AU2019246817B2 - Electrical monitoring and evaluation process - Google Patents
Electrical monitoring and evaluation process Download PDFInfo
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- AU2019246817B2 AU2019246817B2 AU2019246817A AU2019246817A AU2019246817B2 AU 2019246817 B2 AU2019246817 B2 AU 2019246817B2 AU 2019246817 A AU2019246817 A AU 2019246817A AU 2019246817 A AU2019246817 A AU 2019246817A AU 2019246817 B2 AU2019246817 B2 AU 2019246817B2
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- neutral line
- voltage
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- neutral
- site
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/086—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution networks, i.e. with interconnected conductors
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/26—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents
- H02H3/32—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at corresponding points in different conductors of a single system, e.g. of currents in go and return conductors
- H02H3/33—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at corresponding points in different conductors of a single system, e.g. of currents in go and return conductors using summation current transformers
- H02H3/338—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at corresponding points in different conductors of a single system, e.g. of currents in go and return conductors using summation current transformers also responsive to wiring error, e.g. loss of neutral, break
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/40—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to ratio of voltage and current
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H5/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal non-electric working conditions with or without subsequent reconnection
- H02H5/10—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal non-electric working conditions with or without subsequent reconnection responsive to mechanical injury, e.g. rupture of line, breakage of earth connection
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
- Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
- Y04S10/00—Systems supporting electrical power generation, transmission or distribution
- Y04S10/50—Systems or methods supporting the power network operation or management, involving a certain degree of interaction with the load-side end user applications
- Y04S10/52—Outage or fault management, e.g. fault detection or location
Abstract
ELECTRICAL MONITORING AND EVALUATION PROCESS
The invention relates to an automated process for monitoring
5 and evaluating the integrity of an active line and/or neutral
line for a polyphase site. The process uses measurements
obtained at the site to estimate the voltage and impedance of
the neutral line. These estimates are compared with
established operating zones for the site to evaluate the
10 condition of the active and/or neutral line.
An electrical utility meter installed at the site captures
instantaneous usage measurements (typically the voltage and
current for each phase of an electrical supply). The
measurements are transmitted to an evaluation module that
15 derives active and/or neutral line performance
characteristics for the site.
Description
Related Application
This application is a divisional application of
Australian application no. 2015268091, the disclosure of
which is incorporated herein by reference. Most of the
disclosure of that application is also included herein,
however, reference may be made to the specification of
application no. 2015268091 as filed to gain further
understanding of the invention claimed herein.
Field of the Invention
This specification relates generally to electrical
distribution networks and the evaluation of neutral line and
active line function.
Background
Electrical distribution networks transfer electrical
energy from a utility to individual consumer sites. The
electrical energy is typically produced by a power generation
facility (such as a hydroelectric plant) and distributed at
high voltages to localised electrical sub-stations before
being transferred to consumer sites. The electrical utility
typically manages the distribution network. This can include
maintaining the physical network connecting consumer sites to
electrical sub-stations and regulating the electrical
performance of the network.
11978870_1
Electrical energy can be distributed to consumer sites
in either single phase or polyphase (such as three-phase).
Industrial sites typically operate with three-phase
electrical supply. Residential sites may operate on either a
three-phase electrical supply (for high energy consumption
households) or a single phase electrical supply (for lower
household energy consumption).
Three phase instillations typically utilise a single
neutral return line. The neutral line completes the
electrical loop between the consumer site and the
distribution network for each active phase. The neutral line
is ideally maintained at the same potential as an earth
(ground) line.
A voltage difference may develop between the neutral
line and the earth line if the neutral line is damaged or
broken. A 'floating neutral' (where the neutral line and
earth line have different electrical potential) increases the
risk of an electric shock and can interfere with the
operation of electrical devices at the site.
The state of the neutral line for an electrical
installation can be checked by measuring the voltage
difference between the neutral line and an independent earth
connection. Neutral line integrity checks are typically
performed by technicians as a fault finding procedure or
instillation check.
Single phase and three phase instillations utilise at
least one active line. Typically the active line delivers
energy to the consumer site. Ideally the impedance of the
11978870_1 active line is minimised to increase efficiency of the electrical distribution network.
Impedance of the active line may increase if the active line is damaged or broken. This increases energy loss and can interfere with the operation of electrical devices at the site.
The state of the active line for an electrical installation can be checked by measuring the active line voltage while a load current is present. Active line integrity checks are typically performed by technicians as a fault finding procedure or instillation check.
Summary of the Invention
In a first aspect, the invention provides a neutral line evaluation process. The process comprises: recurrently measuring the voltage and current of an electrical supply, the measurements being captured by an electrical meter installed at the site; deriving an instantaneous neutral line indicator from the voltage and current measurements obtained by the electrical meter, the neutral line indicator representing the function of the site neutral line; and tracking fluctuations of the derived neutral line indicator and determining a volatility index for the site neutral line.
