An online oil filtering device for large transformer under voltage and a control method thereof

Abstract

The application discloses an online live oil filtering device for large transformers and a control method thereof, and belongs to the technical field of power equipment maintenance. The application is characterized in that an oil inlet mass flowmeter and an oil outlet mass flowmeter are arranged, data collected by a temperature sensor is combined, a controller is used to execute a closed-loop mass-volume balance algorithm based on temperature compensation, and whether micro leakage exists in an oil filtering pipeline is accurately judged, so that high safety under live working is realized. The application solves the technical problem that the prior art cannot safely and efficiently filter oil for large transformers under a non-power-off state, and has the remarkable advantages of high leakage detection precision, fast response speed and safety and reliability.

Description

Technical Field

[0001] This invention relates to the field of insulating oil purification and treatment technology for large transformers in power systems, specifically to an online live-line oil filtration device for large transformers and its control method. Background Technology

[0002] Power transformers are core equipment in power grid systems, and transformer oil, as their primary insulating and heat dissipation medium, directly determines the operational safety of the transformer. With increasing operating time, transformer oil deteriorates under the influence of electromagnetic fields, high temperatures, and oxygen, producing moisture, gases, and solid particulate impurities, leading to a decrease in insulation strength.

[0003] Traditional oil filtration methods require shutting down the transformer and using a vacuum oil filter for dehydration, degassing, and filtration. This shutdown oil filtration method has significant technical drawbacks: firstly, a power outage of a large transformer for 6 to 8 days can cause huge economic losses and affect power supply reliability; secondly, current technology cannot perform high-precision real-time monitoring of leakage risks in connecting pipelines during the oil filtration process. Once a leak occurs, a large amount of transformer oil will leak out, not only wasting resources but also potentially causing serious environmental pollution or even fire accidents.

[0004] While some online oil filtration devices have been reported in the existing technology, most are limited to small transformers below 220 kV, and their temperature and pressure detection accuracy is low, failing to overcome the fundamental impact of oil temperature changes on the flow meter's measurement accuracy, leading to frequent false alarms or leakage alarms. Therefore, developing an online live oil filtration device capable of being used in large transformers and possessing high-precision leakage detection capabilities is a technical problem urgently needing to be solved in this field. Summary of the Invention

[0005] The present invention aims to provide an online live-line oil filtration device for large transformers and its control method, so as to solve the technical problems in the prior art that transformer oil filtration requires power outage and that pipeline leakage cannot be detected with high precision during the oil filtration process.

[0006] To achieve the above objectives, the present invention provides an online live-line oil filtration device for large transformers, comprising:

[0007] The oil inlet pipeline is equipped with an oil inlet mass flow meter and an oil inlet temperature sensor;

[0008] The oil outlet pipeline is equipped with an oil outlet mass flow meter and an oil outlet temperature sensor;

[0009] The controller is electrically connected to the inlet mass flow meter, the outlet mass flow meter, the inlet temperature sensor, and the outlet temperature sensor, respectively.

[0010] And a cut-off execution module, electrically connected to the controller, for performing shutdown protection actions;

[0011] The controller is configured to execute a temperature-compensated closed-loop mass volume balance algorithm. Based on the inlet temperature value collected by the inlet temperature sensor and the outlet temperature value collected by the outlet temperature sensor, the controller corrects the inlet flow rate reading of the inlet mass flow meter and the outlet flow rate reading of the outlet mass flow meter, respectively. The controller then calculates the difference between the corrected inlet flow rate value and the corrected outlet flow rate value. When the difference exceeds a preset safe mass flow rate threshold, a leak is identified, and a shutdown protection action is executed through the cut-off execution module.

[0012] The "closed loop" mentioned in this article refers to the closed-loop judgment logic of mass-volume balance between inlet and outlet oil flow rates. That is, by comparing and correcting the inlet oil flow rate value and the outlet oil flow rate value in real time, a "measurement-comparison-judgment" closed-loop detection loop is formed, rather than the feedback adjustment and control of pump speed or valve opening.

