JP6803025B2 - Remaining life diagnosis method and diagnostic equipment for oil-immersed transformers - Google Patents

Description

The present invention relates to a diagnostic method and a diagnostic apparatus for determining the remaining life of an oil-immersed transformer from the average degree of polymerization residual ratio of the wound insulating paper housed in the oil-immersed transformer.

It is believed that the life of a transformer depends on the decrease in mechanical strength of the coil insulating paper, especially the decrease in tensile strength (tensile strength).
When a short-circuit failure occurs outside the transformer, a large electromagnetic force is generated in the coil inside the transformer. The transformer is designed so that the stress applied to the coil copper wire at this time is 1200 kg weight / cm ² or less, and the coil insulating paper is damaged when it cannot withstand the expansion and contraction of the coil copper wire at this time, and the transformer The internal insulation of the is threatened. When the insulating paper is in such a state, the transformer is judged to have reached the end of its life.

It is known that the mechanical strength of wound insulation paper correlates with the average degree of polymerization (DP) of the cellulose molecules that compose it. According to the Japan Electrical Manufacturers' Association standard JEM1463, the life level is DP450 and the danger level is It is specified as DP250. In addition, the Electrical Cooperation Study Group recommends DP450 as the life level of wound insulating paper (Non-Patent Document 1, P177).
As a method of predicting the remaining life of a transformer, the degree of deterioration of the transformer at the present time is investigated, and if the same operation is continued in the future, the DP of the winding insulating paper will decrease and the minimum value will reach the life level. It has been made to predict the time until (Non-Patent Document 2, P40).

As a method of investigating the degree of deterioration of the transformer at present, a method of estimating the degree of deterioration of the wound insulating paper by collecting the insulating paper of the part that does not affect the insulation from the inside of the transformer, and the method of generating the deterioration of the insulating paper in the insulating oil. Non-Patent Document 2 describes a method for measuring the amount of CO ₂ + CO, furfural, etc. of an object.
The former is direct, but it is difficult to collect insulating paper without stopping the transformer. Therefore, the latter method, which can be collected even during operation, is widely implemented.

For a method of predicting the time required for the DP of the wound insulating paper to decrease and the minimum value to reach the life level when the transformer continues to operate in the same manner, refer to P180 to P181 of Non-Patent Document 1. It is described as a life prediction method. There are two types of life prediction methods: a method based on the estimated value of DP and a method (ARY-Map method) for mapping the amount of insulation paper deterioration product produced (A), production rate (R), and years of operation (Y). It is shown.
However, as shown in P172 to P174 of Non-Patent Document 1, the method of estimating the degree of deterioration of the transformer from the components in oil such as CO ₂ + CO and furfural has a certain range of diagnosis, and further. There is a demand for a highly accurate diagnostic method for the degree of deterioration.

Therefore, a method of quantitatively evaluating the decrease in DP from the initial stage of operation based on the operation results of the transformer without using the measured value of the deterioration product for the prediction of deterioration has been studied (Non-Patent Document 3). , P43-4, equation (2)).
In Non-Patent Document 2 and the like, the relationship between the deterioration temperature and the decrease rate of DP has been clarified and reported by various experiments by a test in which an insulating paper is thermally accelerated and deteriorated in a test tank simulating a transformer. It is stated that the temperature rise history can be grasped from the load of the transformer and the ambient temperature, and the deterioration of the insulating paper can be estimated accurately by combining the thermal deterioration characteristics of the insulating paper.

On the other hand, it is known that the winding insulating paper used in the oil-immersed transformer is also deteriorated by moisture, and its influence is formulated (Non-Patent Document 4, P21-17 to P21). -8 (1) to (3), and Non-Patent Document 5, P7-7 (4) and (5)).
Therefore, it is considered important to grasp the moisture absorption state of the winding upper insulating paper, which is expected to have the highest temperature in the transformer, in performing the deterioration diagnosis.
However, since it is usually difficult to collect insulating paper from an operating transformer and measure the water content, the water content in the insulating oil collected from the transformer and the water balance relationship between the insulating paper and the insulating oil are used. A method of indirectly estimating the water content in the winding upper insulating paper has been studied (Non-Patent Document 6, P335).

Further, Patent Document 1 describes a method of measuring the water content of an insulating paper from the temperature and the water content of the insulating oil. The principle is "The moisture moves from the higher vapor pressure to the lower vapor pressure until the moisture vapor pressure of the insulating paper and the moisture vapor pressure of the insulating oil become equal. When the vapor pressure becomes equal, the movement of water ends. It reaches a state of equilibrium. " In this Patent Document 1, a graph of the water vapor pressure in oil with respect to the oil temperature and a graph of the water vapor pressure in paper with respect to the oil temperature are shown in Tables 2 and 3, and the oil temperature and the water content in oil are given. It is stated that the amount of water in the paper is determined.

In Non-Patent Document 7, Electrical Collaborative Research Vol. 61, No. 2, P43, "In general, oil is collected from a valve near the bottom of the tank. Therefore, in a transformer during operation, the upper temperature indicated by a dial thermometer and There is a difference in the temperature of the insulating oil collected. However, since this temperature difference is taken into consideration in the coefficient in the formula, the value of the dial thermometer at the time of oil extraction should be applied. "
However, in Non-Patent Document 7, although the water content in oil and the water content in paper in the transformer are represented by one representative value, the water content in oil and the water content in paper in the transformer are constant. Therefore, a more accurate method for estimating the moisture content in paper is required.

Patent Document 2 is a document describing a technique for providing a device and a method for estimating the moisture content in the insulating paper on the upper part of a new winding in consideration of the temperature distribution inside the oil-immersed transformer. In the technique described in Patent Document 2, it is described that the temperature change with time is taken into consideration, and the water content in oil and the water content in paper change with a first-order lag with different time constants with respect to the changing oil temperature. ing.

Patent Document 3 relates to a remaining life diagnostic device and a remaining life diagnosis method for a power transformer, and estimates the history of the winding maximum temperature at which the transformer has been operated from the outside temperature record and the load history during operation. The technology to be used is described. Then, it is a technique that claims that the diagnostic accuracy can be improved by using the thermal history as compared with the conventional method of measuring the deterioration product in the insulating oil, but Patent Document 3 still states that the moisture content in the insulating paper is high. The effects of deterioration are not taken into account.

Patent Document 4 proposes a method of considering the moisture in the paper for the DP estimation of the wound insulating paper. The method of estimating the water content in paper is a method of measuring the water content in oil during transformer operation and obtaining it using a diagram showing the relationship between the water content in oil and the water content in paper. At that time, the temperature of the upper insulator is calculated, and the water content equilibrium value in paper at the temperature of the insulating oil and the water content in the oil is estimated from the relationship diagram.

Patent Document 5 proposes a method for estimating the amount of water in paper in consideration of the fact that the water equilibrium relationship between paper and oil changes due to aged deterioration of paper and oil. Assuming that the water content in oil circulating in the transformer is determined by the water content in the press board, when estimating the average value throughout the year, the water content in oil during transformer operation is measured multiple times, and the paper-oil content is measured. It is obtained using the water equilibrium relationship of. Since the moisture in the oil corrected by the moisture content in the press board returns in the transformer, it is used to estimate the moisture in the wound insulating paper.

Japanese Patent No. 3709444 Japanese Unexamined Patent Publication No. 2008-192775 Japanese Patent No. 4323396 Japanese Patent No. 4703519 Japanese Patent No. 5704965

Power Transformer Maintenance and Management Expert Committee, "4-1 Average Degree of Polymerization as a Guideline for Life", published by the Electric Cooperative Research Association, February 1999, Vol. 54, No. 5 (Part 1), No. Chapter 4, P177 Teruo Miyamoto, "4. Transformer Life Diagnosis Method", Life Diagnosis Technology for Transformers with Oil in Operation, Institute of Electrical Engineers of Japan Study Group Materials, Industrial Power Electrical Application Study Group IEA-94-5, P40 Yoshinobu Mizutani et al., "Heat deterioration evaluation method based on temperature history analysis of 154 to 275 kV oil-immersed transformer insulating paper", 2012 Institute of Electrical Engineers of Japan Power and Energy Division Conference No. 343, P43-3 to P43-4 Shun Nakatsuka et al., "Study on Thermal Deterioration Characteristics of Transformer Winding Insulation Paper for Electric Power by Accelerated Aging Test", 2006 IEEJ Electric Power and Energy Division Conference No. 271, P21-17 to P21-18 Shun Nakatsuka et al., "Estimation of Average Degree of Polymerization of Transformer Winding Insulation Paper for Electric Power Using Thermal History", 2007 IEEJ Electricity and Energy Division Conference No. 158, P7-7 to P7-8 Tomoyuki Sekiguchi et al., "Method for estimating the amount of water in insulating paper of oil-immersed transformers", 2007 IEEJ National Convention No. 5-216, P335 Substation Equipment Operation Limit Evaluation Expert Committee, "6-1-5 How to Determine the Limit Value of Insulating Paper Based on Bubble Generation Temperature (1) Method of Estimating the Moisture Content in Insulating Paper", Electric Cooperative Research, Electric Cooperative Published by the study group, November 2005, Vol. 61, No. 2, P43

What is common to the patent documents and non-patent documents described above is that the water equilibrium relationship between paper and oil is used. In the conventional technology, the water content in the paper has been estimated assuming that an equilibrium relationship is established between the coil insulating paper on the winding upper part and the water content in the oil.
However, in an operating transformer, insulating oil must be collected from the oil extraction port (for example, the drain valve at the bottom of the tank) installed in the transformer, and the amount of water in the oil at the time of oil extraction must be actually estimated at the top of the winding. It is possible that the value is different from the value in the vicinity.
Moreover, since the insulating oil in the transformer is always convected, the water relationship between the paper and the oil is locally non-equilibrium. Therefore, if the amount of water in the oil near the upper part of the winding, which is actually desired to be estimated from the amount of water in the insulating oil collected from the oil sampling port of the transformer, is estimated by the conventional technique, there is a problem that the accuracy is low.

Further, in the case of the technique described in Patent Document 5, the average value of the water content in the paper is used throughout the year. However, in reality, the water content in the paper changes every moment as the ambient temperature changes, the water content in the paper decreases when the temperature of the insulating paper is high, and vice versa when the temperature of the insulating paper is low. Since it is the amount, it is considered that the values of the temperature and the amount of water at the same time are necessary to accurately calculate the deterioration of the insulating paper. If the values of temperature and water content at the same time are obtained, the state in which the DP of the insulating paper decreases momentarily under those conditions is calculated by the deterioration formula (average degree of polymerization residual rate) as shown in Non-Patent Document 5. It is possible to do.

An object of the present invention is to propose a new method for estimating the amount of water in the oil near the upper part of the winding to be actually estimated from the amount of water in the insulating oil, and based on this, estimate the deterioration state of the winding insulating paper and add oil. It is to provide a method for diagnosing the remaining life of a transformer and a device for diagnosing the remaining life.

The method for diagnosing the remaining life of an oil-immersed transformer of the present invention includes an iron core, a winding coil provided around the core, an insulating paper for coil insulation, a press board, a water-containing solid insulator including a wooden object, and a solid insulating material containing water. It is an oil-filled transformer in which the contents of the transformer provided with the above are immersed in insulating oil contained in a tank, and is a method for diagnosing the remaining life of the oil-filled transformer having a configuration in which an oil flow is generated in the insulating oil. In the input transformer, the vertical cross section including the region where the contents of the transformer are present excluding the iron core and the region where the insulating oil is present is divided into a plurality of regions in the vertical and horizontal directions, and exists in each of the divided regions. The distribution of the winding coil, the solid insulator, and the insulating oil is grasped, the relationship of mutual diffusion of water between the solid insulator and the insulating oil in each area is grasped, and a predetermined relationship is determined in each area. Understand the situation in which insulating oil containing water flows, grasp the mutual diffusion relationship of the amount of water between them for each area, and actually start from a part of the divided area when operating the oil-immersed transformer. The measured value of the water content of the insulating oil collected in the above oil was compared with the value of the water content of the insulating oil derived from the mutual diffusion relationship with respect to the area where the insulating oil was collected. If the difference between the measured value and the water content in the oil derived from the mutual diffusion relationship is less than or equal to a predetermined threshold value, the water content distribution in the insulating oil for each area is determined, and oil is added based on the determined water content distribution. It is characterized by diagnosing the remaining life of the transformer.

