This paper describes the characteristic parts of the hydroelectric power plant, which includes the upper water, dam, supply and pressure pipeline, surge and latch tank, turbines, and lower water. In addition to each of the described parts, data are also given for HPP Vinodol, such as length and diameter of the pipeline. Further description is related to losses within the HPP system, how losses are divided and characteristic equations for the calculation. The main division of losses is into local and longitudinal ones. Due to the lack of data, only the longitudinal losses are calculated, from the supply pipeline to the end of the pressure pipeline. Local losses could not be calculated because data for coefficients of resistance, 𝑘, are not known, and it is assumed that the total losses of HPP are equal to longitudinal losses. Calculation of the losses was verified by computer program Fathom. Fathom is a program that calculates the output size of the system, such as losses, which use fluid as a working medium. The program provides a diagram showing the change of the losses with the change of flow. Also described is the occurrence of a hydraulic hammer and how waves propagate with regard to the velocity of sound, 𝑐. In additions to the description of the oscillations, there are also characteristic equations that represent the relationship between the change of flow and the height difference between the upper water and the water level inside the surge tank over time 𝑡. Part of calculations and the diagram were obtained with Python.