Diverted neutral current detector, apparatus, and method

Abstract

There is provided a diverted neutral current (DNC) detector 100, an apparatus 200, a method 400, and a computer program 206. The DNC detector 100 comprises a sensor arrangement CTP, CTN, CTE, VS. The DNC detector 100 further comprises circuitry 201 configured to determine whether a condition is satisfied in dependence on information from the current sensor arrangement, and output one or more signals in dependence on satisfaction of the condition.

Description

[0001] TITLE

[0002] Diverted Neutral Current detector, apparatus, and method

[0003] TECHNOLOGICAL FIELD

[0004] Examples of the disclosure relate to a Diverted Neutral Current detector, an apparatus, and a method.

[0005] BACKGROUND

[0006] In a TN-C-S (terra-neutral combined-separated) electrical supply, a single ‘PEN’ conductor (protective-earthed neutral conductor) is used for neutral and earth, up to the installation of an electricity consumer. The PEN conductor is also referred to as a CNE (combined-neutral-and-earth) conductor.

[0007] A single-phase TN-C-S electricity supply network comprises just two supply conductors: a phase conductor and a PEN conductor. A three-phase TN-C-S supply comprises just four conductors: three phase conductors and a PEN conductor. The supply network does not comprise a separate earth conductor. Instead, the PEN conductor is earthed at various points.

[0008] Each installation is connected to the phase conductor and PEN conductor by service laterals, including: a service lateral phase conductor and a service lateral PEN conductor.

[0009] The service lateral PEN conductor of the electricity supply network splits into separate neutral and earth conductors at the installation. The split is implemented by a neutralearth link at the installation, such as a busbar or other conductive connector.

[0010] The earth conductor in the installation is connected to a main earthing terminal (MET). The MET is often connected to bondings such as metal gas pipes, metal water pipes, or steel building elements, for example. A dedicated earth electrode could be used, but these may not always be present. The bondings at multiple installations may be connected to each other. For example, the gas and water pipes to which an installation is earthed may be connected to central street-connected service pipes which serve multiple consumers. Multiple electrical installations may be earthed to gas and water pipes served by the same street- connected service pipes. If the pipes are formed from metal, this creates a conductive path between the bondings of the installations. Therefore, the same conductive bondings may be shared by multiple installations, for earthing purposes.

[0011] Another example of shared bondings comprises a single building hosting several installations, wherein the METs of the installations are electrically connected to the same steel frame of the same building, or water or gas pipes.

[0012] The sharing of bondings between installations has the side effect of creating parallel neutral circuits, so that neutral currents of each installation are to some extent divided. Each parallel branch comprises a separate installation that shares the bonding. Some neutral current at the installation is diverted into the earth conductor via the neutralearth link. A low level of diversion is regarded as normal. The diverted neutral current (DNC, or NCD) reaches the main earthing terminal (MET), and flows into the shared bonding. The DNC flows through the shared bonding into the MET of other nearby installations such as neighbouring properties, where it can find its way to the service lateral PEN conductor of the second installation and back to the source.

[0013] The DNC flowing in the earth conductor may be lower in magnitude than the current flowing directly to the PEN conductor, due to the higher electrical resistance of the shared bonding.

[0014] A problem can arise when a supply PEN conductor or service lateral PEN conductor breaks before the neutral-earth link, such that one or more first installations lose their neutral return path to the source while one or more second installations retain intact neutral return paths to the source. The neutral current of all the installations will return to source through the intact PEN conductors of the one or more second installations, via the shared bonding shared by the installations. In some cases, the break may even go unnoticed for a long time because the installations with the broken PEN conductors do not experience an open circuit; in other words, the neutral current finds a new path to source via other nearby installations.

[0015] If the DNC is of a high magnitude, for example due to a PEN fault, this can result in resistive heating of the bonding carrying the DNC and a potential risk of fire. Furthermore, if the bonding at the second installation is disconnected from the MET, the current will stop flowing but the bonding will now be at an elevated potential difference, potentially in the high tens or hundreds of volts (e.g., 230V UK, or 120V US). This potential difference gives rise to the risk of electric shock in the second installation if somebody touches any exposed metal part of the bonding while also providing a path to ground.

[0016] There is a lack of awareness of DNCs particularly among tradespeople such as plumbers and gas engineers. They may assume that it is sufficient to isolate the electrical supply to a property at the distribution unit, without realizing that on rare occasions significant electrical current may be flowing into the installation from the bonding. They may not realise that if they disconnect an electrical earth wire from a water or gas pipe, to service said pipe, the pipe may now be at an elevated electrical potential. They may possess tools such as shorting cable and voltmeters and current clamp meters, but this does not guarantee that they will take steps to reduce the risks due to their assumptions and lack of awareness of DNCs.

[0017] BRIEF SUMMARY

[0018] According to various, but not necessarily all examples there is provided a diverted neutral current (DNC) detector comprising: a current sensor arrangement to detect electrical current in a current carrier conductor and an earth conductor of an electrical supply; and circuitry configured to: determine whether a first condition is satisfied in dependence on information from the current sensor arrangement, wherein satisfaction of the first condition is dependent on comparison of electrical current between the current carrier conductor and the earth conductor; determine whether a second condition is satisfied in dependence on information from the current sensor arrangement, wherein satisfaction of the second condition is dependent on a direction of electrical current flow in the earth conductor; output one or more first signals in dependence on satisfaction of the first condition; and output one or more second signals in dependence on satisfaction of the second condition.

