System grounding will be a key factor in many of the decisions related to fault management, component sizing, voltage quality, and the resulting socioeconomic impact.
Background
Historically, the 132 kV grid in Norway has been built as a resonant grounded system. This operating mode has generally proven effective—resonant grounding allows for the self-extinguishing of arcs in single-phase ground faults, ensuring good voltage quality for the end user.
However, more recently, single-phase ground faults have caused damage to other components in the grid. While there is no clear cause for this, it is likely related to the voltage rise that occurs on healthy phases in resonant grounded networks. This voltage rise can cause excessive stress on components, which are typically designed according to international standards that mainly consider directly grounded and resistance-grounded systems, both of which experience much lower voltage rises compared to isolated and resonant grounded networks. Additionally, aging components may have reduced tolerance for voltage stress.
Building resonant grounded networks is also cost-intensive, as it requires more additional equipment (such as reactors) and increased insulation in the components.
Society’s expectations for better supply security mean that existing and new overhead lines are being replaced by underground cables, which drives the need for more reactor capacity. Switching from one grounding system to another is a time-consuming process that must be based on solid technical expertise.
Main Objective
The project aims to develop new principles, guidelines, and software tools for the planning and operation of the regional distribution network, including the significance of system grounding.
This will be based on existing knowledge, studies, and new findings. The results will provide a foundation for safer and more robust grid operation, including guidelines and software tools for any transition to a different system grounding.
Project Owner: REN AS