[0013] As a preferred technical solution, the temperature-compensated closed-loop mass volume balance algorithm includes the following steps:

[0014] Acquire the first temperature value T1 collected by the oil inlet temperature sensor and the second temperature value T2 collected by the oil outlet temperature sensor;

[0015] Based on the pre-stored viscosity-temperature characteristic curve μ(T) of the transformer oil, calculate the first compensation coefficient k1 corresponding to T1 and the second compensation coefficient k2 corresponding to T2 according to the formula k(T)=μ(T0) / μ(T), where T0 is the preset reference temperature;

[0016] Multiply the original reading of the inlet mass flow meter by the first compensation coefficient to obtain the corrected inlet flow value Q_in;

[0017] Multiply the original reading of the oil outlet mass flow meter by the second compensation coefficient to obtain the corrected oil outlet flow value Q_out;

[0018] Calculate the flow difference, which is the absolute value of the difference between the corrected inlet flow rate Q_in and the corrected outlet flow rate Q_out;

[0019] When the flow difference is greater than or equal to the preset safety threshold, a leakage alarm signal is triggered.

[0020] As a further preferred technical solution, both the inlet mass flow meter and the outlet mass flow meter are Coriolis mass flow meters, and both the inlet temperature sensor and the outlet temperature sensor are platinum resistance temperature sensors.

[0021] As a further preferred technical solution, the preset safety threshold is the mass flow rate value corresponding to a volumetric flow rate of 6 liters per hour.

[0022] As a further preferred technical solution, the oil inlet pipeline is also equipped with an oil inlet pressure sensor, and the oil outlet pipeline is also equipped with an oil outlet pressure sensor; the controller is also used to calculate the pressure difference based on the oil inlet pressure value collected by the oil inlet pressure sensor and the oil outlet pressure value collected by the oil outlet pressure sensor, and compare the pressure difference with a preset pressure difference threshold; the controller only determines that a leak has occurred when the flow difference exceeds a preset safety threshold and the pressure difference between the oil inlet pressure value and the oil outlet pressure value is less than a preset lower limit threshold for pressure difference, so as to form a dual judgment logic of flow and pressure.

[0023] As a further preferred technical solution, an alarm module is also included, which is electrically connected to the controller and is used to issue an audible and visual alarm signal when a leak is detected.

[0024] As a further preferred technical solution, the cut-off execution module is disposed on the oil inlet pipeline and the oil outlet pipeline, including a first pneumatic cut-off valve installed on the oil inlet pipeline and a second pneumatic cut-off valve installed on the oil outlet pipeline. Both the first pneumatic cut-off valve and the second pneumatic cut-off valve are electrically connected to the controller. When the controller determines that there is a leak, it outputs a cut-off signal to close the first pneumatic cut-off valve and the second pneumatic cut-off valve within a preset time.

[0025] As a further preferred technical solution, a remote monitoring terminal is also included. The remote monitoring terminal is connected to the controller via an Ethernet or 5G wireless network. The remote monitoring terminal is used to display the detection data of the inlet mass flow meter, the outlet mass flow meter, the inlet temperature sensor, and the outlet temperature sensor in real time, and is used to remotely send a shutdown command to the controller.

[0026] The present invention also provides a control method based on the above-mentioned device, comprising the following steps:

[0027] Step S0: Fill the device with oil and vent the air, and purge the air from the oil inlet pipe, oil outlet pipe and oil filter unit;

[0028] Step S1: Start the inlet and outlet oil pumps to establish external circulation of transformer oil;

[0029] Step S2: Use the inlet mass flow meter and the outlet mass flow meter to collect the raw values ​​of the inlet flow rate and the outlet flow rate in real time, and use the inlet temperature sensor and the outlet temperature sensor to collect the inlet temperature value and the outlet temperature value in real time.

[0030] Step S3: The controller corrects the original values ​​of the inlet flow rate and the outlet flow rate according to the inlet temperature value and the outlet temperature value, respectively, to obtain the compensated inlet flow rate value and the compensated outlet flow rate value;

[0031] Step S4: Calculate the difference between the compensated inlet flow rate and the compensated outlet flow rate;

[0032] Step S5: If the difference is greater than the preset safety threshold, the controller immediately cuts off the power supply to the oil inlet pump, the oil outlet pump and the heater, and issues an audible and visual alarm signal.

