What Stator Current Processing Based Technique to Use for Induction Motor Rotor Faults Diagnosis?

Transcription

1 What Stator Current Proceng Baed Technque to Ue for Inducton Motor Rotor Fault Dagno? Mohamed Benbouzd, Gerald Klman To cte th veron: Mohamed Benbouzd, Gerald Klman. What Stator Current Proceng Baed Technque to Ue for Inducton Motor Rotor Fault Dagno?. IEEE Tranacton on Energy Converon, Inttute of Electrcal and Electronc Engneer, 003, 8 (), pp <hal > HAL Id: hal Submtted on Jul 04 HAL a mult-dcplnary open acce archve for the depot and demnaton of centfc reearch document, whether they are publhed or not. The document may come from teachng and reearch nttuton n France or abroad, or from publc or prvate reearch center. L archve ouverte plurdcplnare HAL, et detnée au dépôt et à la dffuon de document centfque de nveau recherche, publé ou non, émanant de établement d enegnement et de recherche frança ou étranger, de laboratore publc ou prvé.

2 What Stator Current Proceng Baed Technque to Ue for Inducton Motor Rotor Fault Dagno? Mohamed Benbouzd, Senor Member, IEEE and Gerald B. Klman, Lfe Fellow, IEEE Abtract In recent year, marked mprovement ha been acheved n the degn and manufacture of tator wndng. However, motor drven by old-tate nverter undergo evere voltage tree due to rapd wtch-on and wtch-off of emconductor wtche. Alo, nducton motor are requred to operate n hghly corrove and duty envronment. Requrement uch a thee have purred the development of vatly mproved nulaton materal and treatment procee. But cage rotor degn ha undergone lttle change. A a reult, rotor falure now account for a larger percentage of total nducton motor falure. Broken cage bar and bearng deteroraton are now the man caue of rotor falure. Moreover, wth advance n dgtal technology over the lat year, adequate data proceng capablty now avalable on cot-effectve hardware platform, to montor motor for a varety of abnormalte on a real tme ba n addton to the normal motor protecton functon. Such multfuncton montor are now tartng to dplace the multplcty of electromechancal devce commonly appled for many year. For uch reaon, th paper devoted to a comparon of gnal proceng baed technque for the detecton of broken bar and bearng deteroraton n nducton motor. Feature of thee technque whch are relevant to fault detecton are preented. Thee feature are then analyzed and compared to deduce the mot approprate technque for nducton motor rotor fault detecton. Index Term Inducton motor, rotor fault dagno, tator current. I. INTRODUCTION It well known that nducton motor domnate the feld of electromechancal energy converon. Thee machne fnd a wde role n mot ndutre n partcular n the electrc utlty ndutry a auxlary drve n central power plant of power ytem, a well a retrcted role n low MVA power upply ytem a nducton generator, mnng ndutre, petrochemcal ndutre, a well a n aeropace and mltary equpment. Therefore, aement of the runnng condton and relablty of thee drve ytem crucal to avod unexpected and catatrophc falure. Conequently, the ue of preventve mantenance and nonnvave dagno of the condton of thee nducton motor drve of great concern, and becomng ncreangly mportant [-]. In recent year, marked mprovement ha been acheved n the degn and manufacture of tator wndng. However, motor drven by old-tate nverter undergo evere voltage tree due to rapd wtch-on and wtch-off of emconductor wtche. Alo, nducton motor are requred to operate n hghly corrove and duty envronment. Requrement uch a thee have purred the development of vatly mproved nulaton materal and treatment procee. But cage rotor degn ha undergone lttle change [3]. A a reult, rotor falure now account for a larger percentage of total nducton motor falure (Fg. ) [4]. Broken cage bar and bearng deteroraton are now the man caue of rotor falure (Fg. ). In general, condton-montorng cheme have concentrated on enng pecfc falure mode n one of three nducton motor component: the tator, the rotor, or the bearng. Even though thermal and vbraton montorng have been utlzed for decade, mot of the recent reearch ha been drected toward electrcal montorng of the motor wth empha on npectng the tator current of the motor [5]. Fault detecton baed on motor current rele on nterpretaton of the frequency component n the current pectrum that are related to rotor or bearng aymmetre. However, the current pectrum nfluenced by many factor, ncludng electrc upply, tatc and dynamc load condton, noe, motor geometry, and fault condton. Thee condton may lead to error n fault detecton. Wth advance n dgtal technology n recent year, adequate data proceng capablty now avalable on coteffectve hardware platform, to montor motor for a varety of abnormalte on a real tme ba n addton to the normal motor protecton functon. Such multfuncton montor are now tartng