Method for measuring and analyzing residual magnetism characteristics of iron core

Abstract

The invention discloses a method for measuring and analyzing residual magnetism characteristics of an iron core. According to the method, a to-be-detected iron core is demagnetized, preset residual magnetism is set, direct-current voltage excitation with opposite polarities, the same amplitude and the same duration is applied to a primary winding of the to-be-detected iron core, and transient current response signals are synchronously collected; two groups of current under positive / negative polarity excitation are extracted, and the residual magnetism direction is judged by comparing the change rate of the current; a curve of equivalent resistance changing along with time is calculated based on forward current and voltage, a resistance value corresponding to a characteristic inflection point moment is selected, the resistance value is substituted into a pre-established residual magnetism-equivalent resistance empirical formula to deduce the magnitude of residual magnetism, and a matched iron core residual magnetism detection and demagnetization integrated system integrates information management, residual magnetism detection, demagnetization and display modules. And closed-loop automation of detection, analysis and demagnetization is realized. According to the method, a magnetic field sensor is not needed, the residual magnetism direction and size can be synchronously obtained in a high-precision and robust mode only through port electric signals, and the method is suitable for on-site off-line or live detection.

Description

Technical Field

[0001] This invention relates to the field of power transformer condition detection and maintenance technology, and in particular to a method for measuring and analyzing the residual magnetism characteristics of the iron core. Background Technology

[0002] Transformers are key equipment in power systems for voltage transformation, power transmission, and distribution, and their operating status directly affects the stability, economy, and security of the power grid. With the continuous development of my country's smart grid, the new generation of power systems also places higher demands on transformer performance.

[0003] With the development of the power grid, the requirements for power transformers are increasing, and their performance requirements are also becoming more stringent. As a crucial part of the power grid, power transformers play a vital role in voltage step-up and step-down, and are an indispensable link in the power transmission process. The problem of residual magnetism within the core magnetic circuit of power transformers is widespread. After rapid development in recent years, my country's power system has reached a world-leading level, with power transformer capacities increasing significantly, with the largest single unit exceeding 1000 MVA. Furthermore, voltage levels are rising, reaching as high as 1000 kV. The problem of residual magnetism within the cores of large power transformers is becoming increasingly serious, especially in step-up transformers in power plants, converter transformers used for DC transmission, and main transformers in substations, where the residual magnetism problem is most severe.

[0004] In existing technologies, the open-loop DC demagnetization method or the direct magnetic field measurement method based on Hall sensors is often used to evaluate residual magnetism. The former relies on empirical voltage amplitude and the number of times it is applied, and cannot quantitatively determine the magnitude and direction of residual magnetism. The latter requires high-precision magnetic field probes to be placed in the air gap or on the surface of the iron core. Due to limitations in installation location, temperature drift and spatial resolution, it is difficult to achieve non-destructive, online, closed-loop measurement at the winding port. Summary of the Invention

[0005] To address the aforementioned problems, this application provides a method for measuring and analyzing the remanence characteristics of iron cores, the method comprising: S1. Demagnetize the iron core under test by applying a DC voltage excitation to a preset winding of the iron core under test to generate a controllable preset residual magnetism in the iron core under test. S2. Apply a set of small DC signal voltage excitations with opposite polarity, the same amplitude, and the same duration to the primary winding of the iron core under test; S3. During the application of each group of DC small-signal voltage excitation, the first transient current response signal under positive DC small-signal voltage excitation and the second transient current response signal under negative DC small-signal voltage excitation are collected respectively. S4. Compare the instantaneous change rates of the first transient current response signal and the second transient current response signal at the same observation time; S5. Determine the remanent magnetization direction of the core under test based on the comparison result of the rate of change, and determine the transient current response signal collected under the excitation of the DC voltage signal with the same remanent magnetization direction as the positive transient current response signal. S6. Based on the positive transient current response signal and the corresponding DC voltage signal, calculate the curve of the equivalent resistance of the core during the transient process as a function of time according to Kirchhoff's law of the circuit. S7. Select the equivalent resistance value at the characteristic inflection point on the curve of the equivalent resistance changing with time. S8. Substitute the equivalent resistance value into the pre-established empirical formula of remanence-equivalent resistance to calculate the magnitude of the remanence of the iron core under test.

[0006] Furthermore, in step S1, the demagnetization process is achieved by applying an alternating voltage excitation with progressively decreasing amplitude to the preset winding until the hysteresis loop of the core contracts to near the origin. The alternating voltage excitation is a sinusoidal signal.

[0007] Further, in step S5, the direction of remanence of the core under test is determined based on the comparison result of the rate of change, specifically including: If the rate of change of the first transient current response signal at the same observation time is less than the rate of change of the second transient current response signal, then it is determined that the direction of the remanence of the iron core is opposite to the direction of the DC voltage excitation corresponding to the application of the first transient current response signal. If the rate of change of the first transient current response signal at the same observation time is greater than the rate of change of the second transient current response signal, then it is determined that the direction of the residual magnetism of the iron core is the same as the direction of the DC voltage excitation corresponding to the application of the first transient current response signal.

[0008] Furthermore, the rate of change is determined by calculating the first derivative of each transient current response signal with respect to time at the same observation time.

[0009] Furthermore, in step S7, the characteristic inflection point is the moment when the decay rate on the curve of the equivalent resistance changing with time changes from fast to slow, and the moment corresponds to the starting point of irreversible displacement of the magnetic domain walls inside the core.

