Presenting to the ISO-NE Planning Advisory Committee on Feb. 26, Eversource Energy introduced a new set of asset-condition projects that could cost the region billions over multiple decades.
The company is proposing the staged replacement of its aging network of underground high-pressure fluid-filled (HPFF) transmission lines in Eastern Massachusetts. The company’s HPFF lines are reaching the end of their expected lifespan, and leaks from the lines have become larger and more frequent as the lines have aged, Eversource’s Chris Soderman said.
“Failures can lead to monthslong outages due to the difficulty of repairs,” he said, adding that the company is still working on the environmental cleanup for a leak that occurred Dec. 24, 2023. Most of the 6,000 gallons of dielectric fluid that leaked from the line during the incident flowed into the Charles River, he said.
Eversource outlined its plans to gradually replace its HPFF lines with cross-linked polyethylene (XLPE) technology, which it described as the “preferred technology for new underground transmission line construction.”
Soderman said the supply chain for HPFF technology is fragile, and the only remaining HPFF manufacturing plant in the world has signaled its intent to exit the market in the long term.
“If HPFF cable manufacturing were discontinued today, Eversource estimates that spare inventory would be sufficient to maintain existing HPFF lines during the conversion to XLPE — but not over the long term,” Soderman said. “The most responsible solution to ensure long-term reliability for customers and protection of the environment is to transition away from HPFF cables as the assets reach [their] end of usable life.”
He said the company plans for roughly three to four phases of work to replace its HPFF network, which includes “approximately 179 miles of [pool transmission facility] HPFF circuits.”
The company expects the replacements to continue into the 2040s, with the first phase aiming to construct about 35 miles of double-circuit underground ductbank, which will likely cost “somewhere between $1.5 [billion] and $2 billion,” Soderman said. He added that it is too early to make reliable cost projections for later phases of the replacements.
In recent years, the New England states have raised alarm about the rapidly increasing costs of asset-condition projects in the region, prompting some changes to the process of reviewing the projects at the PAC. However, asset-condition projects are under FERC jurisdiction, and the states have limited power to regulate the projects.
The asset-condition project forecast database published by the New England Transmission Owners — created at the request of the states in 2024 — outlines $5.8 billion in spending for projects expected to come online between 2024 and 2030. This includes only projects with full cost estimates, and the total cost will increase as additional projects move out of the conceptual stages.
Beyond the cost estimate, Eversource did not provide an official cost estimate for the HPFF replacement program. Soderman said the first phase of replacements will be broken into 11 individual projects with in-service dates from 2028 to 2033. Eversource plans to provide cost estimates to the PAC in the summer, he said.
Also at the PAC, Joe Dobiac of National Grid detailed a nearly $9 million cost increase for a transmission upgrade project in Massachusetts. He attributed the increase to permitting delays, which have pushed the expected in-service date from December 2025 to December 2026.
Rafael Panos of National Grid presented a nearly $12 million asset-condition project in Eastern Massachusetts, driven by worn shieldwire assemblies, deteriorated insulation, damaged shieldwire and cracks in a river crossing tower foundation.
Joshua Cefaratti of Avangrid provided an update on the final cost of a project to build a flood wall protecting a substation in Connecticut. The project was completed in August 2024 at a cost of $53.9 million, a significant increase over the initial estimate of $16.5 million in 2016. He attributed the price increase to permitting and construction delays and increased labor and materials costs.
