ABSTRACT
The North American Electric Reliability Council (NERC) term “Available Transfer Capability” addresses Federal Energy Regulatory Commission requirements, but has a more detailed and complete definition and application. There are three limiting factors to be considered in determining transmission transfer capability first; “thermal limits” must be taken into account. “Voltage limits” are the second limiting factor. For every transmission line or flowgate there are minimum and maximum acceptable voltage limits. “Stability limits” are the third limiting factor. Following a power system fault, very high current flows may occur during the subtransient period or dynamic period. The determination of available transfer capability (ATC) can at best be based on an approximation of the effects and the use of judgement to identify the most likely contingencies and system variations over time. Recognizing the importance and complexity of the issues, the NERC took the lead in developing uniform ATC definitions and ATC methodologies.
