Method and system for on-line positioning of partial ageing of cable insulation in distributed power-rich areas
By establishing a distributed parameter model and series resonant frequency analysis, combined with broadband impedance spectrum and inverter control algorithm, efficient and accurate online positioning of cable insulation in distributed power source rich areas was achieved, solving the problem of difficulty in identifying local aging in existing technologies, and improving system operation reliability and power supply safety.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- BEIJING JIAOTONG UNIV
- Filing Date
- 2026-03-13
- Publication Date
- 2026-06-23
AI Technical Summary
Existing technologies struggle to achieve efficient and accurate local positioning in cable insulation within distributed power source-rich areas, particularly in cable positioning methods and systems within these areas. Furthermore, existing technologies often fail to address cable insulation issues, particularly in achieving efficient and accurate local aging identification and positioning within cable insulation in distributed power source-rich areas.
By establishing a distributed parameter model of the cable, using series resonant frequency analysis, combining it with broadband impedance spectrum, and employing inverter control algorithm to superimpose broadband signals, Fourier analysis is performed to obtain the precise location of local aging of cable insulation.
It enables efficient and accurate online monitoring and location of cable insulation in areas rich in distributed power sources, avoiding the impact of power grid impedance fluctuations and improving the efficiency of fault diagnosis and repair.
Smart Images
Figure CN122260027A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of online monitoring of cable insulation aging, specifically relating to an online location method and system for local aging of cable insulation in distributed power source rich areas. Background Technology
[0002] To achieve its "dual carbon" goals and address the shortage of fossil fuels, my country is actively promoting the construction of a new energy system represented by wind and solar power. Distributed power sources are rapidly forming concentrated areas in regions with superior resource conditions. These areas are typically remote, scattered, and far from the main grid load centers, relying on long transmission lines for power transmission. Furthermore, because these concentrated areas are often located in deserts, Gobi, and grasslands with complex climates and significant temperature differences, the working environment for cable insulation is much harsher than in conventional areas. The natural climate and environmental conditions in these regions exacerbate cable insulation aging and the risk of failure. To ensure safe and reliable power transmission, online monitoring is currently widely used to assess the overall insulation status of cables in real time. However, simply knowing the overall insulation parameters is insufficient to accurately identify localized problems—in actual operation, insulation defects often manifest as localized aging. If the specific aging section cannot be identified in time, it will significantly affect the efficiency of fault diagnosis and repair. Therefore, there is an urgent need to develop online monitoring technologies with the ability to identify and locate localized aging, enabling early detection and precise location of insulation problems in transmission lines in concentrated areas of distributed power sources, thereby improving system reliability and power supply security.
[0003] Cable insulation aging location technology is a crucial link in ensuring the safe transmission of power from distributed power sources. Existing location methods mainly include traveling wave-based methods and broadband impedance spectroscopy (BIS)-based methods. The traveling wave-based method injects a modulated pulse signal into the cable and collects the reflected signals generated at both ends of the locally aging section to locate the localized aging of the cable insulation. The BIS-based method injects a set of excitation signals with progressively increasing frequencies into the cable under test, obtaining an impedance spectrum over a frequency range. In this case, the locally aging section of the cable insulation will exhibit changes in electrical parameters, leading to non-uniform characteristic impedance. By collecting the impedance spectrum of the cable over a wider frequency band and performing an inverse Fourier transform on the collected impedance spectrum, the time-domain energy distribution of the signal can be obtained. Ignoring the wave velocity differences between different cable segments, the spatial energy spectrum can be obtained based on the time-domain energy distribution. According to the correspondence between the time and frequency domains of the signal, the two ends of the locally aging section of the cable insulation will correspond to abrupt peaks in the spatial energy spectrum. The location of these abrupt peaks allows for the location of the localized aging of the cable insulation. While the two methods described above can pinpoint uniform, localized aging within cables, they require high spectral range and frequency resolution in practical systems, often needing to reach megahertz levels. Therefore, these methods can only locate locally aged sections of cable insulation offline and are difficult to apply in actual power distribution networks. Summary of the Invention
