Method and device for measuring direct-current resistance of on-load voltage regulating transformer

Abstract

The invention discloses an on-load tap changing transformer direct current resistance measuring method and device, and the method comprises the steps: carrying out the sampling of the current of each phase winding of a transformer in the same gear state at a plurality of moments, obtaining the first sampling current data, and obtaining the time constant estimation value of each phase winding based on the first sampling current data; selecting sampling current values at a plurality of continuous sampling moments from the first sampling current data as second sampling current data, and obtaining a direct current resistance estimation value of each phase winding based on the current stability of the second sampling current data; and fitting the first sampling current data, and obtaining the optimal direct current resistance value of each phase of winding after optimization through iteration as the direct current resistance measurement value of the corresponding winding. The method can effectively avoid the defects of long measurement time, high measurement time point requirement and large measurement result error, improves the accuracy and reliability of direct current resistance measurement, is suitable for direct current resistance measurement of various transformers, and has a wide application scene.

Description

Technical Field

[0001] The invention relates to the technical field of on-load transformers, and in particular to a method and a device for measuring the direct current resistance of an on-load voltage regulating transformer. Background Art

[0002] In the power industry, the normal operation of transformers is crucial to ensuring power supply. Transformer DC resistance testing is a key link to ensure its performance and safety, and can effectively identify hidden dangers such as manufacturing defects of transformer coils, loose connections, missing strands or broken wires. According to the requirements of the "Power Equipment Maintenance Test Regulations", power transformers need to undergo winding DC resistance testing every 3 or 6 years, and measurements must be taken at all tapping positions during the test.

[0003] However, there are many problems with traditional testing methods. First, the transformer's on-load tap changer stays in only one gear most of the time during actual operation, which may cause oxidation of the joints in other gears, thus affecting the accuracy of the measurement results. In order to ensure the effectiveness of the test, the tester needs to manually adjust the tap changer from one gear to another, usually requiring 3 to 5 rounds of repeated adjustments. In the case of severe oxidation, the number of adjustments may reach more than 10 rounds. This process is not only time-consuming and labor-intensive, but also requires special personnel to operate it, which increases labor costs.

[0004] Secondly, the current test of DC resistance of power transformers mainly relies on static measurement methods, such as loop resistance mutation method, high-voltage charging and low-voltage measurement method, magnetization method and short-circuit demagnetization method, etc. Most of these methods are based on measuring resistance after the test circuit reaches a steady state, and usually take several minutes or even longer to complete a test. This traditional "static" measurement method has shortcomings: First, since the power transformer winding can be equivalent to a series circuit model of an inductor L with a large inductance value and a resistor R with a small resistance value, the time constant τ=L / R, so the inherent time constant of the large-capacity transformer is relatively large. In the process of using the traditional measurement method, due to the existence of the above-mentioned large inductance, the self-inductance effect on the changing electric quantity is large, so that the current flowing through the winding cannot change suddenly. It is necessary to wait for the time constant τ for the current to reach the steady-state value before measurement can be performed. Since the measurement time required to wait for the current to reach the steady-state value is relatively long, the requirements for the measurement time point are extremely high, which can easily lead to large errors in the measurement results; Second, the stability and accuracy are insufficient: For transformers with star-delta (Y / Δ) connection, the traditional static measurement method is easily affected by the winding inductance and the connection method, resulting in current circulation interference test results and affecting measurement accuracy. Summary of the invention

[0005] The technical problem to be solved by the present invention is as follows: In view of the above-mentioned problems in the prior art, a method and a device for measuring the DC resistance of an on-load tap-changing transformer with high measurement efficiency and wide applicability are provided to achieve high-precision measurement of the DC resistance of the transformer.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: A method for measuring the DC resistance of an on-load voltage-regulating transformer, wherein the on-load voltage-regulating transformer comprises three-phase windings of phase A, phase B and phase C, including: Step S1, sampling the current of each phase winding of the transformer in the same gear state at multiple times to obtain corresponding first sampled current data, and obtaining a time constant estimation value of each phase winding based on the first sampled current data; Step S2, selecting a plurality of sampling current values ​​at consecutive sampling moments from the first sampling current data as second sampling current data, and obtaining an estimated value of a DC resistance of each phase winding based on the current stability of the second sampling current data; Step S3, fitting the first sampled current data and obtaining the optimal time constant value and the optimal DC resistance value of each phase winding after optimization through iteration, and taking the optimal DC resistance value as the DC resistance measurement value of the corresponding winding.

