Abstract:
An electrical instrument includes an input terminal block that allows customers to configure input power as either single-phase, three-phase delta, or three-phase wye, using shorting bars to connect appropriate line and/or neutral terminals to each other without the need for an external adaptor or converter, and without modifying the internal circuitry or programming of the instrument.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electrical instrument, and in particular to an electrical instrument such as an AC power source having an input terminal block that allows customers to configure input power as either single phase, three phase delta, or three phase wye, without the need for an external adaptor or converter, and without modifying the internal circuitry or programming of the instrument or power source. 
     2. Description of Related Art 
     The present invention provides an improvement over the power input illustrated in FIGS. 3 and 4 of U.S. Patent Publication No. 2011/0080692, in which single phase and three phase wye and delta input connections are configured by connecting different “wiring blocks” 13 (in the form of multiple input/multiple output trace patterns shown in FIGS. 6-8) between two fixed terminal blocks T2,T3, the first of which (T1) includes three line terminals and a neutral terminal, and the second of which (T2) includes six terminals connectable to either the line or neutral terminals depending on the desired input configuration. 
     The power input arrangement of U.S. Publication No. 2011/0080692 has the disadvantage that, in order to change the configuration of the power input, it is necessary to replace the entire distribution circuit with another distribution circuit having a different trace pattern. This arrangement is both expensive and subject to operator error since it is possible to confuse the trace patterns and inadvertently misconnect the respective line and neutral terminals of the two fixed terminal blocks. 
     In contrast, instead of configuring the power input by using two fixed terminal blocks connected together by a configurable wiring blocks, a three-phase power input embodiment of the present invention utilizes a single terminal block having three line and three neutral terminals directly connectable to wires of an input power cable, with configuration being accomplished by attaching shorting bars to connect together the three line terminals or the three neutral terminals, or respective line and neutral terminals, to achieve the desired input configurations. According to the invention, there is no need to select from among multiple similarly-appearing pre-wired wiring blocks, as in U.S. Publication No. 2011/0080693, or to use an external adapter or converter. Furthermore, the invention may be adapted for additional phases by expanding the single terminal block to include additional line and neutral terminals so that the total number of line terminals and the total number of neutral terminals each equals the maximum number of input phases, and by providing appropriately dimensioned shorting bars for connecting together the line and neutral terminals according to the desired wiring configuration. 
     In an exemplary embodiment, the terminal block of the invention is applied to an AC power source. AC power sources are electrical instruments that convert an AC voltage and/or frequency level into another AC voltage or frequency level. For example, the AC power source may be used to convert a single phase line voltage input into a single or multiple phase electrical test voltage, to provide enhanced metering and current protection capabilities, to condition the output power to minimize power factor related losses, or to simulate voltage surges and drops during transient testing. 
     In typical AC power sources used for electrical testing, or to supply power for other electrical instruments, the power input is through an input terminal block having a neutral (N) screw terminal, a line (L) screw terminal, and a ground (G) connection, and is designed to accept typical line or mains voltages of between 180-284 VAC at frequencies of 47-63 Hz. Examples of AC power sources with fixed input terminal block configurations include modular AC power source model nos. 310XAC, 320XAC, and 340XAC, sold by Associated Power Technologies, Inc., of Diamond Bar, Calif. Such input power connections are simple and reliable but can only be directly connected to a single phase AC line voltage. As a result, the problem arises that when the only available external power source is a multiple phase external power source, an adapter or converter must be provided to convert the multiple phase input power into single phase input power for input through the included single phase terminal block. 
     The present invention provides an improvement to the single input block of the conventional power source, which allows direct connection to three phase input power supplies as well as single phase power supplies, without the need to modify the internal input circuitry or programming of the power source, without the need for an external adapter or power converter, and without the need for the multiple terminal blocks and connecting “wiring blocks” described in the above-cited U.S. Patent Publication No. 2011/0080693. While it may be used in the Associated Power Technologies™ AC power sources mentioned above, it is not limited to any particular AC power source, or even to AC power sources in general. In addition, the input terminal block of the invention may be applied to converters having a DC output, which are not strictly “AC power sources,” as well as to any power conditioner, controller, protection device or other electrical instrument having an AC input(s), including multiple function, programmable, or modular devices. 
