A method and device for measuring the direct current resistance of a load regulating transformer

Abstract

The application discloses a kind of on-load voltage regulating transformer DC resistance measurement method and measuring device, method includes: the current of each phase winding of transformer in the same gear state is sampled at multiple time to obtain first sampling current data, based on the time constant estimation value of each phase winding of first sampling current data;Select the sampling current value of several continuous sampling time in first sampling current data as second sampling current data, based on the current stability of second sampling current data to obtain the DC resistance estimation value of each phase winding;First sampling current data is fitted and is obtained by iteration The optimized best DC resistance value of each phase winding is as the DC resistance measurement value of corresponding winding.The application can effectively avoid the shortcomings of long measurement time, high measurement time point requirement and large measurement result error, improve the accuracy and reliability of DC resistance measurement, suitable for DC resistance measurement of various transformers, with wide application scenarios.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of on-load tap-changing transformers, in particular to a method and device for measuring the direct current resistance of an on-load tap-changing transformer. BACKGROUND

[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, which can effectively identify manufacturing defects of transformer coils, looseness of connection parts, broken strands or broken wires, etc. According to the requirements of the Power Equipment Overhaul Test Regulations, power transformers need to be tested for winding DC resistance every 3 or 6 years, and measurements must be taken at all tap positions during the test.

[0003] However, the traditional testing method has many problems. First, the on-load tap-changing switch of the transformer stays in a certain position most of the time in actual operation, which may cause oxidation of the joints at other positions, affecting the accuracy of the measurement results. In order to ensure the effectiveness of the test, the test personnel need to manually adjust the tap-changing switch from one position to another, usually requiring 3 to 5 rounds of repeated adjustment, or even more than 10 rounds in severe cases of oxidation. This process not only consumes time and effort, but also requires special personnel to operate, increasing labor costs.

[0004] Secondly, the current testing of power transformer DC resistance mainly relies on static measurement methods, such as loop resistance jump method, high voltage charging low voltage measurement method, magnetic assistance method and short circuit demagnetization method, etc. These methods are mostly based on resistance measurement after the test circuit reaches a steady state, usually requiring several minutes or even longer to complete a test. This traditional "static" measurement method has the following shortcomings: first, since the power transformer winding can be equivalent to a series circuit model of a large inductance L and a small resistance R, the time constant τ=L / R, therefore the inherent time constant of large-capacity transformers is large, and due to the existence of the above-mentioned large inductance, the self-induction effect of the changing electric quantity is large, so that the current flowing through the winding cannot be suddenly changed, and the current needs to be waited for a time constant τ to reach a steady state value before measurement. Since the current needs to be waited for a long time to reach a steady state value, the requirement for the measurement time point is extremely high, which easily leads to large measurement result errors; second, lack of stability and accuracy: for star-delta (Y / Δ) connected transformers, the traditional static measurement method is easily affected by the winding inductance and the connection mode, which leads to current circulation interference with the test results, affecting the measurement accuracy. SUMMARY

[0005] The technical problems solved by the present application are: in view of the above problems of the prior art, a load regulation transformer DC resistance measurement method and device with high measurement efficiency and wide applicability are provided to realize high-precision transformer DC resistance measurement.

[0006] To solve the above technical problems, the technical scheme adopted by the present application is:

[0007] A load regulation transformer DC resistance measurement method, the load regulation transformer includes three-phase windings of A phase, B phase and C phase, comprising:

[0008] Step S1, the current of each phase winding of the transformer in the same gear state is sampled at multiple time points to obtain corresponding first sampling current data, and the time constant estimation value of each phase winding is obtained based on the first sampling current data;

[0009] Step S2, in the first sampling current data, the sampling current values of several continuous sampling time points are selected as the second sampling current data, and the DC resistance estimation value of each phase winding is obtained based on the current stability of the second sampling current data;

[0010] Step S3, the first sampling current data is fitted and the optimized best time constant value and the best DC resistance value of each phase winding are obtained through iteration, and the best DC resistance value is taken as the DC resistance measurement value of the corresponding winding.

[0011] Further, the step S1 comprises:

[0012] In the first sampling current data, the sampling current values of 3 or more than 3 different sampling time points are selected, and the time constant estimation value of the corresponding winding is calculated according to the ratio of the difference value of the sampling time corresponding to the adjacent sampling current values and the difference value of the adjacent sampling current values.

