Category Archives: Fără categorie

Load Flow Analysis of Unbalanced Distribution Networks using Symmetrical Components Based Software

14 December 2016Fără categoriecburada

Abstract

This paper presents the algorithm and the main features of a Matlab (R2014a)-based software conceived by the authors for analysis of the asymmetrical operation of the three-phase distribution networks. The software’s algorithm is based on an iterative procedure of Newton-Raphson type. This algorithm is independently applied on three equivalent sequence networks and includes an equivalent model for the unbalanced loads supplied from the analysed distribution grid. In order to outline the capabilities of this software tool named PFASYM and illustrate the key concepts a comprehensive case study was considered. This one summarizes the results of a three-phase load flow analysis performed for a real representative 110/20 kV distribution network supplying industrial unbalanced loads. The PFASYM’s results are validated by comparison with those generated by a proprietary software package. The analysis methodology used in this illustrative case study and the results generated for different grid configurations could assist the grid operator in conducting the power flow studies of operational areas of interest. This work is part of an overall energy systems modelling and analysis project developed by the authors, in collaboration with the local power distribution operator. This one has as objective to facilitate the understanding of the power flow concepts for the present distribution networks operating in asymmetry conditions and to assist the grid operator in applying optimal mitigation measures.

Aspects of Behavior Regarding Certain Electronic Equipment Subject to Electrostatic Discharge

14 December 2016Fără categoriecburada

Abstract

Electrical discharge due to human operators may cause disturbances with very fast variation reaching the sensitive equipment by conduction and radiation and can affect and even destroy them. Therefore, between a human, possible to load electrostatic voltages of 10-15kV ordinal, and an electronic device (computer, laptop, memory stick, etc.), system connected to the grounding, an electrostatic discharge can occur as a result of electric charging (electrification) the person wearing clothes made of synthetic fibers, due to friction with the air. This paper proposes a study of the transient arrangement produced by human electrostatic discharge and the disruptive or destructive effects that may occur. Experimental tests have been performed to determine the degree of immunity to electrostatic discharge (ESD) into the air and through direct contact, in accordance with the regulations in force, in the specialized laboratory of ICMET Craiova, subjecting a memory stick and a wireless Internet connection stick to electrostatic discharge. The results obtained revealed the individualized behavior for each device tested.

On the Immunity of Data Acquisition Systems Used in Power Systems

14 December 2016Fără categoriecburada

Abstract

The paper deals with some tests regarding the immunity for radiated emissions and compliance with international standards for electromagnetic compatibility (EMC) measurements for an industrial data acquisition system (DAS) used in power systems. The behavior of the DAS, when functioning near electromagnetic disturbance sources, is studied. The goal is to test its robustness in similar conditions as those encountered in its normal environment. It is known that multiple factors may affect the accuracy of data acquired by DAS. The Equipment Under Test (EUT), witch in this case is represented by DAS is tested for immunity in a specialized enclosure (GTEM Cell). The immunity based on the analysis of the influences of an electric field with constant magnitude and variable frequency in the range of 80 MHz…1 GHz is studied. After analyzing the initial tests results, partial and, afterwards, full shielding of the EUT’s case is performed in order to remove the EM influence. The tests’ results drive to the conclusion that it is necessary to design and build an enclosure from conductive material for the DAS. After the implementation of the measures, the EUT passed the tests concerning the immunity. The GTEM Cell construction, GTEM model, generation and distribution of electric and magnetic field inside the GTEM Cell, equipment under test (EUT), radiated emission measurement scheme, EMC standards for GTEM Cell, are exposed.

Comparisons Among p – Channel, n-Channel and Mixed n/p Channel OTFTs

14 December 2016Fără categoriecburada

Abstract

Some theoretical approaches of an alternative organic semiconductor device are presented in this work. The Organic transistors are based either on n-type or p-type or mixed p/n overlapped layers. The carrier modulation insides different films is carried out by two gates electrodes, as is usual in the thin film transistor field. This paper introduces some novel aspects for these kinds of organic transistors, selecting a suitable biasing regime. The simulations emphasize a stronger influence on the static characteristics when the superior gate is acted. One of the novelties of this paper concerns the electrical conduction occurrence by two simultaneous channels, in comparison with one volume channel conduction, for different gate voltage regimes. A similar work regime is also encountered in the SOI devices with ultra-thin films that develop a volume channel. The volume channel regime is advantageously when the technology of fabrication of the organic semiconductors on different insulators provides an extremely charged interface, which can degrade the surface currents. Comparisons and applications for both situations – with one volume channel or two accumulation channels – are finally discussed. The vertical n/p junction arose between the upper n-channel and the bottom p-channel, offers novel physical properties and prevented any interaction among channels. The device simulations revealed multiple behaviors, depending on the Top and Bottom Gate voltages, if a positive drain-source voltage is applied.

The Analysis of Magnetic Field Measurements in a Public Access Area

14 December 2016Fără categoriecburada

Abstract

This paper describes a case study referring to the magnetic field measurements performed in a public access area. Compared to the standard limits regarding the human exposure to electromagnetic fields, the measurement results were significantly higher. Based on these results and the scarce data regarding the magnetic field sources in the area, there are discussed several cases of power lines configurations and their corresponding magnetic field levels.

