Patent Description:
Digital branch current monitors may incorporate data processing systems that can monitor a plurality of circuits and determine a number of parameters related to electricity consumption by the individual branch circuits or groups of circuits. A branch current monitor for measuring electricity consumption by respective branch circuits comprises a plurality of voltage and current transducers that are periodically read by the monitor's data processing unit which, in a typical branch current monitor, comprises one or more microprocessors or digital signal processors (DSP). For example, a branch current monitor from Veris Industries, Inc. enables up to ninety circuits to be monitored with a single meter and utilizes the MODBUS® RTU network communication interface to enable remote monitoring as part of a building or facility management system. The data processing unit periodically reads and stores the outputs of the transducers quantifying the magnitudes of current and voltage samples and, using that data, calculates the current, voltage, power, and other electrical parameters, such as active power, apparent power and reactive power that quantify the distribution and consumption of electricity. The calculated parameters are typically output to a display for immediate viewing or transmitted from the meter's communication interface to another data processing system, such as a building management computer for remote display or further processing, for example formulating instructions to the facility's automated equipment.

The voltage transducers of digital branch current monitors commonly comprise a voltage divider network that is connected to a conductor in which the voltage will be measured. The power distribution panel provides a convenient location for connecting the voltage transducers because typically each phase of the electricity is delivered to the power distribution panel on a separate bus bar and the voltage and phase is the same for all loads attached to the respective bus bar. Interconnection of a voltage transducer and the facility's wiring is facilitated by wiring connections in the power distribution panel, however, the voltage transducer(s) can be connected anywhere in the wiring that connects the supply and a load, including at the load's terminals.

The current transducers of digital power meters typically comprise current transformers that encircle each of the power cables that connect each branch circuit to the bus bar(s) of the distribution panel. <CIT>, discloses a branch current monitoring system that includes a plurality of current transformers mounted on a common support facilitating installation of a branch current monitor in a power distribution panel. Installation of current transformers in electrical distribution panels is simplified by including a plurality of current transformers on a single supporting strip which can be mounted adjacent to the lines of circuit breakers in the panel. The aforementioned branch current monitor from Veris Industries, Inc. is commonly used to monitor up to four strips of current sensors, each comprising <NUM> current transformers on a common support. In addition, the branch current monitor provides for eight auxiliary current transformer inputs for sensing the current flow in two <NUM>-phase mains with two neutrals and six voltage connections enabling voltage sensing in six bus bars of two <NUM>-phase mains.

<CIT> shows a system according to the preamble of claim <NUM>. <CIT> shows monitoring a conductor using a capacitive voltage sensor and an inductive current sensor. <CIT> shows obtaining separate voltage signals from a Rogowski coil at a conductor using a stray capacitance to the conductor and a switchable external capacitance. <CIT> shows voltage and current measurements for a primary conductor via a current transformer secondary winding.

With the power metering devices mentioned above, it is problematic to determine whether a load is "turned off" in some manner or if a circuit breaker has tripped. It is hence one object of the invention to provide an improved monitoring system.

Further details and advantages will become apparent from the following description with reference to the drawings, wherein <FIG> and the pertaining description are of exemplary nature for the characteristic aspect of the invention, while <FIG> and the pertaining description show a reference system not according to the invention, and the invention is defined in the claims.

Referring in detail to the drawings where similar parts are identified by like reference numerals, and, more particularly to <FIG>, a monitoring system has a capability of a branch current monitor <NUM> arranged to monitor the voltage and current in a plurality of branch circuits comprises, generally, a data processing module <NUM>, a current module <NUM> and a voltage module <NUM>. The branch current monitor <NUM> is preferably housed in a housing and/or the data processing module <NUM> is preferably housed in a housing and/or the current module <NUM> is preferably housed in a housing and/or the voltage module is preferably housed in a housing. In some embodiments, the branch current monitor and/or the data processing module and/or the current module and/or the voltage module includes one or more connectors suitable to detachably connect a separate power meter to sense electrical properties of the branch current monitor and/or the data processing module and/or the current module and/or the voltage module. The data processing module <NUM> comprises a data processing unit <NUM> which, typically, comprises at least one microprocessor or digital signal processor (DSP). The data processing unit <NUM> reads and stores data received periodically from the voltage module and the current module, and uses that data to calculate the current, voltage, power and other electrical parameters that are the meter's output. The resulting electrical parameters may be output to a display <NUM> for viewing at the meter or output to a communications interface <NUM> for transmission to another data processing system, such as a building management computer, for remote display or use in automating or managing facility functions. The data processing module may also include a memory <NUM> in which the programming instructions for the data processing unit and the data manipulated by the data processing unit may be stored. In addition, the branch current monitor typically includes a power supply <NUM> to provide power to the data processing unit and to the voltage and current modules.

