Simulation method for operating characteristics of gas relay in arc fault of transformer

Abstract

The invention discloses a simulation method for operating characteristics of a gas relay in an arc fault of a transformer. The method comprises the following steps: S1, establishing a 1: 1 equivalent transformer and gas relay three-dimensional simulation model; s2, the three-dimensional calculation model is imported into an ANSYS Fluent platform, and grid model construction and simulation setting are completed; s3, transformer arc fault heavy gas oil flow surging calculation is achieved in an ANSYS Fluent platform, and an oil flow velocity result at the installation position of a gas relay of a transformer oil conservator connecting pipe is obtained; s4, simulating the transient action characteristics of the gas relay under the impact action of the fault oil flow; according to the method, the fault oil flow evolution rule under the arc fault in the transformer can be revealed, and transient simulation calculation of the action process of the gas relay under dynamic oil flow impact during the internal fault of the transformer is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of non - electrical protection of power system transformers, and particularly to a simulation method for the action characteristics of a transformer arc - fault gas relay. Background Art

[0002] The transformer gas - actuated relay plays a crucial role in transformer fault protection. In the case of a severe gas fault, the gas relay detects a serious fault through the surge of oil flow and issues a tripping signal, effectively preventing further damage to the transformer and ensuring equipment safety. However, in recent years, transformers equipped with gas protection have still experienced explosion and fire accidents during internal faults, which has raised doubts in the industry about its response ability and accuracy in dealing with arc faults. Especially in the face of high - energy faults, the transient action characteristics of the gas relay under the impact of oil flow are not clear, and there is a certain degree of uncertainty in setting the trigger angle of the baffle flip and the flow velocity action threshold value when it faces high - energy faults. Summary of the Invention

[0003] The purpose of the present invention is to overcome the above - mentioned deficiencies and provide a simulation method for the action characteristics of a transformer arc - fault gas relay, which can reveal the evolution law of fault oil flow under internal arc faults of the transformer and realize the transient simulation calculation of the action process of the gas relay under dynamic oil flow impact during internal faults of the transformer.

[0004] To solve the above - mentioned technical problems, the technical solution adopted by the present invention is as follows: A simulation method for the action characteristics of a transformer arc - fault gas relay, which includes the following steps; S1. Establish a 1:1 equivalent three - dimensional simulation model of the transformer and the gas relay; S2. Import the three - dimensional calculation model into the ANSYS Fluent platform to complete the construction of the mesh model and simulation settings; S3. Implement the calculation of the severe gas oil flow surge of the transformer arc - fault in the ANSYS Fluent platform to obtain the oil flow velocity results at the installation location of the gas relay on the connecting pipe of the transformer conservator; S4. Simulate the transient action characteristics of the gas relay under the action of the fault oil flow impact.

[0005] Preferably, the step S1 is specifically: Select SolidWorks to establish a 1:1 equivalent three - dimensional simulation model of the transformer and the gas relay.

[0006] Preferably, the step S2 includes the following steps: S2.1. Import the three - dimensional calculation model of the transformer and the gas relay into the ANSYS Fluent platform; S2.2. Set the solver as a transient pressure - based solver; S2.3. Select the structured grid as the grid model division method and adjust the grid size according to the calculation requirements; check the quality of the grid to ensure that there are no highly distorted grid cells; S2.4. Set the turbulence model and solution parameters.

[0007] Preferably, in S2.3, the process of adjusting the grid size according to the calculation requirements is as follows: for regions with boundary layers or drastic changes in the flow field, select a smaller grid size.

[0008] Preferably, the turbulence model in S2.4 is model.

[0009] Preferably, the step S3 includes the following steps: S3.1. Calculate the bubble-liquid boundary velocity under arc fault; S3.2. Update the instantaneous fluid field according to the bubble-liquid boundary velocity; S3.3. Calculate the heavy gas oil flow surge during transformer arc fault on the ANSYS Fluent platform according to the mass conservation equation, momentum conservation equation and energy conservation equation; S3.4. Set a flow velocity monitoring point at the installation location of the gas relay in the conservator connecting pipe to observe the flow velocity change and obtain the oil flow velocity result at the installation location of the gas relay in the transformer conservator connecting pipe.

