Transformer overheating fault diagnosis and evaluation method based on temperature field rapid calculation

Abstract

The invention relates to a transformer overheating fault diagnosis and evaluation method based on temperature field rapid calculation, and belongs to the technical field of electrical engineering. The method aims at solving the problems that an existing method is insufficient in fault positioning, accuracy and safety, and a finite element analysis method is low in calculation speed. According to the method, a transformer iron core side column and an upper winding are divided into a plurality of sections, and temperature measuring points are arranged at corresponding positions of the outer wall of an oil tank. And establishing an internal thermal field model of the transformer based on a thermal circuit method, and constructing a fault temperature rise vector by using the actually measured temperature rise vector and the calculated temperature rise vector under normal operation. By simulating overheating faults at different positions, a fault temperature rise threshold vector is constructed, and positioning of a fault section is realized. And establishing a temperature identification model in the fault section, solving a specific temperature rise value of a fault point through an optimization algorithm, and realizing quantitative diagnosis and evaluation of the severity of the overheating fault. The method has the advantages that the fault can be positioned, the overheating degree can be quantified, and the calculation speed is high.

Description

Technical Field

[0001] The invention belongs to the technical field of electrical engineering and relates to a transformer overheating fault diagnosis and evaluation method based on rapid temperature field calculation. Background Art

[0002] Oil-immersed transformers are one of the core equipment of the power system. Ensuring the safe and stable operation of oil-immersed transformers is crucial to the normal operation of the power system. Transformers will generate energy loss during operation and convert it into heat energy. The main heat sources inside the transformer are the iron core and windings. The alternating magnetic field in the iron core will generate hysteresis loss. When the load current flows through the metal copper winding, Joule loss will be generated. The heat generated by these two energy losses is transferred to the surroundings and eventually dissipated to the surrounding air through the surface of the transformer box. This heat transfer process will form a temperature field distribution inside the transformer. During normal operation, the temperature rise of the transformer core and windings and the temperature rise caused to the surrounding insulation paper, insulating oil and other insulation main parts are generally within the design range. However, when a turn-to-turn short circuit fault occurs in the winding, or the iron core is abnormally heated, the overheating temperature will far exceed the normal hot spot temperature, which will cause the insulation temperature near it to rise too high, which will accelerate the aging of the insulation material, cause deformation and cracks in the insulation structure, and even insulation failure, seriously shortening the insulation life. Therefore, it is necessary to promptly detect this overheating fault of the transformer, find out the location of the fault point in the winding or core, and infer the temperature of the overheating point, and then determine the severity of the overheating fault.

[0003] At present, the commonly used methods for diagnosing transformer overheating faults include dissolved gas analysis in oil, infrared temperature measurement diagnosis method, and optical fiber temperature measurement method. However, it is difficult to identify the specific location of the fault with the dissolved gas analysis method in oil; the infrared temperature measurement diagnosis method can only measure the surface temperature of the transformer box, and it is difficult to accurately reflect the location and severity of thermal defects inside the equipment; although the optical fiber temperature measurement method has high temperature measurement accuracy and fast response speed, it is expensive, the process required for embedding in the transformer winding is complex, and it needs to fit closely with the winding. Its negative impact on the oil-paper insulation performance of the winding is still unclear. Therefore, the existing test methods based on direct physical measurement are difficult to meet the diagnostic needs of transformer overheating faults.

[0004] The use of temperature field analysis can identify the specific state of the overheating point in the transformer according to a certain calculation method. It is an effective theoretical method to achieve the above purpose. It mainly includes two methods: finite element calculation and thermal circuit calculation. However, due to the large spatial scale of the transformer, the use of finite element for thermal field analysis has the problems of large calculation scale and slow calculation speed, which makes it difficult to meet the needs of rapid diagnosis and treatment of transformer faults on site. The use of thermal circuit method to analyze the temperature field can take into account both calculation speed and calculation accuracy. However, the thermal circuit method can only calculate the internal temperature distribution of the transformer under normal operation, and cannot be directly used to diagnose overheating faults.

