'DYNAMIC RESPONSE OF TURBO-GENERATOR FOUNDATIONS'

Abstract

Increasing power requirement has led to construct a number of high capacity thermal power plants in the country. High speed Turbine-Generator sets are installed in these power plants. Turbo-Generators are supported on Large framed founda-tions which are designed to transmit static machine weights as well as dynamic forces caused by the operation of the machine. Dynamic behaviour of these foundations largely governs the performance of turbo generators. So these foundations are very important structures and their unique feature is that the economic consequences of a failure far exceed the cost of the structure itself. Hence a detailed analysis of dynamic response of the structure is very necessary to arrive at a safe and economical design. In this dissertation, various methods of dynamic analysis of space framed structures have been reviewed and' it has also been summarised how shear deformations, soil structure inter-action and shaft stresses etc. affect the dynamic response of the structure. The members of turbo generator foundations generally have large cross sectional dimensions and high depth to span ratio; so the effect of finite width of joints needs consideration for better understanding of the dynamic behaviour of these foundations. To study the effect of finite width of joints on the dynamic response of the structure, an actual 110 MW turbo generator foundation is analysed taking this effect into consi-deration. For this purpose members previously defined by centre to centre dimensions are replaced by clear span and joints are assumed to be rigid. Stiffness matrix of the _member is written for the clear span and then modified by transforming it to member ends to include effect of finite width of joints. Formulation of the problem has been done using 'Frequency Domain Analysis' method. Consistent mass matrix and Rayleigh type damping matrix has been adopted. Complex frequency response is evaluated at the bearings supporting the machine due to harmonic ground motion in longitudinal, transverse and vertical directions as well as due to machine excitation. Response, thus obtained is compared to response of the laructure obtained by neglec- ting the effect of finite width of joints. The response of the structure indicates that some bear-ings undergo excessive vibration amplitudes ln the vicinity of the operating speed. The members supporting these bearings are strengthened and response has been evaluated. Effect of strengthening on natural frequencies of the structure and amplitudes of the bearings is studied by comparing the response with the response of the structure before strengthening. Finally some practical methods of controlling these large vibration amplitudes are suggested,