Extra-high voltage converter transformer network side bushing fault detonation simulation test method and platform

Abstract

The invention discloses a fault detonation simulation test method and platform for an extra-high voltage converter transformer network side bushing, and the method comprises the steps: providing a critical value calculation method for primary physical explosion and secondary chemical explosion of the extra-high voltage converter transformer network side bushing under different arc fault energy conditions; and the critical conditions of primary physical explosion and secondary chemical explosion can be accurately judged. According to the invention, the whole dynamic evolution process from rapid cracking of transformer oil and sudden pressure increase caused by converter transformer fault arc to superposition of physical explosion and explosion chemistry can be truly simulated, a grid-side bushing fault detonation critical discrimination method is provided, and technical parameters and theoretical support are provided for the explosion-proof and pressure-relief design of the converter transformer.

Description

Technical Field

[0001] The present invention relates to the technical field of UHV fire protection, and particularly to a method and platform for simulating the explosion and combustion of a UHV converter transformer's line side bushing failure. Background Art

[0002] The converter transformer is one of the important component devices in the UHV DC transmission project, and its normal operation is the basis of the UHV DC transmission system. The line side bushing of the converter transformer is affected by electricity, heat, mechanical stress and the environment. At the same time, the high voltage and large current it bears will damage its insulation performance, and it is a component with relatively fast aging in the converter transformer. In recent years, converter transformer accidents caused by bushing explosions have occurred many times at home and abroad. The explosion problem of the line side high-voltage bushing of the converter transformer has become one of the important factors affecting its safe and stable operation.

[0003] Currently, the fault detection and diagnosis of the line side bushing of UHV converter transformers is one of the research hotspots. The existing technologies mainly focus on detecting potential faults in advance by monitoring various parameters of the bushing, such as oil temperature, oil chromatography, partial discharge, etc. These technologies can help maintenance personnel discover problems in time and take corresponding measures to avoid the further development of faults. However, for the research on the fire protection technology of the line side bushing of UHV converter transformers, the previous related research mainly includes using special fire extinguishing agents, designing reasonable fire extinguishing systems, and developing bushing structures with self-extinguishing functions.

[0004] The Chinese invention patent with the patent publication number CN114636901A discloses a test system for the explosion characteristics of a transformer line side bushing, including a detonating charge column arranged in the conducting rod, a high-speed camera for taking images of the explosion fireball, and a number of pressure sensors arranged in sequence along the horizontal ray direction of the geometric center of the detonating charge column. These sensors are used to collect the overpressure data of the explosive explosion. This patented technology uses explosives to simulate the explosion. The explosion process of the converter transformer is as follows: a large amount of rapid cracking of the transformer oil caused by the high-energy arc of the converter transformer will produce a physical explosion, resulting in the rupture of the fuel tank. After the high-temperature cracked gas sprays out from the rupture port and contacts the air, a chemical explosion occurs. This process is significantly different from the overpressure characteristics of the explosive explosion, and the overpressure of the explosive explosion usually only lasts for several milliseconds, while the overpressure process generated by the deflagration of the transformer oil can last for hundreds of milliseconds. Therefore, using explosives to simulate the explosion cannot present the process of the line side bushing deflagration with a physical explosion first and then a chemical deflagration, nor can it obtain the critical energy values of the arc energy leading to the first physical explosion and the second chemical explosion under real conditions to provide support for explosion protection and pressure relief design.

[0005] Chinese invention patent with the publication number CN111122195A discloses an experimental platform for simulating the fire of ultra-high voltage converter transformers. By changing the oil tank model, the simulation and reproduction of the fire with riser and the full liquid surface fire can be realized respectively. In addition, by changing the fire extinguishing medium and the setting method of the fire extinguishing system, the fire extinguishing efficiency of different fire extinguishing systems can be compared and verified. The following problems exist in this patent:

[0006] First, the patented technology only simulates the high-temperature environment of pool fire and cannot simulate the process of a large amount of rapid cracking of transformer oil caused by a high-energy arc generated by a fault in the line side bushing of the converter transformer, resulting in a physical explosion that causes the oil tank to rupture, and the chemical explosion that occurs when the high-temperature cracked gas ejects from the rupture and meets the air. Therefore, the patented technology cannot obtain the critical energy values of the primary physical explosion and the secondary chemical explosion caused by arc energy under real conditions, nor can it provide support for explosion protection and pressure relief design.

[0007] Second, in the patented technology, the pool fire takes 1 minute or even longer to reach the fully burning stage, while the deflagration fire of the converter transformer often reaches the maximum fire power within a few seconds. Therefore, the patented technology cannot reproduce the real deflagration fire of the converter transformer.

[0008] Chinese invention patent with the publication number CN116430185A discloses an ultra-high voltage converter transformer fault signal simulation test platform. The platform design includes key components such as a simulation test oil tank and a high-voltage simulation test bushing. The platform can realize accurate simulation tests of various fault signals such as gas production, oil temperature, current-carrying, and internal discharge. However, this document focuses on the detection of early internal faults of the transformer and cannot simulate the process of a large amount of rapid cracking of transformer oil caused by a high-energy arc in the converter transformer, resulting in a physical explosion that causes the oil tank to rupture, and the chemical explosion that occurs when the high-temperature cracked gas ejects from the rupture and meets the air. Therefore, it is impossible to obtain the critical energy values of the primary physical explosion and the secondary chemical explosion caused by arc energy under real conditions, nor can it realize the real-time monitoring of dynamic data such as the temperature inside the riser, the vibration and deformation of the cylinder body.

[0009] In summary, the existing test devices and methods have the following deficiencies:

[0010] First, it is impossible to simulate the complete process from the generation of a high-energy arc caused by a fault in the line side bushing of the converter transformer, which leads to rapid cracking of transformer oil and a sudden increase in pressure, to the physical explosion superimposed on the chemical explosion, and it is impossible to truly reproduce the deflagration process of the converter transformer. Moreover, there is a lack of a complete test method for the deflagration test of the converter transformer.

[0011] Second, there is a lack of a critical calculation method for the primary physical explosion and secondary chemical explosion of the UHV converter transformer's line-side bushing failure deflagration under different arc energy conditions, making it impossible to accurately obtain key data such as the pressure, temperature, and deformation of the oil tank and riser under different arc energies, and thus it is difficult to comprehensively support the theoretical research and technical improvement of transformer explosion protection and pressure relief design. Summary of the Invention

[0012] The technical problem to be solved by the present invention is to provide a method that can accurately simulate the dynamic evolution characteristics of physical explosion and chemical explosion during the failure deflagration of the UHV converter transformer's line-side bushing.

[0013] To solve the above technical problem, the present invention provides the following technical solutions:

[0014] A method for simulating the failure deflagration test of the UHV converter transformer's line-side bushing, characterized by including: based on the arc energy fault model, by setting different simulated fault arc energy conditions, calculating the arc energy value under the short-circuit condition of the riser of the UHV converter transformer's line-side bushing, and thereby determining the critical energy threshold for the primary physical explosion and the secondary chemical explosion, so as to obtain the critical conditions for the bushing failure deflagration.

[0015] Among them, the arc energy fault model is obtained through the following steps:

[0016] S10, set the test groups under different voltages to simulate the internal arc discharge test of the riser.

