Integrated Approaches to Offshore Wind Farm Electrical Design and Grid Code Compliance — Insights from Philip Johnson, Jonathan Horn, and Omer Guksu

The Taiwan Power and Energy Engineering Association-Technology Development Council and Ørsted jointly hosted the "2024 Offshore Wind and Power System Technology Forum: Resilient, Reliable and Sustainable Renewable Energy Supply" on November 19, 2024, exploring the integration of offshore wind and power system technologies to develop a resilient, reliable, and sustainable renewable energy grid. Christy Wang (8th from left), Chairperson of Ørsted Taiwan, emphasized that close collaboration between developers and grid operators is crucial for ensuring cost-effectiveness and technical reliability of wind farm projects.

This article synthesizes expert perspectives on the design and integration of offshore wind farms, drawing upon the contributions of the joint seminar "2024 Offshore Wind and Power System Technology Forum: Resilient, Reliable and Sustainable Renewable Energy Supply" held on November 19, 2024, co-organized by the Taiwan Power and Energy Engineering Association-Technology Development Council and Ørsted's grid experts Philip Johnson, Jonathan Horn, and Omer Guksu. The discussion covers the iterative design process, critical data requirements, grid code compliance, and stability analysis. Emphasis is placed on the importance of early data acquisition, rigorous risk management, and robust collaboration between developers and grid operators to ensure a cost‐effective and technically sound project. Key findings are highlighted throughout the text.

Offshore wind energy has become a cornerstone of renewable energy strategies worldwide. However, the technical challenges inherent in electrical design, grid integration, and regulatory compliance demand a systematic and iterative approach. This article integrates the insights provided by three domain experts—Philip Johnson, Jonathan Horn, and Omer Guksu—to provide a comprehensive overview of the design methodologies, critical data considerations, and stability analyses necessary for successful offshore wind farm projects. The following sections detail the major themes and key points identified by each speaker.

Offshore Wind Farm Electrical Design Process
(Based on the Presentation by Philip Johnson)

Philip Johnson outlines the foundational steps in designing an offshore wind farm, emphasizing the need to begin with clear objectives and initial assumptions. As real data become available, these assumptions are systematically replaced to refine the design. His approach underscores the importance of regulatory compliance, risk management, and peer review throughout the design process.

Chief Senior Grid Integration Engineer Philip Johnson of Ørsted

Key Points from Philip Johnson:

• Initial Assumptions & Data Replacement:
o　Start with technical assumptions based on published information and surveys.
o 　Gradually update the design with real-world data as it becomes available.

• Grid Code Compliance:
o　Understand and incorporate grid regulations from the outset.
o　Ensure that the design complies with transmission company requirements and quality standards.

• Risk Management & Specialist Involvement:
o　Manage project risks through detailed risk assessments and mitigation strategies.
o　Leverage the expertise of specialists and ensure designs undergo rigorous peer review.

• System Bottlenecks & Cable Design:
o　Evaluate the wind farm area relative to wind speed, turbine installation capacity, and export cable lengths.
o　Identify landfall as a potential bottleneck, especially when transitioning from subsea cables to onshore substations.

• Reactive Compensation & Harmonic Filters:
o　Design reactive compensation strategies to minimize charging currents in critical sections such as landfall areas.
o　Incorporate harmonic filters and stability assessments into the design to ensure smooth energization and operation.

Johnson concludes by emphasizing the iterative nature of offshore wind farm design: early assumptions are refined through surveys, detailed manufacturer inputs, and continuous consultation with grid operators.

Critical Data and Iterative Design Studies
(Based on the Presentation by Jonathan Horn)

Jonathan Horn expands the discussion by detailing the extensive studies required to ensure an offshore wind farm’s electrical design is both feasible and compliant. His presentation categorizes the studies into four main groups and highlights the challenges associated with iterative design adjustments driven by study outcomes, procurement changes, and evolving grid requirements.

