CN111753449A - A simulation method for obtaining hot spot temperature of power transformer under different working conditions - Google Patents

Abstract

The purpose of the present invention is to provide a simulation method for obtaining the hot spot temperature of a power transformer under different working conditions. Based on the actual structure of the oil-immersed transformer, a three-dimensional simulation model of the temperature rise of the transformer is established by combining the finite element method and the finite volume method. The influence of electromagnetic field and oil flow on the temperature is considered, and the simulation of the temperature distribution of the transformer hot spot is realized. The method includes the following steps: S1: establishing a three-dimensional physical model of the power transformer; S2: calculating the theoretical analysis of the electromagnetic field of the power transformer; S3: calculating the theoretical analysis of the fluid and thermal fields of the power transformer; S4: theoretical analysis based on the electromagnetic field and fluid-solid heat, Add the corresponding physical field; S5: Carry out the field-circuit coupling connection under different working conditions according to the actual operation, and set the parameters and boundary conditions; S6: Carry out the multi-physics coupling setting; S7: Carry out the model based on the finite element method The mesh is divided, and the simulation results of the temperature distribution of the power transformer and its hot spot temperature position under different working conditions are obtained.

Description

A simulation method for obtaining hot spot temperature of power transformer under different working conditions

technical field

The invention belongs to the research field of load performance of electrical equipment, and relates to a simulation method for obtaining hot spot temperatures under different working conditions of a power transformer.

Background technique

The key factors that affect the working state of power transformers in actual operation are their thermal problems and insulation problems. The temperature rise of the transformer is an important indicator to measure whether the transformer is in a safe and stable working state. Oil-immersed transformers mainly use A-class insulation. In the process of operation, the insulation materials will age due to the influence of the environment and various physical and chemical effects. High temperature will directly cause the insulation materials to age. During the operation of the power transformer, the high temperature will accelerate the chemical reaction, and the mechanical strength and electrical strength of the insulation will decrease very quickly. According to the statistical data of transformer operation accidents released by the State Grid every year, it can be seen that due to the high temperature rise of the hot spot on the winding wire, the transformer operation accident accounts for a large proportion. Domestic and foreign countries have begun to pay attention to the hot spot temperature of the transformer. To ensure the safe operation of the transformer, not only the average temperature rise of the winding should not exceed the allowable temperature value, but also the temperature rise of the winding hot spot should not exceed the allowable temperature value. When designing the transformer, the temperature rise test of the transformer is carried out. Measurement is necessary. If the hot spot temperature in the transformer can be accurately calculated, it can provide a reference for the heat dissipation and cooling design of the transformer, thereby improving the operating efficiency of the transformer, reducing the occurrence of thermal accidents and prolonging the service life of the transformer.

Combined with the structural characteristics of oil-immersed power transformers, a 50MVA/110kV natural oil-circulating oil-immersed power transformer is used as a prototype. The characteristics of the transformer are studied, and the temperature and location of the hot spot in the transformer can be predicted, so that the accident can be detected in time, so as to prolong the service life of the transformer as much as possible.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a simulation method for obtaining the hot spot temperature of a power transformer under different working conditions. Based on the actual structure of the oil-immersed transformer, a three-dimensional simulation model of the temperature rise of the transformer is established by combining the finite element method and the finite volume method. The influence of electromagnetic field and oil flow on the temperature is considered, and the simulation of the temperature distribution of the transformer hot spot is realized.

To achieve the above object, the present invention provides the following technical solutions:

S1: Establish a three-dimensional physical model of the power transformer;

S2: theoretical analysis of electromagnetic field calculation of power transformers;

S3: Computational theoretical analysis of power transformer fluid and thermal field;

S4: Based on the theoretical analysis of electromagnetic fields and fluid-solid heat, add corresponding physical fields;

S5: According to the actual operating conditions, the field-circuit coupling connection under different working conditions is carried out, and the parameters and boundary conditions are set;

S6: Make Multiphysics Coupling Settings

S7: The model is meshed based on the finite element method, and the temperature distribution of the power transformer and its hot spot temperature location results under different working conditions are obtained by simulation.

