A method for on-line monitoring of oil-immersed electrical connection components of a converter transformer

Abstract

The present application relates to the technical field of oil chromatography monitoring, and specifically discloses an online monitoring method for oil-immersed electrical connection components of a converter transformer. The contact resistance is measured to divide the watchband contact fingers into three grades of excellent, good and poor. The oil chromatography experiment is used to determine the gas production rate of the characteristic gas of the contact fingers of different grades under different operating currents. An electromagnetic-thermal flow coupling simulation model with a valve side riser is established to obtain the internal thermal field and flow field distribution under the operating condition. Then, the measured gas production rate is taken as the boundary condition of the contact interface of the watchband contact finger. The diffusion path of the characteristic gas under the action of the thermal gradient is simulated to accurately determine the optimal oil chromatography online monitoring site in the valve side riser. A overheating early warning strategy is constructed to match the oil chromatography online monitoring device for online deterioration early warning. The online, quantitative and accurate early warning of the deterioration state of the oil-immersed electrical contact components is realized, and the operation safety and 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:

[0009] An online monitoring method for a converter transformer oil-immersed electrical connection component, comprising the following steps:

[0010] 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;

[0011] Step A2: The production amount 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 an oil chromatography experiment;

[0012] 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 map describing the distribution of the internal thermal field and flow field of the valve side riser under the working state is obtained;

[0013] Step A4: The contact interface between the watchband contact finger and the inner wall of the insert sleeve is taken as the boundary of the marker gas production, the production amount 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 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, 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;

[0014] 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.

[0015] Further, in step A1, after obtaining the contact resistance value, a multi-level state division threshold is established, and the state of the watchband contact finger is graded by the corresponding contact resistance value.

[0016] Further, the established multi-level state division threshold includes:

[0017] When the contact resistance value R of a single watchband contact finger belongs to: R≤10μΩ, the watchband contact finger belongs to an excellent level;

[0018] When the contact resistance value R of a single watchband contact finger belongs to: 10μΩ

[0019] When the contact resistance value R of the single watchband contact finger corresponding to the contact resistance value R belongs to: R≥50μΩ, the watchband contact finger belongs to the deterioration level.

[0020] Further, in step A2, the marker gas includes but is not limited to: hydrogen, methane, ethylene, ethane, acetylene.

[0021] Further, in step A2, the watchband contact finger entering the deterioration level is supplied with a working current of 1500A for 12 hours, and the gas production of each marker gas is measured at intervals of 60 minutes during the continuous current supply, and the corresponding gas production efficiency is calculated.

[0022] Further, in step A3, the electromagnetic-thermal flow coupling simulation model of the valve side riser of the measured watchband contact finger is constructed as follows:

[0023] Firstly, the valve side operating current waveform is Fourier decomposed, the main harmonic components are extracted, 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%;

[0024] Subsequently, the heat source power of the valve side sleeve plug-in structure: plug-in sleeve, plug and watchband contact finger under the action of each harmonic current is calculated, and the total heat source power under the actual operating condition is obtained by superposition;

[0025] 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 picture is obtained.

[0026] Further, in step A3, the flow field distribution calculation formula is as follows:

[0027]

[0028] In the formula,

[0029] In the formula, u The transformer oil flow rate is represented by m / s, ∇ represents the Hamiltonian operator, p The pressure is represented by Pa, g The gravitational acceleration is represented by m / s 2 , F The volume force suffered by the fluid element in the solution domain is represented by N, p The fluid density is represented by kg / m 3 , α t The gas volume fraction is represented by, p t The gas phase density is represented by kg / m 3 ,x m represents the gas mass proportion, D n represents the diffusion coefficient, unit: m 2 / s, S m represents the gas generation rate, unit: kg / m 3 ·s, T represents temperature.

[0030] The thermal field distribution calculation formula is as follows:

[0031]

[0032] In the formula, Q e represents the active loss, unit: W / m³, J represents the current density vector, unit: A / m², E represents the electric field strength, unit: V / m, p represents the fluid density, unit: kg / m³, Cp represents the specific heat capacity, unit: J / (kg·K), T represents the temperature, unit: K, t represents time, unit: s, k represents the thermal conductivity, unit: W / (m·K).

[0033] Further, in step A4, 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:

[0034] Based on the obtained thermal field cloud picture, the contact interface between the watchband contact finger and the inner wall of the insert sleeve is taken as the marker gas generation boundary, the marker gas generation amount and the gas generation rate of the watchband contact finger entering the deterioration level are taken as the bubble injection boundary conditions, and the diffusion rate of the marker gas is set. The DPM discrete phase model is used to calculate and track the motion trajectory and distribution of the marker gas.

