Construction of lightning observing system and an example of its application

Telecommunications systems for supplying services are installed in various buildings such as telecommunication buildings, office buildings and remote radio stations. The endurance to lightning surges and high-frequency noises in the systems has been decreased because the processing speed of information technology equipment is getting higher and operation voltage of electronic circuits has been decreased. Any breakdown or malfunction of the systems is likely to disrupt business and social activities. Therefore, it is important for the systems to be furnished with lightning protection countermeasures and to be evaluated about the effect. To establish suitable countermeasures for lightning surges in a building, we investigate and compare the effect of some countermeasures by a simulation using small current, in which small currents are injected from the top of the building and the distribution of the current is measured. We can estimate the effect of the countermeasures from the current measured in the power cables, telecommunication signal lines and earthing conductors. This method has disadvantage, however, that it can not include nonlinear effects such as arrester operation and the reduction of earth resistance which can occur by lightning. Therefore, we think that the lightning observation is necessary to understand the difference between the obtained value by our small current injection method and the observation value at actual lightning strike. In this paper, the outline of the lightning observation system we constructed is described. We also describe the difference between the results obtained by the small current injection method and the observation value of the surge current measured from an actual lightning strike.