The voltage module <NUM> includes one or more voltage transducers <NUM> each typically comprising a resistor network, a voltage sampling unit <NUM> to sample the output of the voltage transducers and convert the analog measurements to digital data suitable for use by the data processing unit and a multiplexer <NUM> that periodically connects the voltage sampling unit to selected ones of the voltage transducers enabling periodic sampling of the magnitude of the voltage at each of the voltage transducers. Typically, each phase of the electricity supplied to a distribution panel is connected to a bus bar <NUM> to which are connected the circuit breakers <NUM> that provide a conductive interconnection to each of the respective loads, by way of examples, a single-phase load 21A and a three-phase load 21B. Since the voltage and phase supplied to all commonly connected loads is the same, a meter for measuring three-phase power typically includes three voltage transducers 42A, 42B, 42C each connected to a respective bus bar 23A, 23B, 23C. A clock <NUM>, which may be included in the data processing unit, provides periodic timing signals to trigger sampling of the outputs of the voltage transducers by the voltage sampling unit. The voltage module may also include a voltage sensor memory <NUM> in which voltage sensor characterization data, including relevant specifications and error correction data for the voltage transducers are stored. If a portion of the voltage module requires replacement, a new voltage module comprising a voltage sensor memory containing sensor characterization data for the transducers of the new module can be connected to the data processing unit. The data processing unit reads the data contained in the voltage sensor memory and applies the sensor characterization data when calculating the voltage from the transducer data output by the replacement voltage module.

The current module <NUM> typically comprises a current sampling unit <NUM>, a multiplexer <NUM> and a plurality of current transducers <NUM> communicatively connected to respective sensor positions <NUM> of the current module. The multiplexer <NUM> sequentially connects the sampling unit to the respective sensor positions enabling the sampling unit to periodically sample the output of each of the current transducers <NUM>. The current sampling unit comprises an analog-to-digital converter to convert the analog sample at the output of a current transducer selected by the multiplexer, to a digital signal for acquisition by the data processing unit. The clock <NUM> also provides the periodic timing signal that triggers sampling of the current transducer outputs by the current sampling unit. The current module may also include a current sensor memory <NUM> in which are stored characterization data for the current transducers comprising the module. The characterization data may include transducer identities; relevant specifications, such as turns ratio; and error correction factors, for examples equations or tables enabling the phase and ratio errors to be related to a current permitting correction for magnetization induced errors. The characterization data may also include the type of transducers, the number of transducers, the arrangement of transducers and the order of the transducers' attachment to the respective sensor positions of the current module. At start up, the data processing unit queries the current sensor memory to obtain characterization data including error correction factors and relevant specifications that are used by the data processing unit in determining the monitor's output.

Referring also to <FIG>, and <FIG>, monitoring current in a plurality of branch circuits requires a plurality of current transducers, each one encircling one of the branch power cable(s) <NUM> that connect the power distribution panel to the load(s) of the respective branch circuit. Current sensing may be performed by an individual current sensor, such as the current transformer 54D, which is connected to the current module. On the other hand, a branch current monitor may comprise one or more sensor strips <NUM> each comprising a plurality of current sensors attached to a common support, such as sensors 54A, 54B, 54C.

The sensors <NUM> are preferably current transformers but other types of sensors may be used, inclusive of split-core transformers. Each current transformer comprises a coil of wire wound on the cross-section of a toroidal metallic or non-metallic core. The toroidal core is typically enclosed in a plastic housing that includes an aperture <NUM> enabling the power cable <NUM> to be extended through the central aperture of the core. The openings <NUM> defined by the toroidal cores of the transformers are preferably oriented substantially parallel to each other and oriented substantially perpendicular to the longitudinal axis <NUM> of the support <NUM>.

To provide a more compact arrangement of sensors, the sensors <NUM> may be arranged in substantially parallel rows on the support and the housings of the sensors in adjacent rows may be arranged to partially overlap in the direction of the longitudinal axis of the support. To facilitate routing the power cables of the branch circuits through the cores of the current transformers, the common support maintains the current transformers in a fixed spatial relationship that preferably aligns the apertures of the toroidal coils directly opposite the connections of the power cables <NUM> and their respective circuit breakers <NUM> when the strip is installed in a distribution panel <NUM>. For protection from electrical shock, a transient voltage suppressor <NUM> may be connected in parallel across the output terminals of each sensor to limit the voltage build up at the terminals when the terminals are open circuited.

The transducer strip <NUM> may include the current sensor memory <NUM> containing characterization data for the current transformers mounted on the support <NUM>. The current sensor memory may also include characterization data for the transducer strip enabling the data processing unit to determine whether a transducer strip is compatible with the remainder of the meter and whether the strip is properly connected to the data processing module. Improper connection or installation of an incompatible transducer strip may cause illumination of signaling lights or a warning message on the meter's display. In addition, the transducer strip <NUM> may comprise a current module of the power meter with one or more current transformers <NUM>, the multiplexer <NUM>, the current sampling unit <NUM> and the current sensor memory all mounted on the support <NUM>. A connector <NUM> provides a terminus for a communication link <NUM> connecting the current transducer strip (current module) to the data processing module <NUM>.

The branch current monitor may also include one or more errant current alarms to signal an operator or data processing system that manages the facility or one or more of its operations of an errant current flow in one of the monitored branch circuits. When a current having a magnitude greater or lesser than a respective alarm current limit is detected in one of the branch circuits an alarm annunciator is activated to notify the operator or another data processing system of the errant current flow. An alarm condition may be announced in one or more ways, including, without limitation, periodic or steady illumination of a light <NUM>, sounding of an audible alarm <NUM>, display of a message on the meter's display <NUM> or transmission of a signal from the communications interface <NUM> to a remote computer or operator.

