XLPE cable aging influence analysis method and system based on RTDS

Abstract

The invention relates to the technical field of cables, and particularly provides an RTDS-based XLPE cable aging influence analysis method and system, and the method comprises the steps: building a RTDS-based hybrid operation system simulation model; acquiring a plurality of XLPE insulation aging samples at different time; measuring the insulation resistance of each XLPE insulation aging sample, and calculating the volume resistivity; measuring the dielectric constant and the dielectric loss factor of each XLPE insulation aging sample; inputting into a simulation model, and after the simulation model operates under different working conditions, outputting cable parameters, active power, key point three-phase phasor voltage data and key point three-phase phasor current data of each insulation aging sample; obtaining the influence of cable aging on the maximum transmission power; and obtaining the imbalance influence of the cable aging on the system. The influence of XLPE cable aging on a hybrid operation system is comprehensively explored, and a key basis is provided for operation maintenance, optimization and upgrading of a power system.

Description

Technical Field

[0001] This invention belongs to the field of cable technology, specifically relating to a method and system for analyzing the effects of aging on XLPE cables based on RTDS. Background Technology

[0002] With the growth of global energy demand and the increasing requirements for the reliability of power transmission, submarine cables, as critical infrastructure, have attracted much attention regarding their performance and reliability. Cross-linked polyethylene (XLPE) cables, due to their superior mechanical strength, electrical properties, and heat resistance, have gradually replaced traditional oil-filled cables.

[0003] In existing power transmission projects, when one of the three traditional oil-filled cables fails, a new XLPE submarine cable is built to operate in combination with the original two oil-filled cables, forming a three-phase AC hybrid operating system.

[0004] Because XLPE cables differ significantly from the original oil-filled cables in structure and parameters, they affect power transmission performance and system balance. Furthermore, XLPE cables age over long-term operation, which further impacts power transmission performance and system balance. Summary of the Invention

[0005] To address the aforementioned shortcomings of existing technologies, this invention provides a method and system for analyzing the effects of aging on XLPE cables based on RTDS, thereby resolving the aforementioned technical problems.

[0006] In a first aspect, the present invention provides a method for analyzing the aging effects of XLPE cables based on RTDS, including: A simulation model of a hybrid operation system based on RTDS was built based on the cable wiring, operating conditions and operating parameters in actual engineering. XLPE insulation layer samples were obtained, and multiple XLPE insulation aging samples were obtained at different times using a constant temperature aging oven. The insulation resistance of each XLPE insulation aging sample was measured using a resistance meter, and the volume resistivity was calculated based on the parameters of the XLPE insulation layer sample and the insulation resistance. The dielectric constant and dielectric loss factor of each XLPE insulation aging sample were measured using a broadband dielectric spectrometer. The volume resistivity, dielectric constant and dielectric loss factor of the insulation aging samples at different times are input into the simulation model. After the simulation model runs under different operating conditions, it outputs the cable parameters, active power, key point three-phase phasor voltage data and key point three-phase phasor current data of each insulation aging sample. The impact of cable aging on maximum transmission power is obtained based on cable parameters and active power; the impact of cable aging on system imbalance is obtained based on three-phase phasor voltage data and three-phase phasor current data.

[0007] In an optional implementation, calculating the volume resistivity based on the parameters of the XLPE insulation layer sample combined with the resistivity specifically includes: For each XLPE insulation aging sample, repeated measurements were performed. The arithmetic mean of the obtained insulation resistance was taken, and the volume resistivity was calculated by combining the sample contact area and sample thickness. The calculation formula is as follows:

[0008] in, R is the volume resistivity; S is the measured resistance value; h is the sample contact area; and h is the sample thickness.

[0009] In one optional implementation, the impact of cable aging on the maximum transmission power is obtained based on cable parameters combined with active power, specifically including: The total power is calculated based on the active power under different operating conditions. The active power and total power under different operating conditions are compared to obtain the transmission power under each operating condition. The maximum transmission power is obtained. The maximum transmission power under different operating conditions at different aging times is compared to obtain the impact of cable aging on the maximum transmission power. The reasons for the maximum power change were analyzed based on cable parameters combined with the formulas for functional loss and power loss.

[0010] In an alternative implementation, the functional loss is calculated according to Ohm's law:

[0011]

[0012] Where R represents the measured resistance value, ρ is the resistivity of the material, l is the length of the cable, A is the cross-sectional area, and I is the transmission current; when the resistivity decreases, the functional loss increases, reducing the transmission capacity of the cable and causing a decrease in the maximum transmission power. The specific calculation of power loss is as follows:

[0013]

[0014] In the formula, Where is the dielectric constant. Where is the vacuum dielectric constant, A is the effective contact area of ​​the electrode, d is the cable insulation thickness, ω is the angular frequency, tanδ is the dielectric loss factor, and V is the voltage of the cable during operation. During the aging process, the dielectric constant increases with time, leading to an increase in capacitance and a decrease in the loss factor, resulting in increased power loss, reduced cable transmission capacity, accelerated material degradation, and a decrease in maximum transmission power.

[0015] In one optional implementation, the voltage and current imbalance is calculated based on three-phase phasor voltage data and three-phase phasor current data to obtain the impact of cable aging on system stability, specifically including: The positive-sequence, negative-sequence, and zero-sequence components are obtained by transforming the three-phase phasor voltage data and three-phase phasor current data using Clarke and Fortescue sequence component transformations. Calculate the unbalance of negative sequence voltage:

[0016] in, , These are the root mean square values ​​of the positive-sequence and negative-sequence voltages, respectively. Calculate the unbalance of the negative sequence current:

[0017] in, , These are the root mean square values ​​of the positive-sequence and negative-sequence currents, respectively. The imbalance of zero-sequence voltage is calculated using the same method as that for negative-sequence voltage, and the imbalance of zero-sequence current is calculated using the same method as that for negative-sequence current. Comprehensive analysis shows that the imbalance of negative sequence voltage, zero sequence voltage, negative sequence current, and zero sequence current increases with aging time, and the overall system imbalance also increases with aging time.

