Thermal Protection for Locomotive Main Traction

Europaisches Patentamt (19) European Patent Office Office europeenpeen des brevets EP 0 587 849 B1

(12) EUROPEAN PATENT SPECIFICATION

(45) Date of publication and mention (51) intci.e: H02H7/06, B60L 11/02 of the grant of the patent: 04.09.1996 Bulletin 1996/36 (86) International application number: PCT/US93/02279 (21) Application number: 93907462.1 (87) International publication number: (22) Date of filing: 12.03.1993 WO 93/20608 (14.10.1993 Gazette 1993/25)

(54) THERMAL PROTECTION FOR LOCOMOTIVE MAIN TRACTION ALTERNATORS THERMISCHER SCHUTZ FUR WECHSELSTROMGENERATOR DES HAUPTANTRIEBES EINER LOKOMOTIVE PROTECTION THERMIQUE POUR LES ALTERNATEURS DE TRACTION PRINCIPAUX D'UNE LOCOMOTIVE

(84) Designated Contracting States: • MCGRATH, Robert, Gerald DE ES FR GB IT SE North East, PA 16428 (US)

(30) Priority: 03.04.1992 US 862673 (74) Representative: Pratt, Richard Wilson et al London Patent Operation (43) Date of publication of application: G.E. Technical Services Co. Inc. 23.03.1994 Bulletin 1994/12 Essex House 1 2/1 3 Essex Street (73) Proprietor: GENERAL ELECTRIC COMPANY London WC2R 3AA (GB) Schenectady, NY 12345 (US) (56) References cited: (72) Inventors: DE-A- 3 143 840 US-A- 4 626 753 • VANEK, Laurence, Dean Girard, PA 16417 (US) • PATENT ABSTRACTS OF JAPAN vol. 007, no. 149 (M-225)30 June 1983 JP-A-58 058804

DO O) ^- 00

00 Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice the Patent Office of the Notice of shall be filed in o to European opposition to European patent granted. opposition a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. a. 99(1) European Patent Convention). LU Printed by Jouve, 75001 PARIS (FR) 1 EP 0 587 849 B1 2

Description through a rectifier to a plurality of traction motors. The system and method comprise sensing ambient inlet air Background of the Invention temperature to the alternator and providing a sensor temperature. An individual traction motor current limit is The present invention relates to thermal overloads 5 then calculated using the inlet air temperature and the and, more specifically, to thermal overload protection for sensor temperature. Finally, thermal overload is control- locomotive traction alternators. led in response to the traction motor current. It is well known in the art to provide overload pro- Accordingly, it is an object of the present invention tection for rotating electrical machinery. Existing meth- to provide thermal overload protection. It is a further ob- odology employed relies on the use of stator winding 10 ject to provide thermal overload protection automatical- temperature sensors to provide a signal for either alarm, ly, in a manner compatible with diesel engine loading load reduction, or "trip" of the alternator, if temperatures requirements. These and other objects will become ap- beyond a given limit are encountered. This would usu- parent from a reading of the ensuing description togeth- ally be the result of some type of electrical overload, the er with the appended drawings and claims. protective action function would be carried out by either 15 reducing the load manually or tripping the alternator cir- Brief Description of the Drawings cuit breaker. Overload protection for rotating electrical machin- FIG. 1 is an illustration of a conventional locomotive ery is intended to provide a means of preventing exces- utilizing the thermal overload protection system de- sive overheating of the electrical winding insulation sys- 20 scribed herein; and tem. The protection used has been similar for most FIG. 2 is a flow diagram of the thermal overload pro- types of rotating electrical machines and the devices tection system shown in FIG. 1. employed typically fall into one of several categories. For example, the device employed may be a time-delay Detailed Description of the Preferred Embodiments overcurrent device or relay, a thermal relay or device 25 operated by machine electrical current, a temperature Referring now to the drawings, in FIG. 1 there is il- relay or device operated by an embedded winding tem- lustrated a diesel electric locomotive 10 controlled by a perature sensor or thermostat, or a combination of these thermal overload protection system 12 described here- devices. in. Generally, the locomotive 10 is shown in this partic- The protection option chosen is usually to provide 30 ular example as having an engine 1 4 and a main traction an alarm to an operator, to disconnect or trip the alter- alternator 16. The main traction alternator 16 typically nator from its load, or to permit short overload excur- has a field excitation controlled by an on-board micro- sions compatible with the inverse-time overload limit computer system 1 8 to maintain a constant horsepower curve of the machine. The use of embedded winding load on the engine 14 when the locomotive 10 is oper- sensors is currently the preferred method for thermal 35 ating within its normal continuous rating performance protection. Most large machines usually employ Resist- envelope. Regulating the alternator field excitation var- ance Temperature Detectors (RTD's) embedded in the ies the tractive effort delivered by traction motors mount- stator windings for the purpose of directly sensing stator ed on each axle on the locomotive trucks 20. The mi- winding temperatures. crocomputer system 18 controls the locomotive 10 and Unfortunately, locomotive traction alternators have 40 may comprise one or more microcomputers for control not typically been protected against damaging thermal and protection against damaging operating conditions. overloads due to the philosophy that permissible trac- The locomotive propulsion system 14, traction al- tion motor short-time rating limits will prevent alternator ternator 16, and traction motors (not shown), may be temperatures from reaching excessive levels. It is seen required to operate for short times beyond the continu- then that there exists a need for a thermal protection es ous ratings of its members. In this case, the traction al- control which provides a smooth and gradual reduction ternator thermal overload protection system 12 contin- in the alternator electrical load. uously calculates a limiting value for alternator load current, in terms of traction motor current, and locomotive Summary of the Invention tractive effort is automatically adjusted accordingly. The so objective is to prevent overheating of the alternator This need is met by the method and the system ac- winding insulation. The means, which may be any suit- cording to the present invention, which provides loco- able means but is preferably a computer software pro- motive traction alternator protection against thermal gram, for performing this calculation is contained in the overloads. The invention utilizes stator winding temper- microcomputer 18. ature information obtained from an embedded sensor. 55 It is to be understood that the thermal overload pro- The present invention also provides for a thermal tection system 12 described herein may be used to ad- overload protection control system and method for a lo- vantage with any type of rotating electrical machinery. comotive having an alternator supplying dc power The thermal protection overload system 12 is illustrated

