A wave process calculation method considering corrugated aluminum sheath structure of high voltage cable

Abstract

The application provides a wave process calculation method considering the corrugated aluminum sheath structure of a high-voltage cable, and the steps include: deducing the inner radius formula of the corrugated aluminum sheath of the high-voltage cable according to the geometric characteristics of the corrugated aluminum sheath; using the average geometric radius technology to equivalently convert the corrugated aluminum sheath into a uniform cylindrical shell; using a sine function to fit the corrugation of the actual corrugated aluminum sheath; solving the effective length of the equivalent uniform cylindrical shell; deducing the conductor impedance calculation approximate formula based on the effective length and the equivalent uniform cylindrical shell structure; deducing the admittance calculation formula based on the actual corrugated aluminum sheath structure of the high-voltage cable; calculating the cable wave transmission process characteristic parameters considering the corrugated aluminum sheath structure based on the above formula; and verifying the calculation results by building a low-voltage pulse verification test loop. The application is not only suitable for the distributed parameter equivalent circuit calculation of the corrugated aluminum sheath power cable of different sizes, voltage grades and lengths, but also can improve the electromagnetic transient simulation accuracy of the cable.

Description

Technical Field

[0001] This invention patent belongs to the field of high-voltage cable transmission technology, specifically relating to a method for wave process calculation and verification considering the corrugated aluminum sheath structure of high-voltage cables. Background Technology

[0002] With the development of wind power generation, cross-sea power grid interconnection, and urban power transmission, high-voltage cables have become increasingly widely used as important equipment in power transmission and distribution networks due to their advantages such as small footprint, high power supply reliability, and improved urban appearance. During operation, high-voltage cables are susceptible to unbalanced transient waves, such as switch operation overvoltage, lightning overvoltage, and grounding faults. In severe cases, these can lead to insulation breakdown, threatening the safe and reliable operation of the cables. Therefore, accurately calculating the electromagnetic transient wave process of cables and accurately understanding the transmission laws of overvoltage and overcurrent can guide the insulation design of high-voltage cables and the selection of system protectors, significantly reducing the huge economic losses caused by cable faults.

[0003] The calculation of electromagnetic transients in cables primarily relies on commercial software for modeling and simulation, such as ATP and PSCAD. However, because current software mainly focuses on the system level, it often oversimplifies the modeling of cable structures, frequently neglecting the influence of the inner and outer semiconductive layers, water-blocking buffer layers, and metal sheath structures on the calculated distributed parameters. Related experiments show that these cable layer structures cause changes in propagation characteristic parameters such as wave velocity, attenuation coefficient, and characteristic impedance during the propagation of transient waves, thereby affecting voltage and current distribution patterns. This results in a lack of effective data support for cable insulation condition assessment and insulation coordination strategy formulation. Therefore, achieving refined modeling of each layer of the cable, rather than simply considering the cable as a coaxial cylindrical structure of core-insulation-metal shield, is a major challenge currently facing accurate calculations of cable electromagnetic transients.

[0004] For the metal sheath of high-voltage cables, corrugated aluminum sheaths and aluminum-plastic composite sheaths are commonly used. Meanwhile, smooth aluminum sheath structures are increasingly being adopted to avoid the impact of cable buffer layer ablation on cable safety. In constructing the equivalent circuit for the distributed parameters of the metal sheath, existing EMTP-type transient software often equates it to a single-layer coaxial structure, i.e., a smooth aluminum sheath. However, the widely used corrugated aluminum sheath is actually a spiral corrugated structure, as shown in Figures 7(a) and 7(b). Its geometric characteristics are that the geometry is the same at any interface perpendicular to the thread axis; the sheath cross-section is cylindrical, and it contacts the cable buffer layer at one point on the cross-section. The sheath moves along the cable axis, rotates around the cable core, maintains a constant inner and outer radius, and has a certain offset from the center of the core. Therefore, the effective length of the corrugated aluminum sheath is actually longer than the cable core length. When current flows in the aluminum sheath, its effective length will affect the calculation of the cable model's impedance and admittance; at the same time, due to a certain eccentricity, the equivalent coaxial cylindrical form also differs from the actual structure. Therefore, an electromagnetic transient modeling method conforming to the corrugated aluminum sheath structure is proposed to achieve accurate calculation of the impedance and admittance of the equivalent distributed parameter circuit. This method has important engineering value for understanding the voltage and current transmission characteristics in cables and formulating accurate cable protection strategies. Summary of the Invention