to dplace the multplcty of electromechancal devce commonly appled for many year. For uch reaon, th paper devoted to a comparon of gnal proceng baed technque for the detecton of broken bar and bearng deteroraton n nducton motor. Feature of thee technque whch are relevant to fault detecton are preented. Thee feature are then analyzed and compared to deduce the mot approprate technque for nducton motor rotor fault detecton. M.E.H. Benbouzd wth the Centre de Robotque, d Electrotechnque et d Automatque (CREA) of the Unverty of Pcarde Jule Verne at Amen, 7, Rue du Mouln Neuf, Amen, France (e-mal: m.benbouzd@eee.org). G.B. Klman wth the Electrcal, Computer & Sytem Engneerng Department, Renelaer Polytechnc Inttute, Troy, NY USA (klmag@rp.edu). A. Broken Bar II. MOTOR CURRENT SPECTRAL COMPONENTS The broken rotor bar frequence n the motor current are gven by []

3 f brb f k p () eccentrcte movng n both drecton. A wth the argap eccentrcty, thee varaton generate tator current at frequence gven by Where f the electrcal upply frequency, k/p =, 5, 7,, 3,... (due to the normal wndng confguraton), the per unt lp, and p the number of pole par. Even though the predcted frequence are the ame for both argap dynamc eccentrcty [5] and broken bar, the deband ampltude correpondng to a partcular harmonc number are dfferent allowng the two fault to be dtnguhed. The ampltude of the deband frequency component roughly proportonal to the number of broken rotor bar. In fact, the ampltude I brb of frequency component f ( ) can be approxmated by [7] I brb I n p Where I the tator current fundamental frequency component, R p b (3) R R b the number of broken bar. By analyzng the tator current, t poble to evaluate the general condton of the rotor. If there are broken bar n varou part of the rotor, the current analy not capable of provdng nformaton on the confguraton of noncontguou broken bar. For example, the frequency component f ( ) doe not ext f broken bar are electrcally / radan away from each other. It hould be noted that ome expermental tude have demontrated that both kewng and nonnulaton of rotor bar lead to reduce the broken rotor bar harmonc component. It ha been demontrated expermentally that when the ampltude of thee harmonc over 50 db maller than the fundamental frequency component ampltude, the rotor may be condered healthy [7]. B. Bearng Fault Bearng problem are often caued by mproperly forcng the bearng onto the haft or nto the houng. Th produce phycal damage n the form of brnellng or fale brnellng of the raceway, whch lead to premature falure. Malgnment of the bearng, whch occur n the four way depcted n Fg. 3, alo a common reult of defectve bearng ntallaton. The relatonhp of the bearng vbraton to the tator current pectra can be determned by recallng that any ar gap eccentrcty produce anomale n the ar gap flux denty. Snce ball bearng upport the rotor, any bearng defect wll produce a radal moton between the rotor and tator of the machne. The mechancal dplacement reultng from damaged bearng caue the machne argap to vary n a manner that can be decrbed by a combnaton of rotatng () f bng f m f (4),o Where m =,, 3,... and f,o one of the charactertc vbraton frequence whch are baed upon the bearng dmenon hown n Fg. 4. f n f r,o bd pd co Where n the number of bearng ball, f r the mechancal rotor peed n Hz, bd the ball dameter, pd the bearng ptch dameter, and the contact angle of the ball on the race [5]. It hould be noted from (5) that pecfc nformaton concernng the bearng contructon requred to calculate the exact charactertc frequence. However, thee charactertc race frequence can be approxmated for mot bearng wth between x and twelve ball [8]. f o 0. 4n f r f 0. n f r Th generalzaton allow for the defnton of frequency band where the bearng race frequence are lkely to how up wthout requrng explct knowledge of the bearng contructon. C. Load Effect If the load torque doe vary wth rotor poton, the current wll contan pectral component, whch concde wth thoe caued by a fault condton. In an deal machne where the tator flux lnkage purely nuodal, any ocllaton n the load torque at a multple of the rotatonal peed mf r wll produce tator current at frequence of [9] f load f m f r f (5) () m (7) p Where m =,, 3,... Snce the ame frequence are gven by () and (3), t clear that when the nducton machne operate wth a typcal tme-varyng load, the torque ocllaton reult n tator current that can obcure, and often overwhelm, thoe produced by the fault condton a llutrated by Fg. 5 [0]. Therefore, any tator current nglephae pectrum baed fault detecton cheme mut rely on montorng thoe pectral component, whch are not affected by the load torque ocllaton [0]. However, broken bar detecton tll poble nce the current typcally contan hgher order harmonc than thoe nduced by the load.