[0010] Furthermore, in step S8, the pre-established empirical formula for remanence-equivalent resistance is obtained through finite element simulation, specifically as follows: S8.1. Based on the actual size and material properties of the iron core to be tested, establish a three-dimensional finite element model including the primary winding, the geometry of the iron core and the circuit parameters, and set the magnetization characteristics of the iron core material. S8.2 In the primary winding circuit of the three-dimensional finite element model, by applying DC excitation of different amplitudes until the iron core is saturated and then withdrawing it, preset residual magnetism of different magnitudes and directions is generated in the simulated iron core. S8.3. Based on the preset residual magnetism, simulate the application of a small DC signal voltage excitation with the same parameters as in step S2 in the primary winding circuit, perform transient field-circuit coupling simulation, and extract the transient current waveform obtained from the simulation. S8.4. Based on the transient current waveform obtained from the simulation and the applied DC small-signal voltage excitation, calculate the curve of the equivalent resistance changing with time according to circuit theory, and extract the simulated value of the equivalent resistance at the characteristic inflection point. S8.5. Perform mathematical fitting on discrete data points composed of different preset remanent magnetization values ​​and their corresponding equivalent resistance simulation values ​​to obtain the empirical formula of remanent magnetization-equivalent resistance describing the functional relationship between remanent magnetization and equivalent resistance.

[0011] Furthermore, in step S8.5, the mathematical fitting adopts the least squares curve fitting method, and the resulting empirical formula for remanence-equivalent resistance is in the form of a nonlinear function, the function type of which is determined according to the goodness of fit.

[0012] On the other hand, this application provides an integrated system for core residual magnetism detection and demagnetization, used to implement the above-described method for measuring and analyzing the residual magnetism characteristics of cores. The system includes an information management module, a residual magnetism detection module, a demagnetization module, and a display module. The information management module is used to manage the parameters of the transformer under test, historical measurement data, demagnetization process parameters, and user permissions, including: The parameter input unit is used to receive or import the nameplate parameters and core material magnetic characteristic parameters of the transformer under test. The process management unit is used to store and recall preset residual magnetism detection parameters and demagnetization strategy parameters for transformers of different capacities and voltage levels. The data storage unit is used to store the raw data, process data, and result data of each measurement and demagnetization process; The user management unit is used to implement login verification, permission allocation, and operation log recording for operators; The residual magnetism detection module is connected to the primary winding of the transformer under test, and is used to perform the core residual magnetism characteristic measurement and analysis method described above, and output the polarity and magnitude information of the residual magnetism, including: The power supply excitation unit is used to generate a DC small-signal voltage excitation with controllable amplitude applied to the primary winding of the transformer under test; it includes a PWM modulation circuit, which compares the modulation wave with the carrier signal through a carrier signal generator and a comparator to generate a PWM waveform with adjustable duty cycle, and outputs it as the DC small-signal voltage excitation after power amplification; The current measurement unit is connected in series in the primary winding circuit of the transformer under test and is used to collect the transient current response signal during the application of DC voltage excitation. The voltage measurement unit is connected in parallel across the primary winding of the transformer under test to acquire the applied DC voltage excitation signal. The signal conditioning circuit is connected to the current measurement module and the voltage measurement module respectively, and is used to filter, amplify and condition the acquired current and voltage signals. The control loop is connected to the power module, the signal conditioning circuit and the demagnetizing module respectively. It is used to control the timing, amplitude and polarity of the excitation output by the power module, and to calculate the equivalent resistance based on the conditioned signal output by the signal conditioning circuit, so as to perform the remanent magnetization direction judgment and magnitude calculation as described above. The demagnetizing module is connected to the control loop, receives the residual magnetism information output by the residual magnetism detection module, and generates demagnetizing control commands according to the predetermined demagnetizing strategy, controlling the power supply module to output a series of demagnetizing voltage waveforms with attenuated amplitude and alternating polarity to the primary winding of the transformer under test. The display module is connected to the control loop and information management module, and is used to display the transient current waveform, voltage waveform, equivalent resistance change curve, calculated residual magnetism information, demagnetization process status and historical records in real time during the measurement process.

[0013] Furthermore, in the demagnetization module, the control logic of the demagnetization strategy is specifically as follows: The control loop controls the initial demagnetizing voltage output by the power supply module to have a polarity opposite to the remanent magnetization direction based on the remanent magnetization direction information output by the remanent magnetization detection module. During the demagnetization process, the control loop determines whether the core flux has reached positive or negative saturation based on the current waveform fed back by the current measurement module, and controls the power supply module to switch the polarity of the output voltage when saturation is detected, and reduces the amplitude of the output voltage according to a preset attenuation coefficient in each subsequent cycle. The control loop continuously monitors the magnetic flux difference between the positive and negative saturation points within a complete cycle during the later stage of demagnetization. When the difference is less than the preset demagnetization completion threshold, the demagnetization is determined to be complete and the power module is controlled to stop outputting.

[0014] Furthermore, in the power supply excitation unit, the method for determining the duty cycle of the waveform generated by the PWM modulation circuit is as follows: When the residual magnetism detection module performs the measurement, the control loop controls the PWM modulation circuit to output a PWM waveform with a fixed duty cycle, which is used to generate DC voltage excitation with the same amplitude but opposite polarity. When the demagnetizing module performs demagnetization, the control loop dynamically adjusts the duty cycle of the PWM waveform according to the magnitude and polarity information of the residual magnetism output by the residual magnetism detection module, based on preset rules. These preset rules include: The initial output polarity of the PWM waveform is opposite to the remanent magnetization polarity; In the initial stage of demagnetization, the initial duty cycle of the PWM waveform is positively correlated with the magnitude of the residual magnetism; During the demagnetization process, the control loop periodically reduces the duty cycle of the PWM waveform according to a preset attenuation coefficient.