[0005] To overcome the shortcomings of existing electromagnetic transient modeling of metal sheaths, this patent provides a wave process calculation method that considers the corrugated aluminum sheath structure of high-voltage cables. It fully considers the influence of the eccentricity and equivalent length of the spiral corrugated aluminum sheath structure on the distributed parameter equivalent circuit impedance and admittance. It is not only applicable to the distributed parameter equivalent circuit calculation of corrugated aluminum sheath power cables of different sizes, voltage levels and lengths, but also improves the accuracy of electromagnetic transient simulation of cables.

[0006] The technical solution adopted by this invention to solve its technical problem is:

[0007] This invention provides a wave process calculation method considering the corrugated aluminum sheath structure of high-voltage cables. It constructs a planar equivalent circuit of the corrugated aluminum sheath using the average geometric radius technique and solves for its equivalent extension length. Based on Maxwell's equations, an approximate formula for calculating the impedance of the eccentric conductor is derived. Based on the multi-layer cable structure and average geometric radius, an admittance calculation formula is derived. Based on the above formulas, the characteristic parameters of the cable wave transmission process considering the corrugated aluminum sheath structure are calculated, thereby analyzing the wave process law. A single-core cable circuit with a corrugated aluminum sheath structure is constructed, and a low-voltage pulse test is conducted. The voltage and current waveforms at the cable's beginning and end are collected to verify the calculation results.

[0008] A wave process calculation method considering the corrugated aluminum sheath structure of high-voltage cables includes the following steps:

[0009] S1. Derive the formula for the inner radius of the aluminum sheath based on the geometric characteristics of the corrugated aluminum sheath structure of high-voltage cables;

[0010] S2. Based on the inner radius formula, the corrugated aluminum sheath is equivalent to a uniform cylindrical shell using the average geometric radius technique.

[0011] S3. Use a sine function to fit the corrugations of the actual corrugated aluminum sheath;

[0012] S4. Based on the fitting results, solve for the effective length of the equivalent uniform cylindrical shell;

[0013] S5. Based on the effective length, derive an approximate formula for calculating conductor impedance;

[0014] S6. Based on the cable structure and average geometric radius, derive the admittance calculation formula;

[0015] S7. Based on the inner radius formula, the approximate formula for conductor impedance calculation, and the admittance calculation formula, calculate the characteristic parameters of the cable wave transmission process considering the corrugated aluminum sheath structure.

[0016] Preferably, the method further includes the following steps:

[0017] S8. A low-voltage pulse verification test circuit is constructed to verify the calculation results. Furthermore, if the measurement error of the verification test meets the requirements, there is no case of verification failure in this method. The modeling method itself is more in line with the actual cable structure in the theoretical derivation process, thus improving the calculation accuracy compared with the traditional simplified method.

[0018] Preferably, the geometric feature is:

[0019] The corrugated aluminum sheath of high-voltage cables is a spiral corrugated aluminum sheath with a cylindrical cross-section. It contacts the cable buffer layer at one point on the cross-section. The sheath moves along the cable axis, rotates around the cable core, maintains a constant inner and outer radius, and has a certain offset from the center of the cable core.

[0020] Preferably, the formula for the inner radius of the aluminum sheath is:

[0021] r i，s =(r o，w +r i,p -d s ) / 2

[0022] in,

[0023] r i，s The inner radius of the aluminum sheath.

[0024] r o，w The outer radius of the water-blocking layer,

[0025] ri,p The inner radius of the PVC outer sheath.

