Transient Behaviour of Grounding System in a Two-Layer Soil Using the Transmission Line Theory

Abstract

Original scientific paperThe present work deals with modeling of the transient behavior of grounding systems in the presence of layered media. A simple and efficient Transmission Line (TL) model featuring the use of the Finite Difference Time Domain (FDTD) is proposed. The proposed approach easily accounts for the influence of semi-infinite media (soil or air) and imposes conditions at the interfaces. The TL model is verified through the direct solution of the Maxwell's equations in the time domain by means of the FDTD method. Some illustrative computational examples addressing some engineering applications stemming from industry are given in the paper. Tranzijentni odziv uzemljivačkog sustava u dvoslojnom tlu primjenom teorije prijenosnih linija. U radu se razmatra modeliranje tranzijentnog odziva uzemljivačkog sustav au prisutnosti slojevitih sredina. Predložen je jednostavan i efikasan model prijenosne linije uz upotrebu metode prijenosnih linija u vremenskom području. U okviru predloženog pristupa lako se uzima u obzir utjecaj polubeskonačnih sredina (tlo ili zrak) te postavljaju uvjeti na granici sredina. Model prijenosne linije verificira se direktnim rješenjem Maxwellovih jednadžbi u vremenskom području primjenom metode konačnog diferencija u vremenskom području. U radu se daju neki ilustrativni računalni primjeri koji se odnose na neke inženjerske primjene proizašle iz prakse.Ključne riječi: Tranzijentni odziv, uzemljivački sustav, teorija prijenosnih linija, pristup preko Maxwellovih jednadžbi, dvoslojno tlo, metoda konačnih diferencija u vremenskom područjuThe principal task of grounding systems is to ensure the safety of personnel and prevent damage of installations and equipment. Defect on grounding systems may cause operation error, malfunction and destruction of components in electric and electronic systems connected to the grounding systems. During a short circuit or lightning discharge, the assessment of fault currents in the grounding systems is rather important task, as these currents cause an increase of ground potential and related high intensity electromagnetic fields. The increase in ground potential is dangerous for the technical staff inside the substation, while the radiated fields may affect the measuring equipment required for the control and management of the power network. The model proposed in this work has been developed as an extension of the homogeneous soil model, based on the Transmission Line (TL) theory and the FDTD solution method. The two-layer soil effects are taken into account by means of the concept of apparent resistivity.An alternative approach used in this work for the transient analysis of grounding systems is the FDTD solution of Maxwell's equations in inhomogeneous media (layers of soil, air and the conductors of the ground).First, a rather simple case of a single horizontal buried electrode is considered. What follows up is the configuration of a grounding grid. Some illustrative computational examples are presented throughout the paper. TRANSMISSION LINE APPROAC...

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