A method and device for recovering insulating oil of oil-immersed transformer

Abstract

The invention discloses a method and device for recovering insulating oil of an oil-immersed transformer. The method comprises the following steps: firstly, the insulating oil inside the oil-immersed transformer is extracted, and then hot air circulation heating and low-frequency induction heating are performed alternately. The hot air is heat-exchanged with the residual oil inside the oil-immersed transformer, thereby improving the fluidity of the residual oil and reducing the adhesion of the residual oil. The residual oil attached to the internal components of the oil-immersed transformer is precipitated through low-frequency induction heating. The hot air circulation heating and low-frequency induction heating are performed alternately to rapidly increase the temperature of the residual oil inside the transformer, so that the residual oil is gasified, thereby improving the gasification efficiency of the residual oil inside the oil-immersed transformer, effectively removing the insulating oil in the oil-immersed transformer, and reducing the probability of insulating oil leakage. Finally, the gas generated by the gasification is subjected to tail gas treatment, thereby reducing the risk of environmental pollution.

Description

Technical Field

[0001] The invention relates to the technical field of transformers, and in particular to a method and a device for recovering insulating oil of an oil-immersed transformer. Background Art

[0002] As the service life of oil-immersed transformers increases, their performance gradually declines. When oil-immersed transformers are scrapped, they need to be recycled and disassembled. At present, the recycling industry lacks scientific and standardized recycling technology, and it is impossible to effectively remove the insulating oil in the oil-immersed transformer before disassembly. As a result, insulating oil leakage is prone to occur during the disassembly of oil-immersed transformers, causing a greater risk of environmental pollution. Summary of the invention

[0003] Based on this, the present invention provides a method and device for recovering insulating oil of an oil-immersed transformer, which can effectively remove the insulating oil in the oil-immersed transformer by gasifying and treating the exhaust gas of the residual oil inside the oil-immersed transformer after extracting the insulating oil from the oil-immersed transformer, thereby reducing the probability of insulating oil leakage and thus reducing the risk of environmental pollution.

[0004] To achieve the above object, an embodiment of the present invention provides a method for recovering insulating oil of an oil-immersed transformer, comprising:

[0005] Extract the insulating oil inside the oil-immersed transformer;

[0006] After the insulating oil extraction is completed, hot air circulation heating and low-frequency induction heating are alternately performed on the inside of the oil-immersed transformer to gasify the residual oil inside the oil-immersed transformer;

[0007] After the residual oil is gasified, the gas generated by the gasification is subjected to tail gas treatment to complete the recovery of the insulating oil of the oil-immersed transformer.

[0008] To achieve the above object, an embodiment of the present invention further provides an oil-immersed transformer insulating oil recovery device, comprising:

[0009] Waste oil extraction module, used to extract the insulating oil inside the oil-immersed transformer;

[0010] A residual oil gasification module, used for alternately performing hot air circulation heating and low-frequency induction heating on the inside of the oil-immersed transformer after the insulating oil extraction is completed, so as to gasify the residual oil inside the oil-immersed transformer;

[0011] The tail gas treatment module is used to treat the gas generated by the gasification after the residual oil is gasified, so as to complete the recovery of the insulating oil of the oil-immersed transformer.

[0012] Compared with the prior art, the insulating oil recovery method and device for oil-immersed transformers disclosed in the embodiments of the present invention first extract the insulating oil inside the oil-immersed transformer; then, after the insulating oil extraction is completed, hot air circulation heating and low-frequency induction heating are alternately performed on the inside of the oil-immersed transformer to gasify the residual oil inside the oil-immersed transformer; finally, after the residual oil is gasified, tail gas treatment is performed on the gas generated by the gasification to complete the insulating oil recovery of the oil-immersed transformer. It can be seen that the embodiment of the present invention first extracts the insulating oil inside the oil-immersed transformer, and then alternately performs hot air circulation heating and low-frequency induction heating. The hot air exchanges heat with the residual oil inside the oil-immersed transformer, thereby improving the fluidity of the residual oil and reducing the adhesion of the residual oil. The residual oil attached to the internal components of the oil-immersed transformer is precipitated through low-frequency induction heating. By alternately performing hot air circulation heating and low-frequency induction heating, the temperature of the residual oil inside the transformer is rapidly increased, and the residual oil is gasified, thereby improving the gasification efficiency of the residual oil inside the oil-immersed transformer, effectively removing the insulating oil in the oil-immersed transformer, and reducing the probability of insulating oil leakage. Finally, the gas generated by gasification is subjected to tail gas treatment, thereby reducing the risk of environmental pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the technical solution of the present invention, the drawings required for use in the implementation mode will be briefly introduced below. Obviously, the drawings described below are only some implementation modes of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0014] Figure 1 It is a schematic flow chart of a method for recovering insulating oil of an oil-immersed transformer provided by one embodiment of the present invention;

[0015] Figure 2 It is a structural schematic diagram of an oil-immersed transformer insulating oil recovery device provided by one embodiment of the present invention;