[0019] An advantage is that a single DNC detector with a limited number of current sensors is able to detect the effects of a broken PEN conductor, regardless of whether the break occurs at a PEN conductor servicing the electrical supply (installation) such that the electrical supply no longer has a direct neutral path to source, or occurs at a PEN conductor servicing another electrical supply of another installation, resulting in DNC entering the electrical supply via the earth conductor, i.e., flowing in the wrong direction.

[0020] More specifically, this is because the first, comparative condition detects a DNC resulting from a locally broken PEN conductor by detecting that most or all of the neutral current has diverted into the earth conductor. The second, direction-based condition detects excessive diverted neutral current entering the installation via the earth conductor, which may occur as a consequence of a remote broken PEN conductor.

[0021] Optionally, satisfaction of the first condition is dependent on electrical current in one of the conductors, such as the earth conductor, being greater than a threshold, and wherein the threshold is dependent on electrical current in the other conductor, such as the neutral conductor. Optionally, the threshold defines a similarity threshold such as an equality threshold. Optionally, the threshold of the first condition is equal to or approximately equal to electrical current in the other conductor. Optionally, satisfaction of the first condition is dependent on electrical currents of the conductors matching or approximately matching.

[0022] In practice, it is likely that the currents in the earth and neutral conductors will match if the PEN conductor is broken. However, the threshold could be set to less than equality. Therefore, alternatively the threshold may be a variable which is based on but less than the electrical current in the other conductor. For example, the threshold may be a variable that is at least 50% or at least 80% or at least 90% of the electrical current in the other conductor.

[0023] Optionally, satisfaction of the first condition is further dependent on electrical current in at least one of the conductors being greater than a lower limit. Optionally, the lower limit is at least one Amp or at least 1.5 Amps. An advantage is improved reliability because there is a slight possibility that in some situations, there may be zero power on the neutral conductor and zero power on the earth conductor and their currents would match despite the absence of an DNC fault.

[0024] An advantage is that users are protected from or warned of a DNC fault.

[0025] Optionally, satisfaction of the second condition is dependent on the direction of electrical current flow in the earth conductor being towards a neutral-earth link. If second condition may be unsatisfied in dependence on the direction being away from the neutral-earth link.

[0026] An advantage is that DNC fault currents entering the installation from an external neutral break are detected.

[0027] Optionally, satisfaction of the second condition is further dependent on electrical current flow in the earth conductor being greater than a threshold. Optionally, the threshold of the second condition is five Amps. Alternatively, the threshold may be lower than five Amps, for example greater than or equal to four Amps.

[0028] Optionally, the one or more second signals comprise a supply disconnection control signal and / or an alert triggering signal.

[0029] Optionally, the current sensor arrangement comprises first and second current sensors to respectively detect phase current and neutral current in a pair of current carrier conductors including a phase conductor and a neutral conductor. Optionally, the current sensor arrangement comprises a third current sensor to detect earth current in the earth conductor. The first current sensor may be a phase current sensor. The second current sensor may be a neutral current sensor. The third current sensor may be an earth current sensor.

[0030] Optionally, determining whether the first condition is satisfied comprises comparing electrical currents indicated by the neutral current sensor and the earth current sensor. An advantage is that by comparing earth current with neutral current rather than with phase current, the same DNC detector can be used for both single-phase and three- phase / multi-phase electrical supplies.

[0031] Optionally, determining whether the second condition is satisfied comprises determining a direction of electrical current flow through the earth current sensor.

[0032] Optionally, the circuitry is further configured to: determine whether a third condition is satisfied in dependence on the information from the phase and neutral current sensors (first and second current sensors), wherein satisfaction of the third condition is dependent on comparison of the phase current and neutral current; and output one or more third signals in dependence on satisfaction of the third condition.

[0033] An advantage is that the DNC detector is able to detect a further type of DNC fault which has the symptom of causing the neutral current to significantly differ from the phase current. Normally, the phase current and neutral current should be equal between the distribution unit and the neutral-earth link. However, if for example DNC occurs somewhere within the installation, perhaps in one of the load circuits serviced by the distribution units, then electrical current may find one or more additional return paths other than the neutral conductor. Such a fault may not be detectable by the first or second conditions.

[0034] Collectively, the first to third conditions allow most or all types of DNC fault to be detected with a single DNC detector and just three current sensors.

[0035] Optionally, satisfaction of the third condition is dependent on one of the neutral or phase current being less than a lower threshold dependent on the other of the neutral or phase current, and / or greater than an upper threshold dependent on the other of the neutral or phase current. For example, satisfaction of the third condition may be dependent on the neutral current being less than a lower threshold dependent on the phase current, and / or greater than an upper threshold dependent on the phase current.

[0036] Optionally, the lower threshold and / or the upper threshold define a range relative to the other of the phase or neutral current. Optionally, the lower threshold and / or the upper threshold is at least multiple Amps different than the other current. Optionally, the lower threshold is approximately five Amps less than the other current and / or the upper threshold is approximately five Amps greater than the other current.

[0037] An advantage is that this creates an allowable range of ± several Amps within which the neutral and phase currents may vary without an DNC fault being detected, for example due to imbalanced loads or acceptable ground leakage. The exact thresholds may vary depending on the country, whether the installation receives a single-phase or multi-phase / three-phase supply, and whether the installation is a residential or commercial consumer, for example.

[0038] Optionally, the DNC detector further comprises a voltage sensor to detect a phase-to- neutral voltage, and wherein the circuitry is configured to: determine whether a fourth condition is satisfied in dependence on information from the voltage sensor, wherein satisfaction of the fourth condition is dependent on the phase-to-neutral voltage being less than a lower voltage threshold and / or greater than an upper voltage threshold; and output one or more fourth signals in dependence on satisfaction of the fourth condition.