[0035] Further, in step A5, the overheating warning strategy includes the following steps:

[0036] Step B1: Real-time monitoring of acetylene content in the valve side riser based on the multi-point oil chromatography online monitoring device;

[0037] Step B2: When the acetylene content is monitored to be greater than or equal to the acetylene content threshold value, step B3 is entered;

[0038] Step B3: Monitoring other marker gases;

[0039] Step B4: When the acetylene gas generation rate is monitored to be greater than or equal to the acetylene gas generation rate threshold value, step B5 is entered, otherwise continue to monitor;

[0040] Step B5: when the hydrogen production rate is monitored ≥ hydrogen production rate threshold, enter step B6, otherwise continue to monitor;

[0041] Step B6: when the production rate of all alkanes is monitored ≥ all alkanes production rate threshold, enter step B7, otherwise continue to monitor;

[0042] Step B7: check if the online oil chromatography three-ratio code is 002, if yes, enter step B8, otherwise continue to monitor;

[0043] Step B8: determine that the watchband contact finger has an overheating defect and enter the degradation state.

[0044] Further, the acetylene content threshold is 0.5uL / L, the acetylene production rate threshold is 0.01mL / day, the hydrogen production rate threshold is 3.92mL / day, and the production rate threshold of all alkanes is 6.42mL / day.

[0045] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0046] In the present application, through steps A1 to A5, an overheating early warning strategy for the watchband contact finger is constructed, realizing online early warning for the watchband contact finger in the degradation level. Under the premise of not stopping power, the valve side electrical connection component can be early warned. The contact degradation and overheating risk of the watchband contact finger effectively prevent overheating, discharge, and even fire and explosion caused by poor contact, ensuring the safe and stable operation of the power grid, improving the operation safety and operation efficiency of the converter transformer, and solving 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 stop power, but also has difficulty in diagnosing the early degradation state of the watchband contact finger due to the large loop resistance. BRIEF DESCRIPTION OF DRAWINGS

[0047] 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 considered 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:

[0048] Figure 1 is a flow chart of an online monitoring method for oil-immersed electrical connection components of a converter transformer according to an embodiment of the present application;

[0049] Figure 2 is a flow chart of an overheating early warning strategy according to an embodiment of the present application;

[0050] Figure 3 is a schematic diagram of a superheating gas production test platform proposed by an embodiment of the present application;

[0051] Figure 4 is a broken line graph of the gas production rates of the hydrogen, methane, ethylene, ethane, and acetylene of the watch winder contact finger entering the degradation grade after the through-flow 1500A according to an embodiment of the present application;

[0052] Figure 5 is a schematic diagram of the Fourier decomposition result of the valve side operating current according to an embodiment of the present application;

[0053] Figure 6 is a schematic diagram of the physical model of the valve side raised seat according to an embodiment of the present application;

[0054] Figure 7 is a thermal field cloud chart according to an embodiment of the present application;

[0055] Figure 8 is a schematic diagram of the optimal oil chromatography monitoring point according to an embodiment of the present application.

[0056] The marks in the drawings and the corresponding names of the parts are as follows:

[0057] Oil tank cover 1, oil tank 2, plug 3, watch winder contact finger 4, plug sleeve 5, current generator 6. DETAILED DESCRIPTION

[0058] In order to make the purpose, technical solutions and advantages of the present application clearer and more apparent, the present application is further described in detail below with reference to the embodiments 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.

[0059] A method for on-line monitoring of an oil-immersed electrical connection component of a converter transformer, as shown in Figure 1 , includes the following steps:

[0060] Step A1: An oil-immersed watch winder contact finger 4 superheating gas production test platform is built, the contact resistance values of the watch winder contact finger 4 in different states are measured based on the superheating gas production test platform, and a multi-level threshold value is established to divide the state of the watch winder contact finger 4 into excellent grade, good grade, and degradation grade in turn according to the contact resistance value.

[0061] Specifically, as shown in Figure 3 , the built superheating gas production test platform includes:

[0062] Oil tank 2, oil tank cover 1, the oil tank 2 is filled with dry insulating oil, and the oil tank cover 1 is provided with a sealable gas inlet, gas outlet, and oil outlet;

[0063] The plug-in structure is arranged in the oil tank 2, and includes a plug 3 and a bushing 5 for fixing the watchband contact finger 4.

[0064] A current generator 6 is used to generate a working current, and after the plug-in structure is fixed with the watchband contact finger 4, the plug-in structure is electrically connected to form a loop, and the overall resistance of the loop is measured. In this embodiment, the generated working current value is 5000A.

