Vibration Characteristics And Fault Diagnosis For Hydraulic Generator Units

With the rapid development of social economy and the sustained and rapid growth of electricity demand, the single unit capacity of the hydro-generating unit continues to increase; the safe and reliable operation of the units is directly related to the safety of hydropower plants and the stability of interconnected power system. Once a failure for generating units occurs, it may cause the plant to non-planned shutdown or reduce capacity, even serious heavy casualties and serious damage to the system may appear when encountering major accidents of units. Due to the universality of the vibration when the unit in the operation, the theoretical analysis of the vibration characteristics on hydro-generator shaft system is made, which studies the dynamic characteristics of two rotors connected by rigid coupling with parallel misalignment and the rotor rubbing under the axial thrust. At the same time, the vibration fault diagnosis strategies for the hydro-generating units are further researched. The main contents of the paper as follows:(1) The dynamical equation of parallel misalignment rotor-bearing systems is derived using Lagrangian dynamics. The effect of the rigid coupling parallel misalignment and the rotor unbalance is examined with theoretical and numerical analysis, where the numerical simulation methods are applied to verify the conclusions of the theoretical analysis. At steady state condition, the 1X-rotational speed excitation is presented in the lateral vibration direction, which indicates that parallel misalignment of the rigid coupling can be a source of lateral excitation. The axial locus of the rotor systems is a steady circle after full decay. Simulation results showed the changes of the amplitude of the driving shaft and the driven shaft are more complicated with the changes of the rotor mass eccentricity, the rigid coupling parallel misalignment, the rotor mass of the driving shaft and the driven shaft etc. The effect of the transient response on the parallel misalignment to the rotor-bearing systems with less bearing stiffness is stronger.(2) A model of a rigid rotor system under axial thrust with rotor-to-stator is developed based on the classic impact theory and analyzed by the Lagrangian dynamics. The effects of rotating speed, mass eccentricity, friction coefficient, and damping coefficient on dynamic characteristics of the rotor system are researched. With the changes of these parameters, the changes of vibration characteristics of rotor system turn to be very complicated, and the periodic motion, complicated quasi-periodic motion, or chaotic motion may occur in the response of the rotor system.(3) The kinetic equation for a hydrogenerator set system is deduced and the motion differential equation is simulated using numerical methods. Considering the effect of generator rotor's mass eccentricity, hydraulic turbine rotor's mass eccentricity, blades mass and the distance of guide bearings, the lateral vibration characteristics of the hydrogenerator set system are analyzed. Research results demonstrated that the radial displacement of generator rotor and hydraulic turbine rotor increases linearly with the increase of hydraulic turbine rotor's mass eccentricity. There mainly appears relatively simple periodic motion of the rotor systems, but accidentally the more complicated quasi-periodic motion may occur with the changes of blades mass, generator rotor's mass eccentricity, and the distance of guide bearings.(4) Considering that the complexity of diagnosis process and the diagnosis conclusion is not satisfying as expected for the vibration fault diagnosis of the hydraulic generator units, the information fusion technology is introduced to the units fault diagnosis, which enable us to make full use of different information sources of data and expertise to obtaine the relevant faults information of units. On this basis, the vibration fault diagnosis model of the hydraulic generator units is established using entropy weight coefficient, grey incidence analysis and information fusion technology. Taken the vibration spectrum characteristics and amplitude characteristics as the fault diagnosis samples, an initiative vibration fault diagnosis of hydraulic generator units is accomplished based on grey incidence analysis and entropy weight coefficient. The final diagnosis results are deduced by fusing different evidences using Dempster-Shafter theory. This diagnosis method can take full advantage of the effective information of different faults source of the hydraulic generator units, and also can restrain the diagnosis limitations of the single fault source. Thus this diagnosis method is able to better determine the type and location of unit faults. Diagnosis example demonstrated that the proposed method is a good candidate to be used as an online diagnosis tool for hydraulic generator units.