     Finally, by way of general background, it has long been known to provide terminal blocks to facilitate connections between different circuits. Examples of terminals blocks in contexts other than the electrical instrument input of the present invention include the terminal block of U.S. Pat. No. 5,007,156, which is used to connect the windings of a three-phase electrical motor in either wye or delta configurations, or the terminal blocks of U.S. Pat. No. 2,785,324 and U.S. Patent Publication No. 2004/0017120, which enable switching between high and low voltage configurations by changing the interconnections between terminals of the terminal block. The present invention differs from these terminal blocks both in the specific configuration of the terminals, and in that it is applied to the particular context of providing a configurable input for an instrument, so as to enable the instrument to receive both single and multiple phase input power with different wiring configurations. 
     SUMMARY OF THE INVENTION 
     It is accordingly an objective of the invention to provide a simplified configurable input power arrangement for an electrical instrument having an input power terminal block that enables configuration of the input power as either single phase or multiple phase input power without the need for an external adaptor or converter. 
     It is also an objective of the invention to provide a configurable input power terminal block, in which configuration is achieved by using at least one shorting bar to appropriately interconnect the line terminals, the neutral terminals, or respective line and neutral terminals. 
     These objectives are achieved, in accordance with the principles of a preferred embodiment of the invention, by providing an electrical test instrument having an input terminal block that is capable of being configured to have anywhere from one to N input phases, wherein N is at least three, the input terminal block including at least two sets of N input terminals and an additional ground terminal. 
     The invention provides an improvement over the input power arrangement disclosed in U.S. Patent Publication No. 2011/0080693, in which configuration is achieved by connecting one of a plurality of pre-wired “wiring blocks” connecting two fixed input terminals, the first of which is a four terminal line input and the second of which is a six terminal configurable output. Instead, of pre-wired “wiring blocks” between multiple fixed terminals, the invention provides a single terminal block, each terminal of which is directly connectable to wires of an input power cable, and which are configurable through the use of shorting bars to connect appropriate sets of terminals to each other to achieve the desired input wiring configuration. 
     In an exemplary embodiment of the invention, the maximum number N of input phases is three, and the individual terminals may be connected in either three-phase wye or three-phase delta configurations. Although the invention is not limited to a particular type of terminal, the terminals may be in the form of screw terminals. Alternatively, the terminal block of the preferred embodiment may include plug-in terminals, clip-on terminals, or any other type of terminal to which individual wires of an input power cable or line may be connected. 
     The term “input terminal block” is intended to encompass any structure having multiple terminals arranged to be connected to input circuitry of an electrical instrument, and is not limited to a single integral or discrete member, but may also include, by way of example, a set of terminals extending from an electrical instrument. The internal circuitry to which the terminals are connected forms no part of the present invention, and may include voltage/frequency conversion circuitry, power conditioning circuitry, control circuitry, and/or power monitoring/sensing circuitry. The electrical instrument in which the input terminal block of the invention is included is also not limited to a particular type of electrical instrument, but rather may include AC test instruments, AC and DC power sources, and other electrical devices having an AC input. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram showing the layout of an input terminal block constructed in accordance with the principles of a preferred embodiment of the invention. 
         FIGS. 2A-2C  are schematic circuit diagrams showing electrical equivalents of single and three phase connections for the terminal block of  FIG. 1 . 
         FIGS. 3A-3C  show connections corresponding to the single and three phase equivalent circuits of  FIGS. 2A-2C  for the input terminal block of  FIG. 1 . 
         FIG. 4  is a schematic diagram showing respective connections between the terminal block of  FIGS. 3A-3C  and electrical test instrument input circuitry. 
         FIG. 5  is a rear elevation of an electrical test instrument that includes a terminal block corresponding to the terminal block of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows the layout of a terminal block  1  constructed in accordance with the principles of a preferred embodiment of the invention. 
     Terminal block  1  includes one earth terminal G, and two sets (L 1 ,L 2 ,L 3 ) and (N 1 ,N 2 ,N 3 ) of three terminals for connection to respective line and neutral wire of a three-wire or four-wire input cable. The specific connections of the terminals to the respective wires of the input cable are shown in  FIGS. 2A-2C  and  3 A- 3 C, while internal connections to the terminals are shown in  FIG. 4 . 
