Lightning surges in hybrid cable-overhead lines. Part I: Voltage estimation for shielding failure

The increasing usage of hybrid cable-overhead lines raises concerns over the protection of short cable sections against lightning surges, because of voltage build-up in the cable section. To set a simulation model of the phenomenon is time consuming, with numerous parameters impacting the overvoltage. This paper (Part I) presents formulas able to perform a fast estimation of the maximum overvoltage at a cable-overhead line transition point in the event of shielding failure. The formulas estimate the overvoltage with and without surge arrester, as well as the energy absorbed by the surge arrester. These formulas do not require an electromagnetic transients software and they can be implemented as a script, requiring solely the geometric data of the cable and overhead line, information available in the respective datasheets. The main usefulness is a tool for a fast screening of the overvoltages and a fast evaluation of the impact of different parameters such as cable length, lightning waveform and grounding impedance.