On-line monitoring method for oil immersed electric connection component of converter transformer

Abstract

The invention relates to the technical field of oil chromatography monitoring, and particularly discloses an on-line monitoring method for an oil immersed electric connection part of a converter transformer, watchband contact fingers are divided into an excellent grade, a good grade and a deteriorated grade by measuring contact resistance, and gas production rates of symbolic gases of the contact fingers of different grades under different operation currents are measured by utilizing an oil chromatography experiment; an electromagnetic-heat flow coupling simulation model of the valve side ascending flanged base is established, internal heat field and flow field distribution under the operation working condition is obtained, then the actually-measured gas production rate serves as the boundary condition of a watchband contact finger contact interface, and the gas production rate of the watchband contact finger contact interface is calculated by simulating the diffusion path of symbolic gas under the thermal gradient effect. According to the method, the optimal oil chromatography on-line monitoring site in the valve side ascending flanged base is accurately determined, an overheating early warning strategy is constructed to be matched with the oil chromatography on-line monitoring device for on-line degradation early warning, on-line, quantitative and accurate early warning of the degradation state of the oil immersed electric contact part is achieved, and the operation safety and the operation and maintenance efficiency of the converter transformer are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil chromatography monitoring, and particularly relates to an on-line monitoring method for oil-immersed electrical connection components of a converter transformer. BACKGROUND

[0002] The oil-immersed electrical connection component is a key current-carrying connecting piece between a valve-side winding lead-out wire and a valve-side bushing of an extra-high voltage converter transformer, is usually installed at the valve side of the converter transformer, and includes a riser and a watchband connecting structure, i.e., a watchband contact finger, between a conductive terminal installed in the riser and a wiring end of the valve-side bushing. The oil-immersed electrical connection component is mainly applied in converter stations of extra-high voltage direct current transmission in western regions. According to statistics, among the currently operated extra-high voltage direct current converter stations, 1344 valve-side bushings adopt the same oil-immersed watchband connecting structure as the valve-side oil-immersed electrical connection component.

[0003] In a long-term use process, the state of the watchband contact finger in the oil-immersed watchband connecting structure is gradually deteriorated. When the watchband contact finger is deteriorated, the valve-side direct current resistance value of the converter transformer is out of standard, and then the converter transformer is caused to be out of operation due to a fault.

[0004] In the prior art, the valve-side loop direct current resistance measurement value of the converter transformer is the only index for evaluating the contact state of the watchband contact finger, and the valve-side loop direct current resistance measurement value of the converter transformer can only be obtained during the annual power-off maintenance of the converter station. When the watchband contact finger is in a normal state, the detected valve-side loop direct current resistance measurement value is more than 300 times the resistance of the watchband contact finger insertion structure, because the amplification multiple of the resistance is too large. When the watchband contact finger forms electrochemical corrosion and is in an early deterioration state, the defect state is difficult to identify due to being hidden by the valve-side loop direct current resistance.

[0005] Moreover, the watchband contact finger has a nonlinear corrosion deterioration characteristic. When the watchband contact finger forms electrochemical corrosion, the accelerated deterioration stage thereof causes the valve-side loop direct current resistance of the converter transformer to increase by 10% per year, which reflects the contradiction between the nonlinear corrosion deterioration characteristic of the watchband contact finger and the existing detection method of the valve-side loop direct current resistance of the converter transformer, i.e., the early corrosion deterioration is easily hidden by the valve-side loop direct current resistance and is difficult to identify, and the defect identification time is seriously delayed due to the limitation of the annual inspection period in the accelerated corrosion stage.

[0006] The present application provides an on-line monitoring method for oil-immersed electrical connection components of a converter transformer, so as to solve the above problems. SUMMARY

[0007] The present application provides an on-line monitoring method for oil-immersed electrical connection components of a converter transformer, so as to solve the above problems.

