Analyzing and Solving Stability Problems during the Commissioning of the Steam Turbine

The commissioning of the steam turbine in the CCPP of Vlore (Albania) was carried out after a shutdown of about one year. During previous operation of the unit, in particular in a couple of shutdowns, were observed high vibration at bearing MAD 21. Before the restart, the oil deflector of the MAD21 bearing (the bearing located in the front standard, on the inlet side of the steam turbine and adjacent to the clutch) was modified increasing the radial clearance on the part of the oil deflector acting as a thermal shield with the aim of eliminating / preventing the risk of rubbings. Rubs at the location of the above mention oil deflector were considered as the very likely cause of high vibration at bearing MAD 21. A lot of tests were carried out during the recommissioning phase and the data received were analyzed. This paper details the discovery of the problems, initial attempts to address them and the use of the rotor dynamics tools to find a solution of the problem by the optimization of the bearings. The bearings were not optimized as per rotordynamics analysis (RDA) findings, because it was a too expensive solution. The solution was found making some modification on control system of the ST, without affecting the mechanical integrity of the machine.