A New Method for Synchronous Generator Core Evaluation

576 IEEE TRANSACTIONS ON ENERGY CONVERSION, VOL. 19, NO. 3, SEPTEMBER 2004

A New Method for Synchronous Generator CoreQuality Evaluation

Gerald B. Kliman, Life Fellow, IEEE, Sang Bin Lee, Member, IEEE, Manoj R. Shah, Fellow, IEEE, R. Mark Lusted,and N. Kutty Nair, Life Senior Member, IEEE

Abstract—A new technique for detecting the presence andseverity of inter-laminar short circuits as well as estimating thestatus of core compression (or looseness) in laminated magneticcores of synchronous generators, with a single test equipment isdemonstrated in this paper. The core loss measurement obtainedfrom a flux injection probe that injects flux (of varying amplitude,frequency, and wave-shape) into two nominally adjacent teethover a localized region, is used as an indicator for detecting anddistinguishing the two fault conditions. An injection probe systemwas developed and tested, in the laboratory, using stacks of fullsize generator laminations with various induced fault conditions.The injection probe was shown to detect the presence of shortedlaminations at the bottom of the slot and to gauge the degree ofcore compression or looseness. In addition, a unique differentialprobe was developed and tested to demonstrate the capability ofdetecting as few as five shorted laminations.

Index Terms—AC generators and motors, core looseness detec-tion, core loss, differential signals, fault detection, fault diagnosis,fault location, insulation testing, magnetic laminated cores.

I. INTRODUCTION

THE importance of stator core quality evaluation for syn-chronous generators cannot be overemphasized consid-

ering the impact of generator failure caused by stator coreproblems. According to reports on recent generator failures[1], [2], the repair or rebuild process for stator core failuresare costly since it usually requires replacement of the entirecore. In most cases, it is required to remove the generatorfrom its foundation, ship it to the manufacturer, disassemblethe machine, restack the laminations, and reinstall it at thecustomer site, which takes several months. The total finan-cial loss that results from such a forced outage is hundredsof millions of dollars for the cost of repair and replacementpower. Moreover, the loss of reputation and fallout for futurebusiness is a serious concern to the manufacturer. Therefore,it is critical to reliably assess the condition of a generatorstator core for both the OEM and the customer. The mostcommon generator stator core problems are inter-laminar corefaults, relaxation of core stack pressure, and core end region

Manuscript received August 19, 2003. Paper no. TEC-00216-2003.G. B. Kliman, deceased, was with Rensselaer Polytechnic Institute, Troy, NY

12180-3590 USAS. B. Lee is with Korea University, Seoul, Korea (e-mail: sang-

[email protected])M. R. Shah is with the GE Global Research Center, Schenectady, NY 12309

USA.R. M. Lusted and N. K. Nair are with GE Energy, Schenectady, NY 12345

USADigital Object Identifier 10.1109/TEC.2004.832058

heating. This paper proposes a method for detecting inter-lam-inar insulation failure and core loosening with a single testequipment.

A. Inter-Laminar Insulation Failure

Shorting between laminations due to electrical failure ofinter-laminar insulation can result from 1) abrasion by foreignmaterials introduced during manufacturing, inspection, orrepair, 2) vibration of loose windings, wedges, or laminations,3) mechanical damage on the core surface during manu-facturing, inspection, or repair, 4) manufacturing defects inlaminations and its insulation, etc. Once an inter-laminar shortis introduced, a fault current path is formed in the laminationsand building bars or frame, which creates hot spots. If unde-tected, the fault progresses in severity and results in burningor melting of the laminations, which can eventually causegenerator failure, as shown in Fig. 1(a).

