Imagine a world where a new product is introduced that works so flawlessly, it can be used seamlessly in a third-generation application. Is this a dream world? Pie in the sky? Nothing ever works this well, especially in the harsh and unforgiving world of extra-high-voltage (EHV) transmission, right?
In this case, the product is a new three-phase bundle configuration for 765-kV transmission. In fact, it is the first six-wire bundle on an operating line in North America. American Electric Power's (AEP; Columbus, Ohio, U.S.) Wyoming-Jacksons Ferry line was energized in June 2006. This 90-mile (145-km) line, built almost entirely in the Appalachian Mountains, runs from the company's Wyoming station near Oceana, West Virginia, U.S., to its Jacksons Ferry station near the New River between Wytheville and Pulaski, Virginia, U.S.
This configuration will likely play a key role in an even more ambitious 550-mile (885-km) US$3 billion proposed transmission line project from West Virginia to New Jersey slated for completion in 2014.
To find out what's behind the enthusiasm for the new design, a little history is in order. Keep in mind that a smooth transition from four- to six-wire bundles would be a pleasant outcome for AEP. Its earlier advances in transmission technology typically required minor adjustments.
AEP announced its intent in 1990 to build a 765-kV line from West Virginia to Virginia. Routing would undergo considerable alteration during the permitting process. In early 1991, AEP assembled a team of five engineers and system planners to recommend the best new conductor bundle design at a reasonable cost for the proposed line, which would be constructed at an average elevation of 2500 ft (762 m) above sea level. Specifically, the team sought to find a solution to the problem of audible noise from existing four-wire bundle 765-kV lines in the low relative air density (thinner air) at higher elevations.
AEP had been monitoring its 765-kV lines since the first line was energized in 1969, largely from its mobile labs. In addition, AEP operated a monitoring station in the Blue Ridge Mountains near Floyd, Virginia, to record weather and electrical operating data on its Jacksons Ferry-Axton 765-kV line, which was built with 4-Dipper, 1351.5-kcmil cross-sectional area aluminum conductor steel reinforced (ACSR) 1.385-inch (35-mm) bundles and went on-line in 1985.
In addition to studying four to seven conductors per bundle, the AEP team evaluated six alternative conductor sizes — Grosbeak, Tern, Rail, Ortolan, Dipper and Lapwing — ranging from 636-kcmil to 1590-kcmil ACSR or 0.99-inch to 1.5-inch (25-mm to 38-mm) diameter, and four to seven conductors per bundle.
AEP determined that either 6-Tern, 795-kcmil ACSR 1.063-inch (27-mm) diameter or 5-Dipper bundles and phase spacing of 45 ft (14 m) would reduce noise by 4 to 5 dBA, compared with 4-Dipper, at the edge of a 200-ft (61-m)-wide right-of-way in foul weather. This would achieve the goal of 51 dBA at a right-of-way edge of 2500-ft (762 m) elevation in foul weather.
Cost was an important consideration for the five-person team in its analysis. Each of the two (6-Tern and 5-Dipper) prospective new designs would reduce line losses due to corona by almost 150 MWh/mile per year. While each new design would be more expensive than the existing four-wire system (greater operating efficiencies would offset much of the higher capital costs), the cost premium for 5-Dipper was about 2.5 times higher than the premium for 6-Tern.
So, the decision was made to go with the 6-Tern bundle because it met the noise goal, reduced line losses and was less expensive to build than its nearest competitor. Other study conclusions about 6-Tern included no corona in fair weather, significant improvements in radio interference (RI) and television interference (TVI), slightly increased ground-level electric field strengths, no change in magnetic fields, and comparable overvoltage and lightning performance, compared with 4-Dipper.
While 6-Tern construction costs were estimated to be about 6% higher than 4-Dipper, reduced line losses cut in half the additional construction costs.
Given the peripheral problems encountered with early operation of both 345-kV and 765-kV lines, AEP decided to install 6-Tern bundles in its operating 765-kV system, and observe and analyze its characteristics.
It just so happened that the 765-kV Blue Ridge monitoring station (see “AEP EHV Chronology” on page 32) was situated near five spans (1.1 miles [1.8 km]) between two dead-end towers, which is a perfect location for a six-wire demonstration project.
With the help of hardware, wire and spacer manufacturers, AEP installed 6-Tern bundles arranged in a 30-inch (760 mm)-diameter hexagonal design. At the Blue Ridge site the new conductors were even scrubbed of their manufacturing oils to speed the aging process.
To evaluate long-term corona performance, data on audible noise, radio interference, magnetic fields and weather were collected from January to December 1994. Voltage and power flow were also recorded.
“In conclusion, the results show that in rain an audible noise improvement of about 5 to 6 dBA over the 4-Dipper bundle was obtained for this new bundle design of 6-Tern conductors,” according to a June 1995 report on the Blue Ridge demonstration project. This section of 6-Tern line is still in operation today.
