Simulation test method for improving combustion performance of cable

Abstract

The invention discloses a simulation test method for improving the combustion performance of a cable. A simulation test environment capable of accurately simulating the combustion process of the cable in a fire disaster is constructed by using fire dynamics software FDS; the method comprises the following steps: constructing Fortran compilation and automatically constructing a make environment; creating a combustion chamber three-dimensional model in the FDS according to the standard, and simulating the combustion test environment of the cable; fuel is directly defined as a mixture of propane and air in a simulation test environment so as to simulate a real combustion source; performing grid division on the three-dimensional model of the combustion chamber; in the modeling of the cable system, the geometric layout of the cable is input in detail, and the cable is decomposed into corresponding components according to the layered structure of the cable; arranging a virtual thermocouple and a smoke concentration sensor in the three-dimensional model of the combustion chamber; through simulation operation, a temperature curve and a flue gas concentration change process captured by the thermocouple and the flue gas concentration sensor are recorded in real time. The method can help to improve the design level of the cable.

Description

Technical Field

[0001] The invention belongs to the technical field of detection and inspection, and in particular relates to a simulation test method for cable combustion performance. Background Art

[0002] The safety and reliability of cables are directly related to the stable operation of the power system.

[0003] Cable combustion performance mainly refers to the combustion behavior and characteristics of cables under fire conditions. According to different standards, the combustion performance of cables can be divided into flame retardant, fire resistant, halogen-free, low smoke, low toxicity and other categories. For example, according to the national standard "Classification of Combustion Performance of Cables and Optical Cables" (GB 31247-2014), the combustion performance of cables is divided into four levels: A, B1, B2, and B3. In addition, there are other international standards such as EN 13501-6:2018, which are used for flame retardant performance testing of cables exported to the European market.

[0004] Flame-retardant cables refer to cables that, under specified test conditions, after the fire source is removed, the flame spreads only within a limited range, and the residual flame or residual burning can extinguish itself within a limited time. Fire-resistant cables refer to cables that can maintain safe operation for a certain period of time under flame burning conditions.

[0005] Among the many cable properties, fire resistance is particularly critical, especially in extreme environments such as fire. Unlike ordinary cables, the ability of fire-resistant cables to maintain circuit integrity at high temperatures is one of their most notable features. This ability is mainly due to their special material composition and structural design. When a fire occurs, the fire-resistant layer of the fire-resistant cable can effectively prevent the spread of flames and the transfer of heat, so that the conductor and insulation layer inside the cable maintain a certain temperature and electrical properties. Therefore, even under extremely high temperature conditions, fire-resistant cables can maintain the integrity of the circuit and provide necessary power support for fire-fighting equipment and emergency lighting, thereby ensuring the safety of life and property.

[0006] However, there are still many challenges in the evaluation, testing and product upgrade of the fire resistance performance of fire-resistant cables. Traditional cable combustion test methods are often carried out by actual combustion. Although this method is intuitive, it has many shortcomings. For example, the actual combustion test is costly, and the test process is difficult to control. The test results are easily affected by many factors, and the variables in the test are difficult to control accurately, which makes the pass rate of the fire-resistant cable combustion test very low, and at the same time causes the accuracy and reliability of the test results to be questioned. In addition, the actual combustion test may also pose potential safety risks to the environment and testers.

[0007] In order to overcome these shortcomings, simulation combustion test technology has gradually attracted attention in recent years.

[0008] The simulation combustion test technology simulates the actual combustion environment of the cable in a fire, and combined with advanced testing equipment and data analysis methods, can accurately and reliably evaluate its fire resistance performance without actually burning the cable. This test method not only reduces the test cost and improves the test efficiency, but also can better control the test conditions and reduce the error of the test results. It can also help technicians modify the test parameters and explore the impact of various parameters of fire-resistant cables on the test results.

[0009] However, the existing simulation technology does not perform combustion simulation on fire-resistant cables. The test standards, test requirements, test environment and structural parameters of fire-resistant cables are very different from those of ordinary cables, and extremely high requirements are placed on the modeling accuracy and material pyrolysis process. Summary of the invention

[0010] In order to solve the above technical problems, the present invention aims to improve the accuracy and reliability of fire resistance performance evaluation of fire-resistant cables by optimizing the simulation combustion test method.

[0011] Specifically, the present invention will use the fire dynamics software FDS (Fire Dynamics Simulator) to build a simulation test system that can accurately simulate the combustion process of cables (such as fire-resistant cables) in fire. The test results will provide more accurate and reliable technical support for cable performance evaluation and design optimization.

