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Qualitrol-Iris
Power
DIAGNOSTIC NEWS
April 2012
Why Do So Few Plants Perform Rotor Hipot Testing?
By: Greg Stone
Inside this issue:
Why Do So Few Plants
Perform Rotor Hipot Testing?
1,4
IRMC—Las Vegas
1
Training Courses
2
New Condition-Based
Maintenance Technology
2
Iris Introduces Advanced
3,4
Endwinding Vibration Technology
Expanded Qualitrol-Iris
Power Offices Around the
World
4
QCMC—Beijing and Dubai
4
In past articles I have talked about maintenance high potential (hipot) testing of stator
windings. It seems that about 50% of large utilities do such routine hipots every 5 to 10 years or
so to find serious stator winding insulation defects. Few industrial operators of motors and
generators seem to do stator hipot testing. But it
is apparent that almost no machine owners do
routine hipot testing on their synchronous rotor
windings. This was pointed out by Relu Ilie of
Israel Electric at an EPRI conference last year.
Since then Relu and I wrote an extensive article
on maintenance hipot testing that was published
in the March 2012 issue of the IEEE Electrical
Insulation Magazine. Part of that article focused
on rotor hipot testing.
The stator winding hipot level for new stators
has been set for years in IEC and IEEE/ANSI standards. The acceptance test is 2E + 1 kV rms, AC
applied between phase and ground, where E is
the rated phase-to-phase voltage. IEEE 56 (which
is withdrawn but a revised version is near to
completion) suggests that the stator winding be
given a routine or maintenance hipot on a regular basis. The hipot level suggested in IEEE 56 is
about 60 – 80% of the new winding hipot. This
voltage is approximately the voltage that a stator
winding would experience during a severe voltage transient.
A new rotor winding (rated less than 500 V
DC) is subject to an AC hipot of about 10 times
normal rated DC voltage, with a minimum test
voltage of 1500 V AC. Thus a 400 V DC rotor is
tested with 4 kV rms AC before it is put into service. These acceptance hipot levels are set by IEC
and ANSI standards. For rotor routine or maintenance testing, no hipot test is suggested in IEC or
IEEE standards, although some OEMs do suggest
one. Not surprisingly, there is also no suggested
rotor winding hipot level. The reason for the lack
of a suggested maintenance hipot test is not
clear. Of course every plant manager is wary of
maintenance hipots, since they bring with them
the risk of a failure, and thus an extended outage. But the same reason holds for stator windings, and yet surveys show that many plants do
perform this test. Perhaps it is because rotor
windings are usually isolated from the rotor
body, and a single ground fault can be tolerated.
Continued on page 4...
UPCOMING EVENTS 2012
EPRI
Australian
Reliability
Workshop
Brisbane,
Australia
Apr 12-14
GE 7F Users
Conference
San Antonio,
TX May 14-18
HydroVision
2012
Louisville, KY
July 17-20
IRMC/QCMC 2012
June 25-28, 2012
For the first time, the Iris Rotating Machine Conference will be held in Las Vegas, NV! For this
15th annual conference the program has changed to provide attendees with parallel sessions
on Rotating Machines, Gas Insulated Switchgear, and Transformers. This conference will be
devoted not just to presentations on condition monitoring tools, but also to educating attendees on the
practical aspects of implementing condition-based maintenance in transformers, switchgear, large motors and generators. There will be ample time for participants to take in the local sites as well as network
with colleagues.
Renaissance Las Vegas Hotel
3400 Paradise Road
Las Vegas, NV 89169
Visit www.irispower.com for more information or email Karen Howard at [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
Page 2
Iris Power Introduces New Condition-Based Maintenance Technology
2012 Training Courses

