Underground Cable Assessment

A Complex Asset

Almost all electric power utilities distribute a portion of the electric energy they sell via underground cable systems. Collectively, these systems form a vast and valuable infrastructure. Estimates indicate that underground cables represent 15 % to 20 % of installed distribution system capacity. These systems consist of many thousands of miles of cables and accessories installed under city streets, suburban developments and rural areas. 

Cable systems are designed to have a long life with high reliability. However, the useful life is not
infinite. These systems age and ultimately reach the end of their reliable service lives. Appropriate maintenance and repair practices enable system aging to be controlled and helps manage end of life replacements. Sophisticated and modern commissioning and maintenance diagnostics are critical in determining the health of the cable system thus maximizing the lifecycle value. 

Some Cable Defects and Aging Factors

  • Manufacturing Imperfections:
    • Voids
    • Contaminants in insulations
    • Poor application of shield material
    • Protrusions on the shields
    • Poor application of jacket
  • Poor Workmanship:
    • Cuts
    • Contamination
    • Missing applied components or connections
    • Misalignment of accessories
  • Aggressive Environment:
    • Chemical attack
    • Transformer oil leaks
    • Floods
    • Petrochemical spills
    • Neutral corrosion

  • Wet Environment:
    • Bowtie trees
    • Vented water trees
    • High rates of corrosion
  • Overheating:
    • Excessive conductor current for a given environment and operating condition
    • Proximity to other cable circuits for short distances
  • Mechanical:
    • Damage during transportation
    • Damage during cable pulling
    • Improper application at vaults/chambers and switchgear entry

Our Comprehensive list of Cable Diagnostic Techniques

  • Time Domain Reflectometry (TDR). 
  • Frequency Domain Reflectometry(FDR).
  • DC conductor and neural resistance.
  • AC impedance measurements.
  • Monitored Withstand (60Hz & VLF).
  • Offline Partial Discharge (PD) via applied overvoltage @ 60Hz. 
  • Offline Partial Discharge (PD) via applied overvoltage @ 0.1Hz VLF.
  • Very Low Frequencies (VLF Tan δ).
  • Low Frequency Dielectric Spectroscopy.
  • Fault location.