[0007] Furthermore, the step S1 comprises: Three or more sampling current values ​​at different sampling times are selected from the first sampling current data, and the time constant estimation value of the corresponding winding is calculated according to the ratio of the difference between the sampling times corresponding to adjacent sampling current values ​​and the difference between adjacent sampling current values.

[0008] Furthermore, the calculation expression of the estimated value of the time constant of the corresponding winding is:

[0009] In the above formula, is the estimated value of the time constant of the corresponding winding of the transformer, are three different sampling moments, for The sampled current value of the same winding corresponding to the sampling moment.

[0010] Furthermore, the step S2 comprises: Selecting three or more sampling current values ​​at three consecutive sampling moments from the first sampling current data, and calculating an estimated current value after the corresponding winding is stabilized according to the sampling current values; The current stability of the corresponding winding is obtained according to the ratio of the sampling current values ​​at the two most recent sampling moments among the sampling current values; After determining that the current stability of the three-phase windings is greater than the stability threshold, the DC resistance estimation value of the corresponding winding at the current gear is calculated according to the ratio of the transformer capacity and the estimated current value.

[0011] Furthermore, the calculation expression of the estimated current value after the corresponding winding is stabilized is:

[0012] In the above formula, are the estimated current values ​​of the A-phase, B-phase and C-phase windings respectively, They are the sampling current values ​​corresponding to three consecutive sampling moments of the A-phase winding, They are the sampling current values ​​corresponding to three consecutive sampling moments of the B-phase winding, They are the sampling current values ​​corresponding to three consecutive sampling moments of the C-phase winding.

[0013] Furthermore, the calculation expression of the current stability of each phase winding is:

[0014] In the above formula, They are the current stability of phase A, phase B and phase C windings respectively.

[0015] Furthermore, the calculation expression of the estimated value of the DC resistance of the corresponding winding at the current gear is:

[0016] In the above formula, are the estimated DC resistance of phase A, phase B and phase C windings at the current gear, and E is the transformer capacity.

[0017] Furthermore, the step S3 comprises: Obtaining an error function associated with a time constant and a DC resistance by fitting a plurality of sampling current values ​​of the first sampling current data and corresponding sampling moments based on a least square method; The error function is optimized according to the gradient descent method or the Newton-Raphson method with the estimated time constant and the estimated DC resistance as initial values, the values ​​of the time constant and the DC resistance are updated in each iteration, and the iteration is stopped when the error value of the error function is less than a preset threshold, and the DC resistance value obtained by the last update is used as the DC resistance measurement value of the corresponding winding.

[0018] Furthermore, the expression of the error function is:

[0019] In the above formula, S is the error function, n is the number of current data collected by the corresponding winding, and are the i-th sampling current value and the i-th sampling time of the corresponding winding, τ is the time constant of the corresponding winding, and R is the DC resistance of the corresponding winding; The calculation expression for updating the time constant value and DC resistance value is:

[0020] In the above formula, is the current updated DC resistance value, Indicates the DC resistance value before updating, is the time constant after the current update, is the time constant before updating, and η is the learning rate.

[0021] Furthermore, after step S3, the following steps are further included: Step S4, converting the obtained DC resistance measurement value of each phase winding to a DC resistance value at a preset temperature, and calculating the unbalance coefficient of the DC resistance of the three-phase winding according to the ratio of the difference between the maximum value and the minimum value of the converted DC resistance values ​​of each phase winding to the average value, and determining whether the transformer is operating normally according to the unbalance coefficient.

[0022] Furthermore, after step S4, the following steps are further included: Step S5, adjust the transformer gear to the next gear and repeat steps S1-S3 to measure the DC resistance value of the three-phase winding at the next gear, and repeat the operation until the measurement at all gears is completed.

