A method for predicting temperature distribution of transformer windings

Abstract

The present invention discloses a method for predicting the temperature distribution of oil-immersed transformer windings, and belongs to the field of power transformers. The present invention aims at the problem that it is difficult to balance the accuracy of temperature prediction of existing oil-immersed transformers with the complexity of calculation methods. The present invention includes repeatedly correcting the flow part of the winding inlet boundary condition based on the linear assumption of the flow resistance in the winding, so that the pressure in each winding quickly reaches equilibrium; the present invention starts from the winding inlet boundary condition, obtains the corresponding pressure and temperature in the radiator and oil tank, and adjusts the flow in the winding boundary condition according to the pressure on both sides, and adjusts the inlet temperature in the winding boundary condition according to the temperature at the radiator outlet and the oil tank inlet, so that the winding boundary condition finally reaches the actual situation, and then obtains the winding temperature distribution. The present invention corrects different assumed values ​​so that the winding boundary conditions quickly approach the actual situation, and then quickly and effectively obtains the transformer winding temperature distribution.

Description

Technical Field

[0001] The invention relates to the field of power transformers, and in particular to a method for predicting temperature distribution of oil-immersed transformer windings. Technical Background

[0002] Oil-immersed transformers are an important part of the power system, and they play a role in energy conversion and energy transmission in the power system. Therefore, ensuring the stable operation of power transformers during use is crucial to ensuring economic production and people's lives. In the actual use of power transformers, the life of the transformer and most of the transformer failures are affected by the degree of aging of the transformer winding insulation, and the degree of aging of the transformer insulation is closely related to the transformer winding temperature. Therefore, accurate prediction of the transformer winding temperature during the transformer design process plays a very important role in improving the transformer life and reducing transformer failures.

[0003] Most of the existing transformer winding temperature prediction methods have their limitations. For the thermal network method to predict the transformer temperature distribution, the prediction results will be affected by the model parameters in the thermal network. The complex structure of the transformer winding makes it difficult to determine the model parameters. For the numerical analysis method, it is necessary to model the transformer as a whole and then divide it for calculation. The calculation cycle is long and has certain requirements on the computer configuration used. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a transformer winding temperature distribution prediction method which can accurately predict the transformer winding temperature distribution without placing excessive demands on computer computing power and is time-saving.

[0005] The present invention provides a method for predicting the temperature distribution of oil-immersed transformer windings, the method comprising determining the inlet boundary conditions of each winding and calculating the fluid-temperature field of each winding, comprising the following steps:

[0006] S1. Draw the 3D models of the heat sink and windings of each voltage level at a ratio of 1:1 and use existing software to mesh the models to prepare for the subsequent calculation of the fluid-temperature field of the windings and heat sink;

[0007] S2. Determine the inlet temperature θ of the fluid-temperature field calculation of the high-voltage winding drawn in S1 rr With the inlet flow Q g The initial value of calculation;

[0008] S3, set the high voltage winding at the inlet temperature θ rr With the inlet flow rate Q g Perform temperature-fluid field calculations and determine the temperature-fluid field conditions of other windings when the pressure is balanced with that of the winding, including:

[0009] S31, the inlet temperature θ rr With the inlet flow Q g Substitute it into the high voltage winding and calculate its temperature-fluid field;

[0010] S32. Determine the low voltage winding inlet flow Q d and medium voltage winding inlet flow Q z The initial value of

[0011] S33, according to the low voltage winding inlet flow Q d and medium voltage winding inlet flow Q z Calculate the temperature-fluid field of the winding;

[0012] S34. Based on the temperature-fluid field calculation results of S33, the oil flow resistance pressure of each oil flow rate in the winding is estimated according to the proportional relationship between the oil flow resistance pressure in the winding and the flow rate; the gravity pressure of the oil flow in the winding at each oil flow rate is determined according to the loss in the winding; and then the calculated value Q of the low-voltage winding inlet flow rate that is balanced with the high-voltage winding pressure under the current proportional relationship is obtained. dq And the calculated value of the medium voltage winding inlet flow Q zq ;

[0013] S35, determine the low voltage winding inlet flow Q d The calculated value of low voltage winding inlet flow Q dq And the medium voltage winding inlet flow Q z The calculated value of the medium voltage winding inlet flow Q zq Is the error within 1%? If so, jump to S4 to continue calculation; if not, continue to execute S36;