[0005] At present, the direct physical test methods such as oil dissolved gas analysis, infrared temperature measurement diagnosis, and optical fiber temperature measurement commonly used to diagnose overheating faults in transformer core-winding systems have deficiencies in fault location, fault accuracy, safety, etc., and the finite element analysis method has the problem of slow calculation speed. In view of these problems, the present invention uses a fast calculation method for the internal temperature field of the transformer based on the thermal circuit method, and combines the measured temperature rise values ​​of the top oil temperature, bottom oil temperature value and other temperature measurement points of the transformer to achieve the section location of the overheating fault of the transformer winding-core system, and establishes a temperature identification model for the transformer core and winding overheating points. By solving the model, the quantitative diagnosis and evaluation of the severity of the transformer winding-core overheating fault is achieved, which has the advantages of fault location, quantification of overheating degree, and fast calculation speed. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide a transformer overheating fault diagnosis and evaluation method based on rapid temperature field calculation. A method for rapid calculation of the internal temperature field of a transformer based on the thermal circuit method, combined with the measured temperature rise values ​​of the top oil temperature, bottom oil temperature and other temperature measurement points of the transformer, to achieve the section location of the transformer winding-core system overheating fault, and establish a temperature identification model for the transformer core and winding overheating points. By solving the model, the severity of the transformer winding-core overheating fault can be quantitatively diagnosed and evaluated, which has the advantages of fault location, quantification of overheating degree and fast calculation speed.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A transformer overheating fault diagnosis and evaluation method based on rapid temperature field calculation includes the following steps:

[0009] S1. Combine a transformer core leg and the high-voltage winding and low-voltage winding around the core leg as a whole research object, divide the high-voltage winding, low-voltage winding and core leg of the transformer into n sections with exactly the same spatial position distribution, each section contains a number of coil turns and each core leg small section;

[0010] S2. Set the temperature measurement points at the same height of the transformer box body corresponding to the above sections, and record them as S1…S n ; The temperature rise of each temperature point measured compared to the ambient temperature is recorded as the measured temperature rise vector Θ Μ =[θ M 1,θ M 2,θ M 3…θ M n];

[0011] S3. According to the installation of the temperature measurement points of the transformer winding outer oil channel, at least two measurement points, the bottom oil temperature and the top oil temperature, are included. The temperature rise values ​​of the top oil temperature and the bottom oil temperature inside the transformer, as well as the temperature at other internal and external oil channel temperature measurement points compared to the ambient temperature are measured respectively, and recorded as the calibration temperature rise vector θ C =[θ C top ,θ C bottom …];

[0012] S4. Based on the thermal circuit method, the temperature of each position inside the transformer is analyzed and obtained under normal operation under a certain load, and the normal temperature rise calculation vector Θ of the transformer is obtained. Ν ;

[0013] S5, based on the measured temperature rise vector Θ in S2 Μ , and the calculated temperature rise vector Θ under normal operation in step S44 Ν , construct the transformer overheating fault temperature rise vector Θ D =Θ Μ –Θ Ν =[θ D 1,θ D 2…θ D n ];

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

[0015] S7. Further determine the severity of overheating within the specific fault section located above, that is, the specific temperature rise value of the fault point.

[0016] Further, the S4 comprises the following steps:

[0017] S41. Establish a thermal circuit calculation model for the internal thermal field of the transformer; where Φ IRON,i is the equivalent current source of the core heating, and its magnitude is the heating power value of the i-th section of the core divided according to S1; Φ L,i is the equivalent current source for heating of the low-voltage winding, and its magnitude is the heating power value of the i-th section of the low-voltage winding divided in S1; Φ H,i is the equivalent current source of the high-voltage winding heating, and its magnitude represents the heating power value of the i-th section of the high-voltage winding divided in S1; each resistor R xx Indicates the thermal resistance on the corresponding heat flow path; the node corresponds to three types of positions: θ iron,i represents the temperature rise of the i-th section of the core; θ iron,bot Indicates the temperature rise at the bottom of the core; θ L,irepresents the temperature rise of the i-th section low-voltage winding; θ L-H,i Represents the temperature rise of the oil gap between the high and low voltage windings in the i-th section; θ H,i represents the temperature rise of the i-th section high voltage winding; θ oil,i represents the temperature rise of the i-th section of the external oil channel; θ oil,bot Indicates the bottom oil temperature; θ oil,top Top oil temperature; θ surf,i represents the temperature rise of the i-th section housing; θ surf,bot Indicates the temperature rise at the bottom of the housing;

