Offshore wind power generation requires the deployment of complex transmission infrastructure, which significantly impacts the capital and operational expenditures of the overall project. The spatial separation between offshore substations—where wind turbine arrays are interconnected—and the onshore grid connection point can range from a few kilometers to well over 100 kilometers in some case studies. While high-voltage alternating current (HVAC) transmission systems are predominantly employed, high-voltage direct current (HVDC) systems are increasingly utilized for remote installations due to their superior efficiency over long distances. The breakeven distance at which HVDC becomes economically favourable over HVAC is a subject of ongoing research and is generally estimated to lie between 120 km and 160 km, contingent upon a multitude of technical and economic parameters.

In AC transmission configurations, reactive power management is a critical design consideration. Long submarine cables exhibit substantial capacitive behaviour, necessitating the integration of shunt reactors to supply inductive reactive power and maintain voltage stability. The inductance of these reactors must be dynamically adjusted in accordance with wind power output, as reactive power requirements are inherently linked to generation levels. Additionally, offshore transformers are typically equipped with on-load tap changers to facilitate voltage regulation within the offshore network.

This paper introduces an automated computational tool developed to address the aforementioned challenges and to optimize the design of offshore wind transmission systems. The tool supports hybrid configurations incorporating both overhead/underground lines (onshore) and submarine cables (offshore), and allows for the use of multiple voltage levels across different segments of the network. It also includes the strategic placement and sizing of reactive power compensation equipment. The tool evaluates a range of operational scenarios, characterized by varying wind power availability and grid voltage conditions at the point of interconnection, each associated with a defined probability. It ensures that the transmission system remains compliant with grid code requirements under all considered scenarios, avoiding violations of voltage, current, and power thresholds.

The optimization framework integrates deterministic mathematical techniques—specifically Optimal Power Flow (OPF) analyses—for fixed operating conditions, with heuristic algorithms to explore a diverse set of feasible technical solutions. The results are synthesized into a Pareto front that balances total project cost against the quantity of energy delivered to the grid.

A case study is presented to demonstrate the tool’s capabilities, highlighting the optimal technical configurations under varying prioritization criteria derived from the Pareto analysis. For each selected configuration, the corresponding OPF results across multiple operating conditions are detailed, illustrating the robustness and efficiency of the proposed design methodology.