A method and system for monitoring the abnormal operation status of a transformer based on magnetic flux leakage

Abstract

The present invention belongs to the technical field of abnormal monitoring of transformers, and discloses a method and system for monitoring the abnormal operation status of transformers based on magnetic flux leakage. The method includes: using ANSYS Maxwell and ANSYS Workbench to model and analyze a 110 kV oil-immersed power transformer, and combining with Circuit software to enable the transformer to operate under different overload conditions. Using finite element analysis (FEM), calculate the overall magnetic field of the transformer and the vibration intensity under overload conditions. And combining the leakage magnetic induction intensity (LMIS) to conduct numerical analysis on the overload and vibration conditions of the transformer, and establish a mapping relationship between the overload and vibration conditions of the transformer and the magnetic flux leakage amount through the least squares method (LS). The present invention proposes a warning method that can predict the overload and vibration of the transformer, and perform human intervention in advance before more serious disasters occur to avoid greater losses and ensure the stability of the power system.

Description

Technical Field

[0001] The present invention relates to the technical field of abnormal monitoring of transformers, and specifically relates to a method and system for monitoring the abnormal operation status of transformers based on magnetic leakage monitoring. Background Art

[0002] The overload and severe vibration of power transformers pose a major threat to the safety, reliability, and continuous power supply capacity of power systems. Due to the cascading nature of power systems, any fault in the system may affect the entire system, such as large-scale power outages and wire fires. With the continuous growth of electricity demand, the load faced by transformers is gradually increasing, and the overload phenomenon has become more common. According to the investigation data of more than 600 faulty distribution transformers, the occurrence frequency of overload faults is much higher than that of other types of faults, posing a great challenge to the safety of power systems. If the transformer is severely overloaded, it can lead to severe vibration and excessive heating, which will accelerate the aging of the equipment, shorten the service life, and even cause irreparable damage. In severe cases, it will lead to the permanent failure of the transformer. Summary of the Invention

[0003] To solve the above technical problems, the present invention provides a method and system for monitoring the abnormal operation status of transformers based on magnetic leakage monitoring, and studies a non-contact method to quantify the magnetic field outside the transformer tank to determine the overload and vibration intensity of the transformer. The results show that the overload and vibration levels of power transformers can be monitored using non-contact micro-magnetic sensors placed at the proposed sensing points.

[0004] The present invention provides a method for monitoring the abnormal operation status of transformers based on magnetic leakage monitoring, and the method includes:

[0005] Performing three-dimensional visualization modeling on an oil-immersed power transformer using ANSYS Maxwell, and analyzing the established transformer model using FEM to obtain magnetic data, where the transformer model includes: iron core, winding, clamping parts, and outer shell;

[0006] Coupling the magnetic data with the transient result analysis module of ANSYS Maxwell and ANSYS Workbench to obtain mechanical results, and calculating the vibration intensity under the overload condition of the transformer;

[0007] Then, combining LMIS to perform numerical analysis on the overload and vibration conditions of the transformer, establishing a mapping relationship between the overload and vibration conditions of the transformer and the magnetic leakage amount through LS, and comprehensively judging the damaged degree of the transformer.

[0008] Preferably, using FEM to calculate the magnetic field of the whole transformer and the vibration intensity under the overload condition includes: analyzing the vibration situation through the magnitude of the magnetic force;

[0009] Wherein, the magnetic force received by the iron core is:

[0010] ;

[0011] Among them, is the magnetic field force generated by the remaining local magnetic flux leakage; is the magnetic field force generated by the main magnetic flux;

[0012] The electromagnetic force received by the winding is:

[0013] ;

[0014] Among them, is the maximum value of the current flowing in the winding; is the conductor resistance value; is the Coulomb constant; is the operating angular frequency.

[0015] Preferably, the numerical analysis of the overload and vibration conditions of the transformer in combination with LMIS includes: using the integral value of the magnetic flux leakage magnetic induction intensity at the transformer shell and time within a preset operating cycle time to judge the overload and vibration conditions of the transformer; the calculation formula is:

[0016] ;

[0017] Among them, is a preset operating cycle; is the integral of the magnetic flux leakage magnetic induction intensity and time, is the magnetic induction intensity value of the A-n region of the A side of the transformer, and n is 1-9.

