IEEE Power & Energy Magazine - May/June 2019 - 81

The design of a reliable, effective HVdc grid-protection
scheme depends on both system characteristics and
the strategy used for fault clearing.

the algorithm must wait for signals communicated from the
remote line end to make a tripping decision.
Differential line protection compares the currents or
traveling waves seen at both line ends. the basic principles
of traveling-wave differential protection, originally developed for ac overhead line systems, may be applied to HVdc
systems. However, the algorithm may need an adaptation
for cable systems because of the larger influence of wave
distortion and attenuation in cable systems. for these algorithms, the delay caused by the wave propagation is subtracted from the communication delay, which favors a high
speed of operation. Because these algorithms rely on the
exchange of measured quantities rather than logical signals,
they impose a larger communication burden compared to
directional algorithms.
communicationless algorithms have the advantage of
fast fault detection due to the absence of communication
delays but face difficulties with detecting remote faults.
By contrast, communication-based algorithms can detect
remote faults while having an acceptable communication
delay. therefore, a combination of communication-based
and communicationless algorithms may be suitable for protecting long lines.

Summary
the design of a reliable, effective HVdc grid-protection
scheme depends on both system characteristics and the strategy used for fault clearing. system characteristics determine
the requirements for protection by fixing the relationship
between the probability of faults and their impact and by
setting constraints on secure system operation. the strategy used for fault clearing determines the technology to be
used (e.g., whether or not to use HVdc circuit breakers) and
determines the final impact of a fault on the system and its
components. for HVdc grid protection, fault-clearing strategies can be classified into three philosophies: nonselective, partially selective, and fully selective. the impact of
the fault on an ac or dc system can be determined from the
actions taken by ac-dc converters during fault clearing. in
all cases, the fault-clearing strategies benefit from fast fault
detection and, in the case of a fully selective strategy, fast
fault identification. the overview of protection algorithms
given here shows that these algorithms operate mainly on
traveling waves and may use a scheme without or with communication. the algorithms not using communication must

may/june 2019

rely on an impedance between the protection zones, which,
for HVdc grids, may be provided by an inductor in series
with the HVdc circuit breaker. for algorithms using communication, the algorithms may employ a traveling-wave differential or directional-comparison protection scheme and must
rely on a fast communication channel, such as a dedicated
fiber optic cable.

Acknowledgments
the authors acknowledge contributions from the members
of Work Package 4 in the european Horizon 2020 project
Progress on Meshed HVDc offshore transmission networks (ProMotion). this work was funded by ProMotion under grant 691714.

For Further Reading
cigre, "Local control and protection of HVDc grids,"
cigre, Paris, techn. Brochure 739, tech. rep. JWg B4/
B5.59, 2017.
ProMotion consortium, "D4.2-Broad comparison of
fault clearing strategies for Dc grids," oct. 2017. [online].
Available: https://www.promotion-offshore.net/fileadmin/
PDfs/D4.2_Broad_comparison_of_fault_clearing_strategies_for_Dc_grids.pdf
D. Van Hertem, o. gomis-Bellmunt, and J. Liang, eds.
HVDC Grids for Offshore and Supergrid of the Future.
Hoboken, nJ: Wiley, 2016.
i. Jahn, n. Johannesson, and s. norrga, "survey of methods for selective Dc fault detection in MtDc grids," in
Proc. 13th IET Int. Conf. AC and DC (ACDC) Power Transmission, 2017.

Biographies
Willem Leterme is with energyVille, the university of Leuven (Katholieke universiteit Leuven), Belgium.
Ilka Jahn is with the royal institute of technology,
stockholm, sweden.
Philipp Ruffing is with rheinisch-Westfälische technische Hochschule, Aachen, germany.
Kamran Sharifabadi is with equinor, stavanger,
norway.
Dirk Van Hertem is with energyVille, the university of
Leuven (Katholieke universiteit Leuven), Belgium.
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IEEE Power & Energy Magazine - May/June 2019

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