an iron core probe based inter-laminar core fault detection technique for generator stator cores

344 IEEE TRANSACTIONS ON ENERGY CONVERSION, VOL. 20, NO. 2, JUNE 2005

An Iron Core Probe Based Inter-Laminar Core FaultDetection Technique for Generator Stator Cores

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

Abstract—A new technique for detecting incipient inter-laminarinsulation failure of laminated stator cores of large generators isproposed in this paper. The proposed scheme is a low flux induc-tion method that employs a novel probe for core testing. The newprobe configuration, which uses magnetic material and is scannedin the wedge depression area, significantly improves the sensitivityof fault detection as well as user convenience compared to existingmethods. Experimental results from various test generators testedin factory, field, and lab environments under a number of fault con-ditions are presented to verify the sensitivity and reliability of theproposed scheme.

Index Terms—AC generators, fault diagnosis, fault location, in-sulation testing, magnetic cores, maintenance, reliability.

I. INTRODUCTION

THE stator core of electric machines is built from thin insu-lated steel laminations to reduce the eddy current losses for

high efficiency operation. For large generators, the laminationsare individually stacked by selectively placing one of the dove-tail grooves on the outer edge of a lamination in the dovetail ofa key bar, a set which is integral to the frame, as schematicallyshown in Fig. 1. Since the material used for inter-laminar insula-tion is subject to deterioration and damage, shorts between lam-inations can be introduced due to mechanical damage during as-sembly/inspection/rewind, vibration of loose coil wedges/lami-nations, electrical arcs during winding failure, presence of for-eign material, manufacturing defects, etc [1]–[7]. If the lamina-tions are shorted together for one of the reasons above, a circu-lating eddy current larger than that compared to normal oper-ation is induced in the fault loop that consists of the fault, theshorted laminations, and the key bar as shown in Fig. 1. The cir-culating fault current causes additional power loss in the coreand results in localized heating, which may progress in severityand eventually cause burning or melting of the laminations. Asa result, the stator insulation and windings can also be damagedcausing ground current through the stator core, which has a po-tential for complete machine failure.

Manuscript received October 1, 2003; revised January 31, 2004. Paper no.TEC-00283-2003.

S. B. Lee is with Korea University, Seoul 136-701, Korea (e-mail: [email protected]).

G. B. Kliman, deceased, was with Rensselaer Polytechnic Institute, Troy, NY12180-3590 USA (e-mail: [email protected]).

M. R. Shah is with the GE Global Research Center, Schenectady, NY 12309USA (e-mail: [email protected]).

N. K. Nair and R. M. Lusted are with General Electric Energy, Schenectady,NY 12345 USA (e-mail: [email protected]; [email protected]).

Digital Object Identifier 10.1109/TEC.2005.847977

Fig. 1. Inter-laminar core faults in laminated stator core.

The financial loss due to such a forced outage would be sig-nificant to both the original equipment manufacturer (OEM) andthe customer. It can be measured in terms of the capital and in-surance expenses along with loss of revenue generation. Also,the adverse impact on reputation and its subsequent fallout onfuture business cannot be overemphasized. Therefore, it is crit-ical to detect and repair inter-laminar core faults to prevent fur-ther damage, improve the reliability of generator operation andreduce maintenance costs.

II. PRIOR ART AND REQUIREMENTS

A. Prior Art

Before any thermal/electromagnetic techniques were devel-oped for detecting inter-laminar insulation failure, detection ofcore faults relied on visual inspection. The stator bore was in-spected for localized darkening of varnish, paint, or insulationcaused by stator core problems. The traditional method for mon-itoring the health of stator cores is the full ring test, also knownas the loop test [1]. In the loop test, an external winding isformed around the yoke of the core in a toroidal manner (statorcore is encircled through the main bore and around the outerframe) to excite the yoke of the stator core at 80% to 100% ofrated flux. The excitation flux in the yoke excites the inter-lam-inar faults, if any, and induces the fault currents, as shown inFig. 1. After the stator core heats up, a thermal imaging camerais used for hot spot detection on the inner surface of the core.The main disadvantage of the ring test is the requirement for anMVA level low PF power source (requires hundreds of amps) to

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LEE et al.: AN IRON CORE PROBE BASED INTER-LAMINAR CORE FAULT DETECTION TECHNIQUE 345

provide the required flux as well as the long setup, test, and re-moval time requirement for inspection. Other shortcomings ofthe ring test include difficulty of detecting deep-seated faults,expensive thermal sensing equipment, and safety issues.

