Improved Governing of Kaplan Turbine Hydropower Plants Operating Island Grids

Abstract: To reduce the consequences of a major fault in the electric power grid, functioning parts of the grid can be divided into smaller grid islands. The grid islands are operated isolated from the power network, which places new demands on a faster frequency regulation. This thesis investigates a Kaplan turbine hydropower plant operating an island grid. The Kaplan turbine has two control signals, the wicket gate and the turbine blade positions, controlling the mechanical power. The inputs are combined to achieve maximum turbine efficiency at all operating points. In relative terms, the wicket gate has a fast dynamic but small effect on the mechanical power, while the turbine blade has slow dynamic and large effect on the output, seen around an operating point. The proposed method to get a faster frequency control uses a different combination of the turbine inputs, transferring control effect from the turbine blades to the wicket gates at the cost of loss of turbine efficiency. The method is investigated with time domain simulations on a model containing all essential parts of a Kaplan turbine hydropower plant.