[0039] An advantage is that evidence of an DNC fault can be detected because when the neutral current diverts through the earth conductor to the bonding to find another path to source, the overall resistance is higher which reduces the voltage. Therefore, a phase-to-neutral voltage being less than the lower voltage threshold can indicate an DNC fault. If the confidence is not high, the voltage detection may be combined with a current detection such as checking the earth current in the earth conductor, to satisfy the fourth condition. Optionally, the lower voltage threshold is at least 6% less than nominal supply voltage, and / or the upper voltage threshold is at least 6% or at least 10% greater than nominal supply voltage. For example, in the United Kingdom where the nominal supply voltage is 230 Volts, the lower voltage threshold may be 216.2 Volts (-6%) or less, and / or the upper voltage threshold may be 253 Volts or more (+10%).

[0040] An advantage is that normal fluctuation of voltages is accepted.

[0041] Optionally, the electrical supply is a three-phase supply, and wherein the voltage sensor and fourth condition are replicated for each phase conductor of the three-phase supply.

[0042] Optionally, the one or more first / second / third / fourth signals comprise an alert triggering signal. For example, the alert triggering signal may control an audio rendering device and / or a visible light rendering device of the DNC detector. Additionally, or alternatively, the alert triggering signal may be transmitted to a communication interface.

[0043] Optionally, the one or more first / second / third fourth signals comprise one or more supply disconnection control signals. Optionally, the one or more supply disconnection control signals comprise an isolation signal configured to isolate one or more conductors of the electrical supply. Optionally, the one or more supply disconnection control signals comprise a microgenerator isolation signal to isolate a microgenerator circuit.

[0044] Optionally, the electrical supply is a TN-C-S electrical supply. The neutral conductor and earth conductor may be connected to each other and to a PEN conductor by a neutral-earth link.

[0045] Optionally, the condition(s) determined by the DNC detector are without reference to true earth. According to various, but not necessarily all examples there is provided an electrical supply comprising the DNC detector, wherein the current sensor arrangement comprises one or more of: a phase current sensor connected to a phase current carrier conductor between a supply point and a distribution unit; a neutral current sensor connected to a neutral current carrier conductor between the supply point and the distribution unit; or an earth current sensor connected to the earth conductor between a neutralearth link and a main earthing terminal. Furthermore, the voltage sensor may be included.

[0046] According to various, but not necessarily all examples there is provided a handportable test instrument comprising the DNC detector.

[0047] According to various, but not necessarily all examples there is provided an apparatus (e.g., controller) comprising at least one processor, and at least one memory including computer program code, the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to perform at least: receiving information from a current sensor arrangement, indicating electrical current in a current carrier conductor and an earth conductor of an electrical supply; determining whether a first condition is satisfied in dependence on the information from the current sensor arrangement, wherein satisfaction of the first condition is dependent on comparison of electrical current between the current carrier conductor and the earth conductor; determining whether a second condition is satisfied in dependence on the information indicating the electrical current in the earth conductor, wherein satisfaction of the second condition is dependent on a direction of electrical current flow in the earth conductor; outputting one or more first signals in dependence on satisfaction of the first condition; and outputting one or more second signals in dependence on satisfaction of the second condition. According to various, but not necessarily all examples there is provided a method of detecting diverted neutral current, the method comprising: receiving information from a current sensor arrangement, indicating electrical current in a current carrier conductor and an earth conductor of an electrical supply; determining whether a first condition is satisfied in dependence on the information from the current sensor arrangement, wherein satisfaction of the first condition is dependent on comparison of electrical current between the current carrier conductor and the earth conductor; determining whether a second condition is satisfied in dependence on the information indicating the electrical current in the earth conductor, wherein satisfaction of the second condition is dependent on a direction of electrical current flow in the earth conductor; outputting one or more first signals in dependence on satisfaction of the first condition; and outputting one or more second signals in dependence on satisfaction of the second condition.

[0048] According to various, but not necessarily all examples there is provided a computer program comprising instructions, which, when executed by an apparatus or DNC detector, cause the apparatus or DNC detector to perform the method.

[0049] According to various, but not necessarily all examples there is provided an DNC detector comprising: a sensor arrangement; circuitry configured to determine whether any two or more of the first condition, second condition, third condition, or fourth condition are satisfied, in dependence on information from the sensor arrangement, and output one or more signals in dependence on satisfaction of one of the conditions.

[0050] According to various, but not necessarily all examples there is provided an apparatus comprising at least one processor, and at least one memory including computer program code, the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to perform at least: receiving information from a sensor arrangement; determining whether any two or more of the first condition, second condition, third condition, or fourth condition are satisfied, in dependence on the information from the sensor arrangement; and outputting one or more signals in dependence on satisfaction of one of the conditions.

[0051] According to various, but not necessarily all examples there is provided a method of detecting diverted neutral current, the method comprising: receiving information from a sensor arrangement; determining whether any two or more of the first condition, second condition, third condition, or fourth condition are satisfied, in dependence on the information from the sensor arrangement; and outputting one or more signals in dependence on satisfaction of one of the conditions.

[0052] According to various, but not necessarily all examples there is provided a computer program comprising instructions, which, when executed by an apparatus or DNC detector, cause the apparatus or DNC detector to perform the method.

[0053] According to various, but not necessarily all, embodiments there is provided an apparatus comprising means for performing at least part of one or more methods described herein. The description of a function and / or action should additionally be considered to also disclose any means suitable for performing that function and / or action. Functions and / or actions described herein can be performed in any suitable way using any suitable method.