[0004] To address the aforementioned technical problems and ensure the safe and stable operation of the power system, this invention proposes an efficient and accurate online monitoring and location technology solution for the potential issue of localized insulation aging in cables in distributed power generation-rich areas. This solution can avoid resonant frequency changes caused by variations in the equivalent impedance of weak power grids, and further estimate the distance of localized insulation aging by analyzing the resonant frequency changes in the cable's broadband impedance spectrum, thereby achieving accurate location. The online location method for localized insulation aging of cables in distributed power generation-rich areas provided by this invention includes the following steps: Step 1: Based on the cable type in the distributed power source enrichment area, establish a distributed parameter model for the cable, determine the equivalent electrical parameters per unit length of the cable, and adopt a Γ-type equivalent circuit per unit length of the cable, with an equivalent resistance of [missing value]. R 0. Equivalent inductance is L 0. Equivalent capacitance is C 0; for a total length of l The cable uses n The ladder-shaped iterative network constructed from the segment Г-type equivalent circuit is used as a replacement; Step 2: Write the equivalent circuit model based on the unit Γ type. s Formula (1) under the domain is: ;
[0005] in h 0 indicates that in the unit Γ type equivalent circuit R 0 and L The impedance formed by 0, s 0 indicates that in the unit Γ type equivalent circuit C Admittance composed of 0 h g Represents the equivalent resistance of the power grid R g and equivalent inductance L g The impedance formed; at the same time let ,according to n A trapezoidal iterative network constructed from a segment Г-type equivalent circuit is used to calculate the mathematical model of the impedance of the back-end cables and power grid system of the new energy power plant using a recursive method. Z s See formula (2): ; in and All are about polynomials; Step 3: Starting from the grid connection point, the total length is... l The cable in x=l f Localized aging occurs at a point, dividing the cable into two parts: the first region is denoted as Г. I The cable length is l f The impedance formed by the resistive and inductive components corresponding to the cable segment is Z LI The admittance formed by the capacitor is Y LI The second region is denoted as Г. Ⅱ The cable length is l - l f The impedance formed by the inductor and resistor portion corresponding to the cable segment is Z LII The admittance formed by the capacitor is Y LII ; from x=l f Impedance looking towards the power grid side Z Ⅱ The localized aging capacitance to ground is C f That is, the capacitive reactance expression is X f =1 / sC f Therefore, it was introduced from x=l f Including the impedance looking towards the grid from the aging point Z f Formula (3) is: ; Impedance viewed from the grid connection point towards the grid side Z I Formula (4) is: ; Step 4: According to the definition of series resonant frequency, Z I The series resonant frequency is calculated by equation (7), and the specific calculation process includes: Z I The series resonant frequency is determined by the root of formula (5): ; Simplify formula (5) into formula (6): ; Definitions include the back-end impedance of aging capacitors. Z f The impedance formed by the resistive and inductive components corresponding to the cable segment after localized aging capacitance is: Z LI The modulus of the ratio is K s Based on the amplitude-frequency and phase-frequency characteristic curves of the impedance, equation (6) is simplified to real equation (7): ; use r pk This indicates the first... k One solution. Z I The k Series resonant frequency and r pk The general expression for the resonant frequency between them (8) is: ; The inverter control algorithm is set to superimpose every hour into the modulated wave. f 1±1kHz and fA broadband signal around 2±1kHz was collected, and the three-phase voltage and current at the outlet of the distributed power source enrichment area were continuously acquired and Fourier analyzed during system operation to obtain the amplitude-frequency characteristics of the three-phase voltage and current. The amplitude of each phase voltage and current at each frequency point was divided to obtain the broadband impedance spectrum of each phase of the grid-connected point downstream system. The broadband impedance spectrum of each phase includes the impedance of the downstream cable and the power grid system. After data processing, the broadband impedance spectrum of the grid-connected point downstream system was obtained, and the current operating status was recorded. Z I The second series resonant frequency f 2, r p2 The second solution to formula (7) is obtained from the above analysis. f The expression for 2 (9) is: ; From formula (7), we can deduce that the root r pk The value is a polynomial and The x-coordinate of the intersection point, according to the knowledge of polynomials, polynomial The first root Represented as: ; r p2 Approximately equal to Therefore, by combining formulas (9) and (10), we obtain the expression for the local aging distance of cable insulation (11): ; Step 5: Measure the second series resonant frequency under the current operating state. f Substituting 2 into formula (11), the distance of local aging of the cable insulation at this time can be obtained. l f This allows for precise location of localized aging in cable insulation.
