Combined arc shield/wire tray for switchgear and switchgear assemblies incorporating same

[0002] Commonly owned, concurrently filed U.S. Patent Application entitled “Switchgear Assembly With Integral Control Wiring Wireway” and identified by Ser. No. 09/325,308.

[0003] 1. Field of the Invention

[0004] This invention relates to switchgear used in low voltage electric power distribution systems, and more particularly, to an arrangement for channeling arc gases generated by an electrical switching apparatus such as a circuit breaker incorporated into the switchgear, and also for guiding and protecting from the arc gases control and instrumentation wiring for the electrical switching apparatus.

[0005] 2. Background Information

[0006] Switchgear for electric power distribution systems includes electrical switching apparatus and their line and load terminations together with related equipment mounted in metal cabinets. Switchgear used in sections of electric power distribution systems operating at voltages up through 600 volts is classified as low voltage switchgear. Typically, the electrical switching apparatus is a circuit breaker, but other switching apparatus such as for instance, network protectors, disconnect switches and transfer switches are also mounted in such switchgear cabinets. Henceforth, the electrical switching apparatus will be referred to as circuit breakers, although it will be understood that other types of electrical switching apparatus can be used as well.

[0007] Typically in such low voltage switchgear, multiple circuit breakers are mounted in each cabinet in cells stacked vertically in a forward compartment. The line and load conductors are mounted in rearward compartments and engage the circuit breakers through quick disconnects as the circuit breakers are installed in the cells.

[0008] Power circuit breakers can generate significant amounts of arc gases when interrupting large currents such as those associated with a short circuit in the distribution system. It is common for the arc gases to be vented through the rear of the circuit breaker. Other power circuit breakers discharge the gases through vents in the top of the circuit breaker housing. Generally, the approach is to slow the arc gases down and cool them before they leave the switchgear cabinet.

[0009] Other considerations in the design of low voltage switchgear is the placement of the terminals for the secondary wiring, such as the control and instrumentation wiring. Generally, there is not much room for these secondary wiring terminations within the circuit breaker cabinet. One approach is to terminate the secondary wiring in the rear of the switchgear cabinet. However, this can expose personnel tending the secondary terminations to power conductors which are located there.

[0010] It is preferable to have the secondary wiring terminations at the front of the switchgear cabinet both for safety and accessibility. Hence, one approach has been to mount the secondary terminations alongside the circuit breakers. However, such space is very limited in the typical switchgear cabinet which is of standardized width.

[0011] Another approach has been to use an entire cell for terminations. Obviously this limits the number of circuit breakers that can be mounted in a switchgear cabinet. In some switchgear, the secondary terminations are mounted on trays which slide between the vertically mounted cells. In one arrangement, the trays pull out horizontally and then swing vertically for better access. One non-domestic manufacturer has fixed mountings for secondary terminations between the cells.

[0012] Placing the secondary terminations between the circuit breakers and accessible from the front of the cabinet must include protection of wiring from the arc gases discharged from top vents on the breakers. The non-domestic manufacturer referred to above utilizes a rectangular channel extending transversely above the top vents to deflect the arc gases out sideways. The fixed secondary terminations are then mounted separately in front of the transverse channel.

[0013] The switchgear utilizing the pull out trays have a flat, horizontal arc shield at the top of the cells above the top vents. In some switchgear, this type of flat horizontal shield also extends under the pull out tray which is forward of the top vents. In this arrangement, where the pull out tray swings vertically after being pulled out, the flat wall is lower under the tray and there is an inclined transition section to this lower forward section. However, this is well in front of the arc vents. The switchgear also has flanges extending downward along the side edges of the flat ceiling panel.

[0014] There is a need for improvement in low voltage switchgear for containing the arc gases generated by the newer power circuit breakers with top arc vents and higher interruption ratings, and for safe and convenient secondary terminations which are protected from the high volumes of the arc gases.

[0015] This need and others are satisfied by the invention which is directed to an arc shield/wire tray for secondary wiring terminations for electrical switching apparatus having arc chute vents in an upper surface thereof and mounted in a switchgear cabinet. The arc shield/wire tray comprises an upward and rearwardly inclined rear panel positioned over the arc chute vents for deflecting arc gases rearward. A floor panel extends forward from a front edge of the inclined rear panel and a front wall extends upward from a front edge of the floor panel. Secondary terminations provided on terminal blocks are mounted to the front wall for access from the front of the cabinet. Where the electrical switching apparatus has secondary wiring connectors on an upper surface forward of the arc chute vents and forward of the inclined rear panel, the floor panel of the wire tray has a cut-out for the secondary wiring connectors.

