Fluke 434 II, 435 I, 435 II, 437, 437 II Case Studies

Hospital Technician Develops
His Power Quality Knowledge

with the Fluke 434

Power
Quality

Case
Study

Measuring tools: Fluke 434 Power
Quality Analyzer

Application Note

Operator: Stan Benoit, CRES
Radiology/Oncology Maintenance
Supervisor at Geisinger Health System

Functions used: Three-phase
scope, dips and swells, autotrend,
system monitor and transients

Stan Benoit often finds himself
engaged in politics, even
though his expertise is in
electronics and medical imag­ing. A CRES Radiology/Oncol­ogy Maintenance Supervisor
at Geisinger Health System,
Benoit is responsible for keep­ing dozens of complex imaging
systems at peak performance
for five hospital campuses and
31 satellite facilities. Suspected
PQ issues can put him between
equipment manufacturers and
in-house electricians.

Downtime is costly, both
in terms of patient wellbe­ing and monetary costs—the
X-Ray, mammography, and

other systems themselves cost
millions and a failure can also
idle technicians or surgical
teams. Most of the facilities
have motor/generators and
can maintain operations inde­pendent of the utility, making
the power system robust but
also complex. In addition, the
facilities are constantly being
improved to accommodate
the best medical technol­ogy available. Engineers and
electricians have to work with
power systems that are always
changing. For Benoit and the
people he works with, talking
about power quality is part of
everyday life.

When complex CAT Scan­ners, MRI, and cardiac cath­eterization systems experience
problems, the first question
is: “Is it the electronics or is it
the power?” To answer this
question, and ultimately fix the
problem, Benoit has to work
with several different orga­nizations. Equipment vendors
support the imaging electron­ics under contract. An in-house
facilities department maintains
electrical systems, often with
support from outside electri­cal contractors. This situation
naturally turns “is it electron­ics or power?” into “whose
problem is it?”

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

Benoit is a 23 year veteran
of medical electronics, but he
was not an expert on power
quality. And without hard
facts he found it difficult to
orchestrate the electrical and
electronic teams. Last year he
acquired a Fluke 434 Power
Quality Analyzer and started
learning more about power
quality.

Charging up the
learning curve

Benoit wanted to be able to
do basic tests on three-phase
power to get his facts straight
before talking to manufacturers
or electricians. He also wanted
a tool that would provide more
details as he learned more
about power quality. One of
his most important require­ments was the ability to
share data among the various
parties—sometimes this means
a detailed report but it can also
mean standing at a panel and
looking at a real-time display.
He had to have a tool that his
colleagues inside and outside
of his organization would trust.
The Fluke 434 was a good fit.

Sometimes tracing through
the electrical system can be
challenging. He is careful to
have professional electricians
help make connections and
identify the circuits. Benoit
read the 434 manuals, some
of the Fluke app notes, and
browsed a couple of books, but
mostly he’s learned by looking
at measurements on the 434
and working with equipment
vendors, electricians and PQ
experts.

How Stan Benoit
uses the Fluke 434

Since he got his 434 last
year he has used it almost
constantly. He has applied it
on X-Ray, CAT, MRI, and linear
accelerators. In addition to
troubleshooting, he also uses
the 434 to check power quality
before installing new imaging
systems. And in many cases
he uses it to demonstrate that
power quality is probably not
the cause of a failure.

He really likes the color
graphical display, especially
the connection screens that
help him set things up prop­erly. The display lets him
share and discuss (argue over)
waveforms and trends in real
time. Then he uses the PC
interface to download the data
to his computer and generate a
complete report. He customizes
his reports to suit his audience,
“I have to talk about this stuff
with doctors and administra­tors. I have to make it clear.”

For troubleshooting, Benoit
turns first to the three-phase
scope display on the 434 to
check the shape of the voltage
waveform. The phasor display
helps confirm that the connec­tions are good and gives a
quick snapshot of system
balance.

To help track intermittent
problems, he often uses the
dips and swells mode. In this
mode the 434’s autotrend
capability immediately analyzes
voltage and current without
any setup, identifying changes
as short as ½ line cycle.
While he is in dips and swells
mode, he can run the imaging
system through its paces, cycle
nearby equipment, or trans­fer to backup power systems
and observe the effects on the

434. On the instrument screen,

Benoit can view the events
using the cursors and zoom
tools while background record­ing continues.

