Online and Offline Vibration Analysis of Stator End Windings of Large Power Generators

Abstract

An overview of different techniques to monitor vibrations of the generator end winding (impact tests, online vibration measurements using fiber optic accelerometers or a laser vibrometer) are presented. Data from online vibration measurements to investigate the vibration modal shapes of the stator end winding basket during operation is correlated with the generator operation parameters. These analyses are compared to results of finite-element-model calculations of a stator end winding. To evaluate the vibrations of a generator stator end winding during operation, it is necessary to relate vibrational modes to the generator operation parameters. In situ recording of, i.e. local accelerations or strain together with generator operating parameters allows deeper insight into the correlation of operating parameters and vibrations of the stator end windings.

Finite element modelling of turbine generator stator end windings for vibration analysis

“…where g xy is an applied shear strain. Shear modulus G xy is obtained from an equation similar to (12). In the case of shear loading in the yz plane, the constraints applied to the model are (9) and…”

“…Owing to the complex geometries of the bindings, if FE meshes of end windings reproduce the binding geometries exactly, computational costs become unreasonably high. To reduce these costs, the bindings are generally modelled with simple spring elements connecting the stator bars and the rings, which are modelled with solid elements [11, 12]. This spring model, however, cannot take the bending, twisting, and shearing rigidities of the binding into account.…”

“…The rigidities of bindings and stator bars are especially difficult to model because of their complex geometries. In FE models, the geometries of the bindings are simplified, and the bindings are generally modelled with spring elements [11][12][13]; however, these so-called 'spring models' neglect to take the bending, twisting, and shearing rigidities of the binding into account and this may lead to inaccurately calculated natural frequencies of the stator end windings. Moreover, in FE models, stator bars comprising several materials are simplified.…”