Physical Model Research On Leader Discharge Of Long Air Gap Under Low Atmospheric Pressure

Reasonable external insulation design has become an important factor to ensure the safely and reliable operation for EHV/UHV transmission and transformation project.As the increasing of altitude,atmospheric pressure decreases,air insulation drops.There exists certain differences of macroscopic and microscopic characteristics of long air gap discharge between low atmospheric pressure area and normal atmospheric pressure area.At present,in order to meet the needs of the EHV/UHV transmission technology research in our country,carried out a lot of long air gap discharge characteristic research.Most of the researches focused on the experimental study of long air gap discharge characteristics of power transmission and transformation project,few studies in terms of discharge mechanism,less studies in terms of discharge mechanism while under the condition of low atmospheric pressure.Studying leader discharge development process of long air gap under the condition of low atmospheric pressure,and comparing with the results which obtained under the condition of normal atmospheric pressure in low altitude areas will help us to further understand the mechanism of long gap discharge.Due to the high dispersion of long air gap discharge characteristics,we need to do lots of experiments research,and that is costly,strenuous and time-consuming.While the simulation analyses of physical model of leader discharge can make up for the inadequacy of experimental research.Taking the rod-plate air gap as the study object,this paper mainly focuses on the modeling of physical model of long air gap leader discharge under low atmospheric pressure condition,theoretical analysis of discharge,physical modeling,simulating and experimental tests has been conducted.The leader discharge processes of lm,2m and 3m rod-plate air gap under the condition of 0.06MPa atmospheric pressure were simulated by using MATLAB software,physical parameters such as the discharge channel image,the development speed of leader channel,accumulated discharge charge,discharge current,intensity of the space electric field were obtained.Carried out a series of positive switching impulse discharge experiment test for 1m,2m and 3m rod-plane air gaps in Tibet's High Altitude Test Base of State Grid Corporation where altitude is about 4300 m by using high speed photography and integrated optical electric field sensor(OEFS)synchronous observation system.Parameters such as the discharge channel image,intensity of space electric field in certain position were obtained,results revealed that the critical electric field of the air medium is about 1850 kV/m?2100 kV/m kV/m.Compared the physical parameters which obtained from experimentation with the results which obtained under the condition of normal atmospheric pressure in low altitude areas and the ones from simulation.The simulation leader discharge channels and electric fields broadly in line with the experimental tests results,while the leader initial time and breakdown time deviate from the measured values to some extent.Considering the randomness and dispersion of long air gap leader discharge,the model is rational and valid.