[0065] In the loop formed by the current generator 6, the plug 3, the watchband contact finger 4 and the bushing 5, the current generator 6, the plug 3 and the watchband contact finger 4 are equivalent to a resistance R1, and the bushing 5 is equivalent to a resistance R2. The resistance values of the resistance R1 and the resistance R2 are measured before the test. During the test, the watchband contact finger 4 is fixed in the groove of the plug 3, and the plug 3 is inserted into the bushing 5. In the test, 1500A of current flows through a single watchband contact finger 4, the voltage of the loop 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:

[0066] R=R3-R2-R1.

[0067] In this embodiment, a plurality of state division threshold values are established, and the state of the watchband contact finger 4 is graded according to the obtained contact resistance value. The plurality of state division threshold values established and the corresponding state grades divided include:

[0068] When the contact resistance value R of a single watchband contact finger 4 belongs to: R≤10μΩ, the watchband contact finger 4 belongs to an excellent grade;

[0069] When the contact resistance value R of a single watchband contact finger 4 belongs to: 10μΩ

[0070] When the contact resistance value R of a single watchband contact finger 4 belongs to: R≥50μΩ, the watchband contact finger 4 belongs to a deterioration grade.

[0071] Step A2: Measure the gas production amount and gas production rate of the watchband contact finger 4 entering the deterioration grade under the working current in the overheat gas production test platform through the oil chromatography experiment.

[0072] Specifically, the measurement process is as follows:

[0073] Select the watchband contact finger 4 entering the deterioration grade, fix it in the groove of the plug 3, insert the plug 3 into the bushing 5, fill the oil tank 2 with dry insulating oil, and seal it with the oil tank cover 1.

[0074] Before the experiment starts, nitrogen is introduced from the gas inlet for 30 minutes, the gas between the surface of the dry insulating oil and the oil tank cover 1 is discharged from the gas outlet, and then the gas inlet and the gas outlet are sealed.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] Specifically, the process of constructing the electromagnetic-thermal-fluid coupling simulation model of the valve-side riser of the converter transformer is as follows:

[0079] 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%.

[0080] 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.

[0081] Next, a physical model of the valve-side riser is established. The total heat source power corresponding to the aforementioned harmonic components is imported into the multiphysics simulation software along with the physical model. Finally, the flow field and thermal field distribution within the valve-side riser under the rated operating current are calculated, and a thermal field cloud map is obtained. In this embodiment, the valve-side operating current is decomposed using Fourier decomposition, and the obtained Fourier decomposition results are as follows: Figure 5 As shown.

[0082] In this embodiment, as Figure 6 As shown, the physical model of the valve-side riser seat, from the outside to the inside, includes:

[0083] The shell, the capacitor core, the outer guide rod and the conductive rod, the shell is further provided with a pressure equalizing ball, the conductive rod is divided into two sections, the end of the two sections is protected inside the pressure equalizing ball, the end of the one section of the conductive rod inside the pressure equalizing ball is formed with a plug, an insert sleeve is arranged outside, the insert sleeve is connected with the plug through an oil-immersed electric connecting part: watchband contact finger, the end of the other section of the conductive rod inside the pressure equalizing ball is formed with a socket for inserting the plug.

[0084] 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 guide rod and the conductive rod, the conductive rod is hollow and the inside is air.

[0085] 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 heat field distribution calculation of the valve side riser are carried out based on the following formula:

[0086] The flow field distribution calculation formula is as follows:

[0087]

[0088] In the formula, u The transformer oil flow rate is represented by m / s, ∇ represents the Hamiltonian operator, p The pressure is represented by Pa, g The gravity acceleration is represented by m / s 2 , F The volume force suffered by the fluid element in the solution domain is represented by N, p The fluid density is represented by kg / m 3 , alpha t The gas volume fraction is represented by, p t The gas phase density is represented by kg / m 3 , x m The gas mass ratio is represented by, D n The diffusion coefficient is represented by m 2 / s, S m The gas generation rate is represented by kg / m 3 ·s, and T represents the temperature.

[0089] The heat field distribution calculation formula is as follows:

[0090]

[0091] In the formula, Q e The active loss is represented by W / m³, Jrepresents the current density vector, unit: A / m2, E represents the electric field strength, unit: V / m, p represents the fluid density, unit: kg / m3, Cp represents the specific heat capacity, unit: J / (kg·K), T represents the temperature, unit: K, t represents the time, unit: s, k represents the thermal conductivity, unit: W / (m·K).

[0092] Finally, the thermal field nephogram as shown in Figure 7 is obtained.

