Service Restoration Overview

The service (or outage) restoration process is perhaps the most complicated operational process at any electric utility. It requires coordination and communication across all of the key functions of the distribution business and is implemented in a time-critical environment (often in extreme weather conditions and non-standard working hours). It requires an extraordinary focus on safety while key participants are making innumerable real-time decisions to satisfy operational, engineering, and customer-related demands.

These extreme and complex performance requirements have led utilities to take a highly process-focused approach to managing and monitoring these critical reliability-related activities. While no two utilities implement these processes in precisely the same manner, they all follow a general flow as outlined below:

Outage Detection and Analysis

This first step in the process begins with the first call, which is usually initiated by a customer but sometimes originated from police/fire agencies or the public at large when they observe wire down, street lights out, etc. In the more advanced system configurations, this initial notification may be provided by sensing devices. Regardless of the manner in which an outage is reported, it is important to properly group multiple calls with a common root cause into a “case” or “outage”, with each representing a group of one or more customers who are electrically “behind” the same isolating device (e.g. fuse, recloser, circuit breaker, substation, bus, or transmission line). Though the outage management system uses an algorithm to indicate the connectivity of customers to a common device, a human intervention is usually required to analyze the outage and confirm or change any automated assignment. Final determination will be made based on the crews’ on-site observation, but initially a dispatcher or case analyst working with the dispatcher will need to correlate calls to cases or outages.

Trouble Dispatch

Once the dispatcher has identified a “case” or outage, a trouble man will be dispatched to the assumed location of the fault (or alternatively to the location of the isolating device). As soon as the first call comes in, it is normally handled as a “single no-light” (i.e., an outage involving only one customer) and the trouble man is directed to start moving in that direction. As the calls increase and the case is analyzed, the location will likely change from the premise of the original call to a common isolating device (fuse, recloser, etc.). The availability of a trouble man (or other first response resource) is a key factor at this stage of the process, as is the dispatcher’s determination of the size and anticipated duration of the outage. During major storms, outages will queue up until the next available resource can be assigned, accumulating minutes of customer interruptions.

Deploy / Drive Time

Inevitably, the trouble man (or alternate first responder) will be directed to proceed to the assumed location of the outage. There are a number of variables that impact travel duration, namely:

• Size of territory
• Time of day
• Deployment of required resources
• Factors related to mobilizing off-duty resources

Patrol and Diagnose

During transit (and certainly once on site), the trouble man will inspect to determine the cause of the fault (i.e. broken limbs, fallen trees, automobile accident, dig in, etc.). This action offers two benefits:

• Focuses on public safety (i.e. locates and isolates any wire down situation)
• Locates the fault.

Often the fault will clear itself (i.e. a singed branch often will no longer make contact with the line or an animal may no longer bridge the gap between conductor and ground, etc.). Should this occur, the trouble man will re-energize the line (e.g. replace the fuse, re-set the recloser or breaker), but only after patrolling to ensure that such an action can be accomplished safely.

Switch and Restore

Should the trouble man properly identify and locate the fault-causing device or occurrence, and determine the fault to be permanent pending repair, the next course of action will involve partial restoration (referred to as “cut and run” to restore some, if not most of the customers). This is typically accomplished by isolating the faulted section of line, and then re-energizing the unfaulted sections by:

• Operating two disconnect switches on the line – which are placed at various points along the line, or
• “Cutting in the clear” (i.e., cutting the conductor on each side of the faulted section, with the intention of splicing the line back once the repair is done).

If the permanent repair is straightforward and can be accomplished quickly, or if the number of customers affected is small and not easily restored by other means, this switch and restore step can be skipped (with the concurrence of the dispatcher) and the process will then transition to permanent repair and restoration.

Repair Dispatch

Rarely can a lone trouble man do more than a minor repair. Therefore, once a faulted section is isolated, a full line crew is usually mobilized to perform the necessary permanent repair. This requires going through the dispatch function as the line crews that are typically scheduled to perform new construction, forced relocation, or planned replacement/upgrade work need to be shifted to this higher priority work.

Repair and Restore

Once the repair crew arrives at the site of the outage, permanent repair can be made and the remaining out-of-service customers are restored.

Within the context of the outage restoration process, one can isolate each step and identify opportunities for improving service restoration (i.e. reducing customer minutes of interruption). And every utility should, as a matter of course, challenge each step in the process to identify improvement opportunities and incorporate any findings into its overall service restoration program.

Service Restoration Performance

Service restoration, typically measured in terms of the average time required to restore service to the average customer per sustained interruption (CAIDI), can be analyzed from three perspectives:

• Mobilization (with an emphasis on being proactive in terms of planning and establishing contingencies),
• Work flow (focusing on partial restoration and follow through for permanent restoration), and
• Communication (both externally with the customers and internally in terms of timely reporting of customer restoration).

From a “best practices” perspective, this analysis yields a number of recurrent themes:

• Accurate prediction and assessment of damage is essential
• Command structure needs to be flexible in terms of switching modes of operation and decentralizing control as the weather changes from non-storm to storm
• Technology must be adaptable to ever-changing volume of service interruptions
• Internal communication related to planning and managing contingencies and external communication in managing customer expectations are the primary differentiators between outstanding and poor performance