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Using adjustable speed drives employing fast switching components to supply low voltage asynchronous motors may be detrimental to their reliability in some cases. The premature failures of the insulating materials are often attributed to the existence of partial discharges (PD) in the windings. Nevertheless, a clear evidence of any PD existence in such systems is far from being established. Also, their location may not be in the turn-to-ground or phase-to-phase insulation but in the turn-to-turn insulation due to the voltage waveforms, and as such, the classical ac test is no longer applicable. The aim of this paper is to present an off-line test procedure capable of overcoming this problem. The results of the test carried out on the representative population of different motors are presented. Index Terms--Partial discharge (PD), adjustable speed drive (ASD), insulating materials, asynchronous machines, PD detectors, premature Failure.

The problem of premature failure of rotating machines fed by inverters appears to be of crucial importance. Understanding of the phenomena caused by this new type of supply on the stator insulation of motors provides enhanced reliability of the inverter/motor set. After identifying the stresses created by this type of device, a study of aging of the materials used as models, and subjected to similar stresses, is undertaken. For the voltage, rise time and frequency under study, the intrinsic part of the aging is studied. The results are presented and discussed according to the nature of the interaction existing between the electrical stress and the material properties.

When standard low voltage induction motors are supplied by pulse-width modulated (PWM) adjustable speed drives, some of the traditional sinusoidal system concepts cannot be applied. This paper reports the results of an investigation of the effect of PWM drives on the insulation of the stator winding. The characteristics of the employed dielectric material and the magnitude of the applied voltages led to the hypothesis of the possible existence of partial discharges within the insulation. Practical experiments were carried out and high frequency signals which could be associated with such a phenomenon were observed. These measurements also showed that the interturn insulation undergoes some high electrical stresses and that the nominal rotation speed (50 Hz) appears to be a point of high disturbance in the working of the motor Further work is required, since most of the points identified here need to be understood fully.

The molecular mobility of cooperative segmental (α-process) and local (β-process) motions in semicrystalline fluorinated parylene (PA-F) films has been studied using broadband dielectric spectroscopy in a wide temperature range. Particularly, the α-relaxation is, for the first time in a semicrystalline polymer, probed well above the glass transition temperature (∼10Tg) based on the PA-F strong difference between Tg and the crystallization temperature (Tc ∼ 16Tg). The influence of the amorphous phase confinement on the chain dynamics, induced by increasing crystallinity, is also explored. Thus, in the range of Tg, the α-relaxation is described by two crossover Vogel-Fulcher-Tamman characteristics, and the high temperature one presents an exacerbated low fragility. The space confinement of the amorphous regions, as characterized by x-ray diffraction, shows an important mobility restriction of both the α- and β-relaxations. The β-process, which has been related to CF2 group local motions, does not present a modification of its activation energy (Ea ∼ 30.8 kJ mol-1) with confinement, showing that it happens in the pure amorphous regions. The dielectric strength analysis of each process, through the Onsager-Kirkwood-Fröhlich (OKF) theory, has demonstrated that a rigid amorphous phase is strongly involved in the very high temperature range well above Tg. In the range around Tg, a peculiar behavior of the low temperature α-relaxation dielectric strength is reported, in agreement with the OKF temperature decreasing dependency that has been related to cooperative rearranging regions in the pure amorphous phase. The disappearance of the α-relaxation with the amorphous phase confinement leads to a transformation from 2D to 3D crystallite arrangements of the PA-F chains in correlation with the formation of spherulitic structures. [ABSTRACT FROM AUTHOR]

Deals with a study which investigated the space-charge injection (SCI) and electroluminescence (EL) threshold fields in polyethylene, in order to determine the threshold field for aging. Information on SCI and EL; Methodology of the study; Results and discussion.

The problem of premature failure of low voltage rotating machines fed by inverters could have serious economic impact if it is not addressed. Indeed, even though much already has been written on the different topics related to the use of such power supplies, there is a great need for a better understanding of the physical mechanisms involved, particularly with regards to aging mechanisms of insulating materials. The aim of this paper is to highlight the effect of adjustable speed drives (ASD) on the stator winding insulating materials. Pulse-like electrical stresses have been applied to three types of samples (thin film, twisted pair, and layer to layer). Physical characterization and/or lifetime measurements have been performed. The results are presented and discussed according to the nature of the interaction existing between the electrical stress main characteristics (magnitude, frequency, dV/dt) and the material properties. According to these results, the development of a standardized insulation quality control test, based on a physical understanding of involved stresses and material behavior, appears now to be necessary.

We present in this paper a study on the thermal behavior of an integrated circular inductor. We determinate a mathematical expression giving the evolution of temperatures in an integrated inductor using the separation of variables method and a visualization of the thermal behavior is determined in 3D space dimension using the finite element method. [ABSTRACT FROM AUTHOR]

This paper presents the dimensioning and modeling of a circular inductor integrated in a Boost micro converter. At first, we define the characteristics of the Boost micro converter, which is the starting point for the design our component, taking into account the electrical and magnetic characteristics of the materials selected. The second, a Boost micro converter schematic simulation coupled with ideal and integrated inductor was presented. This conceptual model of the Boost is best understood in terms of the relation between voltage and current of the inductor. Finely, we have simulated the electromagnetic effects in integrated inductor in the air, and with substrate using the finite element method. [ABSTRACT FROM AUTHOR]