CASE HISTORY:OIL WHIP INDUCED VIBRATION OF RETROFITTED STEAMTURBINE

摘要

In April 2002, Mitsubishi Power Systems, Inc. was awarded the retrofitting project of arn49 year old 202 MW fossil plant owned and operated by Exelon Power. This retrofitrnincluded the replacement of the HP rotor and diaphragms, LP blades L-0 and L-1 and thernupgrading of the vibration measuring system. Orthogonal vibration measurementrncapability was implemented to have a better monitoring and understanding of thernvibration behavior of the unit.rnDuring the start- up activities that followed completion of the retrofit work, vibrationrninstability was observed in the HP bearings that were triggered by rubbing at low-loadrnoperating conditions. Thanks to the vibration data provided by perpendicular sensors inrneach bearing, the orbit and the average centerline of all the bearings were recorded duringrnthe start-up activities. The data revealed a combination of contributing factors that madernthe vibration analysis fairly complex. In addition to evidence of rubbing and sub-synchronousrnvibration, the average shaft centerline of bearing # 2 showed a peculiar trendrnthat seemed to indicate either a) a relative movement of the sensor with respect to thernbearing center, or b) an actual lateral movement of the shaft center in the oppositerndirection of the expected shaft locus.rnA joint vibration analysis performed by Mitsubishi Power Systems and Exelon Powerrnvibration specialists quickly determined the contributing factors for the oil- whirl sub-synchronousrnvibration. In order to increase the stability margin of the HP rotor-bearingrnsystem under rubbing conditions the loading on the bearing was increased by slightlyrnmodifying the bearing geometry.