Electrical Switchboard Apparatus Including Welded Bus Connector

The present invention is related to copending U.S. patent applications Ser. No. 755,705, entitled "Electrical Switchboard Apparatus With Center Fed Vertical Riser Bus" filed 12/30/76 by G. N. Kovatch and R. Rosey; Ser. No. 756,036, entitled "Electrical Switchboard Apparatus Including Double-Flanged Vertical Riser Conductors filed 12/30/76 by G. N. Kovatch, R. Rosey, N. H. Simon, and N. A. Tomasic; and Ser. No. 755,540 entitled "Electrical Switchboard Apparatus Including Bus System With Individual Phase Isolation" filed 12/30/76 by G. N. Kovatch, R. Rosey, and N. H. Simon. All of the above-mentioned copending U.S. patent applications are assigned to the assignee of the present invention.

1. Field of the Invention

The invention relates to electrical switchboard apparatus having welded bus and more particularly to means for welding the main horizontal bus to the vertical riser bus forming a part of such switchboard apparatus.

2. Description of the Prior Art

An electrical distribution switchboard distributes the main incoming power among various site functions such as heating, lighting, and air conditioning. It typically consists of a number of vertical cabinet sections containing circuit breakers for switching and protecting the various load circuits. Three-phase electrical power enters a switchboard via cable or bus duct connected to a main bus which runs horizontally within the switchboard between the various sections. The main bus is connected to vertical, or riser, bus in each vertical cabinet section. Various circuit interrupters stacked vertically have their inputs connected to the vertical riser bus and their outputs connected to horizontal load size extensions which run toward the rear of the cabinet perpendicular to the main horizontal bus. Bus duct or cable is then attached to the load side extensions to permit the power to exit the switchboard and flow to the load (air conditioning, lights, motors, etc.).

The primary requirements for a switchboard are that it be safe and dependable, and that it exhibit low cost in construction, installation, and maintenance. Material cost and availability has influenced the choice of aluminum as the bus conductor material in some switchboard applications, since aluminum is readily available at an attractive cost and can be easily formed or extruded into any desired configuration. However, aluminum bus systems having joints formed with nuts and bolts (as is standard with copper bus systems) require periodic maintenance to assure satisfactory performance. This maintenance is costly and usually requires de-energization of the switchboard, causing great inconvenience to the users of the building being supplied by the switchboard.

Aluminum bus systems having welded connections eliminate the need for such maintenance. However, assembly of the switchboard can be much more costly and complicated due to the increase in complexity of welding precedures over bolting assembly methods in the confines of the switchboard cabinet framework. It is therefore desirable to provide a switchboard having a welded bus system suitable for a maximum of bench assembly operations prior to installation within the switchboard cabinet.

It has been found that savings can be achieved in the use of horizontal bus members having a plurality of spaced parallel-connected conductors rather than a single larger conductor having the same current carrying capacity. This is due primarily to greater cooling capability of parallel conductors, plus the increase in surface area which takes advantage of the "skin effect", whereby alternating current tends to flow at the surface of a conductor rather than its interior.

The use of such spaced parallel conductors means more complicated connections between the horizontal bus and the vertical riser bus. Prior art connections were often made by interleaving the incoming and outgoing horizontal bars at a horizontal-vertical junction, but this required an external jig fixture to properly position the bars during the welding operation. It is therefore desirable to provide a switchboard having a welded bus system which eliminates the need for an external fixture and which simplifies the welding operation required at a bus junction.

In accordance with a preferred embodiment of the present invention, there is provided an electrical power distribution switchboard comprising a cabinet structure and a welded bus system. The bus system comprises a main bus mounted within the cabinet and connected to a source of electrical power. The main bus comprises a plurality of spaced parallel-connected conducting bars. The bus system also comprises a distribution bus perpendicular to the main bus and connected to an electrical load.

A connector block provided for joining the main supply bus to the distribution bus is defined by two end surfaces, a bottom surface connected to the distribution bus, and side surfaces, one or more of the side surfaces comprising locating means being adapted to receive the ends of the spaced parallel-connected main bus bars.

The ends of the main bus bars are positioned by the connector block locating means and are welded thereto.

