Patent Grant
9829519
Field
The disclosed concept relates generally to electric power or energy meters in polyphase electric power systems, and more particularly to the commissioning and diagnosis of voltage sensors and current sensors under different wiring configurations for branch circuit monitoring systems used in polyphase electric power systems.
Background Information
In a branch circuit monitoring system, a service panel typically has bus bars that have polyphase voltages that can be measured using voltage sensors. In addition, the panel also has multiple main current sensors on the bus bars. Furthermore, the service panel can have branches and associated branch circuit current sensors. For proper metering, it is critical that those voltage and current sensors be configured correctly. Incorrect configurations often involve voltage sensors wired to wrong phases, branch circuit current sensors associated with wrong phases, or branch circuit current sensors incorrectly grouped.
A conventional approach for commissioning and diagnosing a branch circuit monitoring system is based on an understanding of the physical layout of the system and the values measured by the voltage and current sensors, which values are used to calculate real, reactive, and apparent power values. Branch circuit current sensors are grouped based on the physical layout, which are used to calculate branch power. A failure in the understanding of the physical layout of the system often results in an incorrect configuration. Incorrect configurations may produce similar real, reactive, apparent, and branch power values.
In one embodiment, a method for a branch current monitoring system employing a 2-Phase Wye, a Single-Phase 3-Wire or a Single-Phase 2-Wire wiring configuration is provided, wherein the branch current monitoring system has at least a first phase. The method includes obtaining a voltage measurement using a voltage sensor associated with the first phase, obtaining a current measurement using a branch circuit current sensor, wherein the branch circuit current sensor is intended to measure a phase current of the first phase, determining a phase angle between the voltage measurement and the current measurement, and using the phase angle and a set of rules including a plurality of predetermined rules to identify at least one phase association and at least one polarity for the branch circuit current sensor.
In another embodiment, a branch circuit meter module for a branch current monitoring system employing a 2-Phase Wye, a Single-Phase 3-Wire or a Single-Phase 2-Wire wiring configuration is provided, wherein the branch current monitoring system has at least a first phase. The branch circuit meter module includes a control system, wherein the control system stores and is structured to execute a number of routines. The number of routines are structured to receive a voltage measurement from a voltage sensor associated with the first phase, receive a current measurement from a branch circuit current sensor, wherein the branch circuit current sensor is intended to measure a phase current of the first phase, determine a phase angle between the voltage measurement and the current measurement, and use the phase angle and a set of rules including a plurality of predetermined rules to identify at least one phase association and at least one polarity for the branch circuit current sensor.
In another embodiment, a method for an electric power system having at least a first phase, a main current sensor structured to measure a main current of the first phase and a main voltage sensor structured to measure a main voltage of the first phase is provided. The method includes identifying that each of a plurality of branch circuit current sensors is associated with the first phase using a phase angle between a voltage measured by the main voltage sensor and a current measured by the branch circuit current sensor, and determining whether each of the plurality of branch circuit current sensors has been properly identified as being associated with the first phase by: determining a total branch real power quantity and a total branch reactive power quantity for the plurality of branch circuit current sensors using the voltage measured by the main voltage sensor and the current measured by the branch circuit current sensor; determining a total main real power quantity and a total main reactive power quantity for the first phase using measurements made by the main current sensor and the main voltage sensor; and comparing the total branch real power quantity to the total main real power quantity and the total branch reactive power quantity to the total main reactive power quantity.
In still another embodiment, a branch circuit meter module for an electric power system having at least a first phase, a main current sensor structured to measure a main current of the first phase and a main voltage sensor structured to measure a main voltage of the first phase is provided. The branch circuit meter module includes a control system, wherein the control system stores and is structured to execute a number of routines. The number of routines are structured to identify that each of a plurality of branch circuit current sensors is associated with the first phase using a phase angle between a voltage measured by the main voltage sensor and a current measured by the branch circuit current sensor; and determine whether each of the plurality of branch circuit current sensors has been properly identified as being associated with the first phase by: determining a total branch real power quantity and a total branch reactive power quantity for the plurality of branch circuit current sensors using the voltage measured by the main voltage sensor and the current measured by the branch circuit current sensor; determining a total main real power quantity and a total main reactive power quantity for the first phase using measurements made by the main current sensor and the main voltage sensor; and comparing the total branch real power quantity to the total main real power quantity and the total branch reactive power quantity to the total main reactive power quantity.