[0026] d s This refers to the thickness of the aluminum sheath.

[0027] Preferably, the average geometric radius technique uses the average geometric radius GMR as the equivalent radius of the helical corrugated aluminum, thereby equating the helical corrugated aluminum structure to a uniform cylindrical shell, wherein...

[0028] GMR = r i，s +d s / 2.

[0029] Preferably, in step S3, the fitting method is as follows:

[0030] f(x) = Asin(Bx)

[0031] in,

[0032] A represents the crest of the corrugated aluminum, and B = 2π / l p , l p This represents the pitch length.

[0033] Preferably, the effective length L of the equivalent uniform cylindrical shell is:

[0034]

[0035] in,

[0036] Δx is the original length.

[0037] Δl is the equivalent extension length of the corrugated aluminum sheath.

[0038] f′(x) is the derivative of the corrugated sine fitting function of the actual corrugated aluminum sheath.

[0039] Preferably, the approximate formula for calculating the conductor impedance is as follows:

[0040] Correcting the mutual impedance Z between the conductor and the sheath 12 Mutual impedance Z′ between the protective layer and the ground 23 Inner surface impedance Z′ of the sheath 2i , Sheath outer surface impedance Z′ 2o Sheath mutual impedance Z′ 2m They are respectively:

[0041]

[0042] in,

[0043] j is the imaginary unit in mathematics.

[0044] ω is the angular frequency.

[0045] μ0 is the free permeability.

[0046] b is the eccentricity between the aluminum sheath and the wire core, and its value is r. i，s -r o，w ,

[0047] r o，c The outer radius of the wire core;

[0048]

[0049] in,

[0050] r o，s The outer radius of the aluminum sheath.

[0051] r o，P The radius of the PVC outer sheath;

[0052] Z′ 2i =Z 2i ·L / Δx

[0053] Z′ 2m =Z 2m ·L / Δx

[0054] Z′ 2o =Z 2o ·L / Δx

[0055] Z′ 23 =Z 23 ·L / Δx

[0056] in,

[0057] Z 2i Z represents the inner surface impedance of the sheath before correction. 2m Z represents the sheath mutual impedance before correction. 2o Z represents the outer surface impedance of the sheath before correction. 23 Considering only the eccentricity, the mutual impedance between the sheath and the ground is calculated.

[0058] Furthermore, the coaxial mode impedance is calculated as follows:

[0059] Z coaxial ≈Z 11 +Z 12 +Z′ 2i

[0060] in,

[0061] Z coaxial For coaxial mode impedance,

[0062] Z 11 The resistance is the internal resistance of the outer surface of the wire core.

[0063] Preferably, the admittance Y(ω) is calculated using the following formula:

[0064]

[0065] Wherein, Y1(ω), Y2(ω), Y3(ω), Y4(ω), and Y5(ω) are the admittances of the inner semiconducting layer, insulation layer, outer semiconducting layer, water-blocking buffer layer, and air layer of the cable, respectively;

[0066]

[0067]

[0068]

[0069]

[0070]

[0071] In the formula, ε0 is the vacuum permittivity. The relative complex permittivity of the inner semiconducting layer, insulating layer, outer semiconducting layer, and water-blocking buffer layer are respectively obtained from material testing. The complex permittivity value at the corresponding frequency is selected according to the dominant frequency f = ω / 2π, thus fully considering the influence of the frequency-dependent characteristics of the material on the admittance calculation; r1, r o，i r3, r i，s These are the outer radii of the inner semiconductive layer, the outer radii of the insulating layer, the outer radii of the outer semiconductive layer, and the inner radii of the aluminum sheath, respectively.

[0072] Preferably, the feature parameters are calculated as follows:

[0073]

[0074]

[0075] α=Re(γ)

[0076] Where Z0 is the characteristic impedance, v is the wave velocity, and α is the attenuation coefficient.

[0077]

[0078] β=Im(γ)

[0079] Where γ is the propagation constant and β is the phase constant.

