Effect of Rotor Speed Change on Electromagnetic Transient and Angular Swing of Synchronous Generators

Abstract In the existing reduced model of the electromagnetic transient for synchronous generators, rotor speed change is ignored together with the stator transient. This treatment is based on the conclusion that the effects of the stator transient and the rotor speed change can be counteracted. However the preconditions of the conclusion are very strict and nearly impossible to satisfy for practical power systems, which has not been fully investigated yet. In this article, the precondition to ignore stator transient and rotor speed change in the electromagnetic transient is derived, showing that two components cannot be counteracted in practical systems, whether under small or large disturbance. The reduced model ignoring the stator transient but including the rotor speed is newly proposed. Proportionality of the transient/subtransient reactances/voltages to the rotor speed is newly proved. For the synchronous generators either strongly or weakly connected to a power system, it is shown that the effects of the stator transient and rotor speed are dominant at different time scales, and cannot be counteracted. Numerical results shows that during a large disturbance, the proposed electromagnetic model including rotor speed change coincides with the full model more perfectly than the existing reduced model.