480 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 21, NO. 1, JANUARY 2006

Collecting and Categorizing Information Related toElectric Power Distribution Interruption Events:

Data Consistency and Categorization forBenchmarking Surveys

Val G. Werner, Member, IEEE, Donald F. Hall, Senior Member, IEEE, Rodney L. Robinson, Member, IEEE, andCheryl A. Warren, Senior Member, IEEE

AbstractReliability of electric power systems remains an im-portant societal issue. While transmission disturbances draw na-tional attention and scrutiny, service interruptions at the distribu-tion level are the primary concern of the end-use customer andtheir regulatory and governmental representatives. Much efforthas been expended in developing methods to uniformly and con-sistently quantify the reliability of distribution service based onelectric system performance. However, the results of a nationwidesurvey of recorded information used for calculating distributionreliability indices performed in 1998 by the Working Group onSystem Design indicate that significant inconsistencies exist in thedata, categorization of that data, and in the collection processesused within the industry. This paper is one in a series of papers thatdiscuss the collection and categorization of information related toelectric power distribution interruption events and will be used inthe development of industry guidelines. This paper presents a min-imal set of data and a consistent categorization structure that whenused in combination with IEEE Std. 1366 will promote consistencyin how the industry collects data for the purpose of benchmarkingdistribution system performance.

Index TermsPower distribution reliability, reliability manage-ment, sampling methods.

I. INTRODUCTION

B ENCHMARKING of distribution reliability performancehas become commonplace in the electric power industryover the past several years, despite the fact that useful com-parisons are often difficult to make due to the data collectionmethods employed, differences in system design and operation,and differences in the environments. Many benchmarkingstudies have been established, each with its own criteria todefine how data should be provided and analyzed. In order toarrive at meaningful conclusions, consistent interruption eventdata and categorization of that data are desirable. IEEE Std.1366-2003 [1] has defined a methodology that, if used, willprovide a common way to segment data thereby eliminatingone of the two major hurdles to benchmarking. The purpose ofthis IEEE Task Force on Interruption Reporting Practices is to

Manuscript received Novenber, 16, 2004. Paper no. TPWRD-00536-2004.V. G. Werner is with We Energies, Milwaukee, WI 53203 USA (e-mail:

val.werner@we-energies.com).D. F. Hall is with SPL WorldGroup, Inc., San Francisco, CA 94105 USA.R. L. Robinson is with Westar Energy, Topeka, KS 66601 USA.C. A. Warren is with National Grid USA, Albany, NY 12203 USA.Digital Object Identifier 10.1109/TPWRD.2005.852303

define data collection procedures. Clearly, this is a large topicand therefore the group has elected to start with benchmarkingdata collection issues.

This paper presents suggestions on comparison of utilitiesbased on a high-level categorization of interruption relateddata. It is not meant to limit how detailed the collection of datacould be, or to say what must be collected, rather to definethe minimum set of data collection categories required forbenchmarking and to give consistency to those categories.

The Task Force used a survey they performed in 1998 as abasis for their continuing work [2]. They also reviewed other ap-proaches to data categorization, before developing the approachoutlined in this paper [3], [4].

When performing benchmarking studies, the differences be-tween the collection methods, the locations, and the differencesin system design, can make comparison difficult. Examples ofthe types of items that may be relevant when performing bench-marking studies are listed below.

Collection Methods: differences in the interruption data collection systems

(ranging from manually entered paper systems to com-pletely automated computer based systems);

ability to collect interruption data from the system(ranging from the substation level down to the customerservice drop);

use, or nonuse, of step restoration when collecting inter-ruption data;

determination of the start time; definition of sustained interruption, which may play a role

(ranging from greater than 1 min to greater than 5 min); definition of a customer (account, meter, premise, etc.); interruption delineations (unplanned interruptions,

planned interruptions, major events, etc.).Location: system characterization (rural, suburban, urban); climatic information (hot, cold, wet, dry, lightning, etc.).

System Design: system layout (radial, loop, two transformer station, etc.); system placement (underground, overhead, etc.).

This paper presents a minimal set of data and a consistent cat-egorization structure necessary for comparison of distribution

0885-8977/$20.00 2006 IEEE

WERNER et al.: COLLECTING AND CATEGORIZING INFORMATION RELATED TO ELECTRIC POWER DISTRIBUTION INTERRUPTION 481

system performance. Categories for system characterization, in-terruption causes, responsible systems, conditions, voltages, de-vices, device initiation, and restorations are presented.

II. SYSTEM CHARACTERIZATIONIt is important to identify the composition of the utilities par-

ticipating in a benchmarking study. The characterizations of theutility system are usually broken into the three categories below.The categories are defined by the customer density per kilo-meter, as shown.