[0080] Preferably, the verification method is as follows: a broadband pulse voltage wave is injected into the cable head end, and voltage waveforms are collected at both ends of the cable using a voltage differential probe. A Rogowski coil is used to collect the current waveform at the cable head end. Since the voltages at both ends are synchronized, the experimental result v′ of the wave velocity can be obtained using the difference between the cable length l and the voltage propagation time Δt.

[0081] v′=l / Δt

[0082] Compare the experimental result v′ with the calculated result v to verify the accuracy of the simulation modeling.

[0083] The technical advantages of this invention are as follows:

[0084] 1) Compared with the existing technology, which simply considers the coaxial cylindrical structure of wire core-insulation-metal shield, the present invention uses the geometric average radius technology to construct the planar equivalent structure of corrugated aluminum sheath, and fully considers the influence of the equivalent extension length of corrugated aluminum on impedance and admittance calculation.

[0085] 2) Compared with the existing technology that uses coaxial cylindrical equivalents to calculate the impedance of each layer of the cable, the present invention fully considers the error of the impedance calculation result caused by the eccentricity of the spiral structure.

[0086] 3) This invention designs a single-core cable circuit with a corrugated aluminum sheath structure, conducts low-voltage pulse tests, establishes the relationship between voltage propagation time difference and cable length, and proposes to use wave velocity to verify the accuracy of simulation modeling, filling the gap in the lack of verification links in existing transient calculations. Attached Figure Description

[0087] Figure 1 This is a flowchart of the steps of the present invention;

[0088] Figure 2 This is a diagram showing the equivalent structure of the corrugated aluminum sheath.

[0089] Figure 3 This is a schematic diagram of a low-voltage pulse verification test circuit.

[0090] Figures 4(a) and 4(b) show the coaxial mode impedance Z. coaxial Comparison chart of calculation results;

[0091] Figure 5(a) and Figure 5(b) are comparison charts of the calculated admittance of the multilayer cable structure;

[0092] Figures 6(a) to 6(c) Comparison of calculation results of characteristic parameters of coaxial cable body wave process;

[0093] Figures 7(a) and 7(b) are schematic diagrams of the spiral corrugated aluminum sheath;

[0094] Figure 8 Inject waveforms into the acquired voltage pulses. Detailed Implementation

[0095] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will describe them in conjunction with the embodiments of the present invention and the accompanying drawings. Figures 1 to 8 The technical solutions in the embodiments of the present invention are clearly and completely described herein. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0096] This invention provides a wave process calculation method considering the corrugated aluminum sheath structure of high-voltage cables, such as... Figure 1 As shown, a planar equivalent circuit of the corrugated aluminum sheath is constructed using the average geometric radius technique, and its equivalent extension length is solved. Based on Maxwell's equations, an approximate formula for calculating the impedance of the eccentric conductor is derived. Based on the multilayer cable structure and the average geometric radius, the admittance calculation formula is derived. Based on the above formulas, the characteristic parameters of the cable wave transmission process considering the corrugated aluminum sheath structure are calculated, thereby analyzing the wave process law. A single-core cable circuit with a corrugated aluminum sheath structure is built, a low-voltage pulse test is carried out, and the voltage and current waveforms at the beginning and end of the cable are collected to verify the calculation results.

[0097] In one embodiment, the wave process calculation method considering the corrugated aluminum sheath structure of high-voltage cables specifically includes the following steps:

[0098] S1. As shown in Figures 7(a) and 7(b), the cross-section of the spiral corrugated aluminum sheath is cylindrical, and it contacts the cable buffer layer at one point on the cross-section. The sheath moves along the cable axis, rotates around the cable core, maintains a constant inner and outer radius, and has a certain offset from the center of the cable core. Based on the above geometric characteristics, the inner radius of the aluminum sheath can be derived as follows:

[0099] r i，s =(r o，w +r i,p -d s ) / 2

[0100] in,

[0101] r i，s The inner radius of the aluminum sheath.