For many years, the only methods available to evaluate lami-nated magnetic cores of electrical machines for the presence ofshorted laminations were the “ring test” and visual inspection[2]–[4]. The ring test requires a power source of several MVA toexcite the core close to the rated flux, which raises safety risks.Several turns of rather heavy gauge, high voltage insulated ca-bles are wound through the stator bore to establish a circumfer-ential flux in the yoke but not in the teeth, as shown in Fig. 1(b).The excitation is applied for a duration long enough to start thecore heating but short enough not to allow it to reach a thermalequilibrium. The presence of inter-laminar faults is then ascer-tained by observing the resulting hot spots on the stator boredue to heat diffusing to the surface from them. Careful timingis needed so that the hot spots are not blunted by heat diffusionas the core approaches thermal equilibrium. In the past, detec-tion of the hot spots was done qualitatively by turning off thepower and immediately crawling into the bore and feeling thesurface. In recent times, this is done by means of an infraredimaging camera set outside the machine. Because robust traysare required to hold the heavy cables, significant portion of thecore may be hidden from view. Usually the rotor is removedhence it becomes an expensive and difficult test to run so it israrely done in the field and not often in the factory.

In the last decades of the 20th century, a low power test, called“EL CID” for Electromagnetic Core Imperfection Detector, wasdeveloped and is now widely used [5]–[7]. The core is wound,as in the ring test, but excited only to about 4% of rated flux sothat only a few kVA are required, greatly simplifying the powersupply and winding issues. In most cases, the rotor must still

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KLIMAN et al.: A NEW METHOD FOR SYNCHRONOUS GENERATOR CORE QUALITY EVALUATION 577

Fig. 1. (a) Inter-laminar core failure and (b) core ring test excitation.

be removed. Detection of inter-laminar faults is done by meansof a small, air core coil of many turns bent into a “horse shoe”shape such that it spans two adjacent teeth (“Chattock Coil” or“Maxwell Worm”). This coil is then scanned axially along thestator bore for each tooth pair and anomalies in the leakage fluxare noted. When the anomalous leakage flux, as measured bythe Chattock coil, reaches a particular magnitude it is concludedthat there is a fault in the core somewhere close to that point.The resulting signal tends to be noisy and difficult to interpretproperly. Both the ring test and the EL CID test can be run onlyon completed cores. Also, both tests encounter problems whenapplied to the end stepping portions of the core.

B. Relaxation of Core Stack Pressure

Relaxation of stator core stack pressure can result from1) loosening of core tightening means at the core end due tovibration during machine operation, 2) relaxation of laminationmaterial due to compression or wear of insulation material withtime and temperature, 3) manufacturing defects—non uniformthickness within lamination sheets causes accumulative nonuni-form pressure distribution, and so on. If the laminations are freeto vibrate due to core loosening, lamination steel and insulationfatigue is accelerated and eventually results in inter-laminarinsulation failure or a tooth fracture, as shown in Fig. 2(a).Broken laminations can migrate into the ground wall andcause ground faults, or severe inter-laminar insulation damageif it migrates into the gap. Stator winding insulation wear isalso accelerated by lamination vibration, which increases thepotential for ground faults [2]–[4].

The only generally recognized methods for evaluating coretightness (or looseness) are visual observation [3], the so-called“knife test”, and bolt torque measurement. In the knife test, oneattempts to insert a knife blade between laminations at the statorbore, as shown in Fig. 2(b). If the knife cannot be inserted thecore is judged to be tight (or compressed) enough. If the knifeblade can be inserted, the core is judged to be “loose”. The knifetest clearly carries a risk of creating inter-laminar faults. In thebolt torque measurement method, the bolt torque is checked andthe bolt is tightened if the bolt torque is below the threshold.This only provides the overall pressure within the core, and aloose local portion of the core cannot be detected. Several, morescientific, tests utilizing vibration, space block dimensions or

Fig. 2. (a) Fractured laminations due to vibration and (b) knife test.

ultrasonics have been proposed but none have been universallyadopted.

C. Requirements for Core Quality Evaluation

In response to the shortcomings of the available core testmethods revealed in the prior art survey, specifications for anew core quality test instrument were developed. They includedrequirements for 1) improved sensitivity to detect two shortedlaminations, 2) improved fault position identification, 3) localcore compression pressure measurement, 4) portability, 5) non-invasive testing, 6) low power, 7) ease of core-end step testing,and 8) the capability for use on partially assembled cores. Alow power flux injection concept was selected as the most likelyto meet all of these requirements. The flux injection concept ispresented in detail along with experimental verifications for arange of inter-laminar core faults with varying severity and forcore compression measurements. It should be emphasized thatone of the most difficult cases to detect with the conventionaltechniques is a fault at the bottom of the slot. In this paper, allof the lamination faults examined were placed at the bottom ofthe slots.