[0012] FDS (Fire Dynamics Simulation) is a computational fluid dynamics simulation software jointly developed by the National Institute of Standards and Technology (NIST) of the United States and VTT Technical Research Center of Finland. It is used to simulate large eddy currents (LES) of low-speed flows. The simulation focuses on the generation and diffusion of smoke and heat in fires.

[0013] According to GB / T 19216.11-2003 and the combustion test standard -TICW 8-2012, a three-dimensional model of the combustion chamber is established in the fire dynamics simulation software, the model parameters of the fire-resistant cable system are set, combustion simulation is performed, and the data of the oxygen concentration, the combustion temperature of each layer of the cable, and the change of smoke concentration over time during the combustion process are obtained. The specific steps are as follows:

[0014] (1) To run the FDS software, you must first build the Fortran compilation and automated build (make) environment to ensure that the Fortran-based source code can be compiled and executed smoothly.

[0015] (2) In accordance with GB / T 19216.11-2003 and TICW 8-2012 standards, a three-dimensional virtual space was created in FDS to simulate the combustion test environment of medium-voltage fire-resistant cables (for example, simulating a laboratory size of 3m×3m×3m).

[0016] (3) For propane blowtorches, the standard stipulates that air and propane are mixed in the blowtorch and then sprayed out, and partial premixed combustion occurs when encountering a fire source. Because the premixing and ignition processes are difficult to achieve simultaneously in FDS, the model is simplified and the fuel is directly defined as a mixture of propane and air. Air is also defined as the background gas. Based on accurate mass flow calculations, a corresponding blowtorch model is constructed to simulate a real combustion source.

[0017] (4) In order to improve the accuracy and efficiency of the simulation, a differentiated meshing strategy was adopted for the model: a fine mesh (one tenth of the diameter of the blowtorch nozzle and the cable conductor, respectively) was used in key areas (such as the area covered by the blowtorch flame and the cable section), while the mesh size was appropriately relaxed in the remaining areas to achieve the optimal allocation of resources.

[0018] (5) In the modeling of the cable system, the geometric layout of the cable was input in detail, and the cable was carefully decomposed into multiple components such as the outer sheath, insulation layer, conductor, fire-resistant layer and stainless steel belt. At the same time, segmented parameter settings were implemented for the temperature-dependent characteristics of each layer of material (such as the ceramicization process of ceramic silicone rubber). Different densities, thermal conductivity coefficients, and specific heat capacities of the ceramic layer materials were set before and after sintering according to the combustion time to ensure accurate reflection of the material properties. In addition, basic environmental parameters (such as temperature and humidity) were also set, and all were solidified in the model in the form of code.

[0019] (6) In order to deeply analyze the combustion behavior of the cable, a thermocouple and a smoke concentration sensor are arranged every 10 cm in the model. These virtual sensors can capture point data that are difficult to reach with traditional tests (such as the temperature changes of each layer of the cable's internal structure in the heat source and non-heat source sections), providing strong support for the comprehensive analysis of the combustion behavior.

[0020] (7) Through simulation operation, the temperature curve and flue gas concentration change process captured by the thermocouple and flue gas concentration sensor were recorded in real time. These data laid a solid foundation for the subsequent combustion characteristics analysis.

[0021] (8) Based on the above simulation results, the effects of cable structure (such as different layer thicknesses) and material parameter adjustment on combustion performance were further explored. Since there are many factors that affect the fire resistance and thermal insulation performance of cables, it is not possible to rely solely on a certain thermal insulation and fire resistance technology. Instead, it is necessary to coordinate the fire resistance and thermal insulation of each area with the overall optimization design to comprehensively improve the fire resistance performance of the cable. The purpose is to design a medium-voltage fire-resistant cable with a more reasonable structure and better material performance to meet higher safety standards.

[0022] This process can not only help improve the design level of cables, but also provide strong support for the innovative development of the cable industry.

[0023] Advantages of the invention:

[0024] (1) It has various functions and can adjust environmental parameters such as ambient temperature, air flow rate, ambient humidity, and pressure.

[0025] (2) You can define the surface temperature, density, thermal conductivity, specific heat capacity and other thermophysical properties of solid materials. Based on the customized parameters, you can research more suitable materials.

[0026] (3) Thermocouples, smoke detectors, vents, air outlets and other detection and actuation devices can be set up as needed to study the different burning characteristics of cables.

[0027] (4) High degree of visualization, the entire combustion process can be observed.