[0054] According to various, but not necessarily all, embodiments there is provided examples as claimed in the appended claims.

[0055] While the above examples of the disclosure and optional features are described separately, it is to be understood that their provision in all possible combinations and permutations is contained within the disclosure. It is to be understood that various examples of the disclosure can comprise any or all the features described in respect of other examples of the disclosure, and vice versa. Also, it is to be appreciated that any one or more or all the features, in any combination, may be implemented by / comprised in / performable by an apparatus, a method, and / or computer program instructions as desired, and as appropriate. The description of a function should additionally be considered to also disclose any means suitable for performing that function.

[0056] BRIEF DESCRIPTION

[0057] Some examples will now be described with reference to the accompanying drawings in which:

[0058] FIG. 1 illustrates an example electrical supply to a first installation;

[0059] FIG. 2 illustrates an example controller;

[0060] FIG. 3 illustrates an example non-transitory computer-readable storage medium;

[0061] FIG. 4 illustrates an example method;

[0062] FIG. 5 illustrates a first example DNC fault;

[0063] FIG. 6 illustrates a second example DNC fault; and

[0064] FIG. 7 illustrates a third example DNC fault.

[0065] DETAILED DESCRIPTION

[0066] FIG. 1 illustrates a single-phase electricity supply network and a first installation 1 providing an electrical supply 10 for a building. The electrical supply 10 and the electricity supply network are interfaced with each other by a service point SP, which represents the boundary between the two.

[0067] A single-phase network and electrical supply 10 is shown, with one phase conductor and one PEN conductor entering the installation. In another example, the electricity supply network and electrical supply 10 are three-phase, with three phase conductors and one PEN conductor entering the installation.

[0068] The electricity supply network is a TN-C-S network. The electricity supply network comprises two supply conductors: a supply phase conductor P and a supply PEN conductor. They are connected upstream to a source (not shown) such as a generator. The supply PEN conductor is earthed at various points (not shown) along its length. In other embodiments, the electricity supply network is other than a TN-C-S network.

[0069] The supply phase conductor P and supply PEN conductor may service multiple installations. They may run along a street, either overground or below ground.

[0070] A service lateral phase conductor P1 connects the electrical supply 10 of the first installation 1 to the supply phase conductor P. At the service point SP, the service lateral phase conductor P1 connects to or continues as a phase conductor P1 of the electrical supply 10.

[0071] A service lateral PEN conductor PEN1 connects the electrical supply 10 of the first installation 1 to the shared PEN conductor.

[0072] The service lateral PEN conductor PEN1 of the electricity supply network terminates at a neutral-earth link NEL such as a busbar or other electrically conductive connector. The neutral-earth link NEL is located either at the service point SP, or just before or just after the service point SP.

[0073] A neutral conductor N1 and an earth conductor E1 each terminate at the neutral-earth link NEL, and are each electrically connected to the PEN conductor PEN1.

[0074] The phase conductor P1 , neutral conductor N1 , and earth conductor E1 extend to a distribution unit DU, optionally via a meter (not shown). The distribution unit DU is a distribution board that divides the phase conductor P1 , neutral conductor N1 , and earth conductor E1 to a plurality of subsidiary / load circuits LC. For example, the load circuits LC may comprise one or more of a lighting circuit, a socket circuit, an alarm circuit, an outbuilding circuit, etc. The distribution unit DU may further comprise one or more circuit breakers, fuses, and / or a residual current device.

[0075] The earth conductor E1 comprises a MET between the neutral-earth link NEL and the distribution unit DU. The MET. The MET is a busbar or comprises a plurality of terminals, to facilitate additional electrical connections. A first electrical connection of the MET connects the earth conductor E1 to the distribution unit DU. The MET comprises a further electrical connection to a wire connecting the MET to a bonding B1 in the form of a metal pipe. In some examples, multiple different bondings are connected, but only one is shown. The bonding B1 may comprise a water pipe or gas pipe, for example. In other examples, the bonding B1 is a metal building element such as steelwork.

[0076] The bonding B1 in FIG. 1 is connected to a street-connected service SCS (shared bonding). This can comprise a street water pipe or a district water pipe, or a street gas pipe or district gas pipe, for example. The street-connected service SCS may be buried underground or may be overground.

[0077] The DNC detector 100 is also illustrated in FIG. 1. The DNC detector 100 comprises circuitry (controller 201) connected to a current sensor arrangement including a phase current sensor CTP, a neutral current sensor CTN, and a bidirectional earth current sensor CTE. The current sensors may comprise current transformers, for example. The controller 201 is further connected to a voltage sensor VS connected to the phase conductor P1 and neutral conductor N1 to detect a voltage therebetween.

[0078] The DNC detector 100 may be either hard-wired into the electrical supply 10 as part of the installation, or may be implemented as part of a hand-portable test instrument.

[0079] Turning now to FIG. 2, a schematic of an apparatus 200 is illustrated, the apparatus

[0080] 200 comprising the controller 201 of the DNC detector 100 and one or more output devices. The apparatus 200 may further comprise the sensors (not shown in FIG. 2).

[0081] FIG. 200 illustrates an example of a controller 201 suitable for use in an apparatus 200. Implementation of a controller 201 may be as controller circuitry. The controller

[0082] 201 may be implemented in hardware alone, have certain aspects in software including firmware alone or can be a combination of hardware and software (including firmware).

[0083] As illustrated in FIG. 200 the controller 201 may be implemented using instructions that enable hardware functionality, for example, by using executable instructions 206 in a general-purpose or special-purpose processor 202 that may be stored on a machine readable storage medium (disk, memory etc.) to be executed by such a processor 202.

