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[On Screen: US Department of the Interior Bonneville Power Administration
Presents 25,000 Volts Under The Sea
A Pictorial Record of the laying of the Submarine Electric Transmission Cable to serve the San
Juan Islands] [Music]
[Off Screen Narrator] In the spring of 1951 the San Juan Islands,
off the Northwest coast of the United States, became the scene of the laying of the world's
longest single-length submarine high-voltage cable. The project was designed and carried
out by the Bonneville Power Administration. Have you heard of the Pig War of 1870? Well,
it was on the San Juan Islands, the last part of the United States Territory on which the
British flag was flown, where this war was waged.
At that time, the treaty establishing the boundary between Canada and the United States
was not definite, and a dispute arose as to the ownership of the San Juan Island group.
An American settler shot a pig owned by a British settler. Both countries immediately
moved troops on the Island of San Juan. For thirteen years this joint occupation continued,
until the boundary was finally settled in 1872 by Kaiser Wilhelm the First of Germany.
An old British fort still stands today as a memorial of a war in which no shot was fired
-- except the shot that killed the pig. The people of the beautiful and economically
important San Juan Islands were promised power a long time ago. To serve these islands, it
was necessary to find a way to transmit power from the great Federal projects on the Columbia
River over hundreds of miles of high voltage lines.
Several alternate plans of service were investigated, including a submarine cable from the mainland
to Orcas Island on the north, then overhead lines spanning the narrow reaches of water
from island to island, using high precipitous banks to obtain sufficient clearance for the
long spans required. The plan finally selected included a four
and a half mile submarine crossing of Rosario Strait, a wood pole line on Decatur Island,
and another two-mile submarine cable to Lopez Island.
The core of the entire plan was the submarine cable. To select the proper cable, Bonneville
engineers investigated several different types of designs. Final specifications called for
a submarine cable covered for mechanical protection by galvanized steel armor wires laid in a
jute bedding around the three rubber-insulated copper conductors.
Each conductor was wrapped with a Monel metal shielding tape and a little over one-half-inch
wall of rubber insulation. The cable was manufactured in one continuous 7 ½ mile length, weighing
nearly three-quarters of a million pounds. The first step in manufacturing the cable
was to strand the sixty-one individual lead-coated copper wires into phase conductors. Next these
were insulated by folding rubber compound strips around each conductor and compressing
them by forming wheels. After eight separate layers were built up, a temporary lead sheath
was put over the outside to serve as a mold. The cable was then placed in a large vulcanizing
tank, in which it was cured under pressure and heat for several hours. After the curing
process had been completed, the temporary lead sheath was peeled off like a banana skin.
The conductor was then immersed in water for twelve hours and tested with 170,000 volts
DC for 15 minutes, and 49,000 volts AC for five minutes to ensure that the insulation
had been properly applied and cured. Three of these individual Monel-type conductors
were then twisted together with jute fillers to make a firm rounded core. This assembly
was wrapped with a heavy tape binder and place on reels in 23,000 foot lengths.
Factory splices were required to join the 2300 foot cable lengths. The 61 copper wires
in each conductor were separated and silver soldered. When the birdcage of wires had been
individually soldered, the strands were compressed back into a smooth, firm assembly, very little
larger than the original conductors. The individual conductors were then reinsulated
with rubber tape. An electric heating strip was wound around the joint, and an asbestos
blanked wrapped around it to vulcanize the rubber tape.
These splices were tested with the same AC and DC voltages as the original insulation.
The core was covered with a cushion of jute then wound in one continuous operation with
400 miles of quarter-inch galvanized steel armor wire.
From the armoring machine, the completed cable was fed directly over a capstan 40 feet above
the ground into the gondola cars where it was coiled about a wooden core in the center.
The cable was carried from one car to the next by means of vertical loops, and the cars
were sealed with lumber. As a safety precaution, the gondola cars were
linked with two heavy chains and a bar welded through the coupling pin to prevent accidental
opening of the coupling in the freight yards or during transit.
After a final test, the shipment was appropriately launched by breaking a bottle of Atlantic
Ocean water on the end car, and started on its 3,000 mile trip to the West Coast.
In the meantime, Bonneville engineers were completing plans for installation of the cable.
Studies of weather records of the Spring period for the previous six years were made to determine
probability of favorable weather. This record had to be matched with tidal information,
since the velocity of the water in the channel would be one of the major factors during the
cable laying operation. To assist the Bonneville Power Administration
in this problem, a special study was prepared by the Coast and Geodetic Survey, predicting
the actual velocity of the water in Rosario Strait for each hour of the day from April
1 to June 1, 1951. From this prediction and the weather studies,
the dates of April 16 to April 18 were selected. On these dates the tidal currents would be
near zero for several hours in the late morning and early afternoon.
