Early detection of voltage instability in distribution system utilizing phasor measurement units

Abstract

Power system automation leads to a great jump in detecting and solving the system problems. Due to the serious problems of system voltage collapse, an early prediction online voltage instability detector is discussed in this paper. The voltage instability detector utilizes the voltage and current phasor readings of connected phasor measurement units to the distribution terminals. The detector works according to two parallel algorithms. The first algorithm is a comparison for terminal current and voltage phasors with an offline calculated Look-up table, in which particle swarm optimization technique is used. The Look-up table represents the permissible maximum current and minimum voltage phasors for each terminal. The second algorithm is based on the online computation of the ratio of the Thevenin equivalent system impedance to the terminal load impedance. The simulated voltage detector is applied to two different unified power systems. It gives good and reasonable results.