ACE Diversity Interchange (ADI) Discussion OC Meeting Marina Del Ray, CA Mark C. Willis SMUD October 30-31, 2008

Current Operation Two ADI “Bubbles” within WECC NW Bubble with seven participants SW Bubble with five participants Each participating BA limited to 30 MW ACE deviation Suspended for concerns about system reliability BA operator falls back to original ACE

Current = 30 MW NW Bubble 7 BAs ACE=0 SW Bubble 5 BAs ACE=0

Proposed Operation One ADI “Bubble” within WECC Proposal for each participating BA limited to 50 MW ACE deviation, but starting with 30 MW One/Two Bubble operation with 14 entities will be operational by 11/1/08 All entities scheduled to participate by January 2009r Again, suspended for concerns about system reliability BA operator falls back to own ACE

WECC Bubble NW Bubble SW Bubble Current = 30 MW NW Bubble ACE=0 7 BAs “TOT2” 150 40 MW ACE=+150 SW Bubble 5 BAs 110 MW 150 “COI” ACE=-150

Reliability Concerns (1) Two “bubble” system No concerns for two “bubble” system currently in place

Reliability Concerns (2) One “bubble” system concerns: Oversight responsibility of entire WECC transmission system ADI Participants unaware of all transmission impacts/conditions between NW and SW bubbles Within California, multiple constrained 500 kV paths, many of which are dynamically rated in real-time operations, both N-S and S-N Separation of unscheduled flow versus ADI on USF qualified WECC Paths, such as COI SOL (OTC) mitigation impacted by ADI flows – scheduled and/or forced outages and resulting mitigation requirements Increased COI SOL (OTC) mitigation requirements

Northern California Transmission Usage Concerns Usage of California-Oregon Transmission Project (COTP), as part of the California-Oregon Intertie (COI) Impacts multiple COI owners, including TANC, WASN, and PG&E Unscheduled transfer of energy between BAs across various TO/TOP systems

Recommendations Open the ADI Operating Group to all interested WECC entities Form a Task Force under Operating Practices Subcommittee (OPS) as assigned by the Operating Committee to study and evaluate reliability impact to WECC Transmission Usage – Mitigation of “take of transmission”

Questions/Discussion

Talking Points (1) Parties in California, which are not participating, are not held harmless due to significant flow of ADI on the 500 kV system between the Northwest and Southwest, during “one bubble” operation, resulting in usage of other’s transmission through unscheduled transfers of energy between participating Balancing Authorities (BAs).

Talking Points (2) Multiple WECC 500 kV paths within California are impacted both North-to-South and South-to-North during “one bubble” operation, resulting in a potential for unreliable operation and mitigation of SOL overloads, since the ADI participants are not the Transmission Operators (TOPs) of many of these paths. These WECC 500 kV paths include COI[1], Path 15, Path 26, West-of-River, and East-of-River[2], of which many of the System Operating Limits (SOLs) are dynamically determined in real-time by the respective TOP. [1] BPA will be monitoring the COI SOL in real-time to change ADI operation from “one bubble” to “two bubble.” [2] APS is the path operator for East-of-River.