Abstract
The increase in contributions from non base load renewables, such as wind and solar, can have adverse effects on the stability of an electrical grid. In this study, the possibility of rapidly loading a Francis turbine from a tail water depression (TWD) mode for providing additional system frequency control is investigated. Based on the analysis of full-scale TWD test results and key findings from the transient testing of a micro-hydro scale turbine unit, a detailed description of the TWD transition process is given. The formulation of an improved turbine model for use in one-dimensional hydro-electric plant models is presented with simulation results compared to full-scale data. The analytical model, which calculates output power according to the conservation of angular momentum and identified sources of loss, is used in parallel with full-scale and model scale test observations to elucidate the events and mechanisms occurring during this proposed transition. The output response, in terms of active power, was found to be highly dependent on guide vane opening rate in both full-scale and model tests. For an approximate doubling in opening rate, the duration of the reverse power flow was reduced by 38% and 21%, for full-scale and model units, while the low pressure transient increased by 16% and 8%, respectively. The analytical model was shown to capture the general response characteristic in all cases tested; however, output power response was over predicted due to two identified model assumptions made, while, for the more rapid opening, the penstock pressure was under predicted by approximately 15%.
Highlights
Hydropower is a key base load provider of electricity generation for many power systems throughout the world
As noted by [5], the rotating wave reaches a maximum amplitude at a tail water depression (TWD) level of approximately 1.0D, but, more importantly, the amplitude diminishes as the level is decreased towards the runner and at no level is the surface seen to impinge on the turbine runner prior to transition
This paper presents full-scale test data and results from laboratory testing of a micro-hydro turbine unit to investigate the transition that occurs when a Francis turbine is rapidly brought online from a proposed tail water depression mode for the purpose of providing fast system frequency control
Summary
Hydropower is a key base load provider of electricity generation for many power systems throughout the world. Due to the ability of hydropower plants to be brought online comparatively faster and more economically than conventional fossil fuel plants and other base load providers, hydropower has been used to an increasing degree for peak load management. In a market with ever increasing penetration of often intermittent renewable energy resources, hydropower can provide flexible and reliable generation options for maintaining system stability and ensuring a secure electricity supply. In the modern liberalised market, the flexible and comparatively rapid response of hydropower presents additional opportunities for operators in the form of ancillary service markets. There is a growing need for large-scale operators to develop a more comprehensive understanding of the full dynamic capabilities and safety limitations of a given hydropower plant. Greater confidence in the transient response characteristics of hydro generators will, in turn, enable and Energies 2017, 10, 496; doi:10.3390/en10040496 www.mdpi.com/journal/energies
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