Control of a pelton turbine with partial jet cutting driven by a cut-in jet deflector

In hydropower plants with Pelton turbines, the output is normally regulated by controlling the flow rate using a needle valve in the injector. However, movement of the needle is slow; as rule of thumb, the power gradient should be less than 3 % per second to avoid excessive pressure variations in the system. The temporal response of the needle valve is limited in most plants due to water hammer problems. This challenge of fast response can be met by diverting the jet using a jet deflector. Partial cutting of the jet enables fast control of power and the associated positive effect on stabilizing the electrical grid. In the present study, the implementation of the cut-in jet deflector has been analyzed with CFD (Computational Fluid Dynamics), with a particular focus on the effects on the torque of the Pelton runner and the hydraulic efficiency. The flow cut and diverted away from the runner at three angular positions of cut-in jet deflector at 3 degrees, 6 degrees, and 9 degrees are obtained as 1 %, 6%, and 11 % relative to the full jet flow at the nominal operating condition, the load decreased by 4.1 %, 11.6 %, and 26.1 % respectively for best efficiency point.