Abstract:
A ground loop detection and prevention system includes multiple electric power generators driven by one or more rotational power sources. Each of the electrical generators has a set of generator windings with a neutral point. A transformer having a number of primary windings as well as a secondary winding is connected to the neutral points via the primary transformer windings. An interrupter device such as a GFCI is connected across the transformer&#39;s secondary winding, such that when a ground loop current occurs in any of the generator windings, the interrupter device detects the loop and stops the operation of the generators.

Description:
TECHNICAL FIELD 
       [0001]    This patent disclosure relates generally to electrical power generation, and more particularly to a system for ground loop detection in generator neutral lines. 
       BACKGROUND 
       [0002]    Electrical power generators are commonplace today, both as stand-alone generators and as components of another system. For example, a utility backup generator facility contains a number of electrical generators as well as a power source for providing rotational energy to the generators. These components are housed in a stationary enclosure and are connected to remote consumers via electrical power cables. Similarly, in the transportation field, a railway locomotive typically includes a number of electrical generators and a diesel engine for driving the generators, with all of these components being carried on a common mobile chassis. 
         [0003]    Whatever the setting, there are certain issues that are common to both stationary and mobile generator sets (gensets). A significant issue is the existence of ground loops, and the harm such loops can cause. A ground loop is a current loop within lines that are ostensibly at the same voltage. In other words, while electrically interconnected points are theoretically assumed to be at the same electrical potential, the material actually utilized for such interconnections has resistance, and thus differs from the ideal resistance-free conductor assumed in the theoretical models. 
         [0004]    As such, voltage changes at one of the interconnected points may result in a voltage differential between interconnected points. This differential gives rise to a current within the associated conductors. This unwanted current is referred to as a ground loop. In addition to wasting electrical energy and providing unexpected radio frequency interference, such loops are also capable of destroying conductive components of the generator such as windings, cabling, etc. 
         [0005]    In multiphase generator systems, generator neutral lines may be linked and grounded to ground the system and its output. In this context, ground loops often arise in the interconnected neutral lines, causing damage to system components. Thus, it is important to be able to locate and remedy any such ground loops. 
         [0006]    While the first step in remedying a ground loop in a generator system is the identification of the loop, ground loop currents through generator neutrals are notoriously difficult to detect using conventional methods. For example, the use of hand held clamp n current meters may not detect sporadic loop issues, and will also not allow the detection of more continuous loop currents that do not induce a strong reaction in inductive sensors. 
         [0007]    While the disclosed principles herein are directed at least in part to overcoming one or more disadvantages, noted or otherwise, it will be appreciated that the innovation herein is defined by the attached claims without to regard to whether and to what extent the specifically claimed embodiment overcomes one or more of the noted problems in the existing technology. Moreover, it will be appreciated that any discussion herein of any reference or publication is merely intended as an invitation to study the indicated reference itself, and is not intended to replace or supplement the actual reference. To the extent that the discussion of any reference herein is inconsistent with that reference, it will be appreciated that the reference itself is conclusive as to its teachings. 
       SUMMARY 
       [0008]    In one aspect, the disclosed generator system includes a plurality of electrical generators configured for connection to one or more rotational power sources, with each of the electrical generators having a set of generator windings with a neutral point. A transformer having a number of primary windings as well as a secondary winding is connected to the neutral points via the primary transformer windings. An interrupter device such as a GFCI is connected across the transformer&#39;s secondary winding, and is configured to stop the operation of the generators when a ground loop current occurs in any of the generator windings. 
         [0009]    In another aspect, a method of detecting a ground loop current in a generator system includes connecting a plurality of multi-phase electrical generators to a rotational power source, and linking the neutral point of each set of generator windings to a respective primary winding of a multi-phase transformer. A secondary winding of the multi-phase transformer is linked to an interrupter device configured to stop the operation of the plurality of generators when triggered. In this way, a ground loop current occurring in any set of the generator windings will create a voltage differential across the secondary winding, triggering the interrupter device and stopping the operation of the plurality of generators. 
         [0010]    In yet another aspect, a generator ground loop detection system includes a multiphase transformer having a secondary winding and a plurality of primary windings inductively linked to the secondary winding. A ground link is connected to one end of each primary winding, and the opposite end of each primary winding is configured or made available for attachment to respective generator winding neutral points. An interrupter device is attached across the secondary winding to trigger based on current flow in any of the primary windings. 
         [0011]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention. Further aspects and features of the disclosed principles will be appreciated from the following detailed description and the accompanying drawings, of which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a circuit diagram of a genset and ground loop detection and prevention system in accordance with the described principles; 
           [0013]      FIG. 2  is a linearized schematic of a multiphase transformer usable in various implementations of the described principles; 
           [0014]      FIG. 3  is a circuit diagram of a four-generator genset and ground loop detection and prevention system in accordance with the described principles; and 
           [0015]      FIG. 4  is a linearized schematic of an extended multiphase transformer having linked three-phase transformers usable in various implementations of the described principles. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    This disclosure relates to detection of ground loop faults in genset systems. As noted above, in multiphase generator systems, generator neutral lines may be linked and grounded to ground the system and its output. The occurrence of ground loops, while potentially damaging, may be difficult to detect using conventional methods prior to such damage. 