Further, step S1 is specifically as follows: the power transformer is a three-dimensional physical model, and during coupling analysis, an important feature of the internal structure of the model is valid and invalid, that is, some features may sometimes need to be ignored according to the type of analysis problem. Therefore, on the basis of the following assumptions, the 50MVA/110kV natural oil circulation oil-immersed power transformer is used as the prototype to carry out 3D modeling:

(1) The high and low voltage windings are simplified into a cylindrical shape, which is convenient for calculation;

(2) The thickness of the insulating layer next to the winding is very thin, so its thickness is ignored;

(3) Both the iron core and the iron yoke are simplified as cylinders;

(4) The electromagnetic relationship of the transformer is mainly determined by the iron core and winding, so the influence of the radiator and structural parts outside the tank is not considered.

Step S2 is specifically, electromagnetic field calculation theory: Maxwell equations are the basis for analyzing the electromagnetic heat field problem, which describe the macroscopic properties of the electromagnetic field, and its differential form is as follows:

Where: D is the electrical displacement; H is the magnetic field strength; B is the magnetic flux density; E is the electric field strength; ρ is the charge density; J is the current density.

In the constitutive relationship, the properties of the material are all set to be isotropic, that is, the magnetic field permittivity ε, the material permeability μ and the electrical conductivity σ are all scalars, E, D, B, H and the properties of the material related.

The specific step S3 is to calculate the temperature field of the transformer based on the fluid flow continuity equation, the momentum equation and the energy equation. The internal temperature field distribution characteristics of oil-immersed power transformers can be studied by numerical calculation method, that is, finite element analysis method.

The oil flow of the oil-immersed power transformer must obey the continuity equation, that is, the mass conservation equation. When the law of mass conservation is applied to the fluid domain of the oil-immersed power transformer, its physical meaning is the difference between the mass of the transformer oil in the oil tank per unit time. The increase is equal to the net mass of transformer oil flowing into the tank in the same time, and the differential form of its fluid flow continuity equation is

where is ρ fluid density, the unit is kg/m ³ ; μ _x , μ _y , μ _z are the velocity components of the velocity vector on the x, y, z axes; t is the time, the unit is s.

If the transformer oil flow is an incompressible flow, ρ is a constant number, and its continuous equation form is:

The momentum equation can be derived according to Newton's second law. When the momentum equation is applied to the fluid domain of an oil-immersed power transformer, its physical meaning is: the increase in the oil flow in the transformer tank is equivalent to the effect of the transformer tank. sum of power. The three components of the momentum equation can be expressed as:

In the formula: p is the pressure, the unit is Pa; τ _xx , τ _xy , τ _xz are the components of the viscous stress τ, the unit is Pa; f _x , f _y , and f _z are the components of the unit mass force.

The energy conservation equation can be derived from the law of thermodynamics, and the law of energy conservation must be obeyed when heat exchange occurs in the fluid. The increment of thermal energy in the transformer tank per unit time is equal to the sum of the heat transferred by the oil flow per unit time, the work done by the force on the transformer tank, and the amount of heat generated in the transformer tank.

Where: E is the total energy of the fluid micelle; h is the enthalpy per unit mass; k _eff is the effective heat transfer coefficient.

Step S4 is specifically, based on the theoretical analysis of the electromagnetic field and the fluid-solid heat, adding corresponding physical fields; that is, adding four physical fields: circuit, magnetic field, heat transfer, and laminar flow.

Step S5 is specifically: according to the actual operation situation, the field-circuit coupling connection under different working conditions is carried out; according to the actual situation of the transformer on-site operation, the model parameters and boundary conditions of each physical field are set, including the heat source of the three-phase iron core, the primary and secondary side Winding heat source, temperature boundary conditions, fluid flow velocity and direction, etc.

