THE ASSET MANAGEMENT INFRASTRUCTURE PLANNING ORGANIZATION OF PACIFICORP has adopted geographic information systems (GIS)-based spatial-load forecasting for high-growth areas of its service territory. This method is giving PacifiCorp's long-term planning efforts a new perspective.

Spatial-load forecasting moves network planning engineers beyond spreadsheet-based trend analysis into the spatial analysis capabilities of GIS. It gives geographic answers to the questions: Where will demand grow, and where is this new growth relative to substation service areas? The planning department can identify changing end-use patterns, predict future load centers, identify substation property requirements, and ensure the most defendable and cost-effective capital expenditures for substation reinforcement. This new approach has the potential to improve our relationships with the communities we serve, developing a more cooperative approach with our customers and improving service delivery. Long-term forecasting will extend the planning horizon beyond five years, increasing the lead time given to the permitting and land acquisition departments.

WHAT IS SPATIAL-LOAD FORECASTING?

Spatial-load forecasting uses GIS to merge distribution system data with land-use and development data. The model uses data such as current land use, transportation infrastructure, mountain slopes and urban centers to forecast the extent, location and timeline of community development. Every land use is related to a predefined profile of load on the distribution system. The model then translates the land use into a system-load forecast, identifying where new load additions are to be expected. This analysis of the community's projected growth helps target where infrastructure investments should be directed.

WHY SPATIAL-LOAD FORECASTING?

Spatial-load forecasting allows PacifiCorp's planning engineers to predict large load additions to the system years in advance of other methods. Planning engineers typically use trend analysis to forecast future loads, but they are now able to use the power of GIS to visualize new load and system additions. It will help them determine where new infrastructure should be added and inform others who need to know. This approach will help the company's Property Management Department better acquire real estate, apply for permits and acquire needed rights-of-way.

Spatial-load forecasting produces a forecast of electric load growth inside a region of the service territory, suitable as a base for comprehensive transmission and distribution expansion planning. Forecast results are used to predict future load centers, identify substation property requirements, prioritize projects and obtain budgeting approval while minimizing risk. Spatial-load forecasting also helps to explore the impacts of new initiatives or localized development events, as well as demonstrates effects to the system due to end-use changes, conversion from winter-to-summer peaking and community redevelopment.

Spatial-load forecasting does have limitations. It is not a design package and does not replace the knowledge and experience of T&D planning engineers. It is primarily used to complement traditional approaches to system planning to challenge planning assumptions. Spatial-load forecasting can support the transmission system planning process but does not predict the routing of transmission lines. Spatial load can forecast expected load demand in a way that creates productive interaction with the communities being served.

APPLICATION AT THE WASATCH FRONT

A greater appreciation of the value of spatial-load forecasting is evident through PacifiCorp's experience in modeling its Wasatch Front Range. The forecasted area in Utah comprises approximately 2000 sq miles (5180 sq km) with boundaries that include 56 cities currently served by 133 distribution substations. The area's population has grown at a rate of 2.6% per year for the last 15 years, which has driven electric load growth. This growth has been further inflated by conversion from evaporative cooling (EV) systems (i.e. swamp coolers) to central air conditioning (AC) systems. PacifiCorp's spatial-load forecast predicted the locations of large load additions due to rapid development, as well as where AC conversion will likely occur.

The spatial-load forecast consists of six main steps to the model setup. The following briefly discusses these steps and the hurdles the GIS and engineering team encountered while working on the project:

1. Determining the load classes

   The initial step is to determine the load classes to be represented. The foundation of the spatial-load forecast is a representation of the study region according to current land use; however, to represent the regional load, land use is actually defined by its consumer load class. A load class distinguishes customers based on energy consumption, defined in kilowatts per acre and a unitized daily load curve. For example, a typical land-use classification might be “medium-density residential,” and the representative load class or customer class would be “medium-density residential with EV” or “medium-density residential with AC.”