         [0017]    In an embodiment of the described principles, a three-phase transformer is configured for linkage to the neutral connection on each genset, causing any circulating currents to induce an output voltage on the secondary coil of the linked three-phase transformer. This induced output voltage is then detected in one embodiment via connection of the three-phase transformer output to a current sensor such as the sensing inputs of a single GFCI. In this way, the GFCI can provide a ground fault detection function. 
         [0018]    Given this overview, and turning now to  FIG. 1 , this figure illustrates a circuit schematic of a multiple generator ground loop detection system and configuration  100 . The illustrated configuration includes genset having a plurality of three-phase generators  101 ,  102 ,  103 . Although three generators are shown, it will be appreciated that a greater or lesser number of generators may be used depending upon user preference. 
         [0019]    Each generator includes three windings, such that the first generator  101  includes winding  109 , winding  110 , and winding  111 , the second generator  102  includes winding  112 , winding  113 , and winding  114 , and the third generator  103  includes winding  115 , winding  116 , and winding  117 . Each generator  101 ,  102 ,  103  is powered by an engine or other power source (not shown in  FIG. 1 ), which turns a rotor (not shown) within the respective windings, also referred to as stator windings. The motion of the rotor induces a current and related voltage within each winding, which is collected as the generator output. As will be appreciated by those of skill in the art, other generator components such as voltage regulators, diode bridges, etc. are omitted from  FIG. 1  for clarity. 
         [0020]    Each generator winding set has a neutral point tied in DC to the neutral points of the other winding sets. Thus, the neutral point N 1  ( 104 ) of generator  101  is tied to the neutral point N 2  ( 105 ) of generator  102  and the neutral point N 3  ( 106 ) of generator  103 . Although tied with respect to DC, the neutral points  104 - 106  may experience potential differences with respect to AC activity. In particular, such tying is usually by way of conductors having an inherent though ideally minimal resistance value. Moreover, in the illustrated embodiment, respective windings of a three-phase transformer  118  are interposed in the connectors  125 - 127  between winding neutral points. 
         [0021]    In particular, the three-phase transformer  118  includes three primary windings  119 ,  120 ,  121 , inductively linked to a secondary coil  122 . In an embodiment, the output leads  123   a,    123   b  of the three-phase transformer  118  are connected to a GFCI (ground fault circuit interrupter) device  124 . A GFCI traditionally operates by sensing a current imbalance indicative of a ground fault, which is a fault to ground rather than a ground loop. However, in the illustrated implementation, the GFCI device  124  will react to the three-phase transformer by triggering if the transformer is energized by ground loop currents. In this way, any ground loop currents between connectors  125 - 127  induced by differential voltages will be transformed by the three-phase transformer  118  into a voltage signal that triggers the GFCI device  116 . When the GFCI device  116  is triggered, it interrupts power to the generators and stops electrical power generation until the operator corrects the ground loop condition, resets the GFCI device  116 , and restarts power generation. 
         [0022]    It will be appreciated that the three-phase transformer  110  is adapted in size and capacity to withstand and react to the possible ground loop current levels in any given implementation. Thus, for example, the three-phase transformer used to implement the described principles in a stationary municipal power facility may differ from the three-phase transformer used to implement the described principles in a locomotive application. 
         [0023]      FIG. 2  is a schematic diagram of a multi-phase transformer usable in the system configuration of  FIG. 1 . The illustrated multi-phase transformer  200  may be physically implemented as a toroidal transformer, though illustrated in linear form for clarity. The multi-phase transformer  200  exposes multiple inputs  201 ,  202 ,  203  for tying to three separate generator neutral points. The multi-phase transformer  200  provides two outputs  204 ,  205  configured to show a voltage differential in the event that any of the inputs  201 ,  202 ,  203  provides a current signal. 
         [0024]    Each input, e.g., input  201 , input  202 , and input  203 , is in series with a respective primary coil, e.g., primary coil  206 , primary coil  207 , and primary coil  208 . The opposite ends of the primary coils are linked. A secondary coil, e.g., secondary coil  209 , secondary coil  210 , and secondary coil  211 , is associated with each primary coil  206 ,  207 ,  208 . The secondary coils  209 ,  210 ,  211  are linked in series with one another, with the ends of the series serving as the multi-phase transformer  200  outputs  204 ,  205 . 