1) rural (less than 31 customers/km);2) suburban (31 though 93 customer/km);3) urban (greater than 93 customers/km).Percentages of the total customers are applied to each of the

categories above to describe the make-up of each utility.

III. INTERRUPTION CAUSE CATEGORIES

Ten general interruption cause categories are suggested forcomparison in benchmarking studies. These are intentionallybroad categories that will make possible more precise bench-mark comparisons between different distribution utilities. Thereare numerous categories that could be chosen, but with the goalof uniformity for comparison purposes, the Task Force arrivedat the following ten categories:

1) equipment;2) lightning;3) planned;4) power supply;5) public;6) vegetation;7) weather (other than lightning);8) wildlife;9) unknown;10) other.The recommended categories do not prevent a utility from

collecting more detailed data, and that is indeed encouraged.However, the data collected should be able to be rolled up intoone of the ten categories recommended.

The following paragraphs describe the types of interruptionsthat should be put into each category. Of course, not every pos-sible interruption can be discussed, but for most interruptions,the choice of category is apparent. The cause categories are dis-cussed in the order as presented above.

1) Equipment: Any piece of the distribution systemequipment that is defective or fails and causes an inter-ruption to customers should be put in the Equipmentcategory. A few examples of equipment types includeControls, Conductors, Insulated Transitions, Inter-rupting Devices, Arresters, Structures and Supports,Switches, and Transformers.

2) Lightning: The Lightning category includes all inter-ruptions caused by lightning. This may be by directstroke, contacting the wires or another piece of equip-ment, or by lightning-induced flashover of the wiresand/or another piece of equipment.

3) Planned:The Planned category includes, but is not lim-ited to, Road construction, maintenance and repairs,load swaps, replacing equipment, and house moves.Typically, Planned interruptions are those interruptionsthat can safely be delayed by the utility personnel andperformed only after the appropriate or required cus-tomer notification. Regulatory commissions have oftenspecified rules describing planned interruptions.

4) Power Supply: The Power Supply category includesinterruptions caused by a failure in the TransmissionSystem, including the transmission portion of a sub-station or the loss of a Generating Unit including theseassociated with distributed generation. It does not in-clude outages due to the loss of a distribution substa-tion component, whether caused by the equipment it-self or another cause, that may impact other distribu-tion substations and/or feeders.

5) Public: Any interruptions resulting as an act of thepublic at large should be put into the Public cate-gory. Examples include customer trouble, nonutilityemployee or contractor dig-in, fire/police requests,foreign contact (such as Mylar balloons, crane boom,aluminum ladder), traffic, vandalism, and fires andexplosions not originating on or within utility ownedequipment.

6) Vegetation: The Vegetation category includes interrup-tions caused by falling trees or limbs, growth of trees,vines, and roots. It should be emphasized that if a treeis involved, the cause category is Vegetation. This isimportant to note during wind storms. It may not bepossible to determine that a feeder may have a forestryissue if wind is listed as the cause when actually a treewas involved.

7) Weather: The category of Weather should includeinterruptions due directly to a weather phenomenon,including wind, snow, ice, hail, and rain, where theweather itself caused the interruption and exceededthe system design limits. Note that if any part of a treeis involved, it would go under the Vegetation category.Wind does not include slapping or galloping conduc-tors; those would go under the Equipment category.Ice forming on conductors and tearing them down orflooding of power facilities would be included in theWeather category.

8) Wildlife: This includes mammals, birds, reptiles, andinsects or any other nonhuman member of the animalkingdom. Wildlife can cause interruptions directlythrough contact like snakes, mice, ants, raccoons,squirrels, or birds, or indirectly like nests and birdexcrement.

9) Unknown: The Unknown category includes any cus-tomer interruptions where a definitive cause cannot bedetermined after investigation.

10) Other: Any interruptions to customers that do not fallinto any of the other cause categories should be as-signed to the Other category. Some examples includeerrors in construction, maintenance, operating or pro-tecting; overload; and contamination.

482 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 21, NO. 1, JANUARY 2006

IV. RESPONSIBLE SYSTEMWhen participating in benchmarking studies, it is useful to

know the responsible system. This is defined as the portion ofthe system in which the fault initiated. There are several respon-sible system categories. These include the following:

1) distribution overhead;2) distribution underground;3) generation;4) substation;5) transmission;6) customer equipment.The first five categories above should be easy to understand,

and no further discussion is included for those. The customerequipment category refers to customer owned equipment that isan integral portion of the utilitys system, and when a fault oc-curs on the customer-owned equipment, it causes interruptionsto one or more of the utilitys other customers.

V. CONDITIONSThe categories under conditions refer to conditions at the

time of the interruption. Many times the condition may be acontributing factor to the number of customer interruptions orthe time it takes to restore customers. The conditions may playan important role when analyzing benchmarking data. The pro-posed Condition categories include

1) routine (day-to-day);2) major event.Routine is defined as daily conditions that do not constitute a

Major Event Day. A Major Event Day is defined by IEEE Std.1366-2003 in the Major Event Day definition [1].