A commercial power distribution panel commonly supplies a substantial number of branch circuits and a branch current monitor for a distribution panel typically includes at least an equal number of current transformers. Referring to <FIG>, an exemplary electrical distribution panel includes two three-phase mains 104A, 104B which respectively are connected to main circuit breakers 106A, 106B. Each of the phases of each main is connected to a bus bar 23A, 23B, 23C. The three bus bars extend behind each of two rows of branch circuit breakers <NUM> that respectively conductively connect one of the bus bars to a conductor <NUM> that conducts current to the branch circuit's load(s).

A single phase load is connected to single bus bar, a two-phase load is typically connected to two adjacent circuit breakers which are connected to respective bus bars and a three-phase load is typically connected to three adjacent circuit breakers which are each connected to one of the three bus bars. Typically, a two-phase load or three-phase load is connected to the appropriate number of adjacent circuit breakers in the same row. The exemplary distribution panel has connections for <NUM> branch circuit conductors which can be monitored by a branch current monitor produced by Veris Industries, Inc. The branch current monitor monitors the current, voltage and energy consumption of each circuit of the distribution panel, including the mains. The accumulated information can be transmitted to a remote consumer through a communications interface or viewed locally on a local display. Data updates occur approximately every two seconds and as a circuit approaches user configured thresholds, alarms are triggered by the monitor.

As illustrated in <FIG>, the main acquisition circuit board <NUM> of the branch current monitor <NUM> is connectable to as many as four current transformer strips or support units 80A, 80B, 80C, 80D each supporting <NUM> current transformers. The transformers of the support units are connectable to the data processing unit of the branch current monitor by communication links <NUM> comprising multi-conductor cables. In addition, the branch current monitor includes connections for six auxiliary current transformers <NUM> which are typically used to monitor the current in the mains. Since the voltage and phase are common for all loads connected to a bus bar, the branch current monitor also includes six voltage connections <NUM>.

A data channel <NUM> connected to the communications interface enables transmission of data captured by the branch current monitor to other data processing devices that are part of a building management system or other network. The main acquisition circuit board <NUM> is preferably housed in a housing. In some embodiments, the main acquisition circuit board <NUM> includes one or more connectors suitable to detachably connect a separate power meter to sense electrical properties of the current and/or voltage being sensed. The strips or support units may be housed in a housing, in whole or in part. In some embodiments, the strips or support units includes one or more connectors suitable to detachably connect a separate power meter to sense electrical properties of the current and/or voltage being sensed.

The branch current monitor is installed in the distribution panel by mounting the current transformer strips to the panel adjacent to the rows of circuit breakers and by passing each of the branch circuit conductors <NUM> through a central aperture in one of the toroidal current transformers and connecting the conductors to the respective circuit breakers. The main acquisition board <NUM> is attached to the electrical panel and the multi-conductor cables <NUM> are connected to the board. The main acquisition board <NUM> is preferably housed in a housing. The mains conductors are passed through the apertures in the auxiliary current transformers and the auxiliary current transformers are connected to the main acquisition board. The voltage taps are connected to respective bus bars and to the main acquisition board. The data channel <NUM> is connected and the branch current monitor is ready for configuration.

Referring to <FIG>, in another embodiment, the strip unit may include a set of connectors at each general location a current sensor is desired. A current transformer may be included with a flexible wire within a connector at the end thereof and a connector on the strip unit. The current transformer is then detachably connectable to the connector of the strip unit. The current transformer may include a solid core or a split core, which is more readily interconnected to existing installed wires. If desired, the strip unit may include one or more power calculation circuits supported thereon. For example, the data from the current transformers may be provided to the one or more power calculation circuits supported thereon together with the sensed voltage being provided by a connector from a separate voltage sensor or otherwise voltage sensed by wires interconnected to the strip unit or signal provided thereto. As a result of this configuration, the connector may provide voltage, current, power, and other parameters to the circuit board. All or a portion of the strip unit is preferably housed in a housing. The strips unit may be housed in a housing, in whole or in part. In some embodiments, the strip unit includes one or more connectors suitable to detachably connect a separate power meter to sense electrical properties of the strip unit.

Referring to <FIG>, another embodiment includes a set of one or more connector boards <NUM> in addition to or as an alternative to the strip units. Each of the connector boards may include a set of connectors <NUM> that may be used to interconnect a current transformer thereto. Each of the connector boards may include a connector <NUM> that interconnects the connector board to the circuit board <NUM>. Each of the connector boards may be labeled with numbering, such as <NUM> through <NUM> or <NUM> through <NUM>, and <NUM> through <NUM> or <NUM> through <NUM>. Often groups of three connectors are grouped together as a three-phase circuit, thus connectors <NUM> through <NUM> may be <NUM> three-phase circuits. For example, the connector board with the number of <NUM> through <NUM> may be intended to be connected to connector A. For example, the connector board with the numbers of <NUM> through <NUM> may be intended to be connected to connector B. All or a portion of the connector board is preferably housed in a housing. In some embodiments, the connector board includes one or more connectors suitable to detachably connect a separate power meter to sense electrical properties of the connector board.