A full understanding of the disclosed concept can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:
As employed herein, the statement that two or more parts are “coupled” together shall mean that the parts are joined together either directly or joined through one or more intermediate parts.
As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality).
As employed herein, the term “processor” means a programmable analog and/or digital device that can store, retrieve, and process data; a computer; a workstation; a personal computer a digital signal processor, a microprocessor; a microcontroller; a microcomputer; a central processing unit; a controller; a mainframe computer; a mini-computer, a server; a networked processor, or any suitable processing device or apparatus.
In one aspect, the disclosed concept provides a method and apparatus that diagnoses current sensor polarities and phase associations in different wiring configurations for protective relays or electric power or energy meters in polyphase electric power systems. The method and apparatus monitors phase angles between voltage and current waveforms, and diagnoses polarity and phase associations of current sensors in different wiring configurations using the monitored phase angles. Voltages and currents are measured via voltage and current sensors, respectively, and the measured voltages and currents are converted into respective discrete-time voltage and current samples by analog-to-digital converters. A phase angle is calculated between the voltage and current for each phase, and the polarities and phase associations of the current sensors under different wiring configurations are diagnosed based on the phase angle. The diagnosis results are output to indicate the determined polarities and phase associations. The diagnosis results may be stored and may be used for troubleshooting or other diagnostic purposes
In another aspect, the disclosed concept provides a method and apparatus for validating branch circuit current sensor diagnoses based on real and reactive power calculations. In still another aspect, the disclosed concept provides a method and apparatus for detecting the wiring configuration of an electric power system based upon a particular voltage ratio that is determined for the electric power system. In still a further aspect, the disclosed concept provides a method and apparatus for diagnosing voltage swap conditions in an electric power system. The particulars of each of these aspects of the disclosed concept according to various exemplary embodiments is described in detail herein.
As seen in
As seen in
In the exemplary embodiment, each branch circuit meter module 14A, 14B comprises a computing device having a control system including a processor 16A, 16B and a memory 18A, 18B. Processor 16A, 16B may be, for example and without limitation, a microprocessor (μP), a microcontroller, or some other suitable processing device, that interfaces with memory 18A, 18B. Memory 18A, 18B can be any one or more of a variety of types of internal and/or external storage media such as, without limitation, RAM, ROM, EPROM(s), EEPROM(s), FLASH, and the like that provide a storage register, i.e., a machine readable medium, for data storage such as in the fashion of an internal storage area of a computer, and can be volatile memory or nonvolatile memory. Memory 18A, 18B has stored therein a number of routines that are executable by processor 16. One or more of the routines implement (by way of computer/processor executable instructions) at least one embodiment of the methods discussed briefly above and in greater detail below for commissioning and diagnosing voltage and current sensors forming a part of branch circuit monitoring system 2 under different wiring configurations.
As seen in
Referring to
Referring to
In branch circuit monitoring system 2 as just described, the voltage and current sensors 24, 26, 28, 30 and 34 are operable to measure voltage and current waveforms, respectively. The voltage measurements are typically acquired by the voltage sensors either from a phase with respect to a separate phase, or from a phase with respect to a voltage reference point (e.g., neutral). In addition, there are two types of current sensors in branch circuit monitoring system 2. The first type of current sensor is the main current sensors 26, which are mounted on the conductors 10A, 10B, and 10C of main busbar 10 at an entry point to, for example, a service panel, and measure aggregate currents for each phase. The second type of current sensor is the branch circuit current sensors 34. Branch circuit current sensors 34 are mounted on each branch circuit associated with a respective load 20, and measure the current of the individual branch circuit.
In the exemplary embodiment, analog-to-digital converters 42, 44 described elsewhere herein (
The voltage and current measurements described above are dependent on wiring configurations. For a branch circuit monitoring system 2 used in a 3-phase electric power system, the wiring configuration is typically one of the following possible cases: 3-Phase 4-Wire Wye; 3-Phase 3-Wire Delta; 3-Phase 4-Wire Delta; 3-Phase Corner-Grounded Delta; 2-Phase Wye; Single-Phase 3-Wire; and Single-Phase 2-Wire. For each wiring configuration, the voltage and current sensors 24, 26, 28, 30 and 34 are configured accordingly to provide voltage and current measurements.
Description of Various Wiring Configurations
The description provided below describes the voltage and current measurements that are associated with each particular wiring configuration listed above. That description will be helpful in understanding the particulars of the various aspects of the disclosed concept described elsewhere herein.
