Review
Issues and Challenges for HVDC Extruded Cable Systems
Giovanni Mazzanti
Citation: Mazzanti, G. Issues and
Challenges for HVDC Extruded
Cable Systems. Energies 2021, 14, 4504.
https://doi.org/10.3390/en14154504
Academic Editor: Pierluigi Siano
Received: 14 June 2021
Accepted: 9 July 2021
Published: 26 July 2021
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Department of Electrical Energy Engineering and Information “Guglielmo Marconi”, University of Bologna,
Viale Risorgimento 2, 40136 Bologna, Italy; giovanni.mazzanti@unibo.it
Abstract:
The improved features of AC/DC converters, the need to enhance cross-country inter-
connections, the will to make massive remote renewable energy sources available, and the fear of
populations about overhead lines have fostered HVDC cable transmission all over the world, leading
in the last two decades to an exponential increase of commissioned HVDC cable projects, particularly
of the extruded insulation type. Comprehensive surveys of the issues to be faced by HVDC extruded
cable systems appeared in the literature some years ago, but they are not so up-to-date, as HVDC
extruded cable technology is developing fast. Therefore, the contribution this paper aims at giving
is a systematic, comprehensive and updated summary of the main present and future issues and
challenges that HVDC cable systems have to face to further improve their performance and com-
petitiveness, so as to meet the growing quest for clean and available energy worldwide. The topics
covered in this review–treated in alphabetical order for the reader’s convenience–are accessories,
higher voltage and power, laying environment (submarine and underground cables), modeling,
multiterminal HVDC, operation and diagnostics, recyclable insulation, space charge behavior, testing,
thermal stability, transient voltages.
Keywords: HVDC cables; XLPE; polymeric insulation; power transmission; RES; smart grids
1. Introduction
Since long time High Voltage Direct Current (HVDC) cables are the ideal—and often
the only—choice available for long subsea links [
1
]. Today, they are appealing for land
usage too,—see German Corridors Projects [
2
]. Indeed, the improved features of AC/DC
converters [
3
], and the fear of populations about the visual impact and the magnetic fields
from overhead lines are making HVDC cables attractive for underground use too. The
spread of HVDC cable systems is regarded as making the whole grid smarter by promoting
availability, flexibility and sustainability via the grid connection of Renewable Energy
Sources (RES)—which lie frequently in remote locations from large consumption areas.
Indeed, the search for huge amounts of clean RES moves power generation towards remote
areas like deep seas and oceans with abundant wind and “blue” energy reservoirs, as well
as deserts with huge solar energy wells, high and broad mountain ranges with plenty of
water power resources. In the past two decades, this yielded a quasi-exponential rise of
HVDC cable systems in services worldwide [
4
,
5
] but has made the working conditions of
HVDC cables harsher, too.
The European Union is particularly sensitive to these issues. Indeed, in 2018 the
European Commission (EC) published its long-term strategy “A Clean planet for all” [
6
],
which identifies offshore RES, amongst others, as a key source to realize the clean energy
transition, and the EC funded “PROMOTioN” project described the advantages of HVDC
technologies—with focus on offshore power, thus on cables—for the integration of large-
scale RES into the energy system and to ensure a future-proof grid, which is affordable,
reliable and sustainable [7,8].
In the HVDC cable market, extruded cables with polymeric insulation [
9
,
10
] are
increasingly competitive vs. “classic” oil-paper insulated cables. Indeed, cables with
Energies 2021, 14, 4504. https://doi.org/10.3390/en14154504 https://www.mdpi.com/journal/energies
