Abstract:
According to one aspect, embodiments of the invention provide a current monitoring device comprising a current transformer configured to be removeably coupled to a power line and to generate a reference signal having a level related to a current level of the power line, a sensor circuit connected to the current transformer and configured to convert the reference signal to a measurement signal, a flexible cable having a first end and a second end, the first end coupled to the sensor circuit, and a connection portion coupled to the second end of the flexible cable and configured to be removeably coupled to a communications bus, wherein the sensor circuit is further configured to provide the measurement signal to the communication bus via the flexible cable and the connection portion.

Description:
This application is a U.S. National Stage application and claims priority under 35 U.S.C. §371 from International Application No. PCT/US2012/034914, filed Apr. 25, 2012, which is hereby incorporated herein by reference in its entirety. 
     BACKGROUND OF INVENTION 
     1. Field of the Invention 
     At least one example in accordance with the present invention relates generally to systems and methods for monitoring a load center for current, power and energy usage. 
     2. Discussion of Related Art 
     A load center or panelboard is a component of an electrical supply system which divides an electrical power feed from a power line into different subsidiary circuit branches. Each subsidiary circuit branch may be connected to a different load. Thus, by dividing the electrical power feed into subsidiary circuit branches, the load center may allow a user to individually control and monitor the current, power and energy usage of each branch circuit and in some instances each load. 
     Current sensors are commonly used to monitor activity of a load center. For example, Current Transformers (CT) are commonly used to monitor current, power and/or energy consumption in a subsidiary or main branch of a load center. A CT may be used to measure current in a branch by producing a reduced current signal, proportionate to the current in the branch, which may be further manipulated and measured. For example, a CT coupled to a branch of a load center may produce a reduced current AC signal, proportionate to the magnitude of AC current in the branch. The reduced current AC signal may then either be measured directly or converted to a digital signal and then measured. Based on the signal received, the level of current in the subsidiary branch may be determined. 
     SUMMARY OF THE INVENTION 
     Aspects in accord with the present invention are directed to a current monitoring device comprising a current transformer configured to be removeably coupled to a power line and to generate a reference signal having a level related to a current level of the power line, a sensor circuit connected to the current transformer and configured to convert the reference signal to a measurement signal, a flexible cable having a first end and a second end, the first end coupled to the sensor circuit, and a connection portion coupled to the second end of the flexible cable and configured to be removeably coupled to a communications bus, wherein the sensor circuit is further configured to provide the measurement signal to the communication bus via the flexible cable and the connection portion. 
     According to one embodiment, the current monitoring device further comprises a first housing containing the sensor circuit and the current transformer, wherein the first housing includes a first portion containing the current transformer and a second portion containing the sensor circuit, and wherein the first portion is rotatably coupled to the second portion. In one embodiment, the first housing is configured to be rotated between a first position and a second position, wherein, in the first position, the first portion of the first housing is rotated about the second portion to allow external access to an interior chamber, and wherein, in the second position, the first portion of the first housing is rotated about the second portion so that the first portion encompasses the interior chamber. 
     According to another embodiment, the connection portion includes a second housing coupled to the second end of the flexible cable. In one embodiment, the second housing includes an insulation displacement connector configured to couple the connection portion to the communication bus. In another embodiment, second housing further includes a lid configured to lock the communication bus in a position adjacent to the insulation displacement connector. In one embodiment, the second housing further includes a comb configured to separate discrete conductors of the communication bus. 
     According to one embodiment, the measurement signal is a digital measurement signal. In another embodiment, the current transformer is a 200 A current transformer. 
     Another aspect in accord with the present invention is directed to a method for monitoring a power line within a load center, the method comprising coupling a current transformer to the power line within the load center, the current transformer coupled to a sensor circuit, the sensor circuit coupled to a connection portion via a flexible cable, coupling the connection portion to a communication bus within the load center, generating, with the current transformer, a reference signal having a level related to a current level of the power line, converting, with the sensor circuit, the reference signal to a measurement signal, and providing, via the connection portion, the measurement signal to the communication bus. 