[0018] Secondly, the present invention provides an XLPE cable aging effect analysis system based on RTDS, comprising: The simulation model building module builds a simulation model of a hybrid operating system based on RTDS, based on cable wiring, operating conditions and operating parameters in actual engineering. The aging sample acquisition module acquires XLPE insulation layer samples and obtains multiple XLPE insulation aging samples at different times using a constant temperature aging oven. The performance data measurement module measures the insulation resistance of each XLPE insulation aging sample using a resistance meter, calculates the volume resistivity based on the parameters of the XLPE insulation layer sample and the insulation resistance, and measures the dielectric constant and dielectric loss factor of each XLPE insulation aging sample using a broadband dielectric spectrometer. The simulation operation module inputs the volume resistivity, dielectric constant and dielectric loss factor of the insulation aging sample at different times into the simulation model. After the simulation model runs under different operating conditions, it outputs the cable parameters, active power, key point three-phase phasor voltage data and key point three-phase phasor current data of each insulation aging sample. The aging impact analysis module obtains the impact of cable aging on the maximum transmission power based on cable parameters and active power; and obtains the impact of cable aging on system imbalance based on three-phase phasor voltage data and three-phase phasor current data.

[0019] In an optional implementation, calculating the volume resistivity based on the parameters of the XLPE insulation layer sample combined with the resistivity specifically includes: For each XLPE insulation aging sample, repeated measurements were performed. The arithmetic mean of the obtained insulation resistance was taken, and the volume resistivity was calculated by combining the sample contact area and sample thickness. The calculation formula is as follows:

[0020] in, R is the volume resistivity; S is the measured resistance value; h is the sample contact area; and h is the sample thickness.

[0021] In one optional implementation, the impact of cable aging on the maximum transmission power is obtained based on cable parameters combined with active power, specifically including: The total power is calculated based on the active power under different operating conditions. The active power and total power under different operating conditions are compared to obtain the transmission power under each operating condition. The maximum transmission power is obtained. The maximum transmission power under different operating conditions at different aging times is compared to obtain the impact of cable aging on the maximum transmission power. The reasons for the maximum power change were analyzed based on cable parameters combined with the formulas for functional loss and power loss.

[0022] In an alternative implementation, the functional loss is calculated according to Ohm's law:

[0023]

[0024] Where R represents the measured resistance value, ρ is the resistivity of the material, l is the length of the cable, A is the cross-sectional area, and I is the transmission current; when the resistivity decreases, the functional loss increases, reducing the transmission capacity of the cable and causing a decrease in the maximum transmission power. The specific calculation of power loss is as follows:

[0025]

[0026] In the formula, Where is the dielectric constant. Where is the vacuum dielectric constant, A is the effective contact area of ​​the electrode, d is the cable insulation thickness, ω is the angular frequency, tanδ is the dielectric loss factor, and V is the voltage of the cable during operation. During the aging process, the dielectric constant increases with time, leading to an increase in capacitance and a decrease in the loss factor, resulting in increased power loss, reduced cable transmission capacity, accelerated material degradation, and a decrease in maximum transmission power.

[0027] In one optional implementation, the voltage and current imbalance is calculated based on three-phase phasor voltage data and three-phase phasor current data to obtain the impact of cable aging on system stability, specifically including: The positive-sequence, negative-sequence, and zero-sequence components are obtained by transforming the three-phase phasor voltage data and three-phase phasor current data using Clarke and Fortescue sequence component transformations. Calculate the unbalance of negative sequence voltage:

[0028] in, , These are the root mean square values ​​of the positive-sequence and negative-sequence voltages, respectively. Calculate the unbalance of the negative sequence current:

[0029] in, , These are the root mean square values ​​of the positive-sequence and negative-sequence currents, respectively. The imbalance of zero-sequence voltage is calculated using the same method as that for negative-sequence voltage, and the imbalance of zero-sequence current is calculated using the same method as that for negative-sequence current. Comprehensive analysis shows that the imbalance of negative sequence voltage, zero sequence voltage, negative sequence current, and zero sequence current increases with aging time, and the overall system imbalance also increases with aging time.

[0030] The beneficial effects of this invention are that the RTDS-based method and system for analyzing the effects of XLPE cable aging provided by this invention, by building a simulation model of a hybrid operation system based on RTDS according to actual engineering, obtaining and testing XLPE insulation aging samples at different times, and inputting the test data into the model for simulation under different operating conditions, can comprehensively and accurately explore the impact of XLPE cable aging on the hybrid operation system from aspects such as the maximum transmission power of the cable and system imbalance, providing key basis for the operation, maintenance, optimization and upgrading of power systems.

[0031] Furthermore, the design principle of this invention is reliable, the structure is simple, and it has a very wide range of application prospects. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic flowchart of an embodiment of the aging effect analysis method for XLPE cables based on RTDS.

[0034] Figure 2 This is a system equivalent wiring diagram according to an embodiment of the present invention.

[0035] Figure 3 This is a graph showing the variation of XLPE volume resistivity under different aging times according to an embodiment of the present invention.

[0036] Figure 4(a) is a graph showing the variation of the dielectric constant of XLPE under different aging times according to an embodiment of the present invention.

[0037] Figure 4(b) is a graph showing the variation of dielectric loss under different aging times according to an embodiment of the present invention.

[0038] Figure 5 This is a graph showing the variation of the power frequency dielectric properties of XLPE under different aging times according to an embodiment of the present invention.

[0039] Figure 6 This is a graph showing the change in voltage imbalance over aging time according to an embodiment of the present invention.