The main hazard in cable laying is paying out the cable faster than the ship moves.
Unless this is prevented, it may result in permitting kinks in the cable as it piles
up on the bottom of the sea, as well as the possibility of running out of cable before
reaching the opposite terminal. To control the rate of payout of the cable,
and underwater profile was made from fathometer readings taken by the Coast and Geodetic survey.
At each station on this profile, the proper tension was calculated and the angle at which
the cable would enter the water. To control the movement of the cable ship
and obtain an accurate record of its position at all times, survey parties were to be established
on shore at each end of the course and at locations off to the side.
Four such points were selected for the Rosario crossing. Radio telephone communication was
provided from each survey party directly to the top deck of the cable ship. Readings determining
the position of the cable ship were to be taken every two minutes.
In the meantime, the cable train was completing its transcontinental trip. The manufacturers
publicized the huge shipment by signs placed on the sides of the cars.
These signs read: Okonite Submarine Power Cable; For 25,000 Volt Electric Transmission;
World's Largest High Voltage Cable; Diameter: Four and two-thirds inches Weight: 19 pounds
per foot; Total Weight: Nearly three-quarter of million pounds, one continuous cable over
seven miles long; for Bonneville Power Administration The Puget Sound Power and Light Company has
installed a number of cables across the deep waters of Puget Sound using a specially equipped
cable ship. Bonneville Power was able to charter this ship, named Puget Power, for the cable
laying operation. To test the ship's equipment, check the communication
facilities and assure complete coordination, all shore and ship crews were assembled for
a trial run in Seattle's Lake Washington. There, an actual operation of laying and picking
up a mile-long piece of used cable was performed. Meanwhile, the nine gondola cars were being
spotted on the dock in Seattle for reloading to the cable ship.
The cable loops between cars had been protected by burlap wrapping, which was pretty well
worn by the time it reached Seattle. Before removing the cable from the cars, both
ends were opened up and connected for a high voltage test to ensure that no damage had
occurred during transit. Forty-six thousand volts DC were applied to
each of the three conductors for a 15-minute period. The final test indicated clearly that
the cable itself was not injured in transit. By this time, the cable ship had been brought
around to the Pier from Lake Washington, and was spotted at the dock for loading operations.
A sheave, 8 feet in diameter was suspended over the gondola cars at approximately the
same height as the capstan at the factory. This was necessary to allow the armor wires
on the outside of the cable to lay back into place, as it had been during the original
manufacturing process. In the cars, this armor wire tended to "basket" and open up.
The end of the cable was threaded through this sheave over the stern of the cable ship.
Upon entering the ship, the cable was wrapped four times around a 92-inch diameter drum.
The purpose of this drum was to pull the cable from the cars and onto the ship.
Later, during the laying operation, this drum would be utilized for providing braking power
to hold the cable back in deep water. Immediately forward of this large drum are
three small sheaves which drive faster than the drum and thus keep the cable tight to
prevent slippage. Two cable wells were available for storage,
one forward and one amidships. It was necessary with the seven-and-a-half mile length of cable
to store portions in each of the two wells. Over each of these wells is located a large
sheave, driven by steam, to pull the cable to the top deck. At all points of sharp angle
on the cable the diameter of the sheaves is quite large, to avoid damage due to bending.
In the wells, a large crew of men was necessary to manhandle the cables snugly into 34-foot
diameter coils. Five-and-a-quarter miles of cable were stored in the forward well, which
required 17 layers of better than 1500 feet per layer.
Normally, an excess length of cable is ordered for submarine jobs. With two separate crossings
it appeared advisable to keep the cable in one continuous length, so that the remaining
cable from the shorter crossing would be available for the second, more difficult crossing. This
also would allow any leftover cable to be in one piece.
A slot was cut in the top deck between the two holes. A loop of the cable was lowered
into the slot and the coiling process was repeated in the second cable well, where the
remaining two-and-a-quarter miles of cable were stored. In this manner, the cable remained
in a single, continuous length. As each car was unloaded, the railroad switch
engine spotted the next one under the large sheave, and the operation was continued without
interruption. The complete loading operation was performed in two normal working days.
The tag end of the cable was opened up, the conductor sealed with rubber tape to keep
out the seawater. Then the armor wires were formed into a pulling eye, for use at the
start of the laying operations. Since it would be necessary to know the actual
tension on the cable during the laying, a special sheave calibrated against a strong
spring was provided at the stern of the boat. The cable was threaded under this sheave to
the fantail. As the tension varied, the sheave was raised and lowered against the spring,
and indicated the tension being applied. Overnight, the ship was towed 65 miles from
Seattle to Lopez Sound. Meanwhile, ship and shore crews were assembling at Anacortes and
completing final preparations for the laying. Early in the morning of April 16, survey,
radio and work crews were loaded on small vessels and transported to their stations.