[0028] (5) It greatly saves the manpower, material and financial resources consumed in cable fire spread experiments, and eliminates the danger of combustion and harmful gases. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the process of this embodiment;

[0030] Figure 2 Schematic diagram of the combustion chamber model and mesh division of this embodiment;

[0031] Figure 3 is a schematic diagram of the sensor arrangement of this embodiment, where the points in the figure are sensors;

[0032] Figure 4 is a schematic diagram of the radial cross section of the cable in this example.

[0033] In the figure: copper conductor 1, conductor shield 2, XLFE insulation 3, insulation shield 4, buffer layer (semi-conductive non-woven fabric) 5, copper tape shield 6, wrapping layer (low-smoke halogen-free flame retardant tape) 7, fire-resistant layer (ceramic silicone rubber tape) 8, low-smoke halogen-free oxygen insulation layer 9, stainless steel tape 10, polyvinyl chloride outer sheath 11. DETAILED DESCRIPTION

[0034] The present invention is further described below with reference to the accompanying drawings and specific implementation methods.

[0035] A simulation test method for improving the burning performance of cables, using the fire dynamics software FDS to build a simulation test environment that can accurately simulate the burning process of cables in fire, and using the test results of cables in the simulation test environment to provide technical support for performance evaluation and design optimization of cables;

[0036] S1. Build Fortran compilation and automate the make environment (using the make tool in Fortran) to ensure that the Fortran-based source code can be compiled and executed smoothly;

[0037] S2. Following GB / T 19216.11-2003 and TICW 8-2012 standards, a three-dimensional virtual space was created in FDS as a three-dimensional model of the combustion chamber to simulate the combustion test environment of the cable;

[0038] S3. For the propane blowtorch mentioned in the standard in S2, the fuel is directly defined as a mixture of propane and air in the simulation test environment; air is also defined as the background gas; and based on the accurate mass flow calculation, the corresponding blowtorch model is constructed to simulate the real combustion source;

[0039] S4. A differentiated meshing strategy was adopted for the combustion chamber 3D model: fine mesh was used in key areas, while the mesh size was relaxed in other areas to achieve the optimal allocation of resources;

[0040] S5. In the modeling of the cable system, the geometric layout of the cables is input in detail, and the cables are decomposed into corresponding components according to their layered structure;

[0041] At the same time, segmented parameter setting is implemented for the temperature-dependent characteristics of the materials in each layered structure;

[0042] In addition, the basic parameters of the environment were set and all solidified in the 3D model of the combustion chamber in the form of code;

[0043] S6. A virtual thermocouple and smoke concentration sensor are arranged at intervals in the three-dimensional model of the combustion chamber. These virtual sensors are used to capture point data that are difficult to reach with traditional tests.

[0044] S7. Through simulation operation, the temperature curve and flue gas concentration change process captured by the thermocouple and flue gas concentration sensor are recorded in real time. These data lay a solid foundation for the subsequent combustion characteristics analysis.

[0045] In S4, the key areas include the area covered by the blowtorch flame and the cable part; the fine grid size of the area covered by the blowtorch flame is one tenth of the diameter of the blowtorch nozzle, and the fine grid size of the cable part is one tenth of the cable conductor.

[0046] In S5, the cable is decomposed into corresponding components according to its layered structure, including: outer sheath, insulation layer, conductor, fire-resistant layer and stainless steel belt;

[0047] In S5, the materials decomposed into corresponding components according to the cable layer structure include ceramic silicone rubber materials. The ceramic silicone rubber materials are ceramicized in the temperature section during the temperature ceramicization process. The ceramic layer materials are set with different densities, thermal conductivity, specific heat capacity, etc. according to the burning time before and after sintering to ensure accurate reflection of material properties.

[0048] In S6, a thermocouple and a smoke concentration sensor are arranged every 10 cm. The point data that are difficult to reach with traditional tests include the temperature changes of each layer structure inside the cable in the heat source and non-heat source sections.

[0049] Specifically in this example, take the medium voltage fire-resistant cable N-YJV62-8.7 / 15kV as an example:

[0050] FDS is used to conduct a fire-resistant combustion simulation test of a medium-voltage fire-resistant cable. Through the following steps, the combustion process of the medium-voltage fire-resistant cable in a fire environment can be accurately simulated, thereby evaluating its fire resistance performance.

[0051] (1) Establishing a simulation model

[0052] First, according to the actual size, material properties and environmental conditions of the medium-voltage fire-resistant cable, the corresponding simulation model is established using FDS software. During the modeling process, it is necessary to set the cable's structural dimensions, material pyrolysis properties (material density, thermal conductivity, specific heat capacity), combustion rate and other parameters in detail to ensure that the model can accurately reflect the actual combustion process of the cable.

