Risk Assessment and Probabilistic Transmission Planning Methods Seattle City Light Risk Assessment and Probabilistic Transmission Planning Methods ColumbiaGrid Puget Sound Area Study Team Kurt Conger, Consultant to Seattle City Light

Transmission Enables: Efficient bulk power markets Hedges against generation outages Hedges against fuel price changes Low-cost access to renewable energy Operational flexibility - Donald Morrow and Richard Brown, InfraSource

All Lines in Service Study Case Planning base case assumption of All Lines In Service (ALIS) and N-1 performance requirements may not reflect operating realities Operating state of the system may be N-2, N-3, or N-k 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. “Planners should model the system as operators would see it in real life.” (Stephen Lee)

Deterministic Approach: NERC Planning Standards NERC TPL-001-0 ALIS Performance NERC TPL-002-0 Single Contingency (N-1) Performance “R1.3.12. Include the planned outage of any bulk electric equipment at those demand levels for which planned outages are performed.”* Question: if we know that planned outages will be likely, but don’t know which elements, what do we study? NERC TPL-003-0 and TPL-004-0 * including maintenance

Risk Assessment Methods, Metrics and Criteria PRA – Probabilistic Reliability Assessment (Stephen Lee, EPRI) “Community Activity Room” (CAR) concept Holistic approaches, including IRP Probabilistic Transmission Planning (Wenyuan Li and Paul Choudhury, BCTC) Monte Carlo simulation or state enumeration Probabilistic Economic Analysis

Factors Affecting Risk Load Growth Age of Equipment Ability to repair and maintain Replacement is inevitable at some point in the future Equipment Load Cycling Frequency and Duration of Forced and Planned Outages Length of Transmission Lines Environmental (weather-related) Factors Generating Resource Constraints and Retirements Changes in gen patterns e.g. emission restrictions, fish biops, RPS

Factors Affecting Future Planned Outages Drivers: Load Growth Need to Restore Ratings – improve reliability performance Changes to Protection Systems Age of Transmission Facilities (repair or replace) External organization (e.g. WSDOT) Requirements Unplanned construction delays Approaches: Repositioning under-built circuits (no outage) Increase Physical Clearance (variable outage duration) Retensioning (long outage duration) Reconductoring (long outage duration) Tower Replacements (long outage duration) Sometimes Double-Circuit towers!

Managing the Model Technical Challenges: Approaches: Computational: N-1-1 combinations on 1,000 elements = 1,000,000 solved cases! Combined Reliability and Congestion modeling (e.g. OPF redispatch) Describing method, assumptions and results Dynamic Stability?! Approaches: Process to “de-clutter” the planning model Probabilistic methods to eliminate improbable system states Use of representative system states and indices

Cost/Benefit Quantification Total Cost Method Total Cost = Investment Cost + Operation Cost + Unreliability Cost* * Unreliability Cost Economic damage function based on GDP considering: LOLP – Loss of Load Probability LOLE – Loss of Load Expectation EENS – Expected Energy Not Served

Planning for Scheduled Outages How should a realistic and manageable set of outage scenarios be developed for a planning case? Develop a Monte Carlo type approach Study the drivers behind historical maintenance outage schedules and identify trends Extend outage planning process milestones into future planning periods Select an outage group based on known maintenance needs, age/mortality (Iowa curves), other.

Survival Rates – Wood Poles (Labrador, NF)

Mitigation Measures Costs and risks of implementing short-term mitigation measures Load shedding  economic damage cost RAS arming  increased risk of tripping Sectionalizing transmission  may affect distribution system reliability Distribution load transfers  increased losses, decreased resilience and operational flexibility Question: At what point will operational mitigation measures no longer be effective or become intolerable without new infrastructure?