Influence of formulation and aging on the dielectric response of ethylene propylene rubber insulation compounds

An electric-utility-sponsored research project was undertaken to systematically explore the effect of compounding on the wet electrical aging behavior of ethylene propylene rubber (EPR) insulating compounds used for medium-voltage power distribution cables. A series of EPR compounds, analogs of commercially available systems, have been prepared for this research. The number, type, and amount of each functional ingredient has been altered in a systematic way so that its effect on the performance of the insulation system can be assessed. A matrix of 72 compounds was developed, where the functional ingredients expected to have a major impact were treated in a full factorial matrix. The functional ingredients that were considered are base polymers, clay fillers, processing aids, antioxidants, ion scavenger levels, and degree of crosslinking. The fundamental dielectric behavior of this series of compounds was characterized using time domain dielectric spectroscopy and thermally stimulated current measurements