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ON LINE MONITORING SYSTEMS FOR BUSHINGS

MIKE Y. LAU1, TYLER SCHWARTZ1, DANNY E. BATES2, CLAUDE F. KANE3, ALEXANDER A.

GOLUBEV3, ANATOLIY B. SELIBER3, VALERIY A. RUSOV4 , SERGEY V. ZHIVODERNIKOV5

1British Columbia Hydro, Vancouver, Canada,2Alabama Power, Alabama, USA,

3Predictive Diagnostics of Eaton Electrical, Minnetonka, USA,

4Vibro-Center, Perm, Russia,

5FSK EES, ElectroSetService, Novosibirsk, Russia

ABSTRACT

Industry statistics suggest that 80% of all plant and equipment failures occur on a random basis and only 20% of the

failures are age related. This means that 80% of failures have not been detected with common test and maintenancepractices and therefore these failures have not been prevented. Based on different sources up to 30-35% of large

power transformer failures are attributed to bushing insulation failures. About half of these bushing failures result in

an explosion and fire.

In today's competitive environment, increasing demands are being placed on the management of physical assets.

Advances in technology are allowing new approaches to maintenance. These include reliability-centeredmaintenance, predictive maintenance, condition monitoring, and expert systems. Trend setting organizations are

increasingly taking advantage of the convergence of these new technologies to implement proactive maintenance

programs.

BC Hydro has recent experience in unexpected failures of 500 kV bushings and has instituted a periodic DGA

program of the bushing oil. See Reference [1] for bushing failures and DGA results. While the oil sampling

program proved to be successful in detecting problem bushings, the program does require a lot of efforts as well as

outages of equipment. In an effort to minimize such effort on some critical transformers, BC Hydro is interested in

on-line monitoring and has installed a bushing monitoring system on a set of three single-phase GSU transformers.

Several similar systems have been installed in other utilities in North America and Russia. The paper will

summarize recorded results and addressees issues affecting the accuracy and interpretation of the results.

INTRODUCTION

During the late sixties and early seventies the former Soviet Union experienced a high rate of catastrophic HV

bushing failures on their 500kV power transmission systems. Root cause of the failures was a combination ofdesign, manufacturing and technological problems. The existing maintenance strategy based on periodical off line

insulation tests were not effective in preventing failures due to the fast rate of defect development. On line bushing

monitoring methods and technology were developed and introduced at that time by P.M. Svi and his colleagues

[2,3]. Implementation of the technology quickly reduced the bushing failure rate by timely detecting developing

insulation defects and replacing failing bushings. The instrumentation with some modifications is still in use in

most of the 500kV and 750kV apparatus in the former Soviet Union republics.

The basis of this on line monitoring method is to compare insulation characteristics of three-phase bushing system.

Technology for several three-phase bushing sets have been developed and tested but has not been widely used due to

more complexity despite of its better noise immunity.

Two basic circuit diagrams reproduced from [2] are shown in Figure 1. Both have sensors connected to the bushing

test tap, summing and balancing units and a null-meter. The circuits differ by their summing and balancing units. In

Figure 1a, a three-phase transformer sums the signal and Figure 1b uses resistive summation.

The first schematic has found initially more application. It provides isolated inputs and therefore eliminates

common mode noise. Another advantage of this schematic is the meter circuit isolation and its additional safety.

One disadvantage isthis circuit requires a high quality transformer with linearity better then 0.5% which is expensive

and bulky. Transformer type summation is also susceptible to transformer stray magnetic flux. This requires

additional magnetic shielding and moving measuring circuit from transformer tank to a distance of several meters.

Resistive summation is more common in modern devices. It is much smaller and is much less expensive. Main

disadvantage of this schematic is susceptibility to common mode noise due to two grounds in the measuring

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circuit. Using good grounding practice allows reduction of this noise to acceptable level on a single three-phase

transformer or three single transformer group. Expanding the technology to several distant transformers of

transformer groups would still require signal circuit isolation.

During commissioning the null-meter is balanced as close to zero value as possible. Normally, 0.1% or better is an

acceptable level of balancing. As a defect develops the complex conductivity of the bushing insulation changes and

the current and its phase angle in one of phases also changes. Therefore, the null-meter will no longer be null. The

amplitude of the change reflects the severity of a problem and the phase angle indicates which phase that isexperiences the change.

