Abstract:
A railroad locomotive includes traction motors for propelling the locomotive, and an isolation switch disposed in signal communication with at least one of the traction motors for isolating a faulting motor from the other traction motors.

Description:
BACKGROUND  
         [0001]    Locomotives may employ a plurality of traction motors, typically four or six, for driving locomotive wheels. However, conventional wiring of these motors has led to certain disadvantages with respect to the interrelationships between respective motors. For example, prior art traction motors were typically hard wired in parallel and/or series with at least three to five other motors. Thus, a fault in one motor would render all of the motors inoperable and thereby render the locomotive inoperable. Accordingly, it is desirable to provide traction motor isolation for railroad locomotives to disable any individual traction motors exhibiting faults while leaving the non-faulting motors operable.  
         SUMMARY  
         [0002]    The aforementioned and other drawbacks and deficiencies of the prior art are overcome or alleviated by a traction motor isolation switch in accordance with the present disclosure.  
           [0003]    A railroad locomotive includes traction motors for propelling the locomotive, and an isolation switch disposed in signal communication with at least one of the traction motors for isolating a faulting motor from the other traction motors.  
           [0004]    These and other features and advantages of the present disclosure may be better understood and appreciated when considered in conjunction with the following detailed description and associated drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    Referring now to the drawings, in which like elements are numbered alike in the several Figures:  
         [0006]    [0006]FIG. 1 is a diagram of a prior art traction motor circuit;  
         [0007]    [0007]FIG. 2 is a diagram of an alternator and ground-fault detection circuit;  
         [0008]    [0008]FIG. 3 is a diagram of the prior art traction motor circuit but showing faults exposing the circuit to ground in several locations; and  
         [0009]    [0009]FIG. 4 is a diagram of a traction motor circuit of this invention with traction motor circuit isolation. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0010]    [0010]FIG. 1 shows a prior art traction motor circuit generally indicated by the reference numeral  10 . The circuit  10  is part of a larger circuit (not shown) having at least two circuits  10  electrically connected in parallel between positive power leads  16  and negative power leads  18 . Each circuit  10  supports a traction motor  12 . Each traction motor  12  has a negative motor lead  14  that is tied to the negative lead of the counterpart traction motors  12  in the larger circuit (not shown), and a positive motor lead  15 .  
         [0011]    A brake grid resistor  20  is connected at a first end to the negative motor lead  14 , and at a second end to a braking switch  22  and a self-load box contactor switch  24 . A contactor switch is a switch that can open under an electrical load, and typically has blowout coils. The braking switch  22  is connected, in turn, to the positive power lead  16 ; and the self-load box contactor switch  24  is connected, in turn, to a junction  26 . The junction  26  is connected to a contactor switch  28 , which is connected, in turn, to the positive motor lead  15 . The junction  26  is also connected to a shunt  30 , which is connected to the positive power lead  16 .  
         [0012]    The negative motor lead  14  is also connected to a braking switch  32 , which has its through terminal connected to a junction  34 . The junction  34  is connected to a reversing switch  36 , which has its through terminal connected to a field inductance  38 . The field inductance  38  is connected, in turn, to a reversing switch  40 . The third terminal of the reversing switch  40  is connected to the junction  34 , and the through terminal of the reversing switch  40  is connected to a junction  42 . The junction  42  is connected to the third terminal of the reversing switch  36 . The junction  42  is also connected to a braking switch  44 , which has its through terminal connected to the negative power lead  18 .  
         [0013]    The third terminal  46  of the braking switch  44  is connected to the field of the next traction motor at the terminal corresponding to reference numeral  48 , while a third terminal  48  of the braking switch  32  is connected to the previous traction motor field, such as from the terminal  46  of the next traction motor field of the previous traction motor. In other words, each terminal  46  is connected to a terminal  48  of another circuit  10  that corresponds to another or next traction motor, and each terminal  48  is connected to a terminal  46  of another circuit  10  that corresponds to another or previous traction motor.  
         [0014]    In FIG. 2, a supply circuit is indicated generally by the reference numeral  50 . The circuit  50  has a positive power lead  16  connected to the positive power lead  16  of FIG. 1, and a negative power lead  18  connected to the negative power lead  18  of FIG. 1. The supply circuit  50  includes an alternator  52  for producing electricity, connected to a regulator  54 . The regulator  54  typically includes diode rectifiers and voltage regulation circuitry as known in the pertinent art. The regulator  54  is connected, in turn, to the positive and negative power leads  16  and  18 , respectively.  