[0017] S20, according to the test voltage and current values to be simulated, connect the fault arc energy test circuit to the simulated UHV converter transformer's line-side bushing platform, first adjust the discharge gap in the simulated UHV converter transformer's line-side bushing platform to the maximum, and then gradually reduce the discharge gap, and conduct the tests in sequence according to the test groups.

[0018] S30, the data acquisition system obtains the deflagration data of the simulated UHV converter transformer's line-side bushing platform during the arc discharge test.

[0019] S40, externally connect a gas chromatography device to conduct chromatographic detection on the transformer oil in the oil tank before and after the test, obtain gas chromatography data, and combine the constructed arc energy fault model to obtain the "energy-gas-explosion" mapping relationship.

[0020] S50, compare the calculation results of the arc energy fault model with the experimental data obtained in step S30 to verify the rationality of the arc energy fault model.

[0021] In an embodiment of the present invention, the arc energy fault model includes an arc energy model inside the UHV converter transformer and a pressure model inside the overheated transformer oil vapor.

[0022] Among them, obtaining the arc energy model inside the UHV converter transformer includes:

[0023] According to Equation (1), calculate the arc energy:

[0024]

[0025] In the formula: W arc is the total arc energy, Δt is the arc duration, u arc and i arc are the voltage drops at both ends of the fault point and the arc current respectively;

[0026] Assume that the arc voltage drop per unit length is constant during the arc burning process, simplify the physical process of the arc fault, and obtain Equation (2):

[0027] u arc = E0l arc , (2);

[0028] In the formula: E0 is the electric field strength per unit length, always a positive value; l arc is the arc length, the arc current i arc is the current value, the arc duration is Δt, and thus substitute Equation (2) into Equation (1), and calculate the arc energy level generated when the transformer fails through Equation (3):

[0029]

[0030] If the current i arc is constant, then Equation (3) is further simplified to obtain Equation (4), which is used as the arc energy model inside the UHV converter transformer:

[0031] W arc = E0l arc i arc Δt, (4);

[0032] b. Obtain the pressure model inside the overheated transformer oil vapor, including:

[0033] Assume that part of the total energy W arc released by the arc is converted into the internal energy of the gas, and part is lost to the surrounding medium. Let there be an energy conversion ratio α, then the energy W heat used to heat and vaporize the oil is:

[0034] W heat = αW arc , (5);

[0035] In the formula: α is the proportion of the arc energy used to heat and vaporize the insulating oil;

[0036] The energy Wheat For heating the liquid transformer oil from the initial temperature to the vaporization temperature and completing vaporization, the absorbed energy is equal to the enthalpy increase:

[0037] W heat = m gas ΔH oil , (6);

[0038] Where: m gas is the mass of the gas, and ΔH oil is the enthalpy increase during the process of the liquid insulating oil rising from the normal operating temperature to the vaporization temperature; from equations (5) and (6), the mass of the cracked gas is obtained:

[0039] m gas = αW arc / ΔH oil , (7);

[0040] Regarding the cracked gas as an ideal gas, it satisfies the state equation (8):

[0041] p gas V gas = nRT, (8);

[0042] Where: n = m gas / M gas is the number of moles of the gas, M gas is the molar mass of the oil vapor, R is the gas constant, T is the gas temperature, V gas is the gas volume, and p gas is the bubble pressure;

[0043] Combining the mass m gas of the gas and substituting equation (7) into equation (8), the expression for the bubble pressure p gas is:

[0044]

[0045] For an ideal gas, the specific internal energy per unit mass μ gas is defined as:

[0046]

[0047] Where: c v is the specific heat at constant volume; and also because:

[0048]

[0049] Where: γ gas is the specific heat ratio, c p is the specific heat at constant pressure. Combining equations (11) and (12) gives:

[0050]

[0051] Substitute the specific internal energy per unit mass μ gas into Equation (10) to obtain:

[0052]

[0053] Substitute Equation (14) into the initial bubble pressure p gas into Equation (9) to obtain:

[0054]

[0055] During the cracking process of transformer insulating oil, take the temperature T of the cracked gas gas as the gasification temperature T of the insulating oil vap :

[0056] T gas = T vap , (16);

[0057] Substitute Equation (16) into Equation (15) to obtain Equation (17), which is used as the pressure model inside the superheated transformer oil vapor:

[0058]

[0059] In an embodiment of the present invention, the critical conditions for the deflagration of the bushing fault include the critical conditions for only physical explosion of the bushing and the critical conditions for physical and superimposed chemical explosion of the bushing; among them,

[0060] Based on the pressure model inside the superheated transformer oil vapor, by calculating the internal pressure value of the bubble, use it as the critical parameter for determining only physical explosion; analyze the fault arc energy through the arc energy model, and combine the dynamic relationship between the cracked gas volume and the arc energy to derive the critical energy thresholds for physical explosion and chemical explosion, as the composite critical parameter for determining the superimposed trigger of physical and chemical explosion.

[0061] In an embodiment of the present invention, the critical condition for only physical explosion of the bushing is:

[0062] When the bubble pressure P gas exceeds the tolerance pressure P of the fuel tank limit , physical explosion occurs:

[0063] P gas ≥ P limit , (18);

[0064] In the formula, P gas is the bubble pressure, and P limit is the tolerance pressure of the fuel tank; among them, the tolerance pressure P of the fuel tank limit is obtained through Equation (19):

[0065] Substitute Equation (17) into Equation (18) and take P gas = P limit , and obtain the physical explosion critical value P of the arc energy limit :

[0066]

[0067] In an embodiment of the present invention, the critical condition for the physical and chemical superposition explosion of the casing is:

[0068] W arc ≥ max(W physical , W chemical )

[0069] Among them, W physical is the physical explosion critical energy, W chemical is the chemical explosion critical energy, and W arc is the arc energy.

[0070] In an embodiment of the present invention, obtaining the chemical explosion critical energy in the critical condition for the physical and superposition chemical explosion of the casing includes:

[0071] Let the proportion of the arc energy used for cracking be β, and the number of moles of hydrogen and acetylene generated is:

[0072]

[0073] Among them, η i is the cracking yield of gas i, and ΔH f,i is the molar formation enthalpy of gas i, and endothermic is positive;

[0074] The total volume of the mixed cracking gas is the fuel tank volume V tank , and the volume concentration is:

[0075]

[0076] In the formula, c i is the volume concentration of gas i;

[0077] Explosion lower limit determination:

[0078] The explosion lower limit of the mixed cracking gas is calculated according to the Le Chatelier's law:

[0079]

[0080] Among them, is the volume fraction of each gas, LEL i is the explosion lower limit of gas i, and LEL mix is the explosion lower limit of the mixed cracking gas;

[0081] When the mixing concentration ∑ i c i ≥LEL mix a chemical explosion is triggered; by combining the gas volume and arc energy relationships in equations (20), (21), and (22), and taking the critical ∑ i c i =LEL mix , the critical energy of the chemical explosion is obtained:

[0082]

[0083] Among them, the critical energy of the physical explosion is obtained through equation (23):

[0084]

[0085] The present invention also provides a test platform for a fault explosion simulation test method of a UHV converter transformer line side bushing, including:

[0086] A platform for simulating the UHV converter transformer line side bushing;

[0087] A fault arc energy test circuit, connected to the platform for simulating the UHV converter transformer line side bushing;

[0088] A data acquisition system, arranged on the platform for simulating the UHV converter transformer line side bushing;

[0089] A data processing terminal, used to calculate the arc energy value under the short - circuit condition of the UHV converter transformer by setting different simulated fault arc energy conditions based on the arc energy fault model, and thereby determine the critical energy thresholds of the primary physical explosion and the secondary chemical explosion, so as to obtain the critical conditions for bushing fault explosion.

