Separating Broken Rotor Bars and Load Oscillations on IM Fault Diagnosis Through the Instantaneous...

IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 56, NO. 11, NOVEMBER 2009 4571

Separating Broken Rotor Bars and Load Oscillationson IM Fault Diagnosis Through the Instantaneous

Active and Reactive CurrentsGuillermo R. Bossio, Member, IEEE, Cristian H. De Angelo, Member, IEEE, José M. Bossio,

Carlos M. Pezzani, and Guillermo O. García, Senior Member, IEEE

Abstract—A new method for broken rotor bars and load oscil-lation diagnosis on induction motors is presented. The proposedstrategy is based on the decomposition of the stator currents intotheir instantaneous active and reactive current components. Suchcomponents allow the decoupling of the effects produced by rotorasymmetries from those produced by oscillating loads. This allowsnot only the proper fault detection but also a correct fault diag-nosis. Simulation and experimental results, both from laboratoryand industrial cases, are presented to validate the proposal.

Index Terms—Broken rotor bar, fault diagnosis, inductionmotor (IM), instantaneous active and reactive currents, loadoscillations.

I. INTRODUCTION

EVEN WHEN vibration analysis has been used for along time as a tool for predictive maintenance and con-

dition monitoring of rotating machines, motor current sig-nature analysis (MCSA) is the most simple and acceptedmethod for detection of rotor asymmetries of induction motors(IMs) [1].

MCSA is based on the analysis of the spectrum componentsof one or more motor currents, when the motor is at steady state.Then, rotor asymmetries are detected through the presenceof sideband components around the fundamental component[2], [3].

However, some load torque oscillations or mechanical loadabnormalities may produce similar effects in the current spec-trum (i.e., sidebands at similar frequencies), making the rotorfault diagnosis difficult.

Manuscript received November 27, 2008; revised May 27, 2009. Firstpublished June 10, 2009; current version published October 9, 2009. This workwas supported in part by the Universidad Nacional de Río Cuarto, by FONCyT-ANPCyT, by MinCyT-Cba, and by the Consejo Nacional de InvestigacionesCientíficas y Técnicas.

G. R. Bossio, C. H. De Angelo, J. M. Bossio, and G. O. García arewith the Grupo de Electrónica Aplicada, Facultad de Ingeniería, UniversidadNacional de Río Cuarto, Río Cuarto X5804BYA, Argentina, and also with theConsejo Nacional de Investigaciones Científicas y Técnicas, Argentina (e-mail:[email protected]; [email protected]; [email protected]; [email protected]).

C. M. Pezzani is with the Grupo de Electrónica Aplicada, Facul-tad de Ingeniería, Universidad Nacional de Río Cuarto, Río CuartoX5804BYA, Argentina, and also with FONCyT-ANPCyT, Argentina (e-mail:[email protected]).

Digital Object Identifier 10.1109/TIE.2009.2024656

In the case of broken rotor bars, they introduce a rotorasymmetry which produces a backward-rotating field. Thisfield introduces a lower sideband component in the currentspectrum at twice the slip frequency (2sf). The amplitudeof this sideband will depend on the rotor asymmetry and themotor load level [4]. A torque pulsation at twice the slipfrequency is also produced by this rotor asymmetry, resultingin a speed oscillation at the same frequency, which introducesthe upper and lower sidebands in the current spectrum. Thisphenomenon continues, producing multiple sidebands whoseamplitude depends on the load level and the drive inertia [5].

On the other hand, load torque oscillations produced byeither an abnormal mechanical load condition (unbalanceand misalignment), the load characteristics (e.g., reciprocatingloads), or a defective transmission produce a speed oscillation atthe perturbation frequency (fl), which is also seen as sidebandcomponents at ±fl in the current spectrum [6], [7]. Thus, ifthe frequency of the speed oscillation is low, close to twicethe slip frequency, it may be difficult to detect and diagnosea rotor asymmetry. A similar problem occurs when trying toseparate the effects of rotor eccentricities and load oscillationsat the rotor frequency [8].