[0040] Figure 7 This is a graph showing the change of current imbalance over aging time according to an embodiment of the present invention.

[0041] Figure 8 This is a schematic block diagram of an XLPE cable aging effect analysis system based on RTDS, according to an embodiment of the present invention. Detailed Implementation

[0042] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0044] The key terms used in this invention will be explained below.

[0045] RTDS, or Real-Time Digital Simulator, is a tool specifically designed for real-time simulation of power systems. It can simulate various operating states and fault conditions of power systems. RTDS typically consists of multiple functional modules, including a processor, input / output interfaces, and communication modules.

[0046] XLPE cables, or cross-linked polyethylene cables, are key equipment in the power transmission field. Their structure generally includes a copper conductor, semi-conductive double-sided water-blocking binding tape and inner shielding layer, XLPE insulation layer, outer shielding layer, semi-conductive water-blocking tape, alloy lead sheath, MDPE sheath, inner lining layer, armor layer, and outer sheath. XLPE material has excellent insulation properties and a high volume resistivity, effectively preventing current leakage. The cross-linked polyethylene molecular structure transforms from linear to network, forming a thermosetting material with significantly improved heat resistance. It also possesses high mechanical strength, capable of withstanding certain tensile, bending, and compressive stresses, making it less prone to damage during cable laying and operation.

[0047] The aging effect analysis method of XLPE cable based on RTDS provided in this embodiment of the invention is executed by a computer device, and correspondingly, the aging effect analysis system of XLPE cable based on RTDS runs in the computer device.

[0048] Figure 1 This is a schematic flowchart illustrating an embodiment of the aging effect analysis method for XLPE cables based on RTDS according to one embodiment of the present invention. Figure 1 The implementing entity can be an XLPE cable aging impact analysis system based on RTDS. Depending on different requirements, the order of steps in this flowchart can be changed, and some can be omitted.

[0049] like Figure 1 As shown, the method includes: Step S1: Based on the cable wiring, operating conditions and operating parameters in the actual project, build a simulation model of the hybrid operation system based on RTDS; Based on the specific wiring conditions of cables in actual projects, including the connection methods and node locations of each cable, as well as operating conditions such as power transmission direction and load size, and operating parameters such as cable resistance, capacitance, and inductance, a hybrid operating system simulation model is built on the RTDS platform to accurately simulate the operating conditions of the actual power system.

[0050] Step S2: Obtain XLPE insulation layer samples, and obtain multiple XLPE insulation aging samples at different times using a constant temperature aging oven. First, XLPE insulation layer samples are prepared. Then, these samples are placed in a constant temperature aging oven. The samples are taken out at the corresponding time points according to different set times, such as 168h, 720h, 1440h, etc., so as to obtain multiple XLPE insulation aging samples at different aging times.

[0051] Step S3: Measure the insulation resistance of each XLPE insulation aging sample using a resistance meter; calculate the volume resistivity based on the parameters of the XLPE insulation sample and the insulation resistance; measure the dielectric constant and dielectric loss factor of each XLPE insulation aging sample using a broadband dielectric spectrometer. The insulation resistance of each XLPE insulation aging sample was measured using a resistance meter, and the data was recorded. Based on the known parameters of the XLPE insulation sample, such as the cross-sectional area and thickness, and combined with the measured insulation resistance, the volume resistivity was calculated using the volume resistivity calculation formula. Then, the dielectric constant and dielectric loss factor of each XLPE insulation aging sample were measured using a broadband dielectric spectrometer.

[0052] Step S4: Input the volume resistivity, dielectric constant and dielectric loss factor of the insulation aging sample at different times into the simulation model. After the simulation model runs under different working conditions, it outputs the cable parameters, active power, key point three-phase phasor voltage data and key point three-phase phasor current data of each insulation aging sample. The volume resistivity, dielectric constant, and dielectric loss factor of XLPE insulation aging samples at different times were input as parameters into the established simulation model. Different operating conditions, such as single-circuit operation, double-circuit operation, and triple-circuit operation, were set, and the simulation model was run under these conditions. After the operation was completed, the cable parameters, active power, key point three-phase phasor voltage data, and key point three-phase phasor current data corresponding to each insulation aging sample were extracted from the simulation results.

[0053] Step S5: Based on cable parameters and active power, obtain the impact of cable aging on the maximum transmission power; based on three-phase phasor voltage data and three-phase phasor current data, obtain the impact of cable aging on the system imbalance.

[0054] Based on the extracted cable parameters and active power data, the changes in cable transmission capacity under different aging stages are analyzed to determine the impact of cable aging on maximum transmission power. By processing the three-phase phasor voltage and current data, such as calculating negative-sequence and zero-sequence components, the voltage and current imbalance is obtained, thereby assessing the impact of cable aging on system imbalance.

[0055] Optionally, as an embodiment of the present invention, in step S1, an AC equivalent model of the main power grid and the interconnection project is established based on RTDS (Real-Time Digital Simulation System). The simulation equipment adopts the latest generation of real-time digital simulator NovaCor developed by RTDS Corporation, which has multiple types of input / output interfaces. The damping controller prototype uses the voltage / current signal output by RTDS as input to generate a reference current signal, all of which are transmitted in the form of analog signals.

[0056] Based on the actual engineering wiring and operating conditions, draw the system wiring diagram and determine the main parameters. The wiring diagram is as follows: Figure 2 As shown, it includes the main network, XLPE submarine cables, oil-filled submarine cables, and key nodes ( Figure 2 The diagram shows A and B as 500kV substations on both sides of the submarine cable, and C and D as terminal stations on both sides of the submarine cable. The simulation model is constructed by simulating the changes in electrical characteristics of these substations in the hybrid operation system.

