Residual magnetism detection method, device and equipment of power transformer and storage medium

Abstract

The embodiment of the invention provides a residual magnetism detection method and device for a power transformer, equipment and a storage medium, and the method comprises the steps: carrying out the voltage reduction and demagnetization processing of the power transformer, enabling the residual magnetism of an iron core to approach zero, carrying out the segmentation fitting of a closing angle-inrush current peak value curve according to the closing angle and historical inrush current peak value data in a no-residual-magnetism state, and carrying out the segmentation fitting of the closing angle-inrush current peak value curve; under rated voltage, the circuit breaker is controlled to be switched on actively at the primary side voltage 90-degree phase of the transformer, the inrush current peak value is monitored, and the monitored inrush current peak value is compared with a switching-on angle-inrush current peak value curve to determine the residual magnetism per unit value. According to the method, the residual magnetism of the transformer iron core can be effectively measured under the conditions that the voltage is not adjusted and other devices are not added. The principle is simple, the steps are simple, the effects of transformer residual magnetism measurement and transformer demagnetization condition verification are good, and the engineering practicability is high.

Description

Technical Field

[0001] This application relates to the field of transformer residual magnetism measurement technology, and in particular to a method, apparatus, equipment and storage medium for detecting residual magnetism in power transformers. Background Technology

[0002] As a core energy conversion device in the power system, the safe operation of power transformers directly affects the stability of the power grid. After a transformer is opened or undergoes tests such as DC resistance testing and partial discharge testing, residual magnetism often remains in the core (the residual magnetism intensity is usually 20%-70% of the steady-state main magnetic flux amplitude). This residual magnetism can trigger a huge inrush current (reaching 6-8 times the rated current) during subsequent no-load closing, leading to malfunctions of relay protection devices, overheating of transformer windings, and even insulation breakdown, seriously threatening the safe operation of the power system. In addition, the presence of residual magnetism can also interfere with the transformer demagnetization verification process, hindering the optimization and standardization of demagnetization technology.

[0003] Currently, residual magnetism measurements are required before transformer commissioning, after maintenance, or after testing in power systems to assess residual magnetism risks and implement demagnetization measures. Existing methods for residual magnetism detection typically involve DC measurements or harmonic analysis.

[0004] However, existing methods for measuring residual magnetism generally suffer from problems such as complex operation, reliance on specialized equipment, and long measurement cycles, making it difficult to meet the needs of engineering sites for efficient, low-cost, and non-invasive measurements. Summary of the Invention

[0005] This application provides a method, apparatus, device, and storage medium for detecting residual magnetism in power transformers, in order to solve the problem of difficulty in measuring residual magnetism in transformer cores.

[0006] In a first aspect, embodiments of this application provide a method for detecting residual magnetism in a power transformer, comprising:

[0007] Voltage reduction and demagnetization treatment is applied to power transformers to reduce the residual magnetism of the iron core to near zero.

[0008] Based on the closing angle and historical inrush peak data under the state of no residual magnetism, the closing angle-inrush peak curve is fitted piecewise;

[0009] Under rated voltage, the control circuit breaker is actively closed at a 90° phase with the primary voltage of the transformer, and the peak inrush current is monitored.

[0010] The per-unit value of residual magnetism is determined by comparing the monitored inrush peak value with the closing angle-inrush peak value curve.

[0011] In one possible implementation, the step of fitting the closing angle-inrush current peak curve piecewise based on the closing angle and inrush current peak data under the no-residual magnetism state includes:

[0012] In the state of no residual magnetism, the circuit breaker is controlled to close at 40° phase and 75° phase of the primary voltage of the transformer, and the peak value of the inrush current is recorded.

[0013] Based on the inrush peak value, the closing angle-inrush peak value curve is segmented and fitted within the range of 0° to 90°, and then extended to the range of 0° to 180° through the principle of point symmetry to obtain the closing angle-inrush peak value curve.

[0014] In one possible implementation, the step of controlling the circuit breaker to actively close at a 90° phase with the primary voltage of the transformer under rated voltage includes:

[0015] The phase angle is extracted by real-time tracking of the primary side voltage waveform using phase-locked loop technology.

[0016] When the phase angle reaches 90°, the circuit breaker is triggered to close.

[0017] In one possible implementation, before segmentally fitting the closing angle-inrush current peak curve based on the closing angle under the no-residual magnetization state and historical inrush current peak data, the method further includes:

[0018] The historical inrush peak data were obtained by normalizing the historical closing test data.

[0019] In one possible implementation, determining the per-unit value of residual magnetism by comparing the monitored inrush current peak value with the closing angle-inrush current peak value curve includes:

[0020] Substitute the monitored inrush peak value into the closing angle-inrush peak value curve to calculate the corresponding closing angle;

[0021] The per-unit value of residual magnetism is determined based on the mapping relationship between the closing angle and the per-unit value of residual magnetism.

[0022] In one possible implementation, the piecewise fitting of the gate angle-inrush peak curve includes:

[0023] The fitting parameters are dynamically adjusted based on the sliding window algorithm, and the closing angle-inrush peak curve is obtained by retaining the latest N test data.

[0024] Based on the temperature and humidity data collected by environmental sensors, the slope and intercept of the closing angle-inrush peak curve are corrected.

[0025] In one possible implementation, the method further includes:

[0026] Close-in tests were conducted at 20°, 50°, and 80° phases, and the peak inrush current was recorded.

[0027] The least squares method was used to perform nonlinear fitting on the test data of multiple combination gates.

[0028] Secondly, embodiments of this application provide a residual magnetism detection device for a power transformer, comprising:

[0029] The voltage reduction and demagnetization module is used to perform voltage reduction and demagnetization treatment on power transformers, so that the residual magnetism of the iron core approaches zero.

