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Electric Power Distribution Handbook

T. A. Short

Overhead Line Performance

Publication details https://www.routledgehandbooks.com/doi/10.1201/b16747-4 T. A. Short Published online on: 19 May 2014

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The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The publisher shall not be liable for an loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material. Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 Overhead Line Performance Line Overhead 3 repair is expensive and time consuming. In addition to long-duration In consuming. interruptions, time and expensive is repair and often equipment,extensive, is damage contact utility trees When interruptions. number one of the or are cause number two trees For expensive. is utilities, many vegetation and management on issues circuits, Trees source of reliability many the are 3.1 for performance. as well normal as tions for resiliency have chapter applica also this in discussed programs of Many the customer impacts. reduce improvements or can resiliency to repair reduce and to reduce times damage of overhead Hardening days. infrastructure to lasting customer interruptions leading repair, response and normal autility’s overwhelm can overhead system distribution reliablemonitored to service. continue safe, providing managed and and The deterioration replacement equipmentof be must infrastructure. have aging but many utilities 50 haveyears, long oftenexceeding tor, life, all hardware line and Poles, conduc infrastructure. and/or distribution of improve their performance the to maintain use chapter, or this options utilities In that programs we explore several and/or mechanically. electrically overhead lines, stress distribution can ofeach these of various sizes— animals and whole branches, trees, tree light, ultraviolet fungi, Wind, References 133 3.6 3.5 3.4 3.3 3.2 3.1 Contents Major storms increase stresses on overhead infrastructure, and damage to the to the damage and on overheadMajor stresses infrastructure, increase storms

Vegetation Management Vegetation Hardening and Resiliency Pole Inspections and Maintenance Inspections and Maintenance 3.3.2 3.3.1 Animal Protection Covered Conductors 3.1.5 3.1.4 3.1.3 3.1.2 3.1.1 Vegetation Management Animal Guards, Wire Coverings, and Protective Other Equipment Animal-Fault Basics Vegetation Program Performance Hazard-Tree Programs Utility Tree Maintenance Programs Physics of Tree Faults Outages and Damage from Trees 104 106 108 123 125 131 114 115 117 99 96 92 91 91 - - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 maintenance and more tree-resistant designs can also reduce maintenance costs. reduce maintenance also more can and designs tree-resistant maintenance more efficient performance, addition to improving budget. So, in the vegetation in infrastructure. to distribution damaging particularly are major trees storms, During interruptions. momentary cause can voltage and cause sags trees from faults the 92 of Alexander Kirichenko. Kirichenko. of Alexander Figure 3.1 (1994) equipment.conductorsor et al. bridging branches Rees or breaking examined of conditions: ahandful from occur generally by trees Faults caused vegetation management. optimize and more design structures tree-resistant utilities should of help that done work been 1990s has deal the A great since faults on tree more managemaintenance. vegetation efficiently help and utilities lines tree-resistant more design help utilities will damage outages how and cause Understanding trees 3.1.1 For most utilities, vegetation management is by far the largest maintenance item maintenance vegetation largest management the byFor is far most utilities, Utility studies of tree outages have shown that most outages are caused from trees outages of trees have from tree most caused outages studies shown are that Utility • • • • Natural tree growth causes a bridge across conductors across abridge causes growth tree Natural conductor to conductor from abridge forms and wires the across falls A branch conductors together push wind Tree by blown the branches point) attachment telecom third-party above the just shows pole breakage acommon 3.1 (Figure pole hardware or break poles down knock or major limbs trees Falling Outages and Damage from Trees Video sequence of a falling tree causing a fault and breaking a pole. (Courtesy (Courtesy a pole. breaking and a fault causing tree of a falling sequence Video http://youtu.be/-gUD31Bqnuo Electric Power Distribution Handbook Distribution Power Electric .) Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 tree-caused outages: tree-caused tree-related of breakdown over outages following over found and the 3000 7years 1, 2001.) 1, outages, tree Understanding Figure 3.2 3.1 outages (see most tree the caused limbs and failures tree that found of 2328 The outages. ECI atotal survey tree and of over utilities 20 survey causes. fault of good outage when recording tance code investigating were caused tree as outages reported sample outage found 25% set Energy’s that of investigations of this addition, Duke In outside of a30-ft (9-m)right-of-way. 45% caused treetrees outages. of limbs or Dead 86% were of line. from these on fell the tree entire when an outagesof occurred tree 62% zone, or and branch. weremaintenance by abroken caused trunk 75% sample, outside from this came the In 64% were and trees. live from trees, dead outages 1995, from asample of In 250 tree-caused 36% were on from ages services. for 14% were of most outages of 3.2), (Figure out that these reported Finch also and zone out covering outside maintenance to 10 their ft (3 86% were faults of from tree permanent of 2000. Grid) National in performed a part growth. from 12% were 18%ruptions and follows: as 70% failure, failure, branch from tree from growth. 2% 11% and tree from branches, trees, falling from outages broke follows: were down as tree-caused results 63% that brokenmain from of Grid). National now is that a part The Massachusetts in (a utility Associates small • • • Detailed tree outage codes allow utilities to target causes more causes precisely. to target utilities See outage allow codes tree Detailed Finch (2003a) (ECI) Inc. of Consultants on a1995 results reported Environmental Taylor (2003) outages where on 73% of a1995 reported tree-caused sample survey Finch (2001) Mohawk Niagara Power that on (now asurvey reported Corporation by Hydro BC tree-related (2004) of inter their 1008480 surveys documents EPRI Simpson Utilities (1997) at Eastern faults of tree-caused on asurvey reported for a breakdown of tree faults and their impact on outages impact for their one for and Note faults utility. of a breakdown tree that 98% of tree-caused outages were from trees or tree parts falling on lines; less than 2% than less on lines; falling parts or tree were trees from outages 98% of tree-caused equipment to utility damage 23% were mechanical from distance alimited across 75% shorts by dead were caused were due to natural growth or burning branch tips beneath the lines the beneath tips branch or burning growth were due to natural Niagara Mohawk survey of tree outage causes. (Data from Finch, K., K., Finch, from (Data causes. outage of tree Mohawk survey Niagara Large limb Small lim Tree fell Growth EEI Vegetation Meeting EEI Managers Overhead Line Performance b 01 Percent ofpermanenttree not 02 caused by trees. This highlights the importhe highlights This by trees. caused faults bycause 03 04 m). accounted only Growth Figure 3.3 Figure 0 , Palm Springs, CA, May CA, Springs, , Palm ). Table Table 93 - - - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 94 Tree on multiplex cable or open-wire secondary Limb fell from inside right-of-way Vines Tree inside right-of-way on (fall/lean primary) Limb fell from outside right-of-way Tree/limb growth Tree outside right-of-way on (fall/lean primary) TABLE 3.1 trends: the moreThey causes faults. following of found about specific Taylor (1993) Energy’s to learn outage database Duke to analyze developed astrategy vegetation to help faults management. Chow guide about and tree-caused to learn have relatively on outage impact less duration. growth tree and vines Likewise, ages. number of out customer of on relative minutes actual interruption the toimpact the (whether or inside from outside right-of-way) of falling the trees amuch cause larger Tree and Outages Clearance Caused Figure 3.3 Note: Source: • • • done has considerable Energy aresource work Duke as its outage on database using of all of Duke’s outages).of all 15 (trees events to 20% outage cause tree of all rate the over is twice which lockouts, 35 of the to 50% caused trees lockouts, recloser and breaker circuit Of devices. tive protec of other were operations than by trees caused to be wererecloser more likely or a line breaker circuit of lockouts a substation lines, same these Along by trees. device protective and Phasing the dayweek. the of by influenced Tree were not greatly ning. faults eveand afternoon the during occurred faults More winter. tree during occurred of day time and Season snow,and rain, ice. also and wind especially faults, tree affects Weather CI Data from aSoutheastern U.S. utility, 2003–2004. = customer interruptions; CMI Percentage of Tree Faults in Category Each ECI survey of tree outage causes. (Data from Finch, K., K., Finch, from (Data causes. outage of tree survey ECI —When looking at the likelihood of tree-caused faults, weather strongly strongly weather faults, of tree-caused likelihood at the —When looking Growth Uproot Trunk Other Limb Cut Electric Power Distribution Handbook Distribution Power Electric —The most tree faults occurred during summer and the least the least and summer during occurred —Thefaults tree most 05 — Multiple-phase faults are more likely to be caused caused to be more are likely faults — Multiple-phase , EEI Natural Resources Workshop, 1, Resources 2003a.) April Natural , EEI Percent oftree-causedfaults = customer minutes of interruptions. 10 15 Outages 20 10.0 12.6 18.0 21.1 26.0 3.6 8.7 25 30 Understanding Line Understanding 14.8 20.1 14.4 37.2 CI 0.2 9.8 3.6 CMI - - 15.2 18.1 13.3 42.5 0.2 7.5 3.1 - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 indicators of the likelihood of a tree-caused interruption. of atree-caused likelihood ofindicators the significant weather,that of day, time were protective most device and statistically interruption. They found tree-caused of a likelihood the influence mostly ables that vari the to identify regression analysis concept the to includeextended astatistical Figure 3.4 rates; fault had similar have utility muchcircuits lower this trees, from rates fault 5-kV held widely that to belief the class Contrary utility. for northeastern another kV averaged customers out 206 per outage. circuits on toages 4.16-kV 2.4 averaged 79 outage, but customers circuits per tree 7.6 to 13.2- out tree-caused that to Finch customers reported on impact less 5-kV circuits. class 3.4. Figure shown in as summer most outages during the (Chow Taylor, and has also 2003). U.S. 1993; utility southeastern Another Xu et al., fall during least the and summer during faults most tree-caused the has Energy Duke removal. hazard-tree backbone, and kV circuit the system, the 13.2- the worstcircuits, target to Mohawk its program Niagara modified results, of basis these the On outages for defects. asample of tree reviewed tree-caused also more They to about learn interruptions. momentary lines distribution contact with in trees with tests live staged Mohawk Niagara also interruptions. on tree-caused details to provide sample more studies used in-depth also and interruptions, of tree-caused 2001, 2003a). source the Mohawk to categorize its outage codes Niagara cause used (Finch, its vegetation systems for management distribution programs restructure Niagara MohawkNiagara (a to company) Grid investigations National several used More recent work (2003) by Xu reported et al. and trends found same of many the Circuit voltage can also impact tree-caused faults. Tree-caused much cause faults. faults tree-caused impact also voltageCircuit can rates. fault on weather, tree impact alarge correlated has with season highly Being