2 3 EP 0 587 849 B1 4 for use with the locomotive 10 for purposes of descrip- tinue block 28 to be repeated. If the sensed traction mo- tion only, and is not to be considered as limiting the in- tor current is determined at decision block 36 to be vention. greater than the calculated traction motor current limit Referring now to FIG. 2, and continuing with FIG. from block 32, the program 12 equalizes the sensed 1, the thermal overload protection system 12 is shown s traction motor current and the calculated traction motor as a flow diagram of computational and measurement current limit at block 38. steps represented as blocks. Each block herein de- If it is determined at decision block 40 that the scribes and operation or step performed by the thermal sensed traction motor current, now equal to the calcu- protection system 1 2. It is noted that the operations may lated traction motor current limit, is greater than or equal also be performed by discrete components wherein 10 to the continuous traction motor current rating, the pro- each block comprises an array of circuits. gram proceeds to block 28 and is repeated. If it is de- The block diagram of FIG. 2 illustrates a method of termined at decision block 40 that the sensed traction providing thermal overload protection for rotating elec- motor current, now equal to the calculated traction motor trical machinery and is intended to provide a means of current limit, is less than the continuous traction motor preventing excessive overheating in a manner compat- 15 current rating, the program proceeds to block 42 to ible with diesel engine loading requirements. There is equalize the continuous traction motor current and the no occurrence of abrupt change or sudden loss of loco- calculated traction motor current limit. The program then motive tractive effort during the execution of the steps proceeds to block 28, where it is continued. illustrated in the flow diagram of FIG. 2. Continuing with FIG. 2, the traction motor current In the flow diagram 12 of FIG. 2, three system var- 20 limit (LIMIT) is calculated by the thermal overload pro- iables are sensed and provide the only inputs required tection system according to the following, Equation (1 ): for the method of providing thermal overload protection, LIMIT = K1 - K2*((T - TA)/TCORR TA) which is typically conducted in real time at one second + intervals. The required system variables include ambi- where ent inlet air temperature to the locomotive traction alter- 25 nator, alternator stator winding embedded temperature LIMIT = Traction Motor Current Limit sensor, and traction motor armature current. The tem- K1 = Constant Related to Maximum Permissible perature sensor reading is converted via a look-up table Winding Temperature (K1 = Iss/NTM + to a temperature in degrees Celsius. The resultant sen- K2*Ths) sor temperature and the sensed value of the ambient 30 Iss = Steady State Alternator Current Corre- air temperature are used to calculate a traction motor sponding to Ths current limit which is then compared to the existing cur- NTM = Number of Traction Motors per Locomotive rent value. If the limit is exceeded, the alternator field Ths = Maximum Permissible Stator Winding Hot current is adjusted such that the sensed traction motor Spot Temperature current is equal to the calculated limit. Thetraction motor 35 K2 = Constant Related to Time Rate of Load Re- current and the traction alternator current are linearly duction and directly related, in that the alternator current limit is T = Stator Winding Sensor Temperature equal to the traction motor current limit multiplied by the TA = Alternator Ambient Air Temperature number of traction motors per locomotive. The traction TCORR = Calibration Factor (sensor rise)/(hot spot motor current is sensed for purposes of convenience. It 40 rise) is the traction alternator current which is to be regulated. The flow diagram 1 2 begins at block 22, where the Thetraction motor current limit value, LIMIT, calcu- winding sensor is read, and continues to block 24 to de- lated in accordance with Equation (1 ) is a direct function termine the winding sensor temperature. If the winding of the winding sensor temperature rise above the alter- sensor temperature is determined at decision block 26 45 nator ambient air temperature. Larger values of sensor to be less than or equal to a preset winding sensor tem- temperature rise give smaller values forthe current limit. perature flag, T|im, the program 1 2 goes to block 28 and The calculated traction motor current limit value varies is repeated. If the winding sensor temperature is deter- as the overload progresses due to the fact that it is con- mined at decision block 26 to be greater than the tem- tinuously calculated during the operation of the thermal perature limit, then the ambient temperature is read at so overload protection system 12. When the calculated block 30. traction motor current limit and sensed current values The program 12 then continues to block 32 where coincide, the alternator load reduction begins. the traction motor current limit is calculated, before pro- The thermal overload protection system and meth- ceeding to block 34 where the sensed traction motor od of the present invention will provide protection current is read. At decision block 36, if it is determined 55 against thermal overloads to the locomotive traction al- that the sensed traction motor current is less than or ternator. The system and method utilize stator winding equal to the calculated traction motor current limit from temperature information obtained from an embedded block 32, the program 12 proceeds directly to the con- sensor. In a preferred embodiment of the present inven-

