Research on influence factors of micro-bubbles generation mechanism in oil paper insulation of 1000 kV transformers

The 1000 kV transformer is one of the most important equipment in ultra high voltage (UHV) power grid, and its service life largely depends on the state of its oil paper insulation system. Especially when micro-bubbles appear in oil paper insulation, the insulation performance of oil paper insulation will be greatly reduced. In this paper, the oil paper insulation micro-bubbles generation platform has been built in the laboratory for 1000 kV transformers. Based on the platform, the influence of temperature rate on oil paper insulation micro-bubbles was studied firstly. By setting the heating power, the micro-bubbles generation experiment of oil paper insulation samples with 3.0% water content was carried out. It is found that with the increase of heating rate, the initial temperature of micro-bubbles generation will increase and the time interval of micro-bubbles escape will be shorten. Then, the oil paper insulation samples aged for 0 day, 20 days and 40 days were tested. It is found that the longer the thermal aging time, the higher the micro-bubbles begin temperature, which directly shows that thermal aging could inhibit the generation of micro-bubbles. In addition, it is found that different layers of insulation paper also have an effect on the generation of micro-bubbles. These results can provide theoretical data support for the operation load setting and fault diagnosis of 1000 kV transformers.