[0018] Preferably, establishing the mapping relationship between the overload and vibration conditions of the transformer and the magnetic flux leakage amount by LS includes:

[0019] Using LS to fit the function, and calculating the slope m of the fitted linear function by finding the minimum value of the sum of the squares of the errors:

[0020] ,

[0021] Among them, are the independent variable and the dependent variable respectively, are the means of the independent variable and the dependent variable respectively, and n is the number of observation quantities;

[0022] And using the existing slope m and mean square value x, calculate the intercept b:

[0023] ,

[0024] According to the slope m and intercept b, obtain the LS and overload degree fitting function expression:

[0025] ;

[0026] Among them, is the integral of the leakage magnetic induction intensity and time in one operating cycle , and is the overload degree of the transformer;

[0027] The overload degree and the maximum vibration equivalent stress value Fitting function expression:

[0028] .

[0029] The present invention also provides a system for monitoring the abnormal operation status of a transformer based on magnetic leakage, and the system is used to implement any one of the above methods. The system includes: a coupling module, a calculation module, and an analysis module;

[0030] The coupling module is used to perform three-dimensional visualization modeling on an oil-immersed power transformer using ANSYS Maxwell, analyze the established transformer model using FEM, and obtain magnetic data. Among them, the transformer model includes: an iron core, windings, clamping parts, and a casing;

[0031] The calculation module is used to couple the magnetic data with the transient result analysis module of ANSYS Maxwell and ANSYS Workbench to obtain mechanical results and calculate the vibration intensity under the overload condition of the transformer;

[0032] The analysis module is used to further perform numerical analysis on the overload and vibration conditions of the transformer in combination with LMIS, establish a mapping relationship between the overload and vibration conditions of the transformer and the magnetic leakage amount through LS, and comprehensively judge the damage degree of the transformer.

[0033] Preferably, using FEM, calculating the magnetic field of the whole transformer and the vibration intensity under the overload condition includes: analyzing the vibration condition through the magnitude of the magnetic force;

[0034] Among them, the magnetic force received by the iron core is:

[0035] ;

[0036] Among them, is the magnetic force generated by the remaining local magnetic leakage; is the magnetic force generated by the main magnetic flux;

[0037] The electromagnetic force received by the winding is:

[0038] ;

[0039] Among them, is the maximum value of the current flowing in the winding; is the resistance value of the conductor; is the Coulomb constant; is the operating angular frequency.

[0040] Preferably, the numerical analysis of the overload and vibration conditions of the transformer in combination with LMIS includes: using the integral value of the magnetic flux leakage magnetic induction intensity at the transformer shell and time within a preset operating cycle time to judge the overload and vibration conditions of the transformer; the calculation formula is:

[0041] ;

[0042] wherein, is a preset operating cycle; is the integral of the magnetic induction intensity of the magnetic flux leakage and time, is the magnetic induction intensity value of the A-n region of the A side of the transformer, and n is 1-9.

[0043] Preferably, establishing the mapping relationship between the overload and vibration conditions of the transformer and the magnetic flux leakage amount by LS includes:

[0044] Using LS to fit the function, and calculating the slope m of the fitted linear function by finding the minimum value of the sum of the squares of the errors:

[0045] ,

[0046] wherein, are the independent variable and the dependent variable respectively, are the means of the independent variable and the dependent variable respectively, and n is the number of observation points;

[0047] And using the existing slope m and mean square value x to calculate the intercept b:

[0048] ,

[0049] According to the slope m and intercept b, obtain the fitting function expression of LS and the overload degree:

[0050] ;

[0051] wherein, is the integral of the magnetic induction intensity of the magnetic flux leakage and time in an operating cycle of, is the overload degree of the transformer;

[0052] Overload degree and maximum vibration equivalent stress value Fitting function expression:

[0053] .

[0054] Compared with the prior art, the beneficial effects of the present invention are:

[0055] The present invention proposes a warning method that can predict transformer overload and vibration, and conducts human intervention in advance before more serious disasters occur to avoid greater losses and ensure the stability of the power system.

[0056] The present invention uses finite element simulation software such as ANSYS Maxwell and ANSYS Workbench to model a 110 kV oil-immersed transformer, and conducts mathematical analysis on the electro-magnetic-mechanical results obtained from the simulation. Aiming at the deficiencies of the existing methods for monitoring transformer faults, it proposes to monitor the overload and vibration conditions of the transformer using magnetic fields. During the experiment, by using the integral value of the magnetic flux leakage magnetic induction intensity at the transformer shell over a running cycle time, it is verified that the overload and vibration conditions of the transformer can be judged by the magnetic flux leakage magnetic induction intensity at the transformer shell. Different functional relationships are established using LS. It is proposed that the constructed relationships can be used to distinguish the vibration and overload conditions of the transformer. At the same time, the areas where the transformer is prone to damage under overload conditions are found, and the influence degree of vibration on the transformer is estimated based on magnetic field monitoring. In the future, this work can be extended to using non-contact micro-magnetic sensors to form a measurement and control system to monitor transformers. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] In order to more clearly illustrate the technical solutions of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0058] Figure 1 Schematic diagram for analysis and processing of the embodiment of the present invention;

