A recent project at Georgia Power, Atlanta, Georgia, U.S., called for upgrading a portion of its system outside of Savannah. The US$3 million job involved adding a new substation and re-conductoring transmission lines from 46 kV to 115 kV. With the increased voltage, the 60 ft (18.3 m) wooden poles needed to be changed to taller concrete ones. The new poles had to be 80 ft to 100 ft (24 m to 30.5 m) high near the power source and 100 ft to 125 ft (30.5 m to 38 m) as the lines were run near a residential area. In all, 100 wooden poles needed to be replaced.
Compicating the job was that a major portion of the pole setting and reconductoring was to be done along a 12-mile (19.3-km) stretch of a busy Georgia state highway. Setting the new poles and pulling cable using the traditional method would have required blocking one or more lanes of the highway over a long period of time. There also would have been extra costs to hire flaggers to control the traffic, increased hazards to ground personnel working along a heavily traveled road and antagonized motorists slowed by the work. Georgia Power rented a Bronto S180 HDT from United Rentals. The Bronto S180 HDT has two features that made it the right choice for the Savannah job-the unit could be "short-jacked" so as not to block traffic, and the boom could be telescoped directly to the overhead work.
The short jacking capability of the Bronto S180 HDT meant that the boom could be rotated and telescoped safely on one side of the truck with the stabilizing outriggers fully extended on the operational side only. Although outriggers were deployed and positioned on the opposite side, they were not extended onto the berm and the opposite side outriggers set up on the shoulder.
The overhang formed by most articulated booms as they are raised would have created another problem on the Savannah job. An articulated boom's "elbow" overhangs the trailer on the opposite side of where the platform is located and in this case, would have extended over traffic lanes. Because the S180 HDT is a straight boom, it can be moved directly to the work area from one side with no overhanging elbow on the opposite side to restrict traffic.
The S180 HDT features platform capacity of 1000 lb (453.6 kg) so Georgia Power could use it to lift both the new cable and the lineman in a single operation. This procedure saved them from having to use an additional crane to lift the cable as it was being attached to the new poles.
Although hampered by bad weather, the crew on the job averaged three poles a day and feels that four poles is a reasonable objective once they have additional experience with the Bronto.
ETECEN Brushes Its Conductors Clean The Peruvian electric utility, Empresa de Transmision Electrica Centro Norte S.A. (ETECEN), operates a 220-kV transmission system that is 1600 km (994.4 miles) long and occupies a 10-km (6.2-mile) wide strip along the Pacific coast. Recently the utility noticed a thin layer of vegetation was accumulating on its lines along with clay, sand and salt deposits. This phenomenon, which causes partial discharges through the corona effect, has led to substantial system losses. A study by the Quebec engineering firm Dessau established that over a 200-km (124-mile) section of line, losses have increased 10 to 12 times since the transmission system was built.
In an effort to resolve the problem, ETECEN requested robotic experts from Hydro-Quebec's IREQ division to develop a device to clean the conductors and remove the contaminants from the lines. The project consisted of designing, manufacturing and testing a cleaning device that could be operated from the ground using a pulling rope. The unit was field tested as part of a testing program conducted in Peru.
The sturdy device weighs 9 kg (19 lb) and consists of two five-brush units (arranged on two levels) set up to clean the conductor twice at each run. Each brush is mounted on a suspension system that allows the device to cross over joints and adapt to any diameter changes on the line. The device is suitable for conductors that are 2 cm to 3.5 cm (.7 inches to 1.4 inches) in diameter. The device is symmetrical and bi-directional, which is crucial for simplifying the operator's work and optimizing the cleaning process.
SRP Benefits from New GIS-Enabled Software The Salt River Project (SRP), Phoenix, Arizona, U.S., realized a need for a geographic information systems (GIS) enabled application to streamline the process of inspecting and maintaining electric power lines. The Transmission Line Asset Management Program (TLAMP) software, developed for SRP by ActiveG and Boers Engineering, integrates field inspection records, computerized maintenance management systems (CMMS) and facility asset data to improve system reliability and safety at lower costs.
TLAMP's field inspection application uses a series of expandable drop-down menus providing thousands of inspection record combinations. The menus were designed around basic RCM philosophies of identifying components, monitoring conditions and prioritizing repairs based on the probability and severity of failure in terms of system reliability, public safety and costs. The final step in recording each condition is to assign it to the appropriate party responsible for providing corrective action. TLAMP's recording application is fast enough to use during aerial patrol inspections, yet detailed enough to capture comprehensive ground patrol inspection results. Connected to a GPS unit, TLAMP plots the path of the inspection vehicle on its Line Route map, expediting inspection patrols and improving data integrity.