   This classification system allows representation of land uses according to their typical load profile and also allows changing end-use analysis. Load classes were selected through analysis of substation SCADA data. The eight load-bearing classes used were:

   • Medium-density residential with AC

   • Medium-density residential with EV

   • Low-density residential

   • High-density residential

   • Commercial retail

   • Commercial office and institutional

   • Light industrial (major industrials were excluded from the model)

   • Commercial business district.

   Several additional nonload-bearing classes also were used to identify vacant available lands, federal nondevelopable lands and municipal service areas not served by PacifiCorp distribution.

2. Data resources and the land-use model

   The land-use model represents current land use and development in the Wasatch Front. Key to the land-use model is reproducing the current land use in the area, as well as indicating the current development environment. In many cases, this is done using zoning regulations that restrict or encourage particular load classes — or that restrict or encourage land-use-type development in certain regions. It is also important to model the land that is currently (or soon will be available) for development. For example, it is possible that land currently considered nonvacant as part of a large multi-acre parcel may be divided later into multiple vacant residential parcels.

   Initially, each of the individual cities were contacted to obtain current land-use information. Unfortunately, many of the communities included in the study area did not maintain accurate enough information to be useful in the land-use model. As part of PacifiCorp's Real Estate Management GIS environment, parcel and ownership data is collected from each of the counties served. Assessor data was also requested from the counties. This allowed each individual parcel to be classified into a load class according to its assessed land use. When assessor data was insufficient, current aerial photographs were used.

   Gathering information from city and county planners was critical in identifying known developments and coordinating with master plans. Spending time with local planners provided insight not otherwise available.

   Cooling system conversions

   The primary concern in the current Wasatch Front development environment is the conversion of older homes from EV systems to centralized AC. This conversion is generating a significant increase of the system electrical load. Therefore, it was important to model this conversion in addition to new development.

   Many assessors maintain a residential housing characteristic regarding AC. However, the information is only collected when a home is reassessed. Additional data was used in cases where an AC characteristic was not available, including square footage, year built and total value. Homes built after 1995 with a square footage greater than 2000 or a total value greater than $150,000 were assumed to have central AC. These homes were placed in the medium-density residential AC class. All other residential parcels were placed in the medium-density residential evaporative cooling class.

   It was important to simulate the end-use conversion in the residential class to show the gradual increase in load growth, which is occurring independent of land development.

   Additional development parameters

   Much of the low-density residential and rural lands of the Wasatch Front will become available for higher-density residential and commercial development in the future. It was important to model the predicted conversion of these lands by incorporating them into a redevelopment model as well. Those areas classified as low-density residential/rural were coded to allow for redevelopment into any of the load classes.

   Future land-use drivers

   An activity center map, locating regions of employment or commercial activity was used as a factor in the model to encourage residential and commercial growth in locations that planners labeled as high-growth regions.

   At this stage of the model it became evident that multiple growth scenarios would be helpful. Running the forecast to show results of development scenarios allowed investigation of the investment needs that may be required if a proposed event occurs. Using these growth scenarios, the company was able to investigate the impacts due to major development activities and proposed transportation corridors, both of which substantially affect load distribution in the study area.

3. Load curve development

   The load profiles or load curves represent the average daily patterns and usage of energy as a function of time for a particular load class. This is used to build a load model from the represented land use. Planners must accommodate peak load conditions; consequently, planners need to know how loads behave during the system peak. The first step in developing the load curves was determining the system peak day. Next, hourly data was extracted from the company's system control and data acquisition (SCADA) system for selected distribution feeders that were representative of each load class. The final curves were presented to the company's metering group for verification.

4. Calibration

   Calibration is the process of matching the model's calculated load for the base year to the actual load on the system and substations. The goal is to achieve the best possible match for the entire system and individual substations, both in magnitude and shape. Matching the magnitude is only a first-order test, but matching the shape ensures the correct type of load has been assigned to each area.