Ua Ub Uc

Ya Yb Yc

Rd

R0

RdRdRc

Rc

Rc

A

B

C

NULL Meter

Ua Ub Uc

Ya Yb Yc

Rd

R0

RdRdRc

Rc

Rc

A

B

C

NULL Meter

a). b).

FIGURE 1.

The change can be approximately represented by the formula under the assumption of a single defective phase [2]:

( )1)tan(2

0

2

0

+

=

CC

I

I

- parameter GAMMA,tan - tangent delta change,

0CC - relative change in bushing capacitance.

Figure 2 explains the method in vector format. Figure 2a show all three currents from the bushing test taps are

perfectly balanced and the sum is equal to zero. For example, if a change in tangent delta in phase A bushing willcreate an additional active current through the A-phase bushing insulation and new current

'

AI . This set the system

out of balance and resultant unbalance vector is equal to the tangent delta change and directed along the phase A

voltage vector (Figure 2b). A change in capacitance is shown in Figure 2c. This additional current is perpendicular

to the A-phase voltage. The resultant unbalance now is positioned along the vector0

AI .

b.

'

I

0

AI

0

CI

0

BI

'

AI

AV

'

AI

a.

0=I0

AI

0

BI

0

CI c.

"

I0A

I

0

CI

0

BI

"

AI

AV

"

AI

FIGURE 2.

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INSULGARDTMG2+

The data presented below has been acquired with the current version of the Eaton Electrical InsulGard TM

G2+

monitor. The monitor has features including phase measurements and temperature correlation that provides for

enhanced knowledge for on line bushing insulation monitors.

The system continuously monitors the power frequency current through the insulation of a 3-phase set of bushingsas well as top oil temperature. Ports are provided that allow the attachment of measurement equipment for making

periodical partial discharge (PD) measurements [4]. The sensors are connected to the bushing capacitor taps, and an

additional neutral PD sensor is installed on the available grounded neutral of the transformer or on the transformer

tank ground for noise cancellation purposes when PD tests are performed.

Each bushing sensor has internal protection for the test tap insulation which limits the residual voltage at the tap to a

level of not more then 135 Volts RMS even if open circuited. In normal operation, the test tap voltage does not

exceed 10 Volts RMS.

FIGURE 3. InsulGardTM

G2+ and bushing sensors installed

FACTORS AFFECTING ACCURACY

Factors affecting accuracy of on line technology may be divided in three groups: Device accuracy; Noise; System voltage variations.

DEVI CE ACCURACY

Accuracy of the device was specified to timely detect dangerous changes in power factor or capacitance that may

lead to bushing insulation failure. Experience indicates that a dangerous change in Gamma is of several percent1.

Ideally, the system should allow the end user some time to make a decision and get ready for correction actions

including bushing replacement. Normally, obtaining a new bushing may take as long as 3-6 months. Therefore, it is

desirable to have enough of a early warning on bushing degradation of about 3 to 6 months before it may fail. Based

on 6 months and 5% of Gamma change and linear defect growth assumption, 0.8% per month rate of change should

be reliably detected. Sliding time window setting for Gamma trend may be as low as 15 days to ensure detectingfast growing defects. Consequently, 0.4% change in 15 days should trigger trend alarm. This requires an accuracy

for magnitude measurements of about 0.1%. It should be noted that the rate of growth of a defect may increase

when it close to a failure that requires less accuracy to be detected. But in any case, the earlier a defect is detected

more time is left for correction actions.

Another aspect influencing accuracy requirements is diagnostics algorithms built in the device. The device

calculates Tan and its temperature coefficient temperature coefficient of parameter Gamma. The temperature1In several decades of Soviet Union experience the warning and alarm setting were 3% and 5% respectively.

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coefficient of 0.03%/C0 in Tan is considered as indicator of significant insulation contamination [3,5]. The

expected variation in parameter Gamma over a common temperature range of 300C (30-60) in this case is about

0.5% and should be reliably detected.

Therefore, the accuracy of 0.1% for relative magnitudes and 0.1O

in phase angle were specified and achieved.

NOISE

The device monitors power frequency currents from bushing potential or test taps. Higher power frequency

harmonics are considered as noise, especially the odd harmonics. The odd harmonics from the three phases are not

balanced in the balancing unit but are summarized. In order to suppress this noise, the device must have high

quality low pass filters. These filters allow for the application on DC/AC converter substations where signals have a

significant high content of power frequency harmonics.