Percent in the given month 10 15 20 5 Tree-caused outage impacts by month. impacts outage Tree-caused Feb Apr Outages Jun Aug Oct Overhead Line Performance Dec Feb Apr Jun CI Aug Oct Dec Table 3.2 Table Feb Apr shows similar trends trends shows similar CMI Jun Aug Oct Dec 95 - - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 96 tree branch must cause a connection between two bare conductors bare two (it between to a connection phase must be branch cause tree can voltages. not The one just touching ute. at fault Atree distribution conductor will for one more min must sustained be than ductors close proximity, usually in which con two must gap branch bridge between the the afault, For to cause branch atree 3.1.2 successfully. reclose or breaker recloser can the restored, is and insulation conductors the the come apart, into conductors to slap push trees together. could them cause and wind Once this: close proximity, notin and conductor just are There to tree. plausiblefor mechanisms must across be they trees, from occur regularly faults temporary So, if below well breakers. reclosers is or what needed tothat is trip circuit 1 than less draws contact but point, contact normally the the near burning be one just conductor There phase may faults. contact with in do not high-current cause not amajor Chapter contributor shown 14, in As interruptions. to momentary trees most To outages. the spacings) following: with on focus the increased to circuits do that, tree-improvement other and maintenance (suchtree strategies covered or as wire maintenance budgets. improve more tree manage and Target efficiently performance onrates 15- 25-kV and systems. class fault tree-caused shows that Table similar utility shows 3.3 asoutheastern from data customersthe impact lower-voltageless on thatfaults is difference main circuits. the Trees are often associated with momentary interruptions, but trees are interruptions, trees probablybut momentary with Trees associated often are • • • • management ofvegetation targeting that should help stronglysuggest findings These Circuits with higher voltage higher with Circuits faults of tree ahistory with Circuits more customers with Circuits circuits of portion Mainline Physics of Tree Faults 25 15 Voltage Class (kV) TABLE 3.3 13.8 4.16 2.4 Voltage (kV) TABLE 3.2 Note: Includes major storms. Tree Faults by U.S. Utility Voltage for aSoutheastern Class Tree Faults by U.S. Utility Voltage for aNortheastern Class Tree SAIDI (min) Electric Power Distribution Handbook Distribution Power Electric 34 22 4 With Major Storms Major With 51 68 Tree Fault Year per 100miles Rate per Tree Fault Year per 100miles Rate per conductor-to-conductor Without Major Storms Major Without 10.8 11.6 9.6 16 27 contacts contacts A, and and A, - - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 can cause faults. ECI (Appelt faults. Finch, cause 2001, Goodfellow, and Goodfellow,can 2004; 2003a; showed that 1994) tests how (Rees et al., branches some tree staged revealing Electric and Gas conditions. Baltimore right the down under wire the enough tobe burn may tree to the arcing the atree, contact with in wires would not small On fault. some may leaves, burn but most 1Aof under conditions; current this it than less or into tophase neutral). branch phase one Atree conductor draws phase normally BioCompliance Consulting, Inc Consulting, BioCompliance Figure 3.5 or the breaker reclosed, recloser opened then is acircuit and If fault. a permanent low-impedance Now, also path. bolted a fault. effectively is high—it is It is current the sec. 80 (1.3-cm)on a0.5-in. at 3 energized red alder diameter develops 3.5 for of example atest Figure track at end movesan each See and inward. Acarbon branch. of the portion unburned to the carbon the from occurs then Arcing carbon path. a compounds.conducting provides The organic good bon by oxidizing andcar creates the branch impedance). arelatively is branch arcing high burns The (the tree small is current the process, the point in At branch. this the contact with in is at end each where wire conductors, occurs the two across arcing falls abranch If of voltagerange gradients. a over covering samples and branch species tree 20 2005) over tested 2000 2000, Once the carbon path is established completely across the branch, the fault is a completely is fault the established branch, is the path across carbon Once the to develop. some conductors time two between branch takes a tree across A fault Progression of arcing and carbonization of a branch. (From J., of Goodfellow, abranch. carbonization and of arcing Progression 60 sec 10 sec . With permission.) . With Overhead Line Performance 70 sec 30 sec Carbon path kV/ft (10 kV/m) in faulted that 75 sec 55 sec 97 - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 98 Goodfellow, J., Goodfellow, Figure 3.7 wires. the off of enough to fall burns branch the unless there be still will low-impedance path carbon J., Goodfellow, from (Data branch. Figure 3.6 • • • • include effects electrical notable Some ops. So, minor leaf and branch burning does not cause faults. not cause does burning branch and leaf minor So, ops. devel track carbon full the before off andfall through burn also can branches Thin is lower. impedance their because faults cause to arelikely more branches Thicker line. the with contact come in and to break more likely are but branches dead gradient, for voltage to agiven fault arelikely more dry.Live is branches wet or the branch if difference little It makes 3.7).gradient the Figure (see voltage on depends occur to forfault a takes it time The 3.6). Figure the branch along(see gradient the voltage on depends fault of a likelihood The Time to fault based on the voltage gradient across the tree branch. (Data from from (Data branch. tree the across gradient voltage on the based to fault Time Percentage of samples faulted based on the voltage gradient across the tree tree the across gradient voltage on the based faulted Percentage of samples Understanding the Way the Understanding Trees Outages Cause

Time of fault (sec) Percentage of samples 100 150 Electric Power Distribution Handbook Distribution Power Electric 100 50 Voltage gradientacrossthebranch(kV/ft) faulted 50 0 Voltage gradientacrossthebranch(kV/ft) 0 01 05 05 01 Understanding the Way the Understanding Trees Outages Cause 02 02 t =1880/(kV/ft) = kV/m 53.2/(kV/m) kV/m 03 03 0 0 3 3 10 , 2000 with the curve fitadded.) curve the with , 2000 10 , 2000.) - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 tree coverage, load and customer densities, and weather between utilities. weather coverage, between and customer loadtree densities, and in widegivenvariances is not surprising This utilities. SAIDI between and spending correlation between direct little Thereis SAIDI index. the using to performance that rates.growth maintenance), tree management rural tree vegetation and cycle, than more difficult is pruning tree coverage, in load anddifferences density suburban reflect (urban and to 2010 to 2005 utility from costs from (CNUC,utility 2013). significantly vary Costs of on $7981 average based upper lower managed and $2497 per mile and quartiles disturbances. do other not and interruptions want also but they pruned, trees not their want people that do It adilemma always is communities. irritate also can maintenance vegetation $1039/mi costs management averaging costs annual ing ($646/km). Tree Vegetation management expensive—see is 3.1.3 longest the (15 lasted pine limbs and (1 fastest the faulted limbs palm tests, their in found variation: 1999)also Florida species. between Power some differences find Corp. (Williams, more fault but more the not likely. does quickly make ECI did occur fault the make of afactor”: “less was moisture it one may guess.” Surface might of afactor than “less grows often shoot that quickly). producedwas factor base ondary Moisture the from and suckers growth sec (a occurring difference”naturally between “no significant to more flashover werebranches likely given also for a ECI gradient. voltagefound (Goodfellow, 2005). Thicker werebranches flashover, 2000, to morelikely live and ECI found that branch characteristics affected the probability of failure thefailure of probability affected characteristics ECI found branch that • Figure 3.9 Figure with managed of showed cost $4754 data per mile a median survey A similar • • • • issues: somekey reveal effects These

a2.7 has circuit of 1 gradient age volt on a10-ftabout a phase-to-phase has A4.8-kV circuit ductors. (3-m)crossarm con across from branches to flashovers more immune are Lower-voltage circuits Three-phase construction is more at risk than single-phase construction. single-phase than is risk more at construction Three-phase spacings. ductor-to-conductor con tighter of because to flashover more likely are designs or armless Candlestick reduced. is branches falling by contact of aphase-to-phase likelihood the may help since construction Vertical above. from falling by branches caused are faults tree most since poorly performs strategy pruning this conductors, above the of trees canopy aheavy (3-m) is there If radius. about a10-ft conductors with the around a“hole” trim crews Traditionally, faults. not prevent does tree canopy aheavy with areas conductors in the around Pruning Utility Tree Maintenance Programs Tree Maintenance Utility shows data on the costs of vegetation management programs and ties of shows ties vegetation costs and on management the data programs kV/ft (9 kV/ft (3 kV/m) to fault. more is likely which gradient, kV/m), very unlikely to fault from tree contact. A 12.47-kV contact. kV/m), tree from to fault unlikely very Overhead Line Performance min). Figure 3.8 Figure for results of a survey show for of asurvey results min in their setup), their in min - - - 99 - - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 100 including major storms. These are primary events with a vegetation cause. Each Each a cause. vegetationwith events are major including primary These storms. include maintenance and metrics performance correlations between with interfere can that Some tricky. be effects can but vegetation this maintenance, mize on depends cycle pruning The should rates. fault cycles optimal lead to higher maintenance tree longer that a3-year expect to One 5-year cycle. use might utilities Many tricky. is Inc.) Consultants, Utility of CN Courtesy 2013. permission; With California, Utility Vegetation 2011–2012 Management Report Figure 3.8

Figure 3.10 Figure • • • • opti helpcan utilities andperformance tree maintenance of effect the Correlating • • • • cycletime Choosing a cycletime. vegetation maintenance afixed use Most utilities Cost per system mile in USD $1000 $1500 $2000 $2500 history of tree fault impacts. fault of tree history Reconfigurations differently. years different impact can Both change. sometimes contractors or specifications pruning Budget and tree maintenance performance. to their circuits to correlate impossible it so is not by circuit, sections, Maintenance approach programs. maintenance of effects the to gauge it difficult but it makes satisfaction, customer Targeting assumptions Economic for pruning tolerance Community conditions growing and rates, growth Type of trees, approaches clearing historical and specifications Tree clearance $500 $0 Cost peroverheadsystemmile=annualroutineandreactiveexpenditures÷totalpolemiles AB Vegetation management costs. (From CNUC, (FromVegetation CNUC, costs. management $219 —Targeting poorly performing circuits for maintenance can help improve can for maintenance circuits —Targeting performing poorly characterizes one utility’s impact of vegetation one impact 1999 from utility’s to 2003, characterizes $261 CD $285 Average: $1039 vegetation managementforNorthAmericanutilitiesin2010 —Circuit reconfigurations can make it difficult to reliably judge the judge reliably to difficult it make can reconfigurations —Circuit $401 Cost peroverheadsystemmileforroutineandreactive EF $417 Electric Power Distribution Handbook Distribution Power Electric —Some utilities schedule vegetation maintenance using map map using maintenance vegetation schedule utilities —Some $512 GH $698

$763 Quartile 1:$698 —Vegetation management budgets often vary and —Vegetation vary often budgets management IJ $780 $786 KL Company code $843

, 2nd ed, CN Utility Consulting, Sebastopol, Sebastopol, Consulting, Utility CN , 2nd ed, $862 MN $972 Median: $972 $1089 OP $1098 CN Utility Consulting Distribution Distribution Consulting Utility CN

$1250 QR $1336

$1358 Quartile 3:$1404 ST $1404 $1578 UV $1588 $1739 WX $1837 $1917 Y $1991 - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 events, including major These events, including but threshold. storms, above days excluding a3.5-beta to 2011. on regions outages Energy’s 2009 based from operating are primary These period. time Theretrend is short strongno this over not does but data show the maintenance, this. tree following steadily would decrease outages tree-caused that previous year. the naively expect One might during tenance main had tree that circuits on all based metric reliability given the is graph each in datapointfirst the So, tree pruning. thelast since time the showsof effect graph the permission.) with Reprinted 2005. Issues Equipment and Faults 1008506, EPRI from 2003; areas, non-integrated and distribution 7. Chapter 2005/06, and Electricity 2004/05 Hydro, BC application Revenue requirement survey; Benchmarking Consulting Figure 3.9

Figure 3.11 Figure Portion exceeding the x-axis value 0.0 0.2 0.4 0.6 0.8 1.0 0 Power Quality Implications of Transmission and Distribution Construction: Tree Construction: of Transmission Distribution and Implications Quality Power Vegetation maintenanceexpenses US$ peroverheadmileyear Vegetation management costs versus performance. (Data from 2003 PA 2003 from (Data performance. Vegetation versus costs management 500 shows the average annual tree-caused event for rates tree-caused one shows average of Duke the annual 1000

Vegetation maintenance expenses

US$ per overhead mile per year 1500 , Electric Power Research Institute, Palo Alto, CA, Copyright Copyright CA, Alto, Palo Institute, Power Research , Electric 1000 1500 2000 2500 500 0 Overhead Line Performance 2000 05 Tree-related SAIDI,minperyear 2500 0

Portion exceeding the x-axis value 0.0 0.2 0.4 0.6 0.8 1.0 100 05 Tree-related SAIDI,minperyear 150 0 100 150 101 - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 102 (Analysis courtesy of Lee Taylor, of Lee Energy.) courtesy Duke (Analysis Figure 3.11 Y have X and common management.etation Areas vegetation approaches. Z Area different had Energy.approachesfor These haveregions to Duke historically veg approaches. clearance torical have into conductors.” grown that systems pruning heavily with associated avoidance costs of the higher and safety but not is public for reliability trimming cycle say that Might outages. increased in results cycle behind (2003b):Guggenmoos substantially is that program atrim “Only Quoting over periods. reasonable time when analyzed maintenance tree between maintenance. after first the 10 years event The fault by overheadrateis relatively miles. flat line for normalized mostare of Figure 3.10 Vegetation maintenance cycles are tied with maintenance specifications and his and specifications maintenance Vegetation with tied are cycles maintenance longer with times outage events do dramatically not tree-caused increase Overall,

