Statistical study of lightning induced overvoltages on distribution power lines and risk analysis

摘要

Owing to the increasing sensitivity of low voltage electrical equipment, it is necessary to be able to assess the magnitude of overvoltages caused by lightning. These are the most problematic overvoltages and, for the most part, they travel through power distribution lines. A risk analysis must be conducted to assist the decision to install a protective device on a given installation. In the French approach, the first stage of this analysis is the evaluation of the level of exposure to lightning induced overvoltages. The second stage consists in allowing for a criterion to evaluate the consequences of these electrical disturbances (destruction or unavailability of equipment) for a given level of exposure and in a given situation. This decision aid method is empirical. It is based on the main characteristics of the electric power supply and on the level of lightning strike density in the relevant area. An analysis of the same type is proposed on a complementary basis by two IEC committees. Finally, a calculation tool (Anastasia) was developed in order to allow the accurate quantification of the level of overvoltages on an installation. It is based on modelling of the coupling of the lightning channel and a power distribution line, allowing overvoltages to be calculated with the EMTP program. The Monte Carlo method is then used, in combination with simulations, to obtain a statistical distribution of the stresses at a given point. A comparison was made between the results obtained with Anastasia and the measurements conducted on an installation in the context of a campaign organized for several years by France Telecom.