[0018] S42. According to the specific nameplate parameters of the target transformer being analyzed, Φ IRON,i Assume 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;

[0019] S43. Consider the thermal circuit as a circuit. After determining all current sources and resistors in the diagram according to S41-S42, use the node voltage method to write out the node voltage equation Gθ=Φ, that is:

[0020]

[0021] The potentials of all nodes except the reference ground node are arranged in a certain order in the θ vector, and each node is numbered in this order; in this order, G xx =1 / R xx represents the self-conductance of the corresponding node and the mutual conductance between the nodes, which are derived from the determined resistance, see the provisions of the node voltage method; corresponding to the above order, the current source associated with each node is sequentially arranged in the Φ vector; solving the equation, the potential of all nodes in the circuit is obtained, that is, θ = G -1 Φ;

[0022] S44. In the above calculation results, the temperature rise values ​​at n positions of the transformer tank wall corresponding to S2 are extracted respectively, and they are combined into a calculated temperature rise vector Θ under normal operation of the transformer Ν =[θ N 1,θ N 2…θN n ].

[0023] Further, the S6 comprises the following steps:

[0024] S61, in the mth segment, m=1…n, representing the three current sources Φ of the core loss, the low-voltage winding loss, and the high-voltage winding loss respectively IRON,m , Φ L,m , Φ H,m Replaced with voltage sources one by one respectively to simulate the three overheating faults of core overheating, low voltage winding short circuit overheating and high voltage winding short circuit overheating in the mth section. The voltage of the voltage source corresponds to the temperature rise value of the overheating point when the overheating fault occurs. According to relevant standards, it is set to the mildest overheating fault temperature rise of 150℃.

[0025] S62. For the thermal paths in the three cases of overheating faults in which core loss, low-voltage winding loss, and high-voltage winding loss are added, respectively, the modified node voltage equations G′θ′=Φ′ containing the fault are written out. Assume that in the mth segment selected in S61, the current source replaced at a certain time is associated with the node i:

[0026]

[0027] Where U i The voltage source to replace the current source has a value of 150;

[0028] The calculated potential of all nodes in the circuit is θ′=G′ -1 Φ′; extract the temperature rise calculation value θ of the node on the upper adjacent tank outer wall of the section in the θ′ vector surf,m+1 , and its temperature under normal operating conditions θ N m+1 The difference between the three cases is taken as the minimum value of the difference, that is, min(θ surf,m+1 –θ N m+1 ) as the overheating fault temperature rise threshold value θ of this winding section T m ;

[0029] S63, for the next segment, that is, m=m+1, repeat S61-S62 to obtain θ T m+1 , until all n sections are traversed; the overheating fault temperature rise thresholds obtained by the above calculations are combined into an overheating fault temperature rise threshold vector Θ T =[θ T 1,θ T 2… θ T n ];

[0030] S64. Construct the transformer overheating fault location vector P = [p1, p2…p n ]; the value of each element in this vector is determined according to the following rules: compare the temperature rise vector Θ of each temperature analysis point in turn D and thermal defect threshold vector Θ T The size of the element at the corresponding position in ; when Θ D An element θ in D i Less than Θ T The corresponding element θ T i When p i = 0, indicating that no overheating fault occurs below the section corresponding to the element; otherwise, p i =1, indicating that an overheating fault has occurred below the section corresponding to the element; when an overheating fault occurs in a section, the value above the section is 1 and the value below is 0, locating the winding section where the transformer thermal defect fault is located.

[0031] Further, the S7 comprises the following steps:

[0032] S71, corresponding to the overheating fault section determined in the above step S64, the current sources of the core loss, low-voltage winding loss, and high-voltage winding loss in the above step S61 in the section are replaced by three voltage sources. The voltage magnitudes of these three voltage sources are the quantities to be determined, which are set as Ux1, Ux2, and Ux3 respectively, and it is assumed that the positions of these three voltage sources are respectively associated with the nodes i, j, and k. In this case, the modified node voltage equation containing the fault is written out G"θ"=Φ", that is:

[0033]

