Method and system for inversely calculating internal temperature of cable joint based on external surface temperature

Abstract

The invention discloses a method and system for calculating the internal temperature of a cable joint based on outer surface temperature inversion, and the method comprises the steps: 1, pre-burying a temperature measurement optical fiber in a buffer waterproof layer of a cable segment containing a middle cable joint, and binding the temperature measurement optical fiber on the outer surface of a cable; 2, establishing an actual measurement value mapping relational expression between the actual measurement data of the outer surface temperature and the actual measurement data of the cable core temperature; 3, establishing a simulation value mapping relational expression between the cable joint heating point temperature simulation data and the cable core temperature simulation data; and 4, constructing an inversion calculation formula between the temperature of the heating point of the cable joint and the temperature of the outer surface of the cable. During work, temperature measurement is carried out through the distributed optical fibers laid on the surface and in the cable body, an inversion calculation method capable of predicting the temperature of a heating point in a cable joint through measurement of the temperature of the outer surface of the cable body is established in combination with simulation calculation, and the accuracy and convenience of temperature measurement are effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of cable detection, and particularly relates to a method and a system for inversely calculating the temperature of an internal heat source of a cable joint based on the temperature of the outer surface of a cable body. Background Technique

[0002] The 220 kV high-voltage cable project is a key power transmission system for high-voltage, low-loss, and fast power transmission between regions and cities. The quality of its performance seriously affects the production safety and stability of the region. The high-voltage cable intermediate joint is an important connection guarantee device in the cable power transmission system. Compared with the cable body, it has a more complex composite interface structure, and the internal heat transfer is relatively complex. When the high-voltage cable operates conventionally, a large current is passed through, and the heat generation is large, especially the heat is relatively concentrated at the cable joint. Under different operating conditions, the temperature of the cable joint rises suddenly, causing abnormal temperature at the joint, which in turn causes material aging or deformation, reduces insulation, and poses serious safety hazards. However, when the large-capacity cable project is operating, it cannot be stopped temporarily and randomly under non-essential circumstances. Therefore, detecting the internal temperature of the cable joint in real time and conveniently has become a key and difficult problem in current engineering applications.

[0003] There are many existing methods for detecting the temperature of high-voltage cable joints, but most of them require power-off and off-line detection. The temperature monitoring of cable joints generally includes direct temperature measurement, indirect temperature measurement, and related numerical calculation methods through analyzing the thermal circuit model, etc. Among them, direct temperature measurement includes thermocouples, temperature sensors, and temperature measurement using distributed optical fibers. The indirect temperature measurement method usually uses the method of inferring and calculating the current-carrying capacity, and the thermal circuit model calculation is to perform thermal circuit equivalence on the structures of the cable and the cable joint, and then perform numerical calculation through the heat transfer theory. The method of placing a thermocouple inside for detection is widely used in medium- and low-voltage cables. Since the voltage level is relatively low, the influence on insulation is relatively small. However, when facing a 220 kV high-voltage cable, the presence of the thermocouple affects the surrounding electric field, and there is an insulation problem under a certain internal insulation condition. Therefore, it can only be placed on the outer sheath surface. Calculating the temperature using the current-carrying capacity is to indirectly obtain the temperature change by detecting the current-carrying capacity fluctuation at both ends of the cable system. This method has a strong hysteresis. The change of the current-carrying capacity is affected by the temperature, and the temperature change generated by the heat source has an accumulation process. Therefore, there is a hysteresis when calculating.

[0004] With the development of distributed fiber optic sensors, passive distributed optical fibers can be used to obtain physical parameters such as ambient temperature, stress, and vibration without affecting the surrounding electrical environment, greatly improving the efficiency and safety of non-destructive testing of power equipment. Distributed fiber optic temperature measurement is a method of laying optical fibers on the outer surface or inside of cables, using their passive characteristics to ensure the safety of normal operation of cables, and detecting optical parameters caused by temperature changes without destroying the electric field and stress field of the cable itself during operation. The detection principle is to apply an optical excitation signal to a section, and then the optical excitation signal is transmitted inside the optical fiber. When the nearby temperature changes, the wavelength and optical power of the returned Stokes light and anti-Stokes light change, which can reflect the changes in the internal temperature.