[0033] As a preferred technical solution, the correction process in step S3 is implemented by linear interpolation or by a lookup table based on the viscosity-temperature characteristic curve, wherein the viscosity-temperature characteristic curve is pre-stored in the memory of the controller.

[0034] Compared with the prior art, the large transformer online live oil filtration device and its control method of the present invention have at least the following beneficial effects:

[0035] By introducing temperature-compensated mass-volume balance technology, the interference of oil temperature changes on detection accuracy is eliminated, enabling accurate identification of minute leaks (detection accuracy reaches 6 liters per hour), effectively avoiding false alarms and missed alarms caused by oil temperature fluctuations.

[0036] The controller can complete data acquisition, compensation calculation and difference comparison within 0.5 seconds. Once a leak is detected, it can automatically cut off the oil circuit within 1.2 seconds, completely eliminating safety accidents caused by oil leaks during live work.

[0037] The system directly measures mass flow rate using a mass flow meter, unaffected by changes in oil density. Combined with a pressure sensor for auxiliary judgment, it forms a dual judgment logic of flow rate and pressure. Leakage is only determined when the flow rate difference exceeds the limit and the inlet and outlet oil pressure difference decreases significantly. This effectively avoids misjudgments caused by flow meter malfunctions or external interference, further improving judgment accuracy and system robustness. It is also equipped with audible and visual alarms and automatic shut-off functions to ensure safety during live-line operations.

[0038] Based on high-precision sensing and closed-loop control logic, coupled with remote monitoring functions, the oil filtration operation of large transformers can be completed without power interruption and without the need for on-site personnel.

[0039] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the overall structure of the large transformer online live oil filtration device provided in an embodiment of the present invention;

[0041] Figure 2 This is a flowchart illustrating the control method provided in an embodiment of the present invention. Detailed Implementation

[0042] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the specific embodiments, structures, features, and effects according to the present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. In the following description, different "embodiments" or "embodiments" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0043] In the description of this invention, it should be clearly stated that the terms "first," "second," etc., in the specification, claims, and accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence; the terms "vertical," "lateral," "longitudinal," "front," "rear," "left," "right," "up," "down," "horizontal," etc., indicate orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, and are merely for the convenience of describing this invention, and do not mean that the device or element referred to must have a specific orientation or position, and therefore should not be construed as a limitation of this invention.

[0044] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0045] Example 1

[0046] Please see Figure 1 This embodiment provides an online live oil filtration device for large transformers, used for online live oil filtration of 500 kV oil-immersed power transformers.

[0047] The device in this embodiment includes: an oil inlet pipeline, an oil outlet pipeline, an oil filter unit, and a leak detection unit.

[0048] The oil inlet pipeline is made of stainless steel with an inner diameter of 32 mm, and its inlet end is connected to the lower oil outlet flange of the transformer via a flange. The oil outlet pipeline is also made of stainless steel with an inner diameter of 32 mm, and its outlet end is connected to the upper oil inlet flange of the transformer via a flange. The oil filter unit is located beside the transformer, with its oil inlet port connected to the output end of the oil inlet pipeline and its oil outlet port connected to the inlet end of the oil outlet pipeline.

[0049] The leakage detection unit includes: an oil inlet flow detection module, an oil outlet flow detection module, an oil inlet temperature detection module, an oil outlet temperature detection module, an oil inlet pressure detection module, an oil outlet pressure detection module, a controller, an alarm module, and a cut-off execution module.

[0050] The inlet flow rate detection module uses a Coriolis mass flow meter, installed on the inlet pipeline, with a measurement range of 0 to 10 cubic meters per hour, and outputs a 4 to 20 mA current signal. The outlet flow rate detection module also uses a Coriolis mass flow meter, installed on the outlet pipeline, with the same specifications as the inlet flow rate detection module, serving as the outlet mass flow meter.

[0051] The oil inlet temperature detection module uses a platinum resistance temperature sensor, installed on the oil inlet line, with a measurement range of 0 to 100 degrees Celsius and an accuracy of ±0.5 degrees Celsius. The oil outlet temperature detection module uses a platinum resistance temperature sensor of the same specifications, installed on the oil outlet line.