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

[0035] S72, based on the arrangement of the temperature measuring points within the outer oil channel of the target transformer determined in S3, according to the verification temperature rise vector θ in S3 C , extract the corresponding θ from the θ" vector obtained in S71 C The temperature rise expression at each position includes at least two temperature measurement points θ: the bottom oil temperature and the top oil temperature oil,bot、 θ oil,top , forming the vector Θ to be solved x =[θ oil,bot， θ oil,top… ], and construct the following optimization model:

[0036] J=min||Θ x -Θ C ||2 (4)

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

[0038] The beneficial effects of the present invention are as follows: by using a fast calculation method for the internal temperature field of the transformer based on the thermal circuit method, and combining the measured temperature rise values ​​of the top oil temperature, the bottom oil temperature and other temperature measuring points of the transformer, the section positioning of the overheating fault of the transformer winding-core system is achieved, and a temperature identification model for the transformer core and winding overheating points is established. By solving the model, a quantitative diagnosis and evaluation of the severity of the transformer winding-core overheating fault is achieved, which has the advantages of fault locating, quantifying the degree of overheating and fast calculation speed.

[0039] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0041] Figure 1 It is the thermal circuit model of transformer. DETAILED DESCRIPTION

[0042] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways 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 only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0043] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0044] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0045] The purpose of the present invention is to use a fast calculation method of the internal temperature field of the transformer based on the thermal circuit method, and combine the measured temperature rise values ​​of the top oil temperature, the bottom oil temperature and other temperature measurement points of the transformer to realize the section location of the overheating fault of the transformer winding-core system, and establish a temperature identification model for the overheating point of the transformer core and winding. By solving the model, the quantitative diagnosis and evaluation of the severity of the overheating fault of the transformer winding-core system are realized, which includes the following steps:

[0046] S1. Combine a transformer core limb, and the high-voltage winding and low-voltage winding around the core limb as a whole research object, divide the high-voltage winding, low-voltage winding, and core limb of the transformer into n segments with exactly the same spatial position distribution, each segment contains a number of coil turns, and each core limb segment;

[0047] S2. Set the temperature measurement points at the same height of the transformer box body corresponding to the above sections, and record them as S1…S n ; The temperature rise of each temperature point measured compared to the ambient temperature is recorded as the measured temperature rise vector Θ Μ =[θ M 1,θ M 2,θ M 3…θ M n ];

[0048] S3. According to the installation of the temperature measurement points of the transformer winding outer oil channel (should include at least two measurement points, the bottom oil temperature and the top oil temperature), respectively measure the temperature rise values ​​of the transformer inner top oil temperature, the bottom oil temperature, and the temperature at other inner and outer oil channel temperature measurement points compared with the ambient temperature, and record it as the calibration temperature rise vector θ C =[θ C top ,θ C bottom …];

[0049] S4. Based on the thermal circuit method, the temperature of each position inside the transformer is analyzed and obtained under normal operation under a certain load, and the normal temperature rise calculation vector Θ of the transformer is obtained. Ν , mainly including the following steps:

[0050] S41. According to the attached Figure 1 Establish a thermal circuit calculation model for the internal thermal field of the transformer; where Φ IRON,i is the equivalent current source of the core heating, and its magnitude is the heating power value of the i-th section of the core divided according to S1; Φ L,i is the equivalent current source for heating of the low-voltage winding, and its magnitude is the heating power value of the i-th section of the low-voltage winding divided in S1; Φ H,i is the equivalent current source of the high-voltage winding heating, and its magnitude represents the heating power value of the i-th section of the high-voltage winding divided in S1; each resistor R xx Represents the thermal resistance on the corresponding heat flow path; Figure 1 The nodes in θ correspond to three types of positions: iron,i represents the temperature rise of the i-th section of the core; θ iron,bot Indicates the temperature rise at the bottom of the core; θ L,i represents the temperature rise of the i-th section low-voltage winding; θ L-H,i Represents the temperature rise of the oil gap between the high and low voltage windings in the i-th section; θ H,i represents the temperature rise of the i-th section high voltage winding; θ oil,i represents the temperature rise of the i-th section of the external oil channel; θ oil,bot Indicates the bottom oil temperature; θ oil,top Top oil temperature; θ surf,i represents the temperature rise of the i-th section housing; θ surf,bot Indicates the temperature rise at the bottom of the housing;