[0005] However, the existing distributed optical fiber temperature measurement method only performs laying detection inside and outside the cable body, and cannot be laid in the face of the complex structure of the cable joint. The high-voltage cable joint in operation cannot be disassembled, and it is difficult to detect the temperature change inside by pre-embedded active wired sensors in it. However, there is currently a lack of corresponding inversion calculation methods to detect the temperature change inside the joint by performing temperature detection on the outer surface of the cable joint.

[0006] In addition, due to the large thickness and complex internal structure of the cable joint, directly measuring the temperature on the surface of the cable joint is difficult to reflect the actual internal temperature changes and is prone to distortion. Summary of the invention

[0007] In view of the shortcomings of the prior art, the present invention provides a method and system for calculating the internal temperature of a cable joint based on the inversion of the external surface temperature. By detecting the outer surface temperature of the cable body and combining it with the inversion calculation method proposed in the present invention, the temperature of the hot spot inside the cable joint can be indirectly estimated, and temperature detection can be achieved quickly, accurately and non-destructively.

[0008] The technical solution adopted by the present invention is as follows: a method for calculating the internal temperature of a cable joint based on the inversion of the external surface temperature, comprising the following steps:

[0009] Step 1: pre-embed a temperature measuring optical fiber in a buffer water-blocking layer of a cable containing an intermediate cable joint, and bundle the temperature measuring optical fibers on the outer surfaces of the cables at both ends of the cable joint;

[0010] Step 2, applying different working currents to the cable, obtaining optical signal data and the measured temperature of the cable outer surface and the measured temperature of the cable core, and establishing a measured value mapping relationship between the measured data of the outer surface temperature and the measured data of the cable core temperature;

[0011] Step 3: Establish a finite element simulation model according to the actual cable joint and line segment structure size and material, obtain the cable joint head hot spot temperature simulation data and the cable core temperature simulation data under different working currents to form a simulation database, and establish a simulation value mapping relationship between the cable joint head hot spot temperature simulation data and the cable core temperature simulation data;

[0012] Step 4, taking the cable outer surface temperature as the independent variable and the hot spot temperature of the cable joint as the dependent variable, using the measured data relationship and the simulation data relationship to construct an inverse calculation formula between the hot spot temperature of the cable joint and the cable outer surface temperature, and then calculate the internal temperature of the cable joint.

[0013] Step 1 includes:

[0014] The cable bodies are connected at both ends of the middle cable joint respectively, and external temperature measuring optical fibers are laid on the outer surfaces of the two sections of the cable bodies in the axial direction of the cable body, and characteristic points are set on the cable surface; internal temperature measuring optical fibers are embedded in the buffer water-blocking layer inside the cable body in the axial direction of the cable core, and corresponding characteristic points are set on the cable core surface radially inwardly corresponding to the characteristic points on the cable surface.

[0015] Step 2 includes:

[0016] Apply different working currents to the cable, collect the optical signals of Raman scattered anti-Stokes light of the internal temperature measurement optical fiber and the external temperature measurement optical fiber, store the optical signals in the optical fiber temperature measurement system for demodulation to obtain the temperature at the characteristic point on the outer surface of the cable and the temperature at the characteristic point on the cable core radially inward;

[0017] The measured temperature values at the characteristic points on the outer surface of the cable and the measured temperature values at the characteristic points on the cable core radially inward are used for fitting to obtain a measured value mapping relationship with the temperature at the characteristic points on the outer surface of the cable as the independent variable and the temperature at the characteristic points on the cable core as the dependent variable.

[0018] Step 3 contains the following sub-steps:

[0019] (1) Establish a finite element simulation model based on the cable connector and cable body structural dimension parameters;

[0020] (2) Set the material parameters and physical parameters of the cable connector, cable body, and ambient air, including electrical conductivity, constant-pressure heat capacity, density, thermal conductivity, and relative dielectric constant;

[0021] (3) Load different working currents, use the finite element method to simulate the finite element simulation model, and obtain the temperature simulation values of the hot spots at the cable joints and the temperature simulation values at the characteristic points of the cable core;

[0022] (4) Use the obtained simulated values of the cable joint heating point temperature and the simulated values of the characteristic point temperature at the cable core to perform fitting, and obtain a simulated value mapping relationship formula with the simulated value of the characteristic point temperature at the cable core as the independent variable and the simulated value of the cable joint heating point temperature as the dependent variable.

