Load Dynamic Impact on Short-Term Voltage Stability

Dynamic load, especially induction motors (IM), represents one of the most critical factors on power system vulnerability to short-term voltage stability (STVS) problems. This paper shows dynamic load modeling impact as IMs on the analysis, identification and improvement of STVS problems in failure events. The STVS problems identification is based on analysis of IM equivalent rotation speed variation with respect to its critical speed. With this information, in addition to identifying the problem, it is also possible to know the causing load, which in turn allows deciding load shedding actions to mitigate STVS problems. Case studies are presented on the IEEE New England 39-bus test system where fast voltage collapses are analyzed, and mitigation actions are proposed. Results show that in order to mitigate fast voltage collapses due to STVS problems, it is necessary to shed enough amount of induction motor load according to its speed deviation during the fault event in sufficient amount and within fast action times.