Reliability HVDC Grids

What is it about?

The availability assessment of a power system is generally used to evaluate the probability of supply power at a given load point adequately. The traditional nodal loss of load probability (LOLP) and the expected energy non-supplied (EENS) are used in previous works. However, unlike AC systems, an HVDC grid has the function of injecting or extracting power from an AC interconnection zone, which implies that traditionally used nodal reliability indices must be modified to indices that reflect the performance of the HVDC network to fulfil its function of interconnection of systems. The availability assessment of an HVDC grid must evaluate its ability to supply power to AC zones that import energy; at the same time, it must evaluate the ability to transport the power from AC zones that export energy. In consequence, a new set of indices to measure these two functions must be proposed, as it is made in this paper.

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Why is it important?

This paper proposes a methodology for assessing the availability of VSC-HVDC grids based on the enumeration methodology of contingency analysis with N-2 criteria and makes contributions in the computation of remedial actions and the definition and computation of reliability indices applied for HVDC grids. Thus, this paper proposes the computation of remedial actions based on an Optimal Power Flow, looking for maintain power exchanges between HVDC and HVAC grids, when a contingency occurs on the HVDC grid and converter stations or HVDC lines are out of their operating limits. On the other hand, an HVDC grid has the function of injecting and extracting power from AC interconnected zones, then traditionally used nodal reliability indices must be modified to indices that reflect the performance of the HVDC network to fulfil its function of interconnection of systems. This paper defines two sets of availability indices applicable to HVDC grids: i) loss of power and energy extracted from the DC grid to the AC zones, and ii) loss of power and energy injected to AC zones from the DC grid. The proposed methodology is applied to perform the availability assessment of the CIGRE B4 DC grid test system and the results are presented.