[0008] The application is achieved by the following technical solutions: A converter transformer oil-immersed electrical connection component online monitoring method, comprising the following steps: Step A1: An oil-immersed watchband contact finger overheating gas production test platform is built, and the contact resistance values of watchband contact fingers in different states are measured, and the states of the watchband contact fingers are divided into multiple different levels including a deterioration level according to the contact resistance values; Step A2: The amount of production and production rate of the marker gas of the watchband contact finger entering the deterioration level under the working current in the overheating gas production test platform are measured through the oil chromatography experiment; Step A3: An electromagnetic-thermal flow coupling simulation model of the valve side riser in which the measured watchband contact finger is located is constructed, and a thermal field cloud picture describing the distribution of the internal thermal field and flow field of the valve side riser under the working state is obtained; Step A4: The contact interface between the watchband contact finger and the inner wall of the plug sleeve is taken as the boundary of the production of the marker gas, the amount of production and production rate of the marker gas of the watchband contact finger entering the deterioration level are taken as the boundary conditions, and based on the obtained thermal field cloud picture, the diffusion law and path of the marker gas under the action of the thermal field gradient of the valve side riser are calculated, and the position with the highest gas concentration on the inner wall of the valve side riser is determined as the optimal oil chromatography monitoring point; Step A5: Based on the determined point, a multi-point oil chromatography online monitoring device is arranged on the valve side riser, the acetylene content when the watchband contact finger enters the deterioration level is taken as the deterioration early warning trigger condition, the production rate of each marker gas is taken as the corresponding deterioration early warning threshold, and an overheating early warning strategy is constructed to issue a watchband contact finger deterioration early warning when all the marker gases monitored by the multi-point oil chromatography online monitoring device exceed the corresponding deterioration early warning threshold.

[0009] Further, in step A1, after the contact resistance value is obtained, a multi-level state division threshold is established, and the state of the watchband contact finger is graded through the corresponding contact resistance value of the watchband contact finger.

[0010] Further, the established multi-level state division threshold includes: When the contact resistance value R of a single watchband contact finger belongs to: R≤10μΩ, the watchband contact finger belongs to the excellent level; When the contact resistance value R of a single watchband contact finger belongs to: 10μΩ When the contact resistance value R of a single watchband contact finger belongs to: R≥50μΩ, the watchband contact finger belongs to the deterioration level.

[0011] Further, in step A2, the marker gas includes but is not limited to: hydrogen, methane, ethylene, ethane, and acetylene.

[0012] Further, in step A2, the watch winder entering the deterioration level is supplied with 1500A working current for 12 hours, and the gas production of each marker gas is measured at an interval of 60 minutes during the continuous current supply, and the corresponding gas production efficiency is calculated.

[0013] Further, in step A3, the electromagnetic-thermal flow coupling simulation model of the valve side of the measured watch winder is constructed as follows: First, the valve side operating current waveform is Fourier decomposed to extract the main harmonic components, and the first several orders of harmonics are selected according to the amplitude ratio, so that the correlation coefficient between the superimposed synthesized current waveform and the measured current waveform is greater than 98%; Subsequently, the heat source power of the valve side sleeve plug-in structure: plug sleeve, plug and watch winder under the action of each harmonic current is calculated, and the total heat source power under the actual operating condition is obtained by superposition; Then, the physical model of the valve side riser is established, the total heat source power corresponding to the above harmonic components is introduced into the multi-physical field simulation software together with the physical model, and finally the flow field and thermal field distribution in the valve side riser under the rated operating current are calculated, and the thermal field cloud diagram is obtained.

[0014] Further, in step A3, the flow field distribution calculation formula is as follows:

[0015] In the formula,

[0016] In the formula, u represents the flow velocity of the transformer oil, unit: m / s, ∇ represents the Hamiltonian operator, p represents the pressure, unit: Pa, g represents the gravitational acceleration, unit: m / s 2 , F represents the volume force suffered by the fluid element in the solution domain, unit: N, p represents the fluid density, unit: kg / m 3 , α t represents the gas volume fraction, p t represents the gas phase density, unit: kg / m 3 , x m represents the gas mass ratio, D n represents the diffusion coefficient, unit: m 2 / s, S m represents the gas generation rate, unit: kg / m 3 ·s, T represents the temperature.