[0015] The beneficial effects of this application are: This application provides a method for measuring and analyzing the remanence characteristics of iron cores, as well as an integrated system for detecting and demagnetizing remanence in iron cores. By applying DC voltage excitation with opposite polarity, equal amplitude, and equal duration to the primary winding, and simultaneously acquiring transient current response signals, the remanence direction is determined by comparing the rate of change of transient current under positive / negative polarity excitation. Then, based on the dynamic curve of equivalent resistance calculated from the positive transient current and voltage, the equivalent resistance value at the characteristic inflection point of the irreversible displacement of the corresponding magnetic domain wall is identified, and the magnitude of the remanence is deduced by substituting it into a pre-built remanence-equivalent resistance relationship model. This application achieves dual discrimination of remanence direction and magnitude, avoiding dependence on magnetic field sensors; it only requires voltage / current signal acquisition, resulting in low hardware cost and strong anti-interference capabilities; it exhibits significant inflection point characteristics and good robustness; the model-driven approach ensures quantization accuracy; and the entire measurement process is electrified, suitable for on-site live or offline testing. Attached Figure Description

[0016] Figure 1 This is a schematic flowchart of the method for measuring and analyzing the residual magnetism characteristics of the iron core according to the present invention.

[0017] Figure 2 This invention relates to a circuit for measuring the residual magnetism of an iron core.

[0018] Figure 3 This is the equivalent circuit model for measuring residual magnetism in this invention.

[0019] Figure 4 This is a graph showing the change of the equivalent resistance of the present invention over time.

[0020] Figure 5 This is a flowchart of the finite element simulation test of the present invention.

[0021] Figure 6 This is a schematic diagram of the three-dimensional model of the iron core of the present invention.

[0022] Figure 7 These are the positive and negative transient current response waveforms of the iron core with remanence in this invention.

[0023] Figure 8 This is the positive transient current response waveform of the iron core under different remanence conditions according to the present invention.

[0024] Figure 9 This invention relates to the magnetic flux density within the iron core under different remanence conditions.

[0025] Figure 10 This refers to the change in equivalent resistance of the iron core under different residual magnetism conditions.

[0026] Figure 11 This is an empirical formula fitting of the discrete points of residual magnetism in the iron core of the present invention. Detailed Implementation

[0027] The technical method of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0028] This application provides a method for measuring and analyzing the remanence characteristics of iron cores. The core of this method lies in mapping the macroscopic magnetic state of remanence to a precisely acquireable and analyzable transient current response difference, further transforming it into the dynamic evolution characteristics of equivalent resistance. Finally, a pre-built, physically consistent remanence-equivalent resistance relationship model is used to complete the quantitative inversion. This method does not rely on direct magnetic field measurement; it only requires applying a controlled DC voltage excitation and simultaneously acquiring the primary side port voltage and current signals to complete the determination of the remanence direction and calculation of its magnitude. It possesses strong robustness, high reproducibility, and engineering deployability.

[0029] Figure 1 The illustrated embodiment shows that the process of the method for measuring and analyzing the remanence characteristics of iron cores according to this application is as follows: S1. Demagnetize the iron core under test by applying a DC voltage excitation to a preset winding of the iron core under test to generate a controllable preset residual magnetism in the iron core under test. S2. Apply a set of small DC signal voltage excitations with opposite polarity, the same amplitude, and the same duration to the primary winding of the iron core under test; S3. During the application of each group of DC small-signal voltage excitation, the first transient current response signal under positive DC small-signal voltage excitation and the second transient current response signal under negative DC small-signal voltage excitation are collected respectively. S4. Compare the instantaneous change rates of the first transient current response signal and the second transient current response signal at the same observation time; S5. Determine the remanent magnetization direction of the core under test based on the comparison result of the rate of change, and determine the transient current response signal collected under the excitation of the DC voltage signal with the same remanent magnetization direction as the positive transient current response signal. S6. Based on the positive transient current response signal and the corresponding DC voltage signal, calculate the curve of the equivalent resistance of the core during the transient process as a function of time according to Kirchhoff's law of the circuit. S7. Select the equivalent resistance value at the characteristic inflection point on the curve of the equivalent resistance changing with time. S8. Substitute the equivalent resistance value into the pre-established empirical formula of remanence-equivalent resistance to calculate the magnitude of the remanence of the iron core under test.

[0030] In step S1, the demagnetization process is achieved by applying an alternating voltage excitation with progressively decreasing amplitude to the preset winding until the hysteresis loop of the iron core shrinks to near the origin. The alternating voltage excitation is a sinusoidal signal.

[0031] In step S5, the direction of remanence of the core under test is determined based on the comparison result of the rate of change, specifically including: If the rate of change of the first transient current response signal at the same observation time is less than the rate of change of the second transient current response signal, then it is determined that the direction of the remanence of the iron core is opposite to the direction of the DC voltage excitation corresponding to the application of the first transient current response signal. If the rate of change of the first transient current response signal at the same observation time is greater than the rate of change of the second transient current response signal, then it is determined that the direction of the residual magnetism of the iron core is the same as the direction of the DC voltage excitation corresponding to the application of the first transient current response signal.

[0032] The rate of change is determined by calculating the first derivative of each transient current response signal with respect to time at the same observation time.