[0059] Figure 2 Schematic diagram of the three-dimensional model and excitation mode of the 110KV oil-immersed power transformer in the embodiment of the present invention;

[0060] Figure 3 Schematic diagram of the B-H curve of the 30Q120 silicon steel sheet in the embodiment of the present invention;

[0061] Figure 4 Schematic diagram of the vibration process of the transformer in the embodiment of the present invention;

[0062] Figure 5 Graph showing the relationship between the integral value of the transformer and the change of the load factor in the embodiment of the present invention;

[0063] Figure 6 Schematic diagram of the maximum displacement and equivalent stress values on the transformer core, fixture and winding in the embodiment of the present invention;

[0064] Figure 7 This is a graph showing the relationship between the maximum stress on the transformer in the embodiment of the present invention and time. Detailed implementation manners

[0065] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0066] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific implementation manners.

[0067] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific implementation manners.

[0068] Embodiment 1

[0069] As can be seen from the background art,

[0070] Power transformers are key equipment in modern power systems. However, due to factors such as overload and vibration, they often face problems of overheating and accelerated aging. Therefore, quantifying the overload state and vibration level of power transformers is crucial for ensuring the stable operation of the power grid.

[0071] To meet the requirements of modern power grids for intelligence, continuity, and stability, the present invention proposes a non-contact method for predicting the overload and vibration of power transformers. The electromagnetic induction principle of transformers shows that various superimposed magnetic fields are distributed around the transformer, and the magnetic field will change with the operating state of the transformer. Through finite element simulation technology, accurate magnetic field data under the operating state of the transformer can be obtained, so as to analyze the relationship between the overload and vibration degree of the transformer and the LMIS (leakage magnetic induction intensity). Based on the LMIS and stress analysis, the optimal installation position of the micro-magnetic sensor can be determined, and the area with the most intense vibration under the overload state of the transformer can be identified. Combining the existing micro-magnetic sensor technology in the world, this method uses the tiny magnetic field to monitor the overload and vibration conditions of the transformer in real time. This non-contact method can not only maintain the original structure of the transformer, but also greatly improve the safety of the staff and the power grid system.

[0072] Power transformers are composed of complex electromagnetic structures, and the interaction between strong magnetic fields determines their performance and operating status. To study the nature and interaction of these forces, FEM (finite element analysis) is widely regarded as an effective solution. Based on this, the present invention proposes a method for analyzing the overload and vibration status of power transformers in combination with leakage magnetic flux monitoring. This method uses ANSYS Maxwell and ANSYS Workbench to model and analyze an 110 kV oil-immersed power transformer, and combines Circuit software to simulate the operating status of the transformer under different overload conditions. Through FEM technology, the magnetic field distribution of the entire transformer can be calculated, and its vibration intensity can be analyzed under overload conditions. Further, this method combines LMIS to numerically analyze the overload and vibration status of the transformer. By introducing LS (least squares method), a mapping relationship between the overload and vibration status of the transformer and the leakage magnetic induction intensity is established. This method can not only accurately predict the abnormal operating conditions of the transformer, but also monitor the operating health status of the transformer in real time through the leakage magnetic flux signal, providing timely early warnings, thereby improving the safety and reliability of the power system.

[0073] The main contributions of the present invention are: proposing a non-invasive method for monitoring the vibration and overload of transformers without changing the transformer structure. Conducting a comprehensive analysis of the optimal sensor positions. There is a correlation between LMIS and the time integral value of a single cycle and the overload level of the transformer, and the results are supported. Calculating and verifying the correlation between the overload degree and the vibration degree.

