A thermo-electrodynamic electric field dependent molecular ionization model to realize positive streamer propagation in a wet-mate DC connector

Complete subsea factory concept, an equivalent of the full topsides processing facility to be operated on the seabed, is envisaged to power longer, deeper and colder subsea oil and gas fields in the future. This concept has been envisioned through a modular stacked subsea DC transmission and distribution system whose subsea umbilical cables and electrical power component on the seabed can be interfaced with each other by wet-mate (WM) DC connectors. Laboratory and theoretical investigations have been carried out to assess various electrical insulation systems and electrode geometries for a WM DC connector which should operate in the steady state as well as switching transients in a corrosive environment for high reliability and minimum maintenance in its lifetime. In this paper, the electrical insulation performance of a needle-sphere electrode geometry defined by IEC 60897 under a positive step voltage is studied. To approach the complicated solid-liquid insulation system envisaged in a WM DC connector after mating, the electrodes are covered by a dielectric solid and oil is enclosed by the dielectric solid as well. A full thermo-electrodynamic electric field dependent molecular ionization Multiphysics model was developed for the simulation of streamer initiation and growth in the oil while dielectric solid is modeled as a perfect insulator. It is shown that stabilization methods, mesh strategies and time step have a great influence on simulation results and guidelines to choose them properly are presented. Based on simulation results, it was found that the higher relative permittivity of the solid insulation the slower streamer propagation in the oil and the less electrical stress on the solid insulation.