High-voltage cable state live detection method and system

Abstract

The invention discloses a high-voltage cable state live detection method, which relates to the technical field of power detection, and is characterized in that a mathematical model of an electric field around a cable is established by using an electrostatic field equation in a Maxwell equation set, and electric field distribution between a cable insulation layer and a conductor is solved; high-frequency electromagnetic pulse signals are measured, and partial discharge detection in the insulating layer of the high-voltage cable is carried out according to a Paschen curve model; the temperature distribution change in the cable is simulated through a heat transfer equation, and the temperature distribution of the cable is monitored in real time by using a fiber bragg grating sensor; and correcting the electric field distribution and the partial discharge detection result based on the obtained temperature distribution of the cable. The partial discharge phenomenon in the cable insulation layer can be accurately identified and positioned, the insulation state of the cable can be monitored in real time, whether the discharge phenomenon exists or not can be rapidly judged, and therefore cable faults can be effectively prevented.

Description

Technical Field

[0001] The present invention relates to the technical field of electric power detection, and more specifically, to a method and system for detecting the state of a high-voltage cable. Background Art

[0002] Live identification and detection of high-voltage cables is an important part of ensuring the safe operation of the power system. It has the following advantages: Through detection, insulation defects and damage of cables can be discovered in time, power outages caused by cable failures can be prevented, and the stable operation of the power system can be ensured; through live detection technology, the cable status can be detected without power outages, reducing the time and cost of power outage maintenance.

[0003] The existing high-voltage cable status live detection method is difficult to accurately reflect the changes in the insulation performance of the cable under actual working conditions. In addition, due to the influence of ambient temperature changes on the insulating material cable, it will lead to misjudgment of discharge detection and the risk of local overheating of the cable not being discovered in time. Therefore, how to research and design a high-voltage cable status live detection method and system that can overcome the above defects is an issue that we urgently need to solve. Summary of the invention

[0004] In order to solve the deficiencies in the prior art, the purpose of the present invention is to provide a method and system for detecting the status of a high-voltage cable. By combining high-frequency electromagnetic pulse signal detection with the Paschen curve model, the accurate identification and positioning of the local discharge phenomenon in the cable insulation layer can be achieved. By measuring the actual air gap size and pressure and calculating the discharge starting voltage, the present invention can monitor the insulation status of the cable in real time, quickly determine whether there is a discharge phenomenon, and thus effectively prevent cable failures.

[0005] The above technical objectives of the present invention are achieved through the following technical solutions:

[0006] In a first aspect, a method for detecting a high voltage cable status is provided, comprising the following steps:

[0007] S1. Using the electrostatic field equations in Maxwell's equations, a mathematical model of the electric field around the cable is established, and the electric field distribution between the cable insulation layer and the conductor is solved;

[0008] S2. Detect local discharge in the insulation layer of high-voltage cables by measuring high-frequency electromagnetic pulse signals and based on the Paschen curve model;

[0009] S3, simulating the temperature distribution change inside the cable through the heat transfer equation, and using the fiber Bragg grating sensor to monitor the temperature distribution of the cable in real time;

[0010] S4. Correcting the electric field distribution and partial discharge detection results based on the obtained temperature distribution of the cable.

[0011] Furthermore, in S1, the electrostatic field equations in Maxwell's equations are used to establish a mathematical model of the electric field around the cable, and solve the electric field distribution between the cable insulation layer and the conductor. The specific steps are as follows:

[0012] S1.1. Establish a mathematical model of the electric field E around the cable through the electrostatic field equations in Maxwell's equations;

[0013] S1.2, using the finite element method to solve the potential value V of the electric field E;

[0014] S1.3. Based on the potential distribution data of the electric field E, the areas of high electric field strength are identified, and the insulation defects and damaged areas are detected by comparing the actually measured electric field data with the calculated electric field distribution.

[0015] Furthermore, in S1.1, a mathematical model of the electric field E around the cable is established by using the electrostatic field equations in the Maxwell equations, and the specific steps are as follows:

[0016] S1.1.1. Determine the electrostatic field equations satisfied by the electric field E;

[0017] S1.1.2, the electric field equation for the potential V;

[0018] S1.1.3. Substitute the electric field equation into the electrostatic field equation to obtain the Poisson equation.

