A method for identifying a point of ignition for a cable tunnel fire scenario

Abstract

The application discloses a kind of ignition point identification methods for cable trench fire scene, comprising the following steps: S1: constructing fire simulation experiment platform, according to the height of cable trench, equidistantly install several temperature detectors in cable trench;S2: obtain the temperature data fed back by each sensor, the position corresponding to sensor and the height of cable trench, adopt single exponential function to establish cable trench roof temperature distribution law prediction.The temperature change of each sensor is used as a measurement index to explore the temperature distribution law of the longitudinal position of the roof, and fire data is obtained.The ignition point position and maximum temperature rise are predicted by fitting the fire data.By combining the influence of fire temperature propagation coefficient and cable tunnel structure parameters, the positioning prediction can be more accurate, with higher reliability and more convenient calculation, providing a basis for cable trench fire prevention.

Description

Technical Field

[0001] This invention relates to the field of cable trench fire technology, and more particularly to a method for identifying ignition points in cable trench fire scenarios. Background Technology

[0002] In recent years, my country's industrialization level has been rising continuously. The use of underground cable power transmission has advantages such as reducing the land area occupied and improving anti-interference ability, and it has been widely used in the power system.

[0003] A fire in a cable trench can cause serious consequences such as explosions and electric arcs, posing a significant threat to personnel safety and the environment. Locating the source of the fire in its early stages can reduce the risk. However, existing fire warning methods are not very accurate, have long calculation times, and are ill-suited for responding to sudden fires.

[0004] The temperature rise pattern of the ceiling is an important part of current research on cable trench fires. Current research focuses on the theoretical basis of fire spread trends and smoke diffusion patterns in underground utility tunnels. There is relatively little research on the temperature distribution pattern of the ceiling in early fires and how to quickly and accurately locate the ignition point. Existing prediction and location methods have a series of problems such as poor accuracy and convenience. There is an urgent need for an ignition point identification method for cable trench fire scenarios to provide a basis for early cable trench fire prevention. Summary of the Invention

[0005] The purpose of this invention is to address the deficiencies in the existing technology by proposing a method for identifying ignition points in cable trench fire scenarios.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for identifying ignition points in cable trench fire scenarios includes the following steps:

[0008] S1: Install several temperature detectors at equal intervals in the cable trench according to the height of the cable trench.

[0009] S2: Obtain the temperature data fed back by each sensor, the corresponding location of the sensor, and the height of the cable trench; use a single exponential function to establish a prediction of the temperature distribution pattern of the cable trench roof.

[0010] S3: Based on the height difference ΔH of the cable trench and the ceiling temperature rise ΔT at different temperature measurement points. max,x1 ΔT max,x2 And the longitudinal distance l, the maximum temperature rise ΔT of the cable trench is obtained by fitting a function. max And the longitudinal distances d1 and d2 between the temperature measuring point and the ignition point are determined by calculation;

[0011] S4: Calculate using known temperature extreme values ​​to detect the location of the maximum temperature in the cable trench and obtain the specific location of the ignition point.

[0012] Furthermore, the temperature detectors are K-type armored thermocouples, which are arranged at least 1m intervals on the ceiling.

[0013] Furthermore, in step S2, the longitudinal temperature decay follows the following pattern:

[0014]

[0015] In the formula, ΔT max,x ΔT represents the maximum temperature rise of the sensor at point X m. max y0 represents the maximum temperature rise in the cable trench, d represents the longitudinal distance between the sensor and the fire source, ΔH represents the vertical height difference between the sensor and the ground, and y0, A, T D T au Represents the coefficients in the formula.

[0016] Furthermore, in step S3, the fitting function is nonlinearly fitted using the formula in step S2.