The ELectromagnetic Core Imperfection Detector alsoknown as the EL CID, uses the same excitation configurationas the ring test, but allows testing at 3 4% rated flux level,which significantly reduces the power requirement and safetyrisks [2]–[5]. An air-core Chattock potentiometer, positionedto span the outer edges of two adjacent teeth, is scanned inthe axial direction along the inner surface to detect changesin the flux pattern caused by an inter-laminar fault. EL CIDoffers many benefits compared to the ring test such as reducedsetup and test time, higher sensitivity to deep-seated faults, andeasier interpretation of results. However, since the output signallevel of the Chattock coil is very small, the noise relative to thesignal level is high, resulting in difficulty of data interpretationand potential for false positive indications. Other shortcomingsof EL CID are the difficulty of scanning and interpretationof signals in the stepped core-end region. Since the Chattockcoil must scan the surface of the teeth, it is difficult to alignthe coil with the surface during the scan, and this results innoisy signals. It is often required to repeat the scans in thestepped iron region due to the obscurity in signal interpretation.A double probe Chattock coil is proposed in [6] along with aquantitative analysis and calibration procedure for improvingthe interpretation of EL CID; however, the fundamental short-comings of EL CID still remain.

A phase-shift sensing iron-core probe method proposed in [7]describes an advanced version of the Chattock coil with an ironcore to enhance the signal level due to a core fault. The difficultyof employing this method is that the tooth surface roughnesscauses the airgap between the core surface and probe to varywidely. This results in signal fluctuation over an unacceptablywide range, obscuring the fault detection. The iron core probeproposed in this method is also required to scan the surface ofthe tooth tip over two adjacent teeth; therefore, it carries all theshortcomings of EL CID related to surface scanning mentionedabove.

B. Requirements of Inter-Laminar Core Fault Testing

The main requirements for core testing based on existingmethods [1]–[7] and end-user feedback are summarized in thefollowing:

• Reliability of fault detection (improved signal/noise level)— Sensitivity to small faults and deep-seated faults— Elimination of false positive (FP) indications

• Speed of inspection— Ease of setup, inspection, and removal— Quick interpretation, Elimination of FP indications

• User convenience— No obscurity in interpretation of results for deter-mining existence, severity, and location of fault— Ease of scanning, safe inspection tool

Given the state-of-the-art in this area and the requirements forrunning the core test, our motivation for this work was to de-velop a more sensitive, reliable, fast, and user-friendly method

(a) (b)

Fig. 2. (a) Probe location and (b) Probe scanning in stepped iron region.

(a) (b)

Fig. 3. (a) Probe location and (b) Probe scanning in stepped iron region.

for detecting inter-laminar core faults. In this paper, we detailour effort in developing an advanced inter-laminar core fault de-tection technique and its analysis.

III. PRINCIPLES OF THE IRON CORE PROBE-BASED

INTER-LAMINAR CORE FAULT DETECTOR

The main idea of the proposed scheme is to replace the probeof existing low-level yoke excitation methods with a small ironcore probe in the wedge depression area. The probe consists of alaminated silicon steel core and 300 turns of fine wire. The probeis positioned in the wedge depression area between the teeth andabove the slot wedge, as shown in Fig. 2. The excitation levelof the yoke flux for exciting inter-laminar core faults is at 0.075T, which is similar to the existing EL CID-based methods (3

4% rated flux). The probe is scanned along the slot in theaxial direction to detect changes in the flux pattern caused byinter-laminar core faults.