[0023] Step 4 includes:

[0024] Fit the measured value mapping relationship formula and the simulated value mapping relationship formula to establish an inversion calculation formula with the cable outer surface temperature as the independent variable and the cable joint heating point temperature as the dependent variable;

[0025] By actually measuring the temperature at the characteristic points on the cable outer surface and substituting it into the inversion calculation formula, calculate the cable joint heating point temperature value.

[0026] The selection of the characteristic points is along the direction of the outer surface optical fiber, starting from the cable joint. The distance between the two nearest characteristic points on both sides to the cable joint heating point is 1.5 m, and 5 characteristic points are selected, with a 10 cm interval between the characteristic points.

[0027] In step 2, apply different working currents of 200 A, 400 A, 600 A, 800 A, 1000 A, 1200 A, and 1400 A respectively. When operating stably, it should be 20 minutes after applying the current.

[0028] A system for inverting the internal temperature of a cable joint based on the outer surface temperature includes:

[0029] A measurement module for pre-burying temperature measurement optical fibers in the buffer water-blocking layer of the cable containing the intermediate cable joint and bundling temperature measurement optical fibers on the outer surfaces of both ends of the cable joint;

[0030] A measured value module for applying different working currents to the cable, obtaining optical signal data, the measured temperature of the cable outer surface and the measured temperature of the cable core, and establishing a measured value mapping relationship formula between the measured data of the outer surface temperature and the measured data of the core temperature;

[0031] A simulation module for establishing a finite element simulation model according to the actual cable joint and the structural dimensions and materials of the line segment, obtaining a simulation database of the cable joint heating point temperature simulation data and the core simulation temperature data under different working currents, and establishing a simulation value mapping relationship formula between the cable joint heating point temperature simulation data and the core temperature simulation data;

[0032] A calculation module for using the measured data relationship formula and the simulation data relationship formula to construct an inversion calculation formula between the cable joint heating point temperature and the cable outer surface temperature with the cable outer surface temperature as the independent variable and the cable joint heating point temperature as the dependent variable, and then calculating the internal temperature of the cable joint.

[0033] In the operation of the present invention, temperature measurement is carried out through distributed optical fibers laid on the surface and inside of the cable body. Combining with the simulation calculation of the finite element model restored in a 1:1 ratio, an inversion calculation method is established to predict the temperature of the heating point inside the cable joint through the temperature measurement on the outer surface of the cable body, effectively improving the accuracy and convenience of temperature measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the structure of the cable joint and the cable body of the present invention;

[0035] Figure 2 It is a schematic diagram of the simulation model and the principle of inversion calculation of the present invention;

[0036] Figure 3 It is a schematic diagram of the experimental platform in the example of the present invention;

[0037] Figure 4 It is a simulated temperature change diagram of the temperature change diagram of the heating point and the internal characteristic points of the cable joint in the example of the present invention;

[0038] In the figure, 1 - cable joint, 2 - cable body, 3 - outer surface of the cable, 4 - cable core, 5 - heating area, 6 - ambient air, 7 - outer surface characteristic point, 8 - radial direction, 9 - internal characteristic point, 10 - axial direction, 11 - heating point. DETAILED DESCRIPTION OF THE INVENTION

[0039] The following further illustrates the application method of the technical solution of the invention in combination with the drawings and specific examples.

[0040] The present invention provides a method for inversely calculating the internal temperature of a cable joint based on the outer surface temperature, including the following steps:

[0041] Step 1, embed temperature measurement optical fibers in the buffer water-blocking layer of a 10-meter cable section containing a 220 kV intermediate cable joint, and bundle temperature measurement optical fibers on the outer surface 3 of a 10-meter cable containing a 220 kV intermediate cable joint.

[0042] Step 1 includes the following sub-steps:

[0043] Connect 5-meter cable bodies to both ends of the 220 kV intermediate cable joint respectively. After connection, make it a whole so that it can be energized and operate normally.

[0044] Lay external temperature measurement optical fibers on the outer surfaces of the two cable bodies, with the direction along the axial direction of the cable body, and set a total of 5 characteristic points on the cable surface; embed internal temperature measurement optical fibers in the buffer water-blocking layer inside the cable body, with the direction along the axial direction 10 of the cable core 4, and set corresponding characteristic points on the surface of the cable core radially corresponding to the characteristic points on the cable surface.

