Helicopter inspections
In July 1999, EPRI and TVA staff conducted the first aerial inspections for corona activity with the DayCor camera. Until then, the use of a helicopter to perform visual inspections of long sections of transmission line for corona activity had been all but impossible: airborne inspections are practical only during the day, but corona could be viewed only at night. “We were confident that the DayCor camera could be used successfully from an airborne platform, and these tests confirmed it,” says Phillips. “Inspections by helicopter will revolutionize the maintenance of transmission lines.”

During such an inspection, the operator observes power lines or components in real time through the DayCor’s viewfinder, and the images can be saved simultaneously on a videotape recorder. This has two benefits, Phillips notes. “It enables the operator to conduct an inspection quickly, which helps to reduce costs—a critical factor with airborne inspections—and it allows a detailed review of the results at a more convenient time and place.” In the not-too-distant future, he goes on, “inspectors will be able to ‘re-fly’ a transmission line and look for corona with a cup of coffee in one hand and a computer joystick in the other.”

For the TVA helicopter inspections, the DayCor MKI prototype was mounted on the lap of an operator who sat in the rear seat and controlled the camera’s viewing direction and settings. The “lap mount” for the camera consisted of a board strapped to the operator’s legs. A three-axis tripod head was mounted on the board, allowing the operator to easily adjust the camera’s view-ing angle. A single-axis gyrostabilizer was installed between the tripod head and the camera to prevent unwanted vibrations from affecting the images—an enhancement that the researchers found unnecessary because of the camera’s wide field of view. The need for a gyrostabilizer will be reassessed for later versions of the DayCor camera, which will have a narrower field of view.

The entire TVA inspection was recorded on 8-mm videotape, which clearly shows corona activity on 500-kV conductor bundles at several points on the TVA system. Subsequent helicopter inspections of NCIs on the Alabama Power and Georgia Power systems also identified problem insulators. “We’re not yet sure what remediation might be required in these cases, but the utilities are happy that we were able to pinpoint potential problems before they created serious difficulties for them and their customers,” says Phillips.

Real-world problem solver
The six months of laboratory and field testing have strongly convinced investigators of the corona camera’s capabilities. But the DayCor’s success is not limited to tests. One utility has already used the camera to resolve a potentially serious problem. When a local radio station in upstate New York began to experience radio interference, the problem was thought to be corona from a nearby New York Power Authority 765-kV transmission line. To resolve the issue quickly, NYPA asked Phillips to use the prototype DayCor camera to identify the source of the problem.

The device found a number of sources of corona activity on the 20-year-old transmission line, but none of these sources were in the beam pattern of the radio station’s antenna. Says NYPA’s Pete Muench, “The technology for daytime corona viewing developed by EPRI allowed us to prove that our line was not the source of radio interference.” The utility avoided a lengthy investigation of its transmission line, which could have resulted in additional expenditures or line repair.

Other utilities involved in the development of DayCor technology are just as enthusiastic. “This device works,” says Rick Stearns, a project manager at the Bonneville Power Administration. “I’m very excited about the promise it holds for use as a routine maintenance inspection tool. The early detection of corona discharge on high-voltage apparatus will allow us to replace defective components before catastrophic failure.” In turn, Stearns continues, “this will help to improve system reliability and greatly reduce the financial risks that are associated with costly line dropping, tower and hardware damage, and unplanned outages.”

Paul A. Dolloff, an engineer with East Kentucky Power Cooperative, shares these sentiments. “The DayCor camera will allow us to routinely check the integrity of NCIs in the field, thereby avoiding a systemwide change-out program.”

Future developments
Even though the technology has met every goal so far, Phillips and his utility partners in the DayCor project are already working to improve the camera. The unit’s weight and size will be reduced, and the ergonomics improved, for easier handling in the field. Technical refinements will include increasing the optical magnification and sensitivity, reducing spurious noise, and developing the capability to capture individual image frames for record-keeping purposes.

Next year EPRI will begin work on a DayCor camera application guide—in effect, a user’s manual for utilities. Publication is slated for 2001. “The guide will not only discuss what you can see with the camera but also explain how to interpret the results,” notes Phillips. “It will present detailed instructions on how to hold, mount, and use the camera, as well as specify appropriate viewing distances and other parameters for obtaining maximum benefit from this new technology.”

Preproduction prototypes of the improved DayCor MKII will be supplied to some of the utilities that have partnered in the camera’s development, including TVA, NYPA, Alabama Power, Allegheny Power, East Kentucky Power Cooperative, and Central Hudson Gas & Electric. And there are still opportunities for funding development and for investigating further applications. DayCor units are expected to be available on the open market by the end of the year 2000.

“The DayCor technology has the ability to fundamentally change the way utilities deal with corona problems,” says Phillips. “Laboratory and field test results have already exceeded our expectations. With further improvements, which are under way, we believe this device will prove indispensable for the inspection of transmission line and substation components.” Not a bad result from a little Net surfing.

Background information

Background information for this article was provided by Andrew Phillips (aphillip@epri.com), EPRI Energy Delivery and Utilization Center, Lenox, Massachusetts.

Reproduced from the EPRI Journal with permission from the Electric Power Research Institute (EPRI)