Small hydro plants

So far, issues related to the frequency stability of an APS have been presented. Maintaining voltage levels in the AC buses of an autonomous power system close to their nominal value is a similar problem. Such an objective can be obtained if equilibrium can be achieved between produced and consumed reactive power in the system. The influence of renewable generators on voltage control depends on the type of the interface used for the connection to the grid. Induction generators in wind turbines or small hydro plants, consume reactive power. A partial compensation can be achieved using local capacitors. Power electronic inverters used for the connection of photovoltaic systems and wind turbines are reactive power neutral. 

Armenia has hydro energy resources that can cover up to 35% of country s energy demand, but according to above mentioned, hydropower development has no much perspective in the country due to limitations of hydro-power resources and this could result environmental degradation, particularly lose of environmental quality of the Lake Sevan. However, the system of small hydropower plants on mountainous rivers could be developed as a support to Armenian energy grid. 

The Dniestr hydroelectric plant of 702 MW capacity with 1 TWh average annual power generation was put into operation on Dniestr river. The Dniestr hydro power cascade will include the biggest in Europe Dniestr hydro accumulating plant of 2,268 MW capacity and buffer hydroelectric plant. Fifty small hydroelectric plants of about 100 MW total capacity with 0.25 TWh annual power production are exploited in Ukraine. 

In Ukraine technically available potential of hydro energy is 81 TWh/year. As for large hydroelectric plants and small hydro energy, total economically expedient unused potential is 17-19 TWh and up to 3. 7 TWh correspon-... 

Hydro power systems utilise the energy of flowing water for the production of electricity. A general consensus for the definition of small hydro power plants does not exist. The upper power limit varies from 2.5 to 25 MW, depending on the country, but 10 MW is the most acceptable one and has been proposed by the European Small Hydro Association (Thematic Network on Small Hydro Power, 2005). 

Small hydro power plants are usually of the run of river type. In such schemes electricity is generated when the water is available and provided by the natural flow of the river. When the river dries up and the flow falls below some predetermined amount, the plant generation ceases. 

The main components comprising a small hydro power plant are the civil works for the water diversion and the necessary mechanical and electrical equipment. Water is diverted from the river at the intake position, where a weir is built at an elevation higher than the power house. From that point, water is driven through a... 

Dennis Norton, Hydro-Chem, Hydro-Chem, presentation to the committee, June 11, 2003 Marvin A. Crews and Howe Baker, Small Hydrogen Plants for the Hydrogen Economy, presentation to the committee, June 11,2003. 

The assumed operating hours per annum are typical for early 2000, where large scale fossil fuel power plants worked predominantly at base load, while hydro-power and small scale plants worked at peak-load. Recently, because of renewable energy diffusion, this value has significantly decreased. 

While several metal-catalysed approaches to solve the task of generating fl tz-l,2-diols have been developed, this method remains remarkable, since it represents the first small molecule-catalysed, catalytic version of this transformation. The starting materials do not need activation or protection, and the reaction can be performed under standard conditions without further precautions. The selectivity of the reaction potentially results from a hydro Q acetone enamine-initiated transition state (5). More recently, Enders et al. applied a related method to the organocatalytic synthesis of sialic acid precursors (Scheme 5.6). Protected pyruvic aldehyde (6) was reacted with several aldehydes, forming the desired aldols (7) in moderate yields, but good selectivities (31-51%, 90-92% de, 73-99% ee). The conditions were optimised to limit detrimental side reaetions sueh as Mannich elimination or formation of the aeetal self-aldolisation produet. While generally easily applicable and robust, the method laeks effieiency in one key parameter, its reaction time. This limitation, combined with moderate yields unfortunately prevents a scale-up to or beyond the pilot plant. 

The biosynthesis of rubber may be divided into three steps (1) initiation, which requires an allylic diphosphate molecule, (2) elongation, in which IPP units are added to a Z-l,4-polyisoprene chain, and (3) termination, in which the polymer is released from the rubber transferase enzyme (Cornish, 1993). In plants, the elongation of Z-l,4-polyiso-prene (natural rubber) requires a small -allylic diphosphate initiator (less than or equal to C20). Famesyl pyrophosphate (FPP) is an effective initiator of polyisoprene biosynthesis (Light et al, 1989) further, because only one molecule of FPP is needed for each molecule of rubber formed, small traces of this substance that are inadvertently present complicate biosynthetic studies. The E-allylic diphosphates are hydrophilic cytosolic compounds, whereas Z-l,4-polyisoprene is hydrophobic and compartmentalized in subcellular rubber particles. A soluble E-prenyl transferase from the latex of Hevea brasiliensis serves as a famesyl diphosphate synthase and plays no direct role in elongation of Z-l,4-polyisoprene (Cornish, 1993). Because the hydro-phobic rubber molecule is produced inside a rubber particle but is formed from hydrophilic precursors from the cytoplasm, the polymerization reaction must take place at the particle surface. 

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