     According to one embodiment, the current transformer is coupled to the power line at a first location within the load center and the connection portion is coupled to the communication bus at a second location within the load center. In one embodiment, the act of coupling a current transformer to the power line includes encompassing the power line within the current transformer. In another embodiment, the act of coupling the connection portion to the communication bus includes piercing an outer insulation layer of the communication bus with at least one contact of the connection portion and connecting the at least one contact to a conductor within the communication bus. 
     According to one embodiment, the measurement signal is a digital measurement signal. In another embodiment, the current transformer is a 200 A current transformer. 
     One aspect in accord with the present invention is directed to a device for monitoring current in a power line within a load center, the device comprising a current transformer configured to be coupled to the power line at a first location within the load center and to generate a reference signal having a level related to a current level of the power line, a sensor circuit configured to convert the reference signal to a measurement signal and provide data related to the measurement signal to a communication bus, and means for coupling the sensor circuit to the communication bus at a second location within the load center. 
     According to one embodiment, the device further comprises a housing containing the sensor circuit and the current transformer, wherein the housing includes a first portion containing the current transformer and a second portion containing the sensor circuit, and wherein the first portion is rotatably coupled to the second portion. In one embodiment, the housing is configured to be rotated between a first position and a second position, wherein, in the first position, the first portion of the housing is rotated about the second portion to allow external access to an interior chamber, and wherein, in the second position, the first portion of the housing is rotated about the second portion so that the first portion encompasses the interior chamber. 
     According to one embodiment, the measurement signal is a digital measurement signal. In another embodiment, the current transformer is a 200 A current transformer. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various FIGs. is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings: 
         FIG. 1  is a circuit diagram of a load center in accordance with aspects of the present invention; 
         FIG. 2  is a schematic diagram of a CT circuit in accordance with aspects of the present invention; 
         FIG. 3  is a schematic diagram of a connection portion in accordance with aspects of the present invention; 
         FIG. 4  is a schematic diagram of a CT circuit within a load center in accordance with aspects of the present invention; and 
         FIG. 5  is another schematic diagram of a CT circuit within a load center in accordance with aspects of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the invention are not limited to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. Embodiments of the invention are capable of being practiced or of being carried out in various ways. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having,” “containing”, “involving”, and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. 
     As discussed above, CT&#39;s may be utilized with a load center of an electrical supply system to monitor circuit branches and assist in providing efficient energy management. For instance, CT&#39;s may be coupled to circuit branches inside or outside of a load center. However, multiple challenges with connecting CT&#39;s in a load center may arise as the electrical supply system grows in size and complexity. 
     Existing methods and systems typically rely on a system of individual CT&#39;s, each connected to a main controller and measurement unit in a “hub and spoke” topology. In such a system, each CT requires dedicated cabling connecting it to the main controller and its measurement unit, so that the number of cables or wires increases linearly with the number of sensors. In addition, some jurisdictions have regulatory requirements on the amount of “gutter space” (i.e., space within the panelboard free of wiring and other electronic devices) available within a panelboard. Therefore, as the number of CT&#39;s increases, the amount of cabling and circuitry within a panelboard may become difficult to manage and violate regulatory requirements. 
     In some instances it may even be difficult to physically place all of the desired CT&#39;s and corresponding circuitry within the load center, and due to the complexity of such a load center; installation, expansion and maintenance may also be expensive, difficult and even hazardous. 
     At least some embodiments described herein overcome these problems and provide a relatively small, less complex and more manageable method and system for utilizing CT&#39;s to monitor circuit branches of a load center. 
       FIG. 1  shows a load center  100  that includes a system for monitoring subsidiary circuit branches  102  of the load center  100  according to one embodiment of the current invention. The load center  100  includes a housing  101 . Within the housing  101 , the load center  100  includes a first input power line  104 , a second input power line  106 , a plurality of circuit branches  102 , a neutral line  108 , and a ground connection  110 . The first and second input power lines  104 ,  106  are each configured to be coupled to an external power source (e.g., a utility power system). Each one of the plurality of circuit branches  102  is configured to be coupled between one of the input power lines  104 ,  106  and an external load  112  (e.g., an appliance, a power outlet, a light etc.). 