[0010] Preferably, the calculation formula for calculating the bubble-liquid boundary velocity under arc fault in S3.1 is: ; In the formula, R is the bubble radius, is the bubble velocity, is the bubble acceleration, l is the straight-line distance from the fluid boundary to the bubble wall boundary, P l is the pressure at the fluid boundary, ρ is the density, γ The value is 1.352, U gas is the internal energy of the bubble, V gas is the volume of the arc bubble, σ is the surface tension coefficient.

[0011] Preferably, in the step S4, take the above oil flow velocity result at the installation location of the gas relay as the input condition of the gas relay inlet, and simulate the transient action characteristics of the gas relay under the impact of the fault oil flow, which specifically includes the following steps: S4.1. Establish a mathematical model based on the principle of moment balance. During the rotation of the baffle, it is subjected to three types of moments: gravitational moment, oil flow impact moment, and spring resistance moment. S4.2. For the surface stress on a plane, which is a function of the radius vector and the surface unit vector, the fluid impact resistance moment acting on the baffle is written as follows: ; where P is the stress tensor, dS is the area element on the surface, n is the surface unit normal vector, , representing the radius vector from any point ( x, y, z ) on the baffle to the rotation axis point ( x 0, y 0, z 0); Since the baffle rotates around the rotation axis at all times in the problem of baffle rotation, only the fluid impact moment in the XY plane is involved, and it is considered that the fluid direction is always horizontal. Therefore, only the impact moment in the X direction needs to be considered when solving. The above formula is written as: ; where, P xz represents the shear stress acting in the z direction on the x-direction surface, P xy represents the shear stress acting in the y direction on the x-direction surface. The gravitational moment can be expressed as: ; where m represents the mass of the baffle, d represents the perpendicular distance from the center of mass to the rotation axis, represents the angle between the baffle and the vertical direction. The resistance moment of the spring can be expressed according to the definition of moment and Hooke's law as: ; where, l represents the length of the lever arm from the spring action point to the rotation axis, represents the angle between the spring force direction and the lever arm, k represents the spring stiffness, is the spring deformation. The rotational equilibrium condition of the baffle is determined by the total moment being zero: ; The total moment divided by the moment of inertia of the baffle is the angular velocity of the baffle rotation, which is expressed in difference format as: ; where, and represent the angular velocities of the baffle at the nth time step and the (n - 1)th time step respectively, M represents the total moment acting on the baffle, J represents the moment of inertia of the baffle, represents the time step; S4.3. Start simulating the movement of the baffle under the impact of the fault oil flow according to the resultant force received, and the movement of the baffle is realized through the dynamic mesh technology; S4.4. Record the calculation results.

[0012] Preferably, in the above S4.3, the calculation formula for starting to simulate the movement of the baffle under the impact of the fault oil flow according to the resultant force received, and realizing the movement of the baffle through the dynamic mesh technology is: ; In the formula, u is the flow velocity vector, Γ is the diffusion coefficient, represents the source term of u g is the mesh velocity of the moving mesh, is the physical quantity being transported the gradient of, dA is the area differential vector, is the control volume boundary, V is the control volume, is the density of the insulating oil.

[0013] Advantages of the present invention: 1. The present invention can reveal the evolution law of the fault oil flow under the internal arc fault of the transformer, and realize the transient simulation calculation of the action process of the gas relay under the dynamic oil flow impact during the internal fault of the transformer.

[0014] 2. The method of the present invention comprehensively considers factors such as the gas production characteristics of the arc fault, the oil flow surging speed, and the mechanical response characteristics of the gas relay, provides a new simulation analysis tool, helps to optimize the protection performance of the gas relay, and ensures the safety of the equipment under fault conditions.

[0015] 3. Through the coupled simulation method of computational fluid dynamics and mechanical system, the present invention can simulate the generation of gas, the oil flow surging, and the response behavior of the gas relay during the internal arc fault of the transformer, and reveals the whole process of how the fault gas promotes the oil flow surging and triggers the relay action; compared with the prior art, the present invention can provide more accurate evaluation data of the action process and protection effect of the gas relay, optimize the setting parameters of the gas relay, and improve its response speed and accuracy under arc fault conditions. Description of the Drawings

[0016] Figure 1 It is the force analysis diagram of the baffle of the transformer gas relay in an embodiment of the present invention.