In some embodiments, the process further comprises determining an instantaneous neutral line voltage estimate for the site and monitoring the neutral line voltage estimate for deviations from a defined operating zone.
11978870_1
In some embodiments, the process further comprises
calculating an instantaneous impedance estimate for the
neutral line from the current measurements obtained by the
electrical meter and an estimated neutral line voltage.
In some embodiments, the process further comprises
determining a correlation coefficient of the instantaneous
neutral line voltage estimate.
In some embodiments, the process further comprises comprising
determining a correlation coefficient of the instantaneous
impedance estimate for the neutral line.
In some embodiments, the process further comprises
recurrently determining instantaneous voltage and impedance
estimates for a neutral line, statistically tracking the
estimated neutral line voltage and impedance, and deriving a
stability indicator from temporal characteristics of the
voltage and current estimates.
In some embodiments, the process further comprises one of the
following:
determining a dynamic threshold for inferring a neutral
line fault from the derived volatility index;
determining a dynamic threshold for inferring an active
line fault from the derived volatility index;
determining a dynamic threshold for inferring an active
line fault from the correlation coefficient.
11978870_1
In a second aspect, the invention provides an electrical
meter that measures energy exchanged between an electrical
utility and a site. The electrical meter is configured for
installation at the site and having a control system that
executes the neutral line evaluation process mentioned above
in respect of the first aspect.
In a third aspect, the invention provides a single phase
active and neutral evaluation process. The process comprises:
obtaining a supply impedance estimate for a single phase
electrical supply, the supply impedance estimate representing
the distribution network impedance between a site and an
electrical utility for an individual phase,
recurrently measuring the voltage and current of the
supply phase at the site, the measurements being captured by
an electrical meter,
determining an instantaneous neutral line voltage
estimate for the site, the instantaneous neutral line voltage
being derived from a function with inputs comprising of;
voltage and current vectors of the supply phase, supply
impedance estimate of the supply phase and an offset voltage,
and
calculating an instantaneous impedance estimate for the
neutral line, the neutral line impedance estimate being
calculated from the estimated neutral line voltage and a
return current derived from the current measurements obtained
by the electrical meter.
11978870_1
The process can comprise one or more of:
monitoring the estimated neutral line impedance for
deviations from a defined impedance operating zone;
tracking fluctuations in neutral line impedance and
determining a volatility index for the site from historic
neutral line impedance characteristics;
tracking fluctuations in neutral impedance.
The process can further comprise one or both of:
tracking neutral voltage estimates for the site and
determining an acceptable operating zone for the neutral
voltage from historic estimate characteristics;
establishing a neutral voltage time profile and
monitoring the neutral line for voltage creep.
The process can comprise one or both of:
tracking neutral impedance estimates for the site and
determining an acceptable operating zone for the neutral
impedance from historic estimate characteristics;
establishing a neutral impedance time profile and
monitoring the neutral line for impedance creep.
The process can comprise deriving statistical characteristics
for the neutral line voltage estimate. The statistical
characteristics comprises:
• a minimum voltage value;
11978870_1
• a maximum voltage value;
• an average voltage value;
• a variability value;
• a median value; or
• a correlation coefficient.
The process can comprise deriving statistical characteristics
for the neutral line impedance estimate. The statistical
characteristics comprise:
• a minimum impedance value;
• a maximum impedance value;
• an average impedance value;
• a variability value;
• a median value; or
• a correlation coefficient.
The process can comprise deriving statistical characteristics
for the active and neutral line currents, the statistical
characteristics comprising:
• a minimum current value;
• a maximum current value;
• an average current value;
• a variability value;
• a median value; or
• a correlation coefficient.
11978870_1
The process can further comprise: inferring a neutral line
fault when the neutral line impedance exceeds an operating
impedance threshold for a defined period of time; or
inferring a neutral line fault when the neutral line voltage
exceeds an operating voltage threshold for a defined period
of time; or both.
The process can further comprise inferring an active line
fault when at least one statistical characteristic exceeds a
threshold for a defined period of time. In some forms, the
process can further comprise inferring an active line fault
when a statistical characteristic includes a variability
value; or when a statistical characteristic includes a
correlation coefficient.
The process can further comprise indicating unreliable active
and neutral integrity evaluation process when at least one
statistical characteristic exceeds a threshold for a defined
period of time.
In a fourth aspect, the invention provides an electrical
meter that measures energy exchanged between an electrical
utility and a site, the electrical meter being configured for
installation at the site and having a control system that
executes the single phase active and neutral evaluation
process mentioned above in respect of the third aspect.
