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This paper presents important results of the European HVDC Study Group founded on an initiative by the German Commission for Electrical, Electronic and Information Technologies in September 2010. The main task of the Study Group has been defining “Technical Guidelines for first HVDC Grids”: 1) to gain a common understanding of basic operating and design principles of HVDC grid systems, and 2) to prepare the ground for more detailed standardization work. The HVDC systems are moving from the stage of point-to-point (PTP) connectors to the stage of the transmission systems interconnecting more than two stations and utilizing multiterminal (MT), multivendor (MTMV) HVDC voltage-source converter (VSC) systems. The development will be modular, for example, in steps, starting with interconnecting PTP connectors and establishing three-pod, radial systems. Then, such simple systems may gradually be interconnected into radial and meshed HVDC–VSC systems comprising more HVDC lines and dc converter stations. This paper describes understanding, specification, and standardization of design and operation principles of the HVDC grids seen as the first needed steps toward such MTMV systems. [ABSTRACT FROM PUBLISHER]

Measurements from an islanding experiment on the Rejsby Hede wind farm, Denmark, are used for the validation of the dynamic model of grid-connected, stall-controlled wind turbines equipped with induction generators. The simulated results are found to be in good agreement with the measurements and possible discrepancies are explained. The work with the wind turbine model validation relates to the dynamic stability investigations on incorporation of large amount of wind power in the Danish power grid, where the dynamic wind turbine model is applied. [Copyright &y& Elsevier]

Ultrastructural study of blood capillaries and muscle fibers in patients with obliterating atherosclerosis was carried out over time. Changes in the fine structure of the capillaries and muscle fibers typical of each stage of the obliterating process are described allowing morphological diagnosis of stages of this disease to be performed.

The time course of quantitative changes in the ultrastructure of capillaries and muscle fibrers was studied by the totality of morphological signs in 33 patients with obliterating endarteritis of the lower extremities. As the disease develops, the area of luminal surface and the volume of basal membrane of the capillaries and mitochondria of muscle fibers increase progressively; the volume and number of micropinocytotic vesicles, the volume of myofibrills and the ratio of myofibrill to the mitochondria volume decrease. In early stages of the disease the size of capillary lumen decreases and subsequently increases along with a decrease in the volume of endothelial cells. An increase in the number of mitochondria in a unit of area of muscle fiber at early stages with subsequent decrease was noted. All the values of observed changes are statistically significant. None of the examined features of the structure can be considered pathognomonic separately, but the totality of the quantitative alterations gives a whole picture of the progressive disease.

The ultrastructure of blood capillaries and muscle fibers was examined in the I, II, III, and IV stages of obliterating endarteritis (OE) of the lower extremities. A number of morphological parameters were analysed quantitatively. The pathogenetic importance of changes in the fine structure of capillaries and muscle fibers for each stage of the disease was demonstrated. Each stage of OE is characterized by definite morphological features of the structure of blood capillaries and muscle fibers which permit to use these data clinically for biopsy diagnosis of different OE stages.