Distribution Lightning Protection Pilot Projects

Reliability Engineering Team

Lightning Arrester Initiative

Presented by Tim Constanzo, PE

Where it all started

Corporate initiative to improve reliability

Reliability Summit

Root cause analysis methodology Relay philosophy/settings Maintenance, allocation of resources Backbone initiative (distribution system design) Lightning arresters (LA’s)

Problem Statement

Lightning arresters (LAs) are believed to be the cause of an unacceptable frequency and duration of customer interruptions and outages.

Probing Questions

How bad is it?Why/how are LA’s failing?How effective is current application of LA’s on system?

How bad is it?Estimated population:

39,000 35kV line LAs300,000 35kV equipment LAs

Total 35kV LAs: 339,00035kV LAs issued for maintenance FYE 2005: 500Ratio of replacements to total population: 0.15%Circuit outages in FYE 2005 LA related: 135LA related rate of circuit outages: 8.7%

How/why are LA’s failing?

Fishbone and Pareto graphs/Root Cause LA failure categories:

Proper isolator operation (not a failure!) Design/Manufacturing defects Installation Design/Practice Thermal Runaway

Normal Operation

Isolator designed to operate when capacity of LA is exceeded Lightning TOV

No outage causedLoss of protection until replacedReduced BIL/CFO until replaced

LA Design/Manufacturing Issues

Poor design/manufacturing Poor seals Voids under sheds

Recommendation: Revise LA standards to eliminate designs with poor seal and voids under sheds.

Failure due to moisture ingress

Installation Design Current installation design/practice Long leads wrapping around primary Reduced Insulation/BIL after isolator

operates

Recommendations: Shorter leads Eliminate insulating bracket

Tracking Failure of Bracket

Installation T & E Option

Thermal RunawayCause: Aging zinc oxide block material Moisture ingress (most common)

Effect: High leakage current Marginalized MCOV Elevated temperature

Recommendations: IR patrol removal when +10°C/18°F above ambient

Current Application of LA’s

Line arresters 27 kV/22 kV MCOV (Heavy Duty) ¼-mile spacing, all phases

Equipment arresters 27 kV/22 kV MCOV (Heavy Duty) All equipment

Evaluating LA Application

TFlash modeling cases: Baseline: no arresters Arresters @ ¼ mile, 3 phases Every pole, center phase only Every pole, raised center phase only Every pole, 3 phases

TFlash Results121

106

2620

00

20

40

60

80

100

120

140

Flashovers/100 miles

Base Case, No LA's

Current Practice, 1/4 Mile,All Phases

LA's Center Phase Only,All Poles

LA's Center Phase Only,All Poles, Raised CenterPhase

LA's All Phases, EveryPole

Conclusions/Recommendations

Discontinue current application: “¼-mile” Let attrition remove line LAs Maintain LAs protecting equipment

Apply only when/where lightning is an issue Circuits requiring higher reliability High exposure Use higher voltage rated LA (27 -> 30 kV)

Lightning Arrestor Initiative Going Forward

T&E lightning arrestor installation arrangements Static wire (no arresters) LA’s center phase only, every pole

Further modeling in TFlashEvaluate costs of various arrangements

Questions?