[0052] The inlet pressure detection module uses a diffused silicon pressure transmitter, installed on the inlet pipeline, with a measurement range of 0 to 1 MPa and an output current signal of 4 to 20 mA, serving as the inlet pressure sensor. The outlet pressure detection module uses a pressure transmitter of the same specifications, installed on the outlet pipeline, serving as the outlet pressure sensor.

[0053] The controller employs a programmable logic controller (PLC), and its analog input modules are electrically connected to the inlet oil flow detection module, outlet oil flow detection module, inlet oil temperature detection module, outlet oil temperature detection module, inlet oil pressure detection module, and outlet oil pressure detection module, respectively. The controller has pre-set temperature compensation algorithms and pressure-assisted judgment logic.

[0054] The alarm module uses an audible and visual alarm, which is electrically connected to the digital output module of the controller. When a leak is detected, the controller drives the alarm module to emit a continuous buzzing sound and a red flashing light signal.

[0055] The cut-off execution module includes a first pneumatic cut-off valve installed on the oil inlet line and a second pneumatic cut-off valve installed on the oil outlet line. The two pneumatic cut-off valves are electrically connected to the digital output module of the controller.

[0056] The controller is the core control unit of this invention, and its specific control logic is as follows:

[0057] First, the controller monitors the oil temperature in real time using inlet and outlet oil temperature sensors. Since the viscosity of transformer oil decreases exponentially with increasing temperature, this causes a change in the resonant frequency of the flow meter's measuring tube, resulting in measurement errors. Therefore, temperature compensation must be performed on the flow readings.

[0058] Specifically, the controller executes the following temperature-compensated leakage detection algorithm:

[0059] The first step is to read the inlet oil temperature value T1 collected by the inlet oil temperature sensor and the outlet oil temperature value T2 collected by the outlet oil temperature sensor. The viscosity-temperature characteristic curve μ(T) of the transformer oil is pre-stored in the controller's internal memory.

[0060] The second step involves using a temperature sensor to indirectly obtain viscosity information for compensation, since the measurement accuracy of the Coriolis mass flow meter is affected by changes in fluid viscosity, and viscosity is a function of temperature. Specifically, based on the viscosity-temperature characteristic curve μ(T), the first compensation coefficient k1 corresponding to the inlet temperature T1 and the second compensation coefficient k2 corresponding to the outlet temperature T2 are calculated using the formula k(T) = μ(T0) / μ(T), where T0 is a preset reference temperature (e.g., 20℃).

[0061] The third step is to multiply the original reading Q_raw_in of the inlet mass flow meter by the first compensation coefficient k1 to obtain the corrected inlet flow rate Q_in = Q_raw_in × k1; and to multiply the original reading Q_raw_out of the outlet mass flow meter by the second compensation coefficient k2 to obtain the corrected outlet flow rate Q_out = Q_raw_out × k2.

[0062] The fourth step is to calculate the absolute flow difference ΔQ = |Q_in - Q_out|.

[0063] The fifth step involves converting the calculated flow difference ΔQ into volumetric flow rate and comparing it with the preset safety threshold of 6 L / h. In this embodiment, the safety threshold is 6 liters per hour. Since the density of transformer oil changes very little with temperature, the conversion error between mass flow rate and volumetric flow rate is negligible. Therefore, the safety threshold can be directly expressed as the volumetric flow rate of 6 L / h.

[0064] Step 6: When ΔQ ≥ 6 liters per hour, the controller determines that there is a leak in the system.

[0065] Once a leak is detected, the controller immediately outputs a shut-off signal within 0.5 seconds, causing the first and second pneumatic shut-off valves to close within 1.2 seconds. At the same time, it activates the audible and visual alarm and sends a "leakage shutdown" fault code to the remote monitoring terminal.

[0066] To verify the effectiveness of the temperature compensation algorithm, the applicant conducted the following comparative experiment. With the oil pressure remaining constant, flow monitoring data was recorded as the oil temperature increased from 25 degrees Celsius to 55 degrees Celsius. The experimental data are shown in the table below:

[0067]

[0068] Experimental data shows that when the oil temperature rises from 25 degrees Celsius to 55 degrees Celsius, the flow meter reading deviation can reach 50 liters per hour. Without temperature compensation, this deviation would far exceed the safety threshold (6 liters per hour), leading to serious false alarms. By employing the temperature compensation algorithm of this invention, the flow readings at each temperature point are corrected to the reference value at the reference temperature, and the flow deviation under steady-state conditions is controlled within ±2 liters per hour, fully meeting the accuracy requirements for leak detection.