[0033] In step S7, the characteristic inflection point is the moment when the decay rate on the curve of the equivalent resistance changing with time changes from fast to slow, and the moment corresponds to the starting point of irreversible displacement of the magnetic domain walls inside the iron core.

[0034] In step S8, the pre-established empirical formula for remanence-equivalent resistance is obtained through finite element simulation. The specific method is as follows: S8.1. Based on the actual size and material properties of the iron core to be tested, establish a three-dimensional finite element model including the primary winding, the geometry of the iron core and the circuit parameters, and set the magnetization characteristics of the iron core material. S8.2 In the primary winding circuit of the three-dimensional finite element model, by applying DC excitation of different amplitudes until the iron core is saturated and then withdrawing it, preset residual magnetism of different magnitudes and directions is generated in the simulated iron core. S8.3. Based on the preset residual magnetism, simulate the application of a small DC signal voltage excitation with the same parameters as in step S2 in the primary winding circuit, perform transient field-circuit coupling simulation, and extract the transient current waveform obtained from the simulation. S8.4. Based on the transient current waveform obtained from the simulation and the applied DC small-signal voltage excitation, calculate the curve of the equivalent resistance changing with time according to circuit theory, and extract the simulated value of the equivalent resistance at the characteristic inflection point. S8.5. Perform mathematical fitting on discrete data points composed of different preset remanent magnetization values ​​and their corresponding equivalent resistance simulation values ​​to obtain the empirical formula of remanent magnetization-equivalent resistance describing the functional relationship between remanent magnetization and equivalent resistance.

[0035] In step S8.5, the mathematical fitting adopts the least squares curve fitting method, and the resulting empirical formula for remanence-equivalent resistance is in the form of a nonlinear function. The function type is determined according to the goodness of fit.

[0036] Specific residual magnetism detection process: like Figure 2 A residual magnetism measurement circuit for the iron core is constructed, including a signal generator, a power amplifier, a digital oscilloscope, and a fluxmeter. The signal generator and the power amplifier are cascaded to form an excitation source, which is then connected to the primary winding of the iron core under test.

[0037] Demagnetization process: A sinusoidal AC voltage signal with an amplitude sufficient to saturate the iron core is generated by a control signal generator and applied to the primary winding through a power amplifier. While keeping the frequency constant, the voltage amplitude is slowly and continuously reduced to zero, causing the hysteresis loop of the iron core to gradually shrink to near the origin, thereby achieving demagnetization and avoiding the influence of other factors on the iron core residual magnetism measurement process.

[0038] Preset Residual Magnetism: A large DC voltage excitation is applied to the preset winding of the iron core. After the iron core is magnetized and stabilized, the excitation is removed. At this time, a certain residual magnetic flux will be generated in the iron core. The iron core magnetic flux after the excitation is removed and stabilized is recorded, which is the preset residual magnetism value. By changing the magnitude and direction of the preset excitation, residual magnetism of different magnitudes and polarities can be obtained.

[0039] Apply measurement excitation and acquire response signals: Apply a set of small DC voltage excitations of opposite polarity to the primary winding of an iron core with a pre-defined residual magnetism. The amplitude of the excitation should be small to avoid significantly changing the residual magnetism state under test. The duration of the excitation is fixed. Acquire and record the transient current response under positive polarity excitation. Similarly, transient current responses under negative polarity excitation were collected and recorded. ; Determining the direction of remanence: The direction of remanence is determined by comparing the transient current waveforms obtained from two measurements. When the current The rate of change is faster than This indicates that when a positive polarity excitation is applied, the direction of the excitation magnetic field is the same as the direction of the remanence, the differential permeability is small, the inductance effect is weak, and the current changes rapidly. Therefore, it can be determined that the direction of the remanence of the iron core is the same as the direction of the positive polarity excitation.

[0040] When the current The rate of change is slower than This indicates that when a positive polarity excitation is applied, the direction of the excitation magnetic field is opposite to the direction of the remanence. Therefore, it can be determined that the direction of the remanence of the iron core is opposite to the direction of the positive polarity excitation.

[0041] The rate of change can be determined by comparing the instantaneous values ​​of the current at the same time point, or by calculating the first derivative of the current waveform at the initial time.

[0042] Extracting the positive transient current: Based on the remanent magnetization direction of the iron core, the current collected under excitation with the same remanent magnetization direction is marked as the positive transient current response signal.

[0043] Calculate the curve of equivalent resistance changing over time: based on, for example... Figure 3 The equivalent circuit model shown is composed of the equivalent inductance. and equivalent resistance The circuit is constructed by connecting the components in parallel and then adding an external resistor R in series. The equivalent resistance is derived by applying Kirchhoff's voltage law. The relationship with the current in the equivalent circuit is as follows: Figure 4 As shown.

[0044] Select the equivalent resistance value at the characteristic inflection point: Analyze the equivalent resistance. The curve shows the decay rate changing over time. At the characteristic inflection point where the decay rate decreases from fast to slow, the time corresponding to this inflection point is selected. Extract the equivalent resistance value at that moment. This inflection point is considered to correspond to the starting moment of irreversible displacement of the magnetic domain walls inside the iron core, and is sensitive to the remanent magnetization state.

[0045] An empirical formula relating core remanence to equivalent resistance was established using finite element simulation. The obtained equivalent resistance value was then used to... By substituting the values ​​into the pre-generated empirical formula, the remanence of the iron core under test can be calculated.

