On July 4, 2007, my home phone rang at 2:30 a.m. The Commonwealth Edison (ComEd) shift manager at the Operations Control Center (OCC) was on the line reporting a substation outage on the west side of Chicago. Seven circuits and several thousand customers were without power. As I left my house, I was on the phone with dispatch and the outage-response team leaders, who directed that we get the area back on-line before we begin the permanent repair process.

Restoration Philosophy

In the past when an emergency outage occurred, an overhead electrician specialist (OES) was typically dispatched to troubleshoot the problem, isolate the faulted section and restore the circuit. Crews would then typically begin the permanent repair process to restore the customers who were impacted by the outage in the faulted section of the line. The duration of a power outage depended on how long it took to repair the problem.

In reviewing these procedures, ComEd's emergency-response team found that the focus was more on repairing the problem than on restoring service. We decided to shift our response effort to doing everything possible to restore the customers' service first, and then repair the faulty equipment or cable. This “restore-first” strategy has changed both the way our field operations crews respond and the kind of equipment being deployed during an unscheduled outage event.

Two First Responders

The most visible change has been with the first responders. ComEd employs approximately 230 OESs who are responsible for troubleshooting outages, isolating the problems and restoring service to customers. Based on our new restore-first philosophy, ComEd typically dispatches two OESs on circuit lockouts. These technicians, stationed at one of ComEd's 34 reporting centers in the greater Chicago metropolitan area and northern Illinois, receive two weeks of classroom training and six to eight weeks of on-the-job training beyond the journeyman lineman apprenticeship.

To improve system reliability, ComEd has invested in overhead fault indicators throughout the system. These fault indicators, installed at the midpoint of all overhead circuits without a midpoint circuit recloser, assist the OCC and troubleshooter in isolating fault locations. Experience has shown that by sending one OES to the midpoint fault indicator on the circuit and a second OES to a designated tie point, important minutes can be saved. This tactic anticipates the likelihood of being able to close the circuit tie switch or the circuit breaker to restore the circuit's unfaulted half, bringing the nonfaulted section back on-line and allowing remediation to commence on the faulted section of the circuit.

To further expedite the troubleshooting process, we have leveraged our recently deployed outage management system (OMS). This computer-based technology provides detailed circuit information on multiple screens at the OCC. The overhead fault indicators are integrated with the OMS through the automated SCADA network. Dispatchers review the graphically displayed circuit information and communicate it to the OESs in the field. Other vital information is also integrated into the OMS such as customers on radial feeds that cannot be switched and critical facilities such as hospitals, nursing homes, water-pumping stations and other large-gathering locations.

If the lockout is caused by a downed conductor, the OES will employ our “cut-and-run” switching procedure, which allows us to restore all customers on the circuit except those directly affected by the downed conductor. Construction crews are then dispatched to the location to restore the remaining customers by replacing the conductor. The goal is to restore service to as many customers as possible.

For our stranded customers, we have developed another new initiative. “Plan B” calls for the deployment of temporary cable or portable generation. ComEd has a vast amount of cable on its underground residential distribution (URD) system. Although most of the URD system features tie points, some radial portions lack switching capability. To improve restoration to these potentially stranded customers, ComEd has expanded its fleet of temporary cable trailers and portable high-capacity field generators.

Temporary Cable Trailers

Temporary cable trailers are typically deployed on URD outage events where a dig-in has occurred, or where a cable has failed underground and alternative switching is not an option. ComEd has stationed 27 cable trailers at various reporting centers throughout its four operation regions. An inventory is maintained by the OCC of the location of each cable trailer, including cable specs and capacity. The cable trailers carry various lengths and diameters of cable from 200 ft to 500 ft. Smaller cable trailers carry a #2 mining cable, which is more flexible and easier to handle than a typical jacketed cable.

If the OES and dispatcher determine that the best solution for restoration is a cable trailer, a construction maintenance crew is dispatched to deliver the trailer. The crew lays the temporary cable from the feed to the affected customers, terminates the feed and re-energizes the conductor. The appropriate work-site protection is implemented at the temporary cable area, including safety cones and safety barricade tape. A radial fault is typically located and repaired in less than four hours. Depending on the location, a watch person may be assigned to guard the construction zone. Once the circuit is restored, the permanent repair process begins.

Portable Generators Mobilized

ComEd also has expanded its temporary generation capability. Additional portable units, ranging in output capacity from 175 kW to 2 MW, have been purchased for emergency-outage events. Each unit has variable low-side output voltages to meet the outage-site requirements. We also lease generators with varying output voltages up to 277 V/480 V. These units can be connected to a step-up transformer to provide primary voltage.

During the July 4 outage, all three of our 2-MW generators were immediately dispatched to the areas affected by the substation failure. Each unit is custom designed with a 7.2-kV/12.6-kV output, which is compatible with ComEd's distribution system. Quick cable connection points on the trailers facilitate a faster site installation by construction crews. Mobile transformers can also be deployed in conjunction with the 2-MW generators to step down the voltage to 2.4 kV/4.6 kV or various other secondary voltages.

Leasing agreements are also in place for additional 2-MW generators. This was the case for the July 4 outage, where a total of six 2-MW generators were installed. Under most conditions, field circuit switching is completed to transfer customers to other substation sources. When it was discovered that the 4-kV bus was completely inoperable, the outage-response team determined that temporary generation was needed. Those customers who could not be switched were restored to service using the six 2-MW generators. Construction crews and supervisors worked diligently throughout the holiday and were able to have all our customers restored by late afternoon.

The next major project in ComEd's restore-first strategy is a three-year implementation plan to install mobile-data technology throughout the workforce. PDAs and laptop computers will provide field personnel with additional data and mapping information in the field.

Measurable Results

By leveraging technology to expedite the troubleshooting and outage-restoration effort, and by expanding our temporary cable and generation capability, our response to outages has improved significantly.

One measure of the success of these efforts has been a decline in our customer average interruption duration index (CAIDI). As of July 17, the year-to-date storm CAIDI has declined by 63 minutes over the same periods beginning in 2005. This 33% decrease, from 193 minutes to 130 minutes, has occurred despite the unusually stronger-than-normal storm year being experienced in 2007.

July 4 was not a normal day for our outage-response team, but for ComEd customers, who experienced only a few hours of outage, it was a typical Fourth of July, thanks to our new motto: “Restore First, Then Repair.”

Jim Conway is director of operations at Commonwealth Edison (ComEd), a unit of Chicago-based Exelon Corp. Conway holds an MBA and has worked as a lineman, and in various other operations, construction and management positions over a span of 24 years. ComEd's Timothy McThenia, operations coordinator, and Mark Quinlan, operations manager, also contributed to this article. jamesm.conway@exeloncorp.com