No abstract

The importance of pumped storage plants (PSPs) is continuously increasing in power systems with more and more variable renewable energies. For the research and development of PSPs, variable speed technology and sea-water PSP are two important new orientations. In this paper, an experimental platform of variable speed pumped storage unit under wave disturbance is introduced. The purpose of the platform is to study the design and operation mechanism of variable speed PSP based on various common technical problems, especially for the four aspects: transient processes, variable speed unit, coordination control, wave disturbance. The platform adopts a Chinese sea-water PSP in feasibility stage as the prototype, and a model scale of 1:4 is applied. It consists of nine sub-systems, including waterway system, variable speed reversible model unit, circulating water system, speed governor system, AC excitation and electric protection, coordination control, monitoring system, intelligent AC load and measurement system. The model unit contains a reversible pump turbine, a doubly fed induction machine, etc. The speed variation range is ±8%, and the rated power is 78.13 kW. The model runner meets the IEC standard with a reference diameter of 284.3 mm. The upstream water tank is a closed pressure tank that can adjust the pressure and discharge. The downstream water tank is an open water tank that can simulate wave level fluctuation. Regarding the control system, it has four core parts: local control unit, speed governor, converter and coordination controller. The experimental study content contains three key aspects: (1) performance validation for variable speed unit; (2) operating stability under complex disturbances; (3) capability of variable speed PSP during transient processes. The experimental study based on the platform aims for laying a theoretical and technical foundation for the follow-up construction and operation of real sea-water PSPs with variable speed units.

Exploring the water sources taken up by plants is necessary for ecological protection. The purpose of this study was to determine the exact proportions of different water sources absorbed by herbaceous plant species in the wetland of Poyang Lake in an inland humid region. This identified the water sources patterns in wetlands and provide Poyang Lake managers information about the lake water level needed to sustain vegetative life. We analysed the deuterium isotope composition (δ2H) and oxygen isotope composition (δ18O) values in the stem water of dominant herbaceous plant during its different growth stages to explore the proportions of water sources in different growth stages by using the Phillips equation, and the results supported the accuracy. The results indicate that the groundwater should not be lower than 0.13 m, otherwise the Carex cinerascens may not be able to absorb it. In previous studies, the lower slopes and intercepts of δ2H–δ18O were attributed to the secondary evaporation under the cloud, but we found that there is a cumulative evaporation effect in rainwater, soil water, and groundwater, which makes the slopes and the intercepts of δ2H–δ18O relationship lines become lower from top to bottom. In this study, the final effect of evaporation on the δ2H and δ18O values of shallow soil water is depleting the δ2H and δ18O values of shallow soil water, which is different from previous studies. The δ2H and δ18O values of groundwater varied little with changes of seasons and rainfalls. The δ2H–δ18O relationship lines established by various substances can also reflect the regulation of d-excess by large lakes through secondary sources.