  The fast protection of meshed HVDC grids requires the modeling of the
transient phenomena affecting the grid after a fault. In the case of hybrid
lines comprising both overhead and underground parts, the numerous generated
traveling waves may be difficult to describe and evaluate. This paper proposes
a representation of the grid as a graph, allowing to take into account any
waves traveling through the grid. A relatively compact description of the waves
is then derived, based on a combined physical and behavioral modeling approach.
The obtained model depends explicitly on the characteristics of the grid as
well as on the fault parameters. An application of the model to the
identification of the faulty portion of an hybrid line is proposed. The
knowledge of the faulty portion is profitable as faults in overhead lines,
generally temporary, can lead to the reclosing of the line.
