Abstract:
A switch has respective open-assist bars fixed to switch blades near the switch contacts. The bars are arranged so that, as the blades are turned by rotation of their supports, the bars come together and serve as a fulcrum mechanism that provides a prying action helping reduce the required opening force. The action of the fulcrum mechanism overcomes friction between the contacts that may otherwise tend to cause bowing of the supports with appreciable increase in the required opening force.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to center break switches, such as for electrical power substations and transmission lines, and particularly to such a switch in an arrangement facilitating opening of the switch. 
   2. Background Art 
   Center break switches have (in a single pole) two switch blades with mating contacts that meet, and separate, between a pair of rotatable blade supports. In a common type, the blade supports include ceramic or polymer insulators that are generally cylindrical with lateral sheds. The supports are joined at one end (nominally, the “bottom”) to a quite rigid metal base with a bearing for rotation of each support relative to the base and a mechanism for imparting rotational force to both supports, hence moving the switch blades into or out of a closed contact position. The supports, and their axes of rotation, are substantially parallel to each other in one switch type or, in another type, are in a substantially V-shaped configuration. Switches of interest include those described and illustrated in Cleaveland/Price Inc. descriptive bulletin DB-126A02, “Aluminum Center Break Switch”, published in 2002, that is representative of prior art to the present invention. 
   Operation of such switches is in some cases manual (e.g., by a handcrank or a swing handle) and in some cases by electric motor. Whether manually or motor operated, it is desirable to operate the switch easily and quickly with only modest requirements on the equipment and personnel. For example, some switches have a handcrank operator for manual operation. The handcrank is connected to the rotatable support apparatus through a gearbox with a gear ratio typically in a range from about 10:1 to 40:1, as specified by a user. A higher gear ratio allows a switch to be opened with less manual force but requires more time, which is generally undesirable. 
   Another factor in switch operation is that a typical installation has three poles, substantially alike, one for each phase of a three phase electrical system, and the operator must apply sufficient force to operate all three poles together. A maximum operating force, for three-phase switches, is typically specified to be in a range from about 35 to 70 pounds. Some installations have switches ganged together in even larger numbers, such as six poles with two poles for each phase of a three phase system. 
   Center break switches are now applied over a wide range of voltages, including high voltage systems up to a nominal rating of at least about 230 kV. Required switch size increases with increasing voltage (for contact clearance when the switch is open and for sufficient distance across the insulative supports) so that the rotatable supports and the contact blades reach up to several feet in length. This makes for a relatively massive structure to be moved and the longer supports make them more subject to bowing that can affect operation. In general, however, considerations affecting the opening force requirements apply to some degree regardless of the switch size or the number of switches operated together. 
   Switches operate in a variety of environments including those that can, particularly with age, change the amount of required operating force. One type of known switch has contacts with engaging surfaces that meet substantially in a horizontal plane like that of the arcuate motion of the contacts resulting from blade supports’ rotation. This produces considerable wiping action between the contacts during opening and closing that helps keep the contact zone free of debris and oxides. In this respect, sliding friction between the contacts enhances switch performance while also having an influence on the required opening force. 
   A variety of contact configurations are used in various center break switches. For example, some have appreciable contact engagement in a vertical plane that is substantially perpendicular to the plane in which the blades move. Still, in any of the contact configurations, there is some degree of sliding friction that can affect switch opening. Prior art has largely relied on a basic assumption that the axes of rotation of the insulative supports are substantially fixed. While prior center break switches have been generally successful, their design has not addressed the fact that sliding friction between the contacts during a switch opening can alter the location of the axes of rotation of the supports, particularly, but not limited to, those of larger units. Altering the axes of rotation by contact friction results in greater required force and time to separate the contacts than if those axes were fixed. 
   SUMMARY OF THE INVENTION 
   The present invention takes into account the effects of friction, including possible bowing movement of the support axes, and provides a simple arrangement for facilitating switch opening despite such friction effects. 
   Without friction, a center break switch would open very easily with no forces to distort the axes of rotation of the supports. With the switch blades at fixed support axes, the blades would swing the contacts from a fully closed position to a point of separation while only traversing a minimum distance. However, friction between contacts can change that by introducing a drag effect altering the geometry. 