[0074] Transformer faults can usually be judged by analyzing the composition of the transformer insulating oil, but this requires shutdown operations, which cannot achieve real-time fault diagnosis. At the same time, because it requires manual operation, it may cause loss or deterioration of the oil sample, affecting the judgment result. Although using fiber optic probes and multiple sensors to assist in monitoring the overload of transformers can achieve real-time and accurate monitoring, this method involves multiple sensors, with high costs and large maintenance expenses. Arsalan et al. verified that there is a certain correlation between the magnetic field of the transformer and the overload, and proposed that the magnetic field can be monitored through magnetic sensors, meeting the requirements of modern power grid systems for high precision, real-time performance, and safety. However, the connection between the magnetic field and vibration was not further clarified in the article, nor was a clear relationship between the magnetic field and the transformer overload established. Lv Jinzhuang et al. proved that the vibration signal shows a positive correlation with the square of the winding current. Guo Lijun used ANSYS Workbanch to conduct vibration analysis on the transformer, reducing the experimental risk.

[0075] Based on existing research, the present invention proposes a non-contact overload and vibration detection method based on the leakage magnetic field of the transformer housing. This method can use micro-magnetic sensors to monitor the leakage magnetic field, achieve electrical isolation, and does not damage the original structure of the transformer, making the installation easier. This method not only meets the requirements of modern power grids for high-precision and real-time monitoring, but also improves the safety of personnel maintenance.

[0076] In addition, the present invention also uses FEM to study the electromagnetic-mechanical interaction of the transformer to deeply understand the characteristics and flow of the internal magnetic field of the transformer. When combined with ANSYS Workbench and ANSYS Maxwell, it can achieve coupled analysis, provide relevant information such as structural mechanics, fluid mechanics, and heat transfer, and conduct visual analysis of its magnetic field and vibration. The overall process is as Figure 1 shown.

[0077] In the present invention, the oil-immersed transformer selected is of the model SZL11-12500 / 110kV, with a rated capacity of 12500 kVA, a rated high-low voltage ratio of , a rated frequency of 50 Hz, three-phase voltage, a total volume of 6350*3800*4350 mm, and a total weight of 28890 kg. The winding parameters of the transformer are shown in Table 1 below. The transformer core is made of 30Q120 silicon steel sheets.

[0078] Table 1: Winding parameters of SZL11-12500 / 110kV oil-immersed transformer

[0079]

[0080] According to the parameters of the transformer, a basic model of the transformer was established in ANSYS Maxwell, which is divided into the core, windings, clamping parts, and housing.

[0081] Since the laminations are always in a tensioned state, the internal magnetic field changes and forces do not affect the overall simulation of the transformer's leakage magnetic field in this experiment. Therefore, a seamless combination treatment is performed on each core to ensure that there is no gap between the laminations.

[0082] Using a hollow cylinder, the number of turns of the winding coil and the excitation value are set to replace the complex multi-coil winding result of the winding. This reduces the model complexity and at the same time reduces the calculation time. According to the real transformer, six windings are set for each of the high-voltage and low-voltage three phases. Among them, the turn ratio is: 1179:195. The windings are connected to ANSYS Circuit, and the primary and secondary side Star-Delta connection methods are set, as Figure 2 shown.

[0083] In the modeling stage, the main parts that play a role in fixing and supporting, such as the transformer base, bracket, insulating board, insulating pad, etc., are retained. While the parts that have little influence on vibration and a relatively deep influence on calculation, such as bolts, nuts, washers, etc., are ignored.

[0084] Most of the space at the top of the transformer is occupied by the lead-out devices, leaving little space for the installation of the micro-magnetic sensor. Moreover, the transformer shell is made of iron material, which has a certain influence on the magnetic field, and the influence will be more obvious in the case of irregular materials. Therefore, the installation of the micro-magnetic sensor is not considered at the top. At the same time, for modeling, the components located at the top of the transformer are also ignored, and only the steel plate at the top of the transformer is retained to form the shell. The bottom constructs the transformer support to ensure that the transformer can be stably fixed on the bottom surface without shaking. However, for the part outside the entire heat dissipation component, the magnetic field change in the heat sink is not affected by the gap between the heat sink fins. Therefore, in the present invention, a cuboid is used to replace the hollow structure of the heat sink, and the number of heat sink fins and the size of the middle gap are increased while retaining the original external structure. The final transformer model is as Figure 2 shown.

[0085] In this embodiment, the mathematical analysis includes: saturation situation analysis and vibration analysis.

[0086] Among them, the saturation situation analysis:

[0087] By analyzing the relationship between the transformer voltage, current, and magnetic field, the connection between the magnetic field and transformer saturation is established.

