Comparing Synthetic Ester and Gas-to-Liquid Insulation Liquids Under Lightning Impulse Voltage Using a Creepage Discharge Test Setup

This article presents the methods and results of an experimental study performed to investigate the partial discharge behavior of synthetic ester and gas-to-liquid insulation liquids using a transformer design-based creepage discharge test setup similar to a two-layer winding with barrier insulation. The test setup consisted of a paper-insulated U-shaped copper rod, a circular pressboard disk and a grounding electrode which were submerged in the respective liquid. The study was focused on positive lightning impulse voltages. Partial discharges were detected optically using a photomultiplier tube. The study revealed that the existing design curves for creepage paths cannot be applied to the insulation arrangement. Furthermore, the synthetic ester liquid exhibited partial discharges at 30 % higher electric stress than the gas-to-liquid insulation liquid.