[0017] Figure 2Fluid domain mesh division diagram of a gas relay according to an embodiment of the present invention.

[0018] Figure 3 Internal three-dimensional streamline diagram of a gas relay according to an embodiment of the present invention.

[0019] Figure 4 Two-dimensional velocity contour diagram of a gas relay according to an embodiment of the present invention. Detailed implementation manners

[0020] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] Embodiment 1: The technical solution in the present invention is based on a profound understanding of the complex coupling relationship between the generation of fault gases and the oil flow surge under the condition of internal arc faults in transformers. This technical solution comprehensively considers the interactions of multiple physical fields such as gas generation, oil flow, and relay mechanical response, providing a solid theoretical basis for accurately simulating the operating characteristics of gas relays under transformer arc faults. Through detailed modeling and simulation calculations, the present invention can reflect the oil flow surge process during internal arc faults in transformers and accurately predict the response behavior of gas relays. This technical solution includes the following steps: S1. Establish a 1:1 equivalent transformer and gas relay three-dimensional simulation model; S2. Import the three-dimensional calculation model into the ANSYS Fluent platform to complete the construction of the mesh model and simulation settings; S3. Implement the calculation of heavy gas oil flow surge at the installation location of the gas relay in the connecting pipe of the transformer conservator in the ANSYS Fluent platform to obtain the oil flow velocity results at the installation location of the gas relay in the connecting pipe of the transformer conservator; S4. Simulate the transient operating characteristics of the gas relay under the impact of fault oil flow.

[0022] Preferably, step S1 is specifically: Select SolidWorks to establish a 1:1 equivalent transformer and gas relay three-dimensional simulation model.

[0023] Preferably, step S2 includes the following steps: S2.1. Import the three-dimensional transformer and gas relay calculation model into the ANSYS Fluent platform; S2.2. Set the solver as a transient pressure-based solver; S2.3. Select structured mesh as the mesh model division method, adjust the mesh size according to the calculation requirements; check the quality of the mesh to ensure that there are no highly distorted mesh elements; S2.4. Set the turbulence model and solution parameters.

[0024] Preferably, in the step S2.3, the process of adjusting the grid size according to the calculation requirements is as follows: for the regions with boundary layers or drastic changes in the flow field, smaller grid sizes are selected.

[0025] Preferably, the turbulence model in the step S2.4 is model.

[0026] Preferably, the step S3 includes the following steps: S3.1. Calculate the bubble-liquid boundary velocity under arc fault; S3.2. Update the instantaneous fluid field according to the bubble-liquid boundary velocity; S3.3. Calculate the heavy gas oil flow surge during transformer arc fault on the ANSYS Fluent platform according to the mass conservation equation, momentum conservation equation and energy conservation equation; S3.4. Set a flow velocity monitoring point at the installation location of the gas relay in the oil conservator connecting pipe to observe the flow velocity change and obtain the oil flow velocity result at the installation location of the gas relay in the transformer oil conservator connecting pipe.

[0027] Preferably, the calculation formula for the bubble-liquid boundary velocity under arc fault in the step S3.1 is: ; In the formula, R is the bubble radius, is the bubble velocity, is the bubble acceleration, l is the straight-line distance from the fluid boundary to the bubble wall boundary, P l is the pressure at the fluid boundary, ρ is the density, γ The value is 1.352, U gas is the internal energy of the bubble, V gas is the volume of the arc bubble, σ is the surface tension coefficient.

