The Impact of Different Vinyl Acetate Content on the DC Electrical Performance of EVA

EVA is a PE copolymer containing vinyl acetate side groups which confer significant polarity to the system. This polymer exhibits high mechanical properties, the ability to incorporate high filler loadings without embrittlement and a thermoplastic behaviour. The EVA properties depend on the VA content, which directly affects the crystalline fraction, the polarity and the thermal stability of the polymeric system. In this work three different VA content have been selected, namely 7%, 19% and 28%, together with a LDPE sample as a 0% VA content reference. The space charge build-up dynamics and the charge mobility have been investigated by means of the PEA technique and conductivity measurements, respectively. Tests have been performed at 20 kV/mm and 25 °C. Although the PEA results of EVA are comparable with LDPE results, over a 7% VA content a significant heterocharge formation close to the cathode is detected. Conductivity increases as the VA content increases, confirming the relationship between the extension of the amorphous phase and the charge mobility. The findings of this study lead to considering the EVA with low VA content suitable as outer insulation for MV and HV transmission system accessories, such as joints and terminations, where components are subjected to high mechanical stress and a reduced temperature gradient.