Total System Reliability Program for Underground Electrical Distribution Networks Essay Shu, Ph.D Winnipeg, MB Sep. 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 Protection Rejuvenation Fluid

Diagnostic Testing Pre-screening Test Catch existing active electrical tree and system components that need to be addressed at a high priority TDR Determine if excessive number of joints Determine if sufficient amount of neutral remaining Pressure Test Ensure existing joints can withstand the injection pressure Flow Test Ensure sufficient flow through cable strands Post-screening Test Ensure craftwork is properly performed Assure switching process did not damage the cable  Pre-injection testing post

Holistic Approach of Feeder Rehabilitation Diagnostic Testing Terminations and Splices Surge Protection Rejuvenation 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) BIL for new cable (kV) % Reduction in impulse strength (kV) % Reduction in impulse strength (kV)577590

Surge Protection for Aged Cables Minimum protective margin recommended by IEEE C62.22 Terminal Pole Protection Scheme

Surge 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 insulation  Reinforcement of cable accessories  Non-destructive proof test of the system  Sufficient 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