[0013] Further, the calculation expression of the time constant estimation value of the corresponding winding is:

[0014]

[0015] In the above formula, is the time constant estimation value of the corresponding winding of the transformer, is 3 different sampling time points, is is the sampling current value of the same winding corresponding to the sampling time.

[0016] Further, the step S2 comprises:

[0017] In the first sampling current data, the sampling current values of 3 or more than 3 continuous sampling time points are selected, and the estimated current value of the corresponding winding after stabilization is calculated according to the sampling current value.

[0018] The current stability of the corresponding winding is obtained according to the ratio of the sampling current values at the last two sampling time points in the sampling current values;

[0019] After judging that the current stability of the three-phase winding 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.

[0020] Further, the calculation expression of the estimated current value of the corresponding winding after stabilization is:

[0021]

[0022] In the above formula, respectively, the estimated current values of the A-phase, B-phase and C-phase windings, respectively, the sampling current values corresponding to the three continuous sampling time points of the A-phase winding, respectively, the sampling current values corresponding to the three continuous sampling time points of the B-phase winding, respectively, the sampling current values corresponding to the three continuous sampling time points of the C-phase winding.

[0023] Further, the calculation expression of the current stability of each phase winding is:

[0024]

[0025] In the above formula, respectively, the current stabilities of the A-phase, B-phase and C-phase windings.

[0026] Further, the calculation expression of the DC resistance estimation value of the corresponding winding at the current gear is:

[0027]

[0028] In the above formula, respectively, the DC resistance estimation values of the A-phase, B-phase and C-phase windings at the current gear, and E is the transformer capacity.

[0029] Further, the step S3 comprises:

[0030] According to the plurality of sampling current values of the first sampling current data and the corresponding sampling time, an error function associated with a time constant and a DC resistance is fitted based on a least square method;

[0031] The error function is optimized according to the gradient descent method or the Newton-Raphson method with the time constant estimation value and the DC resistance estimation value as initial values, the values of the time constant and the DC resistance are updated at 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 taken as the DC resistance measurement value of the corresponding winding.

[0032] Further, the expression of the error function is:

[0033]

[0034] In the above formula, S is the error function, n is the number of current data collected for the corresponding winding, and respectively, the i-th sampling current value of the corresponding winding and the i-th sampling time, τ is the time constant of the corresponding winding, and R is the DC resistance of the corresponding winding.

[0035] The calculation expression for updating the time constant value and the DC resistance value is:

[0036]

[0037] In the above formula, is the current updated DC resistance value, indicates the DC resistance value before updating, is the current updated time constant, is the time constant before updating, and η is the learning rate.

[0038] Further, after step S3, it further includes:

[0039] Step S4, the obtained DC resistance measurement values of the three-phase windings are converted to DC resistance values at a preset temperature, and an unbalance degree coefficient of the DC resistance of the three-phase winding is calculated according to the ratio of the difference between the maximum value and the minimum value to the average value of the converted DC resistance values of the three-phase windings, and whether the transformer is normally operated is determined according to the unbalance degree coefficient.

[0040] Further, after step S4, it further includes:

[0041] Step S5, adjusting the gear position of the transformer to the next gear and repeating steps S1-S3 to measure the DC resistance values of the three-phase windings at the next gear, and repeating the operation until the measurement at all gears is completed.

[0042] The application further provides a DC resistance measurement device for an on-load voltage regulating transformer, comprising:

[0043] A gear adjusting module is configured to adjust the gear state of the transformer.

[0044] The measurement module is used to measure the real-time current data of each phase winding of the transformer at each tap.

[0045] The calculation module is used to calculate the estimated time constant and DC resistance of each phase winding based on real-time current data, and to obtain the optimal DC resistance value of each phase winding through iteration based on the fitted real-time current data, which is used as the DC resistance measurement value of the corresponding winding.