   Sliding friction between contacts can cause the points of rotation of the blades, at the upper end of their supports, to move toward each other due to bowing of the insulative supports. This is because the contacts generate forces to overcome the sliding friction so that during the time contact motion has begun, but the contacts are still not separated, the contacts are not moving in a perfect arc. Their separation will only occur a distance beyond the minimum distance referred to above. With that change, the required torque and operating force is increased. Also, somewhat more time is required. 
   Now, in one embodiment of the present invention, a fulcrum mechanism is combined with the switch elements that may be like the prior art in other respects. It can include two additional members, such as bars (sometimes they may be referred to by alternative expressions such as pry bars, pry-open bars, pry-out bars, pivot bars, easy open bars, or open-assist bars) that are added in combination with a typical center break switch of the prior art. The “bars” need not be very elongated and can be any members that abut each other as described below during a switch opening. The elements of the fulcrum mechanism can be members attached to the respective blades or elements integral with the blades. 
   The bars are, in one example, relatively flat, stiff, metal plates, approximately “L” (or backward “L”) shaped. One bar is on each switch blade, e.g., with the bottom of the “L” (or backward “L”) bolted to the blade behind the contact on that blade and the upper parts of the bars extending beside the contacts to face each other. The facing portions abut and contact each other during a switch opening along with initial contact movement and before full separation. That is, the upper parts of an “L” on a right side blade and the upper part of a reverse “L” on a left side blade are located behind the contacts (with respect to the direction the contacts move) and the ends of the “L” and reverse “L” bars, which have some width and thickness, possibly with a flange-like end, meet to produce the intended effect. 
   While the contacts are engaged in sliding friction, the bars provide a new pivot point, or axis of rotation, during the opening motion that pries the contacts apart and forces them to stay on a more perfect arc as they open. The bars reduce bowing movement of the insulator supports and provide a contact parting at a point substantially like one that would exist if there were no sliding friction, even though the contacts do experience the same friction and wiping action. 
   The bars can be simply formed with the shape mentioned just as an example. Their conductivity is not an issue as far as producing the effect described. They need not touch in the fully closed position and need not have any direct contact with the switch contacts. (If the bars are metal, it is generally preferred to avoid any such contact.) They can be arranged to stay clear of any auxiliary switch elements near the contacts, such as arc horns, and may be attached at any convenient location along the blades, including at the same bolt locations arc horns are attached. Fortunately, the bars assist appreciably in an opening operation without interfering with a switch closing. They can be arranged to have little or no contact with each other during a closing operation and not appreciably alter the closing force. 
   The earlier contact release point that is achieved appreciably reduces the required operating force. A prototype test on a 230 kV, 3000 ampere switch showed a reduction in operating force on a handcrank gearbox (having a gear ratio of 20:1) from about 40 pounds without the bars to about 15 pounds with them in place, with the same contact pressure. Such switches have insulative supports over seven feet long and switch blades with a radius of about five feet. 
   The arrangement can be economical, effective, and readily implemented on switches already in service. It provides a convenient alternative, or a complement to other approaches that could be taken, such as providing a higher ratio gearbox for a handcrank operator. 
   Ancillary benefits include an opportunity to have higher contact pressure because the pry bars alleviate concern that less pressure should be maintained for easier opening. Also, flexibility of insulators can be less of a concern, so they can possibly be made from a wider range of materials. 
   These and other aspects of the present invention will be further understood from the following text and drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIGS. 1 and 2  are, respectively, side elevation and top plan views of a center break switch showing an embodiment of the invention where  FIG. 2  omits for clarity elements of  FIG. 1  below a top portion; 
       FIG. 3  is an enlarged plan view of part of the switch of  FIGS. 1 and 2 ; 
       FIG. 4  is an elevation view of the parts shown in  FIG. 3 ; 
       FIG. 5  is a plan view of the apparatus of  FIGS. 3 and 4  during movement from a fully closed position; 
       FIG. 6  is a schematic plan view of three mechanically interconnected switches; 
       FIGS. 7 and 8  are partial plan views of two alternative embodiments; and 
       FIGS. 9 and 10  are, respectively, partial plan and elevation views of a further embodiment. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1 ,  2 ,  3 ,  4 , and  5  are of the same apparatus although some elements are shown only in FIG.  1 . While each of  FIGS. 1 ,  2 ,  3  and  4  show a fully closed switch position,  FIG. 2  also shows a position after contact separation. 