[0046] The calculated remanence value is compared with the preset remanence value, and the relative error is calculated. The relative error can be controlled within 10%, which shows that the measurement results of the method of this application are in good agreement with the preset value, thus verifying the effectiveness and accuracy of the method of this application.

[0047] Example 2 like Figure 5 As shown, an empirical formula relating the remanence of the iron core to its equivalent resistance is established through finite element simulation. The specific process is as follows: like Figure 6 As shown, the transformer square core sample used in the simulation is made of B30P105 grain-oriented cold-rolled silicon steel sheet with a thickness of 0.3 mm. The overall thickness of the core is 20 mm, and the width is 80 mm. The lamination factor of this sample is 0.96. The overlapping parts of the silicon steel sheets are clamped and fixed to the core using nylon bolts. The yellow part in the figure is an epoxy resin board with an overall thickness of 30 mm. Primary and secondary windings are wound on the core, serving as the preset residual magnetism winding and the measurement residual magnetism winding, respectively. The parameters of the square core sample are shown in Table 1.

[0048] Table 1. Relevant parameters of square iron core sample name numerical values Iron core material B30P105 Cross-sectional area <![CDATA[1600 mm 2 ]]> Average magnetic path length 1920 mm <![CDATA[Power frequency saturation magnetic density B m > 1800 mT Silicon steel sheet density <![CDATA[7650 kg / m 3 ]]> Total mass of the model M 24 kg Preset number of turns of residual magnetization winding 50 <![CDATA[Measuring the number of turns of the residual magnetic winding N 1]]> 50 External series resistor 4 Ω Measurement of voltage excitation loading time 50 ms Based on the numerical range of residual magnetization in the iron core in practical engineering, 10 sets of preset residual magnetization values ​​were set as shown in Table 2, including 5 sets of positive residual magnetization and 5 sets of negative residual magnetization. By observing the transient response current after applying excitation, the equivalent resistance corresponding to the positive current was calculated, and an empirical formula between residual magnetism and equivalent resistance was fitted.

[0049] Table 2 Preset Residual Magnetism Values ​​of Iron Core A square iron core was modeled in the finite element software COMSOL Multiphysics. The material properties of B30P105 were set according to the magnetic properties of the core material shown in Table 1. The applied DC small-signal excitation was set to 150mV, the excitation duration to 50ms, and the external series resistance to 4Ω. During the simulation, a positive DC excitation was first applied to obtain the transient current. Then, a reverse DC excitation is applied to obtain a transient current. Comparing currents and The rate of change of current is used to determine the direction of remanence. The rate of change is faster than that of the current. If the remanence in the core is in the same direction as the applied DC excitation, then the direction is opposite. Choose the positive direction. Equivalent resistance of transient current To solve this problem, we select the equivalent resistance at the same time under different conditions of core remanence, and perform curve fitting between the remanence and the equivalent resistance to obtain an empirical formula for calculating core remanence.

[0050] Figure 7 The figure shows the transient simulation current under positive and negative DC excitation when the iron core has a remanence of 600 mT. As can be seen from the figure, under the same remanence in the iron core, the rate of change of the positive response current is significantly faster than that of the negative response current, and the positive response current is more likely to reach a steady state. Figure 8 The positive transient response current under different remanence conditions of the iron core is shown. It can be seen that the transient process of the response current differs significantly under different remanence conditions, but all eventually reach a steady state. The remanence of the iron core affects the rate of change of the transient current. The larger the remanence in the iron core, the larger the rate of change of the transient current, and the shorter the time required to reach a steady state, making it easier to reach a steady state. Conversely, the smaller the remanence in the iron core, the smaller the rate of change of the transient current, and the longer the time required to reach a steady state. The finite element simulation results are consistent with the above theoretical research and analysis, proving the effectiveness of the theoretical analysis and the feasibility of the proposed measurement method.

[0051] After applying a DC voltage excitation, the magnetic flux density within the square iron core sample also undergoes a slight change during the transient process, such as... Figure 9 The diagram shows the magnetic flux density distribution after applying positive excitation under different remanence conditions of the core. Because the inner magnetic path length of the square core is shorter than the outer magnetic path length, magnetic flux more easily passes through the path with lower magnetic reluctance. Therefore, the magnetic flux density at the four inner corners of the core is greater than that at the four outer corners. Except for the inner and outer corners, the difference between the inner and outer sides of the core is small, and the overall distribution is relatively uniform. Therefore, the remanence measured in the transformer core in this application is the average magnetic flux density.

[0052] The transient response currents obtained after applying DC voltage excitation are compared and analyzed. Utilizing the difference in the rates of change between the forward and reverse response currents, the forward transient response current is selected. By numerically solving for the forward transient response current, its corresponding equivalent resistance is obtained. For example... Figure 10 The figure shows the change in equivalent resistance of the core under different residual magnetism conditions. After the excitation is applied, the equivalent resistance in the transformer core gradually decreases over time until it decreases to a non-zero value. The more residual magnetism in the core, the faster the rate of decrease. That is, at the same time, the greater the residual magnetism in the core, the smaller the corresponding equivalent resistance value.

[0053] The varying residual magnetism within the core of a power transformer leads to significant differences in the response current generated after applying a small DC signal voltage excitation, ultimately affecting the equivalent resistance value within the core. By utilizing the differences in equivalent resistance corresponding to different residual magnetisms at the same time, and selecting equivalent resistance values ​​at inflection points where the differences are significant (as shown in Table 3, where core residual magnetism and corresponding equivalent resistance values ​​are correlated), an empirical formula is fitted between core residual magnetism and equivalent resistance. This empirical formula allows for the calculation of the residual magnetism value within the core, thus achieving the goal of transformer core residual magnetism measurement.