[0069] To improve the accuracy of leak detection and avoid potential misjudgments due to relying solely on flow rate assessment, this embodiment also incorporates a pressure-assisted judgment function. The controller simultaneously collects the inlet and outlet oil pressure values ​​and calculates the pressure difference ΔP = P_in - P_out. Only when the flow rate difference exceeds a safety threshold and the pressure difference simultaneously exceeds the normal range (for example, the lower limit of the pressure difference can be set to 0.15 MPa) does the controller determine a leak and execute protective actions. This dual-judgment mechanism effectively avoids misjudgments caused by flow meter malfunctions or external interference.

[0070] Field application verification

[0071] In January 2024, the device of this invention underwent field application verification at a 500 kV substation of Xinjiang Power Company. The equipment to be processed was a 500 kV, 240 MVA single-phase oil-immersed transformer. After connecting the device of this invention to the transformer, online live oil filtration was performed according to the method described in Example 2, and the system operated continuously for 48 hours. During the oil filtration period, the transformer maintained normal operation without any abnormalities. In the simulated leakage test, when a minor leak was artificially created, the device accurately detected the leak within 1.5 seconds and automatically cut off the oil circuit, verifying the leakage detection accuracy and response speed of the device.

[0072] Example 2

[0073] Please see Figure 2 This embodiment provides a control method for online electrostatic oil filtration using the above-mentioned device, including the following steps:

[0074] Step S0: Equipment Filling and Venting. Close the inlet valve on the inlet pipeline, open the standby inlet valve, and connect the input end of the inlet pipeline to the external standby transformer oil tank via a hose. Start the inlet pump to fill the filter unit with insulating oil from the external oil tank. When the liquid level in the filter unit reaches the set position, the controller automatically stops the oil supply. Close the standby inlet valve, disconnect the external oil tank hose, and open the inlet valve. Then perform internal circulation venting to remove air from the filter unit and connecting pipelines.

[0075] Step S1: Start online oil filtration. Press the "Equipment Oil Filtration" button on the control panel to start the online oil filtration mode. The controller starts the inlet and outlet oil pumps to establish external circulation of the transformer oil.

[0076] Step S2: Real-time data acquisition. The controller uses the inlet and outlet mass flow meters to acquire the raw values ​​of the inlet and outlet flow rates in real time at a frequency of at least 10 times per second. At the same time, it uses the inlet and outlet temperature sensors to acquire the inlet and outlet temperature values ​​in real time.

[0077] Step S3: Temperature Compensation Correction. Based on the collected inlet and outlet oil temperatures, the controller uses a lookup table method based on the viscosity-temperature characteristic curve to correct the original inlet and outlet oil flow rates. Specifically, the controller's internal memory pre-stores the viscosity-temperature characteristic curve of the transformer oil. The compensation coefficient is calculated using the formula: k(T) = μ(T0) / μ(T), where μ(T) is the oil viscosity at temperature T, and T0 is the reference temperature (usually 20 degrees Celsius). The original inlet oil flow rate is multiplied by the compensation coefficient corresponding to the inlet oil temperature to obtain the compensated inlet oil flow rate; the original outlet oil flow rate is multiplied by the compensation coefficient corresponding to the outlet oil temperature to obtain the compensated outlet oil flow rate.

[0078] Step S4: Calculate the flow difference. The controller calculates the difference between the compensated inlet flow rate and the compensated outlet flow rate, i.e., ΔQ = |Q_in_compensated - Q_out_compensated|.

[0079] Step S5: Leakage Judgment and Protection. The controller converts the calculated difference ΔQ into volumetric flow rate and compares it with the preset safety threshold (6 liters per hour). If ΔQ ≤ 6 liters per hour, it indicates that the system is well sealed and there is no leakage, and the device continues to operate normally. If ΔQ > 6 liters per hour, it indicates that there is a leak in the system, and the controller immediately performs the following protection actions: (1) Outputs a cut-off signal to close the first pneumatic cut-off valve and the second pneumatic cut-off valve, cutting off the oil inlet pipeline and the oil outlet pipeline; (2) Stops the operation of the oil inlet pump, the oil outlet pump and the heater; (3) Drives the audible and visual alarm to issue an audible and visual alarm signal; (4) Sends a "leakage shutdown" fault code to the remote monitoring terminal via Ethernet.