[0016] Figure 3 It is a structural schematic diagram of an oil-immersed transformer insulating oil recovery device provided by one embodiment of the present invention;

[0017] Among them, 11. adapter; 112. oil circuit valve; 113. gas circuit valve; 12. oil circuit channel; 121. oil pump; 122. flow sensor; 13. gas circuit channel; 131. vacuum pump; 2. oil-immersed transformer; 21. oil drain hole; 22. oil inlet hole; 3. waste oil recovery box; 4. gas recovery box; 5. hot air blower; 6. heating pipe; 61. heating valve. DETAILED DESCRIPTION

[0018] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] See also Figure 1 , is a flow chart of a method for recovering insulating oil of an oil-immersed transformer provided by an embodiment of the present invention. Specifically, the method for recovering insulating oil of an oil-immersed transformer comprises steps S1 to S3:

[0020] S1. Extract the insulating oil inside the oil-immersed transformer;

[0021] S2, after the insulating oil extraction is completed, alternately performing hot air circulation heating and low-frequency induction heating on the inside of the oil-immersed transformer to gasify the residual oil inside the oil-immersed transformer;

[0022] S3. After the residual oil is gasified, the gas generated by the gasification is subjected to tail gas treatment to complete the recovery of the insulating oil of the oil-immersed transformer.

[0023] Specifically, the specific process of the oil-immersed transformer insulating oil recovery method is as follows: 1. The insulating oil in the box of the oil-immersed transformer is sealed and extracted. 2. After the insulating oil is extracted, there is still residual oil attached to the various components and the box wall in the box, so the residual oil inside the oil-immersed transformer is gasified. Specifically, residual oil is gasified by alternately performing hot air circulation heating and low-frequency induction heating on the inside of the oil-immersed transformer; wherein, the specific implementation method of hot air circulation heating is as follows: hot air is provided into the box body by a hot air blower, and the hot air exchanges heat with the heated object, thereby heating the object; the specific implementation method of low-frequency induction heating is as follows: a low-frequency induction heating module is arranged in the box body of the oil-immersed transformer, the low-frequency induction heating module is a module that uses the principle of electromagnetic induction for heating, mainly includes an induction coil and a power control unit, the power control unit is used to control whether the induction coil is energized or not, when an alternating current passes through the induction coil, an alternating magnetic field is generated around it, and a metal workpiece placed in the magnetic field will generate eddy currents due to electromagnetic induction, and eddy currents will generate Joule heat when flowing inside the metal, thereby rapidly heating the metal workpiece, so that the residual oil attached to the windings, cores and insulating materials in the oil-immersed transformer is precipitated as soon as possible, so as to achieve a quick and thorough drying effect, thereby reducing environmental pollution during the subsequent transformer disassembly process. It is worth noting that alternating hot air circulation heating and low-frequency induction heating of the oil-immersed transformer can ensure uniform temperature distribution in the box during the heating process, and avoid local overheating and damage to some components. 3. In the process of alternating hot air circulation heating and low-frequency induction heating inside the oil-immersed transformer, tail gas containing a variety of harmful substances will be generated, including hydrocarbon gas (such as methane, ethane, ethylene, etc.), hydrogen, carbon monoxide, carbon dioxide, nitrogen oxides, sulfides and a small amount of solid particles. If these tail gases are directly discharged into the atmosphere without treatment, they will cause serious harm to the environment and human health. Therefore, it is necessary to carry out green purification of the tail gas, such as using a tail gas treatment method that combines filtration and adsorption. First, the solid particles in the tail gas are filtered through the fiber filter material, and then the gaseous pollutants are adsorbed by the activated carbon adsorbent. It is worth noting that the specific tail gas treatment method is not limited to the above specific examples, and treatment measures can be taken according to actual conditions, which are not limited here.

[0024] Compared with the prior art, the present embodiment first extracts the insulating oil inside the oil-immersed transformer, and then alternately performs hot air circulation heating and low-frequency induction heating. The hot air exchanges heat with the residual oil inside the oil-immersed transformer, thereby improving the fluidity of the residual oil and reducing the adhesion of the residual oil. The residual oil attached to the internal components of the oil-immersed transformer is precipitated through low-frequency induction heating. By alternately performing hot air circulation heating and low-frequency induction heating, the temperature of the residual oil inside the transformer is rapidly increased, so that the residual oil is gasified, thereby improving the gasification efficiency of the residual oil inside the oil-immersed transformer, effectively removing the insulating oil in the oil-immersed transformer, and reducing the probability of insulating oil leakage. Finally, the gas generated by gasification is subjected to tail gas treatment, thereby reducing the risk of environmental pollution.

