Monthly Archives: December 2015

Active Power Filter Study Using Dedicated Matlab GUI

17 December 2015Fără categoriecburada

Abstract

This paper presents an understandable and friendly Matlab interface, which shows the active filtering role in a simple manner for the users. The created interface allows the active filtering system simulation, choosing the compensation mode. All these are necessary to plot the available workspace variables and to assess the active filtering performance. Moreover it displays the total harmonic distortion values, for the load and grid current, and computes the filtering efficiency The Simulink model was created for a three-phase non-sinusoidal voltage system, the current components being computed using the Conservative Power Theory elaborated by Paolo Tenti. The analyzed system contains a three-phase full wave controlled rectifier with a passive RL load. After the model simulation, the interface will illustrate the grid current and voltage waveforms, before and after the compensation, for both partial and total compensation. The mentioned graphics, as well as the waveform of the reactive current component, will make the user understand the Active Power Filter (APF) functions, i.e. improving the shape of the current absorbed from the power grid and improving the power factor. The created interface can be used as an educational tool in finding that APF is a solution to fix the disturbing effects that non-linear loads, supplied by the power grids, produce to them.

Evolution of the Electric Power Components Definitions

17 December 2015Fără categoriecburada

Abstract

This paper contains a review of the scientific literature published till date in the field of power theory for systems with periodic non-sinusoidal waveforms. Dynamic increase in the number of installed nonlinear loads, that are the sources of higher harmonics in current and voltage waveforms, results in deterioration of electrical energy parameters. Higher harmonics lead to corrupted current and voltage waveforms, hence a much worsened energy quality. The number of power theories and papers concerning these issues give evidence about the importance of the problems of working condition optimisation in power systems.

Object Oriented Video Retrieval System based on Domain Ontologies

17 December 2015Fără categoriecburada

Abstract

This paper presents a method for video information retrieval considering the frames extracted from the video sources through the segmentation of each key frame, the tracking of the salient objects and the domain ontologies. Based on disambiguation algorithms are constructed domain ontologies for annotation of the video contents. An object oriented database is used to store all specific dataextracted by segmenting, tracking, and annotation of the salient objects. The presented technique combines the visual and semantic descriptors with spatial information for a good indexing of data. The object oriented approach used it was imposed by the complex structure of physical objects you can find in the videos as well as the addition of semantic meanings, which must relate to the objects detected. The annotation based on domain ontologies and the pseudonatural query language close to human understanding are a proper contribution of this article, which has led to fulfilling the final goal, the extraction of semantics-based syntax and retrieving the frames with relevant information within a pseudo-natural query language close to human understanding. The results obtained for the sport domain validate the research carried out and represents a model for applying this method on videos from multiple domain of activity.

Fuzzy Control of Centrifugal Pumps Flow

17 December 2015Fără categoriecburada

Abstract

Electronic variable-speed drives can produce large energy and environmental savings in variable-load variable-speed applications when compared with other conventional technologies. There are a very large number of applications which would benefit, both in terms of process improvement and energy savings, through the use of speed control. Previous studies have shown that the variable-flow fluid motion applications (pumps, fans, and compressors) have the largest savings potential. Combined application of inverters and water pumps brings us not only good energysaving benefits but some new problems, such as inverters configuration and overload etc. In systems with high static head the system curve does not follow the curves of constant efficiency. Using the Affinity Laws to calculate energy saving in system with static head is a mistake because it can also lead to major errors. From this element of uncertainty, the thought that we can try a fuzzy approach. This paper presents a theoretical study of use fuzzy logic to control the operation of a variable speed centrifugal pumps. A mathematical model has been realized and a Matlab simulation scheme was attached to it. Based on the mathmatical model of puming systems with or without static head, the article discusses some issues in detail, such as pressure and flow rate regulation. The fuzzy model can be successfully used for the variable speed control of hydraulic systems, whenthe Affinity Lows not observe exactly.

Estimation of the Heat Cumulated Inside a Wall with Cylindrical Symmetry

17 December 2015Fără categoriecburada

Abstract

The issue of mathematical modeling in order to simulate physical processes or physical systems, permanently preoccupy a significant number of researchers. The sustained efforts being made in this direction are determined by the benefits that simulation can provide and by the development of software packages capable of performing such simulations. It is obvious that mathematical modeling followed by simulation allows the study of possible situations that would be difficult to achieve in real systems and could lead to an irremediable defect. If the mathematical modeling of stationary processes with respect to time is pretty well set, for the transient process simulation is still much to study. The mathematical equations describing such processes are generally of higher order, sometimes they are transcendent, and thus harder to solve. In the paper the authors are concerned with the modeling of transient thermal processes. When analyzing electrical heating systems, the main problem occurs due to heat transfer through the walls. This phenomenon appears at multilayered cylindrical walls, when heat is transferred through it, and a part of it is stored into the wall as internal energy. This paper aims to determine some mathematical relationships which describe the heat storage processes in components with cylindrical geometry. Determined mathematical equations will be used furthermore in the modeling of transient thermal processes in structures with cylindrical geometry. This allows the simulation of multilayer insulation systems under a transient thermal regime for a long time, using Matlab-Simulink toolkit.

