GB2571450A

GB2571450A - Apparatus for electrical measurement

Info

Publication number: GB2571450A
Application number: GB1901744.1A
Authority: GB
Inventors: Aydemir Tolga; James Wales Duncan; William Mackay Alan; Jelley Simon
Original assignee: 42 Technology Ltd
Current assignee: 42 Technology Ltd
Priority date: 2018-02-07
Filing date: 2019-02-07
Publication date: 2019-08-28
Anticipated expiration: 2039-02-07
Also published as: GB201806528D0; GB2604571A; GB2604571B; GB201802023D0; GB2571450B; GB201901744D0; GB202209525D0

Abstract

A measurement apparatus for performing electrical measurements of a fuseway comprising a low resistivity busbar, with a pair of contacts 69, 64, arranged to measure voltage-drop across or current through a segment of the busbar between the contacts. Signal lines 63 and 65 are arranged to substantially cancel the magnetic coupling between the busbar and the signal lines. The current passing through the segment may be calculated from a measured voltage and a known resistance. The busbar may form a contact for a fuse or fuse-holder (13 figure 2). Secondarily, an apparatus comprising an interface for connecting to a fuseholder (9 figure 1) is defined, comprising a pair of contacts (13 figure 2) and a measurement circuit (50 figure 7), in addition to an electrical supply circuit (figure 11) arranged to provide power from the fuseway to the measurement circuit when the apparatus is engaged with a fuseway. A control panel (figure 5) may be provided to display or store results of tests.

Description

(57) A measurement apparatus for performing electrical measurements of a fuseway comprising a low resistivity busbar, with a pair of contacts 69, 64, arranged to measure voltage-drop across or current through a segment of the busbar between the contacts. Signal lines 63 and 65 are arranged to substantially cancel the magnetic coupling between the busbar and the signal lines. The current passing through the segment may be calculated from a measured voltage and a known resistance. The busbar may form a contact for a fuse or fuse-holder (13 figure 2). Secondarily, an apparatus comprising an interface for connecting to a fuseholder (9 figure 1) is defined, comprising a pair of contacts (13 figure 2) and a measurement circuit (50 figure 7), in addition to an electrical supply circuit (figure 11) arranged to provide power from the fuseway to the measurement circuit when the apparatus is engaged with a fuseway. A control panel (figure 5) may be provided to display or store results of tests.

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Intellectual

Property

Office

Application No. GB1901744.1

RTM

Date :19 June 2019

The following terms are registered trade marks and should be read as such wherever they occur in this document:

- Kapton

- Bluetooth

Intellectual Property Office is an operating name of the Patent Office www.gov.uk/ipo

Apparatus for Electrical Measurement

The present invention relates to apparatus for performing electrical measurements of low voltage fuseways.

Within the field of electrical distribution there is increasing pressure to save costs while providing a more consistent and reliable service to consumers, specifically fewer drop outs or power cuts.

This requires optimisation of the use of installed infrastructure, such that it is exploited to its full capacity without overloading said infrastructure. To manage this optimisation, it is required to know the conditions experienced by the infrastructure, such as power consumption, current consumption, active and reactive loads, phase balance, etc.. For practical reasons, in reference to low-voltage distribution, this is typically measured within the low-voltage substation.

There are a number of systems for measuring such metrics within a low-voltage installation. In specific relation to a fuseway - fuse holder system, these can be grouped into two categories, first whereby the measurement equipment is integrated into or installed with the fuseway, and secondly whereby the measurement equipment is integrated into the fuse holder.

Examples of the first category are disclosed, for example, in WO 2016/024033, DE 10062644 and DE 202010017635. These systems integrate with the infrastructure without the need for flying leads connecting to other points within the substation beyond the fuseway to be measured; however, they are challenging to retrofit into an installed or existing system. Typically, they require at least to an extent detachment or disassembly of the fuseway, requiring an extended disconnection time or power outage, and as such are most appropriate for installation in new substations or infrastructure, or during refits.

Examples of the second category include, for example, the Lucy™ AcuLok™ Fuse Handle, which is a fuse holder with access for a Rogowski coil, such that current can be measured with an external device without directly accessing the fuse.

-2However, owing to the requirement for an external logging device significant installation time is required, and if logging is to be installed across multiple phases and left installed for a prolonged period of time then a significant number of flying leads are required and must be left in situ. This has the effect of cluttering the substation and thus making fuse replacement more challenging.

