Computational Aspects of Including the Stator and Network Transients in Stability Programs

In power system stability (TS) programs, stator and network transients are neglected to reduce computational burden as the frequency of interest lies within 10 Hz. Network transients, particularly, cannot be ignored when inverter-based resources (IBR) are involved, as these require a broad frequency spectrum in simulations. This paper explores the computational of stability programs including stator and network transients for small and large systems. Two synchronous machine models, discrete domain and continuous domain voltage behind impedance dq0-machine models, for including machine and network transients are compared with the dq0-machine model used in TS programs. The system equations in state-space form are solved using trapezoidal method of integration with 1 ms step size. The discrete dq0-model is found to be better due to fewer network interface equations. A speed optimized C-program bench-marked with commercial EMTP software is used for simulations of WECC 9 Bus system, IEEE 118 Bus system, IEEE 300 Bus system, and Pegase 9241 Bus system. For smaller systems, execution times of models including transients are found to be comparable to TS programs. For large system, the actual time is only 102s for a 10s simulation on a standard desktop which is quite acceptable. Although the number of equations increase by 220%, the computational time only increases by 76% for large systems. The execution time can be reduced further using parallel processing.