[0046] Compared with the prior art, the advantages of the present invention are as follows:

[0047] This invention estimates the time constant and DC resistance of each phase winding of a transformer by sampling the first current data to obtain a reference value. Then, it iterates by fitting the first current data and continuously updates the time constant and DC resistance values ​​based on the reference value, finally obtaining the optimal value as the DC resistance measurement value of the corresponding winding. The operation is simple and efficient, and it can effectively avoid the disadvantages of long measurement time, high requirements for measurement time point and large measurement result error caused by current steady state. Thus, it improves the accuracy and reliability of transformer DC resistance measurement, and is applicable to the DC resistance measurement of various transformers, with a wide range of application scenarios. Attached Figure Description

[0048] Figure 1 This is a schematic diagram illustrating the specific process of the on-load tap-changing transformer DC resistance measurement method according to Embodiment 1 of the present invention. Detailed Implementation

[0049] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0050] Example 1

[0051] like Figure 1 As shown, this embodiment of the invention provides a method for measuring the DC resistance of an on-load tap-changing transformer. The on-load tap-changing transformer includes three-phase windings of phase A, phase B, and phase C, comprising:

[0052] Step S1: Sample the current of each phase winding of the transformer at multiple times under the same tap position to obtain the corresponding first sampled current data, and obtain the estimated value of the time constant of each phase winding based on the first sampled current data.

[0053] Step S2: Select the sampling current values ​​at several consecutive sampling times from the first sampling current data as the second sampling current data, and obtain the estimated DC resistance value of each phase winding based on the current stability of the second sampling current data.

[0054] Step S3: Fit the first sampled current data and iterate to obtain the optimal time constant value and optimal DC resistance value of each phase winding, and use the optimal DC resistance value as the DC resistance measurement value of the corresponding winding.

[0055] It is understood that this embodiment estimates the time constant and DC resistance of each phase winding of the transformer by sampling the first sampled current data to obtain a reference value. Then, it iterates by fitting the first sampled current data and continuously updates the time constant and DC resistance values ​​based on the reference value, finally obtaining the optimal value as the DC resistance measurement value of the corresponding winding. The operation is simple and efficient, and can effectively avoid the disadvantages of long measurement time, high measurement time point requirements and large measurement result errors caused by current steady state. This improves the accuracy and reliability of transformer DC resistance measurement, and is applicable to the DC resistance measurement of various transformers, with a wide range of application scenarios.

[0056] In this embodiment, step S1 includes:

[0057] Select three or more sampling current values ​​at different sampling times from the first sampling current data, and calculate the estimated time constant value of the corresponding winding based on the ratio of the difference between the sampling times corresponding to adjacent sampling current values ​​to the difference between adjacent sampling current values.

[0058] In a specific application embodiment, step S1 will be described in detail using the three-point method as an example. Preferably, a DC resistance tester is used to sample the current of each phase winding of the transformer at the same tap position 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 current sampling refers to sampling at three different times. Collect current values ​​of the same winding respectively The time constant of the corresponding winding is estimated using formula (1) (the time constant of each of the three-phase windings is estimated according to formula 1):

[0059] (1)

[0060] In the above formula, This is an estimated value for the time constant of the corresponding winding of the transformer. For 3 different sampling times, for The sampling current value of the same winding at the sampling time.

[0061] In this embodiment, step S2 includes:

[0062] Select three or more consecutive sampling current values ​​from the first sampled current data, and calculate the estimated current value after the corresponding winding stabilizes based on the sampled current values.

[0063] The current stability of the corresponding winding is obtained by the ratio of the sampling current values ​​at the two most recent sampling times. After determining that the current stability of the three-phase windings is greater than the stability threshold, the estimated DC resistance of the corresponding winding at the current tap is calculated based on the ratio of the transformer capacity and the estimated current value.

[0064] In a specific application embodiment, step S2 will be explained in detail using the three-point method as an example. First, a DC resistance tester is used to measure the resistance at n different time points. Sample n current data points from each phase winding of the transformer. Select three current data points from consecutive sampling times to estimate the DC resistance of the corresponding transformer windings (the estimated DC resistances of the three-phase windings A, B, and C are denoted as follows). The specific steps are as follows:

[0065] Step S21: Estimate the estimated current value of each phase winding of the transformer after stabilization.

[0066] Assuming a 5-second interval between each sampling point, the three consecutive sampling times can be understood as acquiring the current values ​​of each phase winding of the transformer at the start (0 seconds), the middle (5 seconds), and the subsequent (10 seconds), respectively, and denoted as follows: (Sampling current of phase A winding) (Sampling current of phase B winding) (C-phase winding sampling current), calculate the estimated current value after stabilization according to formula (2). :

[0067] (2)

[0068] In the above formula, These are the estimated current values ​​for the windings of phases A, B, and C, respectively. These are the sampled current values ​​corresponding to three consecutive sampling times of phase A winding. These are the sampled current values ​​corresponding to three consecutive sampling times of the B-phase winding. These are the sampling current values ​​corresponding to three consecutive sampling times of the C-phase winding.