[0019] Furthermore, in S1.2, the finite element method is used to solve the potential distribution of the electric field E, and the specific steps are as follows:

[0020] S1.2.1. Divide the calculated cross section of the cable into multiple small units, and the vertex of each unit is called a node;

[0021] S1.2.2. At each unit, the potential V is approximated as a linear combination of the node potentials, and the shape function is used to describe the contribution of each node to the unit potential;

[0022] S1.2.3. Use the weak form of Laplace's equation to multiply by the shape function to construct the weak form equation, and apply Gauss's theorem to optimize the weak form equation;

[0023] S1.2.4. For each unit, construct a local element stiffness matrix and calculate the stiffness matrix elements of each unit using Gaussian integral;

[0024] S1.2.5, assemble the local stiffness matrices of all elements into a global stiffness matrix;

[0025] S1.2.6. Use the conjugate gradient method to solve the global stiffness matrix and obtain the potential value of each node.

[0026] Further, in S2, by measuring the high-frequency electromagnetic pulse signal, and performing partial discharge detection in the insulation layer of the high-voltage cable according to the Paschen curve model, and performing spectrum analysis on the detected discharge signal, the intensity and position of the partial discharge inside the cable are determined, and the specific steps are as follows:

[0027] S2.1. Use a current sensor to capture the high-frequency current pulse signal generated by discharge, use a voltage sensor to measure the high-frequency voltage pulse signal generated by discharge, and use an ultrasonic sensor to capture the ultrasonic signal generated by partial discharge;

[0028] S2.2. Measure the actual air gap size d and pressure p, and calculate the discharge starting voltage V according to the Paschen curve model start ;

[0029] S2.3. By comparing the measured voltage with the starting voltage calculated by the Paschen curve, it is determined whether the current voltage exceeds the discharge starting voltage.

[0030] Furthermore, in S2.3, by comparing the measured voltage with the starting voltage calculated by the Paschen curve, it is determined whether the current voltage exceeds the discharge starting voltage. The specific steps are as follows:

[0031] S2.3.1. Determine the discharge start voltage V start Then, measure the voltage V currently applied to the cable measured ;

[0032] S2.3.2, if V measured >V start , it means that the electric field strength applied to the air gap has exceeded its breakdown strength and partial discharge may occur;

[0033] S2.3.3, if V measured ≤V start , it means that the electric field strength is not enough to cause discharge, the insulation layer is in a safe state, and no local discharge occurs.

[0034] Furthermore, in S3, the temperature distribution change inside the cable is simulated by the heat transfer equation, and the temperature of the cable is monitored in real time using a fiber Bragg grating sensor. The specific steps are as follows:

[0035] S3.1. Use the heat transfer equation to simulate the temperature distribution changes inside the cable;

[0036] S3.2. Use explicit finite difference method to discretize time. Assume that the spacing of spatial grid points is Δx and Δy, and the points are divided into i and j in the x and y directions respectively. Then the temperature field T(x, y, t) at the discrete point (i, j) is expressed as Where n represents the time step;

[0037] S3.3, use explicit finite difference method to discretize the space, set the time step to Δt, and set the initial temperature distribution The temperature field at time step n is expressed as The temperature field at time step n+1 is expressed as

[0038] S3.4. Discretization of the Laplace operator using the central difference method And obtain the finite difference equation in explicit format;

[0039] S3.5. For each time step n, calculate the temperature at all nodes (i, j) And the temperature distribution at time n+1 is used as the initial temperature distribution of the next time step.

[0040] Furthermore, in S4, the electric field distribution and the partial discharge detection result are corrected based on the obtained temperature distribution of the cable, and the specific steps are as follows:

[0041] S4.1. Using the temperature distribution data, calculate the dielectric constant ∈ of the cable internal grid point (i, j) i，j (T), and according to the dielectric constant ∈ i , j (T) Recalculate the electric field E distribution inside the cable;

[0042] S4.2. Using the temperature distribution data, calculate the temperature-dependent breakdown voltage V at the cable internal grid point (i, j). breakdown，i，j , and recalculate the partial discharge starting voltage V start , i , j ;

[0043] S4.3, combined with the updated electric field E distribution and the adjusted partial discharge inception voltage V start , re-determine the current measured voltage V measured , i , j Whether it exceeds the discharge starting voltage V start , i , j .

