Transformer overheat fault diagnosis and evaluation method based on temperature field fast calculation

Abstract

This invention relates to a method for diagnosing and assessing transformer overheating faults based on rapid temperature field calculation, belonging to the field of electrical engineering technology. It aims to address the shortcomings of existing methods in fault location, accuracy, and safety, as well as the slow calculation speed of finite element analysis. This method divides the transformer core and its upper windings into several segments, and sets temperature measurement points at corresponding locations on the outer wall of the tank. A thermal field model of the transformer's internal thermal field is established based on the thermal circuit method, and a fault temperature rise vector is constructed using the measured temperature rise vector and the calculated temperature rise vector under normal operation. By simulating overheating faults at different locations, a fault temperature rise threshold vector is constructed to locate the fault segment. A temperature identification model is established within the fault segment, and the specific temperature rise value at the fault point is solved through an optimized algorithm, achieving quantitative diagnosis and assessment of the severity of the overheating fault. This invention has the advantages of fault location, quantitative overheating degree, and fast calculation speed.

Description

Technical Field

[0001] This invention belongs to the field of electrical engineering technology and relates to a method for diagnosing and evaluating transformer overheating faults based on rapid calculation of temperature field. Background Technology

[0002] Oil-immersed transformers are one of the core pieces of equipment in power systems, and ensuring their safe and stable operation is crucial for the normal operation of the power system. During operation, transformers generate energy losses, which are converted into heat. The main heat sources inside the transformer are the core and windings. The alternating magnetic field in the core generates hysteresis losses, and when the load current flows through the copper windings, Joule losses occur. The heat generated by these two energy losses is transferred to the surrounding environment and eventually dissipated into the air through the transformer tank surface. This heat transfer process creates a temperature field distribution inside the transformer. Under normal operation, the temperature rise of the transformer core and windings, and the temperature rise it causes to the surrounding insulating materials such as insulating paper and insulating oil, are generally within the design range. However, when a short circuit fault occurs between turns in the windings, or when the core overheats abnormally, the temperature of the overheated spot will far exceed the normal hot spot temperature, leading to excessively high insulation temperature rise in the vicinity. This accelerates the aging of the insulation material, causing deformation, cracks, and even insulation failure, severely shortening the insulation life. Therefore, it is necessary to detect this overheating fault in the transformer in a timely manner, find out the location of the fault point in the winding or core, infer the temperature of the overheating point, and then judge the severity of the overheating fault.

[0003] Currently, common methods for diagnosing transformer overheating faults include dissolved gas analysis in oil, infrared thermography, and fiber optic thermography. However, dissolved gas analysis in oil is difficult to pinpoint the exact location of the fault; infrared thermography can only measure the surface temperature of the transformer tank, and cannot accurately reflect the location and severity of internal thermal defects; while fiber optic thermography offers high accuracy and fast response, it is expensive, requires complex manufacturing processes for embedding into the transformer windings, necessitates close contact with the windings, and its negative impact on the winding's oil-paper insulation performance is unclear. Therefore, existing testing methods based on direct physical measurements are insufficient to meet the diagnostic needs of transformer overheating faults.

[0004] Temperature field analysis, using specific calculation methods, can identify the specific state of overheating points in transformers, providing an effective theoretical approach to achieving the aforementioned objectives. This primarily includes two methods: finite element method (FEM) calculation and thermal circuit method (TCM) calculation. However, due to the large spatial scale of transformers, FEM thermal field analysis suffers from large computational scale and slow calculation speed, making it difficult to meet the needs of rapid on-site diagnosis and handling of transformer faults. Thermal circuit method analysis of the temperature field can balance computational speed and accuracy. However, currently, the thermal circuit method can only calculate the internal temperature distribution of transformers under normal operating conditions and cannot be directly used for diagnosing overheating faults.