[0006] To address the aforementioned technical problems, the present invention also provides an online positioning system for localized aging of cable insulation in distributed power source rich areas, comprising a first calculation module, a second calculation module, and a positioning module; The first calculation module is used to determine the mathematical model of the impedance of the back-end cables of the new energy power plant and the power grid system based on the unit Γ-type equivalent circuit model of the standard cable. Z s ; The second calculation module is used to calculate a total length starting from the grid connection point. l The cable in x=l fWhen local aging occurs at a point, the impedance of the back-end cables and power grid system of the new energy power station after local aging is obtained based on the first calculation module. Z I formula; The positioning module is used to determine the location of local aging defects in the cable under test based on the second frequency point of the impedance spectrum of the cable under test when it is determined that the cable under test is aging.
[0007] Furthermore, the first calculation module determines the mathematical model of the impedance of the back-end cables of the new energy power plant and the power grid system based on the unit Γ-type equivalent circuit model of the standard cable. Z s The specific implementation is as follows: Based on the cable type in the distributed power source enrichment area, a distributed parameter model of the cable is established to determine the equivalent electrical parameters per unit length of the cable. A single segment of a Γ-type equivalent circuit is used per unit length of the cable, with an equivalent resistance of [missing value]. R 0. Equivalent inductance is L 0. Equivalent capacitance is C 0; for a total length of l The cable uses n The ladder-shaped iterative network constructed from the segment Г-type equivalent circuit is used as a replacement; Based on the unit Γ type equivalent circuit model, write... s Formula (1) under the domain is: ; in h 0 indicates that in the unit Γ type equivalent circuit R 0 and L The impedance formed by 0, s 0 indicates that in the unit Γ type equivalent circuit C Admittance composed of 0 h g Represents the equivalent resistance of the power grid R g and equivalent inductance L g The impedance formed; at the same time let ,according to n A trapezoidal iterative network constructed from a segment Г-type equivalent circuit is used to calculate the mathematical model of the impedance of the back-end cables and power grid system of the new energy power plant using a recursive method. Z s See formula (2): ; in and All are about The polynomial.
[0008] Furthermore, the second calculation module takes the grid connection point as its starting position, and its total length is...l The cable in x=l f When local aging occurs at a point, the impedance of the back-end cables and power grid system of the new energy power station after local aging is obtained based on the first calculation module. Z I The specific implementation of the formula is as follows: Starting from the grid connection point, the total length is l The cable in x=l f Localized aging occurs at a point, dividing the cable into two parts: the first region is denoted as Г. I The cable length is l f The impedance formed by the resistive and inductive components corresponding to the cable segment is Z LI The admittance formed by the capacitor is Y LI The second region is denoted as Г. Ⅱ The cable length is l - l f The impedance formed by the inductor and resistor portion corresponding to the cable segment is Z LII The admittance formed by the capacitor is Y LII ; from x=l f Impedance looking towards the power grid side Z Ⅱ The localized aging capacitance to ground is C f Its capacitive reactance expression is X f =1 / sC f Therefore, it was introduced from x=l f Including the impedance looking towards the grid from the aging point Z f Formula (3) is: ; Impedance viewed from the grid connection point towards the grid side Z I Formula (4) is: ; Furthermore, when the positioning module determines that the cable under test is aging, the specific implementation of determining the location of the local aging defect in the cable under test based on the second frequency point of the impedance spectrum of the cable under test is as follows: Z IThe series resonant frequency is determined by the root of formula (5): ; Simplify formula (5) into formula (6): ; Definitions include the back-end impedance of aging capacitors. Z f The impedance formed by the resistive and inductive components corresponding to the cable segment after localized aging capacitance is: Z LI The modulus of the ratio is K s Based on the amplitude-frequency and phase-frequency characteristic curves of the impedance, equation (6) is simplified to real equation (7): ; use r pk This indicates the first... k One solution. Z I The k Series resonant frequency and r pk The general expression for the resonant frequency between them (8) is: ; The inverter control algorithm is set to superimpose every hour into the modulated wave. f 1±1kHz and f A broadband signal around 2±1kHz was collected, and the three-phase voltage and current at the outlet of the distributed power source enrichment area were continuously acquired and Fourier analyzed during system operation to obtain the amplitude-frequency characteristics of the three-phase voltage and current. The amplitude of each phase voltage and current at each frequency point was divided to obtain the broadband impedance spectrum of each phase of the grid-connected point downstream system. The broadband impedance spectrum of each phase includes the impedance of the downstream cable and the power grid system. After data processing, the broadband impedance spectrum of the grid-connected point downstream system was obtained, and the current operating status was recorded. Z I The second series resonant frequency f 2, r p2 The second solution to formula (7) is obtained from the above analysis. f The expression for 2 (9) is: ; From formula (7), we can deduce that the root r pk The value is a polynomial and The x-coordinate of the intersection point, according to the knowledge of polynomials, polynomial The first root Represented as: ; r p2 Approximately equal to Therefore, by combining formulas (9) and (10), we obtain the expression for the local aging distance of cable insulation (11): ; The second series resonant frequency measured under the current operating state f Substituting 2 into formula (11), the distance of local aging of the cable insulation at this time can be obtained. l f .
