CN108646156B - A method for judging the insulation state in GIS - Google Patents

Abstract

The invention discloses a method for judging insulation states in GIS, which comprises the following steps of 1, calculating a critical breakdown electric field, 2, calculating electric field distribution under different working conditions, 3, defining an insulation margin as a difference value of the critical breakdown electric field in the step1 and the space electric field intensity in the step2 to be used as a basis for judging insulation in the GIS, 4, calculating coupling between a temperature field and a flow field, 5, calculating SF in the GIS according to the result in the step4₆A gas density distribution; 6. SF based on step5₆And (3) calculating a critical breakdown electric field under the gas density distribution condition through the step1, calculating electric field distribution under different working conditions through the step2, wherein breakdown can occur in the GIS if the insulation margin is less than or equal to 0, and breakdown cannot occur in the GIS if the insulation margin is greater than 0. The invention considers SF caused by temperature rise of the bus and the shell₆The gas distribution variation factor provides sets of GIS operation state comprehensive judgment basis.

Description

A method for judging the insulation state in GIS

technical field

The invention relates to the technical field of high-voltage insulation, and more particularly, to a method for judging the insulation state in a GIS.

Background technique

The sulfur hexafluoride gas-insulated fully enclosed power distribution device is referred to as GIS for short. Among the various fault types of GIS equipment, the probability of insulation faults is relatively high, accounting for about 51% of the total faults. When the insulation failure of GIS equipment occurs, it will cause great harm to the stable operation of the power grid. The fundamental reason for the occurrence of insulation failure is the defect in the design of the main conductor of the existing GIS busbar. The current GIS internal insulation design is based on: 1. Calculate whether the electric field distribution of the busbar under different structures meets the insulation requirements; 2. Calculate whether the temperature rise of the equipment exceeds the allowable operating conditions. In the design of GIS internal insulation, the temperature rise of the main conductor (GIS busbar) has not been fully considered, causing SF ₆ to flow and cause uneven distribution of internal SF ₆ gas, which in turn causes the insulation level at local locations to be much lower than the average. When the electric field is applied, the dielectric strength of the lower part of the SF ₆ gas density will be insufficient and the gas breakdown will occur.

At present, in the design and research of power equipment, partial discharge is often considered when determining the insulation strength of the equipment. Empirical formulas or a single physical field are often used for research, and the influence of SF ₆ gas flow on the internal insulation of GIS is rarely considered. It is impossible to accurately judge the insulation level in the GIS.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to propose a method for judging the insulation state in the GIS. Under the condition of long-term flow of SF ₆ gas, the heating of the bus will affect the distribution of SF ₆ gas density, resulting in uneven distribution of insulation strength inside the GIS, and there are areas with weak insulation. Therefore, the present invention is based on the uneven distribution of SF ₆ gas under long-term flow conditions. A method for judging the internal insulation of GIS is proposed.

The purpose of the present invention is to be achieved through the following technical solutions: design a method for judging the insulation state in a GIS, and the method comprises the following steps:

Step1, calculate the critical breakdown electric field.

In Step 1, the Saha ionization equilibrium equation is used to solve the dielectric breakdown field strength, as described in formula (1),

Among them, n _e , n _r and n _r+1 are the corresponding electron density and particle density, Z _r and Z _r+1 are the partition functions of particles, k, h and _me are Boltzmann constant, Planck Constant and electron mass, _{E 1, r+1} is the ionization energy required for the (r+1) order ionization reaction, Te and _Th are the temperature of the electron and the temperature of the heavy particle, respectively.

According to the ionization equilibrium theory, when the space charge field is approximately equal to the external electric field, the electron avalanche will gradually form a flow column. The electric field E _r when the electron avalanche occurs is in a spherical region with a radius of r. The calculation formula is as shown in formula (2). stated,

Through the derivation of formula (2), we can get,

Among them, _Er is the dielectric breakdown field strength, _e is the amount of charge, ne is the electron density in a unit volume, k is the Boltzmann constant, _E is the space electric field strength, and Te is the electric field temperature. The value is also different from the case of electric field.

