Inertia Estimation and Trend Analysis of the United States Power Grid Interconnections

Transition from conventional to modern power systems is causing an increase in integration of inverter-based resources (IBRs). This generally leads to a decrease in total system inertia which in-turn increases the system's rate-of-change-of-frequency (RoCoF) during disturbances. This poses a threat to the frequency stability of the system and may falsely trigger protective devices. To monitor system status and plan for integrating renewable energy sources like photovoltaic, wind, and energy storage systems, a realistic study of inertia estimation and analysis over the last decade is needed. This paper uses field-measured phasor measurement unit (PMU) data collected throughout the United States (US) from 2013 to 2023 via the Frequency Monitoring Network (FNET/GridEye). The collected data is utilized to estimate the system inertia of the three US interconnections: Eastern,Western, and Texas. Various RoCoF time windows are investigated for estimating the inertia of each interconnection. This is performed by determining the correlation coefficient between the measured RoCoF and power mismatch. The resulting inertia trends over the last decade show approximately a 6% decline in inertia in the Eastern interconnection and a 15% decline in the Western interconnection, while approximately a 16% increase in inertia is observed in Texas. Key insights into how inertia is changing amidst the complex energy landscape are obtained using the fuel mix trend data. This provides valuable information for future energy strategies.