Transmission Line Rating
RSC/MSC/PAC
Agenda Item #4
June 17, 2011
Transmission Ratings in MISO
Processes
Agenda
• Requirements/Submission Process
– NERC/Tariff Obligation
– What/How provided
– TO Rating Methodology
• Application of Ratings – Planning, Forward Ops, &
Real Time Ops horizon
– What ratings applied- types (Normal/Emergency)
– Application of dynamic/short term emergency ratings
– Rating violations trigger mitigation – switching/post
contingency/binding/upgrades
– Maximize use of the transmission system
Rating Requirements/Submission Process
• NERC Requirement/Standard
– FAC -008/009 Facility Ratings Methodology / Communication
• Facility owner documents & provides ratings
• Tariff Obligation
– Transmission Owners Agreement – App B, Sec V
• Owners provide notification of normal and emergency rating changes for
daily/seasonal application or due to facility modifications/enhancements
• Midwest ISO applies TO submitted ratings to various models/processes
• How Rating Provided to the Midwest ISO
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Real Time EMS Model Update Web Tool
Planning Model on Demand (MOD) Tool
Admin Model Engr Group
Model File Exchange (by exception)
Flowgate Email Exploder (Admin Transm Utilization Assessment)
Verbal/Real time operation – temp until verified (Admin RT Ops/OC)
Rating Submission/Verification Requirements
• Rating Types
– Planning (MOD)
• Normal/Continuous – 4 seasons
• Emergency – seasonal (in MOD STE field)
• Conductor – seasonal (MRO only)
– Operations (EMS/AREVA)
• Normal/Continuous – 2 seasons
• Emergency/(post contingency) – seasonal/dynamic
– Flowgate – seasonal
• Rating Verification
– TO designated rating contact
Transmission Owner Rating Methodology
Midwest ISO verifies & comparably applies TO provided
ratings:
• TO rating methodology, philosophies & practices differ
with respect to rating their transmission assets
– Some TOs only have a single rating that they plan to – (normal)
– Many TOs have both Normal & Emergency ratings.
– Some TOs employ three ratings – (normal, emergency, STE/LTE)
•
Considerations:
– Equipment age & manufacture/design differences, risk assessment
– Equip life span/history stress variations, geographic differences
– Design application diff (line sag, expectation of wind speed, local codes,
acceptable loss of life) & line ratings defined by most limiting equipment
– Terminal equipment limitations can exclude dynamic rating applications
Application of Rating (type) - Simplified
• Normal – a continuous rating that is applicable
to system normal conditions and that if
exceeded for system normal planning studies or
operations requires an upgrade/mitigation
• Emergency – rating applicable to contingency
conditions & if exceeded in planning studies or
operations requires an upgrade/mitigation unless a short-term emergency rating or
operating steps are available
Application of Ratings - Planning Time Horizon
• Processes/studies: MTEP, Economic/Congestion studies,
MVP, Assessments, Interconnection/Long Term
transmission Service Studies…..
• Planning Ratings provided by TOP into the MISO MOD bus branch model – normal and emergency ratings –
planning horizon study specific
• Normal/Emergency rating violations trigger upgrade
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MTEP
Congestion
MVP
Transmission Service/Generation Interconnection requests
• Dynamic ratings generally not applicable
Application of Ratings – Near Term/Forward
Operations Time Horizon
• Processes/Studies: Outage Coordination, Transmission
Security Planning (next day assessments), Intra Day Real
Time Ops Look Ahead Assessments, AFC
• Operating Ratings provided by TOP via MISO Web Tool –
MOD bus branch model – normal and emergency ratings
• Normal/Emergency rating violations trigger mitigation
– Dynamic/short term emergency ratings, switching (pre/post
contingency), and/or redispatch
– Economic considerations
• AFCs – bus branch model - ratings input Flowgate Email
Exploder
Application of Ratings – Near Term/Forward
Operations Time Horizon
• Processes/Studies: Day Ahead and FRAC
• Operating Ratings provided by TOP via MISO Web Tool –
EMS node breaker model – normal and emergency
ratings
• Normal/Emergency rating violations trigger mitigation
– Generally (DA) facility binding constraint limits applied at 98%
– Dynamic/short term emergency ratings, and switching (pre/post
contingency) applied per operating guide and/or in anticipation
real time actions
Application of Ratings – Real Time Operations
Time Horizon
• Processes/Studies: RTCA, Binding/SCED, TLR
• Operating Ratings provided by TOP via MISO Web Tool or
TOP provided temporary rating1 – EMS node breaker model –
normal and emergency ratings
• Normal/Emergency rating violations trigger mitigation
– Each potential rating violation confirmed with TOP – verify rating and to
determine if applicable dynamic/short term emergency ratings, or if
switching (pre/post contingency) actions available
– Binding generally occurs at 98% of rating (based on system intact and
the next most limiting contingency – unless real time situation/volatile
flowgates require other action to maintain reliability
• Daily review of constraints to maximize use of the transmission
system
1 Any verbally communicated temporary rating change applied in real time is subsequently
confirmed with the designated TOP rating contact and entered in the Web
Tool/MOD/Flowgate Email Exploder
Application of Transmission Ratings in
Midwest ISO Processes - Summary
• Rating Methodologies are different across TOPs but
documented/communicated/verified – NERC Std
FAC 008 / 009
• Rating are provided by TOs & applied by the Midwest
ISO in reliability & market processes – Tariff
• Ratings are applied on comparable basis
• Maximize use of the transmission system while
ensuring reliable & efficient market operation:
– Ratings verified & updated in the planning/forward/RT processes
– Application of dynamic ratings or operating procedures where
applicable
– Daily review of constraint binding performance