CN108646156B - Method for judging insulation state in GIS - Google Patents
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- CN108646156B CN108646156B CN201810821546.1A CN201810821546A CN108646156B CN 108646156 B CN108646156 B CN 108646156B CN 201810821546 A CN201810821546 A CN 201810821546A CN 108646156 B CN108646156 B CN 108646156B
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- 238000009413 insulation Methods 0.000 title claims abstract description 57
- 238000000034 method Methods 0.000 title claims abstract description 19
- 230000005684 electric field Effects 0.000 claims abstract description 56
- 230000015556 catabolic process Effects 0.000 claims abstract description 48
- 230000008878 coupling Effects 0.000 claims abstract description 4
- 238000010168 coupling process Methods 0.000 claims abstract description 4
- 238000005859 coupling reaction Methods 0.000 claims abstract description 4
- 239000004020 conductor Substances 0.000 claims description 24
- 230000020169 heat generation Effects 0.000 claims description 16
- 238000004364 calculation method Methods 0.000 claims description 12
- 238000010438 heat treatment Methods 0.000 claims description 11
- 238000009421 internal insulation Methods 0.000 claims description 8
- 239000002245 particle Substances 0.000 claims description 8
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- NAWXUBYGYWOOIX-SFHVURJKSA-N (2s)-2-[[4-[2-(2,4-diaminoquinazolin-6-yl)ethyl]benzoyl]amino]-4-methylidenepentanedioic acid Chemical compound C1=CC2=NC(N)=NC(N)=C2C=C1CCC1=CC=C(C(=O)N[C@@H](CC(=C)C(O)=O)C(O)=O)C=C1 NAWXUBYGYWOOIX-SFHVURJKSA-N 0.000 claims 1
- 229910018503 SF6 Inorganic materials 0.000 description 15
- 238000012546 transfer Methods 0.000 description 12
- 230000004907 flux Effects 0.000 description 7
- 238000013461 design Methods 0.000 description 4
- 230000002500 effect on skin Effects 0.000 description 4
- 230000005855 radiation Effects 0.000 description 4
- 230000007774 longterm Effects 0.000 description 3
- 230000009471 action Effects 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 230000005686 electrostatic field Effects 0.000 description 2
- 239000012530 fluid Substances 0.000 description 2
- 230000017525 heat dissipation Effects 0.000 description 2
- 230000035699 permeability Effects 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000011900 installation process Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- SFZCNBIFKDRMGX-UHFFFAOYSA-N sulfur hexafluoride Chemical compound FS(F)(F)(F)(F)F SFZCNBIFKDRMGX-UHFFFAOYSA-N 0.000 description 1
- 229960000909 sulfur hexafluoride Drugs 0.000 description 1
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- G01R31/12—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing
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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
Technical Field
The invention relates to the technical field of high-voltage insulation, in particular to a method for judging insulation states in GIS.
Background
The sulfur hexafluoride gas insulation totally-enclosed power distribution device is called GIS for short, and in various fault types of GIS equipment, the occurrence probability of insulation faults is high and accounts for about 51% of the total faults. When GIS equipment has insulation fault, the GIS equipment causes great harm to the stable operation of a power grid. Root of insulating failureThe reason is that the existing GIS bus main conductor design has defects. The basis of the current GIS internal insulation design is as follows: 1. calculating whether the electric field distribution of the buses under different structures meets the insulation requirement; 2. and calculating whether the temperature rise of the equipment exceeds an operation allowable condition. The temperature rise of a main conductor (GIS bus) is not fully considered in GIS internal insulation design to enable SF6Flow causes internal SF6The gas distribution is uneven, which in turn causes a situation where the insulation level at a local location is much lower than the average. Upon application of an electric field, SF is generated6The dielectric strength of the portion with lower gas density is insufficient to cause gas breakdown.
