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Transmission |
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| Electricity is delivered to homes, schools, hospitals, businesses and industries through an integrated system of generating plants, power lines and substations. Transmission lines, which consist of heavy cables strung between tall towers, carry power from where it is generated to areas where it is needed. The transmission network allows the movement of large amounts of power to travel long distances. | |
TRANSMISSION, SUBSTATIONS AND TELECOMMUNICATION |
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| PPC has entered into extensive partnerships with a view to discovering more efficient means of power transport. The company now has the capacity to own and operate a vast network of transmission facilities that can interconnect Nigeria’s power grids, including 500-kilovolt long-distance transmission lines, AC and DC and 50-60 Hz frequency converter stations. | |
| For telemetering, telecontrolling, and daily operations, PPC currently operates telecommunication facilities by use of optical fiber, microwave and power line carrier of its own design. This will contribute to the reliable and efficient operation of the country's power system and power stations through integrated SCADA systems. As part of our turnkey solution offerings, PPC also provides a unique, high-performance power system analysis program, and a comprehensive power development planning program that allows for high-grade analyses. In all of its nationwide power development projects, PPC has been extending consulting services in planning, design and implementation to form efficient power system networks. Besides, the company also provides the same services on power system formation projects; among such projects is the project interconnecting the networks of the National Integrated Power Projects (NIPP). |
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TRANSMISSION STRUCTURES |
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| PPC employs many different types of transmission line structures (towers, poles) for its project implementations. Many of the country’s transmission lines were built during the 1960s and 19670s, when the common structure design was self-supporting steel lattice towers. The lattice structure is very strong, relatively light and could be erected without the need for heavy equipment and major access roads. However, they take a lot of time to design and build. The base foundations require a large area of land on which to stand, which often interferes with agriculture. | |
 Lattice-style transmission structures, although still in operation today, are generally not used in most of new construction |
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| Today, we use a variety of tower and structure designs that are considered more aesthetically acceptable and leave a smaller footprint. We use both wood and steel structures depending on the conditions of the land and surrounding areas, the height needed for the poles, the price of steel and other factors, such as: | |
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| The land the transmission lines will cross is considered during the planning phase along with legal restrictions (such as zoning and land-use regulations) and the appearance of the structures. The width of a right-of-way depends on the voltage of the line and the height of the structures, but can be 75-150 feet or more depending on the type of facilities. Special consideration is given to the impact the transmission line and construction will have on native vegetation and the environment. | |
Double-circuit, 138-kilovolt transmission line built on wood structures |
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| Local electric distribution lines, cable and telephone lines are sometimes carried on the same structures to make efficient use of space. Taller poles are needed to do this. |  |
| Double-circuit, 138-kilovolt line build on galvanized steel poles | |
| This type of design is often used when the line will carry heavy electric loads. Higher voltage lines require taller poles-sometime 100 feet or more. |  |
| 138-kilovolt single-circuit line on weathering steel | |
| This type of maintenance-free structure will weather (rust) over time to give the appearance of wood and is generally used in wooded areas. |  |
| H-frame wood structure | |
| This type of design allows for shorter spans (the distance between structures.) In general the height of the structures is less than single pole structures. |  |
| Double-circuit 138-kilovolt steel lattice tower | |
| Transmission structures of this design are no longer used for new construction. However, ATC operates many lines on lattice towers. |  |
| 138-kilovolt steel H-frame | |
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| 345-kilovolt, double-circuit on single poles | |
| Higher voltage lines require taller poles and wider rights-of-way. |  |
Wires |
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The wires (conductors) used in large transmission lines are mainly aluminum. Aluminum has replaced copper lines, because of the lower cost and lighter weight. A single-circuit transmission line will have three wires (conductors); a double-circuit line will have six wires. An additional wire (or two), called a shield wire is connected directly to the transmission line towers at the top to protect the main conductors (wires) from a direct lightning strike. If lightning strikes it will hit the shield Transmission lines are connected to the towers by insulators that are usually made of porcelain. They must be strong enough to support the weight of the transmission lines while preventing a contact between the wires and the tower. Contact between the two would cause a short circuit and disrupt supply. |
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