Abstract:
A sensor array including multiple current sensors provides input for power measurement and management systems. The sensor array includes split ferrite cylinder portions connected by a frame, so that when the array is installed around multiple branch circuits in a power distribution panel or raceway, the ferrite cylinders are completed to surround the conductor(s) of the associated branch circuit. Voltage sensing may also be incorporated within the sensors by providing an electrically conductive plate, wire or other element that capacitively couples to the corresponding wire(s).

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention is related to wire managers for managing the position of one or multiple electrical wires, and more specifically to a multi-branch current sensor array with optional voltage sensing. 
         [0003]    2. Description of Related Art 
         [0004]    A need to measure power consumption in AC line powered systems is increasing due to a focus on energy efficiency for both commercial and residential locations. In order to measure power consumption of a circuit, the current drawn by the load must generally be measured, and for precise results, the characteristics of the load may also need to be known. 
         [0005]    Adding current sensors to a power distribution system occupies space and adds complexity. If a large number of circuits must be measured, the installation difficulties are increased and the installation of the current sensor may cause disarray in the power distribution system. 
         [0006]    It is also necessary to provide a safe environment for electrical workers and other personnel in the vicinity of the installations where power is being measured, because installation may be required in an electrical panel that is operational. Installation of current sensors in a live panel requires the use of insulating gloves that make it difficult to perform fine work with the fingers. 
         [0007]    Therefore, it would be desirable to provide a current-sensing device that can provide isolated current draw information and optionally permit load characteristics to be taken into account, while providing safe and efficient installation with little additional space requirements within the power distribution system. It would further be desirable to provide such a device that is easy to operate while an installer is wearing insulating gloves. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    The invention is embodied in a current sensor for sensing currents passing through wires of multiple branch circuits and a method of operation. 
         [0009]    The sensor has a first frame member and a second frame member in which are integrated corresponding portions of ferrite cylinders of the current sensors that, when the frame members are fastened together in a closed position, encircle the corresponding wire(s) of the branch circuit(s) associated with the individual sensors. The frame members may be separate, or may provide a sliding assembly that has an open and closed position for inserting and then retaining the wires, respectively. Measurement and communications electronics may be included in the first and/or second frame member to provide an efficient wireless or wired interconnect to other systems. Branch voltage sensing may be optionally integrated in the sensors, as well. 
         [0010]    The foregoing and other objectives, features, and advantages of the invention will be apparent from the following, more particular, description of the preferred embodiment of the invention, as illustrated in the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0011]    The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives, and advantages thereof, will best be understood by reference to the following detailed description of the invention when read in conjunction with the accompanying Figures, wherein like reference numerals indicate like components, and: 
           [0012]      FIG. 1A  is an isometric view, and  FIG. 1B  is an exploded isometric view, of a multi-branch current-sensing device in accordance with an embodiment of the present invention. 
           [0013]      FIGS. 2A-2B  are illustrations showing details of current-sensing elements that can be used in the multi-branch current sensor of  FIGS. 1A-1B . 
           [0014]      FIG. 3A  is an isometric view, and  FIG. 3B  is an exploded isometric view, of a multi-branch current-sensing device in accordance with another embodiment of the present invention. 
           [0015]      FIGS. 4A-4B  are illustrations showing details of current-sensing elements that can be used in the multi-branch current sensor of  FIGS. 3A-3B . 
           [0016]      FIG. 5  is a pictorial diagram showing current-sensing devices according to embodiments of the present invention installed in an electrical power distribution system. 
           [0017]      FIG. 6  is a pictorial diagram showing wire managers  10  according to the present invention installed in an electrical power distribution system. 
           [0018]      FIG. 7A  is a top view of base portion  10 E and  FIG. 7B  is a side view of cover portion  10 D of wire managers  10  of  FIG. 6 . 
           [0019]      FIG. 8  is an electrical block diagram illustrating circuits that can be interfaced to, and optionally incorporated within, the multi-branch current sensors of  FIGS. 1A-1B  and  FIGS. 3A-3B , according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    The present invention encompasses current sensors for multiple branch circuits, which optionally include voltage sensors and other features for providing input to power measurement systems. For example, the present invention can provide input to power monitoring equipment in computer server rooms, in which multiple branch circuits distribute power to various electronic chassis power supplies, and in which it is beneficial to provide power usage information for the various branch circuits to power monitoring and/or system control utilities within a computer operating environment. Other applications include power monitoring for commercial and/or residential energy management. 