Some proposals addressing this problem have been publishedin the literature in the last several years [6]. By measuring onlyone stator current, the separation of the effects can be possiblein certain applications through the analysis of the sidebands athigher current harmonics [9], [10]. Other techniques such ascurrent Park’s vector approach, space vector angular fluctua-tion, and pendulous oscillation approach [11] have been pro-posed for broken rotor bar detection, but their effectiveness inthe case of time-varying loads is not clear. A technique based onthe negative sequence harmonic information was also presentedfor these cases [12]. Other techniques such as model-basedschemes [13], [14] and Vienna monitoring methods [15] haveshown some good properties for detecting broken rotor barsand rotor eccentricity, even in the presence of some types oftime-varying loads, but they are highly dependent on parametervariations. The analysis of the instantaneous power spectrumwas presented in [16], while the instantaneous reactive power,the complex power, and instantaneous power factor were alsoproposed for rotor fault and mechanical abnormality detectionin [17]–[19]. The use of the instantaneous active and reactivepowers and their ratios to diagnose broken rotor bars androtor eccentricity is proposed in [20]. These techniques have

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4572 IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 56, NO. 11, NOVEMBER 2009

the advantage of avoiding the fast Fourier transform leakageproblem, but their ability to separate load oscillations fromrotor asymmetries is not demonstrated in these papers. Finally,some proposals combining the previous methods with artificialintelligence [5], [21], transient [22], [23], and time-frequencyanalysis [7], [24] have also been proposed.

In this paper, a new strategy for separating the effects ofbroken rotor bars from oscillating loads in the current spectrumof steady-state operating motors is presented. The proposedstrategy is based on current decomposition into their active andreactive components [25] and allows rotor fault detection anddiagnosis in the case of pulsating loads. The main contributionof this paper is a simple and powerful strategy, which allowsa correct detection and diagnosis of broken bars even whenthe frequency of the pulsating load is next to twice the slipfrequency. Moreover, the proposed strategy allows the user to“see” the diagnosis information in the same way as in thewell-known MCSA, i.e., as sidebands next to the fundamentalcurrent component. However, such information is shown in twoseparated spectra, one for rotor asymmetries (broken bars) andthe other for load oscillations.

In the following section, the fault diagnosis strategy is devel-oped, including a detailed analysis of the generation of the side-band components. The behavior of the proposed strategy underdifferent operating conditions is analyzed through simulationin Section III. Experimental results, including laboratory andindustrial cases, are presented in Section IV, while conclusionsare drawn in Section V.

II. FAULT DETECTION THROUGH INSTANTANEOUS ACTIVE

AND REACTIVE CURRENTS

A. Instantaneous Active and Reactive Currents

The theory of the instantaneous active and reactive power (orp–q theory) has been proposed by Akagi et al. in 1983 [26] andused for a long time for power quality analysis and active powerfilter design [25].

A three-phase system can be represented in a stationaryreference frame (α–β) by means of the Clarke transformation.If there is no neutral connection, the three phase currents arerepresented in this frame by two components iα and iβ .

According to the instantaneous power theory, the instanta-neous current iα can be separated into two components: theinstantaneous active current iαp and the instantaneous reactivecurrent iαq .

These components are obtained by first calculating theinstantaneous active power in terms of the Clarke compo-nents, as

p = vαiα + vβiβ (1)

and the instantaneous reactive power as

q = vβiα − vαiβ (2)

where vα and vβ are the instantaneous voltages in the stationaryreference frame.

Then, the instantaneous active current on the α axis is

iαp =vα

v2α + v2

β

p (3)

and the instantaneous reactive current results in

iαq =vβ

v2α + v2

β

q. (4)

For the β axis, the instantaneous active and reactive cur-rents are

iβp =vβ

v2α + v2

β

p (5)

iβq =−vα

v2α + v2

β

q (6)

respectively.By replacing (1) and (2) in (3) and (4), the expressions for

the instantaneous active and reactive currents are obtained as afunction of the α−β voltage and current components

iαp =v2

αiα + vαvβiβv2

α + v2β

(7)

iαq =v2

βiα − vβvαiβ

v2α + v2

β

. (8)

The instantaneous reactive currents do not contribute to theenergy transferred between the source and the load at any time.These currents correspond to the energy exchanged betweenthe three phases [25]. On the other hand, any load oscillationor mechanical disturbance requires the interchange of powerwith the source (active power). Thus, in a first analysis, it seemslogical to think that the effects of the mechanical load will notinfluence these instantaneous reactive currents. Even when amore complicated interaction exists between torque, flux, andcurrents on the IM, this simplified hypothesis suggests the basisfor the proposed separation strategy.