     FIG. 1  shows a switch (one-pole) with a rigid base  10 , e.g., of hot-dip galvanized steel, on which moveable elements of the switch are mounted. Rotatable supports  12  and  13  are mounted at their bottom ends with bearings (not shown) for their rotation relative to the base  10 . In this example, the supports  12  and  13  each include a respective stack of insulators  12   a  and  13   a  with intermediate metal couplings  12   b  and  13   b . The insulators  12   a  and  13   a  are generally of a polymer (e.g., fiber reinforced plastic) or a ceramic material. Even though they are not intended to flex, the insulators are subject to some inherent flexing due to the described friction effects. 
   Contact blades  14  and  15  are respectively joined to the upper ends of supports  12  and  13  (FIG.  1 ). Near the supported ends of the contact blades  14  and  15  there is a respective one of a pair of line terminals  20  and  21  for connection with a conductor of an electrical system. Features for pivoting of the blades  14  and  15  in relation to the relatively fixed terminals  20  and  21  are included but will not be detailed herein and may be the same as prior art. The blades  14  and  15  have ends away from the supports  12  and  13  with blade ends, contacts and members to assist in switch opening (to be discussed later) in an assembly identified collectively by reference numeral  50  in  FIGS. 1 and 2  with more detailed identification of the elements in the subsequent enlarged views. 
   The blades  14  and  15  are, for example, each a single piece, aluminum, square tube. Each blade  14  and  15  has one of a pair of switch contacts  16  and  17  at its end opposite its respective support  12  or  13 . 
   In this example, as shown in  FIGS. 3 and 4 , the left side contact  16  includes four pairs of conductive fingers: two upper pairs each having a top finger  16   a  and a bottom finger  6   b  and two lower pairs each having a top finger  16   c  and a bottom finger  16   d , all of which are conductively joined near their left ends to the blade  14 . 
   The right side contact  17  includes a pair of conductive stabs  17   a  and  17   b , both conductively joined near their right ends to the blade  15 , that are respectively captured (in the closed position) within a jaw formed by the upper pairs of contact fingers  16   a  and  16   b  and within a jaw formed by the lower pairs of contact fingers  16   c  and  16   d . The elements of contacts  16  and  17  are highly conductive, e.g., silver plated or silver overlaid copper. 
   In addition, there is a contact pressure adjusting mechanism  18 , such as one supported from the blade  14  with bolts and adjusting nuts bearing on spring plates that bear against the fingers of contact  16 . 
   The figures omit for greater clarity corona or arc reducing spheres or horns, and also an ice shield, that are conventionally arranged near contacts of such a switch as that shown. 
   At the bottom of the switch ( FIG. 1 ) a mechanism  30  is provided for operation of the switch including a tie rod  31  mechanically coupled to both insulative supports  12  and  13  at metal flange members not detailed here. Bearings (not shown) for rotation of the supports  12  and  13  relative to the rigid base  10  are located near the attachments of rod  31 . 
   In this example, the mechanism  30  further includes a handcrank  32  schematically shown in a mechanically coupled relation through a gearbox  33  to the tie rod  31  that transmits rotational force to the supports  12  and  13 , both together and also typically together with force transmitted to two other switch poles of the same nature, as is later discussed in connection with FIG.  6 . 
   All of the elements discussed so far (not including any open-assist members  40  and  42  as described below) may be in accordance with known prior art switches such as, but not limited to, that described in the above mentioned background publication which is incorporated by reference herein for further description of examples of the construction and use of such switches, including both those with substantially parallel rotatable supports (as shown here) and those with substantially V-oriented supports (not shown herein) with otherwise similar features. 
   While the invention is not so limited, the contacts  16  and  17  in this example have fingers and stabs that engage each other in one or more planes parallel to the arcuate movement of the blades  14  and  15 ; a substantially horizontal interface. ( FIG. 2  gives a general picture of the blades and contacts as they have been moved from a closed to a contact parted position by rotation at their supports.) The contact fingers  16   a-   16   d  are not totally planar, since (as shown in  FIG. 4 ) they have a bend that makes the principal direct contact with the stabs  17   a  and  17   b  along a line  52  (in the closed switch position). Before the switch reaches a position as shown in  FIG. 2 , those bends of the fingers move over the surfaces of the stabs with a wiping action that is favorable for good conduction. The contact pressure adjustment mechanism  18  allows a user to set the pressure to a desired level. 
