Case Studies

Application Note
The technician took a few
readings with his DMM, but the
numerical rms readout didn’t
reveal the problem. Suspecting
the transformer was over-
loaded, he went to the
equipment cage and brought
back the team’s three-phase
power quality analyzer to
calculate the apparent power
(kVA) and see what the scope
tool revealed.
Measurements
To verify the accuracy of his
connections, the technician
checked the View Config
screen on the power quality
analyzer. The one-line diagram
matched up.
As a starting point, the tech
-
nician pushed the Scope button,
to check for distortion. The
wa
veform sig
natures were in
fact suspiciously distorted.
Overheated
transformer
From the Fluke Digital Library @ www.fluke.com/library
Next, he selected Power &
Energy from the menu and
compared the kVA calculated by
the analyzer to the transformer
nameplate’s kVA. Sure enough,
this transformer was heavily
loaded (> 50 %). That meant
harmonics were also a concern.
Measuring tools: Fluke 434 Power
Quality Analyzer
Features: Scope, Power & Energy,
Harmonics
Power
Quality
Case
Study
Problem description
You could almost call it a happy
accident. During a routine job at
a large industrial fac
ility, an
electrical maintenance worker
set a plastic kit on top of a
nearby transformer. By the time
he reached back for it a few
minutes later, it had started to
melt! Obviously, the transformer
was operating well over its
normal temperature range.
Power
Harmonics originate from
loads that generate non-linear
currents, such as adjustable
speed drives, DC-powered
equipment and even computers
and office equipment. When
these harmonic currents travel
through the system impedance,
they distort voltage sinewa
ves
.
The voltage distortion then
spreads the harmonic pollution
throughout the system
.