IEEE Power & Energy Magazine - March/April 2016 - 25

making new, according to the dictionary. It can be that and
so much more if there is a preconceived plan to the refurbishment, especially in an industry such as ours. It is a chance to
introduce totally different state-of-the-art technology to an
existing facility in a cost-effective manner. If refurbishment
is done properly, it sets the stage for unlimited future life
extensions of these critical facilities. Future upgrades can be
accomplished with surgical precision and minimum impact
to the transmission system. It is vial, however, that there is
a strategy for the refurbishment driven by a detailed specification rather than just calling a manufacturer and saying
the facility needs an upgrade. successful life extension starts
with hard work to determine what actually needs to be done.
planning ahead will enhance the facility while extending its
useful life.
one of the first hVdc refurbishments was dubbed a reengineering. the gotland link went into commercial service
in 1954 with mercury-arc valve technology. by the early
1970s, gotland's mercury-arc valves had been in service for
almost 20 years. the mercury-arc valves were aging, and
the link needed more capacity. during that time frame, the
silicon-controlled rectifier (scr) had been developed. the
scr, also known as the thyristor, made the development of
the solid-state valve possible. the designers of the thyristor
valve were looking for a place to prove the new technology.
the operators of the gotland link were interested in increasing the power transfer rating. becoming familiar with the
new technology was a plus too. the reengineering of the
link allowed some thyristor valves to be placed in series with
mercury-arc valves. this adaptation increased gotland's
capacity, and the thyristor valve was given real-world testing
on a utility's transmission system.
It may have been referred to as reengineering, but it met
all of the accepted criteria for what we today consider refurbishment. this refurbishing of the aging link did not result
in the replacement of the entire facility but rather the introduction of newer technology. today all of those pioneering
mercury-arc schemes have all been updated (i.e., replaced)

by solid-state technology. the solid-state thyristor valve
assembly proved to be less complicated and more reliable
than the older technology. It simplified the entire hVdc process, and from that point the industry has never been the
same. this is possibly the first refurbishment project, and it
laid the ground work for the selective life extension process.

Why Refurbishment?
components and systems of hVdc and Facts installations age
at different rates, just as in traditional ac facilities. dollar-conscious utilities typically replace only what is needed at a given
time rather than an entire ac facility, so it makes good business
sense to apply the same strategy for hVdc and Facts installations. Identifying and replacing only those systems that have
aged significantly compared to the rest of the facility allows a
utility to get the most from its existing equipment.
It is not cost-effective to replace 100% of the facility when
the equipment needing replacement represents a much smaller
percentage of the whole (see Figure 2 for an estimated system cost breakdown). a good example is the control system,
which habitually needs attention. an hVdc converter control
system normally represents only about 7% of the total cost.
economically, many components can be replaced before the
replacement of the entire installation is warranted.
Utilities have historically managed their existing assets in
this manner. refurbishment of hVdc converters and Facts
controllers can follow the same philosophy, although the
equipment and systems within these installations are very
closely intertwined, so it takes more research and planning
to perform a refurbishment. creating a strategy of timed
refurbishments allows a facility to remain in service and
useful for an indefinite period of time.

Other
Equipment
10%

Engineering
10%

Erection,
Commissioning
8%
Harmonic
Filters
10%

Valves
20%

Controls
7%
Civil Works
14%

figure 1. Older thyristor valves require a good supply of
spare thyristors to keep them functional. (Photo courtesy of
Gene Wolf.)
24

ieee power & energy magazine

Converter
Transformers
16%
Freight,
Insurance
5%

figure 2. The breakdown of the typical costs for a new
HVdc facility.
march/april 2016

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - March/April 2016