A transformer on-load tap changer precise oil sampling control method and device

Abstract

The application discloses a transformer on-load tap-changer precise oil sampling control method and device, and relates to the field of transformer oil sampling. The application establishes a closed cycle between the oil discharge pipe and the oil injection pipe and confirms that the external oil lead pipe replacement is completed, and formal sampling is carried out after the closed lubrication of the sampling branch. During the formal sampling, the independent oil supplement branch supplements compatible insulating oil into the oil injection pipe simultaneously. The controller determines the equivalent under-supply amount according to the sampling volume, the equivalent oil supplement volume converted by temperature and the pressure elasticity correction amount, so that the equivalent under-supply amount is kept in a controlled under-supply window greater than zero, and the oil supplement front edge is migrated to the sampling source area on the oil discharge side according to the pre-labeled isolation equivalent volume. When the target sample volume is approached, the stop continuation volumes of the sampling side and the oil supplement side are predicted respectively, the sample outlet is closed first, and then the final volume and pressure are recovered through short-time residual oil supplement. The application takes into account the sample representativeness, synchronous oil supplement and small-volume quantitative accuracy.

Description

Technical Field

[0001] This invention relates to the field of on-load tap changer sampling technology, specifically to a method and device for precise oil sampling control of on-load tap changers in transformers. Background Technology

[0002] During load switching, on-load tap changers in transformers experience contact arcing and mechanical wear. The dissolved gas, moisture, and physicochemical properties of the insulating oil in their independent oil chambers reflect the internal operating status of the switch. On-site, it is typically necessary to periodically obtain oil samples ranging from 5 mL to 80 mL for dissolved gas analysis, trace moisture detection, or other oil quality tests.

[0003] The oil inlet and outlet pipes of on-load tap changers are typically led from the top of the equipment to an easily accessible location. Between two samplings, the insulating oil in the inlet pipe is replaced slowly, easily forming stagnant oil that differs from the state of the main oil. If sampling is taken directly from the end of the outlet pipe, the oil obtained initially is insufficient to fully represent the internal state of the on-load tap changer's oil chamber. Discharging large amounts of insulating oil to remove this stagnant oil will cause the oil level to drop and may necessitate additional operations such as oil replenishment, protection deactivation, and cross-shift coordination. Existing sampling methods propose using a pump to establish circulation between the outlet and inlet pipes, allowing the stagnant oil in the inlet pipe to return to the oil chamber for replacement; other methods use flow meters to separately measure the amount of oil discharged and replenished, and control the oil supply pump to replenish the oil chamber with an amount of insulating oil equal to the amount discharged. These methods can reduce oil level deficits, but if the amount of oil removed is directly used as the control target for the formal sampling phase, two problems still exist. On the one hand, the replenishing insulating oil in the oil replenishment and storage unit is usually at ambient temperature, while the on-load tap changer body oil is at operating temperature. The actual volume occupied by the same metering volume after temperature change is not exactly the same, and the oil circuit hoses, valve chambers, and sealing structures also have elastic oil storage and release with pressure changes. Therefore, the fact that the cumulative volumes displayed by the two flow meters are equal does not necessarily mean that the oil chamber has achieved true volume balance under working conditions. On the other hand, during formal sampling, the oil drain side continuously extracts oil, while the oil replenishment side simultaneously replenishes new oil into the oil chamber through the oil injection pipe. If the oil replenishment rate is too high or there is an instantaneous positive volume surplus on the oil replenishment side, the newly replenished oil may migrate quickly to the oil drain side along the low-resistance flow path inside the oil chamber, resulting in the presence of new replenished oil components in the formal sample, thereby reducing the representativeness of the sample to the state of the oil chamber before sampling. The more timely the oil replenishment, the better it is for maintaining the oil level, while the faster the oil replenishment, the more likely it is to shorten the isolation time between the oil replenishment front and the sampling source area, forming a direct technical contradiction.

[0004] Therefore, there is a need for an oil sampling and synchronous oil replenishment technology that can not only replenish oil simultaneously during formal sampling, but also unify the sampling representativeness constraint and volume compensation constraint into the same control process, and coordinate the processing of temperature-volume conversion, oil circuit pressure elasticity, oil replenishment front migration and pump valve stop hysteresis. Summary of the Invention

[0005] In order to solve the above-mentioned technical problems, or at least partially solve the above-mentioned technical problems, and in view of the above-mentioned shortcomings, the present invention proposes a method and device for precise oil sampling control of on-load tap changers of transformers.

[0006] In a first aspect, the present invention provides a precise oil sampling control method for an on-load tap changer of a transformer, applied to an oil sampling device connected to the drain pipe and the injection pipe of the on-load tap changer respectively, and comprising a volumetric sampling pump, a sampling flow detector, a sampling branch, a return path, a sample outlet, a sampling valve group, an oil replenishment and storage unit, an oil replenishment pump, an oil replenishment flow detector, an oil replenishment isolation valve, and an oil replenishment branch connected to the injection pipe; the control method includes: After pre-filling with oil, the sampling valve group is placed in circulation mode, so that the on-load tap changer oil chamber, oil drain pipe, oil sampling and synchronous oil replenishment device and oil injection pipe form a closed circulation oil circuit. The external oil inlet pipeline replacement is confirmed based on the cumulative actual volume of the main circulation and the state of the body oil. After the external oil inlet pipeline is replaced, keep the sample outlet closed, so that the insulating oil returns to the oil injection pipe through the sampling branch and return path, and perform closed-loop reflux rinsing on the sampling branch. After the rinsing meets the preset conditions, the sampling permission state is formed. Under the sampling permission state, reduce the sampling flow rate and complete the soft switching from the sampling branch to the sample outlet. When the actual sampling flow rate enters the stable range, open the oil replenishment isolation valve and slowly increase the output of the oil replenishment pump so that the replenished insulating oil enters the on-load tap changer oil chamber through the oil injection pipe. The cumulative sampling volume is determined based on the actual flow rate of the formal sampling. The cumulative equivalent oil replenishment volume, converted to the operating temperature of the on-load tap changer body oil, is determined based on the actual oil replenishment flow rate and oil replenishment temperature. The equivalent under-replenishment amount is determined based on the cumulative sampling volume, the cumulative equivalent oil replenishment volume, and the oil circuit pressure status. During the formal sampling period, the replenishment pump and the volumetric sampling pump are adjusted together to keep the equivalent under-replenishment amount within the preset under-replenishment window that is greater than zero, while ensuring that the isolation margin of the replenishment front line, determined based on the pre-calibrated isolation equivalent volume from the replenishment inlet to the sampling source area on the drain side, is not lower than the preset isolation threshold. When the cumulative sampling volume is close to the target sample volume, the continued sampling volume after the sampling side stops and the continued oil replenishment volume after the oil replenishment side stops are predicted respectively. First, the sampling side decelerates and closes the sample outlet. After the sample outlet is closed, the supplementary insulating oil used to eliminate the remaining equivalent under-replenishment amount continues to be added until the equivalent under-replenishment amount enters the termination tolerance and the oil circuit pressure is restored to the termination pressure range, and then the oil replenishment stops.

