مدلسازي و محاسبات سيستم زمين، ولتاژ ريل و جريان هاي سرگردان براي شبكه هاي قطار شهري و ارائه روش هاي بهبود آنها

چكيده انگليسي :

128Modeling and Calculation of Grounding System Rail Potential and Stray Currents for Urban Electrical Railways and Methods for its Improvement Mohammad Taghi Raisy mt raisy@ec iut ac ir Date of Submission 28 11 2011 Department of Electrical and Computer Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisors Mehdi moallem moallem@cc iut ac irAbstractNowadays urban electrical railway systems have rapid growth due to such advantages as traffic andpollution reduction Electrical railway is considered the predominant part of transportation systems in largecities Electrical railway is a complex system and constituted of several subsystems Grounding system is oneof the main parts of electrical railway systems that is the subject of this study There are several importantreasons why a grounding system should be installed But the most important reason is to protect passengersagainst electric shock Grounding system of electrical railway systems consists of two important parts first isthe AC grounding system that is used in passenger stations The second are the rails as paths for tractioncurrent This arrangement mainly fucuses on economic considerations since it does not require theinstallation of an additional return conductor The rails along the railway which lie exposed on the ground will cause rail potential and leakage of stray current to the ground So the choice of grounding strategieswithin the electrical railway systems has a profound influence on rail potential and stray current control Thispotential difference could cause electric shock for the passengers The most important effect of stray currentis corrosion of nearby buried metallic structures such as pipelines and concrete reinforcement armatures Sothe goal of this research is to study the methods to reduce the undesired effect of stray current to the ground For this purpose first electrical parameters of railway systems will be studied and short circuit current in ACand DC systems will be calculated To analyze the operation of AC grounding system during a fault toground first the principles of design and analysis for grounding system will be reviewed and the impacts ofdifferent parameters on operation of this system will be analyzed Finally AC grounding system of Esfahanurban railway will be studied for controlling of dangerous voltages Then some techniques will be proposedto improve the operation of the grounding system For reducing the rail potential and stray current in DCelectrical railway systems the methods of modeling the rail ground system and the impacts of differentparameters will be studied Then Esfahan urban railway as a practical case is simulated and rail potential andstray current in this system will be evaluated In practical systems methods such as voltage limiting devicesand stray current collection mats are used to control rail potential and stray current Voltage limiting devicesare located between rails and ground so that when the rail voltage exceeds the allowable limit establish adirect connection between rails and ground to eliminate the risk of electric shock Operation of the voltagelimiting devices cause increasing stray currents Stray current collection mats could be constructed under therails in order to absorb the stray currents and avoid damage to metallic structures Adequacy of thesepractical methods will be studied At the end new methods are proposed to improve the operation of voltagelimiting devices and stray current collection mats in urban electrical railway systems Keywords Electrical railway systems Grounding system Stray currents Rail potential Safety

رئيسي، محمدتقي

مدلسازي و محاسبات سيستم زمين، ولتاژ ريل و جريان هاي سرگردان براي شبكه هاي قطار شهري و ارائه روش هاي بهبود آنها