Mathematical and simulation models enable hydroelectric power unit dynamic behavior analysis using computers. To approximate the power unit dynamics as accurate as; possible, nonlinear high-order model is required. This paper describes a hydroelectric power unit with double regulated Kaplan turbine. The runners of such turbines permit the blades angle to be varied on the run depending on operating conditions. This ensures maximum turbine efficiency under all operating conditions. Detailed mathematical and digital simulation model of the hydroelectric power unit with double regulated turbine was presented for turbine control system analysis. Simulation model developed for Varazdin HPP (power unit 1) is verified by several comparisons with real measurement results.