[0017] Furthermore, in step S4, the method for predicting the ignition point location is as follows:

[0018]

[0019] Among them, ΔT in the system of equations max,x1 ΔT max,x2 Since l, ΔH1, and ΔH2 are all known, substituting them into the equation will yield the maximum temperature rise ΔT in the cable trench. max The longitudinal distances d1 and d2 between the temperature measuring point and the ignition point can be used to further determine the location of the ignition point.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] By using temperature changes from various sensors as a metric, the temperature distribution pattern along the longitudinal direction of the ceiling is explored, and fire data is obtained. By fitting the fire data, the location of the ignition point and the maximum temperature rise are predicted. By combining the fire temperature propagation coefficient and the influence of cable tunnel structural parameters, the location prediction can be made more accurately, with higher reliability and more convenient calculation, providing a basis for fire prevention of cable trenches. Attached Figure Description

[0022] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0023] Figure 1This is a schematic diagram of the thermocouple distribution in the cable trench in an embodiment of the present invention;

[0024] Figure 2 This is a schematic diagram of the cable trench fire location method in an embodiment of the present invention;

[0025] Figure 3 This is a schematic diagram illustrating the verification results of the accuracy of ignition point location in an embodiment of the present invention;

[0026] Figure 4 This is to verify the accuracy of the maximum temperature prediction for the cable trench in the embodiments of the present invention. Detailed Implementation

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0028] In this application, it should be noted that:

[0029] Currently, in theoretical research on the maximum ceiling temperature in tunnel fires, the classic formula for predicting the maximum ceiling temperature rise under natural ventilation conditions is as follows:

[0030]

[0031] Where, ΔT max The maximum temperature rise of the ceiling represents the fire source power; Q represents the effective height of the trench; α is an empirical coefficient, which is 17.5 here.

[0032] A method for identifying ignition points in cable trench fire scenarios includes the following steps:

[0033] S1: Install several temperature detectors at equal intervals in the cable trench according to the height of the cable trench.

[0034] S2: Obtain the temperature data fed back by each sensor, the corresponding location of the sensor, and the height of the cable trench; use a single exponential function to establish a prediction of the temperature distribution pattern of the cable trench roof.

[0035] It should be noted that the experimental fire conditions were reproduced using Pyrosim fire simulation software, and the maximum temperature distribution of the ceiling at different locations was obtained.

[0036] S3: Based on the height difference ΔH of the cable trench and the ceiling temperature rise ΔT at different temperature measurement points. max,x1 ΔT max,x2 And the longitudinal distance l, the maximum temperature rise ΔT of the cable trench is obtained by fitting a function. max And the longitudinal distances d1 and d2 between the temperature measuring point and the ignition point are determined by calculation;

[0037] S4: Calculate using known temperature extreme values ​​to detect the location of the maximum temperature in the cable trench and obtain the specific location of the ignition point.

[0038] In a specific embodiment of this application, the temperature detector uses a type K armored thermocouple, which is arranged at least 1m intervals on the ceiling.

[0039] In step S2, the longitudinal temperature decay follows the following pattern:

[0040]

[0041] In the formula, ΔT max,x ΔT represents the maximum temperature rise of the sensor at point X m. max y0 represents the maximum temperature rise in the cable trench, d represents the longitudinal distance between the sensor and the fire source, ΔH represents the vertical height difference between the sensor and the ground, and y0, A, T D T au Represents the coefficients in the formula;

[0042] In step S3, the fitting function is nonlinearly fitted using the formula in step S2;

[0043] In step S4, the method for predicting the ignition point location is as follows:

[0044]

[0045] Among them, in the system of equations ΔT max,x1 ΔT max,x2 Since l, ΔH1, and ΔH2 are all known, substituting them into the equation will yield the maximum temperature rise ΔT in the cable trench. max The longitudinal distances d1 and d2 between the temperature measuring point and the ignition point can be used to further determine the location of the ignition point.

[0046] To better understand the technical solution of this application, the following explanation is further illustrated with experiments.

[0047] Setting up the experimental platform:

[0048] A 1:1 full-size circular cable trench fire model experimental platform was established within a 10m fire-resistant zone. The effective height of the trench was 1.64m, and the walls were made of cast concrete with a thickness of 0.18m. The platform was supported by a steel frame. Due to the obstruction of the surrounding walls, the trench was highly enclosed during a fire, and the impact of the external environment was relatively small and negligible. The two ends of the trench were designed as open structures for natural ventilation, and fireproof partitions were used to prevent the spread of fire.

