Adaptive switching method of cooling fan for oil-immersed power transformer

Abstract

The invention discloses an adaptive switching method for a cooling fan of an oil-immersed power transformer, comprising: under natural convection conditions, calculating the cooling power of a radiator group under different load rates; calculating the increase in the convective heat transfer coefficient of a single radiator group in combination with the operating limit of the hot spot temperature of an operating transformer winding, the cooling power of the radiator group under different load rates and the average convective heat transfer coefficient of the radiator under natural convection conditions; calculating the number of fans added under different load rates according to the increase in the convective heat transfer coefficient of the single radiator group, the average convective heat transfer coefficient of the radiator under the action of the fan and the average convective heat transfer coefficient of the radiator under natural convection conditions; the invention can accurately formulate an adaptive switching strategy for cooling fans of power transformers.

Description

Technical Field

[0001] The invention relates to the technical field of transformer cooling, and in particular to an adaptive switching method for a heat dissipation fan of an oil-immersed power transformer. Background Art

[0002] As one of the most important and numerous power equipment in the power grid, power transformer plays the role of converting and transmitting electric energy. The safe and stable operation of transformer is directly related to the reliability and safety of power supply. The highest temperature reached by each component inside the transformer is the hot spot temperature, which generally appears on the winding. According to the relevant provisions in the GB / T 1094.7-2008 guidelines, when the hot spot temperature of the transformer is 98℃, the insulation aging rate is defined as 1, and the insulation life is the normal service life; within 140℃, for every 6℃ increase in the hot spot temperature of the transformer, the insulation life is reduced to 1 / 2 of the original, and the insulation aging rate doubles; once the hot spot temperature of the transformer winding exceeds 140℃, the normal operation of the transformer is broken and the failure rate will increase greatly.

[0003] Combined with the operating limit of the hot spot temperature of the transformer winding and the current operating load of the transformer, a design scheme for adaptive switching of the cooling system of the transformer radiator group is proposed to ensure that the hot spot temperature of the winding does not exceed the constraint limit. This is of great significance to ensuring the safe and stable operation of the transformer, reducing the operating energy consumption of the transformer and achieving energy conservation and emission reduction.

[0004] In the related art, the patent application document with publication number CN113946170A proposes that when the oil temperature exceeds the specified value, the fan is started at a precise speed based on the relationship between different fan speeds determined by the initial value and the heat production and ambient temperature; however, this scheme controls the speed of the cooling fan instead of controlling the number of cooling fans put into use. Secondly, its limiting factor is that it is controlled in combination with the oil temperature of the transformer instead of the hot spot temperature, because what is ultimately desired to be controlled is the hot spot temperature, which is more direct and accurate, while the combination with the oil temperature is an indirect method, which is relatively indirect and inaccurate.

[0005] A method for determining the convective heat transfer coefficient of the transformer casing in multi-physical field calculations is proposed in a patent application document with publication number CN112765848A. The equivalent convective heat transfer coefficient of the transformer casing is calculated by combining the transformer casing temperature and the external ambient temperature as well as the heat flux distribution of the transformer casing. However, this scheme uses a finite element calculation method to calculate the convective heat transfer coefficient of the entire transformer under natural convection. Summary of the invention

[0006] The technical problem to be solved by the present invention is how to accurately formulate an adaptive switching strategy for a cooling fan of a power transformer.

[0007] The present invention solves the above technical problems by the following technical means:

[0008] The present invention proposes an adaptive switching method for a heat dissipation fan of an oil-immersed power transformer, the method comprising:

[0009] Under natural convection conditions, calculate the heat dissipation power of the radiator group at different load rates;

[0010] Combined with the operating limit of the hot spot temperature of the transformer winding, the heat dissipation power of the radiator group under different load rates and the average convective heat transfer coefficient of the radiator under natural convection conditions, the increase in the convective heat transfer coefficient of a single radiator group is calculated;

[0011] According to the increase in the convective heat transfer coefficient of a single radiator group, the average convective heat transfer coefficient of the radiator under the action of the fan, and the average convective heat transfer coefficient of the radiator under natural convection conditions, the number of fans added under different load rates is calculated.