For a better understanding of the invention, reference may be had to the preferred embodiment exemplary of the invention shown in the accompanying drawings, in which:

FIG. 1 is a perspective view of a four-section electrical power distribution switchboard;

FIG. 2 is a diagrammatic view of an electrical switchboard employing the principles of the present invention, showing the locations of load and line connectors for a variety of circuit breaker frame sizes;

FIG. 3 is a side view of one section of the switchboard of FIG. 1;

FIG. 4 is a diagrammatic view of the horizontal main bus of the four-section switchboard of FIG. 1;

FIG. 5 is a perspective view of the junction between the horizontal main bus and the vertical riser bus of a single section of the switchboard of FIG. 1;

FIG. 6A is a detail sectional view of the switchboard section of FIG. 5, taken along the line A--A of FIG. 5;

FIG. 6B is a sectional view similar to FIG. 6A taken along the line B--B of FIG. 5;

FIG. 7A is a side view of a phase A vertical phase conductor;

FIG. 7B is a side view of a phase B vertical phase conductor;

FIG. 7C is a side view of a phase C vertical phase conductor;

FIG. 7D is an end view of any of the vertical phase conductors shown in FIGS. 7A-7C; and

FIG. 8 is a detail perspective view of one phase of the bus junction shown in FIG. 5.

Referring now to the drawings, in which like reference characters refer to like components, FIG. 1 shows an electrical distribution switchboard 10 having four vertical section structures 12, 14, 16, and 18. Each of the sections of the switchboard 10 includes a device compartment 20 separated into cells 22, a bus compartment 24, and a cable compartment 26. Each of the cells 22 contains circuit interrupters 23 or instruments used in controlling or monitoring electrical circuits powering loads such as air conditioners, motors, lights, etc.

Generally, each of the vertical sections 12, 14, 16, 18 comprise structural members such as 28 and 30 to which cover sheets 32 and doors 34 are added. Circuit breaker controls and indicators 35 are accessable through the doors 34 to operate and indicate the status of the enclosed circuit breakers.

Incoming main power is connected to a main bus which runs horizontally through the bus compartments 24 of the board 10 connecting the sections 12, 14, 16, 18. The circuit breakers in each section are then connected to the horizontal bus through riser bus extending vertically in the bus compartments of each of the sections 12, 14, 16, 18.

As can be seen in FIGS. 3, 6A, and 6B, each of the circuit breakers 23 includes movable sliding contact connectors, or finger assemblies, 37 cooperating with line stab connectors 36 and load stab connectors 38. The interaction of the fixed stabs 36, 38 and the movable finger assemblies 37 provides sliding contact connection allowing the circuit breakers to be inserted and withdrawn from the cells 22. Other means providing such sliding contact connection could, of course, be used. The line stabs 36 which are connected to the vertical riser bus supply incoming power to the separable contacts within the circuit breaker, from which the power then flows outward through the load stabs 38 and load side runbacks 72 to the distribution circuits and loads which will ultimately be supplied.

As can be seen in FIG. 3, a variety of circuit breaker frame sizes must be provided for. It is desirable to design the bus structure to be compatible with such a variety and mix of circuit breaker frame sizes while at the same time utilizing a minimum amount of material and simplifying the installation of the switchboard. Prior art switchboards often provided for three different locations for the horizontal bus: at the top, the center, and the bottom of the switchboard, the location of the horizontal bus being dependent upon the location and frame size mix of the circuit breakers to be included in each individual switchboard and, specifically, the location of the load side connection. The load side runbacks extend back through the bus compartment and into the cable compartment, complicating the bus layout, since required insulation clearances must be maintained. FIG. 2 (a diagram not related to the specific circuit breaker configuration of FIG. 1) shows the locations of the line and load side stab connectors 36 and 38 for three different circuit breaker frame sizes, 3,000 ampere, 1,600 ampere, and 800 ampere, and the respective breaker horizontal centerlines 40, 42, and 44. The hatched rectangles indicate the location of load stabs 38. Above the horizontal centerline 58 of the switchboard are conventional circuit breakers which are bottom fed, that is, circuit breakers with the input line side stabs 36 at the bottom and the output load side connections 38 at the top. By employing these normal circuit breakers above the horizontal centerline of the vertical section structure and by using top, or reverse, fed circuit breakers below the horizontal bus centerline, it can be seen tht an area around the horizontal centerline becomes free of load side connectors 38 and runbacks 72. This then becomes the ideal position to locate the three phase conductors of the horizontal bus 46.