Typically, to power the logging device, a standard 230V mains socket would also be required within the substation, which may or may not be installed as standard, and as such for installation in all potential scenarios, consideration must be given to the cost of installing a 230V mains socket in those substations that do not have one. Additionally, the chance of damage to the sensitive measurement is increased owing to the need to repeatedly remove and re-install the associated measurement equipment in the fuse holder each time the fuse is replaced.

Another system is the Calmin Group™ Bidoyng™, which uses an intermediary measurement apparatus between the fuseway and fuse holder. This allows the measurement apparatus to be left in situ while the fuse holder and fuse is swapped out. However, such an apparatus still requires a connection to the neutral per fuse to power the measurement apparatus and provide a reference for the phase voltage.

Regardless of powering methods, commercially available current measurement systems for use in three phase fuseways, use magnetic sensing, such as Hall effect sensors, or most commonly, Rogowski coils, to determine the current flowing. Rogowski coils are more expensive and have relatively large dimensions (e.g. compared with shunt resistors) and such measurement methods struggle to achieve high accuracy as they are not immune to other surrounding magnetic fields. In addition, they are typically less sensitive to high frequency transients. Shunt resistors perform better in these areas, but owing to the high currents involved and high temperature variation, shunts have proved too difficult to implement in three phase fuseways in practice.

For lower current systems shunts are more common as an easy to measure voltage drop does not dissipate significant power or generate significant heat. This allows the use of higher resistivity conductors as shunt resistors with higher total

-3resistance. Higher resistivities lead to more even current distribution in the shunt. In lower current systems the magnetic fields generated around conductors are not intense enough to create magnetic coupling issues in wires, especially if the voltage drop across the shunt is relatively high (10s to 100s of millivolts).

In high current systems, such as three phase fuseways where hundreds of amps can flow, even tens of millivolt drops generate significant heat, with further heat generated by the nearby fuse exacerbating this. The magnetic coupling of the sensor wires to the field around the conductor is unacceptably high, even if the wires are brought together and twisted with the minimum wire length (point to point between the sensing contacts either end of the measured length). Parallel paths of higher resistance can be used to infer total current, but as the current in the parallel paths depends on the resistance of each path, this is inaccurate in real world applications where temperature changes and magnetic coupling impact the distribution of current between the paths.

There exists a need to provide improved apparatus for performing electrical measurements of an electrical fuseway.

According to a first aspect of the present invention, there is provided an apparatus to perform measurements of a low voltage electrical fuseway, the apparatus comprising at least one fuseway-side interface with suitable geometry to fit a standard fuseholder interface on the fuseway and further comprising contacts such that when the fuseway-side interface is connected to a standard fuseway the contacts engage electrically with the blade contacts that are provided on the fuseway to engage with the fuse holder, such that the apparatus can be retrofitted to fuseways not designed for fitment of measuring apparatus;

wherein the apparatus comprises a measurement circuit that requires an electrical supply and an electrical supply circuit that provides this electrical supply, where the power to provide this electrical supply may substantially be received directly or indirectly from the fuseway.

When viewed from a second aspect the present invention provides an apparatus for performing electrical measurements of an electrical fuseway, wherein the apparatus comprises:

-4a fuseway-side interface for connecting to a fuseholder interface of a fuseway;

a pair of contacts for electrically connecting to a pair of contacts of the fuseway;

a measurement circuit for performing electrical measurements of the fuseway, wherein the measurement circuit is arranged to perform electrical measurements of the fuseway via one or more of the pair of contacts for electrically connecting to the pair of contacts of the fuseway; and an electrical supply circuit for providing an electrical supply to the measurement circuit;

wherein the electrical supply circuit is arranged such that when the fusewayside interface of the apparatus is connected to the fuseholder interface on the fuseway the electrical supply circuit receives power substantially directly or indirectly from the fuseway to provide the electrical supply to the measurement circuit.

The present invention provides an apparatus for performing electrical measurements of an electrical fuseway. The apparatus includes a fuseway-side interface for connecting to the fuseholder interface of a fuseway. The apparatus also includes a pair of contacts (e.g. as part of the fuseway-side interface) for connecting electrically (and, e.g., mechanically) to a (respective) pair of contacts in the (e.g. fuseholder interface of the) fuseway, when the fuseway-side interface of the apparatus is connected to the fuseholder interface on the fuseway. Thus the fuseway is arranged to receive a fuseholder in its fuseholder interface (e.g. were the apparatus not to be connected thereto).