In a fifth aspect, the invention provides a remote control
system that executes the single phase active and neutral
evaluation process mentioned above in respect of the third
aspect, and having a communication path to one or more
physically separate electrical meters that measure energy
11978870_1 exchanged between an electrical utility and a site, the electrical meters being configured for installation at the site.
Brief Description of the Drawings
Embodiments of the invention are described in this specification (by way of example) with reference to the accompanying drawings, in which:
Figure 1 is a schematic representation of an electrical distribution network connected to a residential site.
Figure 2 is a schematic wiring diagram for a three phase electrical meter depicting two possible neutral line wiring configurations.
Figure 3 is a simplified electrical circuit diagram for a three phase site.
Figure 4a is an equivalent circuit model for a polyphase site exhibiting nominal simulation conditions.
Figure 4b is an equivalent circuit model for a polyphase site exhibiting simulation conditions indicative of degraded neutral line.
Figure 4c is an equivalent circuit model for a polyphase site exhibiting simulation conditions indicative of a broken neutral line.
Detailed Description
An automated process for monitoring and evaluating the
integrity of an active line and/or neutral line for a
polyphase site is disclosed in this specification. The
process uses measurements obtained at the site to estimate
the voltage and impedance of the neutral line. These
11978870_1 estimates are compared with established operating zones for the site to evaluate the condition of the active and/or neutral line.
An electrical utility meter installed at the site
captures instantaneous usage measurements (typically the
voltage and current for each phase of an electrical supply).
The measurements are transmitted to an evaluation module that
derives active and/or neutral line performance
characteristics for the site. Ideally, a management module
interfaces with the evaluation module to monitor the
variability of electrical parameters at the site. The
management module may determine the reliability of
instantaneous neutral line estimates before initiating fault
notifications.
The evaluation module and management module may be
integrated with the electrical meter, implemented by a site
computing system or associated with remote management system
maintained by the electrical utility. The respective modules
may implemented by the same hardware system or divided
between physically separate systems.
The system enables electrical utilities to remotely
monitor the integrity of site active and/or neutral lines
without direct technician intervention. It also supports on
site fault finding and electrical safety precautions. A
faulty neutral line can increase the risk of electric shock,
affect the performance of sensitive electrical components
(particularly motors and instruments), disrupt operation of
electrical networks and damage equipment. A faulty active
11978870_1 line can reduce electrical distribution network efficiency and affect the performance of electrical components.
Conventional active and neutral integrity checks are
performed by an on-site technician. Manual checks can be
susceptible to false diagnosis as they do not evaluate long
term trends.
The exemplary neutral line evaluation process disclosed
in this specification facilitates reliable detection of four
fundamental neutral line states (nominal, degraded broken and
reversed active/neutral) and two active line states (normal
and abnormal) under various operating conditions. The process
passively monitors site electrical properties (i.e. the meter
does not switch an electrical load to obtain measurements) to
derive the active and/or neutral line states. The general
process comprises:
• obtaining supply impedance estimates for the electrical network connecting a polyphase site to an electrical utility, • recurrently measuring the voltage and current of the supply phases at the site,
• validating that voltage and current are within a nominal range, • deriving an instantaneous neutral line voltage estimate for the site from a function of load voltage, load current, supply impedance and error voltage vectors,
• calculating an instantaneous impedance estimate for the neutral line from the estimated neutral line voltage and a return current (derived from the current measurements obtained by the electrical meter), and • calculating statistical characterizations of the neutral line impedance and voltage estimates.
11978870_1
Existing smart meter installations that comply with
established active and neutral wiring conventions can be
upgraded to implement the detection process without
installing dedicated hardware (upgrades are typically
implemented through firmware updates). This reduces the
implementation cost and complexity of active and neutral line
fault detection.
The process is performed recurrently so that degradation
of a site active and/or neutral line can be detected before
affecting operation at the site. Ideally, the electrical
properties of individual sites are recorded to facilitate
performance tracking and statistical parameter
characterization. This enables electrical utilities to
monitor the state of site installations and initiate
preventative maintenance before definitive faults occur.
Historic site records can also be used to improve
classification of instantaneous measurements derived from the
site by identifying deviations from 'normal' operation.
Statistical characterizations (such as an impedance
volatility index) and dynamic operating zone thresholds
reduce the incidence of false fault detections by giving the
system statistical insight into historic trends. The system
is also capable of identifying gradual changes (such as
temporal creep) that are not readily evident in the
instantaneous records.
A schematic representation of a polyphase residential
installation 100 is depicted in Figure 1. The installation
100 comprises a residential site 101 connected to a three
11978870_1 phase, four wire electrical network 102. The network comprises three active phases (represented by wires 106, 107,
108) and a neutral line 105.
The active phase wiring 106, 107, 108 is terminated at a
site utility meter 201 (shown in Figure 2) via fuses or
circuit breakers 205. The meter 201 interfaces the
electrical distribution network 102 with a local site network
200. The neutral line 105 may be terminated at the meter 201
or directly at a neutral block 215 (both arrangements are
depicted schematically with dotted lines in Figure 2).