[0045] The above-mentioned 220 kV cable body includes a copper core, a conductor shielding layer, an XLPE insulation layer, an insulation shielding layer, a buffer water-blocking layer, a corrugated aluminum sheath, asphalt, an outer sheath, and an outer semi-conductive coating, which are arranged in sequence from the inside to the outside.

[0046] The external temperature measurement optical fiber is laid on the outer surface of the cable body in the axial direction of the cable. Two independent optical fibers are bundled and fixed on the outer surface of the cable body using cable ties.

[0047] The above-mentioned characteristic points are selected along the direction of the optical fiber on the outer surface. With the cable joint as the center, the nearest characteristic point is 1.5 m away from the heat source of the cable joint. Five characteristic points are selected, and the characteristic points are spaced 10 cm apart from each other.

[0048] The above-mentioned internal temperature measurement optical fiber is laid in the buffer water-blocking layer inside the cable. Two separate optical fibers are arranged and wrapped with water-blocking tapes to fix the position of the optical fibers.

[0049] Step 2: Build a 220 kV high-voltage cable operation experiment platform, apply different magnitudes of working currents, and after stable operation, obtain the optical signal data obtained by the optical fiber, obtain the measured temperature of the cable outer surface and the measured temperature of the cable core, and establish a measured value mapping relationship between the measured data of the outer surface temperature and the measured data of the cable core temperature.

[0050] Step 2 includes the following sub-steps:

[0051] Apply different working currents to the cable. After stable operation, collect the anti-Stokes light optical signals of the Raman scattering of the internal temperature measurement optical fiber and the external temperature measurement optical fiber, and store the optical signals in the optical fiber temperature measurement system for demodulation to obtain the temperature at the characteristic points on the outer surface of the cable and the temperature at the characteristic points of the cable core radially inward.

[0052] Use the measured temperature values at the characteristic points on the outer surface of the cable and the measured temperature values at the characteristic points of the cable core radially inward obtained to perform fitting, and obtain a measured value mapping relationship with the temperature at the characteristic points on the outer surface of the cable as the independent variable and the temperature at the characteristic points of the cable core as the dependent variable.

[0053] The above-mentioned different working currents applied are 200 A, 400 A, 600 A, 800 A, 1000 A, 1200 A, and 1400 A respectively. Stable operation should be after 20 minutes after applying the current.

[0054] The above-mentioned stable operation should be 20 minutes after applying the current, which means 20 minutes calculated after the current increases uniformly from 0 A to the expected current value.

[0055] The above-mentioned anti-Stokes light optical signal of the Raman scattering is the scattered light power captured by the external detector after the incident light undergoes Raman scattering.

[0056] The above optical signal demodulation is a process of inversely inferring the surrounding temperature from the optical power by utilizing the characteristic that the temperature around the optical fiber affects the anti-Stokes optical power.

[0057] The temperature of the outer surface characteristic point is the temperature at the position of the selected characteristic point, and the internal characteristic point is the point position in the radial direction of the cable core 8 from the surface characteristic point.

[0058] In the above internal temperature measurement optical fiber, in the three-dimensional space, the horizontal direction is the axial direction of the cable core, and the vertical direction is the radial direction of the cable core, corresponding one-to-one with the outer surface characteristic points.

[0059] The above Raman scattering is that the incident light in the optical fiber interacts with molecules in the low energy level, and the anti-Stokes photons released when the molecules are excited to the high energy level and then drop to the low energy level. The anti-Stokes light frequency is as follows, where V as is the anti-Stokes light frequency, v0 is the incident frequency, E1 and E2 respectively represent energy levels, and h is Planck's constant:

[0060]

[0061] The above anti-Stokes optical power is expressed as:

[0062]

[0063] In the above formula, P as is the anti-Stokes optical power, P0 is the incident optical power, K as is the anti-Stokes scattering cross section, α0 and α as are the propagation loss coefficients of the incident light and the anti-Stokes light in the optical fiber, R as (T) is the correlation coefficient related to the molecular energy level layout of the optical fiber, and L is the length of the optical fiber from the laser incident end to the position where the scattering event occurs.

[0064]

[0065] In the above formula, h is Planck's constant, k is Boltzmann's constant, Δv is the Raman frequency shift amount, and T is the thermodynamic temperature.