A measurement circuit in the apparatus is configured to perform electrical measurements of the fuseway (when the fuseway-side interface of the apparatus is connected to the fuseholder interface on the fuseway) and an electrical supply circuit of the apparatus is arranged to provide an electrical supply to the measurement circuit (when the fuseway-side interface of the apparatus is connected to the fuseholder interface on the fuseway). The electrical supply circuit is arranged such that when the fuseway-side interface of the apparatus is connected to the fuseholder interface on the fuseway, the electrical supply circuit receives power substantially directly or indirectly from the fuseway. This enables

-5the electrical supply circuit to provide the electrical supply to the measurement circuit.

Thus it will be appreciated that by connecting to the fuseholder interface of a fuseway, the apparatus is able to connect to, and thus perform electrical measurements of, the fuseway. This allows the apparatus to be (retro)fitted into fuseways that otherwise may not have permitted measurement apparatus to be fitted thereto. Furthermore, the electrical supply circuit which powers the measurement circuit means that there is no need to connect externally to either the neutral or another power source (such as a power socket) in order to power the apparatus or perform (e.g. voltage, phase angle and power parameter) measurements, e.g. in a neutral loss condition. This simplifies the installation process and avoids complex wiring, e.g. where multiple units each have neutral connections. While neutral connection may be included for measurement purposes, the apparatus is flexible to be installed without such a connection, as required, without compromising power supply.

Preferably the apparatus is arranged to perform electrical measurements on a low voltage fuseway. Low voltage is preferably defined (e.g. according to the International Electrotechnical Commission) as being between 50V and 1000V AC (or 120 and 1500V DC).

The pair of contacts of the apparatus may connect with the (respective) pair of contacts on the fuseway in any suitable and desired way. For example, the (fuseway-side interface of the) apparatus may comprise male contacts and the (fuseholder interface of the) fuseway may comprise female contacts, or vice versa.

The apparatus may also comprise energy storage means and include means to supply power from the energy storage means to at least some of the apparatus. This helps to enable beneficial functionality during loss of supply to the fuseway, or when the apparatus is not fitted to a fuseway such as maintaining a real time clock, completing write cycles to non-volatile memory (to avoid data corruption), or storing of volatile memory. It may also provide additional benefits of enabling communications, monitoring or measuring by powering additional circuits as required.

-6The apparatus may comprise charging means to store energy received from the fuseway in the energy storage means. This helps to allow covering more power outages with the energy storage means for a given capacity, enabling longer system life and/or allow higher power consumption when unpowered such as using communication means.

The apparatus may be connected electrically to more than one phase. Thus preferably the apparatus comprises: a plurality of fuseway-side interfaces for connecting to a plurality of fuseholder interfaces of the fuseway; and a plurality of pairs of contacts for electrically connecting to a plurality of pairs of contacts of the fuseway. This may allow power to be received by utilising the voltage between the phases. The apparatus may achieve this by creating a virtual neutral between the three phases of a three-phase supply, or by directly drawing current between phases, or preferably by rectifying power from the phases into a high voltage DC source and stepping that down to low voltage, for example by means of a switch mode power supply. The virtual neutral contact formed between the plurality of pairs of contacts may be used as a reference voltage for measuring the voltage of a phase.

Thus preferably the electrical supply circuit is arranged to receive power from the fuseway by using the voltage (potential difference) between respective pairs of the plurality of pairs of contacts of the fuseway (e.g. between phase modules or the busbars) or between the pair of contacts and a neutral connection (when provided).

Preferably the plurality of fuseway-side interfaces are electrically connected together. Preferably the electrical supply circuit is arranged to receive power from the fuseway by drawing a current from the connections between the plurality of fuseway-side interfaces or between a neutral connection and each of at least one of the plurality of pairs of contacts of the fuseway.

Connection to one phase could enable power scavenging from the electromagnetic field induced by the voltage of and/or current flowing through that phase, such as creating mutual inductance or capacitive coupling. It should be noted that this

-7approach is complex as it will give a low maximum supply power, and may be reliant on current draw through the phase. A preferred approach is a much simpler option: the apparatus comprises direct connection to multiple phases and draws a small current between the connections to power the apparatus. This approach helps to allow power to be received even if no load current is flowing through the phase (such as if the fuse has blown). Preferably the power is less than 1 W (e.g. per phase module). Thus, for example, at about 230 V, the current drawn is less than 5 mA.

