Cable power temperature rise heat transfer simulation test method

Abstract

The invention relates to the field of fire disasters, in particular to a cable power temperature rise and heat transfer simulation test method. The method comprises the following steps that S1, the heat transfer stage of the cable and the temperature rising parameter of the cable under the power-on condition are obtained in real time, the heat transfer stage at least comprises a simulation stage, and the simulation stage specifically comprises the steps that the outer surface of an insulating layer is subjected to the radial heat conduction effect at the same time, and the heat convection effect is generated between the outer surface of the insulating layer and air for heat dissipation; and S2, acquiring basic parameters of the cable, and inputting the basic parameters and the temperature rise parameters into the trained cable core power-on temperature rise model according to a heat transfer stage of the cable to obtain a current-cable outer surface temperature rise characteristic curve in a simulation stage in a power-on process. According to the invention, simulation of temperature rise and heat transfer of the cable under different currents and voltages can be realized under the cable electrification condition, and data support is provided for characteristic parameters of the cable in the early stage of a fire in a cable combustion test.

Description

Technical Field

[0001] The invention relates to the field of fire technology, and in particular to a cable electric power heating and heat transfer simulation test method. Background Art

[0002] The study of the combustion characteristics of wires and cables is the basis for predicting their fire hazards. Currently, cone calorimeters, radiation furnaces, etc. are used to test and evaluate the combustion performance of cables, or combustion experiments are carried out at the actual cable installation site.

[0003] As described in the text of the Chinese patent publication number CN113899850B, entitled Cable Combustion Performance Test Device and Method of Use for Simulating Cable Channel Environment, the cable channel provides a reasonable fire simulation experiment to comprehensively explore the effects of different ambient temperatures, ambient humidity, pressures and gas components on the combustion performance of the cables in the cable channel, so as to be able to study the fire development, smoke patterns and combustion characteristics of the cables in the cable channels in different regions and under different environmental conditions. However, the combustion performance test devices described in the cited patents mostly analyze the combustion fire scene behavior of the cable after it is fused and not energized, and there are few studies on the early characteristic parameters of the cable electric heating and ignition. Since the real cable will produce temperature changes when it is energized, that is, the cable itself has an initial temperature before burning, it is obvious that if the characteristic parameters are not studied in the early stage of the cable fire, it is difficult to replicate the early characteristics of the non-energized cable during the real cable fire, which will eventually lead to inaccurate accuracy of the final flammability research, so it is urgent to solve this problem. Summary of the invention

[0004] In order to avoid and overcome the technical problems existing in the prior art, the present invention provides a cable electric power temperature rise heat transfer simulation test method, which can simulate the cable temperature rise heat transfer at different currents and voltages under energized conditions, and provide data support for the characteristic parameters of the cable in the early stage of cable fire in the cable combustion test.

[0005] A cable power heating and heat transfer simulation test method, comprising the following steps:

[0006] S1. Real-time acquisition of the heat transfer stage of the cable and the temperature rise parameters of the cable under power-on conditions, wherein the heat transfer stage includes at least a simulation stage, and the simulation stage is specifically: the outer surface of the insulation layer is simultaneously subjected to radial heat conduction and generates heat convection with the air to dissipate heat;

[0007] S2. Obtain the basic parameters of the cable, and according to the heat transfer stage of the cable, input the basic parameters and temperature rise parameters into the trained cable core power-on temperature rise model to obtain the current-cable outer surface temperature rise characteristic curve in the simulation stage of the power-on process.

[0008] As a further solution of the present invention: the basic parameters include the real cable radius r p , core radius r0, ambient temperature T a The heating parameters of the cable include the constant heat flux density generated by the power supply of the core Thermal conductivity k, density ρ, specific heat c p .

[0009] As a further solution of the present invention: according to the heat transfer stage of the cable, the basic parameters and the temperature rise parameters are input into the trained cable core power-on temperature rise model to obtain the current-cable outer surface temperature rise characteristic curve in the simulation stage of the power-on process, specifically including:

[0010] According to the heat transfer stage of the cable, the basic parameters and temperature rise parameters are input into the trained cable core power-on temperature rise model to obtain the cable outer surface temperature at each moment in the simulation stage;

[0011] According to the temperature of the cable outer surface at each moment in the simulation stage and the constant heat flux density generated by the core power supply at each moment Generates a current-cable outer surface temperature rise characteristic curve during the simulation phase of the power-on process.

