Numerical Computation on Cold Dielectric Recovery Characteristics in High Voltage SF6 Circuit Breaker

Abstract

In order to study the cold dielectric recovery characteristics of high voltage SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> circuit breaker, a mathematical model is established for the airflow field and electric field inside the circuit breaker arc extinction chamber, and numerical calculation and analysis were made for electric field intensity and airflow characteristics. The variation curve of the electric field non-uniform coefficient f with the contact open distance is obtained by electric field calculation; the electric field calculation result is introduced into the flow field, while the spatial distribution dynamic characteristics like pressure, mass density were analyzed through the flow field, and the critical breakdown field strength of contact gap is calculated according to the stream theory; Based on the electric field calculation result, the circuit breaker arcing chamber structure is a slightly uneven electrical field, the breakdown voltage of the SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas under different pressures is calculated by breakdown voltage empirical formula of SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas under slightly uneven electrical field. The results show that the dielectric recovery strength is affected by the open distance of the circuit breaker, the nonuniformity coefficient of the electric field structure and the particles number density of SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas. Near the open distance of 3mm, there is a sharp point in the electric field nonuniformity coefficient, the minimum particles number density of SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas between the arc contacts, and the low breakdown voltage of SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas, which is the relatively weak area of SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> dielectric insulation strength in breaking process. Under the same conditions, the higher the pressure of arc extinction chamber, the higher the recovery strength of the dielectric. The dielectric recovery strength at 0.5MPa is 71.4% to 0.7MPa. The analytical method of this paper provides a new idea for the study of dielectric recovery characteristics of SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> and its alternative gas.