[0025] Furthermore, in order to precisely control the heating process, a temperature sensor is set inside the oil-immersed transformer to detect the temperature of the hot air in real time, and the power of the hot air blower is adjusted according to the hot air temperature detected in real time. The gasification of insulating oil involves processes such as heat transfer and phase change of matter. The hot air generated by the hot air blower provides heat to increase the temperature of the residual oil inside the oil-immersed transformer. When the temperature reaches the boiling point of the insulating oil, it will begin to gasify. From the perspective of heat transfer, the heat transfer between the hot air and the insulating oil can be preliminarily analyzed using the heat conduction formula, such as Fourier's law. The hot air transfers heat to the insulating oil through heat transfer, causing the temperature of the insulating oil to rise; the gasification process of the insulating oil can be described to a certain extent by the Clapeyron equation. By considering the hot air temperature detected in real time, the heat transfer between the hot air and the insulating oil, and the gasification process of the insulating oil, the heat that the hot air blower needs to blow is derived, and then the power of the hot air blower is controlled to achieve precise heating.

[0026] In a preferred embodiment, based on the above steps S1 to S3, the method further includes: after performing hot air circulation heating on the interior of the oil-immersed transformer and before performing low-frequency induction heating on the interior of the oil-immersed transformer, evacuating the interior of the oil-immersed transformer until the pressure inside the oil-immersed transformer is less than a preset pressure value.

[0027] Specifically, after the duration of hot air circulation heating reaches the set minimum heating time and the change of gas composition inside the oil-immersed transformer tends to be stable, the hot air circulation heating can be suspended and the vacuum pumping step in the box can be started. When the negative pressure in the box of the oil-immersed transformer reaches the preset pressure value, low-frequency induction heating is started. Low-frequency induction heating under negative pressure is a supplement to hot air gasification, which can thoroughly dry the residual oil in the winding and insulating material. Under negative pressure conditions, the boiling point of the gasified insulating oil will decrease accordingly, thereby improving the gasification efficiency. In addition, the negative pressure environment can reduce the degree of oxidation on the surface of the metal workpiece.

[0028] It is worth noting that the preset pressure value can be set according to actual conditions and is not limited here.

[0029] In a preferred embodiment, based on the above steps S1 to S3, the method further includes:

[0030] After the interior of the oil-immersed transformer is subjected to low-frequency induction heating, residual oil in the oil-immersed transformer is extracted.

[0031] It is understandable that the residual oil attached to the internal components of the oil-immersed transformer is precipitated by low-frequency induction heating, and the precipitated residual oil will drip and gather at the bottom of the box. In order to improve the removal efficiency of the insulating oil inside the oil-immersed transformer, the residual oil gathered at the bottom of the box is extracted twice, thereby improving the recovery rate of the insulating oil. In addition, in order to avoid the operation being too complicated, it is often only necessary to extract the insulating oil twice after the first low-frequency induction heating. If necessary, multiple extractions can also be performed, which is not limited here.

[0032] In a preferred embodiment, on the basis of the above steps S1 to S3, before step S3, the method further includes:

[0033] During the gasification process of residual oil inside the oil-immersed transformer, analyzing the gas composition inside the oil-immersed transformer;

[0034] Whether the residual oil inside the oil-immersed transformer has been completely gasified is determined based on the analysis result of the gas composition.

[0035] Specifically, in order to timely determine whether the residual oil has been gasified and improve the efficiency of insulating oil recovery, it is necessary to conduct real-time detection and analysis of the gasified mixture during the heating process to obtain the analysis results of the gas composition. The analysis results include the contents of various gas components. The analysis results are plotted into a curve change diagram in chronological order. The contents and change trends of various gas components can be seen from the curve change diagram to determine whether the residual oil in the box has been gasified. If, after a period of heating, the type of gas component no longer changes and the content of the gas component tends to be stable, it is considered that the gasification is completed, and the exhaust gas generated by the gasification is purified. Otherwise, heating is continued until it is determined that the gasification is complete.

[0036] In a preferred embodiment, based on the above steps S1 to S3, the step S1 of extracting the insulating oil inside the oil-immersed transformer includes:

[0037] The oil drain hole of the oil-immersed transformer is connected to the first interface of the oil and gas recovery pipeline through the first oil and gas tap, and the second interface of the oil and gas recovery pipeline is connected to the waste oil recovery tank; wherein, the oil and gas recovery pipeline is provided with an oil circuit valve for controlling the opening and closing of the first interface and the second interface, and the oil and gas recovery pipeline is provided with an oil pump and a flow sensor near the second interface;

[0038] Open the oil circuit valve and start the oil pump to extract the insulating oil inside the oil-immersed transformer into the waste oil recovery tank until the real-time flow rate detected by the flow sensor is less than the set flow rate value, then turn off the oil pump and replace the first oil and gas tap with an oil suction tap; wherein the rear end of the oil suction tap is connected to the first interface via a hose;

[0039] The front end of the oil suction tap is sent into the oil-immersed transformer through the oil drain hole, and the oil pump is turned on to extract the insulating oil inside the oil-immersed transformer into the waste oil recovery tank until the real-time flow detected by the flow sensor is less than the set flow value, and the oil pump and the oil circuit valve are closed.

