A power system must be able to maintain an operating equilibrium in the state of the network even after potential critical disturbances. The impact of disturbances on the system is determined by the responses of components connected to it. The responses providing additional stability to the system are crucial especially during the faults. Converter based power plants also produce their own portion of these responses. Therefore, for a secure and reliable operation of the power system, determining requirements for their responses is also important. The aim of this thesis was to determine fault current contribution requirements for converter based power plants in Finland. The subjects of this study were variable speed wind power plants. The determination was conducted by studying the impact of fault current contribution on power system stability. In addition to this study, three parameters influencing the contribution were analyzed. The plants were modelled as a part of the Nordic power system. They were located geographically in the western coast area of Finland.The research illustrated that the fault current contribution of the plants can enhance the power system stability. This enhancement was the most substantial when they prioritized reactive fault current contribution. In contrast, some stability study results from plants prioritizing active fault current illustrated that the enhancement was poorer in comparison with results from plants without any fault current injection. With the consistent results, a requirement of prioritizing reactive fault current contribution was able to be determined.Additional results from studying two other parameters influencing the contribution illustrated that in comparison with each other, they had a different impact on the power system stability. Studying their interact with each other was not within the scope of this thesis, but would be useful for determining the remainder of requirements for the fault current contribution of the plants.
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