[0023] The present invention further provides a device for measuring the DC resistance of an on-load voltage-regulating transformer, comprising: A gear adjustment module, used to adjust the gear state of the transformer; A measurement module is used to measure the real-time current data of each phase winding of the transformer at each gear position; The calculation module is used to calculate the estimated time constant and DC resistance of each phase winding according to the real-time current data, and to obtain the optimal DC resistance value of each phase winding through iteration according to the fitted real-time current data as the DC resistance measurement value of the corresponding winding.

[0024] Compared with the prior art, the advantages of the present invention are: The present invention estimates the time constant and the DC resistance of each phase winding of the transformer by sampling the first sampled current data to obtain a reference value, and then iterates by fitting the first sampled current data and continuously updates the time constant and the DC resistance values ​​on the basis of the reference value, and finally obtains the optimal value as the DC resistance measurement value of the corresponding winding. The operation is simple and efficient, and the shortcomings of long measurement time, high measurement time point requirements and large measurement result errors caused by current steady state can be effectively avoided, thereby improving the accuracy and reliability of transformer DC resistance measurement, and then being suitable for DC resistance measurement of various transformers, and having a wide range of application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The figure is a schematic diagram of a specific flow chart of a method for measuring the DC resistance of an on-load tap-changing transformer according to Embodiment 1 of the present invention. DETAILED DESCRIPTION

[0026] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0027] Example 1 like Figure 1 As shown, an embodiment of the present invention provides a method for measuring the DC resistance of an on-load tap-changing transformer, wherein the on-load tap-changing transformer includes three-phase windings of phase A, phase B and phase C, including: Step S1, sampling the current of each phase winding of the transformer in the same gear state at multiple times to obtain corresponding first sampled current data, and obtaining a time constant estimation value of each phase winding based on the first sampled current data; Step S2, selecting a plurality of sampling current values ​​at consecutive sampling moments from the first sampling current data as second sampling current data, and obtaining an estimated value of a DC resistance of each phase winding based on the current stability of the second sampling current data; Step S3, fitting the first sampled current data and obtaining the optimal time constant value and the optimal DC resistance value of each phase winding after optimization through iteration, and taking the optimal DC resistance value as the DC resistance measurement value of the corresponding winding.

[0028] It can be understood that in this embodiment, the time constant and the DC resistance of each phase winding of the transformer are estimated by sampling the first sampled current data to obtain a reference value, and then the first sampled current data is fitted to iterate and the time constant and the DC resistance value are continuously updated on the basis of the reference value, and finally the optimal value as the DC resistance measurement value of the corresponding winding is obtained. The operation is simple and efficient, and the shortcomings of long measurement time, high measurement time point requirements and large measurement result errors caused by current steady state can be effectively avoided, thereby improving the accuracy and reliability of transformer DC resistance measurement, and then being suitable for DC resistance measurement of various transformers, and having a wide range of application scenarios.

[0029] In this embodiment, step S1 includes: Three or more sampling current values ​​at different sampling times are selected from the first sampling current data, and the time constant estimation value of the corresponding winding is calculated according to the ratio of the difference between the sampling times corresponding to adjacent sampling current values ​​and the difference between adjacent sampling current values.

[0030] In a specific application embodiment, the three-point method is used as an example to explain step S1 in detail. Preferably, the current of each phase winding of the transformer in the same gear state is sampled by a DC resistance tester using the three-point method, and the time constant of each phase winding is estimated based on the sampled current data. Specifically, for the A phase, B phase, and C phase windings of the transformer, the three-point method current sampling refers to sampling the current at three different times. Collect the current value of the same winding separately , and use formula (1) to estimate the time constant of the corresponding winding (the three-phase windings estimate their respective time constants according to formula 1): (1) In the above formula, is the estimated value of the time constant of the corresponding winding of the transformer, are three different sampling moments, for The sampled current value of the same winding corresponding to the sampling moment.