[0040] Specifically, the oil-immersed transformer insulating oil recovery method is applied to the oil-immersed transformer insulating oil recovery device. If the device is divided according to function, it mainly includes a waste oil extraction module, a residual oil gasification module and an exhaust gas treatment module, wherein the waste oil extraction module is used to extract the insulating oil inside the oil-immersed transformer; the residual oil gasification module is used to alternately perform hot air circulation heating and low-frequency induction heating on the inside of the oil-immersed transformer after the insulating oil extraction is completed, so as to gasify the residual oil inside the oil-immersed transformer; the exhaust gas treatment module is used to perform exhaust gas treatment on the gas generated by the gasification after the residual oil gasification is completed. Among them, the waste oil extraction module includes an oil and gas recovery pipeline, a first oil and gas tap, an oil suction tap and a waste oil recovery tank, for example, see Figure 2 ,exist Figure 2 In the oil-immersed transformer insulating oil recovery device shown, the oil and gas recovery pipeline includes an adapter 11 and an oil channel 12. The first interface of the adapter 11 serves as the first interface of the oil and gas recovery pipeline, and is connected to the oil drain hole 21 of the oil-immersed transformer 2 through a first oil and gas tap (not shown in the figure) or an oil suction tap (not shown in the figure). The first interface of the oil channel 12 is connected to the second interface of the adapter 11. The second interface of the oil channel 12 serves as the second interface of the oil and gas recovery pipeline, and is used to be connected to the waste oil recovery tank 3. The adapter 11 is provided with an oil valve 112 for controlling the opening and closing of the first interface of the oil channel 12 and the second interface of the adapter 11, and the oil channel 12 is provided with an oil pump 121 and a flow sensor 122.

[0041] Specifically, the specific process of extracting insulating oil is as follows: 1. Connect the drain hole 21 of the oil-immersed transformer 2 to the first interface of the adapter 11 through the first oil and gas tap, and use a ratchet wrench to loosen the nut of the drain hole until the drain hole 21 is fully opened. At this time, start the oil pump 121, open the oil circuit valve 112, and start the oil extraction operation. During the oil extraction process, the current flow rate can be measured by the flow sensor 122. When the flow rate detected by the flow sensor 122 is close to 0, the oil pump 121 is controlled to stop running and the oil circuit valve 112 is closed. 2. In general, there is a height difference of 100-120 mm between the drain hole 21 of the oil-immersed transformer and the bottom of the box, resulting in the inability to achieve the full extraction effect during the process of extracting insulating oil. Therefore, the oil suction tap needs to be passed through the drain hole 21 and penetrated into the bottom of the box to continuously absorb oil. Specifically, the first oil and gas tap is replaced with an oil suction tap. The front end of the oil suction tap is a honeycomb columnar structure, and the rear end is connected to the first interface of the adapter 11 through a hose. The front end of the oil suction tap is sent into the box of the oil-immersed transformer 2 and close to the bottom of the box. The oil pump 121 and the oil circuit valve 112 are turned on to suck out the residual oil in the box as much as possible. The current flow rate can also be measured by the flow sensor 122. When the flow rate is close to 0, it is considered that the residual oil at the bottom is sucked out for the first time. The oil pump 121 and the oil circuit valve 112 are closed to complete the first extraction of insulating oil.

[0042] It is worth noting that the set flow value is set according to the actual situation and is not limited here. The hardware structure of the oil-immersed transformer insulating oil recovery device is not limited to Figure 2 The specific examples shown can be set according to actual conditions.

[0043] Furthermore, the pumping speed is determined according to the size of the oil drain hole, and then the power of the first oil pump is controlled. The relationship between the pumping speed and the oil drain hole diameter is affected by many factors, such as insulating oil viscosity, pressure difference, and pipeline length. Here, a relatively simplified approximate relationship formula is given as a reference based on experience, as follows:

[0044] Assuming the pumping speed is , the aperture is , the following formula can be considered:

[0045] ;

[0046] in, and It is a coefficient and exponent determined by experiments. The principle of this formula is that, generally speaking, the larger the pore size, the more oil is allowed to pass through, and the pumping speed may increase in the form of a power function as the pore size increases. In practical applications, a series of tests are conducted to obtain the pumping speed corresponding to various pore sizes under set insulating oil viscosity and set pipeline length, and the relationship between the two parameters is determined by curve fitting using mathematical software, which is used to select the pumping speed in subsequent applications.

[0047] Optionally, by using high-quality sealing materials and advanced sealing technology, each connection and interface in the extraction path is sealed to prevent the insulating oil from leaking into the environment under pressure, thereby reducing the waste of insulating oil and the risk of causing safety accidents (such as fire, explosion, etc.). Environmental pollution caused by insulating oil leakage is avoided. In addition, the sealed extraction path can maintain the stability of the oil pressure and reduce pressure fluctuations.

