Time response of frequency of the hydro-turbine governing system under the coupled action of surge tank and power grid

For grid connected hydropower plants with surge tanks, the time response of frequency of the hydro-turbine governing system under the coupled action of surge tank and power grid with load disturbance have been examined. On the basis of a mathematical model of a hydro-turbine governing system operating in an isolated grid with a surge tank, a power grid model of the hydro-turbine governing system connected to a grid has been developed. Using Laplace transformation, a comprehensive transfer function, taking the disturbance of the hydro-turbine as the input signal and the speed of the hydro-turbine as the output signal, has been developed for the mathematical model. Finally, by using MATLAB-Simulink to numerically simulate the time response of frequency of the system under the coupled action of the grid at different scales and the surge tank with different sectional areas, the mechanism of the coupled action of the surge tank and the power grid and the effect of grid scale on time response of frequency of system has been analysed. It is concluded that surge tank only affects the tail wave of the time response of frequency, and for surge tanks with large sectional area, the fluctuations in the tail wave are gentler. Hence, the system is easier to become steady. The power grid has an inhibiting effect, which becomes greater for larger grid scale, on both the head wave and the tail wave of the time response of frequency in which the head wave is separated into several wavelets and the tail wave become gentler.