[0044] Furthermore, in S4.3, the updated electric field E distribution and the adjusted partial discharge inception voltage V start , re-determine the current measured voltage V measured,i,j Whether it exceeds the discharge starting voltage V start,i,j , the specific steps are as follows:

[0045] S4.3.1, if V measured,i,j >V start,i,j, it means that the electric field strength applied to the air gap has exceeded its breakdown strength, and partial discharge occurs;

[0046] S4.3.2, if V measured,i,j ≤V start,i,j , it means that the electric field strength is not enough to cause discharge, the insulation layer is in a safe state, and no local discharge occurs.

[0047] In a second aspect, a high-voltage cable status live detection system is provided, the system is used to implement a high-voltage cable status live detection method as described in any one of the first aspects, including:

[0048] The electric field distribution solving module is used to establish a mathematical model of the electric field around the cable using the electrostatic field equations in the Maxwell equations, and solve the electric field distribution between the cable insulation layer and the conductor;

[0049] A partial discharge detection module is used to detect partial discharge in the insulation layer of a high-voltage cable by measuring high-frequency electromagnetic pulse signals and based on a Paschen curve model;

[0050] The temperature distribution simulation module is used to simulate the temperature distribution changes inside the cable through the heat transfer equation and use the fiber Bragg grating sensor to monitor the temperature distribution of the cable in real time;

[0051] The detection result correction module is used to correct the electric field distribution and partial discharge detection results based on the obtained temperature distribution of the cable.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] 1. A method for detecting the charged state of a high-voltage cable provided by the present invention realizes accurate identification and positioning of the local discharge phenomenon in the cable insulation layer by combining high-frequency electromagnetic pulse signal detection with the Paschen curve model; by measuring the actual air gap size and pressure and calculating the discharge starting voltage, the present invention can monitor the insulation state of the cable in real time, quickly determine whether there is a discharge phenomenon, and thus effectively prevent cable failures;

[0054] 2. The present invention corrects the electric field distribution and partial discharge detection model based on temperature distribution data, which can more accurately evaluate the electrical performance of the cable insulation layer, identify potential insulation defects and partial discharge risk areas, and calculate the temperature-dependent dielectric constant and breakdown voltage. This method takes into account the electrical properties of the insulating material that change with temperature, thereby improving the accuracy and reliability of detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0056] Figure 1 is a flow chart of Embodiment 1 of the present invention;

[0057] Figure 2 It is a system block diagram in Example 2 of the present invention. DETAILED DESCRIPTION

[0058] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0059] Embodiment 1:

[0060] See also Figure 1 As shown, this embodiment provides a method for detecting the state of a high-voltage cable, comprising the following steps:

[0061] S1. Using the electrostatic field equations in Maxwell's equations, a mathematical model of the electric field around the cable is established, and the electric field distribution between the cable insulation layer and the conductor is solved;

[0062] By using the electrostatic field equations in Maxwell's equations to establish a mathematical model of the electric field around the cable, we can accurately describe the electric field distribution between the cable insulation layer and the conductor, identify areas with high electric field intensity, and accurately locate possible insulation weaknesses or defective areas in the cable, thereby effectively improving the accuracy and reliability of partial discharge detection and providing an important theoretical basis and data support for the safe operation and maintenance of high-voltage cables.

[0063] In this embodiment S1, the electrostatic field equations in Maxwell's equations are used to establish a mathematical model of the electric field around the cable, and solve the electric field distribution between the cable insulation layer and the conductor. The specific steps are as follows:

[0064] S1.1. Establish a mathematical model of the electric field E around the cable through the electrostatic field equations in Maxwell's equations;

[0065] S1.2, using the finite element method to solve the potential value V of the electric field E;

[0066] S1.3. Based on the potential distribution data of the electric field E, identify areas with higher electric field strength, and detect insulation defects and damaged areas by comparing the actual measured electric field data with the calculated electric field distribution.

[0067] In this embodiment S1.1, a mathematical model of the electric field E around the cable is established by using the electrostatic field equation in the Maxwell equations. The specific steps are as follows:

[0068] S1.1.1. The electric field E satisfies the electrostatic field equation:

[0069]

[0070] S1.1.2 For a potential V, the electric field can be expressed as:

[0071]

[0072] S1.1.3. Substituting into the electrostatic field equation, we get Poisson's equation:

[0073]

[0074] Among them, ∈ is the dielectric constant of the insulating material, which is measured at standard temperature T0; ρ is the space charge density.