3 5 EP 0 587 849 B1 6 tion, the system and method are executed by the loco- to a maximum permissible winding temper- motive on-board microcomputers. The effect on the pro- ature to generate a fourth value which is pulsion system due to the execution of the system and indicative of the calculated traction motor method is a smooth and gradual reduction in the alter- current limit value; and nator electrical load to a new value which simultaneous- 5 ly limits the winding temperature to a predetermined val- (d) controlling the alternator field current in re- ue, without any abrupt change or total loss of locomotive sponse to the calculated traction motor current tractive effort. The alternator is not disconnected from limit value. its load and the system and method of the present invention bring the propulsion system to a safe operating 10 2. A thermal overload protection control method as condition consistent with a preset operating tempera- claimed in claim I wherein the step of controlling the ture limit, without requiring any human intervention. thermal overload further comprises the step of au- The present invention provides for a system and a tomatically adjusting the alternator field current so method of thermal overload protection and prevents that the sensed traction motor current is equal to harmful transient thermal overloads which can cause al- is the calculated traction motor current limit value. ternator failure or drastically reduce its insulation life. An additional benefit of the present invention is that it grad- 3. A thermal protection overload method as claimed in ually and smoothly reduces the prime mover, or diesel claim 1 further comprising the steps of: engine, load. Such action avoids the excessive transient production of engine smoke. Engine transient over- 20 (a) sensing an existing traction motor current speed as would occur with sudden loss or abrupt reduc- value (34); and tion in load is also avoided. Finally, human operator in- (b) comparing the calculated traction motor cur- tervention is not required at any stage of the protection rent limit value to the existing traction motor function or during the recovery from the overload inci- current value (36). dent. 25 Having described the invention in detail and by ref- 4. A thermal protection overload method as claimed in erence to the preferred embodiment thereof, it will be claim 1 wherein the step of providing a sensor tem- apparent that other modifications and variations are perature further comprises the step of using an al- possible without departing from the scope of the inven- ternator stator winding embedded temperature sen- tion defined in the appended claims. 30 sor.