The use of ferromagnetic material in the probe results ina higher flux concentration in the probe since the iron coreprovides a low magnetic reluctance path for the flux. As aresult, the measured probe voltage is several orders of magni-tude higher than using an air core probe. The large measuredsignal level improves the relative signal to noise ratio, whichresults in easier interpretation and reduced chance of falsepositive alarms caused by the noise, as will be shown in theexperimental results.

The position of the probe also enhances stability since themeasured signal is independent of the airgap between the probeand stator teeth (the total airgap on each side of the probe isalways constant). Scanning of the probe is also more convenientcompared to existing methods where the probes are placed onthe surface of the tooth tip, especially in the stepped iron regionsince the probe can be scanned along the slot wedge, as shown inFig. 3. The noncontact between the probe and stator core allowsfaster scanning of the probe and results in lower-noise signalscompared to when there is contact. The small probe size makeshandling and scanning of the probe convenient and also makescarriage trolley design easier.


As the probe is scanned, the variation in the magnitude andphase of the measured voltage are simultaneously monitored inreal time to detect the presence of inter-laminar core faults. TheRMS probe voltage per cycle is calculated and displayed using(1) to monitor changes in the flux, magnitude, where is themeasured probe voltage, and T represents the time interval foreach electrical cycle

(1)

To monitor the phase angle variation in the probe voltage, theexcitation current is also measured and used as a reference forthe angle. The derivative of the excitation current, , is takenand used as the phase reference signal since it is ideally in phasewith . Next, to obtain an accurate value of the phase angle be-tween and the derivative of , , the average power relation-ship shown in (2) is used, where the per cycle RMS value of the

derivative is calculated using (3)

(2)

(3)

The average power can be represented by the average of theinstantaneous product of and derivative and also by theproduct of the RMS values of , derivative, and the displace-ment power factor, as shown in (2). It can be assumed that themeasurements of the flux-induced voltage and current are sinu-soidal for a sinusoidal source. The equation for calculating canbe derived by rearranging (2) as shown in (4), where the valueis updated for each electrical cycle

(4)

As will be shown in the next section, both signals, and, must be simultaneously monitored to determine the existence,

severity, and location of the fault.

IV. ANALYSIS AND INTERPRETATION OF SCAN RESULTS

The variation in the two monitored signals, and ,show different signatures depending on the severity and loca-tion of the fault, when a core fault is present in the stator. Aconceptual phasor diagram analysis is presented in this sectionto map the resulting fault signatures to the actual location andseverity of the fault.

A. Phasor Analysis

The excitation system configuration for the inter-laminar corefault detector system is shown in Fig. 4. The phasor diagram ofthis system for healthy laminations is shown in Fig. 5(a), where

, , and represent the excitation voltage, current, and flux,respectively; , are the measured probe voltage and theprobe voltage due the excitation, and is the excitation fluxcomponent measured in the probe. Assuming an ideal inductive

Fig. 4. Excitation system configuration.

Fig. 5. Phasor diagram for (a) healthy core (b) faulty core (R > ! L ).

excitation system, leads and by 90 and is in phasewith . For healthy laminations without faults, and areequal since the excitation flux is the only flux component in thesystem.

When a fault is present, voltage is induced in the fault loop,, resulting in a fault current flow, . The fault current in-

duces an additional fault flux component, , which changes theflux distribution in the laminations and the probe. The inducedfault voltage, , is in phase with assuming ideal conditions.The phase angle between and depends on the impedancein the faulted loop, which consists of the resistive and induc-tive components, and , where and represent thefault resistance and inductance, and represents the excitationfrequency. The phasor diagram in the presence of a fault when

, is shown in Fig. 5(b), where is the measuredprobe voltage component due to the fault. The measured probevoltage can be assumed as a phasor sum of the voltage compo-nents, and , induced due to the excitation flux and thefault flux in the probe, and .

