Abstract:
A power monitoring system that reduces the need for external power calculation devices while simplifying the configuration of power meters.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional App. No. 61/216,894, filed May 21, 2009. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a branch current monitoring system. 
     Referring to  FIG. 1 , many electrical power distribution systems include a panel enclosure  10  into which is provided electrical power using one or more sets of wires  12 . The electrical power may have any voltage, any current, and any number of phases (e.g., single phase, two phases, or three phases). Each phase of the electrical power to the power panel is normally provided to a separate bus bar  14   a ,  14   b , and  14   c , which are normally elongate conductors within the power panel  10 . A plurality of circuit breakers  16   a ,  16   b , and  16   c , etc., which trip or otherwise selectively disconnect electrical power, are electrically interconnected between one or more of the bus bars  14   a ,  14   b , and  14   c , and respective loads  18  external to the power panel  10 . In many power panels  10  the circuit breakers  16  are vertically aligned in one or more strips. When the load  18  interconnected to a respective circuit breaker  16  within the power panel  10  draws excessive electrical current then the circuit breaker  16  trips or otherwise disconnects the electrical power to the load  18 . In this manner, if a load shorts and thereafter draws excessive current then the circuit breaker will trip. Frequently the load will be a three-phase load having three wires provided thereto, with one or more corresponding circuit breakers. Otherwise, the loads are typically single phase or two phase. 
     In many business environments a set of electrical loads, such as motors, lighting, heating units, cooling units, machinery, etc., may be electrically interconnected to one or more circuits, each of which may be a single phase or multi-phase. Obtaining the total power usage of the business may be readily obtained by reading the power meter provided by the power utility. The power meter is normally electrically interconnected between the power panel and the power utility. In many circumstances, it is desirable to monitor the power consumption of individual loads or groups of loads. The use of power meters permits effective monitoring of the power consumption of particular loads. Also, a set of power meters permits effective sub-metering of different loads, buildings, or groups of loads to attribute and monitor the power usage of the business. For example, the power sub-metering may be used to attribute the power costs charged by the utility to different buildings, departments, or cost centers. The traditional approach to monitoring such power usage is to install a power meter at a location proximate the load itself. To install a typical power meter on a three phase load, a current sensor is located around each wire of the three phases and a voltage connection is electrically interconnected to each wire. Such a power meter is available from Veris Industries, LLC under the name H8035 Power Meter. Unfortunately, it is burdensome to interconnect a significant number of power meters and in particular the voltage connections to the wires, especially if an interconnection to the wires are not readily available. In addition, it is burdensome to interconnect the output of the power meters, if any, to a computer network because of the need to provide communication wiring or other wireless communication channels to each of the remotely located power meters. Also, installing the power meters requires significant expense for the technician to locate a suitable location near each device, in addition to the further expense of servicing the installed power meters. 
     Referring to  FIG. 2 , to monitor the power provided to a particular load from one or more individual circuit breakers  16  a respective current sensor  20  may be interconnected to the wire on the load side of the respective circuit breaker  16 . Typical circuit breakers may include a single phase, two phases, or three phases. The outputs  22  of each of the current sensors  20  may be interconnected to a power monitor  24 . The current sensors  20  may be interconnected to one or more power monitors. Also, the current sensors  20  may likewise be daisy chained together, or interconnected to the power monitor(s) in any other suitable manner. An electrical interconnection from each bus bar to the power monitor(s) normally includes wires  23   a ,  23   b ,  23   c  to sense the voltage and its corresponding phase relationship. Alternatively, the voltage potential and phase relationship for each phase may be sensed from locations other than the bus bars  14   a ,  14   b , and  14   c , such as for example, a wire provided to a load, the load side of a circuit breaker, the utility side of a circuit breaker, a capacitive coupling to the voltage potential, or the wire connection from the utility. It is to be understood that the power monitor may calculate power based upon a single phase, two phases, and/or three phases, etc., as desired. In essence, the power monitoring system may use the electrical path from the power monitor  24  to the bus bars (or otherwise) of at least one of the phases for a plurality of different loads. Typically, the power is calculated by multiplying the voltage, corresponding current, and corresponding power factor which relates to the phase relationship between the voltage and current. 