The breakdown field strength E _b is related to the roughness and curvature of the main conductor surface, therefore, the breakdown field strength E _b is as described in equation (4),

E _b = K _h K _f E _r (4)

Among them, K _h is the main conductor curvature coefficient, K _{f is} the main conductor surface roughness coefficient, and E _r is the dielectric breakdown field strength obtained according to the ionization equilibrium theory.

Step2, calculate the electric field distribution under different working conditions.

The calculation of the electrostatic field involves solving the Laplace equation within the solution region defined by the boundary conditions. Generally, the surface of the electrode is the boundary condition for applying the solution, and the area outside the electrode is the solution domain of the overall model. At this time, the voltage value is generally selected as the load degree of freedom, and it is applied to the electrode surface, and the entire solution domain should satisfy the Laplace equation.

In Step 2, the calculation of the electric field distribution is to solve the pull equation in the restricted region of the second type of boundary conditions, as described in formula (5),

为电位，电场强度与电位之间的关系为：in,

is the electric potential, and the relationship between the electric field strength and the electric potential is:

When calculating the electric field, it is also necessary to consider the situation under different working conditions:

(1) The lightning impulse condition can be expressed by the following formula:

Among them, A is the peak value of lightning impulse voltage, and τ ₁ and τ ₂ are the time constants of wave tail and wave front, respectively.

(2) Very fast transient voltage VFTO, expressed by formula (8):

Among them, k ₀ , k ₁ ...... k ₈ and l ₁ , l ₂ ...... l ₈ are the overvoltage coefficients, and ω is the voltage angular frequency, and the values are given in Table 1 below.

Table 1 Values of Overvoltage Coefficient and Voltage Corner Frequency

k₀ k₁ k₂ k₃ k₄ k₅ -1.496*10⁵ 8.051*10⁶ 8.171*10⁴ 1.143*10⁵ -6.379*10⁴ -2.652*10⁴ k₆ k₇ k₈ l₁ l₂ l₃ 4.041*10³ 4.989*10⁴ 3.477*10⁴ -1.8*10⁵ -3.232*10⁴ 8.983*10⁴ l₄ l₅ l₆ l₇ l₈ ω -3.791*10⁴ -3.065*10⁴ -5.037*10⁴ -3.314*10⁴ 8.635*10⁴ 1.046*10⁷

(3) In the case of power frequency voltage, the power frequency voltage equation is selected as:

u(t)=A×sin(ωt) (9)

Among them, A is the peak value of the power frequency voltage, and ω is the voltage angular frequency. Since it is a power frequency, the value of ω is 100π.

Step 3, define the insulation margin as the difference between the critical breakdown electric field of Step 1 and the spatial electric field strength of Step 2, as the basis for judging the internal insulation of the GIS.

In Step 3, define the insulation margin as the basis for judging the insulation in the GIS, wherein the insulation margin is as described in formula (10),

E _m =E _b -E (10)

Among them, _Em is the breakdown margin, E _b is the breakdown field strength, and E is the space electric field strength.

Step4, the coupling calculation of temperature field and flow field.

For the calculation of the temperature field, an appropriate heat source and heat transfer method should be selected. The heat source mainly includes the resistance loss of the busbar and the heat generated by the eddy current loss of the casing. In the calculation of the resistance loss, the influence of temperature increase on the conductivity and Skin effect of current. In the selection of heat transfer methods, this calculation includes three forms of heat transfer, convection heat transfer and radiation heat transfer. Heat conduction is the heat transfer of the GIS busbar to the surrounding _SF6 gas medium after the temperature rises; convection heat transfer is the heat transfer when the _SF6 gas medium flows relative to the busbar; radiation heat dissipation includes the main conductor and the _SF6 gas, the outer shell and the _SF6 gas , due to the temperature difference between the main conductor and the shell.

