What rating types does MISO support operationally?
- Real-Time AARs (via ICCP/SCADA
- Forecast AARs (LEP/TROLIE or AAR temperature lookup tables)
- Seasonal ratings (via MISO Model Manager, used for planning, certain studies and as recourse/exemptions)
How are Real-Time AARs submitted and how often?
ICCP is the primary vehicle for submitting Real-Time AARs (and optional DLRs) must be submitted at least hourly and can be as frequent as every 5 minutes, with MVA values on the primary equipment (line/transformer/ZBR). Each rating set requires three ICCP points: Normal, Emergency, Load-Shed.
What rating tiers and minimum durations apply in operations?
MISO assumes Normal = Continuous, Emergency ≥ 30 minutes and Load-Shed ≥ 5 minutes (used informationally/reporting). TOs must supply actual effective durations via MISO Model Manager (fields for emergencyRatingDuration and loadshetRatingDuration) and proposals via TROLIE must also carry duration.
Does MISO accept Dynamic Line Ratings (DLR) in real-time?
Yes. If a TO elects DLR, it is telemetered via ICCP at the same cadence. When DLR cannot be calculated or communicated, real-time AARs are required; if neither is available, recourse ratings apply.
Will MISO only send back tie-line ratings per tie line or all ratings?
MISO will provide outbound globally limiting ratings (GLRs) for all facilities with ratings obligations in its footprint, even for singly owned/operated facilities, to ensure the SOL that MISO is operating to can be monitored.
What are the best practices for overriding limits for a line with AARs for an Operator?
The Ratings Provider can implement an override for their ratings obligation at any time. Additionally, MISO can implement an override after coordinating with the Ratings Provider for the facility. Both situations require creating a Temporary AAR Exemption, See the Facility Ratings Procedure Manual for more information.
Can a TO opt out of MISO's real-time recourse method?
Yes - only for real-time - if the TO's alternate risk mitigation is accepted by MISO System Operations. Forecast recourse is uniform.
What will MISO do for external ties in the transition period?
We will document this and work out the finer details. However, I can tell you we are working on two complementary approaches to RC-RC interties:
- We are working with our vendor to complete the implementation of a clearinghouse task to “re-clear” the ties with our adjacent RCs when we obtain new ratings for their end.
- We hope to simplify ratings management on jointly-owned/-operated facilities by using the NERC CORES system to identify the sole registered TOP for each facility, so that either MISO receives the definitive rating directly from that TOP or the adjacent RC does and we receive the rating for them.
During the transition period, if the sole registered TOP is known, we can use AARs from the appropriate source as the globally limiting rating (GLR), assuming we have the needed ratings exchanges working with the adjacent RC.
Note the option to clear ratings from multiple Ratings Providers remains, and the sole registered TOP would still need to update their ratings methodology to reflect that their RC’s clearinghouse is how they obtain the FAC-008 ratings and determine the facility rating. In that case, if only one ratings provider is sending AARs to their RC, the clearinghouse would use seasonal for the other Ratings Provider, and likely clear that as the GLR.