Currently, in the design and research of electric power equipment, partial discharge is considered mostly when the insulation strength of the equipment needs to be determined, an empirical formula or a single physical field is commonly used for research, and the SF is rarely considered6The influence that gas flow brought for GIS internal insulation can't accurately judge GIS internal insulation level.
Disclosure of Invention
The invention aims to solve the technical problem of providing a method for judging the insulation state in GIS, and realizing long-term current-flowing SF6Under gas conditions, bus heating can affect SF6The distribution of gas density causes the uneven distribution of the internal insulation strength of the GIS and the existence of weak insulation areas, therefore, the invention is based on SF under the condition of long-term through-flow6 methods for judging GIS internal insulation are proposed for uneven gas distribution.
The invention aims to realize the following technical scheme that the method for judging the insulation state in GIS comprises the following steps:
step1, calculating the critical breakdown electric field.
At Step1, the dielectric breakdown field strength is solved using the Saha ionization equilibrium equation, as described in equation (1),
wherein n ise、nrAnd nr+1For the corresponding electron density and particle density, ZrAnd Zr+1Being particlesPartition function, k, h and meBoltzmann constant, planck constant and electron mass, EΙ,r+1Ionization energy required for the (r +1) -order ionization reaction to occur, Te、ThThe temperature of the electrons and the temperature of the heavy particles, respectively.
According to the ionization balance theory, when the space charge field is approximately equal to the external electric field, electron avalanche will gradually form a current column in which the electric field E when electron avalanche occursrIn the spherical region with radius r, the calculation formula is as described in formula (2),
as can be derived from the derivation of equation (2),
wherein E isrDielectric breakdown field strength, e electric charge amount, neIs the electron density per unit volume, k is the Boltzmann constant, E is the spatial electric field strength, TeThe values for the temperature of the electric field are different for different pressures and electric fields.
Breakdown field strength EbRelated to the roughness and curvature of the surface of the main conductor, and hence the breakdown field strength EbAs described in the formula (4),
Eb＝KhKfEr(4)
wherein, KhIs a main conductor curvature coefficient, KfIs a main conductor surface roughness coefficient, ErThe dielectric breakdown field strength is obtained according to ionization balance theory.
And Step2, calculating the electric field distribution under different working conditions.
The electrostatic field is calculated by solving Laplace's equation in the solving area defined by the boundary condition, is the boundary condition for applying the solving, and the area outside the electrode is the solving area of the whole model, selects the voltage value as the freedom degree of load to apply to the electrode surface, and the whole solving area should satisfy Laplace's equation.
In Step2, the electric field distribution is calculated by solving a pull type equation in the limited region of the two types of boundary conditions, as described in equation (5),
wherein,
as a potential, the relationship between the electric field strength and the potential is:
the electric field is calculated by considering the conditions under different working conditions:
(1) the lightning surge condition may be represented by the following equation:
wherein A is the peak value of lightning impulse voltage, tau1、τ2Respectively, the tail and wavefront time constants.
(2) The very fast transient voltage VFTO is represented by equation (8):
wherein k is0、k1……k8And l1、l2……l8For the overvoltage coefficient, ω is the voltage angular frequency, the values are given in table 1 below.
TABLE 1 values of the overvoltage coefficient and the voltage angular 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) Under the condition of power frequency voltage, selecting a power frequency voltage equation as follows:
u(t)＝A×sin(ωt) (9)
wherein, A is the peak value of the power frequency voltage, omega is the voltage angular frequency, and because of the power frequency, omega takes the value of 100 pi.
And Step3, defining the insulation margin as the difference value between the critical breakdown electric field of Step1 and the space electric field intensity of Step2, and taking the difference value as the basis for judging the insulation in the GIS.
In Step3, an insulation margin is defined as a basis for insulation judgment in the GIS, wherein the insulation margin is described in equation (10),
Em＝Eb-E (10)
wherein E ismFor breakdown margin, EbFor breakdown field strength, E is the spatial electric field strength.
Step4, calculating the coupling of the temperature field and the flow field.
