The Influence of Introducing an Insulating Barrier into the Point-Sphere Electrode System on Its Lightning Properties When Using Different Dielectric Liquids

An increasing number of different types of dielectric liquids are appearing on the market. This is undoubtedly related to sustainable development goals. This paper presents comparative studies of the lightning impulse breakdown voltage (LIBV) of six dielectric liquids with different chemical compositions: naphthenic uninhibited mineral oil (UMO), naphthenic inhibited mineral oil (IMO), natural ester (NE), synthetic ester (SE), bio-based hydrocarbon (BIO), and an inhibited liquid produced using gas-to-liquids technology (GTL). Tests were conducted in a point to sphere electrode configuration with a 5 mm thick pressboard barrier placed between them. This configuration was designed to more closely replicate the actual configuration found in transformers, where the oil channels are separated by pressboard barriers. Tests were performed for two inter-electrode gap distances of 25 mm and 40 mm, and for both lightning impulse voltage polarities. Pressboard barrier was placed so that the distance between point electrode and the barrier was always the same (10 mm). Measurements were performed using the step method. Before measurements began, pressboard barrier was impregnated in dielectric liquid being tested. The obtained measurement results were compared with previous studies conducted by authors, which used a similar electrode system but without pressboard barrier. The results confirmed that inserting pressboard barrier between electrodes effectively inhibits development of discharges and significantly increases the electrical strength of the entire insulation system.