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