Learnings

Outcomes

2024/25

• A literature review of air clearances has been conducted to establish the current state of the art of compaction.
• The dialogue with manufacturers was successful, particularly with SHEMAR sharing their Compact Composite Substation Frame with us. This solution can achieve more compact access to the substation for the line entry, and we will explore the possibility of extending this approach to the new vertical busbar design.

2025/2026

• The literature review of air clearances has been expanded to understand the process of the clearance distances suggested by international standards and their differences.
• The investigation identified previous attempts in lowering LIWL (Lightning Impulse Withstand Level) and SIWL (Switching Impulse Withstand Level) for air substations.
• The dialogue with manufacturers was extended with GE Vernova and H Nu Australia experts to fully understand the applicability of their existing products to compact substations.
• Preliminary results of the electromagnetic transient studies, lightning and switching overvoltage transients, confirmed the applicability of reduced LIWL and SIWL

Recommendations for further work

This project has delivered a preliminary compact design for a sample bay. The next phase will focus on developing a fully integrated compact design for the entire substation. To make progress toward finalisation, we will establish a clearly defined and agreed design through structured engagement with all relevant stakeholders. Early and active collaboration will ensure the design is practical, implementable, and aligned with operational requirements for substation deployment.

We will move beyond conceptual design into implementation by developing a demonstrator bay based on the proposed compact solution. This demonstrator will be used to validate feasibility, assess performance, and identify integration challenges under real-world conditions. Subject to the demonstrator meeting required maintenance and safety standards, we will take this design forward as the basis for wider deployment.

All stakeholders, including National Grid engineers and external partners, will be actively involved throughout the design, development, and delivery stages. Input of all stakeholders will be critical in defining technical specifications, maintenance requirements, operational procedures, and delivery strategy. This coordinated approach will ensure successful construction of the demonstrator and enable the development of a robust, scalable plan for full substation implementation.

Lessons Learnt

• A key lesson is the value of early stakeholder engagement. Bringing all relevant parties together at the beginning of the project is critical. Identifying and securing the right partners takes time, particularly when their work must align with both National Grid requirements and the objectives of participating companies.
   
• Additionally, coordination with external collaborators must be planned well in advance. Balancing third-party timelines with internal specifications and compliance requirements can be complex, and delays are likely if this is not managed proactively. Engaging partners early, clearly defining expectations, and aligning requirements from the start significantly improves project efficiency and outcomes.

Dissemination 

[1] The first year's work led to a paper entitled “Design concepts for compact air-insulated substations,” and it was submitted to the CIGRE 2025 International Symposium.

[2] Key aspects of the second year’s progress will be presented at UHVnet 2026 in Birmingham under the title “Assessment of Transient Overvoltages in a Compact 400 kV AIS Substation.”