Space charge accumulation in epoxy resin and polyethylene

Accumulation of space charge within a polymeric dielectric material, especially under dc voltage, is associated with its degradation. Space charge accumulation modifies the local field within the material and might contribute to its aging. Further, it would modify the conduction through the material. Formation of space charge within the dielectric material depends on the charge injection from metal-dielectric interface, and the nature of generation and transport of charge within the dielectric material. These are affected by various factors like material composition (including additives or cross linking), applied field, temperature and electrode material. In this work, Pulsed Electro Acoustic (PEA) technique is used to study the effect of field on charge accumulation and distribution in two commonly-used polymeric dielectric materials. The threshold field for space charge accumulation is identified. PE and epoxy resin are chosen since the former is semi-crystalline while the latter is amorphous. An estimate of trap depth and mobility at different fields are also obtained. The effect of two different electrode materials viz. gold and aluminum is also investigated. In this work, information about various parameters related to accumulation of space charge within the material is estimated from measured space charge distribution data obtained from PEA measurements. Maximum amount of charge stored in the material is obtained for different materials and as well as different electrode material under different applied fields.