[0075] In this embodiment, the finite element method is used to solve the potential distribution of the electric field E, and the specific steps are as follows:

[0076] S1.2.1. Divide the calculated cross section of the cable into multiple small units, and the vertex of each unit is called a node;

[0077] S1.2.2. At each unit, the potential V is approximately a linear combination of the node potentials. The shape function is used to describe the contribution of each node to the unit potential. The potential V in each unit is expressed as:

[0078] V(x,y)=N1(x,y)V1+N2(x,y)V2+N3(x,y)V3;

[0079] Among them, N i (x, y) is the shape function at point (x, y); V i is the potential value on the unit node; V(x, y) is the potential at point (x, y);

[0080] Using shape functions to describe the contribution of each node to the unit potential can achieve accurate approximation of the electric field distribution and effective expression of local details. In the high-voltage cable status live detection method of this embodiment, this advantage enables the finite element method to flexibly simulate the potential distribution of complex cable structures and perform higher-precision calculations in key areas, thereby more accurately identifying local defects and high electric field strength areas in the insulation layer, and improving the accuracy and reliability of the detection results.

[0081] S1.2.3. Use the weak form of Laplace's equation multiplied by the shape function N i (x, y) constructs the weak form equation:

[0082]

[0083] Applying Gauss's theorem to optimize the weak form equation is:

[0084]

[0085] in, is the boundary of the solution domain; n is the unit normal vector of the boundary;

[0086] The Laplace equation is a second-order partial differential equation that describes the steady-state field distribution. In the high-voltage cable state live detection method of this embodiment, the weak form of the Laplace equation is multiplied by the shape function to construct a weak form equation, which can transform a complex continuous field problem into a numerical calculation problem in a finite dimension. The advantage is that it allows accurate solution of the electric field distribution in an uneven and complex geometric structure, improves the recognition accuracy of cable insulation defects and partial discharge areas, and thus more effectively detects and prevents potential cable faults.

[0087] S1.2.4. For each element, construct a local element stiffness matrix and use Gaussian integral to calculate the stiffness matrix element of each element

[0088]

[0089] in, is the local element stiffness matrix element; Ω e is the volume of unit e, which refers to the area of ​​a finite element in the cable model; is the shape function N i The gradient of is the shape function N j The gradient of

[0090] The stiffness matrix of each finite element is constructed by calculating the inner product of the dielectric constant ∈ and the gradient of the shape function, and using the Gaussian integration method, these matrix elements can be numerically solved to achieve accurate modeling of the electric field distribution inside the cable.

[0091] S1.2.5. Assemble the local stiffness matrices of all elements into a global stiffness matrix K:

[0092] KV=F;

[0093] Among them, K is the global stiffness matrix, which contains the electric field coupling information of all units; V is the global node potential vector; F is the global load vector, which includes the contribution of boundary conditions and external charges;

[0094] S1.2.6. Use the conjugate gradient method to solve KV=F to obtain the potential value V of each node.

[0095] The conjugate gradient method is an efficient iterative algorithm specifically used to solve large-scale symmetric positive definite sparse linear equations. In the high-voltage cable state live detection method of this embodiment, the advantage of using the conjugate gradient method is that it can quickly and efficiently solve the large-scale linear equations generated by the finite element method discretization, thereby accurately calculating the potential distribution of each node inside the cable.

[0096] S2. Detect local discharge in the insulation layer of high-voltage cables by measuring high-frequency electromagnetic pulse signals and based on the Paschen curve model;

[0097] In this embodiment S2, by measuring the high-frequency electromagnetic pulse signal, and performing partial discharge detection in the insulation layer of the high-voltage cable according to the Paschen curve model, and performing spectrum analysis on the detected discharge signal, the intensity and position of the partial discharge inside the cable are determined. The specific steps are as follows:

[0098] S2.1. Use a current sensor to capture the high-frequency current pulse signal generated by discharge, use a voltage sensor to measure the high-frequency voltage pulse signal generated by discharge, and use an ultrasonic sensor to capture the ultrasonic signal generated by partial discharge;

[0099] S2.2. Measure the actual air gap size d and pressure p, and calculate the discharge starting voltage V according to the Paschen curve model start ;

[0100] S2.3. By comparing the measured voltage with the starting voltage calculated by the Paschen curve, it is determined whether the current voltage exceeds the discharge starting voltage.

