Application Note

Application Note
While we’ve enjoyed enormous
benefits from the evolution of
solid state technology, the fact is
that the microelectronics at the
heart of that technology requires
clean power. Faster speeds and
lower voltages mean that there is
less and less tolerance for any-
thing less than quality power.
Power Quality (PQ) covers a
wide range of issues, from volt-
age disturbances like sags,
swells, outages and transients, to
current harmonics, to perform-
ance wiring and grounding. The
symptoms of poor PQ include
intermittent lock-ups and resets,
corrupted data, premature equip-
ment failure, overheating of
components for no apparent
cause, etc. The ultimate cost is in
downtime, decreased productivity
and frustrated personnel.
Start at the scene of the
crime
T
o troubleshoot PQ problems, one
approach is to start as close to
the “victim load” as possible. The
“victim load” is the sensitive load,
typically electronic, that is some-
how malfunctioning. Poor PQ is
suspected, but part of your job is
to
isolate PQ as a cause from
other possible causes (hardware,
software?). Like any detective,
you should start at the sc
ene of
the crime. This b
ottom-up
approach can take you a long
way. It relies on making use of a
sharp eye and on taking some
basic measurements.
An alternative is to start at the
service entrance, using a three-
phase monitor, and work back to
the “victim load.” This is most
useful if the problems originate
with the utility. Yet survey after
survey has concluded that
the
great majority of PQ problems
originate in the facility
. In fact, as
a general rule, PQ is best at the
service entrance (connection to
utility) and deteriorates as you
move downstream through the
distribution system. That’s
because the facility’s own loads
are causing the problems
. Another
illuminating fact is that
7
5 % of
PQ problems are related to wiring
and gr
ounding pr
oblems!
From the Fluke Digital Library @ www.fluke.com/library
Basic power quality
methodology and
common culprits
For this reason, many PQ
authorities recommend that a
logical troubleshooting flow is to
first diagnose the electrical infra-
structure of the building, then
monitor if necessary. Our bottom-
up troubleshooting proc
edure is
desig
ned to help you do this
detective work.
First steps
1. Make a map: Obtain or
create a current one-line
It’s tough to diagnose PQ prob-
lems without having a working
knowledge of the site being
investigated. You can start by
locating or reconstructing a one-
line diagram of the site. The
one-line will identify the ac
power sources and the loads they
serve. The “as built” one-line, the
one with red-lines, is the one
you want.
If you work on-site, the map
might already exist in your head,
but it will be a big help to every-
one, including yourself, if it
’s on
paper
. If you
’re c
oming to a work
site for the first time, getting an
up-to-date one-line means iden
-
tif
ying new loads or other rec
ent
changes in the system. Why go to
this effort? Systems are dynamic;
they change over time, often in
unplanned and haphazard ways.
F
urthermore, while some prob
-
lems are local in orig
in and effect,
there are many problems that
result from interactions b
etween
one part of the system and
another. Your job is to understand
these system interactions
. The
more c
omplete your documenta-
tion, the better off you’ll be.
Simplified electrical distribution system typical of commercial and industrial facilities.
Recept.
L.C.
ASD
Recept.
XFMR
480/208 Y
Utility
XFMR
MV/480 Y
Switch Gear
Lighting Panel
Lighting
Load
Motor
M.C.C.
PF
Correction
Capacitor
Induction
Motor
Receptacle
Load