ISSN Print ISSN Online nternational ournal of dvanced esearch in lectrical lectronics - PDF document

ISSN (Print) : 2320 – 3765 ISSN (Online): 2278 – 8875 I nternational J ournal of A dvanced R esearch in E lectrical, E lectronics and I nstrumentation E ngineering Vol. 2, Issue 7 , Ju ly 2013 Copyright to IJAREEIE www.ijareeie.com 2901 S TATO R WI N D I N G FAULT DIAGNOSIS OF THREE - PHASE INDUCTION MOTOR BY PARK’S VECTOR APPROACH S.M. Shashidhara 1 , Dr.P. S . Raju 2 Professor . of EC E, Proudhadevaraya Institute of Technology, Hospet, India 1 Professor, Dept . of EEE, SVU College of Engineering, Tirupati , India 2 Abstract: Through this paper issue of on - line detection of short winding fault in three - phase induction motors is presented, and a technique, based on the computer - aided monitoring of the stator current Park’s Vector, is proposed. The park's vector model is realize d by employing Virtual instrumentation. The Virtual Instrumentation is acquired by programming in Lab - view software. Laboratory analysis was performed on a 0.5 hp three phase induction motor. The motor was originally evaluated under optimum circumstances a nd Park's vector model was sketched. Subsequently, the short winding fault is reproduced in the motor. The motor was scrutinized again under erroneous condition and Park's vector model was sketched. Both plots were then scrutinized. It is ascertained that current park's vector pattern of healthy motor was perfect circle meanwhile current park's vector pattern under faulty condition was elliptical in shape. Experimental conclusion, derived by employing a distinct fault producing test rig, illustrate the effi ciency of - phase induction machines. Ke y w o r d s : Induction motor, S tator w i nd i ng inter - turn f au lt , Pa r k’s v e c to r, Lab V I E W . I. I N T R ODU C T I O N There is a consensus that 35 - 40 % of induction motor breakdowns are attribuetd to the stator winding insulation [1]. Furthermore, it is normally assumed that a significant part of stator winding - connected failures are instigated by insulation failures in multiple turns of a stator coil within one phase. This kind of fault is known as a “stator turn fault” [2]. A stator turn fault in a symmetrical three - phase AC machine triggers a high circulating current to flow and therefore produces unwarranted heat in the shorted turns. If the heat relative to the square of the circulating current stator turn fault may be a severe accident concerning loss of life. The organic materials employed for insulation in electric machines are prone to degradation from a combination of thermal overloading and cycling, transient voltage stresses on the insulating material, mechanical stresses, and impurities. Among t he probable causes, thermal stresses are the primary cause for the deterioration of the stator winding insulation. Stator winding insulation thermal stresses are classified into three categories: aging, overloading, and cycling [4]. Even the most superior insulation may fall short if motor is run beyond its temperature li m i t . As a convention , t he l i f e span o f the i nsu l a t i on i s diminished by 50% f o r e v e r y 10 º C raise over t he s t a t or w i nd i ng t e m p e r a t u r e li m i t [ ] . Therefore it is necessa r y t o check t he s t a t or w i nd i ng t e m p e r a t u r e so t hat an e l ec tr i cal m ach i ne won’t ope r a t e past i t s t he rm al capac i t y . For t h i s reason, numerous methods ha v e been put forward [ 6 ] - [ 8 ] . Nonetheless , t he i nhe r ent constric t i on o f t hese methods i s t he i r i ncapacity t o perceive a restricted h ot sp o a t i t s primitive s t a g e. Some m echan i cal difficulties t h a t hasten i nsu l a t i on de g r ad a t i on i nc orporates m o v e m ent o f a co il , v i b r a t i on due to r o t o r unba l ance, slack or w o r n bea r i