Estimation of earth electrode resistance of antenna structures located in non-homogenous geographic terrain using finite element analysis and predictive modelling

Abstract

iv

ABSTRACT The telecommunication sector is consisting of firms that facilitates communication on a mass scale, through the phone or the web, as wired or wireless services. These firms created their infrastructure that permits sending voice, audio, or video and kinds of data or information to be sent anyplace in the world. These companies created their infrastructure that allows transmitting voice, audio, or video and forms of information or data to be sent anywhere in the world. It is observing that the Telecom infrastructure growth is in an aggressive mode even in Sri Lanka due to increase of the user groups and their complex needs for information sharing. As mobile devises become the most attractive device for the customers, operators have to provide these services through higher number of tower structures considering the countries geography and population distribution. With the increasing number of tower constructions and deployment of sensitive equipment with advance features observed due to increasing demand. The tower is a high-elevated structure in the environment. The typical height of the structure may be around sixty meters and may reach up to hundred meters. The towers act as direct grounding path for lightning strike. Providing a sufficient grounding path to such situation is important to mitigate the hazardous nature to the equipment and the livelihood around the structure. A proper earthing system with low earth resistance shall be recommended avoiding possible hazards by ground potential rise. Due to the located small land-plots for tower structures, carefully designed earthing network shall be implemented to achieve a lower earth resistance measurement at the tower. Operators have to maintain the earth resistance at tower sites as per the regulator bench marking. Telecommunications Regulatory Commission Sri Lanka (TRCSL) guideline for antenna structures imposed a recommendation to maintain the resistance level below 5 ohms for classified zones. In order to comply for the guidelines, telecom operators have to deploy optimized earthing networks depending on the tower sites. The tower earthing system consists with copper conductors such as tapes and number of conductive rods to maintain a lower earth resistance value. Estimation of earth resistance is a complicated practice effected by multiple factors due nonhomogeneity of soils. Key observations

are the variance in resistivity and resistance readings. At the time of designing, design itself get complex due to parallel conductor formation and its interconnection conductor’s contribution to the results. In order to identify the earth networks effectiveness to surges and lightnings, the site’s earth resistance measurement is the main parameter which we can be measured at a site. This thesis specifically discusses the effects and reasons for directional deviations observed in measured and theatrical values. Site earth resistance measurements have taken along various directions associated with resistive values and assessed with the measurements in four main directions of the sites along the tower legs. Earth networks would be simulated thorough ANSYS Maxwell to achieve earth resistance values. Numerical model will used to represent the resistance value in a single figure. Earthing network profile has been discussed and elaborated in relation calculate the resistance values from the simulation. Validation of the results has been performed through the comparison between simulation results and measurement values. Analysis has done for various soil types in different geographies in different areas of the Mobitel network and possible limitations for study have been discussed. Thesis concludes with a model to represent the accurate earth resistance for the site. Further includes the general assumptions and the possibilities for the further studies of the model proposed in the thesis.