SAIFI from primary tree contact 0.00 0.05 0.10 0.15 0.20 0.25 Tree maintenance effect performance. on effect Tree maintenance Vegetation fault rate versus time since maintenance for Duke Energy area Z. Z. area Energy for Duke maintenance since Vegetation time versus rate fault Years sincelasttreemaintenance 1 Vegetation events/100 mi/year 10 15 20 25 30 35 0 5 23 Electric Power Distribution Handbook Distribution Power Electric 246 Table 3.4 Table Years sincevegetationmaintenance 4 shows results for several operating regions operating shows for results several

81 Tree outages/100 OH miles 14 10 12 0 2 4 6 8 Years sincelasttreemaintenance 01 1234 21 4 - - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 Z Y X Performance Metrics Performance TABLE 3.4 nance cycle. Several other factors include factors other Several cycle. nance inspections. annual with mainline for three-phase the program ahazard-tree is Z’s to area factor contributing Another performance clearance. that to keep utility the quo, it for easier and is status the accept public the will established, be can clearance if butthe major consistently. clearance, to resist changes will maintained The public zone or right-of-way clearance the and if established been has to easier maintain are longer clearances Larger cycle. this toHerbicides allow help control also undergrowth more at cut even location.longer agiven though vegetation generally is times, cycle of because less are Costs line. into the of falling at risk are branches fewer and trees more With more clearance, clearance. by maintaining partially performance achieves area This intervals. to shorter trends maintenance recent industry challenges mance lower Zhas Area vegetation at rates fault lowerclearances. Z’s Area cost. perfor larger-than-normal but maintains longer-than-normalhas intervals maintenance Region Source: Cost hazard— Fire hazard Shock mainte a only isthereason and interruptions not selecting for on Theeffect faults and dispose off. ECI estimated that for each $1 saved by extending maintenance maintenance that each for saved extending $1 by estimated ECI off. dispose and (3) and to clear have of debris more crews mass calls, to trouble response in tenance (2) to conductors, do more must proximity hot-spot crews close in main are trees (1) when because to prune for crews more higher time are it costs takes increased, 1997; Wiant, Massey, and 1998). are (Browning cycles costs If overall the increase can optimum beyond the cycles maintenance tree extending found that ECI ties, utili of three asurvey In budget. aconsistent maintaining than morebe expensive maintenance. more vegetation frequent requires normally requirements spacing 72 and 2.4 between operating land or grass-covered covered land, 4 of 4293) aclearance requires Section Code Resource (Public California addition, In circuits. transmission and distribution for vegetation all conductors and between an 18-in. (0.46-m)spacing at least specifies Construction Line Electric for Overhead Rules California Theof State more maintenance. frequent more requiring severe, —Longer maintenance cycles may actually cost more as the catch-up phase can can catch-up phase more the cost as may actually cycles maintenance —Longer ft (1.2 Courtesy of Lee Taylor, of Courtesy Lee Energy. Duke (Years) Cycle Time 13 6 4 Duke Energy Cycle Vegetation and Duke Energy with Times Specifications m) for circuits in any mountainous land, or in forest-covered land, brush- forest-covered or in land, land, mountainous any in m) for circuits —See Chapter 14. Chapter —See For areas in high fire-danger areas, tree clearance requirements maybe requirements clearance tree areas, fire-danger high in For areas 30 10 10 to sky and herbicide and down to neutral and down to neutral ft (9.1 ft (3 ft (3 Specification Vegetation m) to sides m) to sides m) ground Overhead Line Performance Vegetation Mile Maintenance per Yearper ($) Cost per per Cost 1154 1998 672 from Vegetation per Vegetativeper Interruptions Customer Mile 24.2 26.8 39.7 kV. such Meeting Incidents/100 Vegetation Vegetation Average Miles 20.8 29.5 25.5 - - 103 - - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 104 found 45% were (Taylor, trees dead from 2003). found 36% were (Finch, trees 2001), dead from Energy Duke sample, another in and Mohawk Niagara Power faults, of tree permanent (now Corporation Grid) National damage. cause and fall they before or trees deterioration to cycle death catch in pruning more the frequent than zone or right-of-way. maintenance normal are that inspections Consider hazard-tree are thethey out of evenif defects, significant with or trees trees dead target programs Hazard-tree zones. trim utility or outside from branches trees from ofare typical azone (e.g.,Tree within pruning circuits. to utility threats largest the are that trees those target programs Hazard-tree 3.1.4 right-of-way. right-of-way a establish to program existing an benefitwidentreeclearance or of a to the estimate to used be approachcan This factors. on these based lines striking trees of risk the (2003a) Guggenmoos for heights. tree amethodology estimating outlines and rates, right-of-wayof the density, tree including mortality factors, other tree and aright-of-way.to clear width the by is determined tree fault theof a Then,probability is treefaults reduce way Thedrastically cycles. only to maintenance between missed brought or trees die are down by severe that healthy either from weather or trees from occur, will faults tree many programs, hazard-tree occur. Even with still faults tree claim. can what you to maintain it advantageous is where get clearance, youplete can circuits, not is possible for clearance Even ground-to-sky com awide if lines. transmission for Such high-voltage right-of-ways or trees. maintained limbs regularly are falling aright-of-wayfrom treewaycontacts clearing theof to chance effective reduce an is Storm repair— Storm Dead trees are the most obvious candidates for hazard-tree removals. In asample In removals. for hazard-tree most candidates obvious the are trees Dead many programs, maintenance tree distribution/subtransmission normal With backbones, or circuit lines, distribution critical lines, subtransmission many On Regulations—

cuits that had not been maintained in 13 years had 5 times the damage of circuits of circuits damage the 5times had 13 years in maintained not had been that cuits cir the territory, service their impacted that of 2002 storm ice the during that ered saved. originally cost 1.47is the to 1.69 times “catch-up” the cost optimum; the past 4years is circuit the if and optimum, its past $1.16 1year from extended require would was cycles cycle the if to $1.23 spending in may impose fines or mandate changes. mandate or fines may impose regulators satisfaction, or customer reliability decreased with coincides that if and cycles maintenance tree and/or increases budgets decreases autility If understand. to for regulators indicator easy an is cycle Tree management. maintenance etation costs. repair storm on reducing based get bud management the vegetation increasing justified Duke of this, cation). Because prior communi (Taylor, 1to 6years from personal 2004, maintained been had that Hazard-Tree Programs Hazard-Tree Regulatory bodies are paying more attention to performance and veg and more to performance attention paying are bodies Regulatory Trees cause considerable damage during storms. Duke Energy discov Energy Duke storms. during damage Trees considerable cause Electric Power Distribution Handbook Distribution Power Electric ± 10 ft) targets tree growth, treebut outages most growth, tree ft)targets ------Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 Finch also reported that much of the extra impact of aspens on of due outages aspens impact was to much that extra of reported the Finch also (see of share damage Table their moreold caused roadside than maples 3.5). also troublesome; large, are particularly aspens and that They state. black foundlocusts New York in species tree to the faults caused Mohawk that species tree compared the Niagara 2000. in astudy Mohawk outages of asample in set tree Niagara evaluated Finch (2001) of trees. types and by area showed varies howto interruptions—this to detect. experience and size)point approximately is more same require the training (two stems nant where neither stems, of stem dominates, at each which abranching disease) or (a codomi to Cankers spot. fungal easy are or splits large trees Dead trees. hazard help that signal defects line). into the tree several the Finch describes to fail likely (defects line tree side on more the inside that are backside, the from trees examining Finch (2001) system, advises the Finch also were trees living. 64% of the that reported where broken cases damaged or branches of trees several study. examination an In 3.12 Figure one defects. of in tree faults led to shows tree that defects some tree of the May 1, CA, 2001.)Springs, K., Finch, from (Data Figure 3.12 Springs, CA, May 1,2001. pine White Sugar maple Silver maple mapleRed Black walnut Black locust Aspen Ash Species TABLE 3.5 For identifying hazard trees, it also helps to know the types of trees that are prone are that of trees helps types to the it know also trees, hazard For identifying types many find to expertise but beneficial, requires highly is trees Targeting hazard Source: Data from Finch, K., Comparison of Trees Causing Permanent Faults with the Tree of Trees the Faults with Permanent Comparison Causing Population Defects causing tree failure for the Niagara Mohawk Power Niagara for Corporation. the failure tree causing Defects Overhead andoverhanging(species) Cracks andsplits—open/visible Understanding TreeUnderstanding Outages Dead alongsideoroverhead Codominant stemsorleads Decay, rotted,andpunky Percent of Outages Understanding Tree Outages Overhead Line Performance 20 14 11 5 9 8 6 5 05 , Percent ofdefectscausing EEI Vegetation Meeting EEI Managers permanent treefaults , EEI Vegetation Managers Meeting, Palm Percent of New York State Population 10 15 N/A 12.0 14.7 20 3.3 0.2 0.3 0.6 7.9 , Palm , Palm 105 - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 intense programs removing 10 removing intense programs to 15 per mile. trees the most with removed programs circuit, of mile aboutper trees hazard-tree five ity old large, roadside from maples decline. serious were in faults mainly often crews overlooked sugar-maple their The which as a canker, defect. hypoxilon 106 reduce the sail effect. On circuits where this was implemented, was customerthis where outage circuits On effect. reduce sail the the treeor height to reducing of a thinning crown mostly was This defects. tural were to remove trees pruned that less-severe struc meaning pruned, “storm-proof” were were Trees trees removed, limbs back. cut unsound overhanging and were dead structurally or weretargeted, circuits 1996). Bossuyt, Three-phase primary implemented project mitigation (Simpson, ahazard-tree 1997; Simpson Van and lines. transmission of approaching their that reliability of achieving goal the with program inspection moved they to abiannual system, 34.5-kV subtransmission the On trees. hazard removed necessary.” as only Crews also to “trim system one-gated two-phase the and and deleimplemented system, three-phase They cyclethe 3-yearon a maintenance attempted and to remove overhangs growth where for possible. natural on pruning 13.2 (mainly system onmanagement its distribution program vegetation to amore switched prioritized 1994), Electric and Gas Baltimore et al., 1019417, (EPRI improve performance and can costs nance 2009). of mainte reliability-centered type This for area. issues and the needs on the based wideor the circuit region even system or on based be optimized can These removals. and application inspections and of hazard-tree retardants, bicides or tree-growth of requirements, her use clearance intervals, maintenance by adjusting targeted Vegetation example. be an as on taps, can single-phase programs than mains phase thecustomers. most spend affect that moretarget, three- To circuits on performing spentarethebest poorest- on reliability, efforts impacting program any with As 3.1.5 USDA including for this, (1996, 2003), Fazio (1989), 1012443 EPRI and (2007). A number available of are resources commondefects. knowledge ofground tree the anyoneforbeneficial involvedfield distribution investigations to in have some back expenditure. aone-time be cannot program ahazard-tree of T&D circuits, distance a striking sheer within number of the trees and order on rates the of to 3% 0.5 annually tality mor tree (2003a) Guggenmoos As with must ongoing be programs. shows detail, in programs Hazard-tree trees. healthy of otherwise failures tree causes weather that from are faults tree regularly. Many occur still Tree notare apanacea. outages will Note that while hazard-tree programs can improve distribution performance, they they improve performance, can distribution programs hazard-tree Note while that (2003a) Guggenmoos of found most seven util utilities, that survey informal an In Eastern Utilities, a small utility in Massachusetts (now of Grid) National Massachusetts apart in utility asmall Utilities, Eastern on how (Rees were faults testing trees causing and of basis outage reviews the On by aprofessional directed forester, best are programs most hazard-tree it is While