         [0021]    Referring now to  FIG. 1A  and  FIG. 1B , a current-sensing device in accordance with an embodiment of the invention is shown.  FIG. 1B  shows an exploded view with details of current sensors formed by ferrite cylinder portions  14 A and  14 B integrated in respective frame members  10 A and  10 B. As illustrated in  FIG. 1A , when frame members  10 A and  10 B are snapped together, they form a current-sensing and voltage-sensing device for measuring the current passing through, and the electrical potentials on, a plurality of wires that generally correspond to multiple branch circuits of a power distribution panel. For the purposes of measuring branch circuit current and voltage within a power distribution panel, the spacing of the current sensors formed by ferrite cylinder portions  14 A and  14 B is generally one inch, which is a standard circuit breaker terminal spacing. Alternatively, other spacings may be provided, such as one-half inch spacing for split breaker applications and two-inch spacing for high current/high voltage applications in which the breaker spacing is larger. Further, the above dimensions correspond to standardized U.S. breaker panels, and spacings may be adapted to accommodate standardized breaker spacings for the countries in which a particular design of the device is intended for use. Frame members  10 A,  10 B are generally non-conductive plastic materials, but may be made from alternative materials, depending on requirements. 
         [0022]    The voltage-sensing elements mentioned above are provided by metal foils or metal layers  18 A and  18 B adhered to or deposited within the central cylindrical voids formed by ferrite cylinder portions  14 A and  14 B when frame members  10 A and  10 B are snapped together in the closed position as illustrated in  FIG. 1A . The illustrated current-sensing devices are provided by semiconductor current sensors  17  disposed within a gap formed between ferrite cylinder portions  14 A and  14 B when frame members  10 A and  10 B are snapped together in the closed position. The high-permeability magnetic flux path around one of the branch circuit wires (not shown) inserted through the central void through a corresponding pair of ferrite cylinder portions  14 A and  14 B is interrupted by the gap and concentrates the field at the corresponding one of current sensors  17  for measurement. A retaining pin  13  or other clip feature on frame member  10 A mates with a mating recess  19  or other suitable feature on frame member  10 B, in order to secure frame members  10 A and  10 B together after installation. An integrated circuit assembly  20  receives electrical connections  15  from current sensors  17  and voltage-sensing elements  18 A and/or  18 B, and can provide a wireless interface to an external power monitoring system. Power for operating integrated circuit assembly  20  can be obtained from a battery integrated within integrated circuit assembly  20 . Alternatively, power can be obtained from a current-sensing winding that provides an alternative type of current sensor as described in further detail below, and which draws power from a branch circuit to which the current-sensing device is coupled. 
         [0023]    Referring to  FIG. 2A , an alternative form of current sensor is shown that can provide for a lower-profile form of frame member  10 B in  FIGS. 1A-1B . In particular, when frame member  10 B is affixed to a power panel and thus acts as a base of the current-sensing device, having a thin structure facilitates the insertion of frame member  10 B behind existing branch circuit wires. To provide a thin structure, the ferrite cylinder halves providing ferrite cylinder portions  14 A,  14 B in  FIGS. 1A-1B  can be replaced by a flat ferrite piece  14 C integrated in base frame member  10 B and a U-shaped structure provided by ferrite cylinder portions  14 D. Current sensor  17  is embedded in frame member  10 A and wires  15  are also generally embedded in frame member  10 A and routed to integrated circuit assembly  20 . While  FIG. 2A  illustrates a current sensor formed from three ferrite portions, a current sensor can be formed by placing sensor  17  at one end of the U-shaped ferrite portion  14 D in a manner similar to that illustrated in  FIG. 1B . Alternatively, U-shaped ferrite portion  14 D can be replaced by a half-cylinder with a sensor disposed at an end, such as ferrite cylinder portion  14 A illustrated in  FIG. 1B . 
         [0024]    Referring to  FIG. 2B , another alternative form of current sensor is shown that can provide a lower-cost device and optionally provide power for operating integrated circuit assembly  20 . The current sensor of  FIG. 2B  uses a winding  16  disposed around ferrite cylinder portion  14 F rather than using a gap and semiconductor current sensor as illustrated above. The ends of winding  16  can be routed within frame member  10 A to integrated circuit assembly  20 . Another ferrite cylinder portion  14 E provides the remainder of the magnetic flux loop, which only requires such gaps as are made by the separate ferrite cylinder portions  14 E and  14 F, since a gap is not required for a semiconductor current sensor. 