[0012] Furthermore, the calculation of the heat dissipation power of the radiator group under different load rates under natural convection conditions includes:

[0013] Calculate the total transformer loss at different load rates of the transformer, and calculate the average temperature difference between the radiator and the ambient temperature based on the total transformer loss at rated load and the total transformer loss at different load rates;

[0014] According to the average temperature difference between the radiator and the ambient temperature, the total area of ​​the radiator and the heat dissipation characteristic parameters of the transformer under natural convection, the heat dissipation power of the radiator group at different load rates under natural convection conditions is calculated.

[0015] Further, the total transformer loss under different load rates of the transformer is calculated, and based on the total transformer loss under rated load and the total transformer loss under different load rates, the average temperature difference between the radiator and the ambient temperature is calculated, including:

[0016] According to the transformer load rate, no-load loss and load loss, the total transformer loss under different load rates is calculated as:

[0017]

[0018] Where: P n is the total transformer loss under different load conditions, n is the transformer load factor, P 0 is the no-load loss, P k is the load loss;

[0019] Based on the total transformer loss at rated load and the total transformer loss at different load rates, the average temperature difference between the radiator and the ambient temperature is calculated as:

[0020] T wcn = T wc × P n / P E

[0021] Where: P E is the total transformer loss under rated load, It is the average temperature difference between the corrected radiator and the ambient temperature under rated load.

[0022] Furthermore, according to the average temperature difference between the radiator and the ambient temperature, the total area of ​​the radiator and the heat dissipation characteristic parameters of the transformer under natural convection, the heat dissipation power of the radiator group under different load rates under natural convection conditions is calculated as:

[0023]

[0024] Where: Q n Different load rates under natural convection conditions n The heat dissipation power of the lower radiator group, A is the total area of ​​the radiator, For different load rates n The average temperature difference between the radiator and the ambient temperature before correction is: It is the overall heat dissipation intensity of the radiator.

[0025] Furthermore, the calculation of the increase in the convective heat transfer coefficient of a single radiator group by combining the operating limit of the hot spot temperature of the transformer winding, the heat dissipation power of the radiator group under different load rates, and the average convective heat transfer coefficient of the radiator under natural convection conditions includes:

[0026] Calculate the hot spot temperature of the transformer winding at different load rates based on the rated hot spot temperature rise of the transformer, the transformer winding index and the ambient temperature;

[0027] According to the hot spot temperature of the winding under different load rates and the hot spot temperature operating limit, the average temperature difference between the radiator and the ambient temperature is corrected to obtain the average temperature difference between the radiator and the ambient temperature under different load rates;

[0028] According to the average temperature difference between the radiator and the ambient temperature at different load rates, the heat dissipation power of the radiator group at different load rates and the average convective heat transfer coefficient of the radiator under natural convection conditions, the increase in the convective heat transfer coefficient of a single radiator group is calculated.

[0029] Furthermore, according to the rated hot spot temperature rise of the transformer, the transformer winding index and the ambient temperature, the winding hot spot temperature of the transformer under different load rates is calculated as:

[0030]

[0031]

[0032] Where: T hst For different load rates n Lower winding hot spot temperature, T a is the ambient temperature, H r is the hot spot temperature rise of the transformer under load, g r is the rated hot spot temperature rise of the transformer, n is the transformer load factor, y is the transformer winding index.

[0033] Furthermore, according to the hot spot temperature of the winding and the hot spot temperature operating limit under different load rates, the average temperature difference between the radiator and the ambient temperature is corrected, and the average temperature difference between the radiator and the ambient temperature under different load rates is obtained as follows:

[0034]

[0035] Where: For different load rates n The average temperature difference between the radiator and the ambient temperature is For different load rates n The average temperature difference between the radiator and the ambient temperature before correction is: T hst For different load rates n Lower winding hot spot temperature, This is the hot spot temperature operating limit.

[0036] Furthermore, according to the average temperature difference between the radiator and the ambient temperature at different load rates, the heat dissipation power of the radiator group at different load rates and the average convective heat transfer coefficient of the radiator under natural convection conditions, the increase in the convective heat transfer coefficient of a single radiator group is calculated as follows:

[0037]

[0038] Where: Add the value of the convection heat transfer coefficient of a single radiator group. Q n For different load rates n The heat dissipation power of the lower radiator group, A is the total area of ​​the radiator, For different load rates n The average temperature difference between the radiator and the ambient temperature is is the average convection heat transfer coefficient of the radiator under natural convection conditions.