In the method for diagnosing the remaining life of an oil-immersed transformer of the present invention, an iron core, a winding coil provided around the iron core, and a water-containing solid insulator including insulating paper for coil insulation, a press board, and a wooden object are used. It is an oil-filled transformer in which the contents of the provided transformer are immersed in insulating oil contained in a tank, and is a method for diagnosing the remaining life of the oil-filled transformer having a configuration in which an oil flow is generated in the insulating oil. In the transformer, a division modeling step of dividing a vertical cross section including a region where the contents of the transformer excluding the iron core and a region where the insulating oil exists into a plurality of regions in the vertical and horizontal directions, and the solid insulation Material distribution, the insulating oil distribution, the weight, thickness and average degree of polymerization of the solid insulating material, the density and saturated water content of the insulating oil, the opening area between adjacent areas, and the temperature distribution. Basic data assumption step that assumes oil flow distribution and initial water distribution, saturated water content of the insulating oil, water diffusion coefficient in the insulating oil, solid insulator-oil equilibrium water content, solid insulator Calculation parameter assumption step that assumes the moving speed of water in and the temperature gradient in solid insulation, and the water in oil of the insulating oil of the transformer in the initial state are mutually diffused with respect to the solid insulation over time. However, the mutual diffusion grasping step of grasping the relationship that the total water content is constant and grasping the mutual diffusion relationship between the water content of the insulating oil in the oil and the water content in the solid insulator for each area, and the oil filling The measured value of the water content of the insulating oil actually collected from a part of the divided area during the operation of the transformer and the insulating oil derived from the mutual diffusion grasping step for the area where the insulating oil was collected. A comparison step of comparing the calculated values of the amount of water in the oil and determining the water distribution in the insulating oil for each area if the difference between the measured value and the calculated value is equal to or less than a predetermined threshold is determined. It is characterized by comprising a diagnostic step of diagnosing the remaining life of the transformer from the amount of water in the paper of the winding coil upper insulating paper derived from the water distribution.

In the present invention, in the mutual diffusion grasping step, the distribution of the amount of insulating oil in each divided area, the distribution of the amount of solid insulator, the distribution of the opening area between adjacent areas, the distribution of the oil flow of insulating oil, and the like. It is preferable to grasp the substantial transfer rate of water molecules in the solid insulator for each area, the water velocity gradient coefficient in the solid insulator, the thickness of the solid insulator for each area, and the initial water content.
In the present invention, when the difference between the measured value and the calculated value exceeds a predetermined threshold in the comparison step, the initial water content, the distribution of the insulating oil amount in each area, and the distribution of the solid insulator amount are determined. Distribution of opening area between adjacent areas, oil flow distribution of insulating oil, substantial movement rate of water molecules in solid insulation for each area, moisture rate gradient coefficient in solid insulation, solid insulation for each area It is characterized by adding a function of reviewing and recalculating at least one of the thickness of the object and the dispersion coefficient and repeating the recalculation until the difference becomes equal to or less than the threshold value.

In the present invention, it is preferable to grasp the mutual diffusion based on the following equation (1) in the mutual diffusion grasping step.

However, in the formula (1), x: the position (mm) of the solid insulator from the copper wire, y: the water content in the solid insulator (%), yn: the water content in the solid insulator in the nth region (section). Amount (%), t: time from the start of operation (min), ∂t: minute time (min), ∂yn: increment of water content in the solid insulator in the nth region in the minute time (%), v ₀ : Substantial movement rate of water molecules in solid insulation in insulating paper in contact with copper wire (mm / min), k': Moisture velocity gradient coefficient in solid insulation (1 / mm), tp: Solid insulation in 1 section It is defined as the thickness of the object (mm).

In the present invention, the amount of water contained in each area is the sum of the amount of water in the solid insulator and the amount of water in oil, and the total amount of water in each area is the total amount of water contained in the oil-filled transformer. The increase in the amount of water in the area is the amount obtained by subtracting the amount of water flowing out from the amount of water flowing into the area, and it is preferable that the increase in the amount of water in the oil satisfies the relationship of the following equation (2).

The diagnostic apparatus of the present invention has a transformer content including an iron core, a winding coil provided around the iron core, an insulating paper for coil insulation, a press board, and a water-containing solid insulator including a wooden object. An oil-immersed transformer immersed in insulating oil contained in a tank, and a remaining life diagnostic device for the oil-immersed transformer having a configuration in which an oil flow is generated in the insulating oil. In the oil-immersed transformer, the iron core A function of storing a plurality of areas in which the vertical cross section including the area where the transformer contents exist and the area where the insulating oil exists excluding the above is divided in the vertical direction and the horizontal direction, and the volume existing in each of the divided areas. The function of memorizing the distribution of the wire coil, the solid insulator, and the insulating oil, and the relationship of mutual diffusion of moisture between the solid insulator and the insulating oil in each area are grasped, and the predetermined moisture is determined in each area. From the function of grasping the flow situation of the insulating oil containing the above and calculating the mutual diffusion relationship of the water content between them for each area and a part of the divided area when the oil-immersed transformer is operated. The measured value of the water content in the oil of the insulating oil actually collected is compared with the value of the water content of the insulating oil derived from the mutual diffusion relationship with respect to the area where the insulating oil was collected, and the water content in the oil is compared. If the difference between the measured value of the above and the water content in the oil derived from the mutual diffusion relationship is equal to or less than a predetermined threshold value, it is characterized by having a function of determining the water content distribution in the insulating oil for each area.

The remaining life diagnostic apparatus according to the present invention is a transformer provided with an iron core, a winding coil provided around the iron core, and a water-containing solid insulator including insulating paper for coil insulation, a press board, and a wooden object. An oil-filled transformer whose contents are immersed in insulating oil contained in a tank, and a remaining life diagnostic device for the oil-filled transformer having a configuration in which an oil flow is generated in the insulating oil. A division modeling function for storing each area in which the vertical cross section including the area where the contents of the transformer excluding the iron core and the area where the insulating oil exists is divided into a plurality of areas in the vertical and horizontal directions, and the above. Solid insulator distribution, the insulating oil distribution, the weight, thickness and average degree of polymerization of the solid insulator, the density and saturated water content of the insulating oil, the opening area between the adjacent areas, and the temperature distribution. , The basic data assumption function to store the oil flow distribution and the initial water distribution, the saturated water content of the insulating oil, the water diffusion coefficient in the insulating oil, the solid insulator-oil equilibrium water content, and the solid. A calculation parameter assumption function that stores the moving speed of moisture in the insulator and the assumed value of the temperature gradient in the solid insulator, and the moisture in the oil of the insulating oil of the transformer in the initial state becomes the solid insulator over time. On the other hand, they diffuse each other, but grasp the relationship that the total water content is constant, and grasp and memorize the mutual diffusion relationship between the water content of the insulating oil and the water content of the solid insulator for each area. The diffusion grasping function, the measured value of the water content in the insulating oil actually collected from a part of the divided area during the operation of the oil-filled transformer, and the mutual diffusion grasping for the area where the insulating oil was collected. The calculated values of the water content of the insulating oil derived from the steps are compared, and if the difference between the measured value and the calculated value is equal to or less than a predetermined threshold value, the water content distribution in the insulating oil for each area is determined. It is characterized by having a comparison function and a diagnostic function of diagnosing the remaining life of the transformer from the amount of water in the paper of the winding coil upper insulating paper derived from the determined water distribution.

In the mutual diffusion grasping function of the remaining life diagnostic apparatus of the present invention, the distribution of the amount of insulating oil in each divided area, the distribution of the amount of solid insulator, the distribution of the opening area between adjacent areas, and the oil flow of insulating oil. It has a function to grasp the distribution, the substantial movement rate of water molecules in the solid insulator for each area, the water velocity gradient coefficient in the solid insulator, the thickness of the solid insulator for each area, and the initial water content. Is preferable.

When the difference between the measured value and the calculated value exceeds a predetermined threshold value, the comparison function of the remaining life diagnostic apparatus of the present invention is adjacent to the distribution of the amount of insulating oil and the distribution of the amount of solid insulator in each area. Distribution of opening area between areas, oil flow distribution of insulating oil, substantial movement rate of water molecules in solid insulation for each area, moisture rate gradient coefficient in solid insulation, and solid insulation for each area It is preferable that a function is added in which at least one of the thickness and the dispersion coefficient is reviewed and recalculated, and the recalculation is repeated until the difference becomes equal to or less than the threshold value.

The mutual diffusion grasping function of the remaining life diagnostic apparatus of the present invention preferably has a function of grasping mutual diffusion based on the following equation (1).

However, in the formula (1), x: the position (mm) of the solid insulator from the copper wire, y: the water content in the solid insulator (%), yn: the water content in the solid insulator in the nth region (section). Amount (%), t: time from the start of operation (min), ∂t: minute time (min), ∂yn: increment of water content in the solid insulator in the nth region in the minute time (%), v ₀ : Substantial movement rate of water molecules in solid insulation in insulating paper in contact with copper wire (mm / min), k': Moisture velocity gradient coefficient in solid insulation (1 / mm), tp: Solid insulation in 1 section It is defined as the thickness of the object (mm).

According to the method for diagnosing the remaining life of a transformer according to the present invention, the conventional method for diagnosing the remaining life does not consider the change in water content in a solid insulator such as insulating paper due to a temperature change, whereas the temperature at the same time It is possible to consider the fluctuation of water content in a solid insulator such as insulating paper or press board, grasp the distribution of water content in oil based on them, and calculate the deterioration of the transformer.
Since the temperature and the amount of water show opposite behaviors, it is corrected that the deterioration of the solid insulator was calculated excessively in the prior art, and the life of the solid insulator such as insulating paper and press board, and eventually the life of the transformer As a result of being able to accurately calculate the remaining life, it is possible to make a diagnosis that accurately grasps the remaining life of the transformer.
Therefore, it is not necessary to determine that the transformer with the remaining life is actually the end of its life and replace it, and the transformer can be operated efficiently.
In addition, it becomes possible to accurately calculate the fluctuation of temperature and moisture during the overload operation of the transformer, and it becomes possible to diagnose the influence of the overload operation on the life of the transformer.

A side sectional view showing an outline of a transformer used for carrying out the remaining life diagnosis method of the first embodiment according to the present invention. The flowchart which shows each step of the remaining life diagnosis method which concerns on 1st Embodiment. Explanatory drawing which shows the state which divided into a plurality of areas with respect to the partial vertical section of the transformer shown in FIG. Explanatory drawing which shows an example which assumed the distribution state of insulating oil with respect to the divided area of the transformer shown in FIG. The explanatory view which shows an example which assumed the distribution state of the winding insulation paper with respect to the division area of the transformer shown in FIG. Explanatory drawing which shows an example which assumed the total weight distribution state of a press board and a wooden object with respect to the division area of the transformer shown in FIG. Explanatory drawing which shows an example which assumed the opening area between the division areas adjacent to the division area of the transformer shown in FIG. Explanatory drawing which shows the position where the thermocouple in paper, the thermocouple in oil, and the thermocouple for measuring the outside air temperature are individually installed in the divided area of the transformer shown in FIG. Explanatory drawing assuming the temperature distribution of the insulating oil for each grouped area when the divided area of the transformer shown in FIG. 3 is grouped into a larger area. The explanatory view which shows an example of the state which classified the flow of the insulating oil into 6 large flows with respect to the divided area of the transformer shown in FIG. It is explanatory drawing which shows the state which classified the flow of the insulating oil with respect to the grouped area into 6 large flow, when the divided area of the transformer shown in FIG. The graph which shows the mutual equilibrium relationship between the moisture in paper in the winding insulating paper provided in the transformer shown in FIG. 1 and the moisture in oil in the insulating oil which is in contact with the winding insulating paper. The graph which shows the mutual equilibrium relationship between the moisture in paper in the press board provided with the transformer shown in FIG. 1 and the moisture in oil in the insulating oil in contact with the press board. The result obtained by the present inventor regarding the moving speed of water in the coil insulating paper provided in the transformer shown in FIG. 1 is shown, (A) is a graph showing the result of a step temperature raising experiment, and (B) is K'=. The graph which shows the calculation result in the case of 0.15. The graph which shows the result of having calculated the temperature dependence about the moving speed of the moisture in a coil insulating paper. A graph showing the moving speed of water in the press board by comparing the experimental results and the calculated results. The results of calculating the water content in oil using the transformer having the configuration shown in FIG. 1 are shown in comparison with the experimental values. (A) is a graph showing the experimental values, and (B) is a graph showing the calculated values. The graph which shows the change with time of the insulating paper temperature and the moisture content in paper in the calculation result using the transformer of the configuration shown in FIG. The result of calculating the oil temperature and the amount of water in the oil corresponding to the divided area of the transformer shown in FIG. 3 is shown. FIG. 3A is a diagram showing the calculation result of the oil temperature in shades, (B). ) Is a diagram showing the result of calculating the water content in oil in shades. The block diagram which shows an example of the residual life determination apparatus suitable for use in carrying out this invention. A model of temperature distribution and moisture distribution when a winding coil (heater), which is regarded as a heating element, winding insulating paper, and insulating oil are arranged adjacent to each other and a boundary film is formed at the boundary between the insulating paper and insulating oil is shown. Explanatory drawing. Explanatory drawing which shows an example of moisture distribution when a heater, an insulating paper, a pleura, and insulating oil are adjacent to each other. Explanatory drawing which shows the temperature distribution model and the moisture transfer rate model in a winding insulation paper. Explanatory drawing for grasping moisture movement when a temperature gradient which changes with time is given when a heater, an insulating paper, a boundary film and an insulating oil are adjacent to each other. The graph which shows the calculation result which estimated the temperature dependence of the kinematic viscosity from the measured value of the kinematic viscosity and the temperature according to JIS regulation. The graph which shows the result of having estimated the temperature dependence of density from the density measurement value of 15 degreeC using the thermal expansion coefficient of one kind of insulating oil according to JIS regulation. The kinematic viscosity and density are the values shown in FIGS. 25 and 26, and the constant const. Is a graph showing the result of calculating the diffusion coefficient temperature dependence of water in oil by Eq. (39) assuming that

<First Embodiment>
Hereinafter, the first embodiment of the method for diagnosing the remaining life of the oil-immersed transformer according to the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram showing an example of a model transformer used to carry out a method for diagnosing the remaining life of an oil-immersed transformer. This model transformer is derived from a collection of components of a transformer actually used. Therefore, the coil winding 2 is provided around the iron core 1 arranged at the center. Each coil winding 2 is covered with insulating paper 3, and the coil winding 2 is sandwiched between the upper and lower press boards 5 and 5, and the coil winding 2 is subjected to tightening force from above and below by the press boards 5 and 5. There is. The spacer press board is also sandwiched between the turns between the windings.
In this embodiment, the transformer content 6 is provided with the iron core 1, the coil winding 2, the insulating paper 3, and the press board 5, and the transformer content 6 is immersed in the insulating oil 8 filled in the cylindrical tank 7. And the transformer A is configured. This transformer A is configured as a single-phase cylindrical transformer. In the transformer A, various wooden objects are provided in addition to the insulating paper 3 and the press board 5, but the wooden objects will be described in detail later.

