Category Archives: Fără categorie

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.

Contributions to the Development of Complementary Equipment for the Romanian Anti-Hail System

29 January 2018Fără categoriecburada

Abstract

The method used in Romania for combating hail is the sowing of the clouds method, with missiles launched from the ground. This paper presents contributions of the University of Craiova, Center for Innovation and Technol-ogy Transfer in the development Hail Suppression System. The primary contribution was the complementary equip-ment that was necessary for developing the anti-hail system in Romania. Two of the systems that contain the anti-hail complementary equipment are showcased: the photovoltaic panels power supply system and the automatic positioning system for missiles launch ramp, respectively. The configu-ration of the accomplished photovoltaic system provides the power for the 12V, 24V, and 48V DC consumers and the 220V AC consumers as well. Likewise, this system can also function independently, interconnected with other energy sources (such as wind turbines, diesel generators, etc.), or synchronized with the national power grid. An energy man-agement system was created, to secure the energy required to launch the anti-hail missiles (high priority consumers). The energy management system controls and monitors the energy flow from the photovoltaic panels to the consumers, using a hierarchy of consumers algorithm. The automatic positioning system for anti-hail missiles launch ramps con-tains intelligent motor drives and a touchscreen human in-terface. Credited to the research work and the accomplished complementary equipment, the University of Craiova – In-novation and Technology Transfer Centre became part of “General designer of the anti-hail Romanian system”.

Design Optimization of an Asynchronous Motor Used in Light Railway Traction

29 January 2018Fără categoriecburada

Abstract

The appropriateness of this work is provided by highlighting some aspects insufficiently treated in the areas of designing and dimensioning of asynchronous traction motors associated with light traction static converters. The traction system is aimed for the light railway vehicles. Through the usage of asynchronous motors supplied by independent converters, the performances concerning the traction and the electric braking system are improved, while the maintenance expenses are reduced. The newly designed motor is aimed for the traction system of a locomotive driv-ing a multiple unit train, while the parameters necessary for the analysis of the regenerative braking system are also ac-counted for. An algorithm for the optimal design of the asynchronous motor is developed, considering the main parameters as the electric and magnetic quantities, the manufacturing and operating costs. The motor dimensions are computed starting from the values of the electromagnet-ic quantities resulted in the optimization process. The opti-mization algorithm is realized in Mathcad, any parameter modification leading to a new motor model. The main objec-tive of the paper is to optimally design the asynchronous traction motor directly rotating the drive wheel of the elec-tric train. The motor design takes into account the statio-nary rated regime, with the speed adjustment within wide limits, frequent starts and stops.

Aspects Regarding Operation of Power Supply System of Cars

29 January 2018Fără categoriecburada

Abstract

In this paper there are presented a few aspects regarding the operation of the direct current power supply system of cars. The operation of the electronic voltage con-troller is specially approached. Theoretical aspects of the problem are presented. In the second part of the paper there are presented a series of experimental determinations car-ried out on a modern stand. The results have been con-firmed by measurements with a car. In order to analyze the rectifier defects there have been viewed the output voltage waveforms for five situations of defect of the diodes. In or-der to analyze the voltage control, there have been obtained the waveforms of the excitation current for three particular situations. In the last part of the paper there are presented the conclusions obtained following the researches. It is em-phasized that: damaging one or more diodes of the rectifier can be identified by viewing, by means of an oscilloscope, the waveform of the output voltage of the alternator; when one of all the diodes is functional, the waveform is symmet-rical, waved and with small variations; for the same number of damaged diodes, the distortion degree of the voltage also depends on their position in the rectifying bridge (e. g. the distortion is higher when two positive diodes are damaged than in case when a positive diode and a negative one are damaged); an existing fault situation can be identified by viewing the output voltage of the alternator.

Dynamic State of Low Power Asynchronous Motors in Direct-on-Line Starting

29 January 2018Fără categoriecburada

Abstract

The research opportunity is explained by the results obtained in modelling and simulation of asynchronous motors, in the purpose of increasing their technical and economic performances when they operate in dynamic states. The study of the dynamic state is compulsory for low and very low power asynchronous motors which are used for driving industrial robots. In order to have simulation results, which are to be close to reality (those established experimentally), it is necessary to know the main inductance and the leakage inductance of the windings, their dependence upon the machine load, so upon the magnetic saturation. In this paper there are presented results, simulations and experimental tests are carried out in order to establish the errors which occur, for correcting the mathematical model used. With the help of the mathematical model presented in this paper, much complex dynamic states can also be studied, caused by the variation of the voltage, of the resistant torque, of the inertia moment etc. The starting characteristics have been computed considering magnetic saturation and current pressing, the results being: starting current Ip=4.208*IN, starting time tp=0.17s. It is considered that this study of asynchronous motor starting is justified, with an eye to obtaining some indications for their optimum construction and operation.

Estimation of Certain Power in Single-phase Network and DC Circuits

29 January 2018Fără categoriecburada

Abstract

Requirement of electrical energy is in order to operate various domestic and industrial devices like ap-pliances, equipment and machinery. Electrical energy per time unit represents electrical power transferred. Well knowing the electrical power is very important because of economical aspects. Electrical power, an important element of an energy system, which considers elements like harmon-ics and phase between voltage and current, influence the cost and elements component of electrical power grid. This paper presents the evaluation of mark-space method of elec-trical power system. This method represents a mathematical approach, simulation, and analog implementation solving the power measurement suitable for single-phase network and DC circuits. The schematics developed consist of well-known electronic circuits like the pulse width modulation (PWM), filtering with operational amplifier, and absolute value of signal. This approach avoids multiplying operations that aid error generating. The main purposes are to track the performance of such a circuit in different operating sit-uations and present the schematic. Thus, influence of phase between voltage and current, influence of waveform shape regarding result using analyzed method, and characteristic linearity are example of tests perform. The results con-firmed the theoretical principle being analyzed using specif-ic simulation programs like LTSpice or Scilab, but not re-stricted to them.