[0009] This invention effectively avoids the influence of power grid impedance fluctuations and aging, thereby achieving precise localization of aging. Attached Figure Description
[0010] Figure 1 This is a schematic diagram of the equivalent circuit model of a cable unit in the form of a Г shape, according to a preferred embodiment of the present invention. Figure 2 A preferred embodiment of the cable of the present invention N Schematic diagram of the equivalent circuit model of the segment Г type; Figure 3 A schematic diagram of partial aging of cable insulation according to a preferred embodiment of the present invention; Figure 4 A preferred embodiment of the present invention A schematic diagram of the amplitude-frequency and phase-frequency characteristic curves. Detailed Implementation
[0011] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.
[0012] To address the aforementioned problems in the prior art, this invention provides an online method for locating localized aging of cable insulation in distributed power source enrichment areas, comprising the following steps: Step 1: Based on the cable type in the distributed power source enrichment area, establish a distributed parameter model for the cable to determine the equivalent electrical parameters per unit length of the cable, such as... Figure 1 As shown, the cable unit length uses a Г-type equivalent circuit, and its equivalent resistance is... R 0. Equivalent inductance is L 0. Equivalent capacitance is C 0; such as Figure 2 As shown, for a total length of l The cable uses n The ladder-shaped iterative network constructed from the segment Г-type equivalent circuit is used as a replacement; Step 2: Write the equivalent circuit model based on the unit Γ type. s Formula (1) under the domain is: ; in h 0 indicates that in the unit Γ type equivalent circuit R 0 and L The impedance formed by 0, s 0 indicates that in the unit Γ type equivalent circuit C Admittance composed of 0 h g Represents the equivalent resistance of the power grid R g and equivalent inductance L g The impedance formed; at the same time let ,like Figure 2 As shown, according to n A trapezoidal iterative network constructed from a segment Г-type equivalent circuit is used to calculate the mathematical model of the impedance of the back-end cables and power grid system of the new energy power plant using a recursive method. Z s See formula (2), ; in and All are about polynomials; Step 3: As Figure 3 As shown, starting from the grid connection point, the total length is l The cable in x=l f Localized aging occurs at a point, dividing the cable into two parts: the first region is denoted as Г. I The cable length is l f The impedance formed by the resistive and inductive components corresponding to the cable segment is Z LI The admittance formed by the capacitor is Y LI The second region is denoted as Г. Ⅱ The cable length is l - l f The impedance formed by the inductor and resistor portion corresponding to the cable segment is Z LII The admittance formed by the capacitor is Y LII ; from x=l f Impedance looking towards the power grid side Z Ⅱ The localized aging capacitance to ground isC f That is, the capacitive reactance expression is X f =1 / sC f Therefore, it was introduced from x=l f Including the impedance looking towards the grid from the aging point Z f Formula (3) is: ; Impedance viewed from the grid connection point towards the grid side Z I Formula (4) is: ; Step 4: According to the definition of series resonant frequency, Z I The series resonant frequency is calculated by equation (7), and the specific calculation process includes: Z I The series resonant frequency is determined by the root of formula (5): ; Simplify formula (5) into formula (6): ; Definitions include the back-end impedance of aging capacitors. Z f The impedance formed by the resistive and inductive components corresponding to the cable segment after localized aging capacitance is: Z LI The modulus of the ratio is K s ,according to Figure 4 The amplitude-frequency and phase-frequency characteristic curves of the impedance are used to simplify equation (6) into a real equation (7): ; use r pk This indicates the first... k One solution. Z I The k Series resonant frequency and r pk The general expression for the resonant frequency between them (8) is: ; The inverter control algorithm is set to superimpose every hour