Space charge accumulation in multilayer insulators

In a multilayer insulator made of two or more materials with different dielectric constants and conductivities, internal space charge accumulates at their interfaces. If the local field is increased by the accumulated charge, the electric durability of the insulator should be decreased. In this paper, we describe the space charge accumulation measured when using oil-impregnated PPLP (polypropylene laminated paper)-consisting of triple layers (craft paper/polypropylene/craft paper)-was subjected to a strong dc electric field. The experimental results suggest that internal space charge accumulates at both surfaces of the PP layer and that the electric field in the craft paper layers disappears.