Aspects of breakdown inhibition in filled composites

Commercial insulation materials are often polymer composites containing additives of a particulate or laminate form. Such additives, in general have (i) a higher permittivity, (ii) a better breakdown resistance, and (iii) a greater mechanical roughness, than the base resin. Thus it can be expected that the electrical breakdown path will be excluded from the filler, a feature that is likely to change the time to breakdown, t/sub b/, beneficially. The lower polymer permittivity (/spl epsi//sub p/) will, however, cause an applied field to be concentrated in the polymer, and thus there will be an upper bound to the filler permittivity (/spl epsi//sub f/) above which it is liable to initiate breakdown. Both these aspects of filled material are investigated.