Abstract:
An electrical bus system is disclosed in which first and second bus bar assemblies are provided for conducting electrical currents of respective first and second polarities. A bus duct enclosure is provided for enclosing the bus bar assemblies. The bus duct enclosure is adapted to provide a heat dissipative configuration. In one aspect of the invention, the bus duct enclosure can be formed of a substantially polycarbonate material, for providing conductive heat dissipation from the bus bar assemblies.

Description:
BACKGROUND OF INVENTION  
         [0001]    The present invention is directed to the field of electrical bus systems, particularly those of the type that carry large currents and thereby produce much excess heat. Electrical bus systems are commonly employed in telecommunications systems such as telephone and fiber optic systems using equipment where low voltages and high currents are required, preferably about 48 volts and 5000-10,000 amperes.  
           [0002]    In a typical telecommunications system, alternating current (AC) is received from a supply, e.g., a utility, and passed through a rectifier to convert the current to direct current (DC). The direct current is used to supply the needs of the telecommunications equipment, e.g. telephone and fiber optic systems. As shown in FIG. 1, a telecommunications system  10  receives alternating current (AC) from a supply, e.g., a utility, and passes it through a rectifier  12  to convert the current to direct current (DC). This DC current is used to “float” one or more battery strings  16  to provide the load to the telecommunications system. The battery strings  16  are typically an array of conventional lead-acid or nickel-cadmium batteries. The batteries also provide an additional function of filtering out any signal noise or power spikes in the power supplied by the utility and thereby provide an electrical load at a consistent voltage and current.  
           [0003]    Battery strings  16  also provide continuous service in the event of a power failure. A telecommunications office provides service to customers over a geographic area. It is therefore imperative that the equipment remain online even in the event of a power failure. In order to insure continuous operation, it is common to provide emergency backup systems, such as diesel-powered generators. However, a certain amount of startup time is required for generators, and it is important to insure against any power interruptions during this period. In the event of a power failure or other interruption of service, the battery strings  16  supply DC current to the telecommunications system  10 , and thereby provide continuous, readily-available power.  
           [0004]    Since the currents between the rectifier  12  and the battery strings  16  are very high, it is common to use an assembly of copper bus bars rather than stranded wire. As also shown in FIG. 1, the direct current is conducted between the battery strings  16  and the rectifier  12  along an assembly of bus bar laminations  14 . In a typical bus work assembly, a number of bus bars are provided, each being copper plates, typically having widths of about eight inches. The bus bars are typically provided in laminations of as many as fourteen for each electrical polarity, and the laminations of each polarity are separated in order to insure safety.  
           [0005]    For safety purposes, one common practice is to enclose the bus bar laminations  14  in a duct work. In this way, the bus bars are protected from external damage, e.g., from water leakage, and accidental short circuits that could result in injury to personnel and damage to equipment. Typically, the two bus bar polarities are retained within a safe proximity, so as to be enclosed within the same duct work assembly. The duct work relies on an air space to provide a degree of electrical isolation. Such duct work has traditionally been fabricated of either galvanized steel or aluminum.  
           [0006]    During non-peak usage periods, a bus assembly may only operate at 10% of a maximum load capacity, a current of about 1000 amperes. However, during peak usage times, current loads can approach 100% capacity, about 10,000 amps. This creates a considerable amount of heat in the bus assembly, which reduces conductivity and can result in an undesirable reduction in available service and even damage to the system. This heat problem can be complicated by the duct work enclosure, since the metal ducts absorb the heat from the bus bars and thus retain a considerable amount of heat within the enclosure.  
         SUMMARY OF THE INVENTION  
         [0007]    The difficulties and drawbacks of previous systems are overcome by the electrical bus system of the present invention in which first and second bus bar assemblies are provided for conducting electrical currents of respective first and second polarities. A bus duct enclosure is provided for enclosing the bus bar assemblies. The bus duct enclosure is adapted to provide a heat dissipative configuration. In one aspect of the invention, the bus duct enclosure can be formed of a substantially polycarbonate material, for providing convective heat dissipation from the bus bar assemblies.  
           [0008]    As will be realized, the invention is capable of other and different embodiments and its several details are capable of modifications in various respects, all without departing from the invention. Accordingly, the drawing and description are to be regarded as illustrative and not restrictive.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a schematic view of a typical bus duct system.  
         [0010]    [0010]FIGS. 2A and 2B are respective oblique and side detail views of a bus duct system with heat dissipating enclosure in accordance with the present invention.  
         [0011]    [0011]FIGS. 3A and 3B are respective side and side detail views of the bus duct system in accordance with the present invention.  
         [0012]    [0012]FIG. 4 is a partially exploded oblique view of the heat-dissipating enclosure of the present invention.  
