Abstract: Aiming at the problem of vibration climbing of the high-medium pressure rotor during the operation of a 300-MW unit, this paper analyzes the abnormal situations such as the differences in vibration characteristics of the rotor between cold and hot(warm) states and the decrease in rotor bending and concludes that the vibration problems are caused by the cracks in the rotor, which lead to the decrease of the rotor stiffness in the hot state and the damage of the rotor balance. The rotor detection shows that there are severe cracks in the rotor shaft. The detection confirms the accuracy of the diagnosis. The timely shutdown and maintenance as well as the detection of the existence of the cracks, have prevented the unit from potential shaft break and collapse. Moreover, the producing process of the rotor cracks and the possible impacts of in-depth peaking load and flexible operation of thermal power units on the rotor safety are also studied in this paper.

Key words: thermal power generation unit, high-medium pressure rotor, abnormal vibration, fault diagnosis, rotor crack