The connection pipe between the tailrace tunnels can effectively improve the minimum pressure at the draft tube during successive load rejection, however its impacts on the system stability under small load disturbance are unclear. The stability of the parameters, such as the rotating speed, water level fluctuations in the surge tank are analyzed by using state space methods. The results of the state space model are compared with the results of elastic model that is based on the method of characteristics to verify the correct of analytical model. Meanwhile, the effect of connection pipe on the system stability are investigated based on the analytical model, and the sensitive analysis of the connection pipe diameters and locations are studied. The conclusions are as follow. The effect of connection pipe as well as its diameters and locations on the system stable area, the dynamic process of rotating speed of runner and water level fluctuation in surge tank can be almost neglected. With the connection pipe between tailrace tunnels, the discharge in the tailrace tunnel will be changed to balance the pressure between tailrace tunnels during the small load disturbance conditions, while the system resistance is not increased. © 2019, China Water Power Press. All right reserved.