The flux distribution in the probe and laminations depends onthe location of the fault. For sub-wedge faults (faults located ator below the wedge), the direction of the flux in the probe dueto the fault, , is close to the excitation flux, , as shownin Fig. 6(b). Therefore, the phasor sum of and can berepresented as shown in Fig. 6(a). From Fig. 6(a), it can be pre-dicted that the magnitude and angle of increase with faultseverity (as increases) The magnitude change is consider-able, whereas the angle change is very small. It should be notedthat the flux distribution and phasors in Fig. 6 do not show theactual flux distribution or phasors, but are conceptual represen-tations for fault-behavior prediction purposes only. In the phasordiagrams of Fig. 6, it was assumed that the inductive componentis larger than the resistive component, .

The main difference in behavior under a surface fault condi-tion is that the direction of is close to the opposite ofas shown in Fig. 6(d), resulting in the phasor diagram shown in


Fig. 6. (a) Phasor diagram and (b) conceptual flux distribution for sub-wedgefault, (c) phasor diagram and (d) conceptual flux distribution for surface fault(R < ! L ).

Fig. 7. Typical fault locations.

Fig. 6(c). It can be seen from Fig. 6(c) that the change in phaseangle of increases significantly with fault severity. The mag-nitude of magnitude decreases initially as the fault severityincreases, but at some point starts to increase as the fault severityincreases.

The simplified phasor analysis shows that the existence ofa fault can be determined by monitoring the deviation of themagnitude and/or phase of . It is also shown that mag-nitude and angle signatures can be used to distinguish surfaceand sub-wedge faults, which is a desirable feature for recom-mending repair actions to the user. The results of the simpli-fied phasor analysis of this section can be used to predict theexistence, severity, and location of the fault. The scan resultsfrom adjacent slots provide more information on the nature ofthe fault, as will be shown in the following section.

B. Interpretation of Scan Results

The expected fault signatures at typical fault locations forthe faulted slots and the slots adjacent to the fault can bepredicted based on the phasor analysis. The typical fault lo-cations—corner of the slot bottom, slot wedge groove, andtooth tip—are shown in Fig. 7 along with slots A, B, C, andD. The predicted results on slots A, B, C, D for each faultcondition are summarized in Fig. 8(a), (b), (c) for faults on thecorner of the slot bottom, slot wedge groove, and tooth tip,

respectively. For all three faults, the scan results on slots A andD show a very small variation from the response obtained witha healthy core, as shown in Fig. 8(a)–(c). The small dips in the

signal are due to the ventilations ducts, which are thespacing intentionally placed between the lamination packages(separated by inside space blocks (ISSB)), for cooling of themachine. When the probe passes the ventilation ducts, theeffective MMF drop across the probe decreases due to reducedflux in the probe, resulting in the dips in . The phaseangle remains constant since it is just the magnitude of flux thatdecreases. The voltage dips due to the ventilation ducts are veryuseful for determining the axial location of the fault within thelamination package when a fault is detected.

For sub-wedge faults, whether the fault is on the slot bottomor the slot wedge groove, increases with the fault severityas shown in Fig. 6(a), when the probe is scanned in the slotwhere the fault is located. Under the same fault conditions, the

signal is narrower if the fault is located closer to the sur-face, as shown in Fig. 8(a), (b). The value of the fault resistancebecomes larger, if the fault is located closer to the surface, sincethe stator tooth resistance is much higher than that of the yoke.Therefore, the phase angle between and is larger, re-sulting in a larger phase angle change. This is shown in the slotB waveforms in Fig. 8(a), (b). The influence of the fault becomesmore noticeable in the measured signals in slot C, if the fault islocated closer to the surface and if the fault is more severe.

The fault signatures for surface faults are shown in Fig. 8(c),when the fault is located closer to slot B as shown in Fig. 7. Itcan be predicted from Fig. 6(c) that initially decreasesand then increases as the fault severity increases (increase in

). This results in the signal “flipping over” for moresevere faults as shown in Fig. 8(c). It can also be predicted fromFig. 6(c) that the phase angle increases with fault severity (rotates clockwise as increases). The fault signatures are nar-rower compared to sub-wedge faults since the faults are locatedcloser to the probe, and show larger variation in slot B comparedto slot C since the fault is located closer to slot B.

