Progress Report for the May 26th 17:31 Event Doug Tucker Associate Staff Engineer Western Electricity Coordinating Council

Western Electricity Coordinating Council Why Model This Event? This event was mentioned at the July PCC meeting Frequency dip was bigger than expected To investigate the feasibility of developing system model validation cases MOD-033 requires Planning Coordinators to perform system model validation through event cases Western Electricity Coordinating Council

Western Electricity Coordinating Council Event Summary At 17:31 Pacific Time one of the DC converters at Celilo blocked BPA-11 Remedial Action Scheme operated and tripped 2826 MW of Northwest generation Investigation led to awareness of other system actions System frequency dropped to 59.66Hz Western Electricity Coordinating Council

Process of Creating Event Case (Power flow) Started with the 14LS1A - Operating Case Gathered data from actual system conditions just prior to disturbance Matched actual generation power output in the 14LS1A case Adjusted loads in each area to actual system conditions Checked major paths to verify flows match actual system conditions Adjusted phase-shifting transformers to match actual flows Western Electricity Coordinating Council

Process of Creating Event Case (Dynamics) Verified output of renewable resources Units turned off in operating cases (1,335 MW) Used typical data for missing dynamics models Used composite load model to better represent actual load behavior Adjusted dynamic model limits for select units to match actual power output Majority of these were hydro units Adjusted simulation plots to match actual system pre-contingency frequency Composite load model- better representation of load. Hydro – were at a different water level ~# Western Electricity Coordinating Council

System Frequency dropped to 59.735 Hz (Initial Simulation) Initial run – appears we are missing generator tripping. Inves Western Electricity Coordinating Council

Additional Information Collected post-contingency data Identified a generator not part of the RAS whose output changed by 83 MW Verified using the Generating Availability Data System (GADS) that another generator was run back by 22 MW These changes only reduced frequency nadir from 59.735 to 59.725 Western Electricity Coordinating Council

System Frequency 59.725 (Simulation 2) Frequency slightly dropped compared to initial simulation Western Electricity Coordinating Council

COI Flows (Simulation 2) Western Electricity Coordinating Council

Adjustments for Simulation 3 Simulated frequency nadir was still too high Blocked governor response for units dispatched above 95% of Pmax Turned off large units that were at low output <10 MW Operational data used for case creation had units at low power output that should be off For this scenario (holiday, light load, generation not preparing for days peak) needed more baseload flags Governors cant reasoned to frequency Western Electricity Coordinating Council

System Frequency 59.692 (Simulation 3) Western Electricity Coordinating Council

COI Flows (Simulation 3) Western Electricity Coordinating Council

Hypothetical Case (Simulation 4) Made assumptions based on known frequency bias Allowed governors to respond to frequency changes Tripped an additional 738 MW of generation Western Electricity Coordinating Council

Additional 738 MW Trip (Simulation 4) Location of generation that we tripped case the COI path to not match due to the flows going to the south Western Electricity Coordinating Council

Western Electricity Coordinating Council Conclusions RAS action in Northwest resulted in unintended generation changes throughout system Simulation did not match actual frequency deviation without data manipulation Potential missing generation tripping or run back Potential governor/turbine response modeling issues Some renewable generation is not being modeled correctly in operational base cases Further model investigation needed Approximately 4 weeks to develop Wonder about turbine/governor models for gas turbines – do they correctly capture reduction in power output with frequency reduction. Wonder if WSM and other reports captured all the under-frequency generator tripping that occurred.  (Get good match to event with minimal data adjustments if another 700 MW of generation tripped with low frequency. Western Electricity Coordinating Council