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Rural
Electrification Magazine, May 1996
The
Relentless Fault Finder
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.
Copyright
© 2000 HD Electric Company
Go
to the IT-4 Insulator Tester product page
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