Category Archives: Fără categorie

Theoretical and Practical Aspects Regarding Radiated Emission Testing in Semi-Anechoic Chambers

29 January 2018Fără categoriecburada

Abstract

This paper presents some theoretical and practical aspects on measurements of radiated emission from a Portable computer. The used Standards are presented and discussed. The measurements were carried out in a Semi-Anechoic Chamber (SAC) in accordance with EN 55022 (CISPR 22) Standard. The test arrangement was in accordance with IEC 61000-4-3 Standard and the following equipment was included: reception antenna, signal generator and emission antenna. The measurements were made at a distance of 3 meters, according to the generic Standard IEC 61000-6-3. The radiated electromagnetic interference (EMI) was assessed in the frequency domain, for the frequency range of 30 MHz – 1 GHz, in compliance with CISPR 22 Standard. The test was performed to verify if the tested item (EUT) – in our case a Portable computer – is operating according to the radiated emission limits imposed by the product Standard of the class in which the equipment is framed: IEC 61000-6-1. Analyzing the values obtained for Quasi-peak during the test period, we noted that none of them exceeded the maximum allowed. The results were in satisfactory agreement with the limits imposed by CISPR 22 Standard, and have demonstrated that the equipment – in our case a Portable computer – works in optimal parameters, passing the radiated emission test.

The Influence of the Output Current Deforming Regime on the Input Current Harmonics for a Three-Phase Rectifier Bridge

29 January 2018Fără categoriecburada

Abstract

The present paper was created based on the desire of the author to realize a systemic approach of static converters in general and especially of rectifiers. Looked as system from energetic point of view, a rectifier could be represented “as a black box” without internal energetic sources. It is connected to external environment with an electric DC load and a power supply (mono-phase or three-phase). On the other side the electric current represents an ordered movement of electric charge carriers. In order to supply a certain current to the DC load, the electrons must be “transferred” by the static converter from power supply. Thus, a certain wave form of the current at the output can be obtained only based on some wave forms of the currents from the supply phases. The present paper answers to two questions: (1): does the modification of the spectrum of the load current produces the modification of the spectrum of the currents from the supply phases; (2):if yes, how it modifies the spectrum of the current from the supply phase, only in the magnitude of the basic harmonics, or it appears new harmonics? The paper proves the fact that the spectrum of the currents from the supply phases of the three-phased bridge rectifier depends on the harmonic spectrum of the output current. This dependence is materialized only on the change of the components of basic harmonic spectrum, without some visible new harmonics.

Control of Flow and Pressure in the Cooling Water Circuit of a Thermal Power Plant Using Fuzzy Logic

29 January 2018Fără categoriecburada

Abstract

Optimum operation of cooling water systems means minimum use of water while maintaining proper temperatures to limit algae growth and cool all equipment properly. Combined, the application of inverters and cooling water pumps brings us not only good energy-saving benefits but some new problems, such as inverter configuration and overload etc. The objective of this paper is to find a suitable solution by designing the intelligent controller for frequency control of cooling water systems, such as fuzzy logic and to investigate the controllability of this model under various changes of static head system. Based on the mathmatical model of puming systems with or without static head, the paper discusses some issues in detail, such as pressure and flow rate regulation. In fuzzy logic control, Mamdani model is used to control the system. The suggested system uses the concept of fuzzy logic system where the fuzzy rule base consists of a collection of fuzzy IF–THEN rules. The fuzzy inference engine uses these fuzzy IF–THEN rules to determine a mapping from fuzzy sets in the input universe of discourse to fuzzy sets in the output universe of discourse based on fuzzy logic principles. The fuzzy model can be successfully used for the variable speed control of hydraulic systems, when the Affinity Lows not observe exactly.