[0017] The thermal field distribution calculation formula is as follows:

[0018] in the formula, Q e represents the active loss, the unit is W / m³, J represents the current density vector, the unit is A / m², E represents the electric field strength, the unit is V / m, p represents the fluid density, the unit is kg / m³, Cp represents the specific heat capacity, the unit is J / (kg·K), T represents the temperature, the unit is K, t represents the time, the unit is s, k represents the thermal conductivity, the unit is W / (m·K).

[0019] Further, in step A4, the calculation process of the diffusion law and path of the marker gas under the action of the valve side elevated seat thermal field gradient is as follows: Based on the obtained thermal field cloud picture, taking the contact interface between the watchband contact finger and the inner wall of the insert sleeve as the marker gas generation boundary, taking the marker gas production rate and production rate of the watchband contact finger entering the degradation level as the bubble injection boundary condition, and setting the diffusion rate of the marker gas, the motion trajectory and distribution of the marker gas are calculated and tracked by the DPM discrete phase model.

[0020] Further, in step A5, the overheating warning strategy includes the following steps: Step B1: Real-time monitoring of acetylene content in the valve side elevated seat based on the multi-point oil chromatography online monitoring device; Step B2: When the acetylene content is monitored to be ≥ the acetylene content threshold value, enter step B3; Step B3: Monitor other marker gases; Step B4: When the acetylene production rate is monitored to be ≥ the acetylene production rate threshold value, enter step B5, otherwise continue to monitor; Step B5: When the hydrogen production rate is monitored to be ≥ the hydrogen production rate threshold value, enter step B6, otherwise continue to monitor; Step B6: When the production rate of all alkanes is monitored to be ≥ the production rate threshold value of all alkanes, enter step B7, otherwise continue to monitor; Step B7: Check whether the online oil chromatography three-ratio code is 002, if yes, enter step B8, otherwise continue to monitor; Step B8: Determine that the watchband contact finger has an overheating defect and enters a degradation state.

[0021] Further, the acetylene content threshold is 0.5 uL / L, the acetylene gas production rate threshold is 0.01 mL / day, the hydrogen gas production rate threshold is 3.92 mL / day, and the all-alkane gas production rate threshold is 6.42 mL / day.

[0022] Compared with the prior art, the present application has the following advantages and beneficial effects: In the present application, through steps A1 to A5, an overheating early warning strategy for the watchband contact finger is constructed, online early warning for the watchband contact finger in the deterioration grade is realized, and the valve side electrical connection component can be early warned under the premise of no power outage. The contact deterioration and overheating risk of the watchband contact finger effectively prevent serious accidents such as overheating, discharge, and even fire and explosion caused by poor contact, ensure the safe and stable operation of the power grid, improve the operation safety and operation and maintenance efficiency of the converter transformer, and do not have the lagging problem caused by the too long span time of annual detection. The problem that the existing direct current resistance method for detecting the valve side oil-immersed electrical connection component of the converter transformer not only needs to be powered off, but also has difficulty in diagnosing the early deterioration state of the watchband contact finger due to the too large loop resistance is solved. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the example embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor. In the drawings: Figure 1 is a flow chart of an online monitoring method for an oil-immersed electrical connection component of a converter transformer proposed by the embodiments of the present application; Figure 2 is a flow chart of an overheating early warning strategy proposed by the embodiments of the present application; Figure 3 is a schematic diagram of an overheating gas production test platform proposed by the embodiments of the present application; Figure 4 is a broken line graph of the gas production rates of hydrogen, methane, ethylene, ethane, and acetylene of the watchband contact finger entering the deterioration grade after passing through 1500 A, proposed by the embodiments of the present application; Figure 5 is a schematic diagram of the Fourier decomposition result of the valve side operating current, proposed by the embodiments of the present application; Figure 6 is a schematic diagram of a physical model of the valve side riser, proposed by the embodiments of the present application; Figure 7 is a thermal field cloud chart proposed by the embodiments of the present application; Figure 8is a schematic diagram of the optimal oil chromatographic monitoring point position proposed by the embodiment of the present application.

