Addition Effect of Nitrogen Fine Bubbles and Nonionic Polymer Surfactant to Pure Water on Resistivity and Negative Lightning Impulse Breakdown Voltage of Pure Water

We have been investigating electrical properties of pure water as one of new liquid insulation materials with environmentally friendly excellent insulation performance. However, if pure water is used as liquid insulating material, there is a disadvantage to increase power loss, because pure water has a lower resistivity than insulating oils. Therefore, it is necessary to increase the resistivity of pure water. In our previous studies, it was confirmed that the resistivity increased when specific nonionic polymer surfactants (nonionic polymers) or nitrogen fine bubbles (N
₂
-FBs) were individually added to pure water. In this paper, we investigated the addition effect of nitrogen fine bubbles and nonionic polymer surfactant to pure water on resistivity and the lightning impulse breakdown voltage (BDV) of pure water. As a result, the resistivity of pure water to which N
₂
-FBs were added (pure water added with N
₂
-FBs) was approximately 1.7 MΩ·cm. On the other hand, the maximum value of the resistivity of each pure water to which N
₂
-FBs and nonionic polymer were added simultaneously (pure water added with N
₂
-FBs and nonionic polymer) was approximately 1.8 MΩ·cm. The resistivity of each pure water added with N
₂
-FBs and nonionic polymer was almost equal to the resistivity of pure water added with N
₂
-FBs. The 50% BDV of pure water added with N
₂
-FBs was approximately -75 kV. On the other hand, the 50% BDVs of each pure water added with N
₂
-FBs and nonionic polymer were approximately -50 to -60 kV. The BDVs of each pure water added with N
₂
-FBs and nonionic polymer were lower than that of pure water added with N
₂
-FBs, which was the same as that 50% BDV of pure water. Assuming that polymers adsorbed at the fine bubble interface since polymers adsorbed at the gas-liquid interface, it can be explained as below. It is possible that each pure water added with N
₂
-FBs and nonionic polymer may have been the same resistivity as pure water added with N
₂
-FBs because the nonionic polymer attached around N
₂
-FBs and there may be few nonionic polymers floating alone. It is also considered that pure water added with N
₂
-FBs and nonionic polymer have been insulation weaknesses because the nonionic polymer was adsorbed to N
₂
-FBs to form clusters.