[0012] The cable core power-on temperature rise model is specifically expressed as:

[0013]

[0014] Among them, T a is the ambient temperature; is the thermal diffusion coefficient, is the Fourier number, is the Biot number; is the constant heat flux density generated by the core power supply; k is the thermal conductivity; ρ is the density; c p is the specific heat capacity; h is the thermal convection coefficient; T i 0 is the core surface at time t=t i Temperature at time; T i+1 0 is the core surface at time t=t i Temperature at +Δt; T i m-1 is the control body of the insulating layer m-1 at time t=t i Temperature at time; T i m is the control volume of the insulating layer m at time t=t i Temperature at time; T i+1 m is the control volume of the insulating layer m at time t=t i Temperature at +Δt; T i m+1is the control volume of the insulating layer m+1 at time t=t i Temperature at time; T i p is the cable surface at time t = t i Temperature at time; T i+1 p is the cable surface at time t = t i Temperature at +Δt.

[0015] As a further solution of the present invention: the training process of the cable core power-on temperature rise model is as follows:

[0016] Obtain a historical experimental measurement data set, and divide the historical experimental measurement data set according to a preset strategy to form a training set, a test set, and a verification data set;

[0017] Obtain the thermal convection coefficient h related to the model, and input the basic parameters at each moment in the training set into the corresponding power-on temperature rise network according to the heat transfer stage to perform model training, so as to obtain the power-on temperature rise model of the cable core;

[0018] The training results are compared with the corresponding historical experimental measurement data sets, and the thermal convection coefficient h is adjusted according to the comparison results until the error between the training results and the corresponding historical experimental measurement data sets meets the preset error range to obtain the corrected cable core power-on temperature rise model.

[0019] As a further solution of the present invention: the preset strategy is specifically: using 70% of the historical experimental measurement data set as a training set, using 20% ​​of the historical experimental measurement data set as a test set, and using 10% of the historical experimental measurement data set as a verification data set.

[0020] As a further solution of the present invention: the heat convection coefficient h is adjusted as follows:

[0021] Get the theoretical value of the cable outer surface temperature at the same time With test value

[0022] The theoretical value With test value Substitute into the Euclidean norm formula to get the NORM value;

[0023] The calculation process of the Euclidean norm formula is as follows:

[0024]

[0025] in, is the theoretical value; is the test value;

[0026] Adjust the heat convection coefficient h so that the NORM value approaches 0;

[0027] Corrected adjusted thermal convection coefficient The calculation process is as follows:

[0028]

[0029] Among them, N u is the Nusselt number, D is the diameter, v is the kinematic viscosity of the fluid, α is the thermal conductivity of the fluid, k is the thermal conductivity of the fluid, Pr is the Prandtl number, g is the gravitational acceleration, and β is the air volume expansion coefficient.

[0030] As a further solution of the present invention: the heat transfer stage also includes a first stage and a second stage located before the simulation stage, wherein the first stage is specifically: the cable core conductor is energized and heated, heat of a certain heat flux density is input into the insulation layer, and the contact surface between the insulation layer and the core is heated and heat is transferred to the inside of the insulation layer; the second stage is specifically: radial heat conduction is generated inside the insulation layer.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] In the present invention, a cable electric power temperature rise heat transfer simulation test method is proposed. During fire simulation, according to the heat transfer stage of the cable, basic parameters and temperature rise parameters are input into the trained cable core power-on temperature rise model, or the heat source is controlled in the un-energized cable combustion experiment to reproduce the real cable electric power temperature rise heat transfer law. The actual situation of cable energized operation can be simulated, so that when it is difficult to achieve the cable energized condition in actual situation, the cable electric power temperature rise heat transfer under different current and voltage conditions can be equivalently simulated. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic diagram of the working process structure of a cable electric power heating and heat transfer simulation test method proposed by the present invention;

[0034] Figure 2 A schematic diagram of radial heat transfer of a cable in a cable power heating and heat transfer simulation test method proposed by the present invention;

[0035] Figure 3 A schematic diagram of the structure of a one-dimensional radial transient heat transfer model of a cable for a cable power heating and heat transfer simulation test method proposed by the present invention;

