Nonlinear Dynamic Analysis Of Shaft System For Hydroelectric Generating Set

With the rapid development of society and economy, the trend for hydroelectric generating sets is moving toward large-scale, high-speed and high-power, with higher degree of integration. The hydropower has more important effect on the stable operation for the grid, due to its increasing proportion in electrical energy structure. Under the interaction of hydraulic, mechanical and electromagnetic factors, the vibration problems for units have become more and more serious, and the consequent nonlinear dynamic phenomena attracted great attention from engineering and academic fields, which became one of the hottest topics in hydropower industry. In this paper, the main shaft system of hydroelectric generating sets is the research object, with the consideration of the universality of vibration during the operation, the dynamic characteristics of rotor-bearing system under the unbalanced magnetic pull (UMP), the nonlinear dynamic behavior of unit shaft with the influence of UMP and sealing force, the stability of runner-seal system, and the dynamic characteristics of a rub-impact rotor-bearing system under UMP are studied systematically. The main contents are as followed:(1) Aiming at the problem that UMP or seal force was considered singly into the dynamic analysis for units previously, the rotor-turbine-seal model and differential equations, taking into account both UMP and Muzynska nonlinear seal force, are developed. The model reflects the nonlinear dynamic behavior of the system well, in addition, the emergence of nonlinear instability and the laws of development and variation can also be revealed by parametric sensitivity analysis, which supply the theoretical support for the design and operation of unit.(2) The analytical expression of UMP with the consideration of pole-pair number, which is suitable for hydroelectric generating set is derived, and the nonlinear electromagnetic model and corresponding vibration equations are established. The influence of bearing parameters, including aspect ratio and clearance, in the lateral vibration characteristics is emphasized with or without UMP by the rotor trjactory and frequency domain, which can provide reference for the fault diagnosis, as well as the dynamic analysis under UMP.(3) In view of the rub-impact problem between stator and rotor due to the UMP, the model of rotor-bearing system with rub-impact for hydraulic generating set under the UMP is set up. The excitation current, which is one of the closest relationships with UMP, is choosen as the important object to focus on its effect on the system dynamics. This model can better reflect the nonlinear dynamical behavior of rub-impact system during the variation process of excitation current. Meanwhile, it can explain the vibration phenomenon, occurrence and development law, with the coupling effect of UMP and rub-impact. The conclusions will provide useful reference for improving the accuracy of vibration fault diagnosis as well as active vibration control.(4) Based on the dynamics analysis of rotor-turbine-seal system, the stability, as well as the instable critical speed of turbine-seal system under linear and nonlinear sealing force are discussed. Depending on the effect of different seal parameters on the critical speed, some measures and suggestions about reducing, even avoiding self-excited vibration are given, in order to provide reference for dynamic design and stable operation of the system.