IN SEPTEMBER 1993, H. BRIAN WHITE STOOD ON KILDALA PASS, NEAR KITIMAT, BRITISH COLUMBIA, Canada, looking south. On that glorious blue-sky day, he could see steep snow-covered mountain peaks to the horizon in every direction. But over his head and stretching out in front of him were the real objects of interest: a pair of 300-kV circuits.

White, a preeminent transmission line designer, worked closely with the authors to address this incredible engineering challenge. According to White, more teachable transmission line engineering has been done at this location than anywhere else in the world.

A LITTLE HISTORY

The two 80-km (50-mile) 300-kV circuits were built in the early 1950s and energized in late 1954 as part of the Aluminum Company of Canada's (Alcan's) Kitimat smelter project. They were White's first effort as a transmission line engineer. The line starts and ends at sea level. Along the route, the typical double-circuit line on lattice-steel towers converts to a more-robust configuration to traverse the higher elevations, including Kildala Pass at a 1550-m (5085-ft) elevation, more than 300 m (984 ft) above the tree line. This is a land of flash-flooding rivers, rock slides, avalanches, glaciers and very deep snow — and mountain goats, moose, wolves, eagles, salmon and grizzly bears. Wild country, as they say.

In January 1955, four months after the line went into service, Mother Nature showed Alcan who is boss. Both circuits were wiped out by a big avalanche in a place called Glacier Bowl. White, then 32, was called on to solve the problem. Another young man on site, 22-year-old Adam Charneski, who was just embarking on a 55-year relationship with the transmission line, said to White, “You need a skyhook.”

From that comment, White conceived the Catenary, a tension-monitoring system for transmission lines. By September of that year, the two circuits were back in service, suspended from two large cables spanning perpendicularly over the conductors. Constructed of galvanized steel, each cable was 76 mm (3 inches) in diameter, 1158 m (3800 ft) in length and anchored into the solid rock of the mountain slopes high above the Glacier Bowl floor. They were in segments up to 365 m (1198 ft) in length, joined end to end with large poured-zinc sockets.

The cable anchorages on each side of the line were about 100 m (328 ft) apart, brought together near their midpoint to a separation of 0.91 m (3 ft). The belly of the cables near their midpoint was 135 m (443 ft) above the valley floor, right where the six conductors' suspension insulator assemblies were attached. The conductor spans on the Catenary were 760 m (2493 ft) and 1200 m (3937 ft), and the weight span was 840 m (2756 ft).

The controlling design load of 60 kg/m (40 lb/ft) of ice-loaded conductors was allowed to run Catenary parts to 100% of their strength. The six conductors were 3364 kcmil (1705 mm²) “Emu” and 58 mm (2.28 inches) in diameter, and weighed 6.9 kg/m (4.6 lb/ft). They had a bare everyday line tension of about 7700 kg (16,976 lb).

Phase separation on the Catenary was 15.2 m (50 ft), and the circuit separation was 45 m (148 ft). For a distance of 122 m (400 ft), the two large Catenary cables were brought 0.91 m apart, serving as handrails for a catwalk suspended from the cables above the circuits. The catwalk was used for inspection and maintenance activities and was accessible by helicopter.

The transmission line has been attacked by rivers, rock slides and avalanches many times since 1955. Some events were close calls, some were damaging and some were destructive. Individual towers were wiped out by avalanches in 1975, 1985 and 1992. The 1992 event occurred at Tower T113R, only 11 months before White had been standing on the mountain pass overlooking his handiwork. His 1955 Catenary was 1200 m (3937 ft) ahead of them, and the site of the destroyed T113R was about 450 m (1476 ft) ahead. White had designed a replacement structure for the T113R site months earlier as part of getting the line back in service. It was a proud day for him, but then Mother Nature stepped in again.

When White's tower was wiped out only 10 months after installation, causing yet another outage, Alcan erected a tower like the original one. The logic was that the first tower had lasted 38 years, and under these tough conditions, that seemed good enough.