     It takes considerable time to install, at significant expense, all of the current sensors  20  and the available space within the power panel  10  may be insufficient for the desired number of current sensors. Also, the limited space available along the circuit breakers  16  may result in significant difficulty installing the current sensors  20 , thus requiring lateral spacing of the current sensors and bending the wires from the circuit breakers to different locations within the power panel  10  in an attempt to locate sufficient available space for the current sensors  20 . In addition, the large number of wires  22  from the current sensors  20  to the power monitor  24  may require considerable space within the power panel  10 . Further, because of the significant number of individual wires  22  an installer has a significant tendency to interconnect the wires  22  to improper places within the power current monitor  24  and in particular to mismatch pairs of wires  22  from the same current sensor  20  rending the current sensors  20  ineffective. Moreover, it is problematic to ensure that the wires  22  indicated by the installer that relate to a particular current sensor  20  actually are interconnected to the desired current sensor  20 . In summary, the potential installation problems are significant, especially when install by untrained technicians. 
     Referring to  FIG. 3 , a set of sensors  60  may be supported by a support  62  which maintains the current sensors  60  in a fixed spatial relationship with respect to one another. Preferably the support  62  is rigid or semi-rigid, while a flexible support  62  that was installed on a rigid or a semi-rigid supporting member(s) may likewise be used. The sensors  60  are preferably current sensors, or alternatively, other types of sensors may be used. The sensors  60  are preferably wire wound torodial coils on a metallic or non-metallic core enclosed within a plastic housing through which a wire  63  may be extended, and the housings are at least partially surrounding the respective coil. Changing current within the wire  63  induces a changing magnetic field around the wire  63 . The changing magnetic field in turn induces a changing current within the wire wound torodial coil. The changing current within the torodial coil may be used directly or converted to any suitable signal, such as for example, a voltage signal, or a different current signal. 
     The openings  64  defined by the sensors  60  are preferably oriented in a substantially parallel relationship with respect to each other and/or oriented in a substantially perpendicular relationship with respect to the longitudinal axis  66  of the support  62  or otherwise the general alignment of the sensors. Preferably, one set of the aligned sensors have a first linear arrangement and another set of the aligned sensors have a second linear arrangement, which may be parallel to each other. Also, preferably at least two of the aligned sensors have a first linear arrangement and at least two others of the aligned sensors have a second linear arrangement. A single aligned set of sensors  60  may be used or more than two sets of sensors  60  may be used, as desired. 
     Referring also to  FIG. 4 , the sensors  60  may be arranged such that the housings surrounding the current sensors have an overlapping region  70  in a substantially perpendicular direction with respect to the longitudinal axis of the support  62  and/or general alignment of the sensors. Preferably, the openings  64  defined by the sensors  60  are in a non-overlapping relationship  72  with respect to one another and a non-overlapping relationship  74  with respect to other housings. This permits the sensors to be arranged in a more compact arrangement within the power panel. 
     Referring also to  FIG. 5 , a respective transient voltage suppressor  80  may be interconnected in parallel across the output terminals of each sensor  60 . The transient voltage suppressors  80  limits the voltage build up at the terminals of the sensors  60 , which may occur if the sensors are sensing a changing magnetic field while the terminals of the sensors  60  are open circuited. This decreases the likelihood that technicians will be the recipient of an unanticipated electrical shock. 
     Referring to  FIG. 6 , the current sensors  60  are preferably arranged in a spatial arrangement such that the openings  64  defined by the current sensors  60  are in a substantially directly opposing relationship with respect to the circuit breakers  16 . In other words, the each of the openings  64  is opposing a respective circuit breaker  16 . In this manner, the wires from the circuit breakers  16  may be readily routed through a respective sensor  60 . 