[0007] Furthermore, the minimum cumulative replacement constraint requires that the cumulative actual volume of the main circulation, obtained by time integration based on the actual flow rate of the main circulation, should not be less than the replacement coefficient multiple of the equivalent retention volume; the equivalent retention volume is determined based on the length and inner diameter of the oil drain pipe and the oil injection pipe, as well as the calibrated volume of the internal cavity of the oil sampling device participating in the main circulation; under maintenance conditions, a reference oil sample is obtained from the near end of the oil chamber, and samples are taken at different cumulative circulation multiples to compare the deviation of the detection index with that of the reference oil sample; a replacement coefficient that makes the deviation stable within the allowable range is selected; The condition of the bulk oil includes temperature difference conditions and temperature stability conditions. The temperature difference condition is that within a continuous observation window, the maximum absolute difference between the oil temperature on the drain side and the reference temperature of the bulk oil is not greater than the temperature difference threshold. The temperature stability condition is that within the same continuous observation window, the maximum rate of change of the oil temperature on the drain side is not greater than the rate of change threshold.

[0008] Furthermore, the rinsing meets the preset conditions as follows: when the cumulative rinsing volume of the branch reaches a preset multiple of the calibrated retention volume of the sampling branch, a sampling permission state is formed. The cumulative rinsing volume is determined based on the calibrated retention volume of the sampling branch and the actual rinsing flow rate. Only when the cumulative rinsing volume reaches a preset rinsing coefficient multiple of the calibrated retention volume of the sampling branch is a formal sampling permission state formed.

[0009] Furthermore, before formal sampling, the oil replenishment branch is pre-charged and vented: the oil replenishment isolation valve is kept isolated from the oil injection pipe, the oil replenishment pump is driven to fill the upstream pipe section of the oil replenishment pump, oil replenishment flow detector and oil replenishment isolation valve with replenishing insulating oil, and the gas in the pipe section is discharged into the oil replenishment storage unit or independent venting chamber; after the establishment of continuous liquid phase in the oil replenishment branch is detected, the oil replenishment isolation valve is allowed to connect with the oil injection pipe.

[0010] Furthermore, the cumulative sampling volume is determined based on the actual flow rate of the formal sampling, and the cumulative equivalent replenishment volume, converted to the operating temperature of the on-load tap changer body oil, is determined based on the actual replenishment flow rate and replenishment temperature. Finally, the equivalent under-replenishment amount is determined based on the cumulative sampling volume, the cumulative equivalent replenishment volume, and the oil circuit pressure status, including: The cumulative sampling volume is determined by integrating the actual flow rate during formal sampling. The cumulative equivalent oil replenishment volume is obtained by integrating the actual oil replenishment flow rate over time and converting the volume according to the temperature difference between the temperature of the replenished insulating oil in the oil replenishment unit and the operating temperature of the on-load tap changer body oil. This is expressed as: ; in, To replenish the actual fuel flow rate, To compensate for the volumetric thermal expansion coefficient of the insulating oil, The operating temperature of the main oil. This is the oil replenishment temperature; The volume required for elastic recovery of the oil circuit is estimated by using the deviation of the pressure on the replenishment side relative to the reference pressure, based on the cumulative sampling volume. Cumulative equivalent oil replenishment volume The equivalent elastic volume correction amount of the oil circuit determines the equivalent under-compensation amount. , represented as: ; in, The equivalent hydraulic compliance coefficient of the oil circuit. The baseline pressure before formal sampling begins. This refers to the pressure readings taken during the formal sampling period, either at the oil replenishment access side or related to the oil chamber pressure.

[0011] Furthermore, the combined adjustment of the replenishment pump and the volumetric sampling pump to maintain the equivalent under-compensation amount within a preset under-compensation window greater than zero includes: setting the preset under-compensation window for the equivalent under-compensation amount as follows: ,and When the equivalent under-compensation amount Approaching the preset under-compensation window limit Increase the output of the make-up pump or reduce the formal sampling flow rate when the equivalent under-compensation amount is... Approaching the lower limit of the preset undercompensation window The output of the replenishing oil pump is limited to prevent a positive volume surplus from forming on the replenishing side during the formal sampling period, which would continuously drive the replenishing insulating oil to migrate toward the sampling source area on the drain side.

[0012] Furthermore, the process of ensuring that the isolation margin at the oil replenishment front, determined based on the pre-calibrated isolation equivalent volume from the oil replenishment inlet to the oil discharge side sampling source area, is not lower than a preset isolation threshold includes: For each type of on-load tap changer and piping layout, the isolation equivalent volume is pre-calibrated. ; After the replenishment side stops, the continued replenishment volume is caused by pump deceleration, valve closure, and elastic release of the oil circuit.

[0013] Based on the equivalent volume of isolation Cumulative equivalent oil replenishment volume And the predicted continuous volume of the refueling side Determine the isolation margin at the oil replenishment front. , represented as: ; During the formal sampling period, it is required to replenish the oil front isolation margin. The oil replenishment flow rate shall not be lower than the preset isolation threshold. When the isolation margin at the oil replenishment front is lower than the first isolation threshold, the oil replenishment flow rate shall be reduced first. When the reduction of the oil replenishment flow rate causes the equivalent under-replenishment amount to approach the upper limit of the preset under-replenishment window, the formal sampling flow rate shall be reduced simultaneously so that the oil replenishment front isolation constraint and the equivalent under-replenishment constraint are satisfied at the same time. When the two cannot be satisfied at the same time, the sample outlet shall be closed first, and then the remaining oil replenishment shall be performed.

[0014] Furthermore, the calibrated isolation equivalent volume is determined by combining the geometric volume of the injection pipe, the effective mixing volume of the oil chamber, the geometric volume of the discharge pipe, and the sampling flow rate conditions. The minimum equivalent transport volume at which the effect of replenishment can be observed to begin reaching the discharge side is used as the conservative isolation equivalent volume. .

[0015] Furthermore, the sustained volume after stopping is estimated separately on both the sampling side and the refueling side: , ; in, , The total actuation delay of the pump valves on the sampling side and the replenishment side are respectively. , This is the correction coefficient for the elastic release of the corresponding oil circuit. The controller operates within the target sample volume. With cumulative sampling volume The difference should not exceed the sampling stop safety margin. and sampling side predicted continuation volume When the sample outlet is closed near the target volume, the sampling side deceleration and stop section is first entered. After the sample outlet is confirmed to be closed, the replenishment pump does not stop immediately, but continues to replenish the remaining equivalent amount of oil at a small flow rate. Corresponding replenishment of insulating oil; when the equivalent under-compensation amount Entering Termination Tolerance Once the pressure on the replenishment access side returns to the allowable range of the reference pressure before formal sampling, close the replenishment isolation valve and stop the replenishment pump.

