Experimental Study on the Flashover Characteristics of Polluted Insulators under Short-tail Lightning Impulse Waveform

Abstract

The pollution flashover accidents of insulator strings do harm to the safe operation of transmission lines. The paper aims to investigate the flashover characteristics of a 2-unit glass suspension string under 0.5/5μs short-tail impulses. Firstly, in order to represent the pre-heating effect of operation voltage, a composite test circuit was established. It can generate a combined voltage waveform consists of the power frequency ac voltage and a subsequent 0.5/5μs impulse. Secondly, adopting the artificial contamination test method with ESDD in the range of 0.010.1mg/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , in the absence of the ac voltage, the U <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50%</sub> of the 2-unit glass suspension string decreases with increasing of ESDD, and reached saturation when ESDD is larger than 0.025 mg/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Comparing to the clean insulator, U <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50%</sub> was reduced by 25%. Thirdly, the result of composite test indicates that the prestressed ac voltage has little influence on the U <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50%</sub> of the insulator. According to the observed flashover paths, most of the flashover was happened between surface of two insulators. The potential distortion caused by the pollutant deposits layer was beneficial to streamer inception. This might be the reason rather than the formation of pre-heated dry bands that leads to a lower U50% when the polluted insulator is subjected to short tail impulses.