Research on Breakdown Characteristics of Phase-change Insulating Coolant Between Self-Heating Electrodes

Phase-change heat transfer can efficiently draw off heat from heat source. Therefore, phase-change materials are wildly used as cooling medium in many kinds of power equipment. Evaporative cooling power transformer is a typical example of the application results in China. In this paper, in order to meet the current development requirements for lightweight and miniaturization of traction transformers, a new type of phase-change insulation coolant QYB_A is selected Its boiling point is higher than the coolant used in existing evaporative cooling power transformers, which is favorable to improving heat transfer efficiency in condensation units and miniaturizing the condensation unit. The cooling performance and insulating property of QYB_A determine whether it can successfully replace the transformer oil in the traditional traction transformer. Hence, a breakdown experimental system for phase-change insulation between self-heating electrodes is designed in this paper. The breakdown characteristics of QYB_A under different thermal loads and different space length between electrodes are tested. The experimental results show: Under the condition of zero pressure in the experimental system, breakdown voltage of the liquid state of QYB_A is 70 kV when the space length between electrodes is 2.5mm, which is comparable(equivalent) to the existing evaporative coolant used in power transformer. As the heat load rises and the proportion of gas phase medium increases, the breakdown voltage of the two-phase insulating coolant shows nonlinear trend, which rises after decreases first, and the lowest value appears when the heat load is 9.S9kW / m². To ensure the safety of phase change insulation systems, further research should closely focus on this phenomenon.