[0036] Figure 4 A schematic diagram of a current-cable outer surface temperature rise characteristic curve calculated by a cable electric power temperature rise heat transfer simulation test method proposed in the present invention;

[0037] Figure 5 It is a schematic diagram of the corrected current-cable outer surface temperature rise characteristic curve of a cable electric power temperature rise heat transfer simulation test method proposed by the present invention. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] For ease of understanding, the specific structure and working mode of the present invention are further described below in conjunction with the accompanying drawings:

[0040] Reference Figure 1-5 The present invention proposes a cable power heating and heat transfer simulation test method, comprising the following steps:

[0041] S1. Real-time acquisition of the heat transfer stage of the cable and the temperature rise parameters of the cable under power-on conditions. The heat transfer stage includes the first stage, the second stage, and the simulation stage.

[0042] In this embodiment, the first stage is as follows: the cable core conductor is energized and heated, and heat of a certain heat flux density is input into the insulation layer, and the contact surface between the insulation layer and the core is heated and heat is transferred to the inside of the insulation layer; the second stage is as follows: radial heat conduction is generated inside the insulation layer; the simulation stage is as follows: the outer surface of the insulation layer is simultaneously affected by radial heat conduction, and heat convection is generated with the air to dissipate heat.

[0043] In this embodiment, the heating parameters of the cable include but are not limited to is the constant heat flux density generated by the core power supply, k is the thermal conductivity, ρ is the density, c p is the specific heat capacity.

[0044] S2. Obtain the basic parameters of the cable. According to the heat transfer stage of the cable, input the basic parameters and temperature rise parameters into the trained cable core power-on temperature rise model to obtain the current-cable outer surface temperature rise characteristic curve in the simulation stage of the power-on process. The basic parameters include the actual cable radius r p , core radius r0, ambient temperature T a .

[0045] In this embodiment, the training process of the cable core power-on temperature rise model is as follows: obtain a historical experimental measurement data set, and divide the historical experimental measurement data set according to a preset strategy to form a training set, a test set, and a verification data set; obtain the model-related thermal convection coefficient h, and input the basic parameters of each moment in the training set into the corresponding power-on temperature rise network according to the heat transfer stage to perform model training to obtain the cable core power-on temperature rise model; compare the training results with the corresponding historical experimental measurement data set, and adjust the thermal convection coefficient h according to the comparison results until the error between the training results and the corresponding historical experimental measurement data set meets the preset error range to obtain a corrected cable core power-on temperature rise model.

[0046] In this embodiment, the preset strategy is specifically: using 70% of the historical experimental measurement data set as a training set, using 20% ​​of the historical experimental measurement data set as a test set, and using 10% of the historical experimental measurement data set as a verification data set.

[0047] In this embodiment, the heat convection coefficient h is adjusted as follows:

[0048] Get the theoretical value of the cable outer surface temperature at the same time With test value

[0049] The theoretical value With test value Substitute into the Euclidean norm formula to get the NORM value;

[0050] When NORM→0, it indicates the test value With theoretical value The more similar;

[0051] The calculation process of the Euclidean norm formula is as follows:

[0052]

[0053] in, is the theoretical value; is the test value;

[0054] The calculation process of the heat convection coefficient h is as follows:

[0055]

[0056] Among them, N u is the Nusselt number, D is the diameter, v is the kinematic viscosity of the fluid, α is the thermal conductivity of the fluid, k is the thermal conductivity of the fluid, Pr is the Prandtl number, g is the gravitational acceleration, and β is the air volume expansion coefficient.

[0057] In this embodiment, the current-temperature rise curve calculated by the cable heat transfer theoretical model is compared with the current-temperature rise curve obtained by the cable power heating heat transfer experiment measurement, and the experimental current temperature rise data ΔT is substituted into the calculation to obtain h(ΔT), and h(ΔT) is substituted into the cable power heat transfer finite difference equation for correction. The theoretical value of the cable temperature is obtained by iterative calculation, and the experimental value and the theoretical value are substituted into the Euclidean norm formula, where is the test value, is the theoretical value. When NORM→0, it indicates that the experimental value is closer to the theoretical value.