[0005] Currently, commonly used methods for diagnosing overheating faults in transformer core-winding systems, such as dissolved gas analysis in oil, infrared thermography, and fiber optic thermography, rely on direct physical testing. However, these methods have limitations in fault location, accuracy, and safety. Finite element analysis, on the other hand, suffers from slow computation speed. To address these issues, this invention employs a rapid calculation method for the internal temperature field of the transformer based on the thermal circuit method. Combined with measured temperature rise values ​​at the top and bottom oil temperatures and other measurement points, this method enables the segmental location of overheating faults in the transformer winding-core system. Furthermore, it establishes a temperature identification model for overheating hot spots in the transformer core and windings. By solving this model, the severity of overheating faults in the transformer winding-core system can be quantitatively diagnosed and assessed. This approach offers advantages such as fault location, quantifiable overheating severity, and rapid computation. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide a method for diagnosing and assessing transformer overheating faults based on rapid temperature field calculation. This method utilizes a rapid calculation method of the internal temperature field of the transformer based on the thermal circuit method, combined with measured temperature rise values ​​at the top and bottom oil temperatures and other temperature measurement points, to locate the section of overheating fault in the transformer winding-core system. Furthermore, it establishes a temperature identification model for overheating hot spots in the transformer core and windings. By solving this model, a quantitative diagnosis and assessment of the severity of transformer winding-core overheating faults can be achieved. This method has the advantages of fault location, quantifiable overheating degree, and fast calculation speed.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for diagnosing and assessing transformer overheating faults based on rapid temperature field calculations, comprising the following steps:

[0009] S1. Take one iron core side column of the transformer, and the high voltage winding and low voltage winding surrounding the iron core side column as a whole research object. Divide the high voltage winding, low voltage winding and iron core side column of the transformer into n segments with the same spatial distribution. Each segment contains several turns of coil and small segments of each iron core column.

[0010] S2. At the same height corresponding to each of the above sections on the outer wall of the transformer tank, set temperature measurement points sequentially, denoted as S1…S2. n The temperature rise of each measured temperature point relative to the ambient temperature is denoted as the measured temperature rise vector Θ. Μ =[θ M 1,θ M 2,θ M 3…θ M n];

[0011] S3. Based on the installation of temperature measurement points in the transformer winding external oil passages, at least two measurement points should be included: bottom oil temperature and top oil temperature. Measure the temperature rise relative to the ambient temperature at the top oil temperature, bottom oil temperature, and other internal external oil passage temperature measurement points. Record this as the verification temperature rise vector Θ. C =[θ C top ,θ C bottom …];

[0012] S4. Based on the thermal circuit method, analyze and obtain the temperature at various locations inside the transformer under normal and fixed load conditions, and obtain the normal temperature rise calculation vector Θ of the transformer. Ν ;

[0013] S5. Based on the measured temperature rise vector Θ in S2 Μ And the calculated temperature rise vector Θ under normal operating conditions in step S44. Ν Construct the temperature rise vector Θ for transformer overheating faults. D =Θ Μ –Θ Ν =[θ D 1,θ D 2…θ D n ];

[0014] S6. Construct the transformer overheating fault temperature rise threshold vector Θ T ;

[0015] S7. Within the specific fault section identified above, further determine the severity of overheating, i.e., the specific temperature rise value at the fault point.

[0016] Furthermore, S4 includes the following steps:

[0017] S41. Establish a thermal circuit calculation model for the internal thermal field of the transformer; where Φ IRON,i The equivalent current source for heating the iron core is Φ, whose magnitude is the heating power value of the i-th segment of the iron core as defined in S1. L,i The equivalent current source for heating the low-voltage winding is the heating power value of the i-th segment of the low-voltage winding as defined in S1; Φ H,i The equivalent current source for heating the high-voltage winding is represented by its magnitude, which indicates the heating power value of the i-th segment of the high-voltage winding as defined in S1; each resistor R xx Represents the thermal resistance along the corresponding heat flow path; nodes correspond to three types of locations: θ iron,i θ represents the temperature rise of the i-th segment of the iron core; iron,bot Indicates the temperature rise at the bottom of the iron core; θ L,iθ represents the temperature rise of the i-th low-voltage winding; L-H,i θ represents the temperature rise in the oil gap between the high and low voltage windings in the i-th segment; H,i θ represents the temperature rise of the i-th high-voltage winding; oil,i θ represents the temperature rise of the i-th segment of the outer oil passage; oil,bot Indicates the bottom oil temperature; θ oil,top Top oil temperature; θ surf,i θ represents the temperature rise of the i-th segment of the outer shell; surf,bot This indicates a temperature rise at the bottom of the casing;