II. FLUX INJECTION CONCEPT

The basic idea of the flux injection system [8]–[10] is shownin Fig. 3 as applied to a typical synchronous generator core (onlyone lamination segment is shown for simplicity). A small lam-inated “U” core is applied to a pair of adjacent teeth as shown.The “U” core is excited by a coil connected to a variable voltageand frequency power supply, as shown in the figure. The ratingof the amplifier need not be more than about 2 kVA. For thisdemonstration, the thickness of the injection test core was madeabout 6.35 mm (0.25”) and the width was selected to approxi-mately match the tooth width. For convenience the test core wasfabricated from a tape wound inductor cut core. A photograph ofthe first test core positioned on a lamination is shown in Fig. 4.

The test works by injecting flux into the teeth and allowingit to spread out through the machine yoke as shown in thefinite element calculations, Fig. 5. The flux configuration in thelocality of the test core is then somewhat similar to the earliertest methods except that flux in the teeth is now considerableinstead of being close to zero. The flux density in the teethand the average flux density in the yoke can now be adjustedto any desired value for a given machine. In the initial testsreported here, the amplifier output was a sine wave voltagewhose amplitude was set to avoid saturation of the magneticcircuit. Capability was provided in the amplifier for frequencies


Fig. 3. Flux injection probe concept applied to a lamination segment.

Fig. 4. Photograph of the first injection probe with a typical laminationsegment. The tooth tip is about 3.3 cm.

other than 60 Hz and for arbitrary waveforms such as squarewaves or pulses. The magnetic circuit inevitably included anair gap, which was set in a range from 0.25 mm to 2.00 mm.The minimum gap is determined by the amount of stagger inthe machine lamination stack, which is usually of the order of0.25 mm. Larger gaps result in reduced sensitivity variationsto the stagger patterns for both types of faults. For most ofthe tests a nominal gap of 0.5 mm was used.

As may be seen in Figs. 3 and 4, a flux-sensing coil waswound around one leg of the test core. A separate sensing coilwas used to avoid problems of temperature dependent resistancedrop in the source winding and possible variations in leakageflux. A signal proportional to the magnetic core loss in the testcircuit may then be obtained by multiplying the output of theflux sensing coil by the exciting coil current and averaging theresult, as shown in (1),

(1)

where, and represent the sense coil voltage and excitationcurrent, and represent the number of turns in the excita-tion and sense coils, and is the time period. Since the presenceof a fault in the machine core when the test core is in its vicinitywill result in circulating currents, the eddy current component ofthe magnetic core loss hence the total loss will increase. Thusas the probe (or test core) is scanned axially along the core, aplot of the magnetic core loss signal will indicate the locationand severity of a lamination fault.

Fig. 5. Simulated flux distribution for a stator core with flux injection.

It is known that the hysteresis losses of steels are sensitive tomechanical pressure. There are data showing that when com-pressive stress, parallel to the flux, is applied to laminations, thehysteresis (and total) losses will increase markedly whereas ten-sile stress will only slightly reduce the losses. Although therehas been no similar data published for compressive stress ap-plied perpendicular to the flux, as is the case for generator andlarge motor cores, it is reasonable to assume that there will bea similar effect. Such an effect is likely to be difficult to findin the gross no load core loss of a large machine, as the me-chanical loading of the core laminations will normally be quitenonuniform both axially and radially and the effect may not belarge. Also looseness may be a quite local effect resulting fromtolerance variations or creepage. However an injection method,such as just described will be effective in ascertaining the localcompression of the core by examination of the local core losses.The very same apparatus as that applied to core faults is used,with only software differences required, to perform both func-tions. Additionally, the flexibility of an electronic power ampli-fier excitation allows testing at different excitation frequencies,

, and flux densities, , to enable separation of the loss datainto eddy current and hysteresis components based on the fol-lowing model.

(2)

where and represent the hysteresis and eddy currentlosses, and represent the hysteresis and eddy current lossconstants, and is the exponential constant that depends onmaterial properties and shape.