[0090] In an embodiment of the present invention, the fault arc energy test circuit includes: a generator K, a short - circuit transformer DB, a grounding resistance Rj, circuit breakers CD1, CD2, CD3, CD4, a power factor adjustment resistor Rt, an adjusting reactor Lt, voltage dividers FY1, FY2, arc voltage dividers FH1, FH2, shunt resistors FL1, FL2;

[0091] On the primary side of the short - circuit transformer DB, the adjusting reactor Lt, the power factor adjustment resistor Rt, the circuit breaker CD1, the generator K, and the circuit breaker CD2 are connected in series; one end of the grounding resistance Rj is connected to the generator K, and the other end is grounded;

[0092] On the secondary side of the short-circuit transformer DB, a voltage divider FY1, a circuit breaker CD3, a shunt FL1, an arc voltage divider FH1, a terminal, an arc voltage divider FH2, a shunt FL2, a circuit breaker CD4, and a voltage divider FY2 are connected in series; the terminal is connected to the bushing platform.

[0093] In an embodiment of the present invention, the simulated UHV converter transformer line side bushing platform includes: a bushing body 1, a riser 2, and an oil tank 3; the bushing body 1 is installed on the top of the riser 2, and the oil tank 3 is arranged at the bottom of the riser 2; moreover, the bushing body 1 is electrically connected to the internal conductor of the oil tank 3; a test bushing 9 is installed on one side of the oil tank 3 as an interface for current input, so that the simulated UHV converter transformer line side bushing platform is connected to the fault arc energy test line.

[0094] In an embodiment of the present invention, the data acquisition system includes: a pressure acquisition system, a vibration acquisition system, and a temperature acquisition system;

[0095] The pressure acquisition system includes a number of dynamic pressure sensors 10, which are arranged at each measuring point of the riser 2 and the oil tank 3;

[0096] The vibration acquisition system includes a number of strain gauges 11, which are arranged outside the cylinder body of the riser 2;

[0097] The temperature acquisition system includes a number of fiber optic thermometers 12, which are installed at each measuring point of the riser 2 and the oil tank 3.

[0098] Compared with the prior art, the beneficial effects of the present invention are:

[0099] First, a large arc is used to ignite the transformer oil, truly simulating the whole process from the fault arc triggering the rapid cracking of the transformer oil, the sudden increase in pressure, to the physical explosion superimposed with the chemical explosion, realizing the measurement of key parameters such as pressure, oil temperature, and strain during deflagration, and providing key technical parameter support for studying the deflagration disaster mechanism and enhancing the design of surrounding fire-fighting facilities.

[0100] Second, a calculation method for the critical values of deflagration, primary physical explosion, and secondary chemical explosion of the UHV converter transformer line side bushing under different arc fault energy conditions is proposed, which can accurately determine the critical conditions of the primary physical explosion and the secondary chemical explosion. This method provides important technical parameters and theoretical support for the explosion-proof and pressure-relief design of the converter transformer, ensuring the safe and stable operation of the UHV converter transformer.

[0101] The present invention can truly simulate the whole process from the initiation of a fault arc that rapidly cracks transformer oil and causes a sudden pressure increase to a physical explosion superimposed with a chemical explosion, enabling the measurement of key parameters such as pressure, oil temperature, and strain during deflagration. It also proposes a critical calculation method for the deflagration of a primary physical explosion and a secondary chemical explosion of the line-side bushing of a UHV converter transformer under different arc fault energy conditions, accurately determining the critical conditions for the primary physical explosion and the secondary chemical explosion, providing key parameter support for a deep understanding of the deflagration damage mechanism, pressure relief design, and the design of surrounding auxiliary fire pipelines and facilities, etc., and providing a reliable basis for the safe design and operation of UHV converter transformers. BRIEF DESCRIPTION OF THE DRAWINGS

[0102] Figure 1 It is a schematic diagram of the platform of the line-side bushing of a UHV converter transformer simulated in an embodiment of the present invention.

[0103] Figure 2 It is a schematic diagram of the fault arc energy test circuit in an embodiment of the present invention.

[0104] Figure 3 It is a schematic diagram of the data acquisition system in an embodiment of the present invention.

[0105] Figure 4 It is a schematic diagram of the sound insulation cover and the data acquisition system in an embodiment of the present invention.

[0106] Figure 5 It is a flow chart of the steps for obtaining the arc energy fault model in an embodiment of the present invention.

[0107] Figure 6 It is a time history curve diagram of the pressure on the upper part of the riser barrel in an embodiment of the present invention.

[0108] Figure 7 It is a curve diagram of the strain change on the riser in an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0109] To facilitate the understanding of the technical solution of the present invention by those skilled in the art, the technical solution of the present invention will be further described below with reference to the accompanying drawings of the specification.

[0110] The terms "first" and "second" are used for descriptive purposes only and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present application, "a plurality" means two or more unless otherwise specifically defined.

[0111] Embodiment 1

[0112] Please refer to Figure 1As shown in the figure, for the convenience of understanding, the UHV converter transformer line side bushing fault explosion simulation test platform will be described first. Specifically, the test platform includes: a simulated UHV converter transformer line side bushing platform, a data acquisition system, a fault arc energy test circuit, and a data processing terminal. Among them, the fault arc energy test circuit is connected to the simulated UHV converter transformer line side bushing platform, and the data acquisition system is set on the simulated UHV converter transformer line side bushing platform. The data processing terminal is used to calculate the arc energy value under the short-circuit condition of the UHV converter transformer by setting different simulated fault arc energy conditions based on the arc energy fault model, and thereby determine the critical energy threshold for the primary physical explosion and the secondary chemical explosion, so as to obtain the critical conditions for bushing fault explosion.

[0113] Please refer to Figure 1 As shown in the figure, in this embodiment, the simulated UHV converter transformer line side bushing platform includes: a bushing body 1, a riser 2, and an oil tank 3. The bushing body 1 is installed on the top of the riser 2. Specifically, the bushing body 1 is vertically installed on the riser 2 through a mounting flange 4. The oil tank 3 is arranged at the bottom of the riser 2, and the bushing body 1 is electrically connected to the internal conductor of the oil tank 3. Specifically, the oil tank 3 is also mechanically fixed to the riser 2 through the mounting flange 4 to ensure sealing and seismic resistance.