         [0015]    The exemplary supply circuit  50  further includes fault detection circuitry  56 . The circuitry  56  detects a ground-fault condition developing on either the positive power lead  16  or the negative power lead  18  by providing a path for the fault current from a neutral terminal  58  of the alternator  52  through a resistor  60  to ground potential. Detection circuit  62  generally senses the voltage drop across the resistor  60  as indicative of the current flow across the resistor  60  due to a ground-fault.  
         [0016]    Thus, the circuit  50  will detect fault current by monitoring the current in the neutral leg  58  of the alternator  52 . Typically, the sensed fault current will be used to disable traction motors of the locomotive as connected in a parallel circuit. A ground-fault condition developing on either the positive side  16  or the negative side  18  of the propulsion voltage will provide a path for the fault current through the resistor  60  to the neutral leg  58  of the alternator  52 . The ground-fault detector  62  will sense the fault current across the resistor  60 .  
         [0017]    There are a number of possible ground-faults. For example, a traction motor ground-fault may develop with a wet traction motor series field, armature or brushes. Alternate faults may originate in the traction motor leads or in the grid resistors.  
         [0018]    [0018]FIG. 3 shows the traction motor circuit  10  of FIG. 1, with three plausible ground-fault conditions. As shown in FIG. 3, a ground-faulting armature is indicated generally by the reference numeral  64 , a ground-faulting field is indicated generally by the reference numeral  66 , and a ground-faulting grid resistor is indicated generally by the reference numeral  68 . Any one of these ground-faults  64 ,  66 , or  68  will provide a path between the alternator neutral  58  of FIG. 2 and the propulsion voltage leads  16  and  18 .  
         [0019]    Turning now to FIG. 4 wherein like reference numerals preceded by the number  1  are used to refer to like elements, an exemplary improved traction motor circuit is indicated generally by the reference numeral  110 . The circuit  110  is part of a larger circuit (not shown) having at least two circuits  110  electrically connected in parallel between positive power leads  116  and negative power leads  118 . Each circuit  110  supports a traction motor  112 . Each traction motor  112  has a negative motor lead  114  that is connected to a junction  172 , and a positive motor lead  115 .  
         [0020]    A brake motor isolation switch  170  is connected at each of its switched terminals to the junction  172 , and at its through terminal to a switched negative lead  174 . The switched negative lead  174  is tied to the switched negative leads  174  of the counterpart circuits  110  in the larger circuit (not shown). The switched negative lead  174  is also connected to a first end of a brake grid resistor  120 . The grid resistor  120  is connected at its second end to a braking switch  122  and a brake motor isolation switch  125 .  
         [0021]    The braking switch  122  is connected, in turn, to the positive power lead  116 ; and the brake motor isolation switch  125  is connected, in turn, to a junction  126 . The junction  126  is connected to a contactor switch  128 , which is connected, in turn, to the positive motor lead  115 . The junction  126  is also connected to a shunt  130 , which is connected to the positive power lead  116 .  
         [0022]    The negative motor lead  114  is also connected to a braking switch  132 , which has its through terminal connected to a junction  134 . The junction  134  is connected to a reversing switch  136 , which has its through terminal connected to a field inductance  138 . The field inductance  138  is connected, in turn, to a reversing switch  140 .  
         [0023]    The third terminal of the reversing switch  140  is connected to the junction  134 , and the through terminal of the reversing switch  140  is connected to a junction  142 . The junction  142  is connected to the third terminal of the reversing switch  136 . The junction  142  is also connected to a braking switch  144 , which has its through terminal connected to a new contactor switch  147 . The switch  147  is connected, in turn, to the negative power lead  118 .  
         [0024]    The third terminal  146  of the braking switch  144  is connected to the field of the next traction motor at the terminal corresponding to reference numeral  148 , while a third terminal  148  of the braking switch  132  is connected to the previous traction motor field, such as from the terminal  146  of the next traction motor field of the previous traction motor. In other words, each terminal  146  is connected to a terminal  148  of another circuit  110  that corresponds to another or next traction motor, and each terminal  148  is connected to a terminal  146  of another circuit  110  that corresponds to another or previous traction motor.  
         [0025]    In operation of the circuit  110 , the brake motor isolation switch  170  switches off between a negative motor lead  114  of a traction motor  112  and a brake grid resistor  120 , to electrically separate the resistor  120  from the traction motor  112 . The resistor  120  is not required during a normal motoring mode when no braking is required, so a faulting resistor  120  is isolated with the brake motor isolation switch  170 . Under normal non-fault conditions, the brake motor isolation switch  170  connects the resistors  120  for dynamic braking and self-load functions. However, during a ground-fault of a resistor  120 , the brake motor isolation switch  170  disables the dynamic braking and self-load function to isolate the fault.  
