System, apparatus and method for localisation of developing faults on power distribution networks

Abstract

A fault detection system for an electrical power distribution network with a plurality of branch circuits comprises one or more magnetic field sensors 30 deployable on the ground over a buried cable 5

Description

Technical Field Of The Invention This invention relates to a system, apparatus and method for localisation of developing faults on power distribution networks. More particularly, this invention relates to a system, apparatus and method for localisation of developing faults on low voltage (LV) networks. In particular, the present invention relates to a system, apparatus and method for detecting and pinpointing the location of a developing fault on a LV network. The present invention further relates to a deployable apparatus that can capture a timestamped magnetic field waveform associated with pre-fault activity. Background For a number of years, it has been known to locate faults on LV cable networks using impedance-based methods, however they require specialist operator intervention and processing to translate the impedance information during network faults by determining cable types and lengths (and hence impedance) and the cable route working away from the substation and then either marking the fault on a cable plan or sending a distance to fault (in metres) from the substation to the field operative or team involved with pinpointing the fault. Time Domain Reflectometry (TDR) is also a recognised method for determining the location of faults on LV networks. In such methods, a short duration voltage pulse with sharp rising edge is injected into a candidate cable of an electrical network on which a fault is known to exist. A change in impedance on the cable, such as that caused by a short circuit fault, will cause a perturbation in the received reflections which is again conceived in terms of a determine the distance along the cable at which the perturbation (fault reflection) occurred. An added complication of communicating the distance to fault obtained via known impedance-based and TDR methods on branched networks with different cable types, is that the fault impedance may relate to different distances from the substation depending on the branch in which the fault has occurred and a given reflection time may relate to points at the same distance on different branches of the network. The practical application of these methodologies and the interpretation of results is a highly-skilled task which often requires the operative to have a great deal of experience in order to produce a reliable fault location. EA Technology Limited already market a commercial product, the CableSniffer®, that can detect the gaseous by-products produced by the burning of an underground cable when it fails catastrophically. This is accomplished by drilling a series of small holes in the vicinity of the fault and identifying where the signal is strongest. Generally, pre-faults do not produce sufficient gaseous by-products to enable reliable detection at the surface. EA Technology Limited already have a significant suite of commercial protection and monitoring devices, such as the ALVIN® Recloser, and VisNet® Hub, that can initially identify the presence of pre-fault activity at a substation, and trigger notifications when network issues arise, but there is still need to pinpoint faults on branched cable networks. It is also known to pinpoint faults using a sensitive microphone operating in either the audible spectrum, or in the ultrasonic range. However, they are usually employed on dead cables in conjunction with a device (often referred to as a “thumper”) that injects a short-duration high-current pulse on to the cable to produce an audible reaction at the point of failure. Hence, they are only effective when working close to the actual faulted dead cable for fine pinpointing its exact location when the approximate fault location is already known. US 5,608,328 (Radar Engineers) is illustrative of another known approach which uses a “thumper” in conjunction with a loop antenna, or other sensors, capable of detecting radio frequency electromagnetic pulses. By moving the antenna along the cable until the point is reached when the polarity of the signal reverses implying that the antenna has moved past the fault. However, US 5,608,328 aims to detect the full fault current (and hence much larger detection signals) when the cable fails or is artificially “thumped”, rather than pre-fault perturbations whilst the cable is still in service and before it faults. US 5,608,328 also relies on detecting electromagnetic signals, as opposed to just magnetic field signals. Electromagnetic (radio type signals) would be subject to much greater attenuation by the earth covering the buried cables than purely magnetic field signals. Another known approach for locating faults in overhead lines (OHL) is by utilising devices known as Fault Passage Indicators (FPIs). FPIs include a sensor coil that can detect a fault current in conductors supported on wood poles. FPIs provide a simple flag or indicator that will tell the operator whether the fault is beyond the pole it is mounted on to localise the fault. The flat laterally-spaced conductor arrangement of OHLs, and their routing generally away from urban areas, means that FPI-detected fault events are more readily discernible from the background noise, rather than the detection of pre-fault perturbations on branched, buried cable networks whilst the cables are in service. It is an object of the present invention to provide a system, apparatus and method for localisation and pinpointing of developing faults on branched cable networks which overcomes or reduces the drawbacks associated with known products of this type. It is an object of the present invention to provide a system, apparatus and method which can detect the passage of pre-fault currents in buried LV power cables. By deploying the apparatus as a mat on the ground above the cable, it detects the residual magnetic field associated with both pre-fault and fault event currents in the cable. When an event occurs, the present invention captures the associated magnetic field waveform, applies a time and date stamp, and then transmits the data back to a remote server. By using synchronous capture (time stamping) it is possible to correlate known pre-fault events measured at the substation with events captured by the apparatus and thereby providing a means of filtering out noise and non pre-fault events and discriminating real pre-fault and fault events. By further matching the date and time stamps from the same event captured on network restoration, control and / or monitoring products in the substation against those associated with events captured by one or more fault detection apparatus deployed out on the network, it is possible to determine the route taken by the pre-fault currents on the LV network to aid pinpointing the fault location. It is a further object of the present invention to provide a reliable, non-contact residual magnetic field prefault localisation apparatus which can be deployed by a single operative and which meets with 18 09 25 regulations, standards and guidelines applicable to the deployment of trench covers, and the like, on public pavements. Summary Of The Invention 5 The present invention is described herein and in the claims. According to a first aspect of the present invention there is provided a fault detection system for an electrical distribution system distributing power from a utility source through a plurality of branch circuits to a load, the fault detection system comprising: 10 residual magnetic field sensors being deployable in one or more branch circuits for capturing one or more fault waveforms when the detected magnetic field disturbance exceeds a predetermined threshold condition, the captured fault waveforms being time stamped and thereby the passage of the same fault event in the one or more branch circuits can be determined for localisation of the fault; 15 wherein the fault waveform being indicative of the magnetic field disturbance from pre-fault currents at a developing or gestating fault, and wherein the developing or gestating fault is a Phase to Neutral / Earth fault (P-E) or Phase to Phase fault (P-P) or Phase to Phase to Neutral / Earth fault (P-P-E) or Phase to Phase to Phase fault (P-P-P) or Phase to Phase to Phase to Neutral / Earth (P-P-P-E). 