Online monitoring and visualizing of a generator’s capability with Simulink

Abstract

The power systems today are becoming more larger, complex and are operating closer to their security and stability limits particularly due to an increase in load demands and number of environmental concerns. Voltage stability has been a major subject of discussion and concern in electric power system operation and planning worldwide. Firstly, this thesis aims to do the survey on voltage stability and collapse phenomena in order to get insights into the mechanisms, causes, and prevention techniques to avoid such. The dynamic long-term voltage stability analysis is carried out using a free and open source, MATLAB based-PSAT software taking a test power system. The influence of load models, overexcitation limiter and transformer load tap changers on voltage collapse are investigated as a part of the thesis. It is observed that the constant power load has a greater impact on the voltage instability as it tries to restore the load unlike constant impedance and the constant current loads. Furthermore, a mathematical model for drawing the generator PQ capability diagram is presented and implemented in MATLAB software environment. For improved visualization and user interactions, a visualization tool is developed using the Graphical User Interface. In addition, the temperature development in the rotor and stator of the 103 MVA hydrogenerator at ‘Åbjøra’ in Norway, is investigated in the same visualization tool utilizing the already developed thermal model. For increased accuracy of the results from dynamic voltage analysis, development and use of more accurate power system component models is recommended. Moreover, the effect of changing armature voltage and the direct axis synchronous reactance on PQ capability diagram can be investigated under further study.