Affected system study: when a project's effects cross a border
The study performed by a neighbouring transmission provider whose system is affected by an interconnection request made elsewhere.
An affected system study examines the effect of an interconnection request on a transmission system other than the one receiving the request. Power flows do not stop at a control area boundary, so a project interconnecting in one region can create constraints in a neighbouring one.
The study is performed by the affected transmission provider under its own tariff, on its own timeline, using its own criteria. The result can be a set of upgrades on the neighbouring system for which the interconnection customer bears responsibility under the terms of an affected system agreement.
Coordination between the two processes has been a recurring subject of FERC proceedings, because an affected system study running on a different schedule from the primary study can delay a project that has otherwise completed its process. Order No. 2023 addressed affected system coordination, and the details now vary by region as implemented in compliance filings.
Questions
- Who performs an affected system study?
- The affected transmission provider, not the one processing the interconnection request, using its own criteria and timelines under its tariff.
- Who pays for upgrades on the affected system?
- Cost responsibility is determined by the affected system's tariff and the applicable agreement, and is a frequent subject of filings and disputes at FERC.
Sources
- 01
Improvements to Generator Interconnection Procedures and Agreements, Order No. 2023
Federal Energy Regulatory Commission · RM22-14-000 · retrieved 2026-08-09
- 02
Pro forma Large Generator Interconnection Procedures and Large Generator Interconnection Agreement
Federal Energy Regulatory Commission · pro-forma-LGIP-LGIA · retrieved 2026-08-09