[0114] In this embodiment, the pressure relief device 5 provided on the riser 2 is located at the connection between the riser 2 and the oil tank 3. The symmetric position of the pressure relief device 5 is a manhole 6. Sensor mounting screw seats 8 are installed at the manhole 6, and at the upper, middle, and lower positions of the riser 2, which is convenient for deploying the data acquisition system. A valve 7 is also provided on the riser 2, and a sound insulation cover 13 is additionally installed outside the simulated UHV converter transformer line side bushing platform, that is, the sound insulation cover 13 houses the entire simulated UHV converter transformer line side bushing platform. Among them, a test bushing 9 is installed on one side of the oil tank 3 as an interface for current input, so that the simulated UHV converter transformer line side bushing platform is connected to the fault arc energy test circuit.

[0115] Please refer to Figure 2 As shown in the figure, in an embodiment of the present invention, the fault arc energy test circuit mainly provides high voltage, large current, and a certain amount of arc energy injection for the simulated UHV converter transformer line side bushing platform, and through the coordinated operation of multiple devices, realizes the precise simulation and data acquisition of the UHV converter transformer line side bushing fault explosion process. Specifically, the fault arc energy test circuit includes: a generator K, a short-circuit transformer DB, a grounding resistance Rj, circuit breakers CD1, CD2, CD3, CD4, a power factor regulating resistor Rt, a regulating reactor Lt, voltage dividers FY1, FY2, arc voltage dividers FH1, FH2, shunt resistors FL1, FL2.

[0116] In this embodiment, on the primary side of the short-circuit transformer DB, the regulating reactor Lt, the power factor regulating resistor Rt, the circuit breaker CD1, the generator K, and the circuit breaker CD2 are connected in series. One end of the grounding resistor Rj is connected to the generator K, and the other end is grounded;

[0117] On the secondary side of the short-circuit transformer DB, the voltage divider FY1, the circuit breaker CD3, the shunt FL1, the arc voltage divider FH1, the terminal, the arc voltage divider FH2, the shunt FL2, the circuit breaker CD4, and the voltage divider FY2 are connected in series. And, the terminal is connected to the simulated UHV converter transformer network-side bushing platform. Figure 2 In, the reference numeral YP is the sample, which can be understood as the simulated UHV converter transformer network-side bushing platform.

[0118] In this embodiment, flexible adjustment is made according to different test parameters. For example, when performing a 21.5 kV voltage test, 1 to 2 6500 MVA generators K are connected in parallel, and 3 short-circuit transformers DB are connected in parallel to provide the high voltage and large current required for the test to simulate the fault arc energy. The circuit breakers CD1 and CD3 with a voltage of 40.5 kV are used to control the on-off of the current in stages. When performing a 43 kV voltage test, 4 6500 MVA generators K are connected in parallel, and 6 short-circuit transformers DB are connected in parallel. The circuit breakers CD2 and CD4 with a voltage of 25.2 kV are selected for control. Other devices provided in the fault arc energy test circuit, such as the grounding resistor Rj, the power factor regulating resistor Rt, and the regulating reactor Lt, etc., can be used to protect the equipment from overload or short-circuit damage. Two sets of voltage dividers FY1 and FY2, arc voltage dividers FH1 and FH2, and shunts FL1 and FL2 are configured in the test circuit to ensure that the test parameters can be normally collected during the test process.

[0119] Please refer to Figure 1 、 3 and Figure 4 As shown in, in an embodiment of the present invention, the data acquisition system includes: a pressure acquisition system, a vibration acquisition system, and a temperature acquisition system, which quantitatively detect various performance parameters and their damage states under the short-circuit state.

[0120] In this embodiment, the positions of the sensors in the data acquisition system at each measurement point on the riser 2 and the oil tank 3 are:

[0121] The pressure acquisition system includes a number of dynamic pressure sensors 10, which are arranged at each measuring point of the lifting seat 2 and the oil tank 3, and are used to detect the pressure change process inside the lifting seat 2 during the test. The vibration acquisition system includes a number of strain gauges 11, which are arranged outside the cylinder of the lifting seat 2 and are used to detect the deformation and vibration of the cylinder of the lifting seat 2 during the test. The temperature acquisition system includes a number of optical fiber thermometers 12, which are installed at each measuring point of the lifting seat 2 and the oil tank 3. Among them, some optical fiber thermometers 12 are installed at the cover plate of the manhole 6, and the probe of the optical fiber thermometer 12 extends into the inside of the lifting seat 2 to detect the temperature change process of the transformer oil inside the lifting seat 2 during the test.

[0122] In this embodiment, the positions of each sensor at each measuring point on the sound insulation hood 13 are as follows: a number of dynamic pressure sensors 10 are installed on the upper middle, middle middle, upper left, upper right and upper right of the network side wall of the valve hall side of the sound insulation hood 13, and a number of strain gauges 11 are installed in the middle of the valve hall side of the sound insulation hood 13 and the middle of the network side wall.

[0123] In an embodiment of the present invention, the test platform further includes a safety protection system, and the safety protection system includes the setting of explosion-proof and fire-fighting equipment and related protection means. Specifically, the safety protection system includes:

[0124] Steel protection plates with a length and width of 8.6m×23.3m and a height of 7.5m are arranged on the four sides of the network side bushing platform of the UHV converter transformer, and are firmly fixed to the ground with bolts. Fire-proof blankets are laid around the network side bushing platform of the UHV converter transformer to prevent debris from splashing. On both sides of the protection plate, multiple sets of dry powder automatic fire extinguishing devices and multiple sets of electric remote control fire fighting water guns are respectively arranged.

[0125] Multiple foam fire extinguishing guns and multiple remote control fire fighting water guns are respectively installed on the surrounding walls of the laboratory. Multiple fire trucks are respectively placed outside the door of the test hall, and at least 2 fire brigades are equipped at the same time.

[0126] An outdoor fire hydrant is provided at the entrance of the test hall, which can be connected to a fire truck to provide water source. The accident oil pool can discharge waste such as oil-water mixture to the second accident oil pool during fire fighting. Control and warning are done around the test site, and it is strictly prohibited for irrelevant personnel to enter the warning range.

[0127] Embodiment 2

[0128] In the theoretical research on the fault characteristics of transformer arc discharge, the test platform of the present invention has obtained effective test data such as pressure, temperature, vibration, and oil tank deformation inside the line side riser 2 and the oil tank 3 under arc discharge faults by equipping with a variety of sensors. It can measure the changes of pressure, temperature, and strain in real time, accurately quantify the performance parameters and damage conditions under short-circuit conditions, reveal the distribution of explosion energy, and thus provide a theoretical basis for the critical value of deflagration overpressure. In addition, gas chromatography technology is used to collect and analyze the gases released during the thermal decomposition of transformer oil samples in real time. Combining the gas chromatography data (such as the concentrations of H2 and C2H2) with the arc energy model, an "energy-gas-explosion" mapping relationship is established.

[0129] Please refer to Figure 5 As shown, the present invention also provides a method for simulating deflagration of the line side bushing fault of a UHV converter transformer, including: based on the arc energy fault model, by setting different simulated fault arc energy conditions, calculating the arc energy value under the short-circuit condition of the UHV converter transformer, and determining the critical energy threshold of the primary physical explosion and the secondary chemical explosion therefrom, so as to obtain the critical conditions for bushing fault deflagration. Among them, the arc energy fault model is obtained through the following steps:

[0130] S10, set test groups under different voltages to simulate the arc discharge test inside the riser.