[0084] The processor 202 is configured to read from and write to the memory 204. The processor 202 may also comprise an output interface via which data and / or commands are output by the processor 202 and an input interface via which data and / or commands are input to the processor 202.

[0085] The memory 204 stores instructions, program, or code 206 that controls the operation of the apparatus 200 when loaded into the processor 202. The computer program instructions, program or code am 206, provide the logic and routines that enables the apparatus 200 to perform the methods illustrated in the accompanying FIGs. The processor 202 by reading the memory 204 is configured to load and execute the instructions, program, or code 206.

[0086] The apparatus / DNC detector 100 further comprises one or more of the following: a display 208, a loudspeaker 210, a wireless communication transceiver 212 (or transmitter), or an isolator 214.

[0087] The display 208 and loudspeaker 210 are configured to render alerts to people in the vicinity of the apparatus 200. The wireless communication transceiver 212 is configured to transmit alerts to a remote service or wide area network, causing a remote application or device outside the property to render an alert.

[0088] The isolator 214 comprises a shunt trip or similar disconnector which disconnects one or more of the phase conductor(s) P1 , neutral conductor N1 , and earth conductor E1. The isolator 214 may be mounted upstream of the load circuits LC, such as to the distribution unit DU, or between the neutral-earth link NEL and the distribution unit DU, or between the service point SP and the neutral-earth link NEL.

[0089] The DNC detector 100 can comprise an input for resetting an alert, such as a button (not shown). The isolator 214 and / or the DNC detector 100 can comprise an input for resetting the isolator 214, such as a button (not shown). As illustrated in FIG. 3, the instructions, program, or code 206 may arrive at the apparatus 200 via any suitable delivery mechanism 300. The delivery mechanism 300 may be, for example, a machine readable medium, a computer-readable medium, a non-transitory computer-readable storage medium, a computer program product, a memory device, a record medium such as a Compact Disc Read-Only Memory (CD- ROM) or a Digital Versatile Disc (DVD) or a solid-state memory, an article of manufacture that comprises or tangibly embodies the computer program 206. The delivery mechanism may be a signal configured to reliably transfer the computer program 206. The apparatus 200 may propagate or transmit the computer program 206 as a computer data signal.

[0090] Although the memory 204 is illustrated as a single component / circuitry it may be implemented as one or more separate components / circuitry some or all of which may be integrated / removable and / or may provide permanent / semi-permanent / dynamic / cached storage.

[0091] Although the processor 202 is illustrated as a single component / circuitry it may be implemented as one or more separate components / circuitry some or all of which may be integrated / removable. The processor 202 may be a single core or multi-core processor.

[0092] The computer program instructions may be comprised in a computer program, a non- transitory computer readable medium, a computer program product, a machine readable medium. In some but not necessarily all examples, the computer program instructions may be distributed over more than one computer program.

[0093] References to ‘computer-readable storage medium’, ‘computer program product’, ‘tangibly embodied computer program’ etc. or a ‘controller’, ‘computer’, ‘processor’ etc. should be understood to encompass not only computers having different architectures such as single / multi- processor architectures and sequential (Von Neumann) / parallel architectures but also specialized circuits such as field-programmable gate arrays (FPGA), application specific circuits (ASIC), signal processing devices and other processing circuitry. References to computer program, instructions, code etc. should be understood to encompass software for a programmable processor or firmware such as, for example, the programmable content of a hardware device whether instructions for a processor, or configuration settings for a fixed-function device, gate array or programmable logic device etc.

[0094] FIG. 4 illustrates a computer-implemented method 400. The method is implemented by the apparatus 200 / controller 201. The apparatus 200 comprises: at least one processor 202; and at least one memory 204 storing instructions that, when executed by the at least one processor 202, cause the apparatus 200 at least to: execute the steps of the method 400.

[0095] The method 400 comprises four separate conditions, for indicating at least three different types of DNC shown in FIGS. 5-7. Different types of DNC depend on where the DNC occurs, which creates different currents or voltages at different points in the electrical supply 10. It is advantageous but not necessary for all four of the conditions to be implemented.

[0096] At block 402, the method 400 comprises receiving information from the current sensor arrangement, indicating electrical current in a current carrier conductor and an earth conductor E1 of an electrical supply 10, and determining whether a first condition is satisfied in dependence on the information from the current sensor arrangement, wherein satisfaction of the first condition is dependent on comparison of electrical current between the current carrier conductor and the earth conductor E1 .

[0097] At block 404, the method 400 comprises outputting one or more first signals in dependence on satisfaction of the first condition. If the first condition is not satisfied, the one or more first signals are not output.

[0098] An example of the first condition is described later with respect to FIG. 5.

[0099] At block 406, the method 400 comprises receiving information from the current sensor arrangement indicating electrical current in the earth conductor E1 , and determining whether a second condition is satisfied in dependence on the information from the current sensor arrangement, wherein satisfaction of the second condition is dependent on a direction of electrical current flow in the earth conductor E1 . At block 408, the method 400 comprises outputting one or more second signals in dependence on satisfaction of the second condition. If the second condition is not satisfied, the one or more second signals are not output.

[0100] An example of the second condition is described later with respect to FIG. 6.

[0101] At block 410, the method 400 comprises receiving information from the current sensor arrangement, indicating electrical current in the phase conductor P1 and the neutral conductor N1 , and determining whether a third condition is satisfied in dependence on the information from the current sensor arrangement (from the phase current sensor CTP and neutral current sensor CTN), wherein satisfaction of the third condition is dependent on comparison of the phase current and neutral current.