3-Phase 4-Wire Wye
In the 3-phase 4-wire Wye wiring configuration, the voltage measurements are typically acquired by voltage sensors either from a phase with respect to a voltage reference point, or from a phase with respect to a separate phase. For instance, when voltage measurements are acquired by voltage sensors from a phase with respect to a voltage reference point in
Alternatively, when voltage measurements are acquired by voltage sensors from a phase with respect to a separate phase in
It is worth noting that voltage measurements VAB, VBC, VCA are related to voltage measurements VAN, VBN, VCN via:
VAB=VAN−VBN (1)
VBC=VBN−VCN (2)
VCA=VCN−VAN. (3)
In
3-Phase 3-Wire Delta
In FIG., the positive direction of phase A current measurement IA is defined as from source to node “A”. Likewise, similar definitions apply to phases B and C quantities IB and IC.
3-Phase 4-Wire Delta
3-Phase Corner-Grounded Delta
2-Phase Wye
The 2-phase Wye wiring configuration is a special case of the 3-phase 4-wire Wye wiring configuration. In a 2-phase Wye system, only 2 out of 3 phases are used. For example,
Single-Phase 3-Wire
According to
VAN=−VBN. (4)
Single-Phase 2-Wire
The single-phase 2-wire wiring configuration is a special case of the single-phase 3-wire wiring configuration. In a single-phase 2-wire system, only 1 out of 2 phases are used. For example, referring to 7, when only ZA is connected, then the original single-phase 3-wire Wye system becomes a single-phase 2-wire system.
Branch Circuit Current Sensor Diagnosis
One particular aspect of the disclosed concept provides a branch circuit current sensor diagnosis methodology that determines whether a branch circuit current sensor has been configured with a correct polarity and associated with a correct phase. The branch circuit current sensor diagnosis of the disclosed concept, described in greater detail below, first obtains wiring configuration information, and then uses the phase angle between voltage and current to determine the current sensor's configuration.
In connection with implementing this aspect of the disclosed concept, a number of methods for calculating phase angle between voltage and current are provided. Also provided are diagnosis methods to determine whether a branch circuit current sensor has been configured with a correct polarity and associated with a correct phase which are particular to each wiring configuration.
As just described, the branch circuit current sensor diagnosis methodology of the disclosed concept determines whether a branch circuit current sensor 34 has been configured with a correct polarity and associated with a correct phase. In particular, the methodology first obtains wiring configuration information, and then uses the phase angle between voltage and current to determine the current sensor's configuration. Described below are two alternative methods that may be used to calculate phase angle between voltage and current in order to implement the branch circuit current sensor diagnosis methodology of the disclosed concept.
In a first method, for each phase, such as phase A, B, or C shown in
TZ=NZ/fS. (5)
where fS is in hertz (Hz).
Because the utility frequency fe (in hertz) of the 3-phase electric power system is typically a known quantity, the time quantity TZ is further converted to a phase angle between voltage and current, typically expressed in degrees (°) via:
φ=rem(360·TZ·fe,360) (6)
where rem(·, 360) denotes the remainder of a quantity after it is divided by 360.
The operation wraps the phase angle between voltage and current to a non-negative value between 0 and 360°, and simplifies the subsequent current sensor diagnosis.
Following the above definition, when the voltage and current waveforms are in phase with each other, then the voltage and current samples' zero-crossing times are identical. Consequently, the phase angle between voltage and current is 0°. Otherwise, the phase angle between voltage and current is a positive value less than 360°.
In a second method, when real power P (in watts), apparent power S (in volts-amperes), and leading/lagging information of each phase are available, the phase angle between voltage and current for each phase is calculated by first calculating an intermediate phase angle φ′ using Table 1 below.
In Table 1, arccos(·) is an arccosine function whose range is between 0 and π inclusive, i.e., 0≦arccos(·)≦π. For example, if P<0 and leading, then φ′=−arccos(P/S).
The phase angle between voltage and current is then obtained from the intermediate phase angle φ′ via:
φ=rem[(φ′+2π)·180/π,360]. (7)
Moreover, as described in detail below, according to a further aspect of the disclosed concept, each different wiring configuration described herein has an associated set of rules for determining whether a branch circuit current sensor in the wiring configuration has been configured with a correct polarity and associated with a correct phase that uses the determined phase angle for the sensor in question.
