Cable tunnel fire risk assessment method for cable joint arc breakdown fault

Abstract

The invention discloses a cable tunnel fire risk assessment method for a cable joint arc breakdown fault. The method comprises the following steps: step 1, constructing an electric arc ignition test platform; step 2, performing an electric arc ignition test under various working conditions to obtain respective temperatures of the various working conditions, respective flame heights of the various working conditions and respective average electric arc power of the various working conditions; 3, new cable intermediate joint simulation models under different simulation test conditions are established, and multiple risk factors influencing the cable tunnel fire risk are obtained; 4, determining the weight of the target layer and the actual score values of the multiple risk factors according to a hierarchy analysis method, and calculating to obtain the score value of the intermediate joint of the sample cable; and step 5, determining the fire risk level and the fire risk state of the sample cable tunnel where the sample cable intermediate joint is located. The technical problem that the risk of cable fire caused by the electric arc grounding fault of the cable joint cannot be quantitatively analyzed is solved.

Description

Technical Field

[0001] The present invention relates to the field of cable joint fire risk assessment, and in particular to a cable tunnel fire risk assessment method for cable joint arc breakdown faults. Background Art

[0002] In order to ensure the reliability of power transmission and ensure the smoothness, sealing and insulation of the transmission line, a cable intermediate joint is usually used as a cable accessory to connect two cable bodies of a certain length. However, during the manufacturing process, the cable intermediate joint is prone to installation process problems such as burrs, air gaps, impurities, scratches, etc., resulting in electric field distortion inside the cable intermediate joint. After the cable has been in operation for a period of time, the internal defects of the joint gradually expand under the action of electrical-thermal stress, so that the cable insulation is broken down and an arc grounding fault occurs, which causes a tunnel fire. In order to avoid the large current generated by the fault from burning electrical equipment, the main network lines of 110kV and above often adopt the method of direct grounding of the neutral point. When a single-phase grounding fault occurs in the cable, the relay protection will immediately operate and cut off the power supply. However, according to relevant national standards, high-voltage cable breakdown characteristics and cable failure cases, it can be seen that after the cable is broken down, there is a continuous arcing process of milliseconds and large current. The arc discharge process manifests itself in the form of electricity, heat, light, magnetism, etc., and at the same time, energy is transferred in the form of heat energy, kinetic energy, etc., which can be visualized as phenomena such as increased air temperature, cable ignition, and molten material splashing. In the cable intermediate joint, the insulating material cross-linked polyethylene and the filler polyurethane are both flammable. The sheath layer polyvinyl chloride can also be ignited under continuous high temperature. Therefore, an arc grounding fault in the cable intermediate joint is likely to cause a cable fire. At present, cable tunnel fires are mostly qualitatively analyzed from the aspects of fire mechanism, combustion phenomenon, spread trend, and influencing factors, which to a certain extent explain the combustion characteristics of cable fires and the law of cable fire development. However, existing studies have not quantitatively analyzed the correlation between fire influencing factors and fire intensity, and have not established a quantitative analysis model for the correlation between factors such as tunnel environment, cable type, arc characteristics, and the size of cable fire.

[0003] To address the above-mentioned problems, no effective solution has been proposed yet. Summary of the invention

[0004] The embodiment of the present invention provides a cable tunnel fire risk assessment method for cable joint arc breakdown faults, so as to at least solve the technical problem that the risk of cable fire caused by arc grounding faults at cable joints cannot be quantitatively analyzed.

[0005] According to one aspect of an embodiment of the present invention, a fire risk assessment method is provided, comprising: step 1: constructing an arc ignition test platform, wherein the arc ignition test platform comprises a target cable intermediate joint, a power frequency current generator, a high voltage probe and an acquisition card, an infrared camera, and a thermocouple;

[0006] Step 2: Under various working conditions, arc ignition tests are performed to obtain respective temperatures and flame heights of the various working conditions, as well as respective average arc powers of the various working conditions, wherein the power supply voltages of the various working conditions are provided by a power frequency current generator, and the power supply voltages of the various working conditions are the same, and the current magnitudes or durations of the various working conditions are different;

[0007] Step 3: Establish a simulation model of the cable intermediate joint according to the arc ignition test, set a simulated combustion surface at the middle copper conductor position of the simulated cable intermediate joint, determine the heat release rate of the simulated combustion surface according to the average arc power obtained in the arc ignition test, and set multiple simulation test conditions that are the same as the arc ignition test to verify that the temperature obtained by the cable intermediate joint simulation model and the arc ignition test is within a predetermined first difference range, and the flame height is maintained within a predetermined second difference range. Change the simulation conditions, including the arc ignition power of the simulated cable intermediate joint and the cable structure parameters, establish a new cable intermediate joint simulation model under different simulation test conditions, and obtain multiple risk factors that affect the fire risk of the cable tunnel;

[0008] Step 4: Analyze multiple risk factors according to the hierarchical analysis method, take multiple risk factors as the indicator layer, and determine the criterion layer and the target layer according to the multiple risk factors, determine the weight of the target layer and the actual score values ​​of the multiple risk factors, and calculate the score value of the sample cable intermediate joint according to the weight of the target layer and the actual score values ​​of the multiple risk factors. i It is obtained according to the cable fire risk factor score table, which is obtained through historical fire conditions and expert scores;

[0009] Step 5: Based on the scoring value of the sample cable intermediate joint, determine the fire risk level and fire risk status of the sample cable tunnel where the sample cable intermediate joint is located.

[0010] Optionally, step 1: building an arc ignition test platform includes the following steps:

[0011] Step 1.1: Select the target cable intermediate joint, use hydraulic pliers to cover the copper terminal on the copper conductor inside the cable body on one side of the target cable intermediate joint, and connect it to the positive pole of the power frequency current generator, fix the screw on the aluminum sheath of the cable body on the other side of the target cable intermediate joint, and connect it to the negative pole of the power frequency current generator, punch a hole from the outside to the inside in the middle position of the target cable intermediate joint until the copper conductor position of the target cable intermediate joint, use copper wire as an arc starting wire to connect the copper conductor at the middle position of the target cable intermediate joint, the copper conductor inside the cable body on one side of the target cable intermediate joint, and the aluminum sheath of the cable body on the other side of the target cable intermediate joint, and use a clamp to fix the target cable intermediate joint on the bracket to obtain an arc ignition test circuit, wherein, punching a hole from the outside to the inside in the middle position of the target cable intermediate joint until the copper conductor position of the target cable intermediate joint is used to simulate the state of insulation breakdown of the target cable intermediate joint;

[0012] Step 1.2, placing high-voltage probes, acquisition cards, and infrared cameras around the arc ignition test, and arranging thermocouples above the middle position of the middle joint of the target cable to obtain an arc ignition test platform, wherein the high-voltage probe and acquisition card are used to collect arc voltage, the infrared camera is used to monitor the temperature of the arc ignition test platform, and the thermocouple is used to monitor the temperature of a specific temperature measuring point of the arc ignition test platform.

[0013] Optionally, step 2: performing arc ignition tests under various working conditions to obtain respective temperatures and respective flame heights under various working conditions comprises the following steps:

[0014] Step 2.1: Detect the circuit and circuit equipment of the arc ignition test platform and start the arc ignition test;

[0015] Step 2.2: Through the arc ignition test, the temperature of each of the various working conditions and the flame height of each of the various working conditions are measured, and the arc voltage of each of the various working conditions and the arc current of each of the various working conditions are obtained;

[0016] Step 2.3: Calculate the arc energy Q of various working conditions according to the arc voltages and arc currents of various working conditions. The calculation formula is: Wherein, P(t) is the instantaneous arc power of each of the various working conditions calculated from the arc voltages of each of the various working conditions and the arc currents of each of the various working conditions; t1 is the start time of the arc generated by each of the various working conditions; t2 is the end time of the arc generated by each of the various working conditions;

[0017] Step 2.4: Determine the average arc power P of various working conditions according to the arc energy Q of various working conditions arc , the calculation formula is:

[0018] Optionally, step 3: establish a simulation model of the cable intermediate joint according to the arc ignition test, set a simulated combustion surface at the position of the middle copper conductor of the simulated cable intermediate joint, determine the heat release rate of the simulated combustion surface according to the average arc power obtained in the arc ignition test, and set a plurality of simulation test conditions that are the same as the arc ignition test, verify that the temperature obtained by the cable intermediate joint simulation model and the arc ignition test is within a predetermined first difference range, and the flame height is maintained within a predetermined second difference range, change the simulation conditions, including the arc ignition power of the simulated cable intermediate joint and the cable structure parameters, establish a new cable intermediate joint simulation model under different simulation test conditions, and obtain a plurality of risk factors that affect the fire risk of the cable tunnel, including the following steps:

[0019] Step 3.1: Based on the arc ignition test, an initial cable intermediate joint simulation model is established, a simulated combustion surface is set at the middle copper conductor position of the simulated cable intermediate joint, the heat release rate of the simulated combustion surface is determined according to the average arc power obtained in the arc ignition test, and multiple simulation test conditions that are the same as the arc ignition test are set, wherein the simulation environment of the initial cable intermediate joint simulation model is consistent with the test environment of the arc ignition test;

[0020] Step 3.2: Conduct simulation tests on the initial simulated cable intermediate joint under multiple simulated working conditions that are the same as the multiple working conditions, obtain the respective temperatures of the initial simulated cable intermediate joint under the multiple simulated working conditions, and compare the respective temperatures of the initial simulated cable intermediate joint under the multiple simulated working conditions with the temperatures under the corresponding working conditions of the arc ignition test, and obtain the respective comparison results under the multiple simulated working conditions;

[0021] Step 3.3: According to the respective comparison results under various simulation working conditions, the proportion of substances participating in the combustion of the insulation layer, filling layer, and sheath layer of the initial simulation cable intermediate joint is adjusted until the temperature difference obtained by simulating the initial simulation cable intermediate joint under various simulation working conditions and the temperature difference of the arc ignition test under the same working conditions are kept within the predetermined first difference range, and the simulated cable intermediate joint and the cable intermediate joint simulation model are obtained, wherein the proportion of substances participating in the combustion of the insulation layer, filling layer, and sheath layer of the initial simulation cable intermediate joint can be expressed as: x1(C2H3Cl)+x2(C9H 14 O3N2)+x3(C2H4), the adjusted formula is: x1(C2H3Cl)+x2(C9H 14 O3N2)+x3(C2H4)+a5O2→bO2+cCO+dC+eH2O+

[0022] fHCl+gHCN, a, b, c, d, e, f, g are the coefficients of the reaction equation, C2H3Cl is the monomer corresponding to the polymer polyvinyl chloride, x1 is the reaction coefficient of C2H3Cl, C9H 14 O3N2 is the monomer corresponding to polyurethane, and x2 is C9H 14 The reaction coefficient of O3N2, C2H4 is the monomer corresponding to cross-linked polyethylene, x3 is the reaction coefficient of C2H4, O2 is oxygen, CO is carbon monoxide, C is carbon, H2O is water, HCl is hydrogen chloride, and HCN is hydrogen cyanide;

[0023] Step 3.4: Simulate the simulated cable intermediate joint under multiple simulation conditions, and when the simulated cable intermediate joint burns stably, obtain the result that the flame height under the multiple simulation conditions and the flame height under the corresponding conditions of the arc ignition test have errors within the predetermined second difference range;

[0024] Step 3.5: Based on the results obtained in step 3.4, change the voltage level and structural parameters of the simulated cable intermediate joint, establish new cable intermediate joint simulation models, and obtain various risk factors that affect cable tunnel fires. The various risk factors include cable position, layer spacing, horizontal spacing, tunnel temperature, tunnel humidity, tunnel wind speed, voltage level, cross-sectional area, cable load, operating years, and duration.

