The present disclosure relates to a method and system for evaluating a grid condition of an AC power grid. A time series of voltage and current signals of the AC power grid is captured and a local frequency of the AC power grid is identified. The time series of the voltage and current signals is transformed at the identified local frequency of the AC power grid into transformed signals. Equivalent circuit parameters are estimated from the transformed signals based on a description of an equivalent circuit of the AC power grid. A value of a grid condition indicator is determined based on the calculated equivalent circuit parameters and the identified local frequency of the AC power grid and processed in a grid monitoring system for evaluating the grid condition of the AC power grid.