         [0025]    In this configuration, if there are no ground loops, there will be no current in any of the primary coils  206 ,  207 ,  208 . Thus, there will be no induced voltage across the multi-phase transformer  200  outputs  204 ,  205 . On the other hand, if there is any current in any primary coil  206 ,  207 ,  208 , there will be a corresponding current and induced voltage in the series connected secondary coils  209 ,  210 ,  211 , resulting in an induced voltage across the multi-phase transformer  200  outputs  204 ,  205 . 
         [0026]    Although  FIGS. 1 and 2  show the use of three generators and three primary transformer coils, it will be appreciated by those of skill in the art that the described principles are applicable to detect ground loops in gensets having any number of generators. In this regard,  FIG. 3  is a schematic illustration of an extendable four-generator ground loop detection system and configuration  300 . The illustrated configuration includes genset having four three-phase generators  301 ,  302 ,  303 ,  304 . As with system  100 , each generator in system  300  includes three windings, such that the first generator  301  includes winding  309 , winding  310 , and winding  311 , the second generator  302  includes winding  312 , winding  313 , and winding  314 , the third generator  303  includes winding  315 , winding  316 , and winding  317 , and the fourth generator  304  includes winding  318 , winding  319 , and winding  320 . 
         [0027]    Each generator  301 ,  302 ,  303 ,  304  includes a rotor (not shown) powered by an engine or other rotational power source. As with  FIG. 1 , other generator components such as voltage regulators, diode bridges, etc. are omitted from  FIG. 3  for clarity. Each generator winding set has a neutral point tied in DC to the neutral points of the other winding sets. Thus, the neutral point N 1  ( 305 ) of generator  301  is tied to the neutral point N 2  ( 306 ) of generator  302 , the neutral point N 3  ( 307 ) of generator  303  and the neutral point N 4  ( 308 ) of generator  304 . Respective windings of a multi-phase transformer  321  are interposed in the connectors  322 - 325  between winding neutral points  305 - 308 . 
         [0028]    In particular, the multi-phase transformer  321  includes four primary windings  326 ,  327 ,  328 ,  329  inductively linked to a secondary coil  330 . In an embodiment, the output leads  331   a,    331   b  of the multi-phase transformer  321  are connected to a GFCI (ground fault circuit interrupter) device  332 . A GFCI traditionally operates by sensing a current imbalance indicative of a ground fault, which is a fault to ground rather than a ground loop. However, in the illustrated implementation, the GFCI device  332  reacts to the three-phase transformer by triggering if the transformer is energized by ground loop currents. 
         [0029]    In this way, any ground loop currents between connectors  322 - 325  induced by differential voltages will be transformed by the multi-phase transformer  321  into a voltage signal that triggers the GFCI device  332 . When the GFCI device  332  is triggered, it interrupts power to the generators  301 ,  302 ,  303 ,  304  and stops electrical power generation until the operator corrects the ground loop condition, resets the GFCI device  332 , and restarts power generation. 
         [0030]    Although the toroidal transformer of  FIG. 2  transforms only three power leads, it is possible to use the same type of transformer for more than three power leads. For example, referring to  FIG. 4 , two such transformers may be configured in series to transform up to six power leads. In the illustrated embodiment, the transformers  400 ,  401  are connected in series to transform six power leads  402 ,  403 ,  404 ,  405 ,  406 ,  407  into a voltage differential output  408 . 
         [0031]    In order to configure the transformers  400 ,  401  to react in this way, in the illustrated embodiment the coil common line  409  of the first transformer  400  is linked to the coil common line  410  of the second transformer  401  via a connector  411 . Similarly, the lower output lead  412  of the first transformer  400  is linked to the upper output lead  413  of the second transformer  401  via a connector  414 . Again, as discussed above, the transformers  400 ,  401  should have appropriate size and capacity for the anticipated load, to avoid damage to the transformers  400 ,  401 . In an embodiment using multiple transformers wired together, it is desirable, though not critical, to match the transformers. 
       INDUSTRIAL APPLICABILITY 
       [0032]    The described principles are applicable to machines and devices requiring the generation of electrical power in an environment where ground loops may occur. Such devices include utility back-up generators, primary utility generators, electric vehicle generators, locomotive generators, and so on. 
         [0033]    The described principles allow the detection of ground loops before such ground loops can extensively damage a generator or associated circuitry. The use of a dedicated transformer group allows the system to react to a ground loop on any generator winding and trip a GFCI when such currents occur. The operator may then remediate the ground loop condition and reset the GFCI prior to restarting power generation, thereby avoiding damage to the generator and other components. 
         [0034]    It will be appreciated that the foregoing description provides examples of the disclosed system and technique. However, it is contemplated that other implementations of the disclosure may differ in detail from the foregoing examples. All references to the disclosure or examples thereof are intended to reference the particular example being discussed at that point and are not intended to imply any limitation as to the scope of the disclosure more generally. All language of distinction and disparagement with respect to certain features is intended to indicate a lack of preference for those features, but not to exclude such from the scope of the disclosure entirely unless otherwise indicated. 
         [0035]    Recitations of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context.