[0057] Optionally, as an embodiment of the present invention, in step S2, taking a 500kV three-core cable as a reference, the experimental XLPE insulation sample is pressed using the same raw materials and manufacturing process as the main insulation of the cable. The raw material components include a crosslinking agent (diisopropylbenzene peroxide), polyethylene particles, and an antioxidant. The materials are mixed by extrusion using a flat vulcanizing machine. First, the insulation material is dried in a drying oven; second, it is preheated without pressure for 4 minutes in a 130°C flat vulcanizing machine; then, it is pressurized at 130°C for 6 minutes; third, it is pressurized at 180°C for 15 minutes; finally, it is placed at room temperature and pressurized for 8 minutes to obtain an insulation layer sample with a thickness of approximately 0.3 mm. A constant temperature aging oven is used, with 120°C selected as the thermal aging temperature, and three sampling time points are selected at 168, 720, and 1440 hours. Performance testing is performed on XLPE insulation aging samples obtained through simulated thermal aging experiments, including the four stages before aging.

[0058] Optionally, as an embodiment of the present invention, in step S3, the sample to be tested is placed between the electrodes of the ZC-90G high insulation resistance measuring instrument, the knob is adjusted to the RV (volume resistivity) setting, the power is turned on, and the measurement button is pressed. After the reading is zeroed, the resistance button is pressed and the high voltage is adjusted to 1kV, and then the hold and balance buttons are activated. The range is adjusted to the display position, and the measurement data is recorded after waiting for one minute. Ten repeated measurements are performed on each sample, and the arithmetic mean of the obtained insulation resistance is taken. The formula for calculating volume resistivity is as follows:

[0059] in, R is the volume resistivity; S is the measured resistance value; h is the sample contact area; and h is the sample thickness.

[0060] Optionally, as an embodiment of the present invention, different operating conditions refer to three operating modes: three-circuit operation, two-circuit operation, and single-circuit operation. In three-circuit operation, submarine cables I, II, and III operate simultaneously, enabling high power transmission and exhibiting unique performance in terms of power transmission and system stability. It can meet the power demand of a large area, but factors such as cable aging may lead to uneven power distribution among the submarine cables. Two-circuit operation involves two submarine cables working together, with transmission power capabilities between three-circuit and single-circuit operation. It requires higher system balance and power transmission stability; significant differences in cable aging can easily cause imbalance problems. Single-circuit operation involves only one submarine cable operating, resulting in relatively limited power transmission capacity. For example, the maximum transmission power of single-circuit II is 583.3MW, lower than the rated power, and it places higher performance requirements on this submarine cable. Severe aging of this cable can lead to a significant decrease in transmission capacity.

[0061] Optionally, as an embodiment of the present invention, the variation law of XLPE volume resistivity under different aging times is as follows: Figure 3 As shown in the figure, the volume resistivity of XLPE exhibits a trend of first slowly increasing and then rapidly decreasing. Before aging, the volume resistivity of XLPE is 1.37 × 10⁻⁶. 17 The volume resistivity of XLPE increased to 1.39 × 10⁻⁶ Ω·cm after aging for 168 h. 17 The resistivity increased slightly in the early stages of aging due to recrystallization, which increased the area of ​​the crystalline region and restricted the free movement of charged particles. After aging for 1440 h, the volume resistivity of XLPE decreased to 1.25 × 10⁻⁶ Ω·cm. 16The Ω·cm decreased by 90.87% compared to the unaged state. This indicates that as the aging time increases, the crystal structure of XLPE is destroyed, the area of ​​the amorphous region increases, and the particle mobility increases. At the same time, the generation of impurity functional groups such as carbonyl, hydroxyl, and ether groups leads to an increase in the concentration of charge carriers such as electrons and charged ions, which promotes the charge conduction process.

[0062] Optionally, as an embodiment of the present invention, in step S3, a broadband dielectric spectrometer is used to test the dielectric constant and dielectric loss factor of XLPE samples under different aging times. To ensure good contact between the metal electrode and the sample surface, a layer of aluminum film is deposited on the sample surface before testing. The test frequency range is set to 10-1 Hz to 106 Hz, and the test voltage is 1 V. The circular sample used for testing has a diameter of 20 mm and a thickness of 0.3 mm.

[0063] Optionally, as an embodiment of the present invention, the variation of the dielectric properties of XLPE under different aging times is shown in Figures 4(a) and 4(b). Figure 4(a) shows that the dielectric constant gradually decreases with increasing test temperature. The figure also shows that the relative dielectric constant of XLPE after thermal aging exhibits a trend of first decreasing and then increasing, with the dielectric constant starting to increase after 168 h. To determine the specific value of the dielectric constant change under different aging times, the variation of the XLPE dielectric constant at 50 Hz is taken, as shown below. Figure 5 As shown, the dielectric constant was 2.28 before aging, and it increased to 2.34 after 1440 h of aging, an increase of 2.6%. This is because the molecular chain broke during the thermal aging process, and the formation of carbonyl and hydroxyl groups led to the increase in dielectric constant, which improved the polarization ability of XLPE.

[0064] The variation of dielectric loss under different aging times is shown in Figure 4(b). As can be seen from the figure, the dielectric loss gradually increases with the extension of aging time. To determine the specific value of dielectric loss variation under different aging times, the variation of XLPE dielectric loss at power frequency under different aging times is shown in Figure 4(b). Figure 5 As shown in the figure. It can be seen from the figure that the loss of the unaged dielectric is 2.30 × 10⁻⁶. -4 Increased to 2.42 × 10 -3 .

[0065] Optionally, as an embodiment of the present invention, the resistivity, relative permittivity and dielectric loss factor of the aged cross-linked polyethylene cable obtained from the experiment are input into the RTDS simulation system, and a detailed statistical analysis is performed on the maximum transmission power of the entire cable system to evaluate the performance changes of the system under different aging conditions and obtain the results.

