Method and system for monitoring abnormal operation condition of transformer based on magnetic flux leakage

Abstract

The invention belongs to the technical field of transformer abnormity monitoring, and discloses a method and system for monitoring the abnormal operation condition of a transformer based on magnetic flux leakage, and the method comprises the steps: carrying out the modeling and analysis of a 110 kV oil-immersed power transformer through ANSYS Maxwell and ANSYS Workbench, and enabling the transformer to operate under different overload conditions through combining with Circuit software. Finite element analysis (FEM) is utilized to calculate the magnetic field of the whole transformer and the vibration intensity under the overload condition. Carrying out numerical analysis on the overload and vibration conditions of the transformer in combination with the leakage flux induction intensity (LMIS), and establishing a mapping relation between the overload and vibration conditions of the transformer and the leakage flux quantity through a least square method (LS). According to the early warning method capable of predicting overload and vibration of the transformer, human intervention is carried out in advance before more serious disasters are caused, so that larger loss is avoided, and the stability of a power system is guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of transformer abnormality monitoring, and in particular to a method and system for monitoring abnormal operation of a transformer based on magnetic flux leakage. Background Art

[0002] Overload and severe vibration of power transformers pose a major threat to the safety, reliability and continuous power supply of power systems. Due to the cascading nature of power systems, any fault in the system may have an impact on the entire system, such as large-scale power outages and power line fires. As the demand for electricity continues to grow, the load faced by transformers has gradually increased, and overload has become more common. According to survey data from more than 600 distribution transformers that have failed, the frequency of overload failures is much higher than other types of failures, posing a great challenge to the safety of the power system. If the transformer is severely overloaded, it can cause severe vibration and excessive heating, which in turn accelerates the aging of the equipment, shortens its service life, and even causes irreparable damage. In severe cases, it can lead to permanent failure of the transformer. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a method and system for monitoring the abnormal operation of transformers based on magnetic flux leakage, and studies a non-contact method to quantify the magnetic field outside the transformer box to determine the overload and vibration intensity of the transformer. The results show that the overload and vibration level 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 abnormal operation of a transformer based on magnetic flux leakage, the method comprising:

[0005] ANSYS Maxwell is used to perform 3D visualization modeling of oil-immersed power transformers. FEM is used to analyze the established transformer model and obtain magnetic data. The transformer model includes: core, winding, clamps and casing.

[0006] 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;

[0007] Combined with LMIS, the overload and vibration conditions of the transformer are numerically analyzed. The mapping relationship between the overload and vibration conditions of the transformer and the leakage magnetic quantity is established through LS to comprehensively judge the damage degree of the transformer.

[0008] Preferably, using FEM, calculating the overall magnetic field of the transformer and the vibration intensity under overload conditions includes: analyzing the vibration conditions by the magnitude of the magnetic force;

[0009] Among them, the magnetic field force on the iron core is:

[0010] ;

[0011] in, The magnetic field force generated by the remaining local leakage flux; The magnetic field force generated by the main magnetic flux;

[0012] The electromagnetic force on the winding is:

[0013] ;

[0014] 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.

[0015] Preferably, the numerical analysis of the 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:

[0016] ;

[0017] in, A preset operation cycle; is the integral of leakage magnetic induction intensity and time, is the magnetic induction intensity value of the transformer A surface area An, and n is 1-9.

[0018] Preferably, establishing a mapping relationship between transformer overload and vibration conditions and magnetic leakage through LS includes:

[0019] 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:

[0020] ,

[0021] 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;

[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, the fitting function expressions of LS and overload degree are obtained:

[0025] ;

[0026] in, For one operation cycle The integral of the leakage magnetic induction intensity and time, is the transformer overload degree;

[0027] Overload degree and maximum equivalent stress value of vibration Fitting function expression:

[0028] .

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

[0030] The coupling module is used to perform three-dimensional visual modeling of an oil-immersed power transformer using ANSYS Maxwell, and to analyze the established transformer model using FEM to obtain magnetic data, wherein the transformer model includes: an iron core, a winding, a clamp and a housing;

[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 perform numerical analysis on the transformer overload and vibration conditions in combination with LMIS, establish a mapping relationship between the transformer overload and vibration conditions and the leakage magnetic quantity through LS, and comprehensively judge the damage degree of the transformer.