[0016] Secondly, the present invention provides a device for precise oil sampling and synchronous oil replenishment of a transformer on-load tap changer, comprising: a first connection end, a second connection end, a volumetric sampling pump, a sampling flow detector, a sampling valve group, a sampling branch, a return path, a sample outlet, an oil discharge side temperature detector, a body oil reference temperature acquisition unit, a pressure detection component, a controller, an oil replenishment and storage unit, an oil replenishment pump, an oil replenishment flow detector, an oil replenishment temperature detector, an oil replenishment isolation valve, a check valve, and an oil replenishment branch; The first connection end is used to connect to the drain pipe of the on-load tap changer, and the second connection end is used to connect to the drain pipe of the on-load tap changer; the volumetric sampling pump, the sampling flow detector, and the sampling valve group are arranged between the first connection end and the second connection end, and the sampling valve group includes a first reversing valve and a second reversing valve. The first reversing valve is used to switch between the main circulation path and the sampling branch, and the second reversing valve is used to switch the outlet of the sampling branch between the return path and the sample outlet; The inlet of the sampling branch is connected to the closed-loop oil circuit via the sampling valve group, and the outlet of the sampling branch can be selectively connected to the return passage or the sample outlet. The return passage is connected to the second connection end. The oil replenishment branch is connected to the second connection end or the oil injection pipe downstream of the second connection end via the oil replenishment storage unit through the oil replenishment pump, oil replenishment flow detector, oil replenishment temperature detector, oil replenishment isolation valve and check valve, so that the replenished insulating oil during the formal sampling period can enter the on-load tap changer oil chamber in the equipment side compensation direction opposite to the sampling oil flow. The controller is connected to the volumetric sampling pump, the sampling flow detector, the sampling valve group, the oil discharge side temperature detector, the body oil reference temperature acquisition unit, the pressure detection component, the replenishment pump, the replenishment flow detector, the replenishment temperature detector, and the replenishment isolation valve, and is configured to execute the control method described above.

[0017] The technical solutions provided in the embodiments of the present invention have the following advantages compared with the prior art: This application reduces the need for separate oil replenishment after sampling and the associated protection operations and multi-shift coordination by simultaneously replenishing oil during the formal sampling process. This is achieved by ensuring that the final sample volume is not uniformly converted into a continuous oil deficit in the on-load tap changer oil chamber. The invention converts the replenishment volume to the operating temperature of the circuit and uses pressure changes to correct the elastic oil storage and release, shifting the control target from flowmeter reading balance to equivalent volume balance under operating conditions. During formal sampling, a controlled under-replenishment window is maintained to prevent a continuous positive volume surplus on the replenishment side. Furthermore, the isolation margin at the replenishment front limits the migration of the replenished insulating oil to the discharge side, which helps maintain the representativeness of the oil sample to the state of the circuit oil before sampling. When the replenishment front constraint conflicts with the volume under-replenishment constraint, this invention can simultaneously reduce the replenishment flow rate and sampling flow rate, and, if necessary, prioritize closing the sample outlet before completing the remaining replenishment, placing sample representativeness before replenishment speed in the control sequence. By predicting the continued volume after the pump valve stops on both the sampling and replenishment sides, and performing residual replenishment after the sample outlet is closed, the quantitative accuracy of small-volume samples and the final oil chamber volume recovery accuracy can be improved simultaneously. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the overall structure of the precise oil sampling and synchronous oil replenishment device of the present invention, which is connected to the on-load tap-out oil control pipe and the oil drain pipe. Figure 2 A block diagram showing the control relationship between the controller and the sampling flow rate, replenishment flow rate, temperature, pressure, sampling pump, replenishment pump, and valve group; Figure 3 This is the overall flowchart of the method for precise oil sampling control of on-load tap changer in transformers according to the present invention; Figure 4 The flowchart for determining the completion of the replacement of the main circulation cumulative volume and the state of the bulk oil as dual criteria; Figure 5 A schematic diagram illustrating the coordinated control of equivalent under-compensation and the isolation margin at the replenishment front during the formal sampling period; Figure 6 This is a time sequence diagram showing the relationship between sampling flow rate, replenishment flow rate, sample outlet, and replenishment isolation valve.

[0021] Reference numerals in the attached diagram: 1. On-load tap changer oil chamber; 2. Drain pipe; 3. Injection pipe; 10. First connection end; 20. Second connection end; 30. Volumetric sampling pump; 40. Sampling flow detector; 50. First directional valve; 60. Sampling branch; 70. Second directional valve; 80. Return passage; 90. Sample outlet; 100. Drain side temperature detector; 110. Body oil reference temperature acquisition unit; 120. Pressure detection component; 130. Controller; 140. Sealed sampling container; 150. Oil replenishment and storage unit; 160. Oil replenishment pump; 170. Oil replenishment flow detector; 180. Oil replenishment temperature detector; 190. Oil replenishment isolation valve; 200. Check valve; 210. Oil replenishment branch. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0024] Example 1 Reference Figure 1 As shown, this invention provides a precise oil sampling control device for on-load tap changers of transformers, comprising: two detachable sealed connection ends. The first connection end 10 is connected to the on-load tap changer oil drain pipe 2, and the second connection end 20 is connected to the oil injection pipe 3. Between the first connection end 10 and the second connection end 20, an inlet pressure detection point, a volumetric pump 30, an outlet pressure detection point, a flow detector 40, and a first reversing valve 50 are sequentially arranged. One path of the first reversing valve 50 forms a main circulation path through the return passage 80 to the second connection end 20, and the other path is connected to a sampling branch 60. The end of the sampling branch 60 is connected to a second reversing valve 70. One path of the second reversing valve 70 is connected back to the second connection end 20 through the return passage 80, and the other path is connected to the sample outlet 90. Thus, the sampling branch 60 has three different states: bypassed during main circulation; oil returns to the oil injection pipe via the return passage after passing through the sampling branch during branch flushing; and oil enters the sealed sampling container 140 via the sampling branch during formal sampling. Pressure detection components 120 are installed at the inlet and outlet pressure detection points to detect the inlet and outlet pressures of the positive displacement pump and obtain the pressure difference between the two ends of the pump.

[0025] The drain side temperature detector 100 is located after the first connection end 10 and before the positive displacement pump 30 to detect the actual oil temperature entering the device from the drain pipe. The body oil reference temperature acquisition unit 110 uses a contact temperature sensor attached to the outer wall of the on-load tap changer oil chamber or to the upper oil pipe near the oil chamber.