[0025] Optionally, step 4: analyzing the multiple risk factors according to the hierarchical analysis method, taking the multiple risk factors as the indicator layer, determining the criterion layer and the target layer according to the multiple risk factors, determining the weight of the target layer and the actual score values ​​of each of the multiple risk factors, and calculating the score value of the sample cable intermediate joint according to the weight of the target layer and the actual score values ​​of each of the multiple risk factors, including the following steps:

[0026] Step 4.1: Analyze multiple risk factors according to the hierarchical analysis method, use multiple risk factors as the indicator layer, and construct the criterion layer and target layer according to the multiple risk factors, where the target layer is the highest level, the criterion layer is the middle level, and the indicator layer is the lowest level. The criterion layer includes cable layout characteristics, environmental characteristics, and cable fault characteristics. The cable layout characteristics include cable position, layer spacing, and horizontal spacing. The environmental characteristics include tunnel temperature, tunnel humidity, and tunnel wind speed. The arc fault characteristics include voltage level, cross-sectional area, cable load, operating years, and duration. The target layer is the cable tunnel fire risk.

[0027] Step 4.2: According to the hierarchical relationship of each risk factor, compare the importance of all risk factors at the same level, and construct the judgment matrix between the target layer and the criterion layer, and between the criterion layer and the indicator layer. The expression of the judgment matrix is: T uis the judgment matrix, x ij is the relative importance of risk factor i to risk factor j, i and j are two risk factors in the same layer, u is the upper-layer risk factor corresponding to the lower-layer risk factor, and n is the number of risk factors in the same layer;

[0028] Step 4.3: Normalize the values ​​in the judgment matrix and calculate the weight of the lower risk factor i relative to the upper risk factor u. The calculation formula is: x ij is the relative importance of risk factor i to risk factor j, where i and j are two risk factors at the same level;

[0029] Step 4.4: Calculate the weights between risk factors at the same level. The calculation formula is: w ij =w iu -w ju +ab, ab is a constant, w iu is the weight of the lower risk factor i relative to the upper risk factor u, w ju The weight of the lower risk factor j relative to the upper risk factor u;

[0030] Step 4.5: Use the formula Obtain a feasibility ratio, and use the feasibility ratio to make a feasibility judgment on the judgment matrix. When the feasibility ratio Z is less than a predetermined threshold, the judgment matrix meets the feasibility requirements;

[0031] Step 4.6: The overall weight of the target layer is: w iz =w iA × iB , w iA is the weight of the risk factor i of the criterion layer relative to the risk factor A of the target layer, w iB is the weight of the risk factor i at the indicator level relative to the risk factor B at the criterion level;

[0032] Step 4.7: According to the overall weight of the target layer, the score value of the sample cable intermediate joint is obtained. The score value S of the sample cable intermediate joint is calculated as follows: R i is the actual score of risk factor i, where R i It is obtained based on the cable fire risk factor scoring table, which is obtained through historical fire conditions and expert scores.

[0033] Optionally, step 5: determining the fire risk level and fire risk status of the sample cable tunnel where the sample cable intermediate joint is located according to the scoring value of the sample cable intermediate joint, comprises the following steps:

[0034] Step 5.1: According to the scoring value of the sample cable intermediate joint, determine the fire risk level and fire risk status of the sample cable tunnel caused by the sample cable intermediate joint; when S is less than S1, the fire risk level of the sample cable tunnel is A, and the fire risk status of the sample cable tunnel is normal; when S is greater than S1 and less than S2, the fire risk level of the sample cable tunnel is B, and the fire risk status of the sample cable tunnel is a light fire; when S is greater than S2 and less than S3, the fire risk level of the sample cable tunnel is C, and the fire risk status of the sample cable tunnel is a moderate fire; when S is greater than S3, the fire risk level of the sample cable tunnel is D, and the fire risk status of the sample cable tunnel is a severe fire.

[0035] According to another aspect of an embodiment of the present invention, a cable tunnel fire risk assessment device for arc breakdown faults of cable joints is provided, including: a test platform construction module, used to construct an arc ignition test platform, wherein the arc ignition test platform includes a target cable intermediate joint, an industrial frequency current generator, a high-voltage probe and an acquisition card, an infrared camera, and a thermocouple; an arc ignition test module, used to perform arc ignition tests under various working conditions to obtain the respective temperatures and flame heights of the various working conditions, as well as the respective average arc powers of the various working conditions, wherein the power supply voltages of the various working conditions are provided by the industrial frequency current generator, and the power supply voltages of the various working conditions are the same, and the current magnitudes or durations of the various working conditions are different; a simulation module, used to establish a cable intermediate joint simulation model by imitating the arc ignition test, and set a simulated combustion surface at the position of the intermediate copper conductor of the simulated cable intermediate joint, and obtain the respective temperatures and flame heights of the various working conditions according to the arc ignition test. The average arc power is used to determine the heat release rate of the simulated combustion surface, and multiple simulation test conditions that are the same as the arc ignition test are set to verify that the temperature obtained by the cable intermediate joint simulation model and the arc ignition test is within a predetermined first difference range, and the flame height is maintained within a predetermined second difference range. The simulation conditions are changed, including the arc ignition power of the simulated cable intermediate joint and the cable structure parameters, and a new cable intermediate joint simulation model under different simulation test conditions is established to obtain a variety of risk factors that affect the fire risk of the cable tunnel; an analysis module is used to analyze the various risk factors according to the hierarchical analysis method, use the various risk factors as the indicator layer, and determine the criterion layer and the target layer according to the various risk factors, determine the weight of the target layer and the actual score values ​​of each of the various risk factors, and calculate the score value of the sample cable intermediate joint according to the weight of the target layer and the actual score values ​​of each of the various risk factors, where R i It is obtained according to the cable fire risk factor integral table, which is obtained through historical fire conditions and expert scores; the risk assessment module is used to determine the fire risk level and fire risk status of the sample cable tunnel where the sample cable intermediate joint is located according to the scoring value of the sample cable intermediate joint.

[0036] According to another aspect of an embodiment of the present invention, a non-volatile storage medium is provided, which stores a plurality of instructions, wherein the instructions are suitable for being loaded by a processor and executing any one of the methods for assessing the fire risk of cable tunnels due to arc breakdown faults of cable joints.

[0037] According to another aspect of an embodiment of the present invention, there is provided an electronic device, comprising: one or more processors and a memory, the memory being used to store one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors implement any one of the methods for assessing the fire risk of cable tunnels due to arc breakdown failures of cable joints.

[0038] According to another aspect of an embodiment of the present invention, there is further provided a computer program product, comprising a computer program, which, when executed by a processor, implements any one of the above-mentioned methods for assessing the fire risk of a cable tunnel due to an arc breakdown fault in a cable joint.

[0039] In an embodiment of the present invention, a method for assessing the risk of cable tunnel fire caused by arc breakdown of cable joints is provided, which has the advantages that:

[0040] (1) Based on cable arc fault and cable arc simulation, the present invention deeply analyzes the arc current size and arc duration when a single-phase grounding fault occurs in the cable. A cable intermediate joint test sample is made to simulate the equivalent arc breakdown insulation, and is equipped with an industrial frequency current generator that can continuously generate large currents to form an arc-starting circuit of the positive pole of the industrial frequency current generator-copper conductor-arc-starting wire-aluminum sheath-negative pole of the industrial frequency current generator. Then, an arc-igniting cable and fire-causing test is carried out, and the test results are more in line with the actual situation.

[0041] (2) Comprehensively analyze the factors affecting cable arc fires, list the risk factors of cable layout, tunnel environment and characteristic factors affecting cable arc faults, and establish a cable arc fault fire risk assessment model of target layer-criteria layer-indicator layer according to the analytic hierarchy process. Compare and analyze the importance of risk factors at the same level, and weaken the coupling relationship between risk factors by calculating the weights between the lower risk factors and their corresponding upper risk factors and the same risk factors.

[0042] (3) Based on the analytic hierarchy process, the overall weights of the target layer fire risk and the indicator layer risk factors can be finally obtained. Combined with the constructed risk factor importance score table, the total fire risk assessment score can be calculated. Then, the risk level of cable arc fault fire can be divided according to the total fire risk assessment score, and the fire risk of cable arc fault can be quantitatively analyzed and evaluated. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0044] Figure 1 It is a flow chart of a cable tunnel fire risk assessment method for cable joint arc breakdown fault provided by an embodiment of the present invention;

[0045] Figure 2 is a schematic diagram of a sample of an optional cable intermediate joint ignition test provided according to an embodiment of the present invention;

[0046] Figure 3 is a schematic diagram of an optional on-site arrangement of an ignition test of a cable intermediate joint provided according to an embodiment of the present invention;

[0047] Figure 4 is a schematic diagram of an optional arc grounding fault provided according to an embodiment of the present invention;

[0048] Figure 5 is a schematic diagram of an optional arc voltage and arc current waveform provided according to an embodiment of the present invention;

[0049] Figure 6 is a schematic diagram of temperature comparison of temperature measuring points in an optional ignition test and a simulation test provided according to an embodiment of the present invention;

[0050] Figure 7 is a schematic diagram of a cable tunnel fire risk assessment device for a cable joint arc breakdown fault provided by an embodiment of the present invention;

[0051] Figure 8 is a schematic diagram of an electronic device provided according to an embodiment of the present invention. DETAILED DESCRIPTION

[0052] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings 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 should fall within the scope of protection of the present invention.

[0053] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0054] According to an embodiment of the present invention, a method embodiment of fire risk assessment is provided. It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and although a logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0055] Figure 1 is a flow chart of a fire risk assessment method according to an embodiment of the present invention. Figure 1 As shown, the method comprises the following steps:

[0056] Step 1: Build an arc ignition test platform, which includes a target cable intermediate joint, a power frequency current generator, a high-voltage probe and acquisition card, an infrared camera, and a thermocouple.

[0057] In this step, a certain cable intermediate joint is selected as the target cable intermediate joint, and the wiring port, arc breakdown channel, and joint fixing equipment are made according to the test requirements; the performance parameters of the power frequency current generator, such as capacity, current range, and duration, are clarified, and monitoring devices such as voltage acquisition, current acquisition, and high-frame cameras are equipped, and the arc ignition test site is arranged according to fault cases and expected situations.

[0058] In an optional embodiment, step 1: building an arc ignition test platform includes the following steps:

[0059] Step 1.1: Select the target cable intermediate joint, use hydraulic pliers to cover the copper terminal on the copper conductor inside the cable body on one side of the target cable intermediate joint, and connect it to the positive pole of the power frequency current generator, fix the screw on the aluminum sheath of the cable body on the other side of the target cable intermediate joint, and connect it to the negative pole of the power frequency current generator, punch a hole from the outside to the inside in the middle position of the target cable intermediate joint until the copper conductor position of the target cable intermediate joint, use copper wire as an arc starting wire to connect the copper conductor at the middle position of the target cable intermediate joint, the copper conductor inside the cable body on one side of the target cable intermediate joint, and the aluminum sheath of the cable body on the other side of the target cable intermediate joint, and use a clamp to fix the target cable intermediate joint on the bracket to obtain an arc ignition test circuit, wherein, punching a hole from the outside to the inside in the middle position of the target cable intermediate joint until the copper conductor position of the target cable intermediate joint is used to simulate the state of insulation breakdown of the target cable intermediate joint;

[0060] Step 1.2, placing high-voltage probes, acquisition cards, and infrared cameras around the arc ignition test, and arranging thermocouples above the middle position of the middle joint of the target cable to obtain an arc ignition test platform, wherein the high-voltage probe and acquisition card are used to collect arc voltage, the infrared camera is used to monitor the temperature of the arc ignition test platform, and the thermocouple is used to monitor the temperature of a specific temperature measuring point of the arc ignition test platform.