THEN CAME 2007

Mother Nature said otherwise, and on March 28, 2007, an avalanche again destroyed T113R. The entire tower and 600 m (1969 ft) of Emu conductor were dragged 4 km (2.5 miles) to the river below. Days after this third failure event at the T113R site, Alcan convened a meeting. Alcan's coordinator of maintenance and operations was designated the owner representative and given two mandates: restore power to the circuit and provide options to senior Alcan management for replacement of the structure at the T113R site.

Clearly, something different was required. POWER Engineers Inc. (Hailey, Idaho, U.S.) had been busy with a variety of tasks on the line since its first visit in 1993 up to 1997. Because of the company's familiarity with the line, and particularly with the T113R site, POWER Engineers was asked to submit a proposal.

POWER Engineers proposed three options:

• Provide an in-kind replacement with some modifications to strengthen the tower legs

• Construct an avalanche deflector to protect the tower

• Use a Catenary.

POWER Engineers calculated that, while the cost of a Catenary was relatively high, it provided the greatest degree of reliability to the T113R line section. What's more, the cost of any effort made in this location paled in comparison to the cost of the outages caused by a structure's loss.

ENGINEERING OF CAT 1

Alcan, now Rio Tinto Alcan, quickly decided to pursue the Catenary solution. After all, the 1955 Catenary was considered the most-secure structure on the entire transmission line after 50-plus years of service.

The first priority for 2007 was to restore power to the R circuit and ensure a reliable source of power to the smelter site through the winter of 2007/2008. The second priority was to build the Catenary. By late July, it was evident that completion of the Catenary project in 2007 would not be feasible. A team — comprised of engineers from POWER Engineers Inc. and Wyllie & Norrish Rock Engineers (Vancouver, British Columbia); contractors from Allteck Line Contractors Inc., a Quanta Services Company, (Langley, British Columbia) and Pacific Blasting and Demolition Ltd. (Burnaby, British Columbia); and Alcan staff — convened to begin detailed planning for the 2008 Catenary construction season.

The terms “Cat 1” and “Cat 2” became the common labels for the two Catenary structures — the one already in place and the new one to come, respectively. When finished, Cat 1 and Cat 2 would be adjacent structures, 960 m (3150 ft) apart. The two circuits and their supports would consist of nothing but wires for a distance of 2.4 km (7874 ft). The ground surface below would have no support structures, as all cable anchors were about 400 m to 600 m (1312 ft to 1969 ft) off to each side of the line and up to 250 m (820 ft) above the circuits they supported.

ENGINEERING OF CAT 2

Cat 1 had been installed within eight-and-a-half months of the 1955 avalanche date that destroyed the circuits. The end of the useful construction season ends in mid-September. Thereafter, the winter brings an average of 15.2 m of snowfall each year. Snow depths reach an average of 3 m to 5 m (10 ft to 16 ft), with ground contours and wind creating depths routinely in excess of 15 m (49 ft).

Since the line had just been completed months earlier in the fall of 1954, infrastructure and manpower to build Cat 1 were all in place. The ground below the site was 1000 m (3281 ft) above sea level, and anchor elevations were near an elevation of 1400 m. Access was available by road, and a crew of about 200 workers lived primarily on site. The cables were laid out on the valley floor, assembled and winched into position for pinning to the four anchorages. The repaired Emu conductors were then raised up to the Catenary from the ground and pinned.

The installation method and design of Cat 2 needed to be quite different than that of Cat 1.

Alcan's goal was to install Cat 2 entirely during the 2007 season, of which there was four-and-a-half months left. The fast decisions leaned heavily on what POWER Engineers and Alcan knew about Cat 1. The valley floor and anchor sites at the new location were at higher elevations of 1370 m (4495 ft) and 1765 m (5791 ft), respectively. Construction crews expected to be “in the clouds” more frequently than the original team that built Cat 1. Road access was long ago terminated near sea level 5 km (3.1 miles) south of the location. For the installation of Cat 2, everything needed to be transported by helicopter.

The 76-mm (3-inch) steel-rope Cat 1 cables are essentially constructed from six 25-mm (1-inch) cables wound around an identical central cable. The Cat 2 design called for installing the large cables by tension stringing seven small cables anchor to anchor and bundling them in place into the large unit. The final configuration included four such cables, placed as pairs, each 57 mm (2.24 inches) in diameter. Each would be formed by bundling seven parallel cables, each 19 mm (0.75 inch) in diameter. Each pair of cables was set 1070 mm (42 inches) apart. All cables were continuous (no joints) between anchorages. Once anchorages were selected, the two cable pairs were calculated to be 1120 m (3675 ft) and 1333 m (4373 ft) in length.