         [0026]    Similarly, if a ground-fault current develops in a traction motor  112 , a controller (not shown) will be able to isolate the motor  112  by locking out the faulting motor  112 . The controller (not shown) will open a motor contactor  128  on a positive motor lead  115  and open the brake motor isolation switch  170  on the negative motor lead  114 . By opening the positive and negative leads,  115  and  114  respectively, the faulting traction motor  112  will be isolated, and the locomotive will again be operational.  
         [0027]    The present embodiment provides the operator or controller with the ability to isolate a grounded traction motor to allow the locomotive to complete its mission, and return to the service shop under its own power. Using this feature, the locomotive will not be disabled with a ground-fault on either a traction motor or a grid resistor. The electrical isolation of the grid resistors allows motoring of the traction motors during a faulting condition. However, the faulting condition will result in some loss of dynamic braking and self-load. One or more grounded traction motor circuits may be detected and reported by appropriate software to limit operation of the locomotive, if necessary. The traction motor isolation may be automatic or may require the operator to manually switch out the faulting motor by trial and error. Isolation of a faulting motor in a trailing locomotive may also be automatic or require the operator to manually switch out the faulting motor.  
         [0028]    In one operating mode, onboard diagnostics may detect fault current from a grounded traction motor and temporarily disable the locomotive. The operator would then be able to isolate the faulting motor by opening the motor contactor switch on the positive propulsion lead and opening a new contactor switch on the negative propulsion lead. By isolating the faulting traction motor, the locomotive will again be operational but with de-rated performance.  
         [0029]    Traction motor isolation may also include isolation of grid resistors. With prior locomotive wiring, the grid resistors were typically wired to the negative motor lead of the even numbered traction motors, and the common wiring of the resistors to the motors would distribute the fault and disable the locomotive, even if the traction motor is cut out with contactors.  
         [0030]    However, since the resistors are not required during motoring, a faulting resistor condition can be isolated during motoring by isolating the resistors from the traction motor to thereby avoid disabling the locomotive. Only the dynamic braking and self-load functions are degraded for the isolated resistor. During normal operating conditions, with no faults on the resistors, the brake motor isolation switch and the existing braking switch will switch the resistors across the traction motors for dynamic braking or self-load.  
         [0031]    Thus, at least the following advantageous improvements and features to traction motors are provided by embodiments of the present disclosure:  
         [0032]    Electrical isolation in the event of a ground or other electrical fault is achieved, thereby leaving all of the remaining traction motors of the locomotive (typically three to five motors) available for use. This feature is in contrast to the prior art wherein each traction motor was hard wired in parallel with typically three to five other motors. Thus, a fault in one motor would render all of the parallel motors inoperable. By providing electrical isolation between motors, the remaining (i.e., operable) motors are available to allow the locomotive to complete its mission and return home for service.  
         [0033]    The ground-fault detector is wired so that it can monitor a ground-fault in any of the multiple (e.g., four or six) traction motors, but remain operable even if a fault occurs. The novel brake motor isolation switch enables this feature. This feature is in contrast to the prior art wherein the ground-fault detector was hard wired to a plurality of motors so that if a fault occurred to any motor, the fault would render the detector inoperable for all of the motors.  
         [0034]    Time-delay switching of a pair of isolating switches is provided for isolating the traction motor. The first isolating switch may be opened while under electrical load (e.g., 1200 amps), so this switch is physically isolated against the resultant arcing, which isolation is costly and requires a lot of space on a locomotive. However, because of the time-delay, the second isolating switch can be opened while electrically unloaded, and thus may be a much smaller and less expensive switch. This feature is in contrast to the prior art wherein the operation of these two switches was not effected by means of the time-delay opening of these switches, and therefore required two large and expensive switches.  
         [0035]    The motors are also associated with a novel mechanical and electrical arcing shield for the isolating switch. In the prior art, a switch opening against a load was housed in a special cab which required significant open space, so that any arcing would not reach the metal enclosure defining the cab. In an embodiment of the present disclosure, a closely spaced substantially non-conductive housing (such as glass) is provided to contain any arcing. This shielded switch is a significant improvement over the prior art, as it requires far less space in the locomotive.  
         [0036]    While exemplary embodiments have been shown and described, various modifications and substitutions may be made thereto by those of ordinary skill in the pertinent art, both now and in the future, without departing from the true scope and spirit of this disclosure. Accordingly, it is to be understood that the present disclosure has been made by way of illustration only, and such illustrations and embodiments as have been disclosed herein are not to be construed as limiting to the claims.