| Summary: | The technology of HVDC systems defines the current return process, which can be through a dedicated metallic conductor or through a conducting medium, such as the earth or sea. Although the magnitude of the earth/sea return current is normally specified in local regulations or project specifications, there is no explicit methodology to estimate the intermittent, time duration of this current, over the life-span of a system. However, dc interference/corrosion impacts related to the development of HVDC links are, to a large extent, associated to the time duration of the earth current. In the absence of any explicit methodology, the potential influence of the earth/sea return current on nearby critical infrastructures is often based on unrealistic or on conservative interference impact studies. The purpose of this paper is to firstly provide a methodology to quantify the expected intermittent duration of the earth return current - in point-to-point bipolar HVDC systems, which arises from their partial-availability or the emergency conditions. Subsequently, the proposed methodology is applied in a realistic dc interference/corrosion study of a critical pipeline system that operates near a HVDC link currently being constructed. In essence, the paper describes a top-down complete approach for HVDC dc interference modelling endeavors in an attempt to avoid conservative and costly mitigation measures concerning third-party critical infrastructures in the nearby vicinity.
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