From the analysis and interpretation presented in this section,the capabilities and procedure for interpreting the results aresummarized as follows:

• The axial position of the fault can be determined byreading the position measurement embedded in the probecarriage trolley. The axial position of the fault withina lamination package can be determined based on thevoltage dips in the signal that result from venti-lation ducts.

• The circumferential position can be narrowed down toone or two slots from the scan results on all the slots byobserving the variation of the waveforms from that of ahealthy slot.

• Once the axial and circumferential position of the faultis identified, the radial position can be determined fromFig. 8. The radial position on the slot side requires carefulobservation, but it is very clear whether the fault is on thesurface or on/below the wedge.

• The magnitude of the variation in the fault signatures in-crease with the fault severity.


Fig. 8. Typical fault signatures for faults on (a) bottom of slot, (b) slot wedge groove, and (c) tooth tip.

A major advantage of using an iron core probe over an aircore probe is the low noise level in the signals shown in Fig. 8;therefore, the shape of the signals can be observed clearly. Thisreduces the false positive indications as well as the guessing andrepetition of tests due to noisy signals, which is typical whenusing methods based on air core probes. The experimental re-sults in the following section will verify that the relative signalto noise ratio is very high.

V. EXPERIMENTAL STUDY

The proposed inter-laminar core fault detector was tested infactory, field, and lab environments under a number of fault con-ditions for verification. There were no inter-laminar core faultindications in the tests run on a new generator in the factoryand in the field (no faults were found with other inter-laminarcore fault detectors as well.). To run tests with faulted lamina-tions, a generator, used for training purposes, shown in Fig. 9,and a generator test rig constructed in the laboratory (Fig. 10),were used. Inter-laminar core faults of varying severity were in-tentionally inserted at several locations for testing the proposedscheme. The results obtained from the two machines are pre-sented in this section.

A. Experimental Setup

To test the validity of the proposed method under a numberof fault conditions, several laminations were welded togetherto simulate inter-laminar fault conditions. For the test generatorshown in Fig. 9, faults that range from seven to 40 welded lam-inations were inserted on the tooth tip and slot wedge groove.All the faults were inserted in the teeth between slots 25 and 26,as shown in Fig. 11, a fault map of the inserted faults, whereeach box represents a lamination package. Faults could not beinserted on the bottom of the slot due to the narrow slot width;therefore, the laboratory test rig (Fig. 10) was used for testingfaults on the bottom of the slot. This test rig has a 125 mm coreof two lamination packages with actual ISSB separators for sim-ulating the response of the probe to ventilation ducts. As shownin Fig. 10(b), the faults were welded on the bottom of the slot(ten shorted laminations in slot 32, and 30 shorted laminationsin slot 5).

Fig. 9. Test generator.

Fig. 10. Lab test rig (a) overall view, (b) welded fault in slot bottom.

To test the concept, a portable field test equipment that con-sists of a 1) data acquisition system, 2) data processing anddisplay system, 3) excitation system, 4) probe carriage system,and 5) sensors was assembled. The overall configuration of thetest setup is shown in Fig. 12. For measuring and at 18kHz, a 16-bit, 200 kHz commercial data acquisition system wasused, and a laptop computer was used for processing the mea-sured data and displaying the fault signatures in real-time. Auser-friendly graphic user interface software was programmedto control the data processing and display. The software also cal-culates the number of excitation winding turns and variac output


Fig. 11. Map of welded faults in slots 25 and 26.

Fig. 12. Overall test setup.

voltage required to excite the stator core at 0.075 T based on thestator core dimensions.

