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Utility
Products Showcase, July 2000
Hi-Test
IT-4 Insulator Tester
by
Bill McNulty, P.E., HD Electric Company
A
69kV transmission line snakes through what used to be farm land
but is now a mix of new subdivisions, shopping malls and office
parks. Most of these new customers are now served by this transmission
line through two new substations.
Starting
this spring, the C phase on this transmission line has been going
down about every other day. Today was the ninth outage so far.
The source dispatcher says the problem isn't due to any overload
on the C phase but is due instead to a fault on the line. Fault
recorders in the two new downstream substations say that the problem
isn't on the load side. It's your job to keep the transmission
line up and this month your job has gotten a lot harder.
Naturally,
the customers are starting to get fed up with these too frequent
outages and the phone calls are pouring in. The shopping malls
are the loudest complainers; even with their expensive automatic
transfer switches, they are finding both sources down since both
of the two new substations are served by your transmission line.
You've already done a visual inspection of all 278 poles, the
insulators hanging from the cross arms and the conductors hanging
from the insulators. You've tested every lightning arrester on
the line, there's no evidence of any wildlife causing these outages
and no storms that coincide with the times of the outages. It's
just starting to get hot outside but it's already a lot hotter
in your office.
You've
already run through your list of the usual causes of these types
of problems but so far nothing has stopped the outages. A second
complete inspection of the line shows no visible flashover damage
on any of the porcelain suspension insulators. Still, you can't
help but suspect a bad insulator somewhere on that C phase. You
don't even want to try telling your boss that you want to replace
all the insulators. After all the unplanned outages, the last
thing you need is a long planned outage. What you really need
is a way to test the insulators quickly and easily and without
a planned outage.
Does
this situation sound all too familiar? Fortunately, there is now
a solution with the Hi-Test Insulator Tester by HD Electric Company.
The Hi-Test Insulator Tester tests energized or deenergized suspension
insulators for non-visible internal failures at any line voltage.
The model IT-4 tester is portable, self contained and designed
for use on the end of a hotstick. Built in test probes contact
the metal ends at the top and bottom of each skirt and the front
panel display readily identifies the high leakage current typical
of bad insulators. A loud buzzer also signals the lineman that
a bad insulator has been found.
The
IT-4 Insulator Tester works by applying a 10kVDC voltage across
each insulator in a string and then measuring the DC leakage current.
Most importantly, it does this while the insulators are still
live. Insulators with non-visible internal failures will show
a high DC leakage current which is then displayed in lights on
the front of the tester. A loud buzzer also signals high leakage
and helps to ensure that nothing is missed. The tester is battery
operated with a rechargeable battery that lasts for several days
of testing. Recharging takes place overnight or in the line truck
during lunch.
Back
in the field, testing of the insulators on your 69kV line is underway.
As long as you're stopping at each pole, you decide to test the
insulators on all three phases. In about two weeks, with some
overtime thrown in, you manage to test every insulator on the
line. Here's what you find: two bad insulators on C phase and
one insulator each on A phase and B phase that weren't completely
bad but looked like they were on their way to failure. After locating
the bad and questionable insulators you go ahead with a planned
outage to replace the four insulators.
After
about two quiet months you realize that you've solved the problem.
You also notice that those nagging TVI complaints that were pushed
to the back burner while you were tracking down the outages have
also disappeared. It's the middle of summer now and plenty hot
outside but things have finally cooled down in your office.
The
Hi-Test Insulator Tester is now used regularly to test your glass
and porcelain suspension insulators on both new installations
and existing lines. It's great for finding defects before they
become problems and is the only way to find the types of defects
that cause those nagging RF/TVI (Radio Frequency/Television Interference)
complaints. You're thinking that once you finally catch up you
might even lend your IT-4 Insulator Tester to another crew.
The
Hi-Test Insulator Tester is supplied complete with long life rechargeable
battery, carrying case and universal spline for attachment to
a hotstick.
Copyright
© 2000 HD Electric Company
Go
to the IT-4 Insulator Tester product page
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