The cable ship itself was anchored offshore from the Lopez terminal. The cable laying
operation was about to begin. Although this operation would require less than 3 hours,
the preparatory work up to this moment took more than a year of planning and preparation.
A helicopter was used to carry a small light rope from shore to ship. This rope was attached
to a steel pulling line which was then drawn to the ship and fastened to the pulling eye
of the submarine cable. A tractor on shore pulled the submarine cable
from the ship into the terminal. In this operation it was necessary to use power from the steam
winches to feed the cable off the ship. During this time the cable ship remained at anchor.
School children and local residents came down en masse to ensure an ample number of "sidewalk
superintendents." Handling and laying this cable was a rugged,
he-man job, and there was little time for relaxation or the more pleasant diversions,
except -- well -- yes, there were a few girls present.
The communities in the area took the event as an important civic affair. They selected
a cable-laying queen and her princesses. In breaking the bottle over the cable as it reached
shore, the Queen cut her finger slightly. This was the only accident during the entire
cable-laying operation. When launching formalities were completed,
the end of the cable was secured to a buried anchor on the shore, and the ship was ready
to proceed across Lopez Sound. [Boat whistle]
Since the ship has no means of self-propulsion, navigation was provided by three tugs, two
secured alongside, near the stern, and one forward.
The navigation officer on the top deck of the cable ship communicated by radio to control
the coordinated operation of these three tugs. Over the loud speakers, throughout the ship
and over the radio, an announcer gave the time every two minutes.
The transit men on shore and the observers on the ship took simultaneous readings at
each of these two-minute intervals. The shore crews transmitted their transit
readings to the plotting table on the top deck, where the information was laid off on
a master control map, and the actual course of the cable ship was thus recorded.
The position of the ship with respect to the course was made available to the navigating
officer. A second crew onboard ship in the meantime was recording the angle of the cable
entering the water, the number of revolutions of the main drum (which gave us the actual
length of cable paid out to that point), the speed of the revolutions of the main drum,
the actual tension of the cable, and the calculated tension desired at each location.
It was impractical to bring the large cable ship into the shallow water near shore, so
as it approached the Decatur-Allen terminal, the cable ship was brought to a stop in deep
water. There a scow was placed in position near the stern so that a sufficient length
of cable could be laid out to reach the shore terminal.
With the measured amount of cable on the scow, workmen bound the armor wire to prevent unraveling
and sawed the cable in two. Shore crews would be coming the next day to
drag the cable up to the terminals from the scow and backfill the ditches.
The cable ship was towed around Decatur Island to Anacortes, where it lay overnight.
Early in the morning she was moved to anchorage off the Fidalgo terminal, in preparation for
the second day's laying across Rosario Strait. Procedure at Fidalgo terminal was similar
to that of the preceding day. Submarine cable was pulled ashore by tractor, anchored, and
the ship began moving across the Strait. The crossing of this Strait, four-and-a-half
miles in length and in much deeper water, was more difficult, due to the greater tensions
required, the stronger wind, and eddy currents at the center of the channel.
Because of these adverse factors, it was necessary to operate the ship at a higher speed -- better
than three miles an hour at times. Deviation from the straight-line course was as much
as 400 feet, although the total amount of cable used in excess of calculated requirements
was only 500 feet. After completing the crossing, the cable ship
was again anchored, the shore length paid off onto a scow, and the cable pulled ashore
to the terminal. At all shore terminal structures, the cable
end was split and each of its conductors was brought out to a separate insulated terminal.
On the Islands, the terminals were mounted on wood pole structures.
At the Fidalgo Island substation, the cable was terminated on a steel frame. The protective
armor wire was anchored in a cast iron casing known as a spreader head. The three individual
conductors were carried through this spreader head up to the potheads.
Shielding tape on the outside of the conductors was protected in this portion by neoprene
rubber and fabric tapes. To relieve the electric stresses between the conductor and the ground-shielding
tape, a tapered stress cone was build up on the end of each conductor.
This stress cone was then inserted through the base of the terminal, and a porcelain
bushing placed over the upper end. This pothead, as it is called, was later filled with a compound
material to keep off moisture and air. A gasketed cap nut was attached to the cap of the pothead,
and provided a terminal for the attachment of the overhead lines.
The cable was energized on July 22, 1951. This event was celebrated by the population
of the San Juan Islands at a large community gathering, with members of Congress, civic
leaders, and the Bonneville Power Administration participating. The cable has been in successful
operation since that time. And so a promise has been fulfilled -- a promise
made more than thirteen years ago -- that someday in the future, power from the mighty
dams on the Columbia River would be brought to the San Juan Islands to light homes and
provide energy for the growing industries of the Islands.
[On Screen: The End]