Analysis of Direct Current Motors in Dynamic Regimes Using Numerical Techniques

29 January 2018Fără categoriecburada

Abstract

The electromechanical converters and the electric drive systems where they are parts are generally nonlinear systems due to the nonlinear properties of the materials they are built from, as well as the multiple dependencies between their electrical, magnetical and mechanical parameters. However, under certain conditions (e.g. operation on the linear part of the characteristics), some simplifying hypo-theses are accepted, which allow the treatment of systems as linear systems. This simplifies their analysis and solutions could be obtained with acceptable errors. So the electrome-chanical converters and the electric drive systems can be analyzed as linear or nonlinear systems, depending on their properties and on the equations that govern them. Thus, analytical or numerical solving techniques can be used in order to obtain the solution, i.e. the variation in time of some electric, magnetic or mechanic quantities. In this paper a separately excited direct current motor that drives a me-chanical load is analyzed. The transient processes due to startup or sudden change of torque are analyzed both ana-lytically and numerically. Two techniques – namely numeri-cal solving using a Runge-Kutta method and respectively using an equivalent electrical scheme corresponding to the entire driving system – were used. By comparing the ob-tained numerical and analytical results a very good correla-tion between the different solving methods was proved. Thus, this paper offers alternative and viable analysis tech-niques, suitable for the dynamic regimes of the driving sys-tems with direct current motors.

Synthesis of the PID Algorithm for Control the Thermal Regime in the 3D Printer

29 January 2018Fără categoriecburada

Abstract

In this paper it is described the automatic system for formation the small pieces from polymer, based on the principle of thermoplastic extrusion and it is proposed the graph – analytical algorithm for identification the mathematical model of the control object first and second order inertia of the industrial process by the experimental curve of the transient process as response at the step signal applied to the entrance of the system.The procedure of calculation the approximation of the control object is based on the experimental curve of the process for which the output level is determined at the value of 0.632k and the respectively time. As control object is used the thermal stabilization regime in the extruder of 3D printer. The obtained results of identification are compared with results obtained in case of identification in MATLAB. For the obtained identified models was synthesized the PID control algorithm by the analytical methods and auto-tuning regime.

Shielding Effectiveness Measurement Using a DTEM Cell

29 January 2018Fără categoriecburada

Abstract

This paper presents a shielding effectiveness evaluation for some metallic threads materials. The tests were performed using a non-standardized method in a dual transversal electromagnetic cell (DTEM). The materials’ shielding characteristics must be properly evaluated in order to choose an appropriate shielding material. The tests were conducted for two different types of material designed for electromagnetic shielding. Material 1 has a low density structure, and Material 2 has a dense structure. The tests were performed with a non-standardized method which uses a simple and economical setup, in two different cases. For the first analyzed case only two components were used: a DTEM cell and an EMI Test Receiver. In comparison with the standardized methods, the non-standardized method one used, does not require large testing space and complicated setup, and the material probe needed for DTEM measurements is considerably smaller than the one necessary for the standardized tests. The second studied case comprised a DTEM cell, an EMI Test Receiver, and a hybrid junction. For the second case, the power level was measured with the hybrid junction connected at the inputs A and B, measuring the sum on the C port, and with the hybrid junction connected in the same way, but measuring the difference from the D port. Analyzing the obtained results with the non-standardized method, in all studied cases for the two materials, one can conclude that the shielding effectiveness is better for the high density material.

Analyzing Signals from a Primary Winding of a Locomotive Transformer with Three Types of Wavelet-Based Transforms

29 January 2018Fără categoriecburada

Abstract

The paper is concerned with the analysis of in-stantaneous values and evaluation of certain power quality indices corresponding to phase currents and voltages ac-quired from the primary winding of a locomotive trans-former. Representative data sets acquired during all operat-ing regimes (acceleration, constant speed, normal and re-spectively regenerative braking) were analyzed. Firstly the background noise was estimated by using a wavelet thrash-ing tree considering a wavelet mother with a short filter. Specific computational aspects related to the use of the Sta-tionary Wavelet Transform were presented and it was used to evaluate the instantaneous values of the fundamental harmonic, respectively the distorting residue. Discrete Wavelet Transform was used for 3 situations to deal with time-frequency localization of deviations from stationarity. A nodal analysis was also made with an original implemen-tation of the Wavelet Packet Transform in a special situa-tion, when the deviation from stationarity nearby the right edge prevents the use of DWT. Excepting the thrashing tree, the wavelet mother used in all transformations relied on a filter of length 40 due to the good properties of selectivity relative to the harmonics’ energies. All methods were used to evaluate the 3 major root mean square values (for fun-damental frequency, for distorting residue and total). The results yielded by different methods were compared. A good convergence of methods was noticed. Explanations for the small differences are suggested.