[0101] In this embodiment S2.2, the actual air gap size d and gas pressure p are measured, and the discharge starting voltage V is calculated according to the Paschen curve model. start , the specific steps are as follows:

[0102]

[0103] Among them, V start is the discharge starting voltage; p is the gas pressure; d is the air gap size; A and B are the gas constants of the Paschen curve; γ is the secondary electron emission coefficient;

[0104] In this embodiment:

[0105] Air gap size d: The air gap size in the cable insulation layer can be accurately measured by non-contact measurement techniques such as ultrasonic rangefinders or electromagnetic wave reflection methods;

[0106] Gas pressure p: The pressure in the air gap can be measured by a pressure sensor. The air gap pressure in the cable insulation layer is usually close to the ambient atmospheric pressure, but may vary due to local air tightness or other environmental conditions;

[0107] The specific value of the secondary electron emission coefficient usually depends on the properties of the electrode material and the type of surrounding gas, and needs to be determined through experimental measurement;

[0108] In this embodiment S2.3, by comparing the measured voltage with the starting voltage calculated by the Paschen curve, it is determined whether the current voltage exceeds the discharge starting voltage. The specific steps are as follows:

[0109] S2.3.1. Determine the discharge start voltage V start Then, measure the voltage V currently applied to the cable measured ;

[0110] S2.3.2, if V measured >V start , it means that the electric field strength applied to the air gap has exceeded its breakdown strength and partial discharge may occur;

[0111] S2.3.3, if V measured ≤V start , it means that the electric field strength is not enough to cause discharge, the insulation layer is in a safe state, and no local discharge occurs.

[0112] S3, simulating the temperature distribution change inside the cable through the heat transfer equation, and using the fiber Bragg grating sensor to monitor the temperature distribution of the cable in real time;

[0113] In this embodiment S3, the temperature distribution change inside the cable is simulated by the heat transfer equation, and the temperature of the cable is monitored in real time using a fiber Bragg grating sensor. The specific steps are as follows:

[0114] S3.1. Use the heat transfer equation to simulate the temperature distribution changes inside the cable;

[0115] S3.2. Use explicit finite difference method to discretize time. Assume that the spacing of spatial grid points is Δx and Δy, and the points are divided into i and j in the x and y directions respectively. Then the temperature field T(x, y, t) at the discrete point (i, j) is expressed as Where n represents the time step;

[0116] S3.3, use explicit finite difference method to discretize the space, set the time step to Δt, and set the initial temperature distribution The temperature field at time step n is expressed as The temperature field at time step n+1 is expressed as

[0117] In this embodiment, the finite difference method is a numerical calculation method, which discretizes the continuous partial differential equation on a discrete grid to approximately solve the evolution of the physical field. The advantage of the finite difference method is that it can discretize the complex heat transfer process inside the cable into a series of time steps and temperature calculations of spatial points, and can quickly iterate and calculate the temperature distribution change using an explicit format. Through this method, the temperature change of the cable insulation layer can be monitored in real time, and potential hot spots and local overheating phenomena can be accurately captured;

[0118] S3.4. Discretization of the Laplace operator using the central difference method And obtain the finite difference equation in explicit format;

[0119] Discretizing the Laplace operator using the central difference method In the context of the method for detecting the state of high-voltage cables in this embodiment, this method can accurately simulate the spatial distribution of the temperature field inside the cable, quickly iterate and calculate the temperature change, and provide accurate temperature data support for subsequent electric field distribution correction and partial discharge detection;

[0120] S3.5. For each time step n, calculate the temperature at all nodes (i, j) And the temperature distribution at time n+1 is used as the initial temperature distribution of the next time step.

