مقالات انگليسي

[ریپورتر]

POWER FACTOR IMPROVEMENT OF SINGLE_PHASE AC VOLTAGE CONTROLLER EMPLOYING EXTINCTION ANGLE CONTROL TECHNIQUE
Abstract
The general study of power converters is to improve the overall efficiency of the power system by some advanced methods of control techniques. Forced commutation of the power semiconductor switches leads to improved power factor in dc converters. Similar techniques may be applied to improve the performance of ac controllers. For example, an ac controller can be used to adjust the stator voltage of an induction motor running under variable load in order to maintain better efficiency. With the present semiconductor technology (MOSFET's, IGBT's, GTO's and improved bipolar transistors), many solutions exist to alter the powerfactor ofdynamic ac loads through an ac controller. In this paper, the performance evaluation of the extinction-angle control technique has been illustrated as applied to a single-phase voltage converter by examples of static load and the widely used single-phase induction motor to verify the feasibility of the proposed technique. Observations on power factor, displacementfactor and motor efficiency make up the results ofthis work.
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Abstract
In today’s demanding business environment, modeling the power system has become necessary in order for utilities to make the right decision when it embarks on any form of asset expansion. Modeling allows the proposed system to be checked for any potential problems, such as mal-operation and incompatibility. The Siemens 7UT6 differential protection relay is used for power transformer differential protection and is capable of protecting transformers of any vector group. This paper covers the steps of modeling the 7UT6 relay and the application of the modeled relay in testing a protection system. A demonstration tripping of vector group D11 will be shown and the fault currents discussed. Graphs showing the phase voltages and currents will be inspected.
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ABSTRACT
This paper presents a power transformer model to evaluate differential element performance. The paper analyzes transformer energization, overexcitation, external fault, and internal fault conditions with this model. Test results with an actual transformer validate the model. The paper includes a guide for properly selecting current transformers for differential protection applications. Accurate power transformer modeling and proper current transformer selection lead us to improved transformer protection.
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Abstract
This paper presents the development of a wavelet based algorithm, for distinguishing between magnetizing inrush currents and power system fault currents, which is quite adequate, reliable, fast and computationally efficient tool. The proposed technique consists of a preprocessing unit based on discrete wavelet transform (DWT) in combination with an artificial neural network (ANN) for detecting and classifying fault currents. The DWT acts as an extractor of distinctive features in the input signals at the relay location. This information is then fed into an ANN for classifying fault and magnetizing inrush conditions. A 220/55/55 V, 50Hz laboratory transformer connected to a 380 V power system were simulated using ATP-EMTP. The DWT was implemented by using Matlab and Coiflet mother wavelet was used to analyze primary currents and generate training data. The simulated results presented clearly show that the proposed technique can accurately discriminate between magnetizing inrush and fault currents in transformer protection.
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Purposes
Abstract
A new approach to CT saturation assessment is presented in the paper. Detailed algorithms for decaying DC component measurement and CT saturation prediction are proposed and their accuracy is discussed. The information on CT saturation period is further used for adaptation of the generator / transformer differential protection. Improved stabilization for external faults is achieved by appropriate temporal adjustment of the differential curve for the time period of CT saturation. The protection developed was tested with both EMTP-generated and real world registered current signals.

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A Novel Digital Relay Model Based on SIMULINK and Its Validation Based on Expert System

Abstract
This paper presents the development of a novel digital relay model and its validation by a digital relay data analysis application. The model is developed as a SIMULINK Sfunction block. MATLAB file I/O functions are employed to generate an oscillography file and an event report. The expert system based digital relay data analysis application validates the relay model and generates diagnosis information for refining the model. An example is used to demonstrate the procedure of simulation, validation, and refining.

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Designing For A Low Resistance Earth Interface (Grounding)



Grounding (or earthing) is the art of making an electrical connection to the earth. The process is a combination of science and “art” as opposed to pure science. This process is required because it is necessary to go through a process of “testing the options,” as opposed to calculations made via some formal process. The options for each site must be determined through visualization and evaluation, individually, using a related analytical process. The earth must be treated as a semiconductor, while the grounding electrode itself is a pure conductor. These factors make the design of an earthing system complex, not derived from a simple calculation or the random driving of a few rods into the soil. Knowledge of the local soil conditions is mandatory and is the first step in the design process. This includes its moisture content, temperature, and resistivity under a given set of conditions.

