Application Note

2 Fluke Corporation Don’t run it backwards - Phase rotation testing in utility power distribution systems
abundantly clear when customer
electricians went to check the
phase rotation on a transformer
whose nameplate read 240
V a using rotating-disc phase
unit. Unfortunately for them,
the system voltage was actually
2400 V, and they smoked their
phase rotation indicator. This
got the utility people to think-
ing: “If it happened to them, and
we have 2400 V secondaries in
our system, there’s a possibility
that someone might misread a
nameplate in our system. Let’s go
ahead and get a Category IV in
case someone messes up.”
So the utility bought 9040s.
Some of the older technicians
resisted at first, insisting they
were more comfortable with the
old rotating dots, but the younger
ones are used to electronic
devices. And what could be sim-
pler: It’s marked L1, L2, L3, red,
white blue, so you can’t easily go
wrong.
More ruined equipment
Of course you have to actu-
ally use the 9040. One time the
utility bought a new motor and
relocated an existing meter base
to power it, but the electrician
didn’t hook it up the way it had
been, and while the meter base
said red white and blue coun-
terclockwise, it was actually
clockwise. A technician checked
rotation at another meter base,
found it correct, and apparently
assumed that this one would
be the same. They plugged in a
meter, threw the breaker, and
ruined the motor.
Another time the job was to
replace a bank of transform-
ers with heavier units with
heavier wire. Despite the fact
that everyone on the job was
experienced, for some reason no
one took a rotation reading. They
finished hooking everything up,
plugged it in, turned it on….. and
then bought all new rotational
equipment for the customer
downstream. The amount that
incident cost doesn’t even com-
pare to the cost for a new 9040
for everyone on the crew.
Standardizing on the
Fluke 9040
Another utility had been using
the old mechanical rotation
devices that had been the indus-
try standard for years, but they
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Let’s get a CAT IV tool in case someone messes up
had started breaking down and
even cross-phasing internally,
and the manufacturer didn’t
respond quickly or even seem to
take the safety issue as seriously
as they might.
The meter technicians and
linemen now use the 9040s to
verify phase rotation on new
installations and mark breaker
panels with the existing rotation.
Later, if they’re troubleshoot-
ing an outage or do a routine
swap, the crews will verify
rotation both before and after,
using those markings and the
9040. Tthe idea is to make sure
to leave the customer with the
same phase rotation. This check
occurs inside transformers, at
disconnects on meter panels,
on the pole to verify overhead
service, on overhead transformer
banks, and in vaults to verify at
the last disconnect point prior
to feeding that source to the
customer.
The utility maintenance chief
has developed a fondness for
Fluke equipment, and says it
has proven its product over the
years. The equipment, he says,
is “made tough for this industry.
These things are going to be
dropped, get wet, get beat up,
dropped from poles and out of
pockets.” And it’s simple to use,
with a yes or no answer. “It’s
about time we got something
other than this mechanical stuff,”
he concludes.