Today, it is fairly common practice in the electric utility industry to use the standard IEEE reliability indices (CAIDI, SAIFI, SAIDI) to track and benchmark reliability performance (Table 1). Indices serve as valuable tools to compare utility reliability performance, as long as similar data is being matched (for example, all data that excludes major storms or defines an interruption in the same manner).

Yet how many electric utilities truly use their reliability data beyond the corporate, division or regional levels? Many utilities simply report reliability indices at the corporate level, as this is a regulatory requirement. Such limited reporting forgoes the potential benefits data could provide at working levels within the organization.

As the electric utility industry moves toward widespread deregulation and open competition, utilities are pushing daily operational responsibility to the lowest levels of the organization in an attempt to reduce costs and remain competitive. The utility's access to accurate and timely outage information is critical in order to maximize daily operational efficiency, minimize customer complaints and maintain electric system reliability.

A Need for Reliability

In 1991, Niagara Mohawk Power Corp. (NIMO), an investor-owned electric and gas utility serving 1.5 million customers in a service area encompassing 24,000 sq miles (62,160 sq km) in New York, U.S., recognized the need to provide reliability performance tracking indices below the system and regional levels. Reliability indices now also are produced at the operating district and crew center levels (subsets of the region) (Fig. 1). NIMO's intent was to drive the corporate level reliability-reporting program to the lowest levels. Its approach included education, data collection, tracking and reporting.

Project Details

The ability to generate reliability indices by area, operating district or crew center permits these entities to be flagged for critical review and for localized corrective actions before severe outages and customer complaints occur. NIMO proactively addressed poorly performing areas by more efficiently assigning budgets and schedules for maintenance and tree trimming, while tracking work crew response and performance levels.

"Utilization of our reliability data at the operating district and line barn levels has allowed us to more accurately pinpoint trouble areas and take specific corrective actions to enhance reliability," says Joe Godlewski, system T&D director at NIMO.

The utility enhanced its ability to report interruptions by revising the field manual for the computer system that records data. It also updated the interruption reporting manuals to reflect current reporting requirements and modernized and updated the interruption report form to include more diverse outage-cause codes.

The utility's educational approach began with teaching employees the definitions of reliability indices, stressing the importance of collection of accurate interruption information and outlining how that information is used to track and resolve reliability issues at the corporate and local levels. The utility then initiated systemwide training to teach personnel how to properly complete the interruption form, when to report and how interruption data is used within the company.

The reporting process includes monthly issuance of reliability charts for regional SAIFI and CAIDI performance to be displayed in each work location. This process reinforces the point that reliability issues at the work location do impact the overall corporate reliability program.

The interruption reporting database (IRD) was converted from an SAS-based system to DB2, which increased its speed and flexibility for users entering or retrieving data. The revised forms tracked interruptions down to the operating district level where the problem occurred and required entry of the crew center code assigned to responding line personnel. Enhancements also required more detailed reporting of transmission and station-caused interruptions. Although the form allowed for identification of an interruption as either transmission or station in origin, the IRD was inconsistent in recording outage data for those facilities. Consequently, every NIMO transmission line was assigned a unique identifier for entry into the IRD to enable faster and easier reliability tracking and analysis.

Interpreting the Data

Interruption reporting enhancements enable the utility to identify and review transmission, station and distribution trouble spots for corrective action, which helps minimize future outages and their impact on CAIDI and SAIFI. In Table 2, the central region indices by facility indicate a longer duration for outages on the distribution feeder (primary) and a shorter duration for the station and transmission outages. This is not unusual, depending on the facility's configuration, as switching schemes and alternate sources would isolate and restore station and transmission outages sooner.

The distribution primary facility can be broken down to the five individual operating districts in the central region to identify the reason the distribution primary facility CAIDI is longer than 2 hr. District C data is shown in Table 3 with a CAIDI of 2.24 hr. For distribution primary outages only, the data is sorted by reported cause to pinpoint the element driving the CAIDI. In District C, lightning, tree contacts and vehicles are the main drivers for primary distribution interruptions.

Detailed interruption data by distribution feeder for multiple years can be retrieved for lightning, tree and vehicle causes by street and pole number in District C and scrutinized for necessary corrective action. Table 4 displays detailed interruption data for a District C distribution feeder.

Corrective actions could include installation of lightning arrestors on sections of the distribution feeder, modification of tree trimming schedules or other actions. Since its inception, this process has successfully identified areas for installation or replacement of lightning arrestors, animal guards, line fuses, switchgear and danger tree removal on distribution feeders.

This analysis also includes transmission lines and stations when the interruption data suggests a problem with those facilities. This review allows NIMO to more efficiently and effectively use its work force resources by focusing reliability improvements where they are needed.

In addition to CAIDI, SAIFI and SAIDI, the statistics include interruptions by hour of the day by crew center, interruptions by crew center for each operating district, interruptions by affected facility, and equipment or cause involved by affected facility.

Table 5 displays indices by crew center in Area 1, District A of the central region. The indices highlight an average CAIDI of more than 3 hr for interruptions to which Crew Center East responded. On the other hand, the Crew Center North frequency of outages or SAIFI tops the five District A crew centers at 0.182. When indices are high for a crew center (such as Crew Center East in this example), their crew center code may be submitted for a date range to print the detailed interruptions for review and possible corrective actions.

Interruption data for the North and East crew centers may indicate high CAIDI and SAIFI values are caused by a facility problem, such as insulator failures. The data also may identify the need to review work force practices. The detailed interruption data may indicate that the damage severity of a few outages, their physical location or recent severe weather that did not qualify as a major storm are driving the indices legitimately, possibly requiring no corrective action.

Project Benefits

In the future, as NIMO moves into the geographic information system age, linking sustained and momentary interruption data with the budgetary process will substantially enhance information to help make critical, effective electric reliability operating decisions.

Do electric utilities truly understand what the reliability indices are telling them and how to react when they are getting worse? Electric utility reliability surveys generally reflect that the equipment and cause of outage are emphasized only at a system or division level. By limiting the focus to these upper levels, utilities fail to take full advantage of their reliability tracking efforts and the benefits such data can provide.

Breaking down outage frequency by cause and duration at the operating district and crew center levels helps distribution engineers, T&D operations, forestry and maintenance managers pinpoint specific reasons for reliability problems. The initiative has resulted in a more reliable and accurate interruption database that tracks electric service problems and outages to the lowest operating levels by crew center, facility or cause. The new procedures and upgraded reporting system help identify locations where proactive mitigation efforts may be needed before a repetitive outage trend develops. This reporting ability enables NIMO to more effectively compete in the newly deregulated competitive marketplace.