The calculation of the flow field should select the corresponding flow state and boundary conditions. The SF ₆ gas flows under the combined action of the heat generated by the bus flow and the heat loss of the casing. From the point of view of hydrodynamics, it belongs to the low-speed Newtonian fluid flow, and the flow state is laminar flow. The selection of boundary conditions includes temperature field boundary conditions and velocity boundary conditions. The temperature boundary conditions need to consider the thermal conductivity and temperature between the main conductor and the outer casing. This time, the velocity boundary conditions are no-slip boundary conditions.

In Step 4, the heat generated by the bus bar and the casing will cause the flow of SF ₆ gas, which will make the gas pressures at different positions different, and the pressure will have an impact on the solution of the medium breakdown field strength. Therefore, when calculating the insulation margin, the flow of gas in the case of the heat generated by the bus flow and the heat generated by the casing loss should be considered.

When calculating the heating of the bus, pay attention to the change of conductivity with temperature. The formula is as follows:

σ=σ ₀ [(1-kΔT ₁ )+(1-kΔT ₂ )]/2 (11)

Among them, σ ₀ is the corresponding conductivity at 20°C, k is the temperature effect coefficient, assuming that the ambient temperature of the temperature rise experiment is 40°C, and the bus temperature is 70°C, that is, ΔT ₁ =(40-20)°C, ΔT ₂ = (70-20)℃;

The obtained electrical conductivity is used to calculate the heat generation of the busbar with the electromagnetic field simulation model, and the skin effect of the main conductor should be considered in the calculation. From the inside to the outside of the main conductor, the magnetic flux density increases gradually, and the magnetic flux density reaches the maximum on the surface of the main conductor; while in the shell, the magnetic flux density gradually decreases from the inside to the outside. The radial depth that current can reach along the surface of the wire is as follows:

where ω is the angular frequency, μ is the magnetic permeability, and γ is the electrical conductivity.

Calculate the heat generation by the magnetic loss of the busbar and the casing, which is expressed in the differential form of Maxwell's equations, as described in formula (13):

为磁场强度矢量，

为总电流密度矢量，

为源电流密度矢量，

为感应电流密度矢量，

为电位移矢量，

为电场强度矢量，

为磁感应强度矢量，ρ为电荷密度。in

is the magnetic field strength vector,

is the total current density vector,

is the source current density vector,

is the induced current density vector,

is the electric displacement vector,

is the electric field strength vector,

is the magnetic induction intensity vector, and ρ is the charge density.

The power loss per unit length is obtained using the electromagnetic loss, as described in Equation (14).

P=∫(J _s ² /σ)dV (14)

Step5: Calculate the density distribution of SF ₆ gas in the GIS according to the results of Step4.

In Step 5, the heat generated by the bus bar and the shell obtained in Step 4 is used as the heat source in the flow field, so the gas flow is expressed by the three-dimensional N-S equation,

The mass conservation equation is:

The momentum conservation equations in the x, y, and z directions are:

The energy conservation equation is:

Among them, ρ represents the density of SF ₆ gas at any point, u _x , v _y , w _z represent the velocity of the gas in the x, y, and z directions, respectively, p is the pressure of the gas, q _v is the energy source term, and e is the unit mass The total energy, τ _ij are the individual components of the viscous stress tensor.

Step6, based on the SF ₆ gas density distribution conditions of Step5, calculate the critical breakdown electric field through Step1, calculate the electric field distribution under different working conditions through Step2, and judge the internal insulation level of the GIS based on the value of the insulation margin defined in Step3. If the insulation margin is less than If it is equal to 0, the breakdown will occur in the GIS. If the insulation margin is greater than 0, the breakdown will not occur in the GIS.

Compared with the prior art, the present invention has the following beneficial effects:

1. Compared with the existing method, the present invention considers the distribution of SF ₆ under long-term current flow when judging the internal insulation, and obtains a set of comprehensive judgment basis for the operation state of the GIS in the above-mentioned way. This method fully considers the busbar and the casing. The temperature rise causes changes in the distribution of SF ₆ gas in the case of gas flow, which is in line with the operating state of GIS in actual operation.

2. The present invention defines the insulation margin, and the Saha ionization equation is used to solve the process involving the calculation of the critical breakdown field strength.