III. EXPERIMENTAL APPARATUS

The test article is a stack of typical generator laminations,such as shown in Fig. 4, piled to a height of about 2.5 cm. Forconvenience in mounting, the laminations were not overlappedor staggered as they would be in a full size machine. Again it wasfound to be useful to conduct inter-laminar fault testing and corecompression testing in the same apparatus. The injection probewas set against the lamination stack in a manner similar to thatshown in Fig. 4. The stack and probe were mounted in a smallhydraulic press as shown in Fig. 6. Since it was impractical,within the constraints of this setup, to actually scan the probe


it was rigidly fixed in place with a strip of plastic shim materialbetween it and the stack to set the gap.

Fig. 6. Test article installed (stacked) in the hydraulic press with the first testprobe.

Instead of scanning the probe along the stack past a fault, theprobe was fixed in place and various inter-laminar faults wereplaced in the stack adjacent to it. After a number of trials themethod used was to solder a group of 20 laminations togetherat the bottom of the slot. This resulted in a fault of about onecm length, which corresponds to the minimum detectable faultsize reported elsewhere. Since there are no key bars on this testarticle, the back of the stack was open circuited. In order toinsert controlled back of core short circuits, a small area on bothsides of each lamination in the group was sanded to removethe inter-laminar insulation. Thin plastic shims were insertedbetween the laminations and sequentially removed to increasethe size of the fault during the test. A nominal pressure wasapplied to the stack, and the back of the core was clamped toassure that there would be contact at the back of the core. Inorder to measure the effect of compression on losses the verysame set up was used except that there were no inter-laminarfaults and the press force was varied. It was not possible to applyforce over the entire lamination. A spreader plate, as illustratedin Fig. 7, was used to apply pressure mainly in the tooth areawhere the major problems of core looseness tend to occur.

Instrumentation of the initial test consisted of an electronicpower meter, a linear power amplifier and a precision waveformgenerator. A computer stored the output of the power meter.The operational characteristics of the electronic power meter ap-peared to introduce considerable “noise” into the measurementsso it was replaced, for the later measurements, by a commer-cial 16-bit data acquisition system, which yielded considerablycleaner results.

IV. EXPERIMENTAL RESULTS—INTER-LAMINAR FAULTS

The test article (stack) was arranged as described in Sec-tion III with all of the plastic shims inserted so that no faultswere apparent. The waveform generator was set for a 60 Hz sinewave at moderate voltage amplitude. Data were logged for sev-eral seconds at no fault. Then data acquisition was stopped whilethe first plastic shim was removed and then resumed. This pro-cedure was repeated until all 19 shims had been removed. Themagnetic core loss for the assemblage is shown in Fig. 8 as afunction of the number of faulted laminations. The core loss, asplotted, includes the laminations losses as well as that of the in-jection core, which is about 15% of the total. The incrementalcore loss, as the fault size is increased, is almost entirely due to

Fig. 7. Application of perpendicular force (stack compression) to testlamination article.

Fig. 8. Measured core loss as a function of the number of faulted laminations.A running average is shown within the raw data.

the eddy currents in the test article. The injection core and testarticle remain fixed in position during this process to avoid in-troducing other sources of variability. It is clear, in Fig. 8, thatthere is a great deal of noise. The trend, however, is clear withthe core loss increasing with the size of the fault according to asquare law up to the 20 laminations faulted. A running averageis superimposed on the raw data. The averaged power shows adiscernible difference all the way down to 3 or 4 laminationsshorted together. This is quite encouraging; however, the entirerange of variation is on the order of only 1.6% and could be im-pacted by local field conditions. While it is possible to resolve atthis level in the laboratory it is probably not readily achievablein the field. This led to considerable re-evaluation of the conceptand, subsequently, to the development of the differential probedescribed in Section VI.

V. EXPERIMENTAL RESULTS—CORE COMPRESSION

Testing to verify the technique of measuring core compres-sion with the injection probe, was carried out in a mannersimilar to that for inter-laminar faults except the fact that anun-faulted stack of laminations was used as the test article.


Fig. 9. Effect of perpendicular compressive stress on the total core loss.

