Pelton turbine deflector control designs for Bradley Lake hydro units

The overspeed deflector control of two Pelton turbine hydro units in the Alaska Railbelt power system has caused many incidents of oscillatory instability. Among the causes is the high controller gains applied to the deflectors, which are essential for load rejection operations but destabilize the power swings. In this paper, the overspeed control is achieved by reducing the feedback gains and using a feedforward control to counter the transient over-frequency condition. An integral part of the design is a reference adjustment scheme for the load setpoint in disengaging the deflectors. Simulation studies show the improved performance of the proposed control design.