Numerical Simulation Study On The Influence Of Air Pressure And Humidity On The Positive Long Air Gap Discharge

UHV transmission is adopted by the power system because it has the advantages of large transmission capacity,long transmission distance low line loss and so on.In UHV transmission project,air is the main external insulation medium,and the insulation distance will directly affect the safety and stability of power system.Scientific insulation level and reasonable air gap are the key issues for optimizing the design of UHV transmission insulation.At present,in the design of power transmission and transformation engineering,the test method is mainly used to determine the insulation gap.The test will consume a lot of manpower and material resources,and the test conditions are less controllable and difficult to simulate complex environmental conditions.To obtain the discharge characteristics of long air gap through numerical simulation modeling is of great significance to the refined design of external insulation in power transmission and transformation engineering and the improvement of test efficiency.The terrain along the transmission line is complex and diverse,and the climate environment is changeable.Some experimental studies have shown that air pressure and humidity will have a great impact on the discharge.Due to the requirement of insulation distance,it is difficult to carry out long gap discharge test in the artificial climate chamber.It is also difficult to simulate all operating environments by conducting discharge tests at high altitudes.Based on this,this paper intends to use MATLAB and COMSOL software to establish a positive long air gap discharge model,and conduct numerical simulation of the discharge process under different gap distances,different air pressures and different humidity environments,and to explore the influence law of air pressure and humidity on the characteristics of positive long air gap discharge.The research results are expected to provide some theoretical support for the study of positive-polarity long-gap discharge mechanism and external insulation design.First of all,based on the existing long air gap discharge model,combined with the previous experimental results about the relationship between the electric field intensity in the streamer region and the air pressure and humidity,the set value of the electric field intensity in the streamer region in the simulation is modified.Then a positive long air gap simulation model considering the influence of air pressure and humidity is obtained.Using the established numerical simulation model,the effect of air pressure on the discharge process of positive long air gaps with different lengths was studied.The research shows that under the same humidity condition,the lower the air pressure is,the lower the electric field intensity and the longer the length of the flow region are.The speed of the streamer and the leader is increased with the air pressure decreases,and the time for gap to break down will be shorter.This phenomenon is more obvious in the short distance gap.The lower the air pressure,the lower the voltage required for gap breakdown.At the same time,the discharge process of 3 m,5 m,7 m and 10 m rod-plane gap at 10%,30%,50%,70% and 90% relative humidity was simulated,and the parameters of the discharge process are obtained,including the three-dimensional structure diagram of the whole discharge process,the streamer length,the curve of the position of the streamer head and the leader head during the discharge process.It is found that in the process of discharge,the length of streamer becomes shorter first and then longer.The longer the gap length is,the greater the difference between the maximum and minimum value of streamer length is.At atmospheric pressure,the lower the humidity is,the longer the stable streamer exists in the discharge process.It can be seen from the curve of the position of the streamer head and the leader head in the discharge process that the higher the humidity is,the slower the development speed of the streamer and the leader is;the lower the humidity is,the faster the development speed of the streamer and the leader is,and the shorter the time of the gap breakdown is.The breakdown voltage of the gap increases with the increase of humidity.