More specifically, for a branch circuit current sensor 34 intended to measure phase A current in a 3-phase 4-wire Wye wiring configuration, there are 6 possible scenarios for this particular branch circuit current sensor 34:
Similarly, a branch circuit current sensor 34 intended to measure phase B or C current also has 6 possible scenarios in each case. According to the disclosed concept, and as described in greater detail below, the branch circuit current sensor diagnosis methodology determines which scenario a particular branch circuit current sensor 34 has by analyzing the phase angle between voltage and current according to a set of rules (in the form of a look-up table in the exemplary embodiment) that is specific to the particular wiring configuration in question, wherein the rules relate the phase angle to a particular sensor association and polarity.
In connection with the disclosed concept, all voltage sensors 24, 28 are assumed to have been correctly configured in polarities and phase associations. For instance, in the 3-phase 4-wire Wye wiring configuration example above, a voltage sensor 24 intended for voltage measurement VAN is configured correctly to measure voltage from phase A to neutral N. A second voltage sensor 24 intended for voltage measurement VBN is configured correctly to measure voltage from phase B to neutral N. A third voltage sensor 24 intended for voltage measurement VCN is configured correctly to measure voltage from phase C to neutral N.
In addition, because most modern 3-phase electric power systems are regulated, 3-phase voltages are hence assumed to be balanced, i.e., the voltage measurements VAN, VBN, VCN, when expressed in phasors, have the same amplitude, and are 1200 degrees apart from each other.
Consequently, according to equations (1)-(3), voltage measurements VAB, VBC, VCA, when expressed in phasors, all have the same amplitude, and are 120° degrees apart from each other, as shown in phasor diagram 60 of
For the purpose of the disclosed concept, a 3-phase symmetric load is assumed, i.e.:
ZA=ZB=ZC=Z, (8)
and the load impedance phase angle, φ, is limited to between 10° leading (capacitive load) and 50° lagging (inductive load). If the load impedance phase angle, φ, is expressed as a non-negative value between 0 and 360°, then the above limit translates to 0°≦φ<50° and 350°<φ<360°.
The above load impedance phase angle range includes: 1) purely resistive loads, in which the load impedance phase angle is φ=0°; 2) a major portion of inductive loads, including induction motors, in which the load impedance has a lagging phase angle, i.e., 0°<φ<50°; and 3) certain capacitive loads, in which the load impedance has a leading phase angle, i.e., 350°<φ<360°.
While the above assumption limits the load impedance phase angle φ to a range 0°≦φ<50° and 350°<φ<360°, other load impedance phase angle ranges can be alternatively used. For example, in a system predominated by inductive loads, the load impedance phase angle φ may be alternatively assumed to range from 20° lagging (inductive load) to 80° lagging (inductive load), i.e., 20°<φ<80°.
As noted above, for each wiring configuration described herein, the branch circuit current sensor diagnosis has a different set of rules for determining sensor phase association and polarity based upon determined phase angle. Thus, according to an aspect of the disclosed concept, each particular wiring configuration described herein has an associated table (referred to as a “Current Sensor Diagnosis Table”) that summarizes the set of rules applicable to particular wiring configuration. The current sensor diagnosis methodology according to the disclosed concept determines the current sensor's polarity and phase association by reading appropriate entries in the appropriate table. The Current Sensor Diagnosis Tables that are applicable to the 3-Phase 4-Wire Wye, 3-Phase 3-Wire Delta, 3-Phase 4-Wire Delta, and 3-Phase Corner-Grounded Delta wiring configurations are described in detail in the United States Patent Application Publication Number 2015/0042311, which is owned by the assignee hereof and incorporated herein by reference in its entirety. As a result, the rationale behind those tables is not discussed in detail herein. Instead, the Current Sensor Diagnosis Table for each of those wiring configurations is provided below (Tables 2-5) for convenience. Furthermore, one aspect of the disclosed concept is the provision of Current Sensor Diagnosis Table for the 2-Phase Wye, Single-Phase 3-Wire, and Single-Phase 2-Wire wiring configurations, each of which is described in detail below (Tables 6-8).
The discussion will now switch to the Current Sensor Diagnosis table for the 2-Phase Wye, Single-Phase 3-Wire, and Single-Phase 2-Wire wiring configurations.
