CN-121980878-A - Plasma dynamics-based perfluoroisobutyronitrile mixed gas lower surface flashover voltage prediction method

Abstract

The invention provides a plasma dynamics-based perfluoroisobutyronitrile mixed gas lower surface flashover voltage prediction method, which comprehensively considers the effects of desorption and collision ionization of gas molecules involved in a gas side, charge accumulation on the surface of a gas-solid interface and carrier traps existing in a solid medium on a solid side, constructs a surface flashover model, and obtains the space-time distribution condition of electric field intensity and the transportation condition of charged particles in space by solving a continuity control equation, a poisson equation and a local field approximation equation of charged particles to be used as a means for predicting the surface flashover voltage. The invention not only can predict the surface flashover voltage, but also is expected to be used as a data reference for research and development of environment-friendly insulating gas equipment, saves test cost and improves research and development efficiency.

Inventors

• ZHONG LIPENG
• YI SHUANG
• LIU YUFANG
• CHAI JUNFENG
• LIU ZULONG
• CHEN SHE
• SUN QIUQIN
• WANG FENG

Assignees

• 湖南大学

Dates

Publication Date

20260505

Application Date

20260407

Claims (6)

1. 1. The method for predicting the flashover voltage of the lower surface of the perfluorinated isobutyronitrile mixed gas based on plasma dynamics is characterized by comprising the following steps: Constructing a surface flashover test platform, wherein the surface flashover test platform comprises a solid side and a gas side, a contact surface of the solid side and the gas side forms a gas-solid interface, the gas side is filled with C 4 F 7 N/CO 2 mixed gas, and the solid side is filled with an insulating material; Constructing an edge surface flashover model of the C 4 F 7 N/CO 2 mixed gas, wherein the geometric shape of the edge surface flashover model is obtained by carrying out equal scaling on an edge surface flashover test platform; In the surface flashover model, electron collision cross section data in the desorption and collision ionization processes of C 4 F 7 N gas molecules and CO 2 gas molecules at the gas side are obtained from a database, and the charge accumulation at the gas-solid interface surface is obtained through simulation by introducing a partial differential equation; simulating a process that carriers of carrier traps existing on the solid side are captured or escaped through a partial differential equation; The gas side processes electron collision cross section data of C 4 F 7 N gas and CO 2 gas by using a Boltzmann equation to obtain electron average energy, mobility, diffusion coefficient and reaction rate, and the solid side sets medium characteristic parameters according to the solid medium characteristics so as to construct an along-plane flashover model of C 4 F 7 N/CO 2 mixed gas; Step three, solving a continuity control equation and a poisson equation of charged particle transport behaviors in the surface flashover model by utilizing finite element software, simulating potential distribution in a discharge process by adopting a local field approximation equation, and extracting voltage applied to an electrode at a flashover moment to serve as a flashover voltage predicted value of the surface flashover model ; Step four, obtaining an actual value of the flashover voltage by using a surface flashover test platform ; Step five, establishing a fitting formula: ; wherein a, b is a fitting parameter; By inputting multiple groups And Obtaining values of a and b by value fitting of (a); step six, solving by adopting an edge surface flashover model of the C 4 F 7 N/CO 2 mixed gas and finite element software to obtain a flashover voltage predicted value of the C 4 F 7 N/CO 2 mixed gas to be detected And inputs the following formula: And obtaining a final predicted value U' of the C 4 F 7 N/CO 2 mixed gas flashover voltage.
2. 2. The method for predicting the flashover voltage of the lower surface of the perfluoroisobutyronitrile mixed gas based on plasma dynamics according to claim 1, wherein in the second step, the accumulation of the surface charge of the gas-solid interface is obtained by simulating by introducing a partial differential equation, as shown in formulas (1) - (3): (1); (2); (3); In the middle of The surface charge density of the gas-solid interface; A normal unit component directed to the gas side for the solid insulating material; Is the solid side bulk current density; is the gas side current density; Tangential component of interface field strength; Is the surface conductivity of the solid medium; Is the electrical displacement vector of the gas side; is the volume conductivity of the solid medium; is the solid side field intensity; e is a meta-charge; Is the gas side field strength; 、 Positive and negative ion mobility respectively; 、 respectively positive and negative ion diffusion coefficients, Or (b) , Or (b) ; 、 The density of positive and negative ion numbers respectively, Is Boltzmann constant, T is ambient temperature, Time is expressed in seconds.
3. 3. The method for predicting the flashover voltage of the lower surface of the perfluoroisobutyronitrile mixed gas based on the plasma dynamics according to claim 1, wherein in the second step, the process of simulating the capture or escape of carriers of carrier traps existing on the solid side through a partial differential equation is shown as the following formulas (4) - (8): (4); (5); (6); (7); (8); Wherein, the And The capturing and detrapping probabilities of the carriers are respectively; Is the trap density; Mobility for initial electron holes; Is vacuum dielectric constant; is the relative dielectric constant of the epoxy resin; et is the trap level; h is the Planck constant; is the Boltzmann constant; And The trapping and detrapping amounts of charge respectively, The capture probability of carriers; The amount of primary charge; Is the trap density; is the probability of carrier detrapping; And The hole-trap recombination rate, the electron-trap recombination rate and the electron-hole recombination rate are respectively; The amount of charge that is free holes; an amount of charge that is an electron trap; Is electron mobility; an amount of charge that is a hole trap; an amount of charge that is free electrons; is hole mobility.
4. 4. The method for predicting the flashover voltage of the lower surface of the perfluoroisobutyronitrile mixed gas based on the plasma dynamics according to claim 1, wherein in the third step, a finite element software is used for solving a continuity equation and a poisson equation for controlling the transport behavior of charged particles, wherein the continuity equation and the poisson equation are shown as formulas (9) - (11): (9); (10); (11); Wherein, the Alpha m and eta m are respectively ionization coefficient and adhesion coefficient in C 4 F 7 N/CO 2 mixed gas; Respectively representing migration coefficients of electrons, positive ions and negative ions; Diffusion coefficients for electrons, positive ions, and negative ions; 、 Respectively representing the recombination coefficients of electrons, positive ions and negative ions and positive ions, wherein E is the electric field intensity, S 0 and S 1 are electrons and positive ions generated by space photoionization, phi is the potential of each node in the domain, E is the unit charge quantity, and ɛ 0 is the vacuum dielectric constant; The relative dielectric constant of the mixed gas is C 4 F 7 N/CO 2 .
5. 5. The method for predicting the flashover voltage of the lower surface of the perfluoroisobutyronitrile mixed gas based on plasma dynamics according to claim 1, wherein in the third step, the potential distribution in the simulated discharge process using the partial field approximation equation is shown in the formula (12): (12); Wherein the method comprises the steps of Representing the potential.
6. 6. The method for predicting the subsurface flashover voltage of a perfluoroisobutyronitrile mixture gas based on plasma dynamics according to claim 1, wherein the dielectric characteristic parameters include relative dielectric constant, conductivity, carrier trap level and carrier capture rate.

