Abstract:
A train including a multi-phase electrical distribution network permitting easy detection and location of ground faults, and a method of detecting a ground fault on such a train are disclosed. Net current tapped at each of the cars is sensed. In the event the net current tapped at a car does not equal zero, an alarm signifying a ground fault at that car is triggered. In this way, ground faults on the train may be easily located and serviced.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to rail vehicles, and more particularly to trains including mobile power distribution networks.  
       BACKGROUND OF THE INVENTION  
       [0002]     In today&#39;s world electricity is required nearly everywhere. In many mobile transport vehicles electricity is used to power auxiliary equipment such as air conditioners, lighting and heaters. Rail based vehicles, such as trains moved by diesel or similar locomotives, for example, typically include an electric generator that generates electricity that is distributed by way of a modular distribution network to cars on the train.  
         [0003]     In such an environment, electricity is generated on the moving vehicle and distributed by way of a mobile distribution network. At each electricity consuming car, electricity is tapped and consumed.  
         [0004]     Because such a distribution network is modular, and electric power is consumed at many locations, faults are difficult to locate. In conventional trains such faults are located by elimination. The fault is initially detected at the generator. After its detection, cars are systematically disconnected from the mobile network until the location of the fault is isolated. This, however, is time consuming and labour intensive.  
         [0005]     Clearly then, there is a need for a method of detecting a fault on a rail transport vehicle having a modular electric distribution system, and an improved rail transport vehicle allowing easy electric fault detection on an associated distribution network.  
       SUMMARY OF THE INVENTION  
       [0006]     In accordance with the present invention multi-phase electric power is distributed in a train. The train includes a plurality of cars, each of which includes a wiring harness for interconnection to an adjacent car to distribute multi-phase electric power. The method includes generating the multiphase electric power; providing the multiphase electric power to a power distribution network formed of a plurality of such wiring harnesses; tapping multiphase power from the power distribution network at at least one of the cars for consumption at the at least one of the cars; sensing net current tapped at the at least one of the cars; and triggering an alarm if the net current tapped at the at least one of the cars does not equal zero, signifying a ground fault at the at least one car.  
         [0007]     A train exemplary of the invention includes, a locomotive; a plurality of cars; a multi-phase electric generator; an electrical distribution network extending from the electric generator to the plurality of cars; at least one of the cars comprising a power providing conductors for providing multi-phase electric power to an electric load on the car; and a ground fault sensor interconnected with the power providing conductors for sensing and indicating a ground fault at the at least one of the cars.  
         [0008]     Other aspects and features of the present invention will become apparent to those of ordinary skill in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     In the figures which illustrate by way of example only, embodiments of the present invention,  
         [0010]      FIG. 1  is an elevational view of a train including a distribution system exemplary of embodiments of the present invention;  
         [0011]      FIG. 2  is a top plan view of the train of  FIG. 1 ;  
         [0012]      FIG. 3  is a schematic diagram of portions of the distribution system of  FIG. 1 ; and  
         [0013]      FIG. 4  is a schematic diagram of a ground fault detection circuit, used in the train of  FIG. 1 . 
     
    
     DETAILED DESCRIPTION  
       [0014]      FIG. 1  illustrates a rail borne vehicle in the form of train  10 , including an electrical distribution network  12 , exemplary of an embodiment of the present invention. As illustrated, train  10  includes a locomotive  18  and a plurality of towed cars  16 . The train  10  may, for example, be a passenger train, with cars  16  suited for passenger transport.  
         [0015]     Locomotive  18  includes a conventional engine (not specifically illustrated) that may, for example, be a diesel engine. In the described embodiment, a generator  14  for generating electricity used to power auxiliary equipment on train  10  is located within locomotive  18 . Electric power generated by generator  14  is distributed throughout train  10  by way of a mobile electric power distribution network  12 .  
         [0016]     Train  10  is illustrated in top plan view in  FIG. 2 . Specifically, distribution network  12  is a three phase distribution network that extends along the top of train  10 . In the disclosed embodiment, distribution network  12  includes a left and right set of three length-wise extending conductors  22   a  and  22   b.  Each of the length-wise extending conductors transports one phase of three-phase electric power from generator  14  to each of cars  16 . Network  12  is modular, in that each car includes two sets of three conductor harnesses  24  (a left and right harness), terminated at each end by a connector  26 . Connectors of adjacent cars may be interconnected so that network  12  may extend from the front to the rear of train  10  providing electric power to each car  16 . As new cars are added to train  10 , harnesses  24  of such cars may be interconnected to an existing network  12 .  
         [0017]     In order to limit the power required to be carried by each harness  24 , by each set of conductors  22   a  or  22   b,  and through connectors  26 , two separate three-phase distribution harnesses  24  are provided on each car  16 . In this way, the total power delivered to each of cars  16  may be delivered by two sets of conductors  22   a  and  22   b,  each only needing to carry half the current required by a single set of conductors.  
         [0018]     Portions of distribution network  12  and generator  14  are schematically illustrated in  FIG. 3 . As illustrated, generator  14  provides two three-phase feeds,  20   a  and  20   b.  In the disclosed embodiment, generator  14  is WYE-connected. A centre tap  28  of generator  14  is connected to ground by way of ground-fault limiting impedance  30 . Ground limiting impedance  30  is preferably sufficiently large to limit ground fault current, preferably to  5 A or less. The two three phase feeds  20   a  and  20   b  emanating from generator  14  terminate at connectors  26   a  and  26   b,  respectively.  