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PERFORMANCE ANALYSIS OF TRADITIONAL AND IMPROVED TRANSFORMER DIFFERENTIAL PROTECTIVE RELAYS

ABSTRACT
This paper describes a new approach for transformer differential protection that ensures security for external faults, inrush, and overexcitation conditions and provides dependability for internal faults. This approach combines harmonic restraint and blocking methods with a wave shape recognition technique. First, we review the concept of transformer differential protection. We then analyze magnetizing inrush, overexcitation, and current transformer (CT) saturation phenomena as possible causes of relay misoperation. After summarizing the existing methods for discriminating internal faults from inrush and overexcitation conditions, we propose a new approach for transformer differential protection and describe the relay that is based on this approach. Finally, we compare the behavior of some of these methods for real cases of magnetizing inrush conditions.
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Programmable Logic Controllers: Programming Methods and Applications
Most textbooks related to programmable controllers start with the basics of ladder logic, Boolean algebra, contacts, coils and all the other aspects of learning to program PLCs. However, once they get more deeply into the subject, they generally narrow the field of view to one particular manufacturer's unit (usually one of the more popular brands and models), and concentrate on programming that device with it's capabilities and peculiarities. This is worthwhile if the desire is to learn to program that unit. However, after finishing the PLC course, the student will most likely be employed in a position designing, programming, and maintaining systems using PLCs of another brand or model, or even more likely, many machines with many different brands and models of PLC. It seems to the authors that it would be more advantageous to approach the study of PLCs using a general language that provides a thorough knowledge of programming concepts that can be adapted to all controllers. This language would be based on a collection of different manufacturer types with generally the same programming technique and capability. Although it would be impossible to teach one programming language and technique that would be applicable to each and every programmable controller on the market, the student can be given a thorough insight into programming methods with this general approach which will allow him or her to easily adapt to any PLC encountered. Therefore, the goal of this text is to help the student develop a good general working knowledge of programmable controllers with concentration on relay ladder logic techniques and how the PLC is connected to external components in an operating control system. In the course of this work, the student will be presented with real world programming problems that can be solved on any available programmable controller or PLC simulator. Later chapters in this text relate to more advanced subjects that are more suitable for an advanced course in machine controls. The authors desire that this text not only be used to learn programmable logic controllers, but also that this text will become part of the student’s personal technical reference library. Readers of this text should have a thorough understanding of fundamental ac and dc circuits, electronic devices (including thyristors), a knowledge of basic logic gates, flip flops, and Boolean algebra, and college algebra and trigonometry. Although a knowledge of calculus will enhance the understanding of PID controls, it is not required in order to learn how to properly tune a PID.
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feedback Control Theory
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Detection of inrush current in distribution transformer using wavelet transform
Abstract
Inrush currents in transformers are non-sinusoidal, high magnitude currents generated due to flux saturation in the core during energization. For protection purpose, in this paper an efficient method for detection of inrush current in distribution transformer based on wavelet transform is presented. Using this method inrush current can be discriminated from the other switching transients such as: load switching, capacitor switching and single phase to ground fault. Inrush current and other events for feature extraction and discrimination are simulated using Electro Magnetic Transient Program (EMTP). Results in all cases show the effectiveness of proposed procedure in identifying inrush current from other transients.
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Current Differential Line Protection Setting Considerations