[0014] S36, Q dq and Q zq The value of is assigned to Q d and Q z , and Q dq and Q zq The value in is cleared, and the process returns to step S33;

[0015] S4, determining an exponential function of the temperature and height of the oil flow in the oil tank that is balanced with the pressure of the winding part, and determining the oil flow rate in the oil tank according to the heat dissipation capacity of the oil tank;

[0016] S5, determine the oil flow, temperature and pressure of the two sections of oil flow from the oil tank inlet to the winding inlet and from the winding outlet to the radiator inlet, specifically including: determining the oil flow through the radiator according to the oil flow of S3 and S4; allocating the core loss of the transformer to the two sections of oil flow from the oil tank inlet to the winding inlet and from the winding outlet to the radiator inlet, and using the unit area heat load of the transformer to determine the heat dissipation of the oil flow through the surface of the oil tank in the above two sections; further determine the functional relationship between the height and temperature of the above two sections of oil flow by energy conservation, and finally determine the gravity pressure of the two sections of oil flow;

[0017] S6, using the radiator inlet temperature and flow obtained in S5 as the inlet boundary conditions for the radiator fluid-temperature field analysis to obtain the radiator fluid-temperature field; using the tank inlet temperature determined in S5 and the tank side gravity pressure calculated by the radiator inlet temperature minus the resistance pressure obtained by the field analysis in S6 as the pressure value on the radiator side;

[0018] S7, judging whether the pressure on both sides of the oil tank and the radiator and the error between the radiator outlet temperature calculated in the field in S6 and the oil tank inlet temperature determined in S5 are within 1%. If the errors of the pressure and temperature are within 1%, it is considered that the temperature field results of each winding obtained in S3 are the actual winding temperature distribution, and the calculation ends; if there is a pressure or temperature error exceeding 1%, continue to execute S8;

[0019] S8. Determine the inlet temperature θ of the high voltage winding during the next cycle by comparing the pressure and temperature in S7. rr With the inlet flow Q g , and returns to S3 to continue the calculation, including:

[0020] S81, determining the temperature of the winding inlet in the next cycle by the difference between the oil tank inlet temperature and the radiator outlet temperature, and assigning the value of the inlet temperature in the current cycle plus the radiator outlet temperature minus the oil tank inlet temperature to the winding inlet temperature in the next cycle;

[0021] S82. Determine the inlet flow rate of the high-voltage winding in the next cycle by the ratio of the gravity pressure difference between the radiator side and the oil tank side to the resistance pressure of the fluid circuit flowing through the radiator and the winding part, and assign the ratio of the gravity pressure difference between the radiator and the oil tank sides in this cycle to the resistance pressure multiplied by the value of the high-voltage winding inlet flow rate to the high-voltage winding in the next cycle.

[0022] Preferably, the winding model in step S1 is a simplified model, and the simplification method is: by enlarging the size of the wire in the corresponding winding so that it completely covers the insulating part in the winding, and uses the insulation as the wall surface.

[0023] For the initial values ​​of the inlet flow and inlet temperature of each winding described in S2 and S32, technicians can make any same reasonable assumptions on the inlet temperature of each winding based on experience within a reasonable range, and make any same or different reasonable assumptions on the flow of each winding, and use them as the initial values ​​for calculation.

[0024] As described above, the present invention provides a method for predicting the temperature distribution of oil-immersed transformer windings, which has the following effects:

[0025] 1. The present invention relates the field analysis results of different parts of the transformer according to the conservation of energy, momentum and mass. On the premise of accurately predicting the temperature distribution of key areas of the transformer, it greatly saves the computing power required for operation and lowers the calculation threshold.

[0026] 2. When calculating the pressure balance between windings, the present invention uses a gradually corrected linear flow resistance to find the pressure balance relationship between windings, so that the calculation can quickly approach the pressure balance from the initial value, greatly reducing the calculation time and improving the calculation efficiency.

