Hydraulic transient simulation and characteristic investigation on Kaplan type hydroelectric power Plant with open channel

Kaplan type of turbines are meant for low head hydro development and sometimes are installed in systems with long open channels. Transient flow analysis in Kaplan hydroelectric power plants (HPP) is one of the most important issues for the prevention of undesirable pressure fluctuations in waterways. To keep efficient operation of a Kaplan turbine, the wicket gates and the runner blades position should be regulated as water head changed. Therefore, the hydraulic transients of Kaplan type HPP with open channel is more complex, exhibiting unique hydraulic characteristic. Based on the transient flow theory, both implicit difference method and method of characteristic are introduced to establish the mathematic model of hydraulic transients calculation for Kaplan type HPP with open channel. Then the fluid transients due to load rejection is simulated to investigate the hydraulic behaviors. The results show that different blades movements give different hydraulic behaviors. If the blades are not involved in the regulation, the hydraulic behavior is exactly the same as that of Francis turbines. If the blades adopt closure mode, the maximum spiral case pressure will slightly increase and the maximum rotating speed rising rate will obviously decrease with the increase of closing time. While the blades adopt opening mode, it will give the opposite hydraulic behavior compared to closure mode. Opening of the runner blades during the turbine shutdown can improve over-speed performance and worsen the spiral case pressure, and vice versa. Additionally, taking open channel into consideration, the influence on hydraulic characteristic is enlarged, while the length of the open channel has little effect on it.