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

[0034] Among them, the magnetic field force on the iron core is:

[0035] ;

[0036] in, The magnetic field force generated by the remaining local leakage flux; The magnetic field force generated by the main magnetic flux;

[0037] The electromagnetic force on the winding is:

[0038] ;

[0039] 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.

[0040] Preferably, the numerical analysis of the 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:

[0041] ;

[0042] in, A preset operation cycle; is the integral of leakage magnetic induction intensity and time, is the magnetic induction intensity value of the transformer A surface area An, and n is 1-9.

[0043] Preferably, establishing a mapping relationship between transformer overload and vibration conditions and magnetic leakage through LS includes:

[0044] 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:

[0045] ,

[0046] 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;

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

[0048] ,

[0049] According to the slope m and intercept b, the fitting function expressions of LS and overload degree are obtained:

[0050] ;

[0051] in, For one operation cycle The integral of the leakage magnetic induction intensity and time, is the transformer overload degree;

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

[0053] .

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] The present invention proposes an early warning method that can predict transformer overload and vibration, and conduct human intervention in advance before causing more serious disasters, so as 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 Workbanch to model a 110kV oil-immersed transformer, and mathematically analyzes the results of the electro-magnetic-mechanical simulation. In view of the shortcomings of the existing methods for monitoring transformer faults, it is proposed to monitor the overload and vibration conditions of the transformer using a magnetic field. During the experiment, the integral value of the leakage magnetic induction intensity at the transformer casing and time during an operating cycle was used to verify that the transformer overload and vibration conditions can be judged by the leakage magnetic induction intensity at the transformer casing. And different functional relationships are established using LS. It is proposed that the constructed relationship can be used to distinguish the vibration and overload conditions of the transformer. At the same time, the areas where the transformer is easily damaged under overload conditions are found, and the degree of influence of vibration on the transformer is estimated based on the monitoring of the magnetic field. In the future, this work can be expanded to use non-contact micromagnetic 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 solution of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0058] Figure 1 This is a schematic diagram of analysis and processing of an embodiment of the present invention;

[0059] Figure 2 A schematic diagram of a three-dimensional model and excitation mode of a 110KV oil-immersed power transformer according to an embodiment of the present invention;

[0060] Figure 3 Schematic diagram of the BH curve of the 30Q120 silicon steel sheet according to the embodiment of the present invention;

[0061] Figure 4 This is a schematic diagram of the transformer vibration process according to an embodiment of the present invention;

[0062] Figure 5 A diagram showing the relationship between the transformer integral value and the load factor change according to an embodiment of the present invention;

[0063] Figure 6 It is a schematic diagram of the maximum displacement and equivalent stress values ​​on the transformer core, the fixture and the winding according to an embodiment of the present invention;

[0064] Figure 7 Graph showing the relationship between the maximum stress on the transformer and time according to an embodiment of the present invention. DETAILED DESCRIPTION

[0065] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0066] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0067] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0068] Embodiment 1

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

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

[0071] In order to meet the needs of modern power grids for intelligence, continuity and stability, the present invention proposes a non-contact method for predicting overload and vibration of power transformers. The electromagnetic induction principle of the transformer shows that various superimposed magnetic fields are distributed around the transformer, and the magnetic field changes 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 LMIS (leakage magnetic induction intensity). Based on LMIS and stress analysis, the optimal installation position of the micromagnetic sensor can be determined, and the area with the most intense vibration under the overload state of the transformer can be identified. Combined with the existing micromagnetic sensor technology in the world, this method uses a 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. In order to study the properties and interactions of these forces, FEM (finite element analysis) is widely considered to be an effective solution. Based on this, the present invention proposes a method for analyzing the overload and vibration status of power transformers combined with leakage magnetic field monitoring. This method uses ANSYS Maxwell and ANSYS Workbench to model and analyze the 110kV oil-immersed power transformer, and combines Circuit software to simulate the operating status of the transformer under different overload conditions. Through FEM technology, the overall magnetic field distribution of the transformer can be calculated, and its vibration intensity can be analyzed under overload conditions. Furthermore, this method combines LMIS to perform numerical analysis on the overload and vibration status of the transformer. By introducing LS (least squares method), a mapping relationship between the transformer overload and vibration status and the leakage magnetic field induction intensity is established. This method can not only accurately predict the abnormal operating status of the transformer, but also monitor the operating health status of the transformer in real time through leakage magnetic field signals, provide timely warnings, and thus improve the safety and reliability of the power system.

