Investigating Outage Rates of 230 kV Transmission Lines Due to Lightning Strike Using Mont Carlo Method: Case Study in West Regions of Iran

Inappropriate design of transmission line towers in areas with high lightning density increases the outage rate of the line due to direct lightning strikes. In this paper, The lightning activities of areas covered by western regional electricity company during five recent years were collected from weather stations. Based on collected datasets, the Isokeraunic level and the lightning density of different areas have been computed. This information were further used to investigate and predict the outage rate of double circuit 230 kV transmission lines with one shield wire (existing plan) due to direct lightning strikes. Due to high density of lightning activities in some areas, the calculation results show high outage rate in these areas, which has been confirmed by actual experiences. In order to overcome this problem, a tower design with two shield wires was proposed for new developments. The outage rate of the transmission line with the two shield wire design with extracted lightning densities were compared with the existing tower installed. The results show high degree of improvement in outage rates. In order to modify the existing transmission line outage rates, installation of surge arresters and their capabilities were studied. Due to statistic nature of lightning, Monte Carlo method along with EMTP simulations were used in investigations. Simulations results show placement of surge arresters on two upper phases can reduce the shielding failure outage rates in the transmission line, significantly. The pros and cons of surge arrester installations in transmission line to compensate inappropriate tower design are discussed. Results of this study can be used for further transmission line developments in these areas.