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 cur- rent, 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.