     Referring to  FIG. 7 , during normal installation the support  62  is initially affixed within the power panel in an adjacent spaced apart relationship with respect to a set of circuit breakers  16 . A support may be located on both sides of a set of circuit breakers  16 , if desired. Another support more suitable for the right hand side of the circuit breakers may also be used. Then, the wires from the loads are passed through the respective sensors and interconnected to a respective circuit breaker  16 . In addition, the wires  23   a ,  23   b , and  23   c , for sensing the voltage potentials on the bus bars are likewise electrically interconnected. In this manner, the installation of the circuit breakers and the power monitor is efficient, less expensive, economical, and the sensors are in a suitable position with respect to the respective circuit breakers. The support  62  may be suitable for supporting a set of electrical traces that interconnect the sensors  60  to a connector  82 . A cable  84  interconnects each connector  82  to a power monitor  24 . While such a set of supports  62  with respective sensors  60  are suitable for use with new installation, it is difficult to install such a set of sensors  60  to an existing set of circuit breakers with wires already installed. To permit the sensors  60  to be readily interconnected with wires already interconnected to the circuit breakers  16  the sensors  60  may be constructed in a split-core manner. In this manner, the opening  64  may be opened, the wire inserted therein, and the opening  64  closed around substantially all of the wire. 
     To provide effective monitoring of the power usage used by the loads, the power monitor  24  may monitor the current levels of each of circuit breakers  16  together with the associated voltage potential and phase relationship. 
     The power monitor  24  may likewise be used to monitor the load balance between the different phases of the power panel  10 . Frequently, the circuit breakers may be interconnected to a single phase when the loads require 120 volts, interconnected to two phases when the loads require 240 volts, and interconnected to three phases when the loads require three phase power. For example, the first phase of the power panel  10  may be supplying 70 amps, the second phase of the power panel  10  may be supplying 30 amps, and the third phase of the power panel  10  may be supplying 150 amps. This significant imbalance in the current supplied by the different phases is sub-optimal. For example, the greater the current levels the greater the voltage drop from the power source to the power panel, which may result in significant variations in the voltage levels provided to the power panel from the three phase power source. By monitoring the current (or power) provided from each phase using the sensors, the loads may be redistributed between the different phases to re-balance the loads. 
     What is desired, therefore, is an effective power monitoring system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a power panel with circuit breakers. 
         FIG. 2  illustrates circuit breakers, associated sensors, and a power monitor. 
         FIG. 3  illustrates a perspective view of a support for a set of current sensors. 
         FIG. 4  illustrates a side view of the support and sensors of  FIG. 3 . 
         FIG. 5  illustrates a top view of the support and sensors of  FIG. 3 . 
         FIG. 6  illustrates a top view of the support and sensors of  FIG. 2  together with circuit breakers. 
         FIG. 7  illustrates a power panel assembly with a power monitor and the support/current sensors of  FIG. 3 . 
         FIG. 8  illustrates a power monitoring system. 
         FIG. 9  illustrates a method of monitoring power with the power monitoring system of  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As a general matter, some existing panels are configured such that the system is configured to determine the single phase power for each respective current sensor for the entire panel. Similarly, some existing panels are configured such that the system is configured to determine the three phase power for each respective contiguous group of three sensors for the entire panel. Likewise, some existing panels are configured such that the system is configured to determine the two phase power for each respective contiguous group of two sensors for the entire panel. However, if the power panel has a mixture of single phase, two phase and/or three phase, 
     Upon reflection of the existing systems, the determination of three phase power requires the selection of three different current sensors, the selection of the corresponding voltage signals, the correlation of the current signals with the respective voltage signals, and subsequent calculation of the three phase power. The determination of two phase power requires the selection of two different current sensors, the selection of the corresponding voltage signals, the correlation of the current signals with the respective voltage signals, and subsequent calculation of the two phase power. The determination of single phase power requires the selection of a current sensor, the selection of the corresponding voltage signal, the correlation of the current signal with the voltage signal, and subsequent calculation of the single phase power. 