4 III. ROTOR FAULT DETECTION TECHNIQUES A. Fat Fourer Tranform (FFT) For th method, the tator current montorng ytem ketched n Fg.. Generally, not denyng the dagnotc value of clacal pectral analy technque, nducton motor fault detecton, va FFT-baed tator current gnature analy, could be mproved by decreang the current waveform dtorton a llutrated by Fg. 7 and 8 []. Moreover, t well known that motor current a nontatonary gnal, the properte of whch vary wth the tme-varyng normal operatng condton of the motor. A a reult, t dffcult to dfferentate fault condton from the normal operatng condton of the motor ung Fourer analy. B. Intantaneou Power FFT In th cae, n place of the tator current, the ntantaneou power ued a a medum for motor gnature analy []. It wa hown that the amount of nformaton carred by the ntantaneou power, whch the product of the upply voltage and the motor current, hgher than that deducble from the current alone. In fact, bede the fundamental and the two clacal deband component, the ntantaneou power pectrum contan an addtonal component drectly at the modulaton frequency a hown by the followng equaton. p LL L t p t co t co 0 MV I t co co t oc oc Where p the ntantaneou power, M the modulaton ndex, V LL the rm value of the lne-to-lne voltage, and I L that of the lne current, whle and denote the upply radan frequency and motor load angle, repectvely, and oc the radan ocllaton frequency. A an llutraton, Fg. 9 how clearly the dfference wth Fg. 7b. In fact, all the fault harmonc are tranlated nto the frequency band 0 00 Hz. Th conttute a great advantage becaue the fault harmonc doman well bounded. However, the power pectra are tll qute noy. Even addng flter ha not brought gnfcant mprovement. Moreover, even though the power pectrum partcularly adapted to mechancal abnormalty detecton (worn or damaged bearng), t tll ha the ame prncpal drawback a the clacal motor current FFT (nontatonary gnal). oc (8) moment equence of a proce [3]. The bpectrum perodc wth a perod of, and preerve both magntude and phae nformaton. It then capable of revealng both the ampltude and phae nformaton of the gnal. Wth thee addtonal dmenon, fault detecton and dagnotc procee can be enrched. Very promng reult were obtaned, a llutrated by Fg. 0. In fact, expermental reult ndcate that the bpectrum magntude of the domnant component, caued by the machne rotaton, ncreaed wth the fault level ncreae. Thee reult clearly ndcate that tator current bpectrum capable of provdng adequate and eental pectral nformaton for nducton motor condton montorng and fault detecton. However, th technque more approprate for the detecton of electrcal baed fault, uch a tator voltage unbalance, becaue thoe fault do not have a welldentfed harmonc frequency component []. D. Hgh Reoluton Spectral Analy A man dadvantage of the clacal pectral etmaton the mpact of de lobe leakage due to the nherent wndowng of fnte data et. Wndow weghtng allow mtgaton of the effect of de lobe at the expene of decreang the pectral reoluton that can be no better than the nvere of acquton tme. In order to mprove the tattcal tablty of the pectral etmate,.e. to mnmze the etmate varance, peudo enemble averagng by egmentng the data wa ntroduced at the prce of further decreang the reoluton. A cla of pectral technque baed on an egenanaly of the autocorrelaton matrx ha been promoted n the dgtal gnal proceng reearch lterature [4]. A an llutraton, two well known egenanaly-baed frequency etmator have been ued: MUSIC (Multple Sgnal Clafcaton) and ROOT-MUSIC for tator voltage unbalance undercorng []. In th cae, one of the prncpal pectral component modfed by the electrc fault the upply frequency thrd harmonc (.e. 50 Hz) whoe ampltude ncreae n a gnfcant way whatever the load. The two prncpal pectral component of the tator current pectrum are the frt and the ffth harmonc (50 Hz - 50 Hz) for a healthy motor, and the frt and thrd harmonc (50 Hz - 50 Hz) for a tator voltage unbalance. The MUSIC algorthm ha been appled for each cae and reult are gven n Fg.. Wth regard to thee reult, MUSIC and ROOT- MUSIC method allow keepng only the man frequence wthout other pectral nformaton. Moreover, tator current hgh-reoluton pectral analy ued a a medum for nducton motor fault detecton wll be ueful for all fault modfyng man pectral component. C. Bpectrum Bpectrum, alo called thrd-order pectrum, derve from hgher order tattc. The bpectrum defned n term of the two-dmenonal Fourer tranform of the thrd-order E. Wavelet Analy Fourer analy very ueful for many applcaton where the gnal are tatonary. The Fourer tranform however not approprate to analyze a gnal that ha trantory