   The actual 24-hour-per-unit load curves for each selected substation were obtained from SCADA for the 2003 system peak day. The calculated 24-hour load curves require three inputs: land-use acreage by load class, per-unit load curves for each load class and load multipliers (kilowatts per acre by load class). The only adjustable parameter input to the calibration process was the load multiplier. This value was adjusted within maximum and minimum set bounds until an indication of success was met. Success was measured by the total load difference at the time of peak, time of system peak, average percent difference for substation peaks and time of substation peaks.

5. Growth rates

   There are two circumstances that cause load growth: new customers and the consumption growth of existing customers. In the former case, new customers are responsible for the steep section of an area's “S” curve. In the latter case, consumption growth drives the flatter sections of the “S” curve. Both types of growth had to be incorporated in the model to accurately simulate load growth and changing patterns.

6. Factors, urban poles and preferences

   Any spatial-load forecast uses a model to simulate the effects of real-world factors to systematically determine the extent and timeline of community development. Forecasts use the theories of urban planning to predict the most likely locations of new land development. To achieve this, the model's growth simulation was based on user-determined factors that tend to influence a region's growth. Factors include transportation infrastructure, locations of employment and commercial centers, barriers to development and general land-use attractors or detractors.

The factors and development influences are mathematically combined to develop suitability maps for each of the load classes. The suitability maps are used to match load classes to their most suitable growth areas. For each forecasted year's growth, the model uses the highest ranked locations on the suitability maps to assign new growth to that particular area. The end result for each year of the forecast was a new land-use map showing the predicted growth in the region.

INTERPRETING THE RESULTS

After the model had been run for each of the forecast years, the new total land-use calculations were broken down by substation boundary to determine the new growth within each substation's service area. Acreage totals for each substation were then converted to megawatt additions. To better understand the systemwide results, the substations were grouped into significant zones according to the planning organization's load flow base cases. The purpose of a spatial-load forecast is to forecast regional load. However, that forecast is of little value without a measure of the impact the projected load will have on the planned and existing infrastructure. Due to the enormous complexity of the entire Wasatch Front electrical system, new infrastructure requirements were evaluated on a purely quantitative level for the distribution transformer level only. Results were analyzed to quantify needed additional capacity by zone according to projected load additions. The results predicted capacity requirements in 30-MVA blocks, corresponding to transformer banks in substations. The results were weather adjusted to look at extreme weather demands. Each zone was analyzed to a standard utilization threshold, and infrastructure enhancement needs were forecasted for each study year.

DELIVERING THE BENEFITS

Last-minute property acquisitions for new facilities can be fraught with conflict, resulting in delays in the siting process. In high-growth regions, acquisition costs are lower when a parcel is secured earlier. If the planning group can anticipate future load centers and equipment utilization issues years in advance, property can be purchased earlier, at a lower price and in a manner that can be incorporated into the local government's master planning process.

The principal benefit of PacifiCorp's spatial-forecasting approach is improved communication. More insightful communication occurs between T&D planning engineers, utility real estate agents and city planners. Spatial-load forecasting creates more flexibility within the distribution system planning process. It helps identify future load centers and changing end-use patterns.

Identifying substation property requirements earlier ensures the most defensible and cost-effective capital expenditures for substation reinforcement. GIS is revolutionizing the ways in which PacifiCorp can visualize and track the changing load patterns throughout its service territory, and provides a basis for comprehensive transmission and distribution planning.

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Jessica C. Noonan is a GIS specialist at PacifiCorp, where she has prepared spatial-load forecasts for the Wasatch Front, Central Oregon and Medford, Oregon, areas. Noonan holds a master's degree in geographic information sciences from the University of Denver and a bachelor's degree in environmental geoscience from Boston College.
jessica.noonan@pacificorp.com

Amy L. Johnson joined PacifiCorp as a planning engineer in 2002, after graduating with a BS degree in electrical engineering from the University of Washington. She provided the engineering data and analysis for the Wasatch Front spatial-load forecast.
amy.johnson@pacificorp.com