into the modulated wave. f 1±1kHz and fA broadband signal around 2±1kHz was collected, and the three-phase voltage and current at the outlet of the distributed power source enrichment area were continuously acquired and Fourier analyzed during system operation to obtain the amplitude-frequency characteristics of the three-phase voltage and current. The amplitude of each phase voltage and current at each frequency point was divided to obtain the broadband impedance spectrum of each phase of the grid-connected point downstream system. The broadband impedance spectrum of each phase includes the impedance of the downstream cable and the power grid system. After data processing, the broadband impedance spectrum of the grid-connected point downstream system was obtained, and the current operating status was recorded. Z I The second series resonant frequency f 2, r p2 The second solution to formula (7) is obtained from the above analysis. f The expression for 2 (9) is: ; From formula (7), we can deduce that the root r pk The value is a polynomial and The x-coordinate of the intersection point, according to the knowledge of polynomials, polynomial The first root Represented as: ; r p2 Approximately equal to Therefore, by combining formulas (9) and (10), we obtain the expression for the local aging distance of cable insulation (11): ; Step 5: Measure the second series resonant frequency under the current operating state. f Substituting 2 into formula (11), the distance of local aging of the cable insulation at this time can be obtained. l f This allows for precise location of localized aging in cable insulation.
[0013] To address the aforementioned technical problems, the present invention also provides an online positioning system for localized aging of cable insulation in distributed power source rich areas, comprising a first calculation module, a second calculation module, and a positioning module; The first calculation module is used to determine the mathematical model of the impedance of the back-end cables of the new energy power plant and the power grid system based on the unit Γ-type equivalent circuit model of the standard cable. Z s ; The second calculation module is used to calculate a total length starting from the grid connection point. l The cable in x=l fWhen local aging occurs at a point, the impedance of the back-end cables and power grid system of the new energy power station after local aging is obtained based on the first calculation module. Z I formula; The positioning module is used to determine the location of local aging defects in the cable under test based on the second frequency point of the impedance spectrum of the cable under test when it is determined that the cable under test is aging.
[0014] Optionally, the first calculation module determines the mathematical model of the impedance of the back-end cables of the new energy power plant and the power grid system based on the unit Γ-type equivalent circuit model of the standard cable. Z s The specific implementation is as follows: Based on the cable type in the distributed power source rich area, a distributed parameter model of the cable is established to determine the equivalent electrical parameters per unit length of the cable, such as... Figure 1 As shown, the cable unit length uses a Г-type equivalent circuit, and its equivalent resistance is... R 0. Equivalent inductance is L 0. Equivalent capacitance is C 0; such as Figure 2 As shown, for a total length of l The cable uses n The ladder-shaped iterative network constructed from the segment Г-type equivalent circuit is used as a replacement; Based on the unit Γ type equivalent circuit model, write... s Formula (1) under the domain is: ; in h 0 indicates that in the unit Γ type equivalent circuit R 0 and L The impedance formed by 0, s 0 indicates that in the unit Γ type equivalent circuit C Admittance composed of 0 h g Represents the equivalent resistance of the power grid R g and equivalent inductance L g The impedance formed; at the same time let ,like Figure 2 As shown, according to n A trapezoidal iterative network constructed from a segment Г-type equivalent circuit is used to calculate the mathematical model of the impedance of the back-end cables and power grid system of the new energy power plant using a recursive method. Z s See formula (2): ; in and All are about The polynomial.
