Electric distribution companies have huge investments in AM/FM/GIS systems and would like to use the AM/FM/GIS circuit information as the foundation for optimizing other systems. Three U.S. utilities — Ameren (St. Louis, Missouri), Detroit Edison (Detroit, Michigan), and Orange and Rockland (O&R, Pearl River, New York) — have chosen EPRI's Distribution Engineering Workstation (DEW) to harness this information and all for surprisingly different reasons.
Ameren had a 25-year investment in programs driven from its AM/FM/GIS system. Over the years, it developed power flow, short circuit, device coordination and feeder tie capacity internally. The programs solved the problem, but the tabular results were difficult to interpret. The utility pursued a graphical solution in order to get a better picture of circuit performance.
Detroit Edison also had a 25-year investment in its AM/FM/GIS system and circuit-analysis programs. Detroit Edison wanted a new graphical circuit-analysis tool to optimize its system. However, the implementation had an additional hurdle to overcome because the AM/FM/GIS system did not have electrical connectivity or phasing information. Detroit Edison needed a program that could intelligently interpret its AM/FM/GIS data to create connectivity and predict the phasing of single-phase taps and distribution transformers.
O&R had yet another set of analysis needs. O&R wanted to perform real-time circuit analysis in its Distribution Control Center (DCC) on operations circuit models. The utility needed a program to import supervisory control and data acquisition (SCADA) measurements and scale the load data to match the present measurements.
While each utility had special software requirements, all three needed a package with an open architecture that they could customize to meet each company's specific analysis requirements.
In 1998, Union Electric (AmerenUE) merged with Central Illinois Public Service Co. (AmerenCIPS) to form Ameren Corp. In the years before the merger, each company had its own circuit-analysis programs. The outputs from the programs were tabular reports, which were cumbersome and hard to interpret. Engineers had to sift through the reports to analyze the system, relating the report back to a system map for the “big picture” of circuit performance.
Over the years, legacy analysis tools were developed, including load flows, short circuits and adjacent feeder tie capacity, as well as protective-device coordination and capacitor-placement programs. The challenge was finding a graphical software tool that would satisfy all of Ameren's analysis needs.
In the mid 1990s, AmerenUE started developing a graphical-analysis program with the functionality of the legacy tools. The utility decided to use EPRI's DEW and finished the first interface with its AM/FM/GIS system by 1997. Ameren deployed DEW as a client-server database application that warehouses analysis models for more than 50 engineers scattered across Illinois and Missouri. A similar interface was developed for the AmerenCIPS' AM/FM/GIS system. These implementations create DEW circuit models automatically from Ameren's AM/FM/GIS system and its legacy transformer load-management system. The interface recognizes any changes made to the AM/FM/GIS system during the day and incrementally updates the DEW models at night. Therefore, the circuit models are never more than one day out of sync with the most recent AM/FM/GIS data.
Ameren's DEW model of the distribution system contains approximately 1.3 million nodes to model 930 substations with 3250 feeders with 600,000 load data points. Interconnected multi-substation models involving more than 40,000 nodes have been created and analyzed. These models are used to study contingency switching in the event that a substation transformer fails. The DEW reconfiguration/restoration module automatically performs the switching to isolate the failed transformer and pick up the load via neighboring feeders. The results show how much load the neighboring feeders can handle, and how much load a mobile substation must serve. The program allows Ameren to study hundreds of scenarios in a matter of minutes, as compared to manual trial-and-error solutions.
The DEW analysis tools have helped Ameren in several ways: critical studies have a much faster turnaround time than in the past; the graphical representation of the results is easy to interpret, the tools reduce the time required to review circuit performance; analysis is easy, resulting in more studies being performed to optimize investment in distribution facilities; and the models have been field verified many times confirming the accuracy of the results.
Detroit Edison had several problems to overcome to achieve its goal. The biggest challenge was digitally interpreting the company's mapping data. These problems were solved using customized applications developed around DEW's open architecture.
The Detroit Edison mapping system does not have information on electrical connectivity or phasing between graphical elements. The maps look great when viewing entire circuits, but closer examination revealed that many parts didn't actually touch. These components are electrically connected in the field, but many components were drawn 50 ft (15 m) from where they should connect in the mapping system. Two application modules were developed so that DEW could intelligently interpret the mapping data.
The connectivity application uses sophisticated logic to extract the discontinuous mapping data to produce a DEW model that has electrical connectivity. In addition to the connectivity problem, there were problems with the maps using many short line sections to traverse a curve. In order to consolidate the line sections, a tool was developed to merge the short line sections into one electrically equivalent line section. The resulting line section maintains geographical accuracy, while reducing the number of nodes in the model. The phase prediction software application determines the phasing of the distribution transformers and taps. Transformer loads are estimated by using a percentage of transformer size or using load research data coupled with kilowatt usage.
Load research data is used to calculate diversified load curves, diversity factors and kilowatt-hour to kilowatt conversion factors as a function of customer class, month and type of day. These load curves are stored in DEW with kilowatt-hour billing data to produce kilowatt load estimates for the distribution transformers. The phase prediction application then uses the distribution transformer loading in conjunction with measurements from the substation breaker (or interior circuit points). The application varies the phasing of transformers and taps on a circuit until a match is achieved between the predicted transformer loading and the known substation readings. Work is ongoing to determine the accuracy of this phase-estimating methodology. If known, actual phasing can be put into the model.
