Abstract:
A transfer switch including: a bus bar; a track parallel to the bus bar; a first power source connection proximate to the track; a second power source connection proximate to the track offset along the track from the first power source connection; a conductive core slidably coupled to the track, wherein the core includes a deformable array of conductive sections and the array includes contacting surfaces on opposite sides of the array; wherein the conductive core has a first position providing a conductive coupling between the bus bar and the first power source and a second position providing a conductive coupling between the bus bar and the second power source.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to transfer switches that transfer electrical power from multiple power sources to a power load. 
     Transfer switches are used, for example, to automatically and quickly connect an emergency power source to a load when a normal power supply fails. Hospitals use transfer switches to maintain continuous electrical power when a power failure occurs in the electrical utility service to the hospital. When a utility power failure occurs, the transfer switch connects the hospital to a backup power generator without significant interruption of electrical power to the hospital. There is a long felt need for mechanically simple and reliable transfer switches which effectively suppress electrical arcs. 
     SUMMARY OF INVENTION 
     A transfer switch has been conceived including: a bus bar; a track parallel to the bus bar; a first power source connection proximate to the track; a second power source connection proximate to the track offset along the track from the first power source connection; a conductive core slidably coupled to the track, wherein the core includes a deformable array of conductive sections and the array includes contacting surfaces on opposite sides of the array; wherein the conductive core has a first position providing a conductive coupling between the bus bar and the first power source, wherein the second power source is electrically isolated from the bus bar when the core is in the first position; wherein the conductive core has a second position providing a conductive coupling between the bus bar and the second power source, wherein the first power source is electrically isolated from the bus bar when the core is in the first position, and wherein the core slides along the track between the first position and the second position. 
     The deformable array may be an array of trapezoidal conductors having abutting surfaces. The trapezoidal conductors may include opposing first trapezoidal conductors each having one of the contact surfaces and opposing second trapezoidal conductors each extending between the first trapezoidal conductors. The abutting surfaces may be planar surfaces and oblique to a plane of the contacting surfaces. 
     The transfer switch may include a spring applying a bias force against the deformable array, wherein the bias force moves the contacting surfaces outward. The transfer switch may also include a pair of arc extinguishers adjacent each of the contacting surfaces when the core is in the first position and a second pair of arc extinguishers adjacent each of the contacting surfaces when the core is in the second position. 
     A transfer switch has been conceived comprising: a main body having a back plate and a cover, parallel the back plate and separated from the back plate by brackets extending between the back plate and cover; a bus bar mounted to the back plate; a first power source connection mounted to the back plate; a second power source connection mounted to the back plate; a track integral or mounted to the back plate, wherein the bus bar is on one side of the track and the first and second power connectors are on the opposite side of the track; a conductive core slidably coupled to the track, wherein the core includes a deformable array of conductive sections and the array includes contacting surfaces on opposite sides of the array; wherein the conductive core has a first position providing a conductive coupling between the bus bar and the first power source, wherein the second power source is electrically isolated from the bus bar when the core is in the first position; wherein the conductive core has a second position providing a conductive coupling between the bus bar and the second power source, wherein the first power source is electrically isolated from the bus bar when the core is in the first position, and wherein the core slides along the track between the first position and the second position. 
     A method has been conceived to transfer a power supply connection comprising: establishing a first electrical connection between a power load and a first power source, wherein the connection includes a conductive core having opposite contacting surfaces and the current flows from the first power, through a first of the contacting surfaces, the core, the second of the contacting surfaces and to the power load; applying a bias force to deform the core and thereby press the contacting surfaces against respective electrical contacts for the power load and first power source; sliding the core out of contact with the first power source and into contact with the second power source, wherein the sliding breaks the electrical connection between the power load and the first power source and establishes a second electrical connection between the power load and second power source. 
