Fluke 1750, 1577, 1743, 1744, 1735 Service Guide

Power quality recording

and analysis: Techniques

and applications

Application Note

Hooking up a power quality recorder and taking
days’ worth of data can give you a rich picture
of your power. In this article we’ll talk about the
various recording techniques available in power
loggers and recorders—understanding the tools
and techniques you have available will be key to
your strategy. What should you be looking for?
And when does recording make sense?

Recording techniques

To really know your power, ideally,
you’d want to look at every line
cycle to see even the smallest
changes. However, since our power
swings through more than four
million cycles per day, it’s impracti­cal to look at tiny changes—and
often unnecessary. Few loads even
notice occasional voltage dips of
one or two cycles.

How long you record depends
somewhat on the rhythm of your
building. If you are working on a
typical commercial or light indus­trial building, then a week is long
enough for a building to go through
its normal cycle. If you are work­ing in a plant that runs special
equipment only periodically (say
a furnace that runs only monthly),
you’ll need to be sensitive to the
timing of these loads.

Different recording techniques
have been developed to look at
small changes over relatively long
time periods. Many instruments
combine several techniques to
improve their coverage. We’ll
describe the common techniques
and some of their pros and cons.

By understanding the different
techniques. you’ll be better able to
choose an appropriate tool for the
job at hand.

Setting up a Fluke 1735 Power Logger at the service entrance for a
30-day load study.

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

Techniques for tracking

3

2

4

10 min.

10 min.

20 min.

20 min.

30 min.

30 min.

40 min.

40 min.

3

2

4

X

X

X

X

Actual variation over time

Plot using fixed 10 minute interval, extremes are lost

trends

Trending tracks power quality
parameters over hours or days.
Power loggers measure param­eters like voltage, current, or
power and log them over time.
Trend recording is good for
tracking normal power, subtle
changes, and exceptional condi­tions but may have a limited
ability to catch fast events.
However, instrument makers
have come up with some creative
ways of showing faster events
while allowing recording lengths
of weeks or even months.

Fixed interval logging

This is the simplest form of
digital recording. To set it up, you
choose a time period, or interval,
between readings—usually in
seconds or minutes. The instru­ment calculates an average of the
rms values during each interval
and stores it in memory. This
technique is useful for tracking
changes longer than the logging
interval. Unfortunately, a very
short measurement interval will
catch fast events, but will also
use memory quickly. So even
though fixed interval logging is
easy to set up, it can’t capture
fast events over hours or days.

Figure 2. Min/Max/Avg trendplot.

Min/Max/Avg logging

This technique is similar to fixed
interval logging since it uses
a preset interval. But instead
of taking just one reading per
interval, the instrument takes
many high-speed measurements
over each interval. Processors
within the instrument crunch
through the measurements and
log three numbers for each
interval: a minimum, a maximum
and an average. The min and
max indicate the worst-case,

short-duration events, in some
instruments as short as a single
power cycle. The average tracks
the overall trend. Graphs from
these instruments will often plot
min, average and max on the
same graph.

Automatic time compression,
TrendPlot

TrendPlot is a logging technique
in some Fluke instruments. It is
a form of min/max/avg recording
in which the timescale auto­matically compresses whenever
the trend approaches the end
of memory. When the recorder
starts to run out of memory,
signal processors quickly go to
work. They combine adjacent
intervals into a new min, max,
and average. You still get to
see the worst-case measure­ments and the overall trend. And
because you choose when to stop
the measurement, you automati­cally get the best time resolution
with the available memory.

Figure 1. Fixed interval voltage trend.

2 Fluke Corporation Power quality recording and analysis: techniques and applications

Event recording

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Dips, swells, interruptions, and
transients are all voltage events.
Power quality events are char­acterized by the time and date
they occur, severity, and dura­tion. 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 instru­ments use an “envelope trigger”.

Figure 3. This event table lists multiple small dips captured within seconds of each other.

An envelope trigger finds
deviations from a clean sine
wave. It builds an envelope
around the sinusoidal voltage
waveform, based on a user­specified tolerance. If the wave­form goes outside the envelope
then the instrument captures and

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 perform­ing comprehensive studies over days,

weeks or even months.
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 4. Envelope trigger example.

3 Fluke Corporation Power quality recording and analysis: techniques and applications

Recording applications

Power quality is recorded in
several general situations. This
section describes the most
common applications.

Troubleshooting with
long-term analysis

Troubleshooting intermittent
failures is challenging. When a
piece of equipment fails or resets
itself mysteriously, it’s tempting
to just swap gear out or reset a
circuit breaker and hope for the
best. For equipment with a high
cost of downtime, the risk of a
repeat failure is too great to rely
on a quick fix. Monitoring the
power after getting your equip­ment running again will reduce
the number of repeat failures
and rule out power problems if a
failure does recur.