         [0025]    Referring to  FIG. 3A  and  FIG. 3B , an alternative form of current-sensing device is shown that can provide for facile and temporary installation from the face of a power distribution panel without requiring insertion of a frame member behind the branch circuit wires. The current-sensing device of  FIG. 3A  and  FIG. 3B  is similar to the current-sensing device of  FIGS. 1A-1B , so only differences between the current-sensing devices will be described below. The current-sensing device of  FIG. 3A  and  FIG. 3B  forms a unitary assembly with frame member  30 A inserted within frame member  30 B to provide a sliding action that, in an open position, provides gaps between the extensions of frame member  30 A and  30 B in which ferrite cylinder portions  14 C,  14 D and  14 E and current sensors  17  are integrated. A spring or other suitable restoring force element can be included within frame member  30 A to push the extensions of frame member  30 B against the extensions of frame member  30 A to bring ferrite cylinder portions  14 C,  14 D and  14 E into contact in the closed position around multiple branch circuit wires. In the open position, which can be maintained by using a finger or tool to move frame member  30 B with respect to frame member  30 A, or which alternatively may be maintained using a locking detent or other locking mechanism (not shown) between frame members  30 A and  30 B. The extensions of frame members  30 A and  30 B are separated to permit insertion of the current-sensing device over the multiple branch circuit wires. Voltage-sensing elements in the form of metal foils or layers  18 C and  18 D are also integrated within frame members  30 A and  30 B. 
         [0026]    Referring now to  FIG. 4A , an alternative current-sensing device similar to the current sensor of  FIG. 2B  is shown. Winding  16  is disposed around the extension of frame member  30 A and around ferrite cylinder portion  14 G, the connections of winding  16  are integrated within Frame member  30 A and routed to integrated circuit assembly  20 .  FIG. 4B  shows details of the current-sensing device including current sensor  17  as illustrated in  FIGS. 3A-3B  and as described above with reference to  FIGS. 3A-3B . 
         [0027]    Referring now to  FIG. 5 , a power distribution system in accordance with an embodiment of the present invention is shown. A power distribution panel  8  receives service entrance wiring  5  and distributes power to branch circuit wires  3  via circuit breakers  9 . Branch circuit wires  3  are routed to supply power to loads via conduits or other raceways  7 . For the purposes of illustration, within power distribution panel  8 , current-sensing devices housed by frame members  10 A, 10 B as illustrated in  FIGS. 1A and 1B  are installed on the left side branch circuits, and current-sensing devices housed by frame members  30 A, 30 B as illustrated in  FIGS. 3A and 3B  are installed on the right side branch circuits. 
         [0028]    Referring now to  FIG. 6 , a wire manager in accordance with an embodiment of the present invention is shown installed in a power distribution system. A power distribution panel  8  receives service entrance wiring  5  and distributes power to branch circuit wires  3  via circuit breakers  9 . Branch circuit wires  3  are routed to supply power to loads via conduits or other raceways  7 . Within power distribution panel  8 , wire managers  10 , in accordance with an embodiment of the invention, are installed. Wire managers  10  include a cover portion  10 D and a base portion  10 E. Wire managers  10  control the position of branch circuit wires  3  and further include sensing elements  40  that are used to determine the current flowing through branch circuit wires  3  and optionally the magnitude and/or phase of the voltage on branch circuit wires  3  to provide for computation of the actual (complex) power delivered to the branch circuit loads. Sensing elements  40  have a split-core construction similar or identical to the sensors incorporated within the sensing device illustrated in  FIG. 1A-1B , with the portion including current-sensing element  17  embedded within base portion  10 E and the other split cores that complete the magnetic paths with the bottom portion of sensors  40  integrated at a corresponding position on the bottom side of cover portion  10 D. Wire managers  10  also include an interface/processing unit  12  that provides a wired or wireless interface to an external processing system and generally provides for computation of power usage-related information prior to transmission to the external processing system, although raw current (and optionally voltage) sensor output information could alternatively be transmitted, with computation of power usage-related information performed in the external processing system. Interface/processing unit  12  may alternatively be placed in locations and be dimensioned other than as shown. For example, interface/processing unit  12  may be physically separate from wire manager  10  and be coupled to wire manager  10  by a wired, wireless, optical or other suitable interface. 
         [0029]    Referring now to  FIG. 7A , details of base portion  10 E of wire manager  10  of  FIG. 6  are shown, in accordance with an embodiment of the invention. Base portion  10 E includes the ferrite cylinder portion  14 A, current-sensing element  17  and optional voltage-sensing element  18 A identical to those elements in  FIGS. 1A-1B . Connections to current-sensing elements  17  are not shown for clarity, but are generally embedded within base portion  10 E and extend to measurement circuits within interface/processing unit  12  of  FIG. 6 . Referring now to  FIG. 7B , details of cover portion  10 D of wire manager  10  of  FIG. 6  are shown, in accordance with an embodiment of the invention. Cover portion  10 D includes ferrite cylinder portion  14 B which completes the magnetic pathway around ferrite cylinder portion  14 A when cover portion  10 D is installed over base portion  10 E. Similarly, cover portion  10 D may include voltage-sensing element  18 B integrated within ferrite cylinder portion  14 B. 