[0039] Furthermore, according to the increase in the convective heat transfer coefficient of a single radiator group, the average convective heat transfer coefficient of the radiator under the action of the fan, and the average convective heat transfer coefficient of the radiator under natural convection conditions, the number of fans added under different load rates is calculated as follows:

[0040]

[0041] Where: N To increase the number of fans, Add the value of the convection heat transfer coefficient of a single radiator group. a is the number of radiator groups, b It means two radiators share one fan. is the average convective heat transfer coefficient of the radiator under the action of the fan, is the average convection heat transfer coefficient of the radiator under natural convection conditions.

[0042] Furthermore, the calculation formula of the average temperature difference between the radiator and the ambient temperature before correction under the rated load is:

[0043]

[0044] Where: is the average temperature of the radiator, is the ambient temperature.

[0045] Furthermore, the average convection heat transfer coefficient of the radiator under natural convection conditions is the average value of the heat dissipation intensity of each part of the transformer radiator under natural convection conditions, and the heat dissipation intensity of each part is the sum of the convection heat transfer coefficient under natural convection conditions and the radiation heat transfer coefficient under natural convection conditions.

[0046] Furthermore, the calculation process of the average convective heat transfer coefficient of the radiator under the action of the fan includes:

[0047] The external flow field simulation analysis model of the transformer radiator group including the fan is established, and the temperature distribution of the radiator group is determined as the temperature boundary condition of the radiator group in combination with the actual temperature rise test results;

[0048] The temperature field and fluid field distribution of the external flow field are obtained by using the finite volume method, and the wind blowing effect of the radiator is equivalent based on the pressure-flow characteristic curve of the radiator to obtain the simulation results;

[0049] Based on the simulation results, the average convective heat transfer coefficient of the radiator under the action of the fan is calculated.

[0050] The advantages of the present invention are:

[0051] (1) The present invention analyzes the equivalent convection heat dissipation coefficient of the transformer radiator group under the action of the fan, further combines the average convection heat transfer coefficient of the radiator under the natural convection of the transformer, and the overall heat generation power of the transformer under different load rates, combined with the operating limit of the hot spot temperature of the operating transformer winding, and formulates an adaptive switching scheme for the cooling fan of a large oil-immersed power transformer to ensure that the hot spot temperature of the winding does not exceed the constraint limit, which can ensure the safe and stable operation of the transformer, while reducing the operating energy consumption of the transformer and achieving energy conservation and emission reduction.

[0052] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is a flow chart of a method for adaptively switching on and off a cooling fan of an oil-immersed power transformer proposed in one embodiment of the present invention;

[0054] Figure 2 It is a schematic diagram of a process for determining an average convective heat transfer coefficient of a radiator under forced convection by a fan in one embodiment of the present invention;

[0055] Figure 3 is a schematic diagram of a simulation boundary setting of a rotating fan in one embodiment of the present invention;

[0056] Figure 4 Schematic diagram of the temperature distribution on the wall of the radiator assembly in one embodiment of the present invention. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0058] like Figure 1 As shown, an embodiment of the present invention provides an adaptive switching method for a cooling fan of an oil-immersed power transformer, the method comprising the following steps:

[0059] S10. Under natural convection conditions, calculate the heat dissipation power of the radiator group under different load rates;

[0060] S20, calculating the increase in the convective heat transfer coefficient of a single radiator group by combining the operating limit of the hot spot temperature of the transformer winding, the heat dissipation power of the radiator group at different load rates, and the average convective heat transfer coefficient of the radiator under natural convection conditions;

[0061] S30, calculating the number of fans added under different load rates according to the increase in the convective heat transfer coefficient of a single radiator group, the average convective heat transfer coefficient of the radiator under the action of the fan, and the average convective heat transfer coefficient of the radiator under natural convection conditions.

[0062] This embodiment analyzes the equivalent convection heat dissipation coefficient of the transformer radiator group under the action of the fan, and further combines the average convection heat transfer coefficient of the radiator under natural convection of the transformer, and the overall heating power of the transformer at different load rates, combined with the operating limit of the hot spot temperature of the operating transformer winding, to develop an adaptive switching plan for the cooling fan of a large oil-immersed power transformer to ensure that the hot spot temperature of the winding does not exceed the constraint limit, so as to ensure the safe and stable operation of the transformer, while reducing the operating energy consumption of the transformer and achieving energy conservation and emission reduction.