     Accordingly, in the event that a power panel includes a mixture of single phase, two phase, and/or three phase power, then the installer is left with measuring the power associated with each current transformer, then sending the data to an external general purpose computer to the power panel. The general purpose computer, in turn, based upon configuration information determines the power associates with the single phase, two phase, and three phase circuits. It is burdensome to route data cables from a power panel to a general purpose computer to do such calculations, and likewise maintain both the power panel and the general purpose computer. Moreover, electricians which are the primary installers of power panels and the electrical components contained therein and generally ill equipped to configure, install, and support an associated general purpose computer. 
     Referring to  FIG. 8 , a panel may include a mixture of single phase circuits  300 , two phase circuits  310 , and three phase circuits  320 . In some cases, the two phase circuits  310  are not necessarily adjacent current transformers, and similarly the three phase circuits  320  are not necessarily adjacent current transformers. In some cases, it is not necessary to measure the output of each of the current transformers because the power usage of a particular current transformer is of no particular interest. Thus, the bandwidth limitations and computational complexity may be reduced by selectively not measuring selected current transformers. 
     However, for a flexible system it was determined that it is desirable to measure the current from all of the current transformers. At a minimum, if not determining the power from all of the current transformers, then obtain the necessary data from current transformers for which power determinations are not needed. Thus, on a regular basis, the system should sense the current from each of the current transformers including one or more that is not necessary for subsequent power determinations together with corresponding voltage measurements. Based upon this measurement of data, the power meter calculates the power usage for each of the sensed current transformers. 
     Referring to  FIG. 9 , for each of the current transformers, including at least one current transformer for which a power measurement is not needed, the current measurements are received by the power meter  350 . In addition, the voltage is sensed for each of current transformers, typically a three phase voltage measurement  360 . The power meter is contained within the power panel for power calculation. The power meter then calculates the power  370  for each of the sensed current transformers by multiplication of the current times the voltage. For single phase circuits the power meter has thus determined the power usage. For multi-phase circuits, a set of preferences determines which single phase power determines should be subsequently combined to calculate the multi-phase power  380 . The system may account for a power factor, as desired. The system may calculate the power for particular multi-phase circuits without separately calculating the corresponding single phase circuits. The resulting power determinations are then provided  382  to an external computer system or power management system  325  via data channel  327 . In some cases, it is desirable by default to calculate one phase power that is subsequently not used by the external computer system or power management system. In this manner, the configuration of the power meter is simplified. The process of sensing and calculating is done on an ongoing basis. In some cases, the data is obtained from the voltage sensors and current sensors in a parallel fashion or a serial sampling fashion. 
     In an alternative embodiment the power factor, the voltage potential, and/or the current may be calculated, sensed, or otherwise measured for a single phase of a multi-phase load. The power monitor may then use the voltage potential and current, together with the power factor if desired, to calculate the power usage of a multi-phase load by presuming that the remaining phases have similar characteristics. For example, in a three phase system the remaining phases may be presumed to have approximately a 60 degree phase difference. Reusing power calculations for other phases reduces the computation complexity of the power monitor while maintaining relatively accurate power measurements. 
     In an alternative embodiment, the power factor of a multi-phase load may be determined based upon one of the voltages and one of the currents, both of which are preferably associated with the same phase. The power factor may then be used for all of the phases, if desired. Reusing the calculated power factor reduces the computational complexity of the power monitor while maintaining relatively accurate power measurements. 
     In an alternative embodiment, the power monitor may, if desired, separate multiple summed alternating voltage signals into their respective phases for power determination, typically by decomposition of the composite signal. 
     The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.