In this study, for the purpose of improving the rotordynamic characteristics of a large power recovery train, PRT, motor-generator rotor fundamentally by design, firstly, a bearing improvement analysis is carried-out by retrofitting from plain partial journal bearings, originally applied for an operation at a rated speed of 1,800 rpm, to final tilting pad journal bearings. Results show that satisfying evenly key basic lubrication performances such as the minimum lift-off speed and maximum oil-film temperature, a careful design solution of 5-pad tilting pad journal bearings may effectively result in enhancing the direct stiffness of bearings by about two times at such a relatively low rated speed. Next, a detailed rotordynamic analysis is performed, applying both of the original plain partial and retrofitted tilting pad journal bearings, in order to confirm the effect of rotordynamic improvement after the suggested bearing retrofit. Results show that the rotor unbalance response vibrations with the tilting pad journal bearings are greatly reduced to as much as about 11% of those with the plain partial journal bearings. In addition, for the tilting pad journal bearings there is no critical speed up to the rated speed while for the plain partial journal bearings there is one critical speed close to the rated speed with some damping but not sufficiently enough.
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