Synchrophasor-assisted detection and control of emergency voltage instability conditions

An impending voltage instability can often be avoided with a timely detection, followed by appropriate control actions. This paper proposes a complete scheme for the detection of impending voltage instability and subsequently, devising an emergency control action using synchrophasor measurements. The impending voltage instability is assessed using voltage and current phasor measurements, which can be obtained from the Phasor Measurement Units (PMUs). These measurements are exploited to find the maximum transferable power to a load bus, which, in turn, is used to deduce a Voltage Stability Monitor (Sy-VSM). The value of the proposed indicator gives the distance to voltage collapse. When the proposed Sy-VSM drops beyond a certain limit, a two-staged Load Shedding (LS) scheme is initiated as an emergency control action. Stage-1 sheds a fixed amount of load in multiple steps, taking into account the time, location and amount aspect of LS. In post-stabilization Stage-2, the amount of load curtailment is optimized using Model Predictive Control (MPC) based approach. The proposed scheme is demonstrated on the New England 39-bus system and a practical Indian Northern Regional Power Grid (NRPG) 246-bus system, and the results are found to be very encouraging.