The apparatus may additionally comprise a fuse-side interface provided to connect electrically and mechanically to a fuse. Preferably, the fuse-side interface is adapted to interface with a standard fuse-holder containing a fuse. This helps to allow the core purpose of the fuseway assembly to be maintained without requiring the inclusion of a fuse within the apparatus. While the Applicant considers their invention to be applicable to a wide range of different types of fuses and fuse holders, in one embodiment the fuse-side interface is arranged to receive a J type fuse link fuseholder, e.g. having a fixating centre of 82 mm or 92 mm and, e.g., a rating of between 20 A and 800 A.

In a preferred embodiment, the fuse-side interface is adapted to interface with a fuse-holder of a type suitable for installation into the fuse holder interface of the fuseway such that the fuse-side interface substantially resembles the fuse holder interface, e.g. the fuse-side interface and the fuse-side contacts are complementary to the fuseway-side interface and the fuseway-side contacts. This helps to allow the apparatus to be installed between a fuseway and fuse holder of a standard matching type, reducing the number of new components that must be installed to install the apparatus, and increasing the familiarity of installation for the installer.

Thus preferably the apparatus (e.g. each phase module) comprises a fuseholder interface for connecting to a fuseholder and a pair of contacts for electrically connecting to a pair of contacts of the fuseholder. The pair of contacts of the apparatus may connect with the (respective) pair of contacts on the fuseholder in any suitable and desired way. For example, the (fuseholder-side interface of the) apparatus may comprise male contacts and the (fuseway interface of the) fuseholder may comprise female contacts, or vice versa.

-8The apparatus may comprise a plurality of phase (measurement apparatus) modules each comprising a fuseway-side interface provided to connect electrically to at least one fuse holder interface ofthe fuseway, wherein the phase modules further comprise connecting means (e.g. a connector) that engage with connecting means (e.g. a connector) on another phase module such that in use the phase modules of the apparatus are connected together electrically. Thus preferably the plurality of fuseway-side interfaces are electrically connected together. Preferably each phase module comprises a pair of contacts for connecting electrically with a respective pair of contacts on the fuseway.

This facilitates installation as each phase module can be installed separately, one at a time, like the way fuse holders would be inserted in existing systems, while the connecting means enable interconnection between phase modules to receive power from multiple phases.

The phase modules may comprise rectifying means to rectify power from the phase module’s phase connection to common high voltage DC lines that are passed between the phase modules, wherein the combination of a plurality of phase modules achieves distributed multiphase rectification. This may avoid the need for any connection to the phase to be passed outside the phase module, in turn making it easier to protect external connections from fault conditions on the phase.

The phase modules may be substantially similar other than their connecting means, or preferably be substantially similar including the connecting means. Connecting means may be fitted with a cap to cover unused connecting means. Caps may be fitted to connecting means that are manually removable such that the installer can remove the unwanted caps. This similarity helps to enable a reduction in the number of variants required, reducing design effort, and stocking and installation complexity.

Phase modules have means to detect or infer the order of installation. This could allow easy indication of which line is which. Such indication is especially important for identifying which line encountered any anomalies that are measured or detected.

-9The measuring circuit may create measurement information based on measurements performed. This measurement information may be transmitted from the apparatus or stored for later communication out of the apparatus. Thus preferably the apparatus comprises a data storage for storing data captured by the measuring circuit and/or a data transmitter for transmitting data captured by the measuring circuit.

The measurements performed may include measuring current flowing through the phase. The measuring circuit may comprise a voltage sensing means across a known shunt resistance. This shunt resistance may be a section of busbar, or a dedicated conductor. The measuring circuit may comprise a magnetic sensing means, such as a Rogowski coil or Hall effect sensor.

The measurements performed may also include phase to neutral voltage, phase to phase voltage, frequency, harmonics, temperatures, voltage to voltage phase angle and/or voltage to current phase angle. From which may be calculated or inferred real and reactive power, peak voltages and currents, fuse status, estimated fuse life, load profile including diurnal usage statistics and monthly usage statistics and/or fault location.

