In November 2006, the city of Naperville's automation system was put to a severe test. A vehicle collided with a transmission pole, knocking out a vital link in the city's (Naperville, Illinois, U.S.) 138-kV transmission grid. The result was a total outage at one of the city's largest substations. Three adjacent substations also experienced partial losses. In an instant, 13,626 customers — almost 25% of the City of Naperville's customer base — lost power.

Within seconds, the city's multilayered automation systems went into action. In less than two minutes, 9103 customers, or 67%, had their electrical service restored automatically. Switches, using distributed intelligence, reconfigured feeders that had lost power to restore service to 5848 of these customers, while the remaining 3255 were re-energized by automatic transfer algorithms implemented at the substation level.

During the next 14 minutes, another 4380 customers — 32% of the originally affected customers — had their power restored by control-room dispatchers using supervisory control and data acquisition (SCADA) to operate substation bus ties and other distribution assets. At this point, only 143 customers, or 1%, were still out of service. Repair crews restored the last customer manually, 81 minutes after the accident. Here again, the distribution automation (DA) switchgear minimized even this outage and allowed repair crews to be immediately dispatched to precisely where they would be most effective.

Although the City of Naperville's DA equipment has successfully operated many times over the past several years to isolate individual incidents of trouble and restore power to unaffected loads, this one nearly catastrophic event succinctly underscores the value of automation and completely validates the city's significant investments in this technology.

Designing for Reliability

The City of Naperville's typical substation design consists of two incoming lines, each supplying a 28-MVA transformer that supplies the 12.47-kV bus. Each bus consists of double-stacked draw-out vacuum circuit breakers in a lineup of metal-clad switchgear. A typical station will have two 12.47-kV buses, each having between four to six feeder breakers to supply station load. Bus ties allow for paralleling transformers when necessary.

Over the last 10 years, the goal of the electric utility department has been to engineer a cost-effective, dependable and maintainable distribution system. The department has additional goals to plan for first-contingency outages and for future growth with a 20-year horizon, and is also alert to opportunities for system-reliability improvement.

The optimum distribution-circuit design consists of a 6-mile (10-km) feeder length that is fed from two substations (above). The feeder length from each substation is half the total length to an open-point switch. By sizing the mainline feeder appropriately, the total feeder length can be fed from either substation during emergency operation. The key reliability component of optimum circuit design is the installation of switchgear at key locations, such as at the open point between feeders and at the midpoint of each feeder. Further, auto-sectionalizing and reconfiguring intelligence allows the switches to operate in automatic teams.

Why is DA a Better Approach?

Open-looped feeders with manual switches provide reasonable restoration time from the utility's perspective. However, what is reasonable for a utility is not always reasonable to a customer without power. Automated feeders drastically reduce the number of customers exposed to a typical outage.

Automated switches reconfigure for faults or loss of power. DA equipment follows the same steps a dispatcher would, only faster. A substation that experiences a loss of power or a faulted cable section is isolated automatically. Half the faulted feeder is restored within 60 seconds. And, fault locating and isolation is reduced, because the fault is isolated before crews arrive.

Good equipment, good design and good installation are only a part of the successful program. Continuing support, maintenance and training are additional keys to success. As every parent knows, it's the “unattended child who gets into trouble.”

Monitor, Support, Maintain

Control-room DA screens allow for daily viewing of the switch team status. The screen has two fields, static and dynamic (on page 49). The static screen reflects the normal feeder configuration, while the dynamic screen shows the existing conditions. The control-room DA interface allows not only monitoring of DA status, but also provides active control over automated switches, if necessary. From the control room, it is possible to disable or enable automatic operation of DA teams, as well as to remotely open or close each switch member.

Proper automatic operation requires the switches to be in a “ready-to-transfer” state. Several conditions can cause teams to be “out of ready,” such as communication issues, the automatic operation being disabled manually or the switches not being in their normal configuration. The DA interface screen indicates the “ready” status of each team and also captures several of the status points that can cause the team to not be ready. All of these status points are monitored on a daily basis to ensure all teams are in the ready mode.

On a monthly basis, technicians visit each automated switch to ensure that basic functionality is intact and all automatic functions are ready for operation. During monthly site checks, a full report is downloaded from each switch control unit and transferred to an automated maintenance program for trending purposes and alarms.

For any problems found, the City of Naperville maintains a test unit for controls that might have trouble. The test set allows the electric utility to inject voltages and currents, and simulates tripping of the circuit breakers. The utility also maintains an inventory of spare critical parts to facilitate immediate repairs to bring teams back in service with minimal delay.

Communication is Key

To design, monitor and maintain optimum communications, the city set up a dedicated vehicle to accomplish all radio surveys, troubleshooting and repair. Included in the vehicle are global positioning systems, multiple radios and various types of antennas.

DA teams communicate with the control room over a backhaul radio that is located at the nearest substation. A Siemens SAS PLC polls DA data in DNP 3 format and transfers it to the control-room server over Ethernet. Substation Ethernet network is supported by GE JungleMUX equipment.

