Non-equilibrium Plasma Model Of Surface Discharge And The Influencing Factors Analysis In The Development Process

Renewable energy,such as wind energy and solar energy has the characteristics of randomness,intermittence and output change fast.DC transmission technology is an important method of new energy consumptive which can effectively solve the above problems,and it has the advantages of flexible operation mode,low cost and low cost.But at present,the technical bottleneck of high voltage and large capacity DC circuit breaker has not yet been broken,which seriously hinders the popularization and development of HVDC technology.The hybrid DC circuit breaker with mechanical fracture is the keystone and hotspot of current research.The insulation between contacts may suffer surface insulation failure at moments of large current interruption.Therefore,it is the key to improve the performance of DC circuit breaker and the insulation performance of the dielectric,to study the dynamic evolution law of surface discharge under HVDC.The research results show that the accumulated charges will affect the insulation performance of the dielectric.To date,there is still a lack of complete physical understanding of dynamic evolution law of surface discharge.It is necessary to study the rules governing the generation,migration,and accumulation of surface charges.Based on the above research background,we present a non-equilibrium plasma model of surface discharge in this paper.The dynamic distributions of micro parameters during surface discharge are studied,considering the parallel plate electrodes and the column plate electrodes.A test platform of electrical characteristics of the dielectric surface insulation is designed to measure the surface charges which are compared with the simulation results to validate the model.The influences of the insulation material and the voltage amplitude on the discharge current,the surface charge distribution and the development speed of surface discharge are analyzed.The main researches of this paper are as follows.(1)A non-equilibrium plasma model of surface discharge is established.According to the physical prototype of the typical mechanical fracture structure of hybrid DC circuit breaker,a geometric model of surface discharge is established,and the appropriate mesh and time step are set up.A two-dimensional(2D)of surface discharges of N2/O2 plasma is presented based on self-consistent fluid simulation.This model solves the continuity equations for charged species and the electron energy balance equation,coupled with Poisson's equation.The chemical reaction of 12 types of particles and 31 chemical reactions are considered in the physical chemistry equation.First,the Poisson equation is solved according to the boundary conditions and the initial charge distribution,and the initial potential and electric field distributions are calculated.The source term and flux in the electron continuity equation are calculated according to the electric field distribution obtained before,and the distributions of electron and electron energy are solved.For the heavy species,the multi-phase diffusion equation is solved,and the spatial concentration distribution is obtained.Finally,according to the boundary conditions and the species number in the discharge space calculated previously,the distributions of the electric field and potential are calculated,and the spatial distribution of species is obtained as well.Based on this model,the distribution of important electrical parameters during surface discharge can be analyzed.The law of dynamic evolution and phase transformation of surface discharge are obtained.(2)The dynamic distributions of the micro parameters during surface discharge under the parallel plate electrodes and the column plate electrodes are studied.A test platform of electrical characteristics of the dielectric surface insulation is designed to measure the surface charges which are compared with the simulation results.It is found that both of them have high consistency,which verifies the correctness of the simulation model and results.Comparing the two kinds of electrodes structures,it is found that the development of the surface discharge is slower and the surface charge is less under the parallel plate electrodes structure.The electrode structure of the HVDC circuit breaker should be with weak vertical component of electric field in order to avoid the surface charge accumulation.(3)The influences of four kinds of insulation materials on the development process of surface discharge,such as polytetrafluoroethylene,polyoxymethylene,nylon and ceramic,were investigate.The study found that the discharge current mainly depends on the conduction current,and the insulation material will affect the space charge distribution,causing the change of the displacement current,which has a certain impact on the discharge current,but the effect is not distinct.When the relative dielectric constant of insulation materials is larger,the surface charge accumulation is more serious,leading to a greater electric field distortion,and accelerating the surface discharge process.The differences of discharge current,surface charge distribution and the development speed of surface discharge under three different voltage amplitudes are studied.The current is generated by the charged particles migrating under the electric field when the voltage amplitude is too low to make the formation of surface discharge,and the space charge density and surface charge density are very small.The stages of surface discharge can be identified from the discharge current when the voltage amplitude is enough to make the formation of surface discharge.The peak value of the spark discharge current is up to several k A,and the surface charge density is about tens of ?C/m~2.The development speed of surface discharge increases with the increase of the electric field,and the speed is 105~106m/s.The further increase of voltage amplitude causes the increase of space charge density,leading to the increase of peak discharge current,up to tens of k A.At the same time,the surface charge density is up to hundreds of ?C/m~2,and the development speed of surface discharge further increases too.