Referring to <FIG>, it was determined that a particular load may have many operational and non-operational states associated with it. For example, in an operational state a particular load may be consuming an insubstantial amount of power, such as no power, when the load is not being used or otherwise in an idle state. When a particular load is consuming an insubstantial amount of power, the current sensed on one or more power conductors (such as one conductor for a single phase load, such as two conductors for a two phase load, and such as three conductors for a three-phase load) will be zero or otherwise an insubstantial amount. In such case, the amount of current sensed will be substantially lower than a value that would be associated with normal operation of the load. However, while the particular load is consuming an insubstantial amount of power, the voltage level sensed to the load from the mains, such as by a voltage sensors interconnected to the main power lines to the panel, will remain at a level typically associated with normal operation of the load. For example, this may be generally <NUM> volts, generally <NUM>, volts, or otherwise. Unfortunately, it is problematic to determine if a voltage source is no longer providing a suitable voltage to a particular load or otherwise a circuit breaker has tripped thereby inhibiting a suitable voltage from being provided to the load.

Referring to <FIG>, for example, in a non-operational state a particular load may be consuming an insubstantial amount of power, such as no power, when the load is not operational or in an alarm related condition. When a particular load is consuming an insubstantial amount of power, the current sensed on one or more power conductors (such as one conductor for a single phase load, such as two conductors for a two phase load, and such as three conductors for a three-phase load) will be zero or otherwise an insubstantial amount. In such case, the amount of current sensed will be substantially lower than a value that would be associated with normal operation of the load such as zero. However, while the particular load is consuming an insubstantial amount of power, the voltage level sensed to the load on the respective conductor, such as by a voltage sensor, will be zero or an insubstantial amount. In such case, the amount of voltage sensed will be substantially lower than a value that would be associated with normal operation of the load such as zero. When both the current sensed and the voltage sensed for a particular load, sensed on the one or more power conductors for a load, it may indicate an alarm condition that would be the result of tripping one or more circuit breakers to the load. In this manner, by sensing the voltage on the conductors to the loads, a more detailed assessment may be made.

When the operational state is determined for a particular load (e.g., insubstantial current level combined with a normal load level), and it is desirable to inspect the operation of the particular load, a technician may be dispatched to the load to determine what the likely cause of the operational state is. When the non-operational state is determined for a particular load (e.g., insubstantial current level combined with an insubstantial voltage level), and it is desirable to inspect the operation of the particular load, a technician may be dispatched to the circuit panel to reset the circuit breaker or otherwise determine the source determining the operational state.

A power meter may provide an indication of the operational and non-operational state of one or more loads, such as whether the device is in an alarm condition and/or a particular type of alarm condition and/or a warning condition. The indication may be provided as a signal to a controller and/or as a register within the power meter that is accessible by the power meter or a remote controller, and/or a visual signal, and/or audio signal, and/or any other manner.

After further consideration it was determined that it is desirable to measure the voltage to each load on the load side of the circuit breakers of the panel using a non-contact voltage sensor. In this manner, it can be more readily determined whether the voltage to a particular load is substantial or insubstantial, indicating whether the circuit breaker has tripped or otherwise power is not being provided to the panel (or otherwise the circuit breaker). While a physical connection, such as a tap, may be interconnected to each wire to obtain an accurate voltage measurement to a respective load, such as would be desirable for a power meter calculation, this is cumbersome to install and may result in safety concerns. It was determined that in order to determine whether a substantial or insubstantial voltage is being provided to a particular load a considerably less accurate voltage measurement technique may be used, namely, the non-contact voltage sensing technique. The non-contact voltage sensing technique is generally considered insufficiently accurate for accurate power measurement determinations. While such a non-contact voltage sensing technique is generally insufficiently accurate for determining an accurate power usage, it is sufficiently accurate to determine a more binary determination, namely, whether or not a substantial voltage is being provided to a particular load.

Referring to <FIG>, it is desirable for a current transformer strip <NUM> to include non-contact voltage sensors 604A, 604B, 604C, etc. associated with each of the sensors 602A, 602B, 602C, etc. In this manner, each of the non-contact voltage sensors is associated with a respective conductor associated with the respective current transformer. Each of the non-contact voltage sensors may be electrically interconnected to the support <NUM> with a wire 608A, 608B, 608C, etc. with each wire electrically interconnected to respective traces supported on the support. The respective traces supported on the support are electrically interconnected to one of the connectors <NUM> of the current transformer strip. As illustrated in <FIG>, there exists a one to one relationship between a respective current sensor and non-contact voltage sensor pair and a corresponding conductor associated therewith. Alternatively, the non-contact voltage sensors may be supported by the support, rather than directly on the current sensor, and each of which is preferably aligned with a corresponding conductor to a load.

Referring again to <FIG>, the connectors are in turn electrically interconnected to the data processing module <NUM>, preferably using the communication link <NUM>, to provide sensor data from respective non-contact voltage sensors to the data processing module <NUM>. The data processing module <NUM> may likewise receive data from each of the respective current sensors to indicate the current levels in the corresponding conductors. The data processing module may include six auxiliary current transformers <NUM> which are typically used to monitor the current in the mains, if desired. The branch current monitor may also include six voltage connections <NUM> attached to the mains typically used to monitor the voltage in the mains, if desired.