Vegetation Program Performance Program Vegetation Electric Power Distribution Handbook Distribution Power Electric kV). less They focused ------­ Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 of growth beneath the lines. They also embarked on a community communications communications embarked community on a also They lines. the beneath of growth did vegetation less They pruning management normal program. toby their changes program the funded they project. mitigation Instead, hazard-tree their to fund gram SAIDI by 62%reduced tree-caused per storm. hours (SAIDI) were due faults program to reduced tree addition, the In by to 30%. 20 circuits. single-phase on rural 6years 5and to between 4years from cycle maintenance the extended utility Another outage database. their from on results based program removal developedalso ahazard-tree They circuits. a5-year for cycle used all they circuits, rural On a 5-year oncycle tion laterals. used to busterscycle catch and a2-year inspec backbone on cycle with a4-year the used one utility circuits, urban On portions. to work reduce cycles focus and most cost on critical maintenance the by about mile 15%. per circuit nance average outage duration measurably. dropped treethe mainte cost They of reduced outages average and the implemented number of tree-caused program, they their where PSE’s circuits along private the On from property system. trees distribution diseased and dying, on dead, Energy, removing was focus 1998, 2003). the in Started improved average an of 67%. More recent show results even more improvement. 2003a,b): 2001, Finch, 2004; 1008480, (EPRI reduction operation), characteristics following had the which (nowCorporation TORO Grid) National implemented (tree called aprogram outage weakness. or structural hadspecies avisible 6% 7% had excessive another overhang, were and spans, weak those along trees the that would They need to be. of found program howtions to their determine extensive from reduced savings outage restorationevencosts. more significant an and from reduced savings hot spotting overall found significant addition, they In not did landowner’s remove the they without trees Also, viable consent.sive pruning. and support treemore forwin removal aggres and customers educateto effort utility Eastern Utilities did not increase funding for their vegetation for management their pro funding not did increase Utilities Eastern Finch (2003b) provides details on several targeted programs. TwoFinch programs. (2003b) adjusted targeted on several utilities provides details (PSE) Energy Sound Puget (Puget implemented Sound program ahazard-tree on 250 feeders based completed, onofAs SAIFI 2002, 92% feeders, tree of the • • • • • Mohawk system, Niagara their outages Poweron tree-caused study a of After sec line random surveyed Utilities Eastern Prior program, to implementing their tions for the presence of single-phase tap fuses. tap of presence single-phase fortions the inspec added also They protection. to improve system for opportunities Looked cycle. to a5-year kept systems suburban and Urban years. to 7or 8 6years from 5-kV systems on rural cycles maintenance tree Lengthened backbone. the where possible on limbs and removed overhanging clearances greater Specified segments. circuit on targeted located trees Removed hazard indicators. tree-caused on specific based circuits Targeted worst-performing work to the Overhead Line Performance - 107 - - - - - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 of cutting needed. Consider pruning performance as improper pruning can trigger trigger can improper as pruning performance Consider needed. pruning of cutting amount reducing the and options clearances to considertors also are for managing regula Herbicides tree-growth lines. hit and can that trees number of and branches reduce the sides above can to more the and clearance lines, bones important and for feeder back Especially cost. and required, intervals maintenance performance, 108 From a design and operating viewpoint, covered conductors viewpoint, bare as From must operating treated be and adesign to 30 150 from range typically tion thicknesses EPR common. and are For insula polyethylene, modern-vintage material, as XLPE, such materials insulation The of types. covering avariety with Tree available is wire configurations. or tight other designs or candlestick armless to use utilities allows and faults animal helps Tree with or weatherproof also wire. wire wire tree called conductors. between covered A conductor flashoveralso falls tree when branch a is conductor voltage, of enough to but line-to-ground reduce chance it the thick full is ( covering insulation cover tree covered use often heavy conductors, thin conductors a with with Utilities 3.2 trees. healthy from zone, many maintenance outside from realistic any falling where ice comes storms, much trees and from major damage nounced wind during is even effect more This zones. pro outside well maintenance from or normal trees by into improved branches caused are of faults translate portion reliability. Alarge not money necessarily at vegetation Just throwing management will performance. clearances. or meetspecified should made be to reduce that hazards cuts tree or were done. tree being that out Education missed defects comes pointing tree from work the is that ensure they that time help same at educate crews audits the can tree targeted programs, and other programs Even hazard-tree ifications. with moreso work done the being is that ensure to spec inspections postwork crews, contract with Especially tree maintenance. audits after do quality-assurance utilities Many mance. include lines help that these along strategies wounds. excess and regrowth exaggerated As noted earlier, clearances and vegetation specifications are tied with reliability reliability with tied are vegetation and noted specifications As earlier, clearances There are limits to what vegetation management can realistically achieve achieve line for whatto realistically vegetationlimits managementcan areThere improve and vegetation manage maintenance perfor help utilities Audits can • • • • • effective)Someis a public relations battle. still (that also is pruning Acceptable tree

Covered Conductors Offering free firewood. free Offering cut/removed.are trees up after Cleaning down). when falls it it “storm-induced fix maintenance”; often practiced of aform the up is (this hacked being beloved trees their to accept willing are more residents outages, after Right cleanups. storm during trees Pruning trees. not on leaves are the much the when as trimming tree not notice will munity com radar”)—the done “under the (or pruning winter tree during trees Pruning pruning. to residents prior to/during tree Talking Figure 3.13 Figure Electric Power Distribution Handbook Distribution Power Electric shows example). an is Thecovering notrated for a mils (1mils mil = 0.001 in. = cm). 0.00254 ------Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 Figure 3.14 cables. underground like just insulation rated have cables fully Aerial a covered use that wire. wires phase holding up three wire a using messenger configuration abundled Spacer are cables areas. treed in for covering. used the of insulation ous grades vari allowed. tighter conductor There are thatare difference spacings only the with C2-2012), (IEEE (NESC) Code Safety conductors Electrical National to the according Energy.)Duke Figure 3.13 • of covered advantages conductorsOther include well Spacer 3.14) cable perform (Figure that alternatives also are cables aerial and in squeezing more circuits on apole structure. more circuits squeezing in more even flexibility allow cables aerial and cables Spacer distribution. underbuilt including lines, multiple-circuit to build it easier making proximity, in placed be more conductors can Also, advantages. have aesthetic spacings Tighter conductors. Spacings Spacer cable. (Courtesy of Hendrix Wire and Cable Inc.) Cable and Wire of Hendrix (Courtesy cable. Spacer —The NESC allows tighter conductor spacings on structures with covered with structures on conductor spacings tighter allows —The NESC Example of a compact armless design using covered conductors. (Courtesy of covered (Courtesy conductors. using design armless of acompact Example Overhead Line Performance 109 - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 110 ratio. The effect on interruption durations is shown in is durations ratio.shown on Theinterruptioneffect faults). permanent 20:1wire and by a cable faults were a bare lower Thethan aerial temporary included both this if by not a10:1 did specify article (although ratio the company were found spacer cable CEMIG faults circuits that bare-wire lower than 2001). Gerais, de Minas and The (Bernis Brazilian areas treed in used cessfully 1994). (Hart, aboutare 3per 100 on rates lines fault bare Finland, In about rates. fault are rates bare-wire 75% than less covered covered-wire conductors with that experience suggests fault European wire. likely. conductor and not is tie used, corrosion insulator more correct is the if ence (RFI) interfer may radio-frequency cause they arcs, fault from more to damage susceptible time. some for may covering prevent the object, flashover ametallic with orintermittent sustained) tion to alow-impedance conductor adowned phase If fault. contact (either comes in transi to likely fault less high-impedance a make also public. Thecovering may the to conductor the hazard less posing deenergize and circuit the to interrupt likely is protective device upstream an and more is a fault then likely degree, down to this conductors, bare it pulled is if with hand, other the On issue. apublicposing safety not covered does afault the occur,covering, then conductor energized may remain but of its because reach of acovered pedestrians, the sags conductor down to within weight deeply the of If a tree preventing not a good is a fault thing! faults, always tree or would away. help jumping that arcing bystanders such keep as to it show energized is that it likely signs less visible is ground, contact the does wire acovered if conductor And, distribution alive ground. on the with scenarios wire to lead to downed- circuits bare-wire Covered than more conductor are likely circuits in are but they ios: covered conductors pointed out it scenar not does that correctly cover they all covered wires, through (1997) currents et al. leakage found Even Landinger small though adisadvantage. is thecovering somein and ways, advantages, offersafety do notsystems necessarily • • In South America, both covered wire and a form of aerial cable have aform suc covered of been and aerial both wire America, South In covered a with wire rates fault of a bare comparing to find hard is data fault Good Covered be to are conductorof. aware They trade-offs have systems additional of covered use the conductorsAdditionally, with for spacer cables and preventing but covered wire, a reason for cited tree as conductor using sometimes is Safety ing between conductors and trees and other debris on the power line. Wildfire Wildfire power line. on the debris other and trees conductors and between ing Fire reduction faults. caused animal- at reducing effective most is that application equipment the is grounded near are conductors that other and jumpers Covering animals. other and squirrels faults Animal-caused (Barber, 1999). coveredin conductors Australia using for justification main prevention the is no way no —Covered conductors reduce the chances of fires starting from arc from starting of fires chances conductors reduce the —Covered km/year on a bare wire and 1per 100 and on wire abare km/year a reliable barrier for workers protection areliable barrier to line public. or the may —Covered conductors add another line of defense against against of defense line conductors another add —Covered Electric Power Distribution Handbook Distribution Power Electric reduce the chance of death from contact in some cases, some contact from cases, in of death reduce chance the km/year on acovered wire km/year Table 3.6 Table . Several spacer . Several - - - - - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 area) could also increase the likelihood of damage from trees during ice storms. during trees from of damage likelihood the increase area) also could on acovered ice loading conductor extra the (due reasoning, surface to increased same Using the damage. force less mechanical to or cause abranch from tree takes load conductor, on the wire’s the weight mechanical and increases covering the it so problem. the eliminate can no pruning of amount tree ance, situation. Short of clear tors. ground-to-sky Covered help conductors this in really twoconduc between andland canopy high thefrom fall tree branches 2006). Often, (Short Taylor, lines and above three-phase the far are overhang, where trees the high contacts. animal and may morespacings levels haveas insulation suchreduced adverse other effects Tighter differences. the to estimate us to allow or testing data no is there industrial as speculative is may but faults not great, this as be tree-caused reduction in the then for used covered conductors. are bare spacings as tighter conductors If (often done), contacts). applicationlimb assumes coveredof This conductors spacings thesame at or small growth damage) mainly to 77%percentage (for with of mechanical utilities a high by (for 30% faults with do to is reduceconductor tree-caused utilities will thatcovered a thebest then fromfaults, damage mechanical not affect will covering conductor the that we If assume on circuits. falling or branches trees entire large Hydro)BC and from Energy damage (Duke were faults of tree due to mechanical alow from utility, of over of Electric) about to ahigh and 70% 23% Gas (Baltimore from benefitcovered conductors.the someus on idea maximum Depending of the costs). maintenance reduction in spacer cable factor of (an the 6 around estimated costs) pruning minor only and factor cable of (an 12 maintenance reduction estimated aerial in an around ing prun minimal did They maintenance. tree reduction by in the ment returned was invest initial the that estimated CEMIG wire. abare more cable cost than aerial areputation spacer cable and has Both for to work hard construction being with. have considerations burndown Spacer acovered some cable same as of the wire. cables on apole. aerial Spacer and cables constructed be can cables orcables aerial A conductor covering may slightly increase the likelihood of mechanical ­ of mechanical likelihood the A conductor increase may covering slightly of covered use best with conductors found the has that areas in is Energy Duke give can treefaults of types chapter the this on of thebeginning data at The utility per year.per March 2001. WorldTransmission Distribution and Aerial cable Spacer cable wire Bare Construction SAIDI TABLE 3.6 Note: Source: SAIDI Data from Bernis, R. A.O. R. Data from Bernis, and deMinas Gerais, C.E., Comparison of the Reliability of Index the Comparison Overhead Line Performance = average hours of interruption customer per , vol. 53,no. 3,pp. 56–61, SAIDI (hours) 3.0 4.7 9.9 damage— 111 - - - - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 of the strength of the messenger and attachment to messenger poles. attachment of and the strength of the because to more poles break into are them, likely fall trees entire if branches, medium for and issues small-to- for growth better should spacer tree cables perform While conductors phase conductors. bundled single much is stronger tightly than the with along cablemessenger Thecombination high-strength the limbs. of tree age from 112 States Navy Naval Postgraduate School, 2007.) School, Postgraduate Naval Navy States et al., Figure 3.15 gap. small this across downs noise break from to microsparking leading two, the between build oxide layer can touches tie conductor, or the touches nearly line that enough so the insulating an then deteriorates insulation the incompatible if from ties: ofa second insulator RFI cause document (2007) more possiblyductor Vincent also causing et al. arcing. insulation, con deteriorate the further conductor. line into the will discharges Arcing then and charges wire tie the gap as air the across occur can arcing repetitive bridged, been has insulation it. Once the may puncture but may covering deteriorate the or lightning conductorcovering may 2007). line voltage, Thethis line holdto the (Vincent et al., order onis the of to pF, 30 50 relative tie conducting the enough to is charge which two conductor. the line the and between tie capacitance insulator The conducting the power-line cause develop noise. can Avoltage that between can scenario arcing prime combinations: following the include conductor. line the from byscenarios insulation These separated ties insulator ing covering. Power-line notis the compatible generated be with noise by can conduct On the other hand, spacer cable systems can be more immune to mechanical dam more be to mechanical immune can spacer cable systems hand, other the On A conducting insulator tie in close proximity to the phase conductors phase to the creates a close proximity in tie insulator A conducting • • tie wire covered insulator the conductors if generate with RFI can Pole structures Insulated conductor tie on a bare or covered line conductor 3.15) (see or covered on line abare conductor Figure tie Insulated insulator at the not is stripped conductor that on acovered conductor line tie Bare The Mitigation of Radio Noise and Interference from External Sources External from and Interference Noise Radio of The Mitigation Example of a covered wire tie on acovered conductor. tie of acovered (From wire W.Example Vincent, R. Electric Power Distribution Handbook Distribution Power Electric , 6th ed, United ed, , 6th - - - - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 conductor damage was found. conductor was damage combinations,insulator and evidence tieof no wire of different tests in that reported Power Company Pennsylvania (PP&L), Light by and the but tests in (1980) et al. Lee theconductor, damage could discharges these that ence. There speculation been has (Courtesy of Duke Energy.) of Duke (Courtesy 3.16 Figure a comparing example the diameter. In increasing conductor.bare with increase Both outside a10% diameter, has and lower-strength rating. conductor XLPE more, 20% weighs a 17% covering has 80-mil an larger ductor with of conductor, abare size con same Relative to the rating. a477-kcmil all-aluminum or fiberglass. afoot and (0.3 insulator an with to astructure insulation cant 3.16). (Figure covering the contact with comes in not add signifi will Thecovering tie thewhereinsulator the at the weakest: is flashoverinsulation pointthe whereis thelikely most and flashoverspossible cause damage; still will strikes Direct small. is insulation indifference theoverall designs, flashovers, American but for most North could helpinsulation induced-voltagereduce wood or fiberglass),theextra (with little should line differences not matter,insulated these but for strike, a weakly For adirect this. than less were values slightly the tie, or apolyethylene-coveredtie aluminum about 145 flashover fromvoltageabout critical the coverthe on115 raises University (Baker, 1984) of 1980s found keeping 15-kV the that in insulators pin class tiecombinations. insulator and differentcovering ence between Clarkson at Tests theresomediffer theimprovementis conductor. left the is on While is marginal, conductor. to the tie on oneinsulator the insulation side bonding the and stripping insulator the compatible are that with To covered reduce interference ties radio conductor insulator with use systems, interfer radio cause they that is discharges partial these problemwith The main The ice and wind loading of a covered conductor is also higher than a comparable a than coveredof a wind loading higher andconductor Thealso ice is Covered conductors heavier, are have diameter, have alarger and alower-strength covering the protection if have lightning better lines that argue Some utilities For a retrofitpossibleis covered ties, by insulator conductors conducting with • • Leave the conductor covering on, and use nonconducting insulator ties insulator nonconducting use on, and conductor covering the Leave or ties insulator metallic bare use and insulator conductor at each the strip Either kV with the coverkV the asemiconductive apreformed on With using tie. with plastic