In both theory and practice at AEP and other utilities, the 6-Tern bundle appeared to be the answer. Confidence was further bolstered by experience in South Africa. Eskom, the South African electric utility, had installed almost 559 miles (900 km) of six-wire (Tern-equivalent) 765-kV transmission lines at 4921 ft (1500 m) above sea level from 1985 to 1990 and pronounced the new line's performance a success.
It had been almost 20 years since AEP built the first 765-kV line in the 20th century. In that time, the world of EHV transmission line design, procurement and construction had changed in many ways. Among the challenges AEP faced, and the subject of a future third and final article of this series (the first article appeared in the February 2006 issue), include the following items concerning the design and testing of materials and structures and, finally, the construction of the line itself:
The company's 765-kV family of towers had to be redesigned, or updated, to current detailing practices and to accommodate the new six-wire bundle.
The skyrocketing price of aluminum had eliminated this metal from consideration in specifying transmission towers. Virtually all of AEP's guyed-V towers in place are aluminum.
To augment its own internal talent and staff, AEP brought in consultants and partners to help design and test many new components.
Engineering and design computing software that had improved by leaps and bounds aided this effort.
In the field of transmission contractors, there was no longer one turnkey or go-to vendor. Also, in part due to the mountainous terrain, AEP decided to use separate contractors for right-of-way clearing, road construction and line construction.
AEP circled the globe, literally, to tap the design, testing and manufacturing capacity to make the line a reality.
Finally, gearing up for and constructing (right-of-way clearing began in December 2003) the 90-mile line through rugged mountains, dealing with severe side slopes, challenging access to tower sites and drenching winter storms, was an ordeal to test the hardiest soul.
Bruce Freimark, AEP principal engineer, has more than 38 years of experience with electric utilities, 32 of which have been with AEP. Since 1982 he has been responsible for maintaining AEP's transmission line design criteria for clearances and loadings. Freimark coordinates revisions to all standards related to transmission line design and materials. For this line, he was responsible for specifying and ordering all materials (excluding tower fabrication). He was also responsible for the design and testing of guy anchor hardware assemblies and the design and corona testing of insulator hardware assemblies. firstname.lastname@example.org
When American Electric Power decided in 1991 that its proposed 765-kV transmission line from West Virginia to Virginia would include the first six-wire bundles in North America, almost 50 years of engineering advances — rarely accomplished easily — were behind the decision. Following are some of AEP's transmission advances.
|1946||AEP's first extra-high-voltage (EHV) lab construction was started adjacent to the Tidd Plant near Steubenville, Ohio. AEP's highest voltage transmission lines operated at 138 kV at the time. Tidd lab voltages could be varied between 265 kV and an unheard of 532 kV. Higher-capacity lines were needed to accommodate the larger output of generating units, 150 MW during the 1940s.|
|1950||AEP concluded that 330 kV (later increased to 345 kV) was the optimal transmission voltage.|
|1953||The first 345-kV line went into service. Problems with audible noise and radio interference caused operating voltage reduction to the familiar 138 kV. Measures implemented included: strict conductor-handling guidelines being adopted and conductor size increased from a 1.6-inch to 1.75-inch (40.6-mm to 44.4-mm) diameter. Performance improved greatly after several years of weathering.|
|1958||The first section of bundled two-wire 345-kV lines went into service. Previously, all 345-kV lines had a single wire per phase. AEP built a total of about 3800 circuit miles (4830 km) of 345-kV lines.|
|1960||A larger transmission test lab at Apple Grove, West Virginia, replaced the Tidd operation. A five-year program was started to test voltages up to 775 kV and combinations of four-wire bundles.|
|1966||Based on this R&D and the need to accommodate 800-MW units, AEP announced it would build a new network — 1050 circuit miles (1658 km) in five states — of 765-kV transmission lines to overlay its existing grid. (The previous November, Hydro-Québec announced plans to build the world's first 735-kV line, which became Canada's Manic-Boucherville line, completed three years later.)|
|1969||Problems arose with corona-caused noise in wet conditions, especially at higher elevations. As a stopgap, new lines were operated at lower voltage while the conductors aged. The original 765-kV phase bundle consisted of four 1.165-inch (30-mm)-diameter Rail (954-kcmil ACSR) wires arranged in a square with sides of 18 inches (457 mm).|
|1972||AEP's originally proposed 1050-mile 765-kV system was essentially completed. The advent of 1300-MW generating units called for additional 765-kV lines.|
|1974||Subsequent 765-kV system expansion used larger 1.385-inch (35 mm) Dipper (1351.5-kcmil ACSR) conductors. This reduced noise and line losses.|
|1968 to 1987|
|These early 765-kV operational problems spawned five generations of mobile laboratories. Increasingly sophisticated data-gathering vans measured and recorded both corona and electromagnetic phenomena throughout the system.|
|1985||Completion of 20th century additions to AEP's 765-kV system: 24 years from planning to completion, 2022 miles (3254 km), 5300 steel towers, 2200 aluminum towers, 24,500 miles (39,429 km) of conductor and 2.5 million ceramic insulators.|
|1990||The need to reinforce the bulk transmission delivery system in southern West Virginia and southwest Virginia led to AEP's proposal to extend its 765-kV system from its Wyoming Station (Oceana, West Virginia) 110 miles (177 km) to its Cloverdale Station (Roanoke, Virginia).|
|1998||During regulatory proceedings in Virginia, however, the line's destination was changed to Jacksons Ferry Station. The West Virginia Public Service Commission approved the project.|
|2001||The Virginia State Corporation Commission issued its final order approving the project.|
|2002||The lead federal agency, the U.S. Forest Service, granted approval to construct the line.|
|2003 to 2004|
|Right-of-way clearing began in December 2003; tower foundation construction started in April 2004; and, the first tower was erected in August 2004.|
|2006||AEP's Wyoming-Jacksons Ferry 765-kV line was energized in June 2006, the first such line in North America with six-wire bundles. |
— Chronology supplied by AEP
|Elevation||Operation voltage on 765-kV base|
|(ft)||(m)||1.0 p.u. (dBA)||1.02 p.u. (dBA)||1.04 p.u. (dBA)|
Approximate foul-weather mean audible noise levels at the edge of a 200-ft (61-m)-wide right-of-way. (Note: Table shows noise levels as a function of elevation and operation voltages for 765-kV line using 6-Tern design.)