[0131] In an embodiment of the present invention, two test groups under different voltages are set to simulate the arc discharge test inside the riser, as shown in Table 1 specifically.

[0132] Table 1 Test parameters under different voltages

[0133]

[0134] S20, connect the fault arc energy test circuit and the simulation platform of the line side bushing of the UHV converter transformer according to the test voltage and current values to be simulated. First, adjust the discharge gap inside the simulation platform of the line side bushing of the UHV converter transformer to the maximum, and then gradually reduce the discharge gap, and conduct tests in sequence according to the test groups.

[0135] In this embodiment, after the simulation platform of the line side bushing of the UHV converter transformer is installed and checked without error, in order to simulate the actual fault situation and explore the characteristics of arc fault deflagration accidents, two test groups under different voltages are set.

[0136] Connect the bushing platform on the line side of the simulated UHV converter transformer to the fault arc energy test circuit, and adjust the discharge gap inside the bushing platform on the line side of the simulated UHV converter transformer to the maximum. In this embodiment, the maximum discharge gap is 20 mm. First, conduct the test with the minimum test current of 5 kA, and observe the arc ignition situation inside the bushing platform on the line side of the simulated UHV converter transformer. If the arc fails to persist within 100 ms, adjust the discharge gap and conduct the test successively from 20 mm, 15 mm, 10 mm, and 5 mm. After each test, check the bushing platform on the line side of the simulated UHV converter transformer:

[0137] a. The riser 2 should not burst due to internal pressure.

[0138] b. The bushing platform on the line side of the simulated UHV converter transformer should not catch fire.

[0139] c. The pressure relief device 5 should open.

[0140] Repeat the test: Determine whether to adjust the discharge gap again according to the test situation, conduct the next test, and adjust the specific discharge gap value.

[0141] S30. The data acquisition system obtains the deflagration data of the bushing platform on the line side of the simulated UHV converter transformer under the arc discharge test.

[0142] In this embodiment, through the data acquisition system, dynamic data of key technical parameters such as pressure, temperature, and strain during the deflagration process can be obtained.

[0143] In this embodiment, specifically, the arc voltage and current data are collected in real time through the arc voltage dividers FH1 and FH2 and the shunt resistors FL1 and FL2 to provide the voltage-current waveform diagram of the test group. As Figure 6 shown, it can be seen that the pressure data waveform on the upper part of the cylinder body of the riser 2 has the following characteristics: The pressure wave first generates a relatively high peak waveform and is transmitted to the cylinder body, and then is transmitted, reflected, and attenuated inside the riser 2. At the same time, due to the damage of the structure of the riser 2, the pressure drops sharply after the first transient pressure wave peak. The pressure wave characteristics can be applied to the internal arc fault detection of the transformer and the energy transfer model of physical explosion.

[0144] By deploying the optical fiber thermometer 12 inside the riser 2 in the arc generation area, the tank 3 and other positions, record the temperature change during the millisecond-level gasification process of the transformer insulation oil, and obtain data such as the initial oil temperature (22.5 °C) and gasification temperature of the transformer insulation oil. This data can be used for theoretical calculation and determination of the deflagration critical value.

[0145] The dynamic strain value induced by the transient pressure wave can be captured through the strain gauge 11 deployed on the riser 2. As Figure 7As shown, the maximum deformation measured by the strain gauge pasted on the lower part of the cylinder of the elevation seat 2 is 1861.36ε, where ε is the unit of deformation. According to Hooke's law, the local stress on the surface of the bushing platform on the network side of the simulated UHV converter transformer can be calculated to determine whether it exceeds the material yield strength. The acquisition of stress parameters is conducive to scientifically setting the pressure relief threshold and avoiding structural overload.

[0146] By performing chromatographic detection on the transformer oil samples in the oil tank 3 before and after the test, the combustible gas components and concentration change data generated by the cracking of the transformer oil vapor can be obtained, realizing the simulation process of chemical explosion when the high-temperature cracked gas ejects from the rupture opening and encounters air. Further analyze the key gas components in the deflagration process, and combine data such as pressure and temperature to establish a more accurate multi-physical-field coupled deflagration model.

[0147] S40, externally connect a gas chromatograph to perform chromatographic detection on the transformer oil in the oil tank before and after the test, obtain gas chromatographic data, and combine the constructed arc energy fault model to obtain the "energy-gas-explosion" mapping relationship.

[0148] In this embodiment, the arc energy fault model includes the arc energy model inside the UHV converter transformer and the pressure model inside the overheated transformer oil vapor.

[0149] a. The arc energy model inside the UHV converter transformer:

[0150] When internal short-circuit faults such as turn-to-turn short circuits occur in the transformer, local arcs usually form at the fault location. For transformers, especially when arc faults occur in the elevation seat 2 area, the generation amount of transformer oil vapor and the generation of pressure waves are closely related to the energy of the arc fault. The arc energy can be calculated according to the following formula, which is expressed as the integral of the product of the arc voltage and current:

[0151]

[0152] In the formula: W arc is the total arc energy, Δt is the arc duration, u arc and i arc are the voltage drop across both ends of the fault point and the arc current respectively. To simplify the physical process of the arc fault, it is assumed that the arc voltage drop per unit length is constant during the arc burning process. Therefore, the arc voltage u arc is only related to the arc length, that is:

[0153] u arc = E0l arc , (2);

[0154] In the formula: E0 is the electric field strength per unit length, which is always positive, and can also be understood as the arc voltage drop per unit length during the arc burning process; l arcis the arc length, generally related to the severity of the fault; the arc current i arc Namely, for the current value and the arc duration Δt, it can be obtained by using the sensors inside the transformer. Substituting Equation (2) into Equation (1), the arc energy level generated when the transformer fails can be calculated as follows:

[0155]

[0156] If the current i arc is approximately constant (such as the short-circuit steady-state current), then Equation (3) is further simplified to:

[0157] W arc = E0l arc i arc Δt, (4);

[0158] b. Pressure model inside the overheated transformer oil vapor:

[0159] Assume that the total energy W arc released by the arc is partially converted into the internal energy of the gas and partially lost to the surrounding medium. Let there be an energy conversion ratio α, that is, the proportion of the energy used to heat and vaporize the insulating oil. Then the energy W heat used for heating and vaporizing the oil is:

[0160] W heat = αW arc , (5);

[0161] In the formula: α is the proportion of the arc energy used to heat and vaporize the insulating oil, and generally takes a value of 40% - 60%. This energy W heat is used to heat the liquid transformer oil from the initial temperature to the vaporization temperature and complete vaporization. The absorbed energy is equal to the enthalpy increase:

[0162] W heat = m gas ΔH oil , (6);

[0163] In the formula: m gas is the mass of the gas, with the unit of kg, and ΔH oil is the enthalpy increase during the process of the liquid insulating oil rising from the normal operating temperature to the vaporization temperature, with the unit of J / kg. From Equation (5) and Equation (6), the mass of the cracked gas can be obtained:

[0164] m gas = αW arc / ΔH oil , (7);

[0165] The cracked gas can be approximately regarded as an ideal gas and satisfies the state equation:

[0166] pgas V gas = nRT, (8);