[0061] Optionally, a typical arc ignition test is carried out using a certain type of cable intermediate joint as an example. The length of the cable body on the left and right sides of the joint is L1, the length of the intermediate joint is L2, and the structural parameters of the cable intermediate joint are shown in Table 1:

[0062] Table 1 Cable intermediate joint structural parameters

[0063]

[0064] In order to facilitate the test wiring and simulate the state of the cable intermediate joint being broken down, the sample is further processed, such as Figure 2 As shown. The cable jacket and insulation material of L3 are stripped off from the right cable body to expose the internal copper conductor; the cable jacket material of L4 is stripped off from the left cable body to expose the internal corrugated aluminum sheath. Put the copper terminal on the copper conductor and crimp it with hydraulic pliers to connect the positive pole of the power frequency current generator. Fix the screw on the aluminum sheath to connect the negative pole of the power frequency current generator. In the middle of the cable intermediate joint, make a hole of d5 from the outer sheath to the copper conductor to simulate the state of insulation breakdown of the cable intermediate joint. Then use the copper wire of d6 as the arc starter wire to connect the copper conductor and the aluminum sheath, and finally form a circuit of positive pole of power supply - copper conductor - arc starter wire - aluminum sheath - negative pole of power supply.

[0065] When alternating current flows through a high-voltage cable, an alternating electromagnetic field is generated. Electrons in the cable are affected by the electromagnetic force and will travel back and forth inside the conductor, causing the cable to oscillate or move. The Biot-Saffar law shows that the greater the cable current, the greater the induced magnetic flux and the greater the cable electromotive force. In order to prevent the continuity of the arc during the test from being affected by cable oscillation, a clamp of appropriate size is required to fix the cable intermediate joint to the bracket.

[0066] Clarify the equipment parameters required for the test, and arrange the test site according to the failure cases and expected situations. The steps for arranging the test site are as follows:

[0067] (1) When a high-voltage cable is broken down and an arc-type grounding fault occurs, the relay protection system will quickly and accurately send a trip command to the circuit breaker closest to the faulty cable, so that the faulty cable can be disconnected from the power system in time to minimize the damage to the power system components themselves and reduce the impact on the safe power supply of the power system. According to "GB / T50064-2014 Overvoltage Protection and Insulation Coordination of AC Electrical Equipment" and "GB / T 14285-2016 Technical Specifications for Relay Protection and Safety Automatic Devices", before the relay protection cuts off the fault, the line power frequency current will remain for several or even dozens of cycles, and the fault duration will be less than tt1. If the main protection fails and the subsequent protection action is initiated, the fault duration can reach tt2. Based on the distributed LC parameters and the lumped resistance Bergeron model, the PSCSD / EMTDC is used to establish a simulation model of a single-phase arc grounding fault at the intermediate joint of the cable, such as Figure 3 As shown. The cable length is L5, and the neutral point is effectively grounded. R0 is the cable equivalent resistance, and Rarc is the arc dynamic resistance. From the simulation results, it can be seen that the rated short-circuit breaking current of the circuit breaker under different current carrying capacities.

[0068] (2) The arc fault grounding of high-voltage cables involves a process of local discharge, insulation degradation - insulation breakdown - grounding arc generation - short-term arc continuation - arc extinguishing by relay protection. Fault analysis shows that the potential of the fault point to the ground before breakdown is U. The voltage drops sharply at the moment of breakdown, and the current rises sharply to I, thus maintaining the arc in a state of low voltage and high current. Since it is difficult to form a test environment that meets both high voltage and high current requirements, the test process focuses on analyzing the arc and cable ignition after insulation breakdown. The breakdown voltage of the air gap is U0, and after the arc is formed, under the influence of temperature, charged particles, and current density, the voltage to maintain the arc is between U1 and U2. Finally, a suitable transformer was selected as the test power frequency current generator, and its specific performance parameters are shown in Table 2:

[0069] Table 2 Performance parameters of power frequency current generator

[0070]

[0071] (3) The test site layout is as follows Figure 4 As shown in the figure, the arc starting circuit is mainly formed by the positive electrode of the power frequency current generator - copper conductor - arc starting wire - aluminum sheath - negative electrode of the power frequency current generator. The power frequency current generator generates a large current of frequency f flowing through the circuit, and the arc starting wire with a smaller cross-section is overloaded, quickly heats up and melts, and then an arc is formed in the air gap.

[0072] The high-voltage probe and acquisition card are used to collect arc voltage. The high-voltage probe ratio is x, and the acquisition card acquisition range is u0. The arc current is directly obtained through the power frequency current generator. The high-speed camera is used to observe the test process of arc ignition. The infrared camera can monitor a large range of temperature, and its temperature monitoring range is T0. The horizontal distance between the high-speed camera and the infrared camera and the simulated breakdown position is d7. In addition, thermocouples are arranged above the simulated breakdown position, from left to right, respectively, temperature measurement point 1, temperature measurement point 2, and temperature measurement point 3, to monitor the local temperature rise characteristics. The vertical interval between the thermocouple and the cable is d8, and the horizontal interval between adjacent cables is d9.

[0073] Step 2: Conduct arc ignition tests under various working conditions to obtain the temperatures and flame heights of the various working conditions, as well as the average arc powers of the various working conditions, wherein the power supply voltages of the various working conditions are provided by an industrial frequency current generator, and the power supply voltages of the various working conditions are the same, and the current magnitudes or durations of the various working conditions are different.

[0074] In this step, multiple groups of arc ignition tests with different durations and current sizes are carried out to obtain and record characteristic information such as voltage, current, temperature, and flame height that characterize the ignition situation.

[0075] In an optional embodiment, step 2: performing arc ignition tests under various working conditions to obtain respective temperatures and respective flame heights under various working conditions, comprises the following steps:

[0076] Step 2.1: Detect the circuit and circuit equipment of the arc ignition test platform and start the arc ignition test;

[0077] Step 2.2: Through the arc ignition test, the temperature of each of the various working conditions and the flame height of each of the various working conditions are measured, and the arc voltage of each of the various working conditions and the arc current of each of the various working conditions are obtained;

[0078] Step 2.3: Calculate the arc energy Q of various working conditions according to the arc voltages and arc currents of various working conditions. The calculation formula is: Wherein, P(t) is the instantaneous arc power of each of the various working conditions calculated from the arc voltages of each of the various working conditions and the arc currents of each of the various working conditions; t1 is the start time of the arc generated by each of the various working conditions; t2 is the end time of the arc generated by each of the various working conditions;

[0079] Step 2.4: Determine the average arc power P of various working conditions according to the arc energy Q of various working conditions arc , the calculation formula is:

[0080] Optionally, the power supply voltage of the power frequency current generator is constant at U3, and the current magnitude and duration are changed to set different test conditions as shown in Table 3:

[0081] Table 3 110kV cable arc ignition condition settings

[0082]

[0083] The ambient temperature is T1 and the humidity is RH. Check the circuit and equipment, and then start the test. At the moment the switch is closed, the arc-starting wire melts quickly and ejects a plasma jet from the hole, generating a strong arc in the air gap. In the arc gap between the conductor and the aluminum sheath, the pressure and temperature of the air rise rapidly, and an obvious, sizzling sound of current appears.

[0084] Take the condition of I2 current and duration t1 as an example. Under the continuous action of current, the temperature of the local area at the arc starting position exceeds T2, the arc column fills the entire air gap, and the arc light tends to emerge from the air gap. The energy generated by the arc diffuses to the surrounding medium in the form of heat convection, heat conduction, heat radiation and combustion jet. The monitored arc voltage and arc current waveforms are as follows: Figure 5 shown.

[0085] From the perspective of electrical characteristics, based on arc gap energy balance and Ohm's law, and ignoring the power of instantaneous heat conduction and heat radiation due to thermal inertia, the arc energy can be further calculated by taking heat convection as the main transfer process of arc heat.

[0086]

[0087] Where Q is the heat generated by the arc; P(t) is the instantaneous power of the arc, which can be obtained from the instantaneous values ​​of the arc voltage and arc current; t1 is the start time of the arc; and t2 is the end time of the arc.

[0088]

[0089] Where P arc is the average arc power during the arcing process.

[0090] Similarly, the arc voltage and arc current waveforms under all working conditions can be obtained through the arc ignition test.

[0091] Step 3: Establish a simulation model of the cable intermediate joint according to the arc ignition test, set a simulated burning surface at the middle copper conductor position of the simulated cable intermediate joint, determine the heat release rate of the simulated burning surface according to the average arc power obtained from the arc ignition test, and set multiple simulation test conditions that are the same as the arc ignition test to verify that the temperature obtained by the cable intermediate joint simulation model and the arc ignition test are within a predetermined first difference range, and the flame height is maintained within a predetermined second difference range. Change the simulation conditions, including the arc ignition power of the simulated cable intermediate joint and the cable structure parameters, establish a new cable intermediate joint simulation model under different simulation test conditions, and obtain a variety of risk factors that affect the fire risk of the cable tunnel.

