ColumbiaGrid Puget Sound Area Study Team Seattle City Light ColumbiaGrid Puget Sound Area Study Team Outage Scheduling Challenges Summer 2007 and Beyond

Planning Assumption: All Lines in Service? Planning base case assumption of All Lines In Service (ALIS) may be creating serious challenges currently experienced in the operating horizon Planning assumptions may not reflect operating realities Operating state of the system may be N-2, N-3, or N-X for extended periods of time due to planned outages The need for maintenance scheduling cannot be ignored in planning studies Increasing frequency and duration of maintenance outages Overlapping outages are common Operating staff assume responsibility for operating a system that is seldom in ALIS state.

Summer 07 ALIS S-N Nomogram

June S-N Nomograms 70 F 85 F Outage 140R2 Outage 140R2: Tacoma - Raver #1&2 500kV, Christopher - O'Brien Tap of Tacoma - Covington #2 230kV, Duwamish - Delridge 230kV,University - Broad St. 115kV, Sedro Woolley 230/115kV Bank O/S

June S-N Nomogram Limits

ALIS WNI N-S Nomogram 85 F North to South

July 9 N-S Nomogram Outage 204 85F Outage 204: University-Broad St #1 115kV, Tacoma-Raver #1 & #2 500kV & Chief Joseph-Snohomish #4 345kV Lines & Bellingham 230/115kV Transformer Bank #1 O/S

July 9 N-S Nomogram Outage 204R3 85F Outage 204R3: Tacoma-Raver #1&2, Chief Jo-Snoh #4, University-Broad St, Sedro W 230/115 Bank, Bellingham 230/115 Bank #1 & Bothell 230/115 Bank O/S; All Massachusetts 230/115 Banks I/S

July N-S Nomogram Limits

Are too many elements simultaneously OPEN? Level of detail being considered Old rules of thumb cannot be used Granularity of operating cases far exceeds planning models – esp. contingency defs. Contingency definitions result in many elements being O/S simultaneously New NWPP COS will help and hurt BFRs that take out multiple facilities should be addressed immediately

Planning for Scheduled Outages How should a realistic set of outage scenarios be developed for a planning case? Develop a Monte Carlo type approach Use historical maintenance outage schedules Extend outage planning process milestones Select a outage group based on known maintenance needs, age (Iowa curves), other. Outage schedule will only be good for one-year into the future max.

Study Methods WECC Basecase (ALIS) Modifications to reflect updated loads, generation patterns, ratings Outage schedules overlaid Contingency Definitions: e.g. BFR at MV#3 ATC Tool and Nomogram Studies

Future Outage Schedules Drivers: Need to Restore Ratings Changes to Relay Protection Systems Age of Transmission Facilities WSDOT Requirements Approaches: Repositioning under-built circuits Increasing Physical Clearance Retensioning Reconductoring Tower Replacements Sometimes Double-Circuit towers!

Labor Issues Resource Commitment Overtime Rescheduling crews is not always an option Overtime Outage schedules are requiring more work during LLH periods During outages, additional crews must be available to address a contingency

Mitigation Measures Risk of implementing mitigation measures Load shedding RAS arming Sectionalizing transmission Distribution load transfers Mass Bank 17 has been in service during entire summer Transformer configuration is not in “normal” state Flow on MA-BR cables is affected by state of Mass transformer banks SCL Downtown Network more vulnerable to certain contingency events

October Outlook BO-UN and BO-NO: to be taken out simultaneously BO-NO is not on the NWPP critical facilities list (but BPA is aware of the outage) Limiting facility may be in SCL service area Other: BO-SK, SE-HO-BO, TAC-RAV 500 See BPA outage plan for October 2007

Other SCL Outages (next summer and beyond) Viaduct cable relocation 115 kV tower replacements SLU substation = extended EP-BR outage BO-UN & BO-VI scheduled for next year. BO-SH 1 & 2 capacity restoration Increase clearance -> increase rating. UN-BR looking at options to increase clearance to restore capacity

Summary Summer 2007 nomograms are a wake-up call – Fall and Winter may also be adverse Transmission system is seldom in ALIS state Planning studies need to more closely reflect probable operating states Future outages are necessary to maintain existing system capability Work-arounds and mitigation plans are not always feasible