         [0013]    [0013]FIGS. 5A, 5B and  5 C are respective side views showing the support pole cap, the cross bar receiver and retainer-insulator assembly in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]    The bus duct system  20  of the present invention is generally depicted in the figures, where like reference numerals are understood to refer to like elements. As can be observed especially from FIGS. 2A, 3A and  3 B, the present system  20  includes a first and second bus bar assemblies  22 ,  24 , each corresponding respectively to either a positive or negative electrical polarity, for delivering electrical current to a plurality of battery strings, preferably for use in telecommunications. Each bus bar assembly  22 ,  24  is formed of a plurality of copper bus bars  26  supported within a bus retainer  28  having top and bottom portions  28 a,  28 b. The embodiment shown in figures depicts bus bars (8 in  20 , 10 in  24 / 26 ) for each polarity, but up to fourteen can be used for a typical application, and any number of bus bars  26  could be employed without departing from the invention.  
         [0015]    In order to provide safety by preventing accidental electrical contact, the bus bar assemblies  22 ,  24  are enclosed within a bus duct enclosure  30 . The present bus duct enclosure  30  is especially configured for heat-dissipation, to prevent the undesirable buildup of heat encountered with previous systems, as will be explained in detail below.  
         [0016]    The present bus duct system  20  includes a plurality of cross bars  40  for supporting the bus bar assemblies  22 ,  24  and the bus duct enclosure  30 . The cross bars  40  are mounted transversely to the bus bar assemblies  22 ,  24 . Each of the bus bar assemblies  22 ,  24  are hung from the respective cross bar  40  by a retainer-insulator assembly  42 , as especially shown in FIG. 5C. Each retainer-insulator assembly includes a pair of two-piece framing clips  42 , secured with a threaded bolt and washer arrangement (as shown) for clamping onto the cross bar  40 . Each framing clip  42  is secured by inserting a bolt  46  and threaded into a dielectric insulator member  44 , which is provided to insure against electrical conduction between the bus bar assemblies  22 ,  24  and the cross bars  40 . In the preferred embodiment, the dielectric insulators  44  are fiberglass standoff insulators of the type manufactured by The Glastic Corporation of Cleveland, Ohio. The top and bottom portions of the bus retainer  28  are supported with bolts that are threaded from below through retainers  28 A and  28 C and into the dielectric insulators  44 , which are threaded to receive and cooperate with the bolts. In this way, the dielectric insulators  44  include a first attachment portion for connecting to the bus bar assemblies  22 ,  24 . In the preferred embodiment, the bus duct enclosure  30  includes openings to admit the bolts of the framing clips  42  and thereby define a second attachment portion of the dielectric insulator  44  for connecting to the bus duct enclosure  30  in a spaced relationship from the bus bar assemblies  22 ,  24 .  
         [0017]    The present cross bars  40  can optionally be affixed to a ceiling structural support member, as is common with previous type systems. However, in the preferred embodiment, as shown especially in FIGS. 2A, 2B and  3 A, the bus duct system  20  is supported by a plurality of stanchion support poles  50 . As shown in the figures, the stanchion poles  50  extend vertically from the floor, and support the frame rail structure  56 , which is attached to the stanchion poles  50 , through the use of the support pole cap assembly  52 , and through these are attached to either end of the cross bars  40 . Preferably, the stanchion pole pairs are spaced about 48 inches apart, so as to insure sufficient support for the weight of the bus duct system  20 . The stanchion support poles  50  thus provide an independent system of support not reliant on the physical structure of the building housing the bus duct system  20 . In this way, the present bus duct system  20  has greater resistance to seismic activity, since the bus bar assemblies  22 ,  24  will be more resistant to damage resulting from slippage of the system  20 .  
         [0018]    As shown especially in FIGS. 2A, 2B,  3 A and  5 A, the stanchion poles  50  include stanchion support pole caps  52  for allowing securement of the stanchion poles  50  to a frame rail  56 . As shown in FIG. 5A, the pole caps  52  are attached to a two-piece framing clip  54 , and bolted with nuts and a threaded rod as illustrated. In this manner, the support caps  52  can be secured directly to the frame rail  56 . In the preferred embodiment, as best shown in FIGS. 2A and 2B, the framing clip  54  is attached to a respective frame rail  56 , mounted parallel on either side of the bus bar assemblies  22 ,  24 . In this way, the frame rails provide additional stability to the stanchion poles  50 . In this preferred embodiment, the frame rails  56  are attached to a cross bar receiver  60 , which attaches to the cross bar  40 . As shown in FIG. 5B, the cross bar receiver  60  includes a pair of framing clips  62  for respectively attaching to the frame rail  56  on the cross bar  40  to be securely bolted. In this way, the present invention provides a sturdy support system that is resistant to seismic disturbances and easily assembled and maintained in accordance with the requirements of the system.  
