by user






April 2011
Stator Winding Endwinding Vibration
By: Greg Stone
Inside this issue:
Stator Winding
Endwinding Vibration
1, 2
Development News
Web-Based Automated
Iris Power News
IRMC & Training
2011 EPRI
European Major
Barcelona, Spain
GE 7EA Users
Houston, TX
St. Louis, MO
IEEE Electrical
Annapolis, MD
Iris Rotating
San Antonio, TX
April 12-13
May 9-13
May 22-26
June 6-7
June 20-23
In the past few years, it seems
that the stator winding endwinding vibration failure process is becoming more common
in large motors and generators, although statistics are
hard to come by. This failure
process is driven by the 120 Hz
magnetically-induced mechanical forces that occur as a result
of the 60 Hz current in the
windings (or 100 Hz forces
created by 50 Hz current). If
the endwinding has been well
designed and has not experienced any aging or transients,
these forces will not result in
any movement of the bars or
coils. However, if the design is
inadequate, the blocking and
bracing materials shrink or lose
strength over time; and/or the
winding is subjected to a dramatic transient force, for example, caused by an out-ofphase synchronization, the
bars or coils may then start to
vibrate in the endwinding. This
vibration can cause the entire
endwinding to move, and
could lead to cracking of the
insulation near the stator core.
More often, coils or bars move
relative to one another, leading to abrasion of the insulation at the blocking and bracing (see Figure). Eventually the
groundwall insulation may be
abraded down to the copper,
increasing the risk of a ground
Sometimes, the endwinding
vibration is severe enough that
the copper conductors in the
endwinding fatigue crack, usually near the connection between bars or on the leads
going to the circuit ring busses.
A cracked stand will arc, rapidly raising the local temperature of the other conductors in
the bar or coil, and increasing
the probability that other conductors will crack. If all the
conductors in the bar or coil
crack, a very heavy arc is
formed that will lead to the
failure of the machine with
considerable collateral damage. This problem seems to be
most common in 2-pole ma-
chines, due to the longer
length of the bars or coils in
the endwinding. However, it
can potentially occur on any
speed machine.
Endwinding vibration has been
known to be a significant cause
of failure since the first large
machines were designed over
100 years ago. Some manufacturers seem to be more prone
to this issue than others –
since the propensity for endwinding vibration is strongly
dependent on the design of
the endwinding.
Continued on page 2..
White powder due to relative movement between the coils and
endwinding support rings.
Qualitrol Iris Power—3110 American Dr.—Mississauga—Ontario—Canada—L4V 1T2
Telephone: 905-677-4824; Fax: 905-677-8498; Email: [email protected]; www.irispower.com—www.qualitrolcorp.com
Page 2
Stator Winding Endwinding Vibration
- continued from page 1 -
If endusers insist on the
lowest cost motor or
generator, then OEMs
may respond by lowering
cost using a less robust
endwinding support
Furthermore, it seems that the
prevalence of the problem
comes and goes in cycles,
probably since OEMs change
their designs over time in response to past problems, or to
reduce manufacturing cost.
We are in one of the periods
where many manufacturers of
air-cooled turbine generators
are experiencing an increased
probability of endwinding vibration. Some spectacular
failures have resulted.
The key design issue is to have
an endwinding blocking and
bracing system that is not mechanically resonant at 120 Hz
(or 100 Hz in 50 Hz machines).
Unfortunately, “Murphy’s Law”
suggests that the endwinding
mass and length will produce a
resonance near the critical 120
(or 100) Hz frequency! OEMs
have developed many alternative methods to make an endwinding non-resonant near a
critical frequency, and brace
the coils/bars to suppress
movement, even while allowing for expansion in the axial
direction due to load cycling.
However, it is apparent that
the more successful designs
cost more to implement. If
endusers insist on the lowest
cost motor or generator, then
OEMs may respond by lowering cost using a less robust
endwinding support system.