Use of Modern Computing Technique to Improve the Energy Indicators of Drive Motors of the Coal Mills

17 December 2015Fără categoriecburada

Abstract

In this paper, the authors present a study on the energetic opportunity to replace derated motors of the five mills which are in service at a power plant with other motors by a rated power closer to the actual load. To this end, it has previously been drawn up a suggestive comparative analysis of diagrams of active and reactive power balance in absolute and percentage values for each case of considered constructive variants. Thus for drawing up, using the complete mathematical model (BEMAS) chosen for the asynchronous machine, of the electric balances for different operating regimes of these asynchronous motors, it was necessary to determine the parameters of the equivalent diagram. Considering the complexity and large volume of computation, the authors developed for this purpose, specific computational algorithms. For all these computational algorithms, computation programs have been drawn, being developed in the programming environment Mathcad Version 7.0, of own conception and which in principle can be used for any other similar motors that have different nominal data. It has also been highlighted that the starting point to establishing the opportunity of replacing of the analyzed asynchronous motors operating derated in steady state, is determining the actual load degree that is achieved through active power measurement for the considered regime.

Virtual Synchronoscope for Connecting Synchronous Generator on the Grid

17 December 2015Fără categoriecburada

Abstract

In this paper is presented in a constructive and functional way an instrument that can be used at connecting synchronous generators at the grid supply that has a constant voltage and frequency. Actually it is about a virtual synchronoscope that verifies the correct instant for the synchronization: phase sequence of the generator must be same with the grid, the generator frequency must be equal to the grid frequency, the generator voltages should be equal to the corresponding grid voltages and the generator voltages should be in phase with the corresponding grid voltages. After the conditions of synchronization between synchronous generator and large power grid are occur, the parallel operation of generator is realized automatically. The virtual synchronoscope is designed from two principal components: hardware (LEMs transducer for measurement six voltages, supply voltage, elements for input/output signals conditioning, USB multifunction I/O module) and software (virtual instrument). The main objective of this paper is to create aneasy to use device for the study of network synchronization synchronous generators. The LabVIEW graphical programming environment is used for designing virtual instrument. The monitored parameters values are displayed using digital indicators. The real-time voltage waveforms for grid and generator are displayed. With three-phase voltage phasors (voltage vectors) we can see the evolution of phase angles and voltages amplitude. This virtual synchronoscope can be used in engineering education from universities or intesting laboratories of electrical machines.

Increasing Safety of the Tests Carried Out in Laboratories by Using Electronic Devices

17 December 2015Fără categoriecburada

Abstract

The ability of the circuit breakers to interrupt the electrical current in circuits with capacitive load it is tested and verified in testing laboratories. During the test, the capacitive type of load impedance simulates an overhead line or an underground cable that works with no load impedance. The transient behaviour which appears at the opening of electric circuits having capacitive load impedance can determine the appearance of some dangerous over-voltages for line, cables and equipments. After testing, at the circuit interruption, it is possible to be residual electrical charge on capacitors. This endangers the lives of people who configures the test scheme. The paper describes a device that monitors the voltage on the capacitors that are connected to busbars and which alerts the staff about the presence of electric charges remaining at the end of the test. A referral unit is mounted near the bars to that are connected capacitors, while warning unit is mounted in the place where can be observed by personnel that configure the test schemes. Two variants of the device are presented. The results, obtained with the device during carrying out tests, both in the laboratory and in operation, are presented into the final section of the paper.

Energetic Influence of Motor Power in Drive Systems with Space-Vector Static Converters and Induction Motors

17 December 2015Fără categoriecburada

Abstract

–The static converters are a vital component of modern drive systems, which in turn are indispensable in industrial equipment designed for small or large complexity, because the achievement of finished goods implies the adjustable mechanical energy available at the output of the system. The aim of this paper is the energetic analysis of two drive systems with the same static converter feeding two different motors which had been performed on an experimental stand for different static operating points. It was considered feeding the both asynchronous motors from the static converter using the space vector modulation command strategy while the mechanical load was assured by a special braking machine and by a DC motor, respectively. It had been taken into consideration feeding the both motors at the same frequencies and with the same RMS voltages. The frequencies considered for the energetic analysis are 20Hz, 30Hz, 40Hz and 50Hz, the mechanical load being adjusted from no load operation up to the nominal value. The power grid energetic parameters were recorded using a Fluke 41b harmonic analyzer, while the current and voltage waveforms at the motor input, were recorded using a Metrix Ox704 digital oscilloscope and later used in Matlab to calculate the AC electric powers.

Study of Indirect Current Control Methods for Urban Traction Active DC Substations

17 December 2015Fără categoriecburada

Abstract

Although the high power DC traction substations are using 12 pulse rectifier which have lower distortion than the classical 6 pulse rectifier, considering the high power, the reactive and harmonic components of the absorbed current are harmful to the power grid. The addition of an active compensator to the classical dc traction substation creates the “active substation”. The active substation allows bidirectional power flow between the power grid and the DC catenary, which means the active power flow from the power grid to the DC catenary and the recovered power flow from the catenary back to the power grid. At the same time, because the compensator acts like an active filter in the first case and like a power inverter in the last case, both the consumed and recovered power are active powers. To achieve this goal the active compensator must inject current to the point of common coupling, and the typical currentcontroller is the hysteresis regulator. At the same time, the typical approach on the injected current regulation is the direct current control, which implies the closed loop controlof the current at the compensator output, i.e. the current through the output inductors. A new approach is the closed loop control of the current absorbed from the power grid, i.e. the indirect control, for which the compensator controls the grid current, and for a given load current, the compensator injected current results from the first two.