A probe carriage was designed and built for positioning andaxial scanning of the probe in the wedge depression area. Theprobe was constructed by stacking small pieces of thin siliconsteel laminations and then winding it with 300 turns. The heightof the probe core was set so that the probe fits in the wedgedepression area, as shown in Fig. 2, and the probe length wasset equal to the height (square cross section). Determining theprobe width is a trade-off between the measured signal leveland ease of probe scanning. If the probe width is too large, con-tact between the probe and the side of the teeth results in noisymeasurements. From several field tests, it was determined ex-perimentally that the minimum total airgap between probe andlaminations required to avoid contact is roughly 5 mm for thecarriage being used. The excitation current was measured usinga commercial current sensor.

B. Experimental Results

The scan results of and on slots without intention-ally inserted faults, slots 13 and 14, are shown in Fig. 13(a) and(b), respectively. It can be seen that the noise levels in both sig-nals are small compared to the typical signals obtained usingexisting core fault detection techniques [2]–[7]. The decreasein the waveform due to ventilation ducts can be clearlyobserved in the signal, which provides a desirable feature fordetermining the exact axial location of the fault within a lam-ination package. When the probe exits the stator core, it canbe seen that decreases as the probe passes the steppediron region, whereas remains constant. The decrease in

Fig. 13. Scan results of V & � for healthy slots: (a) slot 13, (b) slot 14.

can be attributed to the increase in the reluctance seen from theMMF between the teeth, as the probe exits the stator core. Theeffect of the ventilation ducts in the stepped iron region can beclearly observed in the signal. Deviation of orfrom the signals shown in Fig. 13 can be attributed to a fault.For methods that require the probe to be scanned on the sur-face of the teeth, it is very difficult to maintain a constant gapbetween the probe and stator core in this region, which makesscanning difficult and leads to noisy signals. The fact that theprobe can be scanned at the same rate in the stepped iron regionwithout probe-core contact is another advantage of the proposedmethod, since scanning time can be reduced and there is no dif-ficulty of interpretation due to large noise levels in this region.

The scan results on the two slots adjacent to the faults, slots25 and 26, are shown in Fig. 14(a) and (b), respectively. It canbe seen that the noise level is small enough to be able to clearlyobserve the signal variation caused by all the inserted faults.The existence of small faults (7,10 shorted laminations) can beclearly observed in the scan. When the scan is run in slot 25,all the faults appear as a surface fault since the faults insertedon the slot wedge groove are in slot 26, as shown in Fig. 11. Aspredicted in the analysis in Section IV, decreases for smallfaults and shows a decrease-increase signature (flips over) if the


Fig. 14. Scan results of V & � for faulted slots: (a) slot 25, (b) slot 26.

fault is large enough. For all the faults, increases as predictedin Fig. 6(c). It can also be observed that the variations in thefault signatures are smaller for wedge groove faults comparedto tooth tip faults for the same number of shorted laminations.This is because the influence of the faults is smaller since theyare located further away from the probe. When the scan is runin slot 26, the tooth tip faults appear as surface faults, and thewedge groove faults appear as sub-wedge faults since the faultsare located in the same slot as the probe, as predicted in Sec-tion IV. For faults in the wedge groove, the increase inis considerable, and the increase in is small, as predicted inFig. 6(a). It can be observed that variation in the fault signaturesfor tooth tip faults are larger when the scan is run in slot 25,which is because the tooth tip faults are located closer to slot25. The results in Figs. 13 and 14 show that the fault locationcan be distinguished between sub-wedge and surface faults byobserving the fault indicators in adjacent slots.

The scan results on the slots with 10 and 30 shorted lamina-tions on the bottom of the slot are shown in Fig. 15 along withthe scans on the adjacent slots. Fig. 15(a) and (b) show theand signals, respectively, when 10 laminations are shorted inslot 32. There is no noticeable change in , but the showsa small observable increase. For 30 shorted laminations (results

Fig. 15. Scan results for 10 faulted laminations: (a) V , (b) �, scan resultsfor 30 faulted laminations: (c) V , (d) �.

for and shown in Fig. 15(c) and (d)), the increase inand are clearly observable. The variation in the signals

of the adjacent slots (slots 6 and 33) for both cases is very small.The results shown in Fig. 15 match the predictions made in theanalysis and the predictions made in Fig. 8.