20 An advantage of the present invention is that it enables reliable non-contact pinpointing of developing faults on branched cable networks. 25 Preferably, the electrical distribution system is a low voltage (LV) distribution network. Further preferably, the residual magnetic field sensor is selected from the group consisting, but not limited to, any one of the following: multi-turn magnetic flux loop, coaxial loop antenna, Hall effect sensor, magneto-strictive, magneto-diode, magneto-transistor, 30 magnetometer, magneto-optical sensor and the like. 18 09 25 In use, the residual magnetic field sensor may be disposed in a moveable housing provided as a mat, trench cover, commercial traffic analyser instrument, traffic speed reduction / calming ramp or bump, footway board, raised island, ramp, plate, lane delineator, cone or marker or the like. 5 Preferably, a plurality of residual magnetic field sensors are disposed in the moveable housing in various orientations or configurations. Further preferably, the fault detection system further comprises a communications interface 10 configured to send the captured fault waveforms to a web viewer and / or user interface (UI) and / or analysis server for post processing. In use, the fault detection system may further comprise capturing time stamped fault waveforms from a fault event on network restoration, control and / or monitoring products in 15 the feeding substation of the electrical distribution system. Preferably, the fault detection system further comprises transmitting the time stamped fault waveforms from a fault event on network restoration, control and / or monitoring products in the electrical distribution system to a web viewer and / or user interface (UI) and / or analysis 20 server for post processing and comparing the fault events for coincidence. Further preferably the communications interface transmits captured fault waveforms via Global System for Mobile (GSM) cellular telecommunications networks. 25 In use, the predetermined threshold condition may be based upon the magnitude, polarity and / or pulse shape of the disturbance to the background residual magnetic field caused by the passage of the fault event current. Preferably, the predetermined threshold condition being derived by sampling the fault 30 waveforms and comparing successive cycles to discriminate between normal time-varying 18 09 25 changes in load current, and shorter time varying changes associated with pre-fault and fault event currents between successive cycles. Further preferably, the fault detection system further comprising an integrator which integrates 5 the output of the magnetic field sensor over time and generates an integrated signal resembling the pre-fault or fault event current. Preferably, the polarity of the captured fault waveform is indicative of the direction of the passage of the fault event current. 10 In use, further comprising a uniquely identifiable Global Positioning System (GPS) receiver. According to a second aspect of the present invention there is provided an apparatus being deployable in one or more branch circuits of an electrical distribution system for detecting the 15 occurrence of a fault, the apparatus comprising: a surface that abuts the ground adjacent to a section of a branch circuit; at least one residual magnetic field sensor being disposed on the apparatus for capturing a fault waveform when the detected magnetic field disturbance exceeds a predetermined threshold condition; 20 local memory for storing time stamped captured fault waveforms; and communication means for connecting the apparatus to a remote database and transmitting storing time stamped captured fault waveforms from local memory to the remote database for pinpointing the fault, wherein the fault waveform being indicative of the magnetic field disturbance from 25 pre-fault currents at a developing or gestating fault, and wherein the developing or gestating fault is a Phase to Neutral / Earth fault (P-E) or Phase to Phase fault (P-P) or Phase to Phase to Neutral / Earth fault (P-P-E) or Phase to Phase to Phase fault (P-P-P) or Phase to Phase to Phase to Neutral / Earth (P-P-P-E). 18 09 25 Preferably, the apparatus is configured, or has the same general footprint, as a mat, trench cover, commercial traffic analyser instrument, traffic speed reduction / calming ramp or bump, footway board, raised island, ramp, plate, lane delineator or cone or marker or the like. 5 Further preferably, the apparatus is generally planar. In use, the apparatus may meet the relevant standards, regulations and / or statutory guidance that govern the temporary deployment of generally engineered rubber pavement, highways and / or traffic calming and / or access products to a pavement or highway. 10 Preferably, the apparatus further comprises indicia that indicates the correct deployment when in use. Further preferably, the apparatus further comprises mounting apertures through which the 15 apparatus can be temporarily secured to the pavement or highway when in use. According to a third aspect of the present invention there is provided a method for fault detection system on an electrical distribution system distributing power from a utility source through a plurality of branch circuits to a load, the method comprising the steps of: 20 deploying residual magnetic field sensors in one or more branch circuits; capturing one or more fault waveforms when the detected magnetic field exceeds a predetermined threshold condition; and time stamping the captured fault waveforms such that the passage of the same fault event in the one or more branch circuits can be determined for localisation of the fault, 25 wherein the fault waveform being indicative of the magnetic field disturbance from pre-fault currents at a developing or gestating fault, and wherein the developing or gestating fault is a Phase to Neutral / Earth fault (P-E) or Phase to Phase fault (P-P) or Phase to Phase to Neutral / Earth fault (P-P-E) or Phase to Phase to Phase fault (P-P-P) or Phase to Phase to Phase to Neutral / Earth (P-P-P-E). 18 09 25 According to a fourth aspect of the present invention there is provided a computer program product for fault detection on an electrical distribution system distributing power from a utility source through a plurality of branch circuits to a load, comprising: 5 computer program means for capturing time synchronised waveforms from residual magnetic field sensors deployed in one or more branch circuits and from monitoring subsystems deployed in the electrical distribution system; computer program means for correlating the time synchronised waveforms to the same fault event; and 10 computer program means for organising and displaying the time synchronised waveforms for the identification of the fault, wherein the fault waveform being indicative of the magnetic field disturbance from pre-fault currents at a developing or gestating fault, and wherein the developing or gestating fault is a Phase to Neutral / Earth fault (P-E) or 15 Phase to Phase fault (P-P) or Phase to Phase to Neutral / Earth fault (P-P-E) or Phase to Phase to Phase fault (P-P-P) or Phase to Phase to Phase to Neutral / Earth (P-P-P-E). It is believed that a system, apparatus and method for localisation and pinpointing of developing faults on LV networks in accordance with the present invention at least addresses the problems outlined above. It will be obvious to those skilled in the art that variations of the present invention are possible and it is intended that the present invention may be used other than as specifically described herein. Brief Description Of The Dra wings The present invention will now be described by way of example only, and with reference to the accompanying drawings, in which: Figure 1 shows a schematic plan view from above of a deployable fault detection apparatus in accordance with the present invention; Figure 2 illustrates an example of how one or more deployable fault detection apparatuses of Figure 1 can be deployed on a LV network to pinpoint a fault; Figure 3 shows an illustrative screenshot from an application software which provides intelligible and intuitive access to detected pre-fault events recorded from the deployed fault detection apparatus; and Figure 4 is a screenshot from the application software showing captured time stamped waveforms of the same fault event by fault detection apparatus deployed on the network and from monitoring equipment in the substation. Detailed Description Of The Preferred Embodiments The present invention has adopted the approach of utilising a system, apparatus and method for localisation and pinpointing of developing faults on branched cable networks. Advantageously, the present invention provides a system, apparatus and method which can detect the passage of pre-fault currents in buried LV power cables. Further advantageously, by deploying the apparatus as a mat on the ground above the cable, it detects the residual magnetic field associated with both pre-fault and fault event currents in the cable. When an event occurs, it advantageously captures the associated magnetic field waveform, applies a time and date stamp, and then transmits the data back to a remote server. By using synchronous capture (time stamping) it is possible to correlate known pre-fault events measured at the substation with events captured by the apparatus and thereby providing a means of filtering out noise and non pre-fault events and discriminating real pre-fault and fault events. By further matching the date and time stamps from the same event captured on network restoration, control and / or monitoring products in the substation against those associated with events captured by one or more fault detection apparatus deployed out on the network, it is advantageously possible to determine the route taken by the pre-fault currents on the LV network to aid pinpointing the fault location. Further advantageously, the present invention also provides a reliable, non-contact residual magnetic field pre-fault localisation apparatus which can be deployed by a single operative and which meets with regulations, standards and guidelines applicable to the deployment of trench covers, and the like, on public pavements. Referring now to the drawings, a deployable fault detection apparatus 10 for use in detecting and recording the passage of pre-fault currents in buried LV power cables 50a, 50b, 50c is illustrated schematically in Figure 1. The deployable fault detection apparatus 10 being dimensioned such that it can be deployed as a temporary surface-mounted pavement, highways and / or traffic calming and / or access product, and in a preferred embodiment is configured as a generally planar housing or mat 12 having a generally square- or rectangular-shape when in plan view having a top surface 14 and an opposite base surface 16. Between the top surface 14 and the base surface 16, the mat 12 having a low-profile height (not shown in the schematic diagram of Figure 1), and the mat 12 therefore acts as a housing into which the components can be mounted. The skilled person will recognise that the fault detection apparatus 10 can take many other shapes and footprints, and this is in no way intended to be limiting. In use, the fault detection apparatus 10 is intended to be laid flat and temporarily placed and / or anchored to the pavement. The fault detection apparatus 10 must comply with the relevant standards, regulations and / or statutory guidance that govern the temporary attachment of generally engineered rubber pavement, highways and / or traffic calming and / or access products to a pavement and left unattended. Whilst these differ in each country concerned, some general considerations apply. The slope and height of the mat 12 should be such that it is easy to navigate by a pedestrian, pram, wheelchair or mobility scooter, and it could additionally be anchored to the ground securely so that it cannot move when knocked. In use, trench covers, commercial traffic analyser instruments, traffic speed reduction / calming ramps or bumps, footway boards, raised islands, ramps, plates, cones, lane delineators or markers provide the typical infrastructure into which the components of the apparatus 10 can be mounted. The above list is in no way intended to be limiting and exhaustive. In a preferred embodiment, the skilled person will appreciate that the apparatus 10 can be formed from any number of engineered rubber and / or synthetic plastics material, such as a thermoplastic or thermoset material. The above list is in no way intended to be limiting and exhaustive. A textured anti-slip pattern 18 can be formed on the upper surface 14 of the apparatus 10. Located generally at each corner thereof are a series of mounting apertures 20 through which the apparatus 10 can be temporarily secured when in use. The skilled person will understand that the apparatus 10 can be secured to the ground using anchor bolts or fixtures (not shown) through the mounting holes 20. Temporarily anchoring the apparatus 10 to the ground may prevent the mats 12 from moving (if inadvertently knocked, for example), or to prevent or deter the mat 12 from being stolen. Figure 1 also shows that disposed on the top surface 14 of the apparatus 10 is a direction arrow 22 that in use should be aligned with the direction of the centre line of the buried cable 50a. When deployed, the arrow 22 should be pointing in the direction away from the substation 54 that is feeding the buried cable 50a. In use, the sensor 30 (shown in schematically in Figure 1) should be placed over the centre line of the cable 50a as closely as possible. Also disposed on the top surface 14 of the apparatus 10 is a unique ID number 24 to enable each mat 12 to be uniquely identified. Disposed in the top surface 14 of the apparatus 10 are a series of status indicator lights 26 which provide a simple and intuitive means for the operative to ensure the mat 12 is communicating and operating properly, and a means of checking the battery charge level. The status indicator lights 26 are accessed under a removable cover (not shown) such that, when the mat 12 is left unattended, the cover hides the visual indicators 26 from view to avoid attracting unwanted attention to the mat 12. In a preferred embodiment of the invention, the status indicator lights 26 are optically coupled to the electronics module 32 using fibre optics (not shown in Figure 1) which act as an optical waveguide for transporting or conveying light to the indicators 26 disposed in the top surface 14 of the apparatus 10. Fibre optics do not produce nearby magnetic pulse signals associated with high-speed current switching employed on electrical indicator devices that could otherwise interfere with the operation of the residual magnetic flux sensor 30. In addition, fibre optics are also not susceptible to wet conditions or moisture that is likely to be encountered during use. Within the body of the apparatus 10, and sealed into voids or channels (not shown) at the base surface 16 are one or more batteries 28 which are used to power the sensor 30, signal acquisition 32 and communication modules 34 of the apparatus 10. The apparatus 10 is appropriately Ingress Protection (IP) rated to allow extended and continuous outside use. The rechargeable battery pack 28 has a single connector that is used for both charging and connecting it to the mat 12. The percentage remaining charge is displayed through a circular window on the front of the battery whenever it is being used or being charged. During charging, the percentage charge indicator display 26 will flash to show that a charge is taking place and to indicate how much charge is currently stored in the battery. The battery pack 28 can be removed, thus allowing a replacement to be fitted whilst the original pack is recharged. Referring again to Figure 1, which is a high-level schematic diagram, the electronics module 32 comprises a processor which is connected to memory, and to a communications interface 34, via a bus, which is entirely known to the skilled person. The memory stores at least one instruction, a code set, or an instruction set. The at least one instruction, code set, or instruction set is loaded and executed by the processor to implement the system, apparatus and method described herein. The memory can be a volatile memory, a non-volatile memory or a combination thereof such is known to the person skilled in the art. Again, the above list is in no way intended to be limiting. Offsite monitoring and data capture allows the apparatus 10 to be monitored remotely. The communications interface 34 is configured to send signals from the sensor 30 to a web viewer / user interface (UI) and / or data can be uploaded to a cloud 64 or analysis server 62 for post processing, as described in further detail below. In a preferred embodiment, the communications interface 34 is a Global System for Mobile (GSM) cellular telecommunications system. The skilled person will appreciate that other wireless transmission protocols, such as, for example, Wi-Fi (IEEE 802.11 standard), Bluetooth, LoRa, Sigfox could also be appropriate, or the mat 12 could be connected to the analysis server 62 and / or to monitoring equipment 52 in the substation 54 via a wired connection. The magnetic field sensor 30 disposed in the mat 12 is uniquely identifiable in the electronics module 32 as would be known to someone skilled in the art. The sensor 30 utilised in the present application is a magnetic field-based device. In a preferred embodiment, the sensor 30 is a wound multi-turn magnetic flux loop which provides the necessary sensitivity. The skilled person will appreciate that other magnetic field sensors could also be appropriate, including solid-state approaches such as Hall effect sensors, magneto-diodes, magneto-transistors, and more sophisticated magnetometers and optical sensors. The above list is in no way intended to be limiting and exhaustive. In a preferred embodiment, the multi-turn magnetic flux loop described herein comprises a steel, iron or other ferrite type of magnetic core which is utilised to increase the sensitivity of the detection of the residual magnetic field produced by the pre-fault or fault current in the buried cable. An electrical screen is also incorporated to reduce the pick-up of unwanted electrical field strength or electrical interference that would otherwise detract from the detection of the residual magnetic field strength and / or produce unwanted false alarms, as described below. The signal acquisition module 32 is responsible for taking measurements of the magnetic sensor 30 input. As described, the residual magnetic field sensor 30 produces a signal that is proportional to the rate of change of the current in the buried cable 50b. An integrator is used to convert the magnetic field waveform into one that more resembles the pre-fault or fault current waveform present in the cable. This enables waveform shapes captured by the fault apparatus 10 to be compared against each other, and also if required against the current waveforms captured by monitoring equipment 52 in the substation 54 to provide a means of confirming that they are all the same event. For the avoidance of doubt, where the description of the invention refers to detecting the magnetic field waveform associated with the pre-fault or fault current in the buried cable, this is the primary parameter detected, it equally means the waveshape indicative of the residual current waveform present in the buried cable obtained by processing the magnetic field waveform signal using an integration stage. This integrator signal processing can be performed discretely, electronically, digitally, or by any other suitable means that is known to someone skilled in the art. In Figure 1, only a single sensor 30 is disposed in the mat 12. Other sensor arrangements are possible, and more than one sensor 30 can be disposed in the mat 12 in various orientations or placements to further increase sensitivity to pinpoint the fault. Sensors at different spatial locations in the mat 12 could be used to cancel mutually-coupled noise in order to achieve better resolution. In order to ensure that the mat 12 triggers in response to pre-fault currents as described below, a threshold trigger level is set to be slightly above the noise levels to prevent false triggering. These are based upon background waveforms obtained from typical, unfaulted measurements of buried cables. The threshold trigger level is adjustable. The trigger level is appropriately set to a level such that a high level of background noise triggers are not generated, whilst all real pre-fault events are captured. In a preferred embodiment, the system, apparatus and method according to the present invention continuously samples the residual magnetic field and uses a cycle-by-cycle mains waveform comparison threshold to determine when to trigger and capture a waveform. This allows it to discriminate between normal time varying changes in load current, and other unrelated stray magnetic field disturbances, and the much shorter sharper changes associated with pre-fault and fault current pulses. This technique provides a high degree of protection against false triggering, allowing both phase-neutral and phase-phase pre-fault and faults to be recognised reliably. Pre-fault currents in buried cables 50a, 50b, 50c can take several forms. Pre-fault current pulses can occur between phase and neutral / earth conductors, and also between pairs of phase conductors. They are caused by breakdown of insulation in a failing component of the cable system and, although they self-heal before causing circuit protection to operate, they are a sign of an impending damage fault. Where they occur with sufficient frequency, or where their occurrence can be anticipated (or generated), they can be used to give an indication of the location of a developing fault. Single phase pre-fault events are more common than multiphase (phase-phase or phase-phase-phase) pre-fault events present on the network. A typical single-phase pre-fault does not cause protection operation, they can persist unnoticed on the network for a considerable length of time unless equipment to detect them has been installed in the substation. Typically for single phase faults, the phase current is not fully matched by the neutral return as some current finds its way back to the source substation 54 via alternative routes through earth or other conductors (including other neutral conductors). Phase-phase pre-faults tend to produce higher currents and are therefore more likely to cause protection operation. In the case of balanced phase-phase pre-fault or fault events, it is likely that the majority of the current in one phase is matched by an equal and opposite current in the other. Although there will be physical variations from one fault event to another, there is a degree of generalisation in the above pre-fault behaviour description, but it does serve to provide a basic background against which to consider various detection principles applicable to the present invention. In use, when a pre-fault event occurs which exceeds the threshold trigger level, the mat 12 captures the associated magnetic field waveform, applies a time and date stamp, and then transmits the data back via the cellular phone network to a receiving aerial 60 connected to a server 62. By matching the date and time stamps from the events captured on the network restoration, control and / or monitoring products 52 in the substation 54 against those associated with events captured by one or more fault detection apparatus 10 deployed out on the network it is possible to determine the route taken by the pre-fault currents on the branched LV network 50a, 50b, 50c to pinpoint the fault location, as described in Figure 2. The captured pre-fault waveform contains a great deal of information on the pre-fault event. Pertinent information can be obtained from the magnitude, polarity and / or pulse shape. The polarity indicates the relative direction of the passage of the pre-fault current under the mat 12. By using one or more mats 12 in combination, it is possible to therefore pinpoint the location of a developing fault on the branched network 50a, 50b, 50c before it actually fails. The portable mats 12 can be readily deployed at different points on the network. The portable mat 12 can be left in situ temporarily if required to give it sufficient time to capture pre-fault events which, by their very nature, can be unpredictable as to when they will occur. The mats transmit captured magnetic field waveforms back to a remote processing centre 62 automatically so there is no requirement for a worker to be in attendance when the mat 12 has been deployed. In a further embodiment of the invention, the mats 12 are intended to be used in conjunction with monitoring equipment 52 installed in the substation 54 feeding the cable branch 50a under test. Monitoring equipment 52 would normally be the initial means of identifying the presence of a developing fault on the branched network 50a, 50b, 50c through the detection of pre-fault current events in the substation 54 and localising them to the circuit that is sourcing them. By matching the date and time stamps from the events captured on the monitoring equipment 52 in the substation 54 against those associated with events captured by mats 12 deployed on the network, it is possible to determine the route taken by the pre-fault currents on the network and hence, by moving the apparatuses between events, pinpoint the actual location of the developing fault. Figure 2 shows an example of how the deployable fault detection apparatus 10 of Figure 1 can be deployed on a branched LV network 102, 104, 106, 108 to pinpoint a fault. Figure 2 shows the deployment of fault detection apparatus 10 at a test location which was exhibiting high frequencies of pre-fault activity using monitoring equipment 52 operating in the distribution substation 54. The monitoring equipment 52 in the substation 54 was indicating that the Way 2 feeder was experiencing frequent phase-neutral pre-faults on phase L3. The anonymised cable route record 100 for Way 2 is shown in Figure 2. It can be seen that it is a branched feeder 102, and a fault identified as an approximate distance from the substation 54 by monitoring equipment 52 using impedance mapping or TDR, for example could potentially be at one of multiple locations on the network. In this instance, because the monitoring equipment 52 had only just been installed, there was no information available from the monitoring equipment 52 to indicate possible fault locations, so the mats 12 were effectively deployed with no understanding of where the fault might be located on the branched network 102, 104, 106, 108. The waveform captures from the mats 12 were transmitted back to analysis server 62 for post processing and analysis where they could be compared with the pre-fault event captures made by the monitoring equipment 52 in the substation 54. In use, each individual fault detection apparatus 10 may be fitted with a Global Positioning System (GPS) receiver (not shown in Figure 1) such that their current position can be communicated back to the analysis server 62 together with the captured pre-fault residual magnetic field waveform so that the exact location of the fault detector on the network can be automatically displayed on a map, street map or network layout diagram for analysis purposes. Figure 2 shows the locations where the mats 12 were deployed. The sequence of deployment was to move them from one tee-off (branch) to the next in an attempt to identify which branch the fault was on. In practice, it was found useful to only move one or two mats at a time; the remaining one then acted as a reference against which to compare them thus confirming comparative measurements were being made across like-for-like pre-fault events. In Figure 2, the numbers in the rectangles indicate the positions of the mats. The arrow shows the direction that the residual magnetic field indicated the pre-fault current was travelling in. The size of the arrows gives a basic indication of the magnitude of the residual magnetic field, as determined from the relative magnitudes of the captured residual magnetic field waveforms. The mat signals from positions 1 and 3 indicated that the pre-fault current was passing the tee-off at branch 104 and continuing down along feeder 102. The mat at position 4 indicated that very little of the pre-fault current was continuing further down branch 104. The mat at position 5 indicated that the pre-fault current was going down the branch 106. The mat at position 6 did not trigger on pre-fault events at all, effectively ruling out the tee-off to branch 108. Mats at positions 7 and 8 still detected the pre-fault current but at diminishing levels of residual magnetic field. Based on these results the mat measurements appear to indicate that the fault lies somewhere on one of the two feeders 106 on the north side of Street B. The skilled person will understand that Figure 2 shows initial field results from the deployment of the fault detection apparatus 10 at a test location. It is worth restating that the amplitude of the captured magnetic field measurement can be used to indicate the magnitude of the pre fault or fault current, and the polarity of the captured waveform can be used to determine the direction of travel of the pre-fault or fault current towards, or away from, the substation 54. The invention is not intended to be limited to the details of Figure 2 described herein, which is described by way of example only, and the present invention can be utilised for realising the invention in many diverse forms. Figure 3 shows an illustrative screenshot 110 from an application software which provides intelligible and intuitive access to detected pre-fault events recorded from the deployed fault detection apparatus 10 and / or from monitoring equipment 52 that operates in distribution substation 54. The monitoring equipment 52 checks voltage and current data on every LV feeder (and for illustrative purposes is connected to feeder 50a in Figure 1), giving insight about load, faults and condition information across the LV network and undertaking automated data analysis that trigger notifications as network issues arise. The captured data from the monitoring equipment 52 and deployed fault detection apparatus 10 being uploaded to the cloud 64 or analysis server 62 for post processing and analysis. The diagram and table situated towards the left-hand side of the user display 110 shows a summary of the load, faults and condition activity that has been detected by the monitoring equipment 52 on a selected feeder 112. There is a row of data that logs the number of prefaults detected on the selected feeder 112, and clicking on button 114 will cause recent captured waveforms on the LI section, for example, to be displayed in the window 110. This information is used initially to determine which feeders have developing faults and require further investigation. This may include pre-fault impedance measurements, pre-fault TDR distance measurements, and the deployment of one or more fault detectors at various locations on the network to identify which path the pre-fault current has taken and thereby pinpoint its location. When an event detected by the monitoring equipment 52 is determined to have a matching time / date stamp as one or more of the fault detectors deployed on the network this is classified as an “incident” and it will appear in the table 116 that lists pre-fault incidents in chronological order 118 starting with the most recent first. A scroll bar 122 is provided to navigate the list. The second column 124 displays how many fault locators deployed on the network have captured the same pre-fault event and have been grouped together along with the capture from the monitoring equipment 52 to constitute the pre-fault incident. One event will be the prefault waveform captured by the substation monitoring equipment 52, and the remainder will be residual magnetic field waveforms captured any deployed fault detection apparatus 10 that also encountered and captured the coincident pre-fault event. The third column 126 contains an eye iconography that can be selected to view the captured waveforms associated with the incident. Clicking on the eye icon 126 will open a graphical display window, as shown in Figure 4, that illustrates all the captured waveforms associated with the incident, together with the date and time that the incident was detected for further analysis. Figure 4 shows an example of how the invention can be realised where there are more than one deployed fault detection apparatus 10 assigned to this substation monitoring equipment 52, and there is an additional chart displayed for each additional fault detection apparatus 10. The waveforms captured by the substation monitoring equipment 52 may contain the bus bar voltages for each phase together with the neutral currents. By clicking on the legend 130, any unwanted parameters can be hidden from display on the chart, leaving just the key waveforms of interest. Figure 4 shows an illustrative incident waveform capture 128 from the user display 110 where two deployed fault apparatus 10 have captured the same event as the substation monitor 52. In this example, the waveform signals have been derived using simulated signals and are not therefore wholly representative of a real pre-fault event waveform. The two uppermost plots are the waveforms from two fault apparatus 10 and show the ID 24 and location on a street map of each fault locator in the chart title 132. The two plots are opposite in polarity indicating that the pre-fault current is travelling in the opposite direction on one fault detector compared to the other. The lower plot shows the same pre-fault event captured by the monitoring equipment 52 in the substation 54. By comparing the captured magnetic field waveforms from the deployed fault detection apparatus 10 with the current waveforms captured by the monitoring equipment 52 in the substation 54 ensures the pattern of the residual magnetic field matches that of the feeder neutral return current, and thereby gives a high-level of confidence that the two captures correspond to the same pre-fault event. Secondly, providing the fault detection apparatus 10 has been deployed correctly with its direction arrow 22 pointing way from the substation 54, the polarity of the magnetic field waveform, which is representative of the outgoing pre-fault current, can be used to determine the direction of the main current flow in the buried cable relevant to the substation feeder, along with providing an indication of the magnitude of the residual magnetic field. Therefore, the system, apparatus and method according to the present invention quickly and reliably localises pre-fault activity in LV networks. The system, apparatus and method according to the present invention is sensitive enough to localise low-energy pre-fault current pulse activity that occurs before customers go off supply, because it does not rely on waiting for high-energy fault events that blow fuses or the use of thumpers that periodically re-energise a fault on an otherwise dead cable during supply restoration exercises. However, the present invention can work equally as well on full fault current pulses, as it can on pre-fault current pulses. When used in this specification and claims, the terms “comprises” and “comprising” and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components. The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in the terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, separately, or in any combination of such features, can be utilised for realising the invention in diverse forms thereof. The invention is not intended to be limited to the details of the embodiments described herein, which are described by way of example only. It will be understood that features described in relation to any particular embodiment can be featured in combination with other embodiments. It is contemplated by the inventor that various substitutions, alterations, and modifications may be made to the invention without departing from the spirit and scope of the invention as defined by the claims. Examples of these include the following: The present invention also finds application in the localisation of faults on buried cables at voltages other than LV, including high voltage (HV) cables, and overhead lines (OHL) where pre-fault or fault currents are present. In the case of an overhead line, the fault detection apparatus 10 might be attached to the wood pole or other structure supporting the overhead conductors. Figure 2 shows that one or more deployable mats 10 can be placed at strategic points on the branched cable network. There is also opportunity to position a linear line of deployable mats 10 that are spaced-apart by a set distance, and which would enable the present invention to pinpoint faults in a candidate cable branch by comparing at the magnitude and polarity of the obtained residual magnetic fields. For the same reason, the present invention also finds application in the localisation of faults in submarine cables. It is envisaged that a linear line of spaced-apart deployed sensors 30 could be attached to a new submarine cable during installation, or retrofitted to existing cable assets. Again, the residual magnetic field detected from each sensor 30, and its shape, polarity and / or magnitude can used to pinpoint a gestating fault. Equally, the magnetic field sensor 30 could be deployed from a ship or unmanned underwater vehicle (UUV) and traverse a length of the submerged cable continuously capturing the residual magnetic field. For this latter application, the communications link might take the form of an ultrasonic link for communications in underwater environments. 18 09 25

Claims

1. A fault detection system for an electrical distribution system distributing power from 5 a utility source through a plurality of branch circuits to a load, the fault detection system comprising:residual magnetic field sensors being deployable in one or more branch circuits for capturing one or more fault waveforms when the detected magnetic field disturbance exceeds a predetermined threshold condition, the captured fault waveforms being time stamped and 10 thereby the passage of the same fault event in the one or more branch circuits can be determined for localisation of the fault;wherein the fault waveform being indicative of the magnetic field disturbance from pre-fault currents at a developing or gestating fault, andwherein the developing or gestating fault is a Phase to Neutral / Earth fault (P-E) or15 Phase to Phase fault (P-P) or Phase to Phase to Neutral / Earth fault (P-P-E) or Phase to Phase to Phase fault (P-P-P) or Phase to Phase to Phase to Neutral / Earth (P-P-P-E).

2. The fault detection system as claimed in any of the preceding claims, wherein the electrical distribution system is a low voltage (LV) distribution network.

203. The fault detection system as claimed in claim 1, wherein the residual magnetic field sensor is selected from the group consisting, but not limited to, any one of the following: multi-turn magnetic flux loop, coaxial loop antenna, Hall effect sensor, magneto-strictive, magneto-diode, magneto-transistor, magnetometer, magneto-optical sensor and the like.

254. The fault detection system as claimed in claim 1, wherein the residual magnetic field sensor is disposed in a moveable housing provided as a mat, trench cover, commercial traffic analyser instrument, traffic speed reduction / calming ramp or bump, footway board, raised island, ramp, plate, cone, lane delineator or marker or the like.18 09 255. The fault detection system as claimed in claim 4, wherein a plurality of residual magnetic field sensors are disposed in the moveable housing in various orientations or configurations.5 6. The fault detection system as claimed in any of the preceding claims, furthercomprising a communications interface configured to send the captured fault waveforms to a web viewer and / or user interface (UI) and / or analysis server for post processing.