    
    
     
       BRIEF DESCRIPTION OF THE INVENTION 
       The structure, operation and features of the invention are further described below and illustrated in the accompanying drawings which are: 
         FIGS. 1 and 2  show schematically a transfer switch with a top cover removed. 
         FIG. 2  is a perspective view the transfer switch with the top cover removed. 
         FIG. 3  is a perspective view of the transfer switch with the top cover. 
         FIGS. 4 and 5  show a core of the transfer switch electrically connecting a first power source to a power load ( FIG. 2 ) and electrically connecting a second power source to the load ( FIG. 3 ). 
         FIGS. 6 and 7  show the internal components of the core. 
         FIG. 8  is a perspective view of the core wherein the core is shown assembled. 
         FIG. 9  is a perspective view showing the core with a cover removed. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a front view of a transfer switch  10  having a main body  12  and a moveable core  14 . The main body houses a first power connector  16  for a first power source  18 , a second power connector  20  for a second power source  22  and a load connector  24  for a power load  26 . The core  14  provides an electrical connection between one the power connectors  16 ,  20  and a conductive bus bar  28 , which is also connected to the load connector  24 . 
     The core  14  connects the conductive bus bar to one of the power connectors by being a physical and electrical bridge between the power connector and bridge. The core  14  is posited between the power connector and bus bar to form the bridge. The core slides linearly along a track  30  extended between the power connectors  16 ,  20 , and the bus bar  28 . By sliding along the track, the core is positioned between a selected one of the power connectors and the bus bar to establish an electrical connection between the selected power connector and the bus bar. 
     The main body  12  of the transfer switch may include a back plate  32  formed of a rigid insulating material such as a molded plastic or a composite. The back plate provides structural support for the components of the main body. On the back plate are mounted the track  30 , which may have twin parallel rails along which the core slides. The rails may provide a mount to support the core on the back plate. The rails may slidably engage the core and prevent rotation of the core about the rails. Alternatively, the track may be integral with the back plate. 
     The connectors  16 ,  20 ,  24  may be conductive metal blocks having a female or male coupling to receive a male or female coupling from a conductive conduit between the transfer switch  10  and one of the power sources or load. For example, the connector  16  may be an aluminum block having an opening to receive the end of a conductive wire which is connected to the first power source  18 . 
     The first and second connectors  16 ,  20  may be fixed to brackets  34  extending perpendicular to the back plate. Similarly, the connector  24  for the load may be supported by a bracket  36 . The brackets may be attached to the back plate or integral with the back plate. Other brackets for the bus bar  28  and other components of the transfer switch  10  may extend perpendicular to the back plate. The brackets may be integrally molded with the back plate. 
     Junction connectors  38  provide an electrical coupling between the core  14  and each of the connectors  16 ,  20  and the bus bar  28 . The junction connectors  38  may be metal blocks, such as aluminum cubes, that include a protrusion  40  extending towards the core position. The protrusions are each configured to contact the core and provide a low resistance, reliable and releasable connection to the core. 
     Arc extinguishers  42  are adjacent each of the junction connectors  38 . The arc extinguishers may include a chamber to receive high temperature electrical arcs when the core slides between the junction connectors. Arc extinguishers are conventional devices used to capture and suppress electrical arcs. 
     The arc extinguishers  42  may be formed of a non-conducting material and have a chamber divided into passages to receive an arc. The arc extinguishers  42  may have a quarter-circle shape and are adjacent the abutting connection between the core and the junction connectors  38 . The abutting connection tends to be the source of an arc especially as the core slides into engagement with the junction connectors. Because of the proximity of the arc extinguishers to the abutting connection an arc passage is not necessary. 