[0121] In this embodiment S3.1, the heat transfer equation is used to simulate the temperature distribution change inside the cable. The specific steps are as follows:

[0122]

[0123] Where T = T (x, y, z, t) is the temperature field, which depends on the spatial coordinates (x, y, z) and time t; is the thermal diffusion coefficient; k is the thermal conductivity; ρ is the density; c p is the specific heat capacity; Q is the internal heat source intensity;

[0124] In this embodiment S3.4, the central difference method is used to discretize the Laplace operator And get the finite difference equation in explicit format. The specific steps are as follows:

[0125] Laplace operator The discrete form of is:

[0126]

[0127] in, is the temperature value of the temperature field at the discrete grid point (i, j), the temperature at time step n;

[0128] Finite difference equations in explicit form:

[0129]

[0130] Among them, Q i，j is the heat source intensity at the discrete grid point (i, j).

[0131] S4, correcting the electric field distribution and partial discharge detection results based on the obtained temperature distribution of the cable;

[0132] In the context of the method for detecting the state of high-voltage cables in this embodiment, the advantage of correcting the electric field distribution and partial discharge detection results based on the obtained cable temperature distribution is that it can incorporate the temperature change factor under actual operating conditions into the evaluation of the cable insulation state; this correction method can more accurately reflect the changes in the electrical properties of the insulating material at different temperatures, adjust the dielectric constant and breakdown voltage, and thus improve the accuracy of the electric field distribution calculation and partial discharge detection;

[0133] In this embodiment S4, the electric field distribution and the partial discharge detection result are corrected based on the obtained temperature distribution of the cable, and the specific steps are as follows:

[0134] S4.1. Using the temperature distribution data, calculate the dielectric constant ∈ of the cable internal grid point (i, j) i，j (T), and according to the dielectric constant ∈ i , j (T) Recalculate the electric field E distribution inside the cable;

[0135] S4.2. Using the temperature distribution data, calculate the temperature-dependent breakdown voltage V at the cable internal grid point (i, j). breakdown，i，j , and recalculate the partial discharge starting voltage V start , i , j ;

[0136] S4.3, combined with the updated electric field E distribution and the adjusted partial discharge inception voltage V start , re-determine the current measured voltage V measured , i , j Whether it exceeds the discharge starting voltage V start , i , j .

[0137] In this embodiment S4.1, the dielectric constant ∈ of the cable internal grid point (i, j) is calculated. i，j (T), the specific steps are as follows:

[0138] ∈ i , j (T)=∈(1+β(T i ,j -T0);

[0139] Among them, ∈ i，j (T) is the dielectric constant of the grid point (i, j) at temperature T; β is the temperature coefficient of the dielectric constant; T i，j is the actual temperature of the grid point (i, j); T0 is the standard temperature;

[0140] In S4.2, the temperature distribution data is used to calculate the temperature-dependent breakdown voltage V at the grid point (i, j) inside the cable. breakdown , i , j , and recalculate the partial discharge starting voltage V start , i , j , the specific steps are as follows:

[0141] V breakdown , i , j =V breakdown ,0exp(-α(T i , j -T0);

[0142]

[0143] In S4.3, the updated electric field E distribution and the adjusted partial discharge inception voltage V start , re-determine the current measured voltage V measured , i , j Whether it exceeds the discharge starting voltage V start , i , j , the specific steps are as follows:

[0144] S4.3.1, if V measured , i , j >V start , i , j , it means that the electric field strength applied to the air gap has exceeded its breakdown strength, and partial discharge occurs;

[0145] S4.3.2, if V measured , i , j ≤V start , i , j , it means that the electric field strength is not enough to cause discharge, the insulation layer is in a safe state, and no local discharge occurs.

[0146] Embodiment 2:

[0147] See also Figure 2 As shown, this embodiment provides a high-voltage cable status live detection system, which is used to implement a high-voltage cable status live detection method as described in Example 1, including an electric field distribution solution module, a partial discharge detection module, a temperature distribution simulation module and a detection result correction module.

[0148] Among them, the electric field distribution solving module is used to use the electrostatic field equations in the Maxwell equations to establish a mathematical model of the electric field around the cable and solve the electric field distribution between the cable insulation layer and the conductor; the partial discharge detection module is used to measure high-frequency electromagnetic pulse signals and perform partial discharge detection in the insulation layer of the high-voltage cable based on the Paschen curve model; the temperature distribution simulation module is used to simulate the temperature distribution changes inside the cable through the heat transfer equation, and use the fiber Bragg grating sensor to monitor the temperature distribution of the cable in real time; the detection result correction module is used to correct the electric field distribution and partial discharge detection results based on the obtained cable temperature distribution.