5. A thermal overload protection system for a locomo- Claims tive having an alternator supplying dc power to a plurality of traction motors comprising: 1 . A thermal overload protection control method for a 35 locomotive having an alternator supplying dc power (a) means for providing a stator winding sensor to a plurality of traction motors, the method compris- temperature; ing the steps of: (b) means for sensing ambient inlet air temperature to the alternator; (a) providing a stator winding sensor tempera- 40 (c) means for calculating a traction motor cur- ture (22); rent limit to generate a calculated traction motor (b) sensing ambient inlet air temperature to the current limit value, including, alternator (30), (c) calculating a traction motor current limit (32) i. means for dividing a difference between to generate a calculated traction motor current 45 the sensor temperature and the alternator limit value including the steps of: ambient air temperature by a calibration factor to generate a first value, i. dividing a difference between the stator ii. means for summing the first value and winding sensor temperature and the alter- the alternator ambient air temperature to nator ambient air temperature by a calibra- so generate a second value, tion factor to generate a first value, iii. means for multiplying the second value ii. summing the first value and the alterna- and a constant related to a time rate of load tor ambient air temperature to generate a reduction to generate a third value, and second value, iv. means for subtracting the third value iii. multiplying the second value and a con- 55 from a constant related to a maximum per- stant related to a time rate of load reduction missible winding temperature to generate to generate a third value, and iv. subtract- a fourth value which is indicative of the cal- ing the third value from a constant related culated traction motor current limit value;

4 7 EP 0 587 849 B1 8

and Generator-Umgebungslufttemperatur, urn einen zweiten Wert zu erzeugen, (d) means for controlling the alternator field cur- iii. Multiplizieren des zweiten Wertes mit ei- rent in response to the calculated traction motor ner Konstanten, die mit der Zeitrate der current limit value. s Lastreduktion in Beziehung steht, urn einen dritten Wert zu erzeugen, und 6. A thermal protection overload system as claimed in iv. Subtrahieren des dritten Wertes von ei- claim 5 further comprising: ner Konstanten, die mit einer maximalen zulassigen Wicklungstemperatur in Bezie- (a) means for sensing an existing traction motor 10 hung steht, urn einen vierten Wert zu er- current value; and zeugen, der den berechneten Traktions- (b) means for comparing the calculated traction motor-Stromgrenzwert angibt, und motor current limit value to the existing traction motor current value. (d) Steuern des Generatorfeldstroms als Ant- 15 wort auf den berechneten Traktionsmotor- 7. A thermal protection overload system as claimed in Stromgrenzwert. claim 5 wherein the means for sensing ambient inlet air temperature comprises a winding temperature Steuerverfahren fur thermischen Uberlastschutz sensor. nach Anspruch 1, wobei der Schritt des Steuerns 20 der thermischen Uberlast ferner den Schritt enthalt, 8. A thermal protection overload system as claimed in dal3 der Generatorfeldstrom automatisch so einge- claim 5 wherein the means for providing a sensor stellt wird, dal3 der abgetastete Traktionsmotor- temperature comprises an alternator stator winding strom gleich dem berechneten Traktionsmotor- embedded temperature sensor. Stromgrenzwert ist. 25 9. A thermal protection overload system as claimed in Steuerverfahren fur thermischen Uberlastschutz claim 6 wherein the means for calculating a traction nach Anspruch 1 , ferner die Schritte enthaltend: motor current limit comprises a continuous calculation. (a) Abtasten eines bestehenden Traktionsmo- 30 tor-Stromwertes (34) und 10. A thermal protection overload system as claimed in (b) Vergleichen des berechneten Traktionsmo- claim 6 wherein the means for sensing an existing tor-Stromgrenzwertes mit dem bestehenden traction motor current value comprises a dc current Traktionsmotor-Stromwert (36). shunt. 35 4. Steuerverfahren fur thermischen Uberlastschutz nach Anspruch 1, wobei der Schritt des Bereitstel- Patentanspriiche lens einer Sensortemperatur ferner den Schritt enthalt, dal3 ein in die Statorwicklung des Generator 1. Steuerverfahren furthermischen Uberlastschutz fur eingebetteter Temperatursensor verwendet wird. eine Lokomotive mit einem Generator, der mehre- 40 ren Traktionsmotoren Gleichstromleistung zufuhrt, 5. Thermisches Uberlastschutzsystem fur eine Loko- wobei das Verfahren die Schritte enthalt: motive mit einem Generator, der mehreren Trakt- ionsmotoren Gleichstromleistung zufuhrt, enthal- (a) Bereitstellen einer Statorwicklungs-Sensor- tend: temperatur (22), 45 (b) Abtasten von UmgebungseinlaBlufttempe- (a) eine Einrichtung zum Bereitstellen einer ratur zu dem Generator (30), Statorwicklungs-Sensortemperatur, (c) Berechnen einer Traktionsmotor-Strom- (b) eine Einrichtung zum Abtasten von Umge- grenze (32), urn einen berechneten Traktions- bungseinlaBlufttemperatur zu dem Generator, motor-Stromgrenzwert zu erzeugen, enthal- so (c) eine Einrichtung zum Berechnen einer tend die Schritte: Traktionsmotor-Stromgrenze, urn einen berechneten Traktionsmotor-Stromgrenzwert zu i. Dividieren einer Differenz zwischen der erzeugen, enthaltend: Statorwicklungs-Sensortemperatur und der Generator-Umgebungslufttemperatur 55 i. eine Einrichtung zum Dividieren einer Dif- durch einen Kalibrationsfaktor, urn einen ferenz zwischen der Sensortemperatur ersten Wert zu erzeugen, und der Umgebungslufttemperatur des ii. Summieren des ersten Wertes und der Generators durch einen Kalibrationsfaktor,

