Application Note

3 Fluke Corporation Power quality recording and analysis: techniques and applications
Event recording
Dips, swells, interruptions, and
transients are all voltage events.
Power quality events are char-
acterized by the time and date
they occur, severity, and dura-
tion. User-defined thresholds or
triggers determine what qualifies
as an event. Event recording is
great for ensuring your voltage
stays within tolerances, say ± 10
%. Data is usually presented as
a list, making it easy to see all
of the extraordinary conditions
on the power system. Whether
or not an event causes problems
depends on both severity and
duration. For example, a 20 % dip
that lasts for 5 seconds is more
likely to cause problems than
a 20 % dip that lasts for 1 line
cycle. So event data is sometimes
compared to standard tolerance
curves, like the CBEMA curve,
that give limits for severity and
duration. The need to specify
multiple limits can make event
recording tricky to set up. If you
set the tolerances too tightly,
you’ll capture lots of events and if
you set the tolerance too loosely,
you may not see anything at all.
Transient waveform
capture
This technique records the
actual sine wave of the voltage
or current, allowing you to see
any event shorter than one line
cycle. The capture is initiated by
a trigger and uses a high speed
digitizer. Various triggers can
start the capture but most instru-
ments use an “envelope trigger”.
An envelope trigger finds
deviations from a clean sine
wave. It builds an envelope
around the sinusoidal voltage
waveform, based on a user-
specified tolerance. If the wave-
form goes outside the envelope
then the instrument captures and
stores. Some instruments, like the
Fluke 430 Series, can also take a
snapshot of the waveform based
on other criteria like rms events
or current increases.
Full disclosure recording
This technique combines min/
max/avg recording, transient,
and event capture all at the
same time. So you don’t have to
decide whether to look for dips or
transients—you can capture both.
Figure 3. This event table lists multiple small dips captured within seconds of each other.
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These instruments can determine
event thresholds automatically and
adjust the threshold on the fly. This
eliminates the difficulty in setting
event thresholds. Full disclosure
recording is very useful for perform-
ing comprehensive studies over days,
weeks or even months.
Figure 4. Envelope trigger example.