[0028] Preferably, in the step S4, taking the above oil flow velocity result at the installation location of the gas relay as the inlet input condition of the gas relay, the transient action characteristics of the gas relay under the impact of the fault oil flow are simulated, which specifically includes the following steps: S4.1. Establish a mathematical model through the principle of moment balance. The baffle is subjected to three forms of torques during the rotation process: gravitational torque, oil flow impact torque and spring resistance torque; S4.2. For the surface stress received by a plane, which is a function of the vector radius and the surface unit vector, the fluid impact resistance torque received by the baffle is written as: ; where P is the stress tensor, dS is the area element on the surface, and n is the unit normal vector of the surface. , which represents the radius vector from any point ( x, y, z ) on the baffle to the axis of rotation point ( x 0, y 0, z 0); Since the baffle rotates around the axis of rotation at all times in the problem of baffle rotation, it only involves the fluid impact moment in the XY plane. And it is considered that the fluid direction is always horizontal. Therefore, only the impact moment in the X direction needs to be considered when solving. The above formula can be written as: ; where P xz represents the shear stress acting in the z direction on the x-direction surface, P xy represents the shear stress acting in the y direction on the x-direction surface. The gravitational moment can be expressed as: ; where m represents the mass of the baffle, d represents the perpendicular distance from the centroid to the axis of rotation, represents the angle between the baffle and the vertical direction. The resistance moment of the spring can be expressed according to the definition of moment and Hooke's law as: ; where l represents the length of the lever arm from the spring action point to the axis of rotation, represents the angle between the spring force direction and the lever arm, k represents the spring stiffness, is the spring deformation. The baffle rotation equilibrium condition is determined by the total moment being zero: ; The total moment divided by the moment of inertia of the baffle is the angular velocity of the baffle rotation, which is expressed in a difference format as: ; where and represent the angular velocities of the baffle at the nth time step and the (n - 1)th time step respectively, M represents the total moment acting on the baffle, J represents the moment of inertia of the baffle, represents the time step size; S4.3. Start simulating the motion of the baffle under the impact of the failed oil flow according to the resultant force condition. The baffle motion is realized through the dynamic mesh technology; S4.4. Record the calculation results.

[0029] Preferably, in S4.3, the movement of the baffle under the impact of the fault oil flow can be simulated according to the resultant force received. The calculation formula for the movement of the baffle realized by the dynamic mesh technology is as follows: ; In the formula, u is the velocity vector, Γ is the diffusion coefficient, represents the source term of, u g is the grid velocity of the moving grid, is the physical quantity being transported the gradient of, dA is the area differential vector, is the control volume boundary, V is the control volume, is the density of the insulating oil.

[0030] Example 2: Refer to Figure 2 , in this example, theoretical modeling and simulation calculations are carried out for the action characteristics of the typical baffle-float-spring structure of the gas relay.

[0031] Refer to Figure 2 , a simulation method for the action characteristics of a transformer arc fault gas relay in this example includes the following steps: Step 1: Select SolidWorks to establish a 1:1 equivalent three-dimensional simulation model of the transformer and the gas relay.

[0032] Step 2: Import the three-dimensional transformer and pressure relief valve calculation models into the ANSYS Fluent platform; set the solver as the transient pressure-based solver.

[0033] Step 3: Select the structured grid as the grid model division method, adjust the grid size according to the calculation requirements, and select a smaller grid size for areas with boundary layers or drastic changes in the flow field.

[0034] Step 4: Check the quality of the grid to ensure that there are no highly distorted grid cells.

[0035] Step 5: Set the turbulence model as model: ; ; In the formula, is the density, k is the turbulence energy, u j is the velocity component, is the turbulence viscosity, P k is the turbulence energy generation term, is a constant, D k is the turbulent diffusion term, is the turbulent frequency, and are constants.

[0036] Step 6: Calculate the bubble - liquid boundary velocity under arc fault, and the calculation formula is: ; In the formula, R is the bubble radius, is the bubble velocity, is the bubble acceleration, l is the straight - line distance from the fluid boundary to the bubble wall boundary, is the density, the value is 1.352, U gas is the internal energy of the bubble, V gas is the volume of the arc bubble, is the surface tension coefficient.

[0037] Step 7: Update the instantaneous fluid field according to the bubble - liquid boundary velocity.

[0038] Step 8: Set a flow velocity monitoring point at the installation location of the gas relay in the oil conservator connecting pipe to observe the flow velocity change, and obtain the oil flow velocity result at the installation location of the gas relay in the transformer oil conservator connecting pipe during the calculation process.

[0039] Step 9: Calculate the heavy - gas oil flow surging during transformer arc fault on the ANSYS Fluent platform according to the mass conservation equation, momentum conservation equation and energy conservation equation.

[0040] Step 10: Use the above - mentioned oil flow velocity result at the installation location of the gas relay as the input condition at the gas relay inlet, and start the simulation of the transient action process of the gas relay under the impact of the fault oil flow.