[0016] When used in a switchgear cabinet having a vertical passage for wiring, the arc shields/wire trays open on one end for communicating with this vertical passage. This opening can be provided in a side wall of the arc shield/wire tray.

[0017] Preferably, the secondary terminations are mounted in the front panel in at least two substantially horizontal rows with a lower row positioned farther forward than an upper row. This arrangement is provided by the front wall having an upper vertical section and a lower vertical section and a connecting section positioning the lower vertical section further forward than the upper vertical section. When used in switchgear cabinets having a plurality of vertically stacked cells in which the electrical switching apparatus is mounted, the arc shield/wire tray is suspended from a cell above.

[0018] The invention also embraces a wire tray for secondary wiring for electrical switching apparatus mounted in vertically aligned cells in a switchgear cabinet in which the wire tray has a rear wall, a bottom wall and a front wall each extending substantially across the cell and means mounting terminations for the secondary wiring in the front wall. Where the electrical switching apparatus has secondary wiring connectors at a top surface, the bottom wall of the wire tray has a cut-out for the connectors and for passing wiring from the connectors to the terminations. The terminations are mounted in the front wall in two substantially horizontal rows with the lower row forward of the upper row. Where the switchgear cabinet has a vertical wiring passage, the wire tray communicates at one end with this vertical passage. In a preferred arrangement, the wire tray has side walls extending between the rear wall and the front wall and an opening in one of the side walls for communicating with the vertical wiring passage. Where the switchgear cabinet has a plurality of vertically stacked cells, the wire trays are suspended from a cell above.

[0019] The invention is also directed to switchgear apparatus for housing electrical switching apparatus having arc chute vents spaced rearwardly in upper surfaces thereof. A cabinet having a forward compartment for the electrical switching apparatus has an additional compartment behind the forward compartment. At least one cell in the forward compartment houses an electrical switching apparatus and an arc shield mounted over the cell has an arc deflecting member positioned above the arc chute vents and inclined upward and rearwardly to deflect the arc gases ejected through the arc vents rearward. Preferably, the arc shield has an integral downwardly extending lip positioned rearwardly of the arc deflecting member. More preferably, the arc shield has an integral substantially horizontal section extending between the arc deflecting member and the downwardly extending lip. Also, preferably, the cabinet has a vertical passageway extending along at least one side of the arc deflecting member into which the arc gases escape by moving laterally from the downwardly extending lip.

[0020] Where the switchgear apparatus has multiple cells stacked vertically in the forward compartment, arc shields for a plurality of the cells are suspended from a cell above. In a preferred arrangement, at least one cell has a wire tray extending across the cell above the electrical switching apparatus and forward of the arc shield. This wire tray utilizes the arc deflecting member as a rear wall. It further has a bottom wall extending forward of the arc deflecting member, a front wall forward of the bottom wall and secondary terminal blocks supported in the front wall and accessible from a front of the cabinet.

[0021] Where the electrical switching apparatus has quick disconnects extending rearwardly therefrom below the downwardly extending lip on the arc shield, a quick disconnect protector extends between quick disconnects and the downwardly extending lip to protect the quick disconnects from the arc gases. Preferably, this quick disconnect protector is a generally horizontally extending perforated plate.

[0022] 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:

[0023] FIG. 1 is an isometric view of a switchgear assembly incorporating the invention shown with side panels removed for clarity.

[0024] FIG. 2 is a right, front isometric view of a portion of the switchgear assembly of FIG. 1 with parts removed.

[0025] FIG. 3 is a left, front isometric view similar to that of FIG. 2 but with additional parts removed and other parts added.

[0026] FIG. 3ais an enlargement of a section of FIG. 3 showing a lanced section of the wall.

[0027] FIG. 4 is an exploded isometric view of a cell with its corresponding arc shield/wire tray.

[0028] FIG. 5 is a vertical sectional view through the switchgear assembly.

[0029] FIG. 6 is a side elevation view in enlarged scale illustrating the relationship between a circuit breaker and the arc shield/wire tray.

