The paper presents results of a modal analysis for developing a project of a provisory axle of a 69 MW generator’s rotor. The uniqueness of this project, using the modal analysis technique, is that a whole generator set was temporarily (about 90 days) replaced by a sole axle projected, designed, and manufactured by the user. The specific aim of this provisory axle is to provide net 39 MW at 3600 rpm to the blower of the CST’s #1 Blast Furnace during maintenance period of the extracted rotor and without additional risks of interrupting normal operations of steel production. The theoretical modal analysis of the provisory axle was developed with the aid of ANSYS 5.6 with SOLID type elements. The project was based on the geometry of the rotor to be temporarily replaced and main field boundaries conditions were also taken in account as, for example, the clamps in the flanges and the supports in the bearings. After balancing, and under over speed conditions, experimental tests were accomplished successfully, by means of a test “shooting” tunnel, as to check the theoretical critical resonances data and to verify the structural integrity conditions after testing. The results of the theoretical model were also proved successful after the installation, start up, and operation in the field.

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