[0092] In this step, a cable intermediate joint simulation model is established, and after the cable intermediate joint simulation model is corrected according to the arc ignition test, it is verified whether the cable intermediate joint simulation model can obtain the same test results as the arc ignition test. When the cable intermediate joint simulation model can obtain the same results as the arc ignition test, the simulation conditions of the cable joint simulation model are changed, such as the arc ignition power of the cable intermediate joint and the cable structure parameters, to obtain a variety of simulation results, determine which factors will have a greater impact on the fire risk of the cable tunnel, and use these factors as risk factors;

[0093] In an optional embodiment, step 3: establish a simulation model of the cable intermediate joint according to the arc ignition test, set a simulated combustion surface at the position of the middle copper conductor of the simulated cable intermediate joint, determine the heat release rate of the simulated combustion surface according to the average arc power obtained in the arc ignition test, and set a plurality of simulation test conditions that are the same as the arc ignition test, verify that the temperature obtained by the cable intermediate joint simulation model and the arc ignition test is within a predetermined first difference range, and the flame height is maintained within a predetermined second difference range, change the simulation conditions, including the arc ignition power of the simulated cable intermediate joint and the cable structure parameters, establish a new cable intermediate joint simulation model under different simulation test conditions, and obtain a plurality of risk factors that affect the fire risk of the cable tunnel, including the following steps:

[0094] Step 3.1: Based on the arc ignition test, an initial cable intermediate joint simulation model is established, a simulated combustion surface is set at the middle copper conductor position of the simulated cable intermediate joint, the heat release rate of the simulated combustion surface is determined according to the average arc power obtained in the arc ignition test, and multiple simulation test conditions that are the same as the arc ignition test are set, wherein the simulation environment of the initial cable intermediate joint simulation model is consistent with the test environment of the arc ignition test;

[0095] Step 3.2: Conduct simulation tests on the initial simulated cable intermediate joint under multiple simulated working conditions that are the same as the multiple working conditions, obtain the respective temperatures of the initial simulated cable intermediate joint under the multiple simulated working conditions, and compare the respective temperatures of the initial simulated cable intermediate joint under the multiple simulated working conditions with the temperatures under the corresponding working conditions of the arc ignition test, and obtain the respective comparison results under the multiple simulated working conditions;

[0096] Step 3.3: According to the respective comparison results under various simulation working conditions, the proportion of substances participating in the combustion of the insulation layer, filling layer, and sheath layer of the initial simulation cable intermediate joint is adjusted until the temperature difference obtained by simulating the initial simulation cable intermediate joint under various simulation working conditions and the temperature difference of the arc ignition test under the same working conditions are kept within the predetermined first difference range, and the simulated cable intermediate joint and the cable intermediate joint simulation model are obtained, wherein the proportion of substances participating in the combustion of the insulation layer, filling layer, and sheath layer of the initial simulation cable intermediate joint can be expressed as: x1(C2H3Cl)+x2(C9H 14 O3N2)+x3(C2H4), the adjusted formula is: x1(C2H3Cl)+x2(C9H 14 O3N2)+x3(C2H4)+a5O2→bO2+cCO+dC+eH2O+

[0097] fHCl+gHCN, a, b, c, d, e, f, g are the coefficients of the reaction equation, C2H3Cl is the monomer corresponding to the polymer polyvinyl chloride, x1 is the reaction coefficient of C2H3Cl, C9H 14 O3N2 is the monomer corresponding to polyurethane, and x2 is C9H 14 The reaction coefficient of O3N2, C2H4 is the monomer corresponding to cross-linked polyethylene, x3 is the reaction coefficient of C2H4, O2 is oxygen, CO is carbon monoxide, C is carbon, H2O is water, HCl is hydrogen chloride, and HCN is hydrogen cyanide;

[0098] Step 3.4: Simulate the simulated cable intermediate joint under multiple simulation conditions, and when the simulated cable intermediate joint burns stably, obtain the result that the flame height under the multiple simulation conditions and the flame height under the corresponding conditions of the arc ignition test have errors within the predetermined second difference range;

[0099] Step 3.5: Based on the results obtained in step 3.4, change the voltage level and structural parameters of the simulated cable intermediate joint, establish new cable intermediate joint simulation models, and obtain various risk factors that affect cable tunnel fires. The various risk factors include cable position, layer spacing, horizontal spacing, tunnel temperature, tunnel humidity, tunnel wind speed, voltage level, cross-sectional area, cable load, operating years, and duration.

[0100] Optionally, a simulation model is established based on the structural parameters of the cable intermediate joint. The simulation environment is consistent with the actual test environment, and the temperature monitoring position is consistent with the test environment. The simulation environment is windless, the left and right sides are set as open boundaries, and the other boundaries are set as thermal insulation. The thermal physical parameters of each layer of material are shown in Table 4 below:

[0101] Table 4 Thermophysical properties of cable intermediate joints

[0102]

[0103] According to the thermocouple temperature and the burning fire, the gas phase reaction equation of the cable intermediate joint is corrected many times. When the proportion of the substances involved in the combustion of the insulation layer, filling layer and sheath layer is x1, x2 and x3, the corresponding cable intermediate joint model is expressed as x1(C2H3Cl)+x2(C9H 14 O3N2)+x3(C2H4), the corresponding gas phase reaction is shown in equation (3). The average difference between the thermocouple temperature of the modified model and the real combustion is 5.7%, and the equivalence is good.

[0104]

[0105] In the formula, C2H3Cl is the monomer corresponding to the polymer polyvinyl chloride, x1 is the reaction coefficient of C2H3Cl, C9H 14 O3N2 is the monomer corresponding to polyurethane, and x2 is C9H 14 The reaction coefficient of O3N2, C2H4 is the monomer corresponding to cross-linked polyethylene, x3 is the reaction coefficient of C2H4, O2 is oxygen, CO is carbon monoxide, C is carbon, H2O is water, HCl is hydrogen chloride, and HCN is hydrogen cyanide;

[0106] In the middle of the cable joint simulation model, open a Figure 2 A notch with the same air gap size. A burning surface is set at the bottom of the notch, near the copper conductor, to simulate the arc generating heat and igniting the cable. The heat release rate of the burning surface is set according to the power calculated in step 2, and the simulation is divided into 6 working conditions.

[0107] For the ignition of working condition 1, the high temperature area is mainly in the air gap of the cable middle joint in the short time when the simulation starts and the arc ignition is simulated. However, since the arc action time is shorter than the sampling interval of the thermocouple, there is no obvious change in the thermocouple temperature during this period. After the cable is ignited, the temperature changes at the same monitoring point in the test and simulation are as follows: Figure 6 shown.

[0108] In the simulation model, the cable joint was ignited under the action of heat conduction. As time went on, the thermal decomposition of polyurethane and cross-linked polyethylene intensified, and the flame area spread to the surrounding area along the holes in the air gap, and at the same time spread vertically upward along the surface of the cable joint, and the fire in the cable joint gradually increased. After the fire in the cable joint stabilized, the flame height reached H1.

[0109] According to the calculated average arc power, the heat release rate of the combustion surface is changed, and the cable ignition simulation of other working conditions is performed. Working conditions 2 to 6 are all ignited, and when the cable intermediate joint burns stably, the flame heights are H2, H3, H4, H5, and H6 respectively. Under different working conditions, the maximum relative error of the flame height of the cable intermediate joint burning in the arc ignition test and simulation is x4. The results show that the situation where the cable intermediate joint is ignited by arc energy can be simulated by associating arc power and heat release rate, and the simulated cable combustion situation is consistent with the test.

[0110] Similarly, by changing the voltage level and structural parameters of the simulated cable intermediate joint, new cable intermediate joint simulation models are established respectively, and various risk factors affecting cable tunnel fires are obtained. Among them, the various risk factors include cable position, layer spacing, horizontal spacing, tunnel temperature, tunnel humidity, tunnel wind speed, voltage level, cross-sectional area, cable load, operating years, and duration.

[0111] Step 4: Analyze multiple risk factors according to the hierarchical analysis method, take multiple risk factors as the indicator layer, and determine the criterion layer and the target layer according to the multiple risk factors, determine the weight of the target layer and the actual score values ​​of the multiple risk factors, and calculate the score value of the sample cable intermediate joint according to the weight of the target layer and the actual score values ​​of the multiple risk factors. i It is obtained based on the cable fire risk factor scoring table, which is obtained through historical fire conditions and expert scores.

[0112] In this step, a cable arc fault fire risk assessment model is established according to the analytic hierarchy process based on risk factors such as cable location, layer spacing, horizontal spacing, tunnel temperature, tunnel humidity, tunnel wind speed, voltage level, cross-sectional area, cable load, operating years, and duration.

[0113] In an optional embodiment, step 4: analyzing multiple risk factors according to a hierarchical analysis method, taking multiple risk factors as an indicator layer, determining a criterion layer and a target layer according to the multiple risk factors, determining the weight of the target layer and the actual score values ​​of each of the multiple risk factors, and calculating the score value of the sample cable intermediate joint according to the weight of the target layer and the actual score values ​​of each of the multiple risk factors, including the following steps:

[0114] Step 4.1: Analyze multiple risk factors according to the hierarchical analysis method, use multiple risk factors as the indicator layer, and construct the criterion layer and target layer according to the multiple risk factors, where the target layer is the highest level, the criterion layer is the middle level, and the indicator layer is the lowest level. The criterion layer includes cable layout characteristics, environmental characteristics, and cable fault characteristics. The cable layout characteristics include cable position, layer spacing, and horizontal spacing. The environmental characteristics include tunnel temperature, tunnel humidity, and tunnel wind speed. The arc fault characteristics include voltage level, cross-sectional area, cable load, operating years, and duration. The target layer is the cable tunnel fire risk.

[0115] Step 4.2: According to the hierarchical relationship of each risk factor, compare the importance of all risk factors at the same level, and construct the judgment matrix between the target layer and the criterion layer, and between the criterion layer and the indicator layer. The expression of the judgment matrix is: T u is the judgment matrix, x ij is the relative importance of risk factor i to risk factor j, i and j are two risk factors in the same layer, u is the upper-layer risk factor corresponding to the lower-layer risk factor, and n is the number of risk factors in the same layer;

[0116] Step 4.3: Normalize the values ​​in the judgment matrix and calculate the weight of the lower risk factor i relative to the upper risk factor u. The calculation formula is: x ij is the relative importance of risk factor i to risk factor j, where i and j are two risk factors at the same level;

[0117] Step 4.4: Calculate the weights between risk factors at the same level. The calculation formula is: w ij =w iu -w ju +ab, ab is a constant, w iu is the weight of the lower risk factor i relative to the upper risk factor u, w ju The weight of the lower risk factor j relative to the upper risk factor u;

[0118] Step 4.5: Use the formula Obtain a feasibility ratio, and use the feasibility ratio to make a feasibility judgment on the judgment matrix. When the feasibility ratio Z is less than a predetermined threshold, the judgment matrix meets the feasibility requirements;

[0119] Step 4.6: The overall weight of the target layer is: w iz =w iA × iB , w iA is the weight of the risk factor i of the criterion layer relative to the risk factor A of the target layer, w iBis the weight of the risk factor i at the indicator level relative to the risk factor B at the criterion level;

[0120] Step 4.7: According to the overall weight of the target layer, the score value of the sample cable intermediate joint is obtained. The score value S of the sample cable intermediate joint is calculated as follows: R i is the actual score of risk factor i, where R i It is obtained based on the cable fire risk factor scoring table, which is obtained through historical fire conditions and expert scores.

[0121] Optional: The fire of high-voltage cable due to arc is the result of the joint action of multiple risk factors. By assigning different weights to each risk factor, the coupling relationship between the risk factors can be weakened, and then the qualitative evaluation of fire risk can be converted into quantitative analysis, so as to achieve a more objective and reasonable fire risk assessment of high-voltage cable arc faults. The risk factors affecting cable arc fire are divided into target layer, criterion layer and indicator layer according to the hierarchical analysis method, as shown in Table 5, among which the factors in the target layer and criterion layer, and the factors in the criterion layer and indicator layer are all parent-child relationships.

[0122] Table 5 High-voltage cable arc fault fire risk assessment indicators

[0123]

[0124] According to the hierarchical relationship of each risk factor in Table 5, the importance of all sub-risk factors under the same level of risk factors is compared, and the judgment matrix between the target layer A and the criterion layer B, and the criterion layer B and the indicator layer C is constructed respectively. The judgment matrix expression (4) is shown as follows:

[0125]

[0126] Where, T u is the judgment matrix; x ij is the importance of risk factor relative to risk factor; i and j are two risk factors at the same level; u is the upper-level risk factor corresponding to the lower-level risk factor; n is the number of risk factors at the same level and the same parent risk.

[0127] To facilitate calculation, the eigenvalues ​​in the judgment matrix are normalized, and then the risk factors are divided into risk levels by comparing them pairwise based on the fuzzy algorithm. ij = x5, the importance of risk factor i is much less than that of risk factor j; when the risk level is x ij =x6, the importance of risk factor i is much greater than that of risk factor j.

