Abstract: In order to study the electrical insulation performance of water mist for electrical transformers, the breakdown voltages of water mist were tested. The test voltage was nearly 1 000 kV. The breakdown voltage of water mist under different electrode types or
using different water mist nozzles were compared. The results showed that the breakdown voltage of water mist was similar to
that of air, and the insulation ability was good. The electric spray water mist test of 220 kV transformer covered with high voltage
bushing was carried out. By comparison of electric current of transformer before and after spraying, no significant differences were
found, which verifies the electrical insulation ability of water mist.

Key words: water mist, high- voltage, insulation, breakdown voltage, transformer