[0063] As a further preferred technical solution, the step S10: calculating the heat dissipation power of the radiator group under different load rates under natural convection conditions, specifically includes the following steps:

[0064] S11, calculating the total loss of the transformer at different load rates of the transformer, and calculating the average temperature difference between the radiator and the ambient temperature based on the total loss of the transformer at the rated load and the total loss of the transformer at different load rates;

[0065] Specifically, according to the transformer load rate, no-load loss and load loss, the total transformer loss under different load rates is calculated as:

[0066]

[0067] Where: P n is the total transformer loss under different load conditions, n is the transformer load factor, P 0 is the no-load loss, P k is the load loss;

[0068] Based on the total transformer loss at rated load and the total transformer loss at different load rates, calculate the different load rates n The average temperature difference between the lower radiator and the ambient temperature is:

[0069] T wcn = T wc × P n / P E

[0070] Where: P E is the total transformer loss under rated load, It is the average temperature difference between the corrected radiator and the ambient temperature under rated load.

[0071] S12. Calculate the heat dissipation power of the heat sink group under different load rates under natural conditions according to the average temperature difference between the heat sink and the ambient temperature, the total area of ​​the heat sink, and the heat dissipation characteristic parameters of the transformer under natural convection.

[0072] Specifically, the heat dissipation power of the radiator group at different load rates under natural convection is calculated as:

[0073]

[0074] Where: Q n For different load rates n The heat dissipation power of the lower radiator group, A is the total area of ​​the radiator, For different load rates n The average temperature difference between the radiator and the ambient temperature before correction is: It is the overall heat dissipation intensity of the radiator.

[0075] It should be noted that It represents the convection heat transfer coefficient of oil-immersed transformer under natural convection. h c Radiation heat transfer coefficient equivalent to oil-immersed transformer h r The sum is the overall heat dissipation intensity of the radiator corresponding to the oil-immersed transformer.

[0076] Furthermore, the average temperature difference between the radiator and the ambient temperature is Tx = Tw × Pn / P E , the average temperature difference between the radiator and the ambient temperature before correction under rated load The calculation formula is:

[0077]

[0078] Where: is the average temperature of the radiator, is the ambient temperature.

[0079] As a further preferred technical solution, the step S20: combining the hot spot temperature operating limit of the transformer winding, the heat dissipation power of the radiator group under different load rates and the average convective heat transfer coefficient of the radiator under natural convection conditions, calculating the increase in the convective heat transfer coefficient of a single radiator group, specifically includes the following steps:

[0080] S21. Calculate the hot spot temperature of the transformer winding at different load rates according to the rated hot spot temperature rise of the transformer, the transformer winding index and the ambient temperature;

[0081] Specifically, the winding hot spot temperature of the transformer under different load rates is calculated as:

[0082]

[0083]

[0084] Where: T hst For different load rates n Lower winding hot spot temperature; T a is the ambient temperature, °C; H r is the hot spot temperature rise of the transformer under load; g r is the rated hot spot temperature rise of the transformer; n is the transformer load factor; y is the transformer winding index.

[0085] S22, according to the hot spot temperature of the winding and the hot spot temperature operating limit under different load rates, correct the average temperature difference between the radiator and the ambient temperature to obtain the average temperature difference between the radiator and the ambient temperature under different load rates;

[0086] Specifically, the average temperature difference between the radiator and the ambient temperature at different load rates is obtained as follows:

[0087]

[0088] Where: For different load rates n The average temperature difference between the radiator and the ambient temperature is For different load rates n The average temperature difference between the radiator and the ambient temperature before correction is: T hst For different load rates n Lower winding hot spot temperature, This is the hot spot temperature operating limit.

[0089] S23, calculating the increase in the convective heat transfer coefficient of a single radiator group under natural convection conditions according to the average temperature difference between the radiator and the ambient temperature at different load rates, the heat dissipation power of the radiator group at different load rates, and the average convective heat transfer coefficient of the radiator;

[0090] Specifically, the increase in the convective heat transfer coefficient of a single radiator group is calculated as:

[0091]

[0092] Where: Add the value of the convection heat transfer coefficient of a single radiator group. Q n For different load rates n The heat dissipation power of the lower radiator group, A is the total area of ​​the radiator, For different load rates n The average temperature difference between the radiator and the ambient temperature is is the average convection heat transfer coefficient of the radiator under natural convection conditions.