5 9 EP 0 587 849 B1 10

um einen ersten Wert zu erzeugen, tant un alternateur fournissant un courant continu a ii. eine Einrichtung zum Summieren des er- une pluralite de moteurs de traction, ce procede sten Wertes und der Umgebungslufttem- comprenant les etapes de: peratur des Generators, um einen zweiten Wert zu erzeugen, 5 (a) obtention d'une temperature (22) de capteur iii. eine Einrichtung zum Multiplizieren des de temperature d'enroulement statorique; zweiten Wertes mit einer Konstanten, die (b) detection de la temperature de I'air ambiant mit einer Zeitrate der Lastreduktion in Be- d'entree de I'alternateur (30); ziehung steht, um einen dritten Wert zu er- (c) calcul d'une limite (32) de courant de moteur zeugen, und 10 de traction pour generer une valeur limite cal- iv. eine Einrichtung zum Subtrahieren des culee de courant de moteur de traction compre- dritten Wertes von einer Konstanten, die nant les etapes de: mit einer maximalen zulassigen Wick- lungstemperatur in Beziehung steht, um ei- i. division de la difference entre la tempe- nen vierten Wert zu erzeugen, der den be- rs rature de capteur d'enroulement statorique rechneten Traktionsmotor-Stromgrenz- et la temperature de I'air ambiant de I'alter- wert angibt, und nateur a I'aide d'un facteur d'etalonnage pour generer une premiere valeur, (d) eine Einrichtung zum Steuern des Genera- ii. sommation de la premiere valeur et de torfeldstroms als eine Antwort auf den berech- 20 la temperature de I'air ambiant de I'alterna- neten Traktionsmotor-Stromgrenzwert. teur pour generer une deuxieme valeur, iii. multiplication de la deuxieme valeur par 6. Thermisches Uberlastschutzsystem nach An- une constante Nee a un regime de reduc- spruch 5, ferner enthaltend: tion de charge pour generer une troisieme 25 valeur, et (a) eine Einrichtung zum Abtasten eines beste- iv. soustraction de la troisieme valeur d'une henden Traktionsmotor-Stromwertes, und constante Nee a une temperature d'enrou- (b) eine Einrichtung zum Vergleichen des be- lement maximale permise pour generer rechneten Traktionsmotor-Stromgrenzwertes une quatrieme valeur qui est indicative mit dem bestehenden Traktionsmotor-Strom- 30 d'une valeur limite de courant de moteur de wert. traction calculee; et

