Design and Experimental Validation of an Adjustable High-Voltage Test Fixture for Dielectric Strength Characterization of Magnesium Oxide Powder

Magnesium oxide (MgO) powder is widely used as an electrical insulating medium in high-temperature electrical systems; however, reproducible dielectric breakdown characterization remains challenging because the measured response is sensitive to powder-layer thickness, packing state, and electrode configuration. In this study, an adjustable high-voltage test fixture is developed for controlled comparative breakdown testing of loose MgO powder. The fixture integrates an adjustable electrode mechanism, a confined powder chamber, and rounded electrode edges to improve the controllability of the test geometry. An axisymmetric finite difference method (FDM) model was first established to investigate the electric-field distribution at electrode gaps of 2, 3, 5, and 10 mm, and a finite element method (FEM) model in COMSOL Multiphysics was subsequently used for independent numerical comparison. A CNC-machined prototype was experimentally evaluated using MgO powders with different mesh grades at powder-layer thicknesses of 2 and 3 mm. Under controlled ambient conditions, the measured breakdown voltage varied with both powder-layer thickness and mesh grade. Among the investigated powders, the 200-mesh MgO sample exhibited the highest measured breakdown voltage, reaching 5.54 kV at 2 mm and 6.98 kV at 3 mm, corresponding to apparent breakdown field strengths of 2.77 and approximately 2.33 MV·m−1, respectively. These results demonstrate the feasibility of the proposed fixture for controlled comparative breakdown characterization of loose MgO powder.