Experimental research on polarity effect of CF₃I/N₂ mixtures under lightning impulse

Abstract

SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> is a kind of strong greenhouse gas, it is urgent for researchers to seek new alternative insulating gas. This paper studies the discharge characteristics of CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> I/N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas mixture with needle-plane and sphere-plane electrode under standard lightning impulse, which is important for CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> I and its mixtures applied in electrical equipment. The experimental results show that the breakdown strength of CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> I/N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> increases with increasing gas pressure and gap distance. The discharge characteristics of CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> I/N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas mixtures present significantly polarity effect both in highly non-uniform electric field and slightly non-uniform electric field. In the highly non-uniform electric field, the 50% breakdown voltage in negative lightning impulse is greater than that under positive polarity. Under slightly non-uniform field, breakdown voltage in negative lightning impulse is lower than that in the positive polarity. When the electrode gap is 5mm, the polarity reversal phenomenon appeared with the increase of gas pressure. The analysis shows that CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> I/N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas mixture appears polarity effect and polarity reversal phenomenon in the short gap is due to the migration and interaction of space charge between the electrodes gap.