|TOWER TOTER Helicopters are setting 40% of Path 15s structures.|
Relief is in sight for one notorious electric-transmission bottleneck. Steel-lattice towers and poles are rising this month in rugged, remote terrain for a $306-million expansion of Path 15 in central California.
When energized this fall, a new 500-kv line will increase Path 15s capacity from 3,900 Mw to 5,400 Mw, expediting electricity transfers along an 84-mile stretch where three lines now narrow to two. The upgrade is led by an innovative public-private partnership of Trans-Elect Inc., Reston, Va., which is providing most of the financing; Pacific Gas & Electric Inc., a San Francisco-based utility; and the Western Area Power Administration, a Salt Lake City-based U.S. Dept. of Energy agency (ENR 9/29/03 p. 17).
Located some 1,500 to 2,000 ft west of two existing lines in the San Joaquin Valley, the upgrades centerpiece will be an 84-mile line extending from PG&Es Los Banos substation, near Los Banos in Merced County, southeast to its Gates substation near Coalinga in Fresno County. Maslonka & Associates Inc., the projects design-build contractor, is erecting 246 steel-lattice towers and 98 steel poles and stringing the transmission line.
"This is probably some of the most difficult construction that weve run into," says Doug Larson, WAPA civil engineering manager. Mesa, Ariz.-based Maslonka has built or improved over 100 miles of access roads. Access is particularly challenging in one 12-mile leg characterized by steep, eroded hills. A typical spur for a tower site might be 20 ft wide with a 300-ft sheer drop, says Larson.
Maslonka fast-tracked construction, ordering the 100-ft to 160-ft-tall towers before completing foundation design. For optimum production, two concrete batch plants leapfrog down the line, one supplying foundation pours while the other moves. Within 90 days of concrete placement, "were flying steel towers in with the helicopter," reports Martin J. Maslonka, president.
All steel poles and 40% of the towers are too heavy to be flown in. They are being erected instead by a half-dozen all-terrain cranes with up to 200-ton capacity, aided by 25 smaller cranes and winch-equipped bulldozers, Maslonka says.
In the northern five to six miles of the route, WAPA specified steel poles instead of towers to protect endangered wildlife species. Ranging in height from 127 ft to 207 ft, the poles are fitted with 17-in.-tall black polyethylene cones to prevent birds of prey from perching and hunting, says Ross Clark, WAPA electrical engineering manager.
For the 500-kv line, the agency selected standard aluminum conductor, steel-reinforced, in a triangular bundle. "On a project of this size, you want to use proven products that you know are going to last," says Clark.
Kansas City-based Burns & McDonnell is upgrading PG&Es Gates and Los Banos substations. Burns & McDonnell is installing two 500-kv circuit breakers at Gates and 250 megavars of 230-kv shunt capacitors at Gates and Los Banos and modifying Gates 500-kv bus to a breaker-and-a-half design.
PG&E crews are reconfiguring and reinforcing two 230-kv lines "to avoid overloading them in case outage occurs at peak load," says Kevin Dasso, PG&E director of electrical engineering. Some 40 miles south of Gates, PG&E is augmenting foundations to raise about 100 towers an average of 10 ft to 15 ft to offset additional line sag expected from higher loads and higher temperatures, says Dasso.