[0069] Step S22, calculate the current stability c of each phase winding according to formula (3):

[0070] (3)

[0071] In the above formula, These are the current stability values ​​of the A-phase, B-phase, and C-phase windings, respectively.

[0072] Step S23, such as current stability All are greater than the stability threshold (This can be set according to actual needs), then it is determined that the current is stable, and the DC resistance value of each phase winding of the transformer under the current tap is estimated according to formula (4):

[0073] (4)

[0074] In the above formula, These are the estimated DC resistance values ​​of phase A, phase B, and phase C windings at the current tap position, respectively, and E is the transformer capacity.

[0075] It should be noted that if the current stability Not all are greater than the stability threshold Then, from the n current data points of each phase winding of the transformer, select the next set of 3 current data points at the next continuous sampling time and process them again according to steps S21-S23 until the current stability is achieved. All are greater than the stability threshold And determine the DC resistance value of each phase winding. .

[0076] In this embodiment, step S3 includes:

[0077] An error function related to the time constant and DC resistance is obtained by fitting multiple sampled current values ​​of the first sampled current data with the corresponding sampling time.

[0078] The error function is optimized using the estimated time constant and DC resistance as initial values ​​according to the gradient descent method or the Newton-Raphson method. The values ​​of the time constant and DC resistance are updated at each iteration, and the iteration stops when the error value of the error function is less than a preset threshold. The DC resistance value obtained from the last update is used as the measured DC resistance value of the corresponding winding.

[0079] 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:

[0080] Step S31: Test the resistance at n different time points using a DC resistance tester. Sample n current data points from each phase winding of the transformer. The error function S is then fitted. Specifically, in practical applications, to improve accuracy, multiple sets of data points can be collected and fitted using the least squares method. Assume n current data points are collected. and the corresponding time point Then the fitting error function S is:

[0081] (5)

[0082] In the above formula, S is the error function, and n is the number of current data points collected for the corresponding winding. and These represent the i-th sampled current value and the i-th sampled time of the corresponding winding, respectively; τ is the time constant of the corresponding winding; and R is the DC resistance of the corresponding winding.

[0083] Step S32: To ensure measurement accuracy, an iterative optimization algorithm is used to minimize the error function S. Minimizing the error S yields the optimal values ​​of R and τ through an iterative algorithm. Specifically, gradient descent or the Newton-Raphson method can be used to optimize the error function S, adjusting the values ​​of R and τ to ensure measurement accuracy. The update formula is as follows:

[0084] (6)

[0085] In the above formula, This is the currently updated DC resistance value. This indicates the DC resistance value before the update. The current updated time constant. The time constant before the update is η, and the learning rate is the step size used to control parameter adjustment; where The initial value is the estimated DC resistance value determined according to formula (4) in step S23. The initial value is the estimated value of the time constant determined in step S1 according to formula (1).

[0086] Step S33, Convergence Judgment: When the error function S is less than the preset threshold If the parameter changes ΔR and Δτ are sufficiently small, the measurement result is considered to have reached satisfactory accuracy, and iteration is stopped. At this point, the latest... As the time constant τ of the corresponding transformer winding after adaptive update, the latest The DC resistance value obtained after real-time calibration of the corresponding winding of the transformer. .in, , .

[0087] It is understandable that in this embodiment, three consecutive sampling current data points are selected because the time constant of the transformer is unknown during use due to factors such as potentially substandard DC resistance of the windings; and accurate measurement of the DC resistance of each winding requires knowledge of the accurate time constant. In this embodiment, when the time constant is unknown, by continuously sampling n current data points, the iterative algorithm in step S3, when the convergence condition of the iterative algorithm is met in step S33, essentially determines that the sampling time point corresponding to the latest current data point is very close to the transformer's time constant. Therefore, the latest sampling time point is selected. As the time constant τ of the corresponding transformer winding after adaptive update, the latest The DC resistance value obtained after real-time calibration of the corresponding winding of the transformer. .

[0088] Therefore, using the latest three consecutive sampled current data as the basis for subsequent iterative algorithms can improve the iteration accuracy and make the obtained results more accurate. More closely approximating the actual time constant of a transformer, allowing the latest... As a measurement of the DC resistance of the winding The measurement results are more accurate.

