Design validation of high inertia generator rotor

Abstract

The rising urbanization in the developing economies and growing demand from the IT industries are the factors that are driving the global generator sales market. The global electric generator sales market is projected to reach USD 31.6 billion by 2025. Even though the market demand is high, the unbalance force is the vital key role for the vibration of a rotor and also critical speed and torsional vibration. The main goal of the present study is to validate the torsional frequency, critical speed analysis and unbalance response analysis of an operating generator at a speed of 750 rpm. The finite element model was developed using MADYN 2000 software based on the rotor dynamics. The rotor consists of 25 different step diameters. For analysis, the rotor is divided into 42 sections having 43 stations. The stiffness of DE bearings is 3.38E+05 N/mm and 2.32E+05 N/mm in vertical and horizontal directions respectively. The stiffness of NDE bearings is 1.5E+05 N/mm and 1.57E+05 N/mm in horizontal and vertical directions respectively. Analysis is carried out by giving input as 0.1-500 Hz frequency range, relative ratio 10: 20: 500 and speed range from 250 to 5000 rpm. The capacity of the generator is 10MW. The torsional natural frequency is 122.06 Hz and the mode shape is obtained from numerical analysis. Five mode shape frequencies are determined. The displacement of a rotor in static condition is 0.28 mm. The first critical bending speed is 1455.3 rpm and second critical speed is 3194.7 rpm obtained from Campbell diagram. Evaluated torsional natural frequency, static analysis of rotor, critical bending speed and unbalance response analysis are under the design limits, hence they were accepted. Finally, results are validated with a baseline design which are helpful for further researches.