Abstract:
The invention is an apparatus and a method for connecting loads to a polyphase power distribution system in such a way that the loads on the individual phases of the system are balanced. The apparatus includes an equipment rack having multiple electrical equipment mounting positions and multiple electrical outlets wherein contiguous groups of mounting positions are adjacent to groups of outlets connected to different phases. The apparatus also provides for other groups of outlets adjacent to the mounting positions to be connected to different power sources for increased reliability when the equipment has redundant power supplies.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to electrical power distribution systems and particularly to apparatus and methods for balancing the loads on the individual phases of polyphase distribution systems. 
     BACKGROUND OF THE INVENTION 
     In polyphase power distribution systems, it is desirable to balance the loads on the individual phases of the system. Ideally, the loads on all the phases should be equal (that is, balanced) because a polyphase system delivers maximum power when all the phases are supplying their maximum rated current. For example, it would be unacceptable for the loads on one phase to exceed its current rating while the loads on another phase were below its current rating. As used herein, the word “balanced” means that the loads on the individual phases are equal within acceptable limits for the power distribution system in use; however, it does not mean that the loads on each phase are exactly equal or that the loads on all phases are non-zero. 
     Traditionally, load-balancing is accomplished by the electrician wiring the system. To do this the electrician must keep an accounting of the power requirements of all the loads on each phase and add loads to, or remove loads from, each phase as necessary to achieve the desired balance. This method is not only tedious and time consuming during the installation of the system but it also requires the services of a skilled electrician whenever loads are added or removed throughout the life of the system. 
     It is therefore an object of this invention to provide a simple means for achieving acceptable load balancing without the need for wiring, or rewiring, by a skilled electrician. 
     U.S. Pat. No. 5,934,096 discloses a wiring system for commercial refrigeration which permits power to be balanced among three phases of electrical power. Patent &#39;096, in the paragraph extending from column 7, line 50 to column 8, line 4, states that an installer can choose which phases of the electrical power will be sent to the lights and fans and which to the electric defrost by simple rotation of the connectors relative to each other. This requires that the installer know the load distribution on the three phases in order to choose which relative orientation of the connectors to use. In the present invention, such knowledge is not required. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention comprises an apparatus, and a simple method, for connecting loads to a polyphase power distribution system in such a way that the loads on the individual phases of the system are balanced. The balancing is accomplished without requiring the installer to know the load distribution on the, phases. 
     The apparatus comprises an equipment rack or frame having multiple equipment mounting positions and multiple single-phase electrical outlets, or receptacles, adjacent to the mounting positions. Each outlet is connected to one of the N phases of a polyphase power distribution system in such a way that when pieces of equipment are mounted in the rack and plugged into adjacent outlets in an orderly fashion, adequate load balancing is accomplished automatically. 
     For example, in a three-phase system, the outlets are wired to the phases as follows: a first outlet group to phase  1 , a second outlet group to phase  2 , a third outlet group to phase  3 , a fourth outlet group to phase  1 , a fifth outlet group to phase  2 , a sixth outlet group to phase  3 , an i th  outlet group to phase  1 , an ( 1 +i) th  outlet group to phase  2 , an ( 2 +i) th  outlet group to phase  3 , and so on to the total number of outlets in the apparatus. The outlets and the mounting positions for the loads are physically arranged on the rack in rows and columns such that the natural row-and-column order of mounting the loads contiguously in the rack leads to plugging the loads into the outlet groups in counting-number sequence. In other words, the first loads are plugged into the first outlet group, the second loads into outlet  2 , the third loads into outlet  3 , etc. 
     Preferably, the apparatus also provides another group of outlets, adjacent to each mounting position, which is connected to and supplied by a different source. The additional outlets permit redundant power supplies in each piece of equipment to be connected to separate and independent sources for greater reliability. 
     As used herein, the word “outlet” means the point at which a load can be connected to a power distribution system while the word “receptacle” refers to the hardware device for receiving an electrical plug. The term “outlet” is not limited to specific type of hardware. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram of a preferred embodiment of the invention. 
     FIG. 2 is a diagram of a three-phase receptacle. 
     FIG. 3 is a diagram of a three-phase plug. 
     FIG. 4A is a diagram of a power strip. 
     FIG. 4B is a schematic diagram of a power strip wiring. 
     FIG. 4C is an enlarged view of a portion of FIG.  4 B. 
     FIG. 5 is a schematic diagram of a power distribution assembly. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the drawings, like reference numerals indicate like features; and, a reference numeral appearing in more than one figure refers to the same element. The drawings and the following detailed descriptions show specific embodiments of the invention. Numerous specific details including materials, dimensions, and products are provided to illustrate the invention and to provide a more thorough understanding of the invention. However, it will be obvious to one skilled in the art that the present invention may be practiced without these specific details. 
