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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.

These Affected System Operator (ASO) studies seeks to identify whether a projects 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.

Level 1 Transmission Study

Projects between 1.01 and 4.99 MW require a Level 1 Transmission Study. This level of study involves a transfer analysis that will indicate whether or not grid capacity and reliability will be impacted by interconnecting your project.

A transfer study is required to ensure there is no degradation of transfer limits on key ISO-NE transmission interfaces. These studies are needed due to the high level of saturation on circuits that have risk to impact transmission reliability.

If during the Level 1 study it is determined that a more detailed Level 3 study is required, Eversource should be provided with that information from ISO-NE within approximately 3 to 6 months from the time the study commences.

Our goal is to communicate timing and keep you informed on the final determination and next steps, including changes to cost and schedule. If a Level 3 study is required, we will notify you again and let you know if any further additional information is needed.

Examples of what may be needed are: PSS/E models, PSCAD models, executed study agreements, additional fees and other additional potential technical information as needed based on the level of study required.

Your approval to remain in the study, as well as the other projects included, is also needed before the study can commence. We know timing of the transmission study is important to you, but unfortunately, at this stage it’s not possible to predict exact details of your project’s timeline and costs.

For planning purposes, Level 1 studies typically take about 3 months and costs are approximately $500 per MW. This is the current cost range and could change with additional applicants being added to the identified ASO study areas and/or if the composition of the study changes pending applicants who wish to drop out.

Level 3 Transmission Study

Projects that are 5 MW or greater require a Level 3 Transmission Study. This level of study involves a steady state load flow, stability simulation, short circuit analysis and/or model validation to determine how your project impacts the transmission system.

A Level 3 study is also required (including a steady state and transient stability analysis) if the projects is between 1 and 5 MW but the aggregate impact at the transmission station is 20 MW or more. 

Eversource includes all interconnection applications that have been approved and are in queue in the determination of the cumulative injection to the transmission station. These studies are needed due to the high level of saturation on circuits that have risk to impact transmission reliability.

We know the time frame and cost of the transmission study is important to you, but unfortunately, at this stage it’s not possible to predict exact details for your project.

For planning purposes, Level 3 studies typically take about 9 months to complete from the time they commence. Costs are approximately $5,000 to $15,000 per MW. Projects in the Greater Boston or Springfield areas are at the top of this cost range.

These costs pay for the engineering analyses, liaison activity with ISO-NE and system impact analysis and support activities for us to keep you as informed as possible. This is the current cost range and could change with additional applicants being added to the identified ASO study areas and/or if the composition of the study changes pending applicants who wish to drop out.

If during the study process, transmission system issues are identified, additional costs may be incurred for studying how to address and resolve problems on the system.

We will notify you if any further information is needed to complete the Level 3 study. Examples of what may be needed are: PSS/E models, PSCAD models, executed study agreements, additional fees and other additional potential technical information as required based on the level of study required. Your approval to remain in the study, as well as the other projects included, is also needed before the study can commence.  

Notifications & 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 & FAQ

Every two weeks, Eversource will report out to impacted customers and provide answers to frequently asked questions. 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 are currently two groups of ASO customers receiving these monthly reports: post ISA customers who have studies underway prior to the September 25, 2019 Interim Guidance issuance, and customers who are in the Level 0/1 ASO study announced on October 24, 2019. 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 ASOstudyinquiry@Eversource.com.