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.

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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. bfreimark@aep.com