[0030] FIG. 1 illustrates switchgear apparatus 1 which includes a switchgear cabinet 3 having a forward compartment 5 and additional compartments including a middle compartment 7 and a rear compartment 9. The forward compartment 5 has a number, in this case four, vertically stacked cells 11 for housing electrical apparatus. Typically, the electrical apparatus is circuit breakers and associated instrumentation, but other switching apparatus such as, for instance, network protectors, disconnect switches and transfer switches can also be mounted in the cells 11. Each of the cells 11 has a side hinged access door 13, the lower three of which have openings 15 through which the controls of the circuit breaker or other switching apparatus are accessible without opening the door. In the usual arrangement, the upper cell 11 houses instrumentation for the circuit breakers in the cells below and does not have an access opening. Low, wide side hinged doors 17 provide access to wiring terminations to be described below for the circuit breakers.

[0031] The middle compartment 7 houses three-phase power buses 19 connected to the circuit breakers (not shown) mounted in the cells 11. The rear compartment 9 houses connections (not shown) for power cables (also not shown) for connection to the circuit breakers in a manner which is well-known.

[0032] As shown in FIG. 5, the power buses 19 include a set of vertical buses or risers 21 connected to horizontal buses 23. The circuit breakers 25 are inserted into the cells 11 through the open doors 13 (see FIG. 1) on cassettes (not shown) which roll the circuit breakers into position. The circuit breakers 25 have upper and lower quick disconnects 27uand 271 which engage stab connections 29uand 291 as the circuit breakers 25 are fully inserted in the cells 11. The upper stabs 29uare connected to the risers 21 while the lower stabs 291 become runbacks which extend through the middle compartment into the rear compartment 9 for connection to the power cables (not shown).

[0033] Turning to FIGS. 2, 3 and 6, it can be seen that each of the cells 11 has a bottom wall 31 and a pair of side walls 33. A channel member 35 connects the top rear of the side walls 33 and is secured to a panel 37 extending across the rear of the forward compartment 5.

[0034] As mentioned, the circuit breakers 25 are rolled in and out of the cells 11 on the cassette (not shown). FIG. 6 illustrates a circuit breaker 25 shown in place within a cell 11. The circuit breaker 25 has at the rear of an upper surface 39 vents 41 for venting arc gases shown by the arrows 43 generated during the interruption of large currents such as those resulting from a short circuit.

[0035] As also mentioned, terminations 45 for secondary wiring 47 for the circuit breakers 25 are mounted between the circuit breakers. The secondary wiring 47 comprises the control and monitoring wiring for the circuit breakers as opposed to the primary or power conductors connected to the circuit breakers such as the buses 19, the stabs 27uand 271 and the cabling in the rear compartment (not shown). It is important to protect the secondary wiring 47 and terminations 45 from the hot arc gases 43. Thus, an integral arc shield/wire tray 49 is provided. As best seen in FIG. 4, the arc shield/wire tray 49 include an arc shield 51 molded of a resin material such as a polyglass and having an arc deflecting member or panel 53 positioned above the arc vents 41 and inclined upwardly and rearwardly as seen in FIG. 6 to deflect the arc gases 43 rearwardly and away from the secondary wiring 47. The arc shield 51 further includes an integral horizontal section 55 extending rearwardly from the top of the arc deflecting panel and terminating in a downwardly extending lip 57 which extends across the width of the cell 11. The molded arc shield 51 also includes wings 59 on either side of the arc deflecting panel 53 forming side walls. The arc shield also has a lower horizontal wall 61 extending forward from the lower front end of the arc deflecting panel 53. The arc shield 51 is suspended from the bottom walls 31 of the cell 11 above by fasteners 63 extending through molded bosses 65 on the upper horizontal section 55. The forward horizontal panel 61 is secured by fasteners 67 passing through an insulating member to a metal frame 71 extending between the side walls 33 of the cell 11.

[0036] As will be noticed from FIG. 6, the downwardly projecting lip 57 on the arc shield stops the rearward flow of the arc gases 43 and tends to deflect them downward toward the quick disconnects 27. In order to prevent these arc gases from causing arcing at the disconnects, a quick disconnect protector in the form of a perforated plate 73 extends horizontally above the quick disconnects and is supported through an integral flange 75 by the channel member 35 extending across the rear of the cell. This results in the arc gases being diverted laterally, mainly out of the plane of FIG. 6, for further handling in a manner to be discussed.