Abstract
The most common pilot line protection today is directional comparison by use of distance relays. However, the increased availability of digital communications channels has renewed the interest in line differential relaying. Current-only relays have many advantages. One of the most significant advantages is the simplicity of the scheme with regards to settings.
The percentage differential principle originally developed for transformer and generator protection was extended for use on short transmission lines already in the 1930s, and is still widely in use. These Pilot Wire Relays typically use a telephone type pilot wire channel to exchange analog information between the line terminals. The electromechanical pilot wire relays were very easy to set; they either came with factory default fixed sensitivity or had a few tap settings. What tap to use was determined by estimated fault current on the line, making sure that the relay sensitivity was sufficient for the relays to dependably trip for all types of fault on the line. Three phase sensitivity was often limited to current above load levels in order not to trip for open pilot wires.
For digital current differential line relays, the sound and simple setting principles utilized for pilot wire relays seem to have been forgotten. Commonly, the most sensitive setting (10 – 20 % of nominal current) is applied and even recommended without any consideration of actual fault current levels for the application. This practice contradicts fundamental relaying principles that balance security, sensitivity, dependability and operating speed of the protection scheme. For sensitivity, the requirement is to set the relay to detect all faults on the line with a sufficient margin, seldom does this require the most sensitive setting. Higher sensitivity will increase dependability, but decrease security. Too high sensitivity may cause false trips due to ct errors at external faults with high fault currents, or even false trips on load for channel delay measurement errors due to unequal transmit and receive delays.
This paper reviews the basic setting criteria for current differential line protection, and the charge comparison relay in particular. While setting parameters will differ depending on the type of current differential relay, the setting principles and system conditions to consider remain largely the same. Operating time, sensitivity, dependability and security requirements are examined for typical applications. Considerations for weak feed conditions, ct errors and ct saturation, and charging current are discussed. In addition, the effect of channel delay compensation errors and asymmetrical channel delays possible on digital communications networks with regards to setting considerations is examined.
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DISTANCE DIGITAL RELAY MODEL DEVELOPED IN ATP“FOREIGN MODEL”AND C++
This paper presents a new approach in the problem of digital relay development. An interactive model in the simulation program of power system, eg, ATP-EMTP, could properly contribute to the improvement of digital relays. This model is not available and the code for this model has to be created in ATP. There is an internal programming language MODELS in ATP which allows creation of programs themselves but because of its simplicity it is not sufficient for developing sophisticated models as in object oriented programming language. This deficit is compensated for by allowing a suitable interconnection between the ATP computing core and external model developed in another programming language. For this reason, the object oriented programming language C++ was chosen for relay model development. The paper describes the way of linking and compiling of the relay model with ATP. Next, a multifunctional digital relay developed model is introduced with its functional elements, used algorithms and tripping characteristics. Simulation results are presented and correct tripping action is verified at the end.


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Advanced Substation Data Collecting and Processing for State Estimation Enhancement
Abstract
Many functions within a substation can be performed more efficiently if all the substation data is collected from and shared among Intelligent Electronic Devices (IEDs). Gathered measurements and apparatus statuses can be processed by (local) substation computer(s). Processing includes data consistency checking, switching sequence monitoring, predicting switching outcomes, etc. Processed data may be used locally and/or communicated to remote sites (neighboring substations and/or control centers). Substation data integration is facilitated by existence and appropriate connection of IEDs. The paper presents an approach to implementation of substation data integration and information exchange. The emphasis is on the utilization of local data redundancy to enhance power system state estimation, especially topology error detection.
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Modeling and Testing of a Digital Distance Relay Using MATLAB/SIMULINK
Abstract
This paper describes modelling and testing of a digital distance relay for transmission line protection using MATLAB/SIMULINK. SIMULINK’s Power System Blockset (PSB) is used for detailed modelling of a power system network and fault simulation. MATLAB is used to implement programs of digital distance relaying algorithms and to serve as main software environment. The technique is an interactive simulation environment for relaying algorithm design and evaluation. The basic principles of a digital distance relay and some related filtering techniques are also described in this paper. A 345 kV, 100 km transmission line and a MHO type distance relay are selected as examples for fault simulation and relay testing. Some simulation results are given.
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A Sensitive ANN Based Differential Relay for Transformer Protection with Security against CT Saturation and Tap Changer Operation
Abstract
This paper presents an artificial neural network (ANN) based scheme for fault identification in power transformer protection. The proposed scheme is featured by the application of ANN to identifying system patterns, the unique choice of harmonics of positive sequence differential currents as ANN inputs, the effective handling of current transformer (CT) saturation with an ANN based approach, and the consideration of tap changer position for correcting secondary CT current. Performance of the proposed scheme is studied for a wide variety of operating conditions using data generated from simulation. The results indicate that the proposed scheme provides a fast and sensitive approach for identifying internal faults and is secure against CT saturation and transformer tap changer operation.
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PERFORMANCE EVALUATION OF AN ADAPTIVE DIGITAL DISTANCE RELAY IMMUNE TO HARMONIC EFFECTS