[0093] Step A4: Taking the contact interface between the watchband wiper and the inner wall of the bushing as the boundary of the marker gas generation, taking the marker gas generation amount and the gas generation rate of the watchband wiper entering the deterioration level as the boundary conditions, based on the obtained thermal field nephogram, 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 .

[0094] 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:

[0095] Based on the obtained thermal field nephogram, taking the contact interface between the watchband wiper and the inner wall of the bushing as the boundary of the marker gas generation, taking the marker gas generation amount and the gas generation rate of the watchband wiper entering the deterioration level as the bubble injection boundary conditions, setting the diffusion rate of the marker gas, calculating and tracking the motion trajectory and distribution of the marker gas by using the DPM discrete phase model, and determining the position with the highest gas concentration on the inner wall of the valve side riser as the optimal oil chromatogram monitoring point.

[0096] Step A5: Based on the determined point, a multi-point oil chromatogram online monitoring device is arranged in the valve side riser, the acetylene content of the watchband wiper entering the deterioration level is taken as the deterioration early warning trigger condition, and the corresponding gas generation rate of each marker gas is taken as the corresponding deterioration early warning threshold, and a superheat early warning strategy is constructed to issue a watchband wiper deterioration early warning when all the marker gases monitored by the multi-point oil chromatogram online monitoring device exceed the corresponding deterioration early warning threshold.

[0097] In this embodiment, the installed oil chromatogram online monitoring device is the commonly used oil chromatogram online monitoring device in the prior art. And the watchband wiper with the corresponding contact resistance value R as R=50μΩ is taken as the watchband wiper entering the deterioration level, and the corresponding gas generation rate of each marker gas generated by it is taken as the corresponding deterioration early warning threshold, and the superheat early warning strategy as shown in Figure 2 is constructed. Specifically, the superheat early warning strategy includes the following steps:

[0098] Step B1: Real-time monitoring of acetylene content in the valve side elevated seat based on multi-point oil chromatography online monitoring device;

[0099] Step B2: When the acetylene content is monitored to be ≥ acetylene content threshold: 0.5 uL / L, proceed to Step B3;

[0100] Step B3: Monitor other marker gases;

[0101] Step B4: When the acetylene gas production rate is monitored to be ≥ acetylene gas production rate threshold: 0.01 mL / day, proceed to Step B5, otherwise continue monitoring;

[0102] Step B5: When the hydrogen gas production rate is monitored to be ≥ hydrogen gas production rate threshold: 1.92 mL / day, proceed to Step B6, otherwise continue monitoring;

[0103] Step B6: When the production rate of all alkanes is monitored to be ≥ all alkanes production rate threshold: 6.42 mL / day, proceed to Step B7, otherwise continue monitoring;

[0104] Step B7: Check if the three-ratio code of the online oil chromatogram is 002, if yes, proceed to Step B8, otherwise continue monitoring;

[0105] Step B8: Determine that the watchband contact finger has an overheating defect and enter the deterioration state.

[0106] In the present application, through steps A1 to A5, an overheating early warning strategy for the watchband contact finger is constructed, realizing online early warning for the watchband contact finger entering the deterioration level and being in the deterioration level, which can realize early warning of the contact deterioration and overheating risk of the valve side key electrical connection component: the watchband contact finger in the early stage of deterioration, effectively preventing overheating, discharge, even fire explosion and other serious accidents caused by poor contact, ensuring the safe and stable operation of the power grid, improving the operation safety and operation efficiency of the converter transformer, and solving 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 large loop resistance.

[0107] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application. It should be understood that the above description is only a specific embodiment of the present application and is not intended to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present 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 stage in an overheated gas production test platform under the influence of the working current by using 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 strap 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 operating current waveform on the valve side to extract the main harmonic components. The first few harmonics are selected according to their amplitude proportions so 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, ρ=ρ(T), u=u(T); In the formula, u represents the transformer oil flow velocity, with units of m / s. This represents the Hamiltonian operator, p represents pressure in Pa, and g represents gravitational acceleration 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 fraction of the phase. 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 gas generation rate, with units of kg / m³. 3 ·s, where T represents temperature; The formula for calculating the thermal field distribution is as follows: Q e =J·E; In the formula, Q e This indicates active power loss, expressed in W / m. 3 J represents the current density vector, with units of A / m. 2 E represents the electric field strength, with units of V / m, and ρ represents the fluid density, with units of kg / m³. 3 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 taken 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 taken as the boundary conditions for bubble injection. The diffusion rate of the marker gas is set, and the trajectory and distribution of the tracking marker gas are calculated 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 gas production rate of acetylene is detected to be ≥ the gas production rate threshold of acetylene, 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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