[0018] S42. Based on the specific nameplate parameters of the target transformer being analyzed, Φ IRON,i Let P0 / 3 / n be the value, where P0 represents the no-load loss nameplate value of the transformer; Φ L,i =I L 2 R L / n, I L R represents the rated current of the low-voltage winding. L Φ represents the DC resistance of the low-voltage winding; H,i =I H 2 R H / n, I H R represents the rated current of the high-voltage winding. H Represents the DC resistance of the high-voltage winding; each thermal resistance is determined based on a heat flow experiment.

[0019] S43. Treating the thermal circuit as an electrical circuit, after determining all current sources and resistors in the diagram according to S41-S42, use the nodal voltage method to write the nodal voltage equation Gθ=Φ, that is:

[0020]

[0021] The potentials of all nodes except the reference ground node are sequentially arranged in the θ vector, and each node is numbered according to this order; under this order, G... xx =1 / R xx The self-conductance of the corresponding node and the mutual conductance between nodes are represented by the given resistance, as specified in the nodal voltage method. Corresponding to the above order, the current sources associated with each node are sequentially arranged in the vector Φ. Solving the equations yields the potentials of all nodes in the circuit, i.e., θ = G. -1 Φ;

[0022] S44. From the above calculation results, extract the temperature rise values ​​at n locations on the transformer tank wall corresponding to S2, and combine them into a calculated temperature rise vector Θ under normal transformer operation conditions. Ν =[θ N 1,θ N 2…θN n ].

[0023] Furthermore, S6 includes the following steps:

[0024] S61. In the m-th segment, m = 1…n, representing the three current sources Φ for core loss, low-voltage winding loss, and high-voltage winding loss, respectively. IRON,m Φ L,m Φ H,m Each voltage source is replaced individually to simulate three types of overheating faults: core overheating, low-voltage winding short-circuit overheating, and high-voltage winding short-circuit overheating occurring in the m-th segment alone. The voltage of the voltage source corresponds to the temperature rise of the overheating point when the overheating fault occurs. According to relevant standards, it is set to the temperature rise of the mildest overheating fault at 150℃.

[0025] S62. For the three cases of overheating faults with added core losses, low-voltage winding losses, and high-voltage winding losses, respectively, write the corrected node voltage equation G′θ′=Φ′ ​​with fault. Assume that in the m-th segment selected in S61, a current source that is replaced in a certain instance is associated with node i:

[0026]

[0027] In the formula, U i The voltage source, which replaces the current source, has a value of 150;

[0028] The potentials θ′=G′ at all nodes in the circuit are calculated. -1 Φ′; Extract the calculated temperature rise θ of the adjacent outer wall node of the oil tank above the segment in the θ′ vector. surf,m+1 θ, and its temperature under normal operating conditions N m+1 The difference is taken as the minimum of these three cases, i.e., min(θ). surf,m+1 –θ N m+1 θ serves as the overheat fault temperature rise threshold for this winding section. T m ;

[0029] S63. For the next segment, i.e., m = m + 1, repeat S61-S62 to obtain θ. T m+1 This process continues until all n segments have been traversed; the overheating fault temperature rise thresholds calculated in each of the above iterations are then combined to form an overheating fault temperature rise threshold vector Θ. T =[θ T 1,θ T 2… θ T n ];

[0030] S64. Construct a transformer overheating fault location vector P = [p1, p2, ... p n The values ​​of each element in this vector are determined according to the following rules: the temperature rise vector Θ at each temperature analysis point is compared sequentially. D and thermal defect threshold vector Θ T Size of the element at the corresponding position in the middle; when Θ D A certain element θ D i Less than Θ T Corresponding element θ T i When, then p i =0 indicates that no overheating fault has occurred below the segment corresponding to this element; otherwise, p i =1 indicates that an overheating fault has occurred below the section corresponding to the element; when an overheating fault occurs in a certain section, the value above the section is 1 and the value below is 0, thus locating the winding section where the transformer thermal defect fault is located.

