Study On Bulb Tubular Pump’s Transient Process With VFD

Tubular pumping station is a better way in low-head pumping, the bulb tubular pump have been adopted by several pumping station in South-to-North Water Diversion Project, the superiority in hydraulic performance and project cost decided it will become the future development trend of low-head pumping station.The conduct of tubular pumping station is short and straight, moveable gate valve was adopted to cut off flow, close the gate then start-up to prevent the water flow backward make the head in conduct increased rapidly, which can cause the motor overload and then failed in start-up. The control and security of tubular pumping station are influenced by the hydraulic transient process, which become one of the problems that design and operation unit widely concerned about.In the past, the study on the transient process of tubular pumping station is premise with the asynchronous start-up of synchronous motor. There have been4tubular pumping station in the Project of South to North Water Diversion East Route adopted VFD to adjust the working condition. Under the control of VFD, there are a lot of changes in the pump’s transient process, which are not mentioned in any of present research, so the study on the transient process of bulb tubular pump under frequency control is a project that of valuable significance.This article proceed from the frequency control characteristic of VFD, combined with the hydraulic characteristic of pumping station, established the mathematical model of transient process, the frequency controlled start-up and shut-down of Huaiyin3pumping station in the Project of South to North Water Diversion East Route was numerically simulated. it mainly includes the following aspects:(1) Two kinds of complete characteristic of hydraulic model whose specific speed are944and1100was introduced in this paper, a meshless fitting method—move least square method was first applied to the fitting of pump complete characteristic curve and surface, through compare with previous polynomial fitting method, it proves that it have high fitting precision.(2) The basic principle of synchronous motor is introduced, the characteristic and the function of the VFD was analyzed, which provided a reasonable basis for pump speed controlled model in the calculation of transient process.(3) Regarding the bulb tubular pump with moveable gate valve fitted with flaps cutoff as research object, combined the speed controlled synchronous motor, the mathematical model of VFD controlled bulb tubular pump was established, and the simulated block diagram of transient process was given.(4) Take the Huaiyin3pumping station for example, Matlab7.0was used to program, the transient process of VFD controlled start-up and shut-down were simulated, the effects on the start-up process of the motor-pump-system which caused by frequency linear variation and nonlinear variation, the speed of frequency linear variation, the speed of moveable gate valve, the opening delay time of moveable gate valve and different water level of the station were individually discussed.(5) According to the result of numerical simulation, general rules were summarized, scientific guiding basis for the safety and reliable operation of the frequency and speed controlled bulb tubular pumping station was provided.