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Pole and Crossarm Fires May Be Related to Porcelain Cutout Failures
We use EXACTER to locate failing cutouts along with other failing electrical equipment. EXACTER senses and prioritizes failing equipment early in the failure cycle and allows us to avoid costly damage such as pole fires and outages.
We have recognized an apparent failure syndrome in porcelain cutouts. Moisture appears to enter the porcelain causing fractures which we believe are related to freeze-thaw cycles. As the porcelain continues to degrade over time a current path is created from the energized elements to the grounded mounting bracket. As this mounting bracket is either bolted to the crossarm or pole, the current flow results in heating and an eventual pole/crossarm fire.
Don’t Skip the Survey
During the follow-up on an EXACTER Group location field review, we were directed to what seemed to be a mistaken location. Several Events had been aggregated into one significant EXACTER Group, but when we arrived at the location we found it to be midway between two poles. There were splices on the line, so these were inspected with no trouble found. That is when we learned the importance of completing a site survey to its conclusion. We used an RE 330 to do a sweep of the location. That is how we noticed that the Event emission was coming not from the line but from a location perpendicular to the line. We continued to follow the emission source to a house about 200 feet off the road. The survey tool indicated a steadily increasing RF emission. The sweep of the area quickly located the source of the emission: the service Triplex. Using the RE 330 and the RE ultrasonic parabolic sensor, we followed the service entrance to the meter socket. Once we confirmed the source of the emission, an emergency ticket was issued and a meter technician was dispatched. We contacted the owner of the home to let them know that there would be a short interruption of service while the problem in the meter socket was investigated. The Meter Technician removed the meter from service and the emissions ceased, obviously a load-side problem. The problem was immediately apparent. The right-hand load-terminal was badly etched and blackened from arcing and heat. Our first thought was that the meter had not been properly seated in the socket. So, the meter was reinstalled following a thorough safety inspection. At first there were no emissions. But, in about 30 seconds the emissions began again. The emissions were low level at first, but returned to their normal pre-inspection level within a couple of minutes. As a final step, we discussed the hazardous situation with the customer, who agreed that an electrician would be called immediately to replace the failing meter socket before a heat-related failure initiated a fire. Luckily, the weather was mild and there were no heavy loads in the home to exacerbate the problem. The sensitivity of EXACTER located the problem which was hidden from view off the road and avoided a disaster. This really demonstrated the importance of following up on EXACTER Group Events with a site survey to locate the problem and resolve the arc emission. 
Hot-Line Clamp Gets Really Hot
During an EXACTER survey, an emission source was located and logged as an EXACTER Event. Upon review of the location information, it was noticed that this circuit also had a lot of trouble with missed AMR meter readings. We used RE locating tools to quickly pinpoint the arc-emission source that had been located during the EXACTER survey. The source seemed to be the conductor at a hot-line clamp. When the clamp was removed, there was obvious damage to the connector. The clamp was nearly burned through. Luckily, the clamp sustained most of the damage and the conductor seemed to be okay, although we will be watching it. As a secondary benefit, following the replacement of the clamp on a new area of the conductor, the meter-reading system started reporting 100% readings. EXACTER provided the information we needed to avoid a downed conductor and overcome a vexing AMR issue.
Hot line clamps are used in a variety of connection situations. Everyone knows that the conductor must be cleaned to avoid early failure due to high-resistance connections. And proper installation procedures are well understood. But there are times that something can go wrong.
A Continued Source of Flashover and Outages
Finding the insulators that are failing in the field is very difficult. The area of tracking is almost invisible from the ground or even during bucket-truck inspections. Infrared inspections do not locate these devices as little current, therefore no discernable heat signature, is generated across the insulator surface. Using EXACTER, the insulators are easily located at the onset of tracking. Ranking the problems poles with tracking insulators by the EXACTER Maintenance Merit® allows you to develop a pole rebuild strategy. Instead of working an entire line, the Maintenance Merit will pinpoint the poles with the worst problems and these can be dealt with first. click thumbnail to view larger image
The aluminum-porcelain insulator design has not been holding up to Midwest winters. Apparently, the interface between the two materials is affected by freeze/thaw cycles. It is suggested that the coefficients of expansion for the two materials results in cracking of the porcelain surface. This cracking leads to tracking and an eventual flashover and circuit outage.