Abstract

Microprocessor based distance relays use digital filters to process the input current and voltage signals and estimate the system impedance. Distance relays current and voltage input signals are not sinosuidal due to nonlinear and switching loads as well as harmonic frequencies produced by system faults. In this paper, performance of digital distance relays in presence of harmonics is studied. Different filters are proposed to improve the distance relay operational performance. To achieve an adaptive protection method, a fast Total Harmonic Distortion (THD) measurement method is proposed. A benchmark system is used for the development of digital protection simulation. Power system and distance relay model development are reported and some study results are provided.

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The DTP is a digital relay that provides high-speed differential and backup instantaneous differential three-phase protection for power transformers with two, three or four windings.
Differential Protection
For high-magnitude external faults, the DTP uses a current differential with percentage restraint to compensate for unbalance caused by variation in CT outputs. The DTP differential unit has programmable dual-slope percentage restraint with adjustable slope breakpoint. Discrete Fourier Transformation (DFT) provides excellent frequency filtration, making the differential current measurement immune to noise, DC components and wave distortion. This gives the digital DTP relay a clear advantage over other analog and hybrid models. The algorithm used to calculate the RMS value permits a high level of accuracy in the through current measurement. Phase Shift Compensation Internal compensation is selected to adjust for the phase shift across the protected transformer. This selection allows the DTP to make the proper phase adjustments to the applied currents and eliminates the zero-sequence component of the current. Conventional external compensation can also be selected. This setting is useful for testing the relay with single and three-phase test sources that supply in-phase currents.

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AN IMPROVED TRANSFORMER INRUSH RESTRAINT ALGORITHM INCREASES SECURITY WHILE MAINTAINING
FAULT RESPONSE PERFORMANCE
Abstract
This paper presents a new inrush restraint algorithm for the protection of power transformers. The algorithm is an extension of the traditional second harmonic restraint — instead of measuring the ratio between the magnitudes of the second harmonic and the fundamental frequency component, the algorithm considers a ratio between the phasors of the second and the fundamental frequency components of the differential signal, i.e. both the amplitude and phase relations. By making use of the additional dimension that was neglected until now, the new algorithm is capable of making more robust classification of differential currents caused by the magnetizing inrush phenomenon and those caused by true internal faults. The algorithm is presented in detail. Its analytical justification is supported by the results of numerical analysis, including digital simulation and waveforms recorded from physical transformers.

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EARTHING - GROUNDING METHODS: A PRIMER


Abstract :
Grounding and its design is a complex subject encompassing personnel safety, lightning or static protection, electrical power system earthing and computer system grounding. One must define the purpose to be achieved, as each system may accomplish the objective by different means. The paper lists and defines the more common earthing-grounding terms. A brief history of early attempts at grounding electrical and computer systems is covered. The paper answers the questions of why and how an electrical connection is made to earth. It details the methods of connecting the various types of electrical systems to earth. Personal safety with respect to electricity is covered. Misconceptions concerning grounding and earthing are disclosed.

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A CASE STUDY OF RELIABILITY CALCULATIONS AND FAILURES ANALYSIS FOR POWER TRANSFORMERS


Abstract
This paper describes the case study of the reliability of subtransmission transformers (63/20 Kv) installed in MAZANDARAN province, operated in subtransmission system. The information obtained from Mazandaran Regional Electric Company. Failures of transformers in subtransmission systems not only reduce reliability of power system but also have significant effect on power quality since one of the important components of any system quality is reliability of that system. To enhance utility reliability, failure analysis and rates, failure origin and physical damage causes must be study. The results of study on 60 substation including more than 110 transformers installed in subtransmission system show that the failure mode of transformers can be represented by Weibull distribution. Weibull statistics have been widely used and accepted as a successful mathematical method to predict the remaining life time of any equipment. Analysis show that the protective operation is the highest number of failures but the highest Average Time of Fault (ATF) is related to insulation problems. Useful conclusions are presented both for power systems operators and manufactures for improving the reliability of transformers. The methodology used in this study also applied to other equipment in electrical system such as oil switches, capacitor and insulators.