[0024] The marks in the drawings and the corresponding component names are as follows: Tank cap 1, oil tank 2, plug 3, watchband contact finger 4, plug sleeve 5, current generator 6. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the present application clearer, further detailed description of the present application is made below in combination with examples and drawings, the illustrative embodiments of the present application and the description thereof are only used to explain the present application, and do not limit the present application.

[0026] A kind of converter transformer oil-immersed electrical connection component online monitoring method, implementation example as shown in figure Figure 1 As shown, the method comprises the following steps: Step A1: build an oil-immersed watchband contact finger 4 overheating gas generation test platform, measure the contact resistance value of the watchband contact finger 4 in different states based on the overheating gas generation test platform, and establish a multi-level threshold value to divide the state of the watchband contact finger 4 into excellent grade, good grade and deterioration grade in turn according to the contact resistance value.

[0027] Specifically, as shown in Figure 3 The built overheating gas generation test platform comprises: Oil tank 2, tank cap 1, the oil tank 2 is filled with dry insulating oil, and the tank cap 1 is provided with sealable gas inlet, gas outlet and oil outlet; Plug structure, which is arranged in the oil tank 2, comprises plug 3 and plug sleeve 5 for fixing the watchband contact finger 4; Current generator 6 for generating working current, which is electrically connected with the plug structure to form a loop after the watchband contact finger 4 is fixed on the plug structure, and measures the overall resistance of the loop, in the embodiment, the generated working current value is 5000A.

[0028] In the loop composed of the current generator 6, the plug 3, the watchband contact finger 4 and the plug sleeve 5, the current generator 6, the plug 3 and the watchband contact finger 4 are equivalent to the resistance R1, and the plug sleeve 5 is equivalent to the resistance R2, and the resistance values of the resistance R1 and the resistance R2 are measured before the test. In the test, the watchband contact finger 4 is fixed in the groove of the plug 3, and the plug 3 is inserted into the plug sleeve 5. In the test, 1500A of current flows through a single watchband contact finger 4, the loop voltage is measured during the current flow, the overall resistance R3 of the loop is calculated, and the contact resistance value R of the watchband contact finger 4 is calculated according to the following formula: R=R3-R2-R1.

[0029] In the embodiment, a multi-level state division threshold value is established, the state of the watchband contact finger 4 is graded according to the obtained contact resistance value, and the established multi-level state division threshold value and the corresponding divided state grade comprise: When the contact resistance value R corresponding to a single watch band contact finger 4 is: R≤10μΩ, the watch band contact finger 4 is of excellent grade. When the contact resistance value R corresponding to a single watch band contact finger 4 is: 10μΩ < R < 50μΩ, the watch band contact finger 4 is considered to be of good quality. When the contact resistance value R corresponding to a single watch band contact finger 4 is: R≥50μΩ, the watch band contact finger 4 belongs to the deterioration level.

[0030] Step A2: Measure the amount and rate of characteristic gas produced by the watchband contact finger 4, which has entered the deterioration level, in the superheated gas production test platform under the influence of the working current, using an oil chromatography test.

[0031] Specifically, the measurement process is as follows: Select the watch strap contact finger 4 that has entered the deterioration level, fix it in the groove of the plug 3, insert the plug 3 into the socket 5, fill the oil tank 2 with dry insulating oil, and seal it with the oil tank cover 1.

[0032] Before the experiment begins, nitrogen gas is introduced through the gas injection port for 30 minutes to expel the gas between the surface of the dry insulating oil and the oil tank cover 1 from the gas outlet. Then the gas injection port and the gas outlet are sealed.

[0033] Then, a current generator with 6 pairs of watch strap contacts was used to conduct a current of 1500A for 12 hours. During the current conduction period, insulating oil samples were extracted from the oil outlet every 60 minutes. The contents of characteristic gases such as acetylene, hydrogen, carbon monoxide and methane were measured by oil chromatography, and the gas generation rate of each gas was calculated.