[0031] Furthermore, S7 includes the following steps:

[0032] S71. For the overheating fault section determined in step S64 above, replace the current sources of core loss, low-voltage winding loss, and high-voltage winding loss in this section with three voltage sources. The voltage magnitudes of these three voltage sources are to be determined, denoted as Ux1, Ux2, and Ux3 respectively. Assume that the positions of these three voltage sources are associated with nodes i, j, and k respectively. In this case, write the corrected node voltage equation G"θ"=Φ" containing the fault, that is:

[0033]

[0034] Solving for θ, we get θ" = G". -1 Φ"; where each element in the vector θ" is represented as a linear combination expression of the variables to be solved, Ux1, Ux2, and Ux3;

[0035] S72. Based on the arrangement of temperature measurement points within the target transformer's external oil passage determined in S3, and according to the verification temperature rise vector Θ in S3... C From the θ" vector obtained in S71, extract the corresponding Θ C The temperature rise expression at each location should include at least two temperature measurement points θ: the bottom oil temperature and the top oil temperature. oil,bot、 θ oil,top The vector Θ to be determined is formed. x =[θ oil,bot， θ oil,top… Construct the following optimization model:

[0036] J = min||Θ x -Θ C ||2 (4)

[0037] S73. Using any optimization algorithm, solve the above model to obtain the optimal solutions for Ux1, Ux2, and Ux3, which are the specific fault temperature rise values ​​of the core, low-voltage winding, and high-voltage winding within this fault section, thus completing the quantitative diagnosis of the severity of the transformer overheating fault.

[0038] The beneficial effects of this invention are as follows: by using a rapid calculation method for the internal temperature field of a transformer based on the thermal circuit method, and combining the measured temperature rise values ​​of the top oil temperature, bottom oil temperature, and other temperature measurement points, the section location of overheating faults in the transformer winding-core system can be realized. A temperature identification model for overheating hot spots in the transformer core and windings can be established. By solving this model, the severity of overheating faults in the transformer winding-core system can be quantitatively diagnosed and assessed. This invention has the advantages of fault location, quantitative overheating degree, and fast calculation speed.

[0039] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0040] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0041] Figure 1 This is a transformer thermal circuit model. Detailed Implementation

[0042] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0043] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0044] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0045] The purpose of this invention is to address the shortcomings of commonly used direct physical testing methods for diagnosing transformer core-winding overheating faults, such as dissolved gas analysis in oil, infrared thermography, and fiber optic thermography, in terms of fault location, accuracy, and safety. Finite element analysis methods suffer from slow calculation speeds. This invention utilizes a rapid calculation method for the internal temperature field of the transformer based on the thermal circuit method, combined with measured temperature rise values ​​at the top and bottom oil levels and other measurement points, to locate the section of overheating fault in the transformer winding-core system. Furthermore, a temperature identification model for overheating hot spots in the transformer core and windings is established. By solving this model, a quantitative diagnosis and assessment of the severity of transformer winding-core overheating faults can be achieved. The invention includes the following steps:

[0046] S1. Take one iron core column of the transformer, and the high voltage winding and low voltage winding surrounding the iron core column as a whole research object. Divide the high voltage winding, low voltage winding and iron core column of the transformer into n segments with the same spatial distribution. Each segment contains several turns of coil and small segments of each iron core column.

[0047] S2. At the same height corresponding to each of the above sections on the outer wall of the transformer tank, set temperature measurement points sequentially, denoted as S1…S2. n The temperature rise of each measured temperature point relative to the ambient temperature is denoted as the measured temperature rise vector Θ. Μ =[θ M 1,θ M 2,θ M 3…θ M n ];

[0048] S3. Based on the installation of temperature measurement points in the transformer winding external oil passages (at least two measurement points should be included: bottom oil temperature and top oil temperature), measure the temperature rise relative to the ambient temperature at the top oil temperature, bottom oil temperature, and other internal external oil passage temperature measurement points. Record this as the verification temperature rise vector Θ. C =[θ C top ,θ C bottom …];