It is also desirable to reduce the amount of material employed in the horizontal bus structure. FIG. 4 shows a diagrammatic rear view of the horizontal bus structure of the switchboard of FIG. 1. As can be seen, three conductor members of horizontal bus supply the four vertical structures 12, 14, 16, 18, with each section being connected at either end to corresponding vertical individual phase conductors of adjacent riser bus sections. Splice points are indicated by X's on FIG. 4 and occur at the point of connection between corresponding individual phase conductors of the horizontal and vertical bus. By using such connections instead of structure width conductor members spliced at structure boundaries, considerable savings in material can be realized.

In order to minimize the number of different parts required for a variety of switchboard combinations, and to minimize the required cross-section of the vertical riser bus, it is desirable to supply power to the vertical riser bus at its geometric and its electrical center. This is accomplished in the present invention through the use of a tie member, or tie maker bar 52, as is shown in FIG. 5, a perspective view of the bus junction of section 16 of the switchboard of FIG. 1. Various parts have been omitted from FIG. 5 in order to more clearly indicate the method of connecting the vertical and horizontal bus. The tie maker bar 52 is a generally rectangularly sectioned aluminum extrusion having chamferred edges 45 (FIG. 7D) to facilitate welding to I-beams 54 and a connector block 50.

As can be seen most clearly in FIG. 8, each individual phase conductor 47 of the main horizontal bus 46 comprises four spaced parallel aluminum bars 48 welded through the connector block 50 to the tie maker bar 52 which is in turn welded to a pair of I-beams 54 to form an individual phase conductor 57 of the vertical riser bus 56. The two I-beams 54 each have front and rear flanges connected by a web portion and are symmetrically disposed on either side of the centerline 58 (FIG. 5) of the main horizontal bus 46. Each tie maker bar 52 of each phase conductor 57 of the vertical riser bus 56 is similarly disposed with its top and bottom symmetrically located above and below the horizontal main bus centerline 58 and approximately even with the upper edge of the upper horizontal phase conductor and the lower edge of the lower horizontal phase conductors, respectively. Th connector 50 of phase A is seen to be welded to the top portion of its associated tie maker bar 52, while the connector 50 of phase C is welded to the lower portion of its associated tie maker bar 52. The phase B connector is welded to the center of its associated tie maker bar. This can be seen more clearly in FIGS. 7A through 7C, which are side views of the vertical phase conductors of phases A, B, and C, respectively.

The length of the tie maker bar 52 is determined by the amount of available contact area between it and the I-beams, 54 which is in turn determined by the weld bead area. In all cases, however, maximum benefits are obtained where the tie maker bar 52 is located approximately symmetrical with respect to the horizontal bus centerline 58.

As can be seen in FIG. 5, connections for three 800 ampere circuit breakers are mounted above the centerline 58 of the horizontal main bus 46, are bottom-fed through the upper I-beams 54 of the associated vertical riser bus 56, and through tie maker bars 52 to the horizontal main bus 46. Similarly, the lower three circuit breaker connections are connected to the main horizontal bus below the centerline 58 through the bottom I-beams of the associated vertical riser bus 56 and are top-fed. The disclosed construction employing a tie maker bar 52 allows each vertical phase conductor 57 to be fed at its electrical and its geometric center. This allows a single extrusion to be used interchangeably as either the upper half of the vertical phase conductor 57 or the lower half. Similarly, no I-beam 54 is required to carry more than half of the total current which could be supplied through the associated vertical section structure. Of course, for some section configurations it is not necessary to use a full length of I-beam, such as when only a single breaker is to be mounted in the top or bottom half of a section. The two I-beams may also be welded together in certain applications.

The construction of the connector block 50 is shown most clearly in FIGS. 5, 6, 7A-7D, and 8. The connector block 50 is formed from a generally rectangularly cross-sectioned aluminum extrusion with a plurality of locating means such as the rectangularly sectioned channels, or grooves, 53 formed laterally along the largest side surface of the connector block 50. The top and bottom I-beams 54, the tie maker bar 52, and the connector 50 are assembled at a bench location to form each vertical phase conductor 57 of the vertical riser bus 56. Each of the three vertical phase conductors 57 for each vertical section structure is mounted (in the manner to be hereinafter described) to a glass polyester insulating barrier 62 disposed between the device compartment 20 and the bus compartment 24. The horizontal bars 48 are then welded to the connector 50 in the grooves 53 beginning with the groove closest to the tie maker bar 52. The remaining bars 48 are then welded one by one between the connecting blocks 50 of the corresponding phases of adjacent vertical structures. The connector block 50 allows the horizontal bars 48 to be easily located in the proper position during assembly, thereby maintaining the desired spacing between bars. This spacing is provided to reduce the amount of material necessary for a given current carrying capacity of the main horizontal bus, since it has been found that a plurality of parallel spaced conductors is more efficient than a single conductor of the same cross-sectional area. No jig fixture is required to hold all bars in position prior to welding since the bars are positioned one at a time rather than requiring two or more bars to be welded together. In certain cases where maximum current carrying capacity is not required, one or more grooves can be left blank, thereby increasing the spacing between the remaining bars. Tapering of the main horizontal bus is also easily accomplished with the grooved connector 50 by bringing the desired number of bars into the connector 50 on one side and attaching a fewer number of bars on the opposite side, downstream from the power source.