[0034] Ultimately, the result is as follows Figure 4 The contact resistance shown is 52.1 μΩ. The line graph depicts the production rates of characteristic gases—hydrogen (H2), methane (CH4), ethylene (C2H4), ethane (C2H6), and acetylene (C2H2)—after a current flow of 1500 A for the watchband contact finger 4, which is in a deteriorated state. Figure 4 As shown, the production rates of the following characteristic gases with a degradation level of 4 on the deterioration scale obtained by the experiment were: hydrogen, methane, ethylene, ethane, and acetylene, which were 0.88 ppm / h, 12.5 ppm / h, 2.36 ppm / h, 0.407 ppm / h, and 0.0322 ppm / h, respectively.

[0035] Step A3: Construct an electromagnetic-thermal-fluid coupling simulation model of the valve-side riser where the test gauge strap contact finger is located, and obtain a thermal field cloud map describing the internal thermal and flow field distribution of the valve-side riser under working conditions.

[0036] Specifically, the process of constructing the electromagnetic-thermal-fluid coupling simulation model of the valve-side riser of the converter transformer is as follows: Firstly, the valve side operating current waveform is subjected to Fourier decomposition, the main harmonic components are extracted, and the first several orders of harmonics are selected according to the amplitude proportion, so that the correlation coefficient between the superimposed synthesized current waveform and the measured current waveform is greater than 98%; Subsequently, the heat source power of the valve side bushing plug-in structure, i.e., the bushing, the plug and the watchband contact finger, under the action of each harmonic current is calculated respectively, and the total heat source power under the actual operating condition is obtained through superposition; Then, the physical model of the valve side riser is established, the total heat source power corresponding to the above harmonic components is introduced into the multi-physical field simulation software together with the physical model, and finally the flow field and thermal field distribution in the valve side riser under the rated operating current are calculated to obtain the thermal field cloud picture. In this embodiment, the Fourier decomposition result obtained after the valve side operating current is subjected to Fourier decomposition is as shown in Figure 5 .

[0037] In this embodiment, as shown in Figure 6 , the physical model of the valve side riser shown comprises, in sequence from the outside to the inside: a shell, a capacitor core, an outer lead and a conductive rod, a pressure equalizing ball is further arranged in the shell, the conductive rod is divided into two sections, the end portions of the two sections are both protected inside the pressure equalizing ball, the end portion of the conductive rod inside the pressure equalizing ball is formed with a plug, an outer bushing is arranged outside, an oil-immersed electrical connecting component, i.e., a watchband contact finger, is connected between the bushing and the plug, and the end portion of the other conductive rod inside the pressure equalizing ball is formed with a socket for the plug to be inserted into.

[0038] Transformer oil is further filled between the shell and the capacitor core, insulating paper boards are arranged between the shell and the capacitor core, an air gap is formed between the outer lead and the conductive rod, the conductive rod is hollow and the inside is air.

[0039] After the total heat source power superimposed by the multi-frequency current and the physical model of the valve side riser are introduced into the multi-physical field simulation software, the flow field distribution calculation and the thermal field distribution calculation of the valve side riser are carried out based on the following formula: The flow field distribution calculation formula is as follows:

[0040] In the formula, u represents the flow velocity of the transformer oil, the unit is m / s, ∇ represents the Hamiltonian operator, p represents the pressure, the unit is Pa, g represents the gravitational acceleration, the unit is m / s 2 , F represents the volume force suffered by the fluid microelement in the solution domain, the unit is N, p represents the fluid density, the unit is kg / m 3 , α t represents the gas volume fraction, pt represents the gas phase density, with the unit of kg / m 3 , x m represents the gas mass proportion, D n represents the diffusion coefficient, with the unit of m 2 / s, S m represents the gas generation rate, with the unit of kg / m 3 ·s, T represents the temperature.