[0051] S42. According to the specific nameplate parameters of the target transformer being analyzed, Figure 1 Φ IRON,i Assume 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;

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

[0053]

[0054] The θ vector is arranged in a certain order. Figure 1 The potential (temperature rise value) of all nodes except the reference ground node in the following order. xx =1 / R xx represents the self-conductance of the corresponding node and the mutual conductance between the nodes, which can be expressed by Figure 1 The resistance (thermal resistance) determined in the circuit can be deduced by referring to the provisions of the node voltage method; corresponding to the above sequence, the current source (heat source) associated with each node is sequentially arranged in the Φ vector; solving this equation, the potential of all nodes in the circuit can be obtained, that is, θ = G -1 Φ;

[0055] S44. In the above calculation results, the temperature rise values ​​at n positions of the transformer tank wall corresponding to S2 are extracted respectively, and they are combined into a calculated temperature rise vector Θ under normal operation of the transformer 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 operation in step S44 Ν , construct the transformer overheating fault temperature rise vector Θ D =Θ Μ –Θ Ν =[θ D 1,θ D 2…θ D n ];

[0057] S6. Constructing the transformer overheating fault temperature rise threshold vector Θ T , mainly including the following steps:

[0058] S61, in the mth segment, m=1…n, representing the three current sources Φ of the core loss, the low-voltage winding loss, and the high-voltage winding loss respectively IRON,m , Φ L,m , Φ H,m Replaced with voltage sources one by one respectively to simulate the three overheating faults of core overheating, low voltage winding short circuit overheating and high voltage winding short circuit overheating in the mth section. The voltage of the voltage source corresponds to the temperature rise value of the overheating point when the overheating fault occurs. According to relevant standards, it is set to the mildest overheating fault temperature rise of 150℃.

[0059] S62. For the three thermal circuits in the above three cases after adding overheating faults ①-③, write out the modified node voltage equations G′θ′=Φ′ ​​containing the faults (assuming that in the mth segment selected in S61, the current source replaced at a certain time is Figure 1 Node i in association):

[0060]

[0061] Where U i The voltage source is 150, which replaces the current source. The potential of all nodes in the circuit is calculated as θ′=G′ -1 Φ′; extract the temperature rise calculation value θ of the node on the upper adjacent tank outer wall of the section in the θ′ vector surf,m+1 , and its temperature under normal operating conditions θ N m+1 The difference between the three cases ①-③ is taken, that is, min(θ surf,m+1 –θ N m+1 ) as the overheat fault temperature rise threshold value θ of the winding section T m ;

[0062] S63, for the next segment, that is, m=m+1, repeat S61-S62 to obtain θ T m+1 , until all n sections are traversed; the overheating fault temperature rise thresholds obtained by the above calculations are combined into an overheating fault temperature rise threshold vector Θ T =[θ T 1,θ T 2… θ T n ];

[0063] S64. Construct the transformer overheating fault location vector P = [p1, p2…p n ]; the value of each element in this vector is determined according to the following rules: compare the temperature rise vector Θ of each temperature analysis point in turn D and thermal defect threshold vector Θ T The size of the element at the corresponding position in ; when Θ D An element θ in D i Less than Θ T The corresponding element θ T i When p i = 0, indicating that no overheating fault occurs below the section corresponding to the element; otherwise, p i =1, indicating that an overheating fault has occurred below the section corresponding to the element; when an overheating fault occurs in a section, the value above the layer is 1 and the value below is 0, based on which the winding section where the transformer thermal defect fault is located can be located;

[0064] S7. Further determining the severity of overheating, i.e., the specific temperature rise value of the fault point, within the specific fault section located above, including the following steps:

[0065] S71, corresponding to the overheating fault section determined in step S64, replace the current sources ①-③ in step S61 in the section with three voltage sources. The voltages of the three voltage sources are the quantities to be determined, which are respectively set as Ux1, Ux2, and Ux3. It is assumed that the positions of the three voltage sources are respectively the same as those of the attached Figure 1 The nodes i, j, and k in the diagram are connected. In this case, the modified node voltage equation G"θ"=Φ" containing the fault is written out, that is:

[0066]