3. In the present invention, the roughness and curvature of the main conductor surface are also taken into account when calculating the insulation margin, which avoids the influence of errors in the production or installation process on the judgment of the insulation level, and greatly improves the reliability of the judgment of the insulation level. .

4. The invention calculates the electric field distribution under different working conditions. In the actual operation of GIS, in addition to the power frequency voltage, there are also lightning impulse voltage and ultra-fast transient overvoltage. Comprehensive consideration can effectively reduce insulation failures caused by abnormal states.

Description of drawings

The present invention will be further described below in conjunction with the accompanying drawings and embodiments, in which:

1 is a schematic flowchart of a method for judging an insulation state in a GIS;

FIG. 2 is a single VFTO waveform on the load side under a transient working condition according to an embodiment of the present invention;

FIG. 3 is a schematic flowchart of Step 6 in an embodiment of the present invention.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

As shown in Figure 1, the present invention provides a method for judging the insulation state in a GIS, the method comprising the following steps:

Step1, calculate the critical breakdown electric field.

In Step 1, the Saha ionization equilibrium equation is used to solve the dielectric breakdown field strength, as described in formula (1),

Among them, n _e , n _r and n _r+1 are the corresponding electron density and particle density, Z _r and Z _r+1 are the partition functions of particles, k, h and _me are Boltzmann constant, Planck Constant and electron mass, _{E 1, r+1} is the ionization energy required for the (r+1) order ionization reaction, Te and _Th are the temperature of the electron and the temperature of the heavy particle, respectively.

According to the ionization equilibrium theory, when the space charge field is approximately equal to the external electric field, the electron avalanche will gradually form a flow column. The electric field E _r when the electron avalanche occurs is in a spherical region with a radius of r. The calculation formula is as shown in formula (2). stated,

Through the derivation of formula (2), we can get,

Among them, _Er is the dielectric breakdown field strength, _e is the amount of charge, ne is the electron density in a unit volume, k is the Boltzmann constant, _E is the space electric field strength, and Te is the electric field temperature. The value is also different from the case of electric field.

The breakdown field strength E _b is related to the roughness and curvature of the main conductor surface, therefore, the breakdown field strength E _b is as described in equation (4),

E _b = K _h K _f E _r (4)

Among them, K _h is the main conductor curvature coefficient, K _{f is} the main conductor surface roughness coefficient, and E _r is the dielectric breakdown field strength obtained according to the ionization equilibrium theory.

Step2, calculate the electric field distribution under different working conditions.

The calculation of the electrostatic field involves solving the Laplace equation within the solution region defined by the boundary conditions. Generally, the surface of the electrode is the boundary condition for applying the solution, and the area outside the electrode is the solution domain of the overall model. At this time, the voltage value is generally selected as the load degree of freedom, and it is applied to the electrode surface, and the entire solution domain should satisfy the Laplace equation.

In Step 2, the calculation of the electric field distribution is to solve the pull equation in the restricted region of the second type of boundary conditions, as described in formula (5),

为电位，电场强度与电位之间的关系为：in,

is the electric potential, and the relationship between the electric field strength and the electric potential is:

When calculating the electric field, it is also necessary to consider the situation under different working conditions:

(1) The lightning impulse condition can be expressed by the following formula:

Among them, A is the peak value of lightning impulse voltage, and τ ₁ and τ ₂ are the time constants of wave tail and wave front, respectively.

(2) The ultra-fast transient voltage VFTO, as shown in Figure 2, is expressed by formula (8):

Among them, k ₀ , k ₁ ...... k ₈ and l ₁ , l ₂ ...... l ₈ are the overvoltage coefficients, and ω is the voltage angular frequency, and the values are given in Table 1 below.