[0027] 3. The present invention corrects the temperature at the winding inlet by comparing the temperature at the connection between the oil tank and the lower end of the radiator, adjusts the oil flow at the winding inlet by comparing the pressure on both sides of the oil tank and the radiator, and decouples the inlet temperature and flow in the winding boundary conditions, thereby achieving the purpose of simultaneously correcting the inlet temperature and the inlet flow, and reducing the complexity of the calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is an overall flow chart of a method for predicting winding temperature distribution according to a specific embodiment of the present invention;

[0029] Figure 2 It is a medium voltage winding model of a specific embodiment of the present invention, including the position of the 1 / 28 model in the medium voltage winding and a partial enlargement of the model;

[0030] Figure 3 is a positional illustration of a specific embodiment of the present invention;

[0031] Figure 4 This is a prediction result of the temperature distribution of a medium voltage winding according to a specific embodiment of the present invention.

[0032] Explanation of the accompanying drawings: A, transformer winding inlet, the inlet temperature of each winding is the temperature of this point; B, transformer winding outlet, it is assumed that the oil flow in each winding flows out from the winding and is fully mixed here; C, the oil flow in the oil tank that is not completely mixed with the oil flow flowing through the radiator, that is, the oil tank outlet mentioned in the specification; D, is the radiator inlet mentioned in the specification; E, is the radiator outlet mentioned in the specification; F, is the oil tank inlet mentioned in the specification. DETAILED DESCRIPTION

[0033] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0034] It should be noted that the illustrations provided in the following embodiments are only used to illustrate the basic concept of the present invention in a schematic manner, and thus the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0035] In order to ensure the thermal index of the transformer during the design process and the safety during use, a transformer winding temperature distribution prediction method is provided in a specific embodiment. The transformer is an oil-immersed self-cooled three-winding transformer. The method flow is as follows: Figure 1 As shown, the following steps are included:

[0036] S1. Draw the 3D models of the heat sink and windings of each voltage level at a ratio of 1:1 and use existing software to mesh the models to prepare for the subsequent calculation of the fluid-temperature field of the windings and heat sink;

[0037] In this embodiment, step S1 specifically includes the following steps:

[0038] S11. Draw the high, medium and low voltage winding models respectively. The high, medium and low voltage winding models are 1 / 28 models along the circumferential direction of the center line of adjacent pads. In this example, the number of oil channel pads in one layer of high, medium and low voltage windings is 28. The drawn medium voltage winding model is as follows: Figure 2 As shown; and the model is meshed using existing software to prepare for subsequent winding finite element analysis;

[0039] S12. Perform three-dimensional modeling and meshing on one of the many identical heat sinks of the transformer.

[0040] S2. Determine the inlet temperature θ of the fluid-temperature field calculation of the high-voltage winding drawn in S1 rr With the inlet flow Q g The initial value of calculation;

[0041] In this embodiment, the initial value of the winding inlet temperature is 35° C., and the initial value of the high-voltage winding inlet flow rate is 0.03 kg / s.

[0042] S3, set the high voltage winding at the inlet temperature θrr With the inlet flow rate Q g Perform temperature-fluid field calculations and determine the temperature-fluid field conditions of other windings when the pressure is balanced with that of the winding, including:

[0043] S31. Assuming that the paper tube in the transformer is insulated, the heat generated by the transformer winding is completely taken away by the oil flow through the transformer winding. rr With the inlet flow Q g As the inlet boundary condition for the fluid-temperature field analysis of the high-voltage winding, the temperature-fluid field of the high-voltage winding is solved using existing software;

[0044] S32. Determine the low voltage winding inlet flow Q d and medium voltage winding inlet flow Q z The initial value of

[0045] In this embodiment, the low voltage winding inlet flow rate Q d The initial value is 0.02kg / s, and the medium voltage winding inlet flow rate Q z The initial value of is 0.03kg / s;

[0046] S33, according to the low voltage winding inlet flow Q d and medium voltage winding inlet flow Q z Perform temperature-fluid field calculations on medium and low voltage windings;

[0047] S34, let R z and R d are variables representing the flow resistance of the medium and low voltage windings respectively. The pressure loss ΔP flowing through the winding flow path is proportional to the flow rate Q using the S33 field calculation results: ΔP=R*Q, and the R z and R d The value of the low voltage winding inlet flow calculation value Q dq And the calculated value of the medium voltage winding inlet flow Q zq Satisfies the following formula (1):

[0048]

[0049] Where P2 is the sum of the gravity pressure of the high-voltage winding and the pressure loss of the fluid flowing through the winding, P 2g is the gravity pressure in the high voltage winding, h is the winding height, θ rr is the assumed winding inlet temperature, θ rcg is the high voltage winding outlet temperature obtained by finite element analysis, θ rcz is the outlet temperature of the medium voltage winding, θ rcd is the low voltage winding outlet temperature, ΔP g is the pressure loss of the fluid flowing through the high-voltage winding, W z and Wd are the losses of the medium voltage winding and the low voltage winding respectively;

