Nonlinear response of hydraulic turbine generator set caused by unbalanced magnetic pull and oil film force

Hydraulic turbine generator sets are crucial for harnessing water energy. However, the nonlinear phenomena resulting from the combination of unbalanced magnetic pull (UMP) and oil film forces remain unclear. A mathematical model of the rotor-bearing system is introduced to investigate the effects of UMP and the nonlinear oil film force on system. The UMP and nonlinear oil film force are derived from the air-gap magnetic energy and short bearing theory, respectively. The proposed model is verified by the stability experiments of hydraulic turbine generator set in the idling, no-load, and load conditions. The results show that, firstly, the system turns unstable for oil whip and oil swirl, and which experiences bifurcation and undergoes dynamical motions such as period-1 to period-5, quasi-periodic, and chaotic motions. Then, at moderate speeds, the rotor eccentricity has the greatest effect on the bifurcation at idle. While the nonlinear characteristics of the system are most sensitive to the rotor eccentricity at loaded condition. Finally, the existence of UMP reduces the instability caused by oil film forces.