The main horizontal bus 46 is entirely supported by the vertical riser bus 56. Thus, the main horizontal bus can be composed of conducting members equal in length to the spacing between like phases of adjacent vertical riser bus, with mechanical and electrical connections being made only at the ends of the members. This saves considerable material over the section width bus system, as is shown in FIG. 4.

It is not necessary for the connector blocks 50 to have a rectangular cross-section. For example, the sides could converge in steps, with the widest step at the point where the connector block 50 is welded to the tie maker bar 52 and the narrowest step at the top of the block farthest from the tie maker bar 52, thereby forming a "Christmas tree" cross-section. While the benefits obtainable through the use of the tie maker bar are not limited to bus systems employing the grooved connector 50, it has been found that increased versatility and reduced assembly cost result from the use of the connector block 50 as shown and disclosed herein.

Similarly, it is not necessary to employ the tie maker bar construction in order to obtain the benefits provided by the grooved connector block 50. However, the tie maker bar provides a simple and effective means for feeding the vertical riser bus at its geometric and electrical center. These same tie maker bar benefits are also obtained when used in bolted systems.

The insulating glass polyester barrier 62 separates the device compartment 20 and the bus compartment 24. The I-beams 54 of the vertical riser bus 56 are mounted to the glass polyester barrier by bolts 64 passing through the barrier 62 from the device compartment side thereof. The bolts 64 are threaded into fluted press nuts 65 inserted from the rear into holes in the front flange of the I-beams 54. As the bolts 64 are tightened, the I-beams 54 are secured to the polyester barrier 62.

The line stab connectors 36 for the circuit breakers 23 are similarly fastened to the front flange of the I-beams 54 with bolts and press nuts, while the load stab connectors are bolted to the barrier 62 using threaded inserts 67 (FIG. 6B). The connectors 36 and 38 extend through holes in the glass polyester barrier 62 into the device compartment 20. Metering current transformers 66 are mounted upon the connectors 36 and 38 from the device compartment side of the polyester barrier 62. Since the press nuts are fixed into the flange of the I-beams 54, and the threaded inserts 67 are fixed in the polyester barrier 62, access to the press nuts and threaded inserts is not required when inserting or removing the bolts. Thus, the connectors 36 and 38 can be removed or replaced from the device compartment 20 of the switchboard, eliminating the need to deenergize the switchboard and gain access to the bus compartment 24. Since the current transformers 66 are mounted upon the connectors 36 and 38 on the device compartment side of the polyester barrier 62, they can be similarly replaced without requiring access to the bus compartment. This is an important maintenance and safety feature since it is not required to remove any of the cover sheets 32 to replace current transformers or line connectors, nor is it necessary to subject the users of the switchboard to a service interruption for deenergization, as was sometimes required in prior art switchboards.

The rear flange of the I-beams 54 secures riser support members 68, providing needed structural strength to resist forces produced under transient overload current situations. Similarly, members 70 are provided to support the load side runbacks 72 which extend rearwardly into the cable compartment 26 for connection to outgoing cables or bus duct. The members 70 are bolted to the riser bus and bus compartment structure, as seen in FIGS. 6A and 6B, and include notches, or cutouts, through which the load side runback extends. These notches provide lateral rigidity and prevent side-to-side movement of the load side runbacks 72 caused by electromagnetic forces under severe overcurrent conditions.

It can be seen therefore, that the I-shaped cross-section of the vertical riser bus 56 provides an efficient means for mechanical support of the vertical riser bus 56 and associated members while providing a high electrical current carrying capacity in a compact configuration.