The coil winding 2 of the transformer A is wound around an insulating cylinder 4 arranged around the iron core 1 in a state of being insulated and separated by an insulating paper 3, an upper yoke 9 is arranged on the upper side of the iron core 1, and a lower portion of the iron core 1 is arranged. The lower yoke 10 is arranged on the side, and the disk-shaped press board 5 is arranged above and below them. The coil winding on the primary side and the coil winding on the secondary side are each supported in an insulated state around the insulating cylinder 4 via a solid insulator such as an insulating spacer (not shown).
The strut members 11 are erected so as to penetrate the peripheral portions of the press boards 5 and 5, and these strut members 11 press the upper and lower press boards 5 and 5 in a direction approaching each other and are provided inside them. A predetermined tightening force is applied to the coil winding 2.
Although omitted in FIG. 1, the coil winding 2 is surrounded by a winding spacer made of a wooden material equivalent to a press board, an insulating cylinder rail, an insulating cylinder duct rail, an upper yoke insulator, and a lower yoke insulator. Etc. are arranged. Further, although omitted in FIG. 1, an outer barrier made of a wooden object is arranged on the outside of the winding coil 2. Since these wooden objects affect the diffusion and movement of water in oil, they will be analyzed as described later.

In the transformer A shown in FIG. 1, a vertical radiator (radiator) 13 is provided on the right side of the tank 7, the introduction side of the upper part of the radiator 13 and the upper part of the tank 7 are connected by the upper pipe 15, and the radiator 13 is connected. The discharge side of the lower part of the tank 7 and the lower part of the tank 7 are connected by the lower pipe 16.
With the above configuration, the insulating oil 8 contained in the tank 7 is sucked from the upper pipe 15 to the radiator 13 side, dissipated while passing through the inside of the radiator 13, and then radiated through the lower pipe 16. It is circulated so as to return to the lower side of the tank 7.
Further, since the insulating oil 8 stored in the tank 7 is heated by the heat generated by the transformer contents 6, the heated insulating oil generates natural convection from the lower side to the upper side of the tank 7 by natural convection. .. This natural convection and the return flow from the radiator 13 described above are combined, and the upper yoke 9, the lower yoke 10, the upper and lower press boards 5, the coil winding 2 and the like housed inside the tank 7 are insulating oil. Since it becomes a flow resistor against the flow of 8, a complicated flow of a plurality of insulating oils is generated inside the tank 7. The analysis of this complicated flow of a plurality of insulating oils will be described in detail later. Further, the insulating oil may be forcibly circulated by a pump.

In the transformer A shown in FIG. 1 according to the present embodiment, the tank 7 used for the test has an insulating oil amount of 647 L on the upper space side in the tank, an insulating oil amount of 1142 L existing in the coil area, and a tank lower space side. The transformer has a structure in which the amount of insulating oil is set to 311 L, the total amount of insulating oil is 2100 L, and the rated capacity is 10.2 kVA. In this transformer A, the weight of the coil insulating paper 3 is 14.3 kg, the total weight of the upper yoke insulator, the winding spacer, the insulating cylinder rail, the insulating cylinder duct rail, and the lower yoke insulator is 73.7 kg, and it is made of wood. The weight of the strut member 11 is 27.3 kg, and the total weight of the insulating paper, the press board, and the wooden object is 115.3 kg.
The total capacity of the insulating oil on the upper space side in the tank, the insulating oil in the coil area, and the insulating oil on the lower side of the tank includes the insulating oil existing on the radiator 13 side and the pipes 15 and 16. Further, a conservator CS (see FIGS. 3 to 9) omitted in FIG. 1 is installed on the upper side of the tank 7, and 110 L of insulating oil is also stored in this conservator CS, but the conservator CS also contains 110 L of insulating oil. The contained insulating oil will be included in the weight of the insulating oil on the upper space side in the tank.

The insulating paper 3 has a thickness of 80 μm and is wound with four half-wraps around the coil winding 2.
If the transformer A can be regarded as new immediately after the start of operation, it is assumed that the average degree of polymerization (DP) of the insulating paper is all new (around 1100). As the deterioration progresses over time, the DP decreases, so when calculating from the point where the effect of deterioration cannot be ignored after the start of operation, it is necessary to assume the DP distribution as well. In the case of the transformer A of the present embodiment, the transformer A is regarded as a new product, and it is assumed that the DP of the insulating paper 3 is 1174 and the DP of the press board and the wooden object is 1101 in the present embodiment.
The insulating oil was used a density 0.866 g / ^cm 3, 40 insulating oil kinematic viscosity 2.17 mm ² / s in kinematic viscosity 7.68mm ² / s, 100 ℃ at ° C. at 15 ° C..

The change in water content in oil when the transformer A described above was actually used, operated for 20 days at a load factor of 100%, and then operated for 10 days under no load was calculated and compared with the measured value. An example will be described below.
In the present embodiment, first, as shown in the flowchart shown in FIG. 2, the oil-filled transformer A includes a region where the transformer contents 6 excluding the iron core 1 exists and a region where the insulating oil 8 exists. A division modeling step S1 is performed in which a vertical section is taken and the vertical section is divided into a plurality of areas in the vertical direction and the horizontal direction.

"Split modeling step: S1"
In this embodiment, in the division modeling step S1, as illustrated in FIG. 3, a mesh is cut in the vertical cross section on the right half side of the tank 7 in 5 cm increments, and 48 layers in the vertical direction (the bottom side of the tank 7 is the area 1). The inner top side of the tank 7 was set as the area 48), and the tank 7 was divided into 7 layers in the radial direction (the areas A to G were set in order from the inside to the outside of the tank 7), for a total of 296 areas.
Since the transformer A of the present embodiment is single-phase and cylindrical, the structure can be approximated in two dimensions in the radial direction and the vertical direction on the assumption of cylindrical symmetry. Therefore, cutting the mesh in 5 cm increments as shown in FIG. 3 takes a vertical cross section of the transformer A including the region where the transformer contents 6 excluding the iron core 1 exists and the region where the insulating oil exists. It means that the vertical cross section is divided into a plurality of areas in the vertical direction and the horizontal direction.

Further, as shown in FIG. 3, the internal space of the radiator 13 is divided into areas R12 to 43 in the height direction in order from the bottom, and the area RU indicates the upper pipe 15 at the upper end of the radiator 13. The area RL shows the lower pipe 16 at the lower end of the radiator 13. Further, since the vertical direction of the tank 7 is divided into 48 layers and 7 layers in the radial direction, a total of 296 areas, the internal space of the tank 7 is A41 to A48, B1 to B48, C1 to C48, D1 to D48, It is divided into areas E1 to E48, F1 to F48, and G1 to G48.
Since the area corresponding to A1 to A40 is an area in which the iron core 1 exists and the insulating oil does not exist, it is excluded from the area setting in the present division modeling step S1. Further, the internal space of the radiator 13 is divided into 32 and divided into regions (RU, RL) connected by the upper pipe 15 and the lower pipe 16.

"Basic data assumption step: S2"
Next, in the present embodiment, in the basic data assumption step S2, the volume of insulating oil in each area in the transformer A and the solid insulator (insulating paper for coil winding, press board, winding spacer, insulating cylinder rail, insulation). The arrangement, thickness, and weight of the tubular duct rail, upper yoke insulator, lower yoke insulator, etc. are collectively referred to as solid insulator), and the values are known. Is used, and it is assumed that what is not known is consistent with the survey results described later.
With respect to the transformer A adopted in the present embodiment, the distribution of insulating oil (unit: L) is shown in FIG. 4, the distribution of wound insulating paper (unit: g) is shown in FIG. 5, and a press board other than insulating paper is shown. And the distribution of the total weight of the wooden object (unit: g) was assumed as shown in FIG.
Since the details of the structure of the transformer A actually used are known for these assumptions, how much insulating oil, winding insulating paper, press board and wooden objects are present in each divided area? Is the result of allocating.

In each area shown in FIGS. 3 to 6, insulating oil convects through an opening area in contact with adjacent or upper and lower areas, and water in the oil diffuses to each other. Therefore, the opening area between each area was assumed as shown in FIG. 7 in consideration of the geometric shape of the transformer A and the structure of the transformer (unit: cm ² ).
In FIG. 7, the areas B9 to B36 are areas where coil windings are provided, and it is assumed that the opening area between the vertically adjacent areas is half the opening area of the upper and lower areas thereof.
Also, the opening area between the B8 and B9 areas was assumed to be one-fourth of the geometric opening area of the B8 area, considering that the winding supports were further clogged. (864/4 = 216 cm ² ) Furthermore, the upper yoke exists at the boundary between the upper part of the tank and the coil winding area (the area below the thick black solid line above in FIG. 7), and the boundary between the lower part of the tank and the coil winding area (the area below the coil winding area). The area below the thick black solid line in the lower part of the figure) has a lower yoke and is considered not to be open, so the opening area of C to F in those areas was assumed to be 0. That is, it is assumed that the thick black lines at the top and bottom of FIG. 7 become a wall when the insulating oil flows, and the insulating oil convects so as to avoid this wall.

The opening area of the boundary between the vertical direction and the horizontal direction of each region is shown numerically in FIG. 7, and is as follows.
The opening area of the vertical direction, A42～A48 is 1963cm ^2, A2~A8 is 864cm ^2, B10~B37 is 432cm ^2, B38~B48 is 864cm ^2, C2~C48 is 1021cm ^2, B10~B37 is 432 cm ^2, D2 ~D48 is 1178cm ^2, E2~E48 is 1335cm ^2, F2~F48 is 1492cm ^2, G2~G48 was set to 1649cm ^2.
The opening area of the left-right direction, the direction of B42~B48 from A42~A48 773cm ^2, the direction from B37~B48 to C37~C48 927cm ^2, the direction from C37～C48 to D37~D48 is 1082cm ^2, D37~ direction from D48 to E37~E48 is 1237cm ^2, the direction from E37~E48 to F37~F48 1391cm ^2, the direction from F37～F48 to G37~G48 was set to 1546 cm ^2.

The opening area of the left-right direction, the direction from B9~B36 to C9~C36 954cm ^2, direction 1113Cm ² from C9～C36 to D9～D36, direction from D9～D36 to E9~E36 is 1272cm ^2, E9 direction from ~E36 to F9~F36 is 1431cm ^2, the direction from F9~F36 to G9~G36 was set to 1590 cm ^2.
The opening area of the left-right direction, the direction from B1~B8 to C1 to C8 973 cm ^2, direction 1135Cm ² from C1 to C8 to D1 to D8, the direction from D1 to D8 to E1~E8 is 1297cm ^2, E1 direction from ~E8 to F1~F8 is 1459cm ^2, the direction from F1~F8 to G1~G8 was set to 1621 cm ^2.
Radiator opening area of the vertical direction in 13 746cm ^2, the opening area of the opening area of the entrance portion of the upper pipe 15 and the lower pipe 16 connections to 150 cm ^2, CS was set to 13cm ^2.