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Energy Indicators for Sustainable Development:Guidelines and Methodologies


INTRODUCTION
Sustainable development’ has been defined best by the Brundtland Commission as ‘development that meets the needs of the present without compromising the ability of future generations to meet their own needs’.1 Adequate and affordable energy supplies have been key to economic development and the transition from subsistence agricultural economies to modern industrial and service-oriented societies. Energy is central to improved social and economic well-being, and is indispensable to most industrial and commercial wealth generation. It is key for relieving poverty, improving human welfare and raising living standards. But however essential it may be for development, energy is only a means to an end. The end is good health, high living standards, a sustainable economy and a clean environment. No form of energy — coal, solar, nuclear, wind or any other — is good or bad in itself, and each is only valuable in as far as it can deliver this end. Much of the current energy supply and use, based, as it is, on limited resources of fossil fuels, is deemed to be environmentally unsustainable. There is no energy production or conversion technology without risk or without waste. Somewhere along all energy chains — from resource extraction to the provision of energy services — pollutants are produced, emitted or disposed of, often with severe health and environmental impacts. Even if a technology does not emit harmful substances at the point of use, emissions and wastes may be associated with its manufacture or other parts of its life cycle. Combustion of fossil fuels is chiefly responsible for urban air pollution, regional acidification and the risk of human-induced climate change. The use of nuclear power has created a number of concerns, such as the storage or disposal of high-level radioactive waste and the proliferation of nuclear weapons. The noncommercial use of biomass in some developing countries contributes to desertification and loss of biodiversity.
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Subject Definition and Objectives


Introduction:

When an electrical signal is sent to an oscilloscope its waveform is observed in the time domain; that is, the screen shows the signal amplitude at each instant in time. If the same signal is applied to a hi-fi amplifier, the resulting sound is a mix of harmonic frequencies that constitute a complete musical chord. The electrical signal, therefore, can be described either by time-domain or frequency-domain information. This book describes the relationships between these two domains in the power system environment, the causes and effects of waveform distortion and the techniques currently available for their measurement, modelling and control. Reducing voltage and current waveform distortion to acceptable levels has been a problem in power system design from the early days of alternating current. The recent growing concern results from the increasing use of power electronic devices and of waveform-sensitive load equipment. The utilisation of electrical energy is relying more on the supply of power with controllable frequencies and voltages, while its generation and transmission take place at nominally constant levels. The discrepancy, therefore, requires some form of power conditioning or conversion, normally implemented by power electronic circuitry that distorts the voltage and current waveforms. The behaviour of circuits undergoing frequent topological changes that distort the waveforms can not be described by the traditional single-frequency phasor theory. In these cases the steady state results from a periodic succession of transient states that require dynamic simulation. However, on the assumption of reasonable periods of steady-state behaviour, the voltage and current waveforms comply with the requirements permitting Fourier analysis [1], and can, therefore, be expressed in terms of harmonic components. A harmonic is defined as the content of the function whose frequency is an integer multiple of the system fundamental frequency.