[0049] The temperature detectors use type K armored thermocouples, which are arranged at 1m intervals at 1.64m positions on the ceiling from T0 (X=0m) to T5 (X=5m). The thermocouple positions are as follows: Figure 1 As shown.

[0050] Oil bath fire experiments were conducted using high-concentration ethanol, with the ignition source placed in the center of the trench. Due to the small size of the circular cable trench experimental platform, a smaller ignition source power was suitable; therefore, 0.2MW and 0.5MW were selected for the ignition source power. The maximum temperature at each sensor under different ignition source powers is shown in Table 1.

[0051]

[0052]

[0053] Table 1

[0054] Currently, theoretical research on the maximum temperature of the ceiling in tunnel fires is relatively mature. Among them, Li proposed a classic formula for predicting the maximum temperature rise of the ceiling under natural ventilation conditions:

[0055]

[0056] Where, ΔT max The maximum temperature rise of the ceiling in a trench fire is represented by Q; the power of the fire source is represented by H; the effective height of the trench is represented by α, which is an empirical coefficient of 17.5.

[0057] Ignition point location:

[0058] The height difference ΔH of the cable trench can be obtained through measurement. If the ceiling temperature rise ΔT at two different temperature measurement points can be determined... max,x1 ΔT max,x2 And the longitudinal distance l, the maximum temperature rise ΔT of the cable trench can be obtained by solving a system of equations using a fitted function. max The longitudinal distances d1 and d2 between the temperature measuring point and the ignition point are determined by calculation. A schematic diagram of the temperature sensor installation and ignition point location method within the fire-resistant zone is shown below. Figure 2 As shown.

[0059] In summary, the equations for predicting the ignition point location are listed as shown in formula (3). In the equations, ΔT max,x1 ΔT max,x2 Since l, ΔH1, and ΔH2 are all known, substituting them into the equation will yield the maximum temperature rise ΔT in the cable trench. max The longitudinal distances d1 and d2 between the temperature measuring point and the ignition point can be used to further determine the location of the ignition point.

[0060] In this experiment, ceiling temperature sensors T0 and T5 were selected as the temperature sensors on both sides. The fitting function of the maximum temperature rise distribution of the ceiling was substituted into the equation system, and the calculated results were compared with the experimental results to finally determine the most accurate equation system for predicting the ignition point. Based on the above approach, three additional cable fire experiments were conducted, with the ignition points located at X = 1.5m, X = 2.5m, and X = 3.5m, respectively. Temperature sensors T0 and T5 were placed at the ceiling positions of X = 0m and X = 5m, respectively, to obtain the maximum temperature rise ΔT at that location. max,x0 ΔT max,x5 Temperature sensors T1, T2, and T3 were placed at the ceiling locations of the three ignition points to obtain the maximum temperature rise ΔT at the ignition points. max .

[0061] The maximum temperature rise directly above the ignition point can be approximated as the maximum temperature rise inside the tunnel. Taking the ambient temperature as 10℃, the experimental data from three experiments are shown in Table 2.

[0062]

[0063] Table 2

[0064] Based on the fitted curve obtained from the first set of experiments, the parameters y0 = 0.6424, A = 0.5736, and T were set... D =1.5981, T au Substituting 3.3116 into the system of equations, and combining ΔH and the experimental data ΔT... max,x0 ΔT max,x5 Substituting the values, we can obtain the fire source location results for the first set of fitted curves. Similarly, we can obtain the fire source location results for the fitted curves of Experiment 2, Experiment 3, and Experiment 4. The results of the fire point location are summarized in Table 3.

[0065]

[0066] Table 3

[0067] like Figure 3As shown, in fitted curve one, the maximum deviation between the calculated and actual values ​​of the fire source location is 0.239m, the average deviation is 0.124m, and the average accuracy reaches 95.50%; in fitted curve two, the maximum deviation is 0.098m, the average deviation is 0.044m, and the average accuracy reaches 98.77%; in fitted curve three, the maximum deviation is 0.200m, the average deviation is 0.147m, and the average accuracy reaches 95.03%; in fitted curve four, the maximum deviation is 0.330m, the average deviation is 0.256m, and the average accuracy reaches 91.43%. The calculation results show that all four fitted curves can identify the location of the ignition point relatively well. Especially when the parameters y0 = 0.6796, A = 1.8827, and T... D =1.5003, T au When the value is 9.1240, the average accuracy reaches 98.77%, which can provide a basis for the location identification of fire sources.

