Line Arrester Application on a 110 kV High Alpine Overhead Line to reduce Lightning-Caused Outages
Keywords:Line surge arresters, 110 kV overhead line, high alpine region, lightning outages, backflash
This contribution discusses a project, which aims to increase the reliability in an existing 110 kV overhead transmission network by taking measures addressing lightning and grounding issues. Due to the fault statistic in the past, a single overhead line was identified as a main reason for the lightning-caused outages in the area. In this work a number of possibilities for the reduction of lightning-caused outages are discussed and the measures taken in the network are described. All considerations took the special geographical situation of 2300 meter above sea level, the grounding resistance of up to 1200 Ohm and the local lightning activity of more than 6 lightning strikes per km² and year into account (4 to 5 times higher than in other Austrian regions). An analytical process was carried out to evaluate relevant parameters and to develop a concept of practical measures. Within these evaluations, the footing resistance, the effectiveness of the shielding angle of the shielding wires and the line arrester locations were analyzed. A multiplicity of numerical calculations were performed to assess the application of surge arresters regarding the insulation coordination for the system. To improve the line performance and to decrease the line outage rate, a number of practical measures were applied to the 110 kV line. In the past, the double three phase systems of the 110 kV overhead line was constructional converted into one active single three phase system with two additional earth wires. According to the numerical results, 18 surge arresters have been installed in a line section of 9 towers, located in a high alpine part and in an area of high lightning activity. Three years of field experiences have shown that the theoretical investigations and the practical measures led to a significant decrease of lightning caused outages. In the year 2007 a new project was started to evaluate a reconstruction of the line into the original double three phase system. New numerical calculation routines were made to apply line arresters at this important 110 kV system in an Austrian extreme mountain region. Based on this results, a new application of line arresters and the constructional change of the system is planned.