[0048] Furthermore, the oil and gas recovery pipeline is also provided with a third interface, a vacuum pump and a gas circuit valve for controlling the on-off of the first interface and the third interface, and the third interface is used to connect the gas recovery box;

[0049] The hot air circulation heating method is as follows:

[0050] After the insulating oil is extracted, the oil inlet of the oil-immersed transformer is connected to a hot air blower through a heating pipe; a heating valve is provided on the heating pipe;

[0051] replacing the oil suction tap with the first oil and gas tap;

[0052] Open the heating valve, and set the opening of the gas circuit valve to a first set opening value, wherein the first set opening value is greater than zero and less than one;

[0053] Starting the hot air blower to blow hot air into the oil-immersed transformer through the heat supply pipe and the oil inlet hole in sequence, so as to gasify the residual oil in the oil-immersed transformer;

[0054] When it is detected that the change degree of the gas composition inside the oil-immersed transformer is less than the set change value, the hot air blower is turned off, the heating valve is turned off, and the opening of the gas circuit valve is set to a second set opening value, wherein the second set opening value is greater than or equal to the first set opening value;

[0055] The vacuum pump is started to extract the gas inside the oil-immersed transformer into the gas recovery box until the gas pressure inside the oil-immersed transformer is less than a preset pressure value.

[0056] For example, Figure 2As shown, the insulating oil recovery device for oil-immersed transformer also includes a gas recovery box 4, a hot air blower 5 and a heating pipeline 6. A heating valve 61 is provided on the heating pipeline 6. The oil inlet 22 of the oil-immersed transformer 2 is connected to the hot air blower 5 through the heating pipeline 6. In addition to the adapter 11, the oil circuit valve 112, the oil channel 12, the flow sensor 122 and the oil pump 121, the oil and gas recovery pipeline also includes an air channel 13, an air circuit valve 113 provided on the adapter 11 for controlling the first interface and the third interface of the adapter 11 to be turned on and off, and a vacuum pump 131 provided on the air channel 13. The third interface of the adapter 11 is connected to the first interface of the air channel 13. The second interface of the air channel 13 is connected to the gas recovery box 4 as the third interface of the oil and gas recovery pipeline.

[0057] Specifically, after step S1, the oil inlet 22 at the upper end of the oil-immersed transformer 2 is connected to the heating pipeline 6 through the second oil-gas tap (not shown in the figure), and the oil drain hole 21 of the oil-immersed transformer 2 is replaced with the first oil-gas tap again. The heating valve 61 is opened, the oil circuit valve 112 is closed, and the gas circuit valve 113 is partially opened. The hot air blower 5 is started to heat the oil-immersed transformer 2 from top to bottom with hot air circulation, so that the residual oil inside the oil-immersed transformer 2 undergoes a gasification reaction. By monitoring the values ​​of the air pressure sensor and the temperature sensor inside the oil-immersed transformer 2, the power of the hot air blower 5 is adjusted so that the air pressure and temperature inside the oil-immersed transformer 2 remain stable, so that the residual oil on the box wall and the winding is fully gasified. After maintaining the gasification reaction for a period of time, the gas circuit valve 113 can be fully opened, and the vacuum pump 131 can be started to extract the hot air in the box, and the gasified oil-gas mixture can be quickly taken away by accelerating the hot air circulation.

[0058] In a preferred embodiment, based on steps S1 to S3, the method further includes, before step S1, placing the oil-immersed transformer on an inclined box placement rack so that the oil-immersed transformer is tilted toward the oil drain hole, so that the insulating oil in the oil-immersed transformer can be more easily extracted.

[0059] In a preferred embodiment, based on steps S1 to S3, the specific method of low-frequency induction heating is as follows:

[0060] The metal workpiece inside the oil-immersed transformer is subjected to low-frequency induction heating to increase the temperature of the metal workpiece and the insulating workpiece connected to the metal workpiece, so that the residual oil attached to the metal workpiece and the insulating workpiece is precipitated.

[0061] Specifically, during the low-frequency induction heating process, the calculation of the temperature rise of metal workpieces (such as windings) and oil flow inside the oil-immersed transformer is a fluid-temperature field coupling problem. The hot air flow inside the oil-immersed transformer and the heat transfer between the components can be expressed by the mass conservation equation, momentum conservation equation, and energy conservation equation, among which the mass conservation equation, momentum conservation equation, and energy conservation equation are as follows:

[0062] The mass conservation equation:

[0063] ;

[0064] Momentum conservation equation:

[0065] ;

[0066] Energy conservation equation:

[0067] ;

[0068] In the formula, is the fluid flow rate; , , The fluid flow rate exist , , Directional weight; is the unit time; is the fluid density; is the dynamic viscosity of the fluid; is the fluid temperature; is the fluid pressure; , , is the generalized source term of the momentum conservation equation; is the enthalpy per unit mass; is the thermal conductivity of the fluid; is the internal enthalpy generation rate per unit volume; It indicates divergence. From the three conservation equations, we can see that the variables of each equation influence each other, and the density, energy, momentum, etc. in the fluid are interdependent, indicating that the fluid field and temperature field are strongly coupled during fluid flow and heat transfer.