[0102] At block 412, the method 400 comprises outputting one or more third signals in dependence on satisfaction of the third condition. If the third condition is not satisfied, the one or more third signals are not output.

[0103] An example of the third condition is described later with respect to FIG. 7.

[0104] At block 414, the method 400 comprises receiving information from the voltage sensor VS, indicating a phase-to-neutral voltage, and determining whether a fourth condition is satisfied in dependence on the information from the voltage sensor VS, wherein satisfaction of the fourth condition is dependent on the phase-to-neutral voltage being less than a lower voltage threshold and / or greater than an upper voltage threshold.

[0105] At block 416, the method 400 comprises outputting one or more fourth signals in dependence on satisfaction of the fourth condition. If the fourth condition is not satisfied, the one or more fourth signals are not output.

[0106] An example of the fourth condition is described later with respect to FIG. 5.

[0107] The one or more first / second / third / fourth signals may comprise an alert triggering signal. For example, the alert triggering signal may control an audio rendering device such as the loudspeaker 210, and / or a visible light rendering device such as the display 208. Additionally, or alternatively, the alert triggering signal may be transmitted to a communication interface such as the wireless communication transceiver 212. This alerts nearby users to the presence of DNC.

[0108] Alternatively, or additionally, the one or more first / second / third fourth signals comprise one or more supply disconnection control signals. The one or more supply disconnection control signals comprise an isolation signal configured to isolate one or more conductors of the electrical supply 10. For example, the isolation signal may be transmitted to the isolator 214 to cause the isolation / disconnection.

[0109] Alternatively, or additionally, if the property comprises a microgeneration circuit to provide local power generation at the property, the one or more supply disconnection control signals may comprise a microgenerator isolation signal to isolate a microgenerator circuit from the electrical supply 10.

[0110] The blocks illustrated in FIG. 4 may represent steps in a method 400 and / or sections of code in the computer program 206. The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible for some blocks to be omitted.

[0111] FIG. 5 illustrates a first example DNC fault, detectable by one or both of the first condition or the fourth condition.

[0112] A pair of installations 1 , 2 are shown, connected by a shared bonding SCS. The electrical supplies (installations) are shown in two separate buildings but may alternatively be in a same building / property.

[0113] The shared bonding in this case is a street-connected service SCS such as a gas pipe or water pipe. The PEN conductor PEN1 at the first installation 1 is broken. As a result, the arrows show the neutral current returning to source from the distribution unit DU via the following path:

[0114] - neutral conductor N1 of first installation 1 ,

[0115] - neutral-earth link NEL of first installation 1 ,

[0116] - earth conductor E1 of first installation 1 ,

[0117] - MET of first installation 1 ,

[0118] - bonding B1 of first installation 1 ,

[0119] - street-connected service SCS,

[0120] - bonding B2 of second installation 2,

[0121] - MET of second installation 2,

[0122] - earth conductor E2 of second installation 2,

[0123] - neutral-earth link NEL of second installation 2,

[0124] - PEN conductor PEN2 of second installation 2,

[0125] - supply PEN conductor.

[0126] As a consequence, the electrical current in the earth conductor E1 of the first installation 1 is approximately equal to the electrical current in the neutral conductor N1 of the first installation 1. In normal operation, it would be significantly lower.

[0127] Therefore, satisfaction of the first condition is based on a threshold requiring the electrical currents of the conductors detected by the earth current sensor CTE and neutral current sensor CTN to match or approximately match. When they match or almost match, this is a strong indicator of an abnormal DNC resulting from a broken or faulty PEN conductor PEN1 at the first installation 1.

[0128] Therefore, an alert may be triggered and / or the electrical supply 10 of the first installation 1 may be isolated.

[0129] Whether the threshold of the first condition requires equality or is set to less than the neutral conductor N1 depends on calibration. If the threshold is too low, normal DNCs will trigger an unwanted alert or isolation. If the threshold is too high, some abnormal DNCs may not be detected. If an acceptable level of DNC is low, then the threshold may be set substantially lower than requiring equality, such as at least 50% or at least 80%.

[0130] The first condition may also comprise a lower limit of the absolute value of the current in the neutral conductor N1 and / or in earth conductor E1 , requiring it to be greater than 2A, or some other value greater than 1 A or greater than 1 ,5A. This is because in some situations such as evening usage, there may be zero or near-zero power on the neutral conductor N1 and earth conductor E1 so their currents would match despite the absence of a DNC fault.

[0131] Although the above-described first condition compares the currents in the earth and neutral conductors E1 , N1 , in another embodiment the comparison is between the earth and phase conductors E1 , P1.

[0132] The voltage-based fourth condition is also capable of detecting the first DNC fault of FIG. 5. This is because the phase-to-neutral voltage will be significantly lower than the nominal supply voltage due to the electricity now flowing in a longer and higher- resistance path.

[0133] For example, in the United Kingdom the fourth condition may allow a range of 207V to 258V relative to a nominal supply voltage of 230V. Alternatively, the fourth condition may just have a lower limit (e.g., 207V) without an upper limit. When the voltage is outside this range, it indicates a fault such as a DNC.

[0134] The range above is only an example, and may vary depending on the nominal supply voltage of the current, and the percentage variation which is allowed by the network operator. For example, the United Kingdom allows actual voltage to be within -6% or +10% of the nominal supply voltage while being treated as normal, whereas other countries may define a range of ±6% or ±10%, or some other range. Either way, the range or lower limit defined by the fourth condition may be one or more volts wider than the range specified as acceptable by the network operator. The exact values will depend on calibration.

