IEEE Power & Energy Magazine - March/April 2016 - 37

operates and maintains the converter station and the line to
the Oregon border.
On 9 February 1971, shortly after the commissioning of
the PCDI, the San Fernando earthquake heavily damaged
the Sylmar converter station. The intensity of the quake
was in the range of 6.5-6.7. Extensive damage occurred
throughout the San Fernando Valley with the collapse of
buildings and freeway structures, and two men were killed
when an elevated roadway collapsed. At the Sylmar converter station, mercury arc valves were dislodged from
their supporting platforms, oil-filled reactors and capacitor racks tipped over, and switchgear was damaged. The
converter station was out of service for 18 months while
new mercury arc valves were manufactured in Sweden and
a wide variety of other equipment repaired or replaced. As
an interim measure, several mercury arc valves were moved
from Celilo to Sylmar, and the system was configured to
operate with only one pole using the other pole for return
current. This mode, called metallic return, avoids injecting
current into the earth through the ground electrodes at each
station. Metallic return is now a normal operating mode
when a failure at one station takes one of the two poles out
of service.
In 1977, a series of studies and tests established that
the line and converter equipment had latent capacity, and
the current rating was increased to 2,000 A for a power
rating of 1,600 MW. During this period, BPA had vast
amounts of surplus power available and stimulated two
subsequent projects to increase the intertie capacity.
The first upgrade came in 1984 when ASEA provided
100-kV
thyristor converters. These converters were connectfigure 4. 1970 mercury arc valves.
ed in series with the mercury arc
converters raising the rating to
±500 kV and 2,000 A. Later, in
1989, Brown Boveri Corporation
Conv
1
Conv
1
(BBC) provided 500-kV, 1,100Conv 3
Conv 3
A converters that were connected
in parallel with the combination
of mercury arc and thyristor converters. Following installation of
the so-called expansion converters, Celilo and Sylmar were not
the biggest converter stations
in the world, but they were cerConv 2
Conv 4
Conv 4
Conv 2
tainly the most complex. Each
converter station had ten separate
converters that could be configCelilo
Sylmar
ured in a bewilderingly wide
±400 kV, 1,440 MW, 3 × 133 kV, 1,800-A Hg-arc Valve Groups per Pole (~1969)
variety of ways. Fortunately,
160-MW, 2,000-A Inherent Continuous Current Overload Capability (~1972)
the new parallel 1,100-A con±100 kV, 400 MW, 1 × 100 kV, 2,000-A Thyristor Valve Groups per Pole (~1984)
verters were located about 1 km
±500 kV, 1,100 MW, 1 × 500 kV, 1,100-A Thyristor 12p Converter per Pole (~1989)
away from the original Sylmar
converter station on ground that
was not subject to liquefaction
figure 5. A single-line diagram of the PCDI prior to renovations at Sylmar
during an earthquake.
and Celilo.
commissioned in 1970 by ASEA and General Electric
(GE), it consisted of six independent mercury arc converters at each end for a rating of ±400 kV, 1,800 A, and 1,440
MW (see Figures 4 and 5). The transmission line extends
for 1,358 km (842 mi). Ownership is divided at the Oregon-
Nevada border. BPA owns, operates, and maintains the
northern converter station (Celilo) and the line from Celilo
to the Oregon-Nevada border. South of that point, the line
and the Sylmar converter station are owned by a partnership consisting of Southern California Edison; the Los
Angeles Department of Water and Power (LADWP); and
the cities of Burbank, Glendale, and Pasadena. LADWP

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