       FIG. 2  is a perspective view of the transfer switch  10 . The cover of the switch is removed in  FIGS. 1 and 2  to show the internal components of the switch. The main body  12  includes the back plate  32 , the brackets  34 , and other brackets  35 ,  36  that extend perpendicularly from the back plate. The brackets form side support structures for the stationary components of the transfer switch, such as the first and second power connections  16 ,  20 , the load connection  24 , the bus bar  28 , and arc extinguishers. The brackets may also form end stops for the core at opposite ends of the track  30 . The brackets may also separate the back plate from the top cover and provide structural support for the transfer switch which is transverse to the back plate and top cover. 
       FIG. 3  is a perspective view of the transfer switch with the top cover  27  which may attach to the upper ends of the brackets. The top cover may be superimposed over the back plate and generally conform to the planar shape of the back plate. Alternatively, some or all of the brackets may be integrally formed with the top cover rather than with the back plate. An open slot  29  in the top cover corresponds to the track. A similar open slot may be present in the back plate. The open slot may be used to allow an actuator to extend into the transfer switch to move the core. 
       FIGS. 4 and 5  are schematic illustrations showing the core  14  electrically connecting the first power source  18  to the power load  26  ( FIG. 2 ) and the core  14  electrically connecting the second power source  22  to the load  26  ( FIG. 3 ). As shown in  FIG. 2 , electrical current flows (see arrow  43 ) from the first power source  18 , through the core and to the load  26 , when the core is aligned with the first power connection  16 . As shown in  FIG. 3 , electrical current flows (see arrow  44 ) from the second power source  22 , through the core  14  and to the power load  26  when the core is aligned with the second power connection  20 . 
     The core  14  (which is shown in a simplified form in  FIGS. 3 and 4 ) slides between the opposite junction connectors  38  for either the first power source ( FIG. 2 ) or the second power source ( FIG. 3 ). The core has electrical contacts  46  which are biased outwardly to abut against the junction connectors  38 . The spring bias force presses the contacts  46  of the core against the protrusions  40  of the junction connectors. The spring bias force ensures a good electrical contact between the core and the junction connectors. The spring bias force does not prevent sliding of the core along the track  30  ( FIG. 1 ) when a moving force is applied to the core. 
     The core  14  is slid (see arrow  48 ) linearly between the opposite junction connectors to decoupled the first power source from the power load and connect the second power source to the power load, and vice versa. A motor  49  may apply a moving force to move the core and a controller  50 , e.g., computer, made actuate the motor to slide the core when the controller detects a condition, such as a power failure of the first power source. The core may also be configured to be manually moved between the connections for the first and second power sources. 
       FIGS. 6 and 7  are similar views showing the internal components of the core  14  which may have a split core body formed of opposing body covers  51 . A front view of a body cover is shown in  FIGS. 6 and 7 . The covers may be formed of a non-conductive material, such as a plastic or composite material. The covers may be generally rectangular and have cavities or recesses to receive the components of the core. 
     The components of the core include trapezoidal conductors  52 ,  54  arranged in a rectangular deformable array  61 . The trapezoidal conductors  54  are adjacent the sides of the core and physically contact the junction connectors  38  ( FIG. 1 ). The other trapezoidal conductors  52  span between the side trapezoidal conductors  54  and extend transversely through the core. The conductors are arranged in a deformable array  61  that forms a conductive path from one side of the core to the other. The arrows  56  show the current path flowing through each of the trapezoidal conductors  52 ,  54  of the array  61 . The conductive path provides an electrical connection between one of the connections  16 ,  20  to the power source and the bus bar  28 . The trapezoidal conductors may alternatively be arc-shaped and arranged in a ring and need not all have a uniform shape. 
     The trapezoidal conductors  52 ,  54  each have abutment surfaces  58 ,  60  which abut and slide against the abutment surfaces  60 ,  58  of an adjacent trapezoidal conductor. The surfaces  58 ,  60  of the trapezoidal conductors slide against each other to deform the array  61  and cause the trapezoidal conductors  54  firmly abut against the junction connectors  38  ( FIG. 1 ) and ensure good electrical contact between the core  14  and the junction connectors. The abutment surfaces may be planar and oblique, e.g., at 45 degrees, to a plane parallel to the contacting surfaces between core and the junction connectors. 