n g s, a i r gap peculiarity, and damaged r o t or b a r s . T h e cu rr e n t i n t he s t a t o r w i nd i ng results in a f o r ce on t he co il t hat i s p r opo r t i onal t o t he s q u a r e o f t he c u rr e n t . T h i s f o r ce i s at i t s greatest un d er t r ans i ent o v e r l oads, resulting in t he co il s t o pulsate at t w i ce t he s y nch r onous fr e q uency wi t h shifting i n bo t h t he r ad i al and t he t a n g en t i al d i r ec t i on. T h i s m o v e m ent deteriorates t he reliability o f t he i nsu l a t i on s y s t e m . M echa n i cal f au l t s , such as damaged r o t or ba r , w o r n bea r i n g s , and a i r - g ap eccen tr i c i t y , m ay be a cause w hy t he r o t or hits t he s t a t o r w i nd i n g s. Hence , such m echan i cal f a il u r es shou l d be identified b e f o r e t hey breakdown t he s t a t o r ISSN (Print) : 2320 – 3765 ISSN (Online): 2278 – 8875 I nternational J ournal of A dvanced R esearch in E lectrical, E lectronics and I nstrumentation E ngineering Vol. 2, Issue 7 , Ju ly 2013 Copyright to IJAREEIE www.ijareeie.com 2902 w i nd i ng i n s u l a t i on [ 9 , 10 ] . C on t amination due t o unknown m a t e r i a l s can result in undesirable outcomes on t he s t a t or w i nd i ng i nsu l a t i on. T h e p r esence o f f o r e i gn contaminants can cause a decline i n heat d i ss i pa ti on [ 11 ] . I t i s t herefore of utmost i m po r t ant t o k eep t he m o t o r s dirt free and d r y , in particular w hen t he m o t o r s runs i n a ho s t il e en v ir on m e n t . Despite o f t he cau s es, s t a t o r w i nd i n g - r e l a t e d breakdown can be segregated i n t o f i v e types : t u r n - t o - t u r n , co il - t o - co il , li ne - t o - g r ound, line - t o - li ne, and open - c ir cu i t f au l t s . A mong t h e f i v e f a il u r e m odes, t u r n - t o - t u r n f au l t s ( s t a t or t u r n f au lt ) is supposedly t he m o s t cha ll en g i ng one s i nce t h e o t her forms o f breakdowns a r e genera ll y t he result o f t u r n f au l t s . Fig . 1. Stator winding faults of Induction Motor In addition, t u r n f au l t s a r e v e r y arduous t o identify at t he i r primitive juncture. To crack t he d i f f i cu l t y i n identifying t u r n f au l t s , m any techniques ha v e been de v ised [ 12 ] - [ 1 4 ] . I n this thesis, sh o r t wi nd i ng f au l t i s d i a g nos e d w i t h P a r k ' s V ec t o r method. II . D E T E C T I O N O F FAU L T S U SI N G PA R K’S V E C TO R METHOD One of the difficulties encountered in the analysis and description of the behavior of most rotating electric machines is that the inductances are functions of the relative position of the rotor and stator. In order to simplify the study of the electrical machines R.H. Park formulated a transformation that made their analysis more straightforward by transforming the motor equatio ns into a two - phased orthogonal frame of reference. The transformation of the three - phased system to the two - phased orthogonal system can be performed upon: (1) where f is the function to be transformed (it can be the current, voltage or magnet ic flux). The Park transformation matrix is given by: ISSN (Print) : 2320 – 3765 ISSN (Online): 2278 – 8875 I nternational J ournal of A dvanced R esearch in E lectrical, E lectronics and I nstrumentation E ngineering Vol. 2, Issue 7 , Ju ly 2013 Copyright to IJAREEIE www.ijareeie.com 2903 (2) θ=ωt being the angular displacement. By using the above transformation the orthogonal components of the Park's current vector can be computed from the symmetrical three - phase d current system, having the components: ia, ib and ic: (3) If the reference is fixed in the stator of the machine the above equation becomes: (4) When the induction machine , if healthy , its three - phased stator current system is perfectly symmetric: (5) Where