Example of damage on a covered conductor from flashover at the insulator tie. tie. insulator the on acovered flashover at conductor from of damage Example Overhead Line Performance kV with a bare wire to wire kV abare with m) or more of wood 113 - - - - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 the coveredthe conductor conductor versus follows: abare as increase for loadings the covering, XLPE 80-mil conductor an with 477-kcmil all-aluminum 114 Commission (1999). (1996), (1996), Bonham and Frazier Chow Taylor and (1995), Energy California and include TE-114915 EPRI (1999), 1001883 EPRI (2001), 1012437 EPRI (2006), NRECA approaches. relatively using simple faults reduce animal greatly can protection, utilities animal include that practices proper Fortunately, construction with to animals. be likely also are faults on of unknown overhead Many faults cause or circuits. third the second are they For utilities, many lines. distribution with issues many cause Animals 3.3 100°C. as high as rating conductor Abare may75°C. operated EPR be may XLPE up and have to 90°C. a prone it so shouldPolyethylene not operated to be damage, above especially is temperatures. high at degrades insulation temperatures—the higher withstand differencethat is covered conductorsThe to most ability significant lesshave ductors absorb darker, more are but heat they so sun better. radiate heat the from (see temperature operating previous chapter). for same the ties the Covered con better. conductor.into the of corrosion Because water-blocked concerns, conductors are holes pierced by Temperature connectors. water tocause pumped be then changes by abrasion caused cover or erosion, damage at and strikes, by lightning caused of operation years to 20 (Barber, 1999). Water enters conductor the at pinholes 15 in covered wires found complete with has that experience occur corrosion can Australian of moisture. care conductorsbare evaporation takes and periodically, (the evaporate). water cannot washes conductors, bare On corrosion rare—rain is corrosion low at causes the and points it settles covering, the waterIf penetrates should more be and much are to reliable. degradation susceptible less erings abrasion. from and Modern EPR cov or XLPE tracking, from light, ultraviolet from to degradation susceptible PVC, used widely were the including especially materials, covering Early or objects. other trees erosion, abrasion against and rubbing from and tracking radiation, due may to to degradation ultraviolet susceptible be ering • • • A number of useful references for animal protection on distribution circuits circuits protection references on distribution forA number of useful animal Covered conductors close to bare-conductor are have that ampaci ampacities Covered conductors water. from more are to corrosion, susceptible primarily covering. Thecov covered of the conductors with issue integrity Another the is

Animal Protection Resultant Horizontal Vertical —Loading due to ice and conductor weight increases by 14% conductor increases due weight and to ice —Loading —Loading due to the vertical and horizontal component increases by 11% component increases horizontal and vertical due to the —Loading —Loading due to wind increases by 8% increases due to wind —Loading Electric Power Distribution Handbook Distribution Power Electric - - - - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 current path. The fault will cause a voltage sag to nearby customers and an interan andcustomers a cause voltageto sag nearby will The fault path. current low-impedance fault- ionized, create ahighly will phase energized orground another conductor and an energized the thatgapbetween bridges (aftertrees).ties animal An interruptions cause two ofthe for often number utili are by animals Faults caused 3.3.1 on insulators and woodpecker damage to poles. Large groups of flocking birds groups of to poles. Large flocking (such woodpecker damage and on insulators include faults bird-dropping cause contamination birds can ways that Other faults. bird-caused protect against also will faults squirrel-caused protect against that sures equipment protective to mea perch same utility on of for Many the and use nests. Birds for or spacings: arresters unprotected surge bushings tight example, tions with gap loca across the bridging squirrels—by way as much same in the faults cause TE-114915, (EPRI tion circuits 1996). Bonham, 1999; and Frazier normally Birds caused interruptions number of animal-caused the as far as animals. climbing other from faults most protect against also for protective measures squirrels the squirrels, longer than are animals some of these While snakes. and cats, rats, raccoons, including circuits, on overhead faults cause can animals climbing other several common of faults, cause most the are squirrels While unprotected bushing. an across example, ­squirrels—for prone 10 extremely are to in. than less vent Spacings outages. most squirrel-caused conductors enough to energized pre ofrations 18 between normally are to in. 24 1994)) measurements nose (Jackson, to are tip-of-tail (lengths are species main the est, connectors. aluminum coverings and wire chew secondary equipment; will they totive utility have aneed to gnaw, destruc be Squirrels paths. can follow which same edly the of habit development creatures tend are and the to repeat Squirrels of wooded areas. following faults squirrel have in noted increases love utilities suburbs and in trees; flashoverrare. is three-phase uncommon A phase-to-phase happen; flashovertois ground. phase a can but path normally are faults (a fault). reenergized be temporary can Animal-caused circuit away, blown gets off falls theor animal the If permanent. be will fault the and age, not able be to hold volt will circuit leaves the path path, arc aconducting a charred or remains animal the If or fault fault. apermanent atemporary cause can animal An protective covered device. circuit upstream of by the the portion ruption to the Common birds (including starlings and blackbirds) rank second behind squirrels squirrels second blackbirds) behind and Common birds (including rank starlings sepa 2ft, more stretch longest than the can fox that see squirrels we can While • • • • • theFrom aredifferentthe longestshort of to Differentlengths. squirrels of species thrive Squirrels on most faults overhead circuits. the cause distribution Squirrels

