“Unbalance Response and Field Balancing of an 1150-MW Turbine-Generator with Generator Bow,”
This paper presents some of the theoretical and experimental unbalance response characteristics of an 1150-MW turbinegenerator. These large 11-bearing turbine-generators can operate through as many as 10 distinct critical speeds. The balance condition of these units may change over time due to various influences such as turbine blade erosion, alignment and, in particular, generator bowing. Over a period of time, the generator may developed a bowed condition due to the nature of the electrical conductors. It is difficult to directly field balance a generator which is encased in a hydrogen environment. Removal of the generator for high-speed balancing in a balance facility is exceptionally expensive. This study examines the control of the turbine-generator response due to generator bow and turbine unbalance by various combinations of balance weights placed along the turbines. Some experimental responses of the turbine-generator due to various trial weights along the system are also presented. The 11-bearing turbine-generator, including foundation effects, was analytically modeled using transfer matrix and finite element methods. It was determined that in order to correctly model a large turbinegenerator, the foundation effects must be included. Foundation flexibility may cause as much as an 80-90% reduction in effective bearing damping. Various unbalance response simulations were performed with this model with combinations of turbine unbalance and generator bow. It is shown that system response due to turbine unbalance and generator bow at running speed may be controlled by proper application of unbalance weights and couples placed along the couplings and the low pressure turbines.
Turbine-generator response, Multi-plane Balancing, Three-dimensional complex modes
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