Self-coupling transformer winding hot-spot temperature rise prediction method based on line-oil temperature difference

Abstract

The invention provides an autotransformer winding hot-spot temperature rise prediction method based on line-oil temperature difference, which does not need to increase economic cost and can accurately predict the hot-spot temperature of a transformer winding. Comprising the following steps: S1, based on the sizes of an oil tank, a winding and an iron core of the transformer, establishing a three-dimensional numerical model of the transformer in finite element simulation software; s2, electromagnetic field simulation is carried out, and winding loss during operation of the transformer is obtained through frequency domain time-harmonic field calculation; s3, applying the winding loss obtained in the electromagnetic field simulation as a heat source to finite element simulation software so as to carry out electromagnetic field-temperature field coupling simulation and obtain winding hot-spot temperature rise and oil surface average temperature rise under different load currents; s4, according to the winding hot-spot temperature rise and the oil surface average temperature rise under different load currents, line-oil temperature differences under different load currents are obtained, and a curve is drawn to obtain a function relation between the load currents and the line-oil temperature differences; s5, according to the real-time data of the load current and the oil temperature, the winding hot-spot temperature is obtained in combination with the function relation.

Description

Technical Field

[0001] The invention relates to the technical field of transformers, and in particular to a method for predicting hot spot temperature rise of an autotransformer winding based on a line-oil temperature difference. Background Art

[0002] The hot spot temperature rise of transformer windings is an important parameter in transformer design, operation and maintenance. At present, the hot spot temperature rise data of transformers are mainly obtained through the following methods:

[0003] (1) Direct measurement method

[0004] Pre-embed optical fiber temperature measuring probes in transformer windings to monitor winding temperature and hot spot temperature in real time. The optical fiber temperature measurement method is characterized by high data accuracy, real-time and strong distribution, but the distribution position of the probe has a great influence on the results and is costly.

[0005] (2) Theoretical calculation method

[0006] The transformer temperature rise is calculated according to the empirical formula, but the temperature rise calculation is a complicated process involving multiple factors and complex heat conduction processes. It is easily affected by multiple uncontrollable variables such as ambient temperature, transformer oil surface temperature rise, hot spot and temperature rise difference, etc. The accuracy is not high and the reference value is not great.

[0007] (3) Software simulation

[0008] The working conditions are simulated using the more mature simulation software in the industry, and predictions are made in combination with various AI algorithms. However, this method is still in the research stage and has not yet been widely used in the industry.

[0009] In summary, the cost of fiber optic temperature measurement is relatively high. For conventional transformers that have already been put into operation, it is not advisable to spend huge amounts of money to return them to the factory for renovation to add fiber optic temperature measurement. Various AI predictions are not yet mature in the industry. Summary of the invention

[0010] In view of the above problems, the present invention provides a method for predicting the hot spot temperature rise of an autotransformer winding based on the line-oil temperature difference, which can accurately predict the hot spot temperature of the transformer winding without increasing the economic cost.

[0011] The present invention adopts the following technical scheme, a method for predicting the hot spot temperature rise of an autotransformer winding based on the line-oil temperature difference, comprising the following steps:

[0012] S1. Based on the dimensions of the transformer oil tank, windings and core, a three-dimensional numerical model of the transformer is established in the finite element simulation software;

[0013] S2. Based on the three-dimensional numerical model of the transformer, electromagnetic field simulation is performed in finite element simulation software, and the winding loss P of the transformer during operation is obtained by using frequency domain time-harmonic field calculation;

[0014] S3. Apply the winding loss P obtained in the electromagnetic field simulation as a heat source in the finite element simulation software to perform electromagnetic field-temperature field coupling simulation to obtain the winding hot spot temperature rise T under different load currents. r and the average temperature rise of the oil surface T y ;

[0015] S4. According to the winding hot spot temperature rise T under different load currents r and the average temperature rise of the oil surface T y , obtain the line oil temperature difference under different load currents, and then draw a curve to obtain the functional relationship between load current and line oil temperature difference;

[0016] S5. According to the real-time data of load current and oil temperature, and in combination with the functional relationship between load current and line-oil temperature difference, the hot spot temperature of the winding is obtained.