[0149] Working principle: The present invention combines high-frequency electromagnetic pulse signal detection with the Paschen curve model to achieve accurate identification and positioning of local discharge phenomena in the cable insulation layer; by measuring the actual air gap size and pressure and calculating the discharge starting voltage, the present invention can monitor the insulation status of the cable in real time, quickly determine whether there is a discharge phenomenon, and thus effectively prevent cable failures.

[0150] In addition, the present invention corrects the electric field distribution and partial discharge detection model based on temperature distribution data, which can more accurately evaluate the electrical properties of the cable insulation layer, identify potential insulation defects and partial discharge risk areas, and by calculating the temperature-dependent dielectric constant and breakdown voltage, this method takes into account the electrical properties of the insulating material that change with temperature, thereby improving the accuracy and reliability of detection.

[0151] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for detecting the state of a high-voltage cable, characterized in that: The following steps are involved: S1. Using the electrostatic field equations in Maxwell's equations, a mathematical model of the electric field around the cable is established, and the electric field distribution between the cable insulation layer and the conductor is solved; S2. Detect local discharge in the insulation layer of high-voltage cables by measuring high-frequency electromagnetic pulse signals and based on the Paschen curve model; S3, simulating the temperature distribution change inside the cable through the heat transfer equation, and using the fiber Bragg grating sensor to monitor the temperature distribution of the cable in real time; S4. Correcting the electric field distribution and partial discharge detection results based on the obtained temperature distribution of the cable.

2. A method for detecting the state of a high-voltage cable according to claim 1, characterized in that: In S1, the electrostatic field equations in Maxwell's equations are used to establish a mathematical model of the electric field around the cable, and solve the electric field distribution between the cable insulation layer and the conductor. The specific steps are as follows: S1.

1. Establish a mathematical model of the electric field E around the cable through the electrostatic field equations in Maxwell's equations; S1.2, using the finite element method to solve the potential value V of the electric field E; S1.

3. Based on the potential distribution data of the electric field E, the areas of high electric field strength are identified, and the insulation defects and damaged areas are detected by comparing the actually measured electric field data with the calculated electric field distribution.

3. A method for detecting the state of a high-voltage cable according to claim 2, characterized in that: In S1.1, a mathematical model of the electric field E around the cable is established by using the electrostatic field equations in the Maxwell equations. The specific steps are as follows: S1.1.

1. Determine the electrostatic field equations satisfied by the electric field E; S1.1.2, the electric field equation for the potential V; S1.1.

3. Substitute the electric field equation into the electrostatic field equation to obtain the Poisson equation.

4. A method for detecting the state of a high-voltage cable according to claim 2, characterized in that: In S1.2, the finite element method is used to solve the potential distribution of the electric field E. The specific steps are as follows: S1.2.

1. Divide the calculated cross section of the cable into multiple small units, and the vertex of each unit is called a node; S1.2.

2. At each unit, the potential V is approximated as a linear combination of the node potentials, and the shape function is used to describe the contribution of each node to the unit potential; S1.2.

3. Use the weak form of Laplace's equation to multiply by the shape function to construct the weak form equation, and apply Gauss's theorem to optimize the weak form equation; S1.2.

4. For each unit, construct a local element stiffness matrix and calculate the stiffness matrix elements of each unit using Gaussian integral; S1.2.5, assemble the local stiffness matrices of all elements into a global stiffness matrix; S1.2.

6. Use the conjugate gradient method to solve the global stiffness matrix and obtain the potential value of each node.

5. A method for detecting the state of a high-voltage cable according to claim 1, characterized in that: In S2, by measuring the high-frequency electromagnetic pulse signal, and performing partial discharge detection in the insulation layer of the high-voltage cable according to the Paschen curve model, and performing spectrum analysis on the detected discharge signal, the intensity and position of the partial discharge inside the cable are determined. The specific steps are as follows: S2.

1. Use a current sensor to capture the high-frequency current pulse signal generated by discharge, use a voltage sensor to measure the high-frequency voltage pulse signal generated by discharge, and use an ultrasonic sensor to capture the ultrasonic signal generated by partial discharge; S2.

