Estimation of Inertial Transfer Function Coefficients and Algorithm Development for Forecasting Inertia in Indian National Electricity Grid

India plans to supplement 50% of the electricity demand through renewables by 2030. This manuscript primarily aims to estimate inertial transfer functions in the current renewable energy penetration scenario of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$30-35 \%$</tex> by analyzing the frequency response behavior of the generationloss grid disturbances of above 500 MW in the Indian National Electricity Grid between December 2020 to June 2023 from Phasor Measurement Unit-frequency data at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{1}$</tex>-second intervals. The estimation considers the proportional lag-compensator control function to imitate the primary and secondary grid frequency control response. The novelty of this study lies in the methodology for evaluating the transfer functions which are capable of predicting future grid disturbances with high accuracy. The other novelty of the manuscript is the development of an algorithm to calculate real-time universal grid transfer function for forecasting generation-loss grid disturbances. The algorithm can be developed into an artificially intelligent tool that can be exercised by grid operators in India and worldwide to estimate fast-acting energy storage reserve capacities required for frequency control ancillary grid service operations. The research pursued in this manuscript will help uncover opportunities to design, develop, and schedule grid-sale inertial energy storage systems for reliable and flexible electricity grid operations in the future.