If he doesn’t turn up
anything in dips and swells
mode, he works the system
over with the 434 in Transient
mode. In transient mode, the
434 can capture and display
even shorter events—down to
5 uS.

Recently Benoit used the
Dips and Swells mode to track
down problem with a mobile
imaging system. The system
was shutting down intermit­tently and seemed to have
the most trouble during hot
weather. According to Stan,
“We had the recording running
and it looked familiar, like a
paper stripchart recorder. We
saw all three phases drop
when we heard the cool­ers come on.” These truck­mounted systems carry their
own cooling systems and a
high inrush current caused
a voltage dip when the fans
came on. During summer
months, demand on the util­ity is high and voltage levels
can run a bit low, especially
in rural areas that would be
served by a mobile imaging
lab. So during balmy weather
the voltage dips were more
likely to cause the imaging
system to drop off line.”

To judge the quality of
power for a new installa­tion, or to help rule out power
disturbances as a cause for
equipment problems, he uses
the system monitor function
on the 434. This is the func­tion he uses most often. With a
single button he can initiate a
comprehensive study of voltage
quality.

2 Fluke Corporation Tips for learning power quality analysis

The system
monitor function

Most power quality problems
can be detected by taking
detailed voltage measurements
and tracking how they vary
over time. A power system that
consistently delivers strong,
stable voltage is a healthy
system. The system moni-
tor function in the Fluke 434
analyzes dozens of voltage
characteristics against preset
limits for up to a week, and
presents this wealth of data in
a single pass/fail display. To
look at how Benoit uses this
function, we’ll examine an
evaluation he did on the power
feeding an MRI system.

System monitor uses limits
from the EN50160 Power
Quality Standard to determine
if voltage characteristics are
within acceptable tolerances.
The characteristics it looks
at are:

Average rms voltage

•

Harmonics

•

Flicker

•

Voltage events (dips,

•

swells, rapid changes,
or interruptions)

Unbalance

•

Frequency

•

These limits determine when the 434
stores voltage dips in System Monitor.

You can use the EN50160
limits which are the defaults,
or you can adjust them to suit
your needs. In this case Benoit
reviewed manufacturer’s spec­ifications and decided to set
the voltage limits a bit tighter,
to 92 % instead of 90 %.

The details behind pass
or fail

Each of the voltage charac­teristics on the main System
Monitor display as a pass/fail
bar. But behind this simple
display is a lot of detail.

In Benoit’s voltage data you
can see the weekly genera­tor test required for hospitals.
The transfer to backup power
shows up as a dip of roughly
two cycles. You can see the
working rhythm of the build­ing—low currents during the
weekends and nighttime, high
current during working hours.

Stan Benoit has learned a
lot about power quality over
the past year. To some extent
he is becoming a victim of his
own success. He’s worked with
other biomedical engineers
to debug a problem with a
cardiac computer system. He’s
been called in to check power
feeding HVAC chillers. “Since
I’ve gotten the 434 I’ve been
doing favors for people I didn’t
even know!” He’s counting on
two things that will make him
less “popular”: first that he can
teach some of his co-workers
what he’s learned, and second
that other departments will
get their own power quality
analyzer.

System monitor summary shows
pass/fail results for average voltage,
harmonics, flicker, dips, unbalance and
frequency. In this case all parameters
were in tolerance.

System monitor tracks all of
these characteristics for up to
a week. It also records current
to help determine the cause of
voltage changes.

3 Fluke Corporation Tips for learning power quality analysis

Dips and swells trend shows
generator test.

Currrent trend shows lower loading on
weekends and most nights.

The events screen shows the same
event in a different way.

Harmonics monitor shows the
worst-case harmonics and THD
over the week.

Delta correctly connected.

Wye with B and C current reversed.

Check your connections
on a three-phase system

One of the most common
mistakes people make
in checking three-phase
systems is incorrectly
connecting their instrument.
It can take nine connections
to measure a wye system,
so it can be easy to swap
leads or forget to make a
connection. The 434 uses
color coding on leads and on
the display. This will help,
but it’s best to check the
phasor display to confirm
your connections. The
figures below show phasor
diagrams for correct and
incorrect connections.

Wye correctly connected.

Wye with B and C volts reversed.

4 Fluke Corporation Tips for learning power quality analysis

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 2646562 A-EN-N Rev A