Abstract:
A mechanism assembly is for a vacuum circuit interrupter including a vacuum housing including a stationary contact and a moveable contact, and an operating mechanism including a drive rod. The mechanism assembly cooperates with the drive rod to open and close the contacts. The mechanism assembly includes a housing having a pair of first longitudinal openings and a pair of second longitudinal openings, the first longitudinal openings defining a first plane, the second longitudinal openings defining a different second plane. A first trunnion member is pivotally and translationally mounted with respect to the first longitudinal openings. The first trunnion member is coupled to the moveable contact. A second trunnion member is pivotally and translationally mounted with respect to the second longitudinal openings. The drive rod is pivotally connected to the second trunnion member. A pair of compression springs are biased between the first and second trunnion members.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention pertains generally to circuit interrupters and, more particularly, to circuit interrupters, such as, for example, medium voltage vacuum circuit breakers, employing one or more poles each of which includes a vacuum interrupter. The invention also pertains to operating mechanism assemblies for vacuum circuit interrupters. 
   2. Background Information 
   Circuit interrupters provide protection for electrical systems from electrical fault conditions such as, for example, current overloads, short circuits and abnormal level voltage conditions. Typically, circuit interrupters include a spring powered operating mechanism which opens electrical contacts to interrupt the current through the conductors of an electrical system in response to abnormal conditions, although a wide range of driving mechanisms may be employed. 
   Circuit interrupters, such as, for example, power circuit breakers for systems operating above about 1,000 volts typically utilize vacuum interrupters as the switching devices. Vacuum switching devices (e.g., circuit interrupters; circuit breakers; switches; reclosers) include separable main contacts disposed within an insulating housing. Generally, one of the contacts is fixed relative to both the housing and to an external electrical conductor which is interconnected with the circuit to be controlled by the circuit interrupter. The other contact is moveable. In the case of a vacuum circuit interrupter, the moveable contact assembly usually comprises a stem of circular cross-section having the contact at one end enclosed within a vacuum chamber and a driving mechanism at the other end which is external to the vacuum chamber. An operating rod assembly comprising a push rod, which is fastened to the end of the stem opposite the moveable contact, and a driving mechanism provide the motive force to move the moveable contact into or out of engagement with the fixed contact. 
   Vacuum interrupters are typically used, for instance, to reliably interrupt medium voltage alternating current (AC) currents and, also, high voltage AC currents of several thousands of amperes or more. Typically, one vacuum interrupter is provided for each phase of a multi-phase circuit and the vacuum interrupters for the several phases are actuated simultaneously by a common operating mechanism, or separately by separate operating mechanisms (and auxiliary switches). 
   Known medium voltage vacuum circuit interrupters using spring-charged stored energy mechanisms lack the requisite force to maintain necessary contact pressure to withstand current levels dictated by a withstand test for a 75 kA rating. 
   Accordingly, there is room for improvement in circuit interrupters. There is also room for improvement in operating mechanism assemblies for vacuum circuit interrupters. 
   SUMMARY OF THE INVENTION 
   These needs and others are met by the present invention, which employs a conventional stored energy operating mechanism to drive a separate spring-charged toggle mechanism including two movable trunnions coupled to each other by a contact spring assembly. The trunnions move in separate planes and take advantage of the toggle mechanism to increase the contact force at the end of the toggle mechanism travel when the contacts are closed and, also, to assist in separating the fixed and moveable contacts as the contacts are opened. 
   In accordance with one aspect of the invention, a circuit interrupter comprises: first and second terminals; a vacuum housing comprising separable contacts including a stationary contact and a moveable contact, the first terminal being electrically connected to the stationary contact and the second terminal being electrically connected to the moveable contact; an operating mechanism comprising a drive rod, the operating mechanism being structured to move the drive rod in a general first direction to close the separable contacts, and to move the drive rod in a general opposite second direction to initiate opening of the separable contacts; and a mechanism assembly cooperating with the drive rod to open and close the separable contacts, the mechanism assembly comprising: a housing including a pair of first longitudinal openings and a pair of second longitudinal openings, the first longitudinal openings defining a first plane, the second longitudinal openings defining a different second plane, a first trunnion member pivotally and movably mounted with respect to the first longitudinal openings of the housing, the first trunnion member being coupled to the moveable contact, a second trunnion member pivotally and movably mounted with respect to the second longitudinal openings of the housing, the drive rod being pivotally connected to the second trunnion member, and at least one spring biased between the first trunnion member and the second trunnion member. 
