Investigation on the Effects of Magnetic Saturation in Induction Machines During Transients

Magnetic saturation in electrical machines is of major influence on the operating characteristics during transients. For induction machines, the assumption of linear magnetic behavior of the iron core in classical machine models may be adequate for the calculation of steady-state rated operation. In operating points or during transients following a short-circuit or out-of-phase synchronization, where currents can reach values as high as 25 pu, especially the magnetic paths of the leakage fluxes are highly saturated, leading to a significant raise in currents and machine torque. Therefore an investigation on the effect of magnetic saturation has been performed by comparing inductances calculated by analytical methods for assumed linear magnetic behavior with results of static finite-element-method (FEM) models taking magnetic saturation into account. These results are subsequently converted into simplified current-depending parameter functions that can be used in transient machine models. Therefore, based on an enhanced space phasor approach, a newly modified machine model is presented, where the parameters can be used according to the dependencies worked out in the paper in order to identify deviations with the classical approach using constant inductances. Furthermore the newly acquired set of current-depending machine inductances is validated by simulating a series of transients using dynamic FEM calculation, showing a significant improvement in accuracy compared to sets of constant parameters

Determination of Stator End Winding Inductance of Large Induction Machines: Comparison Between Analytics, Numerics, and Measurements

Knowledge of the end winding inductance of electrical machines is decisive for calculating their operating performance. In this article, two different approaches to analytically calculate the stator end winding inductance of large induction machines are discussed. The first method is based on the exact replication of the 3D conductor geometry using serially connected straight filaments, where the inductances are calculated by solving Neumann’s integral. In the second method, the end winding flux is resolved into components excited by the axial and circumferential end winding magnetomotive force, resulting in a far simpler geometrical model. In both cases, end face effects are taken into account by adopting the method of images. The analytical approaches are compared to the known analytical calculation method proposed by Alger [1]. In addition, the stator end winding inductance is computed by means of 3D finite-element analysis. Using experimental validation, it is shown that both the analytical and numerical results reasonably correlate with removed rotor inductance measurements taken for several induction machines with different rated powers and frame sizes, if the permeability of the laminated core is taken into consideration

Modeling autosomal recessive cutis laxa type 1C in mice reveals distinct functions for Ltbp-4 isoforms

Recent studies have revealed an important role for LTBP-4 in elastogenesis. Its mutational inactivation in humans causes autosomal recessive cutis laxa type 1C (ARCL1C), which is a severe disorder caused by defects of the elastic fiber network. Although the human gene involved in ARCL1C has been discovered based on similar elastic fiber abnormalities exhibited by mice lacking the short Ltbp-4 isoform (Ltbp4S(-/-)), the murine phenotype does not replicate ARCL1C. We therefore inactivated both Ltbp-4 isoforms in the mouse germline to model ARCL1C. Comparative analysis of Ltbp4S(-/-) and Ltbp4-null (Ltbp4(-/-)) mice identified Ltbp-4L as an important factor for elastogenesis and postnatal survival, and showed that it has distinct tissue expression patterns and specific molecular functions. We identified fibulin-4 as a previously unknown interaction partner of both Ltbp-4 isoforms and demonstrated that at least Ltbp-4L expression is essential for incorporation of fibulin-4 into the extracellular matrix (ECM). Overall, our results contribute to the current understanding of elastogenesis and provide an animal model of ARCL1C.Peer reviewe

Modeling autosomal recessive cutis laxa type 1C in mice reveals distinct functions for Ltbp-4 isoforms

Recent studies have revealed an important role for LTBP-4 in elastogenesis. Its mutational inactivation in humans causes autosomal recessive cutis laxa type 1C (ARCL1C), which is a severe disorder caused by defects of the elastic fiber network. Although the human gene involved in ARCL1C has been discovered based on similar elastic fiber abnormalities exhibited by mice lacking the short Ltbp-4 isoform (Ltbp4S(-/-)), the murine phenotype does not replicate ARCL1C. We therefore inactivated both Ltbp-4 isoforms in the mouse germline to model ARCL1C. Comparative analysis of Ltbp4S(-/-) and Ltbp4-null (Ltbp4(-/-)) mice identified Ltbp-4L as an important factor for elastogenesis and postnatal survival, and showed that it has distinct tissue expression patterns and specific molecular functions. We identified fibulin-4 as a previously unknown interaction partner of both Ltbp-4 isoforms and demonstrated that at least Ltbp-4L expression is essential for incorporation of fibulin-4 into the extracellular matrix (ECM). Overall, our results contribute to the current understanding of elastogenesis and provide an animal model of ARCL1C.Peer reviewe

Loop Quantum Cosmology

Quantum gravity is expected to be necessary in order to understand situations where classical general relativity breaks down. In particular in cosmology one has to deal with initial singularities, i.e. the fact that the backward evolution of a classical space-time inevitably comes to an end after a finite amount of proper time. This presents a breakdown of the classical picture and requires an extended theory for a meaningful description. Since small length scales and high curvatures are involved, quantum effects must play a role. Not only the singularity itself but also the surrounding space-time is then modified. One particular realization is loop quantum cosmology, an application of loop quantum gravity to homogeneous systems, which removes classical singularities. Its implications can be studied at different levels. Main effects are introduced into effective classical equations which allow to avoid interpretational problems of quantum theory. They give rise to new kinds of early universe phenomenology with applications to inflation and cyclic models. To resolve classical singularities and to understand the structure of geometry around them, the quantum description is necessary. Classical evolution is then replaced by a difference equation for a wave function which allows to extend space-time beyond classical singularities. One main question is how these homogeneous scenarios are related to full loop quantum gravity, which can be dealt with at the level of distributional symmetric states. Finally, the new structure of space-time arising in loop quantum gravity and its application to cosmology sheds new light on more general issues such as time.Comment: 104 pages, 10 figures; online version, containing 6 movies, available at http://relativity.livingreviews.org/Articles/lrr-2005-11

Die Heimat der altsächsischen Denkmäler in den Essener Handschriften und ihre Bedeutung für die Heimatbestimmung des Heliand

von Alexander ConradiZugl.: Münster (Westf), Univ., Diss., 26. Juli 190

On the applicability of digital human models for personal equipment design

Digital Human Models (DHMs) have developed from academic research into valuable engineering tools. They offer a vast amount of functionality for modeling and simulation of anthropometric dimensions, reach, vision, movement, and comfort. Today's DHMs are primarily used in automotive design. As our previous studies have shown, a simple transfer to other application domains (e.g. workplace design) may be possible but result into inaccuracies. With the following study we analyzed the applicability of two typical DHMs for the design of personal equipment and for identifying potential conflicts between different pieces of equipment. Such an application differs strongly from automotive applications, but many similar uses of DHMs can be observed in daily life. The analysis addresses different aspects: At first, the general functionality of the DHMs was screened. Required functions were either available instantly, available by workarounds, or unavailable. A subsequent verificati on and validation study analyzed potential shortcoming for the available functions. It consists of an empirical survey with different typical soldiers' movements. The data include maximum reach, focusing a target with a binocular or aiming with different postures. A number of motion sequences were selected for the analysis. Results show that simple movements were modeled quite accurately. But complex movements were hardly possible to model and large inaccuracies were observed. An important functional shortcoming resulted from limited possibilities to integrate virtual objects of personal equipment into the DHM. This prevented an analysis of conflicts between personal equipment