[0050] S35, determine the low voltage winding inlet flow Q d The calculated value of low voltage winding inlet flow Q dq And the medium voltage winding inlet flow Q z The calculated value of the medium voltage winding inlet flow Q zq Is the error within 1%? If so, jump to S4 to continue calculation; if not, continue to execute S36;

[0051] S36, Q dq and Q zq The values ​​of Q are assigned to d and Q z , and Q dq and Q zq Take it as unknown quantity again and return to step S33;

[0052] By looping steps S33-S36, the medium and low voltage windings are quickly connected to the high voltage winding at an inlet temperature of θ rr And the inlet flow is Q g Pressure balance under boundary conditions.

[0053] S4, determining an exponential function of the temperature and height of the oil flow in the oil tank that is balanced with the pressure of the winding part, and determining the oil flow in the oil tank according to the heat dissipation capacity of the oil tank, specifically comprising the following steps:

[0054] S41, the fluids flowing through the high, medium and low pressures are fully mixed at the winding outlet after passing through the flow paths in each phase winding. The temperature of the mixed fluid is θ rc Satisfies the following formula (2):

[0055]

[0056] Where W is the overall loss of the winding part, Q r =(Q g +Q z +Q d )*28*3;

[0057] S42, oil flow through the oil tank Q oil Satisfies the following formula (3):

[0058]

[0059] where θ a is the ambient temperature, k is the heat transfer coefficient of the oil tank surface, O is the circumference of the oil tank, and c is the specific heat capacity of the transformer oil;

[0060] S43, calculate the temperature θ when the oil flows through the oil tank and reaches the winding inlet without mixing with other oil flows yc , as shown in formula (4):

[0061]

[0062] S5, determining the temperature, flow rate and pressure from the winding outlet to the radiator inlet and from the oil tank inlet to the winding inlet, step S5 specifically includes the following steps:

[0063] S51. Calculate the total oil flow Q through the radiator s , as shown in formula (5):

[0064] Q s =Q r -Q oil (5)

[0065] S52. When the oil flows out of the winding and enters the radiator, the oil flows through the oil tank of the transformer. During this process, the oil flows absorb the heat generated by the transformer core and dissipate part of the heat through the surface of the oil tank.

[0066] In the process of oil flowing out of the winding into the radiator and flowing into the oil tank into the winding, the heat absorbed by the oil flow is half of the loss generated by the transformer core, which is represented by the symbol W. fe / 2 express;

[0067] Calculate the heat dissipation of the fuel tank surface based on the heat dissipation area. The effective heat dissipation area S = 0.75S1 + S2 + S3, where S1 is the area of ​​the fuel tank cover, S2 is the heat dissipation area of ​​the fuel tank wall, and S3 is the heat dissipation area of ​​the radiator.

[0068] Heat load per unit area q = (P0 + P k ) / S, where P0 is the transformer no-load loss, P k is the transformer load loss;

[0069] The heat dissipated by the oil flow through the oil tank after it flows out of the winding and before it enters the radiator is ql1O, where l1 is the vertical distance from the winding outlet to the radiator inlet;

[0070] S53, temperature at the radiator inlet θ sr Satisfies the following formula (6):

[0071]

[0072] S54, calculate the pressure P1 from the winding outlet to the radiator inlet, as shown in formula (7):

[0073]

[0074] S55, oil flow from radiator to oil tank Q s Absorbs half of the transformer core loss before reaching the winding fe / 2 The heat is dissipated through the oil tank, and then the temperature mixed with the fluid in the oil tank reaches the winding inlet temperature. The oil tank inlet temperature θ yr Satisfies equation group (8):

[0075]

[0076] Where W os is the heat absorbed by the temperature change of the oil flow in the oil tank at the winding inlet when it merges with the oil flow passing through the radiator at the winding inlet, l2 is the vertical distance between the oil tank inlet and the winding inlet;

[0077] S56. Calculate the pressure P3 from the oil tank inlet to the winding inlet, as shown in formula (9):

[0078]