[0135] FIG. 6 illustrates a second example DNC fault, detectable by the second condition. The supply PEN conductor is broken between the first and second installations 1 , 2. As a result, the arrows show the neutral current of the second installation 2 returning to source via the first installation 1 along the following path:

[0136] - neutral conductor N2 of second installation 2,

[0137] - neutral-earth link NEL of second installation 2,

[0138] - earth conductor E2 of second installation 2,

[0139] - MET of second installation 2,

[0140] - bonding B2 of second installation 2,

[0141] - street-connected service SCS,

[0142] - bonding B1 of first installation 1 ,

[0143] - MET of first installation 1 ,

[0144] - earth conductor E1 of first installation 1 ,

[0145] - neutral-earth link NEL of first installation 1 ,

[0146] - PEN conductor PEN1 of first installation 1 ,

[0147] - supply PEN conductor.

[0148] As a consequence, the electrical current in the earth conductor E1 is towards the first installation 1. In normal operation, the current would flow out of the first installation 1.

[0149] Therefore, satisfaction of the second condition is based on the direction of electrical current flow detected by the earth current sensor CTE being towards the neutral-earth link NEL, and greater than a minimum threshold such as 5A, or some other value of at least 4A. When the direction along the earth conductor E1 is into the first installation 1 and is at a high magnitude, this is a strong indicator that a PEN conductor has broken somewhere else, resulting in high current flowing into the first installation 1.

[0150] Therefore, an alert may be triggered and / or the electrical supply 10 of the first installation 1 may be isolated.

[0151] The minimum threshold of the second condition depends on calibration. If the threshold is too low, normal DNCs may trigger an unwanted alert or isolation. If the threshold is too high, some abnormal DNCs may not be detected. FIG. 7 illustrates a third example DNC fault, detectable by the third condition.

[0152] The PEN conductors may be intact, but the neutral current in the first installation 1 has somehow found another parallel path into the bonding B1. In FIG. 7, a line has been drawn connecting one of the load circuits LC to the bonding B1 , indicating that one of the load circuits LC has become connected to the bonding B1 , for example due to decomposing insulation.

[0153] Since the diversion occurs before the earth current sensor CTE, the first condition may not detect this type of DNC fault. The second condition will not detect it either. Therefore, the third condition has been devised which comprises comparing the neutral current with the phase current, based on information from the neutral current sensor CTN and phase current sensor CTP. If the neutral current differs from the phase current by more than a range such as ±5A defined by lower and upper thresholds, this is a strong indicator that a DNC fault has occurred somewhere. For example, one would expect the current in the neutral conductor N1 to drop because the rest of the neutral current has found another path to the source which is parallel to the neutral conductor N1.

[0154] Therefore, an alert may be triggered and / or the electrical supply 10 of the first installation 1 may be isolated.

[0155] The lower and upper thresholds of the second condition depend on calibration. If the lower threshold is too low, normal DNCs will trigger an unwanted alert or isolation. If the lower threshold is too high, some abnormal DNCs may not be detected. In other implementations, only the lower threshold is used, rather than a range.

[0156] In summary, a DNC detector for detecting a wide range of DNC faults is disclosed. In other implementations, the DNC may be configured to detect one or more, but not all of the DNC faults disclosed herein.

[0157] In the preceding disclosure, where a structural feature has been described, it may be replaced by means for performing one or more of the functions of the structural feature whether that function or those functions are explicitly or implicitly described. The description of a feature, such as an apparatus or a component of an apparatus, configured to perform a function, or for performing a function, should additionally be considered to also disclose a method of performing that function. For example, description of an apparatus configured to perform one or more actions, or for performing one or more actions, should additionally be considered to disclose a method of performing those one or more actions with or without the apparatus.

[0158] Although features have been described with reference to certain examples, those features may also be present in other examples whether described or not.

[0159] The presence of a feature (or combination of features) in a claim is a reference to that feature or (combination of features) itself and to features that achieve substantially the same technical effect (equivalent features). The equivalent features include, for example, features that are variants and achieve substantially the same result in substantially the same way. The equivalent features include, for example, features that perform substantially the same function, in substantially the same way to achieve substantially the same result.

[0160] In this description, reference has been made to various examples using adjectives or adjectival phrases to describe characteristics of the examples. Such a description of a characteristic in relation to an example indicates that the characteristic is present in some examples exactly as described and is present in other examples substantially as described.

[0161] The above description describes some examples of the present disclosure however those of ordinary skill in the art will be aware of possible alternative structures and method features which offer equivalent functionality to the specific examples of such structures and features described herein above and which for the sake of brevity and clarity have been omitted from the above description. Nonetheless, the above description should be read as implicitly including reference to such alternative structures and method features which provide equivalent functionality unless such alternative structures or method features are explicitly excluded in the above description of the examples of the present disclosure. Whilst endeavoring in the foregoing specification to draw attention to those features believed to be of importance the Applicant may seek protection via the claims in respect of any patentable feature or combination of features hereinbefore referred to and / or shown in the drawings whether or not emphasis has been placed thereon. l / we claim:

Claims

CLAIMS1 . A diverted neutral current detector comprising: a current sensor arrangement to detect electrical current in a current carrier conductor and an earth conductor of an electrical supply; and circuitry configured to: determine whether a first condition is satisfied in dependence on information from the current sensor arrangement, wherein satisfaction of the first condition is dependent on comparison of electrical current between the current carrier conductor and the earth conductor; determine whether a second condition is satisfied in dependence on information from the current sensor arrangement, wherein satisfaction of the second condition is dependent on a direction of electrical current flow in the earth conductor; output one or more first signals in dependence on satisfaction of the first condition; and output one or more second signals in dependence on satisfaction of the second condition.

