Analysis and visualization of progressive erosion in Pelton buckets

Abstract

Hydropower plants operating in fragile mountainous regions face severe hydro-abrasive erosion of hydraulic components, which results in drop in efficiency, frequent interruptions in power generation and downtime for repair/replacement. Due to high flow velocity in components like nozzles and buckets, a Pelton turbine is highly susceptible to erosion. The effect of erosion is observed as cumulative loss of material and study of its gradual progress required frequent measurement. In this study, in-situ images of Pelton buckets were captured throughout a sediment period at a hydropower plant located in Himalayan region, India and analysed for characteristics of progressive erosion damages. A multi-layered paint method was used to visualize the initiation of erosion in different parts of bucket. Removal of colours due to erosion provided the information on erosion initiation and various erosion zones in bucket. The erosion of outer side of bucket was analysed with single layer paint removal and images from past records of the plant. Further, the effect of initial condition of a bucket on cumulative erosion after a sediment season is also presented for both coated and uncoated buckets. The in-situ photographs during the silted water period suggested that the outlet portion inside the bucket faces significant erosion. The technique of image capturing throughout sediment season was successful in obtaining progressive erosion. Such method with a reference scale in the image is an effective method to quantify erosion like width increase of the splitter more frequently. The paint in the buckets was found capable of providing information on erosion initiation and erosion zones inside Pelton buckets. The erosion characteristics of outer side of the bucket confirms the presence of a Coanda effect. This study will facilitate turbine designers and manufacturers in better coating and/or surface treatment to specific zones of bucket to minimize efficiency loss due to distorted profile of the bucket, as more prone surfaces can be coated with thicker coatings to protect it longer from erosion.