[0069] Outside the fluid area, the solid areas such as windings and iron cores inside the oil-immersed transformer transfer heat through heat conduction, and heat is transferred through heat convection on the contact surface between the solid and the fluid. The influence of radiation heat dissipation is ignored, and only the processes of heat convection and heat conduction are considered. The heat transfer area, thermal conductivity, surface transfer coefficient, solid surface temperature and the temperature of the fluid around the solid between the solid and the fluid are used to calculate the heat transfer by convection and heat conduction between the solid and the fluid.

[0070] According to the test, after 2 hours of low-frequency induction heating under negative pressure vacuum, there is basically no residual oil in the windings, core, insulation materials, etc. inside the oil-immersed transformer.

[0071] In a preferred embodiment, based on steps S1 to S3, the method further includes: analyzing the gas composition inside the oil-immersed transformer during the gasification process of the residual oil inside the oil-immersed transformer; and judging whether the gasification of the residual oil inside the oil-immersed transformer is complete according to the analysis result of the gas composition. Wherein, analyzing the gas composition inside the oil-immersed transformer during the gasification process of the residual oil inside the oil-immersed transformer includes:

[0072] During the gasification process of residual oil inside the oil-immersed transformer, real-time detection of gas inside the oil-immersed transformer is performed to obtain gas detection data;

[0073] The gas detection data is input into a pre-trained convolutional neural network, and the analysis result of the gas composition inside the oil-immersed transformer is output.

[0074] Specifically, the training process of the convolutional neural network is as follows: first, a training set containing multiple training samples is obtained, and the training samples include historical gas detection data that has been cleaned and normalized and the analysis results of its gas composition. Optionally, the gas detection data is the gas spectrum information obtained by the acquisition module, and the analysis results of the gas composition include the gas composition and its content. 2. Construct a convolutional neural network model. (1) Design a convolutional neural network architecture, which usually includes an input layer, several convolutional layers, a pooling layer, a fully connected layer, and an output layer; (2) Determine the hyperparameters of the model, such as the convolution kernel size, step size, number of layers, learning rate, etc.; the selection of hyperparameters has a great impact on the performance of the model, and it is usually necessary to determine the best hyperparameter combination through experiments and parameter adjustment. (3) Select appropriate activation functions, loss functions, and optimization algorithms. For example, commonly used activation functions include Rectified Linear Unit (ReLU) and Sigmoid function, among which ReLU and Sigmoid functions are commonly used activation functions in convolutional neural networks, and Sigmoid function is an S-shaped function; the loss function can be Mean Squared Error (MSE) or cross entropy loss; optimization algorithms include adaptive moment estimation (Adam) and stochastic gradient descent (SGD). 3. Model training. Divide the preprocessed data set into training set, validation set and test set. Use the training set to train the convolutional neural network, and make the output of the network as close to the actual gas composition analysis results as possible by continuously adjusting the weights and biases of the network. During the training process, use the validation set to monitor the performance of the model to prevent overfitting. When the performance of the model on the validation set no longer improves, the training can be stopped. 4. Model evaluation and optimization. Use the test set to evaluate the trained model and calculate evaluation indicators such as accuracy and root mean square error (RMSE). Based on the evaluation results, the model is optimized, such as adjusting the network architecture, adding data enhancement operations, adjusting hyperparameters, etc., to improve the performance of the model.

[0075] In order to have a deeper understanding of convolutional neural networks, the following is a brief introduction to the basic operations of convolutional neural networks:

[0076] (1) Convolution operation

[0077] The activation function usually uses the ReLU function. The data after the convolution operation usually introduces nonlinearity through the activation function to enhance the expressiveness of the model.

[0078] (2) Loss Function

[0079] When training a convolutional neural network for gas analysis, it is necessary to define a loss function to measure the difference between the model's predicted values ​​and the true values.

[0080] (3) Parameter optimization

[0081] In order to minimize the loss function, it is necessary to update the parameters (weights and biases) of the convolutional neural network through an optimization algorithm. Commonly used optimization algorithms include stochastic gradient descent.

[0082] Convolutional neural networks minimize the loss function by continuously adjusting parameters, thereby improving the prediction accuracy of the model.

[0083] Specifically, after the convolutional neural network training is completed, it is applied to the residual oil gasification process inside the oil-immersed transformer, and the gas inside the oil-immersed transformer is detected in real time to obtain gas detection data. The gas detection data is analyzed using a convolutional neural network to obtain analysis results of the gas composition. The analysis results are plotted as a curve change graph in chronological order. The content and change trend of various gas components can be seen from the curve change graph, and whether the residual oil in the box has been gasified can be judged based on the content and change trend of various gas components.