Partial Discharge Seminar,
Jakarta, Indonesia
May 28-30

HydroGenerator
Maintenance Course,
Nashville, TN
September 25-27

EL CID ACE Course
Nashville, TN
September 25-27

Advanced Partial
Discharge Course,
Stockholm, Sweden
October 1-2

Partial Discharge Course,
Long Beach, CA
November 13-15
For more information, contact:
[email protected]
Condition-based maintenance (CBM) is the
process of making maintenance decisions based
on the information collected through condition
monitoring. To be effective, CBM requires 3
steps: the acquisition of condition data; data
processing for detection of anomalies and symptoms of problems; and maintenance decision
making. Ideally, CBM allows maintenance personnel to do only the right things, minimizing
spare parts cost, system downtime and time
spent on maintenance.
Condition-based monitoring of specific components of motors and generators has become
common practice for many utility and industrial
customers. For example, CBM of stator winding
insulation systems has been accomplished with a
high degree of confidence and reliability through
on-line PD monitoring.
The following are the 3 steps above:
Acquisition of Condition Data –TracII and
GuardII continuous on-line PD monitors, the
latest generation of this evolving technology.
Data Processing for Detection of Anomalies
– 250,000 record PD database which provides
levels of concern for insulation condition.
Maintenance Decision Making – Interpretation of the PD trend, the effect of load, temperature, etc on PD, and Pulse Phase Analysis data
allows users to determine the failure mechanism(s) occurring and thus the necessary maintenance.
Many other rotating machine components
have similar on-line monitoring technologies
which can be combined with PD to provide a
complete rotor and stator on-line condition assessment. Ideally all these technologies can be
integrated into a single hardware and software
platform with a common interface and installation.
Recognizing this need, Iris Power has now
developed the GuardII platform which encompasses technologies including partial discharge,
air-gap flux, endwinding vibration, shaft voltage
and current monitoring, and current signature
analysis (induction motors) which are appropriate for complete on-line machine condition assessment.
The GuardII system now includes a NEMA 4X
base unit (FPGA-based processor for remote
Ethernet and local USB communications, diagnostics, data archiving memory, and alert calculations) with optional plug-in cards for specific
diagnostic technologies. The GuardII system can
be configured with a combination of inputs, and
field upgraded with new technologies as outages
and sensor installations allow. As well as one
common hardware case, the GuardII platform
includes a common WindowsTM software suite
called the Iris Application Manager. All diagnostic data from the GuardII can be downloaded to
an Iris Information Database (IID) giving users
one common repository for condition-based
monitoring data.
Future developments will add more condition-based monitoring technologies to the
GuardII line as well as more tools to turn the
measured data into actionable knowledge about
the health of your equipment.
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
Iris Introduces an Advanced Endwinding Vibration Monitoring System
EVTracII Monitor
Dual Axis Endwinding Vibration
Accelerometer
As discussed in the last issue of Diagnostic
News, vibration of the stator bars and coils outside of the stator slot (endwinding vibration) is
becoming a more common cause of motor and
generator failure. If one does regular inspections
of the machine, such deterioration can be detected well before a stator winding fault by looking for signs of fretting dust, greasing and/or
cracks in the varnish that often coats the endwindings. However, the preferred method of
detecting stator endwinding vibration without
requiring a machine outage and disassembly has
been the direct measurement of the vibration
using a fiber optic accelerometer mounted at
critical locations of the endwinding. Westinghouse developed the first practical endwinding
vibration monitor using fiber optic accelerometers
in the 1980s, and many machine manufacturers
now supply fiber optic accelerometers based on
various physical phenomena. Iris Power-Qualitrol
has now developed both stand-alone and integrated monitors for use with most installed fiberoptic accelerometers, including our own.
The stand-alone endwinding vibration monitor is called the EVTracII. It is based on the TracII
platform (see page 2), that will enable continuous
monitoring of all the endwinding sensors in a
motor or generator, plus a stator core accelerometer and various operating parameters (stator
temperature, load, etc). The EVTracII trends total
vibration displacement in mils or microns (over
the frequency range 20 to 1000 Hz) as well as the
displacement at various selected frequencies
(such as rotational speed and 100 or 120 Hz).
Alerts and alarms can be set for any of these displacements. In addition, the frequency response
over the range 20-1000 Hz can be displayed for
more in-depth analysis. Assuming dual axis (radial
and tangential) accelerometers are used, EVTracII
has the ability to simultaneously measure the
displacement in the radial and tangential directions so that the exact movement of the stator
winding at that location can be determined. Such
information is critical in designing an upgraded
stator endwinding support system, if it is needed.
EVTracII prototypes have been in use for about a
year. The attached figure shows the output from
a hydrogen-cooled turbine generator located in
the Midwest USA.
EVGuardII is the next evolution of the GenGuard product, first introduced in 1994. EVGuardII facilitates a complete motor or generator
integrated monitoring system. The EVGuardII can
be expanded to include on-line partial discharge