[0049] S4. Based on the thermal circuit method, analyze and obtain the temperature at various locations inside the transformer under normal and fixed load conditions, and obtain the normal temperature rise calculation vector Θ of the transformer. Ν It mainly includes the following steps:

[0050] S41, according to the appendix Figure 1 Establish a thermal path calculation model for the internal thermal field of the transformer; where Φ IRON,i The equivalent current source for heating the iron core is Φ, whose magnitude is the heating power value of the i-th segment of the iron core as defined in S1. L,i The equivalent current source for heating the low-voltage winding is the heating power value of the i-th segment of the low-voltage winding as defined in S1; Φ H,i The equivalent current source for heating the high-voltage winding is represented by its magnitude, which indicates the heating power value of the i-th segment of the high-voltage winding as defined in S1; each resistor R xx This represents the thermal resistance along the corresponding heat flow path; Figure 1 The nodes in the array correspond to three types of positions: θ iron,i θ represents the temperature rise of the i-th segment of the iron core; iron,bot Indicates the temperature rise at the bottom of the iron core; θ L,i θ represents the temperature rise of the i-th low-voltage winding; L-H,i θ represents the temperature rise in the oil gap between the high and low voltage windings in the i-th segment; H,i θ represents the temperature rise of the i-th high-voltage winding; oil,i θ represents the temperature rise of the i-th segment of the outer oil passage; oil,bot Indicates the bottom oil temperature; θ oil,top Top oil temperature; θ surf,i θ represents the temperature rise of the i-th segment of the outer shell; surf,bot This indicates a temperature rise at the bottom of the casing;

[0051] S42. Based on the specific nameplate parameters of the target transformer being analyzed, attach... Figure 1 Φ in IRON,i Let P0 / 3 / n be the value, where P0 represents the no-load loss nameplate value of the transformer; Φ L,i =I L 2 R L / n, I L R represents the rated current of the low-voltage winding. L Φ represents the DC resistance of the low-voltage winding; H,i =I H 2 R H / n, I H R represents the rated current of the high-voltage winding. H Represents the DC resistance of the high-voltage winding; each thermal resistance is determined based on a heat flow experiment.

[0052] S43, will Figure 1 The thermal path is considered as a circuit. After determining all the current sources (simulated heat sources) and resistors (simulated thermal resistances) in the diagram according to S41-S42, the nodal voltage method is used to write the nodal voltage equation Gθ=Φ, that is:

[0053]

[0054] The vectors θ are arranged sequentially in a certain order. Figure 1 The potential (temperature rise value) of all nodes except the reference ground node is given, and the following nodes are numbered in this order; under this order, G xx =1 / R xx This represents the self-conductance of the corresponding node and the mutual conductance between nodes, which can be derived from... Figure 1 The resistance (thermal resistance) determined in the equation is derived from the rules of the nodal voltage method; corresponding to the above order, the current sources (heat sources) associated with each node are sequentially arranged in the vector Φ; solving this equation yields the potentials of all nodes in the circuit, i.e., θ = G. -1 Φ;

[0055] S44. From the above calculation results, extract the temperature rise values ​​at n locations on the transformer tank wall corresponding to S2, and combine them into a calculated temperature rise vector Θ under normal transformer operation conditions. Ν =[θ N 1,θ N 2…θ N n ];

[0056] S5. Based on the measured temperature rise vector Θ in S2 Μ And the calculated temperature rise vector Θ under normal operating conditions in step S44. Ν Construct the temperature rise vector Θ for transformer overheating faults. D =Θ Μ –Θ Ν =[θ D 1,θ D 2…θ D n ];

[0057] S6. Construct the transformer overheating fault temperature rise threshold vector Θ T It mainly includes the following steps:

[0058] S61. In the m-th segment, m = 1…n, representing the three current sources Φ for core loss, low-voltage winding loss, and high-voltage winding loss, respectively. IRON,m Φ L,m Φ H,m Each voltage source is replaced individually to simulate three types of overheating faults: core overheating, low-voltage winding short-circuit overheating, and high-voltage winding short-circuit overheating occurring in the m-th segment alone. The voltage of the voltage source corresponds to the temperature rise of the overheating point when the overheating fault occurs. According to relevant standards, it is set to the temperature rise of the mildest overheating fault at 150℃.

