The effect of high voltage fields on epoxy laminates

This thesis describes the characterisation of epoxy/glass fibre composite material before and progressively through electrical and thermal ageing. Glass fibre reinforced epoxy (GFRE) material is used in pressboard transformers for optical telecommunication systems, typically at voltages between 1 and 2kV. The material was characterised by means of space charge measurements using the Pulsed Electroacoustic (PEA) technique, Dielectric response, Dynamic Mechanical Analysis (DMA), Differential Scanning Calorimetry (DSC), and Scanning Electronic Microscopy (SEM). An ageing programme was set up to follow the thermal and electrical ageing (at DC fields) of the GFRE by the same means. The results show a q-dc transport process with an activation energy of 1.1eV. The qdc process is associated with a charge transport process on the surface of the fibres. The results for the aged samples show delamination and debonding between the epoxy and the glass fibre at the glass epoxy interface. The delamination creates free volumes and voids which lead to partial discharge and hence failure. Electrical ageing can be characterised in term of dielectric, PEA, and DSC responses. Thermal ageing does not produce the same effect as electrical ageing. The samples that were only thermally aged behave in the same way as un-aged samples.