[0026] like Figure 2As shown, the controller 130 is connected to the aforementioned sensor, positive displacement pump 30, and two directional valves. All hoses, seals, and valve bodies inside the device that come into contact with oil are made of materials compatible with transformer insulating oil, and the sampling circuit is kept sealed before operation. The first and second connection ends use quick-connect or flange adapters that match the standard specifications of existing oil filling and draining pipes, and a misconnection prevention structure prevents the two ends from being connected in reverse.

[0027] The first connection end 10 of the oil sampling and synchronous oil replenishment device is connected to the on-load tap changer drain pipe 2, and the second connection end 20 is connected to the oil injection pipe 3. In the main circulation state, the drain pipe 2, the internal passage of the device, the oil injection pipe 3, and the on-load tap changer oil chamber 1 form a closed loop. The sampling branch is selectively connected to the return passage or the sample outlet through the sampling valve assembly.

[0028] The oil replenishment unit is independently located outside the sampling circuit. The oil replenishment and storage unit 150 is connected to the second connection terminal or the oil injection pipe downstream of the second connection terminal via an oil replenishment pump 160, an oil replenishment flow detector 170, an oil replenishment temperature detector 180, an oil replenishment isolation valve 190, and a check valve 200. The check valve 200 only allows the replenished insulating oil to flow towards the oil injection pipe 3, preventing backflow of equipment oil when the oil replenishment pump stops. The oil replenishment isolation valve 190 remains closed during main circulation replacement and sampling branch return flushing; the oil replenishment branch is only allowed to connect to the oil injection pipe after the formal sampling flow rate is established. The oil replenishment pump and the positive displacement sampling pump use independent drive channels, and the controllers adjust the sampling flow rate and oil replenishment flow rate separately. The oil replenishment and storage unit 150 preferably adopts an airtight structure, storing replenished insulating oil of the same grade or with confirmed compatibility. For scenarios requiring dissolved gas analysis in the oil, the replenished insulating oil is pre-degassed, filtered, and its contact with air is minimized. The replenishing pump 160 and the volumetric sampling pump 30 are each equipped with an independent driver, and the controller 130 can provide flow rates to both sides respectively.

[0029] Example 2 like Figure 3 and Figure 6 As shown, this embodiment of the invention provides a precise oil sampling control method for on-load tap changers of transformers, applied to an oil sampling device connected to the drain pipe and injection pipe of the on-load tap changer respectively, and including a volumetric sampling pump, a sampling flow detector, a sampling branch, a return path, a sample outlet, a sampling valve group, an oil replenishment and storage unit, an oil replenishment pump, an oil replenishment flow detector, an oil replenishment isolation valve, and an oil replenishment branch connected to the injection pipe; the control method includes: After the oil sampling device is pre-filled and connected on-site, the controller 130 loads the parameters of the drain pipe 2, fill pipe 3, and main circulation volume corresponding to the device model. The first reversing valve 50 is placed in the main circulation position, the second reversing valve 70 keeps the sample outlet isolated, and the oil replenishment isolation valve 190 remains closed. The volumetric sampling pump 30 first runs at low speed and judges whether the interface is open, whether the oil circuit is continuous, and whether there is obvious leakage based on the inlet pressure, actual flow rate, and valve position feedback.

[0030] After the self-test is passed, the sampling valve group is placed in the circulation state, so that the oil chamber 1, oil drain pipe 2, first connection end 10, volumetric sampling pump 30, sampling flow detector 40, first reversing valve 50, second connection end 20 and oil injection pipe 3 form a closed circulation oil circuit, thereby increasing the main circulation flow.

[0031] like Figure 4 As shown, in the main loop phase, the controller adjusts the flow rate based on the actual loop volume. Calculate the cumulative actual volume of the main loop, and use the cumulative volume of the main loop as the basis. The minimum replacement amount constraint is set at a preset replacement multiple that reaches the equivalent retention volume of the external oil passage. The proximity and stability of the oil temperature on the drain side with the reference temperature of the main body oil are used to confirm that the thermal front of the main body oil has been reached. Only when both the minimum cumulative replacement amount constraint and the main body oil arrival status are met is the replacement of the external oil inlet pipe considered complete.

[0032] The minimum cumulative replacement volume constraint requires that the cumulative actual volume of the main circulation, obtained by time integration of the actual flow rate of the main circulation measured by the sampling flow detector 40, should not be less than the replacement coefficient multiple of the equivalent retention volume; the equivalent retention volume is determined based on the length and inner diameter of the oil discharge pipe and the oil injection pipe, as well as the calibration volume of the internal cavity of the oil sampling device participating in the main circulation, and is expressed as follows: ; in, For equivalent retention volume, and The first The inner diameter and length of the pipeline section. The internal cavity of the oil sampling device participating in the main circulation is calibrated to a certain volume, where n is the number of pipe sections.

[0033] When first applied to a certain type of on-load tap changer, a reference oil sample was obtained from the near end of the oil chamber under maintenance conditions. Simultaneously, the oil removal device of this invention was used to take samples at different cumulative cycle multiples, comparing the deviations of dissolved gas, trace water, or other target detection indicators with the reference oil sample. Based on this, a replacement coefficient was selected to stabilize the deviation within the allowable range. This embodiment takes It is between 1.2 and 3.

[0034] The condition of the bulk oil includes temperature difference conditions and temperature stability conditions. The temperature difference condition is that the oil is in a length of... Oil temperature on the drain side within the continuous observation window Reference temperature of the main oil The maximum absolute difference is not greater than the temperature difference threshold. Temperature stability condition: the maximum rate of change of oil temperature on the drain side within the same continuous observation window does not exceed the rate of change threshold. .

[0035] The initial temperature of the oil discharge side is obtained at the start of the main circulation. The body oil of an on-load tap changer in operation maintains a relatively stable reference temperature due to equipment load, switch operation, and oil chamber heat exchange. Oil that remains in the external oil inlet pipe for an extended period is more likely to approach ambient temperature. As the main circulation proceeds, the oil remaining in the drain pipe enters the unit first, followed by the main body oil gradually flowing out of the oil chamber. Therefore, the temperature on the drain side... Typically, a temperature shift occurs from the initial temperature to the body reference temperature. Transitional situations.

[0036] When the accumulated actual volume of the main circulation has not yet reached the replacement coefficient multiple of the equivalent retention volume, no determination of the oil arrival state is performed; when it reaches the replacement coefficient multiple of the equivalent retention volume, the controller opening length is... The sliding observation window. If the oil temperature on the drain side... Reference temperature of the main oil maximum absolute difference Not greater than the temperature difference threshold And the maximum rate of change of oil temperature on the drain side Not greater than the rate of change threshold Then, the minimum cumulative replacement amount constraint and the condition for the state of the bulk oil are determined.

