IEEE Power & Energy Magazine - September/October 2017 - 99

Almost 15 years later, in 1970, thyristor valves were introduced to the
Gotland converter stations and placed
in series with the mercury-arc valves.
The thyristor valves would be a cornerstone to future HVdc installations, and
it was the first time they were used in a
commercial HVdc link. This allowed
the voltage to be increased to a possible 150 kV with a power capacity of
30 MW.
This would not be the first time the
Gotland HVdc project would be upgraded. A second link, named Gotland 2, was constructed in 1983. An
additional cable lay separate from the
original Gotland link. It was entirely
thyristor based and rated for 150 kV
and 130 MW. It was a much larger capacity than the original Gotland HVdc
project, allowing the island to transition
its oil-fired power station and diesel
to reserve.
Two more links would be constructed. One connected the island of Gotland

with the mainland in 1985. The other
connected the city of Visby to the southern part of the island in 1999. Gotland 3 was another undersea cable
project designed to work together with
Gotland 2 in a bipolar scheme but with
the capability to operate independently.
This doubled the power capacity to Gotland to a total of 260 MW. The cable and
terminal equipment of the original Gotland HVdc scheme was dismantled after Gotland 3 was commissioned. The
second HVdc link, called Gotland HVdc
Light, was the first commercial HVdc
Light project. (The HVdc Light name is
the branded name of ABB for their VSC
technology. The name HVdc PLUS is
used by Siemens.) The VSC link used
underground cables and had a rating of
80 kV, 50 MW.

Pacific DC Intertie
The Pacific DC Intertie project combined long ac and HVdc transmission
systems to move electrical energy from

the hydroelectric generators of the Pacific Northwest of the United States
to southern California, approximately
900 mi away. (See Figure 4.)
The Pacific DC Intertie had one
terminal, named Celilo, outside The
Dalles, Oregon, and another terminal,
Sylmar, north of Los Angeles, California. The initial ratings of the installation were 400 kV with a power capacity
of 1,440 MW. The project was a collaborative effort between General Electric
and ASEA of Sweden.
This HVdc link is notable with respect to Uno Lamm for two reasons.
The first is that it uses the HV mercuryarc valves he developed. The second is
more political and highlights Lamm's
ability to bring ideas to fruition.
The idea to optimize the use of hydroelectric power from the Pacific Northwest
by transmitting it to the southern part
of California when there was an excess
supply of power was nothing new and
went back to the 1930s. It was considered

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Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - September/October 2017