[0066] As the aging time of XLPE submarine cables increases, the maximum transmission power of the system gradually decreases. Simulation results show that from no aging to 1440 hours of aging, the total transmission power decreases by approximately 35.9 MW. This trend is mainly due to the degradation of the electrical properties of the cable material during the aging process. Changes in resistivity, relative permittivity, and dielectric loss factor are the main factors affecting system performance. The reasons for the maximum power change are analyzed based on cable parameters combined with functional loss formulas and power loss formulas.

[0067] Optionally, as an embodiment of the present invention, the resistivity of the XLPE cable decreases over time during the aging process. According to Ohm's law and the power loss formula generated by the transmitted current:

[0068]

[0069] In the formula, R Indicates resistance. ρ The resistivity of the material l The length of the cable. A For cross-sectional area, I For transmitting current. During the aging process, chemical reactions caused by heat and mechanical stress generate conductive impurities and microcracks, leading to a decrease in resistivity, which in turn increases leakage current and power loss. The increase in power loss reduces the cable's transmission capacity, resulting in a decrease in maximum transmission power.

[0070] Secondly, aging leads to an increase in the relative permittivity. According to the capacitance formula:

[0071] In the formula, The relative permittivity, The vacuum permittivity, A The effective contact area of ​​the electrode. d This refers to the cable insulation thickness. During aging, the formation of polar groups and conductive impurities enhances the dielectric polarization, increasing the relative permittivity. While the increased permittivity improves the cable's energy storage capacity, it also leads to higher dielectric stress, increased electric field inhomogeneity, and reduced transmission stability during operation.

[0072] Furthermore, an increase in the dielectric loss factor significantly affects system performance. Power loss can be expressed as:

[0073] In the formula, ω Angular frequency, tanδ For dielectric loss factor, CHere, V represents the capacitance, and V is the voltage at which the cable operates. Experiments show that the loss factor increases over time during aging, significantly increasing the cable's power loss. This not only reduces transmission efficiency but also raises the cable temperature, accelerating material degradation and creating a vicious cycle that further reduces the maximum transmission power.

[0074] In summary, changes in resistivity, relative permittivity, and dielectric loss factor caused by aging of XLPE cables in power systems are the main reasons for the reduction in maximum transmission power. Simulation analysis verifies the significant impact of aging on system performance, providing a clear reference for cable life assessment, optimization of operation strategies, and formulation of maintenance measures.

[0075] Optionally, as an embodiment of the present invention, the voltage imbalance at substation B, terminal station C, and the current imbalance of the II return submarine cable are selected as key indicators for analyzing the system's imbalance characteristics. Location B is on the busbar side, close to the generator end and the main transmission branch, reflecting the voltage imbalance characteristics of the system at the busbar connection point. Location C, located at the remote terminal station, is adjacent to the load, fully demonstrating the changing trend of the remote voltage characteristics. Regarding the selection of the submarine cable current, the II return submarine cable is a circuit combining cross-linked polyethylene submarine cable and oil-filled submarine cable. Due to the differences in physical characteristics and electric field distribution between the two different cable structures, its imbalance characteristics are significant and highly representative.

[0076] The positive-sequence, negative-sequence, and zero-sequence components can be obtained from the three-phase phasor voltage and current data obtained from RTDS real-time simulation by using Clarke and Fortescue sequence component transformations.

[0077] Calculate the unbalance of negative sequence voltage:

[0078] in, , These are the root mean square values ​​of the positive and negative sequence voltages, respectively; the variation patterns of the negative and zero sequence voltage imbalances between the transformer station at point B and the terminal station at point C under different aging times are shown below. Figure 6 As shown.

[0079] Calculate the unbalance of the negative sequence current:

[0080] in, , These are the root mean square values ​​of the positive-sequence and negative-sequence currents, respectively; the trend of the negative-sequence and zero-sequence unbalance of the II return submarine cable current with aging time is obtained after calculation. Figure 7 As shown.

[0081] The imbalance of zero-sequence voltage is calculated using the same method as that for negative-sequence voltage, and the imbalance of zero-sequence current is calculated using the same method as that for negative-sequence current. Comprehensive analysis shows that the imbalance of negative sequence voltage, zero sequence voltage, negative sequence current, and zero sequence current increases with aging time, and the overall system imbalance also increases with aging time.

[0082] Optionally, as an embodiment of the present invention, from Figure 6 and Figure 7 As can be seen, both voltage and current imbalances show a gradual increase with cable aging time. Regarding voltage, both negative-sequence and zero-sequence voltage imbalances at transformer station B and terminal station C increase slowly. Terminal station C is more significantly affected by aging, with zero-sequence imbalance increasing from approximately 0.47% to 0.58%, and negative-sequence imbalance increasing from approximately 0.43% to 0.54%. In contrast, the voltage imbalance at transformer station B increases less, indicating that voltage balance closer to the busbar is less sensitive to aging, while the terminal station, being closer to the load, is more significantly affected by aging.

[0083] For the current section, the imbalance of the II return submarine cable also increased significantly with aging time. The negative sequence current imbalance increased from approximately 8.67% initially to 9.80%, and the zero sequence current imbalance increased from approximately 9.05% initially to 10.37%, with the increase in the zero sequence component being significantly greater than that of the negative sequence component. As the main circuit for the mixed operation of cross-linked polyethylene submarine cables and oil-filled submarine cables, the II return submarine cable is more sensitive to the impact of imbalance during the aging process due to differences in material properties.

[0084] According to GB / T 15543-2008 "Power Quality: Three-Phase Voltage Imbalance", the voltage imbalance at the point of common coupling of a power system shall not exceed 2% during normal operation and shall not exceed 4% for short periods. Based on the analysis results of this study, although the negative-sequence and zero-sequence voltage imbalances at transformer station B and terminal station C increase with the aging time of the cross-linked polyethylene cables, the maximum imbalance over the entire aging cycle is only 0.58%, lower than the 2% limit stipulated by the national standard.