[0037] For example, in operating conditions where there is a significant initial temperature difference between the bulk oil and the external dead oil, the temperature difference threshold... The temperature is set to 0.5℃ to 3℃ based on the temperature sensor accuracy and on-site fluctuations, and the length of the sliding observation window is [not specified]. Set the time to 5s to 60s. Parameters should be determined through calibration. Output a replacement completion flag when both the cumulative volume condition and the condition for the oil to reach its final state are met. When the temperature of the oil and the ambient temperature are close, and the thermal front identification condition is insufficient, a conservative mode is used to continue cycling until a larger cumulative volume is reached before sampling, or an auxiliary state sensor capable of detecting the dielectric and conductive characteristics of the oil is added to form an alternative condition for thermal front identification. The conservative or alternative modes are used to improve field adaptability and do not change the dual-criteria main control process of this embodiment.

[0038] After the replacement is completed, the sample outlet remains closed. The controller connects the end of the sampling branch to the return path, allowing the main body oil to flow through the sampling branch and valve chamber before returning to the oil injection pipe. This performs closed-loop reflux rinsing of the sampling branch, and a sampling-allowed state is established after the rinsing meets preset conditions. The sampling-allowed state is established when the cumulative rinsing volume of the branch reaches a preset multiple of the calibrated retention volume of the sampling branch.

[0039] In the specific implementation process, after the replacement is completed, the first reversing valve 50 controls the oil flow to enter the sampling branch 60, while the second reversing valve 70 remains connected to the return passage 80. After the oil flows through the sampling hose, valve chamber, and upstream area of ​​the sample outlet 90, it returns to the second connection end 20 and the oil injection pipe 3 through the return passage 80. The controller determines the cumulative rinsing volume based on the calibrated retention volume of the sampling branch and the actual rinsing flow rate; when the cumulative rinsing volume reaches a preset rinsing coefficient multiple of the calibrated retention volume of the sampling branch, a formal sampling permission state is formed. During this process, the sample outlet 90 remains closed, and the oil replenishment isolation valve 190 also remains closed. After the replacement, the oil in the device pipeline is determined to be from the on-load tap changer, and the sampling branch is subsequently cleaned.

[0040] The controller pre-stores the calibrated retention volume of the sampling branch. During the branch flushing process, the actual flushing flow rate measured by the integral sampling flow detector 40 yields the cumulative flushing volume, which reaches the calibrated retention volume of the sampling branch. Only after the lubrication coefficient is multiplied by a factor of 2 is the sampling branch deemed ready for formal sampling. The lubrication coefficient is calibrated through a residual test of the sampling branch, for example, taking a value of 2 to 5. Since all the lubrication oil returns to the oil chamber, no increase in the amount of oil discharged during this stage is observed.

[0041] Before formal sampling, the replenishment branch undergoes pre-charging and venting. The replenishment isolation valve remains isolated from the oil injection pipe, and the replenishment pump drives the replenishment insulating oil to fill the upstream pipe section of the replenishment pump, flow meter, temperature detector, and replenishment isolation valve, establishing a continuous liquid phase in the replenishment branch. The replenishment insulating oil is preferably an insulating oil compatible with the oil in the sampled equipment, degassed, filtered, and stored in a sealed container.

[0042] Specifically, the replenishing oil pump 160 operates at a low flow rate, and the replenishing oil isolation valve 190 remains isolated from the oil injection pipe 3, allowing the replenishing insulating oil to fill the replenishing oil pump 160, the replenishing oil flow detector 170, the replenishing oil temperature detector 180, and the upstream pipe section of the replenishing oil isolation valve 190. For structures with an independent venting chamber, the gas is discharged through the venting chamber; for structures with a return pre-charge channel, the pre-charged oil pushes the gas back to the replenishing oil storage unit 150. When the replenishing oil flow detector 170 detects a continuous and stable liquid phase, and the replenishing oil pump outlet pressure can be established normally, the controller marks the replenishing branch as ready. This step is used to avoid pressure disturbances in the oil chamber or the introduction of air bubbles caused by sudden air intake in the replenishing branch during the formal sampling process.

[0043] After formal sampling begins, the controller first reduces the sampling flow rate and completes a soft switch from the sampling branch to the sample outlet. Once the actual sampling flow rate enters the stable range, the controller opens the replenishing oil isolation valve and slowly increases the output of the replenishing oil pump, allowing the replenishing insulating oil to enter the on-load tap changer oil chamber via the oil injection pipe.

[0044] In the specific implementation process, the controller first reduces the volumetric sampling pump 30 to the reversing flow rate, and the second reversing valve 70 switches from the return passage 80 to the sample outlet 90. After the sample outlet is connected to the sealed sampling container 140, the volumetric sampling pump 30 is gradually increased to the formal sampling target flow rate. After the actual sampling flow rate stabilizes, the replenishment isolation valve 190 is opened and the replenishment pump 160 is started.

[0045] During the formal sampling period, the cumulative sampling volume is determined based on the actual flow rate of the formal sampling. The cumulative equivalent replenishment volume, converted to the operating temperature of the on-load tap changer body oil, is determined based on the actual replenishment flow rate and replenishment temperature. The equivalent under-replenishment amount is then determined based on the cumulative sampling volume, the cumulative equivalent replenishment volume, and the oil circuit pressure status. The specific process is as follows: The cumulative sampling volume, determined by integrating the actual flow rate from the formal sampling, is expressed as follows: ; in, To formally sample the actual flow rate, This marks the start time of the formal sampling process.

[0046] The cumulative equivalent oil replenishment volume is obtained by integrating the actual oil replenishment flow rate over time and converting the volume according to the temperature difference between the temperature of the replenished insulating oil in the oil replenishment unit and the operating temperature of the on-load tap changer body oil. This is expressed as: ; in, To replenish the actual fuel flow rate, To compensate for the volumetric thermal expansion coefficient of the insulating oil, The operating temperature of the main oil. The oil replenishment temperature is used. For field conditions with small temperature differences, a linear thermal expansion approximation is adopted; for conditions with large temperature differences, a nonlinear conversion is performed using an oil temperature-density calibration table.

[0047] To incorporate the impact of elastic oil storage and release on volume balance into the control, the volume required for elastic recovery of the oil circuit is estimated by using the deviation of the replenishment inlet pressure relative to the reference pressure, based on the cumulative sampling volume. Cumulative equivalent oil replenishment volume The equivalent elastic volume correction amount of the oil circuit determines the equivalent under-compensation amount. , represented as: ; in, The equivalent hydraulic compliance coefficient of the oil circuit. The baseline pressure before formal sampling begins. This refers to the pressure readings taken during the formal sampling period, either at the oil replenishment access side or related to the oil chamber pressure. When formal sampling causes a pressure drop... This indicates the equivalent elastic volume that needs to be replenished to restore the hydraulic pressure to its pre-sampling state.