[0053] (2) Setting propane torch parameters

[0054] According to the national standards and relevant standards, set appropriate fire source parameters. This includes setting parameters such as the position of the blowtorch, the flow of air and propane, and the duration of combustion. At the same time, environmental factors such as ambient temperature, humidity, and ventilation conditions need to be considered to simulate a real fire environment.

[0055] (3) Run simulation

[0056] After setting the fire scene, run the FDS software for simulation.

[0057] During the simulation, FDS simulates the combustion process of the cable in a fire according to the set parameters and conditions, and uses the set thermocouples and smoke sensors to collect combustion information including flame propagation, smoke generation, and heat transfer.

[0058] (4) Collect simulation data

[0059] After the simulation is completed, the data generated during the simulation are collected. These data include key indicators such as temperature distribution, flame spread speed, and smoke concentration during cable combustion. By analyzing these data, the fire resistance performance of the cable in a fire can be evaluated.

[0060] (5) Result analysis and evaluation

[0061] According to the collected simulation data, combined with the national standard requirements, the fire resistance performance of the cable is analyzed and evaluated. By comparing the simulation results with the performance indicators specified in the national standard, it can be determined whether the cable meets the fire resistance requirements.

[0062] (6) Cable performance improvement

[0063] According to the simulation results, the cable design, material selection and manufacturing process can be optimized and improved. For example, the thickness of a certain structure of the cable can be optimized, or the thermal conductivity can be changed, so as to explore more reasonable structures and materials.

[0064] Through the above steps, using FDS to conduct fire test combustion simulation of medium voltage fire resistant cables can achieve accurate evaluation of cable fire resistance performance. This method not only overcomes the defects and shortcomings of traditional actual combustion test methods, but also has the advantages of high efficiency, safety, and low cost, providing strong support for the performance evaluation and optimization of fire resistant cables.

[0065] For step S1, the main task is to establish a combustion chamber that meets the standards in FDS according to GB / T 19216.11-2003 and the combustion test standard-TICW8-2012. The standard stipulates that the volume of the combustion chamber should not be less than 20m 3 ,like Figure 2 The figure shows a room of 2m×3m×4m. The room size meets the requirements and the grid is divided according to the needs. The cable and the blowtorch are divided into fine grids, and the rest are divided into coarse grids.

[0066] In FDS fire simulation software, meshing is an important step, which has a significant impact on the accuracy and efficiency of the simulation. The way the mesh is divided determines the specific description of the simulation space, which is crucial for accurately reflecting the gas flow, temperature distribution and fire spread in the fire scene.

[0067] First, the division of the grid helps to accurately simulate the physical and chemical changes during the fire process. By dividing the simulation space into several small areas (i.e., grids), FDS can perform detailed calculations for each grid, thereby more accurately simulating parameters such as the speed, direction, and temperature of gas flow during the fire. Secondly, reasonable grid division can improve the computational efficiency of the simulation. By optimizing the size and distribution of the grid, the amount of calculation can be reduced and the simulation time can be shortened. This is especially important for the simulation of large-scale fire scenes, which can save a lot of computing resources.

[0068] For step S2, according to the standard requirements, the cable sample is set at a height of one meter from the ground, and the blowtorch is located 50 cm in front of it.

[0069] First, determine the structural dimensions of the measuring cable and the material properties of each part. Figure 4 Taking the high-pressure fire-resistant cable N-YJV62-8.7 / 15kV as an example, it is necessary to determine the thickness of the sheath, insulation, fire-resistant layer, conductor and other parts in the cable layered structure, and at the same time, it is necessary to obtain the corresponding material properties, including density, thermal conductivity and specific heat capacity.

[0070] Secondly, the temperature, humidity and air pressure of the room (virtual space) need to be measured. In this test, the temperature is 20 degrees Celsius, the humidity is 40% RH, and the initial air pressure in the combustion chamber is 1 bar. The propane torch is 50 cm long, the air inflow rate in the torch is 80L / min, and the propane inflow rate is 5L / min to ensure that the flame temperature reaches 750 degrees Celsius, and the fire supply time is 90 minutes.

[0071] For step S3, it is mainly to set thermocouples, smoke sensors, etc. at the required positions to measure the changes in temperature and smoke concentration during the combustion process. Figure 3 The small blue dot is the set sensor.

[0072] For step S4, after the simulation is completed, the data generated during the simulation are collected. These data include key indicators such as temperature distribution, flame spread speed, and smoke concentration during the cable combustion process. By analyzing these data, the fire resistance performance of the cable in a fire can be evaluated.