     The sidewalls  62  of the trapezoidal conductors are in firm and constant electrical contact with the junction connectors at least in part due to the sliding that occurs between the surfaces  58 ,  60  of the trapezoidal conductors  52 ,  54 . 
     Spring assemblies  64  bias the transverse trapezoidal conductors  52  inward of the deformable conductive array  61  formed by the trapezoidal conductors  52 ,  54 . The spring bias force is applied through the transverse trapezoidal conductors  52  to spread apart the side trapezoidal conductors  54 , as is shown by the arrows  63  in  FIG. 7  that indicate the mechanical force applied to the trapezoidal conductors. The spring assemblies  64  may include a spring  66 , e.g., a helical spring, and a contact block  68  that abuts against the outer wall of the trapezoidal conductor  52 . 
     The spring assembly may be housed in a chamber  70  of the body of the core. The chamber  70  may be capped at an end of the core such that the cap may be removed to replace a spring. 
     A center region  72  of the array  61  of trapezoidal connectors is open to allow movement of the connectors. As the connectors  52 ,  54  move and slide with respect to each other, the center region may be altered in shape and size. 
     During the relative movement of the trapezoidal connectors  52 ,  54 , electrical connections are maintained between each of the connectors due to the sliding contact between the opposing surfaces  58 ,  60  of the connectors. The connectors  52 ,  54  may be formed of a conductive material, such as aluminum or steel, or be coated with a conductive material and have an interior that is non-conductive. Further, one of the transverse connectors  52  need not be conductive. In addition, one of the transverse connectors may be stationary and not require associated spring assemblies. Where one transverse connector is stationary, the other transverse connector alone provides the full bias force to spread apart the other trapezoidal connectors  54 . 
       FIG. 8  is a perspective view of the core  14  wherein the core is shown assembled.  FIG. 9  is a similar perspective view showing the core with one of the covers  51  removed. The opposing covers  51  encase and provide structural support for the trapezoidal conductors  52 ,  54 , and spring assemblies  64 . 
     The sidewalls  74  of the core are formed by the opposing covers  51  and include a recessed center rectangular region  76 . Within this region  76  are seated top and bottom secondary arc extinguishers  78  and an arc runner  80 . The arc runner  80  may be a panel having a center opening through which extends the contact region  46  of the sidewall  62  ( FIG. 6 ) of one of the trapezoidal conductors  54 . The secondary arc extinguishers  78  may be rectangular panels on opposite sides of the arc runner, and formed of a non-conductive material capable of withstanding high temperatures and electrical sparking. 
     The arc runner directs any electrical arc formed as the contact region  46  slides against the junction connectors  38  ( FIG. 1 ). The electrical arc is directed by the runner to the arc extinguisher  42  and the secondary arc extinguisher  78 . 
     The core  14  in the transfer switch  10  is a linear transfer device that may serve as a linear automatic transfer switch (LATS). The core  14  forms two contacts between a power source and a load based on the opposite contacts  46  of the core. When the core moves into or out of engagement of a power source, both contacts of the core come into electrical contact or break electrical contact. 
     The movement of the core provides a double break feature wherein the separation of two points of contacts creates two arcs as opposed to one arc that would be created with a single point of contact. By having two arcs, the distance of arc elongation is effectively doubled resulting in a greater arc voltage gain with respect to time. The greater arc voltage gain achieves faster interruptions in the current through the switch than occurs with smaller arc voltage gains that may occur with cores having a single point of contacts. While the core may be configure to have a single point of contact, the two contacts of the core  14  provide a quicker break in current when the core is moved by the switch. 
     The transfer switch  10  may be formed without conductive braided components and without requiring the braiding of conductive components in the switch. Further, the transfer switch may be formed without a silver based contact pad between the core and the junction connectors. 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.