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Total System Reliability Program for Underground Electrical
Distribution Networks
Essay Shu, Ph.DWinnipeg, MBSep. 2015
Chemical Treatment
• Over 27 years experience, 131 million feet injected since 1989• Conveniently accommodated injection process• Cable dielectric strength is enhanced to comparable of new
cables
2
Feeder ≠ Large URD
Physical Differences Geometry Length
Electrical Differences Loading/Temperatures Stress Profile
Economic Differences More Electric Meters Materials and Installation
Holistic Approach of Feeder Rehabilitation
Diagnostic Testing
Terminations and Splices
Surge ProtectionRejuvenation Fluid
Diagnostic Testing
• Pre-screening TestCatch existing active electrical tree and system components that need to be addressed at a high priority
• TDRDetermine if excessive number of joints
Determine if sufficient amount of neutral remaining
• Pressure TestEnsure existing joints can withstand the injection pressure
• Flow TestEnsure sufficient flow through cable strands
• Post-screening TestEnsure craftwork is properly performed
Assure switching process did not damage the cable

Pre-
inje
ction
testi
ngpo
st
Holistic Approach of Feeder Rehabilitation
Diagnostic Testing
Terminations and Splices
Surge ProtectionRejuvenation Fluid
Remaining Impulse Strength
• Is the surge protection adequate?
• Evaluating the remaining impulse strength of a cable is impossible
• Lightning protection practice based on new cable parameters may not be sufficient for an aged cable system
Voltage Class (kV) 15 25 35
BIL for new cable (kV) 95 125 150
20% Reduction in impulse strength (kV) 76 100 120
40% Reduction in impulse strength (kV) 57 75 90
1001(%)
TTV
BILPM
Surge Protection for Aged Cables
15 kV 25 kV 35kV-40%
-20%
0%
20%
40%
60%
80%
new cable
Aged Cable 20% reduction
Aged Cable 40% reduction
Voltage Class
Prot
ectiv
e M
argi
n
Minimum protective margin recommended by IEEE C62.22
Terminal Pole Protection Scheme
15 kV 25 kV 35kV-20%
0%
20%
40%
60%
80%
100%
120%
140%
160%new cable
Aged Cable 20% reduction
Aged Cable 40% reduction
Voltage Class
Prot
ectiv
e M
argi
nSurge Protection for Aged Cables
Minimum protective margin recommended by IEEE C62.22
Terminal Pole and Open Point Protection Scheme
Suggested Actions
Check if arresters are in place in aged cable systems
Verify if arrester lead length are optimum
Evaluate whether protective levels are adequate for desired protection
Conclusion
• The holistic feeder reliability approach includes Enhancement of cable insulationReinforcement of cable accessoriesNon-destructive proof test of the systemSufficient surge protection to meet today’s standards
• The goal of feeder cable program is to review all aspects of the aging portions of a distribution system for enhanced system reliability and to eliminate an unscheduled electrical outage