Endusers can detect this problem by “bump” tests, inspec-
tion, and/or by monitoring. In
a bump test, the endwinding is
struck with a calibrated hammer at many locations around
the endwinding. The response
to this bump is detected by a
temporarily applied accelerometer. If the response is a
resonance near 120 Hz (or 100
Hz in a 50 Hz machine), then
the endwinding is likely to
experience endwinding vibration. If the endwinding is loosening up as it ages, the resonance frequency and damping
will change. Note this test is
done with the winding cold.
Some change in the resonant
frequencies will occur when
the stator is hot.
Inspection requires the motor
or generator to be shut down
and the endplates removed, at
least at one end. If one cannot
expose both ends, then it
should be the end of the stator
having the circuit ring busses,
since experience shows this
end is more prone to vibration
due to the extension leads to
the ring busses. If the machine
is not contaminated with oil,
then vibration is usually apparent by light colored powder at
blocking points, caused by
fretting, as shown in the picture.
If the winding is contaminated
with oil, then one sees
“greasing”, a viscous, darkcolored paste at the blocking
Finally, the endwinding can be
monitored on-line for vibration
using permanently installed
endwinding vibration sensors,
located at likely vibration
points. The vibration sensors
are usually non-metallic fiber
optic sensors, since they will
not be affected by the high
voltages in the endwinding. As
a minimum, the vibration in
the radial direction is monitored, since this is the force
direction most likely to cause
conductor cracking and/or
insulation fretting.
More information on this issue
can be found in references [1,
2]. The National Electric Coil
website also has frequent contributions on this subject:
In addition, EPRI is preparing a
guide on the endwinding vibration issue that should be available to EPRI member utilities in
a few months. The contact is
Jan Stein, [email protected]
G.C. Stone, Et al,
“Electrical Insulation for
Rotating Machines”, Wiley
–IEEE Press, 2004.
G. Klempner, I. Kerszenbaum, “Operation
and Maintenance of Large
Turbine Generators”,
Wiley -IEEE Press, 2004
Qualitrol Iris Power—3110 American Dr.—Mississauga—Ontario—Canada—L4V 1T2
Telephone: 905-677-4824; Fax: 905-677-8498; Email: [email protected]; www.irispower.com—www.qualitrolcorp.com
Page 3
Web-Based Automated Analysis of
Stator Winding Partial Discharge
Development News
By Blake Lloyd
By Blake Lloyd
Intel co-founder Gordon Moore in
the mid 1960’s predicted that advances in manufacturing would
result in a doubling of the number
of transistors per-inch about every
18 months. This rule of thumb
became known as Moore’s law and
has pretty much held true for the
last three decades. One of the side
effects of these advancements is
that integrated circuit external pin
densities are also growing. With
complicated circuit boards, the days
of hand soldering are ending - as
specialized tools and techniques
become the norm. This brings on
new challenges for low volume
manufacturers like Iris who have
traditionally controlled the manufacturing and testing of our electronics. Now external board stuffing companies who have the technolgy to deal with complex integrated cirucuits are providing complete boards as “components”
which then require rigorous verification and testing. To address this
new challenge, the Product Development group has begun to provide
automated test Jigs along with the
release of new circuit boards. These
test harnesses alllow our Manufacturing team to deeply probe and
document each board function
using computer controlled test
software. With reliable board level
verification passed, instrument
assembly and another round of
automated testing result in a complete functional instrument. The
final stage of the manufacturing
process is a prolonged burn-in to
identify infant mortality issues. The
good news is, this prolonged,
multistep process may be significantly simplified if Moore’s Law
continues to hold. With density
doubling every 2 years, sometime
around 2040 you can expect your
PDA-IV to be a single chip item, with
all testing performed at the silicon
mask level.
This quarter
Iris Power
will be
launching our
automated, web based, partial
discharge (PD) data analysis
tool. Users will be able to access this e-commerce tool
(credit card or bulk PO purchases) from the Iripower.com
website. Using our automated
PD analyzer, determining the
condition of your machine
from PD measurements is as
simple as uploading the IID
database and tagging the assets you want evaluated. The
completed machine assessment report can be viewed
immediately on-line, and a soft
copy is also emailed back to
you. Should the program be
incapable of performing an
analysis due to anomalies in
the data, your database can be
forwarded to Iris Technical
Services for a human expert
assessment and full report.