Southern flying squirrels: 8 to in. to 25 10 (20 squirrels: flying Southern in. 10 to 12 30 squirrels: (25 to flying Northern 10 (25 to 15 in. squirrels: to 38 pine Douglass and Red 16 (41 in. to 20 squirrels: to 51 tassel-eared and squirrels Western and gray Eastern 18 (46 to 27Fox in. to 69 squirrels: Animal-Fault Basics Animal-Fault Overhead Line Performance cm) cm) cm) cm) on overhead distribu cm) 115 ------Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 mals; in most cases, the frequency of large-raptor contacts is small relative to of other frequency large-raptor the small is contacts most cases, in mals; such, endangered As ani it of amatter is protecting electrocution. birds from these needed to protect are measures extra of this, Because overhead circuits. distribution on phase-to-phase separations normal the herons enough to and owls, span wide are the flock suddenly conductor. hawks, leavesthe eagles, including large birds, Many or crows) conductor aconductor into cause another starlings as when to can swing 116 or ground wires near phase conductors). phase near or wires ground (exceptions guys faults grounded poles with are muchare to animal susceptible less employ without Polesequipment utilities protective measures. unless flashover paths have susceptible all capacitor reclosers, and banks regulators, pole installations, Riser tank. arrester, transformer asurge across ajumper from toformer the and bushing, trans the across faults: have to locations animal susceptible many poles normally found pole-mounted equipment Unprotected system. on adistribution transformer most problem at equipment are areas poles. Transformers most widely the by are far equipment tight. where poles, are spacings phase-to-ground ground distribution, substation, and transmission. under between evenly split remainder almost the uted to overhead with distribution outages were attrib 78% interruptions. of animal-caused animal-caused to address TE-114915, 1999). program Out respondents, of 84 77% of had some structured sort animals. actually are faults “unknown” many the estimate how used of to be can strategies classification same These fuse. and tap transformer or for a weather, one only fair affected, phase mornings, during are more likely faults Animal that operated. and device protective affected, phases outage (ID), identity following inputs: on the circuit based of day, time weather code, (1993) faults Chow et al. animal-caused routine to developedidentify aclassification animals. by certain caused being really are faults “unknown” one if as way used to be determine can population data Animal populations. mal ani and flow ebbwith also faults Animal a region. within variation a significant tocustomer more complain. is likely it not or and is interruption voltage stormy, sag, due process to autility the critical poor weather—but during not good weather.bances in acustomer a loses When distur expect customers normally heightened. is Utility faults perception of these winter. during active less are animals as weather patterns, in variations seasonal experience also for Some food. looking utilities are they as morning the in most active are and night sleep at or Squirrels late evening at night. the during few and occurred morning, the during occurred faults animal the of half that than morealso found They system. Energy Duke weather on the fair during occurred faults overthat 85% of animal contacts. animal The EPRI survey also points out where most animal-caused outages occur—at occur—at outages points also outwhere animal-caused most survey TheEPRI (EPRI protective measures animal and faults on animal utilities surveyed EPRI faults. “unknown” have classify to used faults been animal-caused of The patterns considerably also there andis by vary region, faults causing animals of types The weather, power-quality fair the during normally are faults animal-caused Since weather. fair Chow in Taylor and occur faults (1995)Most animal-caused found Electric Power Distribution Handbook Distribution Power Electric Figure 3.17 Figure shows that ------Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 transformers reduced the cost of animal-caused faults by 78% faults 1989). et al., (Hamilton of reduced cost animal-caused the transformers Taylor, 13,000 on all guards 1995). application the of animal Nebraska, Lincoln, In average 12 to from an of per faults year 1.5 (Chow per year reduced and cuit animal cir on the transformers distribution application on all guard animal circuit, Energy in oneForDuke faults. example, prevent effectively animal-caused can most wires covered conjunction jumper in with most common. Properly guards applied bushing the are transformers locations, these Of sectionalizers. reclosers, and tors, regulators, capaci transformers, arresters found andon surge used forbe bushings can These are ment available. (butguards relatively to expensive retrofit). of bushing variety A birds) and squirrels are (particularly animals against ways to prevented.equipment protect two most main easily The the are faults animal equipment and failures— lightning, trees, major of the faults—animals, Of causes 3.3.2 permission.) Construction of Distribution Implications Quality Power Substations and (From TE-114915, EPRI Figure 3.17 Bushing protectors and covered lead wires are inexpensive if installed with equip with installed if protectors inexpensive covered are Bushing and lead wires • • Covered lead wires lead Covered protectors Bushing Animal Guards, Wire Coverings, and Other Protective Equipment Phase-to-phase conductorcontacts Overhead distribution points most susceptible to animal-caused faults. faults. to animal-caused susceptible most points distribution Overhead , Electric Power Research Institute, Palo Alto, CA, 1999; EPRI 1002188, EPRI 1999; CA, Alto, Palo Institute, Power Research , Electric Grounded pole-tophardware Potheads atriserlocations Phase-to-neutral contacts Insulator contamination Pole-top groundwires Jumper wirescontacts Conductor jumping Mitigation of Animal-Caused Outages for Distribution Lines Lines Distribution for Outages of Animal-Caused Mitigation Structural failure Surge arresters Sectionalizers Transformers Overhead Line Performance Switchgear Capacitors Regulators Unknown Reclosers Breakers Cutouts 01 as atop-fiveoutage-frequencyproblem Percentage ofutilitieslistingtheitem 02 . Copyright 2004. Reprinted with with Reprinted 2004. . Copyright 03 0 117 - - - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 full flashover across an animal contact. forFor a momentary retrofitsplit- situations, animal an flashover across full enough to prevent insulation).is 600-V normally a class insulation The normally is have covered and no jumper voltagefor wire workers guards rating, line (animal and rated safety provides of no degree fully is not insulation The of installations. conductors. 3.18ment Figure energized See covering poles by physically for examples 118 Institute, Palo Alto, CA, 2001. Copyright 2001. Reprinted with permission.) with 2001. Reprinted 2001. CA, Copyright Alto, Palo Institute, (From 1001883,ers. EPRI Figure 3.18 covers coverslems bushing or were on missing jumpers (see missing 1999). Commission, Energy (California The common most devices prob installed (PG&E) found 165 that poles (65%) were incomplete found or with improperly Electric & protection,Gas of Pacific 253 shoulda survey poles have that had animal In jumpers. on leads all insulated use and arrester and should cover bushing every incorrect. you certainly are half-way bushing, youIf more down the are than top second bushing. shed of the the from under the guard the you to install ers direct insulator. manufactur the Many bypass to fully guard weso do animal not the want flashover, and track can rated insulators—they not are fully guards Animal tank. the tors, have protector leave crews bushing bottom of and some the the room between (see Height important placement directions. also is manufacturer’s lockedinto to place the and according bushing the around securely covers available. are for insulation jumper wires seam Animal guards and covered jumper wires prevent most animal flashovers covered preventequipat and jumper wires most animal guards Animal The most common mistake is leaving some energized pathways exposed. Crews pathwaysexposed. some energized is leaving The common mistake most shouldbe guard placed The for guards. bushing important is Proper installation Examples of wildlife protection with animal guards and covered jump and guards animal with protection of wildlife Examples Distribution Wildlife and Pest Control Pest and Wildlife Distribution Electric Power Distribution Handbook Distribution Power Electric Figure 3.19 Figure , Electric Power Research Power Research , Electric ). For protec bushing Figure 3.20 Figure ). - - - - - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 Commission, 3.20 Figure polymer in depolymerization causes radiation to ultraviolet Exposure guard. animal tracking. and covers deteriorating ing bush reported new utilities problems. outage caused orsures maintenance Several gap. the removed be can to maintain that knockouts come with not guards Some to gap bushing block on the air-gapped arresters. careful not Also, be crews they properly should thentheapplythat fit. onedoes fit, does guard the If Crews should or notradiation. guards. tape nylon use to secure ties ultraviolet from degradation to withstand tested guards choose animal Also, ing. the andbush capsthe between wedge can animals popand off, determined can cap thatcover the protectors just bushing The small arresters. ciently cover and bushings enough to suffi large are choose models that guards, animal selecting When ware. permission.) with Control Figure 3.19 In a survey (EPRI TE-114915, (EPRI asurvey In mea 1999), some reported animal-mitigating utilities hard line compared distribution to most relativelyother are flimsy guards Animal Electrostatic guardbelowfirstskirt , Electric Power Research Institute, Palo Alto, CA, 2001. Copyright 2001. Reprinted 2001. Reprinted 2001. CA, Copyright Alto, Palo Institute, Power Research , Electric Incomplete jumperinstallation Cover abovebushingmount

Cover overtoomanyskirts Reducing Wildlife Interactions with Electrical Distribution Facilities Distribution Electrical with Interactions Wildlife Reducing Animal guard installation. (From 1001883, EPRI installation. guard Animal Problems with animal protective devices. (Data from California Energy Energy California from (Data devices. protective animal with Problems Two coversperbushing Perch guardmisplaced Cover missing Cover loose Cover cut Overhead Line Performance 01 Figure 3.21 Figure Percentage ofdeviceproblems (N=1 0 shows of example adeteriorated an 20 Distribution Wildlife and Pest Pest and Wildlife Distribution 30 40 65) , 1999.) 50 119 - - - - - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 120 the device’s condition from the ground. A closer examination could reveal other clues other reveal could device’s Acloser examination the ground. condition the from torn, or deformation) respectively: forms of degradation, severe less (discolorationthese or black traces) more and severe (tracking/erosion, and B to A representinto classes thegrouped results They functionality. designed or deformation would have tearing, tracking/erosion, obvious lost someing of their show devices those were while they designed, as of performing greater likelihood would have discoloration or showing black a traces devices those anticipated that and/or (caused erosion, by tracking tearing wear),traces, deformation. and PG&E discoloration (e.g., to was most, damage), least from light black ultraviolet ranked 1999). observed, Commission, of degradation Energy type (California The devices effect. rapid aging create alocalized can present which corona in also is discharge, (of a component) is radiation radiation sunlight ultraviolet which ultraviolet although to exposure through achieved primarily is radiation to ultraviolet rioration. Exposure dete further and arcing more thus to dry-band and susceptible collection pollutant may Thenow roughenedbe surface more to surface. susceptible of the pitting and oftencracking is accompanied by which surface, material of the aroughening tion is (the down). bondsmaterials polymer break depolymeriza the material of Theeffect permission.) with Reprinted Substations (From TE-114915, EPRI Figure 3.21 This ranking of degradation severity is only based on what could be observed of whatbe on observed could based is only severity of degradation ranking This • • poles (32%) 80 by PG&E, 253 the Of poles examined were degraded found with mance such as tears, signs of tracking/erosion, or deformation. of tracking/erosion, signs tears, as such mance B Class performance. affect not likely will that A Class , Electric Power Research Institute, Palo Alto, CA, 1999. Copyright 1999. 1999. CA, Alto, Copyright Palo Institute, Power Research , Electric —Degradation that is of a lesser degree such as discoloration or black traces traces or black discoloration as such degree of a lesser is that —Degradation —Degradation of a greater degree that will likely result in reduced perfor reduced in result likely will that degree of agreater —Degradation Example of a deteriorated animal guard compared to a new animal guard. guard. to animal anew compared guard animal of adeteriorated Example Mitigation of Animal-Caused Outages for Distribution Lines and and Lines Distribution for Outages of Animal-Caused Mitigation Electric Power Distribution Handbook Distribution Power Electric - - - - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 Also, 62% were in residential areas, and 14% were in agricultural areas. 14% 62% and Also, were areas, residential in were agricultural in (no shielding). to sunlight environmental exposed but one fully was all and exhaust, automobile 43% to heavy were devices, exposed degraded poles with 80 the Of discoloredoutside on appeared only the that surface. of adevice surface inside on the occur could For tracking greater or example, would degradation. lesser indicate that other climbing animals. Additionally, some bird-specific practices include Additionally, some bird-specific practices animals. climbing other help include also that Someitems technologies. additional animal-control common effective and specifications. 1016043,(EPRI of purchasing as part test 2008). Consider aflammability including heat removed when source is the self-extinguish others some continue while to burn and others, than faster ignite some guards, animal of tests Fromfires. flammability secondary start and guard the from drip also can material Burning major damage. a temporary, low-damage event turned and into ignited guards animal because equipment incidents ofcompletely significant other reclosersdown and burning radiation. ultraviolet from degradation to resistant more are materials 1999). Commission, Energy (California rubber silicone (EPDM), and methylene diene propylene ethylene copolymers, ene polypropyl such as materials, products base made other from compared to similar Table 3.7 summarizes the extent of deterioration on the poles surveyed by PG&E. by of extent PG&E. deteriorationTable the poles on surveyed the 3.7 summarizes • • • • and squirrels with as well birds as coverings help with wire and guards Animal • • • most coverings—the wire and guards concentrated has section on bushing This There have consider flammability. been their also guards, animal selecting When The older units. than better to resist degradation Newer products expected are 1997 in found PVC tests that their products that poorly perform reported PG&E Electrical Distribution Facilities Distribution Electrical B Class A Class Degradation TABLE 3.7 Removing nearby roosting areas roosting nearby Removing category aseparate as Tracking raptor areas) in (mainly guards perch Installing of nests rid Getting solutions. proper to identify easier it is animal, by an tracked are outages animal—If Identify maintenance. where to target to identify hot pinpoint spots can tem sys tracking outage agood so repeated, are outages tracking—Many outage Good attractive. equipment less is utility away lines, mon). kept from are trees If com less is (pole climbing trees equipment via to get utility trees—Squirrels Clear Note: Source: Survey of locations. 253pole Survey Data from Commission, Energy California