5 charactertc uch a drft, abrupt change and frequency trend. To overcome th problem t ha been ueful to analyze mall ecton of the gnal at varou tme. Th technque known a Short-Tme Fourer Tranform (STFT) or wndowng technque. The technque map a gnal nto a two-dmenonal functon of tme and frequency. The STFT repreent a ort of comprome between tme and frequency baed vew of a gnal and t provde ome nformaton about both. However, we can only obtan th nformaton wth lmted precon, and that precon determned by the ze of the wndow. The fxed ze of the wndow the man drawback of the STFT [5]. The wavelet tranform wa ntroduced wth the dea of overcomng the dffculte mentoned above. A wndowng technque wth varable-ze regon ued to perform the gnal analy, whch can be the tator current. Wavelet analy allow the ue of long tme nterval where we want more prece low frequency nformaton, and horter regon where we want hgh frequency nformaton. The ablty to perform local analy one of the mot nteretng feature of the wavelet tranform. The advantage of ung wavelet technque for fault montorng and dagno of nducton motor ncreang becaue thee technque allow u to perform tator current gnal analy durng tranent. The wavelet technque can be ued for a localzed analy n the tme-frequency or tme cale doman. It then a powerful tool for condton montorng and fault dagno. A an llutraton, Fg. provde the reult where STFT and the wavelet technque are combned. Thee reult how the mprovement ntroduced by the wavelet technque for the gnal frequency montorng []. F. The Park Vector Approach A two dmenonal repreentaton can be ued for decrbng three-phae nducton motor phenomena. A utable one beng baed on the tator current Park vector [7]. A a functon of man phae varable ( a, b, c ) the current Park vector component ( d, q ) are d q 3 a b b c c Under deal condton, three-phae current lead to a Park vector wth the followng component d q M M n t n t (9) (0) Where M the upply phae current maxmum value and the upply frequency. It repreentaton a crcular pattern centered at the orgn of the coordnate. Th a very mple reference fgure that allow the detecton of faulty condton by montorng the devaton of the acqured pattern a llutrated by Fg. 3. The healthy pattern dffer lghtly from the expected crcular one, becaue upply voltage generally not exactly nuodal. Recently, a new mplementaton of the Park vector approach ha been propoed [8]. Under abnormal condton, for example n the preence of rotor cage fault uch a broken bar, (9) and (0) are no longer vald, becaue the nducton motor upply current wll contan deband component at frequence dfferng from the fundamental by the double lp frequency. Thee addtonal component at frequence of ( )f and ( + )f wll alo be preent n both motor current Park vector component ( d, q ). In thee condton, t can be hown that the pectrum of the tator current Park vector modulu the um of a dc level, generated manly by the fundamental component of the nducton motor upply current, plu two addtonal term, at frequence of f and 4f. In th way, the pectrum of the tator current Park vector modulu ac level clear from any component at the fundamental upply frequency, makng t more ueful to detect the component drectly related to the nducton motor fault. Th new mplementaton of the Park vector approach ntended to elmnate ome of the techncal lmtaton of the conventonal FFT technque. In fact, Fg. 4a how that, n the abence of fault, the behavor of the nducton motor motly characterzed by the abence of any relevant pectral component. Moreover, reult obtaned by the extended Park vector approach are more dcrmnatng than thoe obtaned by the tradtonal FFT technque (Fg. 4b). G. Adaptve Stattcal Tme-Frequency Method The motor current can be modeled a a nontatonary random gnal. However, a prevouly mentoned, Fourer tranform technque are not uffcent to repreent nontatonary gnal. Moreover, the uncertanty nvolved n the ytem requre an adaptve tattcal framework to addre the problem n an effcent way. In recent year, advancement of tattcal gnal proceng method ha provded effcent and optmal tool to proce nontatonary gnal. In partcular, tme-frequency and tme-cale tranformaton provde an optmal mathematcal framework for the analy of tme-varyng, nontatonary gnal [9]. Recently, an adaptve tattcal tme-frequency method to detect broken bar and bearng fault ha been propoed. The key dea n th method to tranform the motor current nto a tme-frequency pectrum to capture the tme varaton of the frequency component and to analyze the pectrum tattcally to dtnguh fault condton from the normal operatng condton of the motor. Snce each motor ha a dtnct geometry, a uperved approach adapted. In th approach, the algorthm traned to recognze the normal