B. Effects of Broken Rotor Bars and Oscillating Loads

As stated earlier, broken rotor bars and oscillating loadsproduce sidebands near the fundamental component of thephase currents. In the case of broken bars, these sidebandsare produced by the interaction of the fundamental currentwith a backward-rotating field due to rotor asymmetry whichproduces, in turn, torque oscillations. These oscillations intro-duce a current modulation which is seen as lower and uppersidebands near the fundamental current and its harmonics. Asimilar effect is produced when the stator current is modulatedby an oscillating load torque.

In this paper, only the case of oscillating loads at lowfrequencies, close to twice the slip frequency, is considered,since they can obscure a broken rotor bar diagnosis. Loadoscillations at higher frequencies, close to the rotor frequency,can be confused with eccentricity faults but not with brokenbars [8]. Such load problems are beyond the scope of this paper.

BOSSIO et al.: SEPARATING BROKEN ROTOR BARS AND LOAD OSCILLATIONS 4573

In order to analyze the effects of broken rotor bars or oscil-lating loads over the instantaneous active and reactive currents,the modulated currents are expressed as

iα = If cos(ωt − ϕ) + Il cos ((ω − ωb)t − ϕl)+ Iu cos ((ω + ωb)t − ϕu)

iβ = If sin(ωt − ϕ) + Il sin ((ω − ωb)t − ϕl)+ Iu sin ((ω + ωb)t − ϕu) (9)

where If and ϕ are the magnitude and phase of the fundamentalcurrent component, and Il, Iu and ϕl, ϕu are the magnitudeand angular displacement of the lower and upper sidebandcomponents, respectively. ω is the fundamental frequency, andωb � ω is the disturbance frequency.

Assuming a nondistorted voltage

vα = Vf cos(ωt)vb = Vf sin(ωt) (10)

with Vf being the magnitude of the fundamental voltage, theinstantaneous active and reactive powers will be

p(t) = VfIf cos ϕ + VfIl cos(ωbt + ϕl)+ VfIu cos(ωbt − ϕu) (11)

q(t) = VfIf sin ϕ + VfIl sin(ωbt + ϕl)− VfIu sin(ωbt − ϕu) (12)

respectively.By grouping terms of the same frequency, the instantaneous

active and reactive powers result in

p(t) = P0 + Pb cos(ωbt + ϕp) (13)

q(t) = Q0 + Qb sin(ωbt + ϕq) (14)

where P0 and Q0 are the mean values of the active and reactivepowers, and

Pb =Vf

√I2l + I2

u + 2IlIu cos(ϕl + ϕu) (15)

Qb =Vf

√I2l + I2

u − 2IlIu cos(ϕl + ϕu) (16)

are the amplitudes of the low-frequency oscillating compo-nents, produced by the current sidebands, while ϕp and ϕq aretheir angular displacements.

As shown earlier, if the amplitudes of the upper and lowersidebands are similar and the sum of their angular displacementis close to π, the amplitude of the oscillating term of theinstantaneous active power (Pb) is practically null, while anoscillating term remains in the instantaneous reactive power.This is the case of broken rotor bars, as demonstrated in [4].On the other hand, in the case of load oscillations, the sum ofthese angular displacements is approximately 2π [16], and theamplitude of the oscillating reactive power (Qb) is nearly zero.It must be noted that these considerations are only valid for low-frequency load oscillations (close to twice the slip frequency).In the case of higher frequency load oscillations, close to therotor frequency, their effects over the oscillating reactive powerare more important. For such a reason, more complex strategies

are needed to eliminate the effects of load oscillation for motordiagnosis [13].

A further analysis for the broken bar case shows that, onlyif the motor-load inertia is very high (tending to infinity), theamplitude of the upper sideband is very low (Iu ≈ 0) and theamplitudes of the components of both oscillating powers arepractically the same, while their angular displacement is closeto π/2.

From the preceding analysis, it can be concluded that theeffects of broken rotor bars and low-frequency load torqueoscillations can be separated through the analysis of the oscil-lating active and reactive powers. This property can be extendedto the active and reactive current components, allowing the userto “see” the diagnosis information in the same way as in thecommonly used MCSA.