[0041] The thermal field distribution calculation formula is as follows:

[0042] In the formula, Q e represents the active loss, with the unit of W / m³, J represents the current density vector, with the unit of A / m², E represents the electric field strength, with the unit of V / m, p represents the fluid density, with the unit of kg / m³, Cp represents the specific heat capacity, with the unit of J / (kg·K), T represents the temperature, with the unit of K, t represents the time, with the unit of s, k represents the thermal conductivity, with the unit of W / (m·K).

[0043] Finally, the thermal field cloud map as shown in Figure 7 is obtained.

[0044] Step A4: Taking the contact interface between the watchband contact finger and the inner wall of the plug sleeve as the boundary of the generation of the marker gas, taking the marker gas generation amount and the gas generation rate of the watchband contact finger entering the deterioration level as the boundary condition, based on the obtained thermal field cloud map, the diffusion law and path of the marker gas under the action of the thermal field gradient of the valve side riser are calculated by using the DPM discrete phase model, and the position with the highest gas concentration on the inner wall of the valve side riser is determined as the optimal oil chromatogram monitoring point in the valve side riser, and the result is shown in Figure 8 .

[0045] In this embodiment, the calculation process of the diffusion law and path of the marker gas under the action of the thermal field gradient of the valve side riser is as follows: Based on the obtained thermal field cloud map, taking the contact interface between the watchband contact finger and the inner wall of the plug sleeve as the boundary of the generation of the marker gas, taking the marker gas generation amount and the gas generation rate of the watchband contact finger entering the deterioration level as the bubble injection boundary condition, setting the diffusion rate of the marker gas, the motion trajectory and distribution of the marker gas are calculated and tracked by the DPM discrete phase model, and the position with the highest gas concentration on the inner wall of the valve side riser is determined as the optimal oil chromatogram monitoring point.

[0046] Step A5: Based on the determined point position, a multi-point oil chromatography online monitoring device is arranged on the valve side riser seat. The acetylene content when the watchband contact finger enters the deterioration grade is taken as the deterioration early warning trigger condition, and the corresponding gas production rate of each marker gas is taken as the corresponding deterioration early warning threshold. A superheat early warning strategy is constructed to issue a watchband contact finger deterioration early warning when all marker gases monitored by the multi-point oil chromatography online monitoring device exceed their corresponding deterioration early warning thresholds.

[0047] In this embodiment, the installed oil chromatography online monitoring device is an oil chromatography online monitoring device commonly used in the prior art. The watchband contact finger with a corresponding contact resistance value R of R=50μΩ is taken as the watchband contact finger entering the deterioration grade. The corresponding gas production rate of each marker gas generated by the watchband contact finger is taken as the corresponding deterioration early warning threshold. A superheat early warning strategy as shown in Figure 2 The superheat early warning strategy includes the following steps: Step B1: Real-time monitoring of acetylene content in the valve side riser seat based on the multi-point oil chromatography online monitoring device; Step B2: When the acetylene content is monitored to be≥ acetylene content threshold: 0.5uL / L, proceed to step B3; Step B3: Monitor other marker gases; Step B4: When the acetylene gas production rate is monitored to be≥ acetylene gas production rate threshold: 0.01mL / day, proceed to step B5, otherwise continue monitoring; Step B5: When the hydrogen gas production rate is monitored to be≥ hydrogen gas production rate threshold: 1.92mL / day, proceed to step B6, otherwise continue monitoring; Step B6: When the production rate of all alkanes is monitored to be≥ all alkanes production rate threshold: 6.42mL / day, proceed to step B7, otherwise continue monitoring; Step B7: Check if the online oil chromatography three-ratio code is 002, if yes, proceed to step B8, otherwise continue monitoring; Step B8: Determine that the watchband contact finger has a superheat defect and enters a deterioration state.

