A study on performance of a wet-mate DC connector under overvoltages

Due to diminishing oil and gas reservoirs in existing brownfield sites, offshore drilling activity continues to migrate into new oil and gas sites located in deeper water and further from the shore. For technical and economic reasons, processing of hydrocarbons is preferred on the seabed in ultra-deepwater sites instead of doing it on a host platform at the surface. Since the use of AC subsea transmission and distribution system to supply subsea process becomes impractical once beyond the critical length limit of AC submarine cables due to their capacitive charging current, a modular stacked DC (MSDC) subsea transmission and distribution system emerges as a promising technology alternative. Allowing only the faulty module to be retrieved for repair, wet-mate (WM) DC connectors are key to the reduction of downtime for the complete MSDC system. While there is no commercially available WM DC power connector, a time-dependent full thermo-electrodynamic model comprised of Poisson's equation, three charge continuity equations-one each for the positive and negative ions and one for the electrons-, and a thermal diffusion equation is developed to study the streamer initiation and propagation in the oil portion of a WM DC chamber. The envisaged geometry of a WM DC connector containing oil-solid insulation systems located in a cylindrical electrode geometry is considered for simulation. It is shown that the model developed can be used as an engineering tool to study the performance of compact designs of WM connector under overvoltages. In this regard, for the geometry considered for simulations, it is shown that a dielectric solid layer with a thickness of 1 mm is needed between moving contact and dielectric oil after mating to prevent streamer growth in the oil for a 4 p.u. overvoltage.