[0073] The main contributions of this invention are: A non-intrusive method for monitoring transformer vibration and overload without changing the transformer structure is proposed. A comprehensive analysis of the optimal sensor location is performed. A correlation between the LMIS and the time-integrated value of a single cycle and the transformer overload level is found and supported by the results. The correlation between the overload degree and the vibration degree is calculated and verified.

[0074] Transformer faults can usually be judged by analyzing the composition of transformer insulating oil, but it requires shutdown operation, which cannot achieve real-time fault diagnosis. At the same time, because it requires manual operation, it may cause loss or deterioration of oil samples, affecting the judgment results. Although the use of optical fiber probes and multiple sensors to assist in monitoring the overload of transformers can achieve real-time and accurate monitoring, this method involves multiple sensors, which is costly and has high maintenance costs. Arsalan et al. verified that there is a certain correlation between the magnetic field and overload of the transformer, and proposed that the magnetic field can be monitored by magnetic sensors, meeting the needs of modern power grid systems for high precision, real-time and safety. However, the article did not further clarify the connection between magnetic field and vibration, nor did it establish a clear relationship between magnetic field and transformer overload. Lv Jinzhuang et al. proved that the vibration signal is positively correlated with the square of the winding current. Guo Lijun used ANSYS Workbanch to perform 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. The method can use micromagnetic sensors to monitor the leakage magnetic field to achieve electrical separation without destroying the original structure of the transformer, making installation easier. This method not only meets the needs of modern power grids for high-precision, real-time monitoring, but also improves the safety of personnel maintenance.

[0076] In addition, the present invention also uses FEM to study the electromagnetic interaction of the transformer to gain a deeper understanding of the characteristics and flow of the magnetic field inside the transformer. When combined with ANSYS Workbench and ANSYS Maxwell, coupling analysis can be achieved to provide relevant information such as structural mechanics, fluid mechanics and heat transfer. The magnetic field and vibration are visualized. The overall process is as follows Figure 1 shown.

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

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

[0079]

[0080] According to the parameters of the transformer, a basic model of the transformer was established in ANSYS Maxwell, which is divided into core, winding, clamp and shell.

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

[0082] Using a hollow cylinder, set the number of winding coils and the excitation value to replace the complex multi-coil winding results of the winding. Reduce the complexity of the model and reduce the calculation time. According to the real transformer, set the high voltage and low voltage three phases, a total of six windings. Among them, the turns ratio is: 1179:195. The winding is connected to ANSYS Circuit, and the primary and secondary side Star-Delta connection method is set, such as Figure 2 shown.

[0083] In the modeling stage, the transformer base, bracket, insulation board, insulation pad and other parts that mainly play a fixing and supporting role are retained, while bolts, nuts, washers and other parts that have little impact on vibration and have a greater impact on calculation are ignored.

[0084] The top of the transformer is occupied by most of the lead-out equipment, leaving little space for the installation of the micromagnetic sensor. In addition, the transformer casing is made of iron, which has a certain influence on the magnetic field. When the material is irregular, the influence will be more obvious. Therefore, the installation of the micromagnetic sensor on the top is not considered. At the same time, for modeling, the components located on the top of the transformer are also ignored, and only the steel plate on the top of the transformer is retained to form the outer shell. The transformer support is constructed at the bottom 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 changes in the heat sink are not affected by the gaps between the heat sink fins. Therefore, the present invention uses a rectangular parallelepiped to replace the hollow structure of the heat sink, and increases the number of heat sinks and the size of the gaps in the middle, retaining the original appearance structure. The final transformer model is as follows: Figure 2 shown.

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

[0086] Among them, saturation analysis:

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

[0088] Known magnetic induction intensity and current intensity The relationship can be obtained by , the length vector of the current element , the vector from the current element to the observation point express:

[0089] , (1)

[0090] Magnetic induction intensity describes the number of magnetic lines of force per unit area that pass perpendicular to the direction of the magnetic field. The magnetic flux generated by the current is divided into two parts: the main magnetic flux and the and leakage flux , where the main magnetic flux is much larger than the leakage magnetic flux. The total magnetic flux It is composed of main flux and leakage flux:

[0091] , (2)

[0092] According to the principle of electromagnetic induction, when the core of the transformer is not fully saturated, the primary and secondary voltages , , Current , Number of winding turns , The transformer winding turns ratio of the present invention is .

