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In the long-range planning of electric substation and distribution facilities, a long-range load forecast and a plan for future distribution substation locations and capacity are developed. Corresponding plans for transmission and distribution lines are also prepared. Future substation sites, additional capacity at existing substation sites, transmission rights-of-way, and preliminary feeder costing can be developed, providing a blueprint for an organization to conduct its short-range planning and budgeting process. It is common for long-range plans to begin 5 years into the future and extend to 15 to 20 years in time.

Benefits of long-range planning include:

• Land acquisition for new substations before an area becomes developed. Land can be obtained before the market price of the land escalates as development increases. Substation siting is also facilitated if it is done before the area becomes saturated with development.
• Improved transmission planning, especially right-of-way acquisition
• Selection of best locations for substations from an electrical standpoint, including fewer losses, less distribution voltage problems, and improved reliability
• A coherent blueprint of how the power delivery system will evolve
• A planning process in which inputs from distribution, substation, and transmission personnel are obtained
• Documentation and results from a rigorous planning process that can be shared and defended with customers, government planning agencies, and regulatory authorities

Power delivery organizations face two primary difficulties in developing comprehensive long-range plans. First, in many organizations resources are focused on short-range planning and day-to-day operations of the system. This leaves very little or no time to develop a sound long-range plan. Second, long-range planning utilizes different methods than short-range planning. For example, an area distribution engineer may have local knowledge of how an area will develop in the next 1 – 2 years, which may be instrumental for short-range planning. However, projection of how an area will grow over a longer time frame, say 10 – 15 years into the future, requires different data and methodologies that go beyond what can be seen in the next two years.

In many cases, thorough long-range planning doesn’t get done. At the least, the resulting system is not cost-optimal, but in many cases the consequences are more severe. A reactionary budgeting process develops in which power delivery facilities are energized either at the last minute or after system operating problems have already occurred. Employees in different departments can have different perspectives about the planned long-range development of the system. The result can be additional expedited design and construction costs, additional stress on employees responsible for the system, and sometimes poor public image.

The maturing of Geographic Information Systems (GIS), especially the increased availability of GIS data and information required for long-range planning, has made it easier to develop long-range electric load forecasts and power delivery plans. Organizations can now get the benefits of long-range planning at a fraction of the effort that it used to take.

Using GIS in Long-Range Planning

Future electric load growth, and distribution facilities to serve that load, is heavily dependent upon geographic features in a particular area. Features that influence future electric growth include the presence of major highways, interstates, intersections, roadways, bodies of water, zoning restrictions, and proximity to existing load of various types. GIS provides an excellent platform to obtain and analyze the geographic features on an area.

GIS has become a more accepted technology over the past 20 years, and is used by many government agencies and utilities. Today, there are many sources of GIS data, including city/county governments and their planning agencies, as well as private database providers. Internet map providers such as GoogleTM illustrate the availability of map and satellite imagery (although its data is not typically used in commercial planning studies). The increased availability of GIS data facilitates the production of long-range peak load forecasts that is dependent upon the geographic development in an area, and enables the planner to evaluate different power delivery alternatives from a geographic perspective.

Typical GIS Data That is Used

Some of the GIS data and maps that are typically used in the development of an electric distribution long-range plan includes:

• Transportation infrastructure, such as interstates, roadways, and railroads.
• Tax maps or land-use maps, indicating the present use of developed land.
• Zoning maps or maps showing the projected land-use upon ultimate build-out of the land
• Planned developments of major roads, beltlines, or other developments (such as airports or major employment centers)
• Maps of undevelopable land, such as bodies of water, wetlands, state or national parks, etc.
• Transmission and distribution maps, showing present locations of lines and substations

This data is typically organized into separate maps or layers in the GIS. Local government planning offices often maintain GIS databases, and are often willing to share or sell access rights for a nominal fee.

The maps provide a planner with a geographic model of both the present and future development in the area. Figure 1 contains land-use maps for a small portion of a fast-growing metropolitan area, in the present year (Year 1) and 15 years into the future. In addition to the load-bearing land-use types, major roadways, vacant land available for development, and vacant land unavailable for development are also represented.

Figure 1 – Land-Use Maps for a Small Area of a Fast-Growing Metropolitan Area

Historic Peak Load Data

Collecting and using present peak load data is an important step in developing the model. In the geographic model, a reasonable estimate of spatial load density is needed for each customer class, such as peak kVA/acre. Using load data from the area under study, as opposed to load data from another area or system, is preferred. Some power delivery organizations still maintain customer load research groups which can provide typical peak kVA per customer, as well as typical customer daily load profiles. In other cases, it is possible to estimate peak kVA per acre using historic feeder loading information from SCADA history on feeders that are predominantly one customer type.

The peak load density for each customer type can be applied to the GIS maps of present land use to obtain preliminary load density maps for the area. Calibration is then typically performed to improve the accuracy of the load density maps. Historic substation loading information can be used to adjust the load densities in each substation area. Further calibration and refining can be performed using data from TLM (Transformer Load Management) or AMI (Automated Meter Infrastructure) systems. These methods provide an additional way to insure the loads in the GIS model are as close as possible to the most recent actual loading data.

The Long-Range Electric Load Forecast

There are two ways to develop the long-range electric load forecast in the GIS. One way is to utilize an algorithm which simulates the development of land and the subsequent electric load growth with time. One advantage in such an algorithm is that a geographic representation of peak load is provided over time, making it easier to stage a power delivery infrastructure plan in future years. A second way is to manually develop a representation of the ultimate land use and load densities in the planning area. This does not require as much effort at the first method, but it does not provide a representation of load growth as a function of time.

The Long-Range Power Delivery Plan

Because the GIS maps contain a geographic representation of the load, it is possible to perform mathematical operations on the peak load in the GIS in developing the electric facility plans. For example, a new substation should be located as close as possible to the “center-of-mass” for the electric load that it will serve. The electric load center-of-mass can be calculated within the GIS for each substation area. The GIS enables planners to try different combinations of substations and substation boundaries, while trying to locate the substation as close as possible to the electric center of mass for each substation.

In many cases, the goal of power delivery infrastructure planning is to minimize system total owning costs while meeting system performance criteria. System total owning costs include transmission, substation, and distribution costs. Utilizing GIS facilitates the calculation of transmission costs, since the lengths of future transmission rights-of-way or line upgrades can be calculated directly. Additionally, GIS can be used to estimate future distribution feeder system costs. Mathematical models of distribution feeders can be developed, or projected feeder routes can be developed with accompanying cost estimates. Various scenarios of new transmission lines and transmission upgrades, substation siting and upgrades, and feeder systems can be developed and evaluated in the GIS to determine the most suitable long-range plan. Figure 2 is a depiction of substation locations and service areas in a GIS planning tool, with the substation locations indicated by the boxes.

Figure 2 – Substation Locations and Substation Service Areas Displayed in GIS

Summary: Using GIS in Long-Range Planning

There are many benefits to long-range planning of power delivery systems: acquiring land for substations and rights-of-way before it gets too expensive; identifying best locations for substations from an electrical standpoint; performing a planning process in which inputs from distribution, substation, and transmission personnel are all obtained; and having a defensible blueprint of how the system will evolve.

Long-range power delivery planning is geographically-based, and is highly dependent upon future land usage driven by the characteristics of present land use, future roads, other planned transportation infrastructure such as regional rail, future major developments such as large employment or entertainment centers, and zoning restrictions. GIS is the best platform for representing such data and evaluating various long-range plans. GIS data and information are much more available than they were in the past. GIS technology provides power delivery organizations a way to develop comprehensive long-range facility plans while expending minimal amounts of effort.