Mechanism of Creepage Distance Dependency for Electrical Breakdown of Alumina at High Temperature

Abstract

Solid Oxide Fuel Cells (SOFCs), which work at 600 ∼ 1000°C and have efficiencies of over 60%, are expected to be larger capacity. However, expanding SOFCs will rise operating voltage and increase the risk of insulation failure. Extending creepage distance is one of the ways to reduce the risk. In order to clarify the effect of extending creepage distance on dielectric strength, it is indispensable to elucidate the mechanism of creepage distance dependency for electrical breakdown in high temperature and non-uniform electric field.

In this paper, surface breakdown voltage for alumina (Al₂O₃) at 700 ∼ 900°C was measured, changing creepage distance from 4 mm to 20 mm. As a result, at 4 ∼ 8 mm, breakdown voltage was proportion to the 0.4 ∼ 1.2th power of creepage distance. However, at 8 ∼ 12 mm, breakdown voltage decreased with extending creepage distance and indicated dependency on Paschen's law. At 12 ∼ 20 mm, breakdown voltage was proportion to the 0.25 ∼ 0.3th power of creepage distance. At creepage distance of 8 mm, breakdown voltage was over 3 kV. Therefore, the voltage of primary insulation part should be 3 kV or less to prevent increase in size and cost.