   The separable contacts may include a closed position, a contacts touch position and an open position. The mechanism assembly may include a closed position corresponding to the closed position of the separable contacts, a contacts touch position corresponding to the contacts touch position of the separable contacts, a toggle position between the closed and contacts touch positions of the mechanism assembly, and an open position corresponding to the open position of the separable contacts. During opening of the separable contacts, from the toggle position to the open position of the mechanism assembly, the at least one spring may assist the operating mechanism in driving the second trunnion member in the second longitudinal openings. 
   Between the closed position and the toggle position of the mechanism assembly, the force from the at least one spring may be generally normal to the second longitudinal openings. Between the toggle position and the open position of the mechanism assembly, the force from the at least one spring may be sufficiently close to parallel to the second longitudinal openings, in order that the at least one spring provides additional opening force to open the separable contacts and assist the operating mechanism in the event that the separable contacts are partially welded closed. 
   After the opening of the separable contacts, the second trunnion member may be structured to move in the second longitudinal openings in a third direction to a maintenance position in which the at least one spring is not compressed and can be safely assembled or disassembled. 
   The mechanism assembly may include a closed position and an open position. The first trunnion member may be coupled to the moveable contact by a pin member and a clevis connector having a first end and a second end, the first end of the clevis connector being fixedly coupled to the moveable contact, the second end of the clevis connector being pinned to the first trunnion member by the pin member, in order that the first trunnion member pivots about the pin member between the open and closed positions of the mechanism assembly. 
   The second trunnion member may include a first side and an opposite second side. The first side and the opposite second side may include a trunnion pin carrying a bearing mechanism captured in a corresponding one of the second longitudinal openings. 
   The first trunnion member may be coupled to the moveable contact by a pin member having a first end and an opposite second end. Each of the first and second ends may carry a bearing mechanism captured in a corresponding one of the first longitudinal openings. 
   The mechanism assembly may include an opening dimension, which is defined by a distance between the first trunnion member and the second trunnion member. The at least one spring may be at least substantially compressed in the opening dimension between the first trunnion member and the second trunnion member. 
   The first trunnion member may include a rod member having a first end coupled to the first trunnion member and a second end. The second trunnion member may include a bottom and an opening through which the second end of the rod member passes. A snatch gap may be defined between the bottom of the second trunnion member and a portion of the second end of the rod member, in order to indicate wear of the separable contacts. 
   As another aspect of the invention, a mechanism assembly is for a vacuum circuit interrupter including first and second terminals, a vacuum housing comprising separable contacts including a stationary contact and a moveable contact, the first terminal being electrically connected to the stationary contact and the second terminal being electrically connected to the moveable contact, an operating mechanism comprising a drive rod, the operating mechanism being structured to move the drive rod in a general first direction to close the separable contacts, and move the drive rod in a general opposite second direction to initiate the opening of the separable contacts. The mechanism assembly cooperates with the drive rod to open and close the separable contacts and comprises: a housing including a pair of first longitudinal openings and a pair of second longitudinal openings, the first longitudinal openings defining a first plane, the second longitudinal openings defining a different second plane; a first trunnion member pivotally and movably mounted with respect to the first longitudinal openings of the housing, the first trunnion member being coupled to the moveable contact; a second trunnion member pivotally and movably mounted with respect to the second longitudinal openings of the housing, the drive rod being pivotally connected to the second trunnion member; and at least one spring biased between the first trunnion member and the second trunnion member. 
   The first plane of the first longitudinal openings may be about normal to the second plane of the second longitudinal openings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which: 
       FIG. 1  is a side elevational view of a drawout circuit breaker. 
