Comparative Study Between In-Situ Measured Vibration Data at Bearing and BTT on a LP Turbine Last Stage Blades in a Steam Turbo-Generator Set

Cracking of the last stage blades of the low pressure (LP) turbines has been observed after 2007 in the 2 steam turbo-generator (TG) units out of the 4 units at the West Burton Power Plant UK. These 2 units were retrofitted with the new design LP rotor including blades in 1995 and 1997. Recent vibration measurements during machine transient and steady state operations confirms that the TG sets are running close to the machine critical speed and the blades are expected to have high vibration. Now the Unit 3 is fitted with the blade tip timing (BTT) system to monitor the LP1 last stage blades. Hence the present effort to compare the vibration of the blades by the BTT system with the bearing vibration to establish the correlation such that the status of the blade vibration can be accessed even without BTT measurement and the correlation may be used for other units with similar dynamics. The paper presents the comparison of the in-situ vibration measurement on bearings during machine run-up with online BTT data, observations, and possible correlation.