Jonathan Horn, Chief Power Systems Engineer of Ørsted's Greater Changhua 1 & 2 project

Key Points from Jonathan Horn:

• Study Categories and Effort Estimation:
o　Controller Stability Studies: Typically require up to three person-months, especially when iterations are necessary.
o　Installation Coordination Studies: Focus on EMT-type analyses (e.g., transient recovery voltage) and are time-intensive.
o　General Studies: Include short-circuit and harmonic studies critical for equipment rating and system contingency planning.
o　Long Design Tasks: Encompass the development of operational and control philosophies as well as the final equipment specifications.

• Iterative Design Process:
o　Design iterations may be required when study results uncover technical challenges, when procurement leads to equipment changes, or when grid operator requirements evolve.
o　Early and clear grid data are essential to avoid late-stage modifications that could render projects unviable.

• Grid Data and Fault Level Analysis:
o　Emphasize the importance of obtaining clear default grid fault levels (particularly minimum fault levels) to inform stability studies.
o　Detailed harmonic and impedance data from the grid—including accurate cable geometries and neighboring wind farm contributions—are critical for precise modeling.

• Industry Consultation and Standardization:
o　Active dialogue between developers and grid operators is vital for clarifying ambiguous grid code requirements.
o　Standardization of grid code terminology and consultation processes can help mitigate uncertainties and reduce the cost of energy.

Horn's insights underscore that reducing uncertainty through early data collection and proactive industry engagement is paramount for successful offshore wind farm integration.

Grid Code Compliance and Stability Analysis
(Based on the Presentation by Omer Guksu)

Omer Guksu focuses on the stability challenges posed by the integration of converter-based wind turbine generators into the grid. His presentation explains the concept of the short circuit ratio (SCR) as a measure of grid strength and discusses various methods for stability analysis.

Omer Guksu, Chief Power Systems Engineer of Ørsted's Greater Changhua 4 & 2b project

Key Points from Omer Guksu:

• Converter-Based Generation and Inertia:
o　Wind turbine generators, connected via power electronics, do not inherently provide inertia like traditional synchronous generators.
o　Converter limitations necessitate careful analysis of stability and dynamic performance.

• Short Circuit Ratio (SCR):
o　SCR is defined as the ratio of the grid's short circuit power at the point of interconnection to the wind farm's power rating.
o　An SCR below five indicates a weak grid, while values below three signal very weak conditions.
o　Even when the SCR at the point of common coupling is acceptable, internal network impedances and neighboring generation can further impact stability.

• Stability Analysis Methods:
o　Time-Domain Simulations: Offer detailed insights but require long simulation times and may not clearly pinpoint instability sources.
o　Impedance-Based Stability Analysis: Uses techniques such as Nyquist criteria to evaluate stability margins across various operating conditions.
o　Eigenvalue-Based (State-Space) Analysis: Provides quantitative assessments and identifies the participation factors of various system components, thereby revealing the origins of instability.

• Proactive Mitigation Strategies:
o　Adjusting operational parameters and converter controls at early design stages is critical.
o　Enhancements such as additional passive or active components (e.g., harmonic filters, synchronous condensers) should be planned well in advance to mitigate stability issues.

Guksu's analysis reinforces that early and detailed stability assessments, combined with adaptive control strategies, are essential for ensuring that offshore wind farms operate reliably within evolving grid environments.

Conclusion

The integration of offshore wind farms into modern power grids is a multifaceted challenge that requires a coordinated and iterative design approach. As demonstrated by the insights of Philip Johnson, Jonathan Horn, and Omer Guksu, successful projects depend on:

• Early and Accurate Data Acquisition:
Gathering precise grid parameters, fault levels, and harmonic profiles from the outset.

• Iterative and Collaborative Design Processes:
Continually refining assumptions through specialist input, industry consultation, and detailed simulation studies.

• Rigorous Stability and Compliance Analysis:
Employing a mix of time-domain, impedance-based, and eigenvalue-based analyses to ensure grid code compliance and robust dynamic performance.

Through proactive planning and open communication between wind farm developers and grid operators, offshore wind projects can be designed to maximize energy delivery while minimizing risks and costs. This integrated approach not only supports technical excellence but also contributes to the broader goal of deploying clean, renewable energy efficiently and reliably.