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.
Keywords: Hybrid cable-overhead lines, Lightning, Corona,
Transient Overvoltages