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

[0068] S72, based on the arrangement of the temperature measuring points within the outer oil channel of the target transformer determined in S3, according to the verification temperature rise vector θ in S3 C , extract the corresponding θ from the θ" vector obtained in S71 C The temperature rise expression at each position includes at least two temperature measurement points θ: the bottom oil temperature and the top oil temperature oil,bot、 θ oil,top , forming the vector Θ to be solved x =[θ oil,bot， θ oil,top… ], and construct the following optimization model:

[0069] J=min||Θ x -Θ C ||2 (4)

[0070] S73. Use any optimization solution algorithm to solve the above model and obtain the optimal solutions of Ux1, Ux2, and Ux3, which are the specific fault temperature rise values ​​of the core, low-voltage winding, and high-voltage winding in the fault section, and complete 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 solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A transformer overheating fault diagnosis and evaluation method based on rapid temperature field calculation is characterized by: The method comprises the following steps: S1. Combine a transformer core leg and the high-voltage winding and low-voltage winding around the core leg as a whole research object, divide the high-voltage winding, low-voltage winding and core leg of the transformer into n sections with exactly the same spatial position distribution, each section contains a number of coil turns and each core leg small section; S2. Set the temperature measurement points at the same height of the transformer box body corresponding to the above sections, and record them as S1…S n ; The temperature rise of each temperature point measured compared to the ambient temperature is recorded as the 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 measurement points of the transformer winding outer oil channel, at least two measurement points, the bottom oil temperature and the top oil temperature, are included. The temperature rise values ​​of the top oil temperature and the bottom oil temperature inside the transformer, as well as the temperature at other internal and external oil channel temperature measurement points compared to the ambient temperature are measured respectively, and 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 inside the transformer is analyzed and obtained under normal operation under a certain load, and the normal temperature rise calculation vector Θ of the transformer is obtained. Ν ; S5, based on the measured temperature rise vector Θ in S2 Μ , and the calculated temperature rise vector Θ under normal operation in step S44 Ν , construct the transformer overheating fault temperature rise vector Θ D =Θ Μ –Θ Ν =[θ D 1,θ D 2…θ D n ]; S6. Constructing the transformer overheating fault temperature rise threshold vector Θ T ; S7. Further determine the severity of overheating within the specific fault section located above, that is, the specific temperature rise value of the fault point.

2. The transformer overheating fault diagnosis and evaluation method based on rapid temperature field calculation according to claim 1 is characterized in that: The S4 comprises the following steps: S41. Establish a thermal circuit calculation model for the internal thermal field of the transformer; where Φ IRON,i is the equivalent current source of the core heating, and its magnitude is the heating power value of the i-th section of the core divided according to S1; Φ L,i is the equivalent current source for heating of the low-voltage winding, and its magnitude is the heating power value of the i-th section of the low-voltage winding divided in S1; Φ H,i is the equivalent current source of the high-voltage winding heating, and its magnitude represents the heating power value of the i-th section of the high-voltage winding divided in S1; each resistor R xx Indicates the thermal resistance on the corresponding heat flow path; the node corresponds to three types of positions: θ iron,i represents the temperature rise of the i-th section of the core; θ iron,bot Indicates the temperature rise at the bottom of the core; θ L,i represents the temperature rise of the i-th section low-voltage winding; θ L-H,i Represents the temperature rise of the oil gap between the high and low voltage windings in the i-th section; θ H,i represents the temperature rise of the i-th section high voltage winding; θ oil,i represents the temperature rise of the i-th section of the external oil channel; θ oil,bot Indicates the bottom oil temperature; θ oil,top Top oil temperature; θ surf,i represents the temperature rise of the i-th section housing; θ surf,bot Indicates the temperature rise at the bottom of the housing; S42. According to the specific nameplate parameters of the target transformer being analyzed, Φ IRON,i Assume 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. Consider the thermal circuit as a circuit. After determining all current sources and resistors in the diagram according to S41-S42, use the node voltage method to write out the node voltage equation Gθ=Φ, that is: The potentials of all nodes except the reference ground node are arranged in a certain order in the θ vector, and each node is numbered in this order; in this order, G xx =1 / R xx represents the self-conductance of the corresponding node and the mutual conductance between the nodes, which are derived from the determined resistance, see the provisions of the node voltage method; corresponding to the above order, the current source associated with each node is sequentially arranged in the Φ vector; solving the equation, the potential of all nodes in the circuit is obtained, that is, θ = G -1 Φ; S44. In the above calculation results, the temperature rise values ​​at n positions of the transformer tank wall corresponding to S2 are extracted respectively, and they are combined into a calculated temperature rise vector Θ under normal operation of the transformer Ν =[θ N 1,θ N 2…θ N n ].