[0031] In this embodiment, step S2 includes: Selecting three or more sampling current values ​​at three consecutive sampling moments from the first sampling current data, and calculating an estimated current value after the corresponding winding is stabilized according to the sampling current values; The current stability of the corresponding winding is obtained according to the ratio of the sampled current values ​​at the most recent two sampling moments in the sampled current values; after judging that the current stability of the three-phase windings is greater than the stability threshold, the DC resistance estimated value of the corresponding winding at the current gear is calculated according to the ratio of the transformer capacity and the estimated current value.

[0032] In the specific application embodiment, the three-point method is also used as an example to explain step S2 in detail. First, a DC resistance tester is used to measure the resistance of the resistor at n different time points. Sample n current data of each phase winding of the transformer respectively , select the three current data at the continuous sampling time, and estimate the DC resistance of the corresponding winding of the transformer (the estimated DC resistance of the three-phase windings A, B, and C are recorded as ), the specific steps are as follows: Step S21, estimating the stabilized current value of each phase winding of the transformer.

[0033] Assuming that each sampling time point is 5 seconds apart, the three consecutive sampling moments can be understood as collecting the current values ​​of each phase winding of the transformer at the start time (0 seconds), the middle time (5 seconds), and the subsequent time (10 seconds), respectively, which are recorded as (A phase winding sampling current), (B phase winding sampling current), (C phase winding sampling current), calculate the estimated current value after stabilization according to formula (2) : (2) In the above formula, are the estimated current values ​​of the A-phase, B-phase and C-phase windings respectively, They are the sampling current values ​​corresponding to three consecutive sampling moments of the A-phase winding, They are the sampling current values ​​corresponding to three consecutive sampling moments of the B-phase winding, They are the sampling current values ​​corresponding to three consecutive sampling moments of the C-phase winding.

[0034] Step S22, calculate the current stability c of each phase winding according to formula (3): (3) In the above formula, They are the current stability of phase A, phase B and phase C windings respectively.

[0035] Step S23, such as current stability Both are greater than the stability threshold (can be set according to actual needs), then it is judged that the current current has stabilized, and the direct resistance value of each phase winding of the transformer at the current gear is estimated according to formula (4): (4) In the above formula, are the estimated DC resistance of phase A, phase B and phase C windings at the current gear, and E is the transformer capacity.

[0036] It should be noted that if the current stability Not all above the stability threshold , then select the next set of 3 current data at the continuous sampling time from the n current data of each phase winding of the transformer and process again according to steps S21-S23 until the current stability is Both are greater than the stability threshold , and determine the direct resistance value of each phase winding .

[0037] In this embodiment, step S3 includes: fitting a plurality of sampling current values ​​of the first sampling current data and corresponding sampling moments to obtain an error function associated with a time constant and a DC resistance; The error function is optimized according to the gradient descent method or the Newton-Raphson method with the estimated time constant and the estimated DC resistance as initial values, the values ​​of the time constant and the DC resistance are updated in each iteration, and the iteration is stopped when the error value of the error function is less than a preset threshold, and the DC resistance value obtained by the last update is used as the DC resistance measurement value of the corresponding winding.

[0038] In a specific application embodiment, the time constant of the transformer is dynamically adjusted based on an adaptive multi-point fitting algorithm and the estimated DC resistance of the transformer is corrected and updated in real time. The specific steps are as follows: Step S31, the DC resistance tester is used to test the Sample n current data of each phase winding of the transformer respectively The error function S is generated by fitting. Specifically, in practical applications, in order to improve the accuracy, multiple sets of data points can be collected and fitted using the least squares method. Assume that n current data points are collected and the corresponding time points , then the fitting error function S is: (5) In the above formula, S is the error function, n is the number of current data collected by the corresponding winding, and are the i-th sampling current value and the i-th sampling moment of the corresponding winding respectively, τ is the time constant of the corresponding winding, and R is the DC resistance of the corresponding winding.