I is the maximum value of the supply phase current, ω s is the supply frequency and t is the time variable. In this case by replacing (5) in (4) the following equation can be obtained for the two orthogonal components of Park's current vector in the case of a healthy electrical motor : (6) Upon equation (6) it can be expressed that a healthy machine shows a perfect circle in Park's vector representation, as shown in Fig 4. When any type of fault occurs the three - phased current phase current system becomes unbalanced. This results in an elli ptic representation of the Park's current vector. Its representation is a circular pattern centered at the origin of the coordinators as depicted in Fig 2. It’s a straightforward reference figure that permits the identification of anomalous conditions by observing the deviations of acquired patterns. ISSN (Print) : 2320 – 3765 ISSN (Online): 2278 – 8875 I nternational J ournal of A dvanced R esearch in E lectrical, E lectronics and I nstrumentation E ngineering Vol. 2, Issue 7 , Ju ly 2013 Copyright to IJAREEIE www.ijareeie.com 2904 Fig . 2 : Stator C u r r ent P a r k ’ s v ec t or f o r i deal cond i t i on. Short winding fault can be effectively diagnosed with Park’s vector approach. The study of the three - phase induction motor can be simplified with the help of the Park transformation. This technique is based on the visualization of the motor current Park’s vector model. If it’s a perfect circle then the machine can be considered as healthy. If the observed pattern is elliptical, the machine is errone ous. Using the features of the ellipse, the fault's type can be determined. The ellipticity amplifies with the acuteness of the fault. III. E X PE R I M EN T AL S E TUP To determine the fault of induction motor with high precision, a modern laboratory test bench was arranged . Fig 3 shows schematic diagram of the induction motor test facility. The system consists of an induction motor, variable speed controller, supporting bearings, couplings and DC generator as a load, NI data acquisition card PCI - 6251, data acqui sition board ELVIS and Pentium - IV Personnel Computer with software LabVIEW 8.2. Rated da t a o f t he t e s t ed t h r e e - phase s q u i rr el c a ge i nduc t i on m ach i ne w e r e: 0. 5 hp, 415 V , 1 . 05 A and 1380 ( FL) r/m i n . T he constrain t s o f m o t or employed i n t he e x pe r i m e n t a r e provided i n T ab l e 1. L a b V I E W 8 . 2 s o ft w a r e has been employed t o scrutinize the s i g na l s. I t’s simple t o obtain any m easu r e m ent w i t h N I Lab V I E W . Fig . 3 . Schematic diagram of the experimental setup The measurements may be automated from multiple devices and the acquired data can be evaluated simultaneously using LabVIEW. Data acquisition card PCI - 6251 and acquisition board are employed to obtain the current samples from the motor under load. NI high - speed multifunction data acqu isition (DAQ) device can estimate the signal with enhanced precision at high speed sampling rates. The apparatus has six DMA channels for high - speed data output. Onboard is a NI - PGIA2 amplifier fabricated for fast settling times at high reading rates, whic h ensure 16 - bit accuracy even when estimating all channels at maximum speeds. This apparatus has 24 digital I/O lines, a minimum of 16 analog inputs, seven programmable input ranges and two counter/timers. The NI ELVIS incorporates 12 of the most freque ntly used devices - comprising the oscilloscope, DMM, function ISSN (Print) : 2320 – 3765 ISSN (Online): 2278 – 8875 I nternational J ournal of A dvanced R esearch in E lectrical, E lectronics and I nstrumentation E ngineering Vol. 2, Issue 7 , Ju ly 2013 Copyright to IJAREEIE www.ijareeie.com 2905 generator, and Bode analyzer - into a compressed form suitable for the hardware lab. Based on NI LabVIEW graphical system design