Palo Verde-COI RAS Retirement Philip Augustin August 20, 2017

Overview Historical Background Study Motivation Technical Justification Summary of Study Results Recommendation 08/22/2017

Historical Background Originally developed after a 2004 analysis of system impacts on the transfer capability of Path 66, California Oregon Intertie (COI), following planned upgrades on three Palo Verde generating units: Winter / Summer PV Unit #2 – November 2003 (121MW / 92MW) PV Unit #1 – November 2005 (121MW / 92MW) PV Unit #3 – November 2007 (121MW / 92MW) 2004 Technical Studies indicated impacts on California Oregon Inter-Tie (COI): Pre PV unit upgrades showed minimum of 134MVAR margin on COI system busses Post PV unit upgrades study case diverged, indicated zero MVAR margin on COI system busses Direct Load Tripping of 150MW in Phoenix Area restored MVAR margin to 139MVAR The COI was stressed in multiple cases, and the loss of two upgraded Palo Verde units in certain instances, no positive reactive power margin on the COI system buses 08/22/2017

Historical Background To mitigate a potential voltage collapse, a Direct Load Tripping (DLT) RAS was designed with the following specifications: Scheme is armed when output of any two units at Palo Verde exceeds 2550MW Simultaneous loss of two (2) Palo Verde units is defined as loss of two (2) Palo Verde units within a time period of 5 minutes or less. DLT will occur in one second or less. A minimum of 120 MW of load is to shed, but 150 MW is armed to trip. Load restoration is done by manual commands only. 08/22/2017

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Study Motivation SRP began a project to evaluate the operation, coordination, and effectiveness of the PV-COI RAS in compliance with PRC-012–014 and WECC‐010 TPL‐001‐WECC‐CRT‐3 A third party consultant was hired to perform the technical analysis The transmission system has changed since the PV-COI RAS was installed BPA installed series capacitors on John Day–Grizzly #1 and #2 500 kV lines BPA installed a 308MVAR Shunt capacitor installed at Slatt 500 kV bus All transient stability analysis was conducted using version 19.0_02 of GE PSLF. 08/22/2017

Summary of proposed WECC‐010 TPL‐001‐WECC‐CRT‐3 performance criteria Following fault clearing, the voltage shall recover to 80% of the pre‐contingency voltage within 20 seconds of the initiating events for all P1 through P7 events, for each applicable BES bus serving load. Following fault clearing and voltage recovery above 80%, voltage at each applicable BES bus serving load shall not dip below 70% of pre‐contingency voltage for more than 30 cycles nor remain below 80% of pre‐contingency voltage for more than two seconds, for all P1 through P7. For three phase faults, all oscillations that do not show positive damping within 10 seconds after the start of the studied event were continued out to 30 seconds. Oscillations that do not show positive damping after 30 seconds shall be deemed unstable. 08/22/2017

Technical Study Assumptions Power flow, voltage, and transient stability assessments were performed to determine the present-day need of the PV-COI RAS that direct trips Arizona area load for loss of two (2) Palo Verde units. System performance was evaluated against applicable NERC/ WECC and CAISO Reliability Standards and Performance Criteria. Additionally BPA indicated a VAR minimum requirement of 100 MVAR at several buses in the NW. All voltage stability analysis was conducted using version 19.0_02 of GE PSLF and benchmarked against version 21.0_02. 08/22/2017

Summary of Study Results Power flow results identified that there are no elements that exceed its emergency thermal limit for loss of two Palo Verde units. Voltage stability analysis identified that with WECC Path 66 (COI) increased by 2.5%, the loss of two Palo Verde units solved with adequate reactive margin with or without the load dropping RAS. Transient stability results identified that the system is stable and positively damped for loss of two (2) Palo Verde units with and without the load dropping RAS. The contingency conforms to the WECC‐0100 TPL‐001‐WECC‐CRT‐3 System Performance criteria. 08/22/2017

Study Conclusion The study results show that with the COI stressed to its limit and without the PV-COI RAS in service: The system continues to meet all power flow, voltage, stability, and transient stability criteria There is a minimum of 472MVAR of reactive margin on the COI system busses, well above the 134MVAR of margin that the PV-COI RAS was originally designed to maintain 08/22/2017

Recommendation from the study results Based on the study results, SRP recommends that the PV-COI RAS be removed from service by December 31, 2017 and decommissioned at a later date. The Path Operator BPA, is currently reviewing the study results 08/22/2017