[0093] , (3)

[0094] When the voltage remains unchanged, the secondary load decreases and the secondary current gradually increases. It is known that the transformer leakage flux 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 constants. Therefore, at the same position, the current and magnetic induction intensity are directly proportional. For the ferromagnetic material of the iron core: the iron core itself has magnetic saturation characteristics. When the magnetic induction intensity is low, the magnetic permeability is in a growth state, such as Figure 3 When the core reaches saturation, the magnetic permeability can be regarded as a constant. As the current increases, the magnetic induction intensity also increases.

[0095] In summary, the change of secondary side load will cause transformer overload, and the current will increase accordingly, affecting the increase of magnetic induction intensity. The magnetic induction intensity generated by leakage magnetic flux is proportional to the current, so the leakage magnetic flux has a positive correlation with the transformer overload condition.

[0096] Among them, vibration analysis:

[0097] The vibration of the transformer is mainly caused by the winding and the core. The whole transformer vibration process can be described as follows: Figure 4 As shown. Because ferromagnetic materials generate magnetic force within the magnetic field range. The present invention analyzes the vibration condition by the magnitude of the magnetic force, thereby determining the correlation with the transformer overload condition.

[0098] 1) Core vibration:

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

[0100] , (4)

[0101] in, represents the gradient, .

[0102] in, represents the Lorentz magnetic 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 ignored. The remaining two terms are the determining parts of the core vibration. Discarding the first term, the remaining magnetic field force can be expressed as

[0103] , (5)

[0104] in, is the magnetic permeability, is the magnetic field strength, is the volume density, are the components of the magnetic field intensity on the x, y, and z axes respectively. are 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 flux, and the leakage flux can be ignored. Then the equivalent is:

[0106] , (6)

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

[0108] , (7)

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

[0110] , (8)

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

[0112] 2) Winding vibration:

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

[0114] , (9)

[0115] Couple the component forces and calculate the electromagnetic force for:

[0116] , (10)

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

[0118] According to (10), when a single transformer maintains a single frequency operation, the square of the current is proportional to the electromagnetic force. When the transformer is in saturation, the current increases, the electromagnetic force increases accordingly, and the vibration intensifies. It is known from the previous proof that the current and leakage flux are proportional under saturation. Therefore, the leakage 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 units (finite elements), establishes multiple small computable grids, and then discretizes the calculation using the Maxwell equations and other electromagnetic equations. The discrete algebraic equations are numerically solved 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. Transformation of sensor point data into overload:

[0122] In actual operation, transformer load varies. Therefore, transformer overload is allowed within a certain value and time range. Once a certain current value is exceeded and the operating time specified for the corresponding current is exceeded, the transformer needs to take timely measures and conduct human intervention. The regulations are shown in Table 2.

[0123] Table 2

[0124]

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

[0126] , (11)

[0127] in, is the magnetic induction intensity value of the transformer A surface area An (n: 1-9).

[0128] Observe the integral value It shows a linear growth trend with the transformer overload multiple, such as Figure 5 As shown. The Pearson correlation coefficient formula is used to calculate the correlation between the two, and the final integral value is strongly correlated with the transformer overload multiple, with a correlation coefficient of 0.99983. Therefore, it is verified that the transformer overload degree can be judged by the leakage magnetic induction intensity value at the transformer casing.

[0129] Because the transformer overload degree has a strong correlation with the integral value. As the overload degree increases, the integral value also increases and has a linear trend, so 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 squares of the error:

[0130] , (12)

[0131] 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.

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

[0133] , (13)

[0134] Finally, the fitting function expression (14) is obtained after calculation. The fitting effect is as follows: Figure 5 shown.

[0135] , (14)

[0136] in, For one operation cycle The integral of the leakage magnetic induction intensity and time, The overload degree of the transformer.

[0137] B. Vibration prediction:

[0138] During the operation of the transformer, due to electromagnetic effects, corresponding stress will be generated on the iron material, causing the transformer to vibrate. If stress above a certain intensity is applied cyclically, 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 placed in ANSYS Workbanch for transient result analysis. By analyzing the simulation results, it is found that the area with the maximum equivalent stress is at the bottom of the clamp within one cycle of the transformer, such as Figure 6shown.