The illustrated site network 200 accommodates both
polyphase 210 and single phase 211 electrical loads. A
similar network arrangement may also be used for industrial
sites with limited single phase loading. The site neutral
block 215 is electrically connected to ground through an
earth block 216 and earth stake 217. Ideally this
arrangement provides a low impedance path to earth to prevent
hazardous equipment voltages if a neutral line fault
develops.
A simplified equivalent electrical circuit diagram for a
three phase site installation is presented in Figure 3. The
diagram represents the electrical load of a local site 101
and a section of electrical distribution network 102
connecting the site 101 to an electrical sub-station. The
electrical source for each phase is represented by an
independent power supply 301a, 301b and 301c. The power
supplies 301 produce electrical waveforms that are 1200 out
of phase.
11978870_1
The nominal load for each phase 301 is divided into a
supply impedance 310 and a load impedance 320 that are
connected in series. The supply impedance 310 represents the
impedance of the distribution network between the electrical
utility (typically an electrical sub-station) and the meter
201 for each phase. The site impedance 320 is the
instantaneous electrical load on the local site network 200.
The distribution circuit is completed by a neutral line 105
with neutral impedance 305. The neutral line 105 is tied to
an electrical earth 306.
The supply impedance for a site may be obtained from
impedance estimates maintained by the electrical utility,
derived from network characteristics or captured from
measurements of the relevant network section. The site
impedance 320 is determined from measurements captured by the
electrical utility meter installed at the site.
The disclosed fault detection process derives neutral
line characteristics for a site from measured electrical
parameters. Typical characteristics include the
instantaneous neutral line voltage, current and impedance.
The neutral line voltage is derived from a function with
inputs comprising voltage and current vectors of each supply
phase, supply impedance estimates of each supply phase and an
offset voltage. In the following exemplary embodiment the
function is derived from a vector summation of the voltage
for each supply phase. This process may be simplified by
several constraints that are often applicable to polyphase
electrical networks. These constraints include:
11978870_1
• the vector summation of supply voltages is zero when the
supply voltage is balanced,
• the is no neutral current with a star connected load when the
supply voltage and load are balanced (the neutral current
increases as the load becomes unbalanced), and
• the star point voltage at the load is equivalent to the
voltage differential between ground and neutral with a
grounded balanced lossless supply (ground and neutral are
typically held at the same potential and the star point
voltage is zero when the neutral line is functioning
correctly).
A neutral line voltage derivation process for the
equivalent circuit presented in Figure 3 is summarized
quantitatively in Equations 1 to 6. Equation 1 represents a
voltage summation of the supply phases when the supply is
balanced.
0=V +Vbn+Vn Equation 1
Where: Vxn = the active to neutral (ground at the
generator) supply voltage vector for each
supply phase.
The phase voltage vectors can be resolved into
components based on the voltage drop across each equivalent
load depicted in Figure 3 using Kirchhoff's voltage law. The
decomposition of each phase is presented in Equations 2 to 4.
Van = zsa +Vzia +Vzn Equation 2
Vbn = Vzsb +Vzib +Vzn Equation 3
Vn = Vzsc + Vzic + Vzn Equation 4
11978870_1
Where: Vzsx = the voltage drop across the supply
impedance for each phase.
Vzlx = the load voltage for each phase.
Vzn = the neutral voltage.
Substituting Equations 2 to 4 into Equation 1 produces a
decomposed voltage representation for each phase of the
equivalent circuit.
0 = Vzsa + Vzia + Vzn +Vz V +Vz + Vsc + Vz + n Equation 5
Summing the neutral line voltage components from
Equation 5 produces the reduced equivalent circuit voltage
representation presented in Equation 6.
zn =Vzsa+Vzla+Vzsb+Vzlb+Vzsc+Vzlc == Equation 6
The load voltage (Vzlx) for each phase is measured
directly by metrology units integrated with the site utility
meter. The supply voltage drop (Vzsx) can be derived from a
supply impedance estimate and load current. The neutral
voltage derivation can be simplified if the supply impedance
is negligible. The reduced neutral voltage derivation with
negligible supply impedance is presented in Equation 7.
v=zn == Vzla+Vzlb+Vzlc Equation 7
11978870_1
The current passing through the neutral line is
determined from a vector sum of the instantaneous phase
currents measured by the electrical utility meter. This
assumes negligible current leakage through the site's
electrical earth.
The neutral line impedance is determined from the
derived voltage and current using Ohm's Law. The impedance
derivation can only be performed when there is a load
unbalance at the site as there is negligible neutral current
when the site load 320 is balanced. This limitation does not
restrict application of the evaluation process in practice as
most polyphase installations experience regular load
unbalances.
