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Affected System Operator Studies

In coordination with Eversource, ISO-New England has determined transmission studies are needed for many distributed generation projects interconnecting to Eversource's infrastructure.

The Affected System Operator (ASO) studies seeks to identify whether a project impacts the transmission system and/or the electric power systems of neighboring electric distribution companies, and the extent transmission system modifications are required to maintain the safe and reliable operation of the region's transmission system and distribution infrastructure.

If modifications are needed, projects could share in the cost of that work.

The transmission analysis studies are being performed by Eversource’s transmission staff, consulting with other affected systems operators, including ISO-NE. Results of the study need to be approved by ISO-NE. 

Based on factors such as the size of a generator, operating voltage level and connection with a transmission line, various levels of analysis may be required. Eversource has worked with ISO-NE to determine the initial level of transmission study needed for each project. 

Our goal is to safely expediently get distributed generation projects up and running as quickly as possible. We are committed to transparency and will work with potential project stakeholders to answer questions and expedite the study process.

Additional information about ASO studies is available on the Department of Public Utilities website under docket 19-55.

Distributed Generation Guidelines for Interconnection

We have established Distributed Generation Guidelines for Interconnection (DG Guidelines) in collaboration with the Massachusetts Department of Public Utilities (MA DPU).

This document:

  • Explains the electric distribution company's (EDC) process for screening projects in ASO Impact Screens throughout the application lifecycle

  • Details reporting, communications and updates to affected customers during the application process and throughout any ASO study moving forward 

Current Phase

The ASO study announced on October 24, 2019 is currently underway. The Level 0/1 study has been completed and the Level 3 study is in progress.

Notifications, FAQs & Important Information

As required by the Department of Public Utilities (DPU), Eversource has reached out via email to developers with projects needing a Level 1 or Level 3 ASO study. PDFs of the notification are available below. Information shared during the ASO Customer Kickoff Meeting is also linked below in PDF format.

Reports to Impacted Customers

Every two weeks prior to the study commencing, Eversource reported out to impacted customers. An archive of those reports is available below.

On a monthly basis, Eversource will report out on the status and updates of the ASO studies that we have commenced, until those studies are completed. There is currently one group of ASO customers receiving these monthly reports (customers who are in the Level 3 ASO study announced on October 24, 2019). Previously Level 0/1 ASO study customers and customers who had an interconnection service agreement (ISA) were receiving these reports as well. An archive of those reports is available below. 

ASO Maps

Below are links to comprehensive maps illustrating the Eastern and Western Massachusetts ASO study areas. The maps also show all distributed generation projects, whether they are online, in queue, PPA approved, in study or don't require a study.

Eversource has grouped interconnection requests into five ASO study areas: Springfield, Pittsfield, Greater Boston, Upper Southeastern Massachusetts (Upper SEMA) and Cape.

For More Information

If you have questions, or would like more information about the ASO study process, please email us at