[0068] Maximum temperature prediction:

[0069] The exact location of the ignition point was obtained by calculating using known extreme temperature values, and the maximum temperature rise ΔT in the channel could be determined during the solution of the equations. max The solution is obtained as an unknown quantity.

[0070] The extreme temperature values ​​within the cable trench are calculated based on the fitting formula for identifying the ignition point location obtained from Example 2. The accuracy of the results is judged by the difference between the calculated and experimental values. The parameters y0 = 0.6796, A = 1.8827, and T are set as follows: D =1.5003, T au Substituting 9.1240 into the system of equations, the calculation results are shown in Table 4.

[0071]

[0072]

[0073] Table 4

[0074] Verification of the accuracy of maximum temperature prediction in cable trenches, such as Figure 4 As shown:

[0075] As can be seen from the figure, the temperature prediction method can accurately calculate the maximum temperature in the cable trench. The error range between the calculated temperature and the actual temperature is between 19℃ and 31℃, with an average accuracy of 96.67%, which is a significant improvement in accuracy compared to the traditional method for calculating the maximum temperature in cable trenches.

[0076] As can be seen from the above, through experiments and simulations of cable trench fires with different fire source powers, it was found that the maximum temperature of the ceiling directly above the ignition point is the maximum temperature of the cable trench. Under the same location range, the temperature changes faster closer to the fire source.

[0077] The calculated results of the ignition point identification method show minimal deviation from experimental results, with a location deviation within 0.098m and an average accuracy of 98.77%. The maximum temperature prediction method for the ceiling shows a maximum temperature deviation within 31℃ and an average accuracy of 96.67%. Compared to traditional methods for predicting cable trench location and maximum temperature rise, this method considers the influence of fire temperature propagation coefficients and cable tunnel structural parameters, enabling more accurate location prediction, higher reliability, and more convenient calculation. It provides a scientific basis and theoretical guidance for fire prevention in cable trenches.

[0078] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for identifying ignition points in cable trench fire scenarios, characterized in that, Includes the following steps: S1: Install several temperature detectors at equal intervals in the cable trench according to the height of the cable trench. S2: Obtain the temperature data fed back by each sensor, the corresponding location of the sensor, and the height of the cable trench; use a single exponential function to establish a prediction of the temperature distribution pattern of the cable trench roof. S3: Based on the height difference of the cable trench Temperature rise of the ceiling at different temperature measurement points and longitudinal distance l The maximum temperature rise of the cable trench was obtained by fitting a function. The longitudinal distance between the temperature measuring point and the ignition point was determined by calculation. 、 ; S4: Calculate using known extreme temperature values ​​to detect the location of the maximum temperature in the cable trench and obtain the specific location of the ignition point; In step S2, the longitudinal temperature decay follows the following pattern: ； In the formula, This represents the maximum temperature rise of the sensor at location X m. This represents the maximum temperature rise in the cable trench. d This represents the longitudinal distance between the fire source and the sensor. This represents the vertical height difference between the sensor and the ground. 、A、 Represents the coefficients in the formula; In step S4, the method for predicting the ignition point location is as follows: ； Among them, in the system of equations , , , , All the values ​​are known; by substituting them into the equation, the maximum temperature rise of the cable trench can be calculated. and the longitudinal distance between the temperature measuring point and the ignition point , This allows us to further determine the location of the fire.

2. The method for identifying ignition points in cable trench fire scenarios according to claim 1, characterized in that, The temperature detectors are K-type armored thermocouples, which are arranged at least 1m intervals on the ceiling.

3. The method for identifying ignition points in cable trench fire scenarios according to claim 1, characterized in that, In step S3, the fitting function is nonlinearly fitted using the formula in step S2.

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