   (For general reference, switches of the type described typically go to a fully open position only after the blades have turned 90°. In views such as  FIG. 2 , the contacts have parted and have no more frictional engagement but the blades have not yet reached the fully open position.) 
     FIGS. 3  to  5  show a contact assembly  50  that, in addition to the elements that may be otherwise conventional, include a pair of plate-like bars  40  and  42  that are shown respectively attached (e.g., bolted) near a first end  40   a  and  42   a  to the top of a switch blade  14  or  15  and shaped to extend in front of the contacts  16  and  17  to face each other at their ends  40   b  and  42   b  that may have small flanges, as shown. 
   The bars  40  and  42  need not make physical contact to each other in the fully closed position of the switch, so a gap may occur as shown in FIG.  3 . (The “facing” relation is meant to include either with or without a gap). The bars  40  and  42  assist in switch opening. When blade rotation and contact movement has started, the bars  40  and  42  meet at at least part of their facing ends  40   b  and  42   b  (e.g., edge corners  40   c  and  42   c  as shown in  FIG. 5 ) and establish there a new pivot or axis of rotation that facilitates switch opening. The line (or plane)  52  of principal contact engagement and wiping action shifts as the blades move in the directions of the arrows in FIG.  5 . 
   Now, instead of contact sliding friction causing bowing of the supports  12  and  13  so the switch opening is delayed due to extra travel of the contacts  16  and  17  and requires more force, the locus of the pivot comers  40   c  and  42   c  stays substantially fixed through the duration of their contact to each other despite the contact friction. 
   By way of further example, the bars  40  and  42  are relatively stiff metal plates that are relatively flat although  FIG. 4  shows a small angular variation and the abutting ends  40   b  and  42   b  have small vertical flanges. These bars are, looking in the plane of  FIG. 3 , respectively substantially L-shaped (bar  42 ) and reverse L-shaped (bar  40 ) with the bottom leg of each “L” joined at  40   a  and  42   a  to the respective blades and the ends of the top parts of the “L” configurations being the facing ends  40   b  and  42   b.    
   One factor making it convenient to attach the bars  40  and  42  to the blades as shown is that the bar ends  40   a  and  42   a  can be bolted to the blades at bolt locations as shown that are the same as those used for attachment of arc horns (which are not shown in these views). This is particularly convenient for putting the assembly together on switches already in the field. A variety of other attachment locations and shapes for members performing the function of bars  40  and  42  will be apparent. 
     FIG. 6  illustrates a three phase switch combination with respective switches  61 ,  62  and  63  that can each be like that previously described. This schematically shows how a single mechanical arrangement  130  combining tie rods and related parts of each of the three switches are joined together for common operation from a single motive power source, e.g., a handcrank  132  and gearbox  133 . This is a common situation and is shown to make the point that the inventive combination has further benefit when practiced in multi-switch gangs where opening force requirements are greater than with a single switch. 
   The described embodiment is also one that has the facing ends  40   b  and  42   b  that form the pivot point or axis, where corners  40   c  and  42   c  meet per  FIG. 5 , off of the line  52  of the main contact pressure. This is just one possible location. A general characteristic of the inventive combination is that members comprising the fulcrum mechanism, such as bars  40  and  42 , meet and make a pivot point for the blades  14  and  16  at least some part of the time the contacts  16  and  17  are sliding together during a switch opening. Preferably, but not necessarily, the fulcrum mechanism is such that its pivot action occurs substantially throughout the sliding engagement of the contacts. Some benefit can be obtained even if it occurs only part of that time, for example during early contact movement. After the contacts have parted, the fulcrum mechanism need not operate. 
