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 LAs 300,000 35kV equipment LAs Total 35kV LAs: 339,000 35kV LAs issued for maintenance FYE 2005: 500 Ratio of replacements to total population: 0.15% Circuit outages in FYE 2005 LA related: 135 LA 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 caused Loss of protection until replaced Reduced 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 Runaway Cause: 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 ¼ mile, 3 phases Every pole, center phase only Every pole, raised center phase only Every pole, 3 phases

TFlash Results

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 TFlash Evaluate costs of various arrangements

Questions?