Influence of operating conditions on hydrounit power oscillations

Because of many different instability reasons, power unit stability problems should be analyzed in details for each specific case. This paper describes a specific case of power oscillations problem of hydroelectric power unit with double regulated bulb turbine. In some working conditions, natural frequency of electromechanical oscillations could be close to the rotor speed frequency and small disturbance on turbine would be amplified few times because of electromechanical resonance. Influence of operating conditions on natural frequency is analyzed using mathematical model of synchronous machine with excitation system. Simulation model results show that natural frequency decreases significantly with active power increase and near maximum active power becomes close enough to the rotor speed frequency to enter resonance mode.