[0102] r o，w The outer radius of the water-blocking layer,

[0103] r i , p The inner radius of the PVC outer sheath.

[0104] d s This refers to the thickness of the aluminum sheath.

[0105] S2. To account for the actual length of the corrugated aluminum sheath, the corrugated aluminum sheath is converted into a uniform cylindrical outer shell, such as... Figure 2 As shown, the average geometric radius GMR is used as the equivalent radius of the helical corrugated aluminum, thus transforming the corrugated helical aluminum sheath structure into a uniform cylindrical shell.

[0106] GMR = r i，s +d s / 2.

[0107] Furthermore, by utilizing the average geometric radius technique, the corrugated spiral aluminum sheath structure is equivalent to a uniform cylindrical shell, thereby solving the complex impedance and admittance calculation problems caused by the three-dimensional structure of the spiral corrugated aluminum. This improves the calculation speed of the wave process while maintaining accurate calculation precision.

[0108] At the same time, from Figure 2 As can be seen, the length of the aluminum conductor in the corrugated aluminum structure is significantly greater than the length of the cable core. Therefore, the equivalent extension length of the corrugated aluminum needs to be considered in the impedance calculation to improve the accuracy of the calculation.

[0109] S3. Fit the corrugations of the actual corrugated aluminum sheath using a sine function, i.e.

[0110] f(x) = Asin(Bx)

[0111] in,

[0112] A represents the crest of the corrugated aluminum, and B = 2π / l p , l p The pitch length is given. Furthermore, based on the geometry of the cable's corrugated aluminum sheath, using a sine / cosine function is a more accurate and easily calculated fitting function, avoiding overfitting / underfitting. The error from fitting using these two functions is negligible in subsequent calculations.

[0113] S4, based on the sinusoidal fitting expression of the corrugated aluminum sheath in S3, can be solved. Figure 2 The effective length of the equivalent uniform cylindrical shell corresponding to segment ab of the center core is:

[0114]

[0115] in,

[0116] Δx is the original length.

[0117] Δl is the equivalent extension length of the corrugated aluminum sheath.

[0118] f′(x) is the derivative of the corrugated sine fitting function of the actual corrugated aluminum sheath.

[0119] S5. Considering the equivalent extension length of the metal sheath and the non-coaxial structure, correct the mutual impedance Z between the conductor and the sheath. 12 Mutual impedance Z′ between the protective layer and the ground 23 Inner surface impedance Z′ of the sheath 2i , Sheath outer surface impedance Z′ 2o Sheath mutual impedance Z′ 2m as follows:

[0120]

[0121] in,

[0122] j is the imaginary unit in mathematics.

[0123] ω is the angular frequency.

[0124] μ0 is the free permeability.

[0125] b is the eccentricity between the aluminum sheath and the wire core, and its value is r. i，s -r o,w ,

[0126] r o，c The outer radius of the wire core.

[0127]

[0128] in,

[0129] r o,s The outer radius of the aluminum sheath.

[0130] r o,P The radius of the PVC outer sheath.

[0131] Z′ 2i =Z 2i ·L / Δx

[0132] Z′ 2m =Z 2m ·L / Δx

[0133] Z′ 2o =Z 2o ·L / Δx

[0134] Z′ 23 =Z 23 ·L / Δx

[0135] in,

[0136] Z 2i Z represents the inner surface impedance of the sheath before correction. 2m Z represents the sheath mutual impedance before correction. 2o Z represents the outer surface impedance of the sheath before correction. 23This refers to the mutual impedance between the sheath and the ground when only the eccentricity is considered.

[0137] Furthermore, the coaxial mode impedance is calculated as follows:

[0138] Z coaxial ≈Z 11 +Z 12 +Z′ 2i

[0139] in,

[0140] Z coaxial For coaxial mode impedance,

[0141] Z 11 The resistance is the internal resistance of the outer surface of the wire core.

