Unperturbed and Self-Cleared Fault Simulations of Large Power Systems: Physical Factors Causing Excessive Deviations from Initial Conditions

In unperturbed simulations and simulations of self-cleared faults, which are routine tests performed during verification of dynamic models of large power systems, the deviation of a steady state equilibrium from initial conditions is expected to be negligible. However, evidence exists that in otherwise acceptable large power system models, deviations of generator rotor angles and network bus voltages can exceed thresholds set in industry requirements. This paper considers multiple equilibria and specific nonlinearities of mathematical models as physical factors causing excessive deviations and makes conjectures on energy function landscapes. These conjectures require further exploration, and one of this paper's goals is to provide an impetus for additional research and analytical studies. At the same time, it is clear that deviations exceeding industry requirements can be determined by solely physical factors, which needs to be accounted for in assessment of the applicability of a model for actual stability studies.