     It will be appreciated that terminals G, L 1 -L 3 , and N 1 -N 3 , may be screw terminals, plug-in terminals, quick-connect terminals and any other terminals to which the wires of the input cable may be connected. The structure of the individual terminals forms no part of the present invention and may be freely varied. In addition, terminal block  1  refers to the group of terminals and their arrangement, and not to a particular physical structure for supporting the terminals. The terminals may, by way of example and not limitation, be arranged in a single support structure, multiple support structures, or simply extend from an appropriately configured panel or other structure of an electrical instrument. In addition, the terminals may be arranged in any number of rows, or in arrangements other than rows. 
     The respective single phase and three phase input power connections are achieved by connecting the line wire L (single phase) or line wires A-C (three phase) and neutral wire N (if present) of the input cable in the manner shown in  FIGS. 2A-2C  and  3 A- 3 C, and by adding shorting bars or members  3 - 7  as shown in  FIGS. 3A and 3C . Wires L, A-C, and N may be connected directly to the terminals or, alternatively, to an appropriately shaped terminal structure on the sorting bar itself, such as common screw terminal, or any other suitable connection arrangement. 
     The shorting bars or members  3 - 7  may take a variety of forms, including bars, rods, wires, or any other member capable of being electrically coupled to each of the terminals in a respective set (L 1 -L 3 ) and/or (N 1 -N 3 ), preferably by a clamp, screw, press fit, or other secure connection. The ground terminal G is connected to the ground or earth wire of the cable or the cable shield, depending on the type of cable. 
       FIGS. 2A and 3A  show a single phase connection in which the line wire L is connected to one of terminals L 1 -L 3 , and a first shorting bar or member  3  couples the terminal connected to wire L with the remaining terminals in the set L 1 -L 3 . In addition, a second shorting bar or member  4  connects neutral terminals N 1 -N 3  while neutral wire N is connected to one of the terminals N 1 -N 3  or to the second shorting bar or member  4 . 
       FIGS. 2B and 3B  show a three phase, three wire “delta” input configuration in which wires A-C are respectively connected to terminals L 1 -L 3 , and terminals L 1 -L 3  are connected by shorting bars, members, or jumpers  5 - 7  to respective terminals N 2 , N 3 , and N 1 . To facilitate the cross connections (terminal L 1  to N 2 , L 2  to N 3 , and L 3  to N 1 ), terminals L 1 -L 3  are actually arranged in the order L 3 , L 2 , and L 1 , while terminals N 1 -N 3  are arranged in numerical order. Of course, terminals L 1 -L 3  could also be in the numerical order as terminals N 1 -N 3 , with appropriately configured jumpers, or terminals L 1 -L 3  could be in numerical order with terminals N 1 -N 3  being arranged in a different order. 
     Finally, as shown in  FIGS. 2C and 3C , wires A, B, and C may again be respectively connected to individual terminals L 1 -L 3  while the neutral terminals N 1 -N 3  are connected by shorting bar or member  4  (which may be the same as shown in  FIG. 3A ), and a neutral wire N of the three phase cable is connected to one of the neutral terminals or the shorting bar or member to form a three phase “wye” connection. 
     The opposite ends of the terminals are connected to internal circuitry of the electrical instrument, which in  FIG. 4  is illustrated by way of example and not limitation as three power factor controller boards PFC 1 ,PFC 2 ,PFC 3  of an AC power supply 360XAC. Each of the boards has a line input and neutral input corresponding to a respective one of the line terminals L 1 -L 3  and neutral terminals N 1 -N 3 , as well as a separate connection to ground. 
       FIG. 5  shows a portion of a rear panel  9  of AC power supply 360XAC of  FIG. 4 , which includes a power input terminal block  10  corresponding to terminal block of  FIG. 1  and  FIGS. 3A-3C , as well as a power output terminal block  11  having conventional line, neutral, and ground screw terminals  11   a - 11   c , and an external sense output terminal block  12  having line and neutral voltage sense screw terminals  12   a  and  12   b . It will be appreciate that the layout of the input and sense terminal blocks, and of other components of the rear panel, may be entirely conventional and forms no part of the invention. The input terminal block  10  does not need to be on the rear panel of the instrument, or even on the exterior of the instrument, but may be situated at any convenient location. 
     Having thus described a preferred embodiment of the invention in sufficient detail to enable those skilled in the art to make and use the invention, it will nevertheless be appreciated that numerous variations and modifications of the illustrated embodiment may be made without departing from the spirit of the invention, and it is intended that the invention not be limited by the above description or accompanying drawings, but that it be defined solely in accordance with the appended claims.