Configurations and earthing of HVDC grids

Abstract

HVDC grids are considered to be essential building blocks for the future upgrade of the existing AC power system and as a means to transport the expected massive amounts of renewable energy from remote sources to the load centers. HVDC systems exist for over 50 years, yet meshed DC grids do not exist so far. For point-to-point HVDC connections, there is a certain freedom in choosing the configuration and earthing scheme. For a grid, different converter arrangements and earthing schemes can be considered. The choices made will influence how the grid will look like, the components in the grid and their rating, the operating principles, the protection philosophy, the degree to which the grid is extensible and the overall reliability and inherent redundancy. Clearly, it will influence investment and operating costs as well. This paper provides a qualitative overview of potential grid configurations for DC grids (symmetrical monopole, asymmetrical monopole, bipolar schemes, with and without metallic return and combined systems). The possible earthing options for a meshed HVDC grid are part of this discussion. The extensibility and reliability of the HVDC grid are specifically dealt with.

Substation layout for multi-terminal HVDC systems and neutral conductor arrangements for reduced field emissions

“…Hence, this alternative is not further considered. A more detailed description on this topic can be found in [3].…”

“…Converters located far away from the earthed one can be exposed to voltage shifts of unacceptable values during faults as it is described in [3]. A possible solution for that far extended HVDC system can be additional reactance or resistance earthed converter midpoints that are only activated when the voltage at converter midpoints exceed certain limits.…”

Frequency domain based DC fault analysis for bipolar HVDC grids

“…Moreover it is difficult to gain in-depth understanding of the influencing parameters through time domain simulations. Additionally, the future HVDC grids can be developed into monopolar, bipolar, or more complex configurations, such as a bipolar backbone with monopolar tappings [13][14][15]. Such a complex future system might have various grounding schemes, such as low impedance grounding or ungrounded stations.…”

Effects of grounding configurations on post-contingency performance of MTDC system: A 3-Terminal example

“…For the relatively simple point-to-point HVDC connections a variety of configurations and earthling schemes has been reported in the literature [6].…”

“…The research team leads by D, Van Hertem has made contributions in this area in recent time [6,7], however as other publications, [8,9] the core on those contributions is related to faults currents.…”