Space charge accumulation in epoxy-PET composites

Composite insulation systems are commonly used in high voltage apparatus. In the presence of multiple materials, interfaces between the materials assume considerable significance. Epoxy-PET composites are used as class B insulating materials in transformers but little is known about the interfacial charge behaviour in such a system. In this work, a comprehensive study is undertaken to understand the charge dynamics at the amorphous (epoxy)/semi-crystalline (PET) interface of Epoxy-PET composites. On application of electrical stress, mismatch in permittivities and conductivities at dielectric-dielectric interface leads to accumulation of charge at the interface. This charge accumulation is governed by charge injection at the electrodes and generation of charge within the material due to dissociation. In this work, the Pulsed Electroacoustic (PEA) technique is used to map the space charge distribution in epoxy-PET insulation system. The present study is aimed at understanding the phenomena of space charge distribution in epoxy-PET multi dielectric material. The two-layer multi-dielectric system is first oriented such that the PET layer lies proximal to the high voltage electrode. Subsequently, the epoxy layer is placed in contact with the high voltage electrode. Apart from investigating the space charge behaviour in the specific composite, the broader objective of this work is to understand the effect of a dielectric-dielectric interface on the space charge dynamics of the composite dielectric. Aluminium is used as the electrode material.