Another noise that exists to some extent is a common mode noise resulting from two grounding points in ameasuring circuit. There are two protection issues requiring two grounds. The first is to provide absolute safety

for personnel that may occasionally control the monitor from its keypad or touch its enclosure. Reliable grounding

of the device and the enclosure to a local ground and isolating all interfaces provides for personnel safety.

The second requirement is to protect the bushing itself no matter what even if all links to the device are broken

and device protection is not functional. Sensor must be rugged and adequate protection must be built into a sensor

body. Normally a sensor has impedance connected in parallel to the ground and a surge-protecting device. The

impedance passes power frequency test tap current to the ground, keeping a voltage on the tap to an acceptablerange in case the measuring scheme is disconnected for any reason. The internal surge protector suppresses surges

and lightning strike currents. Therefore, the second path (normally relatively high resistance path) to the ground is

built into the sensor2.

Installing the device enclosure next to a transformer tank and grounding it to the transformer ground would normally

resolve the issue due to a small AC voltage drop across the transformer tank. The only problematic connection is on

three single-phase transformer banks. The banks have some AC voltage between their tanks and this will produce

common mode noise for the summation circuit. Good grounding practice will keep the AC voltage between the

tanks within a few hundred millivolts is commonly a sufficient precaution.

For example, in a BC Hydro the device installed on the middle phase of three single-phase 500kV transformers.

Figure 4 shows the schematic of common noise influence.

RO

U a

Ya

Rd

Ub

Yb

Rd

Uc

Yc

Rd

Vb

Vab Vcb

Ia+Vab/Rd

Ic+Vcb/Rd

Ib

FIGURE 4.

Common mode noise sources are applied between a sensor ground at test tap and measuring scheme ground in the

device enclosure. These sources are labeled as Vab, Vb, Vcb since the device installed on the phase B bank. Vb

2The idea to leave only surge protection in a sensor does not seems to provide reliable protection. In the case of disconnecting

the measuring device at 750kV and 60Hz power frequency, surge protection should carry up to 150mA rms continuously at its

residual voltage. Several different types of commercially available discharge gaps carrying such a current have been destroyed in

our laboratory within weeks.

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voltage is negligibly small, but the other two were measured as 100 200 mV RMS. Attempt to provide additional

low impedance connections between banks did not significantly change common mode voltage. This voltage creates

additional noise current (as it shown in the fig. 4) that is measured by the device. Taking 200mV rms and bushing

capacitance of 500 pF additional noise current impact can be estimated as below 0.1% that is acceptable.

SYSTEM VOLTAGE VARIATI ONS

System voltage behavior is one of the main contributors to method accuracy as a whole. This issue becomes verycritical when the precision of 0.1% is required. A variation in system voltage (magnitude or relative phase shift

between phases) creates an unbalance and may be interpreted as capacitance or power factor change. Magnitude

variation may be interpreted as capacitance change and phase shift variation as power factor.

System voltage variations have been observed at all locations where the device is installed regardless of region or

country. Figure 5 below shows the A-B and A-C phase angles3 from four units in three locations across North

America for a time period of several weeks. Table 1 provides statistical quantities calculated for the data in Figure

5.

Figures 5a and 5b are for standalone units and 5c and 5d for two identical units connected to the same HV buses.

Behavior of phase angle variations are very similar in the last two cases despite the two units were not fully

synchronized in taking their readings (time difference between units taking readings was within 10 minutes). This

confirms a stability of different devices that allows a comparison of two (or more) units connected to the same

voltage busses.

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

11/13/ 03 11/23/ 03 12/3/03 12/13/03 12/23/03 1/2/04 1 /1 2/ 04 1 /2 2/ 04

Time

Variations

[Deg.]

a-b a-c

Fi g. 5a Unit #1, Location #1

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

11/23/03 12/3/03 12/13/03 12/23/03 1/2/04 1/12/04

Time

Variations[Deg.]

a-b a -c

F ig. 5c Unit #3, Location #3

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

11/20/03 11/30/03 12/10/03 12/20/03 12/30/03 1/ 9/ 04 1/19/04 1/29/04

Time

Variations[Deg.]

a-b a -c

Fi g. 5b Unit #2, Location #2

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

11/23/03 12/3/03 12/13/03 12/23/03 1/2/04 1/12/04

Time

Variations

[Deg.]

a -b a-c

F ig. 5dUnit #4, Location #3

FIGURE 5.

