Steam Whirl Detection and Correction in 135 MW Steam Turbine

Steam whirl is the self-excited vibration that causes the rotor of a steam turbine to whirl at its first critical speed. It is caused by the combination of steam excitation (in blade rows and steam glands) and low damping of the journal bearings. Steam whirl usually occurs in the high-pressure rotor at high power output where the steam pressure and flow rate are high. The occurrence of the steam whirl prevents maximum power operation. The steam whirl can be rectified by bearing/seal modifications. A case study was presented on the remote startup support service for a 135 MW steam turbine and generator after a major overhaul. The vibration amplitudes measured at high-intermediate pressure (HP/IP) rotor fluctuated due to subsynchronous vibration frequency when the unit was operated at over 103 MW. Furthermore, the amplitudes significantly increased as the load was further increased and the unit tripped at 134 MW due to the excessive vibration amplitudes at bearing 2. The unit was then restarted and the maximum output was limited to around 103 MW until the following outage where both bearings of the rotor were replaced with the tighter clearance ones and the alignment between bearing 1 and the main oil pump was done. The subsequent startup showed acceptable and stable vibration amplitudes of the HP/IP rotor during baseload operation.