IEEE Power & Energy Magazine - March/April 2016 - 39

table 2. A Celilo upgrade comparison.
1989 Celilo
Expansion

2016 Celilo
Upgrade

Thyristors per valve

120

Maximum voltage as rectifier

500 kV

560 kV

Maximum current

1,100 A

3,410 A

Maximum power as rectifier

1,100 MW

3,800 MW

✔ Alberta east link: This new HVdc transmission system

in Alberta, Canada, was commissioned in 2014 and supplied by Siemens. The rating is 1,000 MW, ±500 kV
and extends for 485 km. Increased power demand in
central and southern Alberta overstressed the 240-kV ac
system, and new capacity was needed to move power
from the Edmonton to the Calgary area. Two HVdc
lines were constructed. The east link line runs from
north and east of Edmonton to southeast of Calgary.
✔ Alberta west link: Similar to the Alberta east line,
this system has the same rating and was also commissioned in 2014. The length of the line is 400 km. It
runs from southwest of Edmonton to Calgary, passing
substantially west of the east link line.

Back-to-Back Converters

figure 7. Scale produced by hard water in an evaporative
cooling system. (Used with permission from EPRI.)

Older Unrenovated HVdc system
Vancouver Island HVdc Cable
Compared with most HVdc transmission systems, the Vancouver Island HVdc cable is quite remarkable; it was built
in two stages by two very different manufacturers with very
different technologies. But the most remarkable aspect is
that it is still in service and there are no plans to replace or
renovate it.
The first pole was built in 1970 using mercury arc technology from ASEA. The line consists of a converter station
south of the city of Vancouver, short overhead lines, a submarine cable between the mainland and Vancouver Island
and a converter station on Vancouver Island north of the city
of Victoria. Vancouver Island has no significant generation
resources of its own and depends on power from the mainland. A second set of converters was added in 1977 using GE
air-cooled thyristors. No upgrades or renovations have been
undertaken since then or are planned, and the system is still
in service. This is the last of the many mercury arc converters to remain in use worldwide. Several years ago, ac cables
were installed to supplement the HVdc cable.

New HVdc Systems in the WECC
Two new HVdc transmission systems have been installed in the
WECC in the province of Alberta, Canada. Reporting on renovation of these systems will have to wait 20-30 years for a future
publication or discussion at IEEE Working Group 15.05.08.
38

ieee power & energy magazine

The WECC area is not synchronous with the rest of the
United States or Canada. To transfer power between these
nonsynchronous areas, one must use back-to-back converters or a device called a variable frequency transformer.
Back-to-back converters are like an HVdc transmission
system without the transmission line. Both converters are
located in the same facility and change ac power to dc
and back to ac. The controlled power transfer is dc power
between the converters.
The variable frequency transformer is a large ac machine
in which the rotor winding is connected to one power system
and the stator winding is connected to a different nonsynchronous power system. Power transfer is effected by applying torque to the shaft of the rotor. Several such devices have
been installed, but none are in the WECC area. Back-to-back
converters are typically based on thyristor valves, although
one using voltage source converters exists between Texas
and Mexico.
In the WECC, there are nine back-to-back converters that
connect with the large eastern interconnection or with Texas.
One installation is in Canada (McNeil), and the rest are in
the United States. The newest is Lamar in Colorado, built
in 2005, and the oldest is David Hamil built in 1977, and
located in Stegall Nebraska.

Blackwater
Built in 1984 by BBC, this thyristor converter is rated at
200 MW, connects between New Mexico and Texas, and
is located near Clovis, New Mexico. The station is connected at 345 kV on the New Mexico side and 230 kV on
the Texas side. The dc voltage is 57 kV. It was renovated in
2009 by ABB when the control and cooling systems were
replaced. The original evaporative cooling system had become a considerable problem due to decreased availability of water and scaling (see Figure 7). New dry coolers
were installed along with new controls. The original BBC
controls were still operable, and the utility had a sizable
stock of spare control equipment. The control systems,
however, were replaced in 2009 because of difficulties
march/april 2016

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