[0093] As a further preferred technical solution, step S30: according to the increase in the convective heat transfer coefficient of a single radiator group, the average convective heat transfer coefficient of the radiator under the action of the fan, and the average convective heat transfer coefficient of the radiator under natural convection conditions, the number of fans added under different load rates is calculated as follows:

[0094]

[0095] Where: N To increase the number of fans, Add the value of the convection heat transfer coefficient of a single radiator group. a is the number of radiator groups, b It means two radiators share one fan. is the average convective heat transfer coefficient of the radiator under the action of the fan, is the average convection heat transfer coefficient of the radiator under natural convection conditions.

[0096] As a further preferred technical solution, the average convection heat transfer coefficient of the radiator under natural convection conditions is the average value of the heat dissipation intensity of each part of the transformer radiator under natural convection conditions, and the heat dissipation intensity of each part is the sum of the convection heat transfer coefficient under natural convection conditions and the radiation heat transfer coefficient under natural convection conditions.

[0097] Specifically, in the calculation of the temperature fluid field of the transformer, the convection heat transfer coefficient is often used to equivalently express the heat exchange process between the transformer and the external environment. The heat dissipation characteristic analysis process of the transformer under natural convection is:

[0098] The heat flux of convection heat transfer between the solid wall of the transformer and the external air fluid can be expressed by Newton's cooling formula, that is:

[0099]

[0100] In the formula, q is the heat flux of transformer outer wall convection heat transfer, W / m 2 ; T w and T f are the temperatures of the wall and the external fluid, K; h c is the convective heat transfer coefficient, W / (m 2 ·K).

[0101] Specifically, the solution process of the transformer convection heat transfer coefficient under natural convection is:

[0102] By simplifying the transformer housing and the radiator housing into smooth planes, the heat dissipation process of the transformer housing can be considered as longitudinal flat plate convection heat transfer. Under natural convection heat transfer conditions, the Nusselt number of the vertical plate is v and the Nusselt number Nu of the horizontal plate h It can be expressed by the following formula:

[0103]

[0104]

[0105]

[0106]

[0107]

[0108] Where Pr is the Prandtl number; Gr is the Grashof number; Ra is the Rayleigh number; g is the acceleration due to gravity, m / s 2 ; β is the corresponding fluid expansion coefficient; L is the characteristic size, m; θ is the temperature difference between the wall and the external fluid, K; μ is the kinematic viscosity of the fluid, (m^2) / s; η is the dynamic viscosity of the fluid, kg / (m·s); c is the specific heat capacity of the fluid, J / (kg·K); k is the thermal conductivity of the fluid, W / (m·K); ρ is the fluid density, kg / m 3 .

[0109] After obtaining the Nusselt number, the transformer convection heat transfer coefficient under natural convection can be obtained as follows:

[0110] .

[0111] Specifically, the solution process of the shell radiation heat transfer coefficient is:

[0112] The heat flow generated by the radiation heat transfer of the transformer housing can be expressed by the following formula:

[0113]

[0114] In the formula, ε is the surface emissivity of the transformer housing; σ b is the Stefan-Boltzmann constant, which is 5.67×10 - 8 W / (m 2 ·K 4 ); T w is the transformer case temperature, T a is the external ambient temperature of the transformer.

[0115] The radiation heat transfer capacity per unit area of ​​the transformer casing to the external environment can be equivalently expressed as the radiation heat transfer coefficient h r ,Right now:

[0116]

[0117] Therefore, considering the ambient temperature and the operating conditions of the transformer shell's external radiation heat exchange, the overall heat dissipation intensity of the oil-immersed transformer radiator is It can be expressed as the convective heat transfer coefficient under natural convection h c and the equivalent radiation heat transfer coefficient h r The sum is:

[0118] .

[0119] Furthermore, this embodiment can use the above-mentioned transformer heat dissipation characteristics analysis process under natural convection to calculate the heat dissipation intensity of each part of the transformer casing, and calculate the heat dissipation intensity of the radiator casing, and then calculate the heat dissipation intensity of each part of the transformer casing and the heat dissipation intensity of the radiator casing. The average value of the heat dissipation intensity of each part of the transformer casing and the heat dissipation intensity of the radiator casing can be obtained to obtain the average convection heat transfer coefficient of the radiator under natural convection conditions.