In general, non-contact voltage sensors operate by detecting the changing electric field around objects conducting an alternating current ("AC"). The non-contact voltage sensors do not actually make direct contact with the conductor to achieve this. The non-contact voltage sensor detects the voltage through capacitive coupling. For example, a capacitor normally has two conductors that are separated by a non-conductor (known as a dielectric). If an AC voltage is connected across the capacitor, an AC current will flow across the dielectric. This forms an AC circuit, even though there is typically not an actual wire completing the circuit. In the case of the conductor to the load conducting an electric AC current, the conductor acts as one side of a capacitor. The other side of the capacitor is the conductive member of the non-contact voltage sensor. The air between the conductive member and the conductor acts as the dielectric. Hence a capacitor is formed between the conductive member and the conductor.

Referring to <FIG>, a particular load may have many operational and non-operational states associated with it, which may be determined, based upon (at least in part) the non-contact voltage sensor(s). For example, in an operational state a particular load may be consuming an insubstantial amount of power, such as no power, when the load is not being used or otherwise in an idle state. When a particular load is consuming an insubstantial amount of power, the current sensed on one or more power conductors (such as one conductor for a single phase load, such as two conductors for a two phase load, and such as three conductors for a three-phase load) will be zero or otherwise an insubstantial amount. In such case, the amount of current sensed will be substantially lower than a value that would be associated with normal operation of the load. However, while the particular load is consuming an insubstantial amount of power, the voltage level sensed to the load, such as by non-contact voltage sensors interconnected to the conductors to the loads, will remain at a level typically associated with normal operation of the load. For example, this may be generally <NUM> volts, generally <NUM>, volts, or otherwise. Alternatively, while the particular load is consuming an insubstantial amount of power, the voltage level sensed to the load, such as by non-contact voltage sensors interconnected to the conductors to the loads, will be lower at a level typically associated with non-operation of the load. For example, this may be generally <NUM> volts, or otherwise. The non-contact voltage sensor is particularly suitable for determination of a difference between a substantial voltage level and an insubstantial voltage level.

Referring to <FIG>, in another embodiment a current transformer strip <NUM> may include non-contact voltage sensors 704A, 704B, 704C, etc. each of which is associated with one of the current sensors 702A, 702B, 702C, etc. The non-contact voltage sensors preferably include a generally planar conductive film <NUM> positioned in the interior of the opening defined by the respective current sensors (e.g., iris). In this manner, each of the non-contact voltage sensors is associated with a respective conductor associated with a respective current transformer. Each of the non-contact voltage sensors may be electrically interconnected to the support <NUM> with a respective wire 708A, 708B, 708C, etc. with each wire electrically interconnected to respective traces supported on the support. The respective traces supported on the support are electrically interconnected to one of the connectors <NUM> of the current transformer strip <NUM>. As illustrated in <FIG>, there exists a one to one relationship between a respective current sensor and non-contact voltage sensor pair, and a corresponding conductor associated therewith. The non-contact voltage sensors may likewise be included with the embodiment illustrated in <FIG>.

Referring to <FIG>, in another embodiment a current transformer strip <NUM> may include non-contact voltage sensors 804A, 804B, 804C, etc. each of which is associated with a respective one of the current sensors 802A, 802B, 802C, etc. The non-contact voltage sensors preferably include a generally planar conductive film <NUM> positioned around the exterior of the respective current sensors. In this manner, each of the non-contact voltage sensors is associated with a respective conductor associated with a respective current transformer. Each of the non-contact voltage sensors may be electrically interconnected to the support <NUM> with a wire 808A, 808B, 808C, etc. with each wire electrically interconnected to respective traces supported on the support. The respective traces supported on the support are electrically interconnected to one of the connectors <NUM> of the current transformer strip <NUM>. As illustrated in <FIG>, there exists a one to one relationship between a respective current sensor and non-contact voltage sensor pair, and a corresponding conductor associated therewith. The non-contact voltage sensors may likewise be included with the embodiment illustrated in <FIG>.

Referring to <FIG>, an exemplary circuit topology for the current measurement and the non-contact voltage measurement is illustrated. A current sensor <NUM> may include a wire wound on a toroidal core where the corresponding conductor <NUM> extends through an opening defined therein. The current sensor may be any suitable type of current sensor, including for example, a current transformer, a low voltage current transformer, a Rogowski coil current transformer, a Rogowski coil current transformer constructed on a circuit board, a fluxgate current transformer, a half effect current transformer, etc. The current transformer <NUM> may be electrically interconnected to a burden impendence R1 <NUM>, which is preferably a relatively small resistance, such as less than <NUM>Ω, more preferably less than <NUM>Ω, and more preferably less than <NUM>Ω. The burden impedance R1 <NUM> may be interconnected to a voltage reference <NUM>, such as a neutral voltage reference or ground (e.g., earth) voltage reference. The burden impedance R1 <NUM> may also be interconnected to an analog-to-digital converter <NUM><NUM>, which includes a Vref input <NUM> referenced to the voltage reference <NUM>. The analog-to-digital converter <NUM><NUM> may provide a digital output <NUM> representative of the current levels in the corresponding conductor <NUM>. In some embodiments, the current sensing circuit may include dual burden resistors with a central voltage reference with the analog-to-digital converter <NUM> operating in a differential mode. When sensing the output of the current sensor, the digitization is preferably performed substantially continuously. Other current sensor topologies may likewise be used, as desired.