VI. VOLTAGE LEVEL

In some benchmarking studies, information is providedusing typical voltage classes (phase to phase) as shown in thelist below. The voltage information for a customer interruptionevent should be based on the highest voltage level affected.

1) secondary/low voltage;2) 5 kV;3) 15 kV;4) 25 kV;5) 35 kV;6) kV;7) transmission/generation.

VII. INTERRUPTING DEVICES

Benchmarking studies may review the type of interrupting de-vices used, their failure rates, how many operations occurred,and the total number of devices deployed. Interrupting deviceis the device that initiates the start of the customer interruption.The following is the recommended list of categories of inter-rupting devices.

1) circuit breaker/substation recloser;2) fuse;3) line recloser;4) sectionalizer;

5) switch;6) other.The following discussion centers on which particular devices

should be put into each category; of course, not every possibledevice can be discussed. The circuit breaker/recloser categoryshould include circuit breakers and reclosers found in substa-tions and those used for protection of entire feeders/lines. Thefuse category should include line, tap, and transformer fuses.Reclosers located along a circuit/line should be in the line re-closer category. Gang switches and blade disconnects are cap-tured in the switch category. Any other interrupting devices notcovered by the first five categories, including an open conductor,are grouped under the other category.

VIII. INTERRUPTING DEVICE INITIATION

Another analysis of interrupting devices may include themanner in which they operated when they were opened andclosed. These operations can fall into the following recom-mended categories.

1) automatic;2) manual.Automatic includes all operations without human interven-

tion. Manual is any operation that involves personnel to operatethe device whether at the location of the device or from a remotelocation.

IX. CUSTOMER RESTORATION

Benchmarking studies may analyze how customers are re-stored after experiencing an interruption to power. There maybe several ways to reenergize customers after an interruption.The suggested categories are as follows:

1) automatic substation transfer;2) automatic circuit sectionalizing;3) manual circuit sectionalizing;4) left disconnected;5) reenergized at station;6) repaired defective equipment;7) replaced defective equipment;8) replaced fuse;9) reset transformer breaker.The first category (automatic substation transfer) includes any

scheme that transfers customers to an alternate supply in theevent that their primary supply is interrupted. This scheme op-erates without any human intervention. Automatic circuit sec-tionalizing refers to any automatic schemes outside the substa-tion that transfers customers experiencing a power interruptionto another energized circuit segment either on the same circuitor a different circuit. Manual circuit sectionalizing refers to anyaction taken by field personnel or remote operation by an op-erations supervisor to transfer interrupted customers to otherfeeders/circuits. This also includes resetting midline reclosersand operating switches to reenergize interrupted customers toanother part of the same feeder/circuit. In some cases, customerswill not ever be put back in service due to fire, flood, or someother destructive force that destroys the entity requiring power.In this case, left disconnected is the category.

WERNER et al.: COLLECTING AND CATEGORIZING INFORMATION RELATED TO ELECTRIC POWER DISTRIBUTION INTERRUPTION 483

Sometimes a feeder/circuit is locked out at the station and nocause is found. The circuit breaker or recloser is closed again(reclosed), and if it holds, the category reenergized at station ischosen. It may also be used for transformer or bus outages inthe station. The last four categories are self-explanatory.

X. EQUIPMENT FAILURE OR DETERIORATIONBenchmarking studies frequently examine equipment perfor-

mance as well. This equipment is usually failed equipment thatinitiated the customer interruption. Typically, pieces of equip-ment are grouped into different categories. Data collected maybe by number of interruption events, number of customers af-fected, or by duration of the interruption. Results from this datamay reveal rates of failure for various types of equipment, ifsome utilities have a problem with a type of equipment as com-pared to other utilities, and how the use of equipment varies fromone utility to another. The following is the recommended list ofcategories of equipment.

1) cable;2) wire;3) connector;4) control;5) insulated transition;6) interrupting device;7) lightning/surge arrester;8) other equipment;9) structural support;10) switch;11) transformer.The cable category includes all cable that is direct buried

or encased in pipe or conduit or U guard. Wire refers to over-head strung conductors and jumpers. Connections, splices, andother hardware are not included in these two categories. Theconnector category includes connectors, insulinks, splices, etc.The control category contains relays, meters, and other controlequipment. Insulated Transition is comprised of bushings, insu-lators, separable connectors, polymeric terminations, potheads,stress relief cones, etc. The interrupting device category con-sists of circuit breakers, reclosers, and fused equipment. Thelightning/surge arrester and other categories are self-explana-tory. The Structural support category includes anchors, poles,towers, cross arms, braces, etc. The switch category containsdisconnect or isolation, load break, blade cutouts, etc. The lastcategory (transformer) can include auxiliary, current, distribu-tion, grounding, potential or voltage, power, rectifying, step-down/conversion, and voltage regulating transformers.