       FIG. 2  is a vertical elevational view of a circuit interrupter including conductive terminals, a vacuum housing having a stationary contact and a moveable contact shown in a closed position, an end mechanism assembly and a drive rod in accordance with the present invention. 
       FIG. 3  is a vertical elevational view of the circuit interrupter of  FIG. 2 , but with the stationary and moveable contacts in the open position. 
       FIG. 4  is a partially exploded isometric view of the end mechanism assembly of  FIG. 2 . 
       FIG. 5  is a cross-sectional isometric view of the circuit interrupter of  FIG. 2 . 
       FIG. 6  is a top plan view of the end mechanism assembly of  FIG. 2  in the closed position. 
       FIG. 7  is a cross-sectional view along lines  7 — 7  of  FIG. 6 . 
       FIG. 8  is a side elevational view of the end mechanism assembly of  FIG. 2  in the open position. 
       FIG. 9  is a side elevational view of the end mechanism assembly of  FIG. 2  in the contacts touch position. 
       FIG. 10  is a side elevational view of the end mechanism assembly of  FIG. 2  in a maintenance position. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention is described in association with a medium voltage vacuum circuit breaker, although the invention is applicable to a wide range of circuit interrupters and operating mechanism assemblies therefor. 
   Referring to  FIG. 1 , a metal-clad or metal-enclosed switchgear apparatus is generally indicated at  11  and includes a metal cabinet or enclosure  13  for enclosing a drawout vacuum circuit breaker  15 . The circuit interrupter  15  is preferably a drawout three-phase vacuum circuit interrupter and may have controls on a front panel  17  for manually operating the circuit breaker. The circuit breaker  15  is movably disposed on wheels  19  on rails  21  into and out of the enclosure  13 . In that manner, terminals  23 , 25  on the circuit breaker  15  are moved into and out of electrical contact with corresponding terminals  27 , 29  within the enclosure  13 . 
   The circuit breaker  15  preferably embodies a three-phase interrupter apparatus having a front low voltage portion  31  adjacent to the front panel  17  and a rear high voltage portion  32  including a vacuum circuit interrupter  35  for each phase (only one phase is shown in  FIG. 1 ). Upper and lower insulators  37 , 39  electrically insulate the high and low voltage portions  32 , 31  from each other. Within each vacuum interrupter  35 , a pair of separable contacts  40  including a stationary contact  41  and movable contact  43  is provided. The separable contacts  40  are operated between open ( FIG. 1 ) and closed (not shown) electrical circuit conditions by a linkage  45 . This linkage  45  includes an insulating link  47  which extends between the low voltage portion  31  and a movable contact stem  48  that moves the moveable contact  43 . Details regarding the operating mechanism  50  for moving the contacts  41 , 43  between the open circuit position and the closed circuit position are described in U.S. Pat. No. 4,743,876, which is incorporated by reference herein. Example manual and electric motor charging mechanisms for the operating mechanism  50  are disclosed in U.S. Pat. Nos. 3,590,192 and 3,750,059, which are incorporated by reference herein. 
   The operating mechanism  50  is contained in the front low voltage portion  31  and operates a number of driven parts one of which is a pole or operating shaft  49  that is rotatably mounted in opposite sidewalls (not shown) of a frame or housing. The shaft  49 , when rotated, opens and closes the contacts  41 , 43  in the phases of the switchgear apparatus  11 . For that purpose, the insulating link  47  is connected by a pair of arms  55  (only one arm  55  is shown), which are fixedly mounted on the shaft  49 . 
     FIG. 2  shows a circuit interrupter  60  in accordance with the present invention. The circuit interrupter  60  includes conductive terminals  62 , 64 , a vacuum housing  66  having a stationary contact  68  (shown in hidden line drawing) and a moveable contact  70  (shown in hidden line drawing) shown in a closed position, a drive rod  72  and an end mechanism assembly  74  in accordance with the invention. As is conventional, the conductive terminal  62  is electrically connected to the stationary contact  68  and the conductive terminal  64  is electrically connected to the moveable contact  70 . 