The non-contact voltage sensor may include a conductive member <NUM> that is maintained in proximity to the current sensor <NUM> and/or the conductor <NUM>, where the conductive member <NUM> is one of the plates of a capacitive sensing structure. The conductive member <NUM> is preferably a flexible metal material, such as foil that preferably surrounds the iris of the current sensor or otherwise the current sensor itself or otherwise in proximity to the conductor. Other conductive structures may likewise be used, as desired. The conductive member <NUM> forms a capacitive structure with the conductor and senses a changing voltage field as a result of the changing current in the conductor. The conductive member <NUM> may be electrically interconnected to a burden impedance R2 <NUM>. The burden impedance R2 <NUM> is preferably a large resistance, such as in excess of <NUM> MΩ, more preferably in excess of <NUM> MΩ, and more preferably in excess of <NUM> MΩ. For example, the burden impedance R2 may be <NUM>,<NUM> times or more, <NUM>,<NUM> times or more, and/or <NUM>,<NUM> times or more than the burden impedance R1 <NUM>. The burden impedance R2 preferably has such a large impendence since the capacitance resulting from the conductive member <NUM> is very low.

The burden impedance R2 <NUM> may be interconnected to the voltage reference <NUM>, such as a neutral voltage reference or ground (e.g., earth) voltage reference. The burden impedance R2 <NUM> may also be interconnected to an analog-to-digital converter <NUM><NUM>, which includes a Vref input <NUM> referenced to the voltage reference <NUM>. The analog-to-digital converter <NUM><NUM> may provide a digital output <NUM> representative of the voltage levels in the corresponding conductor <NUM>. In some embodiments, the non-contact sensing circuit may include dual burden resistors with a central voltage reference with the analog-to-digital converter <NUM> operating in a differential mode. Other voltage sensor topologies may likewise be used, as desired, including the current transformer itself as the conductive member.

The output of the non-contact voltage sensor <NUM> is principally used for determining, at least in part, the status of the circuit breakers and/or alarm condition. When determining the status of the circuit breakers and/or alarm condition the digitization for a particular non-contact voltage sensor is preferably not performed substantially continuously (e.g., at a rate substantially less than the analog to digital converter <NUM>). In this manner, there may be periodic periods of time during which the analog to digital converter <NUM> is not determining the status of the voltage for the non-contact voltage sensor <NUM>. With the sampling for any particular non-contact voltage sensor being relatively infrequent, by using a multiplexer, the same analog-to-digital converter <NUM> may be used for a plurality of different non-contact voltage sensors by temporally sampling different non-contact voltage sensors at different times.

In the configuration illustrated in <FIG>, the current sensing and the non-contact voltage sensing may occur at the same time, since each of the current sensing and the non-contact voltage sensing are independent of one another.

Referring to <FIG>, in general, current sensing may be used to quantify a phase voltage loss. The system typically has data indicating the value of the breaker <NUM>. Based upon receiving a signal from the current sensor <NUM>, if the current temporarily spikes over the breaker value <NUM>, followed by a loss of voltage (e.g., insubstantial voltage value) <NUM> and a loss of current (e.g., insubstantial current value) <NUM>, then the event may be characterized as an overcurrent breaker opening with an alarm being indicated <NUM>. Contrary, if a phase loss indicated by an insubstantial non-contact voltage value <NUM> and an insubstantial current value <NUM>, is not preceded by a current spike over the breaker value <NUM>, the event may be due to a circuit being manually turned off or a further upstream breaker opening <NUM>, and the event is preferably not characterized with an alarm. The event <NUM> may be logged in the system and a warning indictor being signaled.

To determine if a voltage is present or not, the observed voltage signal from the capacitive sensor is preferably calibrated. The signal from the capacitive sensor is larger when the voltage is present, but the amplitude tends to change with the position of the wire, the diameter of the wire, the ambient temperature, drifts over time, etc. When the voltage on the wire is not present, a smaller waveform may still be sensed from the capacitive sensor due to capacitive coupling from adjacent wires. It is preferable to distinguish between these two states.

To more accurately determine when the voltage has been lost (or otherwise substantially reduced), it is desirable to know the amplitude of the voltage signal when voltage is known to be present. The presence of the voltage may be determined based upon the current. If the current is present, the system may assume that the voltage is also present. With the voltage presumed to be present, the system periodically measures and records the amplitude of the voltage signal from the capacitive sensor.

If the observed voltage signal is substantially reduced from a previous "known" present signal, it may be presumed that the phase voltage has been lost.

Referring to <FIG>, another exemplary circuit topology for the current measurement and the non-contact voltage measurement is illustrated. A current sensor <NUM> may include a wire wound on a toroidal core where the corresponding conductor <NUM> extends through an opening defined therein. The current sensor may be any suitable type of current sensor, including for example, a current transformer, a low voltage current transformer, a Rogowski coil current transformer, a Rogowski coil current transformer constructed on a circuit board, a fluxgate current transformer, a half effect current transformer, etc. The current transformer <NUM> may be electrically interconnected to a burden impendence R1 <NUM>, which is preferably a relatively small resistance, such as less than <NUM>Ω. The burden impedance R1 <NUM> may be interconnected to a voltage reference <NUM>, such as a neutral voltage reference or ground (e.g., earth) voltage reference. The burden impedance R1 <NUM> may also be interconnected to an analog-to-digital converter <NUM><NUM>, which includes a Vref input <NUM> referenced to the voltage reference <NUM>. The analog-to-digital converter <NUM><NUM> may provide a digital output <NUM> representative of the current levels in the corresponding conductor <NUM>. In some embodiments, the current sensing circuit may include dual burden resistors with a central voltage reference with the analog-to-digital converter <NUM> operating in a differential mode. When sensing the output of the current sensor, the digitization is preferably performed substantially continuously. Other current sensor topologies may likewise be used, as desired.