2. Measure the actual air gap size d and pressure p, and calculate the discharge starting voltage V according to the Paschen curve model start ; S2.

3. By comparing the measured voltage with the starting voltage calculated by the Paschen curve, it is determined whether the current voltage exceeds the discharge starting voltage.

6. A method for detecting the state of a high-voltage cable according to claim 5, characterized in that: In S2.3, by comparing the measured voltage with the starting voltage calculated by the Paschen curve, it is determined whether the current voltage exceeds the discharge starting voltage. The specific steps are as follows: S2.3.

1. Determine the discharge start voltage V start Then, measure the voltage V currently applied to the cable measured ; S2.3.2, if V measured >V start , it means that the electric field strength applied to the air gap has exceeded its breakdown strength and partial discharge may occur; S2.3.3, if V measured ≤V start , it means that the electric field strength is not enough to cause discharge, the insulation layer is in a safe state, and no local discharge occurs.

7. A method for detecting the state of a high-voltage cable according to claim 1, characterized in that: In S3, the temperature distribution change inside the cable is simulated by the heat transfer equation, and the temperature of the cable is monitored in real time using a fiber Bragg grating sensor. The specific steps are as follows: S3.

1. Use the heat transfer equation to simulate the temperature distribution changes inside the cable; S3.

2. Use explicit finite difference method to discretize time. Assume that the spacing of spatial grid points is Δx and Δy, and the points are divided into i and j in the x and y directions respectively. Then the temperature field T(x, y, t) at the discrete point (i, j) is expressed as Where n represents the time step; S3.3, use explicit finite difference method to discretize the space, set the time step to Δt, and set the initial temperature distribution The temperature field at time step n is expressed as The temperature field at time step n+1 is expressed as S3.

4. Discretization of the Laplace operator using the central difference method And obtain the finite difference equation in explicit format; S3.

5. For each time step n, calculate the temperature at all nodes (i, j) And the temperature distribution at time n+1 is used as the initial temperature distribution of the next time step.

8. A method for detecting the status of a high-voltage cable according to claim 1, characterized in that: In S4, the electric field distribution and the partial discharge detection result are corrected based on the obtained temperature distribution of the cable, and the specific steps are as follows: S4.

1. Using the temperature distribution data, calculate the dielectric constant ∈ of the cable internal grid point (i, j) i，j (T), and according to the dielectric constant ∈ i , j (T) Recalculate the electric field E distribution inside the cable; S4.

2. Using the temperature distribution data, calculate the temperature-dependent breakdown voltage V at the cable internal grid point (i, j). breakdown，i，j , and recalculate the partial discharge starting voltage V start , i , j ; S4.3, combined with the updated electric field E distribution and the adjusted partial discharge inception voltage V start , re-determine the current measured voltage V measured , i , j Whether it exceeds the discharge starting voltage V start , i , j .

9. A method for detecting the state of a high-voltage cable according to claim 8, characterized in that: In S4.3, the updated electric field E distribution and the adjusted partial discharge inception voltage V start , re-determine the current measured voltage V measured,i,j Whether it exceeds the discharge starting voltage V start,i,j , the specific steps are as follows: S4.3.1, if V measured,i,j >V start,i,j , it means that the electric field strength applied to the air gap has exceeded its breakdown strength, and partial discharge occurs; S4.3.2, if V measured,i,j ≤V start,i,j , it means that the electric field strength is not enough to cause discharge, the insulation layer is in a safe state, and no local discharge occurs.

10. A high voltage cable status live detection system, characterized in that: The system is used to implement a method for detecting the status of a high-voltage cable according to any one of claims 1 to 9, comprising: The electric field distribution solving module is used to establish a mathematical model of the electric field around the cable using the electrostatic field equations in the Maxwell equations, and solve the electric field distribution between the cable insulation layer and the conductor; A partial discharge detection module is used to detect partial discharge in the insulation layer of a high-voltage cable by measuring high-frequency electromagnetic pulse signals and based on a Paschen curve model; The temperature distribution simulation module is used to simulate the temperature distribution changes inside the cable through the heat transfer equation and use the fiber Bragg grating sensor to monitor the temperature distribution of the cable in real time; The detection result correction module is used to correct the electric field distribution and partial discharge detection results based on the obtained temperature distribution of the cable.

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