[0041] Step 11: Refer to Figure 1 , during the rotation process of the baffle, it is mainly subjected to three forms of torques: gravitational torque, oil flow impact torque and spring resistance torque. Its motion situation is determined according to the torque balance principle. For the surface stress received by a plane, it is a function of the radius vector and the surface unit vector. Thus, the fluid impact resistance torque received by the baffle can be written as: ; Among them, , represents any point ( x, y, z ) on the baffle to the rotation axis point ( x 0, y 0, z0) radius vector. Since the baffle rotates around the rotation axis at all times in the problem of baffle rotation, it only involves the fluid impact moment in the XY plane. And it is considered that the fluid direction is always horizontal. Therefore, only the impact moment in the X direction needs to be considered when solving. The above formula can be written as: ; The gravity moment can be expressed as: ; The resistance moment of the spring can be expressed according to the definition of moment and combined with Hooke's law as: ; The total moment can be written as: ; The total moment divided by the moment of inertia of the baffle is the angular velocity of the baffle rotation, which is expressed in differential format as: ; Step 12: According to the resultant force situation, the movement of the baffle under the impact of the fault oil flow can be simulated. The movement of the baffle is specifically realized by the dynamic mesh technology, and the calculation formula is: ; In the formula, u is the velocity vector, Γ is the diffusion coefficient, represents the source term of, u g is the mesh velocity of the moving mesh, is the physical quantity to be transported the gradient of, dA is the area differential vector, is the control volume boundary, V is the control volume, is the density of the insulating oil.

[0042] Step 13: Record the calculation results.

[0043] Through the accurate simulation method of fluid-structure coupling, the present invention successfully simulates the action characteristics of the gas relay and the surging process of the internal oil flow when an arc fault occurs inside the transformer. This method can accurately reflect the dynamic changes of the oil flow and the response process of the relay, providing reliable data support for optimizing the design and performance of the gas relay.

[0044] Figure 3 and Figure 4 are the simulation calculation results of specific embodiments. Figure 3 is the three-dimensional streamline diagram inside the gas relay, Figure 4It is the two-dimensional velocity cloud diagram of the gas relay. It can be seen from the simulation results that in the initial stage, the gas relay has not yet felt the impact of the oil flow, so the insulating oil inside it is in a random motion state and no flow velocity is generated. At the moment of 90 ms, the inlet flow velocity of the gas relay has already exceeded 1 m / s. As the inlet flow velocity gradually increases, the impact of the oil flow becomes more significant. With the obvious rotation of the baffle, some insulating oil also begins to flow through the gap opened at the bottom of the baffle when flowing through the internal structure of the relay. Due to the inertia of the insulating oil and the speed maintained by the baffle during rotation, the baffle may continue to rotate and generate a larger horizontal displacement and rotation angle in a period of time afterwards, which will trigger the gas relay to send out an action signal.

[0045] The above embodiments are only the preferred technical solutions of the present invention and should not be regarded as limitations on the present invention. The protection scope of the present invention should be the technical solutions recorded in the claims, including the equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, the equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A method for simulating the action characteristics of a transformer arc fault gas relay, characterized in that: It includes the following steps; S1. Establish a 1:1 equivalent transformer and gas relay three-dimensional simulation model; S2, import the 3D computational model into the ANSYS Fluent platform to complete the mesh model construction and simulation settings; S3. Implement the calculation of heavy gas oil flow surge in transformer arc fault in ANSYS Fluent platform, and obtain the oil flow velocity result at the installation point of gas relay in transformer oil pillow connecting pipe; S4. Simulate the transient action characteristics of the gas relay under the impact of fault oil flow.

2. The method for simulating the action characteristics of a transformer arc fault gas relay according to claim 1, characterized in that: The step S1 specifically includes: using SolidWorks to establish a 1:1 equivalent transformer and gas relay three-dimensional simulation model.

3. The method for simulating the action characteristics of a transformer arc fault gas relay according to claim 1, characterized in that: The step S2 comprises the following steps: S2.

1. Import the three-dimensional transformer and gas relay calculation model into the ANSYS Fluent platform; S2.2, set the solver to transient pressure-based solver; S2.

3. Select structured grid as the grid model division method and adjust the grid size according to the calculation requirements; check the quality of the grid to ensure that there are no highly distorted grid cells; S2.

4. Set the turbulence model and solution parameters.

4. The method for simulating the action characteristics of a transformer arc fault gas relay according to claim 3, characterized in that: In S2.3, the process of adjusting the grid size according to the calculation requirements is: for the boundary layer or the area where the flow field changes drastically, a smaller grid size is selected.