         [0030]    Referring now to  FIG. 8 , details of integrated circuit assembly  20  as illustrated in  FIG. 1B  and  FIG. 3B , and which are generally included in interface/processing unit  12  of  FIG. 6 , is shown. A multiplexer  101 A receives signals from the individual current sensors  17  (or windings  16 ) and selects a sensor for measurement, providing input to a current measurement circuit  108 A, which is an analog circuit that appropriately scales and filters the current sensor output. The output of current measurement circuit  108 A is provided as an input to an analog-to-digital converter (ADC)  106 , which converts the current output waveform generated by current measurement circuit  108 A to sampled values provided to a central processing unit (CPU)  100  that performs power calculations in accordance with program instruction stored in a memory  104  coupled to CPU  100 . Alternatively, a separate current measurement circuit  108 A and multiplexer  101 A may not be necessary, and sensors  17  or windings  16  may be coupled directly to ADC  106 . The power usage by the branch circuit associated with a particular sensor can be determined by assuming that the branch circuit voltage is constant (e.g., 115 Vrms) and that the phase relationship between the voltage and current is aligned (i.e., in-phase). However, while the assumption of constant voltage is generally sufficient, as properly designed distribution systems do not let the line voltage sag more than a small amount, e.g., &lt;3%, the phase relationship between voltage and current is dependent on the power factor of the load, and can vary widely and dynamically by load and over time. Therefore, it is generally desirable to at least know the phase relationship between the branch circuit voltage and current in order to accurately determine power usage by the branch circuit. 
         [0031]    When voltage measurement is implemented, another multiplexer  101 B is provided to receive signals from the individual voltage-sensing elements, e.g., one of voltage-sensing elements  18 A,  18 B or  18 C,  18 D in the above-described current-sensing devices, if voltage-sensing is also implemented. Multiplexer  101 B receives signals from the individual voltage-sensing elements within the devices and selects a sensor for measurement, providing input to a voltage measurement circuit  108 B, which is an analog circuit that appropriately scales and filters the signal received from voltage-sensing elements  18 A,  18 B or  18 C,  18 D. A zero-crossing detector  109  may be used to provide phase-only information to a central processing unit  100  that performs power calculations, alternatively or in combination with providing an output of voltage measurement circuit to an input of ADC  106 . Alternatively, multiplexor  101 B may not be necessary and one or more voltage sensor outputs of sensors  17  (or windings  16 ) may be connected directly to ADC  106 . In particular, it may not be necessary to make voltage measurements at each of sensors  17 , for example, when sensing the phase of the voltage, a single measurement may suffice for providing a phase reference that is then used to determine the voltage-to-current phase difference for multiple branch circuits. Further, if multiple voltage measurements are taken, the voltage measurements may be used as an absolute voltage measurement, or the amplitude may be scaled to a known peak, r.m.s. or average value. An input/output (I/O) interface  102  provides either a wireless or wired connection to an external monitoring system  120 , such as a wireless local area network (WLAN) connection  122 A or wired Ethernet connection  122 B. When power factor is not taken into account, the instantaneous power used by each branch circuit can be approximated as: 
         [0000]    
       
      
       P 
       BRANCH 
       =V 
       rms 
       *I 
       meas  
      
     
         [0000]    where V rms  is a constant value, e.g. 115V and I meas  is a measured rms current value. Power value P BRANCH  may be integrated over time to yield the energy use. When the phase of the voltage is known, then the power may be computed more accurately as: 
         [0000]        P   BRANCH   =V   rms   *I   meas *cos(Φ)
 
         [0000]    where Φ is a difference in phase angle between the voltage and current waveforms. The output of zero-crossing detector  109  may be compared with the position of the zero crossings in the current waveform generated by current measurement circuit  108 A and the time ΔT between the zero crossings in the current and voltage used to generate phase difference Φ from the line frequency (assuming the line frequency is 60 Hz): 
         [0000]      Φ=2Π*60 *ΔT  
 
         [0000]    In general, the current waveform is not truly sinusoidal and the above approximation may not yield sufficiently accurate results. A more accurate method is to multiply current and voltage samples measured at a sampling rate much higher than the line frequency. The sampled values thus approximate instantaneous values of the current and voltage waveforms and the energy may be computed as: 
         [0000]      Σ(V n *I n )
 
         [0000]    A variety of arithmetic methods may be used to determine power, energy and phase relationships from the sampled current and voltage measurements. 
         [0032]    While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form, and details may be made therein without departing from the spirit and scope of the invention.