software, NI ELVIS provides the tenacity of virtual instrumentat ion and permits for speedy and simple measurement acquirement and display. In the study, the speed of the motor is computed by digital tachometer. The virtual instrument (VIs) was set up using programming in LabVIEW 8.2. The VIs was employed both for manip ulating the test measurements and data acquisition . In order to assess the system under practical conditions, numerous measurements were made to obtain the stator current of the motor. The 3 - ph IM is of 415V, 0.5 hp, f=50Hz, 1500 rpm, 2 pole pairs and 36 r otor slots. T o obtain t he P a r k ’ s v ec t or pa tt e r n, t he p r o g r a m m i ng i s performed w i t h s i g nal p r ocess i ng m odu l e o f Lab V I E W s o ft w a r e. The i nduc t i on m o t or was initially scrutinized , i n t he absence o f f au lt s so as t o find t he r e f e r ence cu r r ent P a r k ’ s v e ct or pa t t e r n relative t o t he su p posed optimum m o t o r . Later , sh o r t c i r cu i t ed m o t or w as evaluated . A t i m e w i ndow of 17 5 m s w as employed f or a l l da t a a c q u i s i t i on so as t o obtain a s i m p l e and d e t a il ed pa tt e r n. T he s a m p l e r a t e w as 2000 sa m p l e / secon d . T h e nu m b e r o f s a m p l es taken was 35 0 . IV. OBSERVATIONS Fig 4 illustrates a C u rr e n t P a r k ’ s v ec t o r p a tt e r n f o r optimum m o t or w h i ch i s a pe r f e ct c i r c l e in which i ns t an t aneous m a g n i t ude i s unvarying . Fig . 4. The plot of Park’s current vector for a healthy machine An u nbalance due t o sh o r t w i nd i ng f a u l t s r esu l t s i n diverse r ep r ese n t a t i on o f t he pa r k ’ s v ec t or i s depicted i n Fig 5 . I t can be noted t hat cu rr ent pa tt e r n f or erroneous m o t or i s obviously d i f f e r ent fr om that o f t he optimum m o t o r . T he shape o f t he c u rr e n t' s ph a sor i n Fig 5 i s n o t o f a p e r f e c t c i r cle. The e lli p t i cal shape of cu rr e n t ’ s phasor shows sho r t w i nd i ng f au l t i n t he s q u ir r el c a g e i nduc t i o n m ach i ne. Hence , by evaluating t he cu r r ent p a tt e r n o f hea l t hy and f a u l t y m o t o r , t he sh o r t w i nd i ng f au l t can be eas il y identified. ISSN (Print) : 2320 – 3765 ISSN (Online): 2278 – 8875 I nternational J ournal of A dvanced R esearch in E lectrical, E lectronics and I nstrumentation E ngineering Vol. 2, Issue 7 , Ju ly 2013 Copyright to IJAREEIE www.ijareeie.com 2906 Fig . 5. The plot of Park’s current vector for a faulty machine V. C ON C L U SI O NS With the help of t h i s paper a m e t hodo l o g y by w h i ch i nd u c t i on m o t o r s e l e c tr i cal f au l t s c a n be identified by observing t he s t a t or cu r r ent has been proposed . T he suggested technique w as based on t he P a r k ’ s v ec t or ap p r oach. S t a t o r c u rr e n t P a r k ’ s v ec t or p a tt e r n s were employed t o d istinguish b e t w een ' hea l t h y ' and ' f au l t y ' i n duc t i on m o t o r . T he r es u l t s derived fr o m t he e x pe r i m ent prove t hat c u rr e n t pa r k ' s v ec t or p a t t e r n o f hea l t hy m o t or w as pe r f e c t c i r c l e w h il e cu rr e n t p a r k ' s v ec t or pa tt e r n under f a u l t y cond i t i on w as e lli p t i cal i n shape. Using this , t he sh o r t wi nd i ng f au l t o f i nduc t i on m o t o r can be eas il y determined by evaluating t he P a r k ' s v ec t or r ep r ese n t a t i on s . Hence , t he l abo r a t o r y e x pe r i m ent establishes t he efficiency and e f f e c t i v eness o f t h i s method i n area o f c o m pu t er a i ded c ond i t i on m on i t o r i ng o f i n duc t i on m ach i nes. R EFERENCES [ 1] I AS M R W o r k i n g G r ou p , “ R epo r t o f l a r g e m o t or r e li ab ili t y s u r v ey of i ndus tr i al and co mm e r c i al i ns t a ll a t i on, I EE E T r an s . I n d us tr y A pp li ca t i ons, v o l . I - A - 21, p p . 