XI. SUMMARYThe Task Force is defining data collection methods, proce-

dures and approaches. The first phase of their work is to definea minimum set of categories necessary to compare benchmarkdata. Taking the approach outlined in this paper will allow util-ities to more clearly benchmark performance with one another,since they will be using a common categorization strategy.

The Task Force will continue to work on this project and plansto develop a minimum data set required for accurate collectionof interruption data.

REFERENCES[1] IEEE Guide for Electric Power Distribution Reliability Indices, IEEE

Std. 13662003, 2003.[2] A nationwide survey of background information used for the calcuala-

tion of distribution reliability indices, in Proc. IEEE PES General Mtg.,Toronto, ON, Canada, 2002.

[3] Annual Service Continuity Report on Distribution System Performancein Electrical Utilities, Canadian Electricity Assoc., 2001.

[4] Interruption Reporting and Service Continuity Standards for ElectricDistribution Systems,, REA Bull. 161-1, 1972.

Val G. Werner (S88M90) received the B.Sc. degree in electrical engineeringfrom the University of Wisconsin, Milwaukee, in 1990.

He was with Eaton Corporation, Milwaukee. He is now with We Energies,Milwaukee, as a Senior Engineer in the Distribution Protection and ReliabilityGroup. His main areas of expertise are distribution reliability analysis and trans-mission planning.

Mr. Werner has been an active member of the IEEE Std. Working Group onSystem Design that produced the IEEE Std. 1366-2003 IEEE Guide for ElectricPower Distribution Reliability Indices.

Donald F. Hall (M87SM96) was born in Cheverly, MD. He received the B.S.degree with honors in electronics engineering technology from Capitol College,Laurel, MD, in 1986.

He is currently a Product ManagerDistribution Management with SPLWorldGroup, San Francisco, CA, where his responsibilities include productstrategy, new product definition, product release content, product packaging,and reliability consulting. He has over 22 years of experience in powerdistribution, including real-time software application development; reliabilityconsulting; asset management; information systems development; distributionautomation and control; small area load forecasting and system modeling;system analysis, planning, and design; nondestructive diagnostic testing; andfield resource management. Prior to joining SPL in 2004, he served in variousengineering, management, and product management positions with CESInternational, the Northern States Power Company, and the Potomac ElectricPower Company.

Mr. Hall is a registered Professional Engineer in the District of Columbia andthe state of Maryland.

Rodney L. Robinson (M85) received the B.Sc. degree in electrical engineeringfrom the University of Arkansas, Fayetteville, in 1976.

He has been with Westar Energy, Topeka, KS, or its subsidiaries since grad-uation. He is now DirectorReliability Management. His primary areas of re-sponsibility are the distribution reliability programs.

Mr. Robinson has been an active member of the IEEE Working Group onSystem Design that produced the IEEE Std. 1366-2003 IEEE Guide for ElectricPower Distribution Reliability Indices.

Cheryl A. Warren (S85M87SM99) received the B.Sc. and M.Sc. degreesin electrical engineering from Union College, Schenectady, NY, in 1987 and1990, respectively.

She has been with Central Hudson Gas and Electric Company, Poughkeepsie,NY; Power Technologies, Inc./Stone and Webster, Schenectady, and NavigantConsulting, Inc., Albany, NY. She now works for National Grid USA ServiceCompany, Inc., Albany, as the manager of distribution system engineering.Her main areas of expertise are distribution reliability analysis, power quality,GIS/OMS, and enterprise-wide IT systems integration. She has authored orco-authored 26 technical papers.

Mrs. Warren chairs the IEEE Working Group on System Design that wrotethe IEEE Std. 1366-2003 IEEE Guide for Electric Power Distribution ReliabilityIndices.

tocCollecting and Categorizing Information Related to Electric PoweVal G. Werner, Member, IEEE, Donald F. Hall, Senior Member, IEEEI. I NTRODUCTIONCollection Methods:Location:System Design:

II. S YSTEM C HARACTERIZATIONIII. I NTERRUPTION C AUSE C ATEGORIESIV. R ESPONSIBLE S YSTEMV. C ONDITIONSVI. V OLTAGE L EVELVII. I NTERRUPTING D EVICESVIII. I NTERRUPTING D EVICE I NITIATIONIX. C USTOMER R ESTORATIONX. E QUIPMENT F AILURE OR D ETERIORATIONXI. S UMMARY

IEEE Guide for Electric Power Distribution Reliability Indices, A nationwide survey of background information used for the calcuAnnual Service Continuity Report on Distribution System PerformaInterruption Reporting and Service Continuity Standards for Elec