Eversource Replacing Conductors

Eversource Energy (NYSE:ES) will replace more than 12 miles of 115-kV high-pressure, fluid-filled (HPFF) underground conductors between Waltham and Watertown in central Massachusetts to mitigate environmental and reliability issues, according to a presentation to the ISO-NE Planning Advisory Committee last week. The project is estimated to cost $69.6 million.

The existing 1250 kcmil paper-insulated copper conductor will be replaced with a 2000 kcmil laminated paper-polypropylene-insulated copper conductor, which is standard for Eversource in replacement considerations to minimize the number of spare reels and accessories on hand. Larger conductors also allow the cable to run cooler, which increases asset life and ratings.

There is only one remaining supplier of HPFF cables in the world, and the potential loss of that supplier would make replacement with solid dielectric cable or cross-linked polyethylene the only technically viable option, adding time and considerable cost to the preferred solution, according to Eversource’s Christopher Soderman.

The project will address safety and environmental risks associated with a cable failure or pipe breach. There have been six leaks since 1985 that have spilled more than 24,000 gallons of dielectric fluid/mineral oil, including 45% of those total gallons leaked in two significant events in the last six years. There is also increasing scrutiny from state and federal regulators to eliminate or reduce leaks. In addition, leaks result in high cleanup costs from fluid entering waterways and roadways, resulting in shutdowns.

The alternative is to “do nothing,” which is not an option because of the demonstrated asset condition issues, Eversource said. In addition, rebuilding the lines with cross-linked polyethylene requires new duct banks, civil work and lengthy siting, permitting and construction processes that do not quickly address the critical condition of the HPFF cables.

The proposed in-service date is the third quarter of 2023.

More Results from Tx Planning Pilot Study

ISO-NE’s Dan Schwarting and Meenakshi Saravanan presented additional preliminary results from the RTO’s “Transmission Planning for the Clean Energy Transition” pilot study, quantifying the tradeoffs between cost and the ability of the transmission system to accommodate high amounts of renewable resources.

Among the key takeaways of the study, ISO-NE found that generation reductions in southeastern Massachusetts/Rhode Island would be sufficient to relieve overloads on the Stoughton-K St. 345-kV line caused by future renewable resource additions, including over 3,100 MW of offshore wind and 2,300 MW of solar PV. The study kept approximately 5,150 MW of fossil-fuel generation offline to avoid cable overloads.

The study found that thermal overloads in real-time operations could be “relatively easily managed,” and many options exist for generation reduction that would alleviate the constraint. Operators can quickly identify post-contingency thermal overloads before a contingency occurs and make system adjustments, such as reducing generation to avoid overloads.

In a needs assessment, a thermal overload is not considered a need if it could be resolved by reducing generation. Currently, enough capacity is available outside of SEMA/RI that the reduction does not cause a reliability concern. If significant generator retirements occur, some fossil-fuel capacity may be needed to serve load. The RTO will continue the current practice of reducing generation when necessary to avoid overloads.

ISO-NE will next month make its final PAC presentation on steady-state and stability results and share its proposal for new study assumptions for load, solar generation and wind generation. New study conditions for load, solar generation and wind generation will be finalized and documented at the September PAC meeting.