IEEE Power & Energy Magazine - March/April 2016 - 40

retaining staff with sufficient knowledge of the controls
to maintain them.

Miles City
This back-to-back thyristor converter was installed in 1985 by
GE at Miles City, Montana. It was rated at 200 MW with a dc
voltage of 83 kV. The station is currently retired or out of service.

McNeil
This station interconnects the power grids of the Canadian
provinces of Alberta and Saskatchewan and went into service in 1989. See Figure 8 for an example of new modern
controls. Built by GEC Alsthom, it is rated at 150 MW.
Alstom provided a control replacement and other refurbishments discussed in another article in this issue of IEEE
Power & Energy Magazine.

Unrenovated Back-to-Back Converters

stations were built simultaneously and commissioned in
1993 by ABB. The major justification for the SVCs was to
prevent voltage collapse in the event of loss of major transmission assets bringing power from eastern Washington to
the Portland and Seattle areas during heavily loaded conditions. BPA is in the planning stage for renovation of both
stations. No upgrade in capability or capacity is expected.
It is anticipated that valves, controls, and cooling will be
replaced. Difficulty in maintaining the SVCs has been cited
as the major driving factor in scheduling renovation.

Adelanto
This SVC consists of three thyristor switched capacitor branches rated at 388 Mvar. It was installed in 1995 to
improve stability of power transfer into the Los Angeles
basin. The SVC was designed and built by Siemens. No
upgrade or refurbishment is planned at this time.

Five back-to-back converters in the WECC have not been
renovated or upgraded since their construction. David Hamil
(1977), Eddy County (1983), and Virginia Smith (1987) are all
old enough to be considered for some kind of renovation, but
no plans have been announced for modernizing any of these
stations. Rapid City (2003) and Lamar (2005) are both quite
new, and one would not expect renovation plans for either.

Static Var Converters
Power electronics have been used in a variety of innovative ways to solve power system problems. SVCs use thyristor technology to switch varying amounts of capacitive or
inductive power to control voltage. Fast-acting control makes
SVCs useful devices for maintaining stability in power systems. Smaller SVCs are also used in a large variety of industrial applications such as steel arc furnaces to control flicker
and stabilize the connected voltage. The earliest SVC in the
WECC area is called San Juan, owned by Public Service of
New Mexico, and was installed in 1980. There are a number
of more modern installations, but publicly available information is difficult to obtain. The SVCs discussed below are
indicative of the issues faced by utilities needing to upgrade
or refurbish their SVCs.

figure 8. Modern controls become more compact with
advances in computer hardware technology. (Used with
permission from EPRI).

Keeler and Maple Valley
The Keeler and Maple Valley SVCs are identical designs and
were built by ABB in 1993 at two BPA substations. Keeler is
located west of Portland, Oregon, and Maple Valley is near
Seattle, Washington. Both are rated ±300 Mvar. Each station
has two reactor branches and two capacitor branches. Watercooled thyristor valves are arranged in four separate valve
rooms. Several filter branches are attached to the high side
of the transformers. The low side voltage of the single phase
transformers is 20 kV.
Valve cooling (see Figure 9) is provided by a mixture of
water and glycol. Horizontally mounted outdoor radiators
with fans are located adjacent to the valve building. Both
march/april 2016

figure 9. A typical valve cooling system, often a troublesome component of converters. (Used with permission
from EPRI).
ieee power & energy magazine

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