Study On Dynamic Characteristics Of Large Low-head Pumping Station During Transient Period

The large-scale pumping station with low head is mainly applied in important water-lifting, drainge and irrigation engineering and water regulation of state stragitic importance. The water resource problem has been a most importance event in the 21st century. The north parts of China is very short of water, on another hand drainge in the rain season in southern area as Anhui, Jiangsu, Zhejiang, Hunan, Hubei province and Shanghai City becomes an important event regarding to state economical development and people's lifes. So it is necessary how to make the operation of large-scale pumping station with low head safe and reliable and understand its transient charactistics during start-up and shut-down process.This paper takes the large-scale pumping station of low head with siphon discharge as the objective for transient characteristics research during start-up process. The dynamic process during this transient period with regard to siphon discharge was researched. The flow passage was supposed to be rigid system, also the compressity of water wasn't considered, the expression of torque relate to head at any time during start-up was derived. It is assumed that it is adiabatic compression during start-up process before the atmophere pressure in flow passage rise to relief pressure, the thermodynamic equation, momentum equation and rigid water hammer theroy have been applied for the analysis and calculation the variation law of air during this transient process. Formula for approximate estimation of transient voltage during this process was obtained, also an useful expression for the electromagnetism moment was gained. At the end, expression for various torque calculation was analyzed, so the machematical model for the dynamic characteristics during pump start-up based on the hydro-dynamic characteristics of pump and gas-dynamic characteristics of air was constructed in this paper. A program solution for this problem was found in order to search the specific numerical method with regard to different kind of form of this mathematical model.In large-scale pumping station, the head is low and normally the flow passage is short, thus the phase number for water hammer is high and therefore the system compressiblity can be neglected. During the transient characteristics research based on performance characteristics of large-scal pumping station during shut-down process, the compressible water hammer theroy was not considered, a theretical analysis about the dynamic characteristics of pump unit, and pump system and the flow characteristics of unsteady pipe flow under pressure during shut-down process, and so on, were done. The mathematical model was also obtained for various condition, and the calculation solution for specific mathematical model was carried out. In order to simplify the calculation and meet the practical engineering need, aimed at the specific features of the transient process of low head large-scale pumping station, applying the basic equation of rigid water hammer for one dimensional pipe flow in conjuction with transformation equation of pump's full Suter characteristics curves, the boundary condition at pump when pump been suddenly shut down was adapted. Methamatical model for simple transient calculation during pump shut-down process for large-scale pumping station was put forwad for the first time in conjuction with the hydraulic characteristic of pump system. The main aim of this paper is to discover the relation between various important parameters such as speed, discharge, head, torque with regard to time. In the derivation, full Suter characteristics curves to detetmine the relationship between head and discharge was used, and the torque balance equation during pump shut-down process was built for the first time, and a method using mathematical model based on pump full characteristics curves coupling with the dynamic characteristics during pump shut-down process was applied for the first time. So the transient theroy during pump shut-down stated in this paper has solved the difficulty which is impossible to solve in the past for large-scale low head pumping station, therefore it has significant theoretical meaning and practical value for reasonable design, safe and reliable operation for pumping station.Furthermore, validation about several computation models for start-up and shut-down process established in this paper with regard to specific engineering references, such as Huiyin Pumping Station I, Huiyin Pumping Station II, Fankou Pumping Station and Hualanjiao Pumping Station was made. It was found that the mathematical models constructed in this paper is right and therefore could be applied in research, design and operation of pumping engineering.