[0084] Compared with the prior art, the embodiment of the present invention first extracts the insulating oil inside the oil-immersed transformer, and then alternately performs hot air circulation heating and low-frequency induction heating. The hot air exchanges heat with the residual oil inside the oil-immersed transformer, thereby improving the fluidity of the residual oil and reducing the adhesion of the residual oil. The residual oil attached to the internal components of the oil-immersed transformer is precipitated through low-frequency induction heating. By alternately performing hot air circulation heating and low-frequency induction heating, the temperature of the residual oil inside the oil-immersed transformer is rapidly increased, and the residual oil is gasified, thereby improving the gasification efficiency of the residual oil inside the oil-immersed transformer, effectively removing the insulating oil in the oil-immersed transformer, and reducing the probability of insulating oil leakage. Finally, the gas generated by gasification is subjected to tail gas treatment, thereby reducing the risk of environmental pollution.

[0085] See also Figure 3 , Figure 3 : is a structural schematic diagram of an oil-immersed transformer insulating oil recovery device provided in an embodiment of the present invention, the oil-immersed transformer insulating oil recovery device 30 comprises:

[0086] A waste oil extraction module 31 is used to extract the insulating oil inside the oil-immersed transformer;

[0087] The residual oil gasification module 32 is used to alternately perform hot air circulation heating and low-frequency induction heating on the inside of the oil-immersed transformer after the insulating oil extraction is completed, so as to gasify the residual oil inside the oil-immersed transformer;

[0088] The tail gas treatment module 33 is used to perform tail gas treatment on the gas generated by the gasification after the residual oil is gasified, so as to complete the recovery of the insulating oil of the oil-immersed transformer.

[0089] It is worth noting that the specific working process of the oil-immersed transformer insulating oil recovery device can refer to the working process of the oil-immersed transformer insulating oil recovery method described in the above embodiment, which will not be repeated here.

[0090] Compared with the prior art, the oil-immersed transformer insulating oil recovery device disclosed in the embodiment of the present invention includes a waste oil extraction module, a residual oil gasification module and a tail gas treatment module. The waste oil extraction module is used to extract the insulating oil inside the oil-immersed transformer; the residual oil gasification module is used to alternately perform hot air circulation heating and low-frequency induction heating on the inside of the oil-immersed transformer after the insulating oil extraction is completed, so as to gasify the residual oil inside the oil-immersed transformer; the tail gas treatment module is used to perform tail gas treatment on the gas generated by gasification after the residual oil gasification is completed, so as to complete the insulating oil recovery of the oil-immersed transformer. It can be seen that the device of the embodiment of the present invention first extracts the insulating oil inside the oil-immersed transformer, and then alternately performs hot air circulation heating and low-frequency induction heating. The hot air exchanges heat with the residual oil inside the oil-immersed transformer, thereby improving the fluidity of the residual oil and reducing the adhesion of the residual oil. The residual oil attached to the internal components of the oil-immersed transformer is precipitated through low-frequency induction heating. By alternately performing hot air circulation heating and low-frequency induction heating, the temperature of the residual oil inside the transformer is rapidly increased, so that the residual oil is gasified, thereby improving the gasification efficiency of the residual oil inside the oil-immersed transformer, effectively removing the insulating oil in the oil-immersed transformer, and reducing the probability of insulating oil leakage. Finally, the gas generated by gasification is subjected to tail gas treatment, thereby reducing the risk of environmental pollution.

[0091] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for recovering insulating oil from an oil-immersed transformer, characterized in that: include: Extract the insulating oil inside the oil-immersed transformer; After the insulating oil extraction is completed, hot air circulation heating and low-frequency induction heating are alternately performed on the inside of the oil-immersed transformer to gasify the residual oil inside the oil-immersed transformer; After the residual oil is gasified, the gas generated by the gasification is subjected to tail gas treatment to complete the recovery of the insulating oil of the oil-immersed transformer; The method of extracting insulating oil from the oil-immersed transformer comprises: The oil drain hole of the oil-immersed transformer is connected to the first interface of the oil and gas recovery pipeline through the first oil and gas tap, and the second interface of the oil and gas recovery pipeline is connected to the waste oil recovery tank; wherein, the oil and gas recovery pipeline is provided with an oil circuit valve for controlling the opening and closing of the first interface and the second interface, and the oil and gas recovery pipeline is provided with an oil pump and a flow sensor near the second interface; Open the oil circuit valve and start the oil pump to extract the insulating oil inside the oil-immersed transformer into the waste oil recovery tank until the real-time flow rate detected by the flow sensor is less than the set flow rate value, then turn off the oil pump and replace the first oil and gas tap with an oil suction tap; wherein the rear end of the oil suction tap is connected to the first interface via a hose; The front end of the oil suction tap is sent into the oil-immersed transformer through the oil drain hole, and the oil pump is turned on to extract the insulating oil inside the oil-immersed transformer into the waste oil recovery tank until the real-time flow detected by the flow sensor is less than the set flow value, and the oil pump and the oil circuit valve are closed.

2. The method for recovering insulating oil of an oil-immersed transformer according to claim 1, characterized in that: Also includes: After the oil-immersed transformer is heated by hot air circulation and before the oil-immersed transformer is heated by low-frequency induction, the oil-immersed transformer is evacuated until the pressure inside the oil-immersed transformer is less than a preset pressure value.