     A schematic diagram of a preferred embodiment of the invention is shown in FIG.  1 . This embodiment comprises a first equipment rack  1  and a second equipment rack  2  each having multiple equipment mounting positions, hereinafter referred to as bays, for mounting power consuming equipment, hereinafter referred to as loads. Rack  1  comprises equipment bays  101 - 110  and rack  2  comprises equipment bays  201 - 210 . The loads in bays  101 - 110  are plugged into first power strip  30 A and second power strip  30 B which are mounted on the left and right sides, respectively, of rack  1 . Likewise, the loads in bays  201 - 210  are plugged into third power strip  30 C and fourth power strip  30 D which are mounted on the left and right sides, respectively, of rack  2 . Equipment rack  2  also comprises power distribution assembly  3 . Power strips  30 A- 30 D are plugged into and supplied by power distribution assembly  3 . Assembly  3  is connected to and supplied by two external three-phase power distribution systems (not shown) hereinafter referred to as power sources S 1  and S 2 . Each of the two power sources comprises five conductors (wires) providing the three phases (φA, φB and φC) as well as neutral and ground. Assembly  3  is connected to sources S 1  and S 2  by power input cables  4  and  5  and power input plugs  20 A and  20 B, respectively. 
     FIG. 2 is a drawing of a typical three-phase receptacle  10  comprising three line sockets  11 ,  12  and  13  commonly labeled X, Y and Z, respectively, a neutral socket  14  commonly labeled N, and a ground socket  15 . 
     FIG. 3 is a drawing of a typical three-phase plug  20 , for mating with receptacle  10 , comprising three line blades  21 ,  22  and  23 , commonly labeled X, Y and Z, respectively, a neutral blade  24 , commonly labeled N, and a ground pin  25 . 
     The location and shape of the blades and pin of plug  20  and the corresponding sockets of receptacle  10  are designed to ensure that the plug and socket can be mated only one way. The keys on the neutral blade and socket may point inward or outward, depending on the type and current rating of the plug and socket. 
     The drawings in FIGS. 2 and 3 represent the sockets  10 A- 10 D and plugs  20 A- 20 B in the following descriptions. 
     FIG. 4A is a drawing of a power strip  30  as used for each of the power strips  30 A- 30 D in FIG.  1 . Power strip  30  comprises an enclosure  34  containing ten single-phase duplex receptacles  35  arranged in three groups, a first group  31 , a second group  32  and a third group  33 . FIG. 4B is a schematic diagram of the wiring of power strip  30  and FIG. 4C is an enlarged view of the typical wiring of a receptacle  35 . As shown in FIGS. 4B and 4C, receptacles  35  are connected by a four-conductor (plus ground) power strip cable  40  to a three-phase plug  20 . The neutral conductor  44  of cable  40  connects the neutral socket  36  of all the receptacles  35  to the neutral blade  24  of plug  20 . The conductor  45  of cable  40  connects the enclosure  34  and the ground terminals  37  of all the receptacles  35  to the center pin  25  of plug  20 . The line socket  38  of each receptacle in group  31  is connected by conductor  41  to blade  21  of plug  20 . The line socket  38  of each receptacle in group  32  is connected by conductor  42  to blade  22  of plug  20 . The line socket  38  of each receptacle in group  33  is connected by conductor  43  to blade  23  of plug  20 . 
     Referring back to FIG. 1, the inputs to power distribution assembly  3  are connected to the two external three-phase power distribution systems (not shown) via two four-conductor (plus ground) power input cables  4  and  5  and power input plugs  20 A and  20 B. The outputs of assembly  3  comprise four three-phase, four-conductor (plus ground) receptacles  10 A- 10 D. 
     Referring to FIG. 5, power distribution assembly  3  comprises a first receptacle  10 A, a second receptacle  10 B, a third receptacle  10 C and a fourth receptacle  10 D. Receptacles  10 A- 10 D correspond to and mate with the plugs on cables  40 A- 40 D (respectively) in FIG.  1 . 
     Sockets  14  of receptacles  10 A and  10 C are connected through the neutral conductor of power input cable  4  and blade  24  of plug  20 A to the neutral socket and conductor of source S 1 . Likewise, sockets  14  of receptacles  10 B and  10 D are connected through the neutral conductor of power input cable  5  and blade  24  of plug  20 B to the neutral socket and conductor of source S 2 . 
     Sockets  15  of receptacles  10 A- 10 D are connected through the ground conductors (not shown) of power input cables  4  and  5  and pins  25  of plugs  20 A and  20 B to the ground sockets and conductors (not shown) of both sources S 1  and S 2 . The ground conductors of power input cables  4  and  5  are also bonded to a metallic case (not shown) enclosing power distribution assembly  3 . 
     In plug  20 A, blades  21 ,  22  and  23  obtain φA, φB and φC, respectively, from a receptacle connected to source S 1 . Sockets  11 ,  12  and  13  of receptacle  10 A are connected via circuit breakers  51 and  52  and the line conductors in cable  4  to blades  21 ,  22  and  23 , respectively, of plug  20 A. Likewise, sockets  13 ,  11  and  12  of receptacle  10 C are connected to blades  21 ,  22  and  23 , respectively, of plug  20 A. 