[0066] The above anti-Stokes light demodulation process is as follows:

[0067] When the initial reference temperature is T0, the anti-Stokes optical power is:

[0068]

[0069] When the measured temperature is T, the anti-Stokes optical power is:

[0070]

[0071] In the formula,

[0072] By taking the ratio of the optical powers before and after measurement, we can obtain:

[0073]

[0074] The finally demodulated temperature value is:

[0075]

[0076] In the above formula, the actual ambient temperature T is obtained by calculating two optical powers.

[0077] Step 3: Establish a finite element simulation model according to the actual cable joint and line segment structure dimensions and materials, obtain the simulation database of the cable joint hot spot temperature simulation data and the cable core simulation temperature data under different working currents, and establish the simulation value mapping relationship between the cable joint hot spot temperature simulation data and the cable core temperature simulation data.

[0078] Step 3 includes the following sub-steps:

[0079] Establish a 1:1 restored finite element simulation model according to the cable joint and cable body structure dimension parameters.

[0080] Set the material parameters and physical parameters of the cable joint, cable body, and ambient air 6. The parameters include conductivity, constant pressure heat capacity, density, thermal conductivity, and relative permittivity. Setting the above material parameters and physical parameters is the basis for establishing the finite element simulation model and a necessary condition for obtaining the cable joint hot spot temperature simulation value and the cable core characteristic point temperature simulation value.

[0081] Load different working currents, and use the finite element method to perform simulation calculations on the finite element simulation model to obtain the cable joint hot spot temperature simulation value and the cable core characteristic point temperature simulation value.

[0082] Use the obtained cable joint hot spot temperature simulation value and the cable core characteristic point temperature simulation value to perform fitting, and obtain the simulation value mapping relationship with the cable core characteristic point temperature simulation value as the independent variable and the cable joint hot spot temperature simulation value as the dependent variable.

[0083] The above mapping relationship is obtained by non-linear data fitting.

[0084] The working currents for the above simulation loading are 200A, 400A, 600A, 800A, 1000A, 1200A, and 1400A respectively.

[0085] Step 4: Using the cable outer surface temperature as the independent variable and the cable joint hot spot temperature as the dependent variable, an inversion calculation formula between the cable joint hot spot temperature and the cable outer surface temperature is constructed using the measured data relationship formula and the simulation data relationship formula.

[0086] Step 4 includes the following sub-steps:

[0087] List and fit the measured value mapping relationship formula and the simulation value mapping relationship formula respectively, establish an inversion calculation formula with the cable outer surface temperature as the independent variable and the cable joint hot spot temperature as the dependent variable, and then calculate the internal temperature of the cable joint.

[0088] By actually measuring the temperature at the characteristic points on the cable outer surface and substituting it into the inversion calculation formula, the cable joint hot spot temperature value is calculated to realize the inversion function.

[0089] The fitting of the above-mentioned measured value mapping relationship formula and the simulation value mapping relationship formula is based on the internal characteristic points in the two relationship formulas.

[0090] Figure 1 This is the cable joint and the schematic structural diagram of the present invention. The target of the present invention is the 220 kV cable joint 1 and the cable bodies 2 at both ends. The heating area 5 is mainly inside the cable joint.

[0091] Figure 2 This is the schematic diagram of the simulation model and the inversion calculation principle of the present invention. Characteristic points are set on the outer surface of the cable body. Five characteristic points are set. Along the axial direction of the cable body, the characteristic point closest to the cable joint should have an axial distance of 1.5 m from the cable joint hot spot, and the other characteristic points should be 20 cm apart from each other. By detecting the temperature at the outer surface characteristic point 7 using an optical fiber and combining with detecting the temperature at the internal characteristic point 9 using an optical fiber, and performing radial fitting according to the radial direction 8, the measured value mapping relationship formula with the temperature at the outer surface characteristic point 7 of the cable as the independent variable and the temperature at the internal characteristic point 9 of the cable core as the dependent variable is as follows:

[0092] T j =AT i 2 +BT i +C

[0093] In the formula, T i is the measured temperature of the outer surface characteristic point of the cable, T j is the measured temperature of the internal characteristic point at the cable core. i = j = 1, 2, 3, 4 or 5. The nth characteristic point is n. A, B, and C are the constant values after fitting.