[0080] Step S6: Oil filtration complete. Once the insulating oil treatment parameters meet the requirements, press the "Stop" button on the control panel. The controller first closes the transformer's oil outlet valve and oil inlet valve, then starts the oil suction mode to draw the residual insulating oil in the oil inlet and outlet pipelines back into the oil filtration unit. Finally, the insulating oil inside the oil filtration unit is discharged into an external oil storage container.

[0081] Example 3 (Accuracy Verification Experiment)

[0082] This embodiment quantitatively verifies the detection accuracy of the leak detection unit.

[0083] Experiment 1: Flowmeter Accuracy Verification

[0084] The amount of oil leakage was accurately measured using a measuring cup and compared with the leakage amount measured by a flow meter. The experimental data are shown in the table below:

[0085]

[0086] The experimental data shows that the flow meter's measurement deviation is approximately ±6 liters per hour (i.e., ±0.1 liters per minute).

[0087] Experiment 2: Verification of Temperature Compensation Effect

[0088] With the oil pressure remaining constant, the flow meter readings were measured for both uncompensated and compensated flow meters. The experimental data are as follows:

[0089]

[0090] Experimental results show that, after adopting the temperature compensation algorithm of this invention, the flow rate readings at each temperature point are corrected to the reference value at the reference temperature (25 degrees Celsius), with a maximum deviation of no more than ±0.01 cubic meters per hour (i.e., ±10 liters per hour). After further optimization of the compensation algorithm, the compensation error can be reduced to within ±2 liters per hour, and the overall error is approximately ±8 liters per hour. This invention sets the safety threshold at 6 liters per hour, which ensures both detection sensitivity and avoids false alarms.

[0091] Experiment 3: Response Time Test

[0092] The response time of the test device was measured in a simulated leak test. The test results are as follows:

[0093]

[0094] Test results show that the average response time of the device is 1.52 seconds, which fully meets the safety requirements for live-line work.

[0095] The large-scale transformer online live-line oil filtration device and control method provided by this invention can purify transformer oil without interrupting transformer operation. Compared with existing technologies, this invention has significant advantages such as high leakage detection accuracy, fast response speed, and strong safety and reliability. It can effectively avoid safety accidents caused by oil pipe leaks, significantly reduce the manpower and material costs of oil filtration operations, and has extremely high industrial practical value and economic value.

[0096] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the devices, apparatuses, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0097] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A large transformer online live-line oil filtration device, characterized in that, include: The oil inlet pipeline is equipped with an oil inlet mass flow meter and an oil inlet temperature sensor; The oil outlet pipeline is equipped with an oil outlet mass flow meter and an oil outlet temperature sensor; The controller is electrically connected to the inlet mass flow meter, the outlet mass flow meter, the inlet temperature sensor, and the outlet temperature sensor, respectively. And a cut-off execution module, electrically connected to the controller, for performing shutdown protection actions; The controller is configured to execute a temperature-compensated closed-loop mass volume balance algorithm. Based on the inlet temperature value collected by the inlet temperature sensor and the outlet temperature value collected by the outlet temperature sensor, the controller corrects the inlet flow rate reading of the inlet mass flow meter and the outlet flow rate reading of the outlet mass flow meter, respectively. The controller then calculates the difference between the corrected inlet flow rate value and the corrected outlet flow rate value. When the difference exceeds a preset safe mass flow rate threshold, a leak is identified, and a shutdown protection action is executed through the cut-off execution module.