     FIG. 7  shows an alternative arrangement  150  for pivot members or bars on a switch with other elements as previously described. In this embodiment, the configuration of the blades  14  and  15  and the contacts  16  and  17  is the same as was previously described. The contacts  16  and  17  have a horizontal interface and move in the same direction as the contacts of FIG.  5 . However, now pivot members  140  and  142  are attached to respective contact blades  14  and  16  on the side of the blades toward the front of the switch (considering a view such as that of  FIG. 1 ) near their ends  140   a  and  142   a . The members  140  and  142  are plate-like bars that, in this example, are shown just flat and their ends  140   b  and  142   b  face each other, with a small gap in the closed position. As shown, bars  140  and  142  are equal in length; in general, they can have the same or different shape and size as long as their locations cause the described pivot action. In  FIG. 7 , as the switch opens, with blade movement as shown by the arrows, the pivot axis will occur at rear (or lower in the drawing) corner edges  140   c  and  142   c , substantially as it does in the embodiment of FIG.  5 .  FIG. 7  represents just one alternative form a fulcrum mechanism can take with contacts having horizontal engagement. 
     FIG. 8  shows a further alternative arrangement  150 ′. A fulcrum mechanism comprises elements  140 ′ and  142 ′ that are respectively integral with the blades  14 ′ and  15 ′. For example, blades in the form of square tubes can have three sides partly cut away leaving portions  140 ′ and  142 ′ extending from the full square configuration. The extended material can be formed as desired, such as to form the illustrated flange portions at  140   b ′ and  142   b ′ that face each other and whose back corners  140   c ′ and  142   c ′ initially engage to provide a pivot as the contacts open. 
   A variety of contact arrangements for center break switches are used in the art other than that shown for contacts  16  and  17 . Some have principal contact engagement and a degree of wiping action that is not in a plane parallel to the arcuate blade movement. For example, the contact faces may principally engage in a substantially vertical interface plane. Even so, to the extent the contacts engage with sliding friction in any of these alternative contact configurations, the present invention can be beneficial to facilitate switch opening. 
     FIGS. 9 and 10  show an example of a combination  250  of pry bars with a pair of contacts with a vertical interface. Blade  214  supports a first contact  216  that has a loop forming a jaw within which a stab-like second contact  217  on blade  215  is engaged. A closed switch is shown. The arrows in  FIG. 9  show the directions the blades  214  and  215  will take during a switch opening. During that movement, front and back fingers of contact  116  slide against front and back ends of contact  217  and produce sliding friction. 
   The combination  250  includes pry bars  240  and  242  that are arranged and operate in substantially the same way as bars  40  and  42  previously described. Here the bars  240  and  242  are merely flat from their secured ends  240   a  and  242   a  out to their facing ends  240   b  and  242   b  at which a small vertical flange occurs. Also, it will be noted the bars  240  and  242  will meet and pivot, at the back comers  240   c  and  242   c , along the same line as that on which the contacts engage in the closed position. 
   It is, therefore, apparent that the invention applies either in the case in which the contacts engage with sliding friction in a plane orientated the same as the plane of the movement of the blades or the case in which the plane of contact engagement is perpendicular to the blades’ plane of motion. Also, it can be understood that the contacts can be configured with elements such that they engage, and slide, in both planes. 
   Among the considerations for members in the fulcrum, or open-assist, mechanism is to make any gap between them in the closed position as small as reasonably attainable so the pivot action can commence promptly upon contact movement. The gap can be avoided entirely although it is not generally preferred to have any conduction across the bars, if of metal, when closed. However, the bars need not be metal but may instead be of an insulative material such as fiber reinforced plastic, at least at the facing ends, so direct contact when closed would not be a concern. 
   The illustrated embodiments have a geometry for the open-assist elements with a pivot axis centered in relation to the blades and the blade supports although the contacts have a line of primary engagement, as shown in  FIGS. 3 ,  7 , and  8 , not quite centered between the ends of blades  14  and  15  or  14 ′ and  15 ′. Symmetrical elements  40  and  42 ,  140  and  142 , and  140 ′ and  142 ′ are generally preferred for typical switches, such as those with equal length blades. Variations can be implemented in which the abutting elements are not symmetrical; in general, they can have the same or different shape and size, and the same or different relative locations on the blades, as long as they meet to perform the described pivot action during the sliding engagement of the contacts. 
   While the description sometimes refers to “upper”, “lower”, “top” or “bottom”, “horizontal” or “vertical” orientations (consistent with the Figures), it will be understood the described switches can be mounted in essentially any orientation. 
   The specific embodiments disclosed are merely some examples of the various ways in which the invention can be practiced.