Description

Plasma dynamics-based perfluoroisobutyronitrile mixed gas lower surface flashover voltage prediction method Technical Field The invention relates to the technical field of electrical engineering. The method is used for predicting the surface flashover voltage under different gas mixing ratios, different air pressure conditions and different air gap conditions, and can be applied to the research and development of environment-friendly gas insulation equipment through experimental verification. Background SF 6 is widely used in high-pressure gas insulation equipment due to its excellent insulation and arc extinguishing properties. But its greenhouse effect is extremely strong (global warming potential (GWP) is 24300 times that of CO 2), the atmospheric retention life is as long as 3200 years, and global climate change is seriously threatened. Researches show that the C 4F7N/CO2 mixed gas has excellent insulating property, arc extinguishing property, environmental protection property, biological safety and the like, and is the SF 6 substitution gas with the most potential in the high-voltage field. CIGRE data shows that more than 40% of GIS faults are caused by insulator surface flashover, which seriously threatens the service life of high-pressure gas insulation equipment such as GIL, GIS and the like and the safety stability of a power system. Aiming at the surface flashover characteristic of the C 4F7N/CO2 mixed gas, students demonstrate that the insulating strength of the composite material is hopeful to completely replace SF 6 from multiple dimensions through a power frequency withstand voltage test, a lightning impulse test, an operation impulse test and a nanosecond impulse test. And indicates that most of the surface flashover occurs on the concave side of the basin-type insulator rather than on the convex side during power frequency testing, and that the concave side discharge of the basin-type insulator is observed to have two forms of breakdown along the insulator surface and along the gas gap under the operating impact voltage. The test means can visually observe the development path and process of discharge, and can effectively analyze the insulation strength through electrical parameters such as breakdown voltage, current and the like, but cannot know the transportation behavior of carriers, the electric field distortion capability of surface charges, the microscopic process of solid side carrier traps and the like, thereby limiting the deep understanding of the surface flashover discharge mechanism and the efficient improvement of the surface flashover performance. Partial scholars build a discharge multi-physical field model, and the conditions of electric field intensity distribution, charged particle transportation and the like in the discharge process can be obtained in detail by utilizing numerical calculation. For example, studies on C 4F7 N mixed gas stream discharge, dmitry Levko et al explored the C 4F7N/N2 mixed gas stream discharge process at negative DC voltage. And Cang Yiming et al obtain the distribution conditions of electric field intensity, luminous flux density and the like of the C 4F7N/CO2 mixed gas in the process of developing the direct-current voltage current injection by numerical calculation. The team researches the current injection discharge process under the lightning impulse voltage around the C 4F7N/CO2 mixed gas, and combines the experiment to prove that the model can be applied to the prediction of 50% of the lightning impulse voltage. However, because of the influence of factors such as surface flashover, gas-solid-gas solid interfaces and the like, the numerical calculation difficulty is high, the surface discharge research of the mixed gas is less, only Xinfeng Yan et al construct a C 4F7N/CO2 mixed gas surface discharge model, the optical phenomenon of the mixed gas is macroscopically explored, and the discharge mechanism of the mixed gas is not deeply explored, namely, the microscopic charged particle transportation processes such as impact ionization of gas side mixed gas molecules, accumulation of gas-solid interface surface charges, influence of solid side surface carrier traps and the like are comprehensively considered. According to the invention, the influence of desorption and collision ionization of gas molecules involved in a gas side, charge accumulation on the surface of a gas-solid interface and carrier traps existing in a solid medium on the solid side are comprehensively considered, an along-surface flashover model is constructed, and the space-time distribution condition of electric field intensity and the transport condition of charged particles in space can be obtained by solving a continuity control equation, a poisson equation and a local field approximation equation of charged particles, so that the method can be used as a means for predicting the along-surface flashover voltage, is hopeful to be used as a data reference for research and