The neutral impedance is a direct indicator of neutral
line state. As the neutral line degrades, the neutral
impedance increases. A neutral line impedance of greater
than 5Q is typically unsatisfactory for most residential
applications. Metropolitan sites are often more strictly
regulated by electrical utilities than rural site. A neutral
line impedance greater than 1Q may indicate neutral line
degradation in metropolitan applications, whereas this
threshold is likely to be greater for rural sites (such as a
1Q degradation threshold).
The neutral line voltage is also indicative of neutral
line state. The neutral line voltage will increase with
degradation when there is a load unbalance at the site. The
neutral line voltage and impedance can be monitored to
facilitate automated fault determination. A fault management
11978870_1 module associated with the electrical utility or the site electrical utility meter can perform the monitoring function.
Active and neutral line faults are typically derived
from prolonged deviation of monitored characteristics from
established operating zones. The fault management system may
infer a neutral line fault when the neutral impedance and/or
voltage exceed corresponding operating thresholds for defined
time periods. Alternatively, the fault management system may
infer an active line fault when fluctuations in derived
neutral impedance are correlated with load current for
defined time periods. A fault timer may be integrated with
the management system to facilitate the fault delay
mechanism.
The management system initiates a fault timer when a
fault condition is determined (such as the neutral line
voltage or impedance deviating from a defined operating
zone). The timer delays a corresponding fault notification
by a predefined time to compensate for temporary fluctuations
in active and/or neutral line performance.
The management system typically generates a fault
notification at the expiration of the fault timer if the
fault condition persists. The fault timer is ideally reset
by the management system (i.e. the timer is stopped and
reinitialized with the preset fault time) if the fault
condition subsides before expiration of the fault time. This
process reduces false fault notifications.
The management system may suspend active and/or neutral
integrity fault monitoring or suppress active and/or neutral
11978870_1 integrity fault notifications when the neutral line indicators (such as the derived neutral line impedance and voltage) are determined to be unreliable. Some site conditions that can produce unreliable neutral line indicators include:
• Loss of a supply phase,
• Reversed neutral and active line,
• Incorrect phase sequencing,
• Earthing irregularities,
• Excessive current draw, • Voltage unbalance between the supply phases, and • Incorrect supply impedance estimates.
Abnormal site operating conditions (including operating
conditions that cause suspension of active and/or neutral
integrity checks) are ideally monitored by the management
system. The management system may generate fault
notifications for persistent operating fault conditions
and/or reoccurring faults indicative of abnormal operation.
Incorrect termination of the supply wiring at the site
can produce operating conditions that interfere with the
active and/or neutral integrity evaluation process. Typical
wiring induced faults include 'loss of phase' (indicating one
of the active phases is correctly terminated), 'reversed
neutral' (indicating that the neutral line and an active
phase wire have been interchanged) and 'incorrect sequencing' (indicating that the active phase wires are terminated out of
order).
11978870_1
The management system typically suspends active and/or
neutral integrity checks when the supply voltage for any of
the active phases drops below satisfactory operating levels.
This is characterized as a 'loss of phase' fault condition.
A 'loss of phase' fault is typically determined by comparing
the voltage for each phase to a defined operating voltage
threshold. A 'loss of phase' fault notification is
established when the supply voltage is less than the
threshold for a predefined time. The management system may
also monitor the supply frequency of each phase to supplement
the 'loss of phase' determination.
A 'reversed neutral' fault condition can be determined
from the active line RMS voltage ratio (the ratio of minimum
RMS voltage to maximum RMS). A voltage phase angle
comparison for each active phase may also be used to
establish 'reversed neutral' wiring. A voltage magnitude
comparison with a threshold may also be used to establish 'reversed neutral' wiring. A 'reversed neutral' fault is
established when the active line voltage ratio, active phase
angle or voltage magnitude comparisons deviate from
established operating thresholds for a predefined time.
A 'phase sequencing' fault condition is typically
determined from comparative analysis of the voltage zero
crossing for each active phase. 'Phase sequencing' fault
notifications are similarly delayed by a fault time to reduce
fault notifications from temporary fluctuations.
Earthing irregularities can interfere with the active
and neutral integrity evaluation process governed by
11978870_1
Equations 1 to 6. A low earth impedance relative to the
neutral line is likely to divert neutral current through the
ground stake. The neutral impedance estimate generated by
the evaluation module is lower than the actual neutral line
impedance in this situation.
Low earth line impedance is typically encountered in
sites with conductive soil or installations where the
earthing system is indirectly connected to the neutral line
of an adjacent site (often through metallic piping extending
between the sites). Similarly, additional current in the
neutral line from adjacent sites is likely to influence the
neutral line estimates obtained by the management system.