[0088] It is known that the relationship between the magnetic induction intensity and the current intensity can be represented by the magnetic permeability , the length vector of the current element, and the vector from the current element to the observation point:

[0089] , (1)

[0090] The magnetic induction intensity describes the number of magnetic force lines passing through a unit area perpendicular to the magnetic field direction. The magnetic flux generated by the current is divided into two parts, the main magnetic flux and the leakage magnetic flux , where the main magnetic flux is much larger than the leakage magnetic flux. And the total magnetic flux can be composed of the main magnetic flux and the leakage magnetic flux:

[0091] , (2)

[0092] According to the principle of electromagnetic induction, in the case where the iron core of the transformer is not completely saturated, the primary side and secondary side voltages , , current , Proportional to the number of turns of the winding 、 Among them, the turns ratio of the transformer winding of the present invention is 。

[0093] ,(3)

[0094] When the voltage remains unchanged and the secondary load decreases, the secondary current will gradually increase. It is known that the leakage magnetic flux of the transformer forms a closed loop through non-ferromagnetic materials such as air or oil, and its magnetic permeability is a constant. According to (1), at the same position, except for the current intensity and magnetic induction intensity, other values are fixed values. Therefore, at the same position, the current and the magnetic induction intensity are directly proportional. For the ferromagnetic material of the iron core: due to the self-magnetic saturation characteristic of the iron core, when the magnetic induction intensity is relatively low, the magnetic permeability is in a growing state, such as Figure 3 。When the iron core reaches the saturation state, the magnetic permeability can be regarded as a fixed value at this time. As the current increases, the magnetic induction intensity also increases.

[0095] To sum up, when the secondary load changes, it causes the transformer overload phenomenon, the current will increase accordingly, and the magnetic induction intensity will increase. And the magnetic induction intensity generated by the leakage magnetic flux is proportional to the current. Therefore, the leakage magnetic flux is positively correlated with the transformer overload situation.

[0096] Among them, vibration analysis:

[0097] The vibration of the transformer is mainly caused by the winding and the iron core. The whole vibration process of the transformer can be as Figure 4 shown. Because ferromagnetic materials will generate magnetic forces within the magnetic field range. The present invention analyzes the vibration situation through the magnitude of the magnetic force, so as to determine the correlation with the transformer overload situation.

[0098] 1) Iron core vibration:

[0099] There is a sinusoidal alternating electromagnetic field inside the iron core. These magnetic fields will act on the iron core to generate magnetic field forces, causing the silicon steel sheets to vibrate. For ferromagnetic media, the magnetic force per unit volume under the excitation state and the current density vector 、magnetic field strength 、magnetic induction intensity 、magnetic permeability and the volume density of the medium are related:

[0100] ,(4)

[0101] Among them, represents the gradient, 。

[0102] Among them, Represents the Lorentz force, which is the electromagnetic force between silicon steel sheets. Since the model ignores the force of silicon steel sheets, this part of the force can be omitted. The remaining two items are the decisive parts of the core vibration. Omitting the first item, the remaining magnetic field force can be expressed as

[0103] , (5)

[0104] Among them, is the magnetic permeability, is the magnetic field strength, is the volume density, are the components of the magnetic field strength in the x, y, and z axes respectively. are the unit vectors in the x, y, and z directions.

[0105] Under normal circumstances, the main magnetic flux of the core is much higher than the leakage magnetic flux, and the leakage magnetic flux can be ignored. Omitting the local leakage magnetic flux, the magnetic field force received by the core is equivalent to:

[0106] , (6)

[0107] The remaining magnetic field force generated by the local leakage magnetic flux is:

[0108] , (7)

[0109] After the transformer is saturated, the leakage magnetic flux increases. In the overall magnetic flux of the transformer, the leakage magnetic flux at this time needs to be considered. According to (7), as the magnetic leakage flux increases, the magnetic field force generated by the local leakage magnetic flux increases. In summary, it can be known that the magnetic field force received by the core is:

[0110] , (8)

[0111] In summary, as the saturation degree of the transformer increases, the magnetic field force generated by the local leakage magnetic flux increases, and the influence on the transformer vibration becomes more obvious. The saturation degree of the transformer is positively correlated with the vibration degree of the transformer core.

[0112] 2) Winding vibration:

[0113] Under the action of the magnetic field, the current in the winding will generate the axial electromagnetic force of the winding and the radial electromagnetic force of the winding . They are related to the maximum value of the current flowing in the winding , the leakage magnetic density at and the components of the axis and the conductor resistance .

[0114] , (9)

[0115] Couple the component forces to calculate the electromagnetic force It is:

[0116] , (10)

[0117] Wherein, is the Coulomb constant, is the operating angular frequency.

