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Utility
Products Showcase, July 1999
Quick-Check
Provides Quicker and Safer Transformer and Capacitor Testing
by
HD Electric Company
A
"lights out" is reported from several homes on a warm
summer afternoon. The trouble crew finds that all the houses are
served by one pole transformer and the transformer cutout fuse
is blown. No dead wildlife is found, no nearby tree branches,
and the lightning arrester is on the line side of the fuse. In
short, no obvious suspects. Does the crew refuse and hope for
the best? The last time they did, the cover blew off the transformer
leaving the customers without power for 24 hours and the company
had to replace a customer's backyard shed.
A
blown cutout fuse is hanging from one phase of a three-phase switched
overhead capacitor bank. The unbalanced capacitor load is causing
voltage problems at a nearby manufacturing facility. The trouble
crew finds no bulged or blown capacitors. Refusing and closing
the cutout into a shorted capacitor bank would cause a voltage
dip or an outage that would cause still more problems for the
manufacturer. The load dispatcher says "don't disconnect
the VARs".
A
new padmount transformer is installed and connected to buried
secondaries feeding several homes in a new subdivision. When the
transformer is livened from a nearby pole, the overhead cutout
fuse blows. Where's the problem? Is it the transformer itself?
Is it a shorted secondary cable run? Is it a miswired meter socket
on one of the houses?
Sounds
like yet another typical day for our trouble crew. In fact, all
of these situations now have a solution with a new, portable,
hand held, battery-powered tester for quickly identifying shorted
or open transformers, capacitors and cables.
Until
now, there has been no single piece of test equipment, much less
a portable battery-powered unit, capable of testing the equipment
in all of these situations. While most linemen and trouble crews
now carry portable digital volt-ohmmeters, these instruments are
not very useful for testing transformers or capacitors. To a basic
ohmmeter, every transformer winding looks like a short and every
capacitor looks like an open. The Quick-Check however, can readily
tell the difference between a shorted secondary cable run connected
to a transformer secondary and the transformer secondary coil
itself.
The
Quick-Check is a handheld device with two rugged coiled test leads
and large copper alligator clips for connecting to transformer
or capacitor bushings or lugs. A single push button starts the
tester and super bright lights and a beeper indicate whether the
connected equipment is a transformer or capacitor and whether
it is shorted, open or O.K. That's it, just a single button to
test any connected equipment, no range switches, no on/off switch
or anything else to set. The Quick-Check also contains built-in
self test circuitry so the unit can be tested in the field just
before it is used. It is powered by a single nine volt battery
and includes a low battery indication. In normal use, the battery
lasts several months to a year.
The
Quick-Check uses a special high frequency signal to tell the difference
between a connected transformer or capacitor. It also tells the
unit if it is connected to a short or if the leads are open and
not connected to anything. Analyzing the high frequency signal
tells the Quick-Check it is connected to an inductive circuit,
such as a transformer coil, a capacitive circuit such as a power
factor correction capacitor or a resistance such as a cable fault
or shorted winding. A simple test takes just a few seconds. In
less than a minute, a typical single phase transformer can be
checked across the secondary windings, the primary windings, and
from primary to secondary. The tests will also reveal an open
internal fuse or circuit breaker or a shorted internal lightning
arrester. Three-phase transformers can be checked across all three
phases and from each phase to ground.
In
a transformer shop, the Quick-Check can perform a kind of "triage"
as transformers are removed from service and brought into the
shop. The Quick-Check is used to quickly screen incoming and outgoing
transformers for both primary and secondary shorts or opens, including
any internal fuses or breakers. If all combinations of primary
and secondary connections pass the test, then the transformer
can be more thoroughly inspected, for example, turns ratio analysis
and hipot. If the transformer does not pass the test, it is known
immediately that the transformer has some more significant defect
and will need repair. For those cases such as the transformer
shop where only transformers need to be checked and not capacitors,
a version of the Quick-Check called the TILT tests transformers
only. It has all the features of the Quick-Check except the ability
to test capacitors.
Because
the Quick-Check is designed for quick and easy field testing,
it cannot detect all types of transformer or connection defects.
For example, it may not detect a partially shorted transformer
coil such as a turn to turn short. The Quick-Check may also not
detect such high resistance leakage paths to ground as tracking
on a primary side bushing. The Quick-Check works best as a quick
check for gross defects most typically caused by wiring or connection
errors. It saves time, it saves fuses, it provides a safer test
for trouble crews and it helps to provide a better level of service
to your customers.
Copyright
© 2000 HD Electric Company
Go
to the Quick-Check Transformer & Capacitor Tester product
page
Go
to the TILT II Transformer Tester product page
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