Transition Process Of Accidental Shutdown Of Mixed-flow Pumping Station Research

In large-scale mixed-flow pumping station units,the hydraulic transition process often occurs,especially the water hammer phenomenon caused by the accident shutdown transition process of mixed-flow pumping station has the most serious damage to the unit.Therefore,it is of great engineering practical significance to study the water hammer problem in the pumping station system during the accident shutdown to ensure the safe and stable operation of the pumping station.This article combined with engineering examples to do the following work:The second chapter analyzes the water hammer phenomenon in the transition process of the pumping station,and reveals the connotation of the transition process.Deduced the motion equation and continuity equation for calculating the transition process of the pumping station,combined with the actual operation of the pumping station,simplified the motion equation and the continuity equation preliminarily,so that it can be better applied to the actual transition process of the pumping station Calculating.At the same time,on the basis of the motion equation and the continuous equation,the characteristic line normal equation is derived,and the characteristic line equation is simplified and solved.Combined with the similarity of the water pump,the four-quadrant curve of the water pump in the transition process is analyzed,and the parameter change of each quadrant in the four-quadrant curve is described in detail,which paves the way for the next chapter.The three chapter dynamic characteristics of the transition process of pumping station shutdown are analyzed,and the boundary conditions of the pump end for single pump operation and multi-pump series-parallel operation are established based on the characteristic line method.The boundary condition equation is solved by combining the torque rotation equation of the pump unit,the head balance equation and the similarity characteristics of the pump.Moreover,the mathematical models of constant flow and transient flow of mixed flow pumping station are established respectively,and the control equations at the nodes of pump,air valve,unidirectional pressure regulating tower and outlet pool are derived.The four chapter carried out the simulation calculation of the transient process of a cascade pumping station under constant working conditions and accident pump shutdown conditions combined with engineering examples,and studied the simulation calculation of the transient process under the conditions of no water hammer protection measures,whether the valve at the outlet of the pump is closed,whether there is air valve protection and one-way pressure regulating tower protection,and obtained the maximum rotary speed of the pump,the maximum water hammer pressure and the minimum water hammer pressure of the pump station under these conditions.After checking and calculating the accident pump shutdown conditions of the four pump groups,the optimal water hammer protection measures of each pump group were obtained,namely,pump group 1 and pump group 2 adopted the one-way pressure regulating tower and air valve protection,and the control valve at the outlet of the pump needed to be closed in accordance with the two stages.The outlet control valves of large pump and small pump in pump group 3 need to be closed in two stages and need one-way pressure regulating tower for water hammer protection.Pump group 4 is regulated by the two-stage closing law of the pump outlet control valve under the protective measures of the air valve.The check calculation of pump shutdown provides technical support for the safe operation of the pumping station.It also provides scientific reference for water hammer protection of other large mixed flow pumping stations during shutdown.