[0118] According to (10), when a single transformer operates at a single frequency, the square of the current is proportional to the electromagnetic force. When the transformer is in a saturated state, as the current increases, the electromagnetic force increases accordingly, and the vibration intensifies. As proven before, the current and the leakage magnetic flux are proportional in the saturated state. Therefore, the leakage magnetic flux is also related to the vibration amplitude of the transformer winding.

[0119] In this embodiment, ANSYS Maxwell performs calculations based on the finite element analysis method. It divides the built geometric model into small discrete elements (finite elements), establishes multiple small computable grids, and then discretizes the calculations using Maxwell's equations and other electromagnetic equations. The discrete algebraic equations are solved numerically to obtain the analysis of the entire electromagnetic field. The result we finally see is the result after finite element analysis.

[0120] Among them, data conversion:

[0121] A. Convert the sensing point data into the overload amount:

[0122] In the actual operating state, the load of the transformer changes. Therefore, it is stipulated that the transformer overload can be within a certain value and time range. Once the current value exceeds a certain level and the operating time corresponding to the current specification is exceeded, the transformer needs to take timely measures for manual intervention. The regulations are shown in Table 2.

[0123] Table 2

[0124]

[0125] Because the magnetic induction intensity is a changing curve during the operation of the transformer. Therefore, the present invention proposes to use the integral of the leakage magnetic induction intensity and time over an operating cycle to judge the overload and vibration conditions of the transformer. (unit: )

[0126] , (11)

[0127] Wherein, is the magnetic induction intensity value of the A-n region of the A side of the transformer (n: 1-9).

[0128] Observed integral value shows a linear growth trend with the overload multiple of the transformer, as Figure 5 shown. The correlation between the two is calculated using the Pearson correlation coefficient formula, and finally it is obtained that there is a strong correlation between the integral value and the overload multiple of the transformer, and the correlation coefficient is 0.99983. Therefore, it is verified that the overload degree of the transformer can be judged by the value of the leakage magnetic induction intensity at the transformer shell.

[0129] Because there is a strong correlation between the overload degree of the transformer and the integral value. As the overload degree increases, the integral value also increases and shows a linear trend. Therefore, the least squares method is used to fit the function. The slope m of the fitted linear function is calculated by finding the minimum value of the sum of the squares of the errors:

[0130] , (12)

[0131] where are the independent variable and the dependent variable respectively, are the means of the independent variable and the dependent variable respectively, and n is the number of observation points.

[0132] And using the existing slope m and mean square value x, the intercept b can be calculated:

[0133] , (13)

[0134] Finally, the expression of the fitted function (14) is obtained through calculation, and the fitting effect is as Figure 5 shown.

[0135] , (14)

[0136] where is the integral of the leakage magnetic induction intensity and time in one operating cycle , is the overload degree of the transformer.

[0137] B. Vibration condition prediction:

[0138] During the operation of the transformer, due to electromagnetic action, corresponding stress will be generated on the iron material, causing the transformer to vibrate. If a stress above a certain intensity is cyclically applied, it may cause fatigue and damage to the material. Therefore, when the stress reaches a certain intensity, it will cause irreversible damage to the transformer.

[0139] The results calculated in ANSYS Maxwell are put into ANSYS Workbench for transient result analysis. By analyzing the simulation results, within one cycle of the transformer, the region with the maximum equivalent stress is found at the bottom of the clamping piece, as Figure 6as shown

[0140] Using the equivalent stress, the relationship between the overload degree of the transformer and the vibration intensity is established. The relationship diagram of the maximum stress suffered by the transformer under different overload degrees changing with time is as Figure 7 shown. The maximum stress values are all on the same operating time line. A relationship diagram is established between the maximum stress value of the transformer at the same time and the overload multiple, as Figure 7 shown. The maximum stress value and the overload multiple also show a positive linear correlation. Similarly, using the Pearson correlation coefficient formula to calculate the correlation between the two, it is finally obtained that the maximum stress value and the transformer overload multiple have a strong correlation, and the correlation coefficient is 0.99625. And the functional formula fitted by the least squares method is as follows:

[0141] , (15)

[0142] Because there is a strong correlation between the maximum stress value suffered by the transformer and the overload multiple, it is verified that the overload degree of the transformer can predict the vibration situation of the transformer. Given that the leakage magnetic field intensity at the transformer shell can judge the overload degree of the transformer, so the leakage magnetic field intensity at the transformer shell can estimate the vibration situation of the transformer.

[0143] Using (14), the overload and vibration situations of the transformer can be accurately calculated, and the damage degree of the transformer can be comprehensively judged. Before the transformer causes irreversible damage, artificial intervention can be carried out on the transformer in advance.