TLAMP's Asset Record screen provides field personnel with remote access to the transmission line details required to efficiently plan and execute repairs. TLAMP provides convenient access to photographs, drawings and scanned material lists. The relational database model is designed to efficiently handle the complexities of multiple circuits on shared structures. TLA MP's Line Route screen displays geographic features imported from the customer's GIS application, including ArcView, MapInfo and Smallworld. From the Line Route screen, selected attribute data is instantaneously displayed as the cursor touches each of the plotted features such as circuits, structures, substations and access roads.
TLAMP's Work Order Management application automates the process of generating, updating and tracking work orders through the customer's CMMS using data that was originally captured in the field. TLAMP has built-in criteria selection features that batch work by circuit, priority and responsibility. As work progresses, the status, field repairs and cost data are retrieved from the CMMS, automatically updating inspection records accordingly. TLAMP's GIS map can also be used to monitor progress, ensuring that prioritized items are repaired in a timely manner.
Omaha Utility Approves Aerial Cable System In December 1996, Omaha Public Power District, Omaha, Nebraska, U.S., installed and energized the first 69-kV Aerial Spacer Cable system developed in cooperation with Hendrix Wire and Cable. The system has not had any outages, and its components have operated without mechanical failure.
The close phase spacing of Aerial Spacer Cable conductors minimize the right-of-way required for necessary clearances. Reliability and quality of service are enhanced by precluding fault current flow due to momentary, and to some degree sustained, contact with trees or other objects contacting the heavily covered phase conductors.
The spacer is a critical component in the reliable mechanical and electrical performance of the system. A complete spacer is a multi-component assembly consisting of: the injection molded high density polyethylene structural members that are joined using glass filled nylon bolts; three ethylene propylene dimonomer ring ties for securing the phase conductors in the spacer; and an aluminum suspension clamp used to attach the assembled spacer to the messenger. The spacer was molded using the same material that was used to extrude the outer aerial cable layer. Using the same compound for both the cable "jacket" and the spacers assures that the dielectric constant of the contacting surfaces is equal and thereby prevents degradation of the cable covering through corona cutting.
The 69-kV aerial spacer has the same triangular phase configuration that has been used at distribution voltages. This configuration offers a significant reduction, over bare overhead conductors, in the magnetic field strength at ground level, provides a rigid mechanical structure to withstand short circuit forces and ensures that all three phases fall within the 30 deg shield angle provided by the messenger.
The 26-inch (66-cm) phase separation was selected to balance impulse withstand values, surface charging current and flashover characteristics with the required mechanical properties.
The final component in the aerial spacer assembly is the ring tie. Compression molded using a UV stabilized EPDM, the ring tie was designed to provide a balance of tensile strength and elongation to handle the 30 kA short circuit forces anticipated at this transmission level.
The reliable operation of the Omaha Power District circuit coupled with the performance of the cable design and spacers in laboratory testing indicate a viable 69-kV spacer cable system has been developed.
Bracelet Is More Than a Fashion Statement Specialists from Hydro-Quebec's IREQ division have developed a low-cost device for quick detection of defective synthetic insulators. The detector is constructed in the shape of a bracelet and consists of two nickel plated steel half-circles, around which a warning flag is wound. The bracelet is attached as closely as possible to the upper end of the extension rod, which connects the insulator to the support structure so that it hugs the rod once it has been closed and forms a magnetic circuit with an air gap.
The bracelet operates as follows: in a power leakage, a current surge flows through the rod (i.e., inside the bracelet) creating a magnetic pull that is capable of reducing the air gap to almost zero. As soon as the power leakage reaches 1000 A, the bracelet is unlatched and the warning flag attached to the device becomes visible. The warning flag allows the defective insulator to be rapidly located.
The device was designed for 735-kV transmission lines so that it triggers more quickly than protection relays (i.e., at less than two cycles). However, the device can be modified to meet the requirements of systems operating at lower voltages.
Hydro-Quebec installed 50 devices on its 765-kV transmission system in 1996-97. The devices have performed as expected and there have been no false alarms. Other utilities that have expressed interest in the device include Electricite de France, New Brunswick's electric utility and Florida Power & Light.
ABB Develops Dry-Type Power Transformer Developed by ABB, the Dryformer is a completely oil-free, dry-type power transformer.
The Dryformer has windings of cross-linked polyethylene with cylindrical conductors. The conductors have a uniformly distributed electrical field, which the insulating plastic sheath contains within the cable. However, the cable layers do not obstruct the magnetic field, which is the basis of the transformer's function.
The new oil-free insulation technology also gives a higher level of safety. The risk of breakdowns, fires and explosions is much less, as is also the case with the environmental risks. The new transformer in principle can be installed anywhere, such as close to sensitive lakes and rivers, in underground caverns or in densely populated areas. This is due both to the absence of oil and to the ability of the cable to contain the electrical field inside it.
The transformer is air cooled using fans.