[0048] For example, when the target sample volume is 50 mL, the working window for the equivalent under-compensation is calibrated to a range of several milliliters to tens of milliliters, based on the equipment's allowable oil level changes and pressure characteristics. The controller ensures that the replenishment amount lags slightly behind the sampling amount, always maintaining a small positive under-compensation. This reduces the active flow from the replenishment side to the discharge side while maintaining a relatively stable oil level and pressure.

[0049] During the formal sampling period, the replenishment pump and the volumetric sampling pump are adjusted together to keep the equivalent under-replenishment amount within a preset under-replenishment window that is greater than zero. At the same time, the isolation margin of the replenishment front line, determined based on the pre-calibrated isolation equivalent volume from the replenishment inlet to the sampling source area on the drain side, is not lower than the preset isolation threshold.

[0050] The combined regulation of the replenishment pump and the positive displacement sampling pump to keep the equivalent under-compensation amount within a preset under-compensation window that is greater than zero includes: setting the preset under-compensation window for the equivalent under-compensation amount as follows: ,and When the equivalent under-compensation amount Approaching the preset under-compensation window limit Increase the output of the make-up pump or reduce the formal sampling flow rate when the equivalent under-compensation amount is... Approaching the lower limit of the preset undercompensation window The output of the replenishing oil pump is limited to prevent a continuous positive volume surplus from forming on the replenishing side during the formal sampling period, which would drive the replenished insulating oil towards the sampling source area on the drain side. A controlled, slightly under-replenished state is maintained during sampling. This slightly under-replenished state prevents a continuous positive volume surplus from forming on the replenishing side, thus avoiding the active pushing of newly replenished insulating oil towards the drain side in pursuit of instantaneous equal quantities. Simultaneously, Limit the maximum allowable volume deficit to avoid a significant drop in oil level and pressure in the oil chamber.

[0051] The process of ensuring that the isolation margin at the oil replenishment front, determined based on the pre-calibrated isolation equivalent volume from the oil replenishment inlet to the oil discharge side sampling source area, is not less than a preset isolation threshold includes: To prevent newly added insulating oil from significantly entering the sample source area on the drain side before the sampling is completed, the equivalent isolation volume is pre-calibrated for each type of on-load tap changer and pipeline layout. The isolation equivalent volume To determine the pre-calibrated equivalent transport volume corresponding to the migration of replenished insulating oil from the replenishment access point to the sampling source area on the drain side before it causes a detectable replenishment effect under the current topology of the oil injection pipe, oil chamber, and drain pipe connection, the isolation equivalent volume is calibrated by combining the geometric volume of the oil injection pipe, the effective mixing volume of the oil chamber, the geometric volume of the drain pipe, and the sampling flow rate conditions. The minimum equivalent transport amount at which the replenishment effect can be observed to begin reaching the drain side is used as the conservative isolation equivalent volume. For the same type of on-load tap changer and its oil inlet pipe arrangement, the controller pre-stores the equivalent isolation volume from the oil replenishment inlet to the oil drain side sampling source area. .

[0052] After the replenishment side stops, the continued replenishment volume is caused by pump deceleration, valve closure, and elastic release of the oil circuit. .

[0053] Based on the equivalent volume of isolation Cumulative equivalent oil replenishment volume And the predicted continuous volume of the refueling side Determine the margin of the oil replenishment front , represented as: ; like Figure 5 As shown, during the formal sampling period, it is required to replenish the oil front isolation margin. Not lower than the preset isolation threshold. When the isolation margin at the oil replenishment front is... When the flow rate falls below the first isolation threshold, the replenishment flow rate is preferentially reduced. If reducing the replenishment flow rate causes the equivalent under-replenishment amount to approach the upper limit of the preset under-replenishment window, the formal sampling flow rate is simultaneously reduced to ensure that both the replenishment front isolation constraint and the equivalent under-replenishment constraint are satisfied simultaneously. If both cannot be satisfied simultaneously, the sample outlet is closed first, and then the remaining replenishment is performed. When the replenishment front isolation margin... When the oil supply is sufficient, the replenishment flow rate is mainly determined by the amount of insufficient replenishment and pressure feedback; when the replenishment front has a clearance margin... When the flow rate approaches the first isolation threshold, the replenishment flow rate is first limited. If this causes the equivalent under-replenishment amount to approach the upper limit, the flow rate of sampling pump 30 is reduced, causing both the sampling-side output and the replenishment-side input to decrease simultaneously, thus extending the isolation time. If both constraints cannot be satisfied simultaneously at the minimum allowable sampling flow rate, the sample outlet 90 is immediately closed, and the process switches to residual replenishment mode.

[0054] As the sample approaches the target volume, the controller estimates the volume using the actual flow rate on the sampling side, the execution delay on the sampling side, and the differential pressure in the sampling oil circuit. And it uses the actual flow rate on the replenishment side, the execution delay on the replenishment side, and the pressure difference of the replenishment branch to estimate The estimated sustained volume after stopping is expressed as follows for both the sampling side and the replenishment side: , ; in, , The total actuation delay of the pump valves on the sampling side and the replenishment side are respectively. , This is the correction coefficient for the elastic release of the corresponding oil circuit. The controller operates within the target sample volume. With cumulative sampling volume The difference should not exceed the sampling stop safety margin. and sampling side predicted continuation volume When the sample outlet is closed near the target volume, the sampling side deceleration and stop section is first entered. After the sample outlet is confirmed to be closed, the replenishment pump does not stop immediately, but continues to replenish the remaining equivalent amount of oil at a small flow rate. Corresponding replenishment of insulating oil; when the equivalent under-compensation amount Entering Termination Tolerance Furthermore, once the pressure on the replenishment access side returns to the allowable range of the reference pressure before formal sampling, the replenishment isolation valve is closed and the replenishment pump is stopped. In this way, most of the replenishment during sampling is completed simultaneously with the sampling process, and the final volume balance is restored only through short-term residual replenishment after the sample outlet is closed.

[0055] When insufficient replenishment flow causes a pressure drop, increase the replenishment flow rate within the allowable isolation margin at the replenishment front. When the replenishment pressure rises too quickly or exceeds the upper limit, immediately reduce the replenishment flow rate. If sampling flow interruption, abnormal replenishment flow rate, air intake in the replenishment branch, check valve failure, or inconsistent valve position feedback are detected, the controller first closes the sample outlet 90, then closes the replenishment isolation valve 190, and stops the pump. When the target sample volume... Compared with the current cumulative sampling volume The difference is no greater than the predicted continuation volume on the sampling side. With stopping safety margin When the summation occurs, the controller first reduces the output of the volumetric sampling pump 30 and closes the sample outlet 90. At this time, the replenishing oil pump 160 continues to operate at low speed because the sample is now isolated from the oil chamber, and there is no longer any issue of replenishing insulating oil affecting the current sample composition. Subsequently, the controller applies an equivalent under-compensation amount. The pressure recovery status serves as feedback for residual oil replenishment. When the equivalent under-replenishment amount... Entering Termination Tolerance Furthermore, once the pressure on the replenishment access side returns to the allowable range of the reference pressure before formal sampling, the replenishment isolation valve 190 is closed first, and then the replenishment pump 160 is stopped. Through this asymmetric stopping sequence, synchronous replenishment is achieved during the formal sampling stage, and the remaining slight under-replenishment amount can ultimately be made up.