[0142] S6. Calculate the admittance Y(ω) of the multi-layer cable structure. The calculation equation is as follows:

[0143]

[0144] Wherein, Y1(ω), Y2(ω), Y3(ω), Y4(ω), and Y5(ω) are the admittances of the inner semiconducting layer, insulation layer, outer semiconducting layer, water-blocking buffer layer, and air layer of the cable, respectively;

[0145]

[0146]

[0147]

[0148]

[0149]

[0150] In the formula, ε0 is the vacuum permittivity. The relative complex permittivity of the inner semiconducting layer, insulating layer, outer semiconducting layer, and water-blocking buffer layer are respectively obtained from material testing. The complex permittivity value at the corresponding frequency is selected according to the dominant frequency f = ω / 2π, thus fully considering the influence of the frequency-dependent characteristics of the material on the admittance calculation; r1, r o，i r3, r i，s These are the outer radii of the inner semiconductive layer, the outer radii of the insulating layer, the outer radii of the outer semiconductive layer, and the inner radii of the aluminum sheath, respectively.

[0151] S7. The characteristic parameters of the wave process in the coaxial mode of the cable body with multi-layer structure, namely characteristic impedance Z0, wave velocity v and attenuation coefficient α, are as follows:

[0152]

[0153]

[0154] α=Re(γ)

[0155] Where Z0 is the characteristic impedance, v is the wave velocity, and α is the attenuation coefficient.

[0156]

[0157] β=Im(γ)

[0158] Where γ is the propagation constant and β is the phase constant.

[0159] S8, Build as follows Figure 3 The low-voltage pulse verification test circuit shown verifies the calculation results. A broadband pulse voltage wave is injected into the cable head, and voltage waveforms are collected at both ends of the cable using a voltage differential probe. A Rogowski coil is used to collect the current waveform at the cable head. Since the voltages at both ends are synchronized, the wave velocity test result v′ can be obtained using the difference Δt between the cable length l and the voltage propagation time.

[0160] v′=l / Δt

[0161] Compare the experimental result v′ with the calculated result v to verify the accuracy of the simulation modeling.

[0162] Furthermore, Figure 3 The diagram shows a low-voltage pulse verification test circuit. A high-frequency pulse or broadband sine wave signal is injected into the conductor at the beginning of the cable. An oscilloscope is used to simultaneously acquire the conductor current at the beginning, the voltage between the conductor and the sheath, and the voltage between the conductor and the sheath at the end. By comparing the arrival time difference Δt between the waveforms at the beginning and end, the wave propagation velocity is calculated given the cable length. The wave velocity obtained from the experiment is compared with the calculated wave velocity to verify the accuracy of the simulation model.

[0163] This experimental circuit and procedure fill the gap in the current wave process calculation lack of verification process. It uses variable frequency injection excitation to realize the accuracy verification of wave process calculation over a wide frequency range.

[0164] Taking a ±320kV cable as an example, it uses a spiral corrugated aluminum sheath with a corrugation depth of 5.45mm, a nominal thickness of 2.8mm, and a pitch of 20mm. According to the formula described above, its eccentricity b = 2.725mm, average geometric radius GMR = 64.875mm, and equivalent inner radius r of the corrugated aluminum sheath are calculated. i，s = 63.475mm. When Δx = 20mm, the equivalent extension length of the corrugated aluminum sheath is L = 23.2721mm, L / Δx = 1.1636. The Z-axis considering the corrugated aluminum structure was calculated. coaxialIt was compared with the traditional simplified method (i.e., using a simple smooth aluminum equivalent structure), and the comparison results are as follows: Figures 4(a) to 5(b) .

[0165] Figures 4(a) and 4(b) show the impedance results of the cable in coaxial mode obtained using the traditional smooth aluminum calculation method and the proposed wave process calculation method considering the actual helical corrugated aluminum structure. Considering the helical corrugated aluminum structure, the cable has higher resistance and inductance values, which is more consistent with the wave propagation process of a real corrugated aluminum cable line. This also indicates that the impedance calculation results of the actual corrugated aluminum cable using the traditional smooth aluminum structure are generally lower than the actual impedance.