Introducing (13) and (14) in (3) and (4), the instantaneousactive and reactive currents result in

iαp =P0

Vfcos(ωt) +

Pb

2Vfcos ((ω + ωb)t + ϕp)

+Pb

2Vfcos ((ω − ωb)t − ϕp) (17)

iαq =Q0

Vfsin(ωt) − Qb

2Vfcos ((ω + ωb)t + ϕq)

+Qb

2Vfcos ((ω − ωb)t − ϕq) . (18)

From these equations, it can be seen that the instantaneousactive and reactive currents have the same sideband compo-nents as the motor phase currents. However, in this case, theupper and lower sideband components have exactly the sameamplitude. For the instantaneous active current, the amplitudeof their sideband components depends on the amplitude of theoscillating active power Pb. On the other hand, the amplitude ofthe sideband components of the instantaneous reactive currentsis proportional to the amplitude of the oscillating reactive powerQb. The same will be obtained for the β current components.

From the preceding analysis, it can be seen that sidebandcomponents will appear in the instantaneous reactive currentsonly for rotor asymmetries, such as broken rotor bars, while theamplitude of the sidebands of the instantaneous active currentwill be practically null. Conversely, for oscillating load torque,sideband components will be present only in the instantaneousactive currents, but not in the instantaneous reactive currents.

Then, broken rotor bars can be detected and diagnosed bya proper analysis of the sideband components of the instanta-neous reactive current. Moreover, a suitable severity factor canbe established as

SFq =(Iαql + Iαqu)

If× 100% (19)

where Iαql and Iαqu are the amplitudes of the lower and uppersidebands of the instantaneous reactive current, respectively. Itmust be noted that this severity factor results equal to the oneproposed in [4] when the sum of the angular displacements isreplaced by π in (16) and (18). Thus, the proposed severity fac-tor gives an approximate idea of the percentage of contiguousbroken bars.


Fig. 1. Current spectrum analysis, 75% load, three broken bars, and oscil-lating load of 3.5% at 2 Hz. (a) Total current iα. (b) Active current iαp.(c) Reactive current iαq . Simulation results.

III. SIMULATION RESULTS

The proposed strategy was first evaluated by numericalsimulation for different operating conditions, by means ofa multiple-coupled circuit IM model [27]. When using thismodel, inductances are calculated by the 2-D modified windingfunction approach method [28], considering rotor skew andneglecting the effects of saturation and parasitic currents. Inaddition, the broken rotor bars are assumed to be isolated. Theparameters of the simulated motor correspond to the 5.5-kWmotor used for the experimental validation (see Table I).

The results obtained for the simulation of the motor withthree broken rotor bars, 75% of the rated load, and an oscillatingload torque of 3.5% at 2 Hz are shown in Fig. 1. The slipfrequency at this load level is about 0.72 Hz. The spectrum ofthe α current component is shown in Fig. 1(a), while the spectraof the instantaneous active and reactive currents are shownin Fig. 1(b) and (c), respectively. As it can be appreciated,multiple sidebands appear in the spectrum of the α currentcomponent, and there is no possibility to identify a priori whichsidebands are produced by the rotor asymmetry and which onesare produced by the oscillating load. However, the sidebandsare clearly separated in the two spectra of the active and reactivecurrents (Fig. 1(b) and (c), respectively).

Fig. 2. Amplitude of sideband components as a function of the motor-loadinertia for three broken rotor bars, at 75% load. (a) Current iα. (b) Activecurrent iαp. (c) Reactive current iαq . Simulation results.

Fig. 2 shows the variation of the amplitudes of the sidebandcomponents as a function of the inertia, in the case of a rotorasymmetry with a 75% load. As stated by some authors, theamplitudes of the sideband components of the phase currentsare similar for inertia values between 1 and 30 times the motorinertia. For higher inertia values, the amplitude of the uppersideband decreases, while that of the lower sideband increases.This coincides with the result shown in Fig. 2(a) for theα current component. Fig. 2(b) shows the variation of the am-plitude of the sideband components of the active current, whileFig. 2(c) corresponds to the reactive current. As it can be seen,both the upper and lower sidebands have the same amplitudefor each current. However, the amplitude of the sidebands ofthe active currents is practically zero for low values of inertia,and their value increases with the inertia. On the other hand, theamplitude of the sidebands on the reactive currents is practicallyindependent of the inertia, thus being a good indicator of brokenbar faults. It must be noted that for high inertia value, it could benecessary to compare both the instantaneous active and reactivecurrent spectra for a correct diagnosis of the fault origin.