   As important aspects of the invention, an operating mechanism  76  moves the drive rod  72  generally left (with respect to  FIG. 2 ), as shown by arrow  78 , to close the separable contacts  68 , 70  through the end mechanism assembly  74 , and moves the drive rod  72  generally right (with respect to  FIG. 3 ), as shown by arrow  80 , to initiate the opening of the separable contacts  68 , 70  through the end mechanism assembly  74 . 
   Referring to  FIGS. 2–4 , the end mechanism assembly  74  cooperates with the drive rod  72  and includes an end mechanism housing  82 . The drive rod  72  is pivotally connected to a lower (with respect to  FIGS. 2–4 ) mechanism trunnion block  83  of the end mechanism assembly  74  by a drive rod pin  84 . The end of the drive rod  72  pivots within a slot  85  of the block  83 . The drive rod pin  84  is held in place at each end thereof by an X-washer  86  (both of which are shown in  FIG. 6 ) and a lock washer  87  (only one is shown in  FIGS. 2–4 ) as shown on one of those ends (to the right side of  FIG. 4 ). The end mechanism assembly  74  also includes an upper (with respect to  FIGS. 2–4 ) spring trunnion block  88  and a spring trunnion mass  92 , which is attached to the mechanism trunnion block  83  by suitable fasteners  94  (as shown in  FIG. 6 ) (e.g., without limitation, screws and lock washers). 
   The spring trunnion block  88  is pivotally and movably mounted with respect to the end mechanism housing  82  by an end mechanism pin  98 , which passes through longitudinal vertical (with respect to  FIG. 4 ) openings  99  of the housing  82 . Each of the ends of the pin  98  carries a suitable bearing mechanism, such as an end mechanism bearing spacer  100  and an end mechanism bearing  102 , which are disposed within the corresponding one of the housing openings  99  for translation therein as shown in  FIGS. 7–10 . The spacer  100 , bearing  102  and the corresponding end of the pin  98  are held captured within the opening  99  by a washer (e.g., brass)  104  and an X-washer  106  at each end. 
   A clevis connector  108  is pinned to the spring trunnion block  88  by the pin  98 , such that the spring trunnion block  88  may pivot counterclockwise (with respect to FIGS.  4  and  8 – 10 ) about the pin  98  from the position shown in  FIG. 4 . A trunnion rod  110  is threaded at its upper (with respect to FIGS.  4  and  7 – 10 ) end to the spring trunnion block  88  and its lower (with respect to FIGS.  4  and  7 – 10 ) end freely passes through an opening  111  ( FIG. 7 ) in the mechanism trunnion block  83 . A pair of end mechanism compression springs  112  are disposed between the spring trunnion block  88  and the mechanism trunnion block  83 . Although two example springs  112  are shown, one or more suitable springs may be employed. The springs  112  are held in position by end mechanism spring guides  114  (only one is shown in  FIGS. 8–10 ), which are threaded at their upper (with respect to FIGS.  4  and  7 – 10 ) end to the spring trunnion block  88 . As shown in  FIG. 10 , a lock washer  115  is disposed at the top of the spring guide  114  between its upper (with respect to  FIG. 10 ) end and the spring trunnion block  88 . 
   Two trunnion pins  116  are threaded in corresponding opposite sides of the mechanism trunnion block  83 . This trunnion block  83  is pivotally and movably mounted with respect to the end mechanism housing  82  by the trunnion pins  116 , which pass through horizontal (with respect to  FIG. 4 ) longitudinal openings  117  of the housing  82 . Each of the ends of the pins  116  carries a suitable bearing mechanism, such as an end mechanism inner ring  118 , an end mechanism needle bearing  120  and a roller bearing  122 , which are disposed within the corresponding one of the housing openings  117  for translation therein as shown in  FIGS. 7–10 . The end mechanism inner ring  118 , the end mechanism needle bearing  120 , the roller bearing  122  and the end of the pin  116  are held captured within the corresponding opening  117  by a washer (e.g., brass)  123  and an X-washer  124  at each end. 
