In an arcjet thruster,the cathode and constrictor degrade with time,and the electrical arc discharge may become unsymmetrical.In this work,a three-dimensional numerical model of a hydrogen plasma arcjet is developed a...In an arcjet thruster,the cathode and constrictor degrade with time,and the electrical arc discharge may become unsymmetrical.In this work,a three-dimensional numerical model of a hydrogen plasma arcjet is developed and validated to study the effect of unsymmetrical electric arc discharge on thruster performance.The unsymmetrical arc discharge is realized by introducing a radial shift of the cathode so that the cathode tip offset is 80μm(25%of the constrictor radius).Simulations are conducted for both axially centered cathode(coaxial)and off-centered cathode(non-coaxial)configurations with identical propellant flow rates and input current.Simulations show asymmetrical arc discharge in the non-coaxial cathode configuration,resulting in azimuthally asymmetric Joule heating,species concentrations,and velocity field.This asymmetry continues as the plasma expands in the divergent section of the nozzle.Temperature,species concentrations,and axial velocity exhibit asymmetric radial distribution at the nozzle exit.The computed Joule heating was found to reduce with cathode shift,and consequently,the thrust and specific impulse of the thruster was decreased by about 6.6%.In the case of the non-coaxial cathode,geometric asymmetry also induces a small side thrust.展开更多
输电线路覆冰是造成线路跳闸的重要原因之一。云南电网公司通过对500 k V输电线路进行地线绝缘化改造,实现了线路地线的直流融冰。由于地线绝缘化改造过程中,地线会通过地线绝缘子悬挂于杆塔塔头处,导致地线高度降低,进而使得输电线路...输电线路覆冰是造成线路跳闸的重要原因之一。云南电网公司通过对500 k V输电线路进行地线绝缘化改造,实现了线路地线的直流融冰。由于地线绝缘化改造过程中,地线会通过地线绝缘子悬挂于杆塔塔头处,导致地线高度降低,进而使得输电线路的保护角增大,影响线路的绕击耐雷性能。通过EMTP-ATP平台计算5种不同塔型地线绝缘化改造前后的绕击耐雷水平,并通过电气几何模型(electric geometry model,EGM)计算这些塔型的绕击跳闸率。结果表明:地线绝缘化改造对线路绕击耐雷水平影响较小,但是对绕击跳闸率影响较大。展开更多
超高压(Extra High Voltage,EHV)输电线路多为同塔双回,引雷面积大,更易遭受到雷击,特别是对于山谷间大跨度的杆塔常发生绕击跳闸事故。据运检单位统计表明,绕击是引起线路跳闸的主要原因。因此,对输电线路雷电绕击进行分析,探讨影响同...超高压(Extra High Voltage,EHV)输电线路多为同塔双回,引雷面积大,更易遭受到雷击,特别是对于山谷间大跨度的杆塔常发生绕击跳闸事故。据运检单位统计表明,绕击是引起线路跳闸的主要原因。因此,对输电线路雷电绕击进行分析,探讨影响同塔双回输电线路防雷性能的敏感因素是十分必要的。建立500 kV输电线路的绕击模型,该模型采用电气几何模型(Electrical Geometric Model,EGM)法,通过呼高、地面坡度、保护角、导线相序排列变化所导致的雷电绕击跳闸次数变化来反映出各因素对于绕击耐雷性能的影响。展开更多
基金the Indian Space Research Organization(VSSC-ISRO)for funding this research through ISRO-IITM Cell。
文摘In an arcjet thruster,the cathode and constrictor degrade with time,and the electrical arc discharge may become unsymmetrical.In this work,a three-dimensional numerical model of a hydrogen plasma arcjet is developed and validated to study the effect of unsymmetrical electric arc discharge on thruster performance.The unsymmetrical arc discharge is realized by introducing a radial shift of the cathode so that the cathode tip offset is 80μm(25%of the constrictor radius).Simulations are conducted for both axially centered cathode(coaxial)and off-centered cathode(non-coaxial)configurations with identical propellant flow rates and input current.Simulations show asymmetrical arc discharge in the non-coaxial cathode configuration,resulting in azimuthally asymmetric Joule heating,species concentrations,and velocity field.This asymmetry continues as the plasma expands in the divergent section of the nozzle.Temperature,species concentrations,and axial velocity exhibit asymmetric radial distribution at the nozzle exit.The computed Joule heating was found to reduce with cathode shift,and consequently,the thrust and specific impulse of the thruster was decreased by about 6.6%.In the case of the non-coaxial cathode,geometric asymmetry also induces a small side thrust.
文摘输电线路覆冰是造成线路跳闸的重要原因之一。云南电网公司通过对500 k V输电线路进行地线绝缘化改造,实现了线路地线的直流融冰。由于地线绝缘化改造过程中,地线会通过地线绝缘子悬挂于杆塔塔头处,导致地线高度降低,进而使得输电线路的保护角增大,影响线路的绕击耐雷性能。通过EMTP-ATP平台计算5种不同塔型地线绝缘化改造前后的绕击耐雷水平,并通过电气几何模型(electric geometry model,EGM)计算这些塔型的绕击跳闸率。结果表明:地线绝缘化改造对线路绕击耐雷水平影响较小,但是对绕击跳闸率影响较大。