The calculation of the temperature field needs to select a proper heat source and a proper heat transfer mode, wherein the heat source mainly comprises resistance loss of a bus and heating caused by eddy current loss of a shellThe effect of temperature rise on conductivity and the skin effect of current flow are also taken into account in the calculation of the resistive losses. In the selection of the heat transfer mode, the calculation comprises three modes of heat conduction, convective heat transfer and radiation heat transfer. The heat conduction is SF around after the GIS bus is heated through the through flow6Gas medium heat transfer; the heat convection is SF6Heat transfer when the gaseous medium flows relative to the bus; the radiation heat dissipation comprises a main conductor and SF6Gas, shell and SF6Gas, generated due to a temperature difference between the main conductor and the housing.
The flow field is calculated by selecting the corresponding flow state and boundary condition. SF6The gas flows under the combined action of bus through-flow heating and shell loss heating, belongs to low-speed Newtonian fluid flow from the viewpoint of hydrodynamics, and the flowing state is laminar flow. The boundary conditions are selected to include temperature field boundary conditions and speed boundary conditions, the temperature boundary conditions need to consider the heat conductivity coefficient, the temperature and the like between the main conductor and the shell, and the speed boundary conditions are non-slip boundary conditions.
In Step4, SF is caused by heat generation of the bus bar and the housing6The flow of the gas further causes the gas pressure at different positions to be different, and the pressure has influence on the solution of the dielectric breakdown field strength. Therefore, the flow of gas in the case of bus through-flow heat generation and case loss heat generation is considered in calculating the insulation margin.
When calculating the bus heating, attention is paid to the change of the conductivity along with the temperature, and the formula is as follows:
σ＝σ0[(1-kΔT1)+(1-kΔT2)]/2 (11)
wherein σ0The corresponding conductivity at 20 ℃, k is a temperature effect coefficient, and the temperature of the external environment in the temperature rise experiment is assumed to be 40 ℃, the bus temperature is 70 ℃, namely delta T1＝(40-20)℃，ΔT2＝(70-20)℃；
And calculating the heat generation of the bus by using the electromagnetic field simulation model for the conductivity, wherein the skin effect of the main conductor needs to be considered during calculation. The magnetic flux density is gradually increased from inside to outside of the main conductor, and the magnetic flux density reaches the maximum on the surface of the main conductor; and in the housing, the magnetic flux density gradually decreases from the inside to the outside. The radial depth that the current can reach along the wire surface is as follows:
where ω is angular frequency, μ is magnetic permeability, and γ is electrical conductivity.
Calculating the heat generation of the magnetic loss of the bus and the shell, and expressing the heat generation in a differential form by using Maxwell equations, as described in formula (13):
wherein
Is a vector of the magnetic field strength,
to be the vector of the total current density,
is a vector of the density of the source current,
to be the induced current density vector,
in the form of a vector of electrical displacement,
is a vector of the electric field strength,
is the magnetic induction vector, and ρ is the charge density.
The power loss per unit length is found using the electromagnetic loss, as described in equation (14).
P＝∫(Js 2/σ)dV (14)
Step5, calculating SF in GIS according to the result of Step46Gas density distribution.
In Step5, the heat generated by the busbar and the housing obtained in Step4 is used as a heat source in the flow field, so that the gas flow is expressed by a three-dimensional N-S equation,
the conservation of mass equation is:
the conservation of momentum equation in the directions of the x, y and z axes is as follows:
the energy conservation equation is:
where ρ represents an arbitrary points SF6Density of gas, ux，vy，wzRespectively representing the velocity of the gas in the x, y, z directions, p being the pressure of the gas, qvFor the energy source term, e is the total energy per unit mass, τijAre the components of the viscous stress tensor.
Step6, SF based on Step56And calculating a critical breakdown electric field under the gas density distribution condition through Step1, calculating electric field distribution under different working conditions through Step2, judging the insulation level in the GIS according to the numerical value of the insulation margin defined by Step3, 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.