[0128] According to formulas (5) and (6), the weights between the lower-level risk factor and its corresponding upper-level risk factor and the same-level risk factor are calculated respectively.

[0129]

[0130] In the formula, w iu is the weight of the lower risk factor i relative to the upper risk factor u.

[0131] w ij =w iu -w ju +ab (6)

[0132] In the formula, w ij is the weight of risk factor i relative to risk factor j, and ab is a constant.

[0133] Use formula (7) to calculate the judgment matrix T u Conduct feasibility assessment.

[0134]

[0135] Where Z is the feasibility ratio. When Z≤x7, the judgment matrix meets the feasibility requirements.

[0136] The overall weight of the risk factors at the target layer and indicator layer can be expressed as:

[0137] w iz =w iA × iB (8)

[0138] In the formula, w iA is the weight of the risk factor i of the criterion layer relative to the risk factor A of the target layer; w iB is the weight of the risk factor i at the indicator level relative to the risk factor B at the criterion level; w iz is the overall weight of the risk factor i of the indicator layer relative to the risk factor z of the target layer.

[0139] The fire risk assessment calculation formula for cable arc fault is shown in formula (9).

[0140]

[0141] Where S is the total score of fire risk assessment; R i is the actual score of risk factor i.

[0142] Compare and analyze the importance of each risk factor, construct a risk factor importance score table, and calculate and evaluate the fire risk of cable arc faults.

[0143] The steps for cable arc fault risk assessment are as follows:

[0144] According to step 5, the judgment matrix T between the target layer and the criterion layer, and between the criterion layer and the indicator layer is established. A , T B1 , T B2 , T B3 .

[0145] According to formula (5), the arc fault fire risk w is calculated respectively: A , Cable layout characteristics B1 、Environmental characteristics B2 、Arc fault characteristics w B3 The weight of . According to formula (6) and (7), the feasibility test is calculated to obtain Z. According to formula (8), the overall weight w is calculated. iz .

[0146] A scoring table is established based on cable arc ignition test, cable fire simulation and cable fire accident. The correlation model between cables of different voltage levels and cross-sectional areas and fire intensity is established using equations (10) and (11).

[0147] Q ix =m ix q ix (10)

[0148] In the formula, Q ix The heat released when each layer of fuel in the cable intermediate joint is completely burned; m ix is the mass of the fuel; q ix is the unit calorific value corresponding to the fuel; x is the different cable types; i is the type of cable fuel, i=1, 2, 3 correspond to the fuel cross-linked polyethylene, polyurethane, and polyvinyl chloride respectively.

[0149]

[0150] In the formula, H x is the flame height when the fuel is completely burned; ρ is the ambient gas density; c is the ambient gas specific heat capacity; T is the ambient temperature.

[0151] The importance scores of risk factors at the indicator level are shown in Table 6:

[0152] Table 6 Cable fire risk factor scoring table

[0153]

[0154] Step 5: Based on the scoring value of the sample cable intermediate joint, determine the fire risk level and fire risk status of the sample cable tunnel where the sample cable intermediate joint is located.

[0155] In this step, the cable fire risk can be divided into four levels: A, B, C, and D, which correspond to normal, mild, moderate, and severe fire states respectively. According to the range of the scoring values ​​of the sample cable intermediate joints, the fire risk level and fire risk state of the sample cable tunnel where the sample cable intermediate joints are located are determined.

[0156] In an optional embodiment, step 5: determining the fire risk level and fire risk status of the sample cable tunnel where the sample cable intermediate joint is located according to the scoring value of the sample cable intermediate joint, comprises the following steps:

[0157] Step 5.1: According to the scoring value of the sample cable intermediate joint, determine the fire risk level and fire risk status of the sample cable tunnel caused by the sample cable intermediate joint; when S is less than S1, the fire risk level of the sample cable tunnel is A, and the fire risk status of the sample cable tunnel is normal; when S is greater than S1 and less than S2, the fire risk level of the sample cable tunnel is B, and the fire risk status of the sample cable tunnel is a light fire; when S is greater than S2 and less than S3, the fire risk level of the sample cable tunnel is C, and the fire risk status of the sample cable tunnel is a moderate fire; when S is greater than S3, the fire risk level of the sample cable tunnel is D, and the fire risk status of the sample cable tunnel is a severe fire.

[0158] Optionally, the cable fire risk is divided into four levels: A, B, C, and D, corresponding to the four states of normal, mild, moderate, and severe fire, respectively. The specific division is shown in Table 7:

[0159] Table 7 Cable fire risk levels

[0160]

[0161] Based on factors such as cable layout, cable tunnel environment, cable voltage level, load, arc duration, etc., combined with equations (8) and (9), the risk assessment score S can be calculated when an arc fault occurs in the cable, thereby determining the risk level of the fire.

[0162] Through the above steps 1 to 6, the purpose of quantitatively analyzing the risk of fire caused by arc grounding faults in cable joints is achieved, and the technical problem of being unable to quantitatively analyze the risk of cable fire caused by arc grounding faults in cable joints is solved. Thus, the technical effect of reducing the probability of cable fire is achieved.

[0163] Based on the above embodiments and optional embodiments, the present invention proposes an optional implementation mode:

[0164] Step 1: Select a cable intermediate joint and make the wiring port, arc breakdown channel, and joint fixing device according to the test requirements. 110kV cable has the largest cable mileage and the widest application range in the main network. This type of cable intermediate joint has the highest number of arc grounding faults. Therefore, 110kV / 240mm 2 Taking the cable intermediate joint as an example, a typical arc ignition test was carried out. The cable intermediate joint has not yet been put into operation. The cable body on the left and right sides of the joint is 0.2m long, and the intermediate joint is 0.8m long. The structural parameters of the cable intermediate joint are shown in Table 1:

[0165] Table 1 Structural parameters of cable body and intermediate joint

[0166]

[0167]

[0168] like Figure 2 As shown, in order to facilitate the test wiring and simulate the state of the cable intermediate joint being broken down, the sample is further processed. The cable body on the right side of the cable intermediate joint is stripped of 5cm of cable jacket and insulation material to expose the internal copper conductor, and the cable body on the left side of the cable intermediate joint is stripped of 2cm of cable jacket material to expose the internal wrinkled aluminum sheath. The copper terminal is put on the copper conductor and crimped with hydraulic pliers to connect the positive pole of the power frequency current generator. The screw is fixed on the aluminum sheath to connect the negative pole of the power frequency current generator. In the middle position of the cable intermediate joint, a 5mm hole is punched from the outer sheath to the copper conductor to simulate the state of insulation breakdown of the cable intermediate joint. Then use 0.5mm copper wire as the arc starter wire to connect the copper conductor and the aluminum sheath. Finally, a loop of power supply positive pole - copper conductor - arc starter wire - aluminum sheath - power supply negative pole is formed. When the high-voltage cable is connected to alternating current, an alternating electromagnetic field will be generated. The electrons in the cable are affected by the electromagnetic force and will run back and forth inside the conductor, causing the cable to oscillate or move. According to the Biot-Saffar law, the greater the cable current, the greater the induced magnetic flux and the greater the cable electromotive force. In order to avoid the influence of cable oscillation on the continuity of the arc during the test, a clamp of suitable size is used to fix the cable intermediate joint on the bracket.

[0169] Specify the performance parameters of the power frequency current generator, such as capacity, current range, and duration, equip it with monitoring devices such as voltage acquisition, current acquisition, and high-frame cameras, and arrange the test site according to fault cases and expected situations;

[0170] The test site layout steps are as follows:

[0171] The power frequency current generator can be selected as follows: When the high-voltage cable is broken down and an arc ground fault occurs, the relay protection system will quickly and accurately send a trip command to the circuit breaker closest to the faulty cable, so that the faulty cable can be disconnected from the power system in time to minimize the damage to the power system components themselves and reduce the impact on the safe power supply of the power system. According to the national standards "GB / T 50064-2014 Overvoltage Protection and Insulation Coordination of AC Electrical Devices" and "GB / T 14285-2016 Technical Specifications for Relay Protection and Safety Automatic Devices", before the relay protection cuts off the fault, the line power frequency current will remain for several or even dozens of cycles, and the fault duration will be less than 0.5s. If the main protection fails and the subsequent protection action is initiated, the fault duration can reach 1s.

[0172] Based on the distributed LC parameters and lumped resistance Bergeron model, a simulation model of single-phase arc grounding fault at the intermediate joint of 110kV cable is established using PSCSD / EMTDC. Figure 4 As shown. The cable length is 2km, the load capacity is 37% of the transformer capacity, the frequency is 50Hz, the power factor is 0.95, and the neutral point is effectively grounded. R0 is the equivalent resistance of the cable, R arc is the arc dynamic resistance. From the simulation results, we can see that the rated short-circuit breaking current of the circuit breaker under different current carrying capacities is between 8kA and 30kA.

[0173] like Figure 3 As shown in the figure, the arc fault grounding of high-voltage cables has a process of local discharge, insulation degradation - insulation breakdown - grounding arc - short-term arc continuation - relay protection arc extinguishing. Fault analysis shows that the potential of the fault point to the ground before the breakdown is 110kV. At the moment of breakdown, the voltage drops sharply and the current rises sharply to tens of kA, thus maintaining the arc in a state of low voltage and high current.

[0174] It is difficult to form a test environment that meets both high voltage and high current requirements, so the test process focuses on analyzing the arc after insulation breakdown and cable ignition. The breakdown voltage of the air gap is around 30kV / cm, and after the arc is formed, under the influence of temperature, charged particles, and current density, the voltage of the arc is maintained between 15V / cm and 30V / cm. Finally, a transformer model YS-6300 / 10 was selected as the test power frequency current generator. The specific performance parameters are shown in Table 2:

[0175] Table 2 Performance parameters of power frequency current generator

[0176]

[0177] After the test materials are prepared, the test site can be arranged as follows: Figure 4As shown, an arc-starting circuit is formed, which is composed of the positive electrode of the power frequency current generator, copper conductor, arc-starting wire, aluminum sheath, and the negative electrode of the power frequency current generator. The power frequency current generator generates a high current with a frequency of 50 Hz flowing through the circuit, and the arc-starting wire with a smaller cross-section is overloaded, quickly heats up and melts, and then an arc is formed in the air gap.

[0178] The high-voltage probe and acquisition card are used to collect arc voltage. The high-voltage probe ratio is 1000:1, and the acquisition card acquisition range is 80V. The arc current is directly obtained through the power frequency current generator. The high-speed camera is used to observe the test process of arc ignition, and its frame rate is 8000fps. The infrared camera can perform a wide range of temperature monitoring, and its temperature monitoring range is 0-1500℃. The high-speed camera and the infrared camera are 2m apart horizontally from the simulated breakdown position. In addition, thermocouples are arranged above the simulated breakdown position, from left to right, respectively, temperature measurement point 1, temperature measurement point 2, and temperature measurement point 3, to monitor the local temperature rise characteristics. The vertical interval between the thermocouple and the cable is 0.3m, and the horizontal interval between adjacent cables is 0.2m.