The first decision you’ll have
to make is where to connect
the monitor or analyzer. In

general you should start with the
recorder close to the “victim load”
(the equipment that’s having
problems). This way the monitor
will “see” what the load “sees”. If
you have multiple tools available
it can help to record at different
points in the power system.

Before recording, start by
taking some spot measurements
to answer some basic questions.
Is the voltage level right? Is the
voltage waveform a clean sine
wave or is it noisy or distorted?
If the victim is a 3-phase load,
are the phases balanced? Is the
current being drawn by the load
too high?

The next question is: what
should I record? Unless you are
lucky enough to have a sophis­ticated power analyzer, you’re
probably going to have to decide
whether to start by tracking
trends or hunting for transients.

Trends will uncover more prob­lems so try trend recording first
(use fixed interval logging or min/
max/avg). Recording rms voltage
trends on all relevant phases is
the most basic approach. This
will determine if the supply is
subject to voltage dips or outages
which can cause load dropouts
or resets. Recording voltage will
also uncover swells or unbalance
which can cause overheating.

Current trends can also help
in troubleshooting. Excessive
current draw will cause over­heating. If the voltage is stable,
clean and balanced, high current
indicates a problem with the load
itself. By comparing the voltage
and current recordings you can
tell whether the voltage drop is
being caused by high current
being drawn by the victim load
or is being caused by some other
load upstream.

Voltage distortion can also
cause overheating and should
be recorded if possible. The
most basic way to track voltage
distortion is by recording total
harmonic distortion (THD). Some
analyzers can also track indi­vidual harmonics which can help
point to the source of high THD.

If the victim load shows
evidence of arcing or blown
input circuitry transients may
be to blame, but don’t jump to
this conclusion too quickly. After
you’ve performed some trend­ing, or if the evidence strongly
suggests transient damage, then
it’s time to try transient capture
and look at waveforms.

Checking data during recording with the wireless PDA feature of the
FLuke 1750 Power Recorder.

4 Fluke Corporation Power quality recording and analysis: techniques and applications

Tools from Fluke

Fluke offers a number of power
recording tools for almost any
application. In some cases a

combination of tools is best. For
example, you could use the Fluke
434 for quick troubleshooting

and short term monitoring or for
longer term monitoring you might
select a Power Recorder.

Loggers Recorders

Fluke 434

Power

Quality

Analyzer

Applications

1-Phase / 3-Phase 3-Phase 3-Phase 1-Phase 3-Phase 3-Phase 3-Phase 3-Phase 3-Phase 3-Phase
Frontline troubleshooting

Predictive maintenance
Load study/PQ survey
Quality of service

compliance (EN50160)
Long-term analysis —

Recording capability

Typical recording period 1 week 1 month 1 month 1 month 3 months 3 months 3 months 1 month 3 months
Memory 8 Mb 16 Mb 32 kB 4 MB 4 MB 4 MB 8 MB 2 GB 1 GB
Min/Max/Avg logging

Event capture
Waveform capture
User defined logging —
Full-disclosure — — — — — — —
Powered off of measured

signals
Sample rate

High-speed capture rate 200 kHz 200 kHz
Peak voltage 6 kV 6 kV 2.5 kV

Features

Display Color

Voltage channels

Current channels 4 4 — 4 4 4 4 5 4 (0)
Included current probes 40 A/400 A

Dust/water resistance IP51 IP51 — IP 65 (not

Safety rating 600 V CAT IV 600 V CAT IV 300 V CAT III 600 V CAT III 600 V CAT III 600 V CAT III 600 V CAT III 600 V CAT IV 600 V CAT III
Software Fluke View Fluke Power

Battery Operation /UPS 7 hours 7 hours — 24 hours — — 5 hours 5 min UPS 40 min

Analysis capability

Statistical analysis
(including EN50160)