[0015] Optionally, the second calculation module starts at the grid connection point and has a total length of l The cable in x=l f When local aging occurs at a point, the impedance of the back-end cables and power grid system of the new energy power station after local aging is obtained based on the first calculation module. Z I The specific implementation of the formula is as follows: like Figure 3 As shown, starting from the grid connection point, the total length is l The cable in x=l f Localized aging occurs at a point, dividing the cable into two parts: the first region is denoted as Г. I The cable length is l f The impedance formed by the resistive and inductive components corresponding to the cable segment is Z LI The admittance formed by the capacitor is Y LI The second region is denoted as Г. Ⅱ The cable length is l - l f The impedance formed by the inductor and resistor portion corresponding to the cable segment is Z LII The admittance formed by the capacitor is Y LII ; from x=l f Impedance looking towards the power grid side Z Ⅱ The localized aging capacitance to ground is C f Its capacitive reactance expression is X f =1 / sC f Therefore, it was introduced from x=l f Including the impedance looking towards the grid from the aging point Z f Formula (3) is: ; Impedance viewed from the grid connection point towards the grid side Z I Formula (4) is: ; Optionally, when the positioning module determines that the cable under test has aging, the specific implementation of determining the location of the local aging defect of the cable under test based on the second frequency point of the impedance spectrum of the cable under test is as follows: Z I The series resonant frequency is determined by the root of formula (5): ; Simplify formula (5) into formula (6): ; Definitions include the back-end impedance of aging capacitors. Z f The impedance formed by the resistive and inductive components corresponding to the cable segment after localized aging capacitance is: Z LI The modulus of the ratio is K s ,according to Figure 4 The amplitude-frequency and phase-frequency characteristic curves of the impedance are used to simplify equation (6) into a real equation (7): ; use r pk This indicates the first... k One solution. Z I The k Series resonant frequency and r pk The general expression for the resonant frequency between them (8) is: ; The inverter control algorithm is set to superimpose every hour into the modulated wave. f 1±1kHz and f A broadband signal around 2±1kHz was collected, and the three-phase voltage and current at the outlet of the distributed power source enrichment area were continuously acquired and Fourier analyzed during system operation to obtain the amplitude-frequency characteristics of the three-phase voltage and current. The amplitude of each phase voltage and current at each frequency point was divided to obtain the broadband impedance spectrum of each phase of the grid-connected point downstream system. The broadband impedance spectrum of each phase includes the impedance of the downstream cable and the power grid system. After data processing, the broadband impedance spectrum of the grid-connected point downstream system was obtained, and the current operating status was recorded. Z I The second series resonant frequency f 2, r p2 The second solution to formula (7) is obtained from the above analysis. f The expression for 2 (9) is: ; From formula (7), we can deduce that the root r pk The value is a polynomial and The x-coordinate of the intersection point, according to the knowledge of polynomials, polynomial The first root Represented as: ; r p2 Approximately equal to Therefore, by combining formulas (9) and (10), we obtain the expression for the local aging distance of cable insulation (11): ; The second series resonant frequency measured under the current operating state f Substituting 2 into formula (11), the distance of local aging of the cable insulation at this time can be obtained. l f .
[0016] This invention effectively avoids the influence of power grid impedance fluctuations and aging, thereby achieving precise localization of aging.
[0017] The following describes specific embodiments based on the preferred embodiments described above: A distributed power source enrichment region model was constructed in the simulation software MATLAB / Simulink, and the parameters of the unit Γ-type equivalent circuit cable were set in the simulation model. R 0 = 0.00010Ω L 0 = 0.00012mH C 0 = 2.7178nF, the mains impedance parameters are R g =1Ω, L g =1mH, the total length of the cable is set to 4km, and it is divided into 1800 segments of Г-type equivalent circuit.
[0018] Four cable insulation capacitance aging values and four different aging points were set, totaling twenty sets of data. Table 1 shows the results of local aging location when the cable insulation condition changes.
[0019] Table 1: ;
[0020] Based on the above results, when C When 0 remains constant, the local aging positioning error of the cable insulation is within 5%; when l fWhen the value remains constant, the error in locating local aging of cable insulation decreases as the degree of aging increases, which effectively demonstrates the accuracy of online monitoring of local aging of cable insulation in distributed power supply-rich areas.