[0017] Furthermore, in step S2, the calculation formula of the winding loss P when the transformer is running is:

[0018] P=P 损 +P Fe

[0019] P 损 =I 2 R

[0020] P Fe =P h +P w =k h f x +k w δ 2 f 2 B 2

[0021] Among them, P 损 is the copper loss of the wire; I is the load current; R is the resistance of the wire;

[0022] P Fe is the core loss, P h is the hysteresis loss, P w is the eddy current loss;

[0023] k h , k w are the hysteresis and eddy current loss coefficients, respectively;

[0024] f is the rated current frequency;

[0025] δ is the thickness of silicon steel sheet;

[0026] B is the maximum magnetic flux density;

[0027] x is the power exponent;

[0028] Furthermore, in step S3, the winding hot spot temperature rise T r is the highest point temperature of the winding axial direction in the corresponding transformer; a temperature sensor is installed on the transformer, and the temperature of the top oil surface on the transformer is obtained by real-time detection by the temperature sensor. Then, according to the top oil surface temperature under different load currents, the average value of the entire top oil surface temperature is taken to obtain the average oil surface temperature rise T y ;

[0029] Furthermore, in step S4, the line oil temperature difference under different load currents is the winding hot spot temperature rise T r The average temperature rise of the oil surface T y The difference between

[0030] Furthermore, in step S3, according to the calculation formula:

[0031] Q=Sα(T1-T2)

[0032] ΔT=T1-T2

[0033]

[0034] Get the winding hot spot temperature rise T r ,Right now:

[0035]

[0036] Wherein, Q is the heat dissipated by convection in the transformer;

[0037] α is the unit surface heat transfer coefficient on the transformer; S is the heat dissipation area;

[0038] T1 is the temperature of the cooled surface, and T2 is the temperature of the cooling medium;

[0039] q is the heat transfer per unit area on the transformer; ΔT is the change in the cooling medium temperature over a period of time;

[0040] Nu is the Nusselt number; h is the characteristic length; λ is the thermal conductivity of the cooling medium;

[0041] Gr is the Grashof number; β is the volume expansion coefficient of the fluid; g is the gravitational acceleration; γ is the kinematic viscosity;

[0042] Pr is the Prandtl number; ρ is the density of the fluid, c is the specific heat capacity of the fluid, and v is the fluid velocity;

[0043] Furthermore, the step S4 also includes: comparing the difference between the line oil temperature difference and the factory winding hot spot data of the transformer, if the difference between the line oil temperature difference and the factory winding hot spot data of the transformer is within the threshold range, the data is valid, and according to the line oil temperature difference under different load currents, a curve is drawn to obtain the functional relationship between the load current and the line oil temperature difference; if the difference between the two exceeds the threshold, the heat transfer coefficient α is corrected, and the step S3 is returned to re-perform the electromagnetic field-temperature field coupling simulation calculation;

[0044] Furthermore, in step S5, the functional relationship between the load current and the line oil temperature difference is recorded as Y, and the winding hot spot temperature is the sum of the functional relationship Y and the real-time data of the oil temperature.

[0045] The beneficial effects of the present invention are that its process is simple and the data is reliable, without increasing economic costs. It can overcome the technical problem that the hot spots of the windings of the operated transformers cannot be directly measured, and accurately predict the hot spot temperatures of the windings. This has important practical significance for the safe and economical operation of the transformers, and has good economic use value. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a schematic diagram of the process of the present invention;

[0047] Figure 2 is a curve diagram showing the relationship between the hot spot temperature of the winding and the axial height of the winding in the present invention;

[0048] Figure 3 It is a curve diagram of the relationship between the center line oil temperature difference and the load current of the present invention. DETAILED DESCRIPTION

[0049] like Figure 1 to Figure 3 As shown, the method for predicting the hot spot temperature rise of the autotransformer winding based on the line-oil temperature difference in the present invention comprises the following steps:

[0050] S1. Based on the dimensions of the transformer oil tank, windings and core, a three-dimensional numerical model of the transformer is established in the finite element simulation software;

[0051] S2. Based on the three-dimensional numerical model of the transformer, electromagnetic field simulation is performed in finite element simulation software. In the electromagnetic field, the frequency domain time-harmonic field can accurately calculate the loss value of the winding. Therefore, the frequency domain time-harmonic field is used to calculate the winding loss P when the transformer is running;

[0052] Further, in step S2, the calculation formula of the winding loss P when the transformer is running is:

[0053] P=P 损 +P Fe

[0054] P 损 =I2 R

[0055] P Fe =P h +P w =k h f x +k w δ 2 f 2 B 2

[0056] Among them, P 损 is the copper loss of the wire; I is the load current; R is the resistance of the wire;

[0057] P Fe is the core loss, P h is the hysteresis loss, P w is the eddy current loss;

[0058] k h , k w are the hysteresis and eddy current loss coefficients, respectively;

[0059] f is the rated current frequency;

[0060] δ is the thickness of silicon steel sheet;

[0061] B is the maximum magnetic flux density;

[0062] x is the power exponent;

[0063] In the above formula, the heating of the core is mainly caused by the iron loss of the transformer, that is, the repeated magnetization loss occurring in the transformer core, which is mainly composed of the hysteresis loss and eddy current loss in the silicon steel sheet;

[0064] S3. Apply the winding loss P obtained in the electromagnetic field simulation as a heat source in the finite element simulation software to perform electromagnetic field-temperature field coupling simulation to obtain the winding hot spot temperature rise T under different load currents. r and the average temperature rise of the oil surface T y ;

[0065] When performing electromagnetic field-temperature field coupling simulation, the values ​​obtained in the electromagnetic field simulation calculation are imported into the temperature field. The imported values ​​specifically refer to the heat generated by various losses. They are both the results of the electromagnetic field simulation and the data source (heat source value) of the temperature field simulation. This process is called coupled simulation and is automatically performed within the finite element simulation software.

[0066] Further, in step S3, the winding hot spot temperature rise T rIt is the highest point temperature of the winding axial direction in the corresponding transformer; a temperature sensor is installed on the transformer, and the top oil surface temperature of the transformer is directly detected in real time by the temperature sensor. According to the top oil surface temperature under different load currents, the average value of the top oil surface temperature is taken to obtain the average temperature rise T of the oil surface. y ;

[0067] Further, in step S3, according to the calculation formula:

[0068]

[0069] ΔT=T1-T2

[0070]

[0071] Get the winding hot spot temperature rise T r ,Right now:

[0072]

[0073] Wherein, Q is the heat dissipated by convection in the transformer;

[0074] α is the unit surface heat transfer coefficient on the transformer; S is the heat dissipation area;

[0075] T1 is the temperature of the cooled surface, and T2 is the temperature of the cooling medium;

[0076] q is the heat transfer per unit area on the transformer; ΔT is the change in the cooling medium temperature over a period of time;

[0077] Nu is the Nusselt number; h is the characteristic length; λ is the thermal conductivity of the cooling medium;

[0078] Gr is the Grashof number; β is the volume expansion coefficient of the fluid; g is the gravitational acceleration; γ is the kinematic viscosity;

[0079] Pr is the Prandtl number; ρ is the density of the fluid, c is the specific heat capacity of the fluid, and ν is the fluid velocity;

[0080] It can be seen from this that the transformer winding hot spot temperature rise T r It is related to the cooling medium's density, viscosity, specific heat capacity, thermal conductivity and other parameters.