Excessive load current can interfere with neutral
integrity checks performed by the management system. An
'excessive current' fault condition is typically determined
by comparing the RMS current for each phase to a current
threshold. The management system may suspend active and
neutral integrity checks and establish an 'excess current'
fault when the RMS current for a phase exceeds the current
threshold for a predefined time.
A voltage unbalance between the active phases of the
supply can complicate derivation of neutral line
characteristics. The voltage relationship defined in
Equation 1 is derived for systems with negligible supply
voltage unbalance. The neutral line voltage derivation is
more complicated if the supply voltages are not balanced.
Equation 8 represents a system with supply voltage unbalance.
11978870_1
=Vzsa+Vzla+Vzsb+Vzlb+Vzsc+Vzc-Verr Equation 8 -3
Where: Verr = the voltage error introduced by the supply unbalance.
The neutral line voltage and current both vary as the voltage unbalance between the supply phases increases. The derived neutral line voltage also varies with supply voltage unbalance. However, the unbalance introduces an error component (represented by Verr in Equation 8) that reduces the accuracy of the voltage estimate.
An artificial voltage unbalance may develop when the supply impedance 310 (the impedance of the distribution network between the electrical utility and the site) is high and the site load 320 is relatively high. This loading combination emphasizes any loss differential between the supply phases (the difference in voltage drop experienced across the supply line for each phase), generating an apparent voltage unbalance at the terminal of the site utility meter.
Voltage unbalances (both actual and artificial) can be determined by calculating the voltage unbalance factor using voltage for each active supply line. The management system may suspend the neutral integrity checks when the error component introduced by voltage unbalanced becomes excessive. The error component can be evaluated using a voltage unbalance threshold as the difference between the actual neutral voltage and voltage estimated using Equation 6 is proportional to the degree of unbalance between the supply
11978870_1 phases. The management system may alternatively compensate for expected errors introduced by supply voltage unbalances by incorporating an error component that is proportional to the detected unbalance (represented by Equation 8).
Incorrect supply impedance estimates and/or supply irregularities can interfere with the active and neutral integrity evaluation process governed by Equations 2 to 6. As load current varies on a particular phase the voltage drop Vzlx will vary on that phase due to the supply impedance. An incorrect supply impedance estimate will introduce an error in the calculated voltage drop. The neutral voltage and impedance estimate generated by the evaluation module will vary from the actual neutral line voltage and impedance in this situation. When supply impedance estimates are incorrect, fluctuations in load current will cause fluctuations of the neutral impedance estimate. The management system may suspend the neutral integrity checks when fluctuations become excessive. The management system may alternatively correlate fluctuations with load current on a particular phase and raise a 'degraded active' fault condition.
A monitoring system ideally tracks site operating parameters to facilitate diagnostic analysis and operational evaluations. Records for the tracked parameters may be stored in a memory module associated with the site utility meter, a site computing system or a database maintained by the electrical utility. The monitoring system uses the historic records to establish statistical site profiles. The parameters tracked by the monitoring may include:
11978870_1
• Neutral line voltage estimates,
• Neutral line impedance estimates,
• Neutral line current,
• Supply voltage unbalances (voltage unbalance factor),
• Fault notifications generated by the management system,
• Fluctuations in neutral line performance,
• Supply voltage, and
• Load current.
The monitoring system ideally derives a neutral line
volatility index from historic neutral line parameters
(typically the derived neutral line voltage and impedance).
The volatility index is a stability reference for parameter
evaluation. Typical site parameter volatility measures
include variance, standard deviation, mean difference, median
absolute deviation and average absolute deviation.
Instantaneous parameter deviations may be quantified relative
to historic fluctuations at the site by establishing dynamic
operating zone fault thresholds from the volatility index.
The monitoring module may also establish time profiles
for monitored site parameters. Parametric time profiles
facilitate detection of parameter creep and other gradual
trends not readily discernable from short term parameter
analysis. Statistical parameters for the site can also be
extracted from the time profiles. Typical statistics
parameters for neutral line voltage and impedance include:
• Minimum absolute values;
• Maximum absolute values;
• Historic averages;
11978870_1
• Variability measures;
• Median values; and
• Correlation coefficients.
Control logic for a neutral line evaluation process is presented in Appendix A. The control logic is presented in pseudo-code. The management module may implement similar fault determination logic to check the operating conditions of a polyphase site installation and evaluate the state of a site active and/or neural line.
The control logic embodied in Appendix A classifies the neutral line state as nominal, degraded or broken depending on the neutral line attributes derived by the evaluation module. Several operating preconditions are evaluated before the neutral line state is classified. An incremental counter is used to delay fault notifications once a fault condition is detected.
A set of equivalent circuits used to simulate the neutral state derivation process summarized in Equations 1 to 6 are depicted in Figures 4a to 4c. The neutral line state varies from nominal (Figure 4a) to broken (Figure 4c) in the figures. The site operating conditions (including the supply impedance) are maintained constant for each simulation.