3. The transformer overheating fault diagnosis and evaluation method based on rapid temperature field calculation according to claim 1 is characterized in that: The S6 comprises the following steps: S61, in the mth segment, m=1…n, representing the three current sources Φ of the core loss, the low-voltage winding loss, and the high-voltage winding loss respectively IRON,m , Φ L,m , Φ H,m Replaced with voltage sources one by one respectively to simulate the three overheating faults of core overheating, low voltage winding short circuit overheating and high voltage winding short circuit overheating in the mth section. The voltage of the voltage source corresponds to the temperature rise value of the overheating point when the overheating fault occurs. According to relevant standards, it is set to the mildest overheating fault temperature rise of 150℃. S62. For the thermal paths in the three cases of overheating faults in which core loss, low-voltage winding loss, and high-voltage winding loss are added, respectively, the modified node voltage equations G′θ′=Φ′ containing the fault are written out. Assume that in the mth segment selected in S61, the current source replaced at a certain time is associated with the node i: Where U i The voltage source to replace the current source has a value of 150; The calculated potential of all nodes in the circuit is θ′=G′ -1 Φ′; extract the temperature rise calculation value θ of the node on the upper adjacent tank outer wall of the section in the θ′ vector surf,m+1 , and its temperature under normal operating conditions θ N m+1 The difference between the three cases is taken as the minimum value of the difference, that is, min(θ surf,m+1 –θ N m+1 ) as the overheating fault temperature rise threshold value θ of this winding section T m ; S63, for the next segment, that is, m=m+1, repeat S61-S62 to obtain θ T m+1 , until all n sections are traversed; the overheating fault temperature rise thresholds obtained by the above calculations are combined into an overheating fault 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 value of each element in this vector is determined according to the following rules: compare the temperature rise vector Θ of each temperature analysis point in turn D and thermal defect threshold vector Θ T The size of the element at the corresponding position in ; when Θ D An element θ in D i Less than Θ T The corresponding element θ T i When p i = 0, indicating that no overheating fault occurs below the section corresponding to the element; otherwise, p i =1, indicating that an overheating fault has occurred below the section corresponding to the element; when an overheating fault occurs in a section, the value above the section is 1 and the value below is 0, locating the winding section where the transformer thermal defect fault is located.

4. The transformer overheating fault diagnosis and evaluation method based on rapid temperature field calculation according to claim 1 is characterized in that: The S7 comprises the following steps: S71, corresponding to the overheating fault section determined in the above step S64, the current sources of the core loss, low-voltage winding loss, and high-voltage winding loss in the above step S61 in the section are replaced by three voltage sources. The voltage magnitudes of these three voltage sources are the quantities to be determined, which are set as Ux1, Ux2, and Ux3 respectively, and it is assumed that the positions of these three voltage sources are respectively associated with the nodes i, j, and k. In this case, the modified node voltage equation containing the fault is written out G"θ"=Φ", that is: Solving for θ"=G" -1 Φ"; where each element in the θ" vector is expressed as a linear combination expression of the variables to be determined Ux1, Ux2, and Ux3; S72, based on the arrangement of the temperature measuring points within the outer oil channel of the target transformer determined in S3, according to the verification temperature rise vector θ in S3 C , extract the corresponding θ from the θ" vector obtained in S71 C The temperature rise expression at each position includes at least two temperature measurement points θ: the bottom oil temperature and the top oil temperature oil,bot、 θ oil,top , forming the vector Θ to be solved x =[θ oil,bot， θ oil,top… ], and construct the following optimization model: J=min||Θ x -I C ||2 (4) S73. Use any optimization solution algorithm to solve the above model and obtain the optimal solutions of Ux1, Ux2, and Ux3, which are the specific fault temperature rise values ​​of the core, low-voltage winding, and high-voltage winding in this fault section, to complete the quantitative diagnosis of the severity of the transformer overheating fault.

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