[0073] For step S5, the fire resistance performance of the cable is analyzed and evaluated based on the collected simulation data and in combination with national standards.

[0074] By comparing the simulation results with the performance indicators specified in the national standard, it is possible to determine whether the cable meets the fire resistance requirements. At the same time, the cable design, material selection, and manufacturing process can also be optimized and improved based on the simulation results.

[0075] Through the above steps, using FDS to conduct fire test combustion simulation of medium voltage fire resistant cables can achieve accurate evaluation of cable fire resistance performance. This method not only overcomes the defects and shortcomings of traditional actual combustion test methods, but also has the advantages of high efficiency, safety, and low cost, providing strong support for the performance evaluation and optimization of fire resistant cables.

[0076] The present invention simultaneously considers the influence of fire-resistant cable structure, material properties of each layer, spacing size, and test environment on cable combustion test, and overcomes the shortcomings of physical cable combustion test such as high cost, poor flexibility, and large environmental pollution. In the above-mentioned implementation, the multi-layer structure of the cable, the material properties of each layer of the cable, the test environment, etc., can partially modify the parameters according to different cable models and working conditions, which shows that the present invention has good mobility and interactivity.

Claims

1. A simulation test method for improving the burning performance of a cable, characterized in that Use the fire dynamics software FDS to build a simulation test environment that can accurately simulate the burning process of cables in fire, so that the test results of cables in this simulation test environment can provide technical support for cable performance evaluation and design optimization; The steps of this method include: S1. Build Fortran compilation and automate make environment to ensure that Fortran-based source code can be compiled and executed smoothly; S2. Following GB / T 19216.11-2003 and TICW 8-2012 standards, a three-dimensional virtual space was created in FDS as a three-dimensional model of the combustion chamber to simulate the combustion test environment of the cable; S3. For the propane blowtorch mentioned in the standard in S2, the fuel is directly defined as a mixture of propane and air in the simulation test environment; air is also defined as the background gas; and based on the accurate mass flow calculation, the corresponding blowtorch model is constructed to simulate the real combustion source; S4. A differentiated meshing strategy was adopted for the combustion chamber 3D model: fine mesh was used in key areas, while the mesh size was relaxed in other areas to achieve the optimal allocation of resources; S5. In the modeling of the cable system, the geometric layout of the cables is input in detail, and the cables are decomposed into corresponding components according to their layered structure; At the same time, segmented parameter setting is implemented for the temperature-dependent characteristics of the materials in each layered structure; In addition, the basic parameters of the environment were set and all solidified in the 3D model of the combustion chamber in the form of code; S6. A virtual thermocouple and smoke concentration sensor are arranged at intervals in the three-dimensional model of the combustion chamber. These virtual sensors are used to capture point data that are difficult to reach with traditional tests. S7. Through simulation operation, the temperature curve and flue gas concentration change process captured by the thermocouple and flue gas concentration sensor are recorded in real time. These data lay a solid foundation for the subsequent combustion characteristics analysis.

2. A simulation test method for improving the combustion performance of cables according to claim 1, characterized in that in S4, the key areas include the area covered by the blowtorch flame and the cable part; the fine grid size of the blowtorch flame coverage area is one tenth of the diameter of the blowtorch nozzle, and the fine grid size of the cable part is one tenth of the cable conductor.

3. A simulation test method for improving the combustion performance of a cable according to claim 1, characterized in that in S5, decomposing the cable layer structure into corresponding components comprises: Outer sheath, insulation layer, conductor, fire-resistant layer and stainless steel belt.

4. A simulation test method for improving the combustion performance of cables according to claim 1, characterized in that in S5, the materials decomposed into corresponding components according to the cable layered structure include ceramic silicone rubber materials, and the ceramic silicone rubber materials are ceramicized in the temperature section during the temperature ceramicization process, and different density, thermal conductivity, specific heat capacity, etc. of the ceramic layer material are set according to the combustion time before and after sintering to ensure accurate reflection of the material properties.

5. According to claim 1, a simulation test method for improving the combustion performance of cables is characterized in that in S6, a thermocouple and a smoke concentration sensor are arranged every 10 cm; the point data that are difficult to reach with traditional tests include the temperature changes of each layer structure inside the cable in the heat source and non-heat source sections.

6. According to claim 1, a simulation test method for improving the combustion performance of cables is characterized in that, based on the simulation results of S7, the influence of the adjustment of cable structure and material parameters on the combustion performance is further studied to help design cables with more reasonable structures and better material properties.

Images