[0094] The temperature values at the internal heating point 11 of the cable joint under different working conditions are obtained through simulation. Meanwhile, the simulated temperature values at the internal characteristic point 9 are collected. The mapping relationship of the simulation values is established with the simulated temperature value at the internal characteristic point 9 of the cable core as the independent variable and the simulated temperature value at the heating point 11 of the cable joint as the dependent variable as follows:

[0095] In the formula, T’ is the simulated temperature value at the internal heating point 11 of the cable joint under different working conditions, T j ’ is the simulated temperature value at the internal characteristic point 9 of the cable core, and D, E, and F are the constant values after fitting.

[0096] The mapping relationship of the measured values and the mapping relationship of the simulation values are fitted. When fitting, the simulated temperature value and the measured temperature value at the internal characteristic point 9 are corresponding as the intermediate value, that is, the two are set to have the same numerical value. According to the mapping relationship of the measured values, the temperature value at the external surface characteristic point of the cable under the set numerical value can be calculated. Meanwhile, according to the mapping relationship of the simulation values, the temperature value at the internal heating point of the cable joint can be calculated.

[0097] Taking the temperature value at the internal heating point of the cable joint as the dependent variable and the temperature value at the external surface of the cable body as the independent variable, an inversion calculation formula is established.

[0098]

[0099] In the formula, T is the temperature value at the internal heating point of the cable joint, T i is the measured temperature of the external surface characteristic point of the cable, and G, H, and I are the constant values after fitting.

[0100] Based on this, by measuring the measured temperature at the external surface characteristic point of the cable and substituting it into the calculation, the temperature at the internal heating point of the cable joint can be obtained.

[0101] Taking the 220 kV voltage grade cable as an example, the implementation is described as follows:

[0102] Build a 220 kV cable joint and cable body experimental platform, as Figure 3 shown. The current generating device is a device that can generate sufficient current for the test. The cable joint and the body are the research objects including the cable joint and the cable bodies at both ends. The current detection device is a device used to detect whether the current generated by the current generating device meets the requirements. The distributed optical fiber temperature measurement system refers to a device that includes functions of optical signal transmission, reception, and demodulation. The computer is a device that can perform conversion calculations between optical signals and temperature signals.

[0103] Temperature monitoring is carried out by embedding temperature-measuring optical fibers on the outer surface and inside the cable body. Under the condition that the ambient temperature is 20°C, a uniformly increasing current with load currents of 200 A and 800 A is applied. Starting from the moment t = 0, it increases uniformly at a speed of 100 A / s. After t = 20 min, it is regarded as the stable operating state of the cable, and the measured temperature change curves of 7 characteristic points on the outer surface of the cable body over time are obtained. At the same time, the measured temperature change curves of 9 internal characteristic points over time are obtained.

[0104] The two groups of curves are fitted, and using T i as the measured temperature of the characteristic points on the outer surface of the cable, and T j as the measured temperature of the internal characteristic points at the cable core, the following fitting calculation formula can be obtained:

[0105] T j =-63.09 + 7.5×T i -0.1×T i 2

[0106] The parameters used in the 220 kV cable joint and body simulation model are shown in Table 1.

[0107]

[0108] Table 1 220 kV cable joint and body parameters

[0109] According to the parameters and material parameters in Table 1, a simulation model that is restored 1:1 with the actual 220 kV cable joint and body is constructed.

[0110] During the simulation, the ambient temperature is set to 20°C, and the current is a uniformly increasing current with a load current of 800 A. Starting from the moment t = 0, after t = 20 min, it is regarded as the stable operating state of the cable. During the simulation Figure 2 the temperature change curve of the heating point at 9 internal characteristic points over time is obtained. At the same time, the temperature change curve of the 9 internal characteristic points over time on the same time scale is obtained by simulation, as Figure 4 shown in the temperature change diagram of the joint heating point and the internal characteristic points.

[0111] Using T’ as the simulation value of the temperature at the 11 internal heating points of the cable joint under different working conditions, and T j ’ as the simulation value of the temperature at the 9 internal characteristic points at the cable core, the fitting result is:

[0112]

[0113] From the simulation results and the measured results, it can be seen that under the same working conditions, when the same internal characteristic points are selected to analyze the change of their temperatures over time, the simulation results and the measured results are basically in agreement. Therefore, the simulated temperature and the measured temperature of the internal characteristic points can be averaged and then used as the intermediate nodes connecting the temperature of the outer surface characteristic points of the cable body and the temperature of the heat generation point of the cable joint, obtaining the temperature of the heat generation point of the cable joint as the dependent variable T and the measured temperature of the outer surface characteristic points of the cable body as the independent variable T i The inverse calculation formula is as follows:

[0114]

[0115] Through the above inverse calculation formula, the temperature value of the internal heat generation point of the cable joint can be deduced from the temperature of the outer surface characteristic points of the cable body.