     According to one embodiment, each one of the input power lines  104 ,  106  includes a circuit breaker  113  coupled between the input power line  104 ,  106  and circuit branches  102 . According to another embodiment, each one of the plurality of circuit branches  102  includes a circuit breaker  115  coupled between the input power line  104 ,  106  and an external load  112 . In one embodiment, the current rating of each circuit breaker  113 ,  115  may be configured based on the power required by the external load  112  to which the circuit breaker&#39;s  113 ,  115  associated circuit branch  102  is coupled. The neutral line  108  is coupled to the ground connection  110 . According to one embodiment, the neutral line is coupled to the ground connection  110  via a neutral bus bar  116 . According to another embodiment, the ground connection  110  is coupled to the neutral line  108  via a ground bus bar  118 . 
     Within the housing  101 , the load center  100  also includes a plurality of Current Transformers (CT)  114 , a plurality of smart sensor circuits  120 , a communication bus  122 , and a CT concentrator  124 . According to one embodiment, the communication bus  122  includes a plurality of wires. For example, in one embodiment, the communication bus  122  is a four-conductor cable (e.g., a hi-flex unshielded 4-conductor silicone cable) including 4 wires (a power line, a return line, D+ differential pair line, D− differential pair line); however, in other embodiments, the communication bus  122  may include any number and type of wires. Each one of the plurality of CT&#39;s  114  is coupled to at least one of the plurality of circuit branches  102 . According to one embodiment, CT&#39;s  114  may also be coupled to each input line  104 ,  106 . According to one embodiment, each CT  114  encompasses a corresponding circuit branch  102  or input line  104 ,  106 . Each one of the plurality of CT&#39;s is also coupled to a corresponding smart sensor circuit  120 . Each smart sensor circuit  120  is coupled to the communication bus  122 . 
     According to one embodiment, each smart sensor circuit  120  is coupled to the communication bus  122  so that each smart sensor circuit  120  is in electrical communication with the CT concentrator  124 . The coupling of each smart sensor circuit  120  to the communication bus  122  is described in greater detail below. 
     According to one embodiment, the CT concentrator  124  includes a digital interface  125 , at least one analog interface  127 , a power module  126  and a Zigbee RF interface  128 . The communication bus  122  is coupled to the digital interface  125 . The power module  126  is coupled to at least one input power line  104 ,  106  via at least one branch circuit  102 . According to one embodiment, at least one CT  114  is coupled directly to at least one analog interface  127 . 
     According to one embodiment, AC power is provided from an external source (e.g., a utility power system) to the input lines  104 ,  106 . AC power from the input lines  104 ,  106  is provided to each of the external loads  112 , via the circuit branches  102 . The circuit breakers  113  are configured to automatically open and prevent current in an input line  104 ,  106  if an overload or short circuit is detected in the input line  104 ,  106 . The circuit breakers  115  are configured to automatically open and prevent current in a circuit branch  102  if an overload or short circuit is detected in the circuit branch  102 . 
     The power module  126  of the CT concentrator  124  receives AC power from at least one input line  104 ,  106 . Using the AC power, the power module  126  powers the CT concentrator  124 . In addition, the CT concentrator  124  measures the AC voltage, frequency and/or phase of the AC power. According to one embodiment, the CT concentrator  124  is configured to communicate the measured AC voltage, frequency and/or phase information to the smart sensor circuits  120 , via the communication bus  122 . For example, in one embodiment, the CT concentrator  124  transmits phase information of the AC power to the smart sensor circuits  120  so that the CT concentrator  124  may be synchronized with the smart sensor circuits  120 . According to one embodiment, the CT concentrator is also capable of being powered by a battery. 
