Cause and Impact Analysis for Turbine Low Pressure Rotor Axial Deformation Exceed Protection Threshold at a Nuclear Power Plant

This paper introduces the appearance of turbine Low Pressure (LP) rotor axial deformation value (LPRD) exceeded its manual trip protection threshold (MTPT) during full load trip test at a nuclear power plant, and the LPRD monitoring principle. The LPRD influence factors of HN1000-6.43/280.1/267.9 type turbine were analyzed, and got a conclusion that the LP rotor axial thermal expansion (LPRE) influenced by temperature difference between admission steam and exhaust steam. The main sources analysis results of LPRD are LPRE and LPRP. The LPRD changing trend all year round was drew and analyzed in this paper. The root cause of LPRD exceeded MTPT during the full load trip test was analyzed, and got the root cause was LP rotor occurred axial elongation that affected by Poisson effect. A semi-empirical calculation formula of LPRP was provided in this paper. Analysis result of LP flow path axial clearance indicates MTPT provided by the turbine manufactory was conservative, and the maximum LPRD exceeded MTPT during the test without any pernicious impact on operation safety of the turbine.