Effects of Nitrogen Fine Bubbles Generating Time and Standing Time on Resistivity and Negative Lightning Impulse Breakdown Voltage of Pure Water in Nitrogen or Air Atmosphere

Mineral oil is generally used as a liquid insulating material. However, mineral oil has the problem of having a large environmental load. Therefore, in order to use pure water as an environmentally friendly liquid insulating material as an alternative to mineral oil, we have been researching aimed at improving the electrical properties of pure water. In this paper, we focused on the generating time of nitrogen fine bubbles (N
2
-FBs) and the standing time after generating N
2
-FBs, and investigated the effects of N
2
-FBs generating time and standing time on resistivity and negative lightning impulse breakdown voltage (NLI-BDV) of pure water in nitrogen or air atmosphere. As a result, the resistivity of pure water decreased as increasing of the generating time of N
2
-FBs and standing time after generating N
2
-FBs. However, the NLI-BDVs of each pure water were approximately same value, regardless of the generating time of N
2
-FBs and the standing time after generating N
2
-FBs. From the above results, it was suggested that N
2
-FBs affect the resistivity of pure water and does not affect NLI-BDV of pure water.