Lightning-Originated Overvoltages in a Multiple Voltage Level Overhead Line

The paper presents the analysis of lightning-originated flashovers occurring on a multi-circuit high voltage (HV) - medium voltage (MV) overhead line. Both indirect and direct lightning are considered. We focus on the protection of a 15-kV line with compact configuration that shares the same concrete poles of a 69-kV transmission line. Concerning the indirect lightning performance assessment, the electromagnetic coupling between the lightning electromagnetic field and the multi conductor system is calculated using a version of the LIOV-EMTP-RV tool, suitably adapted by the authors for the non-conventional line configuration. The HV line increases as expected the incidence of direct strikes, but the prevailing effect, as shown in the paper, is the shielding of the MV line by the above HV line. Lightning-originated voltages are presented in the time domain for each conductor of the n-conductor line, with particular focus on the occurring flashover phenomena. The lightning performance of the MV power line calculated for the double-circuit configuration is compared with the one relevant to the case of a MV alone