[0048] The overheat early warning strategy for the watchband contact finger is constructed through steps A1 to A5 in the application, online early warning is realized for the watchband contact finger entering the deterioration grade and being in the deterioration grade, early contact deterioration and overheat risk of the valve side key electrical connection component, the watchband contact finger, are early warned, overheat, discharge and even fire explosion and other serious accidents caused by poor contact are effectively prevented, the safe and stable operation of the power grid is ensured, the operation safety and operation and maintenance efficiency of the converter transformer are improved, there is no lag problem caused by too long annual detection span time, and the problem that the existing direct current resistance method detects the valve side oil-immersed electrical connection component of the converter transformer, needs to be powered off, and early deterioration state of the watchband contact finger cannot be diagnosed due to too large loop resistance is solved.

[0049] The above specific embodiments further specifically explain the purposes, technical solutions and beneficial effects of the application, and it should be understood that the above description is only a specific embodiment of the application and is not used to limit the protection scope of the application, and any modification, equivalent replacement, improvement, etc. within the spirit and principle of the application should be included in the protection scope of the application.

Claims

1. A method for online monitoring of oil-immersed electrical connection components of a converter transformer, characterized in that, Includes the following steps: Step A1: Build an oil-immersed test platform for overheating and gas generation of watch strap fingers, and measure the contact resistance value of watch strap fingers in different states. Classify the watch strap fingers into multiple different levels, including deterioration level, according to the contact resistance value. Step A2: Measure the amount and rate of characteristic gas produced by the watchband contact fingers that have entered the deterioration level in an overheated gas production test platform under the influence of working current by oil chromatography. Step A3: Construct an electromagnetic-thermal-fluid coupling simulation model of the valve-side riser where the test strap contact finger is located, and obtain a thermal field cloud map describing the internal thermal and flow field distribution of the valve-side riser under working conditions; Step A4: The contact interface between the watch strap finger and the inner wall of the socket is taken as the boundary for the generation of the marker gas. The generation amount and rate of the marker gas of the watch strap finger that has entered the deterioration level are taken as boundary conditions. Based on the obtained thermal field cloud map, the diffusion law and path of the marker gas under the action of the thermal field gradient of the valve side riser are calculated. The position with the highest gas concentration on the inner wall of the valve side riser is determined as the optimal oil chromatography monitoring point. Step A5: Based on the determined locations, deploy a multi-point oil chromatography online monitoring device on the valve side riser. Use the acetylene content when the gauge band touch finger enters the deterioration level as the deterioration warning trigger condition, and use the gas production rate corresponding to each characteristic gas as the corresponding deterioration warning threshold. Construct an overheating warning strategy to issue a gauge band touch finger deterioration warning when the multi-point oil chromatography online monitoring device detects that all characteristic gases exceed their corresponding deterioration warning thresholds.

2. The online monitoring method for oil-immersed electrical connection components of a converter transformer according to claim 1, characterized in that, In step A1, after obtaining the contact resistance value, a multi-level state classification threshold is established, and the state is classified according to the contact resistance value corresponding to the watch band finger.

3. The online monitoring method for oil-immersed electrical connection components of a converter transformer according to claim 2, characterized in that, The established multi-level state division thresholds include: When the contact resistance value R corresponding to a single watch band finger is: R≤10μΩ, the watch band finger is considered to be of excellent quality. When the contact resistance value R corresponding to a single watch band finger is: 10μΩ < R < 50μΩ, the watch band finger is considered to be of good quality. When the contact resistance value R of a single watch band finger is R≥50μΩ, the watch band finger belongs to the deterioration level.

4. The method for online monitoring of oil-immersed electrical connection components of a converter transformer according to claim 1, characterized in that, In step A2, the marker gases include, but are not limited to: hydrogen, methane, ethylene, ethane, and acetylene.

5. A method for online monitoring of oil-immersed electrical connection components of a converter transformer according to claim 1 or 4, characterized in that, In step A2, a working current of 1500A is continuously applied to the watchband contacts that have entered the deterioration level for 12 hours. During the continuous current application, the gas production of each characteristic gas is measured at 60-minute intervals, and the corresponding gas production efficiency is calculated.