[0058] According to the modified cable power heat transfer finite difference equation, the core temperature T0 is obtained t The characteristic relationship between the power parameters of the cable and the power-on time t is obtained by inputting the core temperature model under the cable power-on condition into the fire simulation software, or controlling the heat source to reproduce the real cable power heating and heat transfer law in the unpowered cable combustion experiment. In this way, the actual situation of the cable energized operation can be simulated, thereby conducting research on the cable fire and combustion characteristics under different cable energization conditions.

[0059] In this embodiment, according to the heat transfer stage of the cable, the basic parameters and the temperature rise parameters are input into the trained cable core power-on temperature rise model to obtain the current-cable outer surface temperature rise characteristic curve in the simulation stage of the power-on process, specifically including:

[0060] According to the heat transfer stage of the cable, the basic parameters and temperature rise parameters are input into the trained cable core power-on temperature rise model to obtain the cable outer surface temperature at each moment in the simulation stage;

[0061] According to the temperature of the cable outer surface at each moment in the simulation stage and the constant heat flux density generated by the core power supply at each moment Generates a current-cable outer surface temperature rise characteristic curve during the simulation phase of the power-on process.

[0062] The cable core power-on temperature rise model is specifically expressed as:

[0063]

[0064] Among them, T a is the ambient temperature; is the thermal diffusion coefficient, is the Fourier number, is the Biot number; is the constant heat flux density generated by the core power supply; k is the thermal conductivity; ρ is the density; c p is the specific heat capacity; h is the thermal convection coefficient; T i 0 is the core surface at time t=t i Temperature at time; T i+10 is the core surface at time t=t i Temperature at +Δt; T i m-1 is the control body of the insulating layer m-1 at time t=t i Temperature at time; T i m is the control volume of the insulating layer m at time t=t i Temperature at time; T i+1 m is the control volume of the insulating layer m at time t=t i Temperature at +Δt; T i m+1 is the control volume of the insulating layer m+1 at time t=t i Temperature at time; T i p is the cable surface at time t = t i Temperature at time; T i+1 p is the cable surface at time t = t i Temperature at +Δt.

[0065] In the process of constructing the cable core energized temperature rise model, three control bodies are established according to the three stages of heat transfer of the energized cable. The energy conservation principle is applied to obtain three heat equations, which are as follows:

[0066]

[0067] in, is the constant heat flux density generated by the core power supply, k is the thermal conductivity, ρ is the density, c p is the specific heat capacity, h is the thermal convection coefficient, T i 0 is the core surface at time t=t i The temperature at i+1 0 is the core surface at time t=t i Temperature at +Δt, T i m-1 is the control body of the insulating layer m-1 at time t=t i The temperature at i m is the control volume of the insulating layer m at time t=t i The temperature at i+1 m is the control volume of the insulating layer m at time t=t i Temperature at +Δt, T i m+1 is the control volume of the insulating layer m+1 at time t=t i The temperature at i p is the cable surface at time t = t iThe temperature at i+1 p is the cable surface at time t = t i +Δt temperature, A0, A m , A p They are the heat transfer areas of the three heat transfer stages of the cable.

[0068] According to the thermal diffusion coefficient Fourier number Biot number Transforming the above formula yields:

[0069]

[0070] According to the stability criterion principle, we can get:

[0071] 1-2Fo≥0

[0072] 1-2BiFo-2Fo≥0

[0073] Pick The calculation can be obtained:

[0074]

[0075] To simplify the finite difference equation, take the maximum value of Δt allowed

[0076] Iterative calculation can obtain the core surface temperature T0 after power-on time t t and cable outer surface temperature T p t .

[0077] Of course, it is obvious to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, but also includes the same or similar structures that can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-limiting, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention. Any reference numerals in the claims should not be regarded as limiting the claims involved.

[0078] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

[0079] The techniques, shapes, and structural parts not described in detail in the present invention are all well-known techniques.

Claims

1. A cable power heating and heat transfer simulation test method, characterized in that: The following steps are involved: S1. Real-time acquisition of the heat transfer stage of the cable and the temperature rise parameters of the cable under power-on conditions, wherein the heat transfer stage includes at least a simulation stage, and the simulation stage is specifically: the outer surface of the insulation layer is simultaneously subjected to radial heat conduction and generates heat convection with the air to dissipate heat; S2. Obtain the basic parameters of the cable, and according to the heat transfer stage of the cable, input the basic parameters and temperature rise parameters into the trained cable core power-on temperature rise model to obtain the current-cable outer surface temperature rise characteristic curve in the simulation stage of the power-on process.

