A real-time voltage stability index based on local measurements

Existing techniques exploiting local measurements to calculate the long-term voltage stability mostly rely on Thevenin equivalent concept. This notion calls for two or more distinct measurement sets for computation of Thevenin parameters assuming that the power system stays unchanged during the data collection, which is not essentially true. This paper presents a new method for computation of voltage stability margin associated with system load buses using voltage and current magnitudes. The proposed method is independent from the system variations; thus, it does not suffer from the shortcoming of regular Thevenin equivalent method. The new methodology is based on this observation that in the stable region of voltage stability curve, the normalized absolute value of the rate of change of voltage magnitude is greater than that of the current magnitude. This observation is supported by the theoretical analysis as well. To demonstrate performance of the developed method, a simple radial network and the IEEE 14-bus test system are examined.