     AC current passing through a circuit branch  102  or input line  104 ,  106  induces a proportionate AC current in its associated CT  114  which encompasses the circuit branch  102  or input line  104 ,  106 . According to one embodiment, where a CT  114  may be coupled to multiple circuit branches  102 , an AC current proportionate to the combined current in the multiple circuit branches is induced in the CT  114  which encompasses the multiple circuit branches. The smart sensor circuit  120  coupled to the CT  114  converts the proportionate AC current from the CT  114  into a digital value and then transmits the digital value, over the communications bus  122  to the CT concentrator  124 . For example, according to one embodiment, a CT  114  and smart sensor circuit  120  pair produces a proportionate AC current (based on an associated circuit branch), converts the proportionate AC current into digital values, and transmits the digital values to the CT concentrator as described in U.S. patent application Ser. No. 13/089,787 entitled “SMART CURRENT TRANSFORMERS”, filed on Apr. 19, 2011 (hereinafter “the &#39;787 Application”), which is hereby incorporated herein by reference in its entirety. 
     According to one embodiment, the smart sensor circuit  120  may be configured to utilize the voltage, frequency and/or phase information received from the CT concentrator  124  over the communications bus  122 . For example, in one embodiment, the smart sensor circuit  120  utilizes the phase information received from the CT concentrator  124  to synchronize operation with the CT concentrator  124  such that current measurements performed by the smart sensor circuits  120  can by synchronized with voltage measurements made by the CT concentrator  124 . In another example, the smart sensor circuit  120  utilizes the voltage, frequency and/or phase information to calculate power and energy parameters such as RMS current, true and apparent power, and power factor of the circuit branch  102  or input line  104 ,  106 . This information is also converted into digital values and sent to the digital interface  125  of the CT concentrator  124  over the communications bus  122 . According to one embodiment, at least one CT  114  may also provide analog signals, proportionate to the AC current passing through the circuit branch  102 , directly to an analog interface  127  of the CT concentrator  124 . 
     According to one embodiment, upon receiving the current information from the smart sensor circuits  120 , the CT concentrator  124  utilizes the measured voltage, frequency and/or phase information to calculate power and energy parameters such as RMS current, true and apparent power, and power factor of the circuit branch  102  or input line  104 ,  106 . 
     According to another embodiment, upon receiving the current information and receiving and/or calculating the power information, the CT concentrator  124  transmits the current, power and energy information to an external client (e.g., a web server, in-home display, internet gateway etc.) via the wireless Zigbee RF interface  128  to assist in power management of the load center  100  and to assist in power management and control of a residence or other facility containing the system. The CT concentrator  124  may also transmit the current, power and energy information to an external client via a wired connection or a different type of wireless connection. For example, according to one embodiment, a CT concentrator  124  receives current information from the smart sensor circuits  120 , calculates power and energy information using the received current information, and transmits the current, power, and energy information to an external client as described in the &#39;787 Application. 
     As described above, each smart sensor circuit  120  is coupled to the CT concentrator  124  via the communication bus  122 . According to one embodiment, each smart sensor circuit  120  is coupled to the communication bus  122  via a connection portion which is clamped onto the communication bus  122 . For example, in one embodiment, electrical contacts of a connection portion, which is coupled to a smart sensor circuit  120 , are pressed onto the communication bus  122  so that the electrical contacts pierce an insulation layer of the communication bus  122  and become electrically coupled to appropriate conductors within the communication bus  122 . In other embodiments, the connection portion may be coupled differently to the communication bus  122 . For example, according to one embodiment, the connection portion is coupled to the communication bus  122  via a bus bar or daisy chained connectors (not shown). 
     According to one embodiment, the connection portion is located within the same housing as the smart sensor circuit  120  and the associated CT  114 . Thus the connection portion is coupled to the communication bus  122  at substantially the same location within the load center as where the CT  114  is coupled to the circuit branch  102  or input line  104 . For example, in one embodiment, the connection portion and the smart sensor circuit  120  are configured as described in the &#39;787 Application. 
     According to another embodiment, the connection portion is located separately from the smart sensor circuit  120  and the associated CT  114 . Such a configuration may allow for increased connection flexibility within the load center as the connection portion may be coupled to the communication bus  122  at a different location then where the CT  114  is coupled to the circuit branch  102  or input line  104 . This may be beneficial where the communication bus  122  and the circuit branch  102  or input line  104  desired to be monitored are not adjacent to each other. It also may be beneficial where the size of the line desired to be measured (e.g. a mains input line  104 ) requires a large CT  114  that is difficult (or even impossible) to connect to the input line  104  adjacent the communication bus  122 . 