[0144] The present invention uses finite element simulation software such as ANSYS Maxwell and ANSYS Workbanch to model a 110 kV oil-immersed transformer, and conducts mathematical analysis on the electro-magnetic-mechanical results obtained from the simulation. Aiming at the deficiencies of the existing methods for monitoring transformer faults, it is proposed to use the magnetic field to monitor the overload situation and vibration situation of the transformer. During the experiment, using the integral value of the leakage magnetic induction intensity at the transformer shell and time within an operating cycle, the best installation area of the sensor is judged. And through the integral value, it is verified that the overload and vibration situations of the transformer can be judged by the leakage magnetic induction intensity at the transformer shell. And different functional relationships are established using the least squares method. It is proposed that the constructed relationships can be used to distinguish the vibration and overload situations of the transformer. At the same time, the areas where the transformer is easily damaged under overload conditions are found, and the influence degree of vibration on the transformer is estimated based on the magnetic field monitoring. In the future, this work can be extended to using non-contact micro-magnetic sensors to form a measurement and control system to monitor the transformer.

[0145] Embodiment 2

[0146] The present invention also discloses a system for monitoring the abnormal operation status of a transformer based on magnetic flux leakage, which is used to implement any of the above-mentioned methods. The system includes: a coupling module, a calculation module, and an analysis module;

[0147] Use ANSYS Maxwell to perform three-dimensional visualization modeling on the oil-immersed power transformer, and use FEM to analyze it to obtain magnetic data. Among them, the transformer model includes: an iron core, windings, clamping parts, and a casing;

[0148] Couple the magnetic data with the transient result analysis module of ANSYS Maxwell and ANSYS Workbench to obtain mechanical results, and calculate the vibration intensity under the overload condition of the transformer;

[0149] Then, combine LMIS to perform numerical analysis on the overload and vibration conditions of the transformer, establish a mapping relationship between the overload and vibration conditions of the transformer and the magnetic flux leakage amount through LS, and comprehensively judge the damage degree of the transformer.

[0150] In this embodiment, using FEM to calculate the overall magnetic field of the transformer and the vibration intensity under the overload condition includes: analyzing the vibration situation through the magnitude of the magnetic force;

[0151] Among them, the magnetic force received by the iron core is:

[0152] ;

[0153] Among them, is the magnetic force generated by the remaining local magnetic flux leakage; is the magnetic force generated by the main magnetic flux;

[0154] The electromagnetic force received by the winding is:

[0155] ;

[0156] Among them, is the maximum value of the current flowing in the winding; is the conductor resistance value; is the Coulomb constant; is the operating angular frequency.

[0157] In this embodiment, combining LMIS to perform numerical analysis on the overload and vibration conditions of the transformer includes: using the integral value of the magnetic flux leakage magnetic induction intensity and time at the transformer casing within a preset operating cycle time to judge the best area for sensor installation; the calculation formula is:

[0158] ;

[0159] Among them, is a preset operating cycle; is the integral of the leakage magnetic induction intensity and time, is the magnetic induction intensity value of the area A-n on the A side of the transformer, where n is from 1 to 9.

[0160] In this embodiment, establishing the mapping relationship between the transformer overload and vibration conditions and the leakage magnetic flux by LS includes:

[0161] Using LS to fit the function, and calculating the slope m of the fitted linear function by finding the minimum value of the sum of the squares of the errors:

[0162] ,

[0163] where, are the independent variable and the dependent variable respectively, are the means of the independent variable and the dependent variable respectively, and n is the number of observed values;

[0164] And using the existing slope m and the mean square value x, calculating the intercept b:

[0165] ,

[0166] According to the slope m and the intercept b, obtaining the fitting function expression of LS and the overload degree:

[0167] ;

[0168] where, is the integral of the leakage magnetic induction intensity and time in one operating cycle , is the overload degree of the transformer;

[0169] The overload degree and the maximum equivalent stress value of vibration Fitting function expression:

[0170] .

