Atypical numerical effects in stability simulations of large power systems

In stability simulations of large power systems, numerical effects that clearly depend on the numerical solution but somewhat contradict the existing paradigm of numerical integration (“atypical effects”) are not unusual. The paper considers relevant features of the power system mathematical model and related aspects of the numerical solution. Presented is a collection of effects revealed in simulations with real large power system databases. Examples of the effects are a non-monotonic behavior of the solution and unexpected transients developing after the dynamic response to a disturbance seems to have damped out. The paper outlines driving forces and discusses some mechanisms of atypical effects. A thorough assessment of the sensitivity of simulation results to solution options, especially in critical cases, is recommended for power system planning and operation studies.