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Where it all started

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

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Where it all started

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  1. Distribution Lightning Protection Pilot Projects Reliability Engineering TeamLightning Arrester InitiativePresented byTim Constanzo, PE

  2. 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)

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

  4. Probing Questions • How bad is it? • Why/how are LA’s failing? • How effective is current application of LA’s on system?

  5. 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%

  6. 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

  7. 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

  8. 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.

  9. Failure due to moisture ingress

  10. Installation Design • Current installation design/practice • Long leads wrapping around primary • Reduced Insulation/BIL after isolator operates • Recommendations: • Shorter leads • Eliminate insulating bracket

  11. Tracking Failure of Bracket

  12. Installation T & E Option

  13. 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

  14. 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

  15. 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

  16. TFlash Results

  17. 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)

  18. 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

  19. Questions?

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