Solubility and coprecipitation of barium and strontium nitrates in HNO<Subscript>3</Subscript> solutions and multicomponent systems

The solubility of Ba(NO₃)₂ and Sr(NO₃)₂ in HNO₃ solutions at 25–95°C is characterized by the power dependence on the total concentration of the nitrate ion with the exponent for Ba(NO₃)₂ equal to −2 in ∼9 M HNO₃ and −6 in more concentrated acid solutions. The latter exponent is also characteristic of the more soluble Sr(NO₃)₂ throughout the examined range of HNO₃ concentrations. In strongly acidic solutions, Ba(NO₃)₂ coprecipitates with Sr(NO₃)₂. The solubility curve for Ba(NO₃)₂ in NH₄(Na)NO₃ solutions suggests formation of a double salt, whereas in UO₂(NO₃)₂ solutions the dependence is the same as in HNO₃ solutions.     

Oxidation of Hydrazine during Evaporation of Nitric Acid Solutions

The processes of hydrazine oxidation with nitric acid on heating and at continuous evaporation were compared. The latter process was performed in a titanium vessel equipped with an external heating chamber and three removable sieve overflow plates. At evaporation, the yield of HN₃ and primarily NH₄NO₃ decreases with increase in the acidity of the bottoms and decrease in the concentration and feeding rate of hydrazine; the presence of plates in the evaporator and their spraying with the reflux decrease the yields of HN₃ and NH₄NO₃ to a still greater extent.     

Modelling and ride‐through capability of variable speed wind turbines with permanent magnet generators

A model for a variable speed wind turbine with a permanent magnet, multipole, synchronous generator is developed and implemented in the simulation tool PSS/E as a user‐written model. The model contains representations of the permanent magnet generator, the frequency converter system with control, the aerodynamic rotor and a lumped mass representation of the shaft system. This model complexity is needed for investigations of the short‐term voltage stability and ride‐through capability of such wind turbines. Ride‐through capability is a major issue and, for the given concept, can be achieved by applying blocking and restart sequences to the frequency converter at the voltage drop in the power grid. Copyright © 2005 John Wiley & Sons, Ltd.     

Technical aspects of status and expected future trends for wind power in Denmark

The power system of Denmark is characterized by significant incorporation of wind power. Presently, more than 20% of the annual electricity consumption is covered by electricity‐producing wind turbines. The largest increase in grid‐incorporated wind power is expected to come from large (offshore) wind farms operating as large wind power plants with ride‐through solutions, connected to the high‐voltage transmission system and providing ancillary services to the system. In Denmark there are presently two offshore wind farms connected to the transmission system: Horns Rev A (160MW rated power in the western part of the country) and Nysted (165MW rated power at Rødsand in Eastern Denmark). The construction of two more offshore wind farms, totalling 400MW by the years 2008–2010, has been announced. This article presents the status, perspectives and technical challenges for wind power in the power system from the point of view of Energinet.dk, Transmission System Operator of Denmark. Copyright © 2006 John Wiley &Sons, Ltd