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GIS application for power transmission line siting:
An illustrative case

Tyeb Pervaiz
GIS Development

Analyses such as the selection of suitable areas, the optimum path finding, the profile analyses, the engineering design of towers and wires, and the cost estimation can be done using GIS.

Analyses such as the selection of suitable areas, the optimum path finding, the profile analyses, the engineering design of towers and wires, and the cost estimation can be done using GIS.

In the last few decades, the electric power industries have been developing power transmission systems to follow up with the rapid growth of the power demand. On the other hand, the suitable site for new transmission lines has been getting restricted, because of development of rural areas and the growing concern over environmental issues. Analyses such as the selection of suitable areas, the optimum path finding, the profile analyses, the engineering design of towers and wires, and the cost estimation can be done using GIS. This will help planners and engineers in the environmental and engineering analyses for transmission line siting.

Application System
In general, the process of the planning and design of transmission lines consists of the following 5 phases.

• Planning: The master guidelines of route constructions are settled based on the long-range power supply plan. The outline is determined for each transmission line planned, which includes voltage, number of lines, starting and ending substations.
• Survey: Information about natural environment, geological features, local communities and regulations in the area of interest etc. is collected in this phase and several alternative routes are compared in terms of environmental impact, technical issues and cost of construction.
• Basic Route: Basic route is determined by the position of each tower along the proposed routes and interference of radio wave caused by the transmission line is estimated. All this is done using a medium scale toposheet.
• Detailed Route: A photogrammetric surveying is performed along the basic route. Based on the results, the detailed position of each tower is determined in the large scale (1:2,000) . And engineering design process follows, which includes the determination of tower type, tower height and supporting devices, and the cost estimation.
• Route for Implementation: In this phase, the detailed field surveying is performed along the determined route. The towers, wires and basement of towers are designed.

The computer system developed here supports phase 1 to 4, and consists of 5 subsystems. Figure 1 shows the outline of the system



Each project execution components has been described below:

Data Entry System This system installs, checks and edits the geographical database used in all other subsystems. The database includes Topographical Maps in 1:50,000 (raster images), Environmental Information (Coverages), Land Information Database (Governmental boundaries, roads, railroads, rivers, lakes (coverages), altitude (GRID), Photogrammetric Maps in 1:2,000 scale (raster images), DTM (GRID) etc.

Route Zone Evaluation Supporting System The purpose of this subsystem is to select the zone, called the "route zone", which is considered suitable for a transmission line in terms of environmental impact and regulations. The route zone is determined in the medium scale of about 1:50,000.

The functions of this system are:

• Display and plot environmental database
• Create the optimum route
• Create suitability map
• Create aerial view
• Estimate the construction cost

Basic Route Evaluation Supporting System The position of each tower is determined interactively referencing the topographical maps, the suitability maps and the optimum route computed above. Figure 2 displays the functions of the subsystem.



Detailed Route Evaluation Supporting System Once the basic route is determined, the photogrammetric surveying is performed along the route to make planimetric, topographic maps, and DTMs in the large scale of 1:2,000. Based on the database, the detailed position of each tower is determined. Furthermore, the system has various functions to perform the engineering analyses. Figure 3 shows the functions of this subsystem.

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