[0059] S62. For the three cases of thermal circuits after adding overheating faults ①-③ respectively, write out the corrected node voltage equation G′θ′=Φ′ ​​with faults respectively (assuming that in the m-th segment selected in S61, the current source that is replaced in a certain instance is related to...). Figure 1 (Association of node i in the data):

[0060]

[0061] In the formula, U i The voltage source, which replaces the current source, has a value of 150; the potentials θ′=G′ at all nodes in the circuit are calculated. -1 Φ′; Extract the calculated temperature rise θ of the adjacent outer wall node of the oil tank above this section from the vector θ′. surf,m+1 θ, and its temperature under normal operating conditions N m+1 The difference is taken as the minimum value of the difference among the three cases ①-③, i.e., min(θ) surf,m+1 –θ N m+1 θ is used as the overheat fault temperature rise threshold for this winding section. T m ;

[0062] S63. For the next segment, i.e., m = m + 1, repeat S61-S62 to obtain θ. T m+1 This process continues until all n segments have been traversed; the overheating fault temperature rise thresholds calculated in each of the above iterations are then combined to form an overheating fault temperature rise threshold vector Θ. T =[θ T 1,θ T 2… θ T n ];

[0063] S64. Construct a transformer overheating fault location vector P = [p1, p2, ... p n The values ​​of each element in this vector are determined according to the following rules: the temperature rise vector Θ at each temperature analysis point is compared sequentially. D and thermal defect threshold vector Θ T Size of the element at the corresponding position in the middle; when Θ D A certain element θ D i Less than Θ T Corresponding element θ T i When, then p i =0 indicates that no overheating fault has occurred below the segment corresponding to this element; otherwise, p i =1 indicates that an overheating fault has occurred below the section corresponding to this element; when an overheating fault occurs in a certain section, the value above the layer is 1 and the value below is 0, which can be used to locate the winding section where the transformer thermal defect fault is located.

[0064] S7. Within the specific fault section identified above, further determine the severity of overheating, i.e., the specific temperature rise value at the fault point, including the following steps:

[0065] S71. For the overheating fault section determined in step S64 above, replace the current sources ①-③ in S61 within this section with three voltage sources. The voltage magnitudes of these three voltage sources are unknowns, denoted as Ux1, Ux2, and Ux3 respectively. It is assumed that the positions of these three voltage sources are respectively adjacent to the attached... Figure 1 The nodes i, j, and k in the equation are related. In this case, the corrected node voltage equation with fault is written as G"θ"=Φ", that is:

[0066]

[0067] Solving for θ, we get θ" = G". -1 Φ"; where each element in the vector θ" is represented as a linear combination expression of the variables to be solved, Ux1, Ux2, and Ux3;

[0068] S72. Based on the arrangement of temperature measurement points within the target transformer's external oil passage determined in S3, and according to the verification temperature rise vector Θ in S3... C From the θ" vector obtained in S71, extract the corresponding Θ C The temperature rise expression at each location should include at least two temperature measurement points θ: the bottom oil temperature and the top oil temperature. oil,bot、 θ oil,top The vector Θ to be determined is formed. x =[θ oil,bot， θ oil,top… Construct the following optimization model:

[0069] J = min||Θ x -Θ C ||2 (4)

