Using GIS for Efficient Transmission Line Siting

By Barbara Shields, ESRI

Power companies have a new tool for approaching the challenges of transmission line siting. Public web map services such as Google Earth and Yahoo! Maps have made basic mapping functionality and common data layers available to practically everybody who connects to the Internet. However, more sophisticated geographic information system (GIS) technology enhances the methods electricity providers use to consider variables in their line siting processes and is a means for accessing and sharing related geographic data throughout their companies.

Click here to enlarge image

Server technology and lightweight online GIS services allow users to bring in a wide variety of data sources and to examine all types of data relationships associated with transmission line siting tasks. Moreover, GIS continues to benefit these projects by providing a framework for modeling, line siting, land management, job tracking, and, in fact, all phases of transmission line management.

Modern online GIS capabilities set the stage for a new perspective, a change of mindset, about bringing web map services into the corporate environment. GIS server technology allows developers to easily design executive dashboards for management that allow uncomplicated data access. Data consumers can visualize up-to-date infrastructure data, load management, power demand, outage information, land leases, schematics and more, which helps them quickly identify network efficiencies and opportunities for transmission line expansion.

PNM system engineers develop potential transmission routes using a statewide least-cost path model. The user inputs the start and end points, and the model creates the route, taking into consideration predefined criteria such as land status, terrain, environmentally and culturally sensitive areas, and existing utility infrastructure.Click here to enlarge image

Public Service Company of New Mexico (PNM) has vast data resources that it draws on for its transmission siting projects. These include USGS TOPOs, DOQQs, high-resolution aerial photography, satellite data, digital elevation models, hillshades and georeferenced scans. Combining these image layers, engineers can assess land contours and model various corridor scenarios. PNM worked with POWER Engineers Inc. to develop and implement eTAMIS, an online software application built on ESRI’s ArcGIS platform that supports high-voltage transmission line facilities management. This online application can either be connected to the network in the office or disconnected in the field. It includes real-time routing and tracking, online analysis of structure information, a fault location tool, integration of several layers of base information, an inspection and maintenance module, and report functionality. The eTAMIS application also can display current environmental and landowner (right-of-way) data.

Now, PNM is creating GIS models for engineers to create a “first guess” route for transmission line siting, which considers a host of criteria. Michael Prescott is an environmental scientist at PNM who is using ArcGIS Spatial Analyst to build a least-cost path model for the project. He explains, “Engineers can enter the start and end points for a transmission line. The model considers important variables and then automatically generates on a map the power line information. Criteria for guiding the line recommendation include data layers for federal land, open areas, water, current utility corridors, new utilities near existing lines and terrain. The model minimizes the footprint the transmission corridor makes on the land and values cultural consideration such as federally protected lands and Native American pueblos.”

Bonneville Power Administration (BPA) uses web-accessible GIS applications to manage a database that contains data on more than 800,000 transmission towers. BPA’s developers designed an Internet tool for viewing its geographic transmission data. TView2, built using ESRI’s Internet mapping software ArcIMS, allows personnel to access and display asset data such as tower location, a line’s operating name, tower type and the conductor elevation attachment point. The map displays a network representation, and the identifier tool indicates the assets on a specific tower. Users can search layers such as roads and rivers, service area boundaries of cooperatives and public utility districts, land ownership, and threatened and endangered species data.

The same data used for monitoring the transmission system can also be applied to best site analysis for building the transmission system. Therefore, BPA created the Transmission Business Line (TBL) tool, which interacts with GIS for a variety of uses including siting transmission lines and facilities. The GIS group also designed a tool called the Internet Mapping Framework (IFM) that works in conjunction with ArcIMS, making it possible for developers to quickly build Web-based applications in-house. IFM helps designers add functionality and data layers to applications for specific work tasks. The framework concept allows the developer to use XML code to quickly change the buttons and the layers available within the application.

PJM Interconnection puts GIS to work in planning enhancements to its system. Its generating units, transmission lines and substations are an integrated, highly reliable network. In a complex network, however, any change can affect other locations in the system. A change in the schedule for interconnecting a new power plant, for instance, can require changes in a distant substation. PJM monitors and manages more than 325 generator, substation and transmission projects. Projects are coordinated through the use of multiple databases accessible via the corporate intranet.

PJM transmission map shows transmission line coded by kilovolt. Elevation hill shading enhances topography presentation.Click here to enlarge image

GIS aids PJM’s regional transmission expansion planning process by allowing engineers to create visualizations of planned structures so they can see the effects that changes in construction and scheduling will have. It links data regarding major milestones for generator, substation and transmission line construction to spatial data. This type of data visualization allows PJM to make more informed and timely decisions, anticipate bottlenecks and plan for future needs. Instead of independently studying multiple spreadsheets and computer-generated drawings, PJM takes a geographic approach to accessing information. Using a linked map, users can access project data, such as status, digital photographs and business enterprise data. Users can drill down to detailed substation and transmission maps including individual substation diagrams.

PJM’s GIS allows engineers to see geographic relationships between electric transmission facilities spread over its entire footprint. It is streamlining analysis, increasing organizational GIS involvement, and increasing flexibility in the knowledge and decision areas GIS supports. The GIS-produced maps are modified automatically when the project manager’s work plans or other databases are updated.

GIS 3D modeling helped GTC obtain permission from the U.S. Forest Service for a power line. Image provided courtesy of Photo Science.Click here to enlarge image

The widely used EPRI-GTC Siting Methodology designed by the Electric Power Research Institute is being used by Georgia Transmission Corporation (GTC), a not-for-profit cooperative. The power corporation is using an extension to ArcGIS designed by Photo Science called Corridor Analyst 9. This software supports each step of the siting methodology’s rigorous procedures for documenting and consistently applying planning assumptions, evaluation criteria and decisions. GIS successfully integrates with the method for analyzing the factors of suitability surfaces for natural, engineering and man-made conditions. It is used to map all geographic features within an area of interest and offers visualization of corridor options.

The selection process uses ArcGIS to identify macro corridors, define the project area boundaries, identify the alternative corridors within the macro corridors, and select a preferred route. The software maps all geographic features in a study area and assigns numerical suitability values to all features. Features such as open land, agriculture and wetlands are ranked from 1 (most suitable) to 9 (least suitable). Using the cell values, a computer algorithm calculates optimal paths for three types of suitability surfaces: locating with existing transmission lines, locating with existing road rights of way, and crossing less developed areas. The optimal paths identified are called macro corridors. The model creates reports that include maps, applied criteria descriptions and cost implications. Ranks and weights are calculated for each alternative, and the siting team ranks each alternative route.

GIS representation of best route for transmission line. Image provided courtesy of Photo Science.Click here to enlarge image

The ArcGIS desktop transmission siting processing is intensive, but once the maps are authored they can be served to others in the company via a viewing tool called GTCView 02. The web application provides browser-based user access to information.

Integration of GTC’s GIS and the existing corporate database into a common application interface increases the practical use of information across the organization. This means teams throughout the company can use the GIS-based siting model for their work as well, including those working in engineering, land acquisition and environmental departments. Because of this online access to geographic data, GTC employees are beginning to think more spatially than they once did and applying corporate data in new ways.

Barbara Shields is a writer for ESRI and specializes in GIS for natural resources. She is editor of Petroleum GIS Perspectives, Energy Currents, and Environmental Matters.

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