[0089] Of course, the latest sampled current data can also be used to iterate with any two previous discontinuous sampled current data. However, since the current data corresponding to different measurement time points fluctuate greatly, the error in the iteration algorithm in step S3 is relatively large, and the final DC resistance measurement value obtained by the iteration is also relatively small. The accuracy is lower compared to continuously sampled current data. Therefore, this invention preferably uses sampling current data from three consecutive sampling times to make the final DC resistance measurement more accurate.

[0090] In this embodiment, step S3 is followed by:

[0091] Step S4: Convert the obtained DC resistance measurement values ​​of each phase winding to the DC resistance values ​​at a preset temperature, and calculate the unbalance coefficient of the DC resistance of the three-phase winding based on the ratio of the difference between the maximum and minimum values ​​of the converted DC resistance values ​​of each phase winding to the average value. Determine whether the transformer is operating normally based on the unbalance coefficient.

[0092] In a specific application embodiment, the data is first converted to DC resistance values ​​at a temperature of 75°C by converting the obtained DC resistance measurements of each phase winding. The calculation expression is as follows:

[0093] (7)

[0094] In the above formula, T is the temperature constant of the winding conductor (adjusted according to the conductor material, such as 235 for copper conductor and 225 for aluminum conductor). This is the real-time temperature under the current measurement environment (data can be collected via a temperature sensor). Take 75.

[0095] Secondly, the unbalance coefficient of the DC resistance of the three-phase windings of the transformer is calculated based on the converted data. The calculation expression is as follows:

[0096] (8)

[0097] In the above formula, This represents the maximum measured DC resistance of the three-phase winding. This represents the minimum measured DC resistance of the three-phase winding. This represents the average DC resistance of the three-phase windings as measured. If the unbalance coefficient F exceeds the normal range, it reflects an abnormality in the transformer's operating condition and suggests a possible defect in the transformer windings.

[0098] Example 2

[0099] This embodiment provides a DC resistance measuring device for an on-load tap-changing transformer, comprising:

[0100] The gear shifting module is used to adjust the gear position of the transformer.

[0101] The measurement module is used to measure the real-time current data of each phase winding of the transformer at each tap.

[0102] The calculation module is used to calculate the estimated time constant and DC resistance of each phase winding based on real-time current data, and to obtain the optimal DC resistance value of each phase winding through iteration based on the fitted real-time current data, which is used as the DC resistance measurement value of the corresponding winding.

[0103] Specifically, the on-load tap-changing transformer DC resistance measuring device includes an online DC resistance tester and a range adjustment device. The online DC resistance tester provides a constant test current (e.g., adjustable from 0.1A to 10A) 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 connectivity, and can perform fast and accurate DC resistance measurements at each range, with the test time controlled within 1 minute. The generated report includes the resistance value and test time for each range.

[0104] The gear adjustment device is a motor-driven gear adjustment device equipped with a camera, temperature sensor and servo control system. Through program control of motor drive and image transmission, it can realize fast on-demand switching of the on-load tap changer of the transformer between gear 1 and gear 17.

[0105] In a specific application scenario, the procedure for measuring the DC resistance of each phase winding of an on-load tap-changing transformer at each tap position using an on-load tap-changing transformer DC resistance measuring device is as follows:

[0106] (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 a self-test with the online DC resistance tester and wirelessly connect it to the gear adjustment device to ensure the system is operating normally.

[0107] (2) Initial state determination: If the transformer tap is not in the initial tap, the target tap is adjusted to the initial tap (default 1) by tap adjustment device or manual adjustment.

[0108] (3) DC resistance test:

[0109] (3.1) Gear position determination: The camera collects images of the transformer gear position in real time, and the image processing unit uses a convolutional neural network (CNN) to perform image analysis and identify the current gear position.

[0110] (3.2) Image information transmission: The image information collected by the camera and temperature sensor is converted into digital signals through the recognition algorithm and transmitted to the online DC resistance tester through the communication module.

[0111] (3.3) Test the pressure, turn on the instrument current source, and perform the test after the current source data stabilizes.

[0112] (3.4) The time constant is automatically adjusted and the DC resistance measurement value is corrected in real time by the three-point method, multi-point fitting method and other methods in steps S1-S3.