The supply impedance 310 is balanced for each simulation. The equivalent circuits all display a site load 320 unbalance. The site load unbalance is the same for each equivalent circuit. Neutral impedances of 0.25Q (nominal), 2.OQ (degraded) and 1,000,OOOQ (broken) are used for the
11978870_1 respective simulations. The derived site parameters for each simulation are summarized in Table 1 and depicted in the respective figures.
Neutral Impedance 0.25 2 le+06
246V 276V 327V Phase A 8.2A 9.2A 10.9A 2013W 2547W 3557W
228V 221V 217V Phase B 38.OA 36.8A 36.2A 8662W 8118W 7880W
224V 206V 185V Phase C 44.7A 41.2A 36.9A 10012W 8507W 6815W
Voltage estimate 7.9 39.3 90.5
Current estimate 31.67 19.64 0.00
Impedance estimate 0.25 2.00 500000.00
Table 1
The word "comprise" (and variations such as "comprises" or "comprising") is used in the description and claims in an inclusive sense (i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features), except where the context requires otherwise due to express language or necessary implication
It will be appreciated by persons skilled in the art that numerous variations and/or modification may be made to
11978870_1 the invention as shown in the specific embodiments without departing from the scope of spirit or scope of the invention broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.
Further, any reference herein to prior art is not intended to imply that such prior art forms or formed a part of the common general knowledge in Australia or any other country.
11978870_1
Appendix A
State = normal.
If (all load currents less than max limit)
If (all phases are present)
If (neutral current > min limit)
If (neutral impedance > degraded limit)
State=degraded;
Else if (neutral impedance > broken limit)
State=broken;
Else if (neutral voltage > min limit)
If (voltage unbalance > min limit)
State=broken;
Else
State=degraded;
If (State == Old State)
Increment counter;
If (Counter > persistence time)
Generate neutral integrity warning;
Old State= State;
11978870_1
*2019246817*
Please note there is a formatting issue and claim 8 appears along side and at the end off claim 7 (on line 17 on page 30).
Claims (21)
1. A neutral line evaluation process comprising:
recurrently measuring the voltage and current of an electrical supply, the measurements being captured by an electrical meter installed at the site,
deriving an instantaneous neutral line indicator from the voltage and current measurements obtained by the electrical meter, the neutral line indicator representing the function of the site neutral line, and
tracking fluctuations of the derived neutral line indicator and determining a volatility index for the site neutral line.
2. The process of claim 1 comprising determining an instantaneous neutral line voltage estimate for the site and monitoring the neutral line voltage estimate for deviations from a defined operating zone.
3. The process of claim 1 or claim 2 comprising calculating an instantaneous impedance estimate for the neutral line from the current measurements obtained by the electrical meter and an estimated neutral line voltage.
4. The process of claim 2 comprising determining a correlation coefficient of the instantaneous neutral line voltage estimate.
11978870_1
5. The process of claim 3 comprising determining a
correlation coefficient of the instantaneous impedance
estimate for the neutral line.
6. The process of any one of claims 3 to 5 further comprising
recurrently determining instantaneous voltage and impedance
estimates for a neutral line, statistically tracking the
estimated neutral line voltage and impedance, and deriving a
stability indicator from temporal characteristics of the
voltage and current estimates.
7. The process of any one of claims 1 to 6 comprising one of
the following:
determining a dynamic threshold for inferring a neutral line
fault from the derived volatility index;
determining a dynamic threshold for inferring an active line
fault from the derived volatility index;
determining a dynamic threshold for inferring an active line
fault from the correlation coefficient.
8. An electrical meter
that measures energy exchanged between an electrical utility
and a site, the electrical meter being configured for
installation at the site and having a control system that
executes the neutral line evaluation process of any one of
claims 1 to 7.
9. A single phase active and neutral evaluation process
comprising:
obtaining a supply impedance estimate for a single phase
electrical supply, the supply impedance estimate representing
11978870_1 the distribution network impedance between a site and an electrical utility for an individual phase, recurrently measuring the voltage and current of the supply phase at the site, the measurements being captured by an electrical meter, determining an instantaneous neutral line voltage estimate for the site, the instantaneous neutral line voltage being derived from a function with inputs comprising of; voltage and current vectors of the supply phase, supply impedance estimate of the supply phase and an offset voltage, and calculating an instantaneous impedance estimate for the neutral line, the neutral line impedance estimate being calculated from the estimated neutral line voltage and a return current derived from the current measurements obtained by the electrical meter.
10. The process of claim 9 comprising one or more of:
monitoring the estimated neutral line impedance for
deviations from a defined impedance operating zone;
tracking fluctuations in neutral line impedance and
determining a volatility index for the site from historic
neutral line impedance characteristics;
tracking fluctuations in neutral impedance.