The main parameters of the model: the diameter of the iron core is 600mm, the center distance of the core column is 1140mm, and the window height is 1525mm. The type of silicon steel sheet used in the transformer core is 30QG120, the thickness of the lamination is 0.3mm, and the lamination coefficient is 0.97. The rated voltage of the high-voltage side winding is 110kV, the rated current is 262.43A, and the number of winding turns is 629. The rated voltage of the low-voltage side winding is 10.5kv, the rated current is 2749.29A, and the number of winding turns is 104.

Table 1 Physical parameters of winding, iron core and transformer oil

Solid heat transfer includes not only the heat transfer between solids such as windings and iron cores, but also the convective heat transfer of transformers. Therefore, it is necessary to introduce the governing equations of the fluid domain, such as:

为速度场；k为传热系数；Q为内热源。In the formula: ρ is the density of transformer oil; C _p is the heat capacity at atmospheric pressure;

is the velocity field; k is the heat transfer coefficient; Q is the internal heat source.

Set up boundary conditions for heat transfer in solids to constrain the temperature rise characteristics:

where q is the heat flux; n is the normal vector of the outflow on the boundary.

Laminar flow: The research object is a natural oil circulation oil-immersed power transformer, and its internal oil flow velocity is very small, which belongs to the laminar flow model. In engineering research, the transformer oil flow can be approximated as an incompressible fluid:

为主应力张量。Among them: μ is the dynamic viscosity of transformer oil; ρ is the density of transformer oil;

is the principal stress tensor.

The specific step S6 is to perform the coupling setting of the thermal field and the laminar flow field according to the coupling principle, add non-isothermal laminar flow and temperature coupling, and perform the coupling setting of the laminar flow and the heat transfer field.

Step S7 is specifically to mesh the model based on the finite element method, select and refine the meshing accuracy, add coil geometry analysis and transient solution, set the simulation time and step size, and obtain the temperature distribution result of the transformer through simulation.

The beneficial effect of the present invention is that: by adopting the method of the present invention, the hot spot temperature distribution of the transformer under different working conditions can be obtained.

Description of drawings

Fig. 1 is the simulation flow chart of the temperature rise characteristic of oil-immersed transformer of the present invention

Fig. 2 is the heat generation analysis of the oil-immersed transformer of the present invention, that is, the schematic diagram of the transformer loss composition

Fig. 3 is the transformer temperature field solution model diagram of the present invention

FIG. 4 is the equivalent circuit model of the present invention under multiple operating conditions

FIG. 5 is a schematic diagram of the calculation result of the iron core temperature under the rated working condition of the present invention

FIG. 6 is a schematic diagram of the calculation result of the iron core temperature under the overload condition of the present invention

FIG. 7 is a schematic diagram of the calculation result of the iron core temperature when a single-phase ground fault occurs in the present invention

FIG. 8 is a schematic diagram of the calculation result of the temperature of the high and low voltage windings under the rated working conditions of the present invention

FIG. 9 is a schematic diagram of the calculation result of the temperature of the high and low voltage windings under the overload condition of the present invention

Fig. 10 is a schematic diagram of the calculation result of the temperature of the high and low voltage windings during a single-phase ground fault of the present invention

Detailed ways:

The present invention will be described in detail below with reference to the accompanying drawings.