Table 1 Values of Overvoltage Coefficient and Voltage Corner Frequency

k₀ k₁ k₂ k₃ k₄ k₅ -1.496*10⁵ 8.051*10⁶ 8.171*10⁴ 1.143*10⁵ -6.379*10⁴ -2.652*10⁴ k₆ k₇ k₈ l₁ l₂ l₃ 4.041*10³ 4.989*10⁴ 3.477*10⁴ -1.8*10⁵ -3.232*10⁴ 8.983*10⁴ l₄ l₅ l₆ l₇ l₈ ω -3.791*10⁴ -3.065*10⁴ -5.037*10⁴ -3.314*10⁴ 8.635*10⁴ 1.046*10⁷

(3) In the case of power frequency voltage, the power frequency voltage equation is selected as:

u(t)=A×sin(ωt) (9)

Among them, A is the peak value of the power frequency voltage, and ω is the voltage angular frequency. Since it is a power frequency, the value of ω is 100π.

Step 3, define the insulation margin as the difference between the critical breakdown electric field of Step 1 and the spatial electric field strength of Step 2, as the basis for judging the internal insulation of the GIS.

In Step 3, define the insulation margin as the basis for judging the insulation in the GIS, wherein the insulation margin is as described in formula (10),

E _m =E _b -E (10)

Among them, _Em is the breakdown margin, E _b is the breakdown field strength, and E is the space electric field strength.

Step4, the coupling calculation of temperature field and flow field.

For the calculation of the temperature field, an appropriate heat source and heat transfer method should be selected. The heat source mainly includes the resistance loss of the busbar and the heat generated by the eddy current loss of the casing. In the calculation of the resistance loss, the influence of temperature increase on the conductivity and Skin effect of current. In the selection of heat transfer methods, this calculation includes three forms of heat transfer, convection heat transfer and radiation heat transfer. Heat conduction is the heat transfer of the GIS busbar to the surrounding _SF6 gas medium after the temperature rises; convection heat transfer is the heat transfer when the _SF6 gas medium flows relative to the busbar; radiation heat dissipation includes the main conductor and the _SF6 gas, the outer shell and the _SF6 gas , due to the temperature difference between the main conductor and the shell.

The calculation of the flow field should select the corresponding flow state and boundary conditions. The SF ₆ gas flows under the combined action of the heat generated by the bus flow and the heat loss of the casing. From the point of view of hydrodynamics, it belongs to the low-speed Newtonian fluid flow, and the flow state is laminar flow. The selection of boundary conditions includes temperature field boundary conditions and velocity boundary conditions. The temperature boundary conditions need to consider the thermal conductivity and temperature between the main conductor and the outer casing. This time, the velocity boundary conditions are no-slip boundary conditions.

In Step 4, the heat generated by the bus bar and the casing will cause the flow of SF ₆ gas, which will make the gas pressures at different positions different, and the pressure will have an impact on the solution of the medium breakdown field strength. Therefore, when calculating the insulation margin, the flow of gas in the case of the heat generated by the bus flow and the heat generated by the casing loss should be considered.

When calculating the heating of the bus, pay attention to the change of conductivity with temperature. The formula is as follows:

σ=σ ₀ [(1-kΔT ₁ )+(1-kΔT ₂ )]/2 (11)

Among them, σ ₀ is the corresponding conductivity at 20°C, k is the temperature effect coefficient, assuming that the ambient temperature of the temperature rise experiment is 40°C, and the bus temperature is 70°C, that is, ΔT ₁ =(40-20)°C, ΔT ₂ = (70-20)℃;

The obtained electrical conductivity is used to calculate the heat generation of the busbar with the electromagnetic field simulation model, and the skin effect of the main conductor should be considered in the calculation. In the main conductor from the inside to the outside, the magnetic flux density increases gradually, and the magnetic flux density reaches the maximum on the surface of the main conductor; while in the shell, the magnetic flux density gradually decreases from the inside to the outside. The radial depth that current can reach along the surface of the wire is as follows:

where ω is the angular frequency, μ is the magnetic permeability, and γ is the electrical conductivity.

Calculate the heat generation by the magnetic loss of the busbar and the casing, which is expressed in the differential form of Maxwell's equations, as described in formula (13):

为磁场强度矢量，

为总电流密度矢量，

为源电流密度矢量，

为感应电流密度矢量，

为电位移矢量，

为电场强度矢量，

为磁感应强度矢量，ρ为电荷密度。in

is the magnetic field strength vector,

is the total current density vector,

is the source current density vector,

is the induced current density vector,

is the electric displacement vector,

is the electric field strength vector,

is the magnetic induction intensity vector, and ρ is the charge density.