2. The large transformer online live-line oil filtration device according to claim 1, characterized in that, The temperature-compensated closed-loop mass volume balance algorithm includes the following steps: Acquire the first temperature value T1 collected by the oil inlet temperature sensor and the second temperature value T2 collected by the oil outlet temperature sensor; Based on the pre-stored viscosity-temperature characteristic curve μ(T) of the transformer oil, calculate the first compensation coefficient k1 corresponding to T1 and the second compensation coefficient k2 corresponding to T2 according to the formula k(T)=μ(T0) / μ(T), where T0 is the preset reference temperature; Multiply the original reading of the inlet mass flow meter by the first compensation coefficient to obtain the corrected inlet flow value Q_in; Multiply the original reading of the oil outlet mass flow meter by the second compensation coefficient to obtain the corrected oil outlet flow value Q_out; Calculate the flow difference, which is the absolute value of the difference between the corrected inlet flow rate Q_in and the corrected outlet flow rate Q_out, ΔQ = |Q_in - Q_out|. When the flow difference ΔQ is greater than or equal to the preset safety threshold, a leakage alarm signal is triggered.

3. The large transformer online live-line oil filtration device according to claim 1, characterized in that, Both the inlet and outlet mass flow meters are Coriolis mass flow meters, and both the inlet and outlet temperature sensors are platinum resistance temperature sensors.

4. The large transformer online live-line oil filtration device according to claim 1, characterized in that, The preset safety threshold is the mass flow rate value corresponding to a volumetric flow rate of 6 liters per hour.

5. The large transformer online live-line oil filtration device according to claim 1, characterized in that, The inlet pipeline is also equipped with an inlet pressure sensor, and the outlet pipeline is also equipped with an outlet pressure sensor. The controller is also used to calculate the pressure difference based on the inlet pressure value collected by the inlet pressure sensor and the outlet pressure value collected by the outlet pressure sensor, and compare the pressure difference with a preset pressure difference threshold. The controller only determines that a leak has occurred when the flow difference exceeds a preset safety threshold and the pressure difference between the inlet pressure value and the outlet pressure value is less than a preset lower limit threshold for pressure difference. This forms a dual judgment logic of flow and pressure, avoiding misjudgment caused by the flow meter itself malfunctioning.

6. The large transformer online live-line oil filtration device according to claim 1, characterized in that, It also includes an alarm module, which is electrically connected to the controller and is used to issue an audible and visual alarm signal when a leak is detected.

7. The large transformer online live-line oil filtration device according to claim 6, characterized in that, The cut-off execution module is installed on the oil inlet pipeline and the oil outlet pipeline, including a first pneumatic cut-off valve installed on the oil inlet pipeline and a second pneumatic cut-off valve installed on the oil outlet pipeline. Both the first pneumatic cut-off valve and the second pneumatic cut-off valve are electrically connected to the controller. When the controller determines that there is a leak, it outputs a cut-off signal to close the first pneumatic cut-off valve and the second pneumatic cut-off valve within a preset time.

8. The large transformer online live-line oil filtration device according to claim 1, characterized in that, It also includes a remote monitoring terminal, which is connected to the controller via an Ethernet or 5G wireless network. The remote monitoring terminal is used to display the detection data of the inlet mass flow meter, the outlet mass flow meter, the inlet temperature sensor and the outlet temperature sensor in real time, and to remotely send a shutdown command to the controller.

9. A control method for a large transformer online live-line oil filtration device based on any one of claims 1 to 8, characterized in that, Includes the following steps: Step S0: Fill the device with oil and vent the air, and purge the air from the oil inlet pipe, oil outlet pipe and oil filter unit; Step S1: Start the inlet and outlet oil pumps to establish external circulation of transformer oil; Step S2: Use the inlet mass flow meter and the outlet mass flow meter to collect the raw values ​​of the inlet flow rate and the outlet flow rate in real time, and use the inlet temperature sensor and the outlet temperature sensor to collect the inlet temperature value and the outlet temperature value in real time. Step S3: The controller corrects the original values ​​of the inlet flow rate and the outlet flow rate according to the inlet temperature value and the outlet temperature value, respectively, to obtain the compensated inlet flow rate value and the compensated outlet flow rate value; Step S4: Calculate the difference between the compensated inlet flow rate and the compensated outlet flow rate; Step S5: If the difference is greater than the preset safety threshold, the controller immediately cuts off the power supply to the oil inlet pump, the oil outlet pump and the heater, and issues an audible and visual alarm signal.

10. The control method according to claim 9, characterized in that, The correction process in step S3 is implemented using linear interpolation or a lookup table method based on the viscosity-temperature characteristic curve, wherein the viscosity-temperature characteristic curve is pre-stored in the memory of the controller.

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