6. The online monitoring method for oil-immersed electrical connection components of a converter transformer according to claim 1, characterized in that, In step A3, the construction process of the electromagnetic-thermal-fluid coupling simulation model of the valve-side riser where the measuring band contact finger is located is as follows: First, Fourier decomposition is performed on the valve-side operating current waveform to extract the main harmonic components. The first few harmonics are selected based on their amplitude proportions to ensure that the correlation coefficient between the superimposed composite current waveform and the measured current waveform is greater than 98%. Subsequently, the heat source power of the valve side bushing connection structure under the action of each harmonic current is calculated separately: the bushing, plug and the gauge contact finger, and the total heat source power under the actual operating conditions is obtained by superposition. Next, a physical model of the valve-side riser is established. The total heat source power corresponding to the above harmonic components is imported into the multiphysics simulation software along with the physical model. Finally, the flow field and thermal field distribution in the valve-side riser under the rated operating current are calculated to obtain the thermal field cloud map.

7. The online monitoring method for oil-immersed electrical connection components of a converter transformer according to claim 6, characterized in that, In step A3, the flow field distribution is calculated as follows: ； ； In the formula, , ; In the formula, u represents the transformer oil flow velocity in m / s, ∇ represents the Hamiltonian operator, p represents the pressure in Pa, and g represents the acceleration due to gravity in m / s². 2 F represents the volume force acting on the fluid element in the solution domain, in N, and ρ represents the fluid density, in kg / m³. 3 α t ρ represents the gas volume phase fraction. t This represents the density of the gas phase, with units of kg / m³. 3 x m D represents the mass percentage of the gas. n This represents the diffusion coefficient, with units of m. 2 / s, S m This indicates the rate of gas generation, expressed in kg / m³. 3 ·s, where T represents temperature; The formula for calculating the thermal field distribution is as follows: ； ； In the formula, Q e The values ​​represent active power loss in W / m³, J represents current density vector in A / m², E represents electric field strength in V / m, ρ represents fluid density in kg / m³, Cp represents specific heat capacity in J / (kg·K), T represents temperature in K, t represents time in s, and k represents thermal conductivity in W / (m·K).

8. The online monitoring method for oil-immersed electrical connection components of a converter transformer according to claim 1, characterized in that, In step A4, the calculation process for the diffusion law and path of the marker gas under the action of the thermal field gradient on the valve side is as follows: Based on the obtained thermal field cloud map, the contact interface between the strap finger and the inner wall of the socket is used as the boundary for the generation of the marker gas. The generation amount and rate of the marker gas of the strap finger entering the deterioration level are used as the boundary conditions for bubble injection. The diffusion rate of the marker gas is set, and the movement trajectory and distribution of the marker gas are calculated and tracked by the DPM discrete phase model.

9. A method for online monitoring of oil-immersed electrical connection components of a converter transformer according to claim 1 or 4, characterized in that, In step A5, the overheat warning strategy includes the following steps: Step B1: Real-time monitoring of acetylene content in the valve-side riser seat using a multi-point oil chromatography online monitoring device; Step B2: When the acetylene content is detected to be ≥ the acetylene content threshold, proceed to step B3; Step B3: Monitor other marker gases; Step B4: When the acetylene production rate is detected to be ≥ the acetylene production rate threshold, proceed to step B5; otherwise, continue monitoring. Step B5: When the hydrogen production rate is detected to be ≥ the hydrogen production rate threshold, proceed to step B6; otherwise, continue monitoring. Step B6: When the gas production rate of all alkanes is detected to be ≥ the gas production rate threshold of all alkanes, proceed to step B7; otherwise, continue monitoring. Step B7: Check if the online oil chromatography three ratio code is 002. If it is, proceed to step B8; otherwise, continue monitoring. Step B8: Determine that the watch strap contacts have an overheating defect and have entered a deterioration state.

10. The online monitoring method for oil-immersed electrical connection components of a converter transformer according to claim 9, characterized in that, The acetylene content threshold is 0.5 μL / L, the acetylene gas production rate threshold is 0.01 mL / day, the hydrogen gas production rate threshold is 3.92 mL / day, and the gas production rate threshold for all alkanes is 6.42 mL / day.

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