Use the electromagnetic losses to find the power loss per unit length, as described in Equation (14).

P=∫(J _s ² /σ)dV (14)

Step5: Calculate the density distribution of SF ₆ gas in the GIS according to the results of Step4.

In Step 5, the heat generated by the busbar and the shell obtained in Step 4 is used as the heat source in the flow field, so the gas flow is expressed by the three-dimensional N-S equation,

The mass conservation equation is:

The momentum conservation equations in the x, y, and z directions are:

The energy conservation equation is:

Among them, ρ represents the density of SF ₆ gas at any point, u _x , v _y , w _z represent the velocity of the gas in the x, y, and z directions, respectively, p is the pressure of the gas, q _v is the energy source term, and e is the unit mass The total energy, τ _ij are the individual components of the viscous stress tensor.

Step6, as shown in Figure 3, based on the SF ₆ gas density distribution conditions of Step5, calculate the critical breakdown electric field through Step1, calculate the electric field distribution under different working conditions through Step2, and judge the internal insulation level of the GIS based on the value of the insulation margin defined in Step3 , if the insulation margin is less than or equal to 0, the breakdown will occur in the GIS, and if the insulation margin is greater than 0, the breakdown will not occur in the GIS.

The accompanying drawings describe the embodiments of the present invention, but the present invention is not limited to the above-mentioned specific embodiments, and the above-mentioned specific embodiments are only schematic, not restrictive, and those of ordinary skill in the art are familiar with the present invention. Under the inspiration of the present invention, many forms can be made without departing from the scope of protection of the present invention and the claims, which all belong to the protection of the present invention.

Claims (4)

1. a judging method of insulation state in GIS, is characterized in that, this method comprises the following steps: Step1, calculate the critical breakdown field strength: use the Saha ionization equilibrium equation to solve the medium breakdown field strength, as described in formula (1),

Among them, n _e , n _r and n _r+1 are the corresponding electron density and particle density, Z _r and Z _r+1 are the partition functions of particles, k, h and _me are Boltzmann constant, Planck Constant and electron mass, _{E Ι, r+1} is the ionization energy required for the (r+1) order ionization reaction to occur, Te and _Th are the temperature of the electron and the temperature of the heavy particle, respectively; According to the ionization equilibrium theory, when the space charge field is approximately equal to the external electric field, the electron avalanche gradually forms a flow column. The electric field when the electron avalanche occurs is the dielectric breakdown field strength _Er , and the dielectric breakdown field strength Er is at the radius of _r . In the spherical area of , the calculation formula is as described in formula (2),

In formula (2), N _e is the number of electrons, which can be obtained by derivation of formula (2),

Among them, _Er is the dielectric breakdown field strength, _e is the amount of charge, ne is the electron density in a unit volume, k is the Boltzmann constant, _E is the space electric field strength, and Te is the electric field temperature. The value is also different from that in the case of electric field; The critical breakdown field strength E _b is related to the roughness and curvature of the main conductor surface. Therefore, the critical breakdown field strength E _b is as described in formula (4), E _b = K _h K _f E _r (4) Among them, K _h is the main conductor curvature coefficient, K _{f is} the main conductor surface roughness coefficient, and E _r is the dielectric breakdown field strength obtained according to the ionization equilibrium theory; Step2, calculate the electric field distribution under different working conditions: the calculation of the electric field distribution is to solve the pull equation in the restricted region of the second type of boundary conditions, as described in formula (5),

in,

is the electric potential, and the relationship between the electric field strength and the electric potential is:

In formula (6), z is the coordinate in the cylindrical coordinate system, which represents the radial distance in the calculation area; When calculating the electric field, it is also necessary to consider the situation under different working conditions: (1) The lightning impulse condition is expressed by formula (7) Among them, t is the time, A is the peak value of the lightning impulse voltage, and τ ₁ and τ ₂ are the wave tail and wave front time constants, respectively; (2) Very fast transient voltage VFTO, expressed by formula (8):