[0167] Where: n = m gas / M gas is the number of moles of gas, M gas is the molar mass of the oil vapor, R is the gas constant, T is the gas temperature, V gas is the gas volume, p gas is the bubble pressure. Combining m gas , substituting Equation (7) into Equation (8), the expression for the bubble pressure p gas is:

[0168]

[0169] For an ideal gas, the specific internal energy per unit mass μ gas is defined as:

[0170]

[0171] Where: c v is the specific heat at constant volume, M gas is the molar mass of the oil vapor. Also, since:

[0172]

[0173] Where: γ gas is the specific heat ratio, c p is the specific heat at constant pressure. Combining Equation (11) and Equation (12), we can obtain:

[0174]

[0175] Substituting into the expression for the specific internal energy per unit mass μ gas Equation (10) gives:

[0176]

[0177] Substituting the above equation into the original expression for the bubble pressure p gas Equation (9) gives:

[0178]

[0179] During the cracking process of transformer insulating oil, the temperature of the cracking gas can be approximated as the vaporization temperature T vap of the insulating oil:

[0180] T gas = T vap , (16);

[0181] Substituting Equation (16) into Equation (15) gives:

[0182]

[0183] The critical conditions for the deflagration of the bushing failure include the critical conditions for only physical explosion of the bushing and the critical conditions for physical and superimposed chemical explosion of the bushing. Based on the pressure model inside the overheated transformer oil vapor, by calculating the internal pressure value of the bubble, it is used as the critical parameter for judging only physical explosion. Through the arc energy model, the fault arc energy is analyzed, and combined with the dynamic relationship between the volume of cracked gas and the arc energy, the critical energy thresholds for physical explosion and chemical explosion are deduced, as the composite critical parameters for judging the superimposed trigger of physical and chemical explosion.

[0184] c. Critical conditions for physical explosion:

[0185] In this embodiment, when the bubble pressure P gas exceeds the tolerance pressure P limit of the fuel tank, physical explosion occurs:

[0186] P gas ≥P limit , (18);

[0187] Substituting Equation (17) into Equation (18) and taking P gas =P limit the physical explosion critical value of the arc energy can be obtained:

[0188]

[0189] d. High energy state, that is, the critical conditions for physical explosion superimposed with chemical explosion:

[0190] When the arc energy continues to increase, the transformer oil vapor will crack at high temperature to generate a large amount of hydrogen and short-chain acetylene. When the concentration of the cracked gas exceeds the lower explosion limit (LEL), physical explosion occurs first and then chemical explosion is superimposed. Let the proportion of the arc energy used for cracking be β, and the number of moles of hydrogen and acetylene generated is:

[0191]

[0192] where η i is the cracking yield of gas i, which is related to the temperature, and ΔH f,i is the molar formation enthalpy of gas i, and endothermic is positive.

[0193] The total volume of the mixed cracked gas is the fuel tank volume V tank , and the volume concentration is:

[0194]

[0195] In the formula, c i is the volume concentration of gas i.

[0196] Determination of lower explosion limit:

[0197] The lower explosion limit (LEL) of the mixed cracking gas is calculated according to Le Chatelier's law:

[0198]

[0199] in is the volume fraction of each gas, LEL i is the lower explosion limit of gas i, LEL mix is the lower explosion limit of the mixed cracking gas. i c i ≥LEL mix When , the chemical explosion is triggered. Combine the gas volume and arc energy relationship equations (20), (21) and (22), and take the critical ∑ i c i =LEL mix Obtaining critical energy of chemical explosion:

[0200]

[0201] Comprehensive physical and chemical explosion conditions, critical energy W chemical Must also meet the following requirements:

[0202] 1. Physical conditions: W arc ≥W physical ;

[0203] 2. Chemical conditions: W arc ≥W chemical ;

[0204] in,

[0205] Finally, the critical conditions for the physical and chemical superposition explosion of the casing are:

[0206] W arc ≥max(W physical ,W chemical ), (25);

[0207] S50, comparing the calculation result of the arc energy fault model with the experimental data obtained in step S30 to verify the rationality of the arc energy fault model.

[0208] The flashover and deflagration of the line-side bushing of UHV converter transformers are closely related to the arc energy of internal transformer faults. The higher the arc energy of internal transformer faults, the more likely it is to cause the explosion of the oil tank. According to the arc energy fault model of S40, the arc energy level caused by the short circuit of UHV converter transformers and the critical energy values of primary physical explosion and secondary chemical explosion can be accurately calculated. Through this model, the dynamic changes of key parameters such as pressure and temperature inside the oil tank 3 and the riser 2 under different arc energies can also be analyzed. By comparing the theoretical calculation results with the experimental data obtained in S30, the rationality of the theoretical model can be verified, so as to deeply study the deflagration characteristics under different working conditions and provide more perfect theoretical support and technical guarantee for the safe operation of power equipment.

[0209] Specific example

[0210] According to step S10, taking the data obtained under the working condition of "test group parameters: voltage 43 kV, current 30 kA, duration 150 ms, discharge gap 5 mm" as an example for theoretical calculation:

[0211] a. The arc energy model inside the UHV converter transformer:

[0212] W arc = E0l arc i arc Δt;

[0213] Where: E0 is the electric field strength per unit length, with a value of 600 V / mm; l arc is the arc length, with a value of 5 mm; from the test parameters, the arc current i arc = 30 kA, and the arc duration Δt = 150 ms. From this, the arc energy level generated when the transformer fails can be calculated:

[0214] W arc = 600×5×30×10 3 ×0.15 = 13.5 MJ;

[0215] b. The pressure model inside the superheated transformer oil vapor:

[0216]

[0217] Where: the energy conversion ratio α has a value of 50%; the vaporization temperature T vap of the transformer oil has a value of 1200 K; the specific internal energy per unit mass of the gas μ gas has a value of 180 kJ / kg; the specific heat ratio γ gas has a value of 1.25; the enthalpy increase ΔH oil has a value of 500 kJ / kg; the gas volume V gas has a value of 3 m 3, from which the bubble pressure can be calculated as follows:

[0218]

[0219] c. Physical explosion critical condition

[0220] When the bubble pressure P gas exceeds the tolerance pressure P of the fuel tank limit , a physical explosion occurs:

[0221] P gas ≥P limit ;

[0222] According to the measured pressure relief valve value, the tolerance pressure P of the fuel tank limit is taken as 1.0 MPa, that is, 1.15 MPa > 1.0 MPa, triggering a physical explosion, which is consistent with the operation of the experimental pressure relief device.

[0223] d. High energy state:

[0224] Combining the relationship between the combined gas volume and the arc energy, the calculation formula for the chemical explosion critical energy is obtained:

[0225]

[0226] The lower explosion limit LEL of the mixed pyrolysis gas mix is taken as 10%; the fuel tank volume V tank is taken as 25 m 3 , the enthalpy of formation Σ i ΔH f,i is taken as 512 kJ / mol, the pyrolysis energy ratio β is taken as 20%, and the pyrolysis yield ∑ i η i is taken as 50%; thus, the chemical explosion critical energy is obtained as:

[0227]

[0228] Criterion for physical and chemical superimposed explosion of the casing:

[0229] From the physical explosion critical pressure formula Replace each parameter with the critical parameter to obtain the physical explosion critical energy:

[0230] Chemical explosion critical energy:

[0231]

[0232] Finally, according to the critical conditions for physical and chemical superimposed explosion of the casing: W arc ≥max(W physical , W chemical) That is, 13.5 MJ > max(11.79 MJ, 12.80 MJ), then physical and chemical superimposed explosions occur, which is completely consistent with the experimental phenomena.