Contractor Work should be Evaluated
We are using EXACTER to look for problems on our lines that will indicate there is a piece of failing equipment. We have found typical problems like tracking lightning arrestors and cutouts. We are also finding bad splices. This one in particular shows that the splice was not done to our standards. Apparently to hasten the work along, the line worker cut several strands of the line to make an easier fit into the splice. This drops the capacity of the conductor and adds a future maintenance problem to the system. These types of installation problems are detected by our EXACTER system and they can then be quickly followed up on and usually can be located from the ground with binoculars once you know which pole to go to.
During storm recovery we often hire contractors to assist in restoration. This is typical for any utility as a way to manage the maintenance budget. But, it is difficult to review all elements of the work when the job is to get the lights back on. Then, after the contractors are gone, there is little opportunity to follow up and evaluate the performance of the contract workers.
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Sometimes the Problem is the Entire Pole
About a week ago we had a real bad storm with a lot of high winds. We had a lot of circuit damage that was evident. But, when investigating an EXACTER problem location, we found this pole. Apparently the wind had tried to knock the pole over, but the wires – although stretched – managed to keep the pole from falling and taking out the entire neighborhood. EXACTER was able to locate the pole as several pieces of equipment had begun to track to ground as the pole was strained and the cross-arms were twisted. We were surprised and pleased that we were able to locate this damage before the outage occurred or some worse accident occurred. click thumbnail to view larger image
We have been using EXACTER to survey our distribution network for some time. Since the system is automatic, we have installed it in our meter reader vehicles. As the routes are run, we receive our mapped information of problems to follow up on.
Hidden Damage - A Safety Issue
Internal failure will eventually lead to a circuit outage, but a more critical problem is present that can be a real danger to the line mechanic who is going about a normal routine. The single-phase switch shown here was in operation when an EXACTER® Outage-Avoidance System survey was being run. The circuit had been surveyed by IR technology previously and no indication of a problem was noted. Following the EXACTER survey, the pole was scanned with a directional radio “sniffer” to locate the device that was found by EXACTER. When the single-phase switch was located as the emission source, the line mechanic was asked to operate the switch following other switching to unload the circuit. When the switch was operated, the device collapsed. This type of failure can occur during normal switch operation when there would be less assistance nearby. It was lucky that this was a preventive maintenance job where the worst was expected to happen. When the broken insulator was examined, it was easy to see where the arc source had eroded the material, weakening it and leading to the eventual mechanical failure.
There are all types of damage that are precursors to the failure of an electric circuit element. Many times the damage is internal and provides no visible or heat-related indication.
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Lightning Arrestor proximity to gas line creates danger
Sometimes the failing electrical equipment can cause more than just an outage, as these pictures demonstrate. At this site, the failing lightning arrestor was on a pole directly above a gas pipeline access. EXACTER located the failing device before any collateral damage could occur. Danger indeed! Pictures courtesy of Intelligent System Sales
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Exacter finds cutout insulator
This cutout insulator looked fine from the ground and even from a bucket-truck inspection. However, a sharp tap caused the entire assembly to crumble. EXACTER® Outage-Avoidance System located the arc-source emission as the survey vehicle drove by. Luckily no one was hurt when the cutout, which was supported by the conductors, collapsed during the inspection. click thumbnail to view larger image
Failing electrical equipment does not always show symptoms until it is too late. Often the arc source is hidden inside of the insulating components and slowly erodes the mechanical elements. The bonding material between metallic components and insulators seems to be particularly susceptible to damage.
EXACTER vs. Telecom
An example of this happened at a southern EMC installing a new AMR program. Communication difficulty was a constant problem and halted installation work early on. The system provider and the utility worked together to solve the problem and exhausted all conventional troubleshooting methods. The problem could not be located. An EXACTER survey located a corroded ground at a telephone pedestal. When the ground wire was lifted, the meters started communicating.
Deployment of a reliable power-line-carrier (PLC) AMR system is a difficult task, but when power line noise disrupts communication, the meters stop reporting.
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