[0039] Step S32, in order to ensure the measurement accuracy, the error function S is minimized by using an iterative optimization algorithm. Minimizing the error S can obtain the optimal R and τ values ​​through an iterative algorithm. Specifically, the error function S can be optimized by using a gradient descent method or a Newton-Raphson method, and the values ​​of R and τ can be adjusted to ensure the measurement accuracy. The update formula is as follows: (6) In the above formula, is the current updated DC resistance value, Indicates the DC resistance value before updating, is the time constant after the current update, is the time constant before updating, η is the learning rate, which is used to control the step size of parameter adjustment; The initial value of is the estimated DC resistance value determined in step S23 according to formula (4), The initial value of is the estimated value of the time constant determined in step S1 according to formula (1).

[0040] Step S33: Convergence judgment: When the error function S is less than a preset threshold , or the parameter changes ΔR, Δτ are small enough, the measurement results are considered to have reached satisfactory accuracy, and the iteration is stopped. As the time constant τ of the transformer corresponding winding after adaptive update, the latest The DC resistance value of the transformer corresponding winding is measured after real-time correction. .in, , .

[0041] It can be understood that the reason why three consecutive sampling current data are selected in this embodiment is that the transformer may have an unknown time constant during use due to reasons such as unqualified DC resistance of the windings. Accurate measurement of the DC resistance of each winding must be based on the accurate time constant. In this embodiment, when the time constant is unknown, the iterative algorithm of step S3 is used continuously in the process of using n current data. When the convergence condition of the iterative algorithm is met in step S33, it is actually to determine that the sampling time point corresponding to the latest current data is very close to the time constant of the transformer, so the latest current data is selected at this time. As the time constant τ of the transformer corresponding winding after adaptive update, the latest The DC resistance value of the transformer corresponding winding is measured after real-time correction. .

[0042] Therefore, using the latest three consecutive sampling current data as the basis for subsequent iterative algorithms can improve the iteration accuracy and make the iterative results Closer to the real time constant of the transformer, As a measure of the DC resistance of the winding The measurement results are more accurate.

[0043] Of course, the latest sampled current data can also be used to iterate with any two discontinuous sampled current data before, but since the current data corresponding to different measurement time points fluctuate greatly, the error in the iterative algorithm in step S3 is large, and the DC resistance measurement value finally obtained by iteration is The accuracy is poorer than that of the continuous sampling current data. Therefore, the present invention preferably uses the sampling current data of 3 consecutive sampling moments to make the final DC resistance measurement more accurate.

[0044] In this embodiment, after step S3, the following steps are further included: Step S4, converting the obtained DC resistance measurement value of each phase winding to a DC resistance value at a preset temperature, and calculating the unbalance coefficient of the DC resistance of the three-phase winding according to the ratio of the difference between the maximum value and the minimum value of the converted DC resistance values ​​of each phase winding to the average value, and determining whether the transformer is operating normally according to the unbalance coefficient.

[0045] In a specific application embodiment, data conversion is first performed to convert the DC resistance measurement values ​​of each phase winding obtained to the DC resistance data at a temperature of 75°C. , the calculation expression is as follows: (7) In the above formula, T is the resistance temperature constant of the winding wire (adjusted according to the wire material, such as 235 for copper wire and 225 for aluminum wire). is the real-time temperature in the current measurement environment (data can be collected through temperature sensors), Take 75.

[0046] Secondly, the unbalance coefficient of the DC resistance of the three-phase winding of the transformer is calculated based on the converted data. The calculation expression is as follows: (8) In the above formula, Indicates the maximum value of the measured three-phase winding DC resistance, Indicates the minimum value of the measured three-phase winding DC resistance, It indicates the average value of the measured DC resistance of the three-phase winding. If the unbalance coefficient F exceeds the normal range, it reflects that the transformer operation status is abnormal, indicating that the transformer winding may be defective.

[0047] Example 2 This embodiment provides a device for measuring the DC resistance of an on-load tap-changing transformer, comprising: A gear adjustment module, used to adjust the gear state of the transformer; A measurement module is used to measure the real-time current data of each phase winding of the transformer at each gear position; The calculation module is used to calculate the estimated time constant and DC resistance of each phase winding according to the real-time current data, and to obtain the optimal DC resistance value of each phase winding through iteration according to the fitted real-time current data as the DC resistance measurement value of the corresponding winding.

