Breakdown Characteristics of PEEK Insulation Immersed in Synthetic Ester Liquid for Subsea Cable Connectors

ABSTRACT Subsea cable connectors are critical components in offshore power delivery systems. They consist of a plug and receptacle, where current‐carrying parts are enclosed in solid insulation and placed within a liquid‐filled diaphragm. With the growing demand for power transfer and renewable energy integration in subsea environments, there is a need for alternative insulation materials that ensure system integrity while minimising environmental impact. This paper proposes integrating polyether ether ketone (PEEK) with a synthetic ester liquid as the composite insulation system for subsea cable connectors. The study commences with a comparative analysis of the electrical performance of PEEK when immersed in synthetic ester versus mineral oil. The AC breakdown strength (BDS) of PEEK in synthetic ester liquid under varying temperatures and thicknesses is also investigated. Results show that the breakdown strength of PEEK immersed in synthetic ester liquid surpasses that in mineral oil, largely due to the closer permittivity match between PEEK and the ester liquid. Likewise, the BDS decreases with increasing thickness, following a power‐law relationship but remains stable within the tested temperature range of 20°C–80°C. Breakdown locations, estimated using an in‐house MATLAB programme, occurred predominantly near the triple point junction.