The apparatus may have a control (interface) module, within which the measurement information from the phase modules is collated, stored and/or transferred. Calculations and inferences based on the measurement information may take place within the control (interface) module, or the result of calculations and inferences made within the phase modules may be collated, stored and/or transferred within the control (interface) module. The control (interface) module may preferably connect to the phase modules in substantially the same way in which the phase modules connect to each other. Providing a central control module helps to allow all the data collected to be stored and/or transferred from a single component (e.g. into a network), rather than having to be done for each phase.

The apparatus may comprise communication means, e.g. for transmitting information or data captured (e.g. measured) or stored by the apparatus from the apparatus. The communication means may be any of: indicator lights or LEDs; a display; near field communications (NFC); radio communications (such as

- 10Bluetooth, Wi-Fi, Zigbee, LoRa, 6LowPAN, Sigfox, Cell connections such as GSM, 3G or 4G, etc.); optical connections; wired connections; or removable media such as USB keys or SD cards. The communications means may also be via a ‘communications over power-line’ method. This may preferably be over the powerlines to which the fuseway is connected and to which the apparatus is connected.

This helps to allow measurement information to be taken from the apparatus. Wide area network options offer maximum accessibility of measurement information, while local connections may offer simpler implementation and security.

According to a further aspect of the present invention, there is provided an apparatus to perform measurements of a low voltage electrical fuseway, the apparatus comprising at least a conductor (conducting element, e.g. a busbar) per phase to be measured, through which the phase current flows, the apparatus being adapted to measure current flowing through said conductor by measuring the voltage drop across a portion of the conductor (conducting element) of known resistance and measuring the temperature of the conductor.

Any or all of the preferred and optional features described herein with reference to other aspects and embodiments may apply equally to this aspect of the invention.

The apparatus may be calibrated in manufacture by applying a known current to the portion at a known temperature, and measuring the voltage to gain a calibration point with which to calculate the resistance.

The apparatus may comprise a measuring circuit to measure the voltage drop across a portion of the conductor (conducting element) of known resistance. Preferably the apparatus comprises temperature sensing means (a temperature sensor) to measure the operating temperature of the conductor (conducting element). Preferably the apparatus is arranged to use the temperature measured by the temperature sensor to determine the resistance of the conducting element. This helps to enable the current flowing through said conductor (conducting element) to be inferred by compensating for temperature difference between the instantaneous operating temperature and the calibration temperature to infer the instantaneous resistance, and then applying Ohm’s law to the measured voltage over the instantaneous resistance. The apparatus may perform this inference using a processor to perform calculations, e.g. the calibration data (e.g. the temperature calibrated resistance) may be stored on (pre-programmed into) the (e.g. control module of the) apparatus.

The conductor (conducting element) may be made of a low resistivity material such as copper, aluminium, or an alloy of one of these metals. As well as minimising selfheating and wasted power, these materials also have high thermal conductivity, maintaining a low temperature difference across the measured portion, such that even if the fuse connected to one end produces significant heat the temperature in the measured portion does not deviate significantly along the length of the measured portion.

The cross section of the measured portion may be flattened, and may be made to a ratio of at least 4:1 width to thickness. Thus preferably the portion of the conducting element has a cross-section having a width and a thickness, wherein the width is at least four times the thickness. The thickness may be less than 15mm and most preferably may be less than 8mm. If the thickness is maintained at 7mm, skin effect related inaccuracy is kept below 3dB for frequencies up to 350Hz.

The resistance of the measured portion of the conductor (conducting element) may be less than 20 micro-ohms (e.g. at standard temperature, 20 °C), and most preferably may be between 0.5 and 3 micro-ohms.

The measurement circuit may comprise a low noise pre-amp to amplify the signal. This pre-amp may be sensitive to signals of nanovolt scale across the measured portion.

The measured portion of the conducting element may be a section of conducting material of substantially the same material to the conductor either side of the section. The measured portion may be a section of conductor of substantially the same cross-section as the conductor either side of the section.

The conductor (conducting element) may be an integral component of the fuseway, such as a blade for attachment to a fuse or fuse holder, or may be a conductor within the retrofittable measurement apparatus such as the contact that interfaces with the blade of the fuseway, or a blade for attachment to a fuse or fuse holder.