VI. CONCLUSIONS

A new method and apparatus for detecting inter-laminar in-sulation failure that satisfies all the requirements for a core faultdetection test, stated in Section II-B, has been proposed in thispaper. It has been shown that the proposed inter-laminar corefault detector not only provides more reliable and versatile de-tection of faults, but also is more convenient to use and interpret.

A major advantage of the proposed scheme comes fromthe use of an iron core probe. The signal to noise level issignificantly improved, which allows the user to determine theexistence, severity, and location of smaller faults with moreconfidence in a shorter period of time compared to existingmethods. Another advantage comes from the position of theprobe. The noncontact and constant airgap scanning resultsin reduced scanning time and stable signal measurements,especially in the stepped iron region. In addition, the difficultyin interpretation is greatly reduced, which results in reducedchance of false indications and the need for repeating scans.

The phasor diagram analysis and typical signatures for sur-face and sub-wedge faults have been established and verified.Experimental results obtained from a laboratory test rig and anactual generator under a number of fault conditions verified thatthe proposed scheme provides reliable detection of small faultsand the ability to distinguish the fault location between surfaceand sub-wedge faults, which is a powerful feature for makingrepair recommendations to the end user.

ACKNOWLEDGMENT

The authors gratefully acknowledge R. Beaupre, S. Galioto,D. Kim, B. Feldman, J. Bird, and K. Imai, for their assistance


on the testing, and L. Tomaino, P. Robillard, J. Petrozzi-Jones,and G. Stewart for their feedback on the practical issues.

REFERENCES

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

[2] J. Sutton, “El-CID—an easier way to test stator cores,” Elect. Rev., Jul.1980.

[3] J. Sutton and B. F. Chapman, “Electromagnetic detection of damagedregions in laminated iron cores,” in Proc. Int. Conf. Electrical Ma-chines—Design and Applications, 1982.

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

[5] J. Sutton, “Theory of electromagnetic testing of laminated stator cores,”INSIGHT, Apr. 1994.

[6] Z. Posedel, “Inspection of stator cores in large machines with a low yokeinduction method-measurement and analysis of interlamination short-circuits,” IEEE Trans. Energy Convers., vol. 16, no. 1, pp. 81–86, Mar.2001.

[7] V. B. Berezhansky, L. I. Chubraeva, and G. V. Rostik, “Experience withmodified iron fault control technique for the stator cores of electricalmachines,” in Proc. Stockholm Power Tech Int. Symp. Electric PowerEngineering, vol. 3, 1995, pp. 108–112.

Sang Bin Lee (S’95-M’01) received the B.S. andM.S. degrees from Korea University, Seoul, Korea,in 1995 and 1997, respectively, and the Ph.D. degreefrom the Georgia Institute of Technology, Atlanta, in2001.

Currently, he is a Professor of Electrical En-gineering at Korea University, Seoul. From 2001to 2004, he was with the Electric Machines andDrives Laboratory, General Electric Global ResearchCenter, Schenectady, NY, where he was involved inresearch projects related to monitoring and diagnos-

tics of electric machines. His research interests are in protection, monitoringand diagnostics, and control of rotating electric machinery.

Dr. Lee was the recipient of the 2005 PES Prize Paper Award from the IEEEPower Engineering Society and the 2001 Second Prize Paper Award from theElectric Machines Committee of the IEEE Industry Applications Society. He isa member of the Industry Applications Society Electric Machines Committee.

Gerald B. Kliman (S’52–M’55–SM’76–F’92),deceased, received the S.B., S.M., and Sc.D. degreesfrom the Massachusetts Institute of Technology(MIT), Cambridge, in 1955, 1959, and 1965, respec-tively.

