The Mechanism And Expei Mental Study On The Truncated Arc Of A Self Expanding Strong Air Flow With Multiple Breakpoints Method In A Confined Space

With the development of power grid and the improvement of transmission line voltage level,the probability of lightning strike is greatly increased,and how to effectively carry out lightning protection for transmission and distribution lines is urgently needed to solve.The actual operating data for many years shows that the lightning protection effect of the traditional "blocking" measures are not ideal,this is due to the fact that the lightning withstand level of the line is related to the ground network resistance,lightning steepness,insulation level,lightning mode(shielding failure and back flashover)and the probability of lightning intensity exceeds the lightning withstand level,and these are not controllable factors that lead to the probability of insulation impulse flashover is very high,and there is no arcing suppression measures,the lightning accident rate,lightning trip rate and lightning outage rate increased;therefore,a new type of lightning protection measures for transmission and distribution lines is urgently needed.In order to solve the above problems,a kind of multiple breakpoints arc-extinguishing lightning protection gap that can quickly extinguish the arc and effectively suppress the development of the power frequency arc is studied.When the lightning occurred,the gap between the flashover electrode and the wire was broken,the impulse arc entered into the arc-extinguishing chamber,the arc developed along a specific arc-extinguishing chamber structure,the arc divided into multiple short arc.Due to instantaneous heat conduction characteristics of the arc,the arc-extinguishing airflow acted on the arc,arc gradually appeared a break-point.And then the arc break-point developed fracture,thereby the the continuity of the arc energy channel was destructed.With the development of the arc,the arc contacted with the cold inner wall of the arc-extinguishing chamber.The arc temperature dropped rapidly,the energy of the arc was weakened and then the arc was extinguished.The mechanism of arc-extinguishing and related experimental research on the device proposed in this paper are studied,and the specific research work are as follows:1)The change regulation of physical characteristics of arc plasma under strong airflow are studied,including arc temperature,arc diameter,arc self magnetic contraction pressure,arc volt ampere characteristic,arc speed,near cathode effect of arc and arc heating efficiency.The development process of arc is analyzed by establishing the developing arc model under the action of airflow.The deionization process of the arc and the energy emission process of the are in the arc quenching process are analyzed theoretically.The analysis results show that the arc temperature will decrease under the action of airflow,the composite action will be enhanced,the positive and negative charge particles in the arc column will be neutralized,and the diffusion of charged particles in the arc column will increase,which are both good for the arc extinction.When the arc is restrained by the arc-extinguishing chamber,the arc is compressed,then the radius of the arc decreases,and the pressure of the arc column will increase,so that the arc self magrnetic compression effect is enhanced,and the arc will be compressed again.According to the energy conservation law of electric arc,the arc is compressed by two times,which will increase the center temperature of arc column,and increase the temperature of the arc chamber and high-speed airflow was generated,creating a good condition for arc quenching.At the same time,the near the cathode effect is existed in short arc.When the arc current crossed zero,the dielectric recovery strength generated in the the cathode surface,and the arc is cut into multiple short arcs,near cathode effect is existed in every short arc,the overall medium recovery strength is the superposition of multiple short arcs,this two comprehensive factors contribute to extinguishing the arc,creating the perfect conditions for extinguishing the arc when the arc current crossed zero.2)The generating mechanism of the arc-extinguishing airflow is theoretically analyzed,and the heat transfer process of the arc is calculated by the lumped parameter method.The arc chain model is established to calculate the arc-extinguishing time,and the finite element method is used to deduce the airflow control equations,and a model of airflow coupled arc is established.The geometry structure of single arc-extinguishing chamber is modeled by COMSOL software to mesh geometry model,differential equations solver using direct solution is established and the two-dimensional cut-off points are set on the symmetry axis of the arc-extinguishing chamber to analysis the temperature,conductivity,speed of the point.At the same time,the temperature distribution,velocity distribution and conductivity distribution of the simulation results can draw change regulation of physical properties of the arc.The conductivity distribution obtained from the simulation can be seen that the arc begins to appear a break-point in about 0.01ms,then the break point area increases gradually,finally form a fracture,the arc is divided into two isolated arc,the arc energy at the moment can not effectively input,which makes the arc extinction.It can be seen from the velocity cloud diagram that the maximum velocity of airflow can reach 51Om/s.3)The lightning volt-second characteristic test,the power frequency arc-extinguishing test,the impulse current discharge test,the impulse coupling power frequency arc-extinguishing test and the 500kV insulation coordination test of the device are carried out.The arc-extinguishing devices are installed in the distribution lines,the calculation results of the lightning trip-out rate of line after arc-extinguishing devices installed and the calculation results of the lightning trip-out rate of line before arc-extinguishing devices installed are analyzed.The test results show that when the gap distance is 8.5cm,the protection effect of the device on insulators is achieved.The power frequency arc-extinguishing test results show that the device can effectively suppress the power frequency arc with the current amplitude of 2kA.The impulse current discharge test results show that when the impulse arc enters into the arc chamber,the arc-extinguishing airflow is formed through the instantaneous heating of the impulse arc,and the arc is cut off by multiple points,and the arc energy supply channel is cut off.At 0.1ms,the velocity of the arc-extinguishing airflow increased and the energy of the arc is weakened to a great extent under the effect of the arc-extinguishing airflow.The impulse coupling power frequency arc-extinguishing test results indicate:The device can effectively suppress the 3.9kA power frequency arc and extinguish the power frequency arc in 0.3ms.Compared with the calculation results of the lightning trip-out rate,it is concluded that the lightning trip-out rate after the installation of the arc-extinguishing device is 83.75%lower than that before the installation of the device.Theory and experimental applications verify the effectiveness of the device for arcing.It can protect insulators from burning and prevent lightning accidents.