2. The diverted neutral current detector of claim 1 , wherein satisfaction of the first condition is dependent on electrical current in one of the conductors being greater than a threshold, and wherein the threshold is dependent on electrical current in the other conductor.

3. The diverted neutral current detector of claim 2, wherein the threshold of the first condition is equal to or at least 50% of electrical current in the other conductor.

4. The diverted neutral current detector of claim 2 or 3, wherein satisfaction of the first condition is further dependent on electrical current in at least one of the conductors being greater than a lower limit.

5. The diverted neutral current detector of claim 4, wherein the lower limit is at least one Amp or at least 1 .5 Amps.

6. The diverted neutral current detector of any preceding claim, wherein the current carrier conductor is a neutral conductor.

7. The diverted neutral current detector of any preceding claim, wherein the one or more first signals comprise a supply disconnection control signal and / or an alert triggering signal.

8. The diverted neutral current detector of any preceding claim, wherein satisfaction of the second condition is dependent on the direction of electrical current flow in the earth conductor being towards a neutral-earth link.

9. The diverted neutral current detector of any preceding claim, wherein satisfaction of the second condition is further dependent on electrical current flow in the earth conductor being greater than a threshold.

10. The diverted neutral current detector of claim 9, wherein the threshold of the second condition is greater than or equal to four Amps.11 . The diverted neutral current detector of any preceding claim, wherein the one or more second signals comprise a supply disconnection control signal and / or an alert triggering signal.

12. The diverted neutral current detector of any preceding claim, wherein the current sensor arrangement comprises first and second current sensors to respectively detect phase current and neutral current in a pair of current carrier conductors including a phase conductor and a neutral conductor, and wherein the circuitry is configured to: determine whether a third condition is satisfied in dependence on information from the first and second current sensors, wherein satisfaction of the third condition is dependent on comparison of the phase current and neutral current; and output one or more third signals in dependence on satisfaction of the third condition.

13. The diverted neutral current detector of claim 12, wherein satisfaction of the third condition is dependent on one of the neutral or phase current being less than alower threshold dependent on the other of the neutral or phase current, and / or greater than an upper threshold dependent on the other of the neutral or phase current.

14. The diverted neutral current detector of claim 13, wherein the lower threshold and / or the upper threshold define a range relative to the other of the phase or neutral current.

15. The diverted neutral current detector of claim 13 or 14, wherein the lower threshold and / or upper threshold is at least multiple Amps different than the other of the phase or neutral current.

16. The diverted neutral current detector of any one of claims 12 to 15, wherein the one or more third signals comprise a supply disconnection control signal and / or an alert triggering signal.

17. The diverted neutral current detector of any preceding claim, further comprising a voltage sensor to detect a phase-to-neutral voltage, and wherein the circuitry is configured to: determine whether a fourth condition is satisfied in dependence on information from the voltage sensor, wherein satisfaction of the fourth condition is dependent on the phase-to-neutral voltage being less than a lower voltage threshold and / or greater than an upper voltage threshold; and output one or more fourth signals in dependence on satisfaction of the fourth condition.

18. The diverted neutral current detector of claim 17, wherein the lower voltage threshold is at least 6% less than nominal supply voltage, and / or wherein the upper voltage threshold is at least 6% or at least 10% greater than nominal supply voltage.

19. The diverted neutral current detector of claim 17 or 18, wherein the one or more fourth signals comprise a supply disconnection control signal or an alert triggering signal.

20. The diverted neutral current detector of any preceding claim, wherein the one or more first signals and / or one or more second signals comprise a microgenerator isolation signal to isolate a microgenerator circuit.

21. An electrical supply comprising the diverted neutral current detector of any preceding claim, wherein the current sensor arrangement comprises one or more of: a phase current sensor connected to a phase current carrier conductor between a supply point and a distribution unit; a neutral current sensor connected to a neutral current carrier conductor between the supply point and the distribution unit; or an earth current sensor connected to the earth conductor between a neutralearth link and a main earthing terminal.

22. A hand-portable test instrument comprising the diverted neutral current detector of any one of claims 1 to 20.

23. An apparatus comprising at least one processor, and at least one memory including computer program code, the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to perform at least: receiving information from a current sensor arrangement, indicating electrical current in a current carrier conductor and an earth conductor of an electrical supply; determining whether a first condition is satisfied in dependence on the information from the current sensor arrangement, wherein satisfaction of the first condition is dependent on comparison of electrical current between the current carrier conductor and the earth conductor; determining whether a second condition is satisfied in dependence on the information indicating the electrical current in the earth conductor, wherein satisfaction of the second condition is dependent on a direction of electrical current flow in the earth conductor; outputting one or more first signals in dependence on satisfaction of the first condition; and outputting one or more second signals in dependence on satisfaction of the second condition.

24. A method of detecting diverted neutral current, the method comprising: receiving information from a current sensor arrangement, indicating electrical current in a current carrier conductor and an earth conductor of an electrical supply; determining whether a first condition is satisfied in dependence on information from the current sensor arrangement, wherein satisfaction of the first condition is dependent on comparison of electrical current between the current carrier conductor and the earth conductor; determining whether a second condition is satisfied in dependence on the information indicating the electrical current in the earth conductor, wherein satisfaction of the second condition is dependent on a direction of electrical current flow in the earth conductor; outputting one or more first signals in dependence on satisfaction of the first condition; and outputting one or more second signals in dependence on satisfaction of the second condition.

25. A computer program comprising instructions, which, when executed by an apparatus, cause the apparatus to perform the method of claim 24.

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