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PROGRAMMABLE CONTROLLERS THEORY AND IMPLEMENTATION

PREFACE:
Since the first edition of this book in 1988, the capabilities of programmable logic controllers have grown by leaps and bounds. Likewise, the applications of PLCs have grown with them. In fact, in today’s increasingly computercontrolled environment, it is almost impossible to find a technical industry that does not use programmable controllers in one form or another. To respond to these phenomenal changes, we introduce the second edition of Programmable Controllers: Theory and Implementation. This second edition, like the first, provides a comprehensive theoretical, yet practical, look at all aspects of PLCs and their associated devices and systems. However, this version goes one step further with new chapters on advanced PLC topics, such as I/O bus networks, fuzzy logic, the IEC 1131-3 programming standard, process control, and PID algorithms. This new edition also presents revised, up-to-date information about existing topics, with expanded graphics and new, hands-on examples. Furthermore, the new layout of the book—with features like two-tone graphics, key terms lists, well-defined headings and sections, callout icons, and a revised, expanded glossary— makes the information presented even easier to understand. This new edition has been a labor-intensive learning experience for all those involved. As with any task so large, we could never have done it alone. Therefore, we would like to thank the following companies for their help in bringing this book to press: Allen-Bradley Company—Industrial Computer Group, ASI-USA, B & R Industrial Automation, Bailey Controls Company, DeviceNet Vendors Association, ExperTune Software, Fieldbus Foundation, Hoffman Engineering Company, Honeywell—MicroSwitch Division, LANcity—Cable Modem Division of Bay Networks, Mitsubishi Electronics, Omron Electronics, Phoenix Contact, PLC Direct, PMC/BETA LP, Profibus Trade Organization, Schaevitz Engineering Company, Siemens Automation, Square D Company, Thermometrics, and WAGO. We hope that you will find this book to be a valuable learning and reference tool. We have tried to present a variety of programmable control operations; however, with the unlimited variations in control systems, we certainly have not been able to provide an exhaustive list of PLC applications. Only you, armed with the knowledge gained through this book, can explore the true limits of programmable logic controllers.
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Detection of Abrupt Changes Theory and Application1

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Introduction
In this chapter, we describe the purpose and contents of the book. In section 1.1 we give the theoretical and applied motivations for change detection. The last part of this section consists of three possible statistical problem statements for change detection, together with the intuitive definition of the corresponding criteria to be used for the design and performance analysis of change detection techniques. The formal definition of these criteria is given at the end of chapter 4, after the introduction of the key mathematical tools to be used throughout the book. In section 1.2, we introduce five typical application examples, which we will use to introduce the main techniques. In section 1.3, we describe the organization of the book, based on a classification of change detection problems according to the types of characteristics that change. We give a short description of each chapter and a general flowchart of the chapters. Finally, in section 1.4, we comment further on several critical issues concerning the design of change detection algorithms and the investigation of their properties.





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Measured Impedance in Double Circuit Transmission Lines for Faults on Second Circuit

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Abstract:

The increasing demands for electricity energy and the limits for rights for transmission lines paths, lead to utilization of double circuit lines in power systems. The lines are loaded as high as possible and this leads to decrease in the security margin of the system. Here, accurate protective system is required for satisfactorily operation of the power system. Distance relays are widely used in the protection of transmission systems. Main and backup protection of transmission lines are provided by distance protection, which is based on the measured impedance at the relaying point. For the faults on the first circuit, in the case of zero fault resistance, the measured impedance at the relaying point is independent of the power system conditions. But in the presence of the fault resistance, the measured impedance deviates from its actual value according to the system structural and operational conditions and specially the magnitude of the fault resistance. In the case of second circuit, the measured impedance even deviates from its actual value in the absence of the fault resistance. However, this paper studies the measured impedance for the faults on the second circuit of a double circuit transmission line. The tripping characteristic is presented for the faults on the second circuit. The variation of this tripping characteristic is studied as a function of the changes in the operational and structural conditions of the power system.





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Neural Network Two-terminal Approach for Fault Location in Transmission Line Distance Protection


Abstract:
This paper presents a new approach to locate shunt faults in power transmission lines using a two-layer Adaptive Linear Neural Network (ADALINE) in a two-end protection scheme. First, a transmission line with actual parameters is simulated in the PSCAD/EMTDC software and signals are fed to the MATLAB software to implement a real time adaptive filtering. In this approach, twoend unsynchronized measurements are used to estimate the unknown synchronization angle, fundamental frequency components using ADALINE. Finally, the distance to fault is calculated in a special process. The proposed method’s aim is to increase convergence accuracy and speed in the first period after fault inception. In this respect, the simulation results show that fault location, reactance effect and fault impedance cannot affect the proposed protection scheme.





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