Study On Arc Quenching Mechanism Of Pressurized Explosion Airflow In Multi-pipe Structure

With the continuous expansion of the power system,the probability of lightning strikes on transmission lines has gradually increased.The power outages caused by lightning trips have severely affected economic development and the stability of people's daily lives.Although traditional lightning protection methods have been proved effective to some extent,they are still restricted by uncontrollable factors such as the intensity of the lightning strike,the type of lightning strike,and the lightning strike method.Flashover is apt to be caused under lightning impulse overvoltage.The continuous combustion of subsequent power-frequency arcs will not only cause line trips,but may also cause permanent damage to the electrical equipment,resulting in huge economic losses.Therefore,currently,it is urgent to propose new lightning protection measures that can effectively reduce the line trip rate,disconnection rate and accident rate of lightning strikes in order to deal with the increasing threat of lightning damage.The multi-pipe arc quenching device studied in this paper has multiple arc compression pipes,each of which has an arc ignition electrode to control the arc path,and the adjacent pipes constitute an arc quenching chamber and an air jet.The device adopts the lightning protection concept of “impulse dredging and power frequency blocking”.Under lightning overvoltage,the impulse flashover is allowed,but power frequency arc establishing is not allowed.In the impulse arc phase,due to the impact energy,the device can generate the pressurized explosion airflow and act on the unstable power frequency arc,effectively suppressing the power frequency arc in the very early "germination period" to avoid line lightning trips.Through theoretical modeling,numerical analysis,simulation analysis and a series of testing experiments,the impulse quenching mechanism of multi-pipe arc quenchingdevice is studied in this paper.The main work is conducted and the corresponding results are obtained.(1)The development characteristics of arc in a multi-pipe structure are studied,which include identifying conditions conducive to arc quenching through the analysis of the essential physical characteristics of the AC arc,and establishing an arc development and heat transfer model of the unit pipe to explain the reason for the pressurized explosion airflow.The reason is ascribed to the rapid temperature rise after the arc is compressed and the heat is conducted to the pipe air.It is concluded that zero quenching and impulse quenching are two kinds of arc quenching methods of multi-pipe structure,among which the impulse quenching is dominant.(2)Combining the theory of arc magnetohydromechanics with the Euler high-speed airflow field model,a simplified model of arc-coupled pressurized explosion airflow in a multi-pipe structure is established and approximated.The analysis results show that the change of temperature lags behind the change of arc current.After the impulse arc,the arc current picked up briefly,but under the continuous action of the airflow,the arc eventually extinguished.The pressurized explosion airflow begins to develop from the middle of the pipeline where a high-speed,high-pressure airflow with a speed of 840m/s and a pressure of0.9Mpa can be generated during the early arc stage.Accompanying the attenuation of the impact energy,the airflow and the pressure can gradually shift from the middle of the pipe to the ends.After the arc is extinguished,a negative velocity flux appears at both ends.(3)The multi-physics simulation software is used to study the arc quenching process and the optimization of the geometry of the arc quenching chamber.Among them,the simulation results of arc quenching show that the instantaneous change of temperature is the key factor to generate the pressurized explosion airflow.It can be judged from the distribution nephogram of speed,temperature,and electrical conductivity that after the air in the arc quenching chamber is heated sharply,the peak air velocity can reach 900m/s.The high-speed pressurized explosion airflow blows the arc from the arc quenching chamber to form an arc spray phenomenon.The arc energy fracture has basically formed in about 0.2ms,and then the electrical conductivity of the arc drops rapidly,and it is completely extinguished around0.31 ms.The optimization analysis on the geometry of the arc quenching chamber shows thatthe width and depth of the arc quenching chamber can affect the heat dissipation of the arc;reducing the deflection angle of the pipeline can increase the difficulty of arc establishing;augmenting the number of arc quenching chambers is beneficial to the current density of the overall structure.The multi-pipe structure will suck in new air medium after the arc quenching process is completed.This backflow characteristic of the multi-pipe structure enables it to effectively protect against multiple strikes.(4)The main performance of the 10 k V multi-pipe arc quenching device is tested through experiments.Among them,the discharge voltage test and the lightning impulse volt-second characteristic test determine the lightning impulse 50% discharge voltage and power frequency wet endurance voltage of the multi-pipe arc quenching device.The volt-second characteristic curve of the device is obtained,which verifies that the device can protect the insulator from flashover under lightning overvoltage.The high-current impulse test verifies that the multi-pipe arc quenching device can segment the impinging large arc,and the triggering of the pressurized explosion airflow is fast.The power follow current blocking test waveform display device can quickly cut off the system follow current and will not reignite.The impulse-power frequency combined arc quenching test shows that the device operates extremely fast,and can produce high-speed pressurized explosion airflow at 0.01 ms.The power frequency arc is deeply suppressed,and the arc establishing peak of power frequency current is only 1k A,finally the arc is extinguished at around 0.35 ms.The optimum insulation mix ratio of the combined arc quenching device is obtained by the insulation match test of500 k V.(5)The result that the device can significantly reduce the line lightning trip rate by nearly85% is obtained through the comparisons between the arc-building rate,the lightning trip rate before and after installing the multi-pipe arc quenching device.The actual operating conditions show that the multi-pipe arc quenching device has achieved a good lightning protection effect,and the trip rate of lightning strikes on some severely damaged lines has become zero after the device is installed.