[0120] As a further preferred technical solution, Figure 2As shown, the calculation process of the average convective heat transfer coefficient of the radiator under the action of the fan includes:

[0121] (1) Establish a simulation analysis model of the external flow field of the transformer radiator group including the fan, and determine the temperature distribution of the radiator group as the temperature boundary condition of the radiator group based on the actual temperature rise test results;

[0122] Specifically, the simulation analysis model of the external flow field of the transformer radiator group including the fan is established as follows: Figure 3 As shown in the figure, the two radiator groups share a cooling fan. In the simulation model, the upper wall and the rear wall have open boundaries, the left wall and the right wall have symmetrical boundaries, the front wall and the lower wall are wall boundaries, and there is no slip at the fluid-solid interface. The radiator group refers to the plate radiator of the transformer, which does not include the cooling fan. The inlet and outlet oil pipes on the left wall of the radiator group are directly connected to the transformer box, and the cooling fan is directly below the two radiator groups.

[0123] Combined with the actual temperature rise test results, the temperature distribution of the radiator group is determined as the temperature boundary condition of the radiator group, that is, the inlet oil temperature is 75℃, the outlet oil temperature is 44.9℃, and the ambient temperature is 33.5℃. It is assumed that the temperature of the radiator group is evenly distributed from top to bottom. Figure 4 shown.

[0124] (2) The temperature field and fluid field distribution of the external flow field are obtained using the finite volume method, and the wind blowing effect of the radiator is equivalent based on the pressure-flow characteristic curve of the radiator to obtain the simulation results;

[0125] Specifically, after completing the external flow setting of the transformer radiator including the cooling fan, the external flow field is calculated by solving the temperature fluid field control equation. For transformers with natural oil circulation cooling, the natural convection process of the transformer oil realizes the transfer and transfer of heat inside the transformer. The solution of the convection heat transfer process follows the three major fluid dynamics equations of conservation of mass, conservation of momentum, and conservation of energy:

[0126] 1) Mass conservation equation

[0127]

[0128] In the formula, is the Hamiltonian operator; t is the amount of time; v is the fluid velocity vector; ρ is the fluid density, kg / m 3 .

[0129] 2) Momentum conservation equation

[0130]

[0131] In the formula, pis the fluid pressure, Pa; f is the external force per unit volume of fluid, N / m 3 ; η is the dynamic viscosity of the fluid, kg / (m·s).

[0132] 3) Energy conservation equation

[0133]

[0134] In the formula, T is the fluid temperature, K; c p is the specific heat capacity of the fluid, J / (kg·K); k is the thermal conductivity of the fluid, W / (m·K); Φ It is the heat source in the fluid; S h The part of the fluid's mechanical energy that is converted into heat energy under the action of fluid viscosity.

[0135] This embodiment will use the finite volume method to discretely solve the above control equations and obtain the temperature field and fluid field distribution of the transformer external flow field. In the external flow field analysis, the wind blowing effect of the cooling fan is equivalent based on the pressure-flow characteristic curve of the cooling fan.

[0136] (3) Based on the simulation results, calculate the average convective heat transfer coefficient of the radiator under the action of the fan.

[0137] Specifically, the simulation result data obtained by the finite element analysis software includes the heat flux density, wall temperature and other data of the calculation unit. The method for determining the convective heat transfer coefficient of the wall unit is:

[0138]

[0139] Where: q i For wall units i The normal heat flux density is T w，i For wall units i The wall temperature, T 0 It is the reference temperature, generally the ambient temperature.

[0140] The method for determining the average convection heat transfer coefficient of the wall is:

[0141]

[0142] Where: It represents the average convection heat transfer coefficient of the wall under the action of the fan; h i Indicates the wall i Convective heat transfer coefficient of each unit;A i Respectively represent the wall i Unit area.

[0143] The heat dissipation power of the radiator under the action of the fan Q for:

[0144]

[0145] Where: A is the total area of ​​the radiator, T Avg is the average temperature of the radiator, T a is the ambient temperature.

[0146] It should be noted that, in this embodiment, the convective heat transfer coefficient under natural convection is calculated by an empirical formula, while the convective heat transfer coefficient under the action of the radiator cooling fan is obtained by a finite element numerical calculation method.

[0147] It should be noted that the empirical formula can be used to directly calculate the convective heat transfer coefficient of the radiator group more accurately, but the empirical formula is difficult to use for the calculation of the convective heat transfer coefficient of the radiator under the action of the fan. Therefore, under the action of the fan, the convective heat transfer coefficient of the radiator group at different wind speeds can be accurately obtained based on the numerical calculation results.

