Effect of Temperature on Insulation Properties of SF₆/N₂ Mixed Gas Under AC Voltage

Abstract

The insulation properties of SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> mixed gas are important for the insulation design of high-voltage equipment such as gas-insulated switchgear (GIS) and gas-insulated transmission line (GIL). However, the influence of temperature on insulation performance of SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> under alternating current (ac) voltage is rarely studied. In this article, we did gas breakdown experiments with SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> mixed gas at temperatures changing from −50 °C to 100 °C. The experimental results indicate that the breakdown voltages of SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> mixed gas increase with the increase in temperature. In order to explain the phenomenon, the three-body attachment process in compressed SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> is introduced to analyze the electron avalanche process affected by temperature. The streamer and leader discharge criteria are introduced to qualitatively explain the influence of temperature on the breakdown voltages. It is found that the streamer channel radius becomes larger at elevated temperatures, which causes the increase in breakdown voltage.