A similar analysis is performed in Fig. 3, but for a healthyrotor with 75% load and an oscillating load of 3.5% at 2 Hz.As shown, the amplitude of the sidebands slightly decreases


Fig. 3. Amplitude of sideband components as a function of the motor-loadinertia for 75% average load plus an oscillating load. (a) Current iα. (b) Activecurrent iαp. (c) Reactive current iαq . Simulation results.

with the inertia for the α current [Fig. 3(a)] and for the activecurrent component [Fig. 3(b)]. However, their amplitude forthe instantaneous reactive current [Fig. 3(c)] is much lowerthan for the active current, independently of the inertia value.This result confirms that load disturbances do not affect theinstantaneous reactive currents. Therefore, the amplitude of thesideband components of the active currents can be considered agood indicator of mechanical oscillations when the amplitudesof the sidebands in the reactive currents are very small.

The proposed severity factor is evaluated by simulation inFig. 4(a), for one, two, and three broken rotor bars, and consid-ering different load conditions. As it can be seen, the proposedseverity factor gives a good difference between fault conditionswhile presenting a low dependence from the load state. This al-lows setting appropriate threshold for fault detection. Fig. 4(b)shows a fault severity calculated as the sum of the amplitudesof the active current sidebands, referred to the fundamentalcurrent. As shown, this severity factor turns out to be more thanten times lower than the proposed one.

IV. EXPERIMENTAL RESULTS

With the aim of validating the proposed strategy, results wereobtained in a laboratory setup and in some industrial cases.

Fig. 4. Fault severity factors for different number of broken bars and loadconditions. (a) Proposed severity factor. (b) Sum of the active current sidebandsreferred to the fundamental α current. Simulation results.

Fig. 5. Experimental setup. (a) IM rotors: Healthy, one, two, and three brokenbars. (b) Laboratory setup.

A. Laboratory Results

An IM with interchangeable rotors was used to test theproposed diagnosis strategy. Four different rotors were usedin the experiments: a healthy rotor and three rotors with one,two, and three broken bars [Fig. 5(a)]. The parameters of themotor under test are shown in Table I. This motor was coupled


Fig. 6. Current spectrum analysis, three broken bars, and 75% load.(a) Total current iα (SF = 3.67%). (b) Active current iαp. (c) Reactivecurrent iαq (SFq = 3.43%). Experimental results.

to an IM drive which acts as a programmable load [Fig. 5(b)].Two phase currents and two line voltages were measuredand registered with an oscillographic recorder. For each test,56 000 samples at 4-kHz sampling frequency were registered.The data were analyzed in a personal computer.

Fig. 6 shows the results obtained for a motor with threebroken rotor bars at 75% load. The frequency spectrum of thetotal α current is shown in Fig. 6(a). As shown, the sidebandcomponents at ±2sf produced by the rotor asymmetry appeararound the fundamental component. By calculating the severityof the fault as the sum of the normalized current sidebands [4],this results in SF = 3.67%. The spectrum of the instantaneousactive current is appreciated in Fig. 6(b), where the amplitudeof the sidebands is significantly lower than those in the totalcurrent. Finally, Fig. 6(c) shows the spectrum of the instan-taneous reactive current, where it can be appreciated that theamplitude of the sideband components is practically equal tothe amplitude of the sidebands of the total α current. In thiscase, the severity factor (19) results in SFq = 3.43%.

The results obtained for the same motor with a healthy rotorand a pulsating load (3% of oscillation at 1.44 Hz) are shownin Fig. 7. The pulsating load was emulated by means of an IMdrive coupled to the tested motor. The torque of this drive wascontrolled, with torque reference composed by a constant value

Fig. 7. Current spectrum analysis, 75% load, and oscillating load of 3%at 1.44 Hz. (a) Total current iα (SF = 3.41%). (b) Active current iαp.(c) Reactive current iαq (SFq = 0.32%). Experimental results.

plus the desired oscillating torque. By comparing Fig. 6(a)with Fig. 7(a), it is found that no difference practically existsbetween the two spectra. This could lead to a confusion witha broken bar fault, with a fault severity of 3.41%. However, asopposed to the broken bar case, sideband currents of the sameamplitude appear in the instantaneous active current spectrum[Fig. 7(b)], while the sidebands on the instantaneous reactivecurrent spectrum are practically negligible [Fig. 7(c)]. Theproposed severity factor, in this case, results in SFq = 0.32%.