Measurements were made at several frequencies and the corecompression was varied from close to zero to around 2.4 Mpa(350 psi) since typical core stacking pressure is in the vicinityof 200–250 psi. Also the electronic power meter was replacedby a digital data acquisition system. In this case, since only thepress force needed to be changed, the data acquisition systemwas run continuously hence the total magnetic core loss isplotted as a function of time in Fig. 9 but with the pressureat each stage noted. The entire range of magnetic core lossvariation was about 7.5%. This indicates that a good estimateof core looseness can be readily achievable in the field.

The data taken at various frequencies between 30 and 90 Hz in10 Hz intervals and at a flux density of were pro-cessed based on (2), to separate the hysteresis and eddy currentloss components. The results are shown in Fig. 10(a) and (b).As initially expected, the variation in the hysteresis componentwould be dominant. It is about 12.1% over the pressure range.Unlike the parallel compression case, the hysteresis componentdecreases with increasing pressure but shows a small increase atthe higher pressures. Surprisingly the eddy current componentdisplays a 3.9% variation over the pressure range, smaller butnot insignificant. The reason for this is not known but it doesnot appear likely that it is a numerical artifact.

VI. DIFFERENTIAL FLUX INJECTION PROBE

The small variations in measured magnetic core loss for evenlarge (more laminations) inter-laminar faults make the injectionprobe difficult to implement for a “fieldable” instrument anddid not meet the requirement of detecting one faulted pair oflaminations. The solution to this drawback is to eliminate thelarge baseline loss and focus on the incremental losses. Themethod developed to accomplish this task, to meet the specifica-tions, employs what is called the differential probe. The conceptof the differential probe is to examine the difference betweenthe magnetic core losses measured at closely adjacent sectionsof the stator core. One realization of the concept is shown inFig. 11. Two identical injection probes are placed side-by-side.The excitation coils are connected in series so that they haveidentical drive current. Instead of calculating the magnetic coreloss for each one and taking the difference the flux sensing

Fig. 11. Differential injection probe concept.

Fig. 12. Measured apparent differential core loss as a function of the numberof faulted laminations.

coils are connected in opposition. The resultant voltage mea-surement is then multiplied by the current and averaged as in (1).In Fig. 11, winding a single coil around both injection yokes toexcite both cores simultaneously with the same current has ef-fectively merged the excitation coils.

The faulted lamination measurement described in Section IIIwas repeated using the differential probe. The result is shown inFig. 12. The range of variation for a 20 lamination fault is nowabout 33% compared to the 1.6% for the single probe or an in-crease by factor of about 20 making it much more practical foruse in the field. The signal-to-noise ratio is also now far betteropening up the possibility of further processing to improve res-olution to the point where a single pair of shorted laminationsmay reliably be detected. A novel, printed circuit flux sensingsystem was devised to permit implementation of the differentialprobe on a single core to reduce the size of the probe and im-prove spatial resolution.

As a quick demonstration of how an actual scan would ap-pear was made by holding the differential probe in the hand andquickly swiping it past the 20-lamination fault. As expected, theresultant signal, Fig. 13, first goes negative and then positive asone core and then the other passes over the faulted region. Thechange in magnitude corresponds to that found in the static tests.It is difficult to draw conclusions about the effect of laminationstagger but its presence is clearly there. That the probe is handheld means that alignment and gap are uncontrolled especiallyin view of the significant magnetic forces between the probe andthe stack.


Fig. 13. Differential probe output when scanned (hend held) past a 20lamination fault (0.7 cm).

VII. CONCLUSIONS

A laboratory demonstration of a new noninvasive syn-chronous generator integrated core quality evaluation instru-ment was successfully carried out. In addition to detectingshorted laminations it can measure the state of compression ofthe core that has heretofore not been possible. The instrument isbased on injecting flux through adjacent teeth using a portable,low power amplifier and a small iron core probe without theneed to wind the entire stator core and could be applied topartly assembled cores. It has been shown that local injectionof flux with high flux density has the potential to increasethe sensitivity of existing inter-laminar core fault detectionmethods. Experimental results showed that inter-laminar faultsinvolving as few as 4 to 5 laminations can be detected usingthis system. A unique differential probe was also demonstratedto increase the fault signal level and signal-to-noise ratio topractical values. It has also been demonstrated that the sameinstrument can be used to detect loosening of core compressionin a noninvasive manner.

