IEEE Power & Energy Magazine - March/April 2016 - 68

Keeping the
Power Flowing

A

AN INCREASING NUMBER OF HIGH-VOLTAGE
dc (HVdc) transmission links are being built around the
world to efficiently and cost-effectively move large amounts
of power from generation sites to distant centers of consumption. (Figure 1 shows a typical HVdc installation.) Similarly,
flexible alternative current transmission systems (FACTSs)
are increasingly being employed to boost power capacity
and improve stability in existing grids the world over. These
installations represent significant investments for owners, so
it is essential that they are maintained in good condition with
proper service strategies, onsite and remote maintenance,
proper training of maintenance personnel, and, finally, after
many years of successful operation, with upgrades to some
parts of the installation.
A number of transmission links around the world have
been upgraded, and many connections built in the 1970s and
1980s will require some kind of overhaul in years ahead.
Since HVdc and FACTS transmission assets have lifetimes
that are many decades long, newer and better technology often appears by the time the asset has only reached
the middle of its expected lifetime, making it possible to
improve performance or introduce new functionality. Carrying out an upgrade at this point can add many years to the
asset's lifetime as well as further increase its performance,
availability and reliability. This article addresses a variety
of maintenance upgrade strategies, including HVdc midlife
and partial upgrades, control and protection upgrades, and
thyristor valve upgrades. In addition, it examines specific
HVdc project upgrades (Skagerrak and Apollo) as well as
FACTS upgrades (Hasle and Insukamini).

Midlife Upgrades of HVdc Installations
HVdc installations have a long operational life, but after
some years of operation, for example, at the installation's
midlife point, an assessment of certain equipment and systems may show the value of maximizing the installation's
lifetime and reducing downtime. Proactive upgrades can save
Digital Object Identifier 10.1109/MPE.2015.2501223
Date of publication: 18 February 2016

march/april 2016

operators time and money by avoiding equipment failure that
can lead to severe outages. Overall, an upgrade increases the
lifetime of an installation.

Upgrades of Control
and Protection Systems
The lifetime for control and protection systems for HVdc and
FACTS plants is typically at least 20 years. The technical life
of the equipment is probably longer, up to 40 years, but for
plants that are expected to operate for 50-60 years, it is wise
to factor in at least one control system replacement during
the plant's life span. An upgrade of the controls at 20-30
years, at the midpoint of a plant's life cycle, may achieve an
optimum return on investment for the new controls.

Upgrades of Thyristor Valves
Most HVdc and FACTS thyristor converters are still in operation, and the conclusion is that the technical lifetime for
thyristor valves is very long, probably over 30 years with
some up to 50 years. As the development of thyristor performance over the last 40 years has been remarkable, replacing
an old thyristor valve with a new one may be a good investment, resulting in an extended life of the installation, lower
losses, improved serviceability, and decreased maintenance.

In-Depth Description
of Some HVdc Upgrades
Skagerrak (Connecting Denmark and Norway)
The Skagerrak HVdc transmission system comprises several
HVdc links that together provide a total transmission capacity of 1,700 MW between Kristiansand in southern Norway and Tjele on Denmark's Jutland peninsula. As shown
in Figure 2, the link is owned by Statnett in Norway and
Energinet.dk in Denmark.
Skagerrak 1 and 2, rated 500 MW, was commissioned in
1976-1977, and Skagerrak 3, rated 500 MW, became operational in 1993. The latest Skagerrak project was awarded to ABB
in 2011, and comprises a fourth link using HVdc light voltage
source converter (VSC) technology, which was combined with
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http://www.Energinet.dk
Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - March/April 2016