In order to analyze the decoupling of the effects produced bythe rotor asymmetries and the load oscillations, experimentalresults were obtained for the motor with three broken rotor barsand different pulsating loads. Fig. 8 shows the current spectrafor a pulsating load of 3% at 2 Hz. The effects of both theelectrical fault and the mechanical one are appreciated in thespectrum of the total current. However, in the spectrum ofthe instantaneous active current, the effects of the rotor asym-metry are almost negligible, while the sidebands produced bythe oscillating load are still present. The opposite occurs in thespectrum of the instantaneous reactive current.

The results obtained for a pulsating load whose frequency isnext to twice the slip frequency are shown in Fig. 9. In this case,the sidebands are very close in the total α current spectrum.However, the same as in the previous cases, both effects are


Fig. 8. Current spectrum analysis, 75% load, three broken bars, and oscillat-ing load of 3% at 2 Hz. (a) Total current iα (SF = 3.74%). (b) Active currentiαp. (c) Reactive current iαq (SFq = 3.57%). Experimental results.

decoupled in the spectra of the instantaneous active and reactivecurrents [Fig. 9(b) and (c)].

The proposed fault severity factor was also evaluated exper-imentally, and the results for one, two, and three broken rotorbars, and considering different load conditions, are shown inFig. 10(a). The same as for simulation, the proposed severityfactor gives a good difference between fault conditions whilepresenting a low dependence from the load state. The faultseverity calculated for the active current sidebands is shown inFig. 10(b).

B. Industrial Cases

The proposed strategy was also tested on different industrialplants. Two industrial cases are presented: an IM with brokenrotor bars and a healthy motor driving an oscillating load.

Fig. 11 shows the results corresponding to a high-pressurepump, operating at 90% load, whose nameplate data are shownin Table II. Once the machine was analyzed with the proposedstrategy, it was verified that this motor had five broken rotorbars. A significant reduction of the sidebands around the fun-damental component can be appreciated in the instantaneousactive current spectrum, while the amplitude of the sidebandsin the instantaneous reactive current spectrum is very similar to

Fig. 9. Current spectrum analysis, 75% load, three broken bars, and oscil-lating load of 3% at 1.5 Hz. (a) Total current iα (SF = 3.49%). (b) Activecurrent iαp. (c) Reactive current iαq (SFq = 3.35%). Experimental results.

Fig. 10. Fault severity factors for different number of broken bars and loadconditions. (a) Proposed severity factor. (b) Sum of the active current sidebandsreferred to the fundamental α current. Experimental results.


Fig. 11. Current spectrum analysis, high-pressure pump. (a) Total currentiα (SF = 5.67%). (b) Active current iαp. (c) Reactive current iαq (SFq =5.32%). Experimental results.

the amplitude of the sidebands of the total current. The resultswere the same as those obtained in the laboratory.

Finally, Fig 12 shows the results obtained for a healthy motordriving an oscillating load. This load consists of a plansifterfor separating the products of cereal milling. Under normaloperating conditions (α = 0), the plansifter behaves as a con-stant load. However, a common problem of this equipmentis produced by the unequal tension of their suspension rods.When this problem occurs, the plansifter is misaligned, and thecentrifugal weight behaves as an oscillating load for the IM (seeFig. 13). The frequency of this oscillation will be the one of thecentrifugal weight. Technical data of the motor are shown inTable III. Unlike the previous case, the sidebands around thefundamental current component [Fig. 12(a)] are produced bythe load torque oscillation, which is typical for the misalignedplansifter. Even when the sidebands are not so close to twicethe slip frequency, the case is useful for validating the proposal.As it can be seen in Fig. 12(b), the sidebands’ amplitude inthe active current spectrum is practically equal to those of thetotal current. However, the sidebands are much lower in theinstantaneous reactive current spectrum [Fig. 12(c)].

All these results demonstrate the capability of the proposedstrategy to separate the effect of rotor faults (broken rotor bars)from oscillating or pulsating loads.

Fig. 12. Current spectrum analysis, misaligned plansifter. (a) Total currentiα (SF = 2.95%). (b) Active current iαp. (c) Reactive current iαq (SFq =0.67%). Experimental results.

Fig. 13. Effect of plansifter misalignment over the IM.

