INVESTGATION OF SAND EROSION OF PELTON TURBINE IN CHENANI HYDRO ELECTRIC PROJECT-I (5 x 4.66 MW)

Abstract

The erosion of hydro turbines through sand-laden river water is one of the biggest problems in the Himalayan region. Quartz is found as a major component in many of the Himalayan rivers, along with feldspar and other hard minerals, these particles have more than 5 hardness on Moh's scale, which can erode parts of hydro turbine. The problem of hydro-abrasive is usually seen in medium and high head turbines. In high head Run-of-River schemes, even small suspended sediment particles can cause severe hydroabrasive erosion particularly in Pelton turbine due to high impact on account of high velocity. Apart from jet velocity, erosive wear depends upon different parameters such as size, shape, concentration, mineral hardness and base material properties. When this water containing silt impinges on the bucket of the Pelton turbine through nozzle, erosion occurs which in turn results into efficiency drop, increase in maintenance cost and down time of turbine repair. Apart from runner of the turbine, parts which are usually affected due to hydroabrasive erosion are nozzle and its ring, spear and deflector. The erosion concern in hydraulic machines is expected to become more severe in the future due to higher availability of suspended sediments from retreating glaciers and heavy rainfall due to climate change. The problem of hydro abrasive erosion is also observed in Run-of-River based Chenani hydroelectric project-I (CHEP-I, 5 x4.66 MW) located in the state of J&K under Jammu and Kashmir State Power Development Corporation. In the present study, the detailed study of the various components of CHEP-I have been done. The homogenous suspended sediment sample were collected from the forebay on a regular basis during the study period. The suspended sediment properties such as particle size distribution (PSD), suspended sediment concentration (SSC), shape and mineral composition were measured. In the laboratory, the samples were analyzed using the gravimetric method, laser diffraction, turbidity, Scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF) and Petrography. The erosion rate and efficiency reduction of turbine have been estimated using IEC-62364(2013) hydro-abrasive erosion model and correlations developed under earlier studies for High head ROR based hydropower plants. Erosion depth of different regions of the buckets such as Splitter height reduction, erosion in cut-out region and erosion depth in bucket outlet was estimated using IEC-62364 and it was found to be 1.51 mm, 2.10 mm and 0.55 mm respectively. Erosion rate of nozzle and efficiency reduction of Pelton turbine is also estimated by using correlations developed under earlier studies.