The conductor may be a single continuous element with a connector on each end, the first end being a contact adapted to attach to a fuseway blade, the second end being a blade adapted to receive a fuse or fuse-holder. Thus preferably the apparatus further comprises a conducting element extending from the fuseway-side interface to the fuseholder interface, wherein the conducting element comprises one of the pair of contacts for electrically connecting to the pair of contacts of the fuseway and one of the pair of contacts for electrically connecting to the pair of contacts of the fuseholder, wherein the measurement circuit is arranged to perform electrical measurements of the fuseway via the conducting element.

In such an arrangement, the relative quality of electrical contact across the blade interface each time a fuse is connected can bias current to flow unevenly through the conductor, affecting measurement accuracy. This can cause a typical measurement error of 1-2% and a worst case of approximately 10%. The conductor (conducting portion) may comprise geometric features to direct, steer or distribute the current, e.g. through the portion of the conducting element (i.e. in which the measurement(s) are being made). This helps to ensure the current distribution is repeatable however the fuse is connected. These features may comprise narrowing, thinning, notching, kinking, serpentining, perforation or other shaping of the conductor before during or after the measured portion, or a combination of the above.

Preferably the measurement circuit is arranged to measure or determine a voltage drop across or a current flow through a portion of the conducting element. Preferably the portion is an integral part of the conducting element. Preferably the portion of the conducting element comprises a shunt resistance.

This is considered to be novel and inventive in its own right and thus when viewed from a further aspect the invention provides a measurement apparatus for performing electrical measurements of an electrical fuseway, wherein the apparatus comprises:

a low resistivity conducting busbar for an electrical fuseway;

- 13a pair of contacts arranged a distance apart on the conducting busbar and defining a measured portion therebetween; and a measurement circuit arranged to measure or determine a voltage drop across or a current flow through the measured portion of the conducting busbar;

wherein the measurement circuit comprises signal lines connected to the pair of contacts, wherein the signal lines are arranged relative to the conducting busbar so as to substantially cancel the magnetic coupling between the signal lines and the conducting element.

The Applicant has appreciated that by measuring or determining a voltage drop across or a current flow through the integral measured portion of the conducting busbar (e.g. an integral low shunt resistance on the conducting busbar), this allows the necessary electrical measurements to be made of the fuseway in a low resistance portion, which helps to minimise the heat dissipated in the shunt resistance. Preferably the voltage across the measured portion is sensed by the measurement circuit and a current passing through the measured portion (and thus the conducting busbar) is determined (calculated) based on the particular (known) resistance ofthe measured portion and, e.g., the temperature ofthe measured portion.

It will be appreciated that some or all ofthe optional and preferable features outlined herein with respect to other aspects and embodiments of the present invention may be equally applicable to this aspect.

In particular, as mentioned above, the conducting busbar may form (and thus the apparatus may comprise) a contact of a fuseway for receiving a fuse or fuse holder. Alternatively, the conducting busbar may form (and thus the apparatus may comprise) a contact for connecting to a contact (e.g. in a fuseholder interface) of a fuseway. Preferably the conducting busbar also forms (and thus the apparatus may comprise) a contact for connecting to a contact of a fuse or fuseholder, e.g. the conducting busbar comprises both the contact for connecting to contact of the fuseway and the contact for connecting to the fuse or fuseholder.

- 14Preferably the low resistivity conducting busbar is made of a low resistivity material such as copper or aluminium, or an alloy thereof. Preferably the resistance of the measured portion of the conducting busbar is less than 20 micro-ohms.

Preferably the signal lines of the measurement circuit that connect to the pair of contacts comprise (e.g. one of the signal lines forms) a magnetic coupling cancellation signal line path. Thus preferably a signal line is arranged to follow a particular (e.g. geometry of) return path (i.e. the magnetic coupling cancellation signal line path) that is arranged to cancel the magnetic coupling of the signal lines to the conducting busbar.

Preferably the magnetic coupling cancellation signal line path comprises a rectangular path disposed on the surface of the conducting busbar, wherein a dimension of the rectangle comprises a cancellation distance arranged to cancel the magnetic coupling between the conducting busbar and the signal line. Preferably the cancellation distance is approximately equal to the thickness of the conducting busbar (e.g. in its smallest dimension).

Preferably the measurement circuit is arranged to be sensitive to voltages on the order of nanovolts, e.g. using a pre-amp or analogue to digital converter, e.g. isolated as disclosed in WO 2017/158385.

