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.

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 ^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 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 polyphase neutral evaluation process for monitoring the function of a site neutral line. The process comprises: obtaining supply impedance estimates for a polyphase electrical supply, each of the supply impedance estimates 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 phases 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 voltage balance between the respective phases of the electrical supply, 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.

In an embodiment, the process is implemented by a control system that receives measurements obtained by the electrical utility meter installed at the site (the device that measures energy exchanged between the site and an electrical utility) . The control system may be integrated with the electrical utility meter or a remote management system associated with an electrical utility. The control system may perform an automated fault determination process that identifies active line and/or neutral line fault conditions. The fault determination process may categorises faults using established fault criteria. Possible fault categories and associated criteria include:

• Broken neutral line: the neutral line impedance exceeds an operating impedance threshold for a defined period of time,

• Degraded neutral line: neutral line impedance is within a defined operating zone and neutral line voltage exceeds an operating threshold for a defined period of time.

• Supply voltage unbalance: the voltage unbalance factor

exceeds a threshold for a defined period of time.

• Reverse active/neutral: line to neutral voltages exceed a threshold, supply voltage angles are outside normal operating range, ratio of maximum voltage of all phases to minimum voltage of all phases is outside normal operating range, and these persist for a defined period of time.

• Unknown status due to high load current: at least one of the phases exceeds an operating current threshold for a defined period of time.

• Unknown status due to volatility: excessive fluctuations of neutral line voltage and/or impedance persist for a defined period of time.

• Degraded active line: neutral line impedance is correlated with load current In an embodiment, the control system monitors the estimated neutral line parameters (typically the neutral line voltage and impedance) for deviations from defined operating zones. The respective operating zones may be dynamically refined by the control system using historic neutral line characteristics to compensate for cyclic deviations (such as diurnal fluctuations) and/or long term trends (such as gradual parameter creep) .

In a second aspect, the invention provides a polyphase neutral evaluation process for tracking fluctuations of a site neutral line. 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.

Instantaneous parameters obtained for the site (either measured or estimated) may be influenced by transient electrical irregularities (such as ephemeral supply voltage unbalances) . The volatility index is a stability reference for parameter evaluation that is derived from historic neutral line characteristics. Fault monitoring may be suspended when the volatility index indicates that monitored parameters are susceptible to uncharacteristic fluctuations.

In a third aspect, the invention provides a polyphase neutral evaluation process for determining the stability of a site neutral line. The process 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.

The control system may derive a plurality of statistical characteristics for the neutral line voltage and/or impedance estimates. Some statistical characteristics include:

• minimum voltage and/or impedance values;

• maximum voltage and/or impedance values;

• average voltage and/or impedance values;

• voltage and/or impedance variability values; and

• median voltage and/or impedance range .

In an embodiment, the control system typically maintains a record of absolute statistical measures for the site (such as the maximum estimated neutral line voltage experienced at the site) . Parameter characteristics may also be established for defined monitoring periods (such as monthly reporting intervals) .

Some parameters may be actively tracked to ensure fluctuations are within acceptable ranges despite not violating absolute fault thresholds. This facilitates identification of persistent parameter fluctuations that can influence site operation (such as persistent supply voltage fluctuations that do not exceed a corresponding fault

threshold) . The control system may establish time profiles for these parameters to assist the tracking process. Time profiles also enable gradual site changes (such as neutral line voltage and/or impedance creep) to be detected.

In a fourth aspect, the invention provides a polyphase active and neutral evaluation process for monitoring the function of a site neutral line. The process comprises: obtaining supply impedance estimates for a polyphase electrical supply, each of the supply impedance estimates 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 phases 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 each supply phase, supply impedance estimates of each supply phase and an offset voltage, determining an instantaneous neutral line current by either; i) deriving from current measurements of the supply phases. 11) deriving from the direct measurement of the differential current between supply phases and neutral.

in) deriving from the direct measurement of the sum of all supply currents .

IV) directly measuring neutral current. 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 neutral line current.

In a fifth aspect, the invention provides a single phase or polyphase active and neutral evaluation process for tracking fluctuations of a site neutral line. 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, tracking fluctuations of the derived neutral line indicator and determining a volatility index for the site neutral line, and correlating fluctuations of the derived neutral line indicator with time and/or load current and determining correlation coefficients.

Correlation coefficents indicate the influence a parameter may have on the neutral line indicator. If the influence is strong it may be an indication of a fault. An active line fault may be raised if the load current

correlation coefficient is high.

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 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 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.

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 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 120° out of phase. 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:

• 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 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 voltage summation of the supply phases when the supply is balanced .

0 = ^v an + ^v bn + ^V cn 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 = Vzsa + ^zla + ^zn Equation 2

Vbn = Vzsb + Vzib + Vzn Equation 3 vcn = ^v zsc + ^v zic + ^v zn Equation 4

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 + Vzla + ¾n + ^zsb + ^zlb + ¾n + ¾sc + ^zlc + ¾n Equation 5

Summing the neutral line voltage components from

Equation 5 produces the reduced equivalent circuit voltage representation presented in Equation 6. vzsa+ ^v zla+ ^v zsb+ ^v zlb+ ^v zsc+ ^v zlc

V _zn — 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. vzla+ ^v zlb+ ^v zlc

V _zn — Equation 7

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 5Ω 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 1Ω may indicate neutral line degradation in metropolitan applications, whereas this threshold is likely to be greater for rural sites (such as a 1Ω 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 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 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) .

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

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.

I/ _ ^V zsa+Vzla+ ^v zsb+ ^v zlb+ ^v zsc+Vzlc ^~v err

V _zn — Equation 8 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 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 egraded 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:

• 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;

• 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 0.25Ω (nominal), 2.0Ω (degraded) and Ι,ΟΟΟ,ΟΟΟΩ (broken) are used for the respective simulations. The derived site parameters for each simulation are summarized in Table 1 and depicted in the respective figures.

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 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 .

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;