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The Relentless Fault Finder

Rural Electrification Magazine, May 1996

by John Lowrey, Communications Manager for Southwest Arkansas Electric Cooperative

Most insulator problems are hard to detect. Until recently, linemen have resorted to the old way of finding the source of a fault. One lineman recloses the line, while another looks for a flash in the night sky. It's not a high-tech solution, but it works.

The tester fits on a standard hot stick and can be used for energized or de-energized testing of insulators. It works on any AC circuit, ranging from the lowest distribution voltage to the highest transmission voltage. A DC power source imposes a 1O-kVDC potential on the insulator, which is placed between two probes. Resistance is measured in gigohms and displayed on a meter. A 6-volt battery with a recharger is built into the unit, which weighs just 2.5 pounds.

John Farquhar, president of Hi-Test Detection Instruments, says: "We tried to make the tester simple so it wasn't awkward or complicated to use. A lot of equipment goes out that people are loath to try because it takes too long to learn how to use comfortably-"

In 1991, Farquhar worked on a case study of the insulator tester with Frank Talentino, then operations manager for Cloverland Electric Cooperative in Dafter, Mich.

Talentino was frustrated by his inability to fight insulator breakdown. "He told me that on the weekends he hated to go to the shopping center because customers of the system would be on his back telling him about problems they had and that he wasn't doing anything to respond," says Farquhar.

Talentino had tried trimming trees, tightening hardware and patrolling radio/TV interference. Nothing worked until Cloverland tested 35,000 insulators with the Hi-Test Insulator Tester. After finding and replacing more than 2,200 defective insulators, customer complaints dropped significantly.

"Talentino knew from the first circuit that he had the problem beat," says Farquhar, "The nuisance calls went to zero as soon as they changed-out the bad insulators."

Records show that in 1991 Cloverland experienced 719 outages. After completing the insulator testing and change-out in 1994, outages dropped to 498. In addition to reduced outages and power quality complaints, Cloverland reports line loss went from 10.42 percent in 1990 to 9.63 per cent by 1993 when the program was two-thirds complete.

Talentino estimated an annual savings of $75,000 on nuisance complaints alone. Increased reliability, improved customer relations and decreased line loss add to the savings. As a result of Cloverland's experience and other field trials, several general rules of thumb of insulator failure can be drawn. For example, Cloverland found most non-visible insulator failures on suspension insulators at dead-end structures.

"Suspension insulators on dead-end applications are under more mechanical stress because they are carrying tension as well as the weight of the line," says Farquhar. They are also prone to more electrical stress, especially in areas with lots of lightning. Finally, the bonding material around the pin is much more subject to wetting." During development of the insulator tester, Hi-Test cut open insulators and found hard-to-detect cracks caused by freezing in the bonding material.

"There is also a tendency for failures to cascade throughout a string of insulators," says Farquhar. This can have safety implications on transmission structures, "On the transmission side, we try to encourage people to use the insulator tester as a part of their routine maintenance activity for safety reasons," he says. "If line crews are working structures hot it is useful for them to know exactly what the condition of the insulators is on the strings. There may be no visual indication of anything wrong. If the crew is on the structure and they are assuming that they have a certain level of insulation on the structure, when in fact four or five of those insulators are defective, then they are working in a completely different circumstance. Under certain conditions, such as a switching surge, it could be hot."

Besides mechanical stress, freezing moisture or the occasional shot from a rifle slug, insulator problems can sometimes be blamed on the insulators themselves. "We were having quite a bit of problem with one particular manufacturer," says Jim Rowley, manager of electrical operations for Holy Cross Electric Association in Glenwood Springs, Colo. "We were having leakage problems with those insulators and we couldn't look at them and tell anything was wrong."

Rowley first heard about Hi-Test Detection Instrument's Insulator Tester during a demonstration at the Mesa Hot Line School in Grand Junction, Colo. Rowley, secretary-treasurer for the school, says Mesa Hot Line trains 500 linemen from 60 utilities each year.

Once he was able to isolate the problem to a particular brand of insulators, Rowley simply had all the insulators of that type changed-out. But instead of throwing the insulators out, the warehouse staff uses the insulator tester to check each one. Insulators that pass the test can be reused.

"When you can't see the problem and customers are asking, 'What kind of company are you? Why can't you fix this problem?', it gets very frustrating." Says Rowley: the Hi-Test Insulator Tester takes the mystery out of faults.

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