115 kV Transmission Line Modernization
Our team was selected for its experience delivering transmission projects and providing multidisciplinary services to advance the design from concept to construction.
The Opportunity
Project purpose and need:
The 115 kV transmission lines between New Haven and Milford, CT, are supported by the Connecticut Department of Transportation (CTDOT) owned railroad catenary structures and connected through UI-owned bonnet structures. As a result of age, asset deterioration, and increased mechanical loads, it was determined that new 115 kV transmission lines should be installed on new monopoles along the CTDOT railroad corridor.
UI’s objective was clear:
- Maintain system reliability
- Preserve safety within the right-of-way
- Provide technological enhancements to legacy system equipment.
Execution required discipline to address key constraints:
- Construction within an active railroad corridor
- Strict clearance requirements
- Permitting and stakeholder coordination
- Phased sequencing driven by constructability, rail operations, and roadway crossings
The Vision
When replacing aging assets, it is critical to plan for future system demands. United Illuminating’s strategic approach ensured the new structures not only met current loading requirements, but were capable of accommodating 2156 ACSS conductors. The approach supports UI’s long-term system flexibility strategy and anticipated grid demand.
Challenges and Solutions
Railroad Corridor Constraints
- Conducted site visits within an active railroad corridor requiring strict site safety protocols.
- Designed for limited construction windows and elevated clearance standards.
- Leveraged experienced engineers to develop crossing exhibits and solutions that supported complex construction sequencing.
Circuit Relocation
- Relocated existing circuits from railroad structures to new steel monopoles.
- Used PLS-CADD, PLS-POLE, and SAP2000, to validate structural performance.
- Delivered a monopole design supporting higher capacity conductors.
Environmental & Multi-Agency Coordination
- The project spanned multiple municipalities and environmentally sensitive areas, requiring careful coordination.
- We conducted 90 geotechnical explorations.
- Provided Land Surveying Support.
- Led permitting coordination efforts aligned with regulatory requirements.
For regulatory reference, the project is associated with CSC Docket No. 508, available here:
https://portal.ct.gov/csc/decisions/docketlists/docket-list-nos500-999
Innovation in Action
We applied innovation to improve constructability today while enabling long-term system performance.
- Line modeling improved conductor behavior through analysis and clearance optimization
- Structures were designed for future conductor upgrades, extending asset life
- LiDAR-driven geospatial integration enhanced corridor intelligence and access planning
- A phased QA/QC framework helped identify risks early and reduce field rework
Services Delivered
Multidisciplinary support provided the entire project lifecycle:
- Transmission line engineering
- Structural analysis
- Foundation design
- Geotechnical investigations
- LiDAR and geospatial surveys
- Land Surveying
- Property line and right-of-way support
- Environmental permitting
- Highway and railroad crossings
- Fiber optic integration
- SCADA and relay coordination
- Construction sequencing
- Constructability reviews
- Cost estimating
- Quality assurance
The Outcome
In partnership with United Illuminating, we delivered a complete, constructable design solution to modernize existing infrastructure and helped position United Illuminating’s transmission corridor for improved reliability, maintenance access, and expanded system capacity.
For more information about United Illuminating and Avangrid:
https://www.uinet.com/company-overview
To learn more about the project scope and engineering overview:
https://www.uirailroadtlineupgrades.com/project-overview-and-engineering.htm