[0070] S73. Using any optimization algorithm, solve the above model to obtain the optimal solutions for Ux1, Ux2, and Ux3. These are the specific fault temperature rise values ​​of the core, low-voltage winding, and high-voltage winding within the fault section, thus completing the quantitative diagnosis of the severity of the transformer overheating fault.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A transformer overheat fault diagnosis evaluation method based on rapid calculation of a temperature field, characterized in that: The method comprises the following steps: S1, one of the transformer core side column, and the high-voltage winding, low-voltage winding around the core side column combination as a research object whole, respectively for the transformer high-voltage winding, low-voltage winding, core side column is divided into equal intervals, the three are divided into n segments with the same spatial position distribution, each segment contains a number of turns, and each core column segment; S2, at the same height corresponding to each segment of the transformer tank outer wall, set each temperature measurement point in turn, recorded as S1…S n ; each temperature point measured temperature compared to the ambient temperature, the temperature rise, recorded as measured temperature rise vector Θ Μ = [θ M 1, θ M 2, θ M 3… θ M n ] S3, according to the installation of the temperature measuring point of the transformer winding outer oil channel, at least contains two measuring points of the bottom layer oil temperature and the top layer oil temperature, respectively measures the temperature rise value of the transformer internal top layer oil temperature, bottom layer oil temperature and other internal outer oil channel temperature measuring point compared with the ambient temperature, recorded as the calibration temperature rise vector Θ C = [θ C top , θ C bottom …] ; S4, based on the thermal circuit method, the temperature of each position in the transformer under normal load is analyzed to obtain the normal temperature rise calculation vector Θ of the transformer Ν ; S5, the measured temperature rise vector Θ in S2 Μ and the calculated temperature rise vector Θ in the normal operation of S4 step Ν , construct the transformer overheat fault temperature rise vector Θ D = Θ Μ - Θ Ν = [θ D 1, θ D 2 … θ D n ] S6, constructing a transformer overheat fault temperature rise threshold vector Θ T and according to Θ D and Θ T locating the fault specific section; S7, according to the S6 step positioning out of the fault specific section, further determine the severity of overheating, that is, the specific temperature rise value of the fault point.

2. The method for evaluating the overheat fault diagnosis of the transformer based on the fast calculation of the temperature field according to claim 1, characterized in that: The S4 comprises the following steps: S41, according to the thermal circuit calculation model of the transformer internal thermal field is established; wherein, Φ IRON,i The equivalent current source of the core heating, the size is the heating power value of the i section core divided out according to S1; Φ L,i The equivalent current source of the low-voltage winding heating, the size is the heating power value of the i section low-voltage winding divided out according to S1; Φ H,i The equivalent current source of the high-voltage winding heating, the size represents the heating power value of the i section high-voltage winding divided out according to S1; each resistance R xx Indicates the thermal resistance on the corresponding heat flow path; the node corresponds to three types of positions: θ iron,i Indicates the temperature rise of the i section core; θ iron,bot Indicates the temperature rise of the core bottom; θ L,i Indicates the temperature rise of the i section low-voltage winding; θ L-H,i Indicates the temperature rise of the i section high-low voltage winding middle oil gap; θ H,i Indicates the temperature rise of the i section high-voltage winding; θ oil,i Indicates the temperature rise of the i section outer oil channel; θ oil,bot Indicates the bottom layer oil temperature; θ oil,top Indicates the top layer oil temperature; θ surf,i Indicates the temperature rise of the i section shell; θ surf,bot Indicates the shell bottom temperature rise; S42, according to the specific nameplate parameters of the analyzed target transformer, set Φ IRON,i as P0 / 3 / n, P0 represents the no-load loss nameplate value of the transformer; Φ L,i = I L 2 R L / n, I L represents the rated current of the low-voltage winding, R L represents the DC resistance of the low-voltage winding; Φ H,i = I H 2 R H / n, I H represents the rated current of the high-voltage winding, R H represents the DC resistance of the high-voltage winding; each thermal resistance is determined according to the heat flow experiment; S43, the thermal circuit is regarded as an electric circuit, after determining all the current sources and resistors in the graph according to S41-S42, the node voltage method is used to write the node voltage equation Gθ=Φ, that is: The potentials of all nodes except the reference ground node are sequentially arranged in the θ vector, and each node is numbered in this order; under this order, G xx = 1 / R xx represents the self-impedance of the corresponding node, and the mutual impedance between nodes, which is derived from the determined resistance, see the provisions of the node voltage method; in the above-mentioned order, the current sources associated with each node are sequentially arranged in the Φ vector; by solving the equation, the potentials of all nodes in the circuit are obtained, that is, θ = G -1 Φ; S44, in the above calculation results, the temperature rise values corresponding to the n positions of the transformer oil tank wall in S2 are extracted respectively, and they are composed into the calculation temperature rise vector Θ of the normal operation of the transformer Ν = [θ N 1, θ N 2... θ N n ].