[0148] Furthermore, the following takes a SFZ9-50000 / 110 transformer as an example to analyze the switching strategy of the transformer radiator group. The no-load loss of this transformer is 26.077kW, the load loss is 233.681kW, and the total loss is 259.758kW.

[0149] According to the solution process of the transformer convection heat transfer coefficient under the above natural convection condition, the equivalent convection heat transfer coefficient of each part of the transformer under natural convection can be calculated as shown in the following Table 1.

[0150] Table 1 Convective heat transfer coefficients of various parts of the transformer

[0151]

[0152] At the same time, according to the heat dissipation power calculation formula, it can be known that the heat dissipation power of each part of the transformer is shown in Table 2 below. The radiator group includes 8 groups of radiators, and the heat dissipation power of a single group of radiators is 29.6kW.

[0153] Table 2 Transformer heat dissipation characteristics

[0154]

[0155] According to the transformer multi-physics field calculation results, the rated hot spot temperature rise of the SFZ9-50000 / 110 transformer in this embodiment is g r The transformer hot spot temperature rise is 80K under other loads. H r The calculation method can be calculated by the following formula, y is the transformer winding index. y The value is 0.7.

[0156]

[0157] Winding hot spot temperature T hst for:

[0158]

[0159] Where: T a is the ambient temperature, ℃.

[0160] Different load rates under natural convection conditions n Cooling power of lower radiator group Q n For (fan not turned on):

[0161]

[0162] Under other loads, different load rates n The average temperature difference between the lower radiator and the ambient temperature is Tx = Tw × Pn / P E , P E is the total transformer loss under rated load, P n is the total transformer loss under different load conditions, A is the total area of ​​the radiator, Tw It is the average temperature difference between the corrected front radiator and the ambient temperature under rated load, which is 37.5K under rated conditions.

[0163] To ensure hot spot temperature T hst Do not exceed hot spot temperature operating limit T hstMAX (98°C), then the corrected load factor n Average temperature difference between the radiator and the ambient temperature :

[0164] .

[0165] According to the average convection heat transfer coefficient of the radiator under the action of the fan According to the calculation process, the average convective heat transfer coefficient of the radiator under the action of the fan is determined to be 19.66 W / (m 2 K), and according to the solution process of the transformer convection heat transfer coefficient under the above natural convection condition, the average convection heat transfer coefficient of the radiator under natural convection is determined to be 8.81W / (m 2 K), the increase in the convective heat transfer coefficient of a single radiator group is h z for:

[0166]

[0167] Different load rates n The number of fans added N for:

[0168] =

[0169] Where 19.66 is the average convective heat transfer coefficient of the radiator under the action of the fan, W / (m 2 K); 8.81 is the average convection heat transfer coefficient of the radiator under natural convection, W / (m 2 K); 8 corresponds to the number of radiator groups, and 2 corresponds to two radiator groups sharing one fan.

[0170] Considering the most severe outdoor operating environment, that is, when the ambient temperature is 40°C, according to the heat generation power of the transformer itself and the heat dissipation efficiency of different fans of the transformer, the fan switching strategy of the transformer is as shown in Table 3 below:

[0171] Table 3 Transformer fan switching strategy

[0172]

[0173] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0174] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0175] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for adaptively switching on and off a cooling fan of an oil-immersed power transformer, characterized in that: The method comprises: Under natural convection conditions, calculate the heat dissipation power of the radiator group at different load rates; Combined with the operating limit of the hot spot temperature of the operating transformer winding, the heat dissipation power of the radiator group under different load rates and the average convection heat transfer coefficient of the radiator under natural convection conditions, the increase in the convection heat transfer coefficient of a single radiator group is calculated, including: calculating the hot spot temperature of the transformer winding under different load rates according to the rated hot spot temperature rise of the transformer, the transformer winding index and the ambient temperature; correcting the average temperature difference between the radiator and the ambient temperature according to the hot spot temperature of the winding under different load rates and the hot spot temperature operating limit, and obtaining the average temperature difference between the radiator and the ambient temperature under different load rates; according to the average temperature difference between the radiator and the ambient temperature under different load rates, the heat dissipation power of the radiator group under different load rates and the average convection heat transfer coefficient of the radiator under natural convection conditions, the increase in the convection heat transfer coefficient of a single radiator group is calculated as follows: Where: Add the value of the convection heat transfer coefficient of a single radiator group. Q n For different load rates n The heat dissipation power of the lower radiator group, A is the total area of ​​the radiator, For different load rates n The average temperature difference between the radiator and the ambient temperature is is the average convection heat transfer coefficient of the radiator under natural convection conditions; According to the increase in the convective heat transfer coefficient of a single radiator group, the average convective heat transfer coefficient of the radiator under the action of the fan, and the average convective heat transfer coefficient of the radiator under natural convection conditions, the number of fans added under different load rates is calculated as follows: Where: N To increase the number of fans, a is the number of radiator groups, b It means two radiators share one fan. is the average convective heat transfer coefficient of the radiator under the action of the fan, is the average convection heat transfer coefficient of the radiator under natural convection conditions.