[0081] S4. According to the winding hot spot temperature rise T under different load currents r and the average temperature rise of the oil surface T y , and obtain the line oil temperature difference under different load currents. The line oil temperature difference under different load currents is the winding hot spot temperature rise T r The average temperature rise of the oil surface T yThe difference between the two is then plotted, and a curve is drawn to obtain the functional relationship between the load current and the line-oil temperature difference; the line in the line-oil temperature difference refers to the copper wire, and the point with the highest temperature rise on the copper wire is called the winding hot spot in the industry; oil refers to the oil temperature, which is the average oil temperature rise after the oil flow is steady; all heat sources (load loss + iron loss of the wire) are coupled in the fluid temperature field, and the heat is dissipated by convection, and the oil temperature will rise;

[0082] Furthermore, the step S4 also includes: comparing the difference between the line oil temperature difference and the factory winding hot spot data of the transformer, if the difference between the line oil temperature difference and the factory winding hot spot data of the transformer is within the threshold range, the data is valid, and according to the line oil temperature difference under different load currents, a curve is drawn to obtain the functional relationship between the load current and the line oil temperature difference; if the difference between the two exceeds the threshold, the heat transfer coefficient α is corrected, and the step S3 is returned to re-perform the electromagnetic field-temperature field coupling simulation calculation;

[0083] S5. According to the real-time data of load current and oil temperature, and in combination with the functional relationship Y between load current and line-oil temperature difference, the hot spot temperature of the winding is obtained. Specifically, the hot spot temperature of the winding is the sum of the functional relationship Y and the real-time data of oil temperature.

[0084] In the present invention, the normal operation of the transformer must comply with two conditions: the oil temperature does not exceed 95°C (the temperature at which the transformer oil begins to crack) and the winding hot spot does not exceed 105°C (the maximum temperature allowed by the transformer A-level insulation). Specifically, the present invention uses finite element simulation technology to analyze the winding hot spot temperature rise T under different load currents. r and the average temperature rise of the oil surface T y The relationship between the oil temperature and the hot spot temperature of the winding can be determined by the relationship between the temperature sensor installed on the transformer body (the existing oil level thermostat can be used) without any economic cost. Finally, the simulation data can be verified or corrected according to the product factory test data (that is, whether the difference between the line oil temperature difference and the transformer factory winding hot spot data is within the threshold range). The hot spot temperature of the winding can be predicted according to the oil temperature under different working conditions (that is, different loads).

[0085] according to Figure 3 , described with the following examples:

[0086] The relationship between the line oil temperature difference and the load current is a positive proportional relationship, which can be approximated as Y = f(x) = 0.0929x + 15;

[0087] Where, x is the load current at the transformer output;

[0088] When x=70, it means that the load current at the transformer output is 70% of the rated current;

[0089] At this time, the line oil temperature difference is 22K;

[0090] If the real-time oil temperature data is 50°C at this time, then the winding hot spot temperature = 22+50=72°C, and 72°C < 105°C (the maximum allowable temperature for Class A insulation), which means that the transformer is operating safely at this time.

[0091] In addition, when performing data verification or correction, the following embodiments are used for description:

[0092] Generally, the factory temperature rise test will be carried out under 70% and 100% load conditions. The two data will meet the conditions for verifying or correcting the simulation data. The data comparison is shown in the following table:

[0093]

[0094]

[0095] At 70% load, the simulated hot spot temperature rise is 61.2K, and the factory test data is 59.8K, with an error of 1.4;

[0096] Under 100% load, the simulated hot spot temperature rise is 65K, and the factory test data is 64.5K, with an error of 0.5;

[0097] This error is within the acceptable range in the transformer industry, so the simulation results have certain guiding significance. (Note: The temperature measurement error of the MESSKO oil level thermostat used in the transformer is about ±3℃).