If the amount of insulating oil that moves per cycle calculation exceeds half of the volume, the calculation may become unstable. Therefore, the step time of the calculation was devised, and the ∂t: minute time used in the diffusion equation described later was set to 10 seconds. Regarding the minute time, if the number of divisions of the area is small, it may be every minute, but if it is divided into 296 areas, it is set to 10 seconds in order to increase the flow velocity per area.

At the same time, in the case of this embodiment, the time constants used in each of the equations described later are determined as follows. The numerical value on the right side of the following equation is a numerical value applied when the minute time is 10 seconds.
・ Equilibrium time constant of water in paper-water in oil:
τp (81.5 ° C) = 205.9 min = 205.9 x 60 sec = 1235.4 x 10 sec
・ Moisture transfer speed in coil insulating paper:
ν ₀ (80 ° C) = 0.015 mm / min = 0.015 mm / 60 sec = 0.0025 mm / 10 sec
・ Moisture transfer speed in the press board:
ν (80 ° C) = 0.009 mm / 60 sec = 0.009 / 60 sec = 0.0015 mm / 10 sec
As a result, in the present embodiment, the flow velocity of the insulating oil can be increased to 3 mm / s as in the calculation described later, and the convection closer to the actual device can be set.
In the present embodiment, the temperature dependence of the density and viscosity of the insulating oil used in the transformer A is measured in advance, and each value is grasped before being used in the calculation.

In the present embodiment, the temperature dependence of the saturated water content of the insulating oil used in the transformer A is measured in advance.
In the case of the transformer A of the present embodiment, the saturated water content of the oil can be expressed by Griffin's equation. Let p be the actual water content of the insulating oil. An important index of water content in oil is water saturation, which is relative humidity. The water saturation pr in oil is given by the following equation (3).

In this equation (3), R represents the gas constant (1.987 cal / mol / K) and T represents the absolute temperature.
The insulating oil used in transformers A, use a density 0.866g / ^cm 3, 40 insulating oil kinematic viscosity 2.17 mm ² / s in kinematic viscosity 7.68mm ² / s, 100 ℃ at ° C. at 15 ℃ There was. From this measurement result, the temperature dependence of the insulating oil viscosity, which will be described later, can be taken into consideration and used in the calculation described later.

In the present embodiment, the initial water content distribution in oil of the transformer A is assumed to be 4 ppm from the grasp of the actual measurement results based on various tests of the present inventor. This assumption of water content in oil will be described in detail later.

Next, since it is necessary to obtain and input the temperature distribution of each area in the transformer A, in each area of the transformer A shown in FIG. 8, a thermocouple (Double) is formed in the insulating paper of the areas B10, B22, and B35. A thermocouple (Double Moisture Meter) is placed in the areas of C10, C22, C35, D2, G43, and RL, and a thermocouple for measuring the outside temperature outside the G1 area is placed. Placed a pair. In FIG. 8, the area where the thermocouple is arranged is painted in dark gray using dots to indicate the respective positions.

In the transformer A of the present embodiment, the thermocouples on the surface of the winding insulating paper installed at three locations, the upper part (B35), the middle part (B22), and the lower part (B10) of the winding, and the six thermocouples inserted at the above-mentioned positions. In addition to the thermocouple, a total of 10 temperature data including the thermocouple for measuring the outside temperature are collected and used for the calculation described later.
As described above, in the tank 7 of the transformer A, a moisture sensor in oil (moisture meter manufactured by Double) was arranged as shown by reference numerals 20, 21, 22, 23, 24, 25 in FIG. The in-oil moisture sensor 20 is provided inside the upper pipe 15, the in-oil moisture sensor 21 is provided inside the lower pipe 16, and the in-oil moisture sensor 22 is an oil drain valve 26 provided near the bottom of the tank side wall. It is provided in the vicinity. The in-oil moisture sensor 23 is provided near the outside of the bottom of the coil winding 2, the in-oil moisture sensor 24 is provided near the outside of the center of the coil winding 2, and the in-oil moisture sensor 25 is provided near the upper outside of the coil winding 2. It is provided nearby and can measure the amount of water in the oil at each position.

From the studies on the transformer of the present inventors so far, it has been found that the surface temperature of the winding insulating paper is about 10 ° C higher than the insulating oil temperature. Therefore, the oil temperature is higher in the area where the coil winding 2 is located. The temperature in the paper was calculated separately. The outside air temperature thermocouple indicates the temperature around the transformer. The temperature of each area is required to calculate the water content, but since there are only 10 measurement points, it is necessary to calculate the other points for each area assuming the oil temperature and use it for the calculation for each area. Therefore, it is assumed that the temperatures at 10 points that can be measured by the transformer A and the temperatures around them have a proportionally distributed temperature distribution.

Although the temperature proportional distribution is described above, the basic concept will be described below with reference to FIG.
FIG. 9 is a simplified study of a structure in which the tank 7 is divided into a total of 296 areas of 48 layers in the vertical direction and 7 layers in the radial direction as shown in FIG. 3, and the tank 7 is divided into 12 layers in the vertical direction and a radius. It is a figure which shows the result of the temperature distribution proportional calculation at the time of dividing into a total of 74 areas of 7 layers in a direction.
The area is divided into 12 in the vertical direction, and since B to G are divided into 12 in the tank 7, it is divided into a total of 72 areas, and is divided into 74 areas together with the areas A11 and A12 located above the iron core 1. There is.

As shown in FIG. 9, thermocouples are arranged in C3, C6, C9, D1, G11, and RL, respectively, and the oil temperature in areas C3 to C9 is the temperature of the moisture meter inserted in the transformer coil winding portion (Do2 to 2). Do4) is used to assume proportional distribution. The oil temperatures in areas A11 to A12, B1 to 12, and C10 to 12 were assumed by proportionally distributing the thermocouple (thermocouple positions C3, C6, C9) and the temperature of the moisture meter (Do2 to Do4). The temperature (Do1) of the moisture meter inserted into the bottom of the tank is assumed to be the oil temperature of D1, and the oil temperature of C1 to C2 is assumed from the surrounding oil temperature. Assuming that the moisture meter on the top of the radiator represents the oil temperature in the neighboring area G11, the area G1 is close to the outside air temperature H1 (thermocouple TC84) but is also related to the temperature (Do1) of the tank bottom moisture meter. It is assumed that the remaining area G can be expressed proportionally from G11 and G1. The remaining areas D to F are assumed to be mainly proportional distribution of areas C and G. The oil temperature of the radiator was proportionally distributed to the area G11 with the temperature of the moisture meter (Do6) at the bottom. The oil temperature of the conservator CS was assumed to be equal to the outside air temperature (thermocouple TC84).

By assuming as described above, the oil temperature can be obtained by proportional distribution for each divided area of the tank 7.
As shown in FIG. 3, the oil temperature obtained by simply proportionally distributing the oil temperature is applied as the temperature of each area divided into a total of 296 areas of 48 layers in the vertical direction and 7 layers in the radial direction. It should be applied. Of course, as shown in FIG. 3, the method of calculating the temperature distribution when the tank 7 is divided into a total of 74 areas of 12 layers in the vertical direction and 7 layers in the radial direction is 48 layers in the vertical direction and 48 layers in the radial direction. It is preferable to divide into a total of 296 areas of 7 layers, calculate in detail, obtain the temperature distribution, and apply it.

If it is necessary to obtain the temperature history of the transformer when implementing the transformer life diagnosis method described later, it is possible to obtain the temperature rise history from the load of the transformer and the ambient temperature. is necessary. In that case, the temperature history analysis of the oil-filled transformer insulating paper described in Non-Patent Document 3 may be performed.
As a result, the temperature history can be calculated from the load history of the transformer for the degree of polymerization of the insulating paper, and the degree of polymerization can be calculated from the temperature history.
In a general transformer, if only one thermometer is installed and there are only two temperature data of the outside air temperature as other data, the temperature history analysis described in Non-Patent Document 3 may be applied.

Since the inside of the tank 7 of the transformer A used for the measurement has a temperature distribution as described above, natural convection occurs in the insulating oil 8. In the forced circulation type transformer, it is necessary to consider the convection of the forced circulation, but for the convection of the transformer A used in the present embodiment, the natural convection may be considered. As a result of hydrodynamically simulating the flow of the insulating oil 8 in the tank 7, it was decided to assume a 6-loop model (loops a to f) as shown in FIG. 10 for the convection distribution (oil flow distribution).
The flow rate of convection of insulating oil is considered to be proportional to the temperature difference between the top and bottom. Therefore, it is preferable to calculate the temperature difference for each loop and optimize the flow velocity of each loop so that the calculation result is close to the experimental value.

Regarding the flow of insulating oil in the tank 7 in the transformer A, the tank 7 is simply divided into a total of 74 areas of 12 layers in the vertical direction and 7 layers in the radial direction, and the result of examining the flow of the insulating oil is shown in the figure. Shown in 11. In FIG. 11, a press board as a partition plate of the lower yoke is provided on the upper side of the area of B2 to E2 as shown by a thick solid line, and a press board as a partition plate of the upper yoke is provided on the lower side of the area of B10 to E10. It is provided as shown by a thick solid line. Further, the insulating oil in the upper part of the tank 7 is drawn into the radiator 13 through the upper pipe 15, passes through the radiator 13, and is returned to the lower part of the tank 7 through the lower pipe 16.

Therefore, it is considered that there is convection that loops only in the upper tank area above the area where the partition plate of the upper yoke exists. In addition, since the partition plate of the lower yoke exists, it is considered that the inflow of oil due to convection is small in the lower part of the tank. Since the opening area of the gap between the iron core and the coil winding is narrow, it is considered that the flow velocity of the insulating oil is high but the amount of oil is small. Rather, the convection outside the coil winding is considered to be faster and the flow rate is higher. Compared to the tank circumference length of about 3 m, the radiator 13 has a structure in which two pipes with a diameter of 15 cm are connected, so the amount of oil flowing through the radiator 13 is small, and it faces downward along the wall surface of the tank 7. It is thought that the amount of oil flowing into is larger. As a result of hydrodynamic simulation from this situation, it was judged that a 6-loop convection model as shown in FIG. 10 can be introduced to express convection.
In FIG. 11, loop a, loop b, loop c, loop d, loop e, and loop f when the area is divided into 74 are described separately. Assuming that the loop model divided into 74 shown in FIG. 11 can be applied to the transformers segmented by 296 shown in FIG. 10, the calculation described later is performed.

"Calculation method"
(Constant calculation of total water content)
The sum of the water content in the solid insulator (the water content of the solid insulation as a whole including insulating paper, press board, wooden material, etc.) and the water content in the oil is the water content contained in each area. If the generation of moisture due to deterioration of solid insulators such as insulating paper and press board and the moisture flowing into the transformer from the outside air can be ignored, the total moisture content in the transformer is considered to be constant, and the total moisture content in each area is considered to be constant. Consider that the total is the total amount of water contained in the transformer. However, when the solid insulator deteriorates and water is added, it is necessary to consider the water to be added.
In addition, the increment of the amount of water in each area is the amount obtained by subtracting the amount of water flowing out from the amount of water flowing into the area. Therefore, the water content in oil can be calculated by the following equation (4).

(Diffusion method of moisture diffusion equation in solid insulator)
The calculation of the solid insulator is obtained by the diffusion equation shown by the following equation (1).

However, in the formula (1), x: the position (mm) of the solid insulator from the copper wire, y: the water content in the solid insulator (%), yn: the water content in the solid insulator in the nth region (section). Amount (%), t: time from the start of operation (min), ∂t: minute time (min), ∂yn: increment of water content in the solid insulator in the nth region in the minute time (%), v ₀ : Substantial movement rate of water molecules in solid insulation in insulating paper in contact with copper wire (mm / min), k': Moisture velocity gradient coefficient in solid insulation (1 / mm), tp: Solid insulation in 1 section It is defined as the thickness of the object (mm).
When the solid insulator is an insulating paper, the nth zone (section) is 8 because there are 8 layers of insulating paper on the outside of the copper wire when 4 layers are wound around the copper wire with half wrap. It means the number in the insulating paper of the layer.

It is considered that the water content of the insulating oil in contact with the solid insulator has a water saturation equal to that of the outermost surface of the solid insulator and is in equilibrium. Water saturation _{p r} is a value obtained by dividing the in-oil water content p [mg / kg] in a saturation water content _{p 0} of the oil. The water content in oil can be converted into the corresponding water content y [%] in the solid insulator by the following equation (5) and used in the calculation. The parameters used in the following formula are the parameters of kraft paper used in general transformers. If the insulating paper is different, select and calculate the parameters according to the type of insulating paper applied, Manila paper, etc.

"Diffusion type of water in oil"
The diffusion equation shown in Eq. (6) below holds for the water content in oil.

If there is a temperature gradient, the diffusion coefficient D _diffusion is calculated using the temperature of each area. The diffusion coefficient and the water transfer rate ν are related to the following equation (7).