TABLE 1. (Calculated from fig.5)

Tr. ID Unit #1 Loc. #1

Fi g. 5a

Unit #2 Loc. #2

F ig. 5b

Unit #3 Loc. #3

F ig. 5c

Unit #4 Loc. #3

Fi g. 5d

Phase / Param. A - B A - C A - B A - C A - B A - C A - B A - C

Averaged -0.10 0.41 -0.24 -0.04 -0.02 -0.12 -0.01 -0.10

Standard

Deviation

0.06 0.06 0.04 0.04 0.12 0.11 0.11 0.10

Detected

Minimum

-0.24 0.27 -0.37 -0.16 -0.28 -0.39 -0.29 -0.37

Detected 0.14 0.65 -0.09 0.06 0.32 0.36 0.30 0.36

3Phase angles of 1200and 2400subtracted from A-B and A-C angles respectively to scale data to the same origin.

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Maximum

Each location has its unique voltage behavior: phase asymmetry and phase angles variations. Note that phase

asymmetry may be as high as 0.40, variations (two standard deviations) - 0.24

0 and minimum/maximum range -

0.750(see Figure 5c).

Accounting for possible voltage change the formula (1) should be rewritten as below, assuming again a change on

one phase.

( )2)tan(2

00

2

0

+++

=

VV

CC

I

I ,

0VV - relative change in system voltage,

(Rad) - change in phase angle.For changes in all phases the formulas should be changed to vector summations. Gamma will react on asymmetric

changes in system voltage only. All symmetric voltage changes will compensate each other (the same increase of all

voltage magnitudes, for example, will not disturb a balance).

Therefore, accuracy of the method depends upon the statistics of the asymmetric voltage variations in the particular

location and statistical data processing procedure.

Simultaneous data acquisition from two or more units connected to the same voltage buses/lines and combined data

processing may improve method accuracy.

DIAGNOSTICS

The technology as originally introduced and implemented was focused on producing timely alarms and then

suspected bushing should be further evaluated with additional off line tests. This part remains unchanged and

Gamma-parameter is a very reliable indicator of a dangerous trend in bushing insulation system. In addition,

modern microprocessor based instrumentation allows for additional diagnostics performed on line while a unit is

running. On line diagnostics gives additional valuable information and therefore advantages in maintenance strategy

and as a result saves money.

The main goal of on line diagnostics is to locate defective bushing, determine the predominant failure mode and

finally predict timely critical insulation triggering shut down and bushing replacement.The diagnostics has three parts: time trend, temperature dependencies and defect identification. Defect

identification requires determining the tangent delta and capacitance of all three bushings.

The task of diagnostics described above is not 100% defined. This means that a number of independently measured

quantities at any single measurement is less than number of independent variables. The situation will remain similar

regardless to how many transformers connected to the same voltage system are tested simultaneously and their data

processed jointly. Increasing the number of transformer bushings monitored will improve a balance between

variables and measured quantities but will never reach 100%.

In the worst case of a single stand-alone unit installed on one three-phase transformer (or three single-phase

transformers) five independent quantities can be obtained: three current magnitudes from the test tap and two

independent phase angles between the currents. The number of variables is twelve, three of each: tangent deltas,

capacitances, system voltage magnitudes, and phase angle between system voltage vectors. The situation partially

improves by learning the statistical behavior of the system voltage at the particular location for a period of time and

assuming that the tangent deltas and capacitances are known at the time and equal to their off line values. Based onthe voltage behavior statistics we can then compensate for the change in the various quantities over time. This

reduces the number of variables to six: three capacitances and tangent deltas changes. The number of independent

test values is still five.

Additional assumptions are required to resolve a system of five equations with six variables. The reasonableassumption that at least one of the tangent deltas have not changed is used. Therefore, the diagnostics is relative by

its nature with some extent of confidence that does not equal to 100%. Normally, a confidence of over 80% is

achievable.

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FIGURE 6.

None of the units showed significant gamma trend at the time.

TREND

All units were base lined for a month and then used the information on system voltage variations for further

diagnostics. Diagnostics results for tangent delta and capacitance trend are shown in Figure 7. Note that the scales

in the graphs representing trend of capacitance are different for different units.

Trends of both the capacitance and tan delta do not indicate any essential insulation deterioration in all four units.

Even in the worst case of system voltage instability on units #3 and #4 the variations in tangent delta are very small

of about 0.1%. It is noticeable that the parameters variations on units #3 and #4 are very similar, which reflects

system behavior rather than a change in insulation condition.

