity.

7. The method for analyzing impedance mismatch and imbalance characteristics of a hybrid operation system based on XLPE cable aging according to claim 1, characterized in that: Step S105 further includes: The current parameters obtained by the simulation system are input as boundary conditions into the established three-core cross-linked polyethylene cable three-dimensional thermal field analysis model. The single-core energized condition and the three-phase symmetrical operation condition are simulated in the thermal field model. Obtain temperature data inside the insulation layer close to the conductor side and outside under two working conditions; The logarithmic mean temperature calculation method of cylindrical insulators is used to calculate the average temperature of the insulation layer under the two operating conditions, and the difference in the average temperature of the insulation layer under the single-core operating condition and the three-phase symmetrical operating condition is obtained.

8. The method for analyzing impedance mismatch and imbalance characteristics of a hybrid operation system based on XLPE cable aging according to claim 7, characterized in that: The calculation formula for the logarithmic mean temperature of a cylindrical insulator is: in, is the internal temperature of the insulation layer, is the external temperature of the insulation layer; According to the Arrhenius equation: in, is the insulation life, is the activation energy, k is the Boltzmann constant, T is the absolute temperature.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, the steps of the method for analyzing impedance mismatch and unbalance characteristics of a hybrid operation system based on XLPE cable aging are implemented as described in any one of claims 1 to 7.

10. A storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method for analyzing impedance mismatch and unbalance characteristics of a hybrid operation system based on XLPE cable aging are implemented as described in any one of claims 1 to 7.

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