3. The method for recovering insulating oil of an oil-immersed transformer according to claim 1, characterized in that: Also includes: After the interior of the oil-immersed transformer is subjected to low-frequency induction heating, residual oil in the oil-immersed transformer is extracted.

4. The method for recovering insulating oil of an oil-immersed transformer according to claim 1, characterized in that: After the residual oil is gasified, the gas generated by the gasification is subjected to tail gas treatment, and before the insulating oil recovery of the oil-immersed transformer is completed, the method further includes: During the gasification process of residual oil inside the oil-immersed transformer, analyzing the gas composition inside the oil-immersed transformer; Whether the residual oil inside the oil-immersed transformer has been completely gasified is determined based on the analysis result of the gas composition.

5. The method for recovering insulating oil of an oil-immersed transformer according to claim 1, characterized in that: The oil and gas recovery pipeline is also provided with a third interface, a vacuum pump and a gas circuit valve for controlling the opening and closing of the first interface and the third interface, and the third interface is used to connect the gas recovery box; The hot air circulation heating method is as follows: After the insulating oil is extracted, the oil inlet of the oil-immersed transformer is connected to a hot air blower through a heating pipe; a heating valve is provided on the heating pipe; replacing the oil suction tap with the first oil and gas tap; Open the heating valve, and set the opening of the gas circuit valve to a first set opening value, wherein the first set opening value is greater than zero and less than one; Starting the hot air blower to blow hot air into the oil-immersed transformer through the heat supply pipe and the oil inlet hole in sequence, so as to gasify the residual oil in the oil-immersed transformer; When it is detected that the change degree of the gas composition inside the oil-immersed transformer is less than the set change value, the hot air blower is turned off, the heating valve is turned off, and the opening of the gas circuit valve is set to a second set opening value, wherein the second set opening value is greater than or equal to the first set opening value; The vacuum pump is started to extract the gas inside the oil-immersed transformer to the gas recovery box until the gas pressure inside the oil-immersed transformer is less than a preset pressure value.

6. The method for recovering insulating oil of an oil-immersed transformer according to claim 1, characterized in that: Before extracting the insulating oil inside the oil-immersed transformer, the oil-immersed transformer is placed on an inclined box placement rack so that the oil-immersed transformer is inclined toward one side of the oil drain hole.

7. The method for recovering insulating oil of an oil-immersed transformer according to claim 1, characterized in that: The specific method of the low-frequency induction heating is as follows: The metal workpiece inside the oil-immersed transformer is subjected to low-frequency induction heating to increase the temperature of the metal workpiece and the insulating workpiece connected to the metal workpiece, so that the residual oil attached to the metal workpiece and the insulating workpiece is precipitated.

8. The method for recovering insulating oil of an oil-immersed transformer according to claim 4, characterized in that: During the residual oil gasification process inside the oil-immersed transformer, analyzing the gas composition inside the oil-immersed transformer includes: During the gasification process of residual oil inside the oil-immersed transformer, real-time detection of gas inside the oil-immersed transformer is performed to obtain gas detection data; The gas detection data is input into a pre-trained convolutional neural network, and the analysis result of the gas composition inside the oil-immersed transformer is output.

9. An oil-immersed transformer insulating oil recovery device, characterized in that: include: Waste oil extraction module, used to extract the insulating oil inside the oil-immersed transformer; A residual oil gasification module, used for alternately performing hot air circulation heating and low-frequency induction heating on the inside of the oil-immersed transformer after the insulating oil extraction is completed, so as to gasify the residual oil inside the oil-immersed transformer; An exhaust gas treatment module is used to treat the gas generated by the gasification after the residual oil is gasified, so as to complete the recovery of the insulating oil of the oil-immersed transformer; The waste oil extraction module is specifically used for: The oil drain hole of the oil-immersed transformer is connected to the first interface of the oil and gas recovery pipeline through the first oil and gas tap, and the second interface of the oil and gas recovery pipeline is connected to the waste oil recovery tank; wherein, the oil and gas recovery pipeline is provided with an oil circuit valve for controlling the opening and closing of the first interface and the second interface, and the oil and gas recovery pipeline is provided with an oil pump and a flow sensor near the second interface; Open the oil circuit valve and start the oil pump to extract the insulating oil inside the oil-immersed transformer into the waste oil recovery tank until the real-time flow rate detected by the flow sensor is less than the set flow rate value, then turn off the oil pump and replace the first oil and gas tap with an oil suction tap; wherein the rear end of the oil suction tap is connected to the first interface via a hose; The front end of the oil suction tap is sent into the oil-immersed transformer through the oil drain hole, and the oil pump is turned on to extract the insulating oil inside the oil-immersed transformer into the waste oil recovery tank until the real-time flow detected by the flow sensor is less than the set flow value, and the oil pump and the oil circuit valve are closed.

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