Negative Lightning Impulse Breakdown Characteristics of Pure Water with and without N2 Fine Bubbles

Electrical insulating oils have been used for many years in power equipment such as transformers and bushings. However, once oils leak from the equipment, it adversely affects the environment. We therefore focused on pure water as one of environmentally friendly liquid insulating materials, and we have been investigating the basic breakdown characteristics of pure water. This paper presents a study of the negative lightning impulse breakdown voltages of pure water with and without nitrogen fine bubbles (N2-FBs). The breakdown voltages were investigated using sphere-to-sphere and plane-to-plane electrode configurations. As the result, it was found that N2-FBs tend not to be weak points of breakdown, but rather to raise the breakdown voltage. It was also found that the diameters of N2-FBs may vary depending on the produced location in an experimental container.