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سایت اطلاع رسانی صنعت برق ایران - 5

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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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درباره : نیروگاه , تولید , وزارت نیرو ,
بازدید : 191
تاریخ : شنبه 15 اسفند 1394 زمان : 12:39 | نویسنده : admin | لینک ثابت | نظرات ()
  • 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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درباره : نیروگاه , انتقال , وزارت نیرو ,
بازدید : 193
تاریخ : چهارشنبه 12 اسفند 1394 زمان : 12:38 | نویسنده : admin | لینک ثابت | نظرات ()
  • 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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درباره : نیروگاه , تولید ,
بازدید : 196
تاریخ : یکشنبه 09 اسفند 1394 زمان : 12:36 | نویسنده : admin | لینک ثابت | نظرات ()
  • 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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درباره : تولید , توزیع ,
بازدید : 211
تاریخ : پنجشنبه 06 اسفند 1394 زمان : 12:35 | نویسنده : admin | لینک ثابت | نظرات ()
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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درباره : نیروگاه , انتقال ,
بازدید : 265
تاریخ : دوشنبه 03 اسفند 1394 زمان : 12:35 | نویسنده : admin | لینک ثابت | نظرات ()

Protection and Control

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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درباره : انتقال , توزیع ,
بازدید : 205
تاریخ : جمعه 30 بهمن 1394 زمان : 12:34 | نویسنده : admin | لینک ثابت | نظرات ()

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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درباره : تولید , انتقال , مصوبات جدید ,
بازدید : 243
تاریخ : سه شنبه 27 بهمن 1394 زمان : 12:33 | نویسنده : admin | لینک ثابت | نظرات ()

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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درباره : تولید , توزیع , مصوبات جدید ,
بازدید : 191
تاریخ : شنبه 24 بهمن 1394 زمان : 12:33 | نویسنده : admin | لینک ثابت | نظرات ()

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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حجم: 516 KB
رمز: www.power2.ir
تعداد صفحات: 18
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درباره : تولید , وزارت نیرو , قوانین ,
بازدید : 187
تاریخ : چهارشنبه 21 بهمن 1394 زمان : 12:29 | نویسنده : admin | لینک ثابت | نظرات ()

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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درباره : تولید ,
بازدید : 173
تاریخ : یکشنبه 18 بهمن 1394 زمان : 12:28 | نویسنده : admin | لینک ثابت | نظرات ()
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