[0085] Simulation results of current imbalance show that the maximum zero-sequence current of the II submarine cable is 103.5A, which is far lower than the inverse-time trip protection setting of 300A and will not cause maloperation of the line protection. Meanwhile, the zero-sequence current at the neutral point of the main transformer in the 500kV Fushan substation is also far less than the rated reactance current even under maximum cable aging, indicating no risk of overload on the equipment. Therefore, although cable aging has some impact on system balance, the magnitude of its imbalance will not jeopardize the system's protection actions or equipment safety, and the normal operation of the power grid and power quality can be effectively guaranteed.

[0086] In summary, this study investigated the impact of aging of cross-linked polyethylene (XLPE) cables on hybrid operation systems. Through experimental and simulation analyses, the multifaceted effects of cable aging on system performance were explored. Firstly, accelerated aging tests were conducted to obtain data on the changes in electrical performance of XLPE cables at different aging stages. A simulation model of the hybrid operation system based on RTDS was then established, incorporating the cable aging characteristic parameters. The study found that with increasing aging time, the electrical properties of the XLPE cable, particularly its dielectric constant, loss factor, and conductivity, change significantly. This not only affects the cable's transmission capacity but also negatively impacts the stability and balance of the entire hybrid operation system.

[0087] Regarding power transmission capacity, simulation results show that the maximum transmission power of the system gradually decreases with the aging of XLPE cables. This phenomenon is mainly attributed to the increased energy loss and changes in system voltage distribution caused by the deterioration of the electrical parameters of the cable materials during the aging process. As for system balance, the voltage and current imbalances show a certain increasing trend with aging, with the zero-sequence voltage component and the negative-sequence current component being significantly affected by aging. In particular, the II-loop submarine cable, as an important part of mixed operation, shows a more significant increase in imbalance due to the structural and performance differences between XLPE cables and oil-filled cables. However, despite the increase in system imbalance, the maximum voltage imbalance is still far below the 2% limit specified in the national standard GB / T15543-2008, indicating that the power grid can still meet the power quality requirements for normal operation even under the most severe aging conditions. Further analysis of the current imbalance problem shows that its zero-sequence and negative-sequence components do not have a substantial impact on system protection and equipment operation, and the lines and equipment are all within the safe operating range.

[0088] While the aging of cross-linked polyethylene (XLPE) cables can lead to reduced transmission capacity and changes in system balance, its impact on the overall performance of hybrid operation systems remains within a controllable range. This study provides theoretical support for further optimizing the hybrid operation mode of submarine cables, and also provides basic data for developing monitoring and maintenance strategies during the cable aging process, contributing to ensuring the long-term stable operation and safety of power systems.

[0089] In some embodiments, the RTDS-based XLPE cable aging effect analysis system may include multiple functional modules composed of computer program segments. The computer programs for each program segment in the RTDS-based XLPE cable aging effect analysis system may be stored in the memory of a computer device and executed by at least one processor to perform (see details). Figure 1 (Description) Functionality for analyzing the effects of aging on XLPE cables based on RTDS.

[0090] In this embodiment, the RTDS-based XLPE cable aging effect analysis system can be divided into multiple functional modules according to its functions, such as... Figure 8 As shown. The system's functional modules may include: a simulation model construction module, an aging sample acquisition module, a performance data measurement module, a simulation operation module, and an aging effect analysis module. The module referred to in this invention is a series of computer program segments that can be executed by at least one processor and perform a fixed function, stored in memory. In this embodiment, the functions of each module will be detailed in subsequent embodiments. The system includes: The simulation model building module builds a simulation model of a hybrid operating system based on RTDS, based on cable wiring, operating conditions and operating parameters in actual engineering. The aging sample acquisition module acquires XLPE insulation layer samples and obtains multiple XLPE insulation aging samples at different times using a constant temperature aging oven. The performance data measurement module measures the insulation resistance of each XLPE insulation aging sample using a resistance meter, calculates the volume resistivity based on the parameters of the XLPE insulation layer sample and the insulation resistance, and measures the dielectric constant and dielectric loss factor of each XLPE insulation aging sample using a broadband dielectric spectrometer. The simulation operation module inputs the volume resistivity, dielectric constant and dielectric loss factor of the insulation aging sample at different times into the simulation model. After the simulation model runs under different operating conditions, it outputs the cable parameters, active power, key point three-phase phasor voltage data and key point three-phase phasor current data of each insulation aging sample. The aging impact analysis module obtains the impact of cable aging on the maximum transmission power based on cable parameters and active power; and obtains the impact of cable aging on system imbalance based on three-phase phasor voltage data and three-phase phasor current data.

[0091] Optionally, as an embodiment of the present invention, the calculation of volume resistivity based on the parameters of the XLPE insulating layer sample combined with resistivity specifically includes: For each XLPE insulation aging sample, repeated measurements were performed. The arithmetic mean of the obtained insulation resistance was taken, and the volume resistivity was calculated by combining the sample contact area and sample thickness. The calculation formula is as follows:

[0092] in, R is the volume resistivity; S is the measured resistance value; h is the sample contact area; and h is the sample thickness.

[0093] Optionally, as an embodiment of the present invention, obtaining the impact of cable aging on the maximum transmission power based on cable parameters combined with active power specifically includes: The total power is calculated based on the active power under different operating conditions. The active power and total power under different operating conditions are compared to obtain the transmission power under each operating condition. The maximum transmission power is obtained. The maximum transmission power under different operating conditions at different aging times is compared to obtain the impact of cable aging on the maximum transmission power. The reasons for the maximum power change were analyzed based on cable parameters combined with the formulas for functional loss and power loss.

