Zicheng Zhao

Internal steam leakage in steam turbines from the high-pressure side to the low-pressure side through clearances causes loss, resulting in reduced efficiency and potentially compromising the safe operation of the turbine. Therefore, a comprehensive understanding of the flow characteristics of leakage through blade tip clearances is crucial to improve the efficiency of steam turbines. In this paper, the last stage blades of the low-pressure cylinder of a certain 600 MW ultra-supercritical steam turbine unit were studied. A wet steam flow model and a turbulence model were established, and the flow characteristics of the last stage under different inlet parameters, outlet parameters, and tip clearance sizes were analyzed. The results showed that an increase in the clearance size affects the inlet and outlet steam angles of the rotor blades, with significant changes occurring near the blade tip. The main flow velocity inside the rotor blade channel fluctuates violently starting from the 70% axial position. The high entropy region is located near the exit flow region of the rotor blade, with its range expanding as the clearance size increases. The entropy change is significant at 60% blade height and above, with more intense changes occurring in the blade tip area. The relative leakage amount and efficiency change uniformly with clearance variation. Generally, for every 0.1% increase in clearance height, the relative leakage amount increases by ∼0.31%–0.42%, and the stage efficiency decreases by 0.34%–0.44%. The results of this study can provide a theoretical basis and guidance for improving the flow efficiency of steam turbines.

The rapid development of new energy sources has brought a certain impact on the original power grid structure, accelerated the wear of unit equipment, and affected the stability, safety, and economy of thermal power unit operation, so it is proposed to add an energy storage system to solve the above problems. To analyze the secondary frequency regulation effect of thermal power units assisted by a flywheel energy storage system, a mathematical model of the control strategy on both sides of the boiler, steam turbine, and flywheel permanent magnet synchronous motor is proposed, and a two-regional power grid model is built through MATLAB/Simulink to simulate the frequency regulation effect of units with or without energy storage participation through step disturbance and continuous disturbance, which are 0.045 and 0.023 p.u. MW. Under step disturbance, the frequency fluctuation of the coupled energy storage system changed by 0.025 228 p.u. Hz, the time for the system to return to a steady state was shortened by 5.85 s, the maximum change of the frequency of the system in Region 2 was reduced by 0.025 579 p.u. Hz, and under continuous disturbance, the fluctuation of the output power of the steam turbine in Region 1 was reduced by 0.022 982 p.u. MW. In summary, under the same disturbance conditions in the outside world, the use of flywheel energy storage to assist the frequency regulation of thermal power units can effectively reduce the frequency fluctuation of the system, reduce the fluctuation of the output power of the steam turbine, reduce the loss of mechanical equipment, and extend the service life of the unit to a certain extent.