[0098] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0099] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for predicting hot spot temperature rise of autotransformer windings based on line-oil temperature difference, characterized in that: The following steps are involved: S1. Based on the dimensions of the transformer oil tank, windings and core, a three-dimensional numerical model of the transformer is established in the finite element simulation software; S2. Based on the three-dimensional numerical model of the transformer, electromagnetic field simulation is performed in finite element simulation software, and the winding loss P of the transformer during operation is obtained by using frequency domain time-harmonic field calculation; S3. Apply the winding loss P obtained in the electromagnetic field simulation as a heat source in the finite element simulation software to perform electromagnetic field-temperature field coupling simulation to obtain the winding hot spot temperature rise T under different load currents. r and the average temperature rise of the oil surface T y ; S4. According to the winding hot spot temperature rise T under different load currents r and the average temperature rise of the oil surface T y , obtain the line oil temperature difference under different load currents, and then draw a curve to obtain the functional relationship between load current and line oil temperature difference; S5. According to the real-time data of load current and oil temperature, and in combination with the functional relationship between load current and line-oil temperature difference, the hot spot temperature of the winding is obtained.

2. The method for predicting hot spot temperature rise of autotransformer winding based on line-oil temperature difference according to case requirement 1 is characterized in that: In step S2, the calculation formula of the winding loss P when the transformer is running is: P=P 损 +P Fe P 损 =I 2 R P Fe =P h +P w =k h fB x +k w δ 2 f 2 B 2 Among them, P 损 is the copper loss of the wire; I is the load current; R is the resistance of the wire; P Fe is the core loss, P h is the hysteresis loss, P w is the eddy current loss; k h , k w are the hysteresis and eddy current loss coefficients, respectively; f is the rated current frequency; δ is the thickness of silicon steel sheet; B is the maximum magnetic flux density; x is the power exponent.

3. The method for predicting hot spot temperature rise of autotransformer winding based on line-oil temperature difference according to case requirement 1 is characterized in that: In step S3, the winding hot spot temperature rise T r is the highest point temperature of the winding axial direction in the corresponding transformer; a temperature sensor is installed on the transformer, and the temperature of the top oil surface on the transformer is obtained by real-time detection by the temperature sensor. Then, according to the top oil surface temperature under different load currents, the average value of the entire top oil surface temperature is taken to obtain the average oil surface temperature rise T y .

4. The method for predicting hot spot temperature rise of autotransformer winding based on line-oil temperature difference according to case requirement 1 is characterized in that: In step S4, the line oil temperature difference under different load currents is the winding hot spot temperature rise T r The average temperature rise of the oil surface T y The difference between .

5. The method for predicting hot spot temperature rise of autotransformer winding based on line-oil temperature difference according to case requirement 4 is characterized in that: In step S3, according to the calculation formula: Q=Sα(T1-T2) ΔT=T1-T2 Get the winding hot spot temperature rise T r ,Right now: Wherein, Q is the heat dissipated by convection in the transformer; α is the unit surface heat transfer coefficient on the transformer; S is the heat dissipation area; T1 is the temperature of the cooled surface, and T2 is the temperature of the cooling medium; q is the heat transfer per unit area on the transformer; ΔT is the change in the cooling medium temperature over a period of time; Nu is the Nusselt number; h is the characteristic length; λ is the thermal conductivity of the cooling medium; Gr is the Grashof number; β is the volume expansion coefficient of the fluid; g is the gravitational acceleration; γ is the kinematic viscosity; Pr is the Prandtl number; ρ is the density of the fluid, c is the specific heat capacity of the fluid, and v is the fluid velocity.

6. The method for predicting hot spot temperature rise of autotransformer winding based on line-oil temperature difference according to case requirement 5 is characterized in that: The step S4 also includes: comparing the difference between the line oil temperature difference and the factory winding hot spot data of the transformer. If the difference between the line oil temperature difference and the factory winding hot spot data of the transformer is within the threshold range, the data is valid, and according to the line oil temperature difference under different load currents, a curve is drawn to obtain the functional relationship between the load current and the line oil temperature difference; if the difference between the two exceeds the threshold, the heat transfer coefficient α is corrected, and the step S3 is returned to re-perform the electromagnetic field-temperature field coupling simulation calculation.

7. The method for predicting hot spot temperature rise of autotransformer winding based on line-oil temperature difference according to case requirement 1 is characterized in that: In step S5, the functional relationship between the load current and the line oil temperature difference is recorded as Y, and the winding hot spot temperature is the sum of the functional relationship Y and the real-time data of the oil temperature.

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