Therefore, if the moisture transfer rate of area 1 is expressed as ν ₁ and the density of insulating oil in area 1 is expressed as ρ ₁ , it is due to diffusion for 1 minute at the boundary between area 1 and area 2 that are in contact with each other with a certain cross-sectional area S. The amount of water transfer is calculated by the following equation (8).

(Dispersion type of water in oil)
In liquids, it is considered that there is a non-directional micro flow due to fluctuations in density and temperature, vibration of the transformer itself (including sound waves), and the like. Mixing oil by such a local flow is called dispersion.
If the variance coefficient is D _variance , the effect of variance expressed by the difference method is given by the following equation (9).

(Formula of water transfer by convection)
In convection, a certain volume of insulating oil flows in a directional manner. The movement of water is considered to be the movement of water in the oil contained in the volume. Strictly speaking, when oil moves from one area to another area with different temperatures, it is thought that the volume of oil changes due to thermal expansion, but the effect is considered to be small, and the volume change is ignored, and a certain volume of oil is used. I think that will move.
As described above, in the transformer A of the present embodiment, a 6-loop convection model is examined, but the details of which area the oil amount is set to be proportional to the oil temperature will be described later. ..

"Calculation parameter assumption step: S3"
Next, various parameters necessary for calculating the water content in the insulating oil are assumed in the calculation parameter assumption step S3.
(Moisture diffusion coefficient in insulating oil)
According to Eyring, the diffusion coefficient of a liquid is proportional to absolute temperature and inversely proportional to its viscosity. When the diffusion coefficient of the solute is D, the viscosity of the solvent is μ, and the absolute temperature is T, the relationship of the following equation (10) holds.

Here, the constant is assumed to be 4 from the results of various studies conducted by the present inventor on transformers in the past. This constant 4 is a numerical value adopted from the constant of the organic liquid described in the physical handbook. The assumption of this constant 4 will be described in detail later.
As described above, the temperature dependence of the water diffusion coefficient in the insulating oil can be calculated by using the temperature dependence of the viscosity of the insulating oil examined in advance.

The values of the equilibrium moisture content between the coil insulating paper and the oil, the moving speed of the moisture in the coil insulating paper, the temperature gradient in the coil insulating paper, etc. were obtained by experiments.
"Equilibrium water content between coil insulating paper and oil"
The equilibrium water content between the coil insulating paper and the insulating oil can be used as an equation in consideration of DP dependence in the BET equation represented by the following equation (11).

The parameters A to D shown in the above equation (11) are the values shown in Table 1 below. The parameters shown in Table 1 are the parameters of the kraft paper used in the transformer used in the experiment. Therefore, in the case of different types of insulating paper, for example, Manila paper, parameters may be selected accordingly.

The DP (average degree of polymerization) of the coil insulating paper and the press board is a measured value of a new product. It was assumed that the parameters A related to the saturated adsorption amount of the monolayer were different between the coil insulating paper and the press board, and B, C, and D were the same.
A comparison between the result of the coil insulating paper-oil equilibrium experiment and the BET formula calculation result is shown in FIG. 12, and a comparison between the press board-oil equilibrium experiment result and the BET formula calculation result is shown in FIG. Both calculated values roughly reproduce the experimental results.

"Moisture diffusion coefficient in oil"
The effect of dispersion is similar to diffusion, and the effect of dispersion can be included by multiplying the diffusion coefficient by several times.
The variance coefficient can be obtained by optimizing the experimental results described later to a value that satisfies the requirements.

(Moisture transfer rate in coil insulating paper)
In the diffusion equation (1) described above, there are two parameters, v ₀ and k'.
From the analysis of the test results shown in FIGS. 14 (A) and 14 (B), it was determined that v ₀ = 0.015 mm / min and k'= 0.15 / mm were optimal and used in the calculation.
The test result shown in FIG. 14 (A) shows that a heating heater in which insulating paper is wrapped in 6 wraps is immersed in the dehydrated insulating oil filled in a constant temperature bath, and a thermometer and a moisture meter are immersed in the insulating oil and held for 8 hours. It shows the relationship between the elapsed time obtained when the heater is energized and heated to the target temperature in 3 hours and then the constant energization is continued and the displacement of the water content in the oil.
The temperature of the insulating oil rises to the target temperature in response to the heating of the heater, but the water content in the oil does not rise to the equilibrium state immediately, and is gradually delayed in time as shown in FIG. 14 (A). Stand up and rise. From this relationship, the optimum values of v ₀ and k'can be obtained. Since 14 curves when the value of the calculation result as _{v 0} in the case of the shown in (B) k '= 0.15 / mm was set to 0.015 mm / min is close to the experimental result, in the calculation of these values Using.

(Temperature dependence of water transfer rate in coil insulating paper)
Separately when the solid insulator moisture transfer constant tau _p study by the present inventors were able calculated 204.4Min, and 600min at 35 ° C. at 81 ° C.. Further, it is assumed that the temperature dependence of the time constant is approximated by the following equation (12). The relationship of equation (12) is shown in the graph of FIG.

The experimental values of the time constant temperature dependence of Eq. (12) were performed only at two points of 81 ° C. and 35 ° C. In particular, the time constant fluctuates greatly below 25 ° C.

(Moist movement speed in the press board)
Pressboard-oil moisture transfer experiment in which four pieces of press board are immersed in insulating oil at intervals, the insulating oil is heated with a heater, and the amount of moisture in oil is measured with an in-oil moisture meter immersed in insulating oil. Was performed, and the results were analyzed. Assuming that the moisture transfer time constant of the press board is equal to that of the coil insulating paper and the moisture transfer rate v is 0.009 mm / min at an oil temperature of 80 ° C., the experimental values can be reproduced well as shown in FIG.

"Mutual diffusion grasp step: S4"
(Calculation of time evolution of water distribution)
Next, the time evolution of the water distribution is calculated. Moisture in the solid insulator evolves over time according to the diffusion equation shown in Eq. (1) above.
Moisture in insulating oil evolves over time due to diffusion, dispersion and convection. If there is a difference in the water saturation between the solid insulator such as insulating paper and the insulating oil, the boundary will evolve over time in the direction in which the water moves from the higher water saturation to the lower water saturation. The total amount of water in the transformer is considered to be constant over time, ignoring the intrusion from the outside and the generation of water due to the deterioration of the insulating paper. The calculation formula is shown by the following formula (1) shown above.

As a result of calculation by the above formula (1), the water content in the insulating oil collected during operation is compared with the water content in the insulating oil of the insulating oil sampling part obtained by the calculation, and if the difference is equal to or less than the set value (threshold). The calculation ends assuming that the water distribution is fixed. In this embodiment, 3 ppm can be adopted as the threshold value.
In the transformer A of the present embodiment, since the oil collecting portion is the oil drain valve 26, the insulation of the area E1 divided as shown in FIG. 3 is set as a position in consideration of the symmetry of the transformer A. Compare the calculation results of the water content of oil in oil. The initial condition of water content in oil is set to 4 ppm (mg / kg) as described above, and the initial condition of water content in paper is set to 1.45%.

Based on the above equation (1), the change in water content in oil when the transformer A is operated at a load factor of 100% for 20 days and then operated under no load for 10 days is calculated and compared with the measured value. The example performed will be described below.
The measured values are the moisture sensor 20 in oil (upper part of the radiator), the moisture sensor 22 in oil (bottom of the tank), the moisture sensor 23 in oil (lower part of the winding), and the moisture sensor 24 in oil (middle part of the winding) provided in the transformer A. , It is a value measured from the oil moisture sensor 25 (upper part of the winding).

FIG. 17 (A) shows the measured value of the oil content obtained from each oil content sensor, and FIG. 17 (B) shows the calculated value of the oil content calculated from the above equation (1).
As is clear from the comparison of FIGS. 17 (A) and 17 (B), the actually measured value and the calculated result generally agreed.
In this state, it is possible to move to the next step. If there is a difference between the calculated value and the measured value exceeding the threshold value of 3 ppm described above, the values set as described above and various assumed data and parameters are changed, and the above calculation is repeated.
The difference between the calculated value and the measured value is compared during the period from 10 to 20 days after the start of transformer operation when the water content in oil stabilizes, and whether or not the difference exceeds 3 ppm within this period. , I decided to compare.
From this calculation, it is possible to calculate the amount of water in the winding upper insulating paper, which is considered to be the most deteriorated.
For example, in the case of the calculation example shown in FIG. 18, the water content in the winding upper insulating paper on the 20th day can be calculated to be 0.87% on the copper wire side and 1.12% on the insulating oil side.

When the calculation is repeated, among the values determined variously as described above, the initial water content, the distribution of the insulating oil amount in each area, the distribution of the solid insulator amount, and the distribution of the opening area between adjacent areas. At least the oil flow distribution of insulating oil, the substantial movement rate of water molecules in the solid insulator for each area, the water velocity gradient coefficient in the solid insulator, the thickness of the solid insulator for each area, and the dispersion coefficient. One is reviewed and recalculated, and the recalculation is repeated until the difference becomes equal to or less than the threshold value.
As an example, in this embodiment, the transformer A is for model analysis, and among the values determined variously as described above, the distribution of the amount of insulating oil in each area, the distribution of the amount of solid insulation, and the distance between adjacent areas. Since it can be estimated that appropriate values have been introduced for the distribution of the opening area and the thickness of the solid insulator for each area, it is preferable to review the other items first. For example, review either the substantial movement rate of water molecules in the solid insulator, the water velocity gradient coefficient in the solid insulator, or the dispersion coefficient for each area, and oil for 10 to 20 days from the start of transformer operation. Recalculate whether the result that the difference does not exceed 3 ppm is obtained within the period when the medium water content is stable. If the result does not exceed 3 ppm, the recalculation is completed.
If the difference does not exceed 3 ppm, the value of the item estimated to have the appropriate value introduced earlier is reviewed and recalculated. When recalculating, it is preferable to give priority to the initial water content, the number of dispersion systems, and the oil flow distribution.
Regarding the recalculation, in the case of the present embodiment, if the division step is set well, it can be assumed that the calculation can be performed by optimizing the parameters, but if the calculation still does not end, the threshold value should be relaxed. We will review the split modeling steps.

FIG. 18 summarizes the changes over time in the temperature of the winding upper insulating paper and the water content in the insulating paper based on the above calculation.
From the calculation results shown in FIG. 18, the temperature of the insulating paper on the winding top rises to the 80 ° C level immediately after the operation of the transformer A, the water content in the insulating paper decreases, and the high temperature and high water content remain until the 20th day. However, after the operation of transformer A was stopped on the 20th day, the temperature of the insulating paper dropped to about 20 ° C, and the water content in the insulating paper increased to 1.8%. The step of grasping the moisture history in the insulating paper in the transformer A is completed.

FIG. 19 shows an example of the distribution of the oil temperature and the water content in the oil for each area obtained based on the above calculation in shades, and shows the value at 16:00 on the 20th day after the start of operation.
The oil temperature (° C) and the water content in oil (ppm) for each area can be calculated in detail individually, but detailed numerical values are omitted in FIG. 19, and FIG. 19 (A) shows the high temperature side of the oil temperature. It is displayed in dark gray, and the low temperature side is displayed in light gray. In FIG. 19B, the high region of the water content in oil is displayed in dark gray, and the low region is displayed in light gray.
From FIG. 19A, it can be seen that the oil temperature is high on the upper side of the tank 7 and low on the lower side. From FIG. 19B, it can be seen that the water content in oil is high in the region above the region C14 to G14 and below the region C38 to G38.

The next step is to calculate the minimum DP of wound insulation paper. In the case of the new transformer A used in the previous embodiment, the current minimum DP of the wound insulation paper is, of course, the new value.
Since the embodiment shown above is such a calculation example, in the case of a new transformer A, the current minimum DP of the wound insulation paper is the new value used in the calculation (all the wound insulation paper DPs are 1174, Press boards and wooden objects are all 1101).

However, when the transformer in actual use, which is not the transformer A shown in FIG. 1, is the measurement target, that is, when the transformer at the stage of being used over time is the measurement target, the moisture history which is the previous step is taken. In the calculation, it is necessary to substitute the DP distribution appropriately, but since the DP distribution is unknown in the transformer in actual use, the calculation of the previous step at this time cannot be executed immediately.
Therefore, first, it is assumed that the DP at the start time of operation is a new value, the water content in paper and the water content in oil at the initial stage of operation are appropriately assumed, and the water content distribution in paper at the start time of operation is determined by the above-described embodiment. Based on the method described, the calculation is performed for a certain period of time, and the decrease in DP for a certain period of time is calculated for each divided area.

Various study results have been reported so far on the rate at which the DP of the insulating paper decreases in the presence of water, and for example, it can be calculated with reference to the calculation formula shown in Non-Patent Document 5.
Non-Patent Document 5 discloses the following equations (13), (14), and (15).

In each equation, βm and γm are constants determined by the water content m [%] in the insulating paper, and βm and γm in the formula (13) are substituted into the water content m in the insulating paper in the formulas (14) and (15). Since it can be calculated by doing so, the average degree of polymerization residual ratio can be calculated by obtaining Vr (life loss ratio).
In Non-Patent Document 5, the life loss ratio Vr is defined by the following equation (16).

