Current Issue : July - September Volume : 2017 Issue Number : 3 Articles : 5 Articles
This paper takes a typical 220 kV three-phase three-limb oil-immersed transformer as\nan example, this paper building transient field-circuit coupled model and 3D coupled magneto\n-fluid-thermal model. Considering a nonlinear Bââ?¬â??H curve, the magneto model uses the field-circuit\ncoupled finite element method (FEM) to calculate the magnetic flux distribution of the core and the\ncurrent distribution of the windings when the transformer is at a rated current and under direct\ncurrent (DC) bias. Taking the electric power losses of the core and windings as a heat source,\nthe temperature inside the transformer and the velocity of the transformer oil are analyzed by\nthe finite volume method (FVM) in a fluid-thermal field. In order to improve the accuracy of the\ncalculation results, the influence of temperature on the electrical resistivity of the windings and\nthe physical parameter of the transformer oil are taken into account in the paper. Meanwhile, the\nconvective heat transfer coefficient of the FVM model boundary is determined by its temperature.\nBy iterative computations, the model is updated according to the thermal field calculation result\nuntil the maximum difference in hot spot temperature between the two adjacent steps is less than\n0.01 K. The result calculated by the coupling method agrees well with the empirical equation result\naccording to IEC 60076-7....
This paper presents a new 12-bit digital to analog converter (DAC) circuit based on a low-offset bandgap reference (BGR) circuit\nwith two cascade transistor structure and two self-contained feedback low-offset operational amplifiers to reduce the effects of\noffset operational amplifier voltage effect on the reference voltage, PMOS current-mirror mismatch, and its channel modulation. A\nStart-Up circuit with self-bias current architecture andmultipoint voltagemonitoring is employed to keep the BGR circuit working\nproperly. Finally, a dual-resistor ladderDAC-Core circuit is used to generate an accuracyDACoutput signal to the buffer operational\namplifier.The proposed circuit was fabricated in CSMC 0.5 ...
Owing to the installation of autotransformers at regular intervals along the line, distance\nprotection relays cannot be used with the aim of locating ground faults in 2 Ã?â?? 25 kV railway power\nsupply systems. The reason is that the ratio between impedance and distance to the fault point is not\nlinear in these electrification systems, unlike in 1 Ã?â?? 25 kV power systems. Therefore, the location of\nground faults represents a complicated task in 2 Ã?â?? 25 kV railway power supply systems. Various\nmethods have been used to localize the ground fault position in 2 Ã?â?? 25 kV systems. The method\ndescribed here allows the location of a ground fault to be economically found in an accurate way\nin real time, using the modules of the circulating currents in different autotransformers when the\nground fault occurs. This method first needs to know the subsection and the conductor (catenary or\nfeeder) with the defect, then localizes the ground faultââ?¬â?¢s position....
Energy harvesting has become a promising and alternative solution to conventional\nenergy generation patterns to overcome the problem of supplying autonomous electrical systems.\nMore particularly, thermal energy harvesting technologies have drawn a major interest in both\nresearch and industry. Thermoelectric Generators (TEGs) can be used in two different operating\nconditions, under constant temperature gradient or constant heat flow. The commonly used TEG\nelectrical model, based on a voltage source in series with an electrical resistance, shows its limitations\nespecially under constant heat flow conditions. Here, the analytical electrical modeling, taking into\nconsideration the internal and contact thermal resistances of a TEG under constant temperature\ngradient and constant heat flow conditions, is first given. To give further insight into the electrical\nbehavior of a TEG module in different operating conditions, we propose a new and original way\nof emulating the above analytical expressions with usual electronics components (voltage source,\nresistors, diode), whose values are determined with the TEG�s parameters. Note that such a TEG\nemulation is particularly suited when designing the electronic circuitry commonly associated to\nthe TEG, to realize both Maximum Power Point Tracking and output voltage regulation. First, the\nproposed equivalent electrical circuits are validated through simulation with a SPICE environment in\nstatic operating conditions using only one value of either temperature gradient or heat flow. Then,\nthey are also analyzed in dynamic operating conditions where both temperature gradient and heat\nflow are considered as time-varying functions....
This paper discusses the modeling and analysis of three phase double stator slotted rotor\npermanent magnet generator (DSSR-PMG). The use of double stator topology through the double\nmagnetic circuit helps to maximize the usage of flux linkage in the yoke structure of the single stator\ntopology. The analytical computation is done using Permeance Analysis Method (PAM). Finite\nElement Analysis (FEA) is used for numerical verifications and to verify the design structure a\nprototype laboratory is performed. The analysis is done with various loading conditions to derive\nthe electromagnetic torque, output power and efficiency for the proposed structure. The analytical,\nnumerical and experimental results from the analysis are found to be in good agreement. The\nmaximum power developed by this generator at rated speed of 2000 rpm is of 1 kW with the\noperational efficiency of 75%. A rectifier bridge circuit is used to make the generated voltage a\nstorage capable constant voltage to make it suitable for mobile applications (such as Direct Current\nDC generator). The proposed generator structure is highly recommended for applications such as\nmicro-hydro and small renewable plants....
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