NERC study reports interregional transfer capability by region pair

Transfer capability between planning regions has historically been treated as a residual, determined by whatever interties happened to be built for other reasons. Reliability assessments and transfer capability studies have made it an explicit subject of analysis.

The finding that recurs is that the constraint is rarely the interties themselves. It is the internal network on either side, which was planned to serve local load rather than to move power across a seam.

This matters for interconnection because seam constraints appear in interconnection studies as upgrades assigned to individual projects. A developer can find itself allocated a share of a reinforcement whose function is regional transfer, not local injection.

For a planner, the remedy is to move those facilities into regional or interregional planning where their costs can be allocated to the beneficiaries. That is precisely what long-term planning requirements are intended to enable, and precisely where cost allocation agreement is hardest.

What to watch: whether any regional compliance construct identifies a seam facility and allocates it on a beneficiary basis rather than to interconnection customers.