With respect to 2-Phase Wye, the load impedance phase angle is limited to between 10° leading and 50° lagging. Therefore, the phase angle between voltage VAn and current measurement IA ranges from 10° leading to 50° lagging. Likewise, the phase angle between voltage VBn and current measurement IB ranges from 10° leading to 50° lagging. This is demonstrated by the phasor diagram 62A of
The Kirchhoff's current law dictates that the sum of current measurements at node “n” is 0, i.e.,
IA+IB=0. (9)
According to FIG.,
IA=VAn/ZA,IB=VBn/ZB. (10)
Substituting equation (10) into equation (9) yields
VAn/ZA+VBn/ZB=0. (11)
Note that equation (11) can be further simplified using the symmetric load assumption in equation (8).
VAn+VBn=0. (12)
The voltage measurement VAB is related to VAn and VBn via
VAB=VAn−VBn (13)
Adding equation (12) to equation (13) yields
VAB=2VAn (14)
Therefore, VAn=VAB/2, and VBn=−VAB/2. The resulting voltage measurements VAN, VBN, and VCN, when expressed in phasors, are shown phasor diagram 64 of
Because IC=0, therefore, if the amplitude of IA is 0, i.e., |IA|=0, where |·| denotes the amplitude of a phasor quantity, then the current sensor 34 intended to measure phase A current must have been mistakenly associated with phase C current-carrying conductor.
Combining
Table 6 summarizes cases from
In a 2-Phase Wye wiring configuration, if a first branch circuit current sensor 34 is intended to measure phase A current, and a second branch circuit current sensor 34 is intended to measure phase B current, then there are 8 possible scenarios for these particular branch circuit current sensors 34.
According to Table 6, for the first branch current sensor 34, if 140°≦φA<200°, then this first branch current sensor 34 is not correctly wired to phase A current-carrying conductor with a normal polarity. Therefore, cases 2), 4), 5) and 7) from the above list can be detected as incorrect wiring.
According to Table 6, for the second branch current sensor 34, if 200°≦φB<260°, then this second branch current sensor 34 is not correctly wired to phase B current-carrying conductor with a normal polarity. Therefore, cases 3), 4), 5) and 6) from the above list can be detected as incorrect wiring.
According to Table 6, for the first branch current sensor 34, if 0°≦φA<20° or 320°<φA<360°, and for the second branch current sensor 34, if 20°≦φB<80°, then either case 1) or case 8) from the above list can result in such detection results.
In this case, to differentiate whether case 1) or case 8) from the above list is true, other indicators, such as a label of phase attached to the current sensor, and a label of phase attached to the current-carrying conductor, may aid the final determination.
This description below discloses steps to diagnose current sensors 34 for the single-phase 3-wire wiring configuration using the phase angles between voltage measurements VAN, VBN and current measurements IA, IB, respectively.
According to the single-phase 3-wire wiring configuration (
VAN=VAn (15)
VBN=VBn (16)
Therefore, according to equations (15) and (16), VAn=−VBn.
Table 7 summarizes cases from
According to Table 7, φA or φB alone cannot uniquely determine that the current sensor 34 is correctly associated with the intended phase current-carrying conductor, and that the current sensor 34 has a normal polarity. For example, for a current sensor intended to measure phase A current, if 0°≦φA<50° or 350°<φA<360°, the current sensor can be either of the following two possible scenarios:
In this case, other indicators, such as a label of phase attached to the current sensor, and a label of phase attached to the current-carrying conductor, may aid the final determination.
The single-phase 2-wire wiring configuration is a special case of the single-phase 3-wire wiring configuration.
Table 8 summarizes cases from
Validation of Branch Circuit Current Sensor Diagnosis
In branch circuit monitoring system 2, after current sensor diagnosis as described herein is performed for each branch circuit, the final branch circuit current sensor diagnosis results can be further validated if main current sensors 26 have been installed and configured in the same branch circuit monitoring system 2. The discussion below discloses steps to validate branch circuit current sensor diagnosis results using real power P and reactive power Q.
For each branch circuit current sensor 34, the real power P (in watts) and the apparent power S (in volts amperes) are available. In addition, the power factor PF is also available. Given a non-zero PF, the reactive power Q (in vars) is then calculated via
where |PF| is the absolute value of the power factor.
For the following 4 wiring configurations: 3-Phase 4-Wire Wye, 3-Phase 3-Wire Delta, 3-Phase 4-Wire Delta, and 3-Phase Corner-Grounded Delta, once current sensor diagnosis as described herein is completed, each branch circuit current sensor 34 is associated with phase A current-carrying conductor 10A, or phase B current-carrying conductor 10B, or alternatively phase C current-carrying conductor 10C. A total phase A real power PA,total is obtained by summing up real power quantities for all branch circuit current sensors 34 that are associated with phase A current-carrying conductor 10A. Similarly, a total phase B real power PB,total is obtained by summing up real power quantities for all branch circuit current sensors 34 that are associated with phase B current-carrying conductor 10B, and a total phase C real power PC,total is obtained by summing up real power quantities for all branch circuit current sensors 34 that are associated with phase C current-carrying conductor 10C. Likewise, QA,total, QB,total, QC,total are obtained for the branch circuit monitoring system 2.
