Turbine rotor & bearing pedestal support stability testing:

If one or more of the turbine rotors on a unit runs smooth under some conditions and has vibration excursions under other conditions, it might be affected by steam or oil induced whirling of the rotor shaft center, or some other condition that results in main bearing loading or pedestal support related stiffness or damping problems.

These types of problems cannot be solved by balancing, at least until the source of the whirling-related problem (which results is sub-synchronous instead of running-speed instead of running-speed vibration) is addressed and corrected and then the running speed and unfiltered vibration is found to still remain too high.

For this type of problem to be solved the original data collection procedure will be the same as for the general survey (section 1 above), and then continuing, concentrating on the measurement points that are exhibiting the excursions, while changing parameters as required (depending on the results of the spectral data) such as:

2.1 Oil supply temperature

2.2 Sequence of control valve operation

2.3 Increasing shaft preload on main bearings (coupling alignment)

2.4 Improving the lap (or per cent contact) of main bearing spherical seats to saddles

Kro-Magnum LTD, P.O. Box 578, Kennesaw, , US, 30144. Tel: 770-975-3123; Fax: 770-975-3123.