[0054] Table 3 Residual magnetism of iron core and corresponding equivalent resistance values <![CDATA[ B r (mT)]]> <![CDATA[ R fe (Oh)]]> 300 1.38 400 1.27 500 1.18 600 1.08 800 0.82 850 0.74 960 0.54 1100 0.28 1200 0.17 The equivalent resistance is obtained by calculating the positive response current from the finite element simulation results. Then, the least squares method is used to fit an empirical formula at the inflection point of the equivalent resistance. The fitted mathematical expression is:

[0055] Among them, the coefficient of determination (COD) and root mean square error (RMSE) are important indicators for evaluating the performance of nonlinear fitting. The COD measures the degree of model fit to the observed data; it is the distance between each point on the fitted curve and the original data points, i.e., the difference between points on the fitted curve and the original data points. It is the sum of the squares of all residuals, ranging from 0 to 1. The closer the COD is to 1, the stronger the model's interpretability of the data and the better the fit. The RMSE is the square root of the average of the sum of squared residuals, representing the magnitude of the error at each data point. It measures the accuracy of the measurement; the smaller the COD is, the closer it is to 0, the higher the measurement accuracy. Figure 4 The image shown is a curve fitting result, with the iron core having a preset residual magnetism. With equivalent resistance The results show a monotonically decreasing trend, with a coefficient of determination of 9.98×10⁻¹ and a root mean square error of 7.5×10⁻⁴, indicating that the fitting effect of this method is good.

[0056] Example 3 This embodiment provides an integrated system for detecting and demagnetizing residual magnetism in iron cores, used to implement the method described in Embodiment 1. The system includes an information management module, a residual magnetism detection module, a demagnetization module, and a display module. The information management module is used to manage the parameters of the transformer under test, historical measurement data, demagnetization process parameters, and user permissions, including: The parameter input unit is used to receive or import the nameplate parameters and core material magnetic characteristic parameters of the transformer under test. The process management unit is used to store and recall preset residual magnetism detection parameters and demagnetization strategy parameters for transformers of different capacities and voltage levels. The data storage unit is used to store the raw data, process data, and result data of each measurement and demagnetization process; The user management unit is used to implement login verification, permission allocation, and operation log recording for operators; The residual magnetism detection module is connected to the primary winding of the transformer under test, and is used to execute the iron core residual magnetism characteristic measurement and analysis method described in claim 1, and output the polarity and magnitude information of the residual magnetism, including: The power supply excitation unit is used to generate a DC small-signal voltage excitation with controllable amplitude applied to the primary winding of the transformer under test; it includes a PWM modulation circuit, which compares the modulation wave with the carrier signal through a carrier signal generator and a comparator to generate a PWM waveform with adjustable duty cycle, and outputs it as the DC small-signal voltage excitation after power amplification; The current measurement unit is connected in series in the primary winding circuit of the transformer under test and is used to collect the transient current response signal during the application of DC voltage excitation. The voltage measurement unit is connected in parallel across the primary winding of the transformer under test to acquire the applied DC voltage excitation signal. The signal conditioning circuit is connected to the current measurement module and the voltage measurement module respectively, and is used to filter, amplify and condition the acquired current and voltage signals. The control loop is connected to the power module, the signal conditioning circuit and the demagnetizing module respectively, and is used to control the timing, amplitude and polarity of the excitation output by the power module, and to calculate the equivalent resistance based on the conditioned signal output by the signal conditioning circuit, so as to perform the remanent magnetization direction judgment and magnitude calculation as described in claim 1. The demagnetizing module is connected to the control loop, receives the residual magnetism information output by the residual magnetism detection module, and generates demagnetizing control commands according to the predetermined demagnetizing strategy, controlling the power supply module to output a series of demagnetizing voltage waveforms with attenuated amplitude and alternating polarity to the primary winding of the transformer under test. The display module is connected to the control loop and information management module, and is used to display the transient current waveform, voltage waveform, equivalent resistance change curve, calculated residual magnetism information, demagnetization process status and historical records in real time during the measurement process.

[0057] In the demagnetization module, the control logic of the demagnetization strategy is specifically as follows: The control loop controls the initial demagnetizing voltage output by the power supply module to have a polarity opposite to the remanent magnetization direction based on the remanent magnetization direction information output by the remanent magnetization detection module. During the demagnetization process, the control loop determines whether the core flux has reached positive or negative saturation based on the current waveform fed back by the current measurement module, and controls the power supply module to switch the polarity of the output voltage when saturation is detected, and reduces the amplitude of the output voltage according to a preset attenuation coefficient in each subsequent cycle. The control loop continuously monitors the magnetic flux difference between the positive and negative saturation points within a complete cycle during the later stage of demagnetization. When the difference is less than the preset demagnetization completion threshold, the demagnetization is determined to be complete and the power module is controlled to stop outputting.

[0058] In the power supply excitation unit, the method for determining the duty cycle of the waveform generated by the PWM modulation circuit is as follows: When the residual magnetism detection module performs the measurement, the control loop controls the PWM modulation circuit to output a PWM waveform with a fixed duty cycle, which is used to generate DC voltage excitation with the same amplitude but opposite polarity. When the demagnetizing module performs demagnetization, the control loop dynamically adjusts the duty cycle of the PWM waveform according to the magnitude and polarity information of the residual magnetism output by the residual magnetism detection module, based on preset rules. These preset rules include: The initial output polarity of the PWM waveform is opposite to the remanent magnetization polarity; In the initial stage of demagnetization, the initial duty cycle of the PWM waveform is positively correlated with the magnitude of the residual magnetism; During the demagnetization process, the control loop periodically reduces the duty cycle of the PWM waveform according to a preset attenuation coefficient.