11. The process of claim 9 or 10 comprising one or both of:
11978870_1 tracking neutral voltage estimates for the site and determining an acceptable operating zone for the neutral voltage from historic estimate characteristics; establishing a neutral voltage time profile and monitoring the neutral line for voltage creep.
12. The process of any one of claims 9 to 11, comprising one or both of:
tracking neutral impedance estimates for the site and determining an acceptable operating zone for the neutral impedance from historic estimate characteristics;
establishing a neutral impedance time profile and monitoring the neutral line for impedance creep.
13. The process of claim 11 comprising deriving statistical characteristics for the neutral line voltage estimate, the statistical characteristics comprising:
• a minimum voltage value; • a maximum voltage value; • an average voltage value;
• a variability value;
• a median value; or • a correlation coefficient.
14. The process of claim 11 comprising deriving statistical characteristics for the neutral line impedance estimate, the statistical characteristics comprising:
11978870_1
• a minimum impedance value;
• a maximum impedance value;
• an average impedance value;
• a variability value;
• a median value; or
• a correlation coefficient.
15. The process of claim 11 comprising deriving statistical
characteristics for the active and neutral line currents, the
statistical characteristics comprising:
• a minimum current value;
• a maximum current value;
• an average current value;
• a variability value;
• a median value; or
• a correlation coefficient.
16. The process of any one of claims 9 to 15 comprising:
inferring a neutral line fault when the neutral line
impedance exceeds an operating impedance threshold for a
defined period of time; or
inferring a neutral line fault when the neutral line
voltage exceeds an operating voltage threshold for a defined
period of time;
or both.
17. The process of any one of claims 13 to 15 comprising
inferring an active line fault when at least one statistical
11978870_1 characteristic exceeds a threshold for a defined period of time.
18. The process of claim 17 comprising inferring an active line fault when a statistical characteristic includes a variability value; or when a statistical characteristic includes a correlation coefficient.
19. The process of any one of claims 13 to 15 comprising indicating unreliable active and neutral integrity evaluation process when at least one statistical characteristic exceeds a threshold for a defined period of time.
20. An electrical meter that measures energy exchanged between an electrical utility and a site, the electrical meter being configured for installation at the site and having a control system that executes the single phase active and neutral evaluation process of any one of claims 9 to 19.
21. A remote control system that executes the single phase active and neutral evaluation process of any one of claims 9 to 19 and having a communication path to one or more physically separate electrical meters that measure energy exchanged between an electrical utility and a site, the electrical meters being configured for installation at the site.
11978870_1
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| AU2015268091A AU2015268091B2 (en) | 2014-05-30 | 2015-06-01 | Electrical monitoring and evaluation process |
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| US10223906B2 (en) | 2017-01-23 | 2019-03-05 | Florida Power & Light Company | Open neutral detection |
| FR3067118B1 (en) * | 2017-05-31 | 2021-07-02 | Sagemcom Energy & Telecom Sas | SINGLE-PHASE ELECTRIC METER |
| PT3642636T (en) | 2017-06-23 | 2021-11-10 | Ariadna Instr S L | Method for detecting impedances in an electrical power distribution grid |
| JP6896149B2 (en) * | 2018-03-16 | 2021-06-30 | 三菱電機株式会社 | Voltage deviation detector |
| CN108614180B (en) * | 2018-04-12 | 2020-05-29 | 山东钢铁股份有限公司 | Single-phase earth fault line searching method |
| SE544786C2 (en) * | 2020-07-03 | 2022-11-15 | Vattenfall Eldistribution Ab | System and method for detection of broken neutral faults |
| FR3127583A1 (en) * | 2021-09-28 | 2023-03-31 | Sagemcom Energy & Telecom Sas | Detection of faulty tightening |
| FR3137178A1 (en) | 2022-06-28 | 2023-12-29 | Sagemcom Energy & Telecom Sas | Detection of loss of neutral or phase |
| FR3137179A1 (en) * | 2022-06-28 | 2023-12-29 | Sagemcom Energy & Telecom Sas | Loss of neutral detection |
| CN115856714B (en) * | 2023-03-01 | 2023-05-05 | 广州东方电科自动化有限公司 | Branch loop health state assessment method and system |
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| US20100271225A1 (en) * | 2006-08-18 | 2010-10-28 | Aurora Energy Pty Ltd. | Method and apparatus for detecting a fault in a supply line |
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| US20100271225A1 (en) * | 2006-08-18 | 2010-10-28 | Aurora Energy Pty Ltd. | Method and apparatus for detecting a fault in a supply line |
| US20100102826A1 (en) * | 2006-11-24 | 2010-04-29 | Karl Nathan Edwards | Power supply monitoring system |
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| AU2019246817A1 (en) | 2019-10-31 |
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