[0030] The fitting module is used to fit the closing angle-inrush peak curve in segments based on the closing angle and historical inrush peak data under the state of no residual magnetism.

[0031] The monitoring module is used to control the circuit breaker to actively close at a 90° phase with the primary voltage of the transformer under rated voltage, and to monitor the peak inrush current.

[0032] The determination module is used to determine the per-unit value of residual magnetism by comparing the monitored inrush peak value with the closing angle-inrush peak value curve.

[0033] In one possible implementation, the fitting module specifically includes:

[0034] In the state of no residual magnetism, the circuit breaker is controlled to close at 40° phase and 75° phase of the primary voltage of the transformer, and the peak value of the inrush current is recorded.

[0035] Based on the inrush peak value, the closing angle-inrush peak value curve is segmented and fitted within the range of 0° to 90°, and then extended to the range of 0° to 180° through the principle of point symmetry to obtain the closing angle-inrush peak value curve.

[0036] In one possible implementation, the monitoring module specifically includes:

[0037] The phase angle is extracted by real-time tracking of the primary side voltage waveform using phase-locked loop technology.

[0038] When the phase angle reaches 90°, the circuit breaker is triggered to close.

[0039] In one possible implementation, the device further includes:

[0040] The preprocessing module is used to normalize the historical closing test data to obtain the historical inrush peak data.

[0041] In one possible implementation, the determining module specifically includes:

[0042] Substitute the monitored inrush peak value into the closing angle-inrush peak value curve to calculate the corresponding closing angle;

[0043] The per-unit value of residual magnetism is determined based on the mapping relationship between the closing angle and the per-unit value of residual magnetism.

[0044] In one possible implementation, the fitting module specifically includes:

[0045] The fitting parameters are dynamically adjusted based on the sliding window algorithm, and the closing angle-inrush peak curve is obtained by retaining the latest N test data.

[0046] Based on the temperature and humidity data collected by environmental sensors, the slope and intercept of the closing angle-inrush peak curve are corrected.

[0047] In one possible implementation, the fitting module further includes:

[0048] Close-in tests were conducted at 20°, 50°, and 80° phases, and the peak inrush current was recorded.

[0049] The least squares method was used to perform nonlinear fitting on the test data of multiple combination gates.

[0050] Thirdly, embodiments of this application provide an electronic device, including: a memory and a processor;

[0051] The memory stores computer-executed instructions;

[0052] The processor executes computer execution instructions stored in the memory, causing the processor to perform the first aspect and / or various possible implementations of the first aspect as described above.

[0053] Fourthly, embodiments of this application provide a computer-readable storage medium storing computer-executable instructions, which, when executed by a processor, are used to implement the first aspect and / or various possible implementations of the first aspect.

[0054] Fifthly, embodiments of this application provide a computer program product, including a computer program that, when executed by a processor, implements the first aspect and / or various possible implementations of the first aspect.

[0055] The residual magnetism detection method, apparatus, equipment, and storage medium for power transformers provided in this application perform voltage reduction and demagnetization treatment on the power transformer, bringing the residual magnetism of the core close to zero. Based on the closing angle and historical inrush current peak data under the state of no residual magnetism, a segmented closing angle-inrush current peak curve is fitted. Under rated voltage, the circuit breaker is controlled to actively close at a 90° phase with the primary voltage of the transformer, and the inrush current peak value is monitored. The monitored inrush current peak value is compared with the closing angle-inrush current peak curve to determine the per-unit value of residual magnetism. The above method can effectively measure the residual magnetism of the transformer core without adjusting the voltage or adding other equipment. The principle is simple, the steps are easy, and it has good effect on measuring the residual magnetism of transformers and verifying the demagnetization of transformers, with strong engineering applicability. Attached Figure Description

[0056] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0057] Figure 1 Flowchart of the residual magnetism detection method for power transformers provided in this application Figure 1 ;

[0058] Figure 2 Flowchart of the residual magnetism detection method for power transformers provided in this application Figure 2 ;

[0059] Figure 3 A schematic diagram of the closing angle-inrush current first cycle peak curve and piecewise fitting curve;

[0060] Figure 4 Flowchart of the residual magnetism detection method for power transformers provided in this application Figure 3 ;

[0061] Figure 5 Flowchart of the residual magnetism detection method for power transformers provided in this application Figure 4 ;

[0062] Figure 6 This is a schematic diagram of active closing and magnetic flux waveform at a 90° phase.

[0063] Figure 7 A schematic diagram of the residual magnetism detection device for the power transformer provided in this application;

[0064] Figure 8 A schematic diagram of the structure of the electronic device provided in this application.

[0065] The accompanying drawings have illustrated specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to specific embodiments. Detailed Implementation

[0066] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0067] Power transformers are extremely expensive and crucial electrical equipment. Due to the saturation characteristics of the transformer's ferromagnetic materials, residual magnetism often exists in the core when the transformer is switched off, typically around 20% to 70% of the steady-state main magnetic flux amplitude. After tests such as DC resistance testing, the residual magnetism may be even greater. Because of the presence of residual magnetism and the lack of reliable demagnetization methods, large inrush currents are often generated in the transformer windings during no-load switching operations, causing various hazards to the power system and the transformer itself. This can lead to malfunctions in the transformer's relay protection devices, increased maintenance costs, damage to electrical equipment in the system, and seriously affect the safe and stable operation of the power system. In summary, residual magnetism in the transformer core has many harmful effects, and its difficulty in measurement brings numerous challenges to residual magnetism research. Without studying residual magnetism, it is difficult to suppress inrush currents based on its state and characteristics. Furthermore, effective demagnetization methods require quantitative analysis of the residual magnetism after demagnetization to ensure the demagnetization effect. This necessitates the use of effective transformer core residual magnetism measurement devices to measure the magnitude of residual magnetism simply and efficiently. Based on this measurement, we can study the evolution mechanism of residual magnetism and demagnetization methods to minimize the problems caused by residual magnetism in the core.

