Method for Estimating Overvoltage at Distribution Boards in Building using TT System Struck Directly by Lightning

Abstract:
This study investigates an evaluation method for the overvoltage that occurs in the distribution boards on each floor of a building directly struck by lightning. The mathematical method for evaluating each overvoltage is investigated by comparing it with the results of the electromagnetic analysis. The distribution board overvoltage can be calculated from the loop inductance formed by the N-phase and protective earth lines and the differential of the current flowing in each ground line. Moreover, the current flowing through each ground line can be estimated under the condition that the magnetic flux inside the building is zero. The evaluation method using these phenomena is verified under the condition that the power substation is installed on the first floor, and it is confirmed that the overvoltage can be evaluated with practical accuracy of within 30%.