This first release is limited to
80 pF capacitive PD sensors
using either 3 or 6 sensors
covering data from Iris Power
Trac, Guard, and Portable in-
strument lines (TGA-B and PDA
-IV). The program automatically evaluates short term and
long term trends including
operating and ambient condition consistencies, comparisons of the machine phases,
and a comparison of your data
to the 225,000 test statistical
Iris database. Future versions
of the reports will be in multiple languages and may include
the ability to evaluate patterns
in the pulse phase analysis
Example Automated Analysis Output
Qualitrol Iris Power—3110 American Dr.—Mississauga—Ontario—Canada—L4V 1T2
Telephone: 905-677-4824; Fax: 905-677-8498; Email: [email protected]; www.irispower.com—www.qualitrolcorp.com
Iris Power News
By: Joseph Mbuyi
Don Albright, a pioneer in
turbine generator rotor design
as well as rotor winding monitoring, recently passed
away. Don worked most of his
career at GE in Schenectady,
where he played a key role in
designing 2 pole and 4 pole
rotor windings for large turbine
generators. He was also the
first person to propose that
rotor winding shorted turns can
be directly detected on-line by
measuring the leakage magnetic flux using a simple coil
mounted within the TG airgap. His ideas were of course
adopted by GE and subsequently by many major
OEMs. After he retired from
GE, Don started his own company, GeneratorTech, which
produces its own version of his
original technology to this day.
As we approach the end
of the 1st
Quarter of
2011 and the
anniversary of
Iris Power
being acquired by Qualitrol
Corporation, it is important to
recognize the milestones of
success of our associates and
our manufacturer representatives around the globe. In 2010
we met our growth objectives
even as we underwent substantial improvement in our
operations by immersing our
operations in the learning and
deployment of Danaher Business Systems. We will continue
to learn and drive the discipline and rigor of the methodologies into our daily operations.
Iris Power will be hosting the 14th annual Iris
Rotating Machine Conference
(IRMC) June 20-23, 2011 in San Antonio, Texas. This annual conference
is attended by industry professionals
from around the world. The conference will take place at the Sheraton
Gunter San Antonio Hotel.
Visit www.irispower.com for more
information or email Karen Howard
at [email protected]
We have started 2011 with a
very aggressive growth target,
including the launch of several
new products that add to our
capabilities in evaluation of the
condition of salient pole rotors, enhancements to our
data interpretation tools, instrumentation capable of
measurements and assessment
of both stator and rotor issues,
and the addition of sensor
technologies for better diagnostic coverage of rotating
As we deploy all of these technologies it is also important to
point out that we have now
been joined by associates from
PDTech, adding different yet
complementary set of on-line
and off-line diagnostic tools for
rotating machines.
Over the next year you will be
hearing about additional organizational and operational
initiatives that are aimed at
helping us to serve you better
and to improve our responsiveness and product offerings
to support your asset management efforts within power and
industrial plants. I encourage
our customers to follow our
progress through our newsletters and on the web, but best
of all, make a call to one of our
rotating machine experts and
share some of your concerns
and progress on your maintenance actions. We will continue to keep the motor and
generator user interest at the
forefront of all our discussions
and offerings, after all that is
why you have chosen to work
with us over the years.
2011 Training
 ACE EL CID Course, Toronto,
September 13-15
Hydrogenerator Maintenance
Course, Portland, OR, October 11-13
Partial Discharge Course, Orlando, FL,
December 6-8
Partial Discharge Course, Gothenburg,
Sweden, December 13-15
For more information, contact:
[email protected]
Qualitrol Iris Power—3110 American Dr.—Mississauga—Ontario—Canada—L4V 1T2
Telephone: 905-677-4824; Fax: 905-677-8498; Email: [email protected]; www.irispower.com—www.qualitrolcorp.com
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