6 operatng condton of the motor pror to actual fault detecton [0]. Tme localzaton of nontatonary gnal typcally acheved by the STFT above dcued. It mathematcal decrpton gven a follow for a gven gnal f F 0 t,n f t g t nt e dt () Where g an deal cut-off functon, g(t nt 0 ) a tranlate of g, t 0 the length of the cut-off nterval, and n an nteger aocated wth the gnal porton. mlar to the Fourer frequency. The propoed detecton method, a hown by Fg. 5, cont of four man tage: preproceng (typcal gnal condtonng procedure), tranng (current tme-frequency pectrum computed and feature relevant to fault condton are extracted), tetng, and potproceng (tetng repeated to mprove fnal the decon accuracy) [0]. For llutraton, Fg. how a typcal tme-frequency pectrum for bearng fault detecton [0]. H. An addtonal Technque Recently [], an nteretng technque ha been propoed for the detecton of broken bar n nducton motor. Th technque baed on an open termnal tet. In th cae, rotor current wll then nduce voltage n the tator wndng. Thee voltage wll be proceed for the dagno of cracked or broken rotor bar. Th a very nteretng technque, nce nducton motor are generally uppled by nondeal ource wth tme harmonc voltage, voltage unbalance, etc. Moreover, the motor may operate n the aturaton regon. Thee frequent condton wll lead to ome error n the fault detecton proce. It appear that thee effect wll be removed by the open termnal tet. Th technque eem to be nteretng for onte rotor fault detecton (before the motor utlzaton). IV. CONCLUDING REMARKS The paper attempt to brefly preent gnal (manly motor current) proceng technque for nducton motor rotor fault detecton (manly broken bar and bearng deteroraton). The man advantage and drawback of the above-preented technque are alo brefly dcued. In many cae, the conventonal teady tate technque may uffce. From thee dcuon, t appear that, for the mot dffcult cae, tmefrequency and tme-cale tranformaton, uch a wavelet, provde a more optmal tool for the detecton and the dagno of faulty nducton motor rotor. On the one hand they remedy the man drawback of motor current gnal proceng technque for fault detecton,.e. nontatonarty. On the other hand thee technque exhbt ome nteretng applcaton advantage, uch a for coal cruher, where peed vare rapdly and for deterorated bearng where peed and gnature may vary n an unpredctable manner. REFERENCES [] O.V. Thoren et al., A urvey of fault on nducton motor n offhore ol ndutry, petrochemcal ndutry, ga termnal, and ol refnere, IEEE Tran. Indutry Applcaton, vol. 3, n 5, September-October 995, pp [] M.E.H. Benbouzd, Bblography on nducton motor fault detecton and dagno, IEEE Tran. Energy Converon, vol. 4, n 4, December 999, pp [3] A.H. Bonnett et al., Squrrel-cage rotor opton for ac nducton motor, IEEE Tran. 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Schoen et al., Evaluaton and mplementaton of a ytem to elmnate arbtrary load effect n current-baed montorng of nducton machne, IEEE Tran. Indutry Applcaton, vol. 33, n, November-December 997, pp [] M.E.H. Benbouzd et al., Inducton motor fault detecton and localzaton ung tator current advanced gnal proceng technque, IEEE Tran. Power Electronc, vol. 4, n, pp. 4-, January 999. [] A.M. Trzynadlowk et al., Dagnotc of mechancal abnormalte n nducton motor ung ntantaneou electrc power, IEEE Tran. Energy Converon, vol. 4, n 4, December 999, pp [3] T.W.S. Chow et al., Three phae nducton machne aymmetrcal fault dentfcaton ung bpectrum, IEEE Tran. Energy Converon, vol. 0, n 4, December 995, pp [4] S.M. Kay, Modern Spectral Etmaton, Prentce-Hall Sgnal Proceng Sere, 988. [5] A.A. Da Slva et al., Rotatng machnery montorng and dagno ung hort-tme Fourer tranform and wavelet technque, Proceedng of the 997 Internatonal Conference on Mantenance and Relablty, Knoxvlle (USA), vol., pp [] W.J. 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7 Fg.. Inducton motor component falng rate veru urvey [] (a) Current pectrum wth an eccentrc argap and a contant load torque. Fg..Vew of a cage nducton motor. (b) Current pectrum wth an eccentrc argap and a load torque ocllaton. Fg. 5. Load torque ocllaton effect. 3 Source IM Load SAMPLER Analog 50 Hz Notch Flter Low Pa Flter A/D Converter Fg. 3. Four type of rollng-element bearng malgnment. Potproceeur Dagnotc Algorthm Fault Detecton Preproceeur FFT & Averagng Fg.. Sngle-phae tator current montorng cheme. Fg. 4. Ball bearng dmenon. (a) (b) Power pectrum around 50 Hz. Fg. 7. Stator current power pectra of healthy motor.