The invention is a simulation method for obtaining the hot spot temperature of a power transformer under different working conditions. Based on the actual structure of the oil-immersed transformer, a three-dimensional simulation model of the temperature rise of the transformer is established by combining the finite element method and the finite volume method. The influence of factors such as electromagnetic field and oil flow on temperature can be used to simulate the temperature distribution of transformer hot spots. Specific steps are as follows:

1. Establish a three-dimensional physical model of the power transformer

The transformer temperature field is established in the finite element software to solve the three-dimensional model, as shown in Figure 3. During the coupled analysis, an important feature of the internal structure of the model is valid and invalid, that is, depending on the type of analysis problem, some features need to be ignored. . Therefore, on the basis of the following assumptions, the 50MVA/110kV natural oil circulation oil-immersed power transformer is used as the prototype to carry out 3D modeling:

(1) The high and low voltage windings are simplified into a cylindrical shape, which is convenient for calculation;

(2) The thickness of the insulating layer next to the winding is very thin, so its thickness is ignored;

(3) Both the iron core and the iron yoke are simplified as cylinders;

(4) The electromagnetic relationship of the transformer is mainly determined by the iron core and winding, so the influence of the radiator and structural parts outside the tank is not considered.

2. Theoretical analysis of electromagnetic field calculation of power transformer

Electromagnetic field calculation theory: Maxwell's equations are the basis for analyzing electromagnetic heat field problems, which describe the macroscopic properties of electromagnetic fields. The differential form is as follows:

Where: D is the electrical displacement; H is the magnetic field strength; B is the magnetic flux density; E is the electric field strength; ρ is the charge density; J is the current density.

In the constitutive relationship, the properties of the material are all set to be isotropic, that is, the magnetic field permittivity ε, the material permeability μ and the electrical conductivity σ are all scalars, E, D, B, H and the properties of the material related. The heat generation is calculated by the loss, and the transformer loss is shown in Figure 2.

3. Computational theoretical analysis of power transformer fluid and thermal field

The oil flow of the oil-immersed power transformer must obey the continuity equation, that is, the mass conservation equation. When the law of mass conservation is applied to the fluid domain of the oil-immersed power transformer, its physical meaning is the difference between the mass of the transformer oil in the oil tank per unit time. The increase is equal to the net mass of transformer oil flowing into the tank in the same time, and the differential form of its fluid flow continuity equation is

In the formula, ρ is the fluid density, the unit is kg/m ³ ; μ _x , μ _y , μ _z are the velocity components of the velocity vector on the x, y, z axes; t is the time, the unit is s.

If the transformer oil flow is an incompressible flow, ρ is a constant number, and its continuous equation form is:

When the momentum equation is applied to the fluid domain of an oil-immersed power transformer, the physical meaning it represents is that the increase in the oil flow in the transformer tank is equivalent to the sum of the forces acting on the transformer tank. The three components of the momentum equation can be expressed as:

In the formula: p is the pressure, the unit is Pa; τ _xx , τ _xy , τ _xz are the components of the viscous stress τ, the unit is Pa; f _x , f _y , and f _z are the components of the unit mass force.

After simplification, we can get:

S _μx = ρf _x +s _x

S _μy = ρf _y +s _y

S _μz = ρf _z +s _z

Among them, S _μx , S _μy , and S _μz are generalized source terms.

S _x , S _y , S _z can be ignored for incompressible fluids.

The energy conservation equation can be derived from the law of thermodynamics, and the law of energy conservation must be obeyed when heat exchange occurs in the fluid. When the law of conservation of energy is applied to the fluid domain of oil-immersed power transformers, its physical meaning is: the increment of thermal energy in the transformer tank per unit time is equal to the heat transferred by the oil flow per unit time, the work done by the force on the transformer tank, and the work done by the transformer tank. The sum of the enthalpy production in the tank. Its expression is:

where E is the total energy of the fluid micelle.

Where: h is the enthalpy per unit mass; K _eff is the effective heat transfer coefficient.

4. Based on the theoretical analysis of electromagnetic fields and fluid-solid heat, add corresponding physical fields;

Add four physical fields of circuit, magnetic field, heat transfer, and laminar flow, and perform coupling: the loss generated by electromagnetic coupling is used as excitation to input the heat transfer field and then coupled with the laminar flow field to obtain the temperature field distribution of the transformer.