[0140] Using equivalent stress, the relationship between transformer overload degree and vibration intensity is established, where the maximum stress of the transformer under different overload degrees changes with time, as shown in the figure below. Figure 7 As 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 shown in Figure 7 As shown. The maximum stress value and the overload multiple also show a positive linear correlation. Similarly, the correlation between the two is calculated using the Pearson correlation coefficient formula, and finally the maximum stress value and the transformer overload multiple have a strong correlation, with a correlation coefficient of 0.99625. And the function fitted by the least squares method is as follows:

[0141] , (15)

[0142] Because there is a strong correlation between the maximum stress value of the transformer and the overload multiple, it is verified that the transformer overload degree can predict the transformer vibration. The leakage magnetic field strength at the transformer casing is known to determine the transformer overload degree, so the leakage magnetic field strength at the transformer casing can predict the transformer vibration.

[0143] By using (14), the transformer overload and vibration conditions can be accurately calculated, the degree of transformer damage can be comprehensively judged, and human intervention can be carried out in advance before the transformer causes irreversible losses.

[0144] The present invention uses finite element simulation software such as ANSYS Maxwell and ANSYS Workbanch to model a 110kV oil-immersed transformer, and mathematically analyzes the results of the electro-magnetic-mechanical simulation. In view of the shortcomings of the existing methods for monitoring transformer faults, it is proposed to use magnetic fields to monitor the overload and vibration conditions of the transformer. During the experiment, the optimal area for sensor installation was determined by using the integral value of the leakage magnetic induction intensity and time at the transformer housing during an operating cycle. And through the integral value, it was verified that the transformer overload and vibration conditions can be determined by the leakage magnetic induction intensity at the transformer housing. And different functional relationships are established using the least squares method. It is proposed that the constructed relationship can be used to distinguish the vibration and overload conditions of the transformer. At the same time, the area where the transformer is easily damaged under overload conditions is found, and the degree of influence of vibration on the transformer is estimated based on the monitoring of the magnetic field. In the future, this work can be expanded to form a measurement and control system using non-contact micromagnetic sensors to monitor transformers.

[0145] Embodiment 2

[0146] The present invention also discloses a system for monitoring abnormal operation of a transformer based on magnetic leakage, the system is used to implement any one of the methods described above, the system comprises: a coupling module, a calculation module and an analysis module;

[0147] ANSYS Maxwell is used to perform 3D visualization modeling of oil-immersed power transformers, and FEM is used to analyze them to obtain magnetic data. The transformer model includes: core, winding, clamps and casing;

[0148] 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;

[0149] Combined with LMIS, the overload and vibration conditions of the transformer are numerically analyzed. The mapping relationship between the overload and vibration conditions of the transformer and the leakage magnetic quantity is established through LS to comprehensively judge the damage degree of the transformer.

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

[0151] Among them, the magnetic field force on the iron core is:

[0152] ;

[0153] in, The magnetic field force generated by the remaining local leakage flux; The magnetic field force generated by the main magnetic flux;

[0154] The electromagnetic force on the winding is:

[0155] ;

[0156] 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.

[0157] In this embodiment, 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 optimal sensor installation area; the calculation formula is:

[0158] ;

[0159] in, A preset operation cycle; is the integral of leakage magnetic induction intensity and time, is the magnetic induction intensity value of the transformer A surface area An, and n is 1-9.

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

[0161] 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:

[0162] ,

[0163] 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;

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

[0165] ,

[0166] According to the slope m and intercept b, the fitting function expressions of LS and overload degree are obtained:

[0167] ;

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

[0169] Overload degree and 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 are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field 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. FEM is used to analyze the established transformer model and 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, the overload and vibration conditions of the transformer are numerically analyzed. The mapping relationship between the overload and vibration conditions of the transformer and the leakage magnetic quantity is established through LS to comprehensively judge the damage degree of the transformer.

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 transformer A surface area An, and n is 1-9.

4. The method according to claim 1, characterized in that: 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 x, 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. 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 4, 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 an oil-immersed power transformer using ANSYS Maxwell, and to analyze the established transformer model using FEM 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, establish a mapping relationship between the transformer overload and vibration conditions and the leakage magnetic quantity through LS, and comprehensively judge the damage degree of the transformer.

6. The system according to claim 5, 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.

7. The system according to claim 5, 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: ； 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 transformer A surface area An, and n is 1-9.

8. The system according to claim 5, characterized in that 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 x, 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: 。

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