Concerning the Automatic Computation of the Electrical Stresses in the High Voltage Substations during the Transient Regimes

29 January 2018Fără categoriecburada

Abstract

This paper deals with an automatic computation program using a Matlab graphical user interface GUI useful to compute electrical stresses which appear in the high voltage substations; that means the parameters computation of the short circuit currents or transient recovery voltages which appear during the fault regimes in the high voltage networks. The numerical evaluation of the electrical stresses is carried out for the high voltage substations from ST Craiova such as transmission lines Filiasi, Slatina, Turnu Magurele, Isalnita. The parameters of the shortcircuit currents or over voltages are computed and graphical display of their variation in time can be available also. The influence of the high voltage network characteristics, such as the line length or the phase angle of the source voltage on the computed parameters level is pointed out. The Matlab GUI is developed based on the automatic computation program, which was achieved within the research contract with the Transelectrica SA Transport Branch Craiova. The partial results obtained within the above mentioned contract were previously presented in the various papers. Also, the computation algorithm is based on the results presented in the references of this paper. This GUI can be applied for any other high voltage substation whose rated parameters are known.

Modelling and Synthesis of Printed Circuit Boards Testing Systems based on Timed Hard Petri Nets

29 January 2018Fără categoriecburada

Abstract

This paper presents a synthesis method for delay time evaluation in the printed circuit boards based on Timed Hard Petri Nets. For the specification and modeling of the delay time evaluation system, Timed Synchronous Petri Nets (TSPN) are used, which allow conflicts identification and exclusion related to both the processes time synchronization and processes timing constraints. The developed TSPN model of the delay time evaluation system comprises the test signal generator and the time delay analyzer. The transition to the hardware description of the system is achieved by translating the TSPN into Timed Hard Petri Net (THPN). THPN consists of processing elements and logical connections between them. For each processing element analytical model and AHDL code were developed. The implementation of the delay time evaluation system was done by direct mapping of the THPN into the Field-Programmable Gate Array (FPGA) circuits. FPGA architectures present advantages such as high parallelism, control processing speed-up and reconfigurability option. The direct mapping method has a linear algorithmic complexity and is not affected by state explosion problem. The transparent correspondence between the elements of the initial specification and the components of the resultant circuit ensures that the timing constraints under which the evaluation system is designed are respected.

Analysis of Crimped Connections Heat Transfer Coefficient Using Experimental and Numerical Determinations

29 January 2018Fără categoriecburada

Abstract

In this paper is presented an analysis of the influ-ence of heat transfer coefficient on temperature values using numerical and experimental results. The research was car-ried out on a crimped connection used at electrical genera-tors manufacture. It was started by heating the crimped connection in AC regime at different electrical current in-tensities for obtaining the values of stabilised temperature. Then, the coefficient was calculated using two different me-thods. The first method, the analytical – experimental ap-proach, consists in calculation of heat transfer coefficient values using a relation obtained starting from thermal re-gime equilibrium. The second method, calculation – experi-mental approach, involves using a minimize function which can be implemented in MathCad. After that, coefficient values were introduced in numerical simulation in order to determine temperature values. The numerical model was developed in QuickField software starting from a coupled problem AC Magnetics – Steady State Heat transfer. At the beginning the AC magnetic problem was solved with the objective of obtainig the heat source which was introduced in Steady State Heat Transfer problem. Finally, by using numerical and experimental results, errors were calculated with the aim of determining the efficience of these two me-thods. It was then concluded that, for domains which in-clude electrical currents up to 1000 A, errors are relative small. But for high values of electrical currents another me-thod for heat transfer coefficient should be developed.