[0233] Result analysis:

[0234] In this embodiment, typical pressure data measured at various points on the riser and the side wall of the valve hall are selected for analysis. The working conditions are as follows: the test voltage is 43 kV, the test current is 30 kA, with the timing signal as the 0 moment, the current starting time is 0.805 ms, and the duration is 101.4 ms. A physical explosion of the transformer riser bursting is superimposed with a chemical deflagration, and the maximum value (relative to the initial pressure value) of the pressure at each measuring point under this working condition is obtained as shown in Table 2 below:

[0235] Table 2 Pressure test results

[0236]

[0237] It can be seen that the measured maximum pressure at the riser manhole is 1.2986 MPa, and the predicted pressure by the theoretical model is 1.15 MPa. The error source may be that the theoretical model assumes that the gas is completely enclosed and does not consider the dynamic pressure relief effect of the pressure relief device (the pressure relief device operates during the test). In addition, the theoretical model assumes a uniform pressure distribution, while the pressure wave generated by the actual explosion will be reflected, superimposed, and attenuated due to the tank structure (such as the riser, flange), resulting in the theoretical value being slightly lower than the measured value, with an error of about 11.4%, which is within the engineering allowable range, verifying the rationality of the model.

[0238] In addition, under the condition of high-energy discharge, due to the limited deformation ability of the oil tank itself, it is very difficult to avoid the occurrence of combustion and explosion accidents only by strengthening the tank body structure. Therefore, it is one of the key points to prevent the riser from catching fire and exploding by timely discharging the high-pressure oil-gas mixture inside the riser before a sufficient concentration of gas is formed inside the oil tank. Based on the theoretical explosion critical values (W physical = 11.79 MJ, W chemical = 12.80 MJ), an adaptive pressure relief algorithm is developed to adjust the trigger threshold in real time (such as from 1.0 MPa to 0.8 MPa), which can reduce the risk of deflagration.

[0239] The arc energy fault model assumes that the temperature of the cracked gas is approximately the gasification temperature of the insulating oil. However, the actual temperature may be significantly higher than this value because the arc energy heats the surrounding transformer oil through heat conduction and convection, causing the oil to crack and generate combustible gas, and the concentrated energy released by the arc leads to local ultra-high temperature, which in turn triggers secondary chemical deflagration. Therefore, the determination of the temperature range has important guiding significance for optimizing the pressure relief design, improving the effectiveness of the fire protection system, and ensuring the safe operation of the equipment.

[0240] The analysis of the components and contents of pyrolysis gases in transformer oil is a core method for diagnosing internal faults, evaluating insulation status, and predicting risks. By quantitatively analyzing key gases (such as H2, C2H2, C2H4, etc.) and their dynamic changes, the types of faults, such as overheating, discharge, and insulation aging, can be accurately located. At the same time, the concentration of combustible gases, ignition energy, and oxygen content are the key critical conditions for the development from a primary physical explosion to a secondary chemical deflagration. Studying these processes and conditions has important theoretical and practical significance for preventing transformer deflagration accidents and improving the safety and reliability of the power system.

[0241] The key technical parameter of strain can be used as an auxiliary determination for the occurrence of deflagration. When the local stress approaches the yield strength, the test device may undergo plastic deformation or even rupture. Therefore, by monitoring the strain data, the positions with higher strain peaks in the test device can be identified, reminding that the design of this area needs to be thickened or strengthened, which is beneficial to setting the trigger pressure threshold of the pressure relief device.

[0242] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention, and any reference signs in the claims should not be regarded as limiting the claimed rights.

[0243] The above-described embodiments only represent the implementation manners of the invention. The protection scope of the present invention is not limited to the above embodiments. For those skilled in the art, without departing from the concept of the present invention, several modifications and improvements can be made, and these all belong to the protection scope of the present invention.

Claims

1. A method for simulating the explosion and combustion of a grid-side bushing failure of an UHV converter transformer, characterized in that, Including: Based on the arc energy fault model, by setting different simulated fault arc energy conditions, calculate the arc energy value under the short - circuit condition of the riser bushing on the network side of the UHV converter transformer, and thereby determine the critical energy threshold for the primary physical explosion and the secondary chemical explosion, so as to obtain the critical triggering condition for the deflagration of the bushing fault; Among them, the arc energy fault model is obtained through the following steps: S10. Set test groups under different voltages to simulate the internal arc discharge test of the riser bushing; S20. According to the test voltage and current values to be simulated, connect the fault arc energy test circuit with the simulated UHV converter transformer network - side bushing platform. First, adjust the discharge gap in the simulated UHV converter transformer network - side bushing platform to the maximum, and then gradually reduce the discharge gap, and conduct tests in sequence according to the test groups; S30. The data acquisition system obtains the deflagration data of the simulated UHV converter transformer network - side bushing platform during the arc discharge test; S40. Connect an external gas chromatography device to conduct chromatographic detection on the transformer oil in the oil tank before and after the test to obtain gas chromatography data. Combine the constructed arc energy fault model to obtain the "energy - gas - explosion" mapping relationship; S50. Compare the calculation results of the arc energy fault model with the experimental data obtained in step S30 to verify the rationality of the arc energy fault model.

