AC breakdown voltage of thermal bubble induced two-phase flow condition of inflammable fluorocarbon by self-heating electrode

Although it has been found that the insulating characteristics of thermal bubble induced two-phase flow changes with pressure and heat power, its breakdown mechanism has not been known clearly so far. In order to obtain actual working conditions of two-phase flow state of fluorocarbon, a special apparatus with self-heating plane-plane electrodes is fabricated to study the relation of AC breakdown voltage (BDV) and thermal parameters, such as heat density, working pressure, electrode surface temperature, and so on. The pressure in the test apparatus could be adjusted individually by a pressure regulator. The test results under atmosphere pressure (0.1MPa abs.) show the BDV of the fluorocarbon liquids remains relatively flat with the heat density less than 7000W/m², and drops sharply when the heat density increases until 20000 W/m². Then the BDV remains the breakdown value of vapor at higher heat density. The thermal parameters and the flow style are also studied with the BDV decreasing line. The test data can provide design constraints for the inflammable fluorocarbon liquid immersed transformers.