[0079] S6, using the radiator inlet temperature and flow rate obtained in S5 as the inlet boundary conditions for radiator field analysis, obtaining the fluid-temperature field of the radiator, and further obtaining the pressure on one side of the radiator. Step S6 specifically includes the following steps:

[0080] S61, Q s / n s is the flow rate at the radiator inlet, where n s is the number of radiators of the transformer; the radiator inlet temperature and inlet flow are used as the inlet boundary conditions for radiator field calculation to solve the fluid-temperature field of the radiator;

[0081] S62. The outlet temperature θ of the radiator under the corresponding inlet boundary conditions is obtained by solving the radiator fluid-temperature field. sc and the pressure loss ΔP through the radiator s ;

[0082] S63. Calculate the pressure P of the radiator s , as shown in equation group (10):

[0083]

[0084] Where β is a coefficient representing the heat dissipation capacity of the radiator surface, which is solved based on the oil tank inlet temperature and the radiator inlet temperature.

[0085] S7, determine whether the equation group (11) is satisfied:

[0086]

[0087] If the equation group (11) is satisfied, the result of the temperature field of each winding in S3 is the predicted temperature distribution of the oil-immersed self-cooling transformer winding, and the calculation ends; if the condition is not satisfied, continue to execute S8;

[0088] S8, determine the inlet temperature θ of the winding selected in S2 during the next cycle by the pressure and temperature of equation group (11) in S7 rr With the inlet flow Q g , and returns to S3 to continue the calculation, which specifically includes the following steps:

[0089] S81. Calculate the high voltage winding inlet flow coefficient, as shown in formula (12):

[0090]

[0091] Assign Q g＝ QUR g ;

[0092] S81, assign θ rr =θ rr +θ sc -θ or ;

[0093] Then return to step S3 to continue the calculation until the condition in S7 is met and the calculation ends.

[0094] By looping steps S3-S8, the inlet temperature θ of the high voltage winding is rr With the inlet flow Q g Quickly reach the real situation and complete the fluid-temperature field calculation for high, medium and low voltage windings.

[0095] The specific locations of the oil tank, winding and radiator inlet and outlet mentioned in the above steps are as follows: Figure 3 shown.

[0096] Some data in this example:

[0097] The transformer winding height is 1800mm, with 102 high-voltage winding sections, 78 medium-voltage winding sections, and 98 low-voltage winding sections. The number of spacers between each phase section is 28;

[0098] The radiator is a radiator bank consisting of 32 PC 2700-30 / 520 radiators;

[0099] The vertical distance from the oil tank inlet to the winding inlet and from the winding outlet to the oil tank outlet is 450mm;

[0100] The room temperature is 25℃, and the heat dissipation coefficient of the oil tank surface is 11.5W / m 2 k, heat dissipation coefficient of radiator surface 13.5W / m 2 k;

[0101] After calculation, the final winding inlet temperature is 34.3℃, the inlet flow rate of the high-voltage group one-phase 1 / 28 model is 0.0453kg / s, the inlet flow rate of the medium-voltage winding one-phase 1 / 28 model is 0.0280kg / s, and the inlet flow rate of the low-voltage winding one-phase 1 / 28 model is 0.0123kg / s;

[0102] Figure 4 The winding temperature cloud diagram corresponding to the hot spot of the transformer in the embodiment.

Claims

1. A method for predicting the temperature distribution of oil-immersed transformer windings, the method comprising determining the inlet boundary conditions of each winding and calculating the fluid-temperature field of each winding, characterized in that: The steps include: S1. Draw the 3D models of the heat sink and windings of each voltage level at a ratio of 1:1 and use existing software to mesh the models to prepare for the subsequent calculation of the fluid-temperature field of the windings and heat sink; S2. Determine the inlet temperature θ of the fluid-temperature field calculation of the high-voltage winding drawn in S1 rr With the inlet flow Q g The initial value of calculation; S3, set the high voltage winding at the inlet temperature θ rr With the inlet flow rate Q g Carry out temperature-fluid field calculation and determine the temperature-fluid field conditions when other windings are in pressure balance with this winding; S4, determining the exponential function of the oil flow temperature and height in the oil tank when the pressure is balanced with the winding part, and determining the oil flow in the oil tank according to the heat dissipation capacity of the oil tank; S5, determining the oil flow rate, temperature and pressure of the two sections of oil flow from the oil tank inlet to the winding inlet and from the winding outlet to the radiator inlet; S6, using the radiator inlet temperature and flow rate obtained in S5 as the inlet boundary conditions for the radiator fluid-temperature field analysis, obtaining the radiator fluid-temperature field, and further obtaining the pressure on one side of the radiator; S7, judging whether the pressure on both sides of the oil tank and the radiator and the error between the radiator outlet temperature calculated in the field in S6 and the oil tank inlet temperature determined in S5 are within 1%. If the errors of the pressure and temperature are within 1%, it is considered that the temperature field results of each winding obtained in S3 are the actual temperature distribution of the winding. If the error of the pressure or temperature exceeds 1%, continue to execute S8; S8. Determine the inlet temperature θ of the high voltage winding during the next cycle by comparing the pressure and temperature in S7. rr With the inlet flow Q g , and returns to S3 to continue calculation.