ACKNOWLEDGMENT

The authors gratefully acknowledge S. Galioto for Fig. 3,J. Mann and J. Rulison for the construction of the initial experi-ment, J. Bird and K. Imai for their assistance in the testing, andL. Tomaino for his feedback on the practical issues.

REFERENCES

[1] Pacificorp Hunter I Outage Filing. Public Service Commission of Utah.[Online]. Available: http://www.commerce.state.ut.us/ccs/HunterI-Filing.htm

[2] A. J. Gonzalez, M. S. Baldwin, J. Stein, and N. E. Nilsson, Monitoringand Diagnosis of Turbine Driven Generators. Englewood Cliffs, NJ:Prentice-Hall, 1995.

[3] IEEE Guide for Insulation Maintenance of Large Alternating-CurrentRotating Machinery (10,000 kVA and Larger), ANSI/IEEE Std.56-1977, Mar. 1977.

[4] W. G. Moore. (2001) Electric Generators: Potential Problems andRecommended Solutions. National Electric Coil. [Online]. Available:http://www.carilec.com/Assets/Presentations%202 001/Moore-Carilec-7-25-01.pdf

[5] J. Sutton, “El-CID—An easier way to test stator cores,” Elect. Rev., July1980.

[6] J. Sutton and B. F. Chapman, “Electromagnetic detection of damagedregions in laminated iron cores,” in Proc. Int. Conf. Elect. Mach.—De-sign and Applications, 1982.

[7] C. Rickson, “Electrical machine core imperfection detection,” Proc.Inst. Elect. Eng. B, vol. 133, no. 3, pp. 190–195, May 1986.

[8] G. B. Kliman, M. R. Shah, and J. A. Mallick, “Method and System forDetecting Core Faults,” U.S. Patent 6 469 504, Oct. 22, 2002.

[9] G. B. Kliman and M. R. Shah, “Method and System for Detecting CoreFaults,” U.S. Patent 6 489 781, Dec. 3, 2002.

[10] J. M. Bourgeois and F. Lalonde, “Apparatus and Method for Evaluationa Condition of a Magnetic Circuit of an Electric Machine,” U.S. Patent5 990 688, Nov. 23, 1999.

Gerald B. Kliman (S’52–M’55–SM’76–F’92–LF’95) [1931–2004], deceased, received the S.B.,S.M., and Sc.D. degrees from the MassachusettsInstitute of Technology (MIT), Cambridge, in 1955,1959, and 1965, respectively.

From 2001 to 2004, he was a Research Professorat Rensselaer Polytechnic Institute, Troy, NY afterretiring from General Electric. At GE Researchand Development, Schenectady, NY, he conductedfundamental studies of linear, synchronous, perma-nent-magnet (PM) and induction motors, advanced

drive systems for traction, the development of high-efficiency and high-speedmotors, electromagnetic (EM) pumps, and the application of new and de-veloping magnetic and nonmagnetic materials and insulations. A majoremphasis was the development of fault and incipient fault detection tech-niques for electric motors and drives. Following graduation from MIT hewas Assistant Professor of Electrical Engineering at Rensselaer PolytechnicInstitute. Prior to GE Corporate R&D, he had several assignments in GE’sTransportation Systems Division and Nuclear Energy Division where heworked on adjustable speed drives, high-speed linear induction motors, largeelectromagnetic pumps, etc.

Dr. Kliman was a Senior Member of the American Institute of Physics andserved on the Rotating Machinery Theory Committee of the Power EngineeringSociety and the Electric Machines and Land Transportation Committees of theIndustry Applications Society. Dr. Kliman was an associate editor of the journalElectric Power Components and Systems. He is listed in the current edition of“Who’s Who in North America.” He has had 88 patents granted in his name andnumbers of publications including several prize papers.

Sang Bin Lee (S’95–M’01) received the B.S. andM.S. degrees in electrical engineering from KoreaUniversity, Seoul, in 1995 and 1997, respectively,and the Ph.D. degree from Georgia Institute ofTechnology, Atlanta, in 2001.