The measuring circuit may comprise contacts to connect to the conductor (conducting element or busbar) at each end of the measured portion, e.g. to allow the voltage drop or the current flow to be measured between the contacts. These contacts may be attached to the conductor by screwing, soldering, conductive gluing, welding or pressed contacts (such as sprung pins). The contacts may be rigidly spaced prior to attachment.

High currents flowing in the conductor can create unacceptably high magnetic coupling to sensor wires. Even taking usual steps to minimise coupling such as bringing wires directly together and twisting wires together does not give acceptable operation at high currents in combination with the low resistance measured portion that is advantageous in at least embodiments of the present invention, owing to the length of signal line running to the position where they are twisted together. In order

- 15to minimise magnetic coupling beyond bringing the sensing conductors together over the shortest path possible a signal line that follows a specific geometry of return path between the contacts that cancels the magnetic coupling may be used. The Applicant has discovered that a rectangular return path along the surface of the conductor helps to cancel out the coupling.

Preferably the measurement circuit comprises signal lines connected to the contacts of the measurement circuit, wherein the signal lines are arranged relative to the conducting element so to substantially cancel the magnetic coupling between the signal lines and the conducting element. The measuring circuit may comprise a first signal line attached to a first contact, and a second signal line attached to a second contact, such that the signal lines carry away the differential signal from the contacts. The first signal line is arranged to follow a path from the first contact to a position where it is in close proximity with the second signal line, thereby bringing the differential signal together, wherein, the path follows a geometry that substantially cancels the magnetic coupling between the signal lines and the conductor.

Preferably the contacts are attached to the edge of the conductor, the conductor being of a height and thickness, and the path comprising three sides of a rectangle on the wide surface of the conductor, such that it leaves a first contact, passes onto the wide surface, travels across the part of the width in a direction substantially perpendicular to the line between the contacts for a cancellation distance, then turning to travel along a line substantially parallel to but offset from the edge by the cancellation distance for the length of the measured portion of the conductor, and then turns again to travel the cancellation distance back towards the edge to a position proximal to the second contact thereby meeting the signal line from the second contact. The two signal lines may then be twisted together or arranged coaxially to prevent further magnetic coupling.

The cancellation distance may be substantially equal to the thickness of the conductor. This helps to provide a repeatable method for cancelling the magnetic coupling.

- 16Preferably the measuring circuit comprises a contact circuit which comprises the contacts. The contact circuit may define the spacing of the contacts as required for the system sensitivity. The contact printed circuit board (PCB) may further comprise any of: a magnetic coupling cancellation signal line path, a temperature sensor to measure the conductor temperature, a low noise pre-amp to amplify the voltage signal from the measured portion of the conductor, or an analogue to digital converter to convert the signal to digital. The contact circuit may be a printed circuit board. The contact circuit may be flexible. The contact circuit may be adhesive.

Preferably the measurement circuit comprises an isolated voltage measuring chip, wherein the isolated voltage measuring chip is arranged to float with the voltage of the fuseway when the fuseway-side interface of the apparatus is connected to the fuseholder interface on the fuseway. Such an arrangement, e.g. which is optocoupled to the rest of the apparatus, helps to allow measurement of very low voltages, e.g. across the portion of the conducting element.

The present invention also extends to a method of installing measurement apparatus comprising a plurality of phase modules one for each phase on a fuseway, and an optional interface (control) module, each fuse module comprising a fuseway-side interface with suitable geometry to fit a standard fuseholder interface on the fuseway and further comprising contact clamps such that when the fusewayside interface is connected to a standard fuseway the contacts engage mechanically and electrically with the blade contacts that are provided on the fuseway, and a fuse-side interface with blade contacts provided to connect electrically and mechanically to a fuse or a standard fuse-holder containing a fuse, wherein the first fuse module is fitted into a fuseway’s fuse holder interface, then the clamping contacts are activated (for examples by screwing screw clamps by means of an installation tool) so as to mechanically and electrically engage the fuseway’s blade contacts; then each subsequent fuse module is fitted in a similar fashion, wherein the process of inserting the fuseway-side interface into the fuseway’s fuse holder interface also electrically connects the fuse module to the previous fuse module, by means of connecting means, and where the optional interface module (if fitted) is connected to a phase module, such that when the final module is connected (whether fuse module or interface module) the measurement apparatus may be powered by the phases on the fuseway without external

- 17connection. Optionally a neutral connection may be added. This is not required for powering the apparatus but may add accuracy to measurements such as voltage or phase angle measurements, especