IEEE 2009 Paper - Active Stator Winding Thermal Protection

8/21/2019 IEEE 2009 Paper - Active Stator Winding Thermal Protection

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ACTIVE STATOR WINDING THERMAL PROTECTION FOR AC MOTORS

Pinjia ZhangStudent Member, IEEE

Georgia Institute of Technology777 Atlantic Dr

Atlanta, GA 30332USA

Bin LuSenior Member, IEEE

Eaton Corporation4201 North 27th StreetMilwaukee, WI 53216

USA

Thomas G. HabetlerFellow, IEEE

Georgia Institute of Technology777 Atlantic Dr

Atlanta, GA 30332USA

Abstract — AC motors are the main workhorses inprocess industries. Their malfunction may not only leadto repair or replacement of the motor, but also causesignificant financial losses due to unexpected processdowntime. Reliable thermal protection of ac motors iscrucial for reducing the motor failure rate and prolonginga motor’s lifetime. In this paper, conventional thermalprotection devices and state-of-the-art thermal protectiontechniques are reviewed with their advantages andlimitations discussed. Since 2001, the research team atthe author’s company and at the Georgia Institute ofTechnology has been cooperatively developing a series ofactive motor thermal protection methods, as a low-costalternative approach to the traditional passive and sensor-based methods. These active thermal protection methodsmonitor the average stator temperature via statorresistance estimation based on the dc equivalent model ofac motors, using only motor stator voltage and currentmeasurements. In this paper, an overview of the activethermal protection techniques for line-started, soft-starter-connected and inverter-fed ac motors is presented, withtheir advantages and drawbacks discussed. The activethermal protection techniques are capable of providingaccurate, and non-invasive thermal protection of acmotors.

Index Terms – AC motor, inverter, starter, stator

resistance, stator temperature, temperature estimation,thermal protection.

I. INTRODUCTION

In North America, ac motor systems play a critical role inindustrial process, while consuming more than a half of all theelectric power produced. Due to their effectiveness,ruggedness and low maintenance requirements, these acmotors are widely used in applications of pumps, fans, mills,compressors, etc. The malfunction of a motor may not onlylead to the repair or replacement of the individual motor, butalso cause significant financial losses due to unexpectedprocess downtime. Therefore, reliable motor protection is

essential for minimizing the motor failure rate, increasing themean time to a destructive motor breakdown, and prolonging amotor’s lifetime. Over the years, substantial efforts have beenmade in developing preventive monitoring and protectiontechniques for ac motors. As an important feature of anymotor protection system, thermal protection is crucial foravoiding thermal overload and prolonging a motor’s lifetime.

As one of the major underlying root causes of motorfailures, thermal overload can lead to deterioration of keycomponents of a motor, including stator winding insulation,bearing, motor conductors, and core, etc [1-5]. The stator

insulation is typically the most vulnerable component duringthermal overload, since its thermal limit is reached before thatof any other motor component. About 35-40% of inductionmotor failures are related to stator winding insulation failure [1-3]. Stator insulation failures are normally the results of long-term thermal aging [6]. A high stator winding temperature,which also depends on the insulation class, gradually andirreversibly reduces the electrical and mechanical performanceof the insulation materials due to chemical reactions, andeventually leads to insulation failures. The typical thermallimits of the stator winding for different insulation classes arelisted in Table I [7]. As a rule of thumb, it is estimated that amotor’s life is reduced by 50% for every 10°C increase abovethe stator winding temperature limit. Therefore, a motor mustbe de-energized immediately when the thermal limit isreached. As a result, accurate and reliable thermal protectionof ac motors is essential for prolonging a motor’s lifetime andpreventing unexpected process downtime.

TABLE I.TEMPERATURE LIMITS FOR DIFFERENT INSULATION

CLASSES.

InsulationClass

AmbientTemperature

(ºC)

RatedTemperature

Rise (ºC)

Hot SpotTemperature

(ºC)

A 40 60 105

B 40 80 130F 40 105 155

H 40 125 180

Motor thermal overload is typically caused by the followingreasons [8]:

1. transient/starting thermal overload;2. motor overload;3. unbalanced supply voltages;4. high ambient temperature;5. impaired cooling capability.

(a) unbalanced supply voltage (b) overload

Fig. 1. stator winding damage due to thermal overload [9].

PRESENTED AT THE 2009 IEEE IAS PULP & PAPER INDUSTRY CONFERENCE IN BIRMINGHAM, AL: © IEEE 2009 - PERSONAL USE OF THIS MATERIAL IS PERMITTED.


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The stator winding damages caused by unbalanced supplyvoltage and overload are shown in Fig. 1 (a) and (b),respectively. It can be observed that the stator winding maybe totally damaged due to thermal overload.

Since the start of the utilization of ac motors, thermalprotection has drawn special attention due to the relativelysevere consequences of stator insulation failures. Topreventively protect the motor from stator winding insulationfailure and extend a motor’s lifetime, the stator winding

temperature often needs to be continuously monitored duringoperation. Such monitoring is particularly important formedium- to large-size motors due to relatively larger capitalcosts the costs of the associated process downtime due tounexpected failures. Direct measurements of the statorwinding temperature using embedded thermal sensors, suchas thermocouples, resistance thermal detectors (RTDs),infrared thermal sensors, etc, are the most reliable approachfor thermal protection. However, their applications are limiteddue to economic reasons, especially for small- to medium-sizemotors, since the installations of the embedded thermalsensors are difficult and costly.

Many different types of thermal protection devices havebecome commercially available, which by design are notdirectly measuring the motor temperature. Their operating

principles and drawbacks are discussed in Section II and III.The basic concept of an alternative type of thermal protectiontechniques: active thermal protection techniques, is presentedin Section IV. The active thermal protection techniques forline-started, soft-starter-connected, and inverter-fed ac motors,which are previously proposed by the authors, are summarizedand compared in Sections V, VI, and VIII, respectively. Theiradvantages and drawbacks are also discussed. The activethermal protection techniques are capable of providingaccurate and non-invasive thermal protection of ac motors.

II. CONVENTIONAL THERMAL PROTECTION DEVICES

Fig. 2. Typical thermal limit curve [10].

The most commonly used conventional motor thermalprotection devices are: dual-element time-delay fuses andeutectic alloy or bi-metal type overload relays. Motor thermalprotection in industry typically relies on using a combination ofthese devices. They are designed based on the thermal limitcurves, which define the safe operating time for differentmagnitudes of input currents under both transient and runningoverload conditions. The typical thermal limit curve of an ac

motor is shown in Fig. 2 [10]. Although these low-cost thermal protection devices have

been proven to work over the years, they can only roughlyemulate the thermal limit curve. Besides, even the thermallimit curve is also only a rough and conservativerepresentation of the thermal characteristic of ac motors, sincethe effects of ambient temperature, unbalanced supply voltageand the changes of the cooling capability of ac motors areneglected. In addition, since only the magnitude of the inputcurrent is monitored, these devices are not capable ofprotecting motors when high negative-sequence currents arepresent. Therefore, nuisance tripping and under-protection areboth common when these devices are used [8, 11].

III. MICROPROCESSOR-BASED THERMAL OVERLOADRELAYS

To overcome the aforementioned drawbacks ofconventional fuses and relays, microprocessor-based thermaloverload protective relays are often applied. They representthe state of the art in the thermal protection of ac motors.These microprocessor-based relays typically estimate thepower losses in ac motors using current measurements, andthen calculate the stator winding temperature based on thethermal model of ac motors. The motor is tripped immediatelywhen a predetermined maximum permissible temperature isreached.

Fig. 3. First-order thermal model of ac motors.

The first-order thermal models are the most commonlyused thermal model in this type of relays. An example of thefirst-order thermal model is shown in Fig. 3. The statorwinding temperature and the ambient temperature are denotedas T s and T A, respectively; C th represents the equivalent

thermal capacitance, which models the intrinsic thermalcharacteristic of the stator winding; R th represents theequivalent thermal resistance, which models the coolingcapability from the stator winding to the ambient; P loss represents the heat dissipation in the stator winding, which ismainly the copper loss. Since identification of the thermalparameters are typically difficult without embedded thermalsensors, methods have been developed to roughly estimatethe thermal parameters using the motor’s nameplateinformation, including Service Factor and Trip Class [12]. The


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first-order thermal model of induction motors is broadly useddue to its implementation simplicity: only the motor currentneeds to be measured. However, as these approachesneglect the temperature rise caused by the other motor lossesand the change of the motor’s thermal behavior under differentoperating conditions, these thermal models are generallyinaccurate and conservative, and therefore often times use ofthis approach will trip the motor long before the actual thermallimit is reached.

To improve the stator temperature estimation accuracy byconsidering the effect of different losses on stator temperature,high-order thermal models are also developed [13-19]. Thesemethods can model the thermal effects of the losses indifferent motor components, such as winding, core, etc, andtherefore are capable of providing more accurate statortemperature estimation than the first-order thermal models. Anexample of a second-order thermal model is shown in Fig. 4[16], where the stator and the rotor are modeled separately, sothat the thermal effects of the rotor losses and the rotortemperature rise on the stator temperature rise can beestimated. The complexity of the thermal model is a tradeoffbetween the accuracy of temperature estimation and thecomplexity in parameter identification and requiredcomputational effort. The losses in different motor

components are either calculated online using the currentmeasurement, or estimated via offline testing. The thermalparameters in these high-order thermal models are normallydetermined based on the measured temperature at differentlocations in the motor using embedded thermal sensors. Theapplications of high-order thermal models are limited due tothe difficulty in thermal parameter identification, whenembedded thermal sensors are not available. Anotherinherent drawback of the thermal model-based approaches istheir negligence of the changes in the cooling capability of acmotors. Therefore, using a thermal model with fixed thermalparameters can lead to rapid motor failures when the coolingcapability of the ac motor is significantly reduced.

Fig. 4. Second-order thermal model of ac motors [16].

Aside from the aforementioned techniques, the statortemperature can also be monitored based on the estimation ofthe stator resistance, since resistance variation is linearly

proportional to temperature variation, as

00

0

( ) s s

s s

s

R RT T

Rα

∧

∧ −= + , (1)

where T s0 and R s0 represents the stator temperature and

resistance at room temperature; sT ∧

and s R∧

are the estimatedT s and R s; and α is the temperature coefficient of resistivity.Many stator resistance estimation approaches have beenproposed based on the equivalent electrical model of induction

motors [20-22]. However, these techniques are mainly usedfor improving the field-oriented control performance at lowspeed or improving the sensorless speed estimation accuracy.It is shown in [23] that these approaches are inherently toosensitive to the variations of motor parameters due to differentoperating conditions, and therefore, are not capable ofproviding accurate stator resistance estimation for thermalprotection purposes.

IV. OVERVIEW OF ACTIVE THERMAL PROTECTIONTECHNIQUES

The development of active thermal protection techniquescan be traced back to the early 80’s. It is first proposed in [24]to use the dc model of ac motors to estimate the statorresistance and temperature, by creating a dc bias in themotor’s input voltage and current. Since the dc componentdoes not “pass through” the air-gap, stator resistance can becalculated using only the dc component in the input voltageand current, as,

2

3

dc

ab

s dc

a

v R

i

⋅=

⋅

, (2)

where,

dc

abv

and

dc

ai

are the dc components of the motor linevoltage v ab and phase current i a , respectively, when a dc biasis injected between phase a and b, phase b and c , of a Y-connected ac motor. However, since power diodes aretypically used to create the dc bias in this approach, dc biascan only be injected continuously and the magnitude of theinjected dc bias can not be adjusted online, which inducescontinuous and uncontrollable torque pulsation and extra heatdissipation in both the power diodes and also the motor itself.

One novel approach to resolve these design limitations isby use of a newly developed signal-injection-based activethermal protection technique. To minimize the torque pulsationand heat dissipation caused by the injected dc bias,controllable dc signals are intermittently injected to estimatethe stator temperature. The period of stator temperature

update depends on the requirement of practical applications. Active thermal protection approaches have been proposed bythe authors for different applications: ac line-started motors[25, 26], soft-starter-connected motors [27, 28], and inverter-fed motors [29]. These techniques are capable of providingaccurate and non-invasive thermal protection of ac motors,with adaptation to the changes in a motor’s cooling capability.

V. ACTIVE THERMAL PROTECTION FOR AC LINE-STARTED M ACHINES

A. DC Signal Injection for AC Line-started Motors

To inject a controllable dc bias between two phases of acmotors, a dc injection circuit is proposed in [26]. It consists ofa controllable switch (e.g., a mechanical contactor or a solid-state power switch) and an external resistor (R ext ) connected inparallel, as shown in Fig. 5-(a). In [26], the controllable switchis implemented using an n-channel enhancement type powerMOSFET. Under dc signal injection mode, the controllableswitch is turned open when i as>0, and turned closed wheni as


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injected dc signal is dependent on the value of R ext , which canbe adjusted depending on the nominal R s and the rated i as sothat the torque distortion and power dissipation caused by dcsignal injection is within an acceptable level. Under normaloperation, the controllable switch is kept closed to minimizethe heat dissipation in the circuit. Therefore, the effects of dcsignal injection can be minimized by using periodic operationof the circuit: dc signals are only periodically injected for asmall amount of time, which is sufficient to obtain an accurate

estimate of the stator temperature. As one of the fewlaboratory prototypes built to validate the dc injectionapproach, a prototype using a commercial mechanicalcontactor as the controllable switch is shown in Fig. 5-(d).

(d) Fig. 5. DC injection circuit.

B. Experimental Testing

a

c

b

230V Induction

Motor

MOSFET

Driver

+ v sw - i as

DSP

Board

Isolation

Amplifiers

DCGenerator

Load

A / D

Conversion

Thermocouples

T s

R s

Field

Voltage

Resistor

Bank

Development

Software

PC

Thermometer

Fig. 6. Experimental Setup [26].

A series of lab testing has been conducted to validate thisstator temperature estimation approach using both mechanicaland solid-state switches. Fig. 6 shows the overallexperimental setup using a MOSFET-based dc injection circuit[26]. A dc generator supplying a resistor bank serves as thedynamometer. Thermocouples are installed at differentlocations of the induction motor to measure the stator windingtemperature for comparison purposes. The estimated statorresistance and the measurement stator temperature areshown in Fig. 7. The motor is operated under load variation

conditions: no load →100%→50%→75% of the rated load.The estimated stator resistance with different values of R ext isshown in Fig. 7-(a), (b) and (c); the measured statortemperatures with thermocouples at different locations areshown in Fig. 7-(d).

Fig. 7. Experimental results (Motor: Leeson, 5 hp, 230 V, 12.4 A,NEMA-B, ODP, 1745 rpm.)

VI. ACTIVE THERMAL PROTECTION FOR SOFT-STARTER-CONNECTED M ACHINES

A. DC Signal Injection using Soft-starters

The soft-starter normally contains multiple anti-parallelsolid-state power switches (e.g., thyristors) to control thecurrent flow and, in turn, the terminal voltages of the motor.The soft-starter limits the transient voltages and currents,reduces the inrush currents, and results in a “soft” motor start.

After starting, the soft-starter typically enters the “bypass”mode, when integrated contactors are closed to minimize thepower dissipation.

A new thyristor gate drive control scheme has beendeveloped by the authors to inject dc components in the motorline voltages and phase currents [28]. This schemeperiodically switches the soft-starter operation between twostates after the soft-starter completes the ramp-up mode: a

normal bypass operation state and a dc signal injection state.During the dc signal injection state, only one contactor(corresponding to only one phase, e.g., phase a) in the soft-starter is kept open, while the other two contactors still worknormally as in bypass mode. Instead of using symmetricalgate drive signals for all three phases, a short delay isintroduced to the gate drive signal of only the forward-conducting thyristor of phase a (V G1), after the phase a current’s rising zero-crossing. After the dc signal injectionstate, the phase a contactor is closed, so that the soft-starter

0 45 90 135 180 225 270 315 360

0.48

0.5

0.52

0.54

0.56

0.58

0.6

E s t i m a t e o

f R

s

Ω )

Time (min)

No load Half loadFull load 75% load0 45 90 135 180 225 270 315 36

20

30

40

50

60

70

80

90

M e a s u r e d s t a t o r t e m p e r a t u r e ( o C

)

Time (min)

T3T2

T1

75% loadHalf loadFull loadNo load

0 45 90 135 180 225 270 315 360

0.48

0.5

0.52

0.54

0.56

0.58

0.6

E s t i m a t e o f R

s

Ω )

Time (min)

No load

Full load Half load 75% load0 45 90 135 180 225 270 315 360

0.48

0.5

0.52

0.54

0.56

0.58

0.6

E s t i m a t e o f R

s

( Ω )

Time (min)

No load Half loadFull load 75% load

(c) R ext =0.3 Ω (d) measured T s

(a) R ext =0.1 Ω (b) R ext =0.2 Ω


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returns to normal bypass operation state. The equivalentmodel of the motor system during dc signal injection state isshown in Fig. 8. Fig. 9 shows the typical waveforms of themotor line voltage, v ab, phase current, i a, while a small delay

angle of α (α < 40°) is added. The torque pulsation caused bythe injected dc signal can be controlled under acceptable levelby adjusting the delay angle.

i a,dc

v ab,dc RS

RS RS

A

B C

V G1

V G2

Fig. 8. DC equivalent circuit of motor, source and soft-starter.

0.86 0.87 0.88 0.89 0.9 0.91 0.92

-50

0

50

0.86 0.87 0.88 0.89 0.9 0.91 0.92

-500

0

500

( A )

α

( V )

Fig. 9. Motor line voltage, phase current during dc signal injection.


Fig. 10. Experimental setup [27].

0 50 100 150 200 250 30020

30

40

50

60

70

80

measured Ts

estimated Ts

S t a t o r

W i n d i n g T e m p e r a t u r e / ° C

(a) Normal cooling condition

0 50 100 150 200 25020

40

60

80

100

120

140

measured Ts

estimated Ts

S t a t o r W i n d i n g T e m p e r a t u r e / ° C

(b) Cooling fan removed

Fig. 11. Experimental results (Motor: Emerson, 7.5 hp, 230 V, 18.4 A,NEMA-B, TEFC, 3515 rpm.)

The lab setup for the validation of this stator temperatureestimation technique is shown in Fig. 10. The motor isoperated under variable load conditions: noload→50%→75%→100% of the rated load. To test thefeasibility of this approach when the cooling capability of themotor is reduced, the motor’s cooling fan is removed under thesame variable load condition. The estimated statortemperature and the mean measured temperature usingthermocouples under normal condition and cooling capabilitydeterioration condition are shown in Fig. 11-(a) and (b),respectively.

VII. ACTIVE THERMAL PROTECTION FOR INVERTER-FEDM ACHINES

A. DC Signal Injection using Motor Drives

Open-loop ac motor variable frequency drives are widelyused for controlling the rotor speed of ac motors. In suchdrives, motor input voltage commands are generated at acertain fixed ratio to the frequency (or speed) command tocontrol the switching of solid-state power switches, e.g. IGBTs.To inject dc signals, a dc voltage offset can be simply added tothe original input voltage command, which then adjusts theswitching of the power switches automatically. An example of


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dc signal injection method using space vector pulse widthmodulation (SVPWM) is shown in Fig. 12 [29]. Similar to thesoft-starter dc injection method, this scheme also periodicallyswitches the drive operation between two states: a normaloperation state and a dc signal injection state. The typical inputcurrent waveform during dc signal injection state is shown inFig. 13, where a clear dc component is shown in the motorcurrent. Since the dc voltage command is constant, the statortemperature can be estimated using only current

measurements, as,

00

1 1 dca

s s dc

a

iT T

iα α

∧

= − + g , (3)

where0

dc

ai represents the dc component in the phase current

when the stator temperature is T s0 . Therefore, the voltagemeasurement can be avoided, which is highly desirable sincevoltage sensors are typically not present in variable frequencymotor drives.

0 0.02 0.04 0.06 0.08 0.1-20

-15

-10

-5

0

5

10

15

20

25

30

time (sec)

p h a s e a

c u r r e n t I a ( A m p )

Phase current during dc signal injection

with dc signal injection

without dc signal injection

Fig. 13. Stator current with dc signal injection.

Fig. 14. Experimental setup [29].

Fig. 15. Impaired cooling by blocking ventilation.

Fig. 12. Modified space vector PWM for dc signal injection.


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0 20 40 60 80 100 120 1400

10

20

30

40

50

60

70

80Stator Temperature Estimation

time (min)

S t a t o r T e m p e r a t u r e ( o C )

Measured Ts

Estimated Ts

(a) Normal condition.

0 50 100 150

0

10

20

30

40

50

60

70

80Stator Temperature Estimation

time (min)

S t a t o r T e m p e r a t u r e ( o C )

Measured Ts

Estimated Ts

(b) Blocked ventilation. Fig. 16. Experimental results (Motor: Leeson, 7.5 hp, 230 V, 20 A,

NEMA-B, ODP, 1760 rpm.)


The lab setup for the validation of this approach is shownin Fig. 14. The motor is then operated under variable loadconditions: no load→100%→50%→75% of the rated load. Totest the effectiveness of this approach when the motor’scooling capability is deteriorated, the ventilation is blocked,when the motors is operated under the same variable loadcondition, as shown in Fig. 15. The estimated stator

temperature and the average temperature measured usingthermocouples under normal condition and cooling capabilitydeterioration condition are shown in Fig. 16-(a) and (b),respectively. The value of the stator resistance estimatedusing this technique can also be further used for improving thefield-oriented control performance at low speed or improvingthe sensorless speed estimation accuracy.

VIII. SUMMARY OF ACTIVE THERMAL PROTECTIONTECHNIQUES

Conventional passive thermal protection devices,including dual-element time-delay fuses, eutectic alloy or bi-metal type overload relays and microprocessor-basedoverload relays, are typically inaccurate due to the difficulty inthe accurate modeling of a motor’s thermal behavior. Theerror in the stator winding temperature estimation may be

more than 30°C [28]. Therefore, nuisance tripping is commonwhen these devices are used.

On the other hand, the active thermal protectiontechniques are capable of providing accurate monitoring of thestator temperature without embedded thermal sensors, asshown in Section V, VI and VII. The errors in the statorwinding temperature estimation can be smaller than 3°C,depending on the magnitude of the injected dc signals. Onlycurrent and voltage measurements are required, whichguarantees their non-invasive and cost-efficient nature. Thetorque pulsation and extra heat dissipation caused by dc signalinjection can be controlled within acceptable levels. The dcsignals are intermittently injected to minimize the effects of thedc signal injection. The period of dc signal injection dependson the frequency of stator temperature estimation updates

required by the practical application, given a motor’s typicalthermal time constant.

Because of their accuracy in the stator windingtemperature estimation, their robustness to the variations inthe electrical/thermal parameters of ac motors and theircapability of adaptation to the changes in a motor’s coolingcapability, these active thermal protection techniques arehighly preferred over conventional thermal protectiontechniques for the reliable thermal protection of ac motors.

IX. CONCLUSIONS

Thermal protection of ac motors is crucial for preventingcatastrophic motor breakdown, prolonging motor’s lifetime, andavoiding the extraordinary financial losses due to unexpected

industrial process downtime caused by motor failures. Areview of available thermal protection devices and techniqueshas been presented in this paper. The principle and drawbackof conventional overload relays and microprocessor-basedthermal relays have been discussed. It has been concludedthat these thermal protection techniques are not capable ofproviding reliable thermal protection for ac motors underdifferent operating conditions, due to:

1. inaccurate modeling of the thermal characteristics ofac motors under different operating conditions;

2. negligence of the changes in a motor’s coolingcapability.

To overcome the drawbacks of conventional thermalprotection techniques, an alternative type of thermal protectiontechnique: active thermal protection, has been proposed bythe authors for ac line-started, soft-starter-connected, andinverter-fed ac motors. By intermittently injecting dc signalsinto the motors, the dc model of ac motors has been used forthe estimation of the stator winding resistance andtemperature. It has been clearly shown that these techniquesare capable of providing accurate monitoring of the statortemperature without embedded thermal sensors. The errors inthe stator winding temperature estimation can be within 3°C,depending on the magnitude of the injected dc signals. Thetorque pulsation caused by the injected dc signals can be


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controlled under acceptable level. The importance of thesetechniques lies in their non-invasive nature:

1. only current and voltage measurements are required;2. motor’s normal operation is not disturbed.

Therefore, the active thermal protection techniques arecapable of providing non-intrusive, low-cost and reliablethermal protection of ac motors, when moderate torquepulsation is acceptable for the practical applications.

X. ACKNOWLEDGEMENT

The authors would like to thank Dr. Sang-Bin Lee for hisearly contribution in this research project. This work wasfinancially supported in part by the U. S. Department of Energyunder Grant DE-FC36-04GO14000 and such support does notconstitute an endorsement by DOE of the views expressed inthe article.

XI. REFERENCES

[1] "Report of Large Motor Reliability Survey of Industrialand Commercial Installations, Part II," Industry

Applications, IEEE Transactions on, vol. IA-21, pp.865-872, 1985.

[2] "Report of Large Motor Reliability Survey of Industrialand Commercial Installations, Part I," Industry


[3] "Report of Large Motor Reliability Survey of Industrialand Commercial Installations: Part 3," Industry


[4] P. F. Albrecht, J. C. Appiarius, R. M. McCoy, E. L.Owen, and D. K. Sharma, "Assessment of thereliability of motors in utility applications- Updated,,"Energy Conversion, IEEE Transaction on, vol. EC-1,pp. 39-46, 1986.

[5] A. H. Bonnett and G. C. Soukup, "Cause and analysisof stator and rotor failures in three-phase squirrel-

cage induction motors," Industry Applications, IEEETransactions on, vol. 28, pp. 921-937, 1992.

[6] G. C. Stone, I. M. Culbert, and B. A. Lloyd, "Statorinsulation problems associated with low voltage andmedium voltage PWM drives," in Cement IndustryTechnical Conference Record, 2007. IEEE , 2007, pp.187-192.

[7] "Information Guide for General Purpose Industrial ACSmall and Medium Squirrel-Cage Induction MotorStandards," NEMA Standard MG1-2003, August2003.

[8] S. F. Farag, R. G. Bartheld, and T. G. Habetler, "Anintegrated on-line motor protection system," Industry

Applications Magazine, IEEE, vol. 2, pp. 21-26, 1996.[9] "Failures in three-phase stator windings," West Coast

Rewind and Electrical Control Pty Ltd, available athttp://www.westcoastrewind.com.au/repair.php.

[10] "IEEE guide for the presentation of thermal limitcurves for squirrel cage induction machines," IEEEStandard 620-1996, August 1996.

[11] R. J. Brighton and P. N. Ranade, "Why OverloadRelays Do NOT Always Protect Motors," Industry


[12] M. S. Abou-El-Ela, A. I. Megahed, and O. P. Malik,"Thermal model based digital relaying algorithm forinduction motor protection," in Electrical andComputer Engineering, 1996. Canadian Conferenceon, 1996, pp. 1016-1019 vol.2.

[13] A. Boglietti, A. Cavagnino, M. Lazzari, and A.Pastorelli, "A simplified thermal model for variablespeed self cooled industrial induction motor," in proc.37th IAS Annual Meeting, 2002. , 2002, pp. 723-730

vol.2.[14] A. Bousbaine, M. McCormick, and W. F. Low, "In-situ

determination of thermal coefficients for electricalmachines," Energy Conversion, IEEE Transaction on,vol. 10, pp. 385-391, 1995.

[15] D. R. G. Champenois and D. S. Zhu, "Electrical andthermal performance predictions in inverter-fedsquirrel-cage induction motor dirves," ElectricMachines and Power Systems, vol. 22, pp. 355-369,May/June 1994.

[16] Z. Gao, T. G. Habetler, R. G. Harley, and R. S. Colby,"A Sensorless Adaptive Stator Winding TemperatureEstimator for Mains-Fed Induction Machines WithContinuous-Operation Periodic Duty Cycles," Industry

Applications, IEEE Transactions on, vol. 44, pp.

1533-1542, 2008.[17] K. D. Hurst and T. G. Habetler, "A thermal monitoring

and parameter tuning scheme for inductionmachines," in proc. 32nd IAS Annual Meeting, IAS'97 , 1997, pp. 136-142 vol.1.

[18] J. F. Moreno, F. P. Hidalgo, and M. D. Martinez,"Realisation of tests to determine the parameters ofthe thermal model of an induction machine," ElectricPower Applications, IEE Proceedings -, vol. 148, pp.393-397, 2001.

[19] P. S. H. Nestler, "On-Line estimation of temperaturesin electrical machines by an observer," ElectricMachines and Power Systems, vol. 21, pp. 39-50,1993.

[20] T. G. Habetler, F. Profumo, G. Griva, M. Pastorelli,and A. Bettini, "Stator resistance tuning in a stator-flux field-oriented drive using an instantaneous hybridflux estimator," Power Electronics, IEEE Transactionson, vol. 13, pp. 125-133, 1998.

[21] G. Guidi and H. Umida, "A novel stator resistanceestimation method for speed-sensorless inductionmotor drives," Industry Applications, IEEETransactions on, vol. 36, pp. 1619-1627, 2000.

[22] C. B. Jacobina, C. C. de Azevedo, M. N. Lima, and L. A. de Souza Ribeiro, "Online estimation of the statorresistance and leakage inductance of a four-phaseinduction machine drive," Power Electronics, IEEETransactions on, vol. 19, pp. 10-15, 2004.

[23] S.-B. Lee, T. G. Habetler, R. G. Harley, and D. J.

Gritter, "An evaluation of model-based statorresistance estimation for induction motor statorwinding temperature monitoring," Energy Conversion,IEEE Transaction on, vol. 17, pp. 7-15, 2002.

[24] D. A. Paice, "Motor Thermal Protection byContinuous Monitoring of Winding Resistance,"Industrial Electronics and Control Instrumentation,IEEE Transactions on, vol. IECI-27, pp. 137-141,1980.

[25] S.-B. Lee and T. G. Habetler, "A remote andsensorless thermal protection scheme for small line-


9/9

connected ac machines," Industry Applications, IEEETransactions on, vol. 39, pp. 1323-1332, 2003.

[26] S.-B. Lee and T. G. Habetler, "An online statorwinding resistance estimation technique fortemperature monitoring of line-connected inductionmachines," Industry Applications, IEEE Transactionson, vol. 39, pp. 685-694, 2003.

[27] P. Zhang, Y. Du, B. Lu, and T. G. Habetler, "ARemote and Sensorless Thermal Protection Scheme

for Soft-Starter-Connected Induction Motors," inIndustry Applications Society Annual Meeting, 2008.IAS '08. IEEE , 2008, pp. 1-7.

[28] P. Zhang, B. Lu, and T. G. Habetler, "A Remote andSensorless Stator Winding Resistance EstimationMethod for Thermal Protection of Soft-Starter-Connected Induction Machines," IndustrialElectronics, IEEE Transactions on, vol. 55, pp. 3611-3618, 2008.

[29] P. Zhang, B. Lu, and T. G. Habetler, "An Active StatorTemperature Estimation Technique for ThermalProtection of Inverter-Fed Induction Motors withConsiderations of Impaired Cooling Detection," inElectric Machines & Drives Conference, IEEEInternational, IEMDC '09, 2009.

Documents

IEEE 2009 Paper - Active Stator Winding Thermal Protection