From 2001 to 2004, he was with the Electric Ma-chines and Drives Lab, General Electric Global Re-search Center (GE GRC), Schenectady, NY, where hewas involved in research related to monitoring anddiagnostics of electrical machines. He is currently aProfessor of electrical engineering at Korea Univer-

sity, Seoul, Korea. His current research interests are in electric machine protec-tion and drives.

Dr. Lee was the recipient of the 2001 Second Prize Paper Award from theElectric Machines Committee of the IEEE Industry Applications Society. He isa member of the IEEE-IAS Electric Machines Committee.


Manoj R. Shah (S’75–M’78–SM’88–F’03) receivedthe B.Tech. (Hons) from the Indian Institute of Tech-nology, Kharagpur, India, in 1972 and the M.S. andPh.D. degrees from Virginia Polytechnic Institute andState University (Virginia Tech), Blacksburg, in 1977and 1980, respectively.

From 1978 to 1980, he was with GeneratorDevelopment at Westinghouse Electric Corp., EastPittsburgh, PA, focusing on negative-sequenceheating of rotors. From 1980 to 1981, he was aPostdoctoral researcher at Rensselaer Polytechnic

Institute, Troy, NY, working on generator end region analysis and transformerbus connections. From 1981 to 1984, he was with General Electric, Bing-hamton, NY, working on cycloconverters and associated magnetics. During1984 to 1986, he moved to Malta, NY to work on acyclic machines andelectromagnetic (EM) launchers. He worked in GE’s Generator Engineering,Schenectady, NY, from 1987 to 1998. During this tenure, he helped developstate-of-the-art finite-element analysis programs as applicable to electricalmachinery. He helped develop advanced ac machines for Navy’s IntegratedElectric Drive factoring in the system impact. In the last assignment, hedesigned GE’s largest fully Hydrogen cooled generator with higher powerdensity, higher efficiency, and lower manufacturing cost. In early 1998, hejoined the Knolls Atomic Power Laboratory Inc., Niskayuna, NY, a LockheedMartin Co. where he worked on advanced motors and drives for various Navyapplications. He returned to GE in early 1999, joining its Global ResearchCenter, Niskayuna, NY. For the last four years, he has focused on developingadvanced solutions for increasing capability of existing generators and novelmachines and analysis techniques. He has authored/coauthored around a dozenpapers in the electrical machines area

He received the General Electric Power generation’s Most Outstanding Tech-nical Achievement/Contribution Award in 1991. He was awarded 17 U.S. andmany foreign patents with a dozen more pending. Presently, he is a member ofthe Electric Machinery Committee of the Power Engineering Society and Chairof its Synchronous Machines subcommittee, a member and past chair of its Ma-chine Theory subcommittee, and a member of its dc, PM, and Special Machinessubcommittee. He is also a past chair of the Schenectady section of IEEE.

R. Mark Lusted received the B.A. degree in Chem-istry from St. Olaf College, Northfield, MN, in 1977,and the M.S., Mechanical Engineering and Engineer,Naval Engineering degrees from the MassachusettsInstitute of Technology, Cambridge, in 1994.

Currently, he is Manager of Generator ServicesNew Product Introduction, and is Manager ofGenerator Repair Technology for General ElectricPower Systems, Schenectady, NY. He joined GeneralElectric Power Systems in 1999. He joined GEfollowing his retirement from the U.S. Navy, where

he served in both the operational submarine force and in submarine designand construction. His last assignment in the Navy was Director for SystemsEffectiveness, Submarine Towed Acoustic Systems at the Naval UnderseaWarfare Center, Newport, RI.

N. Kutty Nair (M’63–SM’74–LSM’02) received theBachelor’s degree in electrical power engineeringfrom the University of Madras, Madras, India, in1957 and the M.S. degree in administrative sciencefrom the Johns Hopkins University, Baltimore, MD,in 1975.

After his retirement from GE Power Systems in1996, he has been retained as a part-time ConsultingEngineer in GE Energy Services, working on newproducts introduction for generator services. Hisemployment experience includes the Tata Steel Co.,

Jamshedpur, India; Bharat Heavy Electrical Ltd., Hyderabad, India; and GEPower Systems, Baltimore, MD, and Schenectady, NY.

A New Method for Synchronous Generator Core Evaluation

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