as well as magnetic flux monitoring, in a single
box and using a uniform software platform for all
of the different types of sensors.
The products and services Iris Power provides
for endwinding vibration monitoring include:
 Kits composed of 6 or 12 single or dual axis
accelerometers together with an optional
single axis accelerometer for the stator core;
an electro-optical converter and an air or
hydrogen cooled penetration.
 Bump testing together with modal analysis to
help find the optimum locations for the accelerometers (see the January 2012 issue of the
Diagnostic News for information on how critical this step is).
 Either the EVTracII or the EVGuardII continuous monitoring systems. These monitors can
be used with any accelerometers providing a
100 mV/g output.
 Training and/or expert analysis of vibration
data
 Technical support to reduce the endwinding
vibration levels, if they are excessive.
Continued on page 4...
Vibration spectrum with displacements of 6.4 mils
p-p and 3 mils p-p at 120 and 60 Hz, respectively
from an operating 2-pole turbine generator
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
QCMC 2012
With the success of the
first Qualitrol Condition Monitoring Conference in Dubai,
UAE last November, we are
pleased to confirm that there
will be a second QCMC in Dubai in 2012. Also, a QCMC will
be held this year, for the first
time, in Beijing, China.
The QCMC is a technical
conference offering both indepth half-day courses on condition monitoring methods, as
well as presentations on stateof-the-art aspects of electrical
equipment design, failure and
repair. As with the North
American based IRMC, this
information is provided in a
non-commercial environment
by world-class experts offering
a range of points-of-view.
Visit the Qualitrol-Iris
Power website for more details
as they become available.
QCMC Beijing
October 22 and 23, 2012
BJ Broadcasting Tower Hotel
Jianguomenwai Street
Chaoyang District, Beijing
QCMC Dubai
November 19—21, 2012
JW Marriott Dubai
Abu Baqer Al Siddique Road
Dubai, UAE
Why Do So Few Plants Perform
Rotor Hipot Testing?
- continued from page 1 -
Advanced Endwinding Vibration
Monitoring System
However if the rotor winding ground insulation is
weak generally, a second ground can lead to massive
circulating currents and consequent damage to the
rotor body. At the EPRI meeting mentioned above, it
seems few or no maintenance engineers were doing a
hipot on generator rotor windings. Furthermore, few
seemed interested in it.
In spite of this, I think there is an argument for
doing routine hipot testing of rotors. It involves transient voltages. Just like the stator hipot test level is
partly based on simulating the transients that can
occur in service, the same can be done for rotor windings. Mr. Ilie has reviewed the publications that discuss the transients that rotor windings can see. Some
of the causes of transients include:
 Opening of the rotor winding DC supply circuit
breaker can cause an AC transient voltage due to
the chopping of the current and Ldi/dt.
 Transient voltages from thyristor operation in
static excitation systems
 Shorts on the terminals of the stator winding will
“transformer couple” transient voltages from the
stator winding to the rotor winding
 Out of phase synchronization events.
Based on an analysis of these transients, it seems
that these transients could be up to 5 times the DC
voltage. Thus a maintenance hipot of about 50% of
the acceptance hipot seems reasonable. If you want
more detailed information you might want to check
out the March issue of the IEEE Electrical Insulation
Magazine. I would appreciate your opinions on
whether hipot testing should be done on rotor windings.
Although Iris Power-Qualitrol is relatively new to the hardware associated with
endwinding vibration monitoring, it has
broad experience with continuous machine
condition monitoring since it introduced
continuous machine monitoring systems in
1994 (based on prototypes Iris Power staff
had been developing since 1982).
Iris Power’s staff of world-class motor
and generator experts have over 25 years
of experience with fiber optic endwinding
vibration monitoring – both with the technology involved and with interpretation of
the results. In the late 1980s Iris’ Joe
Kapler first used fiber optic endwinding
sensors to monitor the vibration levels in a
two pole, 210 MW, hydrogen-cooled turbine generator that was resonant near 120
Hz. In his 2004 book, “Electrical Insulation
for Rotating Machines”, Dr. Greg Stone
published some of the first guidance for
interpreting such results beyond the simple concept of trending. He was also a coauthor of the 2011 EPRI Report PID
1021774 entitled “Generator Stator Endwinding Vibration Guide”. This expertise
and experience has allowed Iris Power to
develop a monitoring system that offers
the optimal sighting of the sensors, long
lived accelerometers, a state of the art
monitor as well as comprehensive training
on its use and results interpretation.
Contact your Iris Power sales representative for more information.
- continued from page 3 -
Qualitrol—Iris Power Continues to Expand Offices around the World!
Iris now has sales and field service specialists located in 8 counties, and will shortly be expanding to
more. At present we have sales and field service people in the following offices:








Brazil (2 people)
Canada (8 people)
China (6 people)
India (3 people)
Switzerland (2 people)
UAE (1 person)
UK (1 person)
USA (5 people)
This expansion of offices makes serving our customers more timely and cost-effective. Many of these
offices have opened since Iris Power was acquired by
Qualitrol two years ago.
Our staff in China: Rick Wu (Manager), Sales:
David Peng, Jason Lin, and Tiger Wang
Field Service Staff :Len Qin, Feiyu Liu
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