In electrical property test for the different kinds of insulators

it is found that partial discharge of the insulator with specific structure will increase with the increase of storage time. We refer to this phenomenon as the hysteresis characteristic of partial discharge. After the combination of 3D simulation and validation tests

it is confirmed that the main reason of this phenomenon results from micro cracks or gaps occurred in the interface between insulating feet and epoxy resin material in later storage or service. By removing insulating feet

the interface between different materials is eliminated and the internal stress is decreased

so the improvements have been achieved.