[0068] To address the aforementioned problems, this application provides a method, apparatus, equipment, and storage medium for detecting residual magnetism in power transformers, solving the difficulty in measuring residual magnetism in transformer cores. Specifically, currently, power systems require residual magnetism measurements before transformer commissioning, after maintenance, or after testing to assess residual magnetism risks and implement demagnetization measures. Existing residual magnetism detection methods typically employ DC measurement or harmonic analysis. However, existing methods generally suffer from complex operation, reliance on specialized equipment, and long measurement cycles, failing to meet the demands of engineering sites for efficient, low-cost, and non-invasive measurements. Considering these issues, the inventors investigated whether it is possible to simply and efficiently measure transformer residual magnetism by closing the circuit at a 90° angle to a transformer containing residual magnetism, and then monitoring only the peak value of the inrush current in the first cycle. The method is characterized by segmentally fitting the transformer's closing angle-inrush current peak value curve through two specific phase closing tests, and actively closing the circuit at a 90° phase of the transformer's primary voltage, monitoring the transformer current peak value, and comparing it with the fitted curve. This allows for effective measurement of transformer core residual magnetism without voltage adjustment or the addition of other equipment. Based on this, the proposed solution is presented in this application.

[0069] The technical solution of this application and how the technical solution of this application solves the above-mentioned technical problems are described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of this application will now be described with reference to the accompanying drawings.

[0070] Figure 1Flowchart of the residual magnetism detection method for power transformers provided in this application Figure 1 ,like Figure 1 As shown, the method includes:

[0071] S101: Perform voltage reduction and demagnetization treatment on the power transformer to reduce the residual magnetism of the iron core to near zero.

[0072] In this step, to eliminate the original residual magnetism in the transformer core and establish a magnetism-free baseline state, and to avoid the original residual magnetism interfering with the fitting accuracy of the subsequent closing angle-inrush current peak value curve, ensuring that the curve can truly reflect the correlation between the pure closing angle and the inrush current peak value, the power transformer can be pre-treated with voltage reduction and demagnetization, thereby making the residual magnetism of the core close to zero.

[0073] Specifically, the transformer is briefly energized at a voltage level lower than its rated voltage. By controlling the magnitude and direction of the excitation current, the residual magnetic field in the core due to hysteresis is gradually eliminated. The core advantage of voltage reduction is to avoid excessive excitation current generated by high-voltage excitation, thus preventing impact on the transformer windings. After demagnetization, verification can be assisted by a small current test (not a necessary step). When the magnetic state of the core returns to the initial neutral point, the residual magnetism is considered to be close to zero. At this point, the transformer can be used as a reference device with no residual magnetism for subsequent curve fitting.

[0074] For example, eliminating the original residual magnetism in the transformer core and establishing a baseline operating condition with no residual magnetism can be expressed by the following formula:

[0075]

[0076] in, The residual magnetic flux of a transformer core refers to the irreversible magnetic flux remaining in the core after the transformer is switched off or tested. The unit is Weber (Wb).

[0077] The above formula reduces the voltage and demagnetizes the core so that the residual magnetic flux approaches zero, at which point the transformer enters a state with no residual magnetism.

[0078] S102: Based on the closing angle and historical inrush peak data under the state of no residual magnetism, the closing angle-inrush peak curve is fitted in segments.

[0079] In this step, in order to construct a baseline curve relating the closing angle and the peak inrush current under the condition of no residual magnetism, and to serve as a reference for the magnitude of residual magnetism under the condition of residual magnetism, curve fitting is performed based on the closing angle under the condition of no residual magnetism and historical peak inrush current data.

[0080] Specifically, in the absence of residual magnetism, the circuit breaker is controlled to close at 40° and 75° phases of the primary voltage of the transformer, and the peak value of the inrush current is recorded. Based on the peak value of the inrush current, the closing angle-peak value curve in the range of 0° to 90° is fitted in segments, and then extended to the range of 0° to 180° through the principle of point symmetry to obtain the closing angle-peak value curve.

[0081] Optionally, the fitting parameters can be dynamically adjusted based on the sliding window algorithm, retaining the latest N test data to fit the closing angle-inrush peak curve, and correcting the slope and intercept of the closing angle-inrush peak curve based on the temperature and humidity data collected by the environmental sensors.

[0082] In one possible implementation, closing tests can be conducted at 20°, 50°, and 80° phases respectively, recording the inrush peak value. The least squares method is then used to perform nonlinear fitting on the multiple closing test data. By conducting closing tests at 20°, 50°, and 80° phases respectively, more inrush peak data points are obtained, and nonlinear fitting using the least squares method generates a more accurate closing angle-inrush peak value curve.

[0083] S103: Under rated voltage, the control circuit breaker is actively closed at a 90° phase with the primary voltage of the transformer, and the peak inrush current is monitored.

[0084] In this step, in order to collect inrush current peak data that can maximize the influence of residual magnetism under residual magnetism conditions and provide core basis for residual magnetism derivation, the circuit breaker is controlled to actively close at a 90° phase with the primary voltage of the transformer under the preset rated voltage to monitor the inrush current peak.

[0085] Specifically, the phase-locked loop (PLL) technology is used to track the primary voltage waveform in real time, extract the phase angle, and trigger the circuit breaker to close when the phase angle reaches 90°.

[0086] The closing voltage is the rated voltage, which is consistent with the voltage conditions when fitting the reference curve, to avoid distortion of the inrush current peak due to voltage differences and to ensure the effectiveness of subsequent curve comparisons.

[0087] In the absence of residual magnetism, the peak inrush current of 90° phase closing approaches zero. At this time, the residual magnetism of the iron core becomes the dominant factor affecting the peak inrush current. The presence of residual magnetism will cause the maximum magnetic flux after closing to shift, thereby generating a significant excitation inrush current peak. This phase can maximize the influence of residual magnetism on the peak inrush current and improve measurement sensitivity.

[0088] The focus is on monitoring the peak value of the inrush current in the first cycle after closing the circuit. This is because the inrush current in the initial stage of closing is not affected by subsequent factors such as transformer winding losses and system impedance, and the peak value data is the most stable, which can truly reflect the change in magnetic flux corresponding to the residual magnetism.

[0089] S104: Determine the per-unit value of residual magnetism by comparing the monitored inrush peak value with the closing angle-inrush peak value curve.

[0090] In this step, to deduce the magnitude of the residual magnetism in the transformer core by comparing the peak value with the curve, and finally output the quantified residual magnetism result, the inrush current peak value is monitored and then compared with the fitted curve to obtain the per-unit value of the residual magnetism.

[0091] Specifically, the monitored inrush peak value is substituted into the closing angle-inrush peak value curve to calculate the corresponding closing angle. Based on the mapping relationship between the closing angle and the per-unit value of residual magnetism, the per-unit value of residual magnetism is determined.

[0092] The residual magnetism detection method for power transformers provided in this application involves voltage reduction and demagnetization treatment of the power transformer to bring the residual magnetism of the core close to zero. Based on the closing angle and historical inrush current peak data under the state of no residual magnetism, a segmented closing angle-inrush current peak curve is fitted. Under rated voltage, the circuit breaker is actively closed at a 90° phase with the primary voltage of the transformer, and the inrush current peak value is monitored. The monitored inrush current peak value is compared with the closing angle-inrush current peak curve to determine the per-unit value of residual magnetism. The above method can effectively measure the residual magnetism of the transformer core without adjusting the voltage or adding other equipment. The principle is simple, the steps are easy, and it has good effect on measuring the residual magnetism of transformers and verifying the demagnetization of transformers, with strong engineering applicability.

[0093] Figure 2 Flowchart of the residual magnetism detection method for power transformers provided in this application Figure 2 ,like Figure 2 As shown, based on the above embodiment, step S102 specifically includes:

[0094] S201: In the state of no residual magnetism, control the circuit breaker to close at the 40° phase and 75° phase of the primary voltage of the transformer respectively, and record the peak value of the inrush current.

[0095] In this step, under the baseline condition where the residual magnetism of the transformer core approaches zero, representative data reflecting the variation law of the inrush current peak value in the 0°~90° closing angle range are collected. This provides core input parameters for subsequent curve fitting, while minimizing the number of closing tests and reducing the impact of the test on the transformer. Then, under the condition of no residual magnetism, different phases are selected for closing, and the inrush current peak value is recorded.

[0096] Specifically, choosing two specific phases, 40° and 75°, instead of random phases, is based on the changing characteristics of transformer inrush current.

[0097] 40° phase: Located in the middle section of the 0°~90° range, the core magnetic flux generated by closing the circuit is at a moderate level, and the corresponding inrush current peak value has obvious differentiation, which can effectively reflect the basic trend of inrush current peak value in this range.

[0098] 75° phase: close to the 90° critical phase, and the 90° phase is a special critical point in the state of no residual magnetism - the peak inrush current approaches zero when the switch is closed at this phase. Choosing the 75° phase can achieve a smooth transition with the 90° critical point and avoid the fitting curve from having a discontinuity in the 75°~90° range.

[0099] The two phases cover the key change range of 0° to 90°, and only two closing tests are needed to support subsequent segmented fitting, balancing test efficiency and data validity.

[0100] After closing the circuit, the excitation inrush current waveform is monitored in real time. The peak value of the inrush current in the first cycle after closing the circuit is extracted (the inrush current is not affected by subsequent factors such as winding loss and system impedance during this stage, and the data is the most stable). The peak values ​​corresponding to the 40° phase and the 75° phase are recorded respectively.

[0101] For example, the correlation formula between the peak value of the residual flux and the closing angle can be expressed as:

[0102]

[0103] in, This represents the maximum magnetic flux generated in the iron core when the switch is closed in a state of no residual magnetism, expressed in Weber (Wb). This represents the rated magnetic flux amplitude of the transformer core, which is determined by the transformer's rated voltage and frequency. It is an inherent parameter of the transformer. It represents the closing angle of the primary voltage of the transformer, which is the angle between the voltage phase at the moment of closing and the voltage zero-crossing point.

[0104] The peak value of the inrush current in the first cycle after two closing cycles is monitored in real time and recorded as follows: and .

[0105] S202: Based on the inrush peak value, the closing angle-inrush peak value curve is piecewise fitted in the range of 0° to 90°, and extended to the range of 0° to 180° through the principle of point symmetry to obtain the closing angle-inrush peak value curve.

[0106] This step is divided into two sub-steps: piecewise fitting and symmetrical expansion. The final result is a reference curve that covers the entire closing angle range, which is the core reference for subsequent residual magnetism measurement.

