Palmetto Electric uses a thermal imager as a routine part of operations and maintenance.
Do you want an immediate, inexpensive, guaranteed way to enhance system reliability and eliminate some potential outages before they happen? Sure you do. Do you want something to use at your leisure but hopefully as part of an annual inspection routine? Of course you do. Then you need to get a thermal imager, also known as an infrared gun.
Palmetto Electric Cooperative Inc., a distribution cooperative located in Beaufort, Jasper, Hampton and Allendale counties in South Carolina, U.S., began service in the 1940s and has grown to 65,000 customers. The utility plant consists of 22 substations and 3165 miles (5094 km) of 7.2/12.5-kV line. A little more than half the distribution lines are underground.
Palmetto's inspection program consists of a five-year cycle for the overhead portion and a four-year period for the underground portion. There are 27,556 pieces of underground equipment on the system. One of the maintenance goals is to scan every piece of underground equipment on the system with an infrared gun.
In the past, subcontractors were used to inspect and paint the underground equipment. This typically was a visual inspection with detailed reports. A couple of years ago, since there were so many primary underground feeders, Palmetto Electric made the decision to take the underground inspection a step further and use infrared technology to inspect the backbone of its system. The device Palmetto uses is a Fluke Ti 30 thermal imager. Two years ago, the cost was around US$10,000. Remarkably, newer models are not only improved but have a significantly lower cost. Also, the images are easily downloadable and the software is user friendly.
The starting point for using the thermal imager was the Hilton Head Island district office, which has about half of the members of the system customer base. The island has 455 pieces of switchgear and 557 three-phase junction cans — all are exposed to the harsh salt environment of a “barrier island.” Out of a total of 116 items flagged for attention, 37 were infrared related. Numerous hot cable termination lugs, elbow arresters, lighting arresters, stress cones and some 200-A-rated elbows were among the items identified. A few of the switchgear also had bushings in need of repair.
Oddly enough, the first day of using the imager, a lineman was preparing to pull a 200-A elbow off an elbow bushing with his shotgun stick. Because the imager rated the elbow at level one, which means a high probability of failure, the lineman was stopped from pulling it (see “Ratings System by the Manufacturer”). Instead, the cabinet was de-energized and, when pulling the elbow off, the conductor contact pin pulled out of the elbow. This could have had serious consequences had it been done live.
The thermal imager also has been used by other districts and the marketing and the substation departments. Furthermore, because of the great results, the utility has purchased another imager for its New River district. When the vendor came to the office to demonstrate the second infrared imager, it was used to check a few three-phase transformers in the field. The very first transformer was a 75-kVA unit that served a convenience store/gas station. Palmetto found a very hot spot on one of the transformer's secondary blades. In the future, this connection would have resulted in a power outage, single-phase condition. To correct the problem, an outage was scheduled during non-business hours.
In another instance, the infrared imager was useful while troubleshooting a feeder circuit with an unacceptable voltage drop. The circuit was a combination of 750-mcm, 15-kV underground cable and 336 aluminum conductor steel reinforced overhead line. The feeder length was approximately 6.5 miles (10 km) and circuit loading was fairly balanced with approximately 280 A per phase and a ground current of less than 20 A. The engineering model indicated the voltage level on the feeder would be within the ±5% tolerance.
The infrared imager identified a couple of hot spots. One was on an overhead switch and the other was on the system, neutral, about halfway down the feeder. The neutral hot spot seemed odd considering the balanced loading and minimum neutral current at the substation. After some investigation, it was determined that although the feeder was balanced at the substation, the load along the feeder was not distributed evenly. One phase was very heavily loaded near the end of the feeder. The hot spot on the neutral directed Palmetto to the problem.
Recently, the thermal imager played a key part in assisting a local national-chain grocery store. The store's plumber and electrician could not resolve why the hot water heater fuses kept blowing. The Palmetto troubleman immediately pinpointed the issue of loose fuse holders that were overheating and blowing the fuses.
The substation manager also quickly became a user of the imager. The substation department still hires a contractor to inspect stations biannually, but uses the imager during some monthly checks when the system is peaking or at times before switching to take a station out of service. It is not uncommon to find hot spots on switch contacts. These are normally corrected by opening and closing the switch, thus wiping the contacts clean. One anomaly the infrared imager identified was on a newly installed 30-MVA power transformer. The infrared imager showed the radiators to be cooler than the transformer tank. The upper valves on the radiators were found to be in the closed position. This could have been a very costly mistake.
Different people have different approaches for using infrared technology. Palmetto created a switch inspection form, specifically a checklist of items that may need correcting. In lieu of taking photos, there is a switch/fuse wiring diagram that provides a label for each cable compartment on the schematic to see where the cable feeds. This can also be compared to the mapping for accuracy. This enables the lineman to see the exact location of the item needing attention when compared to the thermographic report. The crews have responded favorably to the program. The reports are easily understood, there are fewer surprises in the middle of the night and the goal is accomplished: The lights are kept on.
Palmetto has always been focused on providing a high level of system reliability. A proactive preventive maintenance program is an important part of the coops asset management program. Palmetto has proven that infrared technology should be used in such a program. What once was an operations manager's dream to identify problems before an outage happens now fits securely in the palm of their hands.
Ratings System by the Manufacture
The following categorization of thermal imager readings are used to identify situations that will soon fail. Level one readings require immediate action. Level two indicates that further investigation or corrective action is needed.
Level one - Probability of failure
Is the phase-to-phase temperature difference (for surfaces with high emissivity) greater than 24°C (75°F)?
Is the absolute temperature 94°C (201°F) or greater using a reliable measurement?
Is there a visual indication that metal or insulation has melted or is discoloration severe?
Is the problem on a shiny flat or tubular bus connector?
Is the view of the heat source indirect (i.e., an oil-filled device, bus stab, enclosed bus or inside and unopened enclosure)?
Is loading likely to increase by three times or greater prior to normal repairs?
If “yes” is answered to any single level one question, the condition is red, meaning immediate action is required. Otherwise, proceed to level two.
Level two - Probability of failure
Is the temperature difference (for surfaces with high emissivity) greater than 9°C (48°F)?
Are wind or air currents greater than 5 mph (8 kmph) and likely to decrease to little or nothing?
Is equipment subject to excessive vibration, dust, dirt or ambient temperature swings?
Do loads cycle frequently or will loading increase two times or greater prior to normal repairs?
Will ambient air temperatures increase by 24°C or more prior to normally scheduled repairs?
Does the component have little mass (i.e., smaller than a #10 conductors or lightweight fuse clip)?
Is there a history of failure for this or similar components?
If “yes” is answered to any level two question, the condition is yellow, meaning investigative, and possibly corrective, action is required as soon as possible
Dan Wood (email@example.com) has worked at Palmetto Electric Cooperative Inc. for 27 years. He started his career with Southern Engineering Company of Atlanta, Georgia. He spent his early years in field mapping and line staking. He has worked in safety and engineering services and was promoted to district operations manager in 1993. Wood has an associate's degree in electronics.
Bruce Draper (firstname.lastname@example.org) has been with Palmetto Electric Cooperative Inc. for 28 years and is the substation and metering supervisor. In addition to these responsibilities, he oversees the inspection and maintenance of system capacitors, field reclosers, voltage regulators and automatic transfer switches. He has an associate's degree in occupational technology and is a licensed master electrician. Draper also serves on the South Carolina Electric Cooperatives Statewide Association's steering committees for substation training and also its engineering group.
Companies mentioned in this article:
Palmetto Electric Cooperative Inc. www.palmetto.coop