Statistical analysis and interpretation on lightning impulse breakdown voltages of ester liquids under varying field uniformity

Ester liquids (ELs), as the alternative transformer liquids to the conventional mineral oils (MOs), have been increasingly used in power transformers with high voltage ratings. Among various properties, the lightning impulse breakdown voltages (LIBDVs) have been studied elaborately in the past two decades under different electric field uniformities. The electric field uniformities do have an effect on the breakdown characteristics, for example, breakdown mechanisms, polarity effects, and differences of LIBDV between ELs and MOs, which is quantitatively investigated based on the LIBDVs collected from the literatures. The breakdown mechanism transition phenomenon between streamer initiation dominated breakdown and streamer propagation dominated breakdown has been reviewed firstly. Then, the transition field factor boundaries to observe the polarity effect on LIBDVs are taken at around 20 for ELs and 10 for MOs. Besides, the transition field factor boundaries to observe the LIBDV distinctions between ELs and MOs are about 109 and 14 under positive and negative lightning impulse, respectively. The systematic analysis and interpretation on the transition field factor boundaries among different phenomena can provide insights on insulation design of ELs filled power transformers.