7. Thermisches Uberlastschutzsystem nach An- d) commande du courant inducteur de I'alter- spruch 5, wobei die Einrichtung zum Abtasten von nateur en reponse a la valeur limite calculee de UmgebungseinlaBlufttemperatur einen Wicklungs- 35 courant de moteur de traction. temperatursensor aufweist. 2. Procede de commande de protection de surcharge 8. Thermisches Uberlastschutzsystem nach An- thermique selon la revendication 1 , dans lequel spruch 5, wobei die Einrichtung zum Bereitstellen I'etape de commande de la surcharge thermique einer Sensortemperatur einen in die Statorwicklung 40 comprend, en outre, I'etape de reglage automatique des Generators eingebetteten Temperatursensor du courant inducteur de I'alternateur de maniere aufweist. que le courant detecte du moteur de traction soit egal a la valeur limite calculee de courant de moteur 9. Thermisches Uberlastschutzsystem nach An- de traction. spruch 6, wobei die Einrichtung zum Berechnen ei- 45 ner Traktionsmotor-Stromgrenze eine kontinuierli- 3. Procede de protection contre les surcharges ther- che Berechnung aufweist. miques selon la revendication 1, comprenant, en outre, les etapes de: 10. Thermisches Uberlastschutzsystem nach An- spruch 6, wobei die Einrichtung zum Abtasten eines so (a) detection d'une valeur (34) existante de bestehenden Traktionsmotor-Stromwertes einen courant de moteur de traction; et Gleichstromshunt aufweist. (b) comparaison de la valeur limite calculee de courant de moteur de traction avec la valeur existante (36) de courant de moteur de traction. Revendications 55 4. Procede de protection contre les surcharges ther- 1 . Procede de commande de protection contre les sur- miques selon la revendication 1 , dans lequel I'etape charges thermiques pour une locomotive compor- d'obtention d'une temperature de capteur com-

6 11 EP 0 587 849 B1 12

prend, en outre, I'etape d'utilisation d'un capteur de 8. Systeme de protection contre les surcharges ther- temperature noye dans I'enroulement statorique de miques selon la revendication 5, dans lequel le I'alternateur. moyen pour obtenir une temperature de capteur comprend un capteur de temperature noye dans 5. Systeme de protection contre les surcharges ther- 5 I'enroulement statorique de I'alternateur. miques pour une locomotive comportant un alter- nates fournissant un courant continu a une plura- 9. Systeme de protection contre les surcharges ther- lity de moteurs de traction comprenant: miques selon la revendication 6, dans lequel le moyen pour calculer une limite de courant de mo- (a) un moyen pour fournir une temperature de 10 teur de traction comprend un moyen de calcul con- capteur d'enroulement statorique; tinu. (b) un moyen pour detecter la temperature de I'air ambiant d'entree de I'alternateur; 10. Systeme de protection contre les surcharges ther- (c) un moyen pour calculer une valeur limite de miques selon la revendication 6, dans lequel le courant de moteur de traction afin de generer is moyen pour detecter une valeur existante de cou- une valeur limite calculee de courant de moteur rant de moteur de traction comprend un shunt pour de traction, comprenant, courant continu.

i. un moyen pour diviser la difference entre la temperature de capteur et la temperature de I'air ambiant de I'alternateur par un facteur d'etalonnage afin de generer une premiere valeur, ii. un moyen pour faire la somme de la premiere valeur et de la temperature de I'air 25 ambiant de I'alternateur afin de generer une deuxieme valeur, iii. un moyen pour multiplier la deuxieme valeur et une constante Nee a un regime de reduction de charge afin de generer une 30 troisieme valeur, et iv. un moyen pour soustraire la troisieme valeur d'une constante Nee a une temperature maximale permise d'enroulement afin de generer une quatrieme valeur qui est in- 35 dicative de la valeur limite calculee de courant de moteur de traction; et

(d) un moyen pour commander le courant inducteur de I'alternateur en reponse a la valeur 40 limite calculee de moteur de traction.

6. Systeme de protection contre les surcharges thermiques selon la revendication 5, comprenant, en outre: 45

(a) un moyen pour detecter une valeur existante de courant de moteur de traction; et (b) un moyen pour comparer la valeur limite calculee de courant de moteur de traction avec la 50 valeur existante de courant de moteur de traction.

7. Systeme de protection contre les surcharges thermiques selon la revendication 5, dans lequel le moyen pour detecter la temperature de I'air ambiant d'entree comprend un capteur de temperature d'enroulement.

7 EP 0 587 849 B1 P 0 587 849 B1

READ WINDING I -22 SENSOR

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