Abstract:
A method for locking contacts in an automatic transfer switch is provided. The automatic transfer switch includes a plurality of pole units including a plurality of contact pairs. The method includes mounting an interior locking device in at least one pole unit and locking at least one contact pair individually with the interior locking device housed in that contact pair&#39;s pole unit.

Description:
BACKGROUND OF INVENTION 
     This invention relates generally to electrical switches and, more particularly, to automatic transfer switches. 
     Many businesses use transfer switches for switching power sources, for example, from a public utility source to a private secondary supply, automatically within a matter of seconds. Critical load businesses, such as, for example, hospitals, airport radar towers, high volume data centers are dependent upon automatic transfer switches to provide continuous power. Transfer switches typically utilize a plurality of contacts that can be open or closed. 
     Typically, it is desired that a transfer switch remain closed during a fault or overcurrent condition. During a fault condition, a large and quick influx of electrical energy causes a blow open force between the contacts. Therefore, if not locked together, the contacts will interfere with upstream protection (i.e. circuit breakers) and upset coordination between devices. Known transfer switches incorporate a toggle locking of an external mechanism to keep the switch closed during a fault condition. However, this external locking is distant from the contacts of the switch and, accordingly, a play exists in the structure between the lock and the contacts. This play and a shaft torque allow the contacts to separate slightly during a fault condition due to the blow open force. When the contacts are separated slightly, an arcing across the contacts occurs damaging the contacts. 
     SUMMARY OF INVENTION 
     In one aspect, a method for locking contacts in an automatic transfer switch is provided. The automatic transfer switch includes a plurality of pole units including a plurality of contact pairs. The method includes mounting an interior locking device in at least one pole unit and locking at least one contact pair individually with the interior locking device housed in that contact pair&#39;s pole unit. 
     In another aspect, a pole unit for an automatic transfer switch is provided. The pole unit includes a housing, a load lug housed in the housing, and an interior locking device mounted in the housing to electrically couple to the load lug in a first position and in a second position. The pole unit further includes a plurality of source lugs including a first source lug and a second source lug mounted in the housing, wherein each source lug is electrically isolated from each other and the load lug, and the interior locking device is configured to electrically couple at least one of the first source lug and the second source lug to the load lug. 
     In another aspect, an automatic transfer switch is provided. The automatic transfer switch includes a plurality of pole units including a bore therethrough, wherein the housing units are connected with the bores aligned. The switch further includes at least one interior locking device mounted in at least one of the units, the interior locking device comprising a bore therethrough, wherein the bore of the locking device is aligned with the bores of the units. The automatic transfer switch further includes an end wall comprising a bore aligned with the bores of the units and a shaft axially mounted in the interior locking device bore and the housing unit bore. The shaft extends through the end wall and includes an extended portion, and a flywheel is mounted on the extended portion of the shaft. 
     In a further aspect, a pole unit for an automatic transfer switch includes a housing and at least one of a dual disk and a conjugate cam mounted in the housing. The conjugate cam has a tri-lobal shape and is within a conductor assembly. The dual disk includes a driving disk and a driven disk, wherein the driving disk includes a cammed surface configured to engage at least one locking tab. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is an exploded perspective view of a dual disk including a driving disk and a driven disk; 
     FIG. 2 is a perspective view of a pole unit with the dual disk shown in FIG. 1 positioned thereon; 
     FIG. 3 is a perspective view of an automatic transfer switch including a plurality of the pole units shown in FIG. 2; and 
     FIG. 4 is a perspective view of a pole unit including a conjugate cam. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is an exploded perspective view of a dual disk  10  including a driving disk  12  and a driven disk  14  including a plurality of chambers  16  sized to receive a plurality of resilient members  18 . Driving disk  12  includes a first centering finger that is positioned in a first gap  22  between a first resilient member  24  and a second resilient member  26  when dual disk  10  is assembled. Driving disk  12  further includes a second centering finger (not shown) opposite first centering finger  20  that is positioned in a second gap (not shown) between a third resilient member  28  and a fourth resilient member  30 . 
     Driven disk  14  further includes a plurality of slots  32  to receive a conductor  34  having a plurality of contacts  36  mounted thereon. Slots  32  are in flow communication via a plurality of arcuate channels  38 . Conductor  34  includes a first member  40  and a second member  42  that is substantially identical to first member  40  and is attached to first member  40 . First member  40  includes a first end portion  44  and extends from first end portion  44  substantially in a first plane to a first bend  46  and then extends arcuately to a second bend  48  after which first member  40  extends in the first plane to a second end portion  50 . 
     First member  40  is attached to second member  42  such that arcuate sections of members  40  and  42  form a substantially circular opening  51 . Each end portion  44  and  50  has a contact  36  mounted thereon. Driving disk  12  further includes a polygonal shaped bore to receive a shaft (not shown). The bore is defined by a plurality of inner walls  54 . In an exemplary embodiment, the polygonal shaped bore is a hexagonal shaped bore. Inner walls  54  extend radially outward to a cylindrical surface  56  which extends longitudinally from a bottom surface (not shown) of driving disk  12  forming a cylinder  58 . Driven disk  14  includes a substantially circular bore  60  to receive cylinder  58 . 