     Therefore at least some embodiments described herein provide a CT circuit (e.g. including a CT  114  and smart sensor circuit  120 ) which provides enhanced connection flexibility within a load center. 
       FIG. 2  illustrates one embodiment of a CT circuit  200  in accordance with aspects of the present invention. The CT circuit  200  includes a housing  202 . The housing  202  includes a first portion  204  which encompasses a CT (e.g. a CT  114 ) and a second portion  206  which encompasses a smart sensor circuit (e.g. a smart sensor circuit  120 ). The second portion  206  is coupled to a connection portion  208  via a flexible cable  210 . 
     According to one embodiment, the first portion  204  of the housing  202  is a clamp which includes a top portion  201  and a bottom portion  203 . The bottom portion  203  of the clamp is coupled to the second portion  206 . The top portion  201  of the clamp is coupled to a button  208  of the second portion  206  about a lever point within the second portion  206 . Absent pressure on the button  208 , a spring mechanism within the second portion  206  forces the button  208  to extend outward from the second portion  206 , resulting in the top portion  201  being forced against the bottom portion  203  to form an interior chamber  205 . 
     When connection to a circuit branch  102  is desired, a user may press down on the button  208 , compressing the spring mechanism, forcing the button  208  to rotate about the lever point into the second portion  206  and causing the top portion  201  to rotate about the lever point away from the bottom portion  203 . As a result, the top portion  201  and bottom portion  203  move apart. As the top portion  201  and bottom portion  203  separate, an opening is formed by which a circuit branch  102  may be inserted into the interior chamber  205 . Once a circuit branch  102  is inserted into the interior chamber  205 , removal of pressure on the button  208  results in the spring mechanism forcing the button  208  to rotate out of the second portion  206  and the top portion  201  to rotate back towards the bottom portion  203  until the top portion  203  and bottom portion  203  are compressed together, thereby encompassing a circuit branch  102  within the interior chamber  205  of the clamp  204  (and hence the CT). 
     The second portion of the housing  206  encompasses a smart sensor circuit (as described above). However, the housing  202  does not include the connection portion  208  which is configured to be coupled to a communication bus  122 . 
     The connection portion  208  is configured to be coupled to a communication bus  122 . For example,  FIG. 3  illustrates a connection portion  208  in accordance with aspects of the present invention.  FIG. 3  illustrates the connection portion  208  prior to being connected to a communications bus  122 . According to one embodiment, the connection portion  208  includes a housing  309 . The housing  309  of the connection portion  208  includes an Insulation Displacement Connector (IDC)  302  (e.g., an AVX series 9176 IDC). According to one embodiment, the IDC  302  may include a plurality of blades  304 . For example, if, as discussed above, the connection portion  208  (and hence the smart sensor circuit  120  via the cable  210 ) is configured to be coupled to a four-conductor cable, the IDC  302  will include four blades, each blade configured to be coupled to a corresponding conductor within the cable. However, according to other embodiments, the IDC  302  may include any number of blades to adequately connect the connection portion  208  to the communications bus  122 . According to one embodiment, the housing  309  of the connection portion  208  also includes comb features  305  which are configured to separate the discrete conductors within the communication bus  122 . 
     According to one embodiment, the connection portion  208  may also include a locking lid  306  coupled to the housing  309  via a hinge  308 . Prior to being coupled to the communications bus  122 , the locking lid  306  of the connection portion  208  is swung away from the IDC  302 , allowing a user to place the communication bus  122  adjacent to the IDC  302 . The user presses down on the communication bus  122 , causing the communication bus  122  to press against the IDC  302 . The comb features  305  separate the discrete conductors and the plurality of blades  304  of the IDS  302  pierce the outer insulation layer of the communication bus  122 , each one of the plurality of blades  304  connecting with a corresponding conductor within the communication bus  122 . The user may then swing the locking lid towards the IDC  302  and press down on the locking lid to lock the communication bus  122  into place. 