Among them, k ₀ , k ₁ ...... k ₈ and l ₁ , l ₂ ...... l ₈ are the overvoltage coefficients, and ω is the voltage angular frequency (3) In the case of power frequency voltage, the power frequency voltage equation is selected as: u(t)=A×sin(ωt) (9) Among them, A is the peak value of the power frequency voltage, and ω is the voltage angular frequency. Since it is a power frequency, the value of ω is 100π; Step3, define the insulation margin as the difference between the critical breakdown electric field in Step1 and the spatial electric field intensity in Step2, as the basis for judging the internal insulation of the GIS; Step4, coupling calculation of temperature field and flow field; Step5, calculate the density distribution of SF ₆ gas in the GIS according to the result of Step4; Step 6: Calculate the critical breakdown electric field through Step 1 based on the SF ₆ gas density distribution conditions in Step 5, calculate the electric field distribution under different working conditions through Step 2, and judge the internal insulation level of the GIS based on the value of the insulation margin defined in Step 3. If If the insulation margin is less than or equal to 0, the breakdown will occur in the GIS. If the insulation margin is greater than 0, the breakdown will not occur in the GIS. 2. the method for judging the insulation state in a kind of GIS according to claim 1, it is characterized in that, in described step Step3, define insulation margin as the basis for judging insulation in GIS, wherein, insulation margin is such as formula ( 10) said, E _m =E _b -E (10) Among them, _Em is the breakdown margin, E _b is the critical breakdown field strength, and E is the space electric field strength. 3. The method for judging the insulation state in a GIS according to claim ₂ , characterized in that, in the step Step4, the heat generated by the busbar and the casing can cause the flow of SF gas and then make the gas pressures at different positions different. , the pressure will have an impact on the solution of the dielectric breakdown field strength. Therefore, when calculating the insulation margin in Step 3, the gas flow should be considered in the case of the heat generated by the bus flow and the heat generated by the casing loss; Calculate the change of conductivity with temperature when the bus is heated, the formula is as follows: σ=σ ₀ [(1-k△T ₁ )+(1-k△T ₂ )]/2 (11) Among them, σ ₀ is the corresponding conductivity at 20°C, k is the temperature effect coefficient, assuming that the ambient temperature of the temperature rise experiment is 40°C and the bus temperature is 70°C, that is, ΔT ₁ =(40-20)°C, ΔT ₂ = (70-20) °C; Using the obtained electrical conductivity to calculate the heat generation of the busbar with the electromagnetic field simulation model, the radial depth that the current can reach along the surface of the conductor is as follows: Among them, ω is the angular frequency, μ is the magnetic permeability, and γ is the electrical conductivity; Calculate the heat generation by the magnetic loss of the busbar and the casing, which is expressed in the differential form of Maxwell's equations, as described in formula (13):

in

is the magnetic field strength vector,

is the total current density vector,

is the source current density vector,

is the induced current density vector,

is the electric displacement vector,

is the electric field strength vector,

is the magnetic induction intensity vector, ρ is the charge density; The power loss per unit length is obtained using the electromagnetic loss, as described in Equation (14): P=∫(J _s ² /σ)dV (14) In formula (14), J _s is the source current density vector, and V is the volume of the calculation area. 4. The method for judging the insulation state in a GIS according to claim 3, wherein in the step Step5, the heat generated by the busbar and the shell obtained in the step Step4 is used as the heat source in the flow field, so the gas flow uses The three-dimensional N-S equation says, The mass conservation equation is:

The momentum conservation equations in the x, y, and z directions are:

The energy conservation equation is:

Among them, ρ represents the density of SF ₆ gas at any point, u _x , v _y , w _z represent the velocity of the gas in the x, y, and z directions, respectively, p is the pressure of the gas, q _v is the energy source term, and e is the unit mass The total energy, τ _ij are the individual components of the viscous stress tensor.

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