Impulse (Turgo and Pelton) turbine performance characteristics and their impact on pico-hydro installations

Abstract

Pico-hydropower is a viable technology that can be integrated into a decentralized, off-grid approach to rural electrification in regions that currently have only limited access to electricity. The Turgo turbine is classified as an impulse turbine, similar to the Pelton wheel, often used in pico-hydro systems. Both offer high efficiency for a broad range of site conditions, but the primary difference is that the Turgo can handle significantly higher water flow rates, allowing for efficient operation in lower head ranges and thus potentially expanding the geographic viability. Published data on Turgo operating performance are limited; despite the differences, discussion thereof in design manuals is generally lumped in with the discussion of Pelton wheels. In this study, a laboratory-scale test fixture was constructed to test the operating performance characteristics of impulse turbines. Tests were carried out to determine the effect on turbine efficiency of variations in speed ratio and jet misalignment on two Turgo turbines. The results were compared to similar tests in the same fixture on a Pelton turbine. Under the best conditions, the Turgo turbine efficiency was observed to be over 80% at a speed ratio of approximately 0.46, which is quite good for pico-hydro-scale turbines. Peak efficiencies for both the Pelton and the Turgo turbines occurred at lower than theoretical ideal speed ratios based on a momentum balance; the reduction in speed ratio at which peak efficiency occurs is likely caused by inefficiencies in the turbine. Tests of jet misalignment showed that moving the jet to the inside or outside edge of the turbine blades caused a drop in Turgo efficiency of 10–20% and reduced the optimal speed ratio by 0.03 (6.5%). Radial misalignment had a significant adverse impact on both Turgo and Pelton turbines, however, angular misalignment of the jet is more of a concern for the Turgo turbine. The results stress the importance of proper system design and installation, and increase the knowledge base regarding Turgo turbine performance that can lead to better practical implementation in pico-hydro systems.