[0048] Specifically, the DC resistance measuring device of the on-load tap-changing transformer includes an online DC resistance tester and a gear adjustment device, wherein the online DC resistance tester provides a constant test current (such as 0.1A to 10A adjustable), and calculates the resistance value by measuring the voltage (accuracy ±0.1%). The tester is equipped with a data storage and report generation module, supports USB and Bluetooth connections, and can perform fast and accurate DC resistance measurements at each gear. The test time is controlled within 1 minute, and the generated report includes the resistance value and test time of each gear.

[0049] The gear adjustment device is a motor-driven gear adjustment device equipped with a camera, a temperature sensor and a servo control system. By controlling the motor drive and image transmission through a program, it can realize fast on-demand switching of the transformer's on-load voltage regulating switch between gears 1 to 17.

[0050] In an exemplary specific application scenario, the DC resistance measurement process of each phase winding of the on-load tap-changing transformer at each gear position using the on-load tap-changing transformer DC resistance measurement device is as follows: (1) Operation preparation. Connect all equipment, align the gear adjustment device with the "upshift", "downshift" and "stop" buttons on the gear controller, turn on the camera, perform self-test with the online DC resistance tester and connect it wirelessly to the gear adjustment device to ensure normal operation of the system.

[0051] (2) The initial state is determined. If the transformer gear is not in the initial gear, the target gear is adjusted to the initial gear (the default gear is 1) through the gear adjustment device or manually.

[0052] (3) DC resistance test: (3.1) The gear status is determined. The camera collects images of the transformer gear in real time, and the image processing unit uses a convolutional neural network (CNN) to perform image analysis and identify the current gear.

[0053] (3.2) Image information transmission: The image information collected by the camera and temperature sensor is converted into a digital signal through a recognition algorithm and transmitted to the online direct resistance tester through a communication module.

[0054] (3.3) Test voltage, turn on the instrument current source, and then test after the current source data stabilizes.

[0055] (3.4) Automatically adjust the time constant and correct the DC resistance measurement value in real time by the three-point method, multi-point fitting method, etc. in steps S1-S3.

[0056] (3.5) Test data writing: the online DC resistance tester collects current and voltage data in real time at each gear and automatically generates a test report; the test report generation time is controlled within 30 seconds to facilitate subsequent analysis.

[0057] (3.6) Test pressure relief. The instrument measures the DC resistance of each phase winding in the current gear according to the phase sequence of A, B, and C, and relieves the pressure of the instrument after the DC resistance measurement of each phase winding is completed.

[0058] (3.7) To measure the next gear, set a specific control instruction in the program, such as "shift to the 5th gear". The gear adjustment device controls the motor to rotate to the corresponding position according to the instruction, and repeats the operation process of step (3) until all gears are tested.

[0059] (4) Test data report: After the test is completed, the final report is automatically generated and fed back to the operator; the system can provide detailed gear test data after each test and make suggestions on the direct resistance test during the test process to facilitate subsequent analysis and auditing.

[0060] The advantages of the above DC resistance measurement process are as follows: (1) Fully automatic file adjustment operation: The transformer DC resistance test process is fully automated, and the motor-driven gear shifting device is used to eliminate the tediousness of traditional manual operation, significantly improving the test efficiency and accuracy.

[0061] (2) Intelligent image recognition: The use of high-definition cameras and advanced image processing algorithms can monitor and identify the gear position of the transformer voltage regulator in real time, ensuring the accuracy of each gear adjustment operation. The recognition rate is as high as 95%, effectively reducing human errors.

[0062] (3) Remote control function: Through the Bluetooth or Wi-Fi module, the operator can remotely control the gear adjustment process from a safe distance, which enhances the safety of operation and makes high-voltage operations more controllable.

[0063] (4) Real-time data recording and analysis: The system can automatically record test data and generate test reports in a standard format to facilitate subsequent data analysis and auditing. The data accuracy rate reaches 99%, which improves the efficiency of information management.

[0064] (5) Modular design and versatility: The modular design of the gear shifting device and tester makes the system highly adaptable and can be flexibly configured according to different types of transformers to meet the needs of various application scenarios.

