By Michael Kuser and Rich Heidorn Jr.

MILFORD, Mass. — Only six of 32 interconnection requests studied by ISO-NE in its initial test of its new queue clustering methodology have moved on to the next stage of the process, all of them in western Maine.

The six interconnection requests, totaling 691 MW, will be included in the RTO’s first cluster system impact study (SIS), Al McBride, director of transmission strategy and services, told the Planning Advisory Committee last week.

ISO-NE implemented the clustering methodology to address the queue backlog in Maine, where more than 5,800 MW of proposed resources, mostly wind, want to connect to the grid.

The process allows for two or more interconnection requests in the same area to be analyzed together and to share costs for required transmission upgrades when none of the requests can interconnect without the use of common new infrastructure rated at 115 kV AC or HVDC.

The first Maine Resource Integration Study (MRIS) concluded that the RTO could connect nine Northern Maine requests totaling 1,118 MW and 23 western Maine requests totaling 777 MW with about $1.83 billion in transmission upgrades. The upgrades included a second 345-kV Coopers Mill-Maine Yankee 392 line — which both clusters required — at a cost of $108 million.

With constraints on the system, “we found ourselves hitting a ceiling of around 1,800 MW” in interconnection requests able to be accommodated, “which is a significant addition to the Maine transmission system,” McBride said.

Projects had 30 days after posting of the MRIS on March 12 to inform ISO-NE of their intention to move on to the clustered SIS process.

None of the Northern cluster projects — whose upgrades would have totaled $1.36 billion, including the second 392 line — agreed to proceed.

Seven of the 23 western Maine requesters sought to be included in the cluster SIS, but one, for 1,200 MW, was not permitted because it exceeded the capacity of the “cluster-enabling transmission upgrades.” It will be studied separately.

Costs of the upgrades for the western projects, including the second 392 line, were estimated at $575.5 million. The other upgrades include a new 345-kV line from a new substation near Johnson Mountain to the existing 345-kV substation at Larrabee Road.

Second Study Planned

The RTO is planning a second MRIS to evaluate upgrades needed to accommodate an additional 22 interconnection requests, including about 1,350 MW in Somerset and Franklin counties and about 2,300 MW in Aroostook and Penobscot counties.

McBride said the study will consider new HVDC transmission connecting to the southern part of the RTO’s system, connecting either radially to proposed generation or to the existing network.

The RTO asked stakeholders to email feedback on the proposed study scope to PACmatters@iso-ne.com by July 13.

It hopes to complete the study within 12 months.

“We would be very reluctant to study major transmission proposals, from $500 million to $1 billion, that provide only minimal interconnection capability,” McBride said.