[0107] Using the 40° and 75° phase inrush peak values ​​collected by S201 as two anchor points, the inrush peak value corresponding to any closing angle within this range was fitted using linear interpolation. This range covers most operating conditions from 0° to 90°, and the linear fitting results fully meet the engineering measurement accuracy requirements. Taking advantage of the characteristic that the inrush peak value approaches zero when closing at the 90° phase, the measured peak value at the 75° phase and the zero peak value at the 90° phase were used as anchor points to continue linearly fitting the curve for this range, ensuring that the curve converges smoothly at the 90° phase without obvious discontinuities.

[0108] The specific formula for piecewise fitting the closing angle-inrush peak flow curve within the 0° to 90° range is expressed as follows:

[0109]

[0110] in, Represents the arbitrary closing angle obtained from the fitting. The corresponding peak flow rate, This indicates the closing angle of the primary voltage of the transformer.

[0111] It should be noted that, based on the characteristic that the peak inrush current and the closing angle have an approximately linear relationship within a small interval when the transformer has no residual magnetism, a piecewise fitting of a linear function is adopted.

[0112] The primary voltage of the transformer is a sinusoidal alternating signal. With the 90° phase as the axis of symmetry, the voltage phase in the 0°~90° interval and the 90°~180° interval are distributed in a point-symmetric manner. The peak inrush current is determined by the voltage phase (closing angle), so the closing angle-peak inrush current curve also has the same point-symmetric characteristics.

[0113] Using the 90° phase as the axis of symmetry, the fitted curve in the 0°~90° range is mirrored and extended:

[0114] The curve in the 90°~105° range is symmetrical to the curve in the 75°~90° range;

[0115] The curve in the 105°~180° interval is symmetrical to the curve in the 0°~75° interval.

[0116] Without the need for any additional closing tests, a reference curve covering the entire closing angle range of 0° to 180° can be quickly generated, significantly saving testing costs and time.

[0117] For the closing angle at to The formula for fitting a curve within a given range is expressed as:

[0118]

[0119] For example, Figure 3The diagram shows the closing angle-inrush current first cycle peak value curve and the piecewise fitting curve, as follows: Figure 3 As shown, first use and The peak inrush current curve for the closing angle from 0 to 90° is obtained by fitting a linear function. Then, utilizing the 90° symmetry, a complete closing angle-peak inrush current curve is fitted. The fitting data requirements are relatively small, and the accuracy meets the requirements for residual magnetism measurement.

[0120] Optionally, the piecewise fitting of the gate angle-peak flow curve may also include:

[0121] The fitting parameters are dynamically adjusted based on the sliding window algorithm, and the closing angle-inrush peak curve is obtained by retaining the latest N test data.

[0122] Based on temperature and humidity data collected by environmental sensors, the slope and intercept of the closing angle-inrush peak curve are corrected.

[0123] In application scenarios, the equipment status of field transformers (such as winding resistance and core permeability) changes slowly over time, and outdated test data can lead to distorted fitting curves. The sliding window algorithm dynamically updates the fitting parameters by retaining the latest N test data, ensuring that the curve always closely matches the current equipment status.

[0124] Set the sliding window size to N (e.g., N=5), that is, retain the inrush peak data of the latest 5 40° and 75° phase closing tests, form datasets respectively, take the average value of the datasets in the window to obtain the latest reference peak value, substitute it into the formula of the aforementioned step S202 to recalculate the fitting slope and intercept. Each time a new set of test data is added, the oldest set of data is removed, keep the amount of data in the window to N, and repeat the above process.

[0125] Temperature and humidity affect the permeability of the transformer core and the resistance of the windings. As temperature increases, the permeability of the core decreases, resulting in a lower peak inrush current at the same closing angle. Increased humidity may alter the insulation properties of the winding surface, also slightly affecting the inrush current magnitude. Therefore, an environmental correction factor needs to be introduced to optimize the fitting curve.

[0126] Temperature sensors (T) and humidity sensors (H) are deployed near the transformer to collect environmental parameters during the closing test. Through a large number of experiments, a correlation model (such as a linear correction model) is established between the environmental parameters and the slope k and intercept b of the fitted curve. The corrected slope and intercept are substituted into the formula in step S202 to obtain the closed angle-inrush peak curve after environmental correction.

[0127] In one possible implementation, step S102 may further include:

[0128] Close-in tests were conducted at 20°, 50°, and 80° phases, and the peak inrush current was recorded.

[0129] The least squares method was used to perform nonlinear fitting on the test data of multiple combination gates.

[0130] By increasing the number of phase tests and employing a nonlinear fitting algorithm, the curve accuracy is further improved, making it suitable for scenarios with high measurement accuracy requirements. Under the condition of no residual magnetism, three new phase closing tests at 20°, 50°, and 80° were added. Combined with the existing 40° and 75° phases, a total of five phases of inrush current peak data were collected, forming multiple sets of data pairs.

[0131] Considering the slight saturation characteristics of the iron core, the actual peak inrush current and the closing angle are not completely linear. A nonlinear model is selected to minimize the sum of squared errors. The optimal parameters are obtained by solving the system of equations. The parameters are substituted into the nonlinear model to obtain the fitting curve in the range of 0° to 90°. Then, the range of 0° to 180° is extended by the principle of point symmetry.

[0132] The residual magnetism detection method for power transformers provided in this application involves controlling the circuit breaker to close at 40° and 75° phases of the transformer's primary voltage in a state without residual magnetism, recording the inrush current peak value. Based on the inrush current peak value, a closing angle-inrush current peak value curve is segmentally fitted within the 0° to 90° range. This is then extended to the 0° to 180° range using the principle of point symmetry to obtain the closing angle-inrush current peak value curve. This method allows for the acquisition of core data supporting curve fitting within the 0°~90° range with only two precise closing tests, significantly reducing on-site testing workload and minimizing the impact of testing on normal transformer operation and maintenance. Segment fitting, compared to overall fitting, more closely reflects the actual variation law of the inrush current peak value, avoiding fitting errors caused by large range spans. No additional closing tests are required to quickly generate a reference curve covering the complete 0°~180° closing angle range, significantly saving testing costs and time.

