Hydraulic transients analyses are necessary during the design stage of both new and refurbished hydropower plants (HPPs). In this paper, transients of specified most extreme operational regimes are investigated for a long derivation system, provided with a surge tank as well as pressure relief valves (PRVs) at the turbines spiral casing. The transients analyses are focused on water-mass oscillations and water hammer. Investigations for various exploitation regimes and different operating laws of the PRV's are adopted. Results are obtained by means of an original software developed for these analyses. The model was duly calibrated, and the results were compared with the results of the transient analyses from the original design phase of the existing HPP.

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.

This paper presents recent experimental results of pressure measurements during filling and emptying of a relatively small-scale pipeline at the University of Montenegro. Experimental setup for investigation of water hammer and its special effects (unsteady friction, cavitation, column separation, trapped air, fluid-structure interaction - FSI), and pipeline filling and emptying is installed at the Faculty of Mechanical Engineering. It consists of an upstream end high-pressurized tank, horizontal steel pipeline (total length: 55.37 m, inner diameter: 18 mm, pipe wall thickness: 2 mm), four valve units positioned along the pipeline including the end points, and a downstream end outflow tank. The setup was upgraded in 2018 with the installation of new piezoresistive pressure transducers and pipe displacement sensors as well as additional electro-pneumatically operated ball valve at the upstream end of the pipeline. The filling of an initially empty pipeline is performed by a sudden opening of the valve positioned at the high-pressurized tank filled with water. The pipeline emptying process is accomplished by high-pressurized air supplied from the air reservoir installed in the air supply line. The high-pressurized tank is closed, and the downstream end valve is opened. Experimental runs have been performed with different initial values of pressure in the upstream end high-pressurized tank (filling) and air supply line (emptying). Results of new pressure measurements are analyzed and commented, with a reference to the previous experiments presented at 6^th IAHR WG Meeting in Ljubljana, 2015.

Increased climate changes and environmental pollution cause a decrease of available quality water quantities and increase differences in precipitation amounts by seasons. The question is how to provide sufficient quantities of water to supply the population, agriculture, industry, and electricity generation. Sources of quality water are most often located in areas far from the centers of consumption, so it is necessary to construct large water management systems. In order to mitigate the variations in the available quantities of water during the year, reservoirs of significant, seasonal capacity must be built. The power system stability is additionally endangered by the growing impact of renewable sources with extremely variable electricity generation, which is manifested both on an intraday and seasonal level. Therefore, seasonal accumulations, with multi-purpose and even multiple use of the same amount of water, represent a winning option and a stronghold on which power supply, economic and social security and stability should be built. In the case of Serbia, apart from seasonal ones, there are also a spatial differences in the quantities and quality of water in the river basins. In the areas of Zapadna and Velika Morava, Šumadija, Kolubara and Belgrade, the required quantities of water for the supply exceed their own resources. On the other hand, the Drina basin is rich in water of significantly higher quality, and the possibilities of leveling the waters of river Lim are extremely limited. This paper reaffirms the old idea of building a multi-purpose hydro system „Lim-Zapadna Morava“, which would solve these problems. Beside those in power industry, other positive effects that would be achieved by the realization of this strategic project are also presented in this paper.

Modern approach to the modernization of the power generation capacities in the hydropower sector of PE Electric Power Industry of Serbia (EPS) is seen through intensive rehabilitations and building new hydropower plants (HPPs). Although these priorities are defined by long-term investment plan, there are also improvements that are seen through the optimization of the operational regimes of HPPs. EPS technical expert team, after several months of adjustment and investigation has prepared monthly reports with the operational parameters of the HPP. In this paper, as an example, investigated parameters and results for one particular aggregate of the HPP Iron Gate 1 (ser. Đerdap 1/ rom. Portile de Fier I) are presented. Generally, in the current phase of investigation, monthly report is prepared which includes selected parameters that are archived (such as headrace and tailrace water level, the aggregates’ power and discharge) and based on data from the hill charts, losses in pipeline, generator etc. output parameters are defined. Output parameters which are considered as important for the presentation are efficiency of the turbine, generator, hence aggregate, and losses in the operational regimes with the elevation lower than the maximum headrace level. Basic parameters of the aggregates, and generally HPPs’ operational regimes, are retrieved through SCADA system, averaged on minute time intervals, and presented for the one month period.