2. The method for simulating the explosion and combustion of the grid-side bushing fault of the UHV converter transformer according to claim 1, wherein The arc energy fault model includes the arc energy model inside the UHV converter transformer and the pressure model inside the overheated transformer oil vapor; Among them, obtaining the arc energy model inside the UHV converter transformer includes: Calculate the arc energy according to formula (1); Where: W arc is the total arc energy, Δt is the arc duration, u arc and i arc are the voltage drops at both ends of the fault point and the arc current respectively; Assume that the arc voltage drop per unit length during the arc burning process is a constant to obtain formula (2); u arc = E0l arc , (2); Where: E0 is the electric field strength per unit length, which is always positive; l arc is the arc length; the arc current i arc is the current value, the arc duration is Δt. Thus, substituting Equation (2) into Equation (1), the arc energy level generated when the transformer fails is calculated through Equation (3): If the current i arc is constant, Equation (3) is further simplified to obtain Equation (4) as the arc energy model inside the UHV converter transformer: W arc = E0l arc i arc Δt, (4); b. Obtaining the pressure model inside the overheated transformer oil vapor includes: Suppose the total energy W released by the electric arc arc Part of it is converted into the internal energy of the gas, and part is lost to the surrounding medium. Assuming an energy conversion ratio α, the energy W used for heating and vaporizing the oil heat is as follows: W heat = αW arc , (5); In the formula: α is the proportion of the arc energy used for heating and vaporizing the insulating oil; Energy W heat The energy absorbed for heating the liquid transformer oil from the initial temperature to the vaporization temperature and completing the vaporization is equal to the enthalpy increase: W heat = m gas ΔH oil , (6); Where: m gas is the mass of the gas, and ΔH oil is the enthalpy increase during the process of the liquid insulating oil rising from the normal operating temperature to the gasification temperature; from Equations (5) and (6), the mass of the cracked gas is obtained: m gas = αW arc / ΔH oil , (7); Regard the cracked gas as an ideal gas, which satisfies the state equation (8); p gas V gas = nRT, (8); where: n = m gas / M gas is the number of moles of gas, M gas is the molar mass of oil vapor, R is the gas constant, T is the gas temperature, V gas is the gas volume, p gas is the bubble pressure; The mass m of the combined gas gas , substituting Equation (7) into Equation (8), the bubble pressure p gas is expressed as: For an ideal gas, the specific internal energy μ per unit mass gas is defined as: where: c v is the specific heat capacity at constant volume; and since: Where: γ gas is the specific heat ratio, c p is the specific heat capacity at constant pressure. Combining equations (11) and (12) gives: Substitute the specific internal energy per unit mass μ gas into Equation (10) to obtain: Substitute Equation (14) into the initial bubble pressure p gas Equation (9) gives: During the cracking process of transformer insulating oil, the temperature T of the cracked gas gas is used as the gasification temperature T of the insulating oil vap : T gas = T vap , (16); Substitute formula (16) into formula (15) to obtain formula (17) as the pressure model inside the overheated transformer oil vapor; 3. The method for simulating the explosion and combustion of the grid-side bushing fault of an UHV converter transformer according to claim 2, wherein The critical conditions for the deflagration of the bushing fault include the critical condition for the bushing to only have a physical explosion and the critical condition for the bushing to have a physical and superimposed chemical explosion; among them, Based on the pressure model inside the overheated transformer oil vapor, by calculating the internal pressure value of the bubble, use it as the critical parameter for judging only a physical explosion; analyze the fault arc energy through the arc energy model, combine the dynamic relationship between the cracked gas volume and the arc energy, and deduce the critical energy thresholds for physical explosion and chemical explosion as the composite critical parameter for judging the superimposed trigger of physical and chemical explosions.

4. The method for simulating the explosion and combustion of the grid-side bushing of an UHV converter transformer according to claim 3, wherein The critical condition for the bushing to only have a physical explosion is: When the bubble pressure P gas exceeds the tolerance pressure P limit of the fuel tank, a physical explosion occurs: P gas ≥P limit , (18); Wherein, P gas is the bubble pressure, and P limit is the tolerance pressure of the fuel tank; among them, the tolerance pressure P limit of the fuel tank is obtained through Equation (19): Substitute Equation (17) into Equation (18) and take P gas = P limit , and obtain the physical explosion critical value P limit of the arc energy:

5. The method for simulating the explosion and combustion of the grid-side bushing of an UHV converter transformer according to claim 3, wherein The critical condition for the bushing to have a physical and chemical superimposed explosion is: W arc ≥ max(W physical , W chemical ) Among them, W physical is the critical energy of physical explosion, and W chemical is the critical energy of chemical explosion, and W arc is the arc energy.

6. The method for simulating the explosion and combustion of the grid-side bushing fault of the UHV converter transformer according to claim 5, wherein, Obtaining the critical energy of chemical explosion in the critical condition for the bushing to have a physical and superimposed chemical explosion includes: Let the proportion of the arc energy used for cracking be β, and the number of moles n of hydrogen and acetylene generated i be as follows: Among them, η i is the cracking yield of gas i, and ΔH f,i is the molar enthalpy of formation of gas i, with endothermic being positive; The total volume of the mixed cracked gas is the fuel tank volume V tank , and the volume concentration is: where c i is the volume concentration of gas i; Lower explosion limit determination: The lower explosion limit of the mixed cracked gas is calculated according to Le Chatelier's law: Among them, is the volume fraction of each gas, and LEL i is the lower explosive limit of gas i, and LEL mix is the lower explosive limit of the mixed cracking gas; When the mixed concentration ∑ i c i ≥LEL mix When the chemical explosion is triggered, the gas volume and arc energy are related by equations (20), (21) and (22), and the critical ∑ i c i =LEL mix , obtain the critical energy of chemical explosion: Among them, the critical energy of physical explosion is obtained through formula (23):

7. An experimental platform for the simulation test method of the fault explosion and combustion of the line side bushing of a UHV converter transformer using any one of the methods recited in claims 1-6, characterized in that, Including: Simulated UHV converter transformer network - side bushing platform; Fault arc energy test circuit, connected to the simulated UHV converter transformer network - side bushing platform; The data acquisition system is set on the platform of the bushings on the network side of the simulated UHV converter transformer; The data processing terminal is used to calculate the arc energy value under the short-circuit condition of the UHV converter transformer by setting different simulated fault arc energy conditions based on the arc energy fault model, and thereby determine the critical energy threshold between the primary physical explosion and the secondary chemical explosion, so as to obtain the critical conditions for the deflagration of the bushing fault.

8. The UHV converter transformer line side bushing fault explosion simulation test platform according to claim 7, characterized in that, The fault arc energy test circuit includes: a generator K, a short-circuit transformer DB, a grounding resistor Rj, circuit breakers CD1, CD2, CD3, CD4, a power factor regulating resistor Rt, a regulating reactor Lt, voltage dividers FY1, FY2, arc voltage dividers FH1, FH2, shunts FL1, FL2; On the primary side of the short-circuit transformer DB, the regulating reactor Lt, the power factor regulating resistor Rt, the circuit breaker CD1, the generator K, and the circuit breaker CD2 are connected in series; one end of the grounding resistor Rj is connected to the generator K, and the other end is grounded; On the secondary side of the short-circuit transformer DB, the voltage divider FY1, the circuit breaker CD3, the shunt FL1, the arc voltage divider FH1, the terminal, the arc voltage divider FH2, the shunt FL2, the circuit breaker CD4, and the voltage divider FY2 are connected in series; the terminal is connected to the platform of the bushings on the network side of the simulated UHV converter transformer.

9. The UHV converter transformer line side bushing fault explosion simulation test platform according to claim 7, characterized in that, The platform of the bushings on the network side of the simulated UHV converter transformer includes: a bushing body (1), a riser (2), and an oil tank (3); the bushing body (1) is installed on the top of the riser (2), and the oil tank (3) is arranged at the bottom of the riser (2); moreover, the internal conductors of the bushing body (1) and the oil tank (3) are electrically connected; a test bushing (9) is installed on one side of the oil tank (3) as an interface for current input, so that the platform of the bushings on the network side of the simulated UHV converter transformer is connected to the fault arc energy test circuit.

10. The UHV converter transformer line side bushing fault explosion simulation test platform according to claim 9, characterized in that The data acquisition system includes: a pressure acquisition system, a vibration acquisition system, and a temperature acquisition system; The pressure acquisition system includes a number of dynamic pressure sensors (10) arranged at each measuring point of the riser (2) and the oil tank (3); The vibration acquisition system includes a number of strain gauges (11) arranged outside the cylinder of the riser (2); The temperature acquisition system includes a number of fiber optic thermometers (12) installed at each measuring point of the riser (2) and the oil tank (3).

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