Understanding Regional Inertia Dynamics in CAISO from Real Grid Disturbances

TL;DR

This paper develops a measurement-based framework to estimate and analyze regional inertia dynamics in CAISO using real disturbance data, revealing trends related to renewable integration and storage deployment.

Contribution

It introduces a novel measurement-based method for regional inertia estimation in CAISO using real disturbance data, highlighting regional variations and the impact of renewable resources.

Findings

Regional RoCoF values are up to six times higher than interconnection-wide values.

Inertia has been declining but shows recent recovery due to battery energy storage deployment.

Regional inertia monitoring is crucial for reliable grid operation amid renewable growth.

Abstract

The shift from synchronous generators to inverter-based resources has caused power system inertia to be unevenly distributed across power grids. As a result, certain grid regions are more vulnerable to high rate-of-change of frequency (RoCoF) during disturbances. This paper presents a measurement-based framework for estimating grid inertia in CAISO (California Independent System Operator) region using real disturbance-driven frequency data from the Frequency Monitoring Network (FNET/GridEye). By analyzing confirmed disturbances from 2013 to 2024, we identify trends in regional inertia and frequency dynamics, highlighting their relationship with renewable generation and the evolving duck curve. Regional RoCoF values were up to six times higher than interconnection-wide values, coinciding with declining inertia. Recent recovery in inertia is attributed to the increased deployment of battery energy storage systems with synthetic inertia capabilities. These findings underscore the importance of regional inertia monitoring, strategic resource planning, and adaptive operational practices to ensure grid reliability amid growing renewable integration.