What does Available Transfer Capability (ATC) represent?

Available Transfer Capability (ATC) is a critical concept in transmission operations, representing the maximum amount of electric power that can be transferred over the transmission network from one area to another while considering the current load and generation levels as well as transmission constraints. Specifically, ATC is calculated as the difference between the total transfer capability (TTC) and the total existing transmissions commitments (including both scheduled flows and any reserved capacity).

The significance of considering "available capacity, net of scheduled flow" lies in the practical aspect of ensuring transmission reliability and supporting market operations. It allows system operators to understand how much additional power can be moved through the network without violating operational limits or risking system reliability. Therefore, having a clear definition of ATC is crucial for planning, operational decisions, and market mechanisms within electricity systems.

In this context, while the current load demand on a line, emergency overload conditions, and historic performance metrics may provide valuable information, they do not define ATC. These factors can indirectly influence ATC calculations but are separate considerations within transmission operations.