Compared with the prior art, the invention has the following beneficial effects:
1. compared with the prior art, the method takes SF under long-term flux into consideration when judging the internal insulation6Distribution situation, and the comprehensive judgment basis of sets of GIS running states is obtained according to the mode, and the method fully considers SF under the condition that gas flows caused by temperature rise of the bus and the shell6The gas distribution changes, and the running state of the GIS in actual running is met.
2. The invention defines the insulation margin, wherein a Saha ionization equation is adopted for solving in the process of calculating the critical breakdown field strength.
3. The method takes the roughness and the curvature of the surface of the main conductor into account when calculating the insulation margin, avoids the influence on the judgment of the insulation level caused by errors in the production or installation process, and greatly improves the reliability of the judgment of the insulation level.
4. The invention calculates the electric field distribution under different working conditions, and the conditions of lightning impulse voltage and very fast transient overvoltage exist in addition to power frequency voltage in the actual operation of the GIS.
Drawings
The invention will be further described with reference to the drawings and examples, in which:
fig. 1 is a schematic flow chart of a method for determining insulation states in GIS;
FIG. 2 is a single VFTO waveform at the load side under transient operating conditions in an embodiment of the present invention;
FIG. 3 is a flowchart illustrating Step6 according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in with reference to the accompanying drawings and examples.
As shown in fig. 1, the present invention provides a method for determining insulation state in GIS, comprising the following steps:
step1, calculating the critical breakdown electric field.
At Step1, the dielectric breakdown field strength is solved using the Saha ionization equilibrium equation, as described in equation (1),
wherein n ise、nrAnd nr+1For the corresponding electron density and particle density, ZrAnd Zr+1As a partition function of the particles, k, h and meBoltzmann constant, planck constant and electron mass, EΙ,r+1Ionization energy required for the (r +1) -order ionization reaction to occur, Te、ThThe temperature of the electrons and the temperature of the heavy particles, respectively.
According to the ionization balance theory, when the space charge field is approximately equal to the external electric field, electron avalanche will gradually form a current column in which the electric field E when electron avalanche occursrIn the spherical region with radius r, the calculation formula is as described in formula (2),
as can be derived from the derivation of equation (2),
wherein E isrDielectric breakdown field strength, e electric charge amount, neIs the electron density per unit volume, k is the Boltzmann constant, E is the spatial electric field strength, TeThe values for the temperature of the electric field are different for different pressures and electric fields.
Breakdown field strength EbRelated to the roughness and curvature of the surface of the main conductor, and hence the breakdown field strength EbAs described in the formula (4),
Eb＝KhKfEr(4)
wherein, KhIs a main conductor curvature coefficient, KfIs a main conductor surface roughness coefficient, ErThe dielectric breakdown field strength is obtained according to ionization balance theory.
And Step2, calculating the electric field distribution under different working conditions.
The electrostatic field is calculated by solving Laplace's equation in the solving area defined by the boundary condition, is the boundary condition for applying the solving, and the area outside the electrode is the solving area of the whole model, selects the voltage value as the freedom degree of load to apply to the electrode surface, and the whole solving area should satisfy Laplace's equation.
In Step2, the electric field distribution is calculated by solving a pull type equation in the limited region of the two types of boundary conditions, as described in equation (5),
wherein,
as a potential, the relationship between the electric field strength and the potential is:
the electric field is calculated by considering the conditions under different working conditions:
(1) the lightning surge condition may be represented by the following equation:
wherein A is the peak value of lightning impulse voltage, tau1、τ2Respectively, the tail and wavefront time constants.
(2) The very fast transient voltage VFTO, as shown in fig. 2, is represented by equation (8):
wherein k is0、k1……k8And l1、l2……l8For the overvoltage coefficient, ω is the voltage angular frequency, the values are given in table 1 below.
