Investigation on hydraulic transient flow in hydropower station with air chamber and pressure relief valve

Abstract

The fluid flows in closed conduit systems, the flow control is important part for better operation of the system, for instance, load rejection and load acceptance of turbine, opening and closing of wicket gate, starting and stopping of the pumps; etc. when these operations very quickly performed, they shall cause the hydraulic transient or water hammer phenomena, which may results from catastrophic failures of turbine, valves, pump and the rupture of penstock or waterway in general. The fluid transient analysis is one of the more challenging and complicated flow problems in the design and the operation of water pipeline systems. In this research, we used an accurate analysis and suitable protection devices knows as Air Cushion Surge Chamber and Pressure Relief Valve to protect waterway systems of a hydropower plant. The study was applied on a pipeline composed of five segments of different diameters and elevations with a total length of 2493.32 m. The characteristics method are used for handling the hydraulic transient. This thesis simulates of transient phenomena in hydropower plant systems based on the economic size of Air Cushion Surge Chamber and PRVs. Also, it provides the influence of using the protection devices to protect the waterway systems from damaging due to the gain pressure which occurs in the transient state. FORTRAN was used in the simulation. The aim was to simulate transient at the entrance of spiral case and along the pipeline, in general, this is divided into four cases: simulation without any protection measures, simulation with only Pressure Relief Valve, simulation with only Air Cushion Surge Chamber and simulation with both Pressure Relief Valve and Air Cushion Surge Chamber. Results obtained are 420, 370, 355 and 265 meter of water respectively. The allowable pressure in this project design is 350 meter of water, results obtained provide that combination of Pressure Relief Valve and Air Cushion Surge Chamber are efficient and economic devices to amplify transient flow in hydropower plant system. This showed that the stepwise of wicket gate can reduce transients significantly than the linear closure operation. Pressure relief valve with a high opening stepwise can also reduce transients significantly, this can be achieved by means of FORTRAN. The pipeline diameter and the frictional coefficient were seen to be important factors which affect the hydraulic transient. A high frictional coefficient and small diameter results in transients’ reduction.