[0056] During the formal sampling and simultaneous oil replenishment, the pressure detection component 120 monitors at least the inlet pressure of the sampling pump and the pressure at the oil replenishment access side. It further monitors the pressure difference across the sampling pump and the outlet pressure of the oil replenishment pump. The controller uses the lower pressure limit, upper pressure limit, and upper pressure difference limit as hard safety constraints.

[0057] The controller 130 will record the equipment number, target sample volume, main circulation cumulative volume, replacement completion time, branch rinsing volume, formal sampling cumulative volume, equivalent replenishment volume, and equivalent under-replenishment amount for each sampling. Maximum and minimum values The minimum value, sample outlet closing time, residual oil replenishment volume, and pressure anomaly events are associated with the sample number.

[0058] When first applied to a specific equipment model, the under-compensation window and hydraulic compliance coefficient were adjusted under maintenance conditions. Isolation equivalent volume The execution delays on both the sampling and replenishment sides are calibrated. Subsequent on-site sampling directly calls the corresponding equipment parameters and makes corrections based on the pressure response and replenishment residuals from multiple samplings.

[0059] In the embodiments provided by this invention, it should be understood that the disclosed structures and methods can be implemented in other ways. For example, the structural embodiments described above are merely illustrative. For instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection through some interfaces, structures, or units, and may be electrical, mechanical, or other forms.

[0060] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0061] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0062] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for precise oil sampling control of an on-load tap changer in a transformer, characterized in that, An oil sampling device is applied to the oil drain pipe and oil injection pipe of an on-load tap changer, and includes a volumetric sampling pump, a sampling flow detector, a sampling branch, a return path, a sample outlet, a sampling valve assembly, a replenishment and storage unit, a replenishment pump, a replenishment flow detector, a replenishment isolation valve, and a replenishment branch connected to the oil injection pipe; the control method includes: After pre-filling with oil, the sampling valve group is placed in circulation mode, so that the on-load tap changer oil chamber, oil drain pipe, oil sampling and synchronous oil replenishment device and oil injection pipe form a closed circulation oil circuit. The external oil inlet pipeline replacement is confirmed based on the cumulative actual volume of the main circulation and the state of the body oil. After the external oil inlet pipeline is replaced, keep the sample outlet closed, so that the insulating oil returns to the oil injection pipe through the sampling branch and return path, and perform closed-loop reflux rinsing on the sampling branch. After the rinsing meets the preset conditions, the sampling permission state is formed. Under the sampling permission state, reduce the sampling flow rate and complete the soft switching from the sampling branch to the sample outlet. When the actual sampling flow rate enters the stable range, open the oil replenishment isolation valve and slowly increase the output of the oil replenishment pump so that the replenished insulating oil enters the on-load tap changer oil chamber through the oil injection pipe. The cumulative sampling volume is determined based on the actual flow rate of the formal sampling. The cumulative equivalent oil replenishment volume, converted to the operating temperature of the on-load tap changer body oil, is determined based on the actual oil replenishment flow rate and oil replenishment temperature. The equivalent under-replenishment amount is determined based on the cumulative sampling volume, the cumulative equivalent oil replenishment volume, and the oil circuit pressure status. During the formal sampling period, the replenishment pump and the volumetric sampling pump are adjusted together to keep the equivalent under-replenishment amount within the preset under-replenishment window that is greater than zero, while ensuring that the isolation margin of the replenishment front line, determined based on the pre-calibrated isolation equivalent volume from the replenishment inlet to the sampling source area on the drain side, is not lower than the preset isolation threshold. When the cumulative sampling volume is close to the target sample volume, the continued sampling volume after the sampling side stops and the continued oil replenishment volume after the oil replenishment side stops are predicted respectively. First, the sampling side decelerates and closes the sample outlet. After the sample outlet is closed, the supplementary insulating oil used to eliminate the remaining equivalent under-replenishment amount continues to be added until the equivalent under-replenishment amount enters the termination tolerance and the oil circuit pressure is restored to the termination pressure range, and then the oil replenishment stops.

2. The method for precise oil sampling control of on-load tap changers in transformers according to claim 1, characterized in that, The minimum cumulative replacement volume constraint requires that the cumulative actual volume of the main circulation obtained by time integration based on the actual flow rate of the main circulation should not be less than the replacement coefficient multiple of the equivalent retention volume; the equivalent retention volume is determined based on the length and inner diameter of the oil drain pipe and the oil injection pipe, as well as the calibration volume of the internal cavity of the oil sampling device participating in the main circulation; under maintenance conditions, a reference oil sample is obtained from the near end of the oil chamber, and samples are taken at different cumulative circulation multiples to compare the deviation of the test indicators with the reference oil sample; a replacement coefficient that makes the deviation stable within the allowable range is selected; The condition of the bulk oil includes temperature difference conditions and temperature stability conditions. The temperature difference condition is that within a continuous observation window, the maximum absolute difference between the oil temperature on the drain side and the reference temperature of the bulk oil is not greater than the temperature difference threshold. The temperature stability condition is that within the same continuous observation window, the maximum rate of change of the oil temperature on the drain side is not greater than the rate of change threshold.

3. The method for precise oil sampling control of on-load tap changers in transformers according to claim 1, characterized in that, The rinsing meets the preset conditions as follows: when the cumulative rinsing volume of the branch reaches a preset multiple of the calibrated retention volume of the sampling branch, a sampling permission state is formed. The cumulative rinsing volume is determined based on the calibrated retention volume of the sampling branch and the actual rinsing flow rate. Only when the cumulative rinsing volume reaches a preset rinsing coefficient multiple of the calibrated retention volume of the sampling branch is a formal sampling permission state formed.

4. The method for precise oil sampling control of on-load tap changers in transformers according to claim 1, characterized in that, Before formal sampling, pre-charging and venting are performed on the oil replenishment branch: keep the oil replenishment isolation valve isolated from the oil injection pipe, drive the oil replenishment pump to fill the upstream pipe section of the oil replenishment pump, oil replenishment flow detector and oil replenishment isolation valve with replenishing insulating oil, and vent the gas in the pipe section into the oil replenishment storage unit or independent venting chamber; after the establishment of continuous liquid phase in the oil replenishment branch is detected, the oil replenishment isolation valve is allowed to be connected to the oil injection pipe.