         [0019]     The portion of electric distribution network  10  of a single rail car  16  is similarly schematically depicted in  FIG. 3 . As illustrated, each car is equipped with a left and right harness  24 . Two connectors  26  allow the interconnection of each harness  24  including conductors  22   a  or  22   b  spanning the length of car  16  to connectors  26  of a harness  24  of an adjacent car  16  or to connectors  26   a  and  26   b  of locomotive  18 .  
         [0020]     Conductors  22   a  and  22   b  of each of harnesses  24  extending along the length of the car may be tapped by three-phase power providing conductors  34   a  and  34   b.  Each of these feeds one of electrical loads  36   a  and  36   b.  Loads  36   a  and  36   b  may, for example, be heaters, air conditioners, lights, or similar electrical equipment used in rail car  16 .  
         [0021]     In order to limit the current provided to load  36   a/   36   b  by way of power providing conductors  34   a  and  34   b,  these are preferably fused or fed through circuit breakers. As illustrated, one current limiter  38 , for example in the form of a circuit breaker or fuse, fuses each phase of the provided three-phase power, provided by way of left or right harnesses  24 .  
         [0022]     Additionally, exemplary of an embodiment of the present invention, ground fault detection circuits  32   a  and  32   b  (individually a ground fault detection circuit  32 ) are provided to detect ground faults caused by a load connected by way of power providing conductors  34   a  to left harness  24  or by way of power providing conductors  34   b  connected to right harness  24 .  
         [0023]     As illustrated in  FIG. 4 , each ground fault detection circuit  32  includes a current sensor  40 , preferably in the form of a current-sensing transformer, and a conventional ground fault relay  42 , in the form of a DGF digital ground fault relay, interconnected in series with a ground fault indicator  44 . Ground fault indicator  44  is preferably a light. The series combination of relay  42  and indicator  44  are connected between a potential source which may for example be tapped from one of the phases of power providing conductors  34   a  or  34   b.  An identical ground fault detection circuit  32   b  is interconnected with tap  24   b.    
         [0024]     In operation, generator  14  generates three-phase electrical power. Generator  14  may be driven by the engine within locomotive  18  or by another suitable locomotive force. In the absence of any ground faults along distribution system  12 , generator  14  will be balanced; that is, the total current provided by the three-phase output of generator  14  will sum to zero. As such, no current will flow through ground fault-limiting resistor  30 . Generated electricity is provided along conductors  22   a  and  22   b,  with one phase of each the three phases provided along a single conductor. As a result of the electrical interconnection of cars  16 , the generated power is propagated along conductors  22   a  and  22   b  and along train  10 .  
         [0025]     Within each rail car  16 , power is tapped from conductors  22   a  and  22   b  by power providing conductors  34   a  and  34   b,  depicted in  FIG. 3 . In the absence of any ground fault along any power providing conductors  34   a  or  34   b,  the net current flowing through all three phases of any one set of power providing conductors  34   a  and  34   b  will also be zero. As a result, the current through sensor  40  of each ground fault detection circuit  32  will be zero.  
         [0026]     In the presence of a ground fault anywhere along network  12 , generator  14  will become unbalanced and a current reflecting the ground fault will flow through ground fault resistor  30 . Conventionally, such a ground fault may be difficult to locate or isolate. Advantageously, ground fault in any of car  16  results in detection of the ground fault at power providing conductors  34   a  or  34   b,  as the net current flowing through an associated sensor  40  of ground fault-detection circuit  32   a  or  32   b  will no longer be zero.  
         [0027]     As a result, current through sensor  40  will trip the associated ground fault relay  42  causing it to close. In response, the associated ground fault indicator  44  will be illuminated. As each car  16  includes a separate ground fault detection circuit  32  for each of its power providing conductors  34   a  or  34   b,  a ground fault may be easily located and isolated.  
         [0028]     Preferably, two ground fault indicators  44  (one for the right load, the other for the left load) are located in the panel box of each car. In the presence of a ground fault, an operator may simply inspect the ground fault indicator  44  on each car, thereby allowing for quick detection and location of a ground fault. Complex isolation of ground faults on train  10  is no longer required.  
         [0029]     As should be appreciated, multiple ground fault indicators  44  could be replaced remotely located at a single location. Remotely located ground fault indicators could be signalled through a suitable wired or wireless communications network. Optionally, ground faults could be logged using general purpose computing equipment suitably adapted to perform such logging. Similarly, ground fault detection circuit  32  could be replaced by a conventional ground fault detection circuit, as for example available from IPC Resistors under model number MGFR 20-ZB, or the like. In a further alternate embodiment, the ground fault detection circuit could optionally include a circuit breaker in series with conductors  34   a/   34   b  to limit the flow of current to any car having a detected ground fault.  
         [0030]     Of course, the above described embodiments, are intended to be illustrative only and in no way limiting. The described embodiments of carrying out the invention, are susceptible to many modifications of form, arrangement of parts, details and order of operation. The invention, rather, is intended to encompass all such modification within its scope, as defined by the claims.