85 3 - 86 4 , Ju l / Au g , 198 5 . [ 2] J. S o t t il e et al, “ An on - li ne m e t h o d t o de t ect i nc i p i ent f a il u r e o f t u r n s i nsu l a t i on i n r ando m - w ound m o t o r s , ” I EE E T r ansaction on E ne r gy C onve r s i on, v o l . 8, no 4, pp. 762 - 76 8 , D ec , 199 3 . [ 3] S . B .Lee, R . M . T a ll a m , and T. G . H abe t l e r , “ A r obus t , on - li ne t u r n - f a u l t de t ec t i on t echn i q ue f or i nduc t i on m a ch i nes based on m on i t o r i n g t he se q uence c o m pone n t i m pedance m a tr i x , ” I EE E T r an s actions P o w e r El ec t r on i cs, v o l . 18, n o.3, pp. 865 - 87 2 , M a y , 2003. [ 4] A. H . B onnet and G . C . S ou k up, “ C ause and ana l y s i s of s t a t o r and r o t or f a il u r es i n t h r e e - phase s q u ir r el case i nduc t i on m o t o r s , ” I EE E T r a n s. I ndu s tr y A pp li ca t i on, v o l . , 28, no . , 4, pp.921 - 937, Ju l / Au g , 1 9 92. [ 5] T. A.L i po, “ I n t r oduc ti on of AC m ach i ne des i gn ” , W i scons i n P o w e r El ec tr on i cs R esea r c h C en t e r , 2nd e d i t i on, 20 0 4. [ 6] S . F. F a r a g , R . G . B a rt he l d, and W . E . M a y , “ El ec tr on i ca ll y enha n ced l o w v o l t a g e m o t o r p r o t e c t i on and con tr o l, ” I EE E T r ans. I ndu s tr y A pp li ca t i ons, v o l . 29, no.1, pp. 45 - 5 1 , Jan / Fe b , 1994. [ 7] J . T. B o y s and M . J. M il es, “ E m p i r i cal t h e r m al m odel f or i n v e rt e r - d r i v en ca g e i nduc t i on m ach i nes , ” I E E P r o c . , E l ec t r . P o w er A pp li ca t i on, V o l . 141, pp. 360 - 37 2 , 1 994. [ 8] S . B. Lee and T . G . H abe t l e r , “ An on li ne s t a t or wi nd i ng r es i s t ance e s t i m a t i on t echn i q ue f o r t e m p e r a t u r e monitoring of line - conne c t ed i nduc t i on m ach i nes , ” I E E E T r ans. I nd u s t r y A pp li ca t i ons, v o l . 39, no.3, p p . 68 5 - 694, M a y / Ju n , 200 3 . [ 9] W .L. R ou x et al “ D e t ec t i n g r o t or f au l t s i n pe rm anent m a g net s y nch r onous machines , ” i n C on f . R ec. SDEMPE D ’ 03, pp. 198 - 20 3 , A tl an t a, G A , US A, Au g u s t , 2003. [ 10] J . R . S t a c k, T. G . H abe t l e r , and R . G . H a rl e y , “ B ea r i ng f au l t d e t ec ti on v i a au t o r e g r e ss i v e s t a t o r cu r r ent m ode li ng , ” I EE E T r ans. I ndu s tr y A pp li ca t i ons, v o l . 40, no.3, pp. 74 0 - 747, M a y / Jun, 2004. [ 11] M .A. C ash, “ D e t e c t i on o f t u r n f au l t s a r i s i ng f r om i nsu l a t i on f a il u r e i n t he s t a t o r w i nd i n g s o f AC m ach i nes , ” D o c t o r al Di sse rt a t i o n , D ep t . o f El ec tr i cal and C o m p u t er E n g i nee r i n g , G e o r g i a I ns t i t u t e o f T echno l o g y , US A, 1998. [ 12] D . E . S ch u m p, “ Pr ed i ct m o t or f a il u r e w i t h i nsu l a t i on t es t i n g , ” P u l p and P aper I ndu s t r y Tech C on f e r ence 199 7 , p p . 48 - 5 0 , Ci nc i nna t i , OH , US A, Jun, 1997. [ 13] D . E . S ch u m p, “ R e li ab ili t y t es t i ng o f e l e c tr i c m o t o r s , ” I EE E T r ans I n d us tr y A pp li ca t i ons, v o l . 25, n o . 3 , p p . 38 6 - 390, M a y / Jun, 1989. [ 14] R . M a i e r , “ P r o t ec t i o n o f s q u ir r e l - c a g e i ndu c t i on m o t or u t ili z i ng i ns t a n t aneous po w er and phase i n f o r m a t i on , ” I EE E T r ans. I ndu s tr y A p p li ca t i ons, v o l . 28, pp. 376 - 3 80 , M a r/ Ap r , 1992. [ 15] A.J. M . C a r doso et a l. , “ C o m pu t e r a i ded d e t ec ti on of a ir gap e ccen t r i c it y i n ope r a t i ng 3 - phase i nduc t i on m o t o r s by P a r k ’ s v ec t or ap p r oac h ” I EE E T r an actions . On I nd u s t r i al A pp li ca t i ons , v o l .29, pp. 897 – 901, S e p /O c t 19 9 3.