Performance of common-mode chokes

A low-cost method for experimental investigation of common-mode chokes for reducing high-frequency motor ground-currents of inverter-based drive systems of several hundred kW is presented. It provides a powerful tool during the design stage of such chokes to verify their predicted performance. The method draws from the mainly capacitive behavior of machines at very high frequencies. Results of experimental tests for drives with peak ground-current amplitudes of more than 60 Amperes, carried out on a 4 kW test-bed, are presented. They confirm the feasibility of such tests as well as the capability of small, inexpensive, single-turn chokes to effectively reduce the ground-current

Ипотечное страхование как драйвер роста ипотечного кредитования

В статье рассматривается необходимость и факторы развития ипотечного кредитования. Приводится краткий анализ альтернативных методов разрешения жилищного вопроса для россиян. Дается соответствующая оценка ипотечного страхования как фактора развития ипотечного кредитования

Faunal Subsistence Strategies Among Initial Period Coastal Fishers at the Gramalote Site in the Moche Valley of Peru

This faunal analysis focuses on vertebrate remains from the northern coastal site of Gramalote in the lower Moche Valley of Peru. Gramalote dates to the Initial Period (1800-900 BC), a time of great change due to a rise of inland agricultural and increasing sedentism. This intrasite analysis of fauna at Gramalote seeks to contextualize potential subsistence shifts through time. Subsistence specialization regarding fish exploitation of coastal fishers is explored through faunal analysis of vertebrates at this site. For an ecological perspective, this project examines the application of Moseley\u27s Maritime Foundations of Andean Civilization and Optimal Foraging Theory models. The sample analyzed comes from a stratified unit Unit 18A, resulting from the 2005 excavations at the site directed by Jesus Briceño Rosario (Briceño and Billman 2008). The total sample consisted of 22,940animal bones, of which 14,542 are the focus of this analysis. To understand possible chronological shifts in the importance of fish, three questions were examined. How does the vertebrate composition by class compare between the 2005 sample and the data previously reported by Pozorski? For Unit 18A, does the relative importance of fish steadily increase over time? How can we add the variable of depositional context to our evaluation of change over time

Thermal Finite Element Modeling and Simulation of a Squirrel-Cage Induction Machine

Finite element models of electrical machines allow insights in electrothermal stresses which endanger the insulation system of the machine. This paper presents a thermal finite element model of a 3.7 kW squirrel-cage induction machine. The model resolves the conductors and the surrounding insulation materials in the stator slots. A set of transient thermal scenarios is defined and measured in the machine laboratory. These data are used to assess the finite element model

Scaling issues for common-mode chokes to mitigate ground currents in inverter-based drive systems

The additional high-frequency (HF) common-mode (CM) current of inverter-based drive systems can cause parasitic effects such as HF bearing currents. This HF CM current can be significantly reduced by purpose-designed CM chokes that are inserted in the drive at the inverter output. This paper discusses scaling issues related to the design of such CM chokes, of both wound and feed-through toroidal types. The requirements for the design of chokes for these applications can differ from those for CM chokes designed for use in the inverter input, such as those used for the purpose of electromagnetic interference filtering. This difference is notably due to the comparatively large magnitude of the currents involved. The developed correlations allow taking full advantage of the possibilities offered by such chokes to reduce the HF CM current and mitigate the resultant parasitic effects. The discussed relationships are derived analytically, and the results are supported by measurements

On a new type of inverter-induced bearing current in large drives with one journal bearing

We report on a new type of inverter-induced bearing current (BC) that can occur with large inverter-based drive systems with one journal bearing. This current is a variation of the "high-frequency circulating" BC type that has been described by different authors over the last years. As with the first, the BC mirrors the common-mode (CM) current as a result of inductive coupling. However, the voltage across the bearing also mirrors the stator winding CM voltage and is not reduced to zero by the current flow. We show experimental results of measured currents and give physical explanations from which we then derive an effective mitigation technique, which is also illustrated through measurement results

Calculation of motor capacitances for prediction of the voltage across the bearings in machines of inverter-based drive systems

The occurrence of high-frequency discharge bearing currents (also called '' electric discharge machining (EDM) currents '') that can occur in machines of inverter-based drive systems depends strongly on the value of the capacitive voltage divider '' bearing voltage ratio '' (BVR) of the machine. This paper presents a straightforward approach to calculate the involved motor capacitances in order to predict the voltage across the bearing and, thereby, the likeliness of such EDNI currents that are caused by this voltage to occur. The approach is based on the design parameters of the machine and does not involve additional measurements. It combines ease of application and satisfying accurateness, and allows prediction of the risk of endangerment of an inverter-based drive system due to discharge bearing currents

On a New Type of Inverter-Induced Bearing Current in Large Drives with One Journal Bearing

We report on a new type of inverter-induced bearing current that can occur with large inverter-based drive systems with one journal bearing. This current is a variation of the "high-frequency circulating" bearing current type which has been described by different authors over the last years. As with the first, the bearing-current mirrors the common-mode current as a result of inductive coupling. However, the voltage across the bearing also mirrors the stator winding common-mode voltage and is not reduced to zero by the current flow. We show experimental results of measured currents and give physical explanations, from which we then derive an effective mitigation technique, which is also illustrated through measurement results