Eversource Energy has begun a $315.8 million underground transmission line modernization project in Hartford, replacing existing 115-kilovolt underground transmission lines as part of an ongoing infrastructure upgrade throughout the region.
The Hartford Underground Cable Modernization Project will replace roughly 7 miles of underground cables that were installed in 1974, and are nearing the end of their designed life expectancy.
The existing fluid-filled cables will be replaced with new solid dielectric cross-linked polyethylene lines, called XLPE, increasing the capacity and reliability of the existing transmission system, according to Eversource.
Construction began in April 2025, with completion expected by late 2026 and full commissioning by late 2027. The Connecticut Siting Council approved the project in June 2024.
The project involves replacing two transmission lines that form critical links in Hartford’s power grid. The 1722 Line runs approximately 2.9 miles from Northwest Hartford Substation — located at 1557 Albany Ave. — to Southwest Hartford Substation, at 271 New Park Ave.
Meantime, the 1704 Line extends about 3.8 miles from Southwest Hartford Substation to South Meadow Substation, at 140 Reserve Road.
The replacement cables will follow existing routes through city streets wherever possible, with minor deviations.
The project addresses multiple infrastructure challenges while providing environmental improvements, Eversource said. The existing high pressure fluid-filled transmission lines carry the risk of oil leaks, while the new solid dielectric XLPE cable system eliminates this environmental hazard.
Also, the upgrades will improve system reliability by addressing supply chain issues for system repairs. The new technology has a longer life expectancy, will help reduce unplanned outages and will potentially increase line capacity for future load growth, according to Eversource.
The new cables also offer operational advantages. Repairs and maintenance to XLPE systems occur primarily within manholes and vaults, while the existing fluid-filled system requires excavations.
Repairs on the new system will typically take days rather than weeks, Eversource said.
Most construction will occur within existing city streets, requiring temporary lane closures and traffic management.
