Voltage and Frequency Response of Small Hydro Power Plant in Grid Connected and Islanded Mode

Hydro-based power is gaining more interests as the penetration level of small-scale hydro power plants are being increased to the medium voltage network. This paper investigates the performance of a single unit small hydropower plant in both grid-connected and islanded operation. The overexcitation and volt/hertz excitation limiters have been included in the study to compare their responses in both modes of operation. The plant is evaluated under different loading scenarios considering both resistive and inductive loads. A PI tertiary control for speed reference setting in islanded operation is introduced in the governor to enable regaining of 50 Hz frequency after load changes. The results obtained from the simulation study show the importance and difference of analysing different loading scenarios both in grid-connected and island modes. Also, the inclusion of PI control in governor aids in returning the frequency to its nominal value.