[0171] The embodiments described above are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for monitoring abnormal operation of a transformer based on magnetic flux leakage, characterized in that: The method comprises: ANSYS Maxwell is used to perform 3D visualization modeling of oil-immersed power transformers. The established transformer model is analyzed using FEM (finite element analysis) to obtain magnetic data. The transformer model includes: core, winding, clamps and casing. The magnetic data is coupled with the transient result analysis module of ANSYS Maxwell and ANSYS Workbench to obtain mechanical results and calculate the vibration intensity under overload conditions of the transformer; Combined with LMIS (leakage magnetic induction intensity), the transformer overload and vibration conditions are numerically analyzed. The mapping relationship between transformer overload and vibration conditions and leakage magnetic quantity is established through LS (least square method), and the degree of transformer damage is comprehensively judged. The mapping relationship between transformer overload and vibration conditions and magnetic leakage is established through LS, including: Use LS to fit the function, and calculate the slope m of the fitted linear function by finding the minimum value of the sum of squares of the errors: ， in, are the independent variable and the dependent variable, are the means of the independent variable and the dependent variable respectively, and n is the number of observations; And using the existing slope m and mean square value , calculate the intercept b: ， According to the slope m and intercept b, the fitting function expressions of LS and overload degree are obtained: ； in, For one operation cycle The integral of the leakage magnetic induction intensity and time, is the transformer overload degree; Overload degree and maximum equivalent stress value of vibration Fitting function expression: 。 2. The method according to claim 1, characterized in that Using FEM, the calculation of the transformer's overall magnetic field and vibration intensity under overload conditions includes: analyzing vibration conditions through the magnitude of magnetic force; Among them, the magnetic field force on the iron core is: ； in, The magnetic field force generated by the remaining local leakage flux; The magnetic field force generated by the main magnetic flux; The electromagnetic force on the winding is: ； in, is the maximum value of the current flowing in the winding; is the conductor resistance; is the Coulomb constant; is the operating angular frequency.

3. The method according to claim 1, characterized in that The numerical analysis of transformer overload and vibration conditions in combination with LMIS includes: using the integral value of the leakage magnetic induction intensity and time at the transformer housing within a preset operating cycle to determine the transformer overload and vibration conditions; the calculation formula is: ； in, A preset operation cycle; is the integral of leakage magnetic induction intensity and time, is the magnetic induction intensity value of the nth area on the A side of the transformer, where n is 1-9.

4. A system for monitoring abnormal operation of a transformer based on magnetic flux leakage, the system being used to implement the method described in any one of claims 1 to 3, characterized in that: The system comprises: a coupling module, a calculation module and an analysis module; The coupling module is used to perform three-dimensional visual modeling of the oil-immersed power transformer using ANSYS Maxwell, and analyze the established transformer model using FEM (finite element analysis) to obtain magnetic data, wherein the transformer model includes: an iron core, a winding, a clamp and a housing; The calculation module is used to couple the magnetic data with the transient result analysis module of ANSYS Maxwell and ANSYS Workbench to obtain mechanical results and calculate the vibration intensity under the overload condition of the transformer; The analysis module is used to perform numerical analysis on the transformer overload and vibration conditions in combination with LMIS (leakage magnetic induction intensity), establish a mapping relationship between the transformer overload and vibration conditions and the leakage magnetic quantity through LS (least square method), and comprehensively judge the degree of damage to the transformer; The mapping relationship between transformer overload and vibration conditions and magnetic leakage is established through LS, including: Use LS to fit the function, and calculate the slope m of the fitted linear function by finding the minimum value of the sum of squares of the errors: ， in, are the independent variable and the dependent variable, are the means of the independent variable and the dependent variable respectively, and n is the number of observations; And using the existing slope m and mean square value , calculate the intercept b: ， According to the slope m and intercept b, the fitting function expressions of LS and overload degree are obtained: ； in, For one operation cycle The integral of the leakage magnetic induction intensity and time, is the transformer overload degree; Overload degree and maximum equivalent stress value of vibration Fitting function expression: 。 5. The system according to claim 4, characterized in that Using FEM, the calculation of the transformer's overall magnetic field and vibration intensity under overload conditions includes: analyzing vibration conditions through the magnitude of magnetic force; Among them, the magnetic field force on the iron core is: ； in, The magnetic field force generated by the remaining local leakage flux; The magnetic field force generated by the main magnetic flux; The electromagnetic force on the winding is: ； in, is the maximum value of the current flowing in the winding; is the conductor resistance; is the Coulomb constant; is the operating angular frequency.

6. The system according to claim 4, characterized in that The numerical analysis of transformer overload and vibration conditions in combination with LMIS includes: using the integral value of the leakage magnetic induction intensity and time at the transformer casing within a preset operating cycle to determine the transformer overload and vibration conditions; the calculation formula is: ； Wherein, T is a preset operation cycle; is the integral of leakage magnetic induction intensity and time, is the magnetic induction intensity value of the nth area on the A side of the transformer, where n is 1-9.

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