2. The cable power heating and heat transfer simulation test method according to claim 1 is characterized in that: The basic parameters include the real cable radius r p , core radius r0, ambient temperature T a The heating parameters of the cable include the constant heat flux density generated by the power supply of the core Thermal conductivity k, density ρ, specific heat c p .

3. The cable power heating and heat transfer simulation test method according to claim 1 or 2, characterized in that: According to the heat transfer stage of the cable, the basic parameters and temperature rise parameters are input into the trained cable core power-on temperature rise model to obtain the current-cable outer surface temperature rise characteristic curve in the simulation stage of the power-on process, including: According to the heat transfer stage of the cable, the basic parameters and temperature rise parameters are input into the trained cable core power-on temperature rise model to obtain the cable outer surface temperature at each moment in the simulation stage; According to the temperature of the cable outer surface at each moment in the simulation stage and the constant heat flux density generated by the core power supply at each moment Generates a current-cable outer surface temperature rise characteristic curve during the simulation phase of the power-on process. The cable core power-on temperature rise model is specifically expressed as: Among them, T a is the ambient temperature; is the thermal diffusion coefficient, is the Fourier number, is the Biot number; is the constant heat flux density generated by the core power supply; k is the thermal conductivity; ρ is the density; c p is the specific heat capacity; h is the thermal convection coefficient; T i 0 is the core surface at time t=t i Temperature at time; T i+1 0 is the core surface at time t=t i Temperature at +Δt; T i m-1 is the control body of the insulating layer m-1 at time t=t i Temperature at time; T i m is the control volume of the insulating layer m at time t=t i Temperature at time; T i+1 m is the control volume of the insulating layer m at time t=t i Temperature at +Δt; T i m+1 is the control volume of the insulating layer m+1 at time t=t i Temperature at time; T i p is the cable surface at time t = t i Temperature at time; T i+1 p is the cable surface at time t = t i Temperature at +Δt.

4. The cable power heating and heat transfer simulation test method according to claim 3 is characterized in that: The training process of the cable core energized temperature rise model is as follows: Obtain a historical experimental measurement data set, and divide the historical experimental measurement data set according to a preset strategy to form a training set, a test set, and a verification data set; Obtain the thermal convection coefficient h related to the model, and input the basic parameters at each moment in the training set into the corresponding power-on temperature rise network according to the heat transfer stage to perform model training, so as to obtain the power-on temperature rise model of the cable core; The training results are compared with the corresponding historical experimental measurement data sets, and the thermal convection coefficient h is adjusted according to the comparison results until the error between the training results and the corresponding historical experimental measurement data sets meets the preset error range to obtain the corrected cable core power-on temperature rise model.

5. The cable power heating and heat transfer simulation test method according to claim 4 is characterized in that: The preset strategy is specifically: using 70% of the historical experimental measurement data set as a training set, using 20% ​​of the historical experimental measurement data set as a test set, and using 10% of the historical experimental measurement data set as a verification data set.

6. The cable power heating and heat transfer simulation test method according to claim 4 is characterized in that: The heat convection coefficient h adjustment process is as follows: Get the theoretical value of the cable outer surface temperature at the same time With test value The theoretical value With test value Substitute into the Euclidean norm formula to get the NORM value; The calculation process of the Euclidean norm formula is as follows: in, is the theoretical value; is the test value; Adjust the heat convection coefficient h so that the NORM value approaches 0; Corrected adjusted thermal convection coefficient The calculation process is as follows: Among them, N u is the Nusselt number, D is the diameter, v is the kinematic viscosity of the fluid, α is the thermal conductivity of the fluid, k is the thermal conductivity of the fluid, Pr is the Prandtl number, g is the gravitational acceleration, and β is the air volume expansion coefficient.

7. The cable power heating and heat transfer simulation test method according to claim 1 is characterized in that: The heat transfer stage also includes a first stage and a second stage located before the simulation stage, wherein the first stage is specifically: the cable core conductor is energized and heated, heat of a certain heat flux density is input into the insulation layer, and the contact surface between the insulation layer and the core is heated and heat is transferred to the inside of the insulation layer; the second stage is specifically: radial heat conduction is generated inside the insulation layer.

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