[0113] (3.5) Test data writing: The online DC resistance tester collects current and voltage data in real time at each range and automatically generates test reports; the test report generation time is controlled within 30 seconds to facilitate subsequent analysis.

[0114] (3.6) Test the pressure relief. The instrument measures the DC resistance of each phase winding in the current range according to the phase sequence A, B, C, and then relieves the pressure of the instrument after the DC resistance of each phase winding is measured.

[0115] (3.7) Perform the next gear measurement. Set specific control instructions 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 instructions. Repeat the operation process of step (3) until all gears are tested.

[0116] (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 situation during the test process, which is convenient for subsequent analysis and auditing.

[0117] The advantages of the above DC resistance measurement procedure are as follows:

[0118] (1) Fully automated gear shifting operation:

[0119] The process of testing the DC resistance of transformers has been fully automated. By using a motor-driven range adjustment device, the cumbersome traditional manual operation has been eliminated, significantly improving testing efficiency and accuracy.

[0120] (2) Intelligent image recognition:

[0121] Employing high-definition cameras and advanced image processing algorithms, it can monitor and identify the voltage regulator switch position of the transformer in real time, ensuring the accuracy of each adjustment operation. With a recognition rate of up to 95%, it effectively reduces human error.

[0122] (3) Remote control function:

[0123] With the help of Bluetooth or Wi-Fi modules, operators can remotely control the gear shifting process from a safe distance, which enhances the safety of operation and makes high-voltage work more controllable.

[0124] (4) Real-time data recording and analysis:

[0125] The system can automatically record test data and generate standard-format test reports, facilitating subsequent data analysis and auditing. Data accuracy reaches 99%, improving the efficiency of information management.

[0126] (5) Modular design and versatility:

[0127] The modular design of the adjustment device and the tester makes the system highly adaptable, and can be flexibly configured according to different models of transformers to meet the needs of various application scenarios.

[0128] (6) Integrated feedback mechanism:

[0129] Through a real-time feedback mechanism, the system can promptly confirm the gear status after a gear shift and make corresponding adjustments, ensuring the accuracy and reliability of the test.

[0130] (7) Combination of multiple control methods:

[0131] By combining microcontroller, servo control system and stepper motor control, high-precision motor adjustment can be achieved, which can meet complex gear adjustment requirements.

[0132] (8) Intelligent user interface:

[0133] The user-friendly interface is designed to allow users to intuitively control and monitor the testing process, while providing status feedback to enhance user experience and ease of operation.

[0134] (9) Image recognition and temperature sensing work together: 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 unbalance coefficient calculation. Multi-dimensional data collection and analysis improve the intelligence level of the system.

[0135] Gear Position Recognition: The system captures images of the gear position in real time using a high-definition camera and uses a convolutional neural network (CNN) for gear position recognition, achieving an accuracy of up to 95%. Under different lighting and viewing angle conditions, the camera can identify the current gear position and feed the information back to the control system to ensure accurate gear adjustment.

[0136] Temperature data acquisition and conversion: The temperature sensor synchronously acquires the current winding temperature for DC resistance conversion calculation, ensuring that the measurement data under different temperature conditions are comparable.

[0137] (10) Rapid switching between multiple gears and real-time feedback of test data: The system supports rapid switching between 1 to 17 gears. The gear adjustment and measurement process is automated and requires no manual intervention. 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, which effectively improves the test speed and data accuracy.

[0138] Quick switching: Utilizing a servo-controlled motor system, the gear shifting device can quickly switch between gears within 1 minute, reducing testing time.

[0139] Real-time data feedback: The system provides real-time feedback on resistance and current stability for each speed setting, and automatically records resistance measurement data after each speed adjustment. The system can display the resistance value, current stability, and temperature data for the current speed setting in real time, ensuring data timeliness and accuracy.

[0140] (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 operation after the measurement is completed and performs phase sequence detection to ensure that the resistance measurement sequence is correct:

[0141] Automatic pressure relief: After the DC resistance measurement of each phase winding is completed, the system automatically executes the pressure relief process, controls the pressure relief resistor to ensure safe energy release, and avoids safety hazards caused by high voltage.

[0142] Phase sequence detection and confirmation: After each phase measurement is completed, the system automatically detects the phase sequence to ensure that the A, B, and C phase windings 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, avoiding measurement data confusion caused by incorrect phase sequence.