     During operation of an assembled dual disk  10 , a rotation of the shaft exerts a rotational force on inner walls  54  causing driving disk  12  to rotate. First and second centering fingers  20  exert a rotational force on resilient members  18  causing driven disk  14  and conductor  34  to rotate. When any particular contact  36  on conductor  34  contacts an object, conductor  34  stops rotating while driving disk  12  continues to rotate and, depending upon direction of rotation, either first and third resilient members  24  and  28  are compressed or second and fourth resilient members  26  and  30  are compressed causing a biasing of that particular contact against the object. In an exemplary embodiment, resilient members  18  are springs. 
     FIG. 2 is a perspective view of a pole unit  80  with dual disk  10  (shown in FIG. 1) positioned therein. Pole unit  80  includes a first source lug  82 , a second source lug  84 , and a load lug  86  electrically connected to a first load contact  88  and a second load contact  90 . Pole unit  80  further includes a first source contact  92  electrically connected to first source lug  82  and a second source contact (not shown) electrically connected to second source lug  84 . Conductor  34  includes a first contact  94 , a second contact  96 , a third contact  98 , and a fourth contact  100  mounted thereon. Pole unit  80  further includes a housing  95  including a first slot  97  substantially adjacent first source lug  82 , a second slot  99  substantially adjacent second source lug  84 , and a third slot  101  substantially adjacent load lug  86 . Housing  95  is fabricated from non-conductive material and electrically isolates first source lug  82 , second source lug  84 , and load lug  86 . 
     During operation of pole unit  80 , a shaft (not shown) passes through bore  52  (shown in FIG. 1) and a bore (not shown) of pole unit  80 . When the shaft is rotated to a first position (not shown in FIG.  2 ), dual disk  10  rotates clockwise and first contact  94  contacts first source contact  92  forming a first contact pair with a slight wiping motion which causes an abrading of the surfaces (not shown) of first contact  94  and first source contact  92 . Approximately simultaneously with forming the first contact, third contact  98  contacts first load contact  88  forming a second contact pair with a slight wiping motion which causes an abrading of the surfaces (not shown) of third contact  98  and first load contact  88 . 
     After first and second contact pairs are formed, driven disk  14  remains substantially stationary but driving disk  12  continues to rotate causing first and third resilient members  24  and  28  to compress individually locking first and second contact pairs in their contacted positions. In an alternative embodiment, dual disk  10  includes a cammed surface  102  that locks by engaging a plurality of locking tabs (not shown) extending from a back side  104  of pole unit  80  and a terminal plate (not shown in FIG.  2 ). Beneath cammed surface  102  is a cammed resilient member (not shown) that allows cammed surface  102  to be depressed slightly and biased back to an uncompressed position after the locking tab clears a raised cam portion  106  of cammed surface  102 . In an exemplary embodiment, the cammed resilient member is a wave washer. Slots  97 ,  99 , and  101  provide for overpressure relief during a fault condition by allowing heated gases to escape pole unit  80  without enhancing ingress of foreign material. 
     FIG. 3 is a perspective view of an automatic transfer switch  120  including a plurality of pole units  80  (shown in FIG.  2 ). Pole units  80  are positioned such that bores  52  of their respective dual disks  10  are aligned and a shaft (not shown) extends from a first side  122  of switch  120  through bores  52  to a second side  124  of switch  120 . The shaft extends from first side  122  to a flywheel  126  that is biased in a first position by a switch resilient member  128 . 
     In an exemplary embodiment, switch resilient member  128  is a spring. Flywheel  126  is connected to a solenoid  130  that is controlled by a controller (not shown) electrically connected to a limit switch  132 . Solenoid  130  includes a plunger  134 . First side  122  includes a termination plate  136  including at least one locking tab on an interior side (not shown) of termination plate. Because each pole unit  80  has a back side  104  including at least one locking tab, and termination plate  136  has a locking tab in conjunction with the stacked axial placement of each pole unit  80 , each cammed surface  102  is positioned against a surface having at least one locking tab. 
     Accordingly, each contact pair is locked in close proximity to the contact pair by an interior locking device. Dual disc  10  is interior to pole unit  80  and locks the contact pairs together and, accordingly, dual disc  10  is an interior locking device. Since an interior locking device locks the contact pairs, as parts wear out and play develops, the contact pairs maintain rigid contact together. 
     In operation, transfer switch  120  receives electrical power from first source lugs  82  and delivers that power to load lugs  86 . Under normal operating conditions, first source contact  92  contacts first contact  94  forming a first contact pair and first load contact  88  contacts third contact  98  forming a second contact pair. The contact pairs are locked together by resilient members  18  and by the engagement of cammed surface  102  with the locking tabs. 