[0179] Step 2: After the test environment is arranged, carry out multiple groups of 110kV cable arc ignition tests with different durations and currents, and obtain and record characteristic information such as voltage, current, and temperature that characterize the ignition situation; the power supply voltage of the power frequency current generator is constant at 400V, and different test conditions are set by changing the current size and duration as shown in Table 3:

[0180] Table 3110kV cable arc ignition working condition settings

[0181]

[0182] Set the ambient temperature to 33℃ and the humidity to 42%. Check the circuit and equipment and start the test. At the moment the switch is closed, the arc-starting wire melts quickly and ejects a plasma jet from the hole, generating a strong arc in the air gap. In the arc gap between the conductor and the aluminum sheath, the pressure and temperature of the air rise rapidly, and an obvious current sound appears.

[0183] Take the working condition of 20kA current for 100ms as an example. Under the continuous action of current, the temperature of the local area at the arc starting position exceeds 1200℃, the arc column fills the entire air gap, and the arc light tends to emerge from the air gap. The energy generated by the arc diffuses to the surrounding medium in the form of heat convection, heat conduction, heat radiation and combustion jet. The monitored arc voltage and arc current waveforms are as follows: Figure 5 shown.

[0184] From the perspective of electrical characteristics, based on arc gap energy balance and Ohm's law, and ignoring the power of instantaneous heat conduction and heat radiation due to thermal inertia, and taking heat convection as the main transfer process of arc heat, the arc energy can be further calculated:

[0185]

[0186] Where Q is the heat generated by the arc; P(t) is the instantaneous power of the arc, which can be obtained from the instantaneous values ​​of the arc voltage and arc current; t1 is the start time of the arc; t2 is the end time of the arc:

[0187]

[0188] Where P arc is the average arc power during the arcing process. Through integral operation, we know that P arc =374.2kW.

[0189] Similarly, the arc voltage and arc current waveforms under all working conditions can be obtained through the arc ignition test, and the arc ignition power of working conditions 1 to 6 is calculated to be 264.2kW, 276.6kW, 454.7kW, 476.4kW, 663.2kW and 654.5kW respectively. In addition, the intermediate joints of the cables in working conditions 1 to 6 were all ignited, and the fire source heights when burning stably were 42.3cm, 46.7cm, 53.1cm, 57.5cm, 71.2cm and 75.5cm respectively. The test results show that although the arc ignition power of working conditions 1 and 2, working conditions 3 and 4, working conditions 5 and 6 are almost the same, the longer the arc lasts, the more products of high-temperature pyrolysis of the intermediate joints of the cable are produced, so the fire in working conditions 2, 4 and 6 is more intense after the arc is extinguished.

[0190] Step 3: After the ignition test, a simulation model is established based on the structural parameters of the cable intermediate joint. The simulation environment is consistent with the actual test environment, and the temperature monitoring position is consistent with the test environment. The grid size is 10m×10m×10m, and the grid accuracy is 0.05m. The ambient temperature is 33℃ and the humidity is 42%. The simulation environment is windless, the left and right sides are set as open boundaries, and the other boundaries are set as thermal insulation. The thermal physical parameters of each layer of material are shown in Table 4:

[0191] Table 4 Thermophysical properties of cable intermediate joints

[0192]

[0193]

[0194] According to the thermocouple temperature and the burning fire, the gas phase reaction equation of the cable intermediate joint was corrected several times. When the ratio of the amount of substances participating in the combustion of the insulation layer, filling layer and sheath layer is 0.17, 0.38 and 0.45, the corresponding cable intermediate joint model is expressed as 0.17(C2H3Cl)+0.38(C9H 14O3N2)+0.45(C2H4), and the corresponding gas phase reaction is shown in equation (3). The average difference between the thermocouple temperature of the corrected model and the real combustion is 5.7%, and the equivalence is good.

[0195]

[0196] In the formula, C2H3Cl is the monomer corresponding to the polymer polyvinyl chloride, x1 is the reaction coefficient of C2H3Cl, C9H 14 O3N2 is the monomer corresponding to polyurethane, and x2 is C9H 14 The reaction coefficient of O3N2, C2H4 is the monomer corresponding to cross-linked polyethylene, x3 is the reaction coefficient of C2H4, O2 is oxygen, CO is carbon monoxide, C is carbon, H2O is water, HCl is hydrogen chloride, and HCN is hydrogen cyanide;

[0197] In the middle of the cable joint simulation model, open a Figure 2 A notch with the same air gap size. A burning surface is set at the bottom of the notch, near the copper conductor, to simulate the arc generating heat and igniting the cable. The heat release rate of the burning surface is set according to the power calculated in step 3, and the simulation is performed in 6 working conditions.

[0198] For the ignition of working condition 1, at the beginning of the simulation and within a short period of time when the arc is ignited, the high temperature area is mainly in the air gap of the cable joint. However, since the arc action time is shorter than the sampling interval of the thermocouple (0.5s), the thermocouple temperature changes significantly during this period. After the cable is ignited, the temperature changes at the same monitoring point in the test and simulation are as follows: Figure 6 The average temperature differences of the temperature measuring points 1, 2, and 3 are 6.8%, 9.7%, and 5.6%, respectively, and their equivalence is good.

[0199] In the simulation model, the cable intermediate joint was ignited under the action of heat conduction. As time went on, the pyrolysis of polyurethane and cross-linked polyethylene intensified, and the flame area spread to the surroundings along the holes in the air gap, and at the same time spread vertically upward along the surface of the cable intermediate joint, and the fire of the cable intermediate joint gradually increased. After the fire of the cable intermediate joint stabilized, the flame height reached 39.7cm. According to the calculated average arc power, the heat release rate of the burning surface was changed, and the cable ignition simulation of other working conditions was carried out. Working conditions 2 to 6 were all ignited, and when the cable intermediate joint burned stably, the flame heights were 47.3cm, 51.7cm, 58.6cm, 71.4cm, and 77.3cm, respectively. Under different working conditions, the maximum relative error of the flame height of the cable intermediate joint burning in the arc ignition test and simulation was 6.1%. The results show that the situation of the cable intermediate joint being ignited by arc energy can be simulated by associating arc power and heat release rate, and the simulated cable combustion situation is consistent with the experiment.

[0200] The parameters of the simulation model include but are not limited to voltage level, cross-sectional area, cable position, ambient temperature, ambient humidity, and arc duration in the cable. Under specific parameters, a simulation model of the cable intermediate joint is established to obtain the simulated combustion characteristics of the cable joint under a predetermined environment. If after changing one of the parameters of the simulation model, the obtained simulated combustion characteristics are significantly different from the simulated combustion characteristics before the parameter change, it means that the parameter has a greater impact on the fire risk of the cable joint, so the parameter should be determined as a characteristic parameter. If after changing one of the parameters of the simulation model, the obtained simulated combustion characteristics are not significantly different from the simulated combustion characteristics before the parameter change, it means that the parameter has a small impact on the fire risk of the cable joint, so the parameter should not be determined as a characteristic parameter.

[0201] Step 4: Based on the cable layout, tunnel environment and characteristic factors affecting cable arc faults, a cable arc fault fire risk assessment model is established according to the analytic hierarchy process: The fire caused by arc in high-voltage cables is the result of the joint action of multiple characteristic factors. By assigning different weights to each characteristic factor, the coupling relationship between the characteristic factors can be weakened, and then the qualitative evaluation of fire risk can be converted into quantitative analysis, thereby achieving a more objective and reasonable fire risk assessment of high-voltage cable arc faults.

[0202] The characteristic factors affecting cable arc fire are divided into target layer, criterion layer and indicator layer according to the hierarchical analysis method, as shown in Table 5. Among them, the factors in the target layer and criterion layer, and the factors in the criterion layer and indicator layer are all parent-child relationships.

[0203] Table 5 High-voltage cable arc fault fire risk assessment indicators

[0204]

[0205] According to the hierarchical relationship of each characteristic factor in Table 3, the importance of all sub-characteristic factors under the same level of characteristic factors is compared, and the judgment relationship between the target layer A and the criterion layer B, the criterion layer B and the indicator layer C is constructed respectively.

[0206] Judgment matrix. The expression of judgment matrix is ​​as follows:

[0207]

[0208] Where, T u is the judgment matrix; x ij is the importance of the characteristic factor relative to the characteristic factor; i and j are two characteristic factors at the same layer; u is the upper characteristic factor corresponding to the lower characteristic factor; n is the number of characteristic factors at the same layer and the same parent risk.

[0209] To facilitate calculation, the eigenvalues ​​in the judgment matrix are normalized, and then the risk importance of the feature factors is divided into 0.1, 0.2, ..., 0.9 according to the fuzzy algorithm. ij =0.1, the importance of characteristic factor i is much less than that of characteristic factor j; when the risk level is x ij When =0.9, the importance of characteristic factor i is much greater than that of characteristic factor j.

[0210] According to formulas (5) and (6), the weights between the lower layer feature factors and their corresponding upper layer feature factors and the same layer feature factors are calculated respectively.

[0211]

[0212] In the formula, w iu is the weight of the lower-level feature factor i relative to the upper-level feature factor u.

[0213] w ij =w iu -w ju +0.5 (6)

[0214] In the formula, w ij is the weight of feature factor i relative to feature factor j.

[0215] Use formula (7) to calculate the judgment matrix T u Conduct feasibility assessment.

[0216]

[0217] Where Z is the feasibility ratio. When Z≤0.1, the judgment matrix meets the feasibility requirements.

[0218] The overall weights of the characteristic factors of the target layer and the indicator layer can be expressed as:

[0219] w iz =w iA × iB (8)

[0220] In the formula, w iA is the weight of the characteristic factor i of the criterion layer relative to the characteristic factor A of the target layer; w iB is the weight of the characteristic factor i of the indicator layer relative to the characteristic factor B of the criterion layer; w iz is the overall weight of the characteristic factor i of the index layer relative to the characteristic factor z of the target layer.

[0221] An evaluation value table is established based on the cable arc ignition test, cable fire simulation and cable fire accident. Each cable may have multiple characteristic parameters. The evaluation value of each characteristic parameter is multiplied by the corresponding weight to obtain the risk assessment score of each cable. The calculation formula is shown in formula (9):

[0222]

[0223] Where S is the fire risk assessment score; R i is the actual evaluation value of risk factor i.

[0224] The importance of each risk factor is compared and analyzed, and a judgment matrix is ​​established. Based on the cable intermediate joint arc ignition test, cable intermediate joint fire simulation and typical arc ignition fire accidents, a risk factor importance score table is constructed to calculate and evaluate the fire risk of cable arc fault.

[0225] The steps for cable arc fault risk assessment are as follows:

[0226] Judgment matrix T between target layer and criterion layer, criterion layer and indicator layer A 、T B1 、T B2 、T B3 As shown below.

[0227]

[0228] According to formula (5), the weights of arc fault fire risk, cable layout characteristics, environmental characteristics, and arc fault characteristics are calculated as w A =(0.317,0.267,0.416),w B1 =(0.308,0.358,0.334),w B2 =(0.325,0.283,0.392),w B3 =(0.147,0.189,0.192,0.171,0.301).

[0229] According to formula (6) and (7), the feasibility test is calculated and Z = (0.068, 0.072, 0.052, 0.077). From the result, it can be seen that the verification is passed. According to formula (8), the overall weight w is calculated. iz =(0.098,0.113,0.106,0.087,0.076,0.105,0.061,0.079,0.08,0.071,0.125).

[0230] A scoring table is established based on cable arc ignition test, cable fire simulation and cable fire accident. The correlation model between cables of different voltage levels and cross-sectional areas and fire intensity is established using equations (10) and (11).

