Analysis of Dielectric Properties of Selected Ester Based Dielectric Liquids at Negative Lightning Impulse Voltage

This paper is aimed on presenting results of studies of lightning impulse inception voltage (V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</inf>), lightning impulse breakdown voltage (LIBV) and acceleration voltage (V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</inf>) of three types of esters based dielectric liquids namely synthetic ester (SE), natural ester (NE) and blended ester (BE). Tests are intended to comparatively assess these liquids in terms of resistance against standard lightning impulse voltage (1.2/50 μs) of negative polarity. In addition, results are related also to analogically obtained data concerning other products of similar types, which were tested in past in the same testing conditions. Experiments are carried out in a point-to-sphere electrode configuration with 25 mm gap as per previous author's studies. Applied methodology based on step method with one shot per step. Among measurement techniques the photomultiplier based light emission registration and high-speed camera frames-based movie registration are additionally applied. Before the tests started, liquids are treated to remove moisture and to reach the AC breakdown voltage higher than 70 kV in each case. Results indicate that lightning performance of considered synthetic ester, natural ester and blended ester is similar to lightning performance of their equivalents. Small differences exist, both in the direction of advantages as well as disadvantages but, considering stochastic nature of pre-breakdown and breakdown phenomena in liquids under lightning impulse voltage, there is no way to directly rank any of products tested within studies and testing conditions applied.