In equation (16), V ₃₀ : Life loss when continuously heating at a heating (winding) temperature of 95 ° C. for 30 years, θ _i : Heating (winding) temperature [° C], h: Heating (winding) temperature θ _i Indicates the duration of time.
By using these equations (13) to (16), the decrease in the average degree of polymerization DP can be calculated.

Next, the water content distribution in the paper for a certain period of time is calculated, but it is calculated using the decreased DP of each area calculated earlier in the calculation.
The calculation can be repeated sequentially up to the current time to obtain the current DP distribution. An appropriate value is selected so that the difference between the experimental value and the calculated value of the water content in the insulating oil obtained from the result is equal to or less than the set value (threshold value, for example, 3 ppm).
The fixed time selected to execute the calculation for one cycle is considered to be one year or less under normal operation, but the deterioration of the insulating paper is considered to have progressed rapidly due to overload operation. In that case, it is necessary to shorten one cycle of calculation according to the degree.
When the calculation is completed, the current minimum DP of wound insulation paper can be obtained.
If it is considered that the insulation paper has deteriorated rapidly due to overload operation, the calculation is divided into hours or days, and if the DP drops by 100 a day, the time when the DP drops by 100 on the second day. Recalculate from.

"Diagnosis step of remaining life"
The next step is the remaining life calculation and diagnostic step.
It is assumed that the transformer A is operated under the same conditions as before. That is, the temperature history of transformer A assumes that the average load and ambient temperature from the start of operation to the present will continue in the future.
Using the current DP distribution calculated in the previous step, calculate the DP distribution after the next fixed time and confirm the decrease in DP. By repeating the calculation at regular intervals until the minimum DP of the wound insulation paper reaches the life level, the remaining life of the transformer can be obtained, and the value becomes the result of the remaining life diagnosis of the converter. For example, when operating in the current state, the remaining life can be evaluated as 5 years or so.

FIG. 20 is an explanatory diagram showing an example of a remaining life diagnostic device (personal computer) used for carrying out each step for which the outline has been described so far.
The remaining life diagnosis device 30 is composed of a processing unit 31, a storage unit 32, an interface unit 33, and a display unit 34 connected to the interface unit 33 by wire or wirelessly.
The storage unit 32 contains information on the area divided in the above-mentioned division modeling step S1, various basic data obtained in the basic data assumption step S2, and various calculation parameters obtained in the calculation parameter assumption step S3. A plurality of pieces of information such as the mathematical formula set in the mutual diffusion grasping step S4 are individually stored, and the processing unit 31 is provided with a function of performing a plurality of calculations and processes.
The calculation performed in each of the above steps can be performed using, for example, general commercially available spreadsheet software for personal computers.

As described above, each area divided into 296 areas in the division modeling step S1 is applied to each cell of the spreadsheet software, and a calculation formula is incorporated in each cell so that the calculation for each area can be performed.
For each sheet of spreadsheet software, the calculated oil amount, oil diffusion coefficient, oil density, water content in oil (g), water content in solid insulator (g), and water content in oil (ppm) are for each area. It is configured so that the numerical value input to the cell corresponding to the above cell and input to each cell can be displayed on the display device 34.
As for the calculated oil temperature value, for example, in the transformer A shown in FIG. 1, the temperature measurement data at 10 points is automatically measured at 10-minute intervals, but the temperature data of all the individual areas of the 296 areas is measured for a minute time. For example, since data is required at 10-second intervals, it is automatically calculated for each area (cell) by proportional distribution as described above, converted to temperature data at 10-second intervals for each 296 areas, stored for each area, and used for calculation. Will be done.
When the oil temperature of each area is determined, the oil diffusion coefficient of each area is calculated and stored in each cell of the oil diffusion coefficient sheet, and the density is calculated and stored in each cell of the oil density sheet, and later calculated. Used for.
The sheet of water content in oil records how many liters of oil are contained in each divided area and is used for later calculation.

In the spreadsheet software, in addition to the above-mentioned sheets, sheets for each area of 296 from A41 to R43 are set, and the weight and average degree of polymerization are input and stored for the thickness of the press board and the wooden object for each area. The weight and average degree of polymerization of the insulating paper are input and stored for each area.
Further, the opening area information between the areas described above based on FIG. 7 is recorded corresponding to the boundary position of each area and used for the later calculation.
Assuming that the initial value of the water content in oil starts from the same initial water content in all areas, 4.0 ppm is input at the start time of the time axis and used for later calculation.

The water content in the fixed insulator is divided into the water content in the coil insulating paper and the water content in the press board, and is recorded in the cell corresponding to each area.
The coil insulating paper is calculated by taking as an example a half-wrap winding of four insulating papers having a thickness of 80 μm. In this case, it is assumed that a total of eight layers of insulating papers are overlapped.
The side close to the copper wire (coil winding) has a high temperature, so the water content in the paper is low, and the insulating paper on the side in contact with the insulating oil has a low temperature, so the water content in the paper tends to be high. The spreadsheet software is configured so that the water content in the coil insulating paper can be input for each sheet of insulating paper. In the case of a press board, the water distribution differs in the thickness direction, so the press board is every 0.1 mm thick. Each cell corresponding to each area is configured so that medium moisture can be input.

Regarding the dispersion coefficient, liquids are greatly affected by density, temperature fluctuations, transformer vibration, etc., and generate microscopic flows, so dispersion occurs due to local oil flow, but the size of dispersion is larger than diffusion. Since it is possible to take an order of magnitude larger coefficient, it is necessary to tentatively determine it by tentatively determining it as a parameter so as to satisfy the result described later. Here, a tentative value is selected and used in the calculation as described below.
Regarding the oil flow rate, the flow rate flowing in one time step width was determined from the cross-sectional area of each area in the area having the smallest volume in the flow path of each area when the maximum flow rate was 3 mm / s. Convection occurs when there is a temperature difference. In each of the six convection loops, the areas on the high temperature side and the low temperature side that determine the temperature difference are shown, and the convection flow rate is set to change at a rate with respect to the set temperature.

Further, in order to solve the above-mentioned diffusion equation, the initial water content in oil (4.0 ppm), the initial water content in paper (1.45%), the coil insulating paper thickness (80 μm, 1.0 times), and the dispersion coefficient (60 times), each cell of spreadsheet software is assembled so that each flow velocity (mm / s) of convection a to f can be substituted as a calculation parameter.
Each cell of the spreadsheet software is set every hour for the transformer test operation period of 30 days and up to the 4320th row in 10-minute intervals.

The details of each step that has been outlined so far will be described in more detail below.
The processing unit 31 and the storage unit 32 of the remaining life diagnostic device described above are configured to be capable of inputting the above-mentioned items, the calculation functions corresponding to them, and the formulas and parameters required for the calculation according to the following items. Is calculated.
"Specific calculation method of moisture in transformer winding insulating paper"
The water content in the transformer is the sum of the water content in the insulating oil and the water content in the insulating paper. It is considered that the water does not enter from the outside, and the total amount of water in the transformer is constant. However, in some cases, some moisture generated due to aged deterioration of the insulating paper is taken into consideration.

Moisture in insulating oil can be moved in three ways: diffusion, dispersion, and oil flow. Diffusion is the movement of water from the high concentration side to the low concentration side even if the insulating oil is stationary when the water content in the oil has a concentration gradient. However, even when there is no oil flow as a whole, it is dispersion that a local flow is actually generated in the insulating oil due to local temperature fluctuations and transformer vibrations. The local flow is the same as stirring the insulating oil, and the water moves from the side where the water concentration is high to the side where the water concentration is low, similar to diffusion. Further, if a temperature distribution occurs in the transformer even if there is no forced circulation of the insulating oil, convection occurs in the insulating oil, and the moisture in the oil circulates in the transformer along with the flow of the insulating oil.

Moisture in the insulating paper diffuses and moves in the insulating paper when there is a concentration distribution in the insulating paper. Further, it is known that when there is a temperature distribution in the insulating paper, moisture moves from the high temperature side to the low temperature side, and a moisture concentration distribution occurs in the insulating paper.
On the other hand, the moisture in the insulating oil and the moisture in the insulating paper move to each other. For example, when a dry insulating paper is put into an insulating oil containing water, the water moves from the insulating oil to the insulating paper, and the water content in the insulating oil decreases. It is considered that moisture moves between the insulating oil and the insulating paper from the side where the relative humidity is high to the side where the relative humidity is low. The higher the temperature, the more water the insulating oil can contain. On the other hand, the higher the temperature of the insulating paper, the less water it adsorbs. Therefore, when the temperature rises, the relative humidity of the insulating oil decreases and the relative humidity of the insulating paper increases, so that the moisture in the insulating paper escapes from the insulating paper and is released into the insulating oil.

"Temperature distribution at the boundary between copper wire of winding coil, insulating paper and insulating oil"
There is a transition region at the boundary between paper and oil, and it is considered that the oil comes into contact with the paper at a temperature higher than the oil temperature and the water content is in equilibrium. Schematically showing the temperature distribution in the coil winding, the insulating paper is wound around a copper wire. The copper wire that constitutes the coil winding is a heating element (heater) while the transformer is operating, and is considered to be higher than the oil temperature. Therefore, it is considered that the temperature is high on the insulating paper (paper) copper wire side and low on the oil side, and there is a transition region (boundary film) between the paper and the oil. In the recognition of the present inventor, the self-cooling transformer It is considered that there is a temperature difference of about 10 to 15 ° C. and about 15 to 20 ° C. for oil-feeding transformers.
For example, assuming that the surface of the copper wire is 80 ° C., the temperature gradually decreases in the thickness direction of the insulating paper, and if the outermost surface of the insulating paper is 73 ° C., the transition region (boundary film) outside the insulating paper. The temperature drops sharply, causing a temperature difference such as the temperature of the insulating oil at a position away from the transition region reaching 60 ° C.

"Details of deriving the diffusion equation when the wound insulation paper has a temperature gradient"
As shown in FIG. 21, the winding coil (heater) temperature T ₀ , which is regarded as a heating element, the temperature in paper changes linearly from T ₀ to T ₁ , the temperature in the boundary film changes from T ₁ to T ₂ , and oil. calculating the water distribution in the case where the temperature T _2.
Regarding the water content, as shown in FIGS. 21 and 22, the water balance in the minute time ∂t in the minute interval ∂x is considered per unit area. Let y (x) be the water concentration at the position x in the paper, and let ∂y be the change in the water concentration at the minute time ∂t in the minute interval ∂x. Consider the moisture that passes through x = x during ∂t. Moisture is thermally moving in the ± x direction at a velocity v (T).

Since it is assumed that the temperature in the paper changes linearly from T ₀ to T ₁ , it can be expressed by the following equations (17) and (18).

The average velocity of water molecules is considered to be proportional to the square root of temperature, but the average velocity is given by the following equations (19) and (20) by approximating that the temperature difference is small and the temperature changes linearly. It is supposed to be done. FIG. 23 shows a model of the temperature distribution and the model of the moisture transfer rate in the wound insulating paper.

We think that half of the moving water molecules move to the right and half to the left. The amount of water coming from the left per minute time ∂t is given as follows.

Here, Δx1 is the moving distance of water coming from the left. The water velocity at the position x−Δx1 can be expressed by the following equation (22), and the moving distance per minute time ∂t can be expressed by the following equation (23).

Solving Δx1 from this equation yields the following equation (24).

In equation (24), the denominator k'v ₀ ∂t can be approximated to be sufficiently smaller than 1 and expressed by equation (25) below.

Substituting this relationship into Eq. (21) gives Eq. (26) below.

Further, when y (x−Δ) is expanded and the second term is taken, it can be expressed as the following equation (27), and the following equation (28) is obtained.

In addition, the amount of water coming from the right can be expressed by the following equation (29).

Here, Δx2 is the moving distance of water coming from the left, and can be expressed by the following equation (30). Therefore, the substantial flow of water flowing from left to right can be expressed by the following equation (31).

When ∂t is extremely small, the content of the parentheses of the second item in Eq. (31) can be set to v _x ² . In that case, if (31) is rewritten, the actual flow of water can be expressed by the following equation (32).

Next, we calculate the non-equilibrium water transfer given a time-varying temperature gradient. As shown in FIG. 24, in the thin film region between x and x + ∂x, the water balance between time t and t + ∂t is the amount of water entering from the surface x: F (x), surface x + ∂x. The amount of water discharged from: F (x + ∂x).
The amount of change in water content in the region sandwiched between the two surfaces can be obtained by the following equation (33), and the diffusion equation can be obtained by the following equation (34).

Substituting the above equation (19) into this equation (34), the diffusion equation is given by the following equation (35).