One more tool that is used is Utilinet Radio software, which helps the utility maintain and troubleshoot communications between teams and between the control room and field devices. This software helps verify that adequate signal strength exists and proper data is transmitted over the radio network.

On an annual basis, the electric utility runs a voltage-loss test scenario. S&C IntelliTEAM software provides an option to do this automatically. After installing a test plug and decoupling the motor operators, a simulated voltage-loss test is performed for each team, which causes the switches to reconfigure the feeder as if one of the sources lost power.

This testing essentially proves that the teams will reconfigure properly due to a loss-of-source scenario by:

• Ensuring that all programming inputs are appropriate for team operation

• Verifying that all team members are communicating correctly

• Exercising all mechanical parts of the switchgear

• Conducting the test from both voltage sources of the team.

While the testing is being done, a comprehensive written maintenance procedure is performed and fully documented annually by field technicians. The procedure includes checking all control functions such as enable/disable and open/close; checking all motor-compartment functions such as open/close and remote/local; checking the communication value for strength adequacy; checking for lubrication, general conditions, labels and damage; and ensuring the operation procedure is on hand inside the control compartment.

Training

One of the key components of the successful implementation of Naperville's DA program is training, which is performed on an annual basis and includes all departments of the electric utility involved in the DA: engineering, linemen, control room, installers, and control and communication technicians.

Training covers all the components of an automated switchgear including automated control, voltage and current sensors, battery source, open/close indication and motors/couplers. Training is set up with a demo team of controls to provide a hands-on experience.

Concepts covered during training include defining what an automated team is; identifying how the DA system can be automatically reconfigured; interpreting the state of team and switches; learning what steps to take to ensure safe operation, as well as safe isolation; and what should be done when a team has been reconfigured.

Lessons Learned

The City of Naperville has learned several lessons through its implementation of DA:

• Make any initial pilot program large enough so that the system can be fully tested and completely understood by operating personnel

• Use the pilot program for training

• Use the manufacturer's experts to understand the system and train employees

• Share the goals and expectations of each department of a company

• Think about how these automated devices will work with other devices (relaying and motors)

• Remember that reliability improvement comes gradually with automation system growth

• Perform consistent maintenance of the system to guarantee optimum performance

• Realize that overall reliability improvement comes through good design, good equipment, good construction, good operation and maintenance, and timely asset management practices.

Bottom-line Impact

The graph on page 46 illustrates the impact of DA through 2006 by showing the improvement in the system average interruption duration index (SAIDI) achieved through distribution automation. We estimate that for the last six years, SAIDI has averaged being 28% better than it would have been without DA. In view of this steady trend of outage avoidance in conjunction with the potentially catastrophic event in November 2006, the City of Naperville is more convinced than ever that DA works, and the city feels completely justified in its automation investments.

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Olga Geynisman is the electrical engineering and technical services division manager for the City of Naperville Department of Public Utilities-Electric. She joined the City of Naperville in 1998 as a senior automation and communication engineer and has been responsible for the planning, engineering and deployment of automation, communication, system integration and GIS for the utility. Prior to joining the City of Naperville, Geynisman worked as a facility engineer for Fermi National Accelerator Laboratory. She received her degree in electrical engineering from the Polytechnic Institute (St. Petersburg, Russia). Geynisman is a licensed professional engineer in Illinois, and a member of the National Society of Professional Engineers and the IEEE.
geynismano@naperville.il.us

John Schaub is the supply and control division manager for the City of Naperville Department of Public Utilities-Electric. He started at the City of Naperville in the distribution section, and then moved to the automation and communication section, and then to the substations section. Schaub previously worked seven years in nuclear generation, performing plant modifications and calculations. Schaub received his degree from the University of Illinois at Chicago. He is a member of the IEEE.
schaubj@naperville.il.us

City of Naperville

The City of Naperville is located in the northeastern part of Illinois, which is considered to be the top growth area in the state. Naperville is located 28 miles (45 km) west of downtown Chicago and occupies a land area of 38 sq miles (98 sq km) with a population of nearly 142,000. The city has grown by more than 35,000 residents in the past 10 years, making it the fourth-largest city in Illinois.

The City of Naperville operates its own water/wastewater and electric utility. The electric utility serves 56,300 customers with a peak demand of 388 MW. Ninety percent of Naperville's electrical network is underground, and 70% of the distribution network is equipped with distribution automation.

The City of Naperville buys electric power on the open market, with 138-kV ComEd transmission lines delivering it to several primary metering points, from which the Naperville electric utility distributes it to customers. Sixteen substations located throughout the city support a variety of power requirements, from technology and research corridor customers on the north side of the city, to a dynamic downtown shopping area in the central part of the city, to a rapidly developing residential area on the south side.

In July 2006, CNN/Money and Money magazine ranked Naperville second on its list of the 100 best places to live in the United States.