For the branch circuit monitoring system 2 based on the above 4 wiring configurations, the total real and reactive power quantities are also calculated from the voltage measurements made by main voltage sensors 24 and the current measurements made by main current sensor 26. They are denoted as P′A,total, P′B,total, P′C,total and Q′A,total, Q′B,total, Q′C,total.
Table 9 below shows a method that may be used to validate branch circuit current sensor diagnosis results for the following 4 wiring configurations, 3-Phase 4-Wire Wye, 3-Phase 3-Wire Delta, 3-Phase 4-Wire Delta, and 3-Phase Corner-Grounded Delta, according to an exemplary embodiment of an aspect of the disclosed concept. For example, if PB,total=P′B,total and QB,total=Q′B,total, then the branch circuit current sensor diagnosis results are validated OK for all current sensors 34 associated with phase B current-carrying conductors. As another example, if PC,total≠P′C,total or QC,total≠Q′C,total, then the branch circuit current sensor diagnosis results are not validated OK for all current sensors 34 associated with phase C current-carrying conductors.
Following the method outlined above, for the following two wiring configurations: 2-Phase Wye and Single-Phase 3-Wire, a total phase A real power PA,total and a total phase A reactive power QA,total are obtained by summing up real and reactive power quantities for all branch circuit current sensors 34 that are associated with phase A current-carrying conductor 10A, and a total phase B real power PB,total and a total phase B reactive power QB,total are obtained by summing up real and reactive power quantities for all branch circuit current sensors 34 that are associated with phase B current-carrying conductor 10B.
For same branch circuit monitoring system 2 based on the above 2 wiring configurations, the total real and reactive power quantities are also calculated from the voltage measurements made by main voltage sensors 24 and the current measurements made by main current sensor 26. They are denoted as P′A,total, P′B,total, and Q′A,total, Q′B,total.
Table 10 below shows a method that may be used to validate branch circuit current sensor diagnosis results for the following 2 wiring configurations, 2-Phase Wye and Single-Phase 3-Wire, according to another exemplary embodiment of an aspect of the disclosed concept.
For the Single-Phase 2-Wire wiring configuration, a total phase A real power PA,total and a total phase A reactive power QA,total are obtained by summing up real and reactive power quantities for all branch circuit current sensors 34 that are associated with phase A current-carrying conductor 10A. The total real and reactive power quantities, denoted as P′A,total and Q′A,total, are also calculated from the voltage measurements made by main voltage sensors 24 and the current measurements made by main current sensor 26.
Table 11 shows the method that may be used to validate branch circuit current sensor diagnosis results for the Single-Phase 2-Wire wiring configurations according to a further aspect of the disclosed concept.
Wiring Configuration Determination
Provided below is a description of a methodology for determining the number of phases in a system, such as branch circuit monitoring system 2, and then further determining the wiring configuration of the system according to still a further aspect of the disclosed concept. This methodology is, in the exemplary embodiment, accomplished using only the RMS voltage measurements made by voltage sensors 24, 28 and assumes unused voltage terminals of the branch circuit meter modules 14A, 14B are tied to the neutral voltage node comprising neutral conductor 32.
