Impact of harmonic pollution in junctions between DC cables with different insulating technologies: electrical and thermal analyses

Nowadays, power distribution systems deal with an increasing presence of power electronic devices, with the consequent increase in the harmonic pollution. Moreover, a sustainable upgrade path towards DC power systems implies a delayed substitution of present cables, while intervening at first on the substations. Thus, the presence of both conventional and new cable insulation technologies is foreseeable in the next future, leading to a heterogeneous electrical system. In such a scenario, the impact of distorted voltages on cables with different insulation technologies has to be investigated. In this paper the electrical and thermal effects of current harmonics on heterogeneous DC cable-joints have been analyzed. A DC joint connecting two cables, with different size and insulation technologies, has been simulated in the presence of low and high frequency harmonics. It is shown that over-heating can be generated within the joint and this condition can constitute a weak point for the grid.