[0037] Returning to FIG. 4, the wire tray portion 77 of the arc shield/wire tray 49 utilizes the arc deflecting member or panel 53 as a rear wall, and the forward horizontal panel 61 together with the metal frame 71 as a bottom wall. It also includes a front wall 79. This front wall 79 has an upper vertical section 81 and a lower vertical section 83 connected by an intermediate horizontal section 85 which positions the lower vertical section 83 forward of the upper vertical section 81. Each of the upper vertical section 81 and lower vertical section 83 of the front wall 79 have notched horizontally extending slots 87 in which are mounted in horizontal rows a plurality of the secondary wiring terminal blocks 45 (see FIG. 6). These terminal blocks and the manner in which they are secured in the slots 87 are described in commonly owned patent application Serial No. 09/261,796, filed on Mar. 3, 1999. The offset sections 81 and 83 of the front wall 79 position the lower secondary wiring terminal blocks 45 forward of the upper row for easier wiring.

[0038] As can be seen from FIG. 6, the front wall 79 is suspended from the bottom wall 31 of the cell 11 above by a mounting bracket 89. Tabs 91 and 93 on the lower vertical section 83 of the front wall 79 engage slots 95 and openings 97 in the metal frame 71 to stabilize the lower end of the front wall 79. The openings 97 in the metal frame 71, which as will be recalled, forms part of the bottom wall of the wire tray 77, accommodates passage of secondary wiring 47 between connectors 48 on the circuit breaker 25 and the secondary wiring terminal blocks 45.

[0039] Some of the secondary wiring 47 is routed to other circuit breakers 25 or to the instrumentation usually located in the top most cell 11 in the switchgear cabinet 3. Additional secondary wiring is routed outside of the switchgear cabinet 3 for remote monitoring and control. Referring to FIGS. 2 and 3, a wireway 99 is integrated into the switchgear apparatus 1 in order to organize the routing of the secondary wiring for easy and safe access by technicians, and to protect the secondary wiring. Wireway 99 includes a vertical section or passage 101 in the right forward corner of the compartment 3. This vertical section 101 is formed on one side by the side walls 33 of the cells 11, an outer side panel 103, a transverse vertical wall 105 extending between the side panel 103 and the cell walls 33 and is closed off and made accessible through the cell doors 13 and termination doors 17 (see FIG. 1). This vertical section or passage 101 extends the full height of the right front comer of the forward compartment 5 of the cabinet 3 and joins a horizontal section or passage 107 extending rearward under the top top wall 109 of the cabinet and extends through the middle compartment 7 to the rear compartment 9. A gutter section 111 extending forwardly and downwardly from the horizontal section 107 provides a transition between the horizontal section 107 and the vertical section 101 which more easily accommodates bending of the secondary wiring.

[0040] The wireway 99 provides a great deal of flexibility in routing the secondary wiring into and out of the cabinet 3. For instance, as seen in FIG. 2, the floor panel 113 of the forward compartment 5 has a bottom access opening 115 which communicates with the bottom of the vertical section 101 for routing the secondary wiring into and out of the cabinet. If not used, a bottom cover plate 117 is placed over this opening. A top access opening 119 in the top of the cabinet over the middle compartment 7 provides for alternate routing of the secondary wiring and if not used is closed off by a removable top cover 121. A number of side openings 123 in the side panel 103 provides side access at several levels and are blocked off if not used by side covers 125. As another alternative, the wiring can be directed into the rear compartment 9 for rear access. Generally, this would not be recommended as it would expose the technicians servicing the secondary wiring to the power connections also located there.

[0041] The secondary wiring 47 includes factory wiring 47ainstalled before the switchgear apparatus 1 is shipped to the user site (see FIG. 2), and field wiring 47binstalled during installation in the field (see FIG. 3). The wireway 99 provides for convenient organization of the two types of wiring. More specifically, first wiring attachments 127 are provided for the factory wiring 47aon the transverse vertical wall 105 forming the rear wall of the vertical section 101 of the wireway. Second wiring attachments 129 are provided on the side wall formed by the side panel 103 for the field wiring 47b. These wiring attachments 127 and 129 can conveniently be in the form of lanced sections of the respective metal panels to which the respective wiring can be secured by ties (not shown).

[0042] With the vertical section 101 of the wireway 99 located in the right front corner of the forward compartment 5, this leaves a chamber 131 bounded at the front by the transverse wall 105, at the rear by the panel 37, on the outside by the panel 103 and on the other side by the side walls 33 of the cells. The spaces 133 between the side walls 33 of adjacent cells, allow the arc gases 43 to escape into the chamber 131 where they expand and cool.

[0043] 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 invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.