[0143] The apparatus of the present invention corresponds to the method described above and has the same advantages as the method described above, which will not be repeated here.

[0144] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection 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: Sample the current of each phase winding of the transformer at multiple times under the same tap position to obtain the corresponding first sampled current data, and obtain the estimated value of the time constant of each phase winding based on the first sampled current data. Step S2: Select the sampling current values ​​at several consecutive sampling times from the first sampling current data as the second sampling current data, and obtain the estimated DC resistance value of each phase winding based on the current stability of the second sampling current data. Step S3: Fit the first sampled current data and iterate to obtain the optimal time constant value and optimal DC resistance value of each phase winding, and use the optimal DC resistance value as the DC resistance measurement value of the corresponding winding. Step S3 includes: Based on multiple sampled current values ​​of the first sampled current data and the corresponding sampling time, an error function related to the time constant and DC resistance is obtained by least squares fitting. The error function is optimized using the estimated time constant and DC resistance as initial values ​​according to the gradient descent method or the Newton-Raphson method. The values ​​of the time constant and DC resistance are updated at each iteration, and the iteration stops when the error value of the error function is less than a preset threshold. The DC resistance value obtained from the last update is used as the DC resistance measurement value of the corresponding winding. The expression for the error function is: In the above formula, S is the error function, and n is the number of current data points collected for the corresponding winding. and These represent the i-th sampled current value and the i-th sampling time of the corresponding winding, respectively; 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 as follows: In the above formula, This is the currently updated DC resistance value. This indicates the DC resistance value before the update. The current updated time constant. η is the time constant before the update, and η is the learning rate.

2. The method for measuring the DC resistance of an on-load tap-changing transformer according to claim 1, characterized in that, Step S1 includes: Select three or more sampling current values ​​at different sampling times from the first sampling current data, and calculate the estimated time constant value of the corresponding winding based on the ratio of the difference between the sampling times corresponding to adjacent sampling current values ​​to 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 formula for calculating the estimated time constant of the corresponding winding is: In the above formula, This is an estimated value for the time constant of the corresponding winding of the transformer. For 3 different sampling times, for The sampling current value of the same winding at the sampling time.

4. The method for measuring the DC resistance of an on-load tap-changing transformer according to claim 1, characterized in that, Step S2 includes: Select three or more consecutive sampling current values ​​from the first sampled current data, and calculate the estimated current value after the corresponding winding stabilizes based on the sampled current values. The current stability of the corresponding winding can be obtained by the ratio of the sampled current values ​​at the two most recent sampling times. After determining that the current stability of all three phase windings is greater than the stability threshold, the estimated DC resistance of the corresponding winding at the current tap is calculated based on the ratio of the transformer capacity to 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 formula for calculating the estimated current value after the winding stabilizes is as follows: In the above formula, These are the estimated current values ​​for the windings of phases A, B, and C, respectively. These are the sampled current values ​​corresponding to three consecutive sampling times of phase A winding. These are the sampled current values ​​corresponding to three consecutive sampling times of the B-phase winding. These are the sampling current values ​​corresponding to three consecutive sampling times 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 formula for calculating the estimated DC resistance of the corresponding winding in the current tap position is: In the above formula, These are the estimated DC resistance values ​​of phase A, phase B, and phase C windings at the current tap position, respectively, 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, Step S3 is followed by: Step S4: Convert the obtained DC resistance measurement values ​​of each phase winding to the DC resistance values ​​at a preset temperature, and calculate the unbalance coefficient of the DC resistance of the three-phase winding based on the ratio of the difference between the maximum and minimum values ​​of the converted DC resistance values ​​of each phase winding to the average value. Determine whether the transformer is operating normally based on the unbalance coefficient.

8. A DC resistance measuring device for an on-load tap-changing transformer, characterized in that, The apparatus is used to perform the on-load tap-changing transformer DC resistance measurement method according to any one of claims 1 to 7, the apparatus comprising: The gear shifting module is used to adjust the gear position of the transformer. The measurement module is used to measure the real-time current data of each phase winding of the transformer at each tap. The calculation module is used to calculate the estimated time constant and DC resistance of each phase winding based on real-time current data, and to obtain the optimal DC resistance value of each phase winding through iteration based on the fitted real-time current data, which is used as the DC resistance measurement value of the corresponding winding.

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