Analysis of Shaft System Torsional Vibrations and Fatigue Life in Pump Turbines Under Hydraulic Pulsations
For a designated 306 MW pumped storage power unit,a concentrated inertia model for the main shaft's tor-sional vibrations was established to evaluate the torsional characteristics of the shaft system.Strain gauge testing method-ologies were employed to carry out torque measurements and load shedding tests at various operational loads-specifically,25%,50%,75%,and 100%.The investigations uncovered that at a 25%operational load,the shaft system is subjected to torque fluctuations.These torque fluctuations are correlated with hydraulic instabilities observed under low-load condi-tions.The torque fluctuations are ameliorated when the unit is operated at higher load levels.The frequency of these torque fluctuations aligns with the torsional vibration frequencies ascertained through load-shedding tests.By extrapola-ting from the torque fluctuations observed in the strain-tested cross-sectional areas,the torque oscillation response at the rotor end-face was computed.Fatigue life analyses were executed for both the load-shedding conditions and the torque fluctuations.The findings suggest that load-shedding conditions exert minimal impact on the shaft system's fatigue life.In contrast,the torque fluctuations experienced at a 25%load level have a discernible influence.Consequently,it is advised that the operational time spent in the 25%load zone be minimized to mitigate fatigue life degradation of the shaft system.
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