[0065] (6) Integrated feedback mechanism: Through the real-time feedback mechanism, the system can promptly confirm the gear status after the gear adjustment operation and make corresponding adjustments to ensure the accuracy and reliability of the test.

[0066] (7) Combination of multiple control methods: Combining microcontrollers, servo control systems and stepper motor control, high-precision motor regulation is achieved, which can cope with complex gear adjustment requirements.

[0067] (8) Intelligent user interface: The user-friendly operation interface is designed to facilitate users to intuitively control and monitor the test process, while providing status feedback to improve user experience and operation convenience.

[0068] (9) Collaborative image recognition and temperature sensing: The camera and temperature sensor work together to not only accurately identify the gear status, but also collect temperature data in real time for subsequent resistance conversion and imbalance coefficient calculation. Multi-dimensional data collection and analysis improve the intelligence level of the system.

[0069] Gear position recognition: The system uses a high-definition camera to collect images of gear positions in real time and uses a convolutional neural network (CNN) to recognize gear positions with an accuracy of up to 95%. Under different lighting and viewing angles, the camera can identify the current gear position and feed the information back to the control system to ensure gear adjustment accuracy.

[0070] Temperature data collection and conversion: The temperature sensor synchronously collects the current winding temperature for direct resistance conversion calculation to ensure that the measured data under different temperature conditions are comparable.

[0071] (10) Fast switching of multiple gears and real-time feedback of test data: The system supports fast switching of gears from 1 to 17. The gear adjustment and measurement process is automated without manual intervention, and the test time for each gear is controlled within 1 minute. During the test, the resistance value and current stability of each gear are fed back in real time, effectively improving the test speed and data accuracy.

[0072] Fast switching: Using the servo control motor system, the gear adjustment device can complete the fast switching of each gear within 1 minute, reducing the test time.

[0073] Real-time data feedback: The resistance value and current stability are fed back in real time at each gear, and the resistance measurement data after each gear adjustment is automatically recorded. The system can display the resistance value, current stability and temperature data of the current gear in real time to ensure the real-time and accuracy of the data.

[0074] (11) High-precision automatic pressure relief and phase sequence detection: In order to further improve the safety of operation and the accuracy of measurement, the system performs automatic pressure relief after the measurement is completed and performs phase sequence detection to ensure the correct resistance measurement sequence: Automatic pressure relief: After the DC resistance measurement of each phase winding is completed, the system automatically performs the pressure relief process and controls the pressure relief resistor to ensure safe release of energy to avoid safety hazards caused by high voltage.

[0075] Phase sequence detection and confirmation: After each phase measurement is completed, the system will automatically detect the phase sequence to ensure that the three-phase windings A, B, and C are measured correctly in sequence. By measuring the initial phase sequence and comparing the voltage and current characteristic data, the system automatically confirms the measurement sequence to avoid confusion in the measurement data caused by incorrect phase sequence.

[0076] The device of the present invention corresponds to the above method and also has the advantages of the above method, which will not be described in detail here.

[0077] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for measuring the DC resistance of an on-load tap-changing transformer, wherein the on-load tap-changing transformer comprises three-phase windings of phase A, phase B and phase C, characterized in that: include: Step S1, sampling the current of each phase winding of the transformer in the same gear state at multiple times to obtain corresponding first sampled current data, and obtaining a time constant estimation value of each phase winding based on the first sampled current data; Step S2, selecting a plurality of sampling current values ​​at consecutive sampling moments from the first sampling current data as second sampling current data, and obtaining an estimated value of a DC resistance of each phase winding based on the current stability of the second sampling current data; Step S3, fitting the first sampled current data and obtaining the optimal time constant value and the optimal DC resistance value of each phase winding after optimization through iteration, and taking the optimal DC resistance value as the DC resistance measurement value of the corresponding winding.

2. The method for measuring the DC resistance of an on-load tap-changing transformer according to claim 1, characterized in that: The step S1 comprises: Three or more sampling current values ​​at different sampling times are selected from the first sampling current data, and the time constant estimation value of the corresponding winding is calculated according to the ratio of the difference between the sampling times corresponding to adjacent sampling current values ​​and the difference between adjacent sampling current values.