[0231] Q ix =m ix q ix (10)

[0232] In the formula, Q ix The heat released when each layer of fuel in the cable intermediate joint is completely burned; m ix is the mass of the fuel; q ix is the unit calorific value corresponding to the fuel; x is the different cable types; i is the type of cable fuel, i=1, 2, 3 correspond to the fuel cross-linked polyethylene, polyurethane, and polyvinyl chloride respectively.

[0233]

[0234] In the formula, H x is the flame height when the fuel is completely burned; ρ is the ambient gas density; c is the ambient gas specific heat capacity; T is the ambient temperature.

[0235] The importance scores of risk factors at the indicator level are shown in Table 6:

[0236] Table 6 Cable fire risk factor scoring table

[0237]

[0238] Step 5: Classify the cable fire risk into four levels: A, B, C, and D, which correspond to the four states of normal, mild, moderate, and severe fire respectively. Determine the fire risk level corresponding to each cable according to the risk assessment score of each cable. The specific classification is shown in Table 7:

[0239] Table 7 Cable fire risk levels

[0240]

[0241]

[0242] The optional implementation method described above achieves at least the following effects: the purpose of quantitatively analyzing the risk of fire caused by arc grounding faults at cable joints is achieved, and the technical problem of being unable to quantitatively analyze the risk of cable fire caused by arc grounding faults at cable joints is solved. Thus, the technical effect of reducing the probability of cable fire is achieved.

[0243] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0244] In this embodiment, a cable tunnel fire risk assessment device for cable joint arc breakdown fault is also provided, which is used to implement the above-mentioned embodiments and preferred implementation modes, and the descriptions that have been made will not be repeated. As used below, the terms "module" and "device" can be a combination of software and / or hardware that implements a predetermined function. Although the devices described in the following embodiments are preferably implemented in software, the implementation of hardware, or a combination of software and hardware, is also possible and conceivable.

[0245] According to an embodiment of the present invention, there is also provided an apparatus embodiment for implementing a cable tunnel fire risk assessment method for cable joint arc breakdown failure. Figure 7 is a schematic diagram of a cable tunnel fire risk assessment device for a cable joint arc breakdown fault according to an embodiment of the present invention. Figure 7 As shown, the cable tunnel fire risk assessment device for the above-mentioned cable joint arc breakdown failure includes a test platform building module 71, an arc ignition test module 72, a simulation module 73, an analysis module 74, and a risk assessment module 75. The device is described below.

[0246] The test platform building module 71 is used to build an arc ignition test platform, wherein the arc ignition test platform includes a target cable intermediate joint, a power frequency current generator, a high voltage probe and acquisition card, an infrared camera, and a thermocouple;

[0247] The arc ignition test module 72 is used to perform arc ignition tests under various working conditions to obtain the temperature and flame height of each of the various working conditions, as well as the average arc power of each of the various working conditions, wherein the power supply voltage of the various working conditions is provided by an industrial frequency current generator, and the power supply voltage of the various working conditions is the same, and the current magnitude or duration of the various working conditions is different;

[0248] The simulation module 73 is used to establish a simulation model of the cable intermediate joint according to the arc ignition test, set a simulated combustion surface at the position of the middle copper conductor of the simulated cable intermediate joint, determine the heat release rate of the simulated combustion surface according to the average arc power obtained in the arc ignition test, and set multiple simulation test conditions that are the same as the arc ignition test, verify that the temperature obtained by the cable intermediate joint simulation model and the arc ignition test is within a predetermined first difference range, and the flame height is maintained within a predetermined second difference range, change the simulation conditions, including the arc ignition power of the simulated cable intermediate joint and the cable structure parameters, establish a new cable intermediate joint simulation model under different simulation test conditions, and obtain multiple risk factors that affect the fire risk of the cable tunnel;

[0249] The analysis module 74 is used to analyze the multiple risk factors according to the hierarchical analysis method, take the multiple risk factors as the indicator layer, determine the criterion layer and the target layer according to the multiple risk factors, determine the weight of the target layer and the actual score values ​​of the multiple risk factors, and calculate the score value of the sample cable intermediate joint according to the weight of the target layer and the actual score values ​​of the multiple risk factors, where R i It is obtained according to the cable fire risk factor score table, which is obtained through historical fire conditions and expert scores;

[0250] The risk assessment module 75 is used to determine the fire risk level and fire risk status of the sample cable tunnel where the sample cable intermediate joint is located according to the scoring value of the sample cable intermediate joint.

[0251] The cable tunnel fire risk assessment device for cable joint arc breakdown fault provided by the embodiment of the present invention achieves the purpose of quantitatively analyzing the risk of fire caused by arc grounding fault in cable joints, and solves the technical problem that the risk of cable fire caused by arc grounding fault in cable joints cannot be quantitatively analyzed. Thus, the technical effect of reducing the probability of cable fire is achieved.

[0252] It should be noted that the above modules can be implemented by software or hardware. For example, for the latter, it can be implemented in the following ways: the above modules can be located in the same processor; or the above modules can be located in different processors in any combination.

[0253] It should be noted that the test platform building module 71, arc ignition test module 72, simulation module 73, analysis module 74, and risk assessment module 75 correspond to steps 1 to 5 in the embodiment, and the examples and application scenarios implemented by the modules and the corresponding steps are the same, but are not limited to the contents disclosed in the embodiment. It should be noted that the modules as part of the device can be run in a computer terminal.

[0254] It should be noted that the optional or preferred implementation of this embodiment can refer to the relevant description in the embodiment, which will not be repeated here.

[0255] The cable tunnel fire risk assessment device for the above-mentioned cable joint arc breakdown failure may also include a processor and a memory. The test platform construction module 71, the arc ignition test module 72, the simulation module 73, the analysis module 74, the risk assessment module 75, etc. are all stored in the memory as program units, and the processor executes the above-mentioned program units stored in the memory to realize the corresponding functions.

[0256] The processor includes a kernel, which retrieves the corresponding program unit from the memory. There can be one or more kernels. The memory may include non-permanent memory in a computer-readable medium, random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM, and the memory includes at least one storage chip.

[0257] An embodiment of the present invention provides a non-volatile storage medium on which a program is stored. When the program is executed by a processor, a fire risk assessment method is implemented.

[0258] like Figure 8 As shown, an embodiment of the present invention provides an electronic device, the electronic device 10 includes a processor, a memory, and a program stored in the memory and executable on the processor, and the processor implements the following steps when executing the program: the memory is used to store a computer program, wherein, when the computer program is executed by the processor, the processor implements the cable tunnel fire risk assessment method for the above-mentioned cable joint arc breakdown fault, and the device in this article can be a server, a PC, etc.

[0259] The present invention also provides a computer program product, which, when executed on a data processing device, is suitable for executing a program that initializes the following method steps: computer instructions are executed by a processor to perform the above-mentioned cable tunnel fire risk assessment method for cable joint arc breakdown faults.

[0260] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0261] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0262] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0263] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0264] In a typical configuration, a computing device includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0265] The memory may include non-permanent memory in a computer-readable medium, random access memory (RAM) and / or non-volatile memory in the form of read-only memory (ROM) or flash RAM. The memory is an example of a computer-readable medium.

[0266] Computer readable media include permanent and non-permanent, removable and non-removable media that can be implemented by any method or technology to store information. Information can be computer readable instructions, data structures, program modules or other data. Examples of computer storage media include, but are not limited to, phase change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technology, compact disk read-only memory (CD-ROM), digital versatile disk (DVD) or other optical storage, magnetic cassettes, magnetic tape disk storage or other magnetic storage devices or any other non-transmission media that can be used to store information that can be accessed by a computing device. As defined herein, computer readable media does not include temporary computer readable media (transitory media), such as modulated data signals and carrier waves.

[0267] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0268] It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as methods, systems or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes.

[0269] The above are only embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A cable tunnel fire risk assessment method for cable joint arc breakdown failure, characterized in that: include: Step 1: Building an arc ignition test platform, wherein the arc ignition test platform includes a target cable intermediate joint, a power frequency current generator, a high-voltage probe and acquisition card, an infrared camera, and a thermocouple; Step 2: Under various working conditions, an arc ignition test is performed to obtain the temperature of each of the various working conditions, the flame height of each of the various working conditions, and the average arc power of each of the various working conditions, wherein the power supply voltage of the various working conditions is provided by the power frequency current generator, and the power supply voltage of the various working conditions is the same, and the current magnitude or duration of the various working conditions is different; Step 3: Establish a simulation model of a cable intermediate joint according to the arc ignition test, set a simulated combustion surface at the position of the middle copper conductor of the simulated cable intermediate joint, determine the heat release rate of the simulated combustion surface according to the average arc power obtained from the arc ignition test, and set a plurality of simulation test conditions that are the same as the arc ignition test, verify that the temperature obtained from the simulation model of the cable intermediate joint and the arc ignition test is within a predetermined first difference range, and the flame height is maintained within a predetermined second difference range, change the simulation conditions, including the arc ignition power of the simulated cable intermediate joint and the cable structure parameters, establish a new simulation model of the cable intermediate joint under different simulation test conditions, and obtain a plurality of risk factors that affect the fire risk of the cable tunnel; Step 4: Analyze the multiple risk factors according to the hierarchical analysis method, use the multiple risk factors as the indicator layer, determine the criterion layer and the target layer according to the multiple risk factors, determine the weight of the target layer and the actual score values ​​of the multiple risk factors, and calculate the score value of the sample cable intermediate joint according to the weight of the target layer and the actual score values ​​of the multiple risk factors, wherein the R i It is obtained according to the cable fire risk factor score table, which is obtained through historical fire conditions and expert scores; Step 5: According to the scoring value of the sample cable intermediate joint, determine the fire risk level and fire risk status of the sample cable tunnel where the sample cable intermediate joint is located.

2. The method according to claim 1, characterized in that Step 1: Build an arc ignition test platform, including the following steps: Step 1.1: Select the target cable intermediate joint, use hydraulic pliers to cover the copper terminal block on the copper conductor inside the cable body on one side of the target cable intermediate joint, and connect it to the positive pole of the power frequency current generator, fix the threaded nail on the aluminum sheath of the cable body on the other side of the target cable intermediate joint, and connect it to the negative pole of the power frequency current generator, punch a hole from the outside to the inside in the middle position of the target cable intermediate joint until the copper conductor position of the target cable intermediate joint, use copper wire as an arc starting wire to connect the copper conductor at the middle position of the target cable intermediate joint, the copper conductor inside the cable body on one side of the target cable intermediate joint, and the aluminum sheath of the cable body on the other side of the target cable intermediate joint, and use a clamp to fix the target cable intermediate joint on the bracket to obtain the arc ignition test circuit, wherein a hole is punched from the outside to the inside in the middle position of the target cable intermediate joint until the copper conductor position of the target cable intermediate joint is used to simulate the state of insulation breakdown of the target cable intermediate joint; Step 1.2, placing a high-voltage probe, an acquisition card, and an infrared camera around the arc ignition test, and arranging a thermocouple above the middle position of the target cable intermediate joint to obtain the arc ignition test platform, wherein the high-voltage probe and the acquisition card are used to collect the arc voltage, the infrared camera is used to monitor the temperature of the arc ignition test platform, and the thermocouple is used to monitor the temperature of a specific temperature measuring point of the arc ignition test platform.