Report generator —
Root causeanalysis — — — —

Accuracy

IEC 61000-4-30 Class A
compliant

Volts rms 0.5 % Vnom 0.1 % Vnom ± 2 V

Amps rms 1 % +-5

• •

• •

• •

• •

• • • • • • • • •

• • • • • • • • •

• •

— — — —

10 kHz 10 kHz

Graphical

4 4 1 4 4 4 4 4

Clamps

• •

—

counts

Fluke 435

Logging

Power

Quality

Analyzer

Fluke VR101

Voltage

Event

Recorder

— — — — — — —
— — — — — — —
—

— —

Fluke 1735

Power

Logger

Fluke 1743

Power
Quality
Logger

Fluke 1744

Power
Quality
Logger

Fluke 1745

Power
Quality
Logger

Fluke 1750

Power

Recorder

• • • • • •

• • • • •

• • • • • • • •

— — — — —

•

— —

• • •

• •

—

•

— —

12.8 kHz and

15.36 kHz
5 MHz 0.5 or 10 MHz

6 kV 6 kV

PDA and

LEDs

400 A

Clamps

Analyze

—

• •

0.1 % Vnom 0.1 % Vnom

1 % with

flex CT

Color

Graphical

3000 A

Flexis

Log

•

•

0.5 % +-5
counts

• • •

1/2 cycle

integrated

10.24 kHz 10.24 kHz 10.24 kHz 10.24 kHz

• • • • •

• • • •

LED

— 15 A /150 A/

Fluke Event

View

—

—

Color

Graphical

3000 A Flexis

including

battery

housing)

Fluke Power

Log

LEDs LEDs

15 A/150 A

/1500 A/

3000 A Flexis

IP65 IP65 IP50 IP50 IP50

Fluke PQ Log Fluke PQ Log Fluke PQ Log Fluke Power

15 A/150 A

/1500 A/

3000A Flexis

• • • • • •

• • • • • •

• • •

— — — — —

0 to 200 V

± 4 V

0 to 270 V

—

± (0.5 % +

10 counts)

± (1 % + 10

counts)

0.1 % of
range

2 % of range

with flex CT

0.1 % of
range

2 % of range

with flex CT

LCD and

LEDs

15 A/150 A

/1500A/

3000A Flexis

0.1 % of
range

2 % of range

with flex CT

Fluke 1760

Power

Quality

Recorder

•

—

10.24 kHz

LEDs

4 (8 without

current)

200 A/

1000 A

Flexis

Fluke PQ

Analyze

•

1 % with

flex CT

5 Fluke Corporation Power quality recording and analysis: techniques and applications

Quality of service

In some cases, utilities agree to
provide power that complies with
predetermined specifications. The
specifications may be laid out in
contracts or may take the form
of regulations, like EN50160. In
these agreements, details of the
recording techniques, tolerances
and recording duration may be
spelled out. Standard EN50160,
for example, specifies tolerances
for a 1-week recording and refer­ences standard IEC 61000-4-30
for measurement and recording

Load studies, power
quality studies, and
commissioning

These types of recordings are
generally done to assess the
power prior to installation or
operation of equipment.

A load study is performed to
determine the existing loads on
a system, prior to adding more
loads. This may be required by
local authorities and local norms
or standards dictate the required
measurements, intervals and
durations. For example, the US

techniques. If you believe that
the power your utility is provid­ing does not meet the agreed
upon specifications, test it.

Before you push the RECORD button

National Electrical Code specifies
current or power measurements
average over 15 minute intervals,
taken over 30 days. In addition to
satisfying the authorities, taking
recordings prior to significant
system modifications can help in
debugging the system later.

Power quality studies and
commissioning studies try to
answer the questions: “Is this
system healthy?” The strategy
in these applications is to cast a
wide net and record as much as
possible. Ideally we would record
voltage, current and power
trends, transients, and event logs.

Don’t jump right into record-

•

ing. Gather as much informa­tion as you can with spot
measurements of voltage level,
voltage waveform/distortion,
current, unbalance. These may
point you to the problem or
give you some insight as to
where to go next.

Check your connections. If

•

the instrument has a phasor
or scope display, use it to
verify that the connections are
correct.

To twist the old saying: set

•

twice, measure once. If you
are trending, double check
your recording interval. If you
are using event or transient
capture, recheck your limits.

6 Fluke Corporation Power quality recording and analysis: techniques and applications

Consider doing a short run of

•

an hour or so, before leaving
a monitor for a longer period.
This will help you work any
bugs out of your setup, and
you may get lucky and find
what you’re looking for!

Fluke. Keeping your world
up and running.

Fluke Corporation

PO Box 9090, Everett, WA USA 98206
Fluke Europe B.V.

PO Box 1186, 5602 BD
Eindhoven, The Netherlands

For more information call:
In the U.S.A. [phone] or
Fax [phone]
In Europe/M-East/Africa [phone] or
Fax [phone]
In Canada (800) 36-FLUKE or
Fax [phone]
From other countries [phone] or
Fax [phone]
Web access: http://www.fluke.com

©2006 Fluke Corporation. All rights reserved.
Printed in U.S.A. 4/2006 2646555 A-EN-N Rev A