| dc.description.abstract | Several large hydropower plants in Norway have been upgraded with a higher installed capacity, but unfortunately, this upgrade has also brought with it operational problems because of sediments entering penstock and causing damage to the turbine. This was due to a sand trap which was not functioning as projected after the upgrade. To improve sand trap efficiency, several proposals were considered. One of them was to calm and homogenize the flow by using a flow calming structure.
The main objective of this thesis was to propose the optimum design of a sand trap flow calming structure for Tonstad hydropower plant, which was one of the hydropower plants facing operational problems after an upgrade. To find the optimum designed of such a structure, three different flow calming structures were designed, constructed in the model scale, tested in the hydraulic scale model and compared to each other.
The results showed that the implementation of a flow calming structure improved sand trap efficiency. All three flow calming structures provided very similar, satisfactory, results. Sand trap efficiency increased from 95.67 % to more than 99 %, sedimentation began already in the diffuser and occurred mainly in the upstream half of the sand trap. In terms of headloss were the results various. While flow calming structure No. 3, layout 3, increased sand trap efficiency to 99.96 % with a small headloss of 3.83 mm, flow calming structure No. 2 reached sand trap efficiency of 99.19 % with the headloss 5.2 times higher equal to 19,89 mm. This made flow calming structure No. 3 the one to be recommended for further testing and possibly installation in sand trap 3 in Tonstad HPP. | |
