San Diego Gas Electric has been Using Infrared Cameras on its T&D Lines for Years. When the program was implemented, the infrared work was done with a handheld camera mounted on the side of a vehicle or held by a person sitting in an open doorway of a helicopter.

When the California Independent System Operators (CAISO; Folsom, California, U.S.) was created and the CAISO Tariff, Appendix A, which mandates reliability requirements, was implemented, SDG&E's (San Diego, California) infrared inspections of transmission lines were limited to periods of time when the thermographer was not being used by the generation plants. With the increased reliability requirements imposed by the California Public Utility Commission (Sacramento, California), SDG&E decided to use infrared cameras on distribution lines.

As a result of the CAISO Tariff mandating improved reliability, SDG&E developed the “Transmission Owner Maintenance Practices” for overhead and underground transmission and the “Transmission Substation Practices” for substations. In these practices, SDG&E stated that all overhead lines and substations would be given an infrared inspection on an annual cycle and all underground vaults would be inspected on a three-year cycle.

INFRARED CAMERA ON LINES AND CABLES

In 1997, the SDG&E Transmission Construction & Maintenance (TCM) department developed improved methods for infrared inspections. Instead of mounting a handheld infrared camera on the side of a truck, TCM acquired a 4×4 van and mounted a pan/tilt head with an infrared camera on the roof. With the pan/tilt head on top of the van, the thermographer (with a driver) views the infrared image on a 10-inch (254-mm) monitor inside the van.

In 1998, SDG&E purchased a stabilizing gimbal for airborne infrared work. By using the stabilizing gimbal on a helicopter, SDG&E has made the infrared inspections safer and more efficient than previous methods. SDG&E does approximately 13,100 structures by air and 1400 structures on the ground every year.

For underground vault inspections, the thermographer and supervisor developed a combination visual and infrared camera mounted on a pole to inspect the cables and vaults while the lines are still energized. The thermographer does approximately one-third of the 260 vaults every year. Also, the thermographer and supervisor developed an underwater camera to visually inspect cables, cable ladders and ground connections that are hidden from view of the other underground vault camera, because of water in the vault.

By performing planned infrared inspections of the transmission system, SDG&E has improved its system reliability by minimizing the number of outages caused by heat fatigue.

CORONA CAMERA

In 2000, a camera was developed that can identify corona activity during daytime hours. Prior to 2000, the corona cameras could only be used during evening or morning hours. Corona discharge is a partial discharge from an electric field that ionizes the air. Corona activity creates a corrosive byproduct as a result of the ozone and nitrogen oxides, which yield nitric acid in the presence of water vapor. When corona activity is consistently present on metal components, the nitric acid will damage and shorten component life.

In 2001, SDG&E purchased a daytime corona camera to improve patrol reliability. The corona camera also effectively identifies insulator contamination caused by salt deposits. The thermographer combines the corona camera with the infrared camera on the pan/tilt head on the roof of the van. By using this corona technology, the thermographer identifies areas of concern and investigates the components to determine if their life expectancy has been compromised. To further identify components compromised by corona, SDG&E invested in a gimbal that has a corona camera and mounted it on the helicopter.

TCM first inspected the 230-kV and above overhead lines. The thermographer does approximately 100 structures from the ground and 1950 structures from the air every year.

In the late 1990s, SDG&E started using nonceramic insulators (NCIs) on its transmission system. Recent failures of NCIs on 138-kV lines have caused SDG&E to lower the corona inspection threshold to the 138-kV lines. By lowering the threshold, SDG&E increased the number of structures the thermographer does to approximately 2550 by air and 260 structures by ground.

SUBSTATIONS

SDG&E Transmission Substation Practices require an infrared inspection to be performed on an annual cycle. Since the Substation Construction & Maintenance (SCM) department does not have a thermographer, SCM uses the TCM thermographer to perform inspections.

The thermographer does 160 bulk power substations and 40 step-down stations annually. The inspections cover all connections, breakers, capacitors and transformers on the high and low side of the station. Also, corona inspections have been increased to cover bulk power substations to assist in identifying possible causes of flashover as a result of the salt contamination in the region and the presence of water vapor. The thermographer does both the infrared and corona inspections of a substation at the same time.

The thermographer is required to make two trips around a substation, once with the infrared camera and once with the corona camera. Along with the corona and infrared cameras, the thermographer also carries a notepad and a still camera to capture aspects of the inspection that the specialized cameras do not capture.

With the need to comply with the SF₆ gas regulations, the ability to capture and track the amount of SF₆ gas escaping into the atmosphere needed to be developed. With new cameras on the market that can identify possible gas leaks, SDG&E can lower the amount of SF₆ escaping into the atmosphere from its equipment, but the thermographer would need to make three trips around a substation. Thus, the thermographer and supervisor developed a mobile platform that has the infrared and corona cameras mounted on a pan/tilt head and has compartments that hold the still and gasification cameras. With this mobile platform, the thermographer reduces the number of trips around a substation. The use of the mobile platform in bulk power substations decreases the time needed to complete the annual inspections.

DISTRIBUTION OVERHEAD LINES

Because of the increased requirements on distribution reliability indices (SAIDI, SAIFI and CAIDI), SDG&E distribution districts are making requests for the thermographer inspection of overhead circuits. The emphasis of the inspections is on the main feeders, capacitors and switches. All these inspections are done with the van. One district engineer attributes $250,000 in savings to the SAIDI minutes for one year as a result of this limited infrared inspection program.

These savings were accomplished by increasing the reliability of the system through the identification of potential problems with the limited infrared inspection program. The savings noted previously were calculated from one district that comprises 17% of SDG&E customers. A savings of more than $1 million would be anticipated if the infrared inspection program were expanded to cover all SDG&E distribution districts.

A VALUABLE TOOL

While no specific threshold exists to tell the thermographer that a component will fail, these inspections identify possible weak links in the electric system. Thus, even with all the technology mentioned in this article, the thermographer is still required to make the final determinations concerning the health of the electric system.

All of the applications discussed here — van (pan/tilt head), vault inspection cameras and the substation mobile platform — are always in a state of development. With changes in technology, new systems are always being developed, including high-resolution video and still cameras, smaller corona cameras and higher-accuracy infrared cameras. Nevertheless, this is a valuable tool that has demonstrated its ability to increase the reliability of the electric system.

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David Eaton joined SDG&E in 1972 in gas construction and soon enrolled in the lineman apprentice program. He progressed in responsibility from journeyman lineman to transmission line crew foreman. In 1999, Eaton became a transmission analyst and soon after transitioned to performing infrared and corona inspections. He retired in 2007.
dleaton@cox.net

William “Bill” Hewitt joined SDG&E in 1989 in Land Services as a surveyor. In 1999, he transferred to Land Planning and Project Management as a land project manager. During his time as a land project manager, he initiated a GIS program and became the GIS administrator. He transferred to Transmission Engineering as an engineer in 2003 and was promoted in 2006 to operations and engineering supervisor in the Transmission Construction and Maintenance department.
bhewitt@semprautilities.com