Traditional Patrol Methods

EPRI Line Patrol Research

Helicopter patrol

In order to quantify the effectiveness of current practices, a transmission line inspection experiment was devised in which multiple teams of utility and contract inspectors independently inspected the same segments of selected lines and reported observed defects. The line segments included a steel latticed tower line (100 towers) and a wood pole H-frame line (100 structures). Each of the teams independently inspected the same segments of lines using their standard practices and reporting procedures. The modes of inspection included aerial, detailed aerial, walking/driving, and climbing. The detailed aerial technique consisted of performing the line inspection from a helicopter while hovering at structures and flying spans at low ground speeds (5mph). Subsequent to the inspections, the inspection reports provided by each inspection team were compared and evaluated along with observations about each team’s methods to assess the relative effectiveness of the various practices for identifying line defects/deterioration. (Overhead Transmission Inspection and Assessment Guidelines – 2009. EPRI, Palo Alto, CA: 2009. 1017693)

Steel Tower Line-% Of Defects Reported

Aerial Patrol 0.4%
Ground Patrol 17.1%
Climbing Patrol 29.3%
Detailed Aerial 47.6%

Wood Pole H-Frame-% Of Defects Reported

Aerial Patrol 1.7%
Ground Patrol 12.8%
Climbing Patrol 15.6%
Detailed Aerial 36.3%

The results of the experiment indicated that the effectiveness of inspections is a function of several factors, including:

  • Experience and training of inspectors
  • Data recording/reporting system utilized
  • Utility philosophy on maintenance
  • Time allocation to perform inspection
  • Availability and use of inspection tools
  • Utility responsiveness to inspection findings

Is That Tree Too Close?

BPA completes a critical evaluation of the transmission vegetation management program and compares inspection methods. Read more…

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