3. The method according to claim 1, characterized in that Step 2: Under various working conditions, an arc ignition test is performed to obtain the temperature of each of the various working conditions and the flame height of each of the various working conditions, including the following steps: Step 2.1: Detect the circuit and circuit equipment of the arc ignition test platform and start the arc ignition test; Step 2.2: measuring the temperature of each of the multiple working conditions and the flame height of each of the multiple working conditions through the arc ignition test, and obtaining the arc voltage of each of the multiple working conditions and the arc current of each of the multiple working conditions; Step 2.3: Calculate the arc energy Q of each of the multiple working conditions according to the arc voltages of each of the multiple working conditions and the arc currents of each of the multiple working conditions, and the calculation formula is: Wherein, the P(t) is the instantaneous arc power of each of the multiple working conditions calculated from the arc voltages of each of the multiple working conditions and the arc currents of each of the multiple working conditions, the t1 is the start time of the arc generated by each of the multiple working conditions; t2 is the end time of the arc generated by each of the multiple working conditions; Step 2.4: Determine the average arc power P of each of the multiple working conditions according to the arc energy Q of each of the multiple working conditions. arc , the calculation formula is:

4. The method according to claim 1, characterized in that Step 3: Establish a simulation model of a cable intermediate joint according to the arc ignition test, set a simulated combustion surface at the position of the middle copper conductor of the simulated cable intermediate joint, determine the heat release rate of the simulated combustion surface according to the average arc power obtained by the arc ignition test, and set a plurality of simulation test conditions that are the same as the arc ignition test, verify that the temperature obtained by the simulation model of the cable intermediate joint and the arc ignition test is within a predetermined first difference range, and the flame height is maintained within a predetermined second difference range, change the simulation conditions, including the arc ignition power of the simulated cable intermediate joint and the cable structure parameters, establish a new cable intermediate joint simulation model under different simulation test conditions, and obtain a plurality of risk factors that affect the fire risk of the cable tunnel, including the following steps: Step 3.1: Establish an initial cable intermediate joint simulation model in accordance with the arc ignition test, set a simulated combustion surface at the position of the intermediate copper conductor of the simulated cable intermediate joint, determine the heat release rate of the simulated combustion surface according to the average arc power obtained from the arc ignition test, and set a plurality of simulation test conditions that are the same as the arc ignition test, wherein the simulation environment of the initial cable intermediate joint simulation model is consistent with the test environment of the arc ignition test; Step 3.2: Perform simulation tests on the initial simulated cable intermediate joint under multiple simulated working conditions that are the same as the multiple working conditions to obtain the respective temperatures of the initial simulated cable intermediate joint under the multiple simulated working conditions, and compare the respective temperatures of the initial simulated cable intermediate joint under the multiple simulated working conditions with the temperatures under the corresponding working conditions of the arc ignition test to obtain the respective comparison results under the multiple simulated working conditions; Step 3.3: According to the respective comparison results under the multiple simulation working conditions, the proportion of the substances participating in the combustion of the insulation layer, the filling layer, and the sheath layer of the initial simulated cable intermediate joint is adjusted until the temperature difference obtained by simulating the initial simulated cable intermediate joint under the multiple simulation working conditions and the temperature difference of the arc ignition test under the same working conditions are kept within the predetermined first difference range, and the simulated cable intermediate joint and the cable intermediate joint simulation model are obtained, wherein the proportion of the substances participating in the combustion of the insulation layer, the filling layer, and the sheath layer of the initial simulated cable intermediate joint can be expressed as: x1(C2H3Cl)+ x2(C9H 14 O3N2)+x3(C2H4), the adjusted formula is: x1(C2H3Cl)+x2(C9H 14 O3N2)+ x3(C2H4)+a5O2→bO2+cCO+dC+eH2O+fHCl+gHCN, where a, b, The c, d, e, f, and g are all coefficients of the reaction equation, the C2H3Cl is the monomer corresponding to the polymer polyvinyl chloride, the x1 is the reaction coefficient of the C2H3Cl, the C9H 14 O3N2 is the monomer corresponding to polyurethane, and x2 is C9H 14 The reaction coefficient of O3N2, the C2H4 is a monomer corresponding to cross-linked polyethylene, the x3 is the reaction coefficient of the C2H4, the O2 is oxygen, the CO is carbon monoxide, the C is carbon, the H2O is water, the HCl is hydrogen chloride, and the HCN is hydrogen cyanide; Step 3.4: simulating the simulated cable intermediate joint under the multiple simulated working conditions, and obtaining a result that the flame height under the multiple simulated working conditions and the flame height under the corresponding working conditions of the arc ignition test have errors within a predetermined second difference range when the simulated cable intermediate joint burns stably; Step 3.5: Based on the results obtained in step 3.4, change the voltage level and structural parameters of the simulated cable intermediate joint, establish new cable intermediate joint simulation models respectively, and obtain the multiple risk factors that affect cable tunnel fires, wherein the multiple risk factors include cable position, layer spacing, horizontal spacing, tunnel temperature, tunnel humidity, tunnel wind speed, voltage level, cross-sectional area, cable load, operating years, and duration.

5. The method according to claim 1, characterized in that Step 4: Analyze the multiple risk factors according to the hierarchical analysis method, use the multiple risk factors as the indicator layer, determine the criterion layer and the target layer according to the multiple risk factors, determine the weight of the target layer and the actual score values ​​of each of the multiple risk factors, and calculate the score value of the sample cable intermediate joint according to the weight of the target layer and the actual score values ​​of each of the multiple risk factors, including the following steps: Step 4.1: Analyze the multiple risk factors according to the hierarchical analysis method, use the multiple risk factors as the indicator layer, and construct the criterion layer and the target layer according to the multiple risk factors, wherein the target layer is the highest level, the criterion layer is the middle level, and the indicator layer is the lowest level. The criterion layer includes cable layout characteristics, environmental characteristics and cable fault characteristics. The cable layout characteristics include the cable position, the layer spacing and the horizontal spacing. The environmental characteristics include the tunnel temperature, tunnel humidity and tunnel wind speed. The arc fault characteristics include the voltage level, the cross-sectional area, the cable load, the operating years and the duration. The target layer is the cable tunnel fire risk. Step 4.2: According to the hierarchical relationship of each risk factor, compare the importance of all risk factors at the same level, and construct the judgment matrix between the target layer and the criterion layer, and between the criterion layer and the indicator layer, respectively. The expression of the judgment matrix is: T u is the judgment matrix, x ij is the relative importance of risk factor i to risk factor j, i and j are two risk factors in the same layer, u is the upper-layer risk factor corresponding to the lower-layer risk factor, and n is the number of risk factors in the same layer; Step 4.3: Normalize the values ​​in the judgment matrix and calculate the weight of the lower risk factor i relative to the upper risk factor u. The calculation formula is: The x ij is the relative importance of risk factor i to risk factor j, where i and j are two risk factors at the same level; Step 4.4: Calculate the weights between risk factors at the same level. The calculation formula is: w ij =w iu -w ju +ab, ab is a constant, the w iu is the weight of the lower risk factor i relative to the upper risk factor u, and the w ju The weight of the lower risk factor j relative to the upper risk factor u; Step 4.5: Use the formula Obtaining a feasibility ratio, and using the feasibility ratio to perform feasibility judgment on the judgment matrix, when the feasibility ratio Z is less than a predetermined threshold, the judgment matrix meets the feasibility requirement; Step 4.6: The overall weight of the target layer is: w iz =w iA × iB , the w iA is the weight of the risk factor i of the criterion layer relative to the risk factor A of the target layer, and the w iB is the weight of the risk factor i of the indicator layer relative to the risk factor B of the criterion layer; Step 4.7: According to the overall weight of the target layer, the score value of the sample cable intermediate joint is obtained. The score value S of the sample cable intermediate joint is calculated by the formula: R i is the actual score value of risk factor i, where R i It is obtained according to the cable fire risk factor score table, which is obtained through historical fire conditions and expert scores.

6. The method according to claim 1, characterized in that Step 5: Determine the fire risk level and fire risk status of the sample cable tunnel where the sample cable intermediate joint is located according to the scoring value of the sample cable intermediate joint, including the following steps: Step 5.1: According to the scoring value of the sample cable intermediate joint, determine the fire risk level and fire risk status of the sample cable tunnel caused by the sample cable intermediate joint; wherein, when the S is less than S1, the fire risk level of the sample cable tunnel is A, and the fire risk status of the sample cable tunnel is normal; when the S is greater than S1 and less than S2, the fire risk level of the sample cable tunnel is B, and the fire risk status of the sample cable tunnel is a light fire; when the S is greater than S2 and less than S3, the fire risk level of the sample cable tunnel is C, and the fire risk status of the sample cable tunnel is a moderate fire; when the S is greater than S3, the fire risk level of the sample cable tunnel is D, and the fire risk status of the sample cable tunnel is a severe fire.

7. A cable tunnel fire risk assessment device for cable joint arc breakdown failure, characterized in that: include: A test platform building module, used to build an arc ignition test platform, wherein the arc ignition test platform includes a target cable intermediate joint, a power frequency current generator, a high-voltage probe and acquisition card, an infrared camera, and a thermocouple; An arc ignition test module, used for performing an arc ignition test under various working conditions, obtaining the temperature of each of the various working conditions, the flame height of each of the various working conditions, and the average arc power of each of the various working conditions, wherein the power supply voltage of the various working conditions is provided by the power frequency current generator, and the power supply voltage of the various working conditions is the same, and the current magnitude or duration of the various working conditions is different; A simulation module is used to establish a simulation model of a cable intermediate joint according to the arc ignition test, set a simulated combustion surface at the position of the middle copper conductor of the simulated cable intermediate joint, determine the heat release rate of the simulated combustion surface according to the average arc power obtained by the arc ignition test, and set a plurality of simulation test conditions that are the same as the arc ignition test, verify that the temperature obtained by the simulation model of the cable intermediate joint and the arc ignition test is within a predetermined first difference range, and the flame height is maintained within a predetermined second difference range, change the simulation conditions, including the arc ignition power of the simulated cable intermediate joint and the cable structure parameters, establish a new simulation model of the cable intermediate joint under different simulation test conditions, and obtain a plurality of risk factors that affect the fire risk of the cable tunnel; The analysis module is used to analyze the multiple risk factors according to the hierarchical analysis method, use the multiple risk factors as the indicator layer, determine the criterion layer and the target layer according to the multiple risk factors, determine the weight of the target layer and the actual score values ​​of each of the multiple risk factors, and calculate the score value of the sample cable intermediate joint according to the weight of the target layer and the actual score values ​​of each of the multiple risk factors, wherein the R i It is obtained according to the cable fire risk factor score table, which is obtained through historical fire conditions and expert scores; The risk assessment module is used to determine the fire risk level and fire risk status of the sample cable tunnel where the sample cable intermediate joint is located according to the scoring value of the sample cable intermediate joint.

8. A non-volatile storage medium, characterized in that: The non-volatile storage medium stores a plurality of instructions, and the instructions are suitable for being loaded by a processor and executing the cable tunnel fire risk assessment method for cable joint arc breakdown faults as described in any one of claims 1 to 6.

9. An electronic device, characterized in that: include: One or more processors and a memory, the memory being used to store one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors implement the cable tunnel fire risk assessment method for arc breakdown faults as described in any one of claims 1 to 6.

10. A computer program product comprising computer instructions, characterized in that: The computer instructions are executed by the processor to implement the cable tunnel fire risk assessment method for arc breakdown faults as described in any one of claims 1 to 6.

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