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- Fachbereich Energietechnik (1104) (remove)
Heat production in the windings of the stators of electric machines under stationary condition
(2014)
In electric machines due to high currents and resistive losses (joule heating) heat is produced. To avoid damages by overheating the design of effective cooling systems is required. Therefore the knowledge of heat sources and heat transfer processes is necessary. The purpose of this paper is to illustrate a good and effective calculation method for the temperature analysis based on homogenization techniques. These methods have been applied for the stator windings in a slot of an electric machine consisting of copper wires and resin. The key quantity here is an effective thermal conductivity, which characterizes the heterogeneous wire resin-arrangement inside the stator slot. To illustrate the applicability of the method, the analysis of a simplified, homogenized model is compared with the detailed analysis of temperature behavior inside a slot of an electric machine according to the heat generation. We considered here only the stationary situation. The achieved numerical results are accurate and show that the applied homogenization technique works in practice. Finally the results of simulations for the two cases, the original model of the slot and the homogenized model chosen for the slot (unit cell), are compared to experimental results.
Solar thermal concentrated power is an emerging technology that provides clean electricity for the growing energy market. To the solar thermal concentrated power plant systems belong the parabolic trough, the Fresnel collector, the solar dish, and the central receiver system.
For high-concentration solar collector systems, optical and thermal analysis is essential. There exist a number of measurement techniques and systems for the optical and thermal characterization of the efficiency of solar thermal concentrated systems.
For each system, structure, components, and specific characteristics types are described. The chapter presents additionally an outline for the calculation of system performance and operation and maintenance topics. One main focus is set to the models of components and their construction details as well as different types on the market. In the later part of this article, different criteria for the choice of technology are analyzed in detail.
Bei der Ausarbeitung des nationalen Anwendungsdokumentes zur DIN EN 1998-1 waren die in der ENV-Fassung enthaltenen vereinfachten Regeln im Lichte aktueller Forschungsergebnisse zu überprüfen und zu überarbeiten. Die gleiche Aufgabe stellte sich auch für die Neufassung der DIN 4149. In beiden Fällen sind neben konstruktiven Regeln für die Art und Anordnung der zur Gebäudeaussteifung heranzuziehenden Wände im Grundriss Tabellen enthalten, die unter bestimmten Bedingungen den Entfall eines rechnerischen Nachweises der Tragwände im Erdbebenfall ermöglichen. Dies ist für Schwachbebengebiete, wie sie in Deutschland und anderen Ländern Mitteleuropas anzutreffen sind, sinnvoll, um unnötigen Rechenaufwand sowie Probleme mit der Führbarkeit von Nachweisen so weit wie möglich auszuschalten. Im vorliegenden Beitrag werden die Hintergründe der vereinfachten Regeln diskutiert und die Ergebnisse der Anwendung mit verschiedenen Rechenverfahren verglichen und bewertet.
The 2nd edition of the lightning risk management
standard (IEC 62305-2) considers structures, which may
endanger environment. In these cases, the loss is not limited to
the structure itself, which is valid for usual structures. In the past
(Edition 1) this danger was simply taken into account by a special
hazard factor, multiplying the existing risk for the structure with
a number. Now, in the edition 2, we add to the risk for the
structure itself a “second risk” due to the losses outside the
structure. The losses outside can be treated independently from
what occurs inside. This is a major advantage to analyze the risk
for sensitive structures, like chemical plants, nuclear plants, or
structures containing explosives, etc. In this paper, the existing
procedure given by the European version EN 62305-2 Ed.2 is
further developed and applied to a few structures.