Deterioration Devices of Animal-Protective Number of Poles , 1999. Overhead Line Performance 28 (11%) 69 (27%) Reducing Wildlife Interactions with Number Devices of Degraded 37 91 - - 121 - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 in. (15in. 6 than less top pole, to of the leaving the neutral the from runs pole, wire a ground this problem. the On illustrates 3.22 shows that example Figure an separations. ground conductors create phase phase-to- short near can Ground wires guys. and grounds at cutouts where low orproblems. are there problems clearances occur Other can 122 faults. (Courtesy of Duke Energy.) of Duke (Courtesy faults. Figure 3.22 protections. to provide adequate it important animal is installations, piece of equipment, such On itself. butticular line to of improve the performance the applied not arresters to protect are par any arresters Line notdoes fuse. have alocal reliability. problematic for especially are more for area to crews patrol. CSPs mainline on the much more many or with breaker recloser leaving customers operates, interrupted, circuit or upstream fuse tap the then fuse, (CSP) internal transformer an with acompletely is transformer self-protected the If faults. of animal-caused impacts reduces the fuse external an arrester. Having or an bushing transformer tribution issues. helpalso animal reduce can standoffs and supports Insulated cases. in most unnecessary is wire ground of type solution This to is remove wire. ground the Thebest separation. phase-to-ground short of the because faults have repeated animal Unprotected transformer bushings and arresters are the main sources of animal of sources animal main the are Unprotected arresters and bushings transformer Line surge arresters are another common overhead line application that normally common overhead another are application normally that line arresters surge Line for a dis across faults faults of animal-caused impact the change also can Fusing cm) between the phase and the neutral. This is the type of installation that could thatcould installation of type the is This neutral. the and phase cm) the between Electrocuted cat and the ground wire that made the pole susceptible to animal to animal pole susceptible the made that wire ground the and cat Electrocuted Electric Power Distribution Handbook Distribution Power Electric - - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 maintenance that covers that muchmaintenance equipment. and Now, for have inspection programs utilities many minimal. was maintenance considered to was failure,” and “run hardware as most distribution Historically, 3.4 nance program—With lessons learned, learned, lessons program—With nance preventive mainte thermography infrared feeder Development A., M. of autility Kregg, from Figure 3.23 3.24 followed (see of by 3.23). anomalies transformers portion Figure largest See for 12-kV each anomaly were Connections the feeder for Edison. Commonwealth compression 10% (2001) and cutouts. Kregg were crimps, fuse found over just one Mississippi on tified Powerand 40% feeders were wereconnections arresters, hot (2001)equipment Sullivan of 50% issues. problems that design reported and iden (CEA cycles had ad D975, hoc 290 20% or and inspection other tions, 1995). inspec not 28% did thermal perform 5years, 2and between intervals had inspection of overhead 18% inspections lines, thermal annual did 27% that ofreported utilities problems, capacitorThe CEA and connections. tracking dependent, arresters, such as Some load. heavier under hot not circuit are spots load the when with performed most effective are inspections loading, current with hot-spot vary temperatures Since inspection. drive-bybe done in a can inspections Thermal connectors. with foraccounts currents. operations fault and recloser. byseen the Modern provide recloser monitor” controls a“wear can that currents fault on is based duty hundred operations. Therated for actual to 50 several on operation based Reclosers for may counts. basis be form maintenance the can that duties provide for operating equipment normally will Manufacturers tion counts. or on opera interval either on atime based normally are of these maintenance and now bodies tory require periodic inspections. cutout severely on. regula so deterioratedbroken Many issues, and poles, crossarms, Visual inspections can find many issues, including NESC violations, cracked violations,or cracked NESC including issues, many find can inspections Visual Experience with finding problems with thermal imaging can vary based on utility on based utility vary can imaging thermal problemswith finding with Experience distribution problems,especially helpcan identify imaging infrared or Thermal Inspection Voltage maintenance. and reclosers inspection require and regulators for examples of issues. of examples for Inspections and Maintenance Portion of anomalies found from thermal inspections on 12-kV circuits. (Data (Data on 12-kV circuits. inspections thermal found from of anomalies Portion Capacitor banks Transformers Connections Disconnects Arresters Splices Other Fuses Overhead Line Performance 01 InfraMation Percentage ofanomoliesfound 02 , The Thermographer’s Conference Thermographer’s The 03 04 0 , 2001.) , Figure Figure 123 - - - - - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 124 bringing attention to issues and training has helped reduce this problem. helped has reduce this training attention and to issues bringing out-of-adjustment that an reported tool, improper Sullivan and crimping crimping. die, wrong the crimp, size wrong the using found with issues Sullivan sion crimps, were issues connection due error. most of to that their human reported For compres observable. not and directly heat internal source is the pot heads, and transformers such as “nonline equipment of sight in items” because have temperature criteria a tighter equipmentby type; vary These Edison. shows by Commonwealth prioritizations point. reference parable on absolute relative to but acom temperature, rise atemperature to use it best is Figure 3.24 Connector issues are commonly identified by thermal imaging. Sullivan (2001) Sullivan imaging. thermal identified commonly by are issues Connector based aresometimes priorities assigning and issues forThecriteria identifying Examples of infrared issues. (Courtesy of Osmose Utilities Services, Inc.) Services, Utilities of Osmose (Courtesy issues. of infrared Examples Electric Power Distribution Handbook Distribution Power Electric Table 3.8 Table 151.9°F 169.7°F 130.5°F shows one priority grading system. system. shows one grading priority 80.5 51.9 63.0 177.6°F 176.3°F 57.1°F Table 3.9 Table 71.5 54.1 24.1 - -

Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 content above 20%. Growth increases with temperature, peaking between 60°F and and 60°F between peaking temperature, with content increases above Growth 20%. decay.moisture with grow Fungi affecting variables primary the are temperature and (CCA), or pentachlorophenol (penta) delay decay. For ground-level decay, moisture creosote,chromated as arsenatesuchcopper preservatives chemical decay.initial The of pole cause leading feed on the that wood are Fungi externally. seen be cannot and replacements. optimize can program maintenance and have relatively inspection old utilities an Many plant. pole and populations, pole their to manage program maintenance and apole use inspection Most utilities 3.5 would not tube latch properly. fuse the so wrong, aligned stop was mechanical cutoutonewith thewhere issues had design problems. also ofbig their portion They problems. a hinge nuts, were of and proper clamp connections Bad also tightening with issues had also they caps, they but The loose commonfoundwas most issue reference point is usually asimilar component on another phase that is assumed under to similar load. be maintenance program—With lessons learned, 1 to 17°F 18 to 36°F > D For < 18 to 63°F 64 to 135°F > For Temperature Criteria TABLE 3.9 36°F 18°F 135°F own- Pole decay is most common near the ground line. This decay is normally internal internal is decay normally This Pole line. ground most the decay is common near cutouts Mississippifuse at with Power. (2002) issues several identified Sullivan Note: Source: N Line of Pole Inspections and Maintenance on- F All temperatures All are temperature above rises an appropriately reference selected point. The eed L Adapted from Kregg, M.A.,Development of autility infrared feeder thermography preventive ine of 3 2 1 Priority TABLE 3.8 and Utilities’ Rockland (EPRI infrastructure 1000194,2000). 4 S P ight Thermal Inspection Priority System Priority by Edison Used Commonwealth Inspection Thermal ot Note: H S I tems ight eads, Used by Asplundh for inspections of thermal Infrared Orange Services I

tems S A uch as Anomaly Priority Grading System Grading Priority Anomaly rrester

S uch as B B olted Overhead Line Performance Temperature Rise odies, and 10°C or less 11 to 20°C 21 to 49°C 50°C or more T ransformer and C onnections, Splices,onnections, InfraMation Intermediate—corrective action as scheduling permits Serious—correction as actionas possible soon Critical—corrective action immediately Attention—no corrective action but monitor equipment Intermediate—corrective action as scheduling permits Serious—correction as actionas possible soon Critical—corrective action immediately S o O n , Priority The Thermographer’s Conference C apacitor D isconnect isconnect C Monitor regularly Repair in3months Repair in7days Repair immediately ans, Repair Status C able J aws, and U p- F eed and , 2001. S o O n 125 Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 126 Forest Research Laboratory of Oregon University, State permission.) 2012. Laboratory With Forest Research J. J., Morrell, from Oregon University; State Figure 3.26 thickness of the afunction as strength bending shows 3.26 Figure theoretical critical. outer is the shell not strength, is deep. damage For mechanical external the because more of pole risk decay. Wood America (AWPA);the Association Protection number of zones ahigher have from zonesseverity on decay based with 3.25 forSee different Figure amap regions. in different are decay rates dependency of temperature, of decay on and the moisture Because line. groundthe (16 the worst80°F near typically to 27°C).are factors These Wood Association.) Protection American the Figure 3.25 Most decay occurs internally. Poles can look weathered but can still be good be internally. Poleslook still weatheredMost but decay occurs can can 4 Wood pole deterioration zones from AWPAWood from zones pole deterioration U1 (2013). Standard of (Courtesy Theoretical strength remaining as a function of shell thickness. (Courtesy of (Courtesy thickness. shell of function as a remaining strength Theoretical 3 2 1 3

Residual strength (%) Handbook Distribution Power Electric 100 10 20 30 40 50 60 70 80 90 0 1 De 5 1 Residual shell(in.) ter 3 ioration zone Wood Pole Maintenance Manual: 2012Wood Manual: Edition Pole Maintenance 24 2 3 =Interm 1 =Low 4 =High s 3 4 3 5 ed ia 5 =Se 2 =Mo te

ver derate e , Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 and EPRI 1017703 EPRI and (2009). may where lostwhere pole be and due more preservatives is the to gravity. exposed outer (5 of 2in. shell outer sound of According to (2012), the Morrell shell. asound require most utilities Each providesinformation. Each different second and inspections. inspections initial of data: It types includesprograms. two tricky. is curves failure-rate or curves into survivor data should done.tenance be pole Translating inspection main and andpossiblyhow inspections benefitstailor to poleoften of maintenance 10 for for 3, 5. years 8years zones zones 2and 4and and the 12 years for zone every inspection, inspections RUSfirst recommends 1, the After 1, 10 for 12 10 and 3, years 8and decay zones 2and and for 5. years decay zones 4and 12 15121, for and between years decay zone inspection 1996) initial recommends an (RUSService 1730B- survey).Utilities were The eight to only responses this Rural U.S. of 11.4 average pole inspections an duration between reported (though years there 8.1 1002093, (EPRI also was years pole 2004). inspections report between same The 261 average 1002093,(EPRI the duration responses, with 2004). a1997 In survey tests. destructive full-scale in measured strengths correlated with well technology content this from predictions found the and that moisture and density ground-line (2002) measures that on a reported technology 1010654, (EPRI technology scatter 1021996, EPRI 2005; 2011). Taras and Renforth movement, back and measurements, mechanical resistivity ultrasound, including down further decay. boring: and For more detailed information on pole decay and treatments, see Morrell (2012) Morrell see onFor information pole treatments, decay more and detailed where equipment top pole the of the or the occur near attached is also can Decay • • to generate the used be to understand information can Pole results inspection to surveys according program pole inspection have 85%Over a regular of utilities different approaches, using A number have of technologies pole-testing tried, been treatment to slow fumigant ground-line combined are with Most inspections • • • followed test by inspection asounding involve avisual normally Pole inspections inspected, and whether or not it passed an inspection. an or not it passed whether and inspected, previously it was at which age the pole, We of age the samples. the know interval Second inspection inspection. an or not it passed whether Initial inspection (0.4 to 0.6 in. 24 18 to typically pole, the around excavating after made be can tests boring line, boring and Excavation ahook on it. with bar along steel with measured be wood) can sound of the width Boring needed. be might where boring indicate and wood decayed indicate might test hammer or Sounding —Poles are drilled at an angle to identify soft spots. Then shell thickness (the thickness Then shell spots. soft to identify angle at an —Poles drilled are m) deep. —These are the initial inspections. We know the age of the pole and polethe age the of know We inspections. initial the —Theseare cm). —These are the points labeled “recycle” in Figure 3.27.in Figure are labeled “recycle” points These the —Theseare —Since many instances of decay occur just below the ground ground below the just occur of decay instances many —Since —A hammer is used to test for dull-sounding points that that points for dull-sounding to test used is —A hammer Figure 3.27 Figure Overhead Line Performance shows industry data from pole inspection pole from inspection data shows industry 127 - - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 128 possibilities are possibilities types. forinspection different are differently developed curves” “hazard rates or polefailure region. These age and permission.) with Reprinted 2006. Copyright 2006. CA, Alto, Palo Institute, Power Research Electric Volume Edition) Wood 4: (Expanded Replacement: Poles Asset Intelligent for Guidelines Figure 3.27 We also need to be careful about what type of failure rates we are looking for. we rates looking are of Some failure about what type We need to careful be also of afunction as rates failure it possible is to data, estimate From inspection the Hazard rate (%) Hazard rate (%) Hazard rate (%) 10 15 20 10 15 20 10 20 30 40 0 5 0 5 0 Zone 1 Zone 3/4northeastern Zone 2 10 10 10 Pole inspection rejection rates as a function of pole age. (From 1012500, of pole age. EPRI a function as rates rejection Pole inspection 20 20 20 30 30 30 Age Age Age 40 40 40 Electric Power Distribution Handbook Distribution Power Electric 50 50 50 60 60 60 70 70 70 10 15 20 25 Hazard10 15 rate20 (%)25 30 Hazard rate (%) 0 5 0 5 Zone 5southeastern Zone 3/4northwest 10 10 20 20 Initial 30 30 Age Age 40 40 Recycle 50 50 60 60 70 70 , Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 reduce with age. To account for this factor, use only the hazard curve up to the point up To age. to the reduce with curve factor, hazard account for the only this use to level rates off start or hazard why the explains this so age, become bigger with no longer are field. of The polesportion the they removed in because tendwould to removedinspections thefrom of decay. were because missing are otherwise These or previously, failed years and 50 decayed, became were poles is that set installed the from missing poles is of age What 50. included all of set poles inspected the if an age group.appropriate that be would This estimate poles within by all divided inspection the thethat passed ratepolesof is number the survival of estimate The at age 50. of Consider set poles inspected some the data. missing are inspections the in rejection rates that is missing is What over to decrease time. function hazard likelihoods. maximum by using using curves survival where S for pole is rejections curve survival of the estimate crude (1988) Meeker Escobar and Both Nelson and (1982) problem A this well. describe data. doublycensored called survey sometimes is This time. before inspection the someat age “rejected” became they that leftcensored, are meaning inspection an thattime. fail Poles inspection the at become some “rejected” age after pole will the that meaning censored, right are inspection Poles an pass data. that censored survey withouttreatment. treatmentand with areestimates These • • The pole data in Figure 3.28 does not quite follow this. notdoes the 3.28 in this. quite ThepoleFigure follow data We should notexpect Nelson (1982) function hazard cumulative the provides amoreof estimate refined frombe found can functions Hazard function. ever-decreasingan shouldbe This n r are which poleinspections, initial areon based estimates treatment” The “with 3.28 Figure progressionThe is normal • i i