V. CONCLUSION

A new method for separating the effects of rotor asymmetriesfrom those produced by an oscillating load in the current spec-trum has been presented in this paper. The proposed strategyuses a current decomposition into their instantaneous active andreactive components. The analyses and the results demonstrate


that the effects of mechanical oscillations are clearly seen in theinstantaneous active current spectrum, while such abnormalitiesdo not modify the instantaneous reactive current spectrum. Onthe other hand, rotor asymmetries such as broken bars slightlyaffect the instantaneous active currents, but they introduce, in-stead, significant sidebands in the instantaneous reactive currentspectrum.

The simultaneous analysis of both current spectra (active andreactive) allows the detection of these faults and their correctdiagnosis. Moreover, the proposed technique allows performingthe analysis of both types of faults from the sidebands in thecurrent spectrum, which is actually a well-known and acceptedtechnique for predictive maintenance. This represents a greatadvantage for maintenance technicians and nonexpert users.Experimental results, both from laboratory and industrial cases,validate the proposed strategy.

APPENDIX

TECHNICAL DATA AND PARAMETERS OF IMs

TABLE ITECHNICAL DATA AND PARAMETERS OF IM FOR SIMULATIONS

AND LABORATORY EXPERIMENTAL RESULTS

TABLE IITECHNICAL DATA OF IM–HIGH-PRESSURE PUMP

TABLE IIITECHNICAL DATA OF IM–PLANSIFTER

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Guillermo R. Bossio (S’03–M’07) received theElectrical Engineer degree from the UniversidadNacional de Río Cuarto, Río Cuarto, Argentina, in1999 and the Dr.Eng. degree from the UniversidadNacional de La Plata, La Plata, Argentina, in 2004.

Since 1994, he has been with the Grupo deElectrónica Aplicada, Universidad Nacional de RíoCuarto. He is also currently with the Consejo Na-cional de Investigaciones Científicas y Técnicas,Argentina. His research interests include fault diag-nosis on electric machines, sensorless motor control,

electric vehicles, and renewable energy generation.

Cristian H. De Angelo (S’96–M’05) received theElectrical Engineer degree from the UniversidadNacional de Río Cuarto, Río Cuarto, Argentina, in1999 and the Dr.Eng. degree from the UniversidadNacional de La Plata, La Plata, Argentina, in 2004.

Since 1994, he has been with the Grupo deElectrónica Aplicada, Universidad Nacional de RíoCuarto. He is also currently with the Consejo Na-cional de Investigaciones Científicas y Técnicas,Argentina. His research interests include fault diag-nosis on electric machines, sensorless motor control,

electric vehicles, and renewable energy generation.

José M. Bossio received the Electrical Engineerdegree from the Universidad Nacional de Río Cuarto,Río Cuarto, Argentina, in 2006. He is currentlyworking toward the Ph.D. degree in engineering atthe Universidad Nacional del Sur, Bahia Blanca,Argentina.

Since 2001, he has been with the Grupo deElectrónica Aplicada, Universidad Nacional de RíoCuarto. He is also currently with the Consejo Na-cional de Investigaciones Científicas y Técnicas,Argentina. His research interests include fault diag-

nosis on electric machines.

Carlos M. Pezzani received the Electrical Engineerdegree from the Universidad Nacional de Río Cuarto,Río Cuarto, Argentina, in 2007, where he is currentlyworking toward the Ph.D. degree in engineering.

Since 2007, he has been with the Grupo deElectrónica Aplicada, Universidad Nacional de RíoCuarto. He is also currently with FONCyT-ANPCyT,Argentina. His research interests include fault diag-nosis on electric machines.

Guillermo O. García (M’86–S’90–M’95–SM’01)received the Electrical and Electronics Engineeringdegree from the Universidad Nacional de Córdoba,Córdoba, Argentina, in 1981, and the M.Sc. and Dr.degrees in electrical engineering from COPPE, Uni-versidade Federal do Rio de Janeiro, Rio de Janeiro,Brazil, in 1990 and 1994, respectively.

Since 1994, he has been with the UniversidadNacional de Río Cuarto, Río Cuarto, Argentina,where he is currently the Director of the Grupo deElectrónica Aplicada. He is also with the Consejo

Nacional de Investigaciones Científicas y Técnicas, Argentina. His researchinterests include power electronics, electric vehicles, and renewable energyconversion.

Separating Broken Rotor Bars and Load Oscillations on IM Fault Diagnosis Through the Instantaneous...

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