This meant the fundamental design arrangement required installing 28 cables across the valley and bundling them into a Catenary. The weight of each cable on a reel was about 2700 kg (5952 lb), and the installation tension was about 2300 kg (5071 lb). The available heavy-lift helicopters would be capable of lifting these reels and the stringing equipment to install them. There would be no circuit outages during the Catenary assembly.

CONSTRUCTION

Fourteen cables spanned between anchors A and B (a northeast position to a southwest position). The other 14 cables spanned between anchors C and D (a northwest position to a southeast position). The longer C-D cables crossed over the A-B cables, forming an elongated X configuration. Anchors A and C on the east side of the line are about 300 m (984.25 ft) apart, and B and D anchors on the west side are about 120 m (394 ft) apart. All cables were brought together over the circuits to support a catwalk and helipad. The 142-m (466-ft) catwalk was made up of 28 aluminum frame panels, each 4.8 m (15.8 ft) in length. The catwalk and centrally positioned helipad are 152 m (499 ft) above the ground.

The everyday bare-wire weight of each of the six conductors suspended from Cat 2 is 10 tons. The design weight that can bring parts to the ultimate capacity is 75 tons each. The design cable tension for each of the four anchorages is the sum of the breaking strength of the attached cables: 476 tons. The rated strength of the aluminum conductor steel-reinforced (ACSR) Emu conductor is 68 tons. Since this is near the design strength of the suspension assemblies on the Catenary, the arrangement was configured to allow the assembly to support a broken-phase condition that involves considerable displacement along the line.

Detailed planning and scheduling for the 2008 construction window was completed by early March 2008 and a startup date of May 15, 2008, was set. Snow on the ground in this region begins to subside in early May, but avalanche activity remains common into mid-June, which means developing a work site before mid-May is basically an exercise in futility. Any work on or below most slopes requires snow slope management and having evacuation and rescue plans in place into mid-June.

KEYS TO SUCCESS

Allteck had a crew of about 14 — not the 200 count of that from the original Cat 1 installation — who lived 15 km (9.3 miles) from the site. Canadian Helicopters (Terrace, British Columbia) dedicated two A-Star helicopters to the project for daily transportation of people and smaller items to the site. The first of 28 cables was pulled on July 2. Access to the site up to that date had been 50%, well below what had been planned. It got worse. The second cable was pulled on July 8, and the final cable was pulled on July 30. Access in July averaged a miserable 34%.

Work crews began the R line outage on Aug. 29 in the pouring rain and hung that circuit from the Catenary for the winter. Then in June 2009, a smaller Allteck crew mobilized for a five- to six-week period to raise the L line to the Catenary. The project was 100% complete by July 20, 2009. It closed within 5% of budget and without a single reportable accident. There are now two large transmission line Catenary structures in the world.

Brian White was correct to say there was much to learn from that patch of transmission line. The lessons were learned and applied right there, 14 years after that initial visit. Three of the four engineers who participated in the Cat 2 project's engineering and construction management are well under 30 years old. They are each now armed with the knowledge that imagination, skill, good judgment and teamwork can conquer some amazing challenges.

Finally, the success of this once-in-a-lifetime challenge relied completely on a win-win, collaborative approach between all parties involved. Every person on site contributed to the planning with a look-ahead meeting held on a daily basis. This was the key to the project's success.

Peter Catchpole (pcatchpole@powereng.com) is a 1971 civil engineering graduate of Queen's University in Kingston, Ontario, Canada. He has been in the T&D business since 1977 and with POWER Engineers in Idaho since 1992. Prior to joining POWER, he was employed at Great Lakes Power and Ontario Hydro, now Hydro One, both in Ontario. He is a registered professional engineer.

John Rilkoff (jrilkoff@allteck.ca), an electrician by trade, has been with Rio Tinto Alcan Power Operations in Kitimat, British Columbia, Canada, since 1990. He is responsible for the facility's reservoir, generation site and transmission line maintenance.