In equation (35), the first and second terms on the right side represent the movement of water caused by the presence of a temperature gradient. Due to the temperature gradient, there is a gradient k'in the moisture velocity. Assuming that there is no temperature gradient and the water velocity is constant, that is, k'= 0, the right side has only the third term, and the equation (35) becomes the following equation (36).

Here, if the following equation (37) is set, the equation (36) can be expressed as the following equation (38), which is an equation expressing the diffusion phenomenon of the linear equation due to constant temperature. It becomes the equation (6) described above.

"Driving the difference equation"
Since it is difficult to solve the above equation (35) analytically, we consider solving it by the difference method. In the difference method, a continuum is considered as an aggregate of minute regions, and the derivative is represented by the difference from the adjacent region to solve the problem. It is an analysis method usually used when simulating a thermo-fluid phenomenon.
The first-order differential ∂y / ∂x of y is expressed in the difference form by the following equation (39).

The subscript n represents the nth minute region from the copper wire. For example, in the case of the previous experimental result, 12 rolls are obtained in the case of 6 wraps, so that it can be considered as the nth roll of insulating paper. In that case, t _p represents a sheet of paper with a thickness of 0.167 mm.
Further, the second-order differential ∂ follows represent ² y / ∂x ² in differential form (40) equation of y.

Using the above relationship, the calculation formula of equation (35) can be expressed by the difference equation of equation (41) below.

Equation (41) is an equation for calculating the movement of water in the insulating paper. As the boundary condition, it is necessary to consider the computational treatment of the paper that is wound directly around the coil winding (heater: copper wire) on the innermost side and the paper that is in contact with oil on the outermost side. .. Moisture transfer occurs only between the first sheet of paper on the heater side and the second sheet of paper. Therefore, as the calculation of the first derivative of y on the first sheet, we decided to approximate it by the following equation (42) instead of equation (39).

Further, the second derivative of y on the first sheet is approximately equal to that on the second table of contents, and is calculated as the relationship shown by the following equation (43).

In the paper that is in contact with oil on the outermost side, water movement occurs so that the water content in the paper and the water content in the oil move toward equilibrium, and it is considered that the relative humidity of the two is the same in the equilibrium state. It is considered that the outermost surface of the coil winding and the oil are in contact with each other at the temperature of the outermost paper. When the heater temperature (copper wire temperature) is 80 ° C., it is considered that there is a temperature difference of about 13 ° C. from the oil temperature.
Strictly speaking, in the present embodiment, it is considered that the water content in oil in the boundary film is not a constant value, but since it is very difficult to handle the boundary film, the water content in oil in the boundary film is also the water content in oil outside the boundary film. Let's assume that they are equal.
The relative humidity in the oil water is saturation p _r, the use of expressions of Griffin, can be expressed by the following equation (44).

Here, R represents a gas constant and T represents an absolute temperature. On the other hand, the water content in paper is given by the following equation (45) based on the results of studies by the present inventor so far.

Here, a represents 0.260 and k represents 8.49 × 10 ^-4 e ^{2010 / RT} . However, here, the calculation is performed using 1.98 cal / mol / K as R. Solving this for _pr gives the following equation (46). (46) y _r in expression may be considered a saturation Kamichu water.

On the contrary, the value y _oil of the moisture in the insulating paper calculated by the equation (45) using the moisture content p in the _oil is considered as the moisture concentration in the paper (equivalent to the insulating paper) of the oil, and the outermost layer is insulated by using it. Performs paper difference calculation. That is, instead of the equation (39) as the calculation of the first derivative of y of the outermost layer of insulating paper (12th sheet: in the case of 6-wrap winding as in the experimental example shown in FIG. 14 (A) above), The following equation (47) can be used, and the following equation (48) can be used instead of the equation (40) for the calculation of the second derivative of y.

In addition, the water content of the insulating paper is subtracted from the water content of the entire system to obtain the total water content in the oil, and the water content in the oil is calculated by dividing by the oil content.
In equation (41), there are two parameters, v ₀ and k'. v ₀ represents the ease of moisture transfer in the insulating paper, and is a physical quantity having a meaning close to the diffusion constant as seen in Eq. (37).
In the present embodiment, the oil in water are also considered in paper moisture concentration y _oil equivalent in the paper, moisture migration is to be related to v ₀ even in a region where paper and oil are in contact. k'is related to the moisture velocity gradient, that is, the difference in moisture velocity between the high temperature part (heater side) and the low temperature part (oil side) of the insulating paper.

Therefore, both parameters will be optimized based on the experimental results. As an experimental result, v ₀ = 0.0025 mm / 10 s and k'= 0.15 / mm are adopted for the wound insulating paper as parameters that give a change in water content in oil close to the measured value. These are the optimum values obtained from the experimental results as described above based on FIGS. 14 (A) and 14 (B).
As a result of an experiment, v ₀ of the press board was 0.0015 mm / 10 s, but it was considered that the press board was immersed in insulating oil without being directly wound around the copper wire, and k'was set to zero. As explained earlier based on FIG. 16, v _{0 of} this press board was obtained because the experimental value can be reproduced well when it is 0.009 mm / min, but it is set to a value at intervals of 10 seconds in the diffusion equation. Therefore, 0.0015 mm / 10 s is adopted.

"Time constant of insulating paper and temperature dependence of k and k'"
As approximated in the explanation of FIG. 15, the time constant τp of the insulating paper is approximated by the above equation (12). Here, it is assumed that the time constant and the moving speed of water molecules are inversely proportional to each other. That is, it is assumed that the following equation (49) holds for an arbitrary temperature T.

Therefore, if τ _p (80 ° C.) = 204.4 min and v ₀ (80 ° C.) = 0.015 mm / min from the experimental results so far, G = 204.4 min × 0.015 mm / min = 3.07 mm. , Consider the following equation (50).

When the heater temperature is 80 ° C., the following equation (51) is used. However, considering that both the insulating paper and the insulating oil are constant at 35 ° C. at 35 ° C., k has a temperature dependence. Therefore, k is represented by the following equation (52), and similarly, the velocity of the water molecule also loses its position dependence at 35 ° C., and therefore, it is considered to be the following equation (53).

"About diffusion"
According to Eyring, the diffusion coefficient of a liquid is considered to be proportional to absolute temperature and inversely proportional to its viscosity. As described above, when the diffusion coefficient of the solute is D, the viscosity of the solvent is μ, and the absolute temperature is T, the relationship of the equation (10) is obtained.
As shown in equation (10), the viscosity of insulating oil is expressed as the product of kinematic viscosity and density. The results of measuring the kinematic viscosity and density of the insulating oil used in the experiment are shown in Table 2 below.

FIG. 25 shows the calculation results of estimating the temperature dependence of the kinematic viscosity from two points of 40 ° C. and 100 ° C. according to JIS K2283. FIG. 26 shows the calculation result of estimating the temperature dependence of the density from the measured value at 15 ° C. using the coefficient of thermal expansion of one type of insulating oil 7.4 × 10 ^-4 / ° C. (example described in JIS C2101) according to JIS C2101. ..

The const. Of the above equation (10). Is a constant depending on the solvent and solute. Since there is no data on the value of water in oil, the value is assumed from the constants due to different solvents and solutes. Data on the diffusion coefficient and viscosity of (solute) water for three types of solvents, water, methanol, and ethanol, were examined from the Chemical Handbook (Revised 4th Edition) and the Chemical Engineering Handbook (Revised 4th Edition), and the constant const. The results of obtaining the above are shown in Table 3 below.
Compared with the case where the solvent is water, methanol and ethanol have a constant const. Since is small, it is considered that water tends to be difficult to diffuse in an organic solvent. Therefore, in the case of water content in oil, the constant const. Is considered to be close to the value of methanol or ethanol, and the constant const. Is assumed to be 4, and the calculation is performed.
The kinematic viscosity and density are the values in FIGS. 25 and 26, constant const. The result of calculating the diffusion coefficient temperature dependence of the water content in oil by Eq. (39) is shown in FIG. 27.

From the results shown in FIG. 27, the viscosity of the insulating oil is high at a low temperature, and the diffusion coefficient is smaller than that of the high temperature insulating oil. Therefore, at the interface where high-temperature oil and low-temperature oil are in contact, it is necessary to consider water transfer due to the difference in diffusion coefficient in addition to normal diffusion.

"About variance"
It was thought that the water content in the insulating paper would move due to diffusion, but the water content movement in the insulating oil has other effects. Moisture transfer only by diffusion is extremely slow, and it is necessary to consider the effect of local micro oil flow when considering actual water propagation. In the insulating oil, innumerable micro vortices (thought to be turbulent flows) are constantly generated at multiple points in the oil, and it is considered that the oil is moving as a group. The phenomenon of movement of water in oil due to such non-directional micro oil flow is referred to as "dispersion" here. As for dispersion, a dispersion coefficient can be considered as in diffusion, and the dispersion coefficient is considered to be orders of magnitude larger than the diffusion coefficient.
The diffusion equation can be expressed in the same manner as in the equation (40) for the water content in the insulating oil, and can be expressed by the following equation (54) when the water content in the oil is p.

However, since the diffusion coefficients of adjacent areas are different, it is necessary to devise a calculation method at the boundary. When the equation (54) is rewritten in the differential form, the equation (55) is as follows.

Here, if the following equation (56) is set, the equation (55) becomes a diffusion equation that can be expressed by the following equation (57).

Here, D _diffusion represents the diffusion coefficient, and v represents the average moving speed of water molecules.
If the temperature is changing continuously, the above diffusion equation (35) can be used. However, in this example, since the diffusion coefficient is discontinuous at the boundary, the water movement at the boundary is calculated using the average moving speed of water molecules obtained from the diffusion coefficient.
From the diffusion coefficient of water in oil obtained in the previous section, the average moving speed of water molecules is calculated using equation (56). In the area divided into 296 described above, when three areas n-1, n, and n + 1 are lined up, half of the water molecules contained in the n area are on the n-1 side and half. Is considered to move to the n + 1 side. If the water concentration in oil in area _{n is} pn, the average velocity of water molecules in area _n is v _n , the cross-sectional area of the boundary is S, and the density in area _n is ρ _n , then area n The amount of water W _{n → n + 1} (mg) that moves from 1 to n + 1 per unit time (1 minute) is given by the following equation (58).

Similarly, the water content W _{n + 1 → n} (mg) flowing into the n-th area from the n + 1 area can be considered, and when subtracted, the water content ΔW _n (mg) increases by the following equation (59) in the n-th area. To do.

Assuming that the thickness of one divided area is tp, the amount of oil contained in the nth area is expressed as S × tp × ρ _n (kg), so that the nth area is the value of the following equation (60). so that the oil water Δw _n (ppm) increases only.

The oil flow in transformer A is considered to be mainly convection. However, even if there is no convection, it is considered that there is a micro oil flow with no direction due to the fluctuation of density and temperature and the vibration of the transformer itself (including sound waves).
The dispersion to be considered here is the movement of water in the oil accompanying the movement of the oil, assuming that the oil is always mixed by the local oil flow.
Such a micro oil flow is considered to have the effect of averaging the local concentration regardless of the concentration gradient of the water content in the oil.

It is assumed that the water concentration in oil is p _n-1 , p _n , and p _{n + 1} , respectively, when three areas n-1, area n, and area n + 1 are arranged side by side. The average value of water content in oil in the three areas is ( _pn-1 + p _n + p _{n + 1} ) / 3, and if the proportionality constant is A, then {( _pn-1 + p _n + p _{n + 1} ) with respect to the water content in oil in area n. It results in an increment of / 3- _pn } × A.
When this is transformed, it becomes ( _pn-1 -2p _n + p _n-1 ) / 3 × A, and if 3 × A is set as the dispersion coefficient D _dispersion , the effect of dispersion is given by the following equation.

It can be seen that this equation (61) is similar to the following equation (62) in which the diffusion coefficient shown in the above equation (56) is substituted into the equation (54).

Therefore, it can be seen that the movement of water in oil due to dispersion can be calculated simply by replacing the diffusion coefficient of the diffusion equation (54) with the dispersion coefficient. Further, in the boundary area, the effect of dispersion can be added to the above-mentioned effect of diffusion for calculation.
Since the variance coefficient is unknown, the variance coefficient is changed as a parameter to obtain a value close to the experimental result.

"About convection"
In convection, a certain volume of insulating oil flows in a directional manner. The movement of water is considered to be the movement of water in the insulating oil contained in the volume. Strictly speaking, when oil moves from one region to another region with a different temperature, the volume of oil is thought to change due to thermal expansion, but the effect is considered to be small and ignored, and a certain volume of insulating oil moves. I think that.
The state of convection can be calculated numerically, but it is very complicated and difficult to calculate with an actual transformer structure. Therefore, a simulation was performed assuming a simple structure. as a result,
・ Independent convection in the upper part of the tank ・ Slight convection in the lower part of the tank ・ The flow rate in the gap between the iron core and the coil winding is smaller than that outside the coil winding, but the flow velocity is large. Therefore, as described above, a 6-loop model as shown in FIG. 10 was assumed, and a convection model was examined.
The flow rate of convection is considered to be proportional to the temperature difference between the top and bottom. Therefore, the area name that is the basis for calculating the temperature difference for each loop and the temperature setting value that is the flow rate of 100% are assumed as shown in Table 4 below. Here, the temperature set value was the oil temperature in each region at 16:00 on the 20th day.

