The working principle of a steam turbine

A good paper on steam turbines: Upgrade promptly – Analysis of shaft system vibration in high-power steam turbine generators. Zhang Suxin, He Aping, Li Yuhe, Zhang Weike (Shanghai Steam Turbine Co., Ltd., Shanghai 200240). Abstract: A theoretical analysis is conducted based on the shaft system vibration characteristics of the 600MW Wujing unit. The control of high-speed dynamic balancing accuracy, the selection of methods for on-site installation of the unit, the measurement of shaft system vibration during startup and under load conditions are all considered. The results of the theoretical analysis are compared with the actual measurement data, and finally an evaluation is carried out using international (ISO) standards, indicating that the shaft system vibration characteristics of this unit are satisfactory. Keywords: 600MW unit; shaft system vibration; comprehensive analysis; field testing; characteristic evaluation. Chinese Library Classification Number: TK263.6104. Document Code: A. Analysis of large steam turbine-generator rotor system vibration. MANG Sun*, HE A-ping, LI Yu-he, MANG (Shanghai Turbine Co., Ltd., Shanghai 200240, China). Abstract: By combining the characteristics of the Wujiing 600MW steam turbine shaft system vibration, a theoretical analysis of rotor system vibration is presented in this paper. The high-speed dynamic balancing precision, installation options, methods for measuring shaft system vibration during startup and under load, as well as the results of the theoretical analysis and the measured values are compared. Finally, the shaft system vibration characteristics of the Wujiing 600MW unit are evaluated according to ISO standards. It is shown that the shaft system vibration characteristics are effective. Keywords: 600MW unit; shaft system vibration; comprehensive analysis; field testing; characteristic evaluation. Such accidents cause huge economic losses, and they occur both domestically and internationally. Therefore, it is highly necessary to conduct shaft vibration analysis on high-power steam turbine generators. Shaft vibration is one of the important safety indicators for large steam turbine generator sets; it is directly related to whether the unit can operate stably over the long term. There are many factors that affect shaft vibration, which can basically be divided into three categories: first is the design of the shaft vibration characteristics; second is the machining, assembly, and dynamic balancing of the single rotor, as well as the installation in the field; third are the characteristics of the support system. If the vibration characteristics are poor and the vibration amplitude is high, alarm signals may even be generated, which can pose a threat to the unit. The above three factors pose a risk of accidents at any time; if not handled properly, any issue in any of these aspects can lead to vibrations, and in severe cases, it may result in catastrophic accidents that cause death and damage to the equipment, thereby worsening the situation for the manufacturer. High-power steam turbine generator sets possess excellent performance. Date of receipt: February 14, 2001. Author’s profile: Zhang Suxin (born 1964), male; graduated from the Department of Thermal Engineering at Tsinghua University in 1986. In May 2001, he became the chief engineer at Shanghai Turbine Co., Ltd., where he is primarily involved in the design of axial flow compressors, gas turbines, high-power steam turbines, and combined cycle systems. He is also engaged in the development of 600MW subcritical and supercritical power units, and has published several papers on related topics. Wanfang Data · 2. Vibration Analysis of the Shafting System in High-Power Steam Turbine Generators. Vibration characteristics are an issue of concern to both manufacturers and users, and close cooperation between them is essential. Below, taking the 600MW subcritical intermediate reheat four-cylinder four-exhaust steam turbine generator set at Shanghai Wujing No. 2 Power Plant as an example, the vibration characteristics of the shafting system in high-power steam turbine generators are analyzed. The shafting of the 600 MW Wuji unit consists of a high-pressure rotor (HP), a medium-pressure rotor (IP), a low-pressure rotor I (LPI), a connecting shaft (JSO1), a low-pressure rotor II (LPII), a generator rotor (GEN), and an exciter rotor (EXC). Except that the exciter rotor uses a single support, the other rotors all adopt a dual-support structure. The entire shafting system comprises 11 bearings; aside from bearings No. 6, 7, and 8 on the low-voltage rotor, which are of the viscous pump type, the rest are tilting-pad bearings. The total length of the shafting system is approximately 48.3 meters, and its total weight is about 245 tons. A schematic diagram of the shafting system for the 600MW unit is shown in Figure 1. Figure 1: Schematic diagram of the shafting system of the 600MW Wujiing unit. 2. Design of the vibration characteristics of the shafting system. The design of the vibration characteristics of the shafting system includes the calculation of the static parameters of the shafting system, as well as the calculation of its lateral vibration and torsional vibration characteristics. During these calculations, dispersion is first carried out based on the natural modes of the rotor to establish a computational model; thereafter, the bending stiffness and torsional stiffness are determined. The shafting system of the 600MW Wujiing unit is divided into 320 units for such calculations. The optimized transfer matrix method is used in the calculations; it is fast, prevents the occurrence of additional or missing roots for the lower-order frequencies of shaft system vibrations, and offers high accuracy. The theoretical calculation results match well with the actual measurements taken on site. The vibration equation of the shaft system can be written as: &A + D EC+KX=FSin(wt) (1) In this equation, M, D, and K represent the mass matrix, damping matrix, and stiffness matrix of the shaft system respectively, while F represents the perturbation torque matrix of the shaft system. f is the disturbance frequency of the shaft system, t is time, and X, V, A represent the displacement matrix, velocity matrix, and acceleration matrix respectively. It can be seen from this that the vibration characteristics of a shaft system are determined by the mass of the shaft system, its operating speed, the forces acting on it (centrifugal force, damping force, supporting force, disturbing forces), as well as the frequency of these disturbing forces. Relevantly, once the aforementioned parameters are given, the vibration characteristics of the shafting can be determined. 2.1 Calculation of static parameters of the shafting. The purpose of static calculation is to determine the elevation of each bearing in the shafting as well as the bearing loads; the former serves as a basis for the on-site installation of the unit, while the latter is used as boundary conditions for calculating the lateral and torsional vibrations of the shafting. As is well known, a shafting system with more than two supports is actually a hyperstatic system (for example, the shafting system of a 600MW unit is a ninth-order hyperstatic problem). To solve it, supplementary equations equal to the order of hyperstability must be added. Assuming the rotor between the two bearings to constitute one span, and taking into account the continuity and stress conditions of the rotor across various spans under operating conditions, setting the rotor bending moments at the nine intermediate bearings to zero serves as the supplementary equations, thereby turning the shafting system into a static system. At the cross-sections at both free ends of the shaft system, the bending moment and shear force are both zero; thus, the shear force, bending moment, and displacement at each cross-section of the shaft system can be determined using the method of moment transmission. The static parameters of the shafting are shown in Table 1. Table 1 Bearing numbers, bearing diameter (mm): BRGI, BRG2, BRG3, BRG4. Static parameters of the shafting system: BRG5, BRG6, BRG7, BRG8, BRG9, BRG10, BRG11. Values: 279.4, 330.2, 330.2, 3, 8, 1, 48; 2.6, 482.6, 482.6, 482.6; 501, 501, 305 thousand