1. Effect of Thermal Generation Replacement on System Frequency Response Enoch Davies, PE Staff Engineer W ESTERN E LECTRICITY C OORDINATING C OUNCIL

2. Purpose of Study Changing carbon emission reduction policies – State Renewable Portfolio Standards – EPA has a number of existing and proposed emission policies EPA 111(d) is a proposal to reduce carbon emissions for existing generators on a state-by-state basis Concern over affect of carbon emission reductions on system frequency response 2 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

3. Study Assumptions Study ONLY considered system frequency response 2023 Heavy Summer Base Case was used as the base line for system frequency response – California once through cooling assumptions were largely included Generation replacements were based on – Assumptions from Transmission Expansion Planning Policy Committee (TEPPC) Common Case – Assumptions from the EPA 111(d) proposal Units replaced were least efficient as identified through the Common Case 3 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

4. Study Assumptions (cont) Replacement generation was based on – The resource type with the most limited amount of frequency response (inverter-based technologies) Pseudo inertial or governor response was not considered No changes were made to base case area interchanges Double Palo Verde generator outage used for frequency response comparison 4 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

5. Generator Type Frequency Response Comparison 5 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

6. Case Development Two scenarios were selected – 1: Used TEPPC common case assumptions for initial thermal generation replacement followed by EPA 111(d) assumptions to achieve levels for the proposed rule – 2: Focused on the southwest and reductions were based on task force provided assumptions of the EPA 111(d) proposed rule 6 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

7. Case Development (cont) Case Changes – San Onofre Nuclear Generation Station (SONGS) Turned off in case and generation replaced by existing generation present in the case (~2100MW) – Two scenarios examined – removed large amounts of thermal generation Scenario 1: 7146 MW replaced Scenario 2: 6369 MW replaced 7 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

8. Case Development (cont) Scenario 1 Used inverter based generator model (WT4G) Replaced the stability model for each of the thermal generating units selected with out making any changes to the power flow data Scenario 2 The task force recommendations were – Thermal units to replace – Location of replacement 8 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

9. Scenario 1 Results 9 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

10. Scenario 2 Results 10 W ESTERN E LECTRICITY C OORDINATING C OUNCIL

11. Conclusions The two scenarios examined did not show a significant change in system frequency response from the original base case Thermal units replaced were primarily unresponsive to frequency deviations (blocked governor response) The generation replaced was a small portion of the total generation online in the case (~3.5%) 11 W ESTERN E LECTRICITY C OORDINATING C OUNCIL