Detroit Edison's distribution system contains many 4.8-kV, three-wire, ungrounded circuits that are operated in a looped configuration. Loops may appear in either three-phase or two-phase portions of a circuit. Some of the utility's circuits include as many as 15 loops. In addition, many 13.2-kV grounded wye circuits will feed both three-phase and two-phase 4.8-kV ungrounded areas via isolation transformers. These 4.8-kV looped circuits have been successfully modeled and solved using DEW.
Detroit Edison engineers examine the large system they created and stored on a stand alone 2 GHz, 2 GB processor (Power Flow solves in less than one minute). This single, large static test system contains more than 400 circuits with more than 1.2 million components (reduced to 350,000 components using multi-point line modeling) covering an area of nearly 4000 sq miles (10,360 sq km).
However, engineers use DEW mainly to study smaller systems of circuits. They can use the Microsoft Access version of the DEW database, put it on their laptops, cut a CD of their circuit files and take it to the field with them.
In addition to solving these systems, Detroit Edison uses the program to study various types of inverter and synchronous distributed resource models. It has used power flow and fault analysis to study the effect of distributed resources on the delivery system, and used DEW to study the effects of actual installations. Detroit Edison's corporate vision includes integrating distributed resources into its planning and operating process as an alternative to more traditional methods of solving distribution problems.
Detroit Edison is integrating its cost-estimating system into the DEW planning tool. This allows engineers to compare costs of alternative plans resulting from their graphical changes within the DEW analysis. Hyperlinks are used to obtain additional Web-based device information.
Orange and Rockland Utilities
O&R is building a “virtual SCADA system” based on the DEW analysis engine and the application of load-research statistics. The intent is to use the DEW analysis engine to perform power flow calculations when invoked by O&R's Switch Order Management System, a subsystem of O&R's Distribution Management System (DMS). Distribution operators would use the circuit reconfiguration function in DEW when preparing switching solutions, ensuring that load and voltage constraints are met. This frees distribution engineers to perform other critical tasks.
A crucial part of the design criteria for the Switch Order Management subsystem was that engineers performed analysis on SCADA-supplied real-time data. During the design process, it became apparent that all of the necessary information would be in place to allow DEW to continuously analyze and display results in real time as SCADA measurements change. This allows for the creation of a Virtual Distribution SCADA system. The power and speed of the DEW analysis engine ensures that O&R's entire 236 circuit distribution network could be solved fast enough to be used in a control room environment.
Using DEW's open architecture, O&R is creating an interface between its DMS and DEW. As operators perform switching operations, they will maintain the DEW model. Distribution system measurements will be automatically updated in the DEW model and used to scale load, so that power flow results match existing load conditions.
The DEW models will run in one of two modes: operations or analysis. In operations mode, power-flow solutions run automatically whenever switching operations or changes in measurements occur for circuits. The power flow solutions are performed 24 hours per day, seven days per week for all 236 distribution circuits. Overloads, large phase imbalances, and low and high voltages will be alarmed. In the analysis mode, operators will perform the traditional planning studies. As part of this analysis, protection will be checked and the operator will be informed of switching scenarios that could hinder the performance of the system.
More DEW to Come
Several utilities have used the open architecture to customize DEW to their environments. For DEW users, it has optimized system solutions with greater caseload capability and enhanced analysis to solve complex problems. However, the true value of using DEW open database remains to be exploited. The full potential of using DEW will only be realized when all relevant databases and the data that it contains are linked, and the information is available to all users. As distribution utilities strive to become the more efficient asset managers, they should consider systems like the DEW.
The authors want to recognize the efforts of the following individuals for their decade of effort to develop the DEW into the comprehensive tool it is today.
Harry Ng, EPRI manager, Distribution System, managed DEW conception, development, implementation at Detroit and at Ameren, and commercialization.
Robert Broadwater, an electrical engineering professor at Virginia Tech and president of Electrical Distribution Design, directed the DEW software development and implementations for EPRI.
Richard Seguin is principal engineer in DTE's System Projects and Engineering department. He is responsible for the DEW implementation and Distributed Resources.
Andrew Sugg is currently an Engineer in Ameren's Energy Delivery-Technical Applications department. He is responsible for the DEW system and several other engineering applications. He is a registered professional engineer in Illinois and Missouri.
Charlie Scirbona is division superintendent and is responsible for Division Engineering and Line Operations at Orange and Rockland Utilities.
Open Architecture Features
Non-proprietary, user-extendable database
Corporate SQL-compliant database
User-programmable access to any in-memory data or calculated result
Attach and display data on the circuit model
Add new equipment models and customize graphic symbols
Future Plans for DEW
EPRIsolutions, in partnership with Electrical Distribution Design (Blacksburg, Virginia, U.S.), is providing continued development, support and vision for DEW. The vision addresses specific technical achievements, such as combined T&D analysis of systems with millions of nodes. However, the vision goes far beyond such targeted technical achievements and addresses a seamless approach to asset management.
The key to this vision is DEW's open architecture. Instead of trying to provide a common solution for everyone, an open platform for development is provided. Customized applications are developed in the open marketplace by many different creative users and programmers. In this open marketplace development, the DEW system model can be linked to asset management records, daily operational procedures, events, long- and short-term planning, and more. Eventually the best application approaches will be widely adopted. In this role, DEW serves as a cost-effective focal point for information technology and asset management that provides value to all company employees, from senior level management down.
EPRI has made DEW available to all utilities. Since 1992 EPRI has worked on developing and enhancing DEW. During this period, many open-architecture concepts have been built into and subsequently refined in the DEW. DEW is now commercially available to all companies. EPRI membership is not a prerequisite for acquiring or using DEW.