The current sensor typically includes a coil that wraps around the core of the current sensor. It was determined that the coil wrapped around the core has sufficient capacitance to the conductor <NUM> that may be measured, which may be used as the basis of a non-contact voltage sensor. In this embodiment, the non-contact voltage sensor would not include a separate conductive member that is maintained in proximity to the current sensor and/or the conductor, where the conductive member would have been one of the plates of a capacitive sensing structure. The capacitive structure formed by the current sensor itself senses a changing voltage field as a result of the changing current in the conductor. The current sensor <NUM> may be electrically interconnected to a burden impedance R2 <NUM>. The burden impedance R2 <NUM> is preferably a large resistance, such as in excess of <NUM> MΩ. For example, the burden impedance R2 may be <NUM>,<NUM> times or more, <NUM>,<NUM> times or more, and/or <NUM>,<NUM> times or more than the burden impedance R1 <NUM>. The burden impedance R2 preferably has such a large impendence since the capacitance resulting from the current sensor <NUM> is very low.

The burden impedance R2 <NUM> may be interconnected to the voltage reference <NUM>, such as a neutral voltage reference or ground (e.g., earth) voltage reference. The burden impedance R2 <NUM> may also be interconnected to the analog-to-digital converter <NUM><NUM>, which includes the Vref input <NUM> referenced to the same voltage reference <NUM>. The analog-to-digital converter <NUM><NUM> may provide the digital output <NUM> representative of the voltage levels in the corresponding conductor <NUM>, as described below. In some embodiments, the non-contact sensing circuit may include dual burden resistors with a central voltage reference with the analog-to-digital converter operating in a differential mode. Other voltage sensor topologies may likewise be used, as desired, including the current transformer itself as the conductive member.

The burden impedance R1 <NUM> and the burden impedance R2 <NUM> are both interconnected to the same terminal of the current transformer. To permit sensing two different measurements, namely a current measurement and a non-contact voltage measurement, a switch <NUM> may be interconnected between the terminals of the burden impedance R2 <NUM>. The switch <NUM> includes two operational modes. The first operational mode of the switch <NUM> is a closed position, one side of the burden impedance R1 <NUM> is connected to the neutral reference and the burden impedance R2 <NUM> is shorted out. In the first operational mode, the circuit operates as a current sensing circuit with the output <NUM> being representative of the current levels sensed by the current transformer <NUM>.

The second operational mode of the switch <NUM> is an open position, where the one side of the burden impedance R1 <NUM> is interconnected to one side of the burden impedance R2 <NUM>. The analog to digital converter <NUM><NUM> then digitizes the voltage across the burden impedance R2 caused by the voltage from the conductor <NUM> being capacitively coupled to the coil. The much smaller value of burden impendence R1 <NUM> effectively shorts the two coil leads together, such that the burden impendence R2 <NUM> sees the common mode voltage on those leads. As it may be observed, the neutral is effectively "floated" so that the capacitance may be sensed.

The majority of the time, the circuit preferably operates in the current sensing mode with the switch <NUM> closed. If the output of the analog to digital converter <NUM><NUM> indicates that the current flow has gone to <NUM> (or substantially zero), then the switch <NUM> is opened. With the switch <NUM> opened, the analog to digital converter <NUM><NUM> may determine if the voltage has gone to zero (or substantially zero). If the analog to digital converter <NUM><NUM> indicates that the current is flowing normally, then the voltage may be presumed to be non-zero, and there is no need to change the state of the switch <NUM> to sense the voltage.

In addition, the circuit may include a Nyquist resistor-capacitor low pass filter between the burden impendence R1 <NUM> and the analog to digital converter <NUM><NUM>. Such a Nyquist resistor-capacitor low pass filter preferably has a sufficiently low impedance that it is a relatively small fraction of the input impedance of the analog to digital converter <NUM><NUM>. In addition, the burden impedance R2 <NUM> is preferably much higher than the input impedance of the analog to digital converter <NUM><NUM>.

The neighboring conductor(s) <NUM> may also have a capacitance to the current transformer <NUM>. By including a neutral referenced shielding <NUM> around the current transformer <NUM> will reduce the capacitive coupling from neighboring conductor(s) <NUM>. In addition, selected conductors may include twisted pairs to further reduce the effects of capacitive coupling and noise from external sources.

Referring to <FIG> another non-contact voltage and current sensing circuit topology is illustrated. With the pair of switches in position <NUM> a current sensing mode is used. With the pair of switches in position <NUM> the capacitive non-contact voltage sensing mode is used.