[0166] Figures 5(a) and 5(b) show the admittance results calculated using the average geometric radius technique for the equivalent coaxial cylindrical cable structure and the traditional smooth aluminum structure. In the helical corrugated aluminum structure, an air layer is introduced between the metallic shield and the water-blocking buffer layer, leading to a significant difference between the actual admittance of the corrugated aluminum structure and the smooth aluminum structure. Traditional calculation methods for smooth aluminum sheaths are not applicable to corrugated aluminum structure cables.

[0167] Depend on Figures 4(a) to 5(b) It is evident that, with other geometric dimensions of the cable being equal, the spiral corrugated aluminum sheath structure has higher resistance and inductance, and lower conductivity and capacitance compared to the smooth aluminum sheath structure.

[0168] Furthermore, its wave process characteristic parameters are calculated as follows: Figures 6(a) to 6(c) As shown. Figures 6(a) to 6(c) The characteristic parameters of coaxial mode wave propagation, including characteristic impedance, wave velocity, and attenuation coefficient, are derived from the impedance and admittance calculations described above. The three parameters obtained using the traditional smooth aluminum sheath calculation method show significant differences from those calculated using this method, especially in characteristic impedance and wave velocity. On one hand, this method more closely approximates the actual corrugated aluminum structure, highlighting the inapplicability of traditional methods for calculating corrugated aluminum cables. On the other hand, it can be seen that due to the significant differences in the first two parameters, characteristic impedance / wave velocity can be used as verification parameters. Figures 6(a) to 6(c) It is evident that the typical characteristic parameters of the three types of wave processes of the helical corrugated aluminum sheath are significantly different from those of the smooth aluminum sheath, indicating that considering the special characteristics of the helical corrugated aluminum structure is essential for electromagnetic transient calculations.

[0169] Simultaneously, a single-core cable circuit with a corrugated aluminum sheath was constructed, and a low-voltage pulse test was conducted. The calculation results were verified by collecting voltage and current waveforms at the cable's beginning and end. Figure 8The image shows the collected voltage pulse injection waveform. By comparing the wave velocity v′ calculated from the experimental results using the voltage waveform delay Δt collected at both ends, it was found that the wave velocity obtained by the wave process calculation method considering the corrugated aluminum sheath structure of the high-voltage cable has an error of less than 3% compared with the experimental wave velocity, indicating that the method meets the accuracy requirements for electromagnetic transient calculation. Figure 8 The excitation selected for the low-voltage pulse verification test circuit of this method in the embodiment is given. It is a high-frequency pulse containing a wide range of frequency components, so the method can be verified at multiple frequencies.

[0170] The foregoing general description of the invention and its specific embodiments should not be construed as a limitation on the technical solution of the invention. Those skilled in the art, based on the disclosure of this application, can add, reduce, or combine the disclosed technical features in the foregoing general description and / or specific embodiments (including examples) without departing from the constituent elements of the invention, to form other technical solutions within the scope of protection of this application.