2. The method for adaptively switching on and off a cooling fan of an oil-immersed power transformer according to claim 1, characterized in that: Under the natural convection condition, the heat dissipation power of the radiator group under different load rates is calculated, including: Calculate the total transformer loss at different load rates of the transformer, and calculate the average temperature difference between the radiator and the ambient temperature based on the total transformer loss at rated load and the total transformer loss at different load rates; According to the average temperature difference between the radiator and the ambient temperature, the total area of ​​the radiator and the heat dissipation characteristic parameters of the transformer under natural convection, the heat dissipation power of the radiator group under different load rates under natural convection conditions is calculated.

3. The method for adaptively switching on and off a cooling fan of an oil-immersed power transformer according to claim 2, characterized in that: The calculation of the total transformer loss at different load rates of the transformer, and the calculation of the average temperature difference between the radiator and the ambient temperature based on the total transformer loss at the rated load and the total transformer loss at different load rates, include: According to the transformer load rate, no-load loss and load loss, the total transformer loss under different load rates is calculated as: Where: P n is the total transformer loss under different load conditions, n is the transformer load factor, P 0 is no-load loss, P k is the load loss; Based on the total transformer loss at rated load and the total transformer loss at different load rates, the average temperature difference between the radiator and the ambient temperature is calculated as: T wcn = T wc × P n / P E Where: P E is the total transformer loss under rated load, It is the average temperature difference between the corrected radiator and the ambient temperature under rated load.

4. The method for adaptively switching on and off a cooling fan of an oil-immersed power transformer according to claim 2, characterized in that: According to the average temperature difference between the radiator and the ambient temperature, the total area of ​​the radiator and the heat dissipation characteristic parameters of the transformer under natural convection, the heat dissipation power of the radiator group under different load rates under natural convection conditions is calculated as: Where: Q n Different load rates under natural convection conditions n The heat dissipation power of the lower radiator group, A is the total area of ​​the radiator, For different load rates n The average temperature difference between the radiator and the ambient temperature before correction is: It is the overall heat dissipation intensity of the radiator.

5. The method for adaptively switching on and off a cooling fan of an oil-immersed power transformer according to claim 1, characterized in that: According to the rated hot spot temperature rise of the transformer, the transformer winding index and the ambient temperature, the hot spot temperature of the transformer winding under different load rates is calculated as: Where: T hst For different load rates n Lower winding hot spot temperature, T a is the ambient temperature, H r is the hot spot temperature rise of the transformer under load, g r is the rated hot spot temperature rise of the transformer, n is the transformer load factor, y is the transformer winding index.

6. The method for adaptively switching on and off a cooling fan of an oil-immersed power transformer according to claim 1, characterized in that: According to the winding hot spot temperature and the hot spot temperature operating limit under different load rates, the average temperature difference between the radiator and the ambient temperature is corrected, and the average temperature difference between the radiator and the ambient temperature under different load rates is obtained as follows: Where: For different load rates n The average temperature difference between the radiator and the ambient temperature is For different load rates n The average temperature difference between the radiator and the ambient temperature before correction is: T hst For different load rates n Lower winding hot spot temperature, This is the hot spot temperature operating limit.

7. The method for adaptively switching on and off a cooling fan of an oil-immersed power transformer according to claim 3, characterized in that: The calculation formula for the average temperature difference between the radiator and the ambient temperature before correction under the rated load is: Where: is the average temperature of the radiator, is the ambient temperature.

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