7. The fault detection system as claimed in claim 1, further comprising capturing time 10 stamped fault waveforms from a fault event on network restoration, control and / or monitoring products in the feeding substation of the electrical distribution system.

8. The fault detection system as claimed in claim 7, further comprising transmitting the time stamped fault waveforms from a fault event on network restoration, control and / or 15 monitoring products in the electrical distribution system to a web viewer and / or user interface(UI) and / or analysis server for post processing and comparing the fault events for coincidence.

9. The fault detection system as claimed in claim 6, wherein the communications interface transmits captured fault waveforms via Global System for Mobile (GSM) cellular 20 telecommunications networks.

10. The fault detection system as claimed in claim 1, wherein the predetermined threshold condition being based upon the magnitude, polarity and / or pulse shape of the disturbance to the background residual magnetic field caused by the passage of the fault event current.2511. The fault detection system as claimed in claim 10, wherein the predetermined threshold condition being derived by sampling the fault waveforms and comparing successive cycles to discriminate between normal time-varying changes in load current, and shorter time varying changes associated with pre-fault and fault event currents between successive cycles.18 09 2512. The fault detection system as claimed in any of the preceding claims, further comprising an integrator which integrates the output of the magnetic field sensor over time and generates an integrated signal resembling the pre-fault or fault event current.5 13. The fault detection system as claimed in claim 1, wherein the polarity of the capturedfault waveform is indicative of the direction of the passage of the fault event current.

14. The fault detection system as claimed in claim 1, further comprising a uniquely identifiable Global Positioning System (GPS) receiver.1015. An apparatus being deployable in one or more branch circuits of an electrical distribution system for detecting the occurrence of a fault, the apparatus comprising:a surface that abuts the ground adjacent to a section of a branch circuit;at least one residual magnetic field sensor being disposed on the apparatus for 15 capturing a fault waveform when the detected magnetic field disturbance exceeds a predetermined threshold condition;local memory for storing time stamped captured fault waveforms; and communication means for connecting the apparatus to a remote database and transmitting storing time stamped captured fault waveforms from local memory to the remote 20 database for pinpointing the fault,wherein the fault waveform being indicative of the magnetic field disturbance from pre-fault currents at a developing or gestating fault, andwherein the developing or gestating fault is a Phase to Neutral / Earth fault (P-E) or Phase to Phase fault (P-P) or Phase to Phase to Neutral / Earth fault (P-P-E) or Phase to Phase 25 to Phase fault (P-P-P) or Phase to Phase to Phase to Neutral / Earth (P-P-P-E).

16. The apparatus as claimed in claim 15, wherein the apparatus is configured as, or has the same general footprint, as a mat, trench cover, commercial traffic analyser instrument, traffic speed reduction / calming ramp or bump, footway board, raised island, ramp, plate, cone, 30 lane delineator or marker or the like.18 09 2517. The apparatus as claimed in claim 16, wherein the apparatus is generally planar.

18. The apparatus as claimed in claims 16 or 17, wherein the apparatus meets the relevantstandards, regulations and / or statutory guidance that govern the temporary deployment of 5 generally engineered rubber pavement, highways and / or traffic calming and / or access products to a pavement or highway.

19. The apparatus as claimed in any of claims 15 to 18, further comprising indicia that indicates the correct deployment of the apparatus when in use.1020. The apparatus as claimed in any of claims 15 to 19, further comprising mounting apertures through which the apparatus can be temporarily secured to the pavement or highway when in use.15 21. A method for fault detection on an electrical distribution system distributing powerfrom a utility source through a plurality of branch circuits to a load, the method comprising the steps of:deploying residual magnetic field sensors in one or more branch circuits;capturing one or more fault waveforms when the detected magnetic field exceeds a 20 predetermined threshold condition; andtime stamping the captured fault waveforms such that the passage of the same fault event in the one or more branch circuits can be determined for localisation of the fault,wherein the fault waveform being indicative of the magnetic field disturbance from pre-fault currents at a developing or gestating fault, and25 wherein the developing or gestating fault is a Phase to Neutral / Earth fault (P-E) orPhase to Phase fault (P-P) or Phase to Phase to Neutral / Earth fault (P-P-E) or Phase to Phase to Phase fault (P-P-P) or Phase to Phase to Phase to Neutral / Earth (P-P-P-E).

22. A computer program product for fault detection on an electrical distribution system 30 distributing power from a utility source through a plurality of branch circuits to a load, comprising:computer program means for capturing time synchronised waveforms from residual magnetic field sensors deployed in one or more branch circuits and from monitoring subsystems deployed in the electrical distribution system;computer program means for correlating the time synchronised waveforms to the same5 fault event; andcomputer program means for organising and displaying the time synchronised waveforms for the identification of the fault,wherein the fault waveform being indicative of the magnetic field disturbance from pre-fault currents at a developing or gestating fault, and10 wherein the developing or gestating fault is a Phase to Neutral / Earth fault (P-E) orPhase to Phase fault (P-P) or Phase to Phase to Neutral / Earth fault (P-P-E) or Phase to Phase to Phase fault (P-P-P) or Phase to Phase to Phase to Neutral / Earth (P-P-P-E).18 09 25

Images