         [0019]    An important aspect of the invention is the heat-dissipation functions of the present bus duct enclosure  30 . With the present invention, it was desirable to satisfactorily dissipate heat in an enclosure for bus bar assemblies operating at a maximum current load of 10,000 amperes over a four-hour peak usage interval. Applicants have discovered that heat build up can be satisfactorily controlled by providing a sufficiently large enclosure formed of materials having thermal transfer properties superior to those of the previous-type metal enclosures. It has been discovered that certain polymer materials have a high rate of conductive heat transfer between the air temperatures of the interior and exterior of the enclosure  30 , thereby quickly dissipating heat. In particular, excellent results were obtained using polycarbonate materials such as the type sold under the brand name “Lexan” by General Electric of Schenectady, N.Y.  
         [0020]    It has also been observed that heat dissipation can be improved by providing an enclosure sufficiently large to provide adequate volume within, so as to maintain a desired equilibrium temperature inside the enclosure, preferably in the range of between 74° F. to 98.6° F. It has been found that providing standard enclosures  30  having a width of between 28.375 inches and 32.125 inches would accommodate bus bar assemblies having between six and fourteen laminations and allow between 4.375 and 5.25 inches of clearance along the exterior sides of the enclosure  30 . In this way, sufficient volume is provided and avoid heat build up and allow convection within the volume to transfer heat to the walls of the enclosure  30 , thereby dissipating the heat to the outside environment. Alternatively, it is contemplated to use an integrated fan system operated by the bus voltage, and in connection with the first and second bus bar assemblies.  
         [0021]    It may be desirable for certain applications to use a pigmented polycarbonate enclosure  26  to provide a desired color or appearance. However, it has been discovered to be most advantageous to fabricate the enclosure  26  in an unpigmented state, so as to provide a substantially transparent enclosure  26 . In such an enclosure  26 , heat can be directly radiated through the enclosure  26  from the bus bar laminations  22 ,  24 , and thereby provide radiative heat dissipation.  
         [0022]    As shown especially in FIG. 4, the present enclosure  30  is formed in a sectional configuration. In the preferred embodiment, a T-top section  32  is formed which defines the enclosure  30  and the middle insulator portion for separating and insulating the bus bar assemblies  22 ,  24 . The T-top  32  receives and retains a plurality of outer cover sections  34  for forming the sides and bottom of the enclosure. As especially shown in FIG. 3B, the sections  32 ,  34  are interlocking and are preferably secured using stainless steel screws  47  and nylon nuts and bolts to secure the ends of contiguous sections  32 . In this way, the enclosure  30  defines a substantially rectangular cross-section. Of course, it is to be understood that the T-top  32  and outer covers  34  can be formed of any shape to provide any curved or angular cross section, all without departing from the invention.  
         [0023]    In another aspect of the invention, the enclosure  30  can be made to include a plurality of ventilation apertures  36 . As shown in FIG. 4, these can be formed into the T-top  32 . They can also be optionally formed into the outer covers  34  to provide an open air flow throughout the interior volume of the enclosure  30 . The apertures  36  can be machined into the enclosure sections  32 ,  34 . However, the apertures  36  can also be molded directly into the polycarbonate components during a manufacturing step, thereby obviating the need for a separate machining step. To further improve heat dissipation, the enclosure  30  can also be formed to include a number of radiator fins, thereby increasing the surface area of the enclosure  30  and further improving heat dissipation.  
         [0024]    By fabricating the present enclosure from a polymer material such as polycarbonate, the heat transfer properties of the enclosure are greatly improved. Also, polycarbonate offers many other ancillary benefits as used for the present duct work enclosure. As with other polymer materials, polycarbonate is a better insulator than metal, providing additional safety. Polycarbonate is also light weight, reducing the overall weight of the bus duct assembly. It is also inexpensive and easy to machine or mold, thereby adding an economic benefit. It is also less rigid than metal, providing a degree of resiliency and ease of installation over metal enclosures. Also, in its transparent embodiment, the enclosure can be visually inspected, allowing field personnel to quickly determine if corrosion, slippage or any other type of physical damage occurs with the bus bar assemblies  22 ,  24 .  
         [0025]    As described hereinabove, the present invention solves many problems associated with previous type apparatuses. However, it will be appreciated that various changes in the details, materials and arrangements of parts which have been herein described and illustrated in order to explain the nature of the invention may be made by those skilled in the art within the principle and scope of the invention will be expressed in the appended claims.