Abstract
Adopting adequate operational and safety measures is a significant part of the investigation of transient processes of hydropower plants (HPPs), both throughout the design stage of prospective plants and throughout the planning stage of the HPPs envisaged for refurbishment/uprating. One of the surge tank (ST) types, insufficiently researched so far, with a potential positive techno-economical influence, is the semi-pneumatic surge tank (SPST). Since the detailed analyses of SPST have never been performed or published before, the SPSTs have been examined here by presenting theoretical considerations, a newly developed mathematical model and comprehensive numerical simulations. The aim is to improve the performance of the open-air variations of STs. Multiple numerical simulations for a specific case-study HPP have been performed with the conclusions about the peculiarities and benefits of the SPST implementation. Firstly, numerical results for the existing as-built surge tank and corresponding alternative SPST have been compared, in order to verify the developed model. Variations of the main SPST constructive parameters have been analyzed, with the aim to determine the sensitivity of particular influences on transient processes versus its geometry alterations. The conducted analyses show that the SPST application brings HPP transient behaviour improvement compared to open-air ST. Dimensions of the new surge tank with specific aeration orifice could be smaller than the ones previously defined: both the diameter of the optimized upper and lower chamber and the core could be decreased by 20% and 12.5%, respectively.
Highlights
Inevitable activities aiming at their safe, stable and efficient operation are analyses of transient processes which can generally be divided into several categories: water hammer (WH), water-mass oscillations (WMO), turbine governing (TGOV), hydraulic oscillations (HOSC), headwater level governing (LGOV), and open channel (OPCH)
The choice of tank type and dimensions usually greatly influences the initial investment costs, so the focus of this paper was to find a more rational approach by applying the semi-pneumatic surge tanks. The advantage of such tanks could be noticeable by direct implementation of aeration orifice onto the open-air surge tanks in the existing or new hydropower plants (HPPs)
Since the detailed analyses of semi-pneumatic surge tank (SPST) have never been conducted up to now, research on the SPSTs has for the first time been carried out by detailed theoretical considerations, a newly developed mathematical model and comprehensive numerical simulations
Summary
Contemporary requirements for as much energy generation and output as possible from renewable sources result in the design and construction of new hydropower plants (HPPs) with increasing installed capacity and maneuvering capabilities, as well as in preferential increase in the existing HPPs maximum installed discharge as a part of their refurbishments [1]. Inevitable activities aiming at their safe, stable and efficient operation are analyses of transient processes which can generally be divided into several categories: water hammer (WH), water-mass oscillations (WMO), turbine governing (TGOV), hydraulic oscillations (HOSC), headwater level governing (LGOV), and open channel (OPCH). Water-mass oscillations analyses are necessary whenever an HPP is provided with a surge tank. As a safety measure, is a very reliable solution, but often being indispensable and costly, it should be wisely chosen and optimally designed [3,4,5]
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