11.26.08Kevin Costin, Management Systems Solutions Specialist, Oracle

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Utilities have long been under pressure to reduce outage duration. At stake is service reliability for all customers.

In response, utilities have used the past decade to deploy locally controlled protection devices. They have supplemented these devices with outage and workforce management applications that have improved their reliability records.

Typically, outage management identifies a fault location. Mobile workforce management identifies available repair crews with the needed skills, compares their locations, and directs the appropriate crew to the fault site. Outage management comes back into play by monitoring grid conditions in ways that accelerate the repair crew's work.

That process has built-in delays. Crews must travel to the location -- often miles through heavy traffic. Once they arrive at the site, they must identify the exact location and nature of the problem. They must then implement orderly processes, complete with checks and confirmations that protect themselves and bystanders from life-threatening accidents.

Meanwhile, customers live without power.

A New Era

Today, advances in distribution management can further reduce outage duration and increase repair crew efficiency. Fault Location, Isolation, and Service Restoration (FLISR) (see Ref. 1) automatically:

• Senses trips (faults) in switches that are monitored and controlled by a SCADA [i.e., feeder circuit breakers (CB) and downstream reclosers (ACR)].

• Identifies the faulted section using the telemetered Protection Trip and Fault Indication (FI) flags.

• Isolates the fault.

• Restores power to customers by automatically switching them to non-faulted sections of the line.

From the utility's point of view, FLISR does not "fix" the problem. Outage Management predicts probable outage locations and FLISR identifies the faulted feeder section. Crews must still verify the fault and make permanent repairs. FLISR helps minimize the scope of work and increases crew efficiency, but it does not eliminate human intervention.

From the customer point of view, however, there is only a brief, momentary outage. Customers' power is quickly restored. They are unaware that it arrives via a different route, and its route is of no consequence to them. Thus, from the customer perspective, FLISR is appropriately viewed as a first step toward a self-healing grid -- a grid in which coordinated automatic controls minimize outage durations and the number of affected customers.

Are Utilities Ready for FLISR? The vision of a self-healing grid is not new. Grid experts have predicted its arrival for years. And utilities have not ignored the value of automation. In fact, they have deployed technologies that, while producing immediate results, also lead toward an era of greater automation in outage restoration. These technologies include:

• Fault detection through fault indicators deployed in the engineered feeder network.

• Feeders with more than one isolation point in their design.

• Alternative feeds from tie points such that customers can be restored as soon as faulted sections are isolated.

• Automated analysis of capacity and switching alternatives via:
  • SCADA-controlled devices.
  • Devices controlled by distribution automation.
  • Intelligent Electronic Devices. (Ref. 2)

All these technologies contribute to maximizing FLISR efficiency. It is not necessary, however, to have all of them in order to benefit from this new technology. Utilities with nothing more than fault current indication, widely deployed, can garner immediate benefit for operational efficiency by using the FLISR fault location capability.

Even more is possible when utilities have two or more of these technologies in place. And many do. A 2007 Newton-Evans Research Company survey (Ref. 3) of more than 80 utilities worldwide revealed that:

• Ninety percent of utilities surveyed have already deployed fault detection equipment adequate for FLISR needs. Eighty-eight percent include automatic fault-sensing devices in their standard feeder design.

• Utilities typically have more than one isolation point. In the survey, the average number of automated feeder-sectionalizing switches ranged between two and three per feeder for feeder voltages above 13kV. (Ref. 4) (There was no noticeable difference observed between North American and international utilities.)

• The number of feeder alternate sources through feeder tie points ranges between two and three, regardless of voltage level. (Ref. 5)

• Forty percent of automation devices are currently controllable via SCADA supervisory control actions.

Many more utilities surveyed have clear plans to implement these technologies over the next two to three years.

How Soon Will Utilities Confront Requirements for FLISR?

Grid operators face many competing pressures, only one of which is to reduce outage durations. However, there is clear evidence that the issue is moving higher on the regulatory agenda, at least in North America.

The California Energy Commission (CEC), for instance, is currently looking into the relationship between outage duration [as measured by such industry standards as SAIDI, SAIFI and CAIDI (Ref. 6-8)] and the economic losses from outages, as measured on a Value of Service (VOS) index. VOS (Ref. 9) varies significantly among customer classes, of course; a large industrial plant may suffer heavy productivity losses from a service interruption, while a residential customer may suffer only minor inconvenience.

Thus far, the CEC research has identified the top distribution automation applications that could improve VOS. One of them is "System Restoration After Failure" that would "install automated switching on feeders and enhance existing outage management systems (OMS) to more precisely locate faults."

The CEC has not yet recommended specific VOS standards. The depth of the research, however, serves as an alert that utilities may soon confront such new reliability measures.

No utility will want to automate every feeder in the distribution system. The performance of certain highly reliable feeders is such that there is no need for automation. But FLISR can use existing automation to improve the reliability of poorly performing feeders and service areas.

FLISR can also improve the statistical record for utilities currently struggling with current regulatory reliability mandates. It can significantly reduce the total number of prolonged outages by moving many such events into the category of "momentary outage" (generally one to five minutes).

Benefits

FLISR has immediate benefits.

The first is observability. With more granular data, distribution operations are more efficient. Fault location minimizes the scope of work for field crews for each fault event.

The second benefit lies in coordinated automatic control. Fault response automation cannot automatically clear a hard fault; thus, FLISR does not envision unmanned distribution operations. FLISR can, however, reduce the impact of faults on the operations team's overall responsiveness and performance.

In short, FLISR:

• Temporarily restores power to a significant number of customers who would otherwise experience a prolonged outage.

• Gives the system operator more knowledge, better data, and software environments that improve decision management.

• Has the potential to improve reliability, safety, and restoration speed while also improving the stability of the distribution network under transient conditions (resulting from fault and switching operations).

FLISR is thus a major step forward in the control of active and reactive power flows -- a first step toward a self-healing grid.

References

1. Fault Location, Isolation, and Service Restoration (FLISR) responds to protection trips of SCADA monitored and controlled switches (i.e. feeder circuit breakers (CB) and downstream reclosers (ACR)). FLISR automatically identifies the faulted section using the telemetered Protection Trip and Fault Indication (FI) flags and then (in Auto Mode) automatically executes the isolation and restoration actions to restore the non-faulted areas de-energized by isolating the fault. In Manual Mode, FLISR will present the isolation and restoration actions for review and execution by the user.

2. The distinction between SCADA and fully automatic controlled switches in the number of reclosers planned for installation is important. SCADA-controlled switches allow for both automation observability and coordinated automatic control. Fully automatic switches do not necessarily allow for automation observability and they also have limitations dealing with off-nominal switch positions.

3. Newton-Evans Global Market Study of Fault Detection, Isolation and Restoration.
4. For feeder voltages below 13kV, it is clear that automated and/or supervisory feeder section switching is incorporated into feeder design.

5. Note that the average number of normally open feeder tie points per feeder includes manual and automated feeder tie points. Additionally, utilities reported that the average feeder at all distribution voltages has more than one load transfer or restoration source.

6. System Average Interruption Duration Index.

7. System Average Interruption Frequency Index.

8. Customer Average Interruption Duration Index.

9. Typically, VOS is measured in: a) Cost (US Dollars, Euros, etc.) per kWh unserved, based on outage duration and customer load, and b) Cost per outage based on the number of outages experienced. For more information, see the proceedings of the California Energy Commission, Pier Final Project Report -- Value of Distribution Automation Applications, CEC 500-2007-028, April 2007.

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