Reliability Of Hydraulic Urbine-Generator Units With Multiple Failure Modes Based On Nonlinear Vibration

The vibration phenomena of hydraulic turbine-generator unit strongly affect the normal, safe and stable work of hydropower station. So it is necessary to study the vibration reliability of hydraulic turbine-generator unit in order to ensure the safety of equipment. This paper takes the main shaft system of hydraulic turbine-generator unit as an object, and analyz system reliability with multiple failure modes based on nonlinear vibration theory and sturture reliability theory.By applying finite element method, the nonlinear dynamic equation with uncertain parameters is established. Based on the equation, the nonlinear vibration characteristics of the system are analyzed and the excitation frequencies and nature frequencies of the system are obtained.Considering the randomness of units, according to the criterion that the absolute value of difference between natural frequencies and excitation frequencies should be less than specific values, the failure probability with single failure mode and combined failure probability with two failure modes are calculated by dividing variable space into several simple areas. Then the nonlinear vibration reliability model of hydraulic turbine-generator units with correlated failure modes is constructed and the method by which the nonlinear vibration reliability of system with multiple failure modes can be analyzed is proposed.Considering the interval parameters of units, according to the criterion that absolute values of difference between natural frequencies and excitation frequencies should be less than specific values, the non-probabilistic reliability model of system based on nonlinear vibration is constructed by nonlinear vibration theory and non-probabilistic reliability theory, where the highest non-probabilistic reliability index in sub-functions is considered as single failure modes non-probabilistic reliability index.Considering the random parameters, interval parameters and the fuzziness of units, according to the criterion that absolute values of difference between the natural frequencies and excitation frequencies should be less than specific values, hybrid reliability model of the system with nonlinear vibration is constructed by probabilistic reliability theory and the non-probabilistic reliability theory, where the performance equations in two levels are given.An example is presented and the above mentioned reliability model are proved by the Monte Carlo method. The relations between system reliability and uncertain parameters are given.