[0094] Optionally, as an embodiment of the present invention, the functional loss is calculated according to Ohm's law:

[0095]

[0096] Where R represents the measured resistance value, ρ is the resistivity of the material, l is the length of the cable, A is the cross-sectional area, and I is the transmission current; when the resistivity decreases, the functional loss increases, reducing the transmission capacity of the cable and causing a decrease in the maximum transmission power. The specific calculation of power loss is as follows:

[0097]

[0098] In the formula, Where is the dielectric constant. Where is the vacuum dielectric constant, A is the effective contact area of ​​the electrode, d is the cable insulation thickness, ω is the angular frequency, tanδ is the dielectric loss factor, and V is the voltage of the cable during operation. During the aging process, the dielectric constant increases with time, leading to an increase in capacitance and a decrease in the loss factor, resulting in increased power loss, reduced cable transmission capacity, accelerated material degradation, and a decrease in maximum transmission power.

[0099] Optionally, as an embodiment of the present invention, calculating the voltage and current imbalance based on three-phase phasor voltage data and three-phase phasor current data, and obtaining the impact of cable aging on system stability specifically includes: The positive-sequence, negative-sequence, and zero-sequence components are obtained by transforming the three-phase phasor voltage data and three-phase phasor current data using Clarke and Fortescue sequence component transformations. Calculate the unbalance of negative sequence voltage:

[0100] in, , These are the root mean square values ​​of the positive-sequence and negative-sequence voltages, respectively. Calculate the unbalance of the negative sequence current:

[0101] in, , These are the root mean square values ​​of the positive-sequence and negative-sequence currents, respectively. The imbalance of zero-sequence voltage is calculated using the same method as that for negative-sequence voltage, and the imbalance of zero-sequence current is calculated using the same method as that for negative-sequence current. Comprehensive analysis shows that the imbalance of negative sequence voltage, zero sequence voltage, negative sequence current, and zero sequence current increases with aging time, and the overall system imbalance also increases with aging time.

[0102] Those skilled in the art will clearly understand that the techniques in the embodiments of the present invention can be implemented using software plus necessary general-purpose hardware platforms. Based on this understanding, the technical solutions in the embodiments of the present invention, or the parts that contribute to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium such as a USB flash drive, mobile hard drive, read-only memory (ROM), random access memory (RAM), magnetic disk, or optical disk, or other media capable of storing program code. It includes several instructions to cause a computer terminal (which may be a personal computer, server, or a second terminal, network terminal, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention.

[0103] The same or similar parts between the various embodiments in this specification can be referred to mutually. In particular, the terminal embodiments are basically similar to the method embodiments, so the description is relatively simple, and the relevant parts can be referred to the description in the method embodiments.

[0104] In the embodiments provided by this invention, it should be understood that the disclosed systems and methods can be implemented in other ways. For example, the system embodiments described above are merely illustrative. For instance, the division of modules is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple modules or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between systems or modules may be electrical, mechanical, or other forms.

[0105] The modules described as separate components may or may not be physically separate. The components shown as modules may or may not be physical modules; that is, they may be located in one place or distributed across multiple network modules. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs.

[0106] In addition, the functional modules in the various embodiments of the present invention can be integrated into one processing module, or each module can exist physically separately, or two or more modules can be integrated into one module.

[0107] Although the present invention has been described in detail with reference to the accompanying drawings and preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A method for analyzing the aging effects of XLPE cables based on RTDS, characterized in that, Includes the following steps: A simulation model of a hybrid operation system based on RTDS was built based on the cable wiring, operating conditions and operating parameters in actual engineering. XLPE insulation layer samples were obtained, and multiple XLPE insulation aging samples were obtained at different times using a constant temperature aging oven. The insulation resistance of each XLPE insulation aging sample was measured using a resistance meter, and the volume resistivity was calculated based on the parameters of the XLPE insulation layer sample and the insulation resistance. The dielectric constant and dielectric loss factor of each XLPE insulation aging sample were measured using a broadband dielectric spectrometer. The volume resistivity, dielectric constant and dielectric loss factor of the insulation aging samples at different times are input into the simulation model. After the simulation model runs under different operating conditions, it outputs the cable parameters, active power, key point three-phase phasor voltage data and key point three-phase phasor current data of each insulation aging sample. The impact of cable aging on maximum transmission power is obtained based on cable parameters and active power; the impact of cable aging on system imbalance is obtained based on three-phase phasor voltage data and three-phase phasor current data.

2. The method for analyzing the aging effects of XLPE cables based on RTDS according to claim 1, characterized in that, The calculation of volume resistivity based on the parameters of the XLPE insulation layer sample, combined with resistivity, specifically includes: For each XLPE insulation aging sample, repeated measurements were performed. The arithmetic mean of the obtained insulation resistance was taken, and the volume resistivity was calculated by combining the sample contact area and sample thickness. The calculation formula is as follows: in, R is the volume resistivity; S is the measured resistance value; h is the sample contact area; and h is the sample thickness.

3. The method for analyzing the aging effects of XLPE cables based on RTDS according to claim 1, characterized in that, The impact of cable aging on maximum transmission power, obtained based on cable parameters and active power, specifically includes: The total power is calculated based on the active power under different operating conditions. The active power and total power under different operating conditions are compared to obtain the transmission power under each operating condition. The maximum transmission power is obtained. The maximum transmission power under different operating conditions at different aging times is compared to obtain the impact of cable aging on the maximum transmission power. The reasons for the maximum power change were analyzed based on cable parameters combined with the formulas for functional loss and power loss.