As expected, unit #2 shows the best stability in both tangent delta and capacitance with overall variations within

0.05%.

Bushing Tan Delta Trend

0

0.1

0.2

0.3

0.4

0.5

0.6

25-Nov-03 25-Dec-03 24-Jan-04 23-Feb-04

Time

TanDelta

Tan A Tan B Tan C

Bushing Capacitance Trend

460

480

500

520

540

560

25-Nov-03 25-Dec-03 24-Jan-04 23-Feb-04

Time

CapacitancepF

CapA CapB CapC

Bushing Tan Delta Trend

0

0.1

0.2

0.3

0.4

0.5

0.6

25-Nov-03 25-Dec-03 24-Jan-04 23-Feb-04

Time

TanDelta

Tan A Tan B Tan C

Bushing Capacitance Trend

375

380

385

390

25-Nov-03 25-Dec-03 24-Jan-04 23-Feb-04

Time

CapacitancepF

CapA CapB CapC

Fig. 6c Unit #3

Fig. 6d Unit#4

Fig. 7b

Unit #2

Fig. 7a

Unit #1

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Bushing Tan Delta Trend

0

0.1

0.2

0.3

0.4

0.5

0.6

2 5- No v- 03 1 0- De c- 03 2 5- Dec -03 09 -J an- 04 2 4- Ja n- 04

Time

TanDelta

Tan A Tan B Tan C

Bushing Capacitance Trend

438

440

442

25 -Nov -03 10-Dec-03 25-Dec-03 9-Jan-04 24-Jan-04

Time

CapacitancepF

CapA CapB CapC

Bushing Tan Delta Trend

0

0.1

0.2

0.3

0.4

0.5

0.6

2 5- No v- 03 1 0- De c- 03 2 5- Dec -03 09 -J an- 04 2 4- Ja n- 04

Time

TanDelta

Tan A Tan B Tan C

Bushing Capacitance Trend

600

610

620

630

640

650

25 -Nov -03 10-Dec-03 25-Dec-03 9-Jan-04 24-Jan-04

Time

CapacitancepF

CapA CapB CapC

FIGURE 7.

TEMPERATURE DEPENDENCY

Another very important diagnostic characteristic is temperature dependency primarily in tangent delta and also in

capacitance. During the learning period of 30 days this characteristic is also determined. Results of analysis areshown in Table 3. The table also shows the temperature range containing statistically reliable data (10 or more data

points at the same temperature).

Correlation to the temperature has been detected in the unit #1 with correlation coefficient over 0.6. Temperature

variation range is sufficient. Some temperature dependency has been observed in phase A tangent delta which may

explain the 0.5% Gamma variation over the temperature range.Correlation in units #2 and #3 is very low with a correlation coefficient of about 0.1. In unit #4 the correlation

coefficient approaches 0.3, but both the linear approximation and temperature range are very questionable.

TABLE 3. Parameters Temperature Coefficients.

Parameter Tan Delta [%/0C] Capacitance pF/

0C]

Phase A B C A B C

Temp.

Range

Unit #1 0.008 0.000 0.001 -0.001 0.066 -0.005 24-630C

Unit #2 No Correlation 31-470C

Unit #3 No Correlation 3-300C

Unit #4 Correlation Questionable 15-340C

CONCLUSIONS

High voltage bushing -is on the top of the list of failed components of large power transformers. For over thirty

years, technology has been in place to monitor the insulation condition of bushings on-line but it is not wide spread

in North America. Many bushing defects occur very quickly and performances of periodic off-line tests may not be

the answer. Recent advances in on-line monitoring technology have improved the accuracy, reliability, and the

diagnostics capability of such devices.

Fig. 7c

Unit #3

Fig. 7d

Unit #4

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The described device not only monitors changes in Gamma parameter and provides timely alarm signal on a defect

growth, it also performs diagnostics based on bushing temperature and provides trending of the power factor and

capacitance of each bushing. It is a viable system to monitor critical and important units.

Factors affecting the accuracy, such as noise (harmonics), voltage and phase variations of operating systems are

addressed. The achieved accuracy allows for reliable information in planning and implementing predictive

maintenance strategy. Monitoring a unit load current along with monitored parameters may allow for furtherimprovement in diagnostics accuracy. Data is presented from four transformers installed in North America.