[0021] The above-described technical solutions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A method for online location of localized aging of cable insulation in distributed power source enrichment areas, characterized in that, Includes the following steps: Step 1: Based on the cable type in the distributed power source enrichment area, establish a distributed parameter model for the cable, determine the equivalent electrical parameters per unit length of the cable, and adopt a Γ-type equivalent circuit per unit length of the cable, with an equivalent resistance of [missing value]. R 0. Equivalent inductance is L 0. Equivalent capacitance is C 0; for a total length of l The cable uses n The ladder-shaped iterative network constructed from the segment Г-type equivalent circuit is used as a replacement; Step 2: Write the equivalent circuit model based on the unit Γ type. s Formula (1) under the domain is: ; in h 0 indicates that in the unit Γ type equivalent circuit R 0 and L The impedance formed by 0, s 0 indicates that in the unit Γ type equivalent circuit C Admittance composed of 0 h g Represents the equivalent resistance of the power grid R g and equivalent inductance L g The impedance formed; at the same time let ,according to n A trapezoidal iterative network constructed from a segment Г-type equivalent circuit is used to calculate the mathematical model of the impedance of the back-end cables and power grid system of the new energy power plant using a recursive method. Z s See formula (2): ; in and All are about polynomials; Step 3: Starting from the grid connection point, the total length is... l The cable in x=l f Localized aging occurs at a point, dividing the cable into two parts: the first region is denoted as Г. I The cable length is l f The impedance formed by the resistive and inductive components corresponding to the cable segment is Z LI The admittance formed by the capacitor is Y LI The second region is denoted as Г. Ⅱ The cable length is l - l f The impedance formed by the inductor and resistor portion corresponding to the cable segment is Z LII The admittance formed by the capacitor is Y LII ; from x=l f Impedance looking towards the power grid side Z Ⅱ The localized aging capacitance to ground is C f That is, the capacitive reactance expression is X f =1 / sC f Therefore, it was introduced from x=l f Including the impedance looking towards the grid from the aging point Z f Formula (3) is: ; Impedance viewed from the grid connection point towards the grid side Z I Formula (4) is: ； Step 4: According to the definition of series resonant frequency, Z I The series resonant frequency is calculated by equation (7), and the specific calculation process includes: Z I The series resonant frequency is determined by the root of formula (5): ; Simplify formula (5) into formula (6): ; Definitions include the back-end impedance of aging capacitors. Z f The impedance formed by the resistive and inductive components corresponding to the cable segment after localized aging capacitance is: Z LI The modulus of the ratio is K s Based on the amplitude-frequency and phase-frequency characteristic curves of the impedance, equation (6) is simplified to real equation (7): ; use r pk This indicates the first... k One solution. Z I The k Series resonant frequency and r pk resonant frequency between f k The general term expression (8) is: ; The inverter control algorithm is set to superimpose every hour into the modulated wave. f 1±1kHz and f A broadband signal around 2±1kHz was collected, and the three-phase voltage and current at the outlet of the distributed power source enrichment area were continuously acquired and Fourier analyzed during system operation to obtain the amplitude-frequency characteristics of the three-phase voltage and current. The amplitude of each phase voltage and current at each frequency point was divided to obtain the broadband impedance spectrum of each phase of the grid-connected point downstream system. The broadband impedance spectrum of each phase includes the impedance of the downstream cable and the power grid system. After data processing, the broadband impedance spectrum of the grid-connected point downstream system was obtained, and the current operating status was recorded. Z I The second series resonant frequency f 2, r p2 The second solution to formula (7) is obtained from the above analysis. f The expression for 2 (9) is: ; From formula (7), we can deduce that the root r pk The value is a polynomial and The x-coordinate of the intersection point, according to the knowledge of polynomials, polynomial The first root Represented as: ; r p2 Approximately equal to Therefore, by combining formulas (9) and (10), we obtain the expression for the local aging distance of cable insulation (11): ； Step 5: Measure the second series resonant frequency under the current operating state. f Substituting 2 into formula (11), the distance of local aging of the cable insulation at this time can be obtained. l f .
2. An online positioning system for localized aging of cable insulation in distributed power source enrichment areas, characterized in that: It includes a first computing module, a second computing module, and a positioning module; The first calculation module is used to determine the mathematical model of the impedance of the back-end cables of the new energy power plant and the power grid system based on the unit Γ-type equivalent circuit model of the standard cable. Z s ; The second calculation module is used to calculate a total length starting from the grid connection point. l The cable in x=l f When local aging occurs at a point, the impedance of the back-end cables and power grid system of the new energy power station after local aging is obtained based on the first calculation module. Z I formula; The positioning module is used to determine the location of local aging defects in the cable under test based on the second frequency point of the impedance spectrum of the cable under test when it is determined that the cable under test is aging.