|Bundle diameter for 6-Tern||Audible noise reduction below 4-Dipper at 25.5-inch (648-mm) bundle diameter|
Audible noise reduction of various 6-Tern bundle diameters, compared with 4-Dipper at a 25.5-inch diameter.
You want to string and tension a six-wire bundle on your latest transmission line project. The device that does this is a tensioner. So you go to your local transmission line building supply store and find the tensioner aisle. There are single-, dual-, triple- and quad-conductor tensioners. But, the six-conductor version seems to be out of stock. No, a stock check reveals the store never ever had them. It's a special order item.
PAR Electrical Contractors (Kansas City, Missouri, U.S.), a division of Quanta Services, was in such a situation when it contacted Lloyd Morgan at Morpac Industries Inc. (Vancouver, Canada) regarding a six-conductor bundle tensioner for AEP's new 765-kV line. The good end to this story is that PAR ordered two machines, and Morgan designed, built and delivered the first unit in 120 days. But, there is, of course, more to the story.
Born in 1918 and still working every day, Lloyd Morgan started as a line contractor in 1956 and subsequently began developing his own line of high-quality line-stringing equipment. Early field experience led Morgan to an important realization: smaller line crews outfitted with the best tools and equipment resulted in safer, more cost-effective and productive line-stringing operations. Founded as Morgan Power Apparatus, and currently doing business as Morpac Industries Inc., the Morgan name has always been associated with state-of-the-art stringing equipment known for exceptional quality and ruggedness.
Morpac has built many tensioners over the decades ranging from one-wire to four-wire configurations, most of which are built to customers' specifications. Never having built a six-wire tensioner, this new design was loosely based on a tensioner that can be configured in several combinations of bullwheel sizes and bundle numbers. But, this machine required mostly custom parts to fit all six pairs of bullwheels and their associated hardware.
As with all Morgan equipment, this tensioner is equipped with both innovative and decades-old, time-tested features. Half of the bullwheels on the tensioner are tilted to allow the conductor to advance to the next groove on the straight bullwheels without having side load on the wire. The side load often generates a twisting force in the wire, which can eventually lead to failure of the pulling line or conductor if not dealt with properly.
The tensioner is also equipped with an ecologically friendly Cummins 130-hp engine. It is run during tensioning as a giant flywheel to eliminate wire oscillations during the stringing operation. It also allows the tensioners to be used for sagging up to 20,000 lbs per wire.
Providing the tensioning force to Morpac's tensioners is a huge water-cooled brake manufactured by Eaton (Cleveland, Ohio). The coolant runs through a gigantic twin-core radiator capable of expelling up to 540 hp worth of heat in the harshest conditions. This brake has a fine and coarse adjustment and each conductor is individually controlled via its own clutch.
Each drive bullwheel has its own expanding-bladder clutch, which allows it to be operated independently for operations such as sagging, leveling the running board while tensioning or steering the running board through angle towers. This clutch, measuring 20.25 inches (51 cm) in diameter and 7 inches (17 cm) wide, was originally developed by B.F. Goodrich for the U.S. Air Force as aircraft wheel brakes, but is now manufactured in-house. Morpac has been using this device as a clutch and brake on reel stands successfully for decades, and has found that the 445 sq inches (2871 sq cm) of braking surface area provides exceptionally smooth conductor payout.
These features are common among many of Morpac's machines and are why many of its machines are still in use after more than 40 years of service. Morpac Industries has, in the decades it's been in business, branched out into other markets, but its core business and the bailiwick of founder has always been high-quality line-stringing equipment.