2. The method for predicting the temperature distribution of oil-immersed transformer windings according to claim 1, characterized in that: The winding model in step S1 is a simplified model, and the simplification method is: by enlarging the size of the wire in the corresponding winding so that it completely covers the insulating part in the winding, and the insulation is used as the wall surface.

3. The method for predicting temperature distribution of oil-immersed transformer windings according to claim 1, characterized in that: Step S3 includes: S31, the inlet temperature θ rr With the inlet flow Q g Substitute it into the high voltage winding and calculate its temperature-fluid field; S32. Determine the low voltage winding inlet flow Q d and medium voltage winding inlet flow Q z The initial value of S33, according to the low voltage winding inlet flow Q d and medium voltage winding inlet flow Q z Calculate the temperature-fluid field of the winding; S34. Based on the temperature-fluid field calculation results of S33, the oil flow resistance pressure of each oil flow rate in the winding is estimated according to the proportional relationship between the oil flow resistance pressure in the winding and the flow rate; the gravity pressure of the oil flow in the winding at each oil flow rate is determined according to the loss in the winding; and then the calculated value Q of the low-voltage winding inlet flow rate that is balanced with the high-voltage winding pressure under the current proportional relationship is obtained. dq And the calculated value of the medium voltage winding inlet flow Q zq ; S35, determine the low voltage winding inlet flow Q d The calculated value of low voltage winding inlet flow Q dq And the medium voltage winding inlet flow Q z The calculated value of the medium voltage winding inlet flow Q zq Is the error within 1%? If so, jump to S4 to continue calculation; if not, continue to execute S36; S36, Q dq and Q zq The values ​​of Q are assigned to d and Q z , and Q dq and Q zq The value in is cleared and return to step S33.

4. The method for predicting the temperature distribution of oil-immersed transformer windings according to claim 1, characterized in that: The total pressure mentioned in step S6 is the pressure value obtained by subtracting the resistance pressure obtained by the field analysis in S6 from the gravity pressure calculated according to the fuel tank inlet temperature and the radiator inlet temperature determined in S5.

5. The method for predicting temperature distribution of oil-immersed transformer windings according to claim 1, characterized in that: Step S5 includes: The oil flow rate flowing through the radiator is determined according to the oil flow rates of S3 and S4; the core loss of the transformer is evenly distributed to the two oil flows from the oil tank inlet to the winding inlet and from the winding outlet to the radiator inlet, and the heat load per unit area of ​​the transformer is used to determine the heat dissipation of the oil flow through the surface of the oil tank in the above two processes; the functional relationship between the height and temperature of the above two oil flows is further determined by the law of conservation of energy, and finally the gravity pressure of the two oil flows is determined.

6. The method for predicting temperature distribution of oil-immersed transformer windings according to claim 1, characterized in that: Step S8 includes: S81, determining the temperature of the winding inlet in the next cycle by the difference between the oil tank inlet temperature and the radiator outlet temperature, and assigning the value of the inlet temperature in the current cycle plus the radiator outlet temperature minus the oil tank inlet temperature to the winding inlet temperature in the next cycle; S82. Determine the flow rate of the high-voltage winding in the next cycle by the ratio of the gravity pressure difference between the radiator side and the oil tank side to the resistance pressure of the fluid circuit flowing through the radiator and the winding part, and multiply the ratio of the gravity pressure difference between the radiator and the oil tank on both sides of this cycle to the resistance pressure by the value of the high-voltage winding inlet flow rate to assign the high-voltage winding inlet flow rate in the next cycle.

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