The methodology of this aspect of the disclosed concept uses Line to Line and Line to Neutral voltage measurements to determine the wiring configuration without phase angle information. In particular, the voltage sensors 24, 28 will provide Line to Neutral voltage measurements for each of the conductors 10A, 10B, 10C of main busbar 10 (i.e., each phase) to branch circuit meter modules 14. From that information, branch circuit meter modules 14 are able to determine Line to Line voltage measurements for each of the conductors 10A, 10B, 10C of main busbar 10 (i.e., each phase). In order to distinguish between single phase and polyphase systems, the methodology first establishes the number of non-zero Line to Neutral voltage measurements being made by voltage sensors 24, 28. If there are only two non-zero measurements, it can be established that the system is a Single-Phase 2-Wire configuration. If there are three non-zero measurements, the system could be a 2-phase Wye, Single-Phase 3-Wire, or a 3-phase configuration. Furthermore, Vmin refers to the smallest Line to Line voltage measurement, and Vmax, refers to the largest Line to Line voltage measurement. If Vmax is equal to Vmin, the methodology will establish that the system is a 3-phase system. If Vmax is twice the value of Vmin, the methodology will establish that the system is a 2-phase Split. If Vmax is larger than Vmin by a factor of the square root of 3, the methodology will establish that the system is a 2-phase Wye. One particular exemplary embodiment determines the phase mathematically by determining the ratio of Vmin:Vmax and using the following boundaries (boundaries determined as the midpoint between the two expected values):
if Vratio>0.789 then the wiring configuration is a 3-phase configuration
if Vratio<0.539 then the wiring configuration is a Single-Phase 3-Wire configuration
if 0.789≧Vratio≧0.539 then the wiring configuration is a 2-phase Wye configuration
If, under the methodology, the system is determined to be a 3-phase system, the system can be further categorized as a Corner-Grounded Delta, 4-Wire Delta, or a balanced 4-Wire Wye depending on the Line to Neutral voltage measurements. A 3-Phase 3-Wire Delta can be categorized by the absence of a Line to Neutral voltage measurement. In this aspect, Vmin refers to the phase with the smallest Line to Neutral voltage measurement, and Vmax refers to the phase with the largest Line to Neutral voltage measurement. Next, the methodology divides Vmin by Vmax. In the case of a Corner-Grounded Delta, the min value should be zero or close to it. In the case of a 4-Wire Delta, also known as a High-Leg Delta or Center-Tapped Delta, the Vratio value is expected to be close to 1/1.73 or one over the square root of 3. In the case of a 4-Wire Wye configuration, Vratio value will be 1 if the system is perfectly balanced, but certainly not much lower than 1. Therefore, an adequate method of distinguishing between the three configurations identified above is as follows:
if Vratio<0.366 then Voltage Configuration is Corner-Grounded Delta
if 0.366≦Vratio·0.732 then Voltage Configuration is 4-Wire Delta
if Vratio>0.732 then Voltage Configuration is 4-Wire Wye
Diagnosis of Voltage Swap Conditions
A further aspect of the disclosed concept relates to diagnosing voltage swap conditions. For balanced wiring configurations, voltage phases are interchangeable and indistinguishable from each other. However, configurations that utilize a Neutral Voltage can be miswired by swapping the Neutral with a Phase voltage (referred to as a neutral swap). Also, in configurations with imbalanced voltages, miswiring can occur between Phases (referred to as a phase swap). Both of these miswiring errors can be diagnosed.
Neutral Swap can occur in 3-Phase 4-Wire Wye, 3-Phase 4-Wire Delta, and Single-Phase 3-Wire configurations. To diagnose Neutral Swaps with any of the 3-phase configurations, one sample of the Line to Line voltage measurements (ie, each phase is sampled) is taken. Vmin refers to the phase with the smallest Line to Line voltage measurement, and Vmax refers to the phase with the largest Line to Line voltage measurement. Next, the methodology divides Vmin by Vmax. The following tables 12 and 13 show the possible Vratio values of a 120VLN-based system for the correct wiring, and the swapping of Neutral with any phase of a 4-Wire Wye or 4-Wire Delta:
Therefore, an adequate method of detecting if the measurement point of neutral conductor 32 has been wired correctly is as follows:
if Vratio>0.732 then the Neutral Has Been Wired Correctly
if Vratio≦0.732 then the Neutral Has Been Wired Incorrectly
To diagnose a neutral swap condition with the Single-Phase 3-Wire configuration, tone sample of the Line to Neutral voltages of each phase is taken. VA refers to the first voltage and VB refer to the second voltage. If one is lower than the other by ½, then the lower one is swapped with neutral. The following table 14 shows example values of a 120VLN-based system for the correct wiring, and the swapping of Neutral with either phase:
A phase swap condition can be detected in the unbalanced phase configuration of 3-Phase 4-Wire Delta with its identification of the Hi-leg. According to another aspect of the disclosed concept, one sample of the Line to Neutral voltages of each phase is taken. VA, VB, and VC refer to the voltages of each phase. The Hi-leg can then be identified by the voltage with the highest value. The following table 15 shows example values of a 120VLN-based system:
A mismatch in the expected Hi-leg from the identified Hi-leg would be a miswire.