8 (a) Stator voltage unbalance. (b) Stator open phae. Fg. 8. Stator current power pectra of faulty motor. (a) STFT. Fg.. Malgnment detecton. (b) STFT and wavelet technque. 8 Healthy motor q-ax tator current (A) Fg. 9. Power pectrum of the ntantaneou power Voltage unbalance d-ax tator current (A) Fg. 3. Stator current Park vector pattern. (a) Healthy motor. Fg. 0. Bpectrum. (b) Stator wndng fault Condton. Ampltude (A) Frequency (Hz) (a) Healthy nducton motor. (a) Healthy motor. Ampltude (A) (b) Stator voltage unbalance. Fg.. MUSIC frequency etmate. Frequency (Hz) (b) Four contguou broken rotor bar. Fg. 4. Spectrum of the tator current Park vector ac level.

9 Tranng Data Tetng Data Preproceng Preproceng Tranng Tetng Pot Proceng Decon Fg. 5. Block dagram of the adaptve tattcal tme-frequency fault detecton technque. Data Bae Mohamed El Hachem BENBOUZID (S 9- M 94-SM 98) wa born n Batna, Algera, n 98. He receved the B.Sc. degree n Electrcal Engneerng, n 990, from the Electrcal Engneerng Inttute of Batna Unverty, Algera; the M.Sc. and Ph.D. degree both n Electrcal and Computer Engneerng, from the Natonal Polytechnc Inttute of Grenoble, France, n 99 and 994 repectvely. After graduaton, he joned the Unverty of Pcarde Jule Verne, France, where he an Aocate Profeor of Electrcal and Computer Engneerng at the Profeonal Inttute of Amen. In November 00, he receved the Habltaton à Drger de Recherche degree from the Unverty of Pcarde Jule Verne. H current reearch nteret nclude electrc machne and drve, computatonal of electromagnetc, and electromechancal actuaton, a well a technque for energy avng. (a) Normal mode. Gerald B. Klman (S 5 M 55 SM 79 F 9) receved the S.B., S.M., and Sc.D. degree from Maachuett Inttute of Technology, Cambrdge, n 955, 959, and 95, repectvely. Followng graduaton, he wa an Atant Profeor of Electrcal Engneerng at Renelear Polytechnc Inttute, Troy, NY. He then had everal agnment n the Tranportaton Dvon of General Electrc Company, where he worked on adjutablepeed drve, hgh-peed lnear nducton motor, and large electromagnetc pump. He wa wth Corporate Reearch and Development, General Electrc Company, Schenectady, NY, where he conduct fundamental tude of lnear, ynchronou, permanent-magnet, and nducton motor, advanced drve ytem for tracton, the development of hgh-effcency and hgh-peed motor, and the applcaton of new developng magnetc and nonmagnetc materal and nulaton. A major empha ha been the development of fault and ncpent fault detecton technque for electrc motor and drve. He retred from GE n November 00 and became a Reearch Profeor at the Electrcal, Computer & Sytem Engneerng department of the Renelaer Polytechnc Inttute, Troy, NY. Prof. Klman an Aocate Edtor of Electrc Machne and Power Sytem. He the holder of 45 US patent and the author of numerou publcaton. (b) Faulty bearng. Fg.. Tme-frequency pectrum of an nducton motor.