= = (2) the rate at which poles become rejected when decayed. when (2) the rejected become poles at which rate orhere: or (1) decayed good either when rejected become poles at which rate the rates hazard have two actually One can or reinforced. replaced be normally pole will Rejected inspections. by aredetermined “decayed” and of states The “good” “decayed.” Decayed system. Failed

number of rejections of poles within a given age range age agiven within of poles of rejections number number of poles within a given age range age agiven within of poles number —The rate at which poles actually break or are otherwise removed from the from removed are otherwise or break —Theactually poles ratewhich at —The rate at which poles turn to the state of “rejected.” Once rejected, the of state the Once rejected, “rejected.” to —Theturn poles ratewhich at —The rate at which poles turn from the state of “good” to the state of state the to of state the “good” from —Theturn poles ratewhich at shows estimates of failure rates with age using the data in in data the age using with rates of failure shows estimates decayed Overhead Line Performance λ=− → i

= 1– rejected dt d log( r i / n S i → ) failed. Figure 3.27 Figure 129 . Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 130 sometime between age 30 and age 40). With interval-censored data, we can directly directly we can data, age 40). and age 30 between interval-censored With sometime censored “rejected” (they became interval are at age 40 inspection the failed that those and censored, right are at age 40 passed that those at age 40, again inspected were at and age 30 inspection passed poles that we If take data. censored inspection kneepoint. that beyond extrapolate butlinearly you could become significant, point where failures thebeyond does towhat level offit really or wherereduce. unknown it starts is It permission.) with Reprinted 2006. Copyright 2006. CA, Alto, Palo Institute, Volume Edition) Wood 4: Replacement: (Expanded Poles Asset Figure 3.28

The data also includes rejection rates on the second inspection. This is is interval- This includesthesecondinspection. rates also onrejection data The Hazard rate (%) Hazard rate (%) Hazard rate (%) 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Zone 5southeastern Zone 3/4northeastern Zone 1 10 10 10 Estimates of pole failure rates. (From 1012500, EPRI rates. of pole failure Estimates 20 20 20 30 30 30 Age Age Age 40 40 40 Electric Power Distribution Handbook Distribution Power Electric 50 50 50 60 60 60 70 70 70

Hazard rate (%) Hazard rate (%) 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Zone 2 Zone 3/4northwest 10 10 No treatment 20 20 , Electric Power Research Power Research , Electric 30 30 Guidelines for Intelligent Intelligent for Guidelines Age Age 40 40 With treatment 50 50 60 60 70 70 Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 where andsecondinspection: first the between into groups data by time the age and by breaking function hazard the estimate sibly conductors, from due loading pole-top to higher equipment, and/or third-party events, pos to wind more are vulnerable mainlines that suggesting taps, on lateral of poles that were rates twice pole more failure than Mainline damage. wind-only mainly (creosote event caused an that pole treatment or type Wilma, CCA) during on based difference for evidence solid performance Brown found Light. little and for storm category Power Florida with exponentially increased ofrates pole failures events, Brown (2008)For hurricane found the that characteristics. head construction more is events. that larger common pole such major in as breakage ing damage on focus reduc programs resiliency 25 to outage 45 events.every Overhead structure one was pole ratio replaced for this thunderstorms, outage events, but for typical Sandy, hurricane For one in replaced pole example, age increase. six for was every 2013). (CT PURA, Connecticut events in dam and costs storm events, both larger In See increase. costs more major is severe repair storm events, damage and During programs. reliability mainlines. such as system, of the parts at certain or targeted are construction implement conditions. Most on programs new based wind changes extreme NESC coveredpole-top reconductoring conductors, for with refurbishments, design and drops, breakaway connectors on treatment, service and pole inspection aggressive more options include guying, stronger-class concrete poles, or enhanced poles, steel automation, vegetation management. For expanded and overhead improvements, to improve includeties overhead resiliency improvements, more undergrounding, it more make and “resilient” to major events. The options for utili infrastructure distribution impact Theof major on hardening increased focus eventsstorm has 3.6 1012500, (EPRI programs maintenance and 2006). inspection years). 15 in results The industry has only a few examples of correlations between damage and over damage a examples correlationsof few only has between industry The utility normal than different require focus sometimes resiliency and Hardening pole to optimize to try used be can knowledge of pole abetter performance Having in data the With t n r

i i

=

Hardening and Resiliency and Hardening = =

time between the first andsecondinspections first the between time

number of rejections of poles within a given age range and time between between time and age agiven range number of of rejections poles within number of poles within a given age agiven range number of poles within inspections Figure 3.28 Figure Table 3.10 Table Figure 3.27 Figure are based on a 10-year interval (it on a10-year based are probably is interval 10 between and for storm damage from several different types stormof types different several from for storm damage Overhead Line Performance , we do not know the time between inspections. The inspections. between , we do time not the know λ

=

r i / n i / t 131 - - - - - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 Storm type dateStorm TABLE 3.10 132 ologies for calculating conductor of concentrated alarge tensions stress ologies for the under calculating considers orderthat of the equipment. of failure (1995) Yu et al. developed method to amuch leading poles, longer break time. spacer cable can repair the line, the on fall does tree aheavy When link. weakest to the conductors be the likely less are open-wire would spacer not.an strongcable enough system that is But, the that tact con some branch tree withstand tion.” they so quite strong, are Spacer cable systems 3.29. Figure in example point the at poles in tend which as to break anchoring an also provide They structures. weight existing and to the loading wind it moreto repair quickly. and crews havewould beenthe poles able may broken havestanding, been first, left conductors had the if ties orshows of example insulator ahard-to-repair an failure; restore and service. damage the able are crews repair to more quickly but occurs, Thestill fault supports. other poles and breaking than rather insulators conductors the it off just breaks if of have repair easier an will crews on a line, falls for easier is to atree that crews repair. When amanner in equipmentoccur, the fails failures limb large and when such tree that design mechanical to the is coordinate One trees from approach of repaired. damage be impact to reducing the expense and most time the require that faults the are major these and storms, during especially for that lower 30% woodonly poles. than rate for concrete failure being poles, high noted asurprisingly He also attachments. State of Public Connecticut Utilities Authority, Regulatory 2013. Recover Its 2011–2012Major Storm Costs, Joint Testimony of William J. Quinlan and Kenneth B. Bowes outage per Cost per Cost Crossarms Poles replaced Transformers Outage events Customer event outage customer replaced replaced outages Kaempfferand Wong an approach design (1996) to describe overheadstructure “miscoordina amechanical cause can that example an are Spacer cable systems addextra these considerto important as The also role is of telecom attachments outages, of tree-caused portion up alarge make damage Trees mechanical causing Source: Data from CTPURA, Damage and Costs for Connecticut Light and Power Light and for Connecticut for Several Storms Costs and Damage June-2011 Storm $4187 $52 438 95 332 2603 209,045 Thunderstorm 6/8/2011 Electric Power Distribution Handbook Distribution Power Electric Petition of the Connecticut Light and Power Company for Approval to $6906 $109 3204 1297 1748 16,101 1,024,032 Tropical storm 8/27/2011 Storm Irene $122 5590 1655 1964 25,475 1,438,797 Nor’easter 10/29/2011 $6873 Nor’easter October October September-2012 $114 126 33 111 1483 80,575 Thunderstorm 9/18/2012 $6204 Storm Figure 3.29 Figure Storm Sandy $182 4745 2763 2198 16,460 856,184 Hurricane 10/29/2012 $9478 - - - ,

Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 Baker, J., R. Impulse breakdown characteristics of 13.2 Appelt, P. J. and Goodfellow, J. W., Research on how trees cause interruptions—Applications to References to structure. aharder-to-repair supporting link weakest plays arole. some In also applications, ACSR may strong enough to be move the Thechoice storms. conductor during of to easier repair them (AAC versus ACSR) to make structures distribution should considerationgiven be dination designing in results: general of Hydro’s BC several following found and the designs approach to standard analyze for Kaempfferandanalytical sequence design. agiven of failures this Wongused a provides This next. components fail what might for remaining to determine the recalculated are probabilities and stresses the to fail, member determined is weakest of component. each of failure Then,the once likelihood the to rank used is of failure of components. failures component’s Each approachlistic to determining probability or branch). tree a probabiload tension use (the the With they information, falling Figure 3.29 Although this method of distribution design is not widely used, mechanical coor mechanical not is used, widely design of distribution method this Although • • • • • distribution systems, Master of Thesis,Clarkson Science University, 1984. vegetation management, For deadend structures, the guy grip tended to fail first. to fail tended grip guy the For structures, deadend first. failed ally usu neutral for the wire tie the and phase for the grip guy the structures, For angle first. to pole fail tended conductor. ACSR, on the either fell For 336.4-kcmil tree when a first failed neutral and phase ACSR, #2 the with structures, For tangent apole were similar. near falling those and midspan near Trees falling results. affected or pole classes pole length, pole species, Neither Example of a pole broken by a tree in a large wind storm. wind alarge of in apole broken by atree Example Rural Electric Power Conference Overhead Line Performance kV polyethylene covered conductor , 2004. - 133 - - Downloaded By: 10.3.98.104 At: 12:25 25 Sep 2021; For: 9781466598669, chapter3, 10.1201/b16747-4 Bernis, R. A.O. R. Bernis, and deMinas Gerais, C.E.,CEMIG addresses urban dilemma, Hydro,BC Revenue requirement application 2004/05and 2005/06,Chapter dis 7.Electricity Barber, K.,Improvements performance inthe and reliability of covered conductor distribution 134 EPRI 1016043, EPRI 1012500, EPRI 1012443, EPRI 1012437, EPRI 1010654, EPRI 1008506, EPRI 1008480, EPRI 1002188, EPRI 1002093, EPRI 1001883, EPRI 1000194, CT PURA, CNUC, Chow, M.Y., Yee, S.O., and Taylor, animal-caused L.S.,Recognizing faults inpower distribu Chow, M.Y. and Taylor, L.S.,Analysis and prevention of animal-caused faults inpower distribu Chow, M.Y. and Taylor, L.S.,Anovel approach for distribution fault analysis, CEA 290D975, Commission, Energy California Browning, D. 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