[0133] Figure 4 Flowchart of the residual magnetism detection method for power transformers provided in this application Figure 3 ,like Figure 4 As shown, based on the above embodiments, step S103 specifically includes:

[0134] S401: Real-time tracking of primary side voltage waveform and extraction of phase angle using phase-locked loop technology.

[0135] The core of this step is to use a phase-locked loop circuit to track, filter, and calculate the phase of the primary voltage waveform of the transformer in real time, and output continuous and accurate voltage phase angle data to provide a basis for the closing trigger of S402.

[0136] The analog voltage signal is obtained from the primary voltage transformer (PT) of the transformer. This signal is in phase and has the same frequency as the primary voltage, and its amplitude is reduced to a safe level (e.g., 100V) to facilitate subsequent circuit processing. During the acquisition process, the real-time performance of the signal must be ensured, and the sampling frequency should not be less than 20 times the fundamental voltage frequency (e.g., for a 50Hz power frequency system, the sampling frequency should be ≥1000Hz) to avoid loss of phase information.

[0137] The phase-locked loop circuit consists of three core modules: a phase detector (PD), a loop filter (LF), and a voltage-controlled oscillator (VCO). Its operation process is as follows:

[0138] Phase detector phase comparison: The acquired voltage fundamental signal is compared with the reference signal output by the voltage-controlled oscillator, and the phase difference between the two is calculated; if a phase difference exists, the phase detector outputs the corresponding error voltage signal.

[0139] Loop filter to remove interference: Low-pass filtering is performed on the error voltage signal to eliminate high-frequency interference caused by power grid harmonics and voltage fluctuations, and output a smooth DC control voltage. This step is the key to ensuring phase tracking accuracy and can effectively suppress the influence of power grid noise on phase detection.

[0140] Voltage-controlled oscillator frequency adjustment: Adjust the frequency and phase of the output reference signal according to the DC control voltage until the reference signal is in phase and frequency with the fundamental signal of the input voltage. At this time, the phase-locked loop enters the locked state.

[0141] Once the phase-locked loop (PLL) enters the locked state, the phase calculation module converts the output signal of the voltage-controlled oscillator (VCO) into a continuously varying digital phase angle from 0° to 360°, and transmits it to the circuit breaker control unit in real time. The output phase angle accuracy can reach ±0.1°, fully meeting the accuracy requirements for 90° phase closing.

[0142] The phase angle data is updated at the same frequency as the sampling frequency to ensure real-time tracking of the voltage phase.

[0143] S402: When the phase angle reaches 90°, the circuit breaker is triggered to close.

[0144] The core of this step is to accurately determine the 90° phase point based on the precise phase angle output by S301 and trigger the circuit breaker to close. At the same time, the delay compensation eliminates the influence of the mechanical action delay of the circuit breaker, ensuring that the phase is exactly 90° at the moment of actual closing.

[0145] Confirm that the transformer is in a state of residual magnetism and ready to be closed, and that the primary voltage is the rated voltage, consistent with the voltage conditions when the reference curve is fitted; confirm that the circuit breaker is in a state of ready to be opened, that the mechanical mechanism is not stuck, and that the operating parameters (such as closing time) have been calibrated in advance.

[0146] The circuit breaker control unit receives the phase angle data output by S301 in real time. When the phase angle reaches 90°, it triggers the closing command.

[0147] Optionally, if the circuit breaker has a mechanical action delay, an early triggering compensation strategy must be adopted. The specific compensation strategy can be designed according to the actual application scenario, and this application embodiment does not impose specific limitations.

[0148] After receiving the trigger signal, the circuit breaker activates its mechanical mechanism to complete one side circuit closing. After closing, the status feedback module sends a closing success signal to the control system and simultaneously starts the inrush current peak monitoring module to prepare for collecting the inrush current peak value of the first cycle after closing.

[0149] The residual magnetism detection method for power transformers provided in this application uses phase-locked loop (PLL) technology to track the primary voltage waveform in real time, extract the phase angle, and trigger the circuit breaker to close when the detected phase angle reaches 90°. This method improves the stability of operation under complex field conditions and avoids errors caused by manual operation.

[0150] Figure 5 Flowchart of the residual magnetism detection method for power transformers provided in this application Figure 4 ,like Figure 5 As shown, based on the above embodiment, step S104 specifically includes:

[0151] S501: Substitute the monitored inrush peak value into the closing angle-inrush peak value curve to calculate the corresponding closing angle.

[0152] In this step, the peak inrush current monitored under residual magnetism conditions will be... By comparing the closing angle-inrush current peak value reference curve with that under the state of no residual magnetism, the equivalent closing angle corresponding to the peak value is found. .

[0153] It should be noted that the equivalent closing angle is a core concept here: when there is no residual magnetism, different closing angles correspond to different inrush current peak values; when there is residual magnetism, the inrush current peak value generated by closing at a 90° phase can be found at a peak point on the reference curve that is equal to it, and the closing angle corresponding to this point is the equivalent closing angle. .

[0154] The peak value of the remanent magnetization surge detected The peak range of each interval of the baseline curve is compared to determine its corresponding fitting interval (e.g., 0°~75°, 75°~90°, 90°~105°, etc.). Based on the interval, the corresponding piecewise fitting formula is called to solve for the equivalent closing angle. .

[0155] S502: Determine the per-unit value of residual magnetism based on the mapping relationship between the closing angle and the per-unit value of residual magnetism.

