抄録
Overspeed analysis is one of the critical issues in turbines. In order to protect turbines against excessive overspeed, non-return valves (NRVs) are needed in extraction pipes. The traditional overspeed calculation method at a failure of NRV will add all the energy of steam and flashing water in extraction pipes and heaters, thus requires numbers parameters such as number, size and closing time of NRVs and shutoff valves, volume of steam in extraction pipes between the NRVs and heaters, volume of steam in the heaters, and volume of water in the heaters at normal and high level. Furthermore, the traditional method can't obtain the overspeed of the leaking main valves. In this paper, a new overspeed calculation method of steam turbine under the condition of NRV failure or main valve leakage is proposed. This method considers that the steam flowing into the cylinders through a pipe is limited within a certain time, and use iterative approach to calculate the volume of the steam flowing into the cylinders within the acceleration time and the maximum speed. Compared with the results of traditional method, this proposed method which uses only the diameter of extraction or leaking pipe is efficient and convenient.