In general, to reduce the cross-talk from nearby conductors to loads, the non-contact voltage sensor is preferably referenced to a neutral voltage and/or a ground voltage. Moreover, the current sensor depending on the configuration tends to act as a shield for the non-contact voltage sensor.

In general, for solid core current sensors, the non-contact voltage sensor preferably wraps around the entire iris.

In general, for split core current sensors, the non-contact voltage sensor preferably wraps around a majority of the iris.

It is to be understood that the current sensor may be any suitable structure, including non-toroidal cores.

By comparing signals from neighboring voltage sensors, the effect of cross talk between the non-contact voltage sensors may be compensated.

Typically, the spacing between conductors is approximately <NUM>, <NUM>, <NUM> or <NUM>.

In some embodiments, the second burden impendence R2 may be omitted, especially if a sufficiently high input impedance analog to digital converter.

In some embodiments, the configuration may include a single current transformer (such as a split core current transfer) together with a non-contact current sensor (or the capacitance of the current transformer itself) together with the sensing electronics to permit individualized measurements. In addition, multiple such single current transformers may be used together, such as two for two phase circuits or three for three-phase circuits, to permit measurements of multi-phase circuits.

The non-contact voltage sensing technology is likewise applicable to a single current sensor (or one or more non-contact voltage sensor technology associated with a plurality of current sensors). Preferably, the current sensor is interconnected to associated electronics using a shielded twisted pair of wires. The twisted pair of wires may be interconnected to the terminals of the current sensor. The shield wire of the twisted pair may, for example, be interconnected to the digital converter (neutral) reference <NUM> on the meter and on the shield <NUM> of the current transformer. For example, the non-contact voltage sensing technology may be associated with a single current sensor and make a determination of the status of the voltage level therein. The determination of the status of the voltage level may also be used together with current measurements to determine the status of an associated circuit breaker.

Referring to <FIG>, one type of Rogowski coil <NUM> is generally fabricated from a conductor <NUM>, which may include a wire, which is coiled or wound on a substantially non-magnetic core, which may be, for example, air or a substantially non-magnetic material. The <NUM> coil may be placed around a conductor or conductors <NUM> whose current(s) is to be measured with the coil <NUM>. A primary current flowing through the conductor <NUM> generates a magnetic field that, in turn, induces a voltage in the coil <NUM>. A voltage output v(t) of the coil <NUM> is generally governed by the following Equation:
<MAT>
where µo, is the magnetic permeability of free space, µr is the relative permeability (the ratio of the permeability of the coil <NUM> to the permeability of free space µo), n is the winding density (turns per unit length), S is the cross sectional area of the core in the Rogowski coil, and M represents the mutual reactance or mutual coupling between the coil <NUM> and the conductor <NUM>. In a similar manner, the output of the coil may be a current signal i(t).

For an ideal Rogowski coil <NUM>, M is independent of the location of the conductor <NUM> within the coil <NUM>. The Rogowski coil output voltage v(t) is proportional to the rate of change of the measured current i(t) flowing in the conductor <NUM>. The coil output voltage v(t) may be integrated to determine the current i(t) in the conductor <NUM>.

Referring to <FIG>, the Rogowski coil and its secondary leads may include a shielded coaxial cable <NUM> that is connected to a coil <NUM>. Referring to Fig. 4B, a twisted pair wire <NUM> is connected to the coil <NUM>. The twisted wires carry equal but opposite signals and are less susceptible to noise issues and cross talk issues from adjacent signal conductors. The shielded cable <NUM> and the twisted pair wire <NUM> provide protection against noise and electromagnetic influences in the environment of the coils <NUM>.

Referring to <FIG>, the Rogowski coil may be constructed on a single side of a substrate or on two sides of a substrate, such as printed circuit board. The Rogowski coil may include a shield layer over all or a portion of the traces (not shown). Alternatively, the Rogowski coil may include a shield layer on one or more surfaces of the substrate at a location exterior to the traces (not shown).

As described, the Rogowski coil may be flexible in shape in order to readily open and close it on the conductor to be measured. This flexibility is especially useful when installing the Rogowski coil around conductors with limited or irregular space constraints.

As a general matter, the shield may extend around the entire Rogowski coil, extend around a portion of the Rogowski coil, or may extend around the interior portion of the Rogowski coil. In this manner, the shield may be used as a portion of a non-contact voltage sensor in a manner as indicated in <FIG> and <FIG>.

Claim 1:
A monitoring system (<NUM>) comprising:
(a) a current sensor suitable to sense a current level in a power conductor (L1) and providing a first signal indicating said current level;
(b) a non-contact voltage sensor suitable to sense a voltage level in said power conductor (L1) and said non-contact voltage sensor providing a second signal indicating said voltage level, where there is a respective pair of said current sensor and said non-contact voltage sensor associated with said power conductor;
(c) a monitoring device (<NUM>) that receives said first signal and receives said second signal, characterized in that,
said monitoring device (<NUM>) provides an indication of whether a circuit breaker (<NUM>) has tripped based upon said first signal and whether said second signal indicates an insubstantial voltage level for said power conductor, wherein
(d) the monitoring device (<NUM>) is configured to determine whether a corresponding circuit breaker for said power conductor (L1) is tripped based upon said first signal being greater than a threshold and subsequently said first signal indicating a corresponding current level and said second signal are insubstantial.