Enhancing the dynamic frequency of microgrids by means of PV power plants with integrated energy storage

14 December 2016Fără categoriecburada

Abstract

Achieving a high-level of stability represents one major concern in autonomous microgrids (MGs) with high penetration levels of renewable energy sources. The aim of this paper is to study how photovoltaic (PV) power plants can provide dynamic frequency support in MGs, in order to obtain an improved stability for the entire power system. On the PV side an energy storage subsystem is added, with the main purpose of better control and higher power reserve of the PV power plant. By this way the necessary input power is provided by the PV system along with the battery block. The required output power is supplied by a three-phase voltage source converter (VSC). The VSC control is implemented in a rotating dq reference frame, including a harmonic compensation loop for the output current. To improve the dynamic frequency stability of the MG, specific functions are implemented within the PV inverter control. To highlight the performance of the proposed system, a comparative analysis is provided, which cover four cases of interest depending on the status of the storage system and dynamic support (i.e. with/without storage and with/without dynamic support). Simulation results are included to validate the power control system, showing that the dynamic frequency control can be improved by the proposed solution.

Dynamic Regime Electromagnetic Torque in Brushless Direct Current Motors

14 December 2016Fără categoriecburada

Abstract

This study aimed at establishing the mathematical model for determining the dynamic regime torque and at emphasizing constructive aspects which influence its magnitude and variation. Brushless direct current motors are very present and there have been carried out researches regarding their design and optimum construction. The technology evolution in several areas has caused an increase in production of permanent-magnet BLDC motors, which has good technical-economic performances for a large range of controlled-speed applications. The study carried out, by the simulations we presented, shows that these motors have high torque oscillations in a complete rotation. There are identified the slots which create high torques, respectively low torques, in a complete rotation, thus justifying the oscillations. In this paper there is emphasized that the optimum variant of maximum torque involves a supply by six pulses per period in direct direction, also indicating the value of the control angle. The most unfavourable variant occurs at brushless direct current motor supplied by three pulses per period and reverse succession of phases, where the average value of the torque decreases by 56.7% over the optimum machine. A complete elimination of oscillations in this type of motor is not possible, but an optimal design can reduce them considerably

Small Scale Model of Automatic Barrier Powered by Photovoltaic Panel

14 December 2016Fără categoriecburada

Abstract

Access control systems offer numerous benefits and are able to constitute extremely good solutions for securing an area of high or very high importance. An access control system allows restriction, monitoring and directing human trafficking as cars to a location or from a location. In generally at access control systems call the managers of circulated spaces or areas where must enter only authorized persons. To access the vehicles in different areas are frequently used automatic barriers. This paper presents such an access system, achieved a small scale named ˝automatic barrier model˝, that uses photovoltaic panels (PV) as main energy source. Automatic operation of barrier is provided by a development system achieved around a microcontroller. In the first part of paper is presents the structure and minimum requirements of development system. Also are highlighted aspects of dimensioning and design for both parts hardware and software respectively. To achieve electrical diagrams and PCBs was used a dedicated software. Finally was tested the achieved automatic barrier model. The tests consist of verifying the correct operation of the automated system. Were made test regarding to automation and to power supply from PV panel. Experimental results show a smooth functioning of experimental automatic barrier powered by PV panel and can be successfully expanded at real scale.

Design and Simulation of Wireless Power Transfer Systems

14 December 2016Fără categoriecburada

Abstract

This paper presents a set of diagrams for wireless power transfer systems (WPTS) with a lot of applications in key domains such as: medical, electrical engineering, military etc. Our research is based on circuits working as WPTS. All the circuits are using sets of two magnetically coupled coils whose parameters were extracted by simulations using the specialized software ANSOFT Q3D EXTRACTOR. The simulations of the circuits were performed using TINA, SPICE and SIMULINK in MATLAB. We used existing parts from Texas Instruments libraries. WPTS are more appropriate for small distances transmission, distances up to twice the coils dimensions, because the magnetic field strength produced by the transmitter becomes very weak when the distance increases. In contrast to other WPTS methods, the efficiency of the system can reach up to 95% for short distance. The circuits were also physically built and tested and the results were very close to the numerical ones. We also compared the results with data in existing literature and we obtained a bound of the error of less than 5%. We also studied the efficiency of the power transfer and presented some practical applications for these systems such as low power battery chargers. The results done by simulations were almost identical with the experimental ones and those in existing literature, the error being less than 5%.

Modeling and Simulation of the Coal Flow Control System for the Longwall Scraper Conveyor

14 December 2016Fără categoriecburada

Abstract

In this paper, the modeling and simulation of a coal flow control system for the longwall scraper conveyor is presented. The coal flow on the scraper conveyor, it is controlled by the following variables: the coal flow, advance speed and cutting speed of the longwall shearer. The electrical drive system of the longwall scraper conveyor together with the electrical drive system of the advancement and the cutting mechanism of the longwall shearer are done by means of induction motors. The control of speeds and electromagnetic torque of induction motors is realized by using sensorless vector control systems. Within these control systems, the estimation of position and of components of the rotor flux space-phasor, as well as the rotor speed of the induction motor, is done by an extended Gopinath observer. The advantages of a coal flow control system are control of productivity and also that electric motors of the flow of transport can be optimally chosen, leading ultimately to a much lower consumption of electricity for coal extraction. Modeling and simulation of control systems is done taking into account the mathematical equations that make the connection between constructive and functional parameters of the longwall shearers with the features of the strata of mining coal, specifically the coal deposits from the Jiu Valley, Romania.