Breakdown of polyurethane hard-foam insulation under short-time HV stress

Breakdown performance of dielectric material with microporous structure is investigated under short-term voltage stress. The material is a self-skinning polyurethane hard foam. Experimental research on impulse voltage strength and partial-discharge behavior in AC run-up tests shows aspects of gas breakdown in the pores. The structure of the material and the form and size of pores are investigated by optical means and SEM. The composition of the gas in the pores and the diffusion processes are analyzed. These results lead to a model of short-time breakdown of the complete microporous dielectric insulating system, taking into account the breakdown of a single pore according to the relevant theory of gas breakdown.< >