TABLE 1 values of the overvoltage coefficient and the voltage angular 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) Under the condition of power frequency voltage, selecting a power frequency voltage equation as follows:
u(t)＝A×sin(ωt) (9)
wherein, A is the peak value of the power frequency voltage, omega is the voltage angular frequency, and because of the power frequency, omega takes the value of 100 pi.
And Step3, defining the insulation margin as the difference value between the critical breakdown electric field of Step1 and the space electric field intensity of Step2, and taking the difference value as the basis for judging the insulation in the GIS.
In Step3, an insulation margin is defined as a basis for insulation judgment in the GIS, wherein the insulation margin is described in equation (10),
Em＝Eb-E (10)
wherein E ismFor breakdown margin, EbFor breakdown field strength, E is the spatial electric field strength.
Step4, calculating the coupling of the temperature field and the flow field.
The calculation of the temperature field needs to select a proper heat source and a heat transfer mode, the heat source mainly comprises resistance loss of a bus and heating caused by eddy current loss of a shell, and the influence of temperature rise on electric conductivity and the skin effect of current are also considered in the calculation process of the resistance loss. In the selection of the heat transfer mode, the calculation comprises three modes of heat conduction, convective heat transfer and radiation heat transfer. The heat conduction is SF around after the GIS bus is heated through the through flow6Gas medium heat transfer; the heat convection is SF6Heat transfer when the gaseous medium flows relative to the bus; the radiation heat dissipation comprises a main conductor and SF6Gas, shell and SF6Gas, generated due to a temperature difference between the main conductor and the housing.
The flow field is calculated by selecting the corresponding flow state and boundary condition. SF6The gas flows under the combined action of bus through-flow heating and shell loss heating, belongs to low-speed Newtonian fluid flow from the viewpoint of hydrodynamics, and the flowing state is laminar flow. The boundary conditions are selected to include temperature field boundary conditions and speed boundary conditions, the temperature boundary conditions need to consider the heat conductivity coefficient, the temperature and the like between the main conductor and the shell, and the speed boundary conditions are non-slip boundary conditions.
In Step4, SF is caused by heat generation of the bus bar and the housing6The flow of the gas further causes the gas pressure at different positions to be different, and the pressure has influence on the solution of the dielectric breakdown field strength. Therefore, the flow of gas in the case of bus through-flow heat generation and case loss heat generation is considered in calculating the insulation margin.
When calculating the bus heating, attention is paid to the change of the conductivity along with the temperature, and the formula is as follows:
σ＝σ0[(1-kΔT1)+(1-kΔT2)]/2 (11)
wherein σ0The corresponding conductivity at 20 ℃, k is a temperature effect coefficient, and the temperature of the external environment in the temperature rise experiment is assumed to be 40 ℃, the bus temperature is 70 ℃, namely delta T1＝(40-20)℃，ΔT2＝(70-20)℃；
And calculating the heat generation of the bus by using the electromagnetic field simulation model for the conductivity, wherein the skin effect of the main conductor needs to be considered during calculation. The magnetic flux density is gradually increased from inside to outside of the main conductor, and the magnetic flux density reaches the maximum on the surface of the main conductor; and in the housing, the magnetic flux density gradually decreases from the inside to the outside. The radial depth that the current can reach along the wire surface is as follows:
where ω is angular frequency, μ is magnetic permeability, and γ is electrical conductivity.
Calculating the heat generation of the magnetic loss of the bus and the shell, and expressing the heat generation in a differential form by using Maxwell equations, as described in formula (13):
wherein
Is a vector of the magnetic field strength,
to be the vector of the total current density,
is a vector of the density of the source current,
to be the induced current density vector,
in the form of a vector of electrical displacement,
is a vector of the electric field strength,
is the magnetic induction vector, and ρ is the charge density.
The power loss per unit length is found using the electromagnetic loss, as described in equation (14).
P＝∫(Js 2/σ)dV (14)
Step5, calculating SF in GIS according to the result of Step46Gas density distribution.