One bushing (phase A of the unit #1) has been identified as having an insulation problem. Its trend is stable over the

observation period and the temperature coefficient is below the dangerous threshold. It is planned to continue

monitoring and to make a decision based on its future behavior.

ACKNOWLEDGMENTS

The authors want to thank V. Sokolov of ZTZ Services, Ukraine for great support and interest to the project and Z.

Berler who first started introducing the technology in North America.

REFERENCES

[1] Lau, M. Y.; 500KV Bushing Failures and Bushing Oil Sampling Program; 2002 Doble International Client

Conference.

[2] Svi P. M., Diagnostics of Insulation of High Voltage Equipment; 2-nd edition, EnergoAtomIzdat, 1988 (In

Russian);

[3] Svi P. M., Methods and Techniques of Diagnostics of High Voltage Equipment; 2-nd edition,

EnergoAtomIzdat, 1992, 240pp, (In Russian);

[4] Golubev A. A., Kane C. F., Seliber A. B., Blokhintsev I. D., On-Line Predictive Diagnostics Technologies forPower Transformers, The Proceedings of TechCon 2003 North America, pp.263-279, February 5-6, 2003, St

Petersburg, FL.

[5] Sokolov V., Kurbatova A., Mayakov V., Assessing the Condition of 330-750 kV Current Transformers, 67th

Annual International Conference of Doble Clients, March 27-31, Boston, MA, USA.

Mike Y. Lau, a Senior Engineer in the Generation Technical Service Department of BC Hydro. He is a registered ProfessionalEngineer in the Province of British Columbia and a member of IEEE Transformer Committee.

Tyler Schwartz, received his BEng from the University of Victoria in Electrical Engineering in 2000. His pre-graduation work

experience included electrical & instrumentation in the oil sands of northern Alberta, hardware design for paging system

infrastructure and for multi-axis motion controllers, dielectric resonator antenna design for broadband terrestrial applications, andpoint to point design of 900MHz communication systems. Tyler has worked for BC Hydro since 2000 in a variety of engineering

positions and is currently employed as a Maintenance Engineer at a 2730MW generating station. Tyler is registered as an EIT

with the Association of Professional Engineers and Geoscientists of British Columbia and is a member of the IEEE and the ISA.

Danny E. Bates, equipment tests team leader of Alabama Power. He is an author of technical publications.

Claude F. Kane, is a manager of Cutler-Hammer Predictive Diagnostics He graduates from the Milwaukee School of

Engineering, Milwaukee, WI in 1972 with a BS-ET. Claude started with Westinghouse as a Field Service Engineer in 1972.

Over the years he has held a variety of technical and management positions. He also has taken a leadership role in developing and

introducing the Westinghouse Insulation Systems Evaluation Services into the North American market. He is an author of patentsand technical publications.

Dr. Alexander A. Golubev is an engineering team leader for Cutler-Hammer Predictive Diagnostics. He has MS in

Experimental Physics and Ph.D. in Physics and Mathematics from the Moscow Physical Technical Institute (Russia). He has an

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extensive experience in research and design in Laser and Electron Beam Generation, Plasma Coatings, High Frequency

Measurements. He is an author of patents and technical publications.

Dr. Anatoliy B. Selibera Senior Engineer of Cutler-Hammer Predictive Diagnostics Division. He got his MSEE and Ph.D in

Electronics Measurements from the University of Telecommunications ( St. Petersburg, Russia Prior to joining CHPD he

worked as senior engineer in the Laboratory of Electronics Measurements of the University of Telecommunications developing

micro processor based analog and digital measurement equipment. He is an author of patents, books and technical publications.

Dr. Valery A. Rusov . CEO and director of Vibro-Center Company specializing in on-line monitoring of electrical equipment.

He has MSEE and Ph.D. from the State Perm Polytechnic University. During 17 years he lectured, as an Associate Professor, in

this University. He is an author of patents, books and technical publications.

Sergey V. Zhivodernikov,received the degrees electrical engineer from the Novosibirsk State Technology University in 1984.

He was a research engineer of high voltage department and senior engineer of the Siberian research power institute from 1984 to

2000, where he carried out gaseous discharges, insulation diagnostics and tests. The background in scientific and design workexperience has resulted in 35 publications in electro-physics, HV insulation, diagnostic methods and arrangements, insulating

compositions, long spark discharge. Now he is head of diagnostics department Novosibirsk Office of Federal Greed Company

United Energy System (inspections of high voltage equipment in substations and overhead transmission lines of extra high

voltage).