An improved method of including detailed synchronous machine representations in large power system models for fault analysis

An efficient approach for combining time- and frequency-domain analysis techniques to produce improved fault analysis results is presented in this paper. The developed approach is applied to fault analysis to determine the time-domain solutions for synchronous machine terminal variables while utilizing frequency-domian techniques to model the transmission network. In general, the transmission network is modeled using steady-state AC circuit theory to form a constant impedance network description, while the rotating machines are represented by sets of coupled differential equations. The interface between the time-domain machine models and the frequency-domain transmission network model transforms the differential equation solutions into the appropriate frequency-domain phasors using time series analysis to obtain least-square-error approximations of the phasor magnitudes and angles. The combination of time and frequency-domain analysis allows the total number of calculations required for a solution to be considerably less than the number required for a complete time-domain solution