     In plug  20 B, blades  21 ,  22  and  23  obtain φA, φB and φC, respectively, from a receptacle connected to source S 2 . Sockets  12 ,  13  and  11  of receptacle  10 B are connected via circuit breakers  51  and  52  and the line conductors in cable  5  to blades  21 ,  22  and  23 , respectively; of plug  20 B. Likewise sockets  11 ,  12  and  13  of receptacle  10 D, are connected to blades  21 ,  22  and  23 , respectively, of plug  20 B. 
     Referring now to FIG. 1, on the left side of rack  1 , in power strip  30 A, the four receptacles in group  33  adjacent to the four equipment bays  101 - 104  are connected to φA; the three receptacles in group  32  adjacent to bays  105 - 107  are connected to φB; and the three receptacles in group  31  adjacent to bays  108 - 110  are connected to φC. Power strip  30 A is connected through cable  40 A, assembly  3 , cable  4  and plug  20 A to source S 1 . 
     On the right side of rack  1 , in power strip  30 B, the four receptacles in group  33  adjacent to the four equipment bays  101 - 104  are connected to φB; the three receptacles in group  32  adjacent to bays  105 - 107  are connected to φC; and the three receptacles  31  adjacent to bays  108 - 110  are connected to φA. Power strip  30 B is connected through cable  40 B, assembly  3 , cable  5  and plug  20 B to source S 2 . 
     On the left side of rack  2 , in power strip  30 C, the four receptacles in group  33  adjacent to the four equipment bays  201 - 204  are connected to φC; the three receptacles in group  32  adjacent to bays  205 - 207  are connected to φA; and the three receptacles in group  31  adjacent to bays  208 - 210  are connected to φB. Power strip  30 C is connected through cable  40 C, assembly  3 , cable  4  and plug  20 A to source S 1 . 
     On the right side of rack  2 , in power strip  30 D, the four receptacles in group  33  adjacent to the four equipment bays  201 - 204  are connected to φA; the three receptacles in group  32  adjacent to bays  205 - 207  are connected to φB; and the three receptacles in group  31  adjacent to bays  208 - 210  are connected to φC. Power strip  30 D is connected through cable  40 D, assembly  3 , cable  5  and plug  20 B to source S 2 . 
     Typically, present generation Information Technology equipment is equipped with dual redundant power supplies intended to be powered by separate power sources for more reliable operation. Such equipment therefore utilizes, for each load, two separate power cables with attached plugs for connecting to two receptacles. Supplying power from different phases or sources to each of the two receptacles enhances the reliability of the power delivery in addition to balancing the loads. 
     Normally, loads are installed in racks sequentially from top to bottom and plugged into the nearest receptacles. Following this procedure for rack  1  as shown in FIG. 1, each piece of equipment installed in bays  101 - 104  will have one redundant power supply plugged into one of the receptacles in group  33  of power strip  30 A and the other redundant power supply plugged into one of the receptacles in group  33  of power strip  30 B. Each piece of equipment in bays  101 - 104  will thereby have one power supply connected to φA of source S 1  and the other power supply connected to φB of source S 2 . Likewise, each piece of equipment in bays  105 - 107  will have one power supply connected to φB of source S 1  and the other power supply connected to φC of source S 2 . And, each piece of equipment in bays  108 - 110  will have one power supply connected to φC of source S 1  and the other power supply connected to φA of source S 2 . 
     Continuing this process to rack  2 , each piece of equipment in bays  201 - 204  will have one power supply connected to φC of source S 1  and the other power supply connected to φA of source S 2 . Likewise, each piece of equipment in bays  205 - 207  will have one power supply connected to φA of source S 1  and the other power supply connected to φB of source S 2 . Also, each piece of equipment in bays  208 - 210  will have one power supply connected to φB of source S 1  and the other power supply connected to φC of source S 2 . 
     In this way, no more than four loads in one rack will be connected to any one phase supplied by the same source. As additional racks are populated, preferably each rack is filled before the next one is started. Then, for each source, the maximum number of loads on any phase will not exceed the minimum number on any other phase by more than four. 
     The embodiment described herein is optimum for a particular rack of computer equipment using three-phase power. However, in other applications, it may be preferable to use split-phase power (i.e., single-phase center-tapped) or to connect to a distribution system using a three-phase delta configuration instead of the wye configuration described. Or, for example, it may be preferable to arrange the connections to the outlets in such a way that the phases rotate sequentially down the racks (columns) in groups of only one or two receptacles (or one dual receptacle) per phase instead of the six or eight receptacles (or three or four dual receptacles) per phase shown in this embodiment. Many such alternate spatial arrangements providing a desired phase rotation sequence will be readily understood by those skilled in the art. Such alternate arrangements can be economically embodied by only altering the connections within the power strip. For example, in FIG. 4B, instead of all three dual receptacles  35  in group  31  being connected to conductor  41 , one could be connected to each of the three conductors  41 ,  42  and  43 . Likewise, in groups  32  and  33 , each adjacent receptacle could be connected to a different one of conductors  41 ,  42  and  43 . Regardless of the phase rotation within the strips, because of the phase rotation within the power distribution assembly, load sharing and balancing will still tend to occur at the power sources as the number of loads is increased (including when more racks are added). 
     All references mentioned herein are hereby incorporated by reference to the extent that they are not inconsistent with the present disclosure.