Lightning surges in hybrid cable-overhead lines: Part I—voltage estimation for shielding failure

Abstract

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 (EMT) 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.

Accurate Surge Arrester Modeling for Optimal Risk-Aware Lightning Protection Utilizing a Hybrid Monte Carlo–Particle Swarm Optimization Algorithm

“…For modeling the oil-immersed distribution transformer in a high-frequency surge, a model based on interleaved disk winding of a single-phase transformer is given from the presented methods in [17] and extended to the three-phase transformer, based on the stored energy method presented in [28] [27]. Capacitance in both ends of the winding section C shown in Figure 5 is written as…”

“…Maximum frequency, which can be presented by a Pi-cell corresponding length of the overhead distribution lines (l), is written as follows [28,29]:…”

Lightning surges in hybrid cable-overhead lines: Part II—voltage estimation for strikes to shield wire

“…The currents are expressed using the voltage and the impedance (2), which allows to relate the sheath voltage (V S ) with the injected voltage (V EW_I ), the earth wire impedance (Z EW ), the grounding impedance (Z G ) and the sheath impedances…”

“…However, it is not relevant to estimate this core voltage. Reference [2] shows that the ground mode is the main propagation mode in a cable in the event of a back-flashover and this mode does not depend on the voltage at the cable core. The low magnitude of the coaxial propagation modes when compared with the ground mode means that the core and sheath have approximate the same voltage and the main insulation is not particularly stressed.…”