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

2. 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

3. 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

4. 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

5. 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

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

7. 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 to
Western Electricity Coordinating Council

8. System Frequency 59.725 (Simulation 2)
Frequency slightly dropped compared to initial simulation
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9. COI Flows (Simulation 2)
Western Electricity Coordinating Council

10. 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

11. System Frequency 59.692 (Simulation 3)
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12. COI Flows (Simulation 3)
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13. 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
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14. 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

15. 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