Branch Circuit Sensor Grouping
In accordance with a further aspect of the disclosed concept, as part of the commissioning process for branch circuit monitoring system 2, branch circuit sensors 34 are grouped together into virtual meters. These are highly dependent on the physical layout of branch circuit monitoring system 2, and can be diagnosed with information about the physical layout, and with data from the voltage and current sensors of the associated pairs.
For a polyphase system, the physical layout of branch circuits (each branch circuit being associated with a single pole of a circuit breaker 22) is typically in repeating phase order, or in repeating reverse phase order. By identifying the position of each branch circuit in the physical layout of branch circuit monitoring system 2, phase errors can be found if the branches do not follow one of the prescribed orders.
Below in Table 16 are typical physical layouts for 6 branches of 3-phase and 2-phase systems. 3-phase or 2-phase systems that don't use one of these layouts would generate an error.
One, two, or three branch circuit current sensors 34 can be grouped together to create a virtual meter. A virtual meter typically monitors different phases of the same balanced load 20, such as an HVAC or 3-phase motor, and are typically adjacent to each other physically. Thus, a typical virtual meter can define its branch circuits for active loads according to the following criteria: (i) each branch circuit and the associated branch circuit current sensor 34 in a virtual meter should link to a different phase with no duplicate phases; (ii) all branch circuits and the associated branch circuit current sensor 34 in a virtual meter should have the same or similar phase angle; (iii) all branch circuits and the associated branch circuit current sensor 34 in a virtual meter should have the same or similar current; (iv) all branch circuits and the associated branch circuit current sensor 34 in a virtual meter should be adjacent in the physical layout By analyzing each current, phase angle, and position in the physical layout of each branch circuit and the associated branch circuit current sensor 34, virtual meters can be identified with a high degree of confidence.
In accordance with the disclosed concept, analysis begins with identifying the possible virtual meters for each branch circuit and the associated branch circuit current sensor 34 according to the physical layout of branch circuit monitoring system 2. For example, Table 17 below shows a typical branch circuit in a 3-phase system can be part of up to 3 possible 3-phase meters or 2 possible 2-phase meters, as illustrated below.
Branches and the associated branch circuit current sensor 34 located near the edge of the physical layout will have fewer possible meters than those located away from the edge. This method only identifies 3-phase meters on 3-phase 4-wire wye and 3-phase 3-wire delta systems, and 2-phase meters on 1-phase 3-wire systems.
Next, for each possible virtual meter, its branch circuit phase angle variance is calculated using this variance equation:
where x is each of the branch circuit phase angles in the possible virtual meter, u is the average of the branch circuit phase angles in the possible virtual meter, and N is the number of branches and associated branch circuit current sensors 34 in the possible virtual meter. The branch circuit current variance for each possible virtual meter is also calculated using the same equation, where x is each of the branch circuit currents in the possible virtual meter, u is the average of the branch circuit currents in the possible virtual meter, and N is the number of branches and associated branch circuit current sensors 34 in the possible virtual meter.
Then for each branch circuit and the associated branch circuit current sensor 34, a candidate virtual meter is determined by comparing all of the variances of all the possible virtual meters that include it. If one of the virtual meters that includes the branch circuit has the lowest branch circuit phase angle variance and the lowest branch circuit current variance, it is determined to be a candidate virtual meter. Otherwise, there is no candidate virtual meter for that branch.
If there is a possible virtual meter where each of its branch circuits have determined the possible virtual meter to be their candidate virtual meter, then that possible virtual meter is identified as a virtual meter with high confidence. To increase confidence, a filter can be placed on the variances, such that if the variance between the phase angles or currents is too high, no candidate meter is identified.
While specific embodiments of the disclosed concept have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the disclosed concept which is to be given the full breadth of the claims appended and any and all equivalents thereof.
| Number | Name | Date | Kind |
|---|---|---|---|
| 6112159 | Bond | Aug 2000 | A |
| 7660776 | Kious | Feb 2010 | B1 |
| 20060238932 | Westbrock, Jr. et al. | Oct 2006 | A1 |
| 20120089354 | Holdsclaw | Apr 2012 | A1 |
| 20140333286 | Wang et al. | Nov 2014 | A1 |
| 20150042311 | Gao et al. | Feb 2015 | A1 |
| Entry |
|---|
| European Patent Office, “International Search Report and Written Opinion” PCT/US2016/033400, dated Sep. 1, 2016, 12 pp. |
| Number | Date | Country | |
|---|---|---|---|
| 20160349311 A1 | Dec 2016 | US |
