Application of an electromagnetic modeling method for railway grounding systems subjected to lightning strikes

Abstract

This document presents the work done for the Belgian railway operator Infrabel with respect to the modeling of grounding systems. Infrabel needed information on how to design the lightning protection systems of the recently deployed GSM-R installations. There exist many methods for simulating lightning strikes on grounding systems. One of these techniques, an electromagnetic method based on Moment Methods, is used to solve the problem. The theory behind the method is described and a novel technique is presented for simulating cylindrical cables without metal sheets. The method is applied to the grounding of the Infrabel GSM-R base station. The influence of the soil conductivity, the length of cables and grounding rods and the type of lightning strike on the effectiveness of the grounding system is researched.Index Terms-Grounding, grounding electrodes, lightning, moment methods, power system lightning effects I. FORMULATION OF THE PROBLEM NFRABEL, the infrastructure company which manages the Belgian railway lines, recently installed approximately 480 GSM-R base-transceiver stations (BTS) across Belgium. The purpose of this cellular network is to have a communication system for the personnel and a system for the transmission of signaling information (detection of trains and controlling switches). The nominal power of the BTS is 1.3 kVA and it is fed by a single-phase grid of 230 V. This voltage is rectified and stepped down in order to feed the BTS at 48 V. There are several options for supplying the BTS with electrical power, the most important one being a dedicated local connection with the distribution system. However, in some cases, because of economical reasons, another technique is used where the BTS is fed from a supply station that was normally used for the electrical supply of critical signaling infrastructure (SI). This latter situation is presented in Fig. 1. There is a cable between the supply station and the BTS and the SI is supplied from the same bus as the BTS. The supply station is a This work was part of a project supported by the Interuniversitary Attraction Poles (IAP) programme and Infrabel N.V. redundant three-phase IT-system at 1000 V. Normally, the SI is well protected against overcurrents and -voltages due to lightning because of the type of grounding and because the supply station is situated in a zone of overhead wires, connected with each other through an overhead grounding wire. The BTS have antennas on metal towers and are therefore prone to lightning strikes. Therefore, if the supply station also feeds the BTS, the chances of overvoltages in the station increase. Fig. 1. Topology of the supply and grounding system of the signaling infrastructure and the GSM base station.In order to provide a good protection against lighting, the BTS and the supply station are kept away from each other as well as possible. Infrabel enforces a minimum distance between BTS and supply station of 80 meters. Current arrestors are installed at both stations and voltage arrestors at the supply post. An isola...