مقالات انگليسي

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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

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

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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[ریپورتر]

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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