Application Note

Application Note
F r o m t h e F l u k e D i g i t a l L i b r a r y @ w w w . f l u k e . c o m / l i b r a r y
new, more efficient system for
the customer, it still was left with
egg on its face—and a large bill.
All of this could have been
prevented, if the utility crew had
better understood the instruc-
tions on the new equipment
and had used a phase rotation
indicator like the Fluke 9040 to
check the phase rotation at the
480 volt output of the transform-
ers that fed the compressors.
Those few minutes would have
saved the customer considerable
downtime and the utility a pile of
money.
Doing it right
A different utility, after many
years of using the old-style
rotating-disc units, changed out
to Fluke 9040s instead. They
use them most commonly after a
meter base or transformer bank
has been changed out, to make
sure the rotation is correct before
connecting the load. Interest-
ingly, this isn’t a consideration in
a new installation, because then
the responsibility falls on the
customer’s electrician to make
sure the rotation is right before
hooking up the motors. If he’s
wise, he’ll have his own 9040.
The utility has now been
using the 9040s for about three
years. They were initially drawn
to the tool because it was the
only Category IV unit they could
find. The need for this was made
Operator: Municipal electric utilities
Measurements: Phase rotation, tests
during installation, maintenance, and
troubleshooting
Tools: 9040 Phase Rotation Indicator
Don’t run it backwards
Phase rotation testing in
utility power distribution systems
Ruining compressors
Here’s an example of what can
go wrong. A public utility in the
Northwest was installing a new
piece of computerized switch-
gear. It was intended to service a
rather large area that comprised
both industrial customers and
some miscellaneous commercial
facilities. The crew doing the
installation was experienced, but
the piece of equipment was new
to them. The foreman, who was
responsible for specifying which
leads were connected where,
inadvertently reversed phases.
Once the utility had finished
its work, it turned the power
back on.
Down the road, at a major
manufacturer, a whole set of
screw compressors for the HVAC
system—ranging from 25 to
50 hp—started running back-
wards. Screw compressors are
lubricated by internal oil pumps,
“and if they run backwards, they
don’t pump oil,” said the manu-
facturer’s maintenance chief. In
a few seconds, all the compres-
sors were toast. “Thank God our
chillers didn’t come on before we
discovered the problem,” said the
maintenance chief, “because that
would have been really bad.”
The utility ended up paying
for all new compressors, plus
the rent on units brought in on
a temporary basis. While it also
did energy studies and set up a
Testing Functions
Case Study
There’s an old saying that the first time you hook up a
three-phase motor it will run backwards. If you’re lucky,
it will only make you look foolish. If you’re not, it could
severely damage expensive equipment and cost you or
your employer substantial money.