     According to other embodiments, the connection portion  208  (and hence the smart sensor circuits  120  via the cable  210 ) may be coupled to the communication bus  122  in a different manner. For example, connection portions of smart sensor circuits may also be coupled to the communication bus  122  via a bus bar. Upon the connection portion  208  being coupled to the communication bus  122 , the corresponding smart sensor circuit  120  (and associated CT  114 ) is in electrical communication with the CT concentrator  124  via the cable  210 , the connection portion  208  and the communication bus  122 . 
     According to one embodiment, the connection portion  208  and the flexible cable  210  also include appropriate internal connections which are configured to couple the appropriate connections within the smart sensor circuit  120  to the communication bus  122 . 
     By coupling the smart sensor circuit  120  (and CT  114 ) to the communications bus  122  via a connection portion  208  and a flexible cable  210 , the connection portion  208  is able to be connected to the communication bus  122  at a different location within a load center then where the CT  114  is coupled to a circuit branch  102  or input line  104 , thereby providing enhanced connection flexibility within the load center. 
     For example,  FIGS. 4-5  illustrate the CT circuit  200  within a load center  400  in accordance with aspects of the present invention. The load center  400  includes an enclosure  410 . Within the enclosure  410 , the load center  400  includes circuit branches  102 , an input line  104 , circuit breakers  113 ,  115 , a CT circuit  200  and a communication bus  122 , as discussed above. The circuit breakers  113 ,  115  are coupled to the circuit branches  102  and the input line  104  and are arranged in two columns. According to one embodiment, the load center  400  also includes a cover which separates the circuit breakers  113 ,  115  from the circuit branches  102 , input line  104 , CT circuit  200  and communication bus  122 , thereby allowing a user to operate the circuit breakers  113 ,  114  without contacting live electrical parts within the load center  400 . In one embodiment, the cover may be removed when an individual desires to access live components within the load center  400  (e.g. in order to couple a CT circuit  200  to the input line  104  and communication bus  122 ). 
     As described above, the CT circuit  200  includes a housing  202 . The first portion  204  of the housing  202  is coupled around the input line  104  which provides mains power to the circuit branches  102  and the connection portion  208  is coupled to the communication bus  122 . The second portion  206  of the housing  202  is coupled to the connection portion  208  via a flexible cable  210 . The connection portion  208  and flexible cable  210  allow the CT circuit  200  to monitor the input line  104  while being coupled to the communications bus  122 , even though the input line  104  is not located adjacent the communications bus  122  and the CT within the CT circuit  200  is likely too large (e.g. rated for 200 A to handle input mains power) to be located adjacent the communications bus  122 . 
     According to one embodiment, the flexible cable  210  includes a strain relieving feature. For example, in one embodiment, the flexible cable  210  includes an over molded feature  402  located at the end of the cable  210  attached to the second portion  206  and/or the end of the cable  210  attached to the connection portion  208 . 
     Even though examples in accordance with the present invention are described herein in reference to a load center, other examples may be utilized within any electrical system in which current, power and energy of a power line are desired to be monitored. It also is to be appreciated that examples in accordance with the present invention may be utilized to monitor any type (e.g., commercial or residential) or size system. 
     Even though examples in accordance with the present invention are described herein as utilizing a current transformer capable of being clamped onto a circuit branch or input line, other examples may utilize a different type of current sensor. For example, current sensors utilizing shunt resistance, hall-effect, and toroidal (solid core) current transformers may be used. 
     Even though examples in accordance with the present invention are described herein as utilizing a current sensor capable of monitoring a circuit branch, other examples may utilize any other types of sensor (e.g. temperature or humidity sensors) which is desired to be located at a different location than the communication bus within a load center. 
     By coupling a smart sensor circuit and CT to a communications bus via a connection portion, separate from the smart sensor circuit, and a flexible cable, the connection portion is able to be connected to the communication bus at a different location within a load center then where the CT is coupled to a circuit branch or input line, providing enhanced connection flexibility within the load center. 
     Having thus described several aspects of at least one embodiment of this invention, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.