A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering

Thesis (M.Eng.) - Asian Institute of Technology, 1997

Power utilities are facing major challenges in maintaining and improvement of the system reliability, quality and security. During the last few decades there have been several incidents of blackouts throughout the world triggered by the voltage instability. Voltage instability has been recognized as one of the main operational challenge in the present power system networks. In the past five years, seven major blackouts have been observed in Sri Lankan power system network. However no proper investigation has been carried to understand the phenomena responsible for these events. An effort has been made in the present work to carried out detailed investigation of one of the incidents that took place on 2nd May 1995. Possibility of voltage instability and collapse has been explored. Both static and dynamic voltage stability assessment of the system have been carried out for the pre disturbance condition and also for the line outage cases leading to the collapse. In order to improve the voltage stability of the system, impact of placing the reactive power device on the critical bus facing maximum deficit of reactive power, has been studied. A new method based on sensitivity of reactive power losses to reactive power injection at the buses have been suggested to identify the weakest bus. The results have been obtained on the Sri Lankan system as well as an IEEE 30 bus system. · Investigation revels that the incident on 2nd May, 1995 in Sri Lankan network was a case of dynamic voltage stability. Placement of SVC at the weakest bus enhances both static and dynamic stability of the system.