5. The method for simulating the action characteristics of a transformer arc fault gas relay according to claim 3, characterized in that: The turbulence model in S2.4 is Model.

6. The method for simulating the action characteristics of a transformer arc fault gas relay according to claim 1, characterized in that: The step S3 comprises the following steps: S3.

1. Calculate the bubble-liquid boundary velocity under arc fault; S3.2, updating the instantaneous fluid field according to the bubble-liquid boundary velocity; S3.

3. Calculate the heavy gas oil flow surge of transformer arc fault based on the mass conservation equation, momentum conservation equation and energy conservation equation on the ANSYS Fluent platform; S3.

4. Set a flow rate monitoring point at the installation location of the gas relay on the oil pillow connecting pipe to observe the flow rate changes and obtain the oil flow rate results at the installation location of the gas relay on the transformer oil pillow connecting pipe.

7. The method for simulating the action characteristics of a transformer arc fault gas relay according to claim 6, characterized in that: The calculation formula for calculating the bubble-liquid boundary velocity under arc fault in S3.1 is: ； In the formula, R is the bubble radius, is the bubble velocity, is the bubble acceleration, l is the straight-line distance from the fluid boundary to the bubble wall boundary, P l is the pressure at the fluid boundary, ρ is the density, γ The value is 1.352, U gas is the bubble internal energy, V gas is the arc bubble volume, σ is the surface tension coefficient.

8. The method for simulating the action characteristics of a transformer arc fault gas relay according to claim 1, characterized in that: In the step S4, the oil flow velocity result at the installation location of the gas relay is used as the inlet input condition of the gas relay to simulate the transient action characteristics of the gas relay under the impact of the fault oil flow, which specifically includes the following steps: S4.

1. A mathematical model is established based on the principle of moment balance. The baffle is subjected to three types of moments during rotation: gravity moment, oil flow impact moment, and spring resistance moment. S4.

2. The surface stress on a plane is a function of the radius vector and the surface unit vector. The fluid impact resistance moment on the baffle is written as: ； Where P is the stress tensor, dS is the area element on the surface, n is the surface unit normal vector, , indicating that any ( x, y, z )One point to the pivot point( x 0, y 0, z 0); Since the baffle rotates around the axis of rotation all the time in the baffle rotation problem, it only involves the fluid impact moment in the XY plane, and it is assumed that the fluid direction is always horizontal, so when solving, only the impact moment in the X direction needs to be considered, and the above formula can be written as: ； in, P xz represents the shear stress acting on the x-direction surface along the z-direction, P xy represents the shear stress acting on the x-direction surface along the y-direction, and the gravity moment can be expressed as: ； Where m represents the mass of the baffle, d represents the vertical distance from the center of mass to the axis of rotation, It represents the angle between the baffle and the vertical direction, and the resistance torque of the spring. According to the definition of torque and combined with Hooke's law, it can be expressed as: ； in, l It represents the length of the force arm from the spring action point to the rotating shaft. It represents the angle between the spring force direction and the lever arm. k represents the spring stiffness, is the spring deformation, and the baffle rotation equilibrium condition is determined by the total moment being zero: ； The total torque divided by the moment of inertia of the baffle is the angular velocity of the baffle, which is expressed in differential format as: ； in, and They represent the angular velocity of the baffle at the nth time step and the n-1th time step respectively, M represents the total torque acting on the baffle, J represents the moment of inertia of the baffle, represents the time step; S4.

3. According to the resultant force, the movement of the baffle under the impact of the fault oil flow can be simulated, and the movement of the baffle is realized by the dynamic grid technology; S4.

4. Record the calculation results.

9. The method for simulating the action characteristics of a transformer arc fault gas relay according to claim 1, characterized in that: In S4.3, the movement of the baffle under the impact of the fault oil flow can be simulated according to the resultant force. The calculation formula for the movement of the baffle realized by the dynamic grid technology is: ； In the formula, u is the velocity vector, Γ is the diffusion coefficient, express The source term of u g is the mesh speed of the moving mesh, is the physical quantity transported The gradient of , dA is the area element vector, is the control volume boundary, V is the control volume volume, is the density of the insulating oil.

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