Case Study
Milford on Sea
33/11kV substation — engineering delivered, power enabled
Complete detailed design across civil, electrical and system studies for Keltbray on SSEN’s transformer intervention, with HMF acting as Principal Designer.
The Project
Engineering excellence in action
Our multidisciplinary approach ensured coordinated, practical and reliable engineering solutions through every stage of the project.
13MVA, 33/11kV transformers at Milford on Sea were assessed as being in poor condition, with oil leaking into the soil due to the absence of a suitable bund. The works form part of SSEN’s RIIO-ED2 asset replacement programme, targeted for completion during 2024/25.
The scheme improves transformer Health Index from HI5 to HI1 and lifts declared firm capacity from 13.0MVA to 23.8MVA.
Project Facts
At a glance
HI5 to HI1
Transformer Health Index uplift
13.0 to 23.8 MVA
Declared firm capacity increase
RIIO-ED2
Targeted completion 2024/25
Principal Designer
Civil, electrical and system studies
Scope of Works
Associated plant works
- Removal of existing 2 nos. auxiliary transformers
- Replace existing isolators with new manual isolators
- Install new circuit breakers in both transformer feeders
- Replace protection panels and AVC panels at local and remote ends
- Replace LVAC board
Engineering Delivered
Services on this project
- Civil Engineering Design
- Electrical Engineering Design
- Cable Design
- Principal Designer Services
- CDM Support & Compliance
- Temporary Works Design
Project Highlights
Delivering value through design
Integrated design across civil, electrical and cable disciplines.
Collaborative approach focused on quality and performance.
Supporting a resilient and sustainable energy future.
Key deliverables
- Civil foundation design for the new equipment
- Primary and secondary design including SLDs, stage-by-stage SLDs, MCP and protection schematics
- System studies including earthing, cable design and protection coordination
Key milestone
- Final set of civil and electrical drawings issued for construction
Challenges
Key engineering challenges
-
Oil leakage without bunding
Existing transformers were leaking oil into soil due to the absence of a suitable bund, driving urgent intervention.
-
Health and capacity together
The scheme had to improve Health Index from HI5 to HI1 while lifting firm capacity from 13.0MVA to 23.8MVA.
-
Protection and control refresh
Protection and AVC panels required replacement at local and remote ends alongside primary plant works.
-
Multi-OEM interface
Design integrates Winder Power, Morris Line Disconnectors, Brush Circuit Breakers and TE Connectivity Surge Arrestors.
On Site
Project photography
Solution
Integrated design leadership
HMF delivered complete detailed design across civil, electrical and system studies, liaising with Keltbray throughout and acting as Principal Designer.
Deliverables include civil foundations, primary and secondary design with SLDs and protection schematics, plus earthing, cable design and protection coordination studies.
Outcome
Safer plant, stronger capacity
The design supports SSEN’s RIIO-ED2 target for 2024/25, with civil and electrical drawings issued for construction.
Milford on Sea gains improved transformer health, proper containment, and nearly doubled firm capacity for the Hampshire distribution network.