5. The method for precise oil sampling control of on-load tap changers in transformers according to claim 1, characterized in that, The cumulative sampling volume is determined based on the actual flow rate of the formal sampling. The cumulative equivalent replenishment volume, converted to the operating temperature of the on-load tap changer body oil, is determined based on the actual replenishment flow rate and replenishment temperature. The equivalent under-replenishment amount is determined based on the cumulative sampling volume, the cumulative equivalent replenishment volume, and the oil circuit pressure status, including: The cumulative sampling volume is determined by integrating the actual flow rate during formal sampling. The cumulative equivalent oil replenishment volume is obtained by integrating the actual oil replenishment flow rate over time and converting the volume according to the temperature difference between the temperature of the replenished insulating oil in the oil replenishment unit and the operating temperature of the on-load tap changer body oil. This is expressed as: ； in, To replenish the actual fuel flow rate, To compensate for the volumetric thermal expansion coefficient of the insulating oil, The operating temperature of the main oil. This is the oil replenishment temperature; The volume required for elastic recovery of the oil circuit is estimated by using the deviation of the pressure on the replenishment side relative to the reference pressure, based on the cumulative sampling volume. Cumulative equivalent oil replenishment volume The equivalent elastic volume correction amount of the oil circuit determines the equivalent under-compensation amount. , represented as: ； in, The equivalent hydraulic compliance coefficient of the oil circuit. The baseline pressure before formal sampling begins. This refers to the pressure readings taken during the formal sampling period, either at the oil replenishment access side or related to the oil chamber pressure.

6. The method for precise oil sampling control of on-load tap changers in transformers according to claim 1, characterized in that, The combined regulation of the replenishment pump and the positive displacement sampling pump to keep the equivalent under-compensation amount within a preset under-compensation window that is greater than zero includes: setting the preset under-compensation window for the equivalent under-compensation amount as follows: ,and When the equivalent under-compensation amount Approaching the preset under-compensation window limit Increase the output of the make-up pump or reduce the formal sampling flow rate when the equivalent under-compensation amount is... Approaching the lower limit of the preset undercompensation window The output of the replenishing oil pump is limited to prevent a positive volume surplus from forming on the replenishing side during the formal sampling period, which would continuously drive the replenishing insulating oil to migrate toward the sampling source area on the drain side.

7. The method for precise oil sampling control of on-load tap changers in transformers according to claim 1, characterized in that, The process of ensuring that the isolation margin at the oil replenishment front, determined based on the pre-calibrated isolation equivalent volume from the oil replenishment inlet to the oil discharge side sampling source area, is not less than a preset isolation threshold includes: For each type of on-load tap changer and piping layout, the isolation equivalent volume is pre-calibrated. ; After the replenishment side stops, the continued replenishment volume is caused by pump deceleration, valve closure, and elastic release of the oil circuit. Based on the equivalent volume of isolation Cumulative equivalent oil replenishment volume And the predicted continuous volume of the refueling side Determine the isolation margin at the oil replenishment front. , represented as: ； During formal sampling, it is required to replenish the oil front isolation margin. The oil replenishment flow rate shall not be lower than the preset isolation threshold. When the isolation margin at the oil replenishment front is lower than the first isolation threshold, the oil replenishment flow rate shall be reduced first. When the reduction of the oil replenishment flow rate causes the equivalent under-replenishment amount to approach the upper limit of the preset under-replenishment window, the formal sampling flow rate shall be reduced simultaneously so that the oil replenishment front isolation constraint and the equivalent under-replenishment constraint are satisfied at the same time. When the two cannot be satisfied at the same time, the sample outlet shall be closed first, and then the remaining oil replenishment shall be performed.

8. The method for precise oil sampling control of on-load tap changers in transformers according to claim 7, characterized in that, The calibrated isolation equivalent volume is determined by considering the geometric volume of the injection pipe, the effective mixing volume of the oil chamber, the geometric volume of the discharge pipe, and the sampling flow rate. The minimum equivalent transport volume at which the effect of replenishment begins to be observed reaching the discharge side is taken as the conservative isolation equivalent volume. .

9. The method for precise oil sampling control of on-load tap changers in transformers according to claim 1, characterized in that, Estimate the sustained volume after stopping from both the sampling side and the replenishment side: ， ； in, , The total actuation delay of the pump valves on the sampling side and the replenishment side are respectively. , The corresponding oil circuit elastic release correction coefficient; the controller at the target sample volume With cumulative sampling volume The difference should not exceed the sampling stop safety margin. and sampling side predicted continuation volume When the sample outlet is closed near the target volume, the sampling side deceleration and stop section is first entered. After the sample outlet is confirmed to be closed, the replenishment pump does not stop immediately, but continues to replenish the remaining equivalent amount of oil at a small flow rate. Corresponding replenishment of insulating oil; when the equivalent under-compensation amount Entering Termination Tolerance Once the pressure on the replenishment access side returns to the allowable range of the reference pressure before formal sampling, close the replenishment isolation valve and stop the replenishment pump.

10. A device for precise oil sampling and synchronous oil replenishment from an on-load tap changer of a transformer, characterized in that, include: First connection end, second connection end, volumetric sampling pump, sampling flow detector, sampling valve group, sampling branch, return path, sample outlet, oil discharge side temperature detector, body oil reference temperature acquisition unit, pressure detection assembly, controller, oil replenishment and storage unit, oil replenishment pump, oil replenishment flow detector, oil replenishment temperature detector, oil replenishment isolation valve, check valve and oil replenishment branch; The first connection end is used to connect to the drain pipe of the on-load tap changer, and the second connection end is used to connect to the drain pipe of the on-load tap changer; the volumetric sampling pump, the sampling flow detector, and the sampling valve group are arranged between the first connection end and the second connection end, and the sampling valve group includes a first reversing valve and a second reversing valve. The first reversing valve is used to switch between the main circulation path and the sampling branch, and the second reversing valve is used to switch the outlet of the sampling branch between the return path and the sample outlet; The inlet of the sampling branch is connected to the closed-loop oil circuit via the sampling valve group, and the outlet of the sampling branch can be selectively connected to the return passage or the sample outlet. The return passage is connected to the second connection end. The oil replenishment branch is connected to the second connection end or the oil injection pipe downstream of the second connection end via the oil replenishment storage unit through the oil replenishment pump, oil replenishment flow detector, oil replenishment temperature detector, oil replenishment isolation valve and check valve, so that the replenished insulating oil during the formal sampling period can enter the on-load tap changer oil chamber in the equipment side compensation direction opposite to the sampling oil flow. The controller is connected to the volumetric sampling pump, the sampling flow detector, the sampling valve group, the oil discharge side temperature detector, the body oil reference temperature acquisition unit, the pressure detection component, the replenishing pump, the replenishing flow detector, the replenishing temperature detector, and the replenishing isolation valve, and is configured to execute the control method according to any one of claims 1 to 9.

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