From this result, it can be seen that there is no problem in determining that the convection of the 6-loop model described above occurs.

When each area divided into 296 described above is set, and the numerical values set in each cell of the spreadsheet software are substituted based on the above-mentioned basic data assumption step and mutual diffusion grasp step, the calculation is performed so as to solve the diffusion equation. The calculation result shown in FIG. 17B described above can be obtained.
As is clear from the comparison of FIGS. 17A and 17B, if the measured value and the calculation result are in a state of substantially matching, the next step can be performed.
If there is a difference between the calculated value and the measured value exceeding the threshold value of 3 ppm described above, the values set as described above and various assumed data and parameters are changed, and the above calculation is repeated.
By this calculation, it is possible to calculate the amount of water in the paper of the winding upper insulating paper, which is considered to be the most deteriorated, and by grasping the amount of water in the paper of the winding upper part, the remaining life of the transformer can be diagnosed. ..

A ... Transformer, 1 ... Iron core, 2 ... Coil winding, 3 ... Insulating paper, 5 ... Press board, 6 ... Transformer contents, 7 ... Tank, 8 ... Insulating oil, 9 ... Upper yoke, 10 ... Lower yoke, 11 ... Support member, 13 ... Dissipator, 15 ... Upper pipe, 16 ... Lower pipe, 20, 21, 22, 23, 24, 25 ... Oil moisture sensor, 26 ... Oil drain valve, S1 ... Split modeling step, S2 ... basic data assumption step, S3 ... calculation parameter assumption step, S4 ... mutual diffusion grasping step, S5 ... comparison step, S6 ... diagnosis step.

Claims (11)

Insulating oil containing the contents of a transformer containing an iron core, a winding coil provided around it, and a water-containing solid insulator including insulating paper for coil insulation, a press board, and a wooden object. This is a method for diagnosing the remaining life of an oil-immersed transformer immersed in an oil-immersed transformer and having a configuration in which an oil flow is generated in the insulating oil.
In the oil-filled transformer, the vertical cross section including the region where the contents of the transformer are present excluding the iron core and the region where the insulating oil is present is divided into a plurality of regions in the vertical and horizontal directions.
Grasp the distribution of the winding coil, the solid insulator, and the insulating oil existing in each of the divided areas.
In each area, the relationship of mutual diffusion of water between the solid insulator and the insulating oil is grasped, and in each area, the situation where the insulating oil containing a predetermined water flows is grasped, and the water content between them is grasped. Understand the mutual diffusion relationship of quantity for each area,
The measured value of the water content of the insulating oil actually collected from a part of the divided area during the operation of the oil-filled transformer and the insulating oil derived from the mutual diffusion relationship with respect to the area where the insulating oil was collected. If the difference between the measured value of the water content in the oil and the water content in the oil derived from the mutual diffusion relationship is equal to or less than a predetermined threshold value, the insulating oil in each area is used. A method for diagnosing the remaining life of an oil-immersed transformer, which comprises determining the water distribution of the oil-immersed transformer and diagnosing the remaining life of the oil-immersed transformer based on the determined water distribution. Insulating oil containing the contents of a transformer containing an iron core, a winding coil provided around it, and a water-containing solid insulator including insulating paper for coil insulation, a press board, and a wooden object. This is a method for diagnosing the remaining life of an oil-immersed transformer immersed in an oil-immersed transformer and having a configuration in which an oil flow is generated in the insulating oil.
In the oil-filled transformer, a division modeling step of dividing a vertical cross section including a region where the contents of the transformer excluding the iron core and a region where the insulating oil exists into a plurality of regions in the vertical and horizontal directions, and
The solid insulator distribution, the insulating oil distribution, the weight, thickness and average degree of polymerization of the solid insulator, the density and saturated water content of the insulating oil, the opening area between the adjacent areas, and the temperature. Basic data assumption steps that assume distribution, oil flow distribution, and initial water distribution,
Assuming the saturated water content of the insulating oil, the water diffusion coefficient in the insulating oil, the equilibrium water content between the solid insulator and the oil, the transfer rate of the water content in the solid insulator, and the temperature gradient in the solid insulator. Calculation parameter assumption steps to be performed and
We grasped the relationship that the water content of the insulating oil of the transformer in the initial state is mutually diffused with respect to the solid insulator with the passage of time, but the total water content is constant, and the oil of the insulating oil for each area. Mutual diffusion grasping step to grasp the mutual diffusion relationship between the medium moisture content and the water content in the solid insulator,
It was derived from the measured value of the water content of the insulating oil actually collected from a part of the divided area during the operation of the oil-immersed transformer and the mutual diffusion grasping step for the area where the insulating oil was collected. A comparison step of comparing the calculated values of the water content of the insulating oil in the oil and determining the water content distribution in the insulating oil for each area if the difference between the measured value and the calculated value is equal to or less than a predetermined threshold.
A method for diagnosing the remaining life of an oil-immersed transformer, which comprises a diagnostic step of diagnosing the remaining life of the transformer from the amount of water in the paper of the winding coil upper insulating paper derived from the determined water distribution. .. In the mutual diffusion grasping step, the distribution of the amount of insulating oil in each divided area, the distribution of the amount of solid insulator, the distribution of the opening area between adjacent areas, the oil flow distribution of insulating oil, and the solid in each area. The second aspect of claim 2, wherein the substantial moving speed of water molecules in the insulator, the water velocity gradient coefficient in the solid insulator, the thickness of the solid insulator for each area, and the initial water content are grasped. How to diagnose the remaining life of an oil-immersed transformer. In the comparison step, when the difference between the measured value and the calculated value exceeds a predetermined threshold, the initial water content, the distribution of the insulating oil amount in each area, the distribution of the solid insulating amount, and the space between adjacent areas. The distribution of the opening area, the oil flow distribution of the insulating oil, the substantial movement rate of water molecules in the solid insulator for each area, the water velocity gradient coefficient in the solid insulator, and the thickness of the solid insulator for each area. The oil-immersed transformer according to claim 2 or 3, wherein at least one of the dispersion coefficients is reviewed and recalculated, and a function of repeating the recalculation until the difference becomes equal to or less than the threshold value is added. Remaining life diagnosis method. The method for diagnosing the remaining life of an oil-immersed transformer according to any one of claims 1 to 4, wherein in the mutual diffusion grasping step, the mutual diffusion is grasped based on the following equation (1).

However, in the formula (1), x: the position (mm) of the solid insulator from the copper wire, y: the water content in the solid insulator (%), yn: the water content in the solid insulator in the nth region (section). Amount (%), t: time from the start of operation (min), ∂t: minute time (min), ∂yn: increment of water content in the solid insulator in the nth region in the minute time (%), v ₀ : Substantial movement rate of water molecules in solid insulation in insulating paper in contact with copper wire (mm / min), k': Moisture velocity gradient coefficient in solid insulation (1 / mm), tp: Solid insulation in 1 section It is defined as the thickness of the object (mm). The amount of water contained in each area is the sum of the amount of water in the solid insulator and the amount of water in oil, and the total amount of water in each area is the total amount of water contained in the oil-filled transformer. The increment of is the amount obtained by subtracting the amount of water flowing out from the amount of water flowing into the area, and the increment of the amount of water in the oil satisfies the relationship of the following equation (2). The method for diagnosing the remaining life of an oil-immersed transformer according to any one of 5.

Insulating oil containing the contents of a transformer containing an iron core, a winding coil provided around it, and a water-containing solid insulator including insulating paper for coil insulation, a press board, and a wooden object. It is an oil-immersed transformer immersed in, and is a remaining life diagnostic device of the oil-immersed transformer having a configuration in which an oil flow is generated in the insulating oil.
In the oil-filled transformer, a function of storing a plurality of areas in which a vertical cross section including a region where the contents of the transformer are present excluding the iron core and a region where the insulating oil is present is divided into a vertical direction and a horizontal direction is stored.
A function of storing the distribution of the winding coil, the solid insulator, and the insulating oil existing in each of the divided areas, and
In each area, the relationship of mutual diffusion of water between the solid insulator and the insulating oil is grasped, and in each area, the situation where the insulating oil containing a predetermined water flows is grasped, and the water content between them is grasped. A function to calculate the mutual diffusion relationship of quantity for each area,
The measured value of the water content of the insulating oil actually collected from a part of the divided area during the operation of the oil-filled transformer and the insulating oil derived from the mutual diffusion relationship with respect to the area where the insulating oil was collected. If the difference between the measured value of the water content in the oil and the water content in the oil derived from the mutual diffusion relationship is equal to or less than a predetermined threshold value, the insulating oil in each area is used. A remaining life diagnostic device for an oil-immersed transformer, which has a function of determining the water distribution of an oil-immersed transformer. Insulating oil containing the contents of a transformer containing an iron core, a winding coil provided around it, and a water-containing solid insulator including insulating paper for coil insulation, a press board, and a wooden object. It is an oil-immersed transformer immersed in, and is a remaining life diagnostic device of the oil-immersed transformer having a configuration in which an oil flow is generated in the insulating oil.
In the oil-filled transformer, the vertical cross section including the region where the contents of the transformer are present excluding the iron core and the region where the insulating oil is present is divided into a plurality of regions in the vertical and horizontal directions, and each region is stored. Modeling function and
The solid insulator distribution, the insulating oil distribution, the weight, thickness and average degree of polymerization of the solid insulator, the density and saturated water content of the insulating oil, the opening area between the adjacent areas, and the temperature. Basic data assumption function to store distribution, oil flow distribution, and initial water distribution,
Assumption of saturated water content of the insulating oil, water diffusion coefficient in the insulating oil, equilibrium water content between solid insulator and oil, transfer rate of water content in the solid insulator, and temperature gradient in the solid insulator. Computational parameter assumption function to store values and
We grasped the relationship that the water content of the insulating oil of the transformer in the initial state is mutually diffused with respect to the solid insulator with the passage of time, but the total water content is constant, and the oil of the insulating oil for each area. Mutual diffusion grasping function that grasps and stores the mutual diffusion relationship between the amount of water in the medium moisture and the amount of water in the solid insulator,
It was derived from the measured value of the water content of the insulating oil actually collected from a part of the divided area during the operation of the oil-immersed transformer and the mutual diffusion grasping step for the area where the insulating oil was collected. A comparison function that compares the calculated values of the water content of the insulating oil in the oil and determines the water content distribution in the insulating oil for each area if the difference between the measured value and the calculated value is equal to or less than a predetermined threshold.
An oil-filled transformer remaining life diagnostic device characterized by having a diagnostic function for diagnosing the remaining life of the transformer from the amount of water in the paper of the winding coil upper insulating paper derived from the determined water distribution. .. In the mutual diffusion grasping function, the initial water content, the distribution of the insulating oil amount for each divided area, the distribution of the solid insulating amount, the distribution of the opening area between adjacent areas, and the oil flow distribution of the insulating oil. The claim is characterized by having a function of grasping a substantial moving rate of water molecules in a solid insulator for each area, a water velocity gradient coefficient in a solid insulator, and a thickness of the solid insulator for each area. 8. The remaining life diagnostic device for an oil-immersed transformer according to 8. In the comparison function, when the difference between the measured value and the calculated value exceeds a predetermined threshold, the initial water content, the distribution of the amount of insulating oil in each area, the distribution of the amount of solid insulator, and the space between adjacent areas. The distribution of the opening area, the oil flow distribution of the insulating oil, the substantial movement rate of water molecules in the solid insulator for each area, the water velocity gradient coefficient in the solid insulator, and the thickness of the solid insulator for each area. The oil-immersed transformer according to claim 8 or 9, wherein at least one of the dispersion coefficients is reviewed and recalculated, and a function of repeating the recalculation until the difference becomes equal to or less than the threshold value is added. Remaining life diagnostic device. The remaining life diagnostic apparatus for an oil-immersed transformer according to any one of claims 8 to 10, wherein the mutual diffusion grasping function has a function of grasping mutual diffusion based on the following equation (1). ..

However, in the formula (1), x: the position (mm) of the solid insulator from the copper wire, y: the water content in the solid insulator (%), yn: the water content in the solid insulator in the nth region (section). Amount (%), t: time from the start of operation (min), ∂t: minute time (min), ∂yn: increment of water content in the solid insulator in the nth region in the minute time (%), v ₀ : Substantial movement rate of water molecules in solid insulation in insulating paper in contact with copper wire (mm / min), k': Moisture velocity gradient coefficient in solid insulation (1 / mm), tp: Solid insulation in 1 section It is defined as the thickness of the object (mm).

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