Managing Overhead Transmission Lines
Dr. Andrew Phillips is director of Transmission and Substation Research at the Electric Power Research Institute. Phillips earned bachelor’s, master’s, and doctoral degrees in electrical engineering at the University of the Witwatersrand in Johannesburg, South Africa.
Managing the more than 160,000 miles of U.S. high-voltage overhead transmission lines-including towers, conductors, and insulators, as well as corridors-is a costly and challenging proposition. Utilities' stringent standards for reliability, vegetation management and worker safety often require circuits to be located in remote and rugged environments. While Unmanned Aerial Systems or drones show promise as an option for transmission line inspection, there is still much work to do in order to ensure their safety and operational effectiveness near live lines.
The North American Electric Reliability Council (NERC) mandates that transmission system owners and operators maintain adequate clearances between overhead circuits and vegetation along right-of-ways, and that they take additional measures to minimize or prevent vegetation-related outages. For many utilities, the current practice involves dispatching inspection workers to conduct fast-flyby to assess the condition of lines in remote or inaccessible areas, employing limited helicopter hovering.
Ground inspections of components also are performed in some instances, while certain components can only be examined by climbing towers. Some equipment cannot be inspected at all due to hazardous conditions or access restrictions.
To help utilities meet the strict requirements and perform line inspections easily and more safely, the Electric Power Research Institute has developed Ti, a transmission line inspection robot that is capable of crawling over conductor shield wires and harvesting power from ambient energy sources to support autonomous, high-fidelity condition assessment for these critical assets. The robot carries sensing and imaging systems, interrogates areas inaccessible or unsafe for human inspection, and collects data from remote instrumentation, helping to more precisely inform maintenance decisions, and to reduce the need for helicopter over flights and ground patrols.
Ti's on-board systems support autonomous inspection of corridor segments up to 80 miles long at least twice annually. And deliver data and images for enhancing compliance with reliability and vegetation management standards and supporting just-in-time interventions.
Measuring six feet long, Ti incorporates high-definition cameras and LIDAR sensors to assess component condition, identify trees that could pose a risk to wires, and measure conductor clearance by comparing images taken over time. Electromagnetic interference detectors identify discharge activity and other indicators of faulty equipment, and radio frequency receivers collect data from remote instrumentation deployed on towers and wires, such as EPRI-developed sensors for monitoring vibration, lightning strikes, wind-related damage, and corrosive conditions.
Data processing, global positioning, and communications systems analyze and deliver time- and location-stamped data and images to maintenance personnel. Notification and alarm capabilities flag high-risk issues and potential problems that require further investigation or immediate action, guiding condition-based intervention.
Its mobility system includes a set of rollers for traveling along the shield wire and a diverter mechanism enabling navigation over splices, marker balls, and pylons. The rollers also provide the capability to dock at towers, allowing the robot to short out insulators and harvest power from the shield wire due to its proximity to high-voltage lines.
For transmission system components, robotic inspection systems offer the potential to reduce or eliminate human exposure to potentially higher-risk environments. While they collect the data required for effective maintenance and to meet NERC standards on tight maintenance budgets.
As a line item in utility capital plans for new transmission, Ti is expected to improve inspection and monitoring capabilities and worker safety relative to hovering helicopters at cost savings of at least 30 percent. More importantly, the robot will enable utilities to perform proactive, condition-based management of high-value assets, leading to significant cost reductions and reliability improvements.
American Electric Power (AEP) built 53 miles of 138 kV line to be "robot-ready" with diverters installed on the shield wire and power harvesting charging plates. Week-long tests have been performed with the prototype version of Ti under energized conditions. The first production version of Ti is under construction and is expected to be permanently installed on the AEP line in late 2016.
In 2007, EPRI began exploring a vision for future overhead transmission line inspection and monitoring systems capable of autonomous operation, with the idea for a transmission line inspection crawler emerging at an advanced technology readiness level, a measure of product maturity. Innovation scouting and input from utility personnel supported initial conceptual design of a robot capable of running largely on power harvested from shield wires and of interrogating components in areas not readily accessible to helicopter over flights and otherwise challenging to observe and monitor. The transmission line inspection robot entered EPRI's pipeline in 2010 with the decision to accelerate its development and demonstration as a breakthrough technology.
Since then, the team has made significant progress in taking the product to full maturity. Significant developmental work on the robotics platform was conducted on a dedicated test circuit at EPRI's laboratory in Lenox, Massachusetts. Field demonstrations of Ti began in 2013 in close collaboration with a commercial vendor and several utilities.
In conjunction with the full-scale demonstration currently underway, EPRI will continue monitoring for key performance and safety metrics, and continue to define the value proposition for utilities and stakeholders. Since the EPRI efforts began, other vendors have entered the market.
Updates on Ti can be found at www.epri.com, the Technology Innovation Program, and Power Delivery & Utilization Sector. To see Ti in action, go to this YouTube site: https://www.youtube.com/watch?v=IXjsH7zx1Ss.