In Step5, the heat generated by the busbar and the housing obtained in Step4 is used as a heat source in the flow field, so that the gas flow is expressed by a three-dimensional N-S equation,
the conservation of mass equation is:
the conservation of momentum equation in the directions of the x, y and z axes is as follows:
the energy conservation equation is:
where ρ represents an arbitrary points SF6Density of gas, ux，vy，wzRespectively representing the velocity of the gas in the x, y, z directions, p being the pressure of the gas, qvFor the energy source term, e is the total energy per unit mass, τijAre the components of the viscous stress tensor.
Step6, SF based on Step5 as shown in FIG. 36And calculating a critical breakdown electric field under the gas density distribution condition through Step1, calculating electric field distribution under different working conditions through Step2, judging the insulation level in the GIS according to the numerical value of the insulation margin defined by Step3, 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.
While the present invention has been described with reference to the particular embodiments illustrated in the drawings, which are meant to be illustrative only and not limiting, it will be apparent to those of ordinary skill in the art in light of the teachings of the present invention that numerous modifications can be made without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (4)
1, GIS internal insulation state judgment method, characterized in that, the method includes the following steps:
step1, calculating the critical breakdown field strength: the dielectric breakdown field strength is solved by adopting a Saha ionization equilibrium equation, as shown in formula (1),
wherein n ise、nrAnd nr+1For the corresponding electron density and particle density, ZrAnd Zr+1As a partition function of the particles, k, h and meBoltzmann constant, planck constant and electron mass, EΙ,r+1Ionization energy required for the (r +1) -order ionization reaction to occur, Te、ThThe temperature of the electrons and the temperature of the heavy particles, respectively;
according to the ionization balance theory, when the space charge field is approximately equal to the external electric field, the electron avalanche gradually forms a current column, wherein the electric field when the electron avalanche occurs is the dielectric breakdown field intensity ErDielectric breakdown field strength ErIn the spherical region with radius r, the calculation formula is as described in formula (2),
n in formula (2)eFor the number of electrons, it can be derived by the derivation of equation (2),
wherein E isrDielectric breakdown field strength, e electric charge amount, neIs the electron density per unit volume, k isBoltzmann constant, E is the spatial electric field strength, TeThe value is different under different pressure and electric field conditions for the electric field temperature;
critical breakdown field strength EbIs related to the roughness and curvature of the surface of the main conductor, and therefore the critical breakdown field strength EbAs described in the formula (4),
Eb＝KhKfEr(4)
wherein, KhIs a main conductor curvature coefficient, KfIs a main conductor surface roughness coefficient, ErThe dielectric breakdown field strength is obtained according to the ionization balance theory;
step2, calculating electric field distribution under different working conditions: the electric field distribution is calculated by solving a pull equation in the limited region of the two types of boundary conditions, as described in equation (5),
wherein,
as a potential, the relationship between the electric field strength and the potential is:
in the formula (6), z is a coordinate in a cylindrical coordinate system and represents a radial distance in a calculation region;
the electric field is calculated by considering the conditions under different working conditions:
(1) the lightning impulse condition is expressed by formula (7)
Where t is time, A is the peak value of lightning impulse voltage, and τ1、τ2Respectively, the wave tail and wave front time constants;
(2) the very fast transient voltage VFTO is represented by equation (8):
wherein k is0、k1……k8And l1、l2……l8Is the overvoltage coefficient, omega is the voltage angular frequency
(3) Under the condition of power frequency voltage, selecting a power frequency voltage equation as follows:
u(t)＝A×sin(ωt) (9)
wherein A is the peak value of power frequency voltage, omega is voltage angular frequency, and because of power frequency, omega takes the value of 100 pi;
step3, defining the insulation margin as the difference value of the critical breakdown electric field in the Step1 and the space electric field intensity in the Step2, and taking the difference value as the basis of insulation judgment in the GIS;
step4, calculating the coupling of the temperature field and the flow field;
step5, calculating SF in GIS according to the result of Step46A gas density distribution;
step6, SF based on Step56And calculating the critical breakdown electric field under the gas density distribution condition through Step1, calculating the electric field distribution under different working conditions through Step2, judging the insulation level in the GIS according to the numerical value of the insulation margin defined in Step3, 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.