3. The method for measuring the DC resistance of an on-load tap-changing transformer according to claim 2, characterized in that: The calculation expression for the estimated value of the time constant of the corresponding winding is: In the above formula, is the estimated value of the time constant of the corresponding winding of the transformer, are three different sampling moments, for The sampled current value of the same winding corresponding to the sampling moment.

4. The method for measuring the DC resistance of an on-load tap-changing transformer according to claim 1, characterized in that: The step S2 comprises: Selecting three or more sampling current values ​​at three consecutive sampling moments from the first sampling current data, and calculating an estimated current value after the corresponding winding is stabilized according to the sampling current values; The current stability of the corresponding winding is obtained according to the ratio of the sampling current values ​​at the two most recent sampling moments among the sampling current values; After determining that the current stability of the three-phase windings is greater than the stability threshold, the DC resistance estimation value of the corresponding winding at the current gear is calculated according to the ratio of the transformer capacity and the estimated current value.

5. The method for measuring the DC resistance of an on-load tap-changing transformer according to claim 4, characterized in that: The calculation expression of the estimated current value after the corresponding winding is stable is: In the above formula, are the estimated current values ​​of the A-phase, B-phase and C-phase windings respectively, They are the sampling current values ​​corresponding to three consecutive sampling moments of the A-phase winding, They are the sampling current values ​​corresponding to three consecutive sampling moments of the B-phase winding, They are the sampling current values ​​corresponding to three consecutive sampling moments of the C-phase winding.

6. The method for measuring the DC resistance of an on-load tap-changing transformer according to claim 4, characterized in that: The calculation expression of the estimated DC resistance of the corresponding winding at the current gear is: In the above formula, are the estimated DC resistance of phase A, phase B and phase C windings at the current gear, and E is the transformer capacity.

7. The method for measuring the DC resistance of an on-load tap-changing transformer according to claim 1, characterized in that: The step S3 comprises: Obtaining an error function associated with a time constant and a DC resistance by fitting a plurality of sampling current values ​​of the first sampling current data and corresponding sampling moments based on a least square method; The error function is optimized according to the gradient descent method or the Newton-Raphson method with the estimated time constant and the estimated DC resistance as initial values, the values ​​of the time constant and the DC resistance are updated in each iteration, and the iteration is stopped when the error value of the error function is less than a preset threshold, and the DC resistance value obtained by the last update is used as the DC resistance measurement value of the corresponding winding.

8. The method for measuring the DC resistance of an on-load tap-changing transformer according to claim 7, characterized in that: The expression of the error function is: In the above formula, S is the error function, n is the number of current data collected by the corresponding winding, and are the i-th sampling current value and the i-th sampling time of the corresponding winding, τ is the time constant of the corresponding winding, and R is the DC resistance of the corresponding winding; The calculation expression for updating the time constant value and DC resistance value is: In the above formula, is the current updated DC resistance value, Indicates the DC resistance value before updating, is the time constant after the current update, is the time constant before updating, and η is the learning rate.

9. The method for measuring the DC resistance of an on-load tap-changing transformer according to claim 1, characterized in that: After step S3, the following steps are also included: Step S4, converting the obtained DC resistance measurement value of each phase winding to a DC resistance value at a preset temperature, and calculating the unbalance coefficient of the DC resistance of the three-phase winding according to the ratio of the difference between the maximum value and the minimum value of the converted DC resistance values ​​of each phase winding to the average value, and determining whether the transformer is operating normally according to the unbalance coefficient.

10. A device for measuring the DC resistance of an on-load tap-changing transformer, characterized in that: include: A gear adjustment module, used to adjust the gear state of the transformer; A measurement module is used to measure the real-time current data of each phase winding of the transformer at each gear position; The calculation module is used to calculate the estimated time constant and DC resistance of each phase winding according to the real-time current data, and to obtain the optimal DC resistance value of each phase winding through iteration according to the fitted real-time current data as the DC resistance measurement value of the corresponding winding.

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