NEW FACTS ABOUT THE BEHAVIOUR OF EARTHWIRE-EQUIPPED ELECTRIC LINES UNDER THE IMPACT OF THUNDERBOLT

The present calculation methods referring to the behaviour of the earthwire-equipped electric lines under the impact of thunderbolt do not consider the actual value of certain parameters. This leads to partly wrong results. The paper examines several parameters which affect the value and the shape of the atmospheric overvoltage. The authors of this paper have studied them and their research correct them to an extent that cannot be ignored, as follows.: - The instantaneous impedance typical of the earthwire, while also considering the corona impulse discharge. - The dynamic coupling parameter acting between the earthwire and the live conductor. - The real shape of the atmospheric overvoltage at the fall of the thunderbolt on the top of an electric tower, when its wave has a short back of a few microseconds. The paper also shows the comparative results of calculations on the one hand on a 400kv S.C. electric line and on the other hand on a line where the real value of the above mentioned parameter has not been taken into account.