Survey of the Reliability of HVDC Systems Throughout World during 2023-2024

Technical Brochure 956 [3], which was updated and published in February 2025 and supersedes previous versions of the protocol, including Technical Brochures 590 [2] and 346 [1].

This paper is a summary of the reliability performance of HVDC systems in operation throughout the world during the years 2023 and 2024. The summary was developed from data prepared and submitted to B4 AG-04 by companies (also referred to as system correspondents) that operate the HVDC systems. Publicly available reliability data for HVDC systems was also included in this paper. The compiled data includes energy availability, energy utilization, forced and scheduled outages, and other information in accordance with the reporting protocol in

Technical Brochure 956. Statistics on the frequency and duration of forced outages are presented for the years 2023 and 2024, as well as a cumulative average of forced outages by frequency and duration covering the years 1989 to 2024. The categories for the cumulative averages are back-to-back stations, two terminal and multi-terminal stations with one converter per pole, and systems with two or more converters per pole.

The data in this report, together with that published in previous reports, provide a continuous record of reliability performance for many of the HVDC systems in the world since they first went into operation. This now constitutes a major record over time on the reliability performance on thyristor valve systems. Results are now also being reported for transistor based

VSC HVDC systems.