Lightning in hybrid cable-overhead lines and consequent transient overvoltages

Whereas lines that consist entirely of underground cable are naturally protected from lightning, the phenomenon must be considered for lines that are a mix of overhead lines and underground cables. The difference between overhead lines and underground cables wave impedances may lead to transient overvoltages caused by reflections at the transitions points. This paper explains the phenomenon and analyses the influence of modelling Corona effect, the grounding of the towers and of the cable’s screen on the overvoltage magnitude. The analysis is made both for direct strokes on the overhead line phase conductor and for hits on the earth wire, with and without back flashover. For the most common situation, stroke on the earth wire, it is demonstrated that the cable’s ground propagation mode is dominant, reducing the impact of the reflections.