     Accordingly, during a short or overload condition, the pairs do not separate and no arcing occurs which can damage the contacts. When the controller senses that the available power from first source lugs  82  is below a pre-set amount, the controller causes solenoid  130  to actuate causing plunger  134  to move linearly which causes flywheel  126  to rotate against switch resilient member  128  and breaks the contact pair of first source contact  92  with first contact  94  and, nearly simultaneously, breaks the contact pair of first load contact  88  with third contact  98 . As flywheel  126  continues to rotate, second contact  96  contacts the second source contact forming a third contact pair and, nearly simultaneously, fourth contact  100  contacts second load contact  90  forming a fourth contact pair and restoring electrical power to load lug  86 . 
     After the third and fourth contact pairs are formed, flywheel  126  continues to rotate further and locks the third and fourth pairs together by compressing resilient members  18  and engaging cammed surface  102  with the locking tabs. During a short or overcurrent condition when load lug  86  is electrically connected to second source lug  84 , the contacts are protected from damaging electrical arcs by dual disc  10  being an interior locking device. Accordingly, dual disc  10  is a cost-efficient and effective interior locking device which reduces the amount of play in an automatic transfer switch and, therefore, reduces damaging arcs providing for a long lasting and reliable automatic transfer switch. 
     FIG. 4 is a perspective view of a pole unit  150  including a conjugate cam  152 . Conjugate cam  152  is shaped tri-lobal with three apexes  154  and three arcuate sections  156 . Each arcuate section  156  extends between two apexes  154 . Conjugate cam  152  further includes a shaft receiving section  158  proximate one apex  154 . Shaft receiving section  158  includes a polygonal bore to receive a shaft (not shown). In an exemplary embodiment, the polygonal bore is a hexagonal bore. 
     Pole unit  150  includes a first source lug  160 , a second source lug  162 , and a load lug  164 . Pole unit  150  further includes a housing  166  fabricated from a nonconductive material. Housing  166  electrically isolates first source lug  160 , second source lug  162 , and load lug  164  from each other. Pole unit  150  further includes a first source contact  168  electrically connected to first source lug  160 , a first load contact  170  electrically connected to load lug  164 , a second source contact  172  electrically connected to second source lug  162 , and a second load contact  174  electrically connected to load lug  164 . 
     A contact assembly  176  is slideably mounted within pole unit  150 . A first conductor  178  and a second conductor  180  extend from assembly  176 . First conductor  178  is electrically connected to second conductor  180 . First conductor  178  includes a first contact  182  and a second contact  184  mounted thereon. Second conductor  180  includes a third contact  186  and a fourth contact  188  mounted thereon. Housing  166  includes a first slot  190  substantially adjacent first source lug  160 , a second slot  192  substantially adjacent second source lug  162 , and a third slot  194  substantially adjacent load lug  164 . Contact assembly  176  further includes an inner surface  200  including two parallel sections  202  joined by two arcuate sections  204 . 
     A plurality of pole units  150  are assembled to fabricate an automatic transfer switch (not shown) substantially similar to switch  124  (shown in FIG. 3) except pole units  80  are replaced with pole units  150 . In operation, the transfer switch receives electrical power from first source lugs  160  and delivers that power to load lugs  164 . Under normal operating conditions, first source contact  168  contacts first contact  182  forming a first contact pair and first load contact  170  contacts third contact  186  forming a second contact pair. 
     The contact pairs are locked together by a locking engagement between inner surface  200  of contact assembly  176  and apexes  1154  and arcuate sections  1156  of conjugate cam  152 . Accordingly, during a short or overload condition, the pairs do not separate and no arcing occurs which can damage the contacts. When a controller senses that the available power from first source lugs  160  is below a pre-set amount, the controller causes a solenoid to actuate causing a plunger to move linearly which causes a flywheel to rotate against a switch resilient member. When the flywheel rotates, conjugate cam  152  rotates counter-clockwise and, after a sufficient rotation, conjugate cam  152  rotates against parallel portion  202  distal from load lug  164 , causing assembly  176  to move away from first source lug  160  breaking the contact pair of first source contact  168  with first contact  182  and, nearly simultaneously, breaking the contact pair of first load contact  170  with third contact  186 . 
     As the flywheel continues to rotate, conjugate cam  176  continues to rotate thus moving assembly  176  closer to second source lug  162  until second contact  184  contacts second source contact  172  forming a third contact pair and, nearly simultaneously, fourth contact  188  contacts second load contact  174  forming a fourth contact pair and restoring electrical power to load lug  164 . After, the third and fourth contact pairs are formed, assembly  176  is stationary, but conjugate cam  176  continues to rotate further providing a positive lock for the third and fourth pairs. During a short or overcurrent condition when load lug  164  is electrically connected to second source lug  162 , the contacts are protected from damaging electrical arcs by conjugate cam  152  being an interior locking device. 
     Accordingly, conjugate cam  152  is a cost-efficient and effective interior locking device which reduces the amount of play in an automatic transfer switch and, therefore, reduces damaging arcs providing for a long lasting and reliable automatic transfer switch. 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.