[0116] The present invention also provides a system for inversely calculating the internal temperature of a cable joint based on the outer surface temperature, including:

[0117] A measurement module for embedding temperature measurement optical fibers in the buffer water-blocking layer of the cable containing the intermediate cable joint and bundling temperature measurement optical fibers on the outer surfaces of the cables at both ends of the cable joint;

[0118] A measured value module for applying different working currents to the cable, obtaining optical signal data, the measured temperature of the outer surface of the cable and the measured temperature of the cable core, and establishing a mapping relationship of measured values between the measured data of the outer surface temperature and the measured data of the cable core temperature;

[0119] A simulation module for establishing a finite element simulation model according to the actual cable joint and the structural dimensions and materials of the cable segment, obtaining simulation database of the temperature simulation data of the heat generation point of the cable joint and the simulation temperature data of the cable core under different working currents, and establishing a mapping relationship of simulation values between the temperature simulation data of the heat generation point of the cable joint and the simulation temperature data of the cable core;

[0120] A calculation module for using the temperature of the outer surface of the cable as the independent variable and the temperature of the heat generation point of the cable joint as the dependent variable, constructing an inverse calculation formula between the temperature of the heat generation point of the cable joint and the temperature of the outer surface of the cable by using the measured data relationship and the simulation data relationship, and further calculating the internal temperature of the cable joint.

[0121] Compared with the prior art, the beneficial effects of the present invention are:

[0122] 1. A method for inversely calculating the temperature of the internal heat source of a cable joint based on the outer surface temperature of the cable body is proposed. This method has the technical characteristics of performing live on-line temperature measurement without power outage, shutdown and disassembly of the in-service cable, ensuring the continuity of the normal operation of the cable.

[0123] 2. The temperature measurement method proposed by the present invention has higher compatibility and can be applied to various cable projects with different grades, working conditions, environments, etc., and has good universality.

[0124] 3. For the temperature inversion calculation method proposed by the present invention, the temperature measurement accuracy is high, the fitting degree of the inversion calculation formula is high, and the measurement of the internal heating points of the cable joint is more realistic.

[0125] 4. The proposed temperature measurement method can continuously monitor the temperature and can be applied to the heating points at different positions inside the cable joint, showing continuity in both time and space scales, effectively ensuring the safe and stable operation of the cable.

[0126] As mentioned above, the above is only the preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes, should be covered by the protection scope of the present invention.

Claims

1. A method for calculating the internal temperature of a cable joint based on the inversion of the outer surface temperature, characterized in that, It includes the following steps: Step 1: Embed temperature measurement optical fibers in the buffer water-blocking layer of the cable with an intermediate cable joint, and bundle temperature measurement optical fibers on the outer surfaces of the cables at both ends of the cable joint; Step 2: Apply different working currents to the cable, obtain optical signal data, the measured temperature on the outer surface of the cable and the measured temperature of the cable core, and establish a measured value mapping relationship between the measured data of the outer surface temperature and the measured data of the cable core temperature; Step 3: Establish a finite element simulation model according to the actual cable joint and line segment structure dimensions and materials, obtain simulation database of the cable joint hot spot temperature simulation data and the cable core simulation temperature data under different working currents, and establish a simulation value mapping relationship between the cable joint hot spot temperature simulation data and the cable core temperature simulation data; Step 4: Using the temperature on the outer surface of the cable as the independent variable and the cable joint hot spot temperature as the dependent variable, construct an inversion calculation formula between the cable joint hot spot temperature and the temperature on the outer surface of the cable by using the measured data formula and the simulation data formula, and then calculate the internal temperature of the cable joint.

