Risk analysis of offshore commissioning during power transmission tests

Unlike HVAC connections, transmission tests involving active power represent the most critical stage of HVDC commissioning. However, securing sufficient active power during commissioning is often challenging due to unsynchronized schedules between offshore wind farms and substations, adverse weather conditions, and long ramp-up periods. Despite these constraints, commissioning remains essential to ensure high reliability during commercial operation.

This paper presents a risk analysis of performing the commissioning test groups defined in

CIGRE Technical Brochure 697 under varying active power conditions prior to system handover. Risks are categorized by severity across thermal, protection, functional limitations, quality issues, and internal performance checks. The analysis is based on extensive test matrices from multiple projects. Furthermore, mitigation strategies to optimize commissioning duration and relevance are discussed, including comprehensive factory and replica testing of control and protection systems, rigorous early-stage verifications, and extrapolation of thermal checks at reduced active power.

Different scenarios are ranked according to topology and available power, considering the implementation of proposed mitigations. Testing at full power presents the lowest risk, whereas tests without active power carry significant risks. Risk decreases progressively with increased inter-array cable connections and turbine availability, with two notable thresholds: minimal active power (a few percent) and near-maximum power for full thermal stress. Exact target levels must be defined on a project-specific basis.

Finally, bipole topology enables round power tests, offering independence from wind farm schedules while introducing slightly higher risks compared to low-power tests. It also may also allow active power redirection between poles in some cases to enhance stress and test relevance.

Overall, risks remain substantially higher for offshore wind farm connections than for interconnectors due to limited power availability.