[0156] The equivalent closing angle obtained based on S501 Based on the basic principles of transformer magnetic circuits, the per-unit value of residual magnetism in the transformer core is calculated through the derivation of the magnetic flux equivalence formula, thus completing the quantitative determination of residual magnetism.

[0157] The formula for the peak flux in the case of remanent magnetization can be expressed as:

[0158]

[0159] in, This represents the maximum magnetic flux of the iron core when the circuit is closed at a 90° phase, while retaining residual magnetism. This indicates the per-unit value of the residual magnetism.

[0160] because corresponding ,and corresponding They are equal, therefore, by combining the formulas, we can obtain:

[0161]

[0162]

[0163] Optionally, this step is used to verify the demagnetization effect of the transformer. The entire measurement process can be repeated on the demagnetized transformer: if the final calculated If the absolute value is less than the threshold, the demagnetization is deemed successful; if it is greater than the threshold, the demagnetization operation must be repeated.

[0164] For example, Figure 6 This is a schematic diagram of active closing and magnetic flux waveform at a 90° phase, as shown below. Figure 6 As shown, the transformer containing residual magnetism is actively closed at a 90° phase, and the inrush current waveform is continuously monitored. The peak value of the first cycle of inrush current is compared with the closing angle-inrush current peak value curve to obtain the corresponding closing angle, thereby reflecting the per-unit value of residual magnetism. Therefore, this scheme can directly obtain the magnitude of residual magnetism, is simple in principle, and is easy to apply.

[0165] The residual magnetism detection method for power transformers provided in this application substitutes the monitored inrush current peak value into the closing angle-inrush current peak value curve to calculate the corresponding closing angle. Based on the mapping relationship between the closing angle and the per-unit value of residual magnetism, the per-unit value of residual magnetism is determined. This method transforms complex magnetic circuit analysis into simple numerical calculations, significantly reducing the operational difficulty on-site. Simultaneously, the per-unit value output format enhances the versatility of the measurement results, facilitating maintenance personnel to quickly determine residual magnetism risks.

[0166] Figure 7A schematic diagram of the residual magnetism detection device for power transformers provided in this application is shown below. Figure 7 As shown, the residual magnetism detection device 700 for power transformers provided in this embodiment includes:

[0167] The step-down demagnetization module 701 is used to perform step-down demagnetization treatment on power transformers, so that the residual magnetism of the iron core approaches zero.

[0168] The fitting module 702 is used to fit the closing angle-inrush peak curve in segments based on the closing angle and historical inrush peak data under the state of no residual magnetism.

[0169] Monitoring module 703 is used to control the circuit breaker to actively close at a 90° phase with the primary voltage of the transformer under rated voltage, and to monitor the peak inrush current.

[0170] The determination module 704 is used to determine the per-unit value of residual magnetism by comparing the monitored inrush peak value with the closing angle-inrush peak value curve.

[0171] In one possible implementation, the fitting module 702 specifically includes:

[0172] In the state of no residual magnetism, the circuit breaker is controlled to close at 40° phase and 75° phase of the primary voltage of the transformer, and the peak value of the inrush current is recorded.

[0173] Based on the peak inrush flow, the closing angle-peak inrush flow curve is fitted piecewise within the range of 0° to 90°, and then extended to the range of 0° to 180° through the principle of point symmetry to obtain the closing angle-peak inrush flow curve.

[0174] In one possible implementation, the monitoring module 703 specifically includes:

[0175] The phase angle is extracted by real-time tracking of the primary side voltage waveform using phase-locked loop technology.

[0176] When the phase angle reaches 90°, the circuit breaker is triggered to close.

[0177] In one possible implementation, the residual magnetism detection device 700 for the power transformer further includes:

[0178] The preprocessing module 705 is used to normalize the historical closing test data to obtain historical inrush peak data.

[0179] In one possible implementation, the determining module 704 specifically includes:

[0180] Substitute the monitored inrush peak value into the closing angle-inrush peak value curve to calculate the corresponding closing angle;

[0181] The per-unit value of residual magnetism is determined based on the mapping relationship between the closing angle and the per-unit value of residual magnetism.

[0182] In one possible implementation, the fitting module 702 specifically includes:

[0183] The fitting parameters are dynamically adjusted based on the sliding window algorithm, and the closing angle-inrush peak curve is obtained by retaining the latest N test data.

[0184] Based on temperature and humidity data collected by environmental sensors, the slope and intercept of the closing angle-inrush peak curve are corrected.

[0185] In one possible implementation, the fitting module 702 further includes:

[0186] Close-in tests were conducted at 20°, 50°, and 80° phases, and the peak inrush current was recorded.

[0187] The least squares method was used to perform nonlinear fitting on the test data of multiple combination gates.

[0188] The residual magnetism detection device for power transformers provided in this embodiment can perform the residual magnetism detection method for power transformers provided in the above method embodiment. Its implementation principle and technical effect are similar, and will not be described in detail here.

[0189] Figure 8 A schematic diagram of the structure of the electronic device provided in this application. Figure 8 As shown, the electronic device 800 provided in this embodiment includes at least one processor 801 and a memory 802. Optionally, the electronic device 800 further includes a communication component 803. The processor 801, memory 802, and communication component 803 are connected via a bus 804.

[0190] In a specific implementation, at least one processor 801 executes computer execution instructions stored in memory 802, causing at least one processor 801 to perform the methods of the above embodiments.

[0191] The specific implementation process of processor 801 can be found in the above-mentioned method embodiments, and its implementation principle and technical effect are similar. Therefore, it will not be repeated here.