[0059] Specifically, the information management module manages transformer parameters, historical data, etc. Its parameter input unit allows input of core dimensions, materials, winding turns, etc. The process management unit stores standard measurement and demagnetization process parameters. The data storage unit saves the original waveform of each measurement, the calculated equivalent resistance, the judgment result, and the calculated residual magnetism value.

[0060] The residual magnetism detection module is the core execution unit. Its power excitation unit uses a programmable DC source or a PWM-controlled power circuit, capable of accurately outputting a small DC signal with controllable amplitude and switchable polarity required in step S2. The current and voltage measurement unit uses high-precision sensors and signal conditioning circuits to ensure the acquisition of clean voltage and current signals. The control loop controls the output timing of the excitation (positive first, then negative, each lasting 50ms), collects data, and executes the algorithm in steps S4-S7: comparing the rate of current change to determine the direction, calculating the equivalent resistance curve, selecting the inflection point value, and calculating the magnitude of residual magnetism from the built-in empirical formula.

[0061] The demagnetizing module starts after residual magnetism detection. The control loop automatically generates a demagnetizing strategy based on the detected direction and magnitude of the residual magnetism. The demagnetizing strategy control power supply excitation unit first outputs a large-amplitude DC or low-frequency AC voltage opposite to the direction of the residual magnetism, causing the iron core to reverse-saturate. Then, the control voltage amplitude periodically decays and automatically switches polarity, forming alternating positive and negative excitations with decreasing amplitudes until the hysteresis loop in the iron core contracts to near its origin. During demagnetization, the current waveform can be monitored in real time to indirectly determine the magnetic flux state.

[0062] The display module shows the current and voltage waveforms, equivalent resistance change curves, determined remanence direction, calculated remanence magnitude, and demagnetization progress status in real time during the measurement process, providing users with intuitive operation and result feedback.

[0063] This application, through the integrated system combining the aforementioned hardware and software, realizes fully automated operation from residual magnetism detection and quantitative analysis to intelligent demagnetization, greatly improving the efficiency and reliability of residual magnetism treatment before transformer commissioning or after maintenance.

[0064] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of this application can be implemented in various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0065] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0066] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0067] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0068] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0069] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A method of measuring and analyzing core remanence characteristics, characterized by: The method comprises: S1, demagnetizing the measured core, generating a controllable preset residual magnetism in the measured core by applying a direct current voltage excitation to a preset winding of the measured core; S2, applying a group of direct current small signal voltage excitations with opposite polarities, same amplitudes and same durations to a primary side winding of the measured core; S3, during the application of each group of direct current small signal voltage excitations, respectively collecting a first transient current response signal under positive polarity direct current small signal voltage excitation and a second transient current response signal under negative polarity direct current small signal voltage excitation; S4, comparing the instantaneous change rates of the first transient current response signal and the second transient current response signal at the same observation time; S5, judging the residual magnetism direction of the measured core according to the comparison result of the change rates, and determining the transient current response signal collected under the direct current voltage signal excitation with the same direction as the residual magnetism direction as the positive transient current response signal; S6, based on the positive transient current response signal and the corresponding direct current voltage signal, calculating the change curve of the equivalent resistance of the core with time in the transient process according to the circuit Kirchhoff's law; S7, selecting the equivalent resistance value at the characteristic inflection point time on the change curve of the equivalent resistance with time; S8, substituting the equivalent resistance value into the pre-established residual magnetism-equivalent resistance empirical formula to calculate the residual magnetism of the measured core.

2. The method of measuring and analyzing a core residual characteristic according to claim 1, characterized by: In step S1, the demagnetization process is realized by applying alternating voltage excitations with gradually decreasing amplitudes to the preset winding until the magnetic hysteresis loop of the core shrinks to the vicinity of the origin, and the alternating voltage excitation is a sinusoidal signal.

3. The method of measuring and analyzing a core remanence characteristic according to claim 1, characterized by: In step S5, the residual magnetism direction of the measured core is judged according to the comparison result of the change rates, which specifically includes: When the change rate of the first transient current response signal at the same observation time is less than the change rate of the second transient current response signal, it is determined that the residual magnetism direction of the core is opposite to the direction of the direct current voltage excitation corresponding to the application of the first transient current response signal; When the change rate of the first transient current response signal at the same observation time is greater than the change rate of the second transient current response signal, it is determined that the residual magnetism direction of the core is the same as the direction of the direct current voltage excitation corresponding to the application of the first transient current response signal.

4. The method of measuring and analyzing a core residual characteristic according to claim 3, characterized by: The change rate is determined by calculating the first order derivative value of each transient current response signal with respect to time at the same observation time.

5. The method of measuring and analyzing a core residual characteristic according to claim 1, characterized by: In step S7, the characteristic inflection point time is the time when the decay rate on the change curve of the equivalent resistance with time changes from fast to slow, which corresponds to the starting point of irreversible displacement of the core internal magnetic domain wall.