2. The method for determining the insulation state in the GIS according to claim 1, wherein in the Step3, an insulation margin is defined as a basis for the insulation determination in the GIS, wherein the insulation margin is as described in the formula (10),
Em＝Eb-E (10)
wherein E ismFor breakdown margin, EbCritical breakdown field strength, E is spatial electric field strength.
3. The method for determining the insulation state in GIS as claimed in claim 2, wherein the heat generation of the bus bar and the housing in Step4 causes SF6The gas flows further to enable the gas pressures at different positions to be different, and the pressures influence the solving of the dielectric breakdown field strength, so that the gas flows under the conditions of bus through-flow heating and shell loss heating need to be considered when the insulation margin is calculated in Step 3;
and (3) calculating the change of the conductivity along with the change of the temperature when the bus generates heat, wherein the formula is as follows:
σ＝σ0[(1-k△T1)+(1-k△T2)]/2 (11)
wherein σ0The corresponding conductivity at 20 ℃, k is a temperature effect coefficient, and the temperature of the external environment in the temperature rise experiment is assumed to be 40 ℃, the temperature of the bus is assumed to be 70 ℃, namely △ T1＝(40-20)℃，△T2＝(70-20)℃；
The electromagnetic field simulation model is used for calculating the heat generation of the bus by utilizing the conductivity, and the radial depth of the current along the surface of the lead can be as follows:
wherein, omega is angular frequency, mu is magnetic conductivity, and gamma is electric conductivity;
calculating the heat generation of the magnetic loss of the bus and the shell, and expressing the heat generation in a differential form by using Maxwell equations, as described in formula (13):
wherein
Is a vector of the magnetic field strength,
to be the vector of the total current density,
is a vector of the density of the source current,
to be the induced current density vector,
in the form of a vector of electrical displacement,
is a vector of the electric field strength,
is the magnetic induction vector, and rho is the charge density;
the power loss per unit length is found using the electromagnetic losses, as described in equation (14):
P＝∫(Js 2/σ)dV (14)
j in formula (14)sIs the source current density vector and V is the volume of the calculated area.
4. The method of determining the insulation state in GIS according to claim 3, wherein in Step5, the bus bar and the case obtained in Step4 generate heat as a heat source in the flow field, so that the gas flow is expressed by a three-dimensional N-S equation,
the conservation of mass equation is:
the conservation of momentum equation in the directions of the x, y and z axes is as follows:
the energy conservation equation is:
where ρ represents an arbitrary points SF6Density of gas, ux，vy，wzRespectively representing the velocity of the gas in the x, y, z directions, p being the pressure of the gas, qvFor the energy source term, e is the total energy per unit mass, τijAre the components of the viscous stress tensor.
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| CN110728071B (en) * | 2019-10-23 | 2021-03-05 | 北京理工大学 | Method for predicting electromagnetic effect generated by explosion |
| CN111143979B (en) * | 2019-12-16 | 2022-08-16 | 国网上海市电力公司 | Memory, basin-type insulator thermodynamic model construction method, device and equipment |
| CN111342388B (en) * | 2020-03-16 | 2021-05-04 | 武汉理工大学 | GIS compact design method under high-voltage grade mixed gas medium |
| CN112800647B (en) * | 2021-01-09 | 2022-11-08 | 国网山西省电力公司超高压变电分公司 | Multi-physical-field coupling simulation method and system for GIS isolating switch under different contact states |
| CN114004187B (en) * | 2021-10-28 | 2022-10-11 | 国网上海市电力公司 | Electric field simulation method for GIS (gas insulated switchgear) basin-type insulator with defects under lightning impulse voltage |
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