A discussion about optimum time step size and maximum simulation time in EMTP-based programs

This paper presents a discussion about the optimum time step size and maximum simulation time in EMTP-based programs. This is of particular importance for new users of EMTP-based programs, since the user is responsible for setting up these parameters before running a simulation case. The selection of the time step size affects the precision of the simulation. The time step size depends on the maximum frequency expected in the phenomena, which is normally unknown, a priori. The calculation of eigenvalues from the state space matrix obtained from the EMTP conductance matrix and history terms algorithm formulation allows the exact ideal values for the optimal time step size and a maximum simulation time. In comparison, a general and robust algorithm is also presented here based on all the input data given for the circuit under simulation. The proposed calculation process is based on single- or multi-phase uncoupled or coupled circuits, with lumped or distributed parameters. Simulations are given demonstrating the effectiveness of the proposed rules.