From 2001 to 2004, he was a Research Professorwith Rensselaer Polytechnic Institute, Troy, NY,after retiring from General Electric (GE). At GEResearch and Development, Schenectady, NY,he conducted fundamental studies on linear, syn-chronous, permanent-magnet (PM), and induction

motors, advanced drive systems for traction, the development of high-efficiencyand high-speed motors, electromagnetic (EM) pumps, and the application ofnew and developing magnetic and nonmagnetic materials and insulations. Amajor emphasis was the development of fault and incipient fault detectiontechniques 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 IEEE Power Engi-neering Society and the Electric Machines and Land Transportation Committeesof the IEEE Industry Applications Society. He was an Associate Editor of thejournal Electric Power Components and Systems. He was listed in the currentedition of Who’s Who in North America. He has 100 patents granted in his nameand many publications, including several prize papers.

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

From 1978 to 1980, he worked in Generator Devel-opment at Westinghouse Electric Corporation, EastPittsburgh, PA. From 1980 to 1981, he was a Post-doctoral Researcher with Rensselaer Polytechnic In-stitute, Troy, NY. From 1981 to 1984, he was with

General Electric, Binghamton, NY, and worked on cycloconverters and asso-ciated magnetics. During 1984 to 1986, he moved to Malta, NY, to work onacyclic machines and electromagnetic launchers. He worked in GE’s GeneratorEngineering, Schenectady, NY, from 1987 to 1998. During this tenure, he helpeddevelop state-of-the-art finite-element analysis programs applicable to electricalmachinery. He helped develop advanced ac machines for the Navy’s IntegratedElectric Drive factoring in the system impact. In the last assignment, he designedGE’s largest fully Hydrogen-cooled generator with higher power density, higherefficiency, and lower manufacturing cost. In early 1998, he joined KAPL, Inc.,Niskayuna, NY, a Lockheed Martin Company, where he worked on advancedmotors and drives for various Navy applications. He returned to GE in early1999, joining its Global Research Center, Niskayuna, NY. He has focused ondeveloping advanced solutions for increasing the capability of existing genera-tors and novel machines and analysis techniques.

Dr. Shah was the recipient of the IEEE Power Engineering Society Prize PaperAward in 2005. He received the 1991 GE Power Generation’s Most OutstandingTechnical Achievement/Contribution Award. He served as the Chair of the Syn-chronous Machines and Machine Theory Subcommittees for IEEE Power En-gineering Society and the IEEE Schenectady section.

N. Kutty Nair (M’63–’74–LSM’02) received theB.Sc. degree in electrical power engineering fromthe University of Madras, India, in 1957 and theM.Sc. degree in administrative science from TheJohns Hopkins University, Baltimore, MD, in 1975.

He has been with the Tata Steel Company,Jamshedpur, India; BHEL, Hyderabad, India; andGE Power Systems, Baltimore, MD and Schenec-tady, NY. After retiring from GE Power Systems in1996, he has been retained as a Part-Time ConsultingEngineer in GE Energy Services, working on the

new products introduction for generator services.

R. Mark Lusted received the B.A. degree in chem-istry from St. Olaf College, Northfield, MN, in 1977,and the M.S. degree in mechanical engineeringand engineer, Naval Engineering degrees, from theMassachusetts Institute of Technology, Cambridge,in 1994.

He joined General Electric Power Systems,Schenectady, NY, in 1999 as Manager of GeneratorServices New Product Introduction, and is currentlythe Manager of Generator Repair Technology forGE Power Systems, Schenectady, NY. He joined

GE following his retirement from the U.S. Navy, where he served in theoperational submarine force and in submarine design and construction. He wasalso Director for Systems Effectiveness, Submarine Towed Acoustic Systems,with the Naval Undersea Warfare Center, Newport, RI.

an iron core probe based inter-laminar core fault detection technique for generator stator cores

Documents

stator core heats

stator core problems

core testing

detection of core faults

stator insulation

iron core probe

toroidal manner stator

interlaminar faults