3. The method for transformer overheat fault diagnosis and assessment based on fast calculation of temperature field according to claim 1, characterized in that: The S6 comprises the following steps: S61, the m=m…n in the first segment, respectively represent the core loss, low-voltage winding loss, high-voltage winding loss of three current source Φ IRON,m , Φ L,m , Φ H,m Single replacement for voltage source, respectively, to simulate the m segment alone occurs core overheating, low-voltage winding short circuit overheating, high-voltage winding short circuit overheating of the three overheating fault conditions, the voltage of the voltage source corresponds to the temperature rise value of the overheating point when the overheating fault occurs, according to the relevant standard, it is set to the lightest overheating fault temperature rise 150 DEG C. S62, for the above three cases of thermal circuit after adding the core loss, low-voltage winding loss and high-voltage winding loss respectively, the modified node voltage equation G'θ'=Φ' containing fault is written, assuming that in the mth segment selected in S61, the current source replaced for the nth time is associated with node i: wherein U i is a voltage source replacing the current source, having a value of 150; The potential θ' of all nodes in the circuit is calculated -1 Φ'; the temperature rise calculation value θ of the upper adjacent tank outer wall node in the section in the θ' vector surf,m+1 N m+1 The difference between the temperature θ surf,m+1 and the temperature θ N of the normal operating state, and the minimum value of the difference in the three cases, i.e. min(θ m+1 - θ T ) is taken as the overheating fault temperature rise threshold θ m of the winding section S63, for the next segment, i.e. m = m + 1, repeat S61-S62, obtain θ T m+1 , until all n segments are traversed; the overheat failure temperature rise threshold values obtained by the above calculation each time form an overheat failure temperature rise threshold vector Θ T = [θ T 1, θ T 2… θ T n ] S64. Construct the transformer overheating fault location vector P = [p1, p2, ... p n The values ​​of each element in this vector are determined according to the following rules: the temperature rise vector Θ at each temperature analysis point is compared sequentially. D and thermal defect threshold vector Θ T Size of the element at the corresponding position in the middle; when Θ D A certain element θ D i Less than Θ T Corresponding element θ T i When, then p i =0 indicates that no overheating fault has occurred below the segment corresponding to this element; otherwise, p i =1 indicates that an overheating fault has occurred below the section corresponding to the element; when an overheating fault occurs in a certain section, the value above the section is 1 and the value below is 0, thus locating the winding section where the transformer thermal defect fault is located.

4. The transformer overheat fault diagnosis evaluation method based on fast calculation of temperature field according to claim 3, characterized in that: The S7 comprises the following steps: S71, corresponding to the overheating fault section determined in S64, replace the current sources of core loss, low-voltage winding loss and high-voltage winding loss in S61 in this section with three voltage sources, the voltage of the three voltage sources is the quantity to be solved, which is respectively set as Ux1, Ux2 and Ux3, and it is assumed that the positions of the three voltage sources are respectively associated with nodes i, j and k. In this case, the modified node voltage equation G"θ"=Φ" containing fault is written, that is: Solving gives θ" = G -1 Φ"; where each element in the θ" vector is expressed as a linear combination of the variables to be solved for, Ux1, Ux2, Ux3. S72, based on the arrangement of the temperature measurement points in the target transformer oil channel range determined in S3, the check temperature rise vector Θ in S3 is determined according to the arrangement of the temperature measurement points in the target transformer oil channel range determined in S3 C In the θ" vector obtained in S71, the corresponding Θ C The temperature rise expression at each position includes at least two temperature measurement points θ oil,bot , θ oil,top , which constitute the to-be-solved vector Θ x =[θ oil,bot， θ oil,top… ], and the following optimization model is constructed: J = min || Θ x - Θ C ||2 (4) S73, any optimization solving algorithm is used to solve the above model, and the optimal solution of Ux1, Ux2 and Ux3 is obtained, that is, the specific fault temperature rise value of the core, low-voltage winding and high-voltage winding in this fault section, and the quantitative diagnosis of the severity of the transformer overheating fault is completed.

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