Vibration Investigation for Low Pressure Turbine Last Stage Blade Failure in Steam Turbines of a Power Plant

West Burton Power Plant, UK owned by EDF energy has 4 steam turbo-generator (TG) units for power generation. These units were installed and commissioned between 1967 and 1969 and have since operated smoothly without any major problems up to 2007. In 1995 and 1996, two TG sets, namely units 2 and 3, were retrofitted with the new design LP rotors and in 2005, retrofitting of HP rotor for all four TG units was commenced. The retrofitting was done without changing the foundation, but only with the aim to enhance the power output by 20MW (10 MW through LP retrofit and 10MW through HP retrofit). Cracking of the last stage blades of LP1 and LP2 turbine, steam-end blades has been observed in TG units 2 and 3 only. Hence the in-situ vibration measurements have been carried out on TG unit 3 and compared with healthy TG unit 1 to understand the dynamics of both units. This paper presents observations made on the dynamics of TG units 1 and 3, and results from the root cause analysis which may possibly lead to the solution to the blade failure problem in TG units 2 and 3.