IEEE Power & Energy Magazine - March/April 2016 - 65

figure 10. Roanoke SVC substation.

condensers. The new machines are rated +50/-25 Mvar and
were purpose built to be synchronous condensers to support
the dc link.
With the commissioning of the new bipole 2 completed in
2014, the replacement of the bipole 1 control system will be
carried out next. In addition, a top-level supervisory control
system will also be provided which will oversee the control
of both bipoles.

AEP Roanoke SVC Refurbishment
The project involved the refurbishment of a static var compensator (SVC), originally installed and commissioned by
Alstom over 20 years ago. (See Figure 10.) SVCs are used
in electricity transmission systems and industrial plants to
stabilize voltage and reduce fluctuations as part of a FACTS.
The project was a power system equipment upgrade for
Appalachian Power Company, a unit of American Electric
Power (AEP), to improve the power quality of the local
electricity network while boosting production and reducing maintenance costs for a steel mill located near Roanoke,
Virginia.
The SVC system is connected directly at a 34.5-kV bus,
and the facility is fed from the electric utility grid at 138 kV.
The original SVC supplied in 1992 was rated at 211 Mvar
(-42/+169 Mvar) at 34.5 kV and includes a thyristor-controlled reactor (TCR) branch and four harmonic filters tuned
to the second, third, fifth, and seventh harmonics. The second harmonic filter is in a damped C-type configuration.
The main driver for the refurbishment project was the
aging SVC and substation equipment and to extend the life of
the SVC. The objectives were to upgrade the SVC with minimum downtime and interruption to the steel mill operations
as well as minimize the impact on the power system with
respect to power quality without the SVC operation. The
existing SVC system has been operating for 20 years, and a
number of factors led AEP to consider extending the life of
the installation and its operational performance through a
partial refurbishment. One of the major pieces of equipment
that was directly impacting the performance and longevity of
the entire SVC was its control system. Based on the original
analog platform, the control system was lacking important
functional features inherent in today's state-of-the-art digital control platforms, with respect to reliability and ease of
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operation. Furthermore, as is common with obsolete analog
controls, the availability of spare parts had become a critical
issue to the operators. The next deciding factor was to bring
the power quality performance of the SVC system in line
with the most recent standards in terms of voltage flicker
and harmonic distortion. Some specific components in the
thyristor valve and cooling system were also showing signs
of aging, which manifested themselves into a degradation of
the systems' reliability and availability as required for Steel
Dynamics, Inc.'s (SDI's) arc furnace operation.
Based on experience and further discussions with the
original equipment supplier, AEP decided to proceed with
the turnkey replacement of a) the SVC controls with complete integration within the existing substation control, protection, and monitoring system; b) the thyristor valves and
its water-cooling system (heat exchangers and pump station
and motor control center); c) the outdoor second harmonic
filter bank (capacitors, reactors, resistors, filter bank protections, and steel structures), with a new frequency response
characteristic to allow for optimized harmonic performance,
and the TCRs and their support structures. A five-year service and maintenance support package for the upgraded
equipment was also part of the project.
With the refurbished SVC operational, Appalachian
Power has achieved a marked improvement in local power
quality with fewer instances of disruptive harmonics or voltage flicker. That improvement is credited in part to the project's further benefit to the nearby Roanoke Bar Division of
SDI, which produces a range of carbon-steel merchant bar
products. The overhaul has improved the power profile of
SDI's electric arc furnace, making it more efficient and less
expensive to operate and maintain, and thereby reducing its
potential to affect other customers served by Appalachian
Power's local grid. The modernized, more efficient SVC also
has contributed to an increase in the mills steel production.
The refurbishment project was completed within ten
months. By upgrading the SVC, power quality has improved
significantly in addition to extending its life.

Factors Affecting Refurbishment Strategy
There are some general points that are significant factors in
the decision to refurbish HVdc and FACTS installations.
✔ Control system obsolescence. The control systems
are likely to become obsolete first. Even though the
HVdc or FACTS facilities are designed to operate
within the required performance limits for 30 years
or more, the progress of the semiconductor industry
is so rapid that control circuit board components may
only be supported by the supplier for up to ten years.
HVdc and FACTS vendors are now supplying control
systems that use industry-standard, third-party components that may be refreshed with backward-compatible systems available into the future. Many HVdc and
FACTS owners are now factoring the refurbishment of
the control system into the lifetime cost-of-ownership
march/april 2016

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