There is a strong focus on new renewable energy sources, such as, solar power, wind energy and biomass, in the context of reducing carbon emissions. Because of its maturity, hydropower is often overlooked. However, there is an era of hydro oriented research in improving many aspects of this well established technology.Representing a physical system of a hydropower plant by mathematical models can serve as a powerful tool for analysing and predicting the system performance during disturbances. Furthermore it can create opportunities in investigating more advanced control method.A simulation model of a reference hydropower station located in northwest of Iceland was implemented using the modelling language Modelica R ⃝ . The main simulation scenarios of interest were: 20 % load rejection, worst-case scenario of full shut-down and pressure rise in the pressure shaft due to the water hammer effect. This paper will show that the different simulation scenarios were successfully carried out based on the given the data available of the Fossárvirkjun power plant. The load rejection simulation gave expected results and was verified against a reference results from manufacturer.