[0192] In the above embodiments, it should be understood that the processor can be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), etc. The general-purpose processor can be a microprocessor or any conventional processor. The steps of the method disclosed in this invention can be directly implemented by a hardware processor, or implemented by a combination of hardware and software modules within the processor.

[0193] The memory may include random access memory (RAM) and may also include non-volatile memory (NVM), such as at least one disk storage device.

[0194] The bus can be an Industry Standard Architecture (ISA) bus, a Peripheral Component Interconnect (PCI) bus, or an Extended Industry Standard Architecture (EISA) bus, etc. Buses can be categorized as address buses, data buses, control buses, etc. For ease of illustration, the buses shown in the accompanying drawings are not limited to a single bus or a single type of bus.

[0195] This application also provides a computer program product, including a computer program that, when executed by a processor, implements the methods of the various embodiments described above.

[0196] This application also provides a computer-readable storage medium storing computer-executable instructions, which, when executed by a processor, implement the methods of the above embodiments.

[0197] The aforementioned readable storage medium can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), magnetic storage, flash memory, magnetic disk, or optical disk. The readable storage medium can be any available medium accessible to a general-purpose or special-purpose computer.

[0198] An exemplary readable storage medium is coupled to a processor, enabling the processor to read information from and write information to the readable storage medium. Of course, the readable storage medium can also be a component of the processor. The processor and the readable storage medium can reside in an Application Specific Integrated Circuit (ASIC). Alternatively, the processor and the readable storage medium can exist as discrete components in the device.

[0199] The division of units is merely a logical functional division; 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 indirect coupling or communication connection through some interfaces, devices, or units, and may be electrical, mechanical, or other forms.

[0200] 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.

[0201] In addition, 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.

[0202] If a function is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this invention, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0203] Those skilled in the art will understand that all or part of the steps of the above-described method embodiments can be implemented by hardware related to program instructions. The aforementioned program can be stored in a computer-readable storage medium. When executed, the program performs the steps of the above-described method embodiments; and the aforementioned storage medium includes various media capable of storing program code, such as ROM, RAM, magnetic disks, or optical disks.

[0204] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A method for detecting residual magnetism in a power transformer, characterized in that, include: Voltage reduction and demagnetization treatment is applied to power transformers to reduce the residual magnetism of the iron core to near zero. Based on the closing angle and historical inrush peak data under the state of no residual magnetism, the closing angle-inrush peak curve is fitted piecewise; Under rated voltage, the control circuit breaker is actively closed at a 90° phase with the primary voltage of the transformer, and the peak inrush current is monitored. The per-unit value of residual magnetism is determined by comparing the monitored inrush peak value with the closing angle-inrush peak value curve.

2. The method according to claim 1, characterized in that, The step of fitting the closing angle-inrush current peak curve piecewise based on the closing angle and inrush current peak data under the no residual magnetism state includes: In the state of no residual magnetism, the circuit breaker is controlled to close at 40° phase and 75° phase of the primary voltage of the transformer, and the peak value of the inrush current is recorded. Based on the inrush peak value, the closing angle-inrush peak value curve is segmented and fitted within the range of 0° to 90°, and then extended to the range of 0° to 180° through the principle of point symmetry to obtain the closing angle-inrush peak value curve.

3. The method according to claim 1, characterized in that, The control of the circuit breaker to actively close at a 90° phase with the primary voltage of the transformer under rated voltage includes: The phase angle is extracted by real-time tracking of the primary side voltage waveform using phase-locked loop technology. When the phase angle reaches 90°, the circuit breaker is triggered to close.

4. The method according to claim 1, characterized in that, Before fitting the closing angle-inrush current peak value curve piecewise based on the closing angle under the no-residual magnetization state and historical inrush current peak value data, the method further includes: The historical inrush peak data were obtained by normalizing the historical closing test data.

5. The method according to claim 1, characterized in that, The step of determining the per-unit value of residual magnetism by comparing the monitored inrush peak value with the closing angle-inrush peak value curve includes: Substitute the monitored inrush peak value into the closing angle-inrush peak value curve to calculate the corresponding closing angle; The per-unit value of residual magnetism is determined based on the mapping relationship between the closing angle and the per-unit value of residual magnetism.

6. The method according to claim 1, characterized in that, The segmented fitted gate angle-inrush peak flow curve includes: The fitting parameters are dynamically adjusted based on the sliding window algorithm, and the closing angle-inrush peak curve is obtained by retaining the latest N test data. Based on the temperature and humidity data collected by environmental sensors, the slope and intercept of the closing angle-inrush peak curve are corrected.

7. The method according to claim 2, characterized in that, The method further includes: Close-in tests were conducted at 20°, 50°, and 80° phases, and the peak inrush current was recorded. The least squares method was used to perform nonlinear fitting on the test data of multiple combination gates.

8. A residual magnetism detection device for a power transformer, characterized in that, include: The voltage reduction and demagnetization module is used to perform voltage reduction and demagnetization treatment on power transformers, so that the residual magnetism of the iron core approaches zero. The fitting module is used to fit the closing angle-inrush peak curve in segments based on the closing angle and historical inrush peak data under the state of no residual magnetism. The monitoring module is used to control the circuit breaker to actively close at a 90° phase with the primary voltage of the transformer under rated voltage, and to monitor the peak inrush current. The determination module is used to determine the per-unit value of residual magnetism by comparing the monitored inrush peak value with the closing angle-inrush peak value curve.

9. An electronic device, characterized in that, include: Memory, processor; The memory stores computer-executed instructions; The processor executes computer execution instructions stored in the memory, causing the processor to perform the residual magnetism detection method for a power transformer as described in any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer-executable instructions, which, when executed by a processor, are used to implement the residual magnetism detection method for a power transformer as described in any one of claims 1 to 7.

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