   As best shown in  FIG. 5 , the upper end (with respect to  FIG. 5 ) of the clevis connector  108  has a threaded shaft  126  that is secured in a threaded opening  125  of the moveable contact  70 . As best shown in  FIG. 7 , on the threaded shaft  126  are disposed a hex nut  128 , a washer  130  and a lock washer  132 , which further secure the upper end of the clevis connector  108  to the moveable contact  70  ( FIG. 5 ). The lower end (with respect to  FIG. 7 ) of the trunnion rod  110  is a threaded shaft  133  on which are secured a lock nut  134  and a lock washer  135 . 
   The end mechanism assembly  74  of  FIG. 7  is preferably calibrated as shown in  FIG. 8  to provide a suitable opening setting  137  of the springs  112 , which setting is measured between the spring trunnion block  88  and the mechanism trunnion block  83 , as shown by the partially compressed length of the springs  112 . The operating mechanism  76  ( FIG. 2 ) drives the drive rod  72 , which compresses the springs  112  and drives the spring trunnion block  88 , the clevis connector  108  and the moveable contact  70  upward (with respect to  FIG. 5 ) to close the separable contacts  68 , 70 . A suitable snatch gap  139  is also preferably calibrated between the bottom (with respect to  FIG. 7 ) of the mechanism trunnion block  83  and the lock washer  135  to provide an indication of wear of the separable contacts  68 , 70 . For example, the gap  139  becomes progressively smaller with wear of the contacts  68 , 70 . 
     FIGS. 6 and 7  show a top plan view and a cross-sectional view, respectively, of the end mechanism assembly  74  of  FIG. 2  in the closed position. In contrast,  FIG. 8  shows the end mechanism assembly  74  in the open position. As the drive rod  72  is driven to the left (with respect to  FIGS. 8 and 9 ) by the operating mechanism  76  ( FIG. 2 ), the springs  112  are compressed and the moveable contact  70  is driven upward (with respect to  FIG. 5 ) by the spring trunnion block  88  and the clevis connector  108  until the contacts  68 , 70  first touch in the position of  FIG. 9 . Then, as the drive rod  72  is further driven to the left (with respect to  FIGS. 9 and 7 ) by the operating mechanism  76  ( FIG. 2 ), the springs  112  are fully compressed and the moveable contact  70  is driven fully upward (with respect to  FIG. 5 ) to the closed position of  FIGS. 5 and 7 . 
   During opening of the contacts  68 , 70 , the process is essentially reversed from  FIGS. 5 and 7 , to  FIG. 9  and to  FIG. 8 , with one exception. There is a “toggle” position of the end mechanism assembly  74 , which occurs between the “closed” position of  FIGS. 5 and 7  and the “contacts touch” position of  FIG. 9 . At this point, the end mechanism springs  112  advantageously begin assisting the opening of the contacts  68 , 70 . During closure, however, the springs  112  are compressed and are fully locked just prior to the toggle position. During opening, from the “toggle” position of the end mechanism assembly  74  to the “contacts touch” position of  FIG. 9  to the “open” position of  FIG. 8 , both the operating mechanism  76  (through the drive rod  72 ) and the springs  112  drive the mechanism trunnion block  83  to the right (with respect to  FIGS. 7–9 ) in the longitudinal openings  117 . However, between the “closed” position and the “toggle” position of the end mechanism assembly  74 , the vector of the force from the compressed springs  112  is sufficiently normal to the longitudinal openings  117 , such that friction between the roller bearings  122  and the corresponding openings  117  resists an opening force from the springs  112 . At the “toggle” position of the end mechanism assembly  74 , the vector of the force from the compressed springs  112  is sufficiently close to parallel to the longitudinal openings  117 , such that the springs  112  provide additional opening force to open the contacts  68 , 70 . This advantageously assists the operating mechanism  76  in the event that the contacts  68 , 70  might be partially welded closed. 
     FIG. 10  is a side elevational view of the end mechanism assembly  74  of  FIG. 2  in a maintenance position. In this maintenance position, the end mechanism springs  112  are not compressed and, hence, can be safely assembled or disassembled upon removal of the spring trunnion mass  92 . 
   While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the claims appended and any and all equivalents thereof