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 system stability has been an area of concern ever since the system utilized two or more alternating current generators in parallel to meet the load demand. Originally it was seen in the form of 'transient (angular) stability' due to lack of synchronizing power. Several measures were implemented to overcome these problems such as use of fast excitation system, fast governoring system, series and shunt compensators etc. With the introduction of these devices, although the transient stability problem was overcome, another form of angular stability 'small signal stability' was experienced due to reduced damping in the system. This has become a severe problem with the growth in the interconnection of the networks. Since the power system is always in a quasi-static state and loads as well as other states undergo continuous, may be gradual change, such type of instability is likely to be triggered. Although several studies have been conducted in the past to study the transient stability of Vietnam Power System, no systematic effort has been made to assess its small signal stability. This thesis has focused on the study of 'small signal stability' of the Vietnam Power System. The thesis describes different models of the dynamic components and solution techniques used for the small signal stability analysis. A commercially available software (PSTOOL) for this analysis based on MATLAB has been utilized. Small-signal stability simulations have been performed for different operating conditions of and configurations of the existing and planned Vietnam Power System network. The impact of adding a new 500kV line in the future on the small signal stability has been studied. The stability simulations also identify the best placement of additional power system stabilizer and its optimum gain setting to improve the system damping to an acceptable value.