Improvement Of Valve Management Of DEH System Of Certain 600MW Steam Turbine

With the development of national economy, the difference between peak and valley of electric grid further enlarged, more and more large-capacity power generating units is taking part in peak load regulation of electric grid. Some 600MW steam turbines are designed to work at basic load and their control system are designed based on single valve control mode. With the increase of the difference between peak and valley of electric grid, these 600MW steam turbines have to take part in peak regulation. If they work at the original designed mode, when the load of electric grid is low, the throttling loss of the governing valve in steam turbine will increase, and the relative internal efficiency of steam turbine will decrease. In order to enhance economical performance of steam turbine, it is necessary to improve the valve management system of steam turbine.Firstly, the working principle of the Digital Electro-Hydraulic Control System (DEH) is analyzed, and the importance of determining the relationship between input and output of valve management in DEH system is pointed out. Then, based on the relationship between output and input of load demand and valve open degree in single valve mode, the characteristic equations of governing valves are given. The characteristic equations can fit for not only the controlling mode in single valve but also the sequence valve mode. Finally, according to the characteristic equations of valves group, the relationship between output and input of load demand and valve open degree in sequence valve mode is proposed. Also, the economic performance of governing stage is calculated and analyzed. The results show that steam turbine work in part load condition, the sequence valve controlling mode is useful to improve the operating economy of steam turbine. The improved control mode has been applied to certain 600MW steam turbine and the satisfactory result is obtained.