This paper investigates multiple-valve closures in a simple reservoir-valve-pipeline-valve system. Multiple closing (or opening) of valves may induce large positive or low negative pressure waves due to wave interference (superposition of the waves). The effect of multiple-valve closure can be either beneficial or detrimental, with the outcome being entirely dependent on the position of the valves and the sequence and delay of the closures. Valves are incorporated as boundary conditions in the method of characteristics model. The staggered (diamond) grid with consideration of unsteady skin friction is applied. Experimental investigations of multiple-valve induced water-hammer have been performed in the University of Montenegro laboratory pipeline apparatus. The apparatus consists of an upstream end high-pressurized tank, horizontal steel pipeline (length 55.37 m, inner diameter 18 mm), four valve units positioned along the pipeline including the end points, and a downstream end tank. The transient event is initiated first by rapid closure of the downstream-end valve followed by the delayed closure of the upstream-end valve. Calculated and measured results are compared and discussed in the light of the effects of pressure wave interference.

Designing a small hydropower plant (SHPP) necessitates fulfillment of energy and ecological constraints, so a well-defined design flow is of the utmost significance. The main parameters of each SHPP are determined by appropriate techno-economic studies, whereas an improved approach to defining more precise SHPP installed parameter is presented in this paper. The SHPP installed parameter is the ratio of the design flow and averaged perennial flow obtained from the flow duration curve at the planned water intake location. Previous experiences in the design of SHPPs have shown that the SHPP installed parameter has a value in a wide range without the existence of an unambiguous equation for its determination. Therefore, with this aim, the thirty-eight (38) small watercources in the territory of Montenegro, denominated for the construction of SHPPs, have been investigated. SHPPs are divided into two groups depending on the installed capacity and the method of calculating the purchase price of electricity. For both groups, the range of SHPP installed parameter is determined according to the technical and economic criteria: the highest electricity production, the highest income, net present value (NPV), internal rate of return (IRR), and payback period (PB).

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.

Small hydropower plants (SHPPs) have evolved in a sustainable way, providing clean, renewable and reliable electricity with minimal impact on the environment. This paper looks at the methodology for planning SHPPs, with a detailed case study of the Bistrica Majstorovina SHPP. The study outlines the technical, environmental and economic aspects of SHPP development, including site selection, design optimization and integration into local energy grids. It also examines the socio-economic benefits of SHPPs, such as improving the living conditions of the local population and promoting local economic growth. The Bistrica Majstorovina SHPP case study demonstrates the practical implementation of sustainable energy solutions and highlights best practices and lessons learned from project implementation. This paper provides a comprehensive framework for future SHPP projects, contributing to the wider adoption of sustainable energy practices.