4. The method for analyzing the aging effects of XLPE cables based on RTDS according to claim 3, characterized in that, Calculate the power loss according to Ohm's law: Where R represents the measured resistance value, ρ is the resistivity of the material, l is the length of the cable, A is the cross-sectional area, and I is the transmission current; when the resistivity decreases, the functional loss increases, reducing the transmission capacity of the cable and causing a decrease in the maximum transmission power. The specific calculation of power loss is as follows: In the formula, Where is the dielectric constant. Where is the vacuum dielectric constant, A is the effective contact area of ​​the electrode, d is the cable insulation thickness, ω is the angular frequency, tanδ is the dielectric loss factor, and V is the voltage of the cable during operation. During the aging process, the dielectric constant increases with time, leading to an increase in capacitance and a decrease in the loss factor, resulting in increased power loss, reduced cable transmission capacity, accelerated material degradation, and a decrease in maximum transmission power.

5. The method for analyzing the aging effects of XLPE cables based on RTDS according to claim 1, characterized in that, Based on three-phase phasor voltage and current data, the voltage and current imbalance is calculated, and the impact of cable aging on system stability is obtained, specifically including: The positive-sequence, negative-sequence, and zero-sequence components are obtained by transforming the three-phase phasor voltage data and three-phase phasor current data using Clarke and Fortescue sequence component transformations. Calculate the unbalance of negative sequence voltage: in, , These are the root mean square values ​​of the positive-sequence and negative-sequence voltages, respectively. Calculate the unbalance of the negative sequence current: in, , These are the root mean square values ​​of the positive-sequence and negative-sequence currents, respectively. The imbalance of zero-sequence voltage is calculated using the same method as that for negative-sequence voltage, and the imbalance of zero-sequence current is calculated using the same method as that for negative-sequence current. Comprehensive analysis shows that the imbalance of negative sequence voltage, zero sequence voltage, negative sequence current, and zero sequence current increases with aging time, and the overall system imbalance also increases with aging time.

6. A system for analyzing the aging effects of XLPE cables based on RTDS, characterized in that the system... include: The simulation model building module builds a simulation model of a hybrid operating system based on RTDS, based on cable wiring, operating conditions and operating parameters in actual engineering. The aging sample acquisition module acquires XLPE insulation layer samples and obtains multiple XLPE insulation aging samples at different times using a constant temperature aging oven. The performance data measurement module measures the insulation resistance of each XLPE insulation aging sample using a resistance meter, calculates the volume resistivity based on the parameters of the XLPE insulation layer sample and the insulation resistance, and measures the dielectric constant and dielectric loss factor of each XLPE insulation aging sample using a broadband dielectric spectrometer. The simulation operation module inputs the volume resistivity, dielectric constant and dielectric loss factor of the insulation aging sample at different times into the simulation model. After the simulation model runs under different operating conditions, it outputs the cable parameters, active power, key point three-phase phasor voltage data and key point three-phase phasor current data of each insulation aging sample. The aging impact analysis module obtains the impact of cable aging on the maximum transmission power based on cable parameters and active power; and obtains the impact of cable aging on system imbalance based on three-phase phasor voltage data and three-phase phasor current data.

7. The XLPE cable aging effect analysis system based on RTDS according to claim 6, characterized in that, The calculation of volume resistivity based on the parameters of the XLPE insulation layer sample, combined with resistivity, specifically includes: For each XLPE insulation aging sample, repeated measurements were performed. The arithmetic mean of the obtained insulation resistance was taken, and the volume resistivity was calculated by combining the sample contact area and sample thickness. The calculation formula is as follows: in, R is the volume resistivity; S is the measured resistance value; h is the sample contact area; and h is the sample thickness.

8. The XLPE cable aging effect analysis system based on RTDS according to claim 6, characterized in that, The impact of cable aging on maximum transmission power, obtained based on cable parameters and active power, specifically includes: The total power is calculated based on the active power under different operating conditions. The active power and total power under different operating conditions are compared to obtain the transmission power under each operating condition. The maximum transmission power is obtained. The maximum transmission power under different operating conditions at different aging times is compared to obtain the impact of cable aging on the maximum transmission power. The reasons for the maximum power change were analyzed based on cable parameters combined with the formulas for functional loss and power loss.

9. The XLPE cable aging effect analysis system based on RTDS according to claim 8, characterized in that, Calculate the power loss according to Ohm's law: Where R represents the measured resistance value, ρ is the resistivity of the material, l is the length of the cable, A is the cross-sectional area, and I is the transmission current; when the resistivity decreases, the functional loss increases, reducing the transmission capacity of the cable and causing a decrease in the maximum transmission power. The specific calculation of power loss is as follows: In the formula, Where is the dielectric constant. Where is the vacuum dielectric constant, A is the effective contact area of ​​the electrode, d is the cable insulation thickness, ω is the angular frequency, tanδ is the dielectric loss factor, and V is the voltage of the cable during operation. During the aging process, the dielectric constant increases with time, leading to an increase in capacitance and a decrease in the loss factor, resulting in increased power loss, reduced cable transmission capacity, accelerated material degradation, and a decrease in maximum transmission power.

10. The RTDS-based XLPE cable aging effect analysis system according to claim 6, characterized in that, Based on three-phase phasor voltage and current data, the voltage and current imbalance is calculated, and the impact of cable aging on system stability is obtained, specifically including: The positive-sequence, negative-sequence, and zero-sequence components are obtained by transforming the three-phase phasor voltage data and three-phase phasor current data using Clarke and Fortescue sequence component transformations. Calculate the unbalance of negative sequence voltage: in, , These are the root mean square values ​​of the positive-sequence and negative-sequence voltages, respectively. Calculate the unbalance of the negative sequence current: in, , These are the root mean square values ​​of the positive-sequence and negative-sequence currents, respectively. The imbalance of zero-sequence voltage is calculated using the same method as that for negative-sequence voltage, and the imbalance of zero-sequence current is calculated using the same method as that for negative-sequence current. Comprehensive analysis shows that the imbalance of negative sequence voltage, zero sequence voltage, negative sequence current, and zero sequence current increases with aging time, and the overall system imbalance also increases with aging time.

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