Capacity Benefit Margin (CBM) is the amount of firm transmission transfer capability preserved by the transmission provider for load-serving entities (LSEs), whose loads are located on that transmission provider’s system, to enable access by the LSEs to generation from interconnected systems to meet generation reliability requirements.  Preservation of CBM for an LSE allows that entity to reduce its installed generating capacity below that which may otherwise have been necessary without interconnections to meet its generation reliability requirements. The transmission transfer capability preserved as CBM is intended to be used by the LSE only in times of emergency generation deficiencies.

ATC planning studies, except those required for Midwest ISO (MISO) transmission service, do not model CBM. CBM is instead accommodated in the planning process through the Loss of Load Expectation (LOLE) studies in the Midwest Transmission Expansion Planning (MTEP) process.

MISO performs annual studies to determine the import requirement of each study area operated as an isolated system to meet a LOLE of 0.1 day/year. All of ATC is defined as a single stand-alone study area. MISO then compares the flowgate CBM with the Automatic Reserve Sharing (ARS) component of the Transmission Reserve Margin (TRM) for that same flowgate. If the ARS component is greater, no CBM will be preserved on that flowgate. If the ARS component is less, the incremental amount of CBM that is needed above the ARS component will be preserved as CBM for that flowgate.

All MISO transmission service studies use CBM in the flow based analysis of transmission service studies performed by ATC. The network analysis for transmission service studies does not use reductions in equipment ratings for CBM.

We will perform periodic analyses to evaluate (considering planned summer peak load and generation, as well as load forecast error and generator outage characteristics) the probable requirement to import power from external sources to meet a LOLE of 0.1 day per year, and ATC's ability to simultaneously import sufficient power from external sources to meet the 0.1 day per year LOLE reliability standard. If a deficiency is identified, we will incorporate any resulting incremental import capability requirements into ATC's overall transmission expansion plan.