distribution lightning protection pilot projects reliability engineering team lightning arrester...
TRANSCRIPT
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.
Installation Design Current installation design/practice Long leads wrapping around primary Reduced Insulation/BIL after isolator
operates
Recommendations: Shorter leads Eliminate insulating bracket
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