6. The method of measuring and analyzing a core residual characteristic according to claim 4, characterized by: In step S8, the pre-established residual magnetism-equivalent resistance empirical formula is obtained by a finite element simulation method, and the specific method is: S8.1, according to the actual size and material properties of the measured core, a three-dimensional finite element model containing primary winding, core geometry and circuit parameters is established, and the magnetization characteristics of the core material are set. S8.2, in the three-dimensional finite element model of the primary winding loop, by applying different amplitude of DC excitation to the core saturation after the withdrawal, in the simulation core to generate different size and direction of the preset residual magnetism; S8.3, on the basis of the preset residual magnetism, in the primary winding loop simulation of the same parameters in step S2 DC small signal voltage excitation, transient field coupling simulation, extract the simulation of transient current waveform; S8.4, according to the simulation of transient current waveform and the applied DC small signal voltage excitation, according to the circuit theory calculation equivalent resistance with time curve, and extract the equivalent resistance simulation value at the characteristic inflection point time; S8.5, the different preset residual magnetism value and its corresponding equivalent resistance simulation value constitute the discrete data points for mathematical fitting, get the residual magnetism and equivalent resistance function relationship of the residual magnetism-equivalent resistance empirical formula.

7. The method of measuring and analyzing a core residual characteristic according to claim 6, characterized by: In the step S8.5, the mathematical fitting adopts the least square curve fitting method, the obtained residual magnetism-equivalent resistance empirical formula is a nonlinear function form, and the function type is determined according to the fitting degree.

8. A core remanence detection and demagnetization integrated system for implementing the core remanence characteristic measurement and analysis method according to claims 1-7, characterized in that: The system comprises an information management module, a residual magnetism detection module, a demagnetization module and a display module; The information management module is used for managing the parameters of the transformer to be measured, historical measurement data, demagnetization process parameters and user permissions, and comprises: a parameter input unit for receiving or importing the nameplate parameters of the transformer to be measured and the magnetic property parameters of the core material; a process management unit for storing and calling the preset residual magnetism detection parameters and demagnetization strategy parameters for different capacity and voltage grade transformers; a data storage unit for storing the original data, process data and result data of each measurement and demagnetization process; a user management unit for realizing login verification, permission allocation and operation log recording of the operating personnel; The residual magnetism detection module is connected with the primary winding of the transformer to be measured, and is used for executing the core residual magnetism characteristic measurement and analysis method of claim 1, and outputting the polarity information and size information of the residual magnetism, and comprises: a power excitation unit for generating a DC small signal voltage excitation with controllable amplitude applied to the primary winding of the transformer to be measured; the unit comprises a PWM modulation circuit, the circuit compares the modulation wave and the carrier signal through a carrier signal generator and a comparator, generates a PWM waveform with adjustable duty cycle, and outputs the DC small signal voltage excitation after power amplification; a current measurement unit connected in series in the primary winding loop of the transformer to be measured, for collecting the transient current response signal during the application of the DC voltage excitation; a voltage measurement unit connected in parallel across the primary winding of the transformer to be measured, for collecting the applied DC voltage excitation signal; a signal conditioning circuit connected with the current measurement module and the voltage measurement module respectively, for filtering, amplifying and level adjusting the collected current and voltage signals; a control loop connected with the power module, signal conditioning circuit and demagnetization module respectively, for controlling the time sequence, amplitude and polarity of the excitation output by the power module, and calculating the equivalent resistance according to the conditioned signals output by the signal conditioning circuit, to execute the residual magnetism direction judgment and size calculation of claim 1. The demagnetization module is connected with the control loop, receives the residual magnetism information output by the residual magnetism detection module, and generates a demagnetization control instruction according to a predetermined demagnetization strategy, so as to control the power module to output a series of demagnetization voltage waveforms with decaying amplitude and alternating polarity to the primary winding of the transformer to be tested. The display module is connected with the control loop and the information management module, and is used for displaying the transient current waveform, the voltage waveform, the equivalent resistance change curve, the calculated residual magnetism information, the demagnetization process state and the historical record in the measurement process in real time.

9. The core remanence detection and demagnetization integrated system of claim 8, wherein: In the demagnetization module, the control logic of the demagnetization strategy is specifically as follows: The control loop controls the initial demagnetization voltage polarity output by the power module to be opposite to the residual magnetism direction according to the residual magnetism direction information output by the residual magnetism detection module; During the demagnetization process, the control loop judges whether the core magnetic flux reaches the positive and negative saturation states based on the current waveform fed back by the current measurement module, controls the power module to switch the output voltage polarity when saturation is detected, and reduces the output voltage amplitude by a preset attenuation coefficient in each subsequent period; The control loop continuously monitors the magnetic flux difference corresponding to the positive and negative saturation points in a complete period in the late demagnetization stage, and determines that the demagnetization is completed and controls the power module to stop outputting when the difference is less than a preset demagnetization completion threshold.

10. The core remanence detection and demagnetization integrated system of claim 8, wherein: In the power excitation unit, the duty cycle determination method of the PWM modulation circuit for generating the waveform is as follows: When the residual magnetism detection module performs measurement, the control loop controls the PWM modulation circuit to output a PWM waveform with a fixed duty cycle, which is used to generate DC voltage excitation with the same amplitude and opposite polarity; When the demagnetization module performs demagnetization, the control loop dynamically adjusts the duty cycle of the PWM waveform according to the residual magnetism size and polarity information output by the residual magnetism detection module according to a preset rule, and the preset rule includes: The initial output polarity of the PWM waveform is opposite to the polarity of the residual magnetism; In the early demagnetization stage, the initial duty cycle of the PWM waveform is positively related to the size of the residual magnetism; During the demagnetization process, the control loop periodically reduces the duty cycle of the PWM waveform according to a preset attenuation coefficient.

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