Claims

1. A wave process calculation method considering the corrugated aluminum sheath structure of high-voltage cables, characterized in that, The method includes the following steps: S1. Derive the formula for the inner radius of the aluminum sheath based on the geometric characteristics of the actual corrugated aluminum sheath structure of high-voltage cables. S2. Based on the inner radius formula, the corrugated aluminum sheath is equivalent to a uniform cylindrical shell using the average geometric radius technique. S3. Use a sine function to fit the corrugation of the actual corrugated aluminum sheath of the high-voltage cable; S4. Based on the fitting results, solve for the effective length of the equivalent uniform cylindrical shell; S5. Based on the effective length, derive an approximate formula for calculating conductor impedance; S6. Based on the actual corrugated aluminum sheath structure and average geometric radius of high-voltage cables, derive the admittance calculation formula; S7. Based on the formula for the inner radius of the aluminum sheath, the approximate formula for calculating conductor impedance, and the formula for calculating admittance, calculate the characteristic parameters of the cable wave transmission process. The approximate formula for calculating the conductor impedance is as follows: Correcting the mutual impedance Z between the conductor and the sheath 12 Mutual resistance between the protective layer and the ground Inner surface resistance of the protective layer outer surface impedance of the protective layer Sheath mutual impedance They are respectively: ， in, j is the imaginary unit in mathematics. Angular frequency, The permeability of free space, The eccentricity between the aluminum sheath and the wire core is [value missing]. , The inner radius of the aluminum sheath. The outer radius of the water-blocking layer, The outer radius of the wire core; ， in, The outer radius of the aluminum sheath. The radius of the PVC outer sheath; ， ， ， ， in, The inner surface resistance of the sheath before correction. The original sheath mutual impedance. The outer surface impedance of the sheath before correction. To consider only the eccentricity, the mutual impedance between the sheath and the ground is given, where L is the effective length of the equivalent uniform cylindrical shell. This is the original length; Furthermore, the coaxial mode impedance is calculated as follows: ， in, For coaxial mode impedance, The resistance is the internal resistance of the outer surface of the wire core.

2. The method according to claim 1, characterized in that, The method also includes the following steps: S8. Construct a low-voltage pulse verification test circuit to verify the calculation results.

3. The method according to claim 1, characterized in that, The formula for the inner radius of the aluminum sheath is: ， in, The inner radius of the aluminum sheath. The outer radius of the water-blocking layer, The inner radius of the PVC outer sheath. This refers to the thickness of the aluminum sheath.

4. The method according to claim 3, characterized in that, The aforementioned average geometric radius technique uses the average geometric radius (GMR) as the equivalent radius of the helical corrugated aluminum, i.e. This allows the corrugated aluminum sheath to be equivalent to a uniform cylindrical shell.

5. The method according to claim 1, characterized in that, In step S3, the fitting formula is: ， in, A represents the crest of the corrugated aluminum, and B = 2π / l p , l p This represents the pitch length.

6. The method according to claim 5, characterized in that, The effective length L of the equivalent uniform cylindrical shell corresponding to segment ab of the wire core is: ， in, The original length, It is the equivalent extension length of the corrugated aluminum sheath. This is the derivative of the corrugated sine fitting function of the actual corrugated aluminum sheath.

7. The method according to claim 2, characterized in that, The admittance calculation formula is as follows: , in, For equivalent admittance, , , , , These are the admittances of the inner semiconductive layer, insulation layer, outer semiconductive layer, water-blocking buffer layer, and air layer of the cable, respectively. ， ， ， ， ， In the formula, The vacuum permittivity, , , , The relative complex permittivity of the inner semiconducting layer, insulating layer, outer semiconducting layer, and water-blocking buffer layer are respectively obtained from material testing and based on the dominant frequency. The value of the complex permittivity is selected at the corresponding frequency to fully consider the influence of the frequency-dependent characteristics of the material on the admittance calculation. , , , These are the outer radius of the inner semiconductive layer, the outer radius of the insulating layer, the outer radius of the outer semiconductive layer, and the inner radius of the aluminum sheath, respectively.

8. The method according to claim 7, characterized in that, The characteristic parameters are calculated as follows: , ， ， in, Here, is the characteristic impedance, and v is the wave velocity. The attenuation coefficient is... ， ， Where γ is the propagation constant and β is the phase constant.

9. The method according to claim 8, characterized in that, The verification process is as follows: a broadband pulse voltage wave is injected into the cable head end; voltage waveforms are collected at both ends of the cable using a voltage differential probe; and current waveforms are collected at the cable head end using a Rogowski coil. Since the voltages at both ends are synchronized, the cable length is used to... Difference between voltage propagation time Experimental results for obtaining wave velocity : ， Comparative test results With calculation results To verify the accuracy of the simulation modeling.

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