5. Carry out field-circuit coupling connection under different working conditions according to the actual operating conditions, and set parameters and boundary conditions; the main parameters of the model: the diameter of the iron core is 600mm, the center distance of the core column is 1140mm, and the window height is 1525mm. The type of silicon steel sheet used in the transformer core is 30QG120, the thickness of the lamination is 0.3mm, and the lamination coefficient is 0.97. The rated voltage of the high-voltage side winding is 110kv, the rated current is 262.43A, and the number of winding turns is 629. The rated voltage of the low-voltage side winding is 10.5kv, the rated current is 2749.29A, and the number of winding turns is 104.

Table 1 Physical parameters of winding, iron core and transformer oil

Solid heat transfer includes not only the heat transfer between solids such as windings and iron cores, but also the convective heat transfer of transformers. Therefore, it is necessary to introduce the governing equations of the fluid domain, such as:

为速度场；k为传热系数；Q为内热源。In the formula: ρ is the density of transformer oil; C _p is the heat capacity at atmospheric pressure;

is the velocity field; k is the heat transfer coefficient; Q is the internal heat source.

Set up boundary conditions for heat transfer in solids to constrain the temperature rise characteristics:

where q is the heat flux; n is the normal vector of the outflow on the boundary.

Laminar flow: The research object is a natural oil circulation oil-immersed power transformer, and its internal oil flow velocity is very small, which belongs to the laminar flow model. In engineering research, the transformer oil flow can be approximated as an incompressible fluid:

为主应力张量。Among them: μ is the dynamic viscosity of transformer oil; ρ is the density of transformer oil;

is the principal stress tensor.

6. Perform multiphysics coupling settings

According to the coupling principle, the coupling setting of the thermal field and the laminar flow field is carried out, the non-isothermal laminar flow and temperature coupling are added, and the laminar flow and the heat transfer field are coupled and set.

7. Meshing and simulation time settings

The model is meshed based on the finite element method, the meshing accuracy is selected to be refined, the coil geometric analysis and transient solution are added, and the simulation time and step size are set, and the temperature distribution results of the transformer are obtained from the simulation. post-processing. The simulation first obtains the temperature distribution of the hot spot core and winding of the transformer under different working conditions. The equivalent circuit diagram under different working conditions is shown in Figure 3. After the simulation is completed, the core temperature distribution under multiple working conditions is shown in Figure 5, Figure 6, As shown in Figure 7, the temperature distributions of the windings under multiple operating conditions are shown in Figure 8, Figure 9, and Figure 10.

The above preferred embodiments are only to illustrate the technical solutions of the present invention, and are not limited thereto. For those skilled in the art, they can modify, replace or optimize the form and details without departing from the scope of the claims. etc. various changes.

Claims (8)

1. a simulation method for obtaining hot spot temperature under different working conditions of power transformer, is characterized in that, comprises: S1: Establish a three-dimensional physical model of the power transformer; S2: theoretical analysis of electromagnetic field calculation of power transformers; S3: Computational theoretical analysis of power transformer fluid and thermal field; S4: Based on the theoretical analysis of electromagnetic fields and fluid-solid heat, add corresponding physical fields; S5: According to the actual operating conditions, the field-circuit coupling connection under different working conditions is carried out, and the parameters and boundary conditions are set; S6: Make Multiphysics Coupling Settings S7: The model is meshed based on the finite element method, and the temperature distribution of the power transformer and its hot spot temperature location results under different working conditions are obtained by simulation. 2. a kind of simulation method of obtaining hot spot temperature under different working conditions of power transformer according to claim 1, is characterized in that: the described power transformer of S1 is a three-dimensional physical model, when carrying out coupling analysis, the internal structure of the model has an important Features are valid and invalid, that is, some features need to be ignored according to the type of analysis problem. Therefore, on the basis of the following assumptions, the 50MVA/110kV natural oil circulation oil-immersed power transformer is used as the prototype to carry out 3D modeling: (1) The high and low voltage windings are simplified into a cylindrical shape, which is convenient for calculation; (2) The thickness of the insulating layer next to the winding is very thin, so its thickness is ignored; (3) Both the iron core and the iron yoke are simplified as cylinders; (4) The electromagnetic relationship of the transformer is mainly determined by the iron core and winding, so the influence of the radiator and structural parts outside the tank is not considered. 3. a kind of simulation method of obtaining hot spot temperature under different working conditions of power transformer according to claim 2, is characterized in that: step S2 is specifically, electromagnetic field calculation theory: Maxwell equation system is the basis for analyzing electromagnetic heat field problem , which describes the macroscopic properties of the electromagnetic field, and its differential form is as follows:

Where: D is the electrical displacement; H is the magnetic field strength; B is the magnetic flux density; E is the electric field strength; ρ is the charge density; J is the current density.

In the constitutive relationship, the properties of the material are all set to be isotropic, that is, the magnetic field permittivity ε, the material permeability μ and the electrical conductivity σ are all scalars, E, D, B, H and the properties of the material related. 4. a kind of simulation method of obtaining hot spot temperature under different working conditions of power transformer according to claim 3, is characterized in that: step S3 is specifically, calculates the temperature field of transformer based on fluid flow continuity equation, momentum equation and energy equation . The increase in the mass of the transformer oil in the oil tank per unit time is equal to the net mass of the transformer oil flowing into the oil tank in the same time. The differential form of the fluid flow continuity equation is:

ρ is the fluid density, the unit is kg/m ³ ; μ _x , μ _y , μ _z are the velocity components of the velocity vector on the x, y, z axes; t is the time, the unit is s. The increase in oil flow in the transformer tank is equal to the sum of the forces experienced by the transformer tank. The three components of the momentum equation are expressed as:

In the formula: p is the pressure, the unit is Pa; τ _xx , τ _xy , τ _xz are the components of the viscous stress τ, the unit is Pa; f _x , f _y , and f _z are the components of the unit mass force. The energy conservation equation can be derived from the law of thermodynamics, and the law of energy conservation must be obeyed when heat exchange occurs in the fluid. The increment of thermal energy in the transformer tank per unit time is equal to the sum of the heat transferred by the oil flow per unit time, the work done by the force on the transformer tank, and the amount of heat generated in the transformer tank.

Where: E is the total energy of the fluid micelle; h is the enthalpy per unit mass; k _eff is the effective heat transfer coefficient. 5. A simulation method for obtaining hot spot temperature under different working conditions of a power transformer according to claim 4, characterized in that: step S4 is specifically, adding four physical fields of magnetic field, circuit, heat transfer, and laminar flow, wherein electromagnetic field The loss caused by the coupling is used as the excitation input heat transfer field and then coupled with the laminar flow field to obtain the temperature field distribution of the transformer. 6. A simulation method for obtaining hot spot temperature under different working conditions of a power transformer according to claim 5, characterized in that: step S5 is specifically: performing field-circuit coupling connection under different working conditions according to actual operating conditions; According to the actual situation of on-site operation, set the model parameters and boundary conditions of each physical field, including the heat source of the three-phase iron core, the heat source of the primary and secondary windings, the temperature boundary conditions, the flow velocity and direction of the fluid, etc. 7. The simulation method for obtaining the hot spot temperature under different working conditions of the power transformer according to claim 6, wherein step S6 is specifically, according to the coupling principle, the coupling setting of the thermal field and the laminar flow field is performed, and a non-isothermal field is added. Laminar flow and temperature coupling. 8. The simulation method for obtaining the hot spot temperature under different working conditions of the power transformer according to claim 7, characterized in that: step S6 is specifically to perform mesh division on the model based on the finite element method, and the division precision is selected Refinement, adding coil geometry analysis and transient solution, and setting the simulation time and step size, the simulation results of the temperature distribution of the transformer.

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