2. The method for inversely calculating the internal temperature of a cable joint based on the outer surface temperature according to claim 1, wherein: Step 1 includes: Connect the cable bodies at both ends of the intermediate cable joint respectively, lay external temperature measurement optical fibers on the outer surfaces of the two cable bodies, with the direction along the axial direction of the cable body, and set characteristic points on the cable surface; Embed internal temperature measurement optical fibers in the buffer water-blocking layer inside the cable body, with the direction along the axial direction of the cable core, and set corresponding characteristic points on the cable core surface radially inward corresponding to the characteristic points on the cable surface.

3. The method for inversely calculating the internal temperature of a cable joint based on the outer surface temperature according to claim 1, wherein: Step 2 includes: Apply different working currents to the cable, collect the anti-Stokes light optical signals of the Raman scattering of the internal temperature measurement optical fibers and the external temperature measurement optical fibers, store the optical signals in the optical fiber temperature measurement system for demodulation to obtain the temperature at the characteristic points on the outer surface of the cable and the temperature at the characteristic points of the cable core radially inward; Use the measured temperature values at the characteristic points on the outer surface of the cable and the measured temperature values at the characteristic points of the cable core radially inward obtained to perform fitting, and obtain a measured value mapping relationship with the temperature at the characteristic points on the outer surface of the cable as the independent variable and the temperature at the characteristic points of the cable core as the dependent variable.

4. The method for inversely calculating the internal temperature of a cable joint based on the outer surface temperature according to claim 1, wherein: Step 3 includes the following sub-steps: (1) Establish a finite element simulation model according to the structural dimension parameters of the cable joint and the cable body; (2) Set the material parameters and physical parameters of the cable joint, the cable body, and the ambient air, including conductivity, constant pressure heat capacity, density, thermal conductivity, relative dielectric constant; (3) Load different working currents, and perform simulation calculations on the finite element simulation model by using the finite element method to obtain the cable joint hot spot temperature simulation value and the cable core characteristic point temperature simulation value; (4) Fit the obtained simulated values of the cable joint hot spot temperature and the simulated values of the characteristic point temperatures at the cable core to obtain a mapping relationship of simulated values with the simulated values of the characteristic point temperatures at the cable core as the independent variable and the simulated values of the cable joint hot spot temperature as the dependent variable.

5. The method for inversely calculating the internal temperature of a cable joint based on the outer surface temperature according to claim 1, characterized in that: Step 4 includes: Fit the measured value mapping relationship and the simulated value mapping relationship to establish an inversion calculation formula with the cable outer surface temperature as the independent variable and the cable joint hot spot temperature as the dependent variable; By actually measuring the temperatures at the characteristic points on the outer surface of the cable and substituting them into the inversion calculation formula, the cable joint hot spot temperature value is calculated.

6. The method for inversely calculating the internal temperature of a cable joint based on the outer surface temperature according to claim 2, characterized in that: The characteristic points are selected along the direction of the outer surface optical fiber. Starting from the cable joint, the distance between the two nearest characteristic points on both sides to the cable joint hot spot is 1.5 m, and 5 characteristic points are selected, with a 10 cm interval between the characteristic points.

7. The method for inversely calculating the internal temperature of a cable joint based on the outer surface temperature according to claim 2, characterized in that: In step 2, the different working currents applied are 200 A, 400 A, 600 A, 800 A, 1000 A, 1200 A, and 1400 A respectively, and the stable operation should be after 20 minutes of applying the current.

8. A system for calculating the internal temperature of a cable joint based on the inversion of the outer surface temperature, characterized in that, It includes: A measurement module for embedding temperature measurement optical fibers in the buffer water-blocking layer of the cable containing the intermediate cable joint and bundling temperature measurement optical fibers on the outer surfaces of both ends of the cable joint; A measured value module for applying different working currents to the cable to obtain optical signal data and the measured temperatures of the cable outer surface and the core of the cable, and establishing a mapping relationship of measured values between the measured data of the outer surface temperature and the measured data of the core temperature; A simulation module for establishing a finite element simulation model according to the actual cable joint and the line segment structure dimensions and materials, obtaining a simulation database of the cable joint hot spot temperature simulation data and the core simulation temperature data under different working currents, and establishing a mapping relationship of simulated values between the cable joint hot spot temperature simulation data and the core temperature simulation data; A calculation module for using the measured data relationship and the simulation data relationship to construct an inversion calculation formula between the cable joint hot spot temperature and the cable outer surface temperature with the cable outer surface temperature as the independent variable and the cable joint hot spot temperature as the dependent variable, and then calculating the internal temperature of the cable joint.

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