3. The online positioning system for localized aging of cable insulation in distributed power supply rich areas according to claim 2, characterized in that: The first calculation module determines the mathematical model of the impedance of the back-end cables and power grid system of the new energy power plant based on the unit Γ-type equivalent circuit model of the standard cable. Z s The specific implementation is as follows: Based on the cable type in the distributed power source enrichment area, a distributed parameter model of the cable is established to determine the equivalent electrical parameters per unit length of the cable. A single segment of a Γ-type equivalent circuit is used per unit length of the cable, with an equivalent resistance of [missing value]. R 0. Equivalent inductance is L 0. Equivalent capacitance is C 0; for a total length of l The cable uses n The ladder-shaped iterative network constructed from the segment Г-type equivalent circuit is used as a replacement; Based on the unit Γ type equivalent circuit model, write... s Formula (1) under the domain is: ; in h 0 indicates that in the unit Γ type equivalent circuit R 0 and L The impedance formed by 0, s 0 indicates that in the unit Γ type equivalent circuit C Admittance composed of 0 h g Represents the equivalent resistance of the power grid R g and equivalent inductance L g The impedance formed; at the same time let ,according to n A trapezoidal iterative network constructed from a segment Г-type equivalent circuit is used to calculate the mathematical model of the impedance of the back-end cables and power grid system of the new energy power plant using a recursive method. Z s See formula (2): ; in and All are about The polynomial.
4. The online positioning system for localized aging of cable insulation in distributed power source enrichment areas according to claim 2, characterized in that: The second calculation module starts at the grid connection point and has a total length of l The cable in x=l f When local aging occurs at a point, the impedance of the back-end cables and power grid system of the new energy power station after local aging is obtained based on the first calculation module. Z I The specific implementation of the formula is as follows: Starting from the grid connection point, the total length is l The cable in x=l f Localized aging occurs at a point, dividing the cable into two parts: the first region is denoted as Г. I The cable length is l f The impedance formed by the resistive and inductive components corresponding to the cable segment is Z LI The admittance formed by the capacitor is Y LI The second region is denoted as Г. Ⅱ The cable length is l - l f The impedance formed by the inductor and resistor portion corresponding to the cable segment is Z LII The admittance formed by the capacitor is Y LII ; from x=l f Impedance looking towards the power grid side Z Ⅱ The localized aging capacitance to ground is C f Its capacitive reactance expression is X f =1 / sC f Therefore, it was introduced from x=l f Including the impedance looking towards the grid from the aging point Z f Formula (3) is: ; Impedance viewed from the grid connection point towards the grid side Z I Formula (4) is: 。 5. The online positioning system for localized aging of cable insulation in distributed power source enrichment areas according to claim 2, 3, or 4, characterized in that: When the positioning module determines that the cable under test is aging, it determines the location of the local aging defect in the cable under test based on the second frequency point of the impedance spectrum of the cable under test as follows: Z I The series resonant frequency is determined by the root of formula (5): ; Simplify formula (5) into formula (6): ; Definitions include the back-end impedance of aging capacitors. Z f The impedance formed by the resistive and inductive components corresponding to the cable segment after localized aging capacitance is: Z LI The modulus of the ratio is K s Based on the amplitude-frequency and phase-frequency characteristic curves of the impedance, equation (6) is simplified to real equation (7): ; use r pk This indicates the first... k One solution. Z I The k Series resonant frequency and r pk resonant frequency between f k The general term expression (8) is: ; The inverter control algorithm is set to superimpose every hour into the modulated wave. f 1±1kHz and f A broadband signal around 2±1kHz was collected, and the three-phase voltage and current at the outlet of the distributed power source enrichment area were continuously acquired and Fourier analyzed during system operation to obtain the amplitude-frequency characteristics of the three-phase voltage and current. The amplitude of each phase voltage and current at each frequency point was divided to obtain the broadband impedance spectrum of each phase of the grid-connected point downstream system. The broadband impedance spectrum of each phase includes the impedance of the downstream cable and the power grid system. After data processing, the broadband impedance spectrum of the grid-connected point downstream system was obtained, and the current operating status was recorded. Z I The second series resonant frequency f 2, r p2 The second solution to formula (7) is obtained from the above analysis. f The expression for 2 (9) is: ; From formula (7), we can deduce that the root r pk The value is a polynomial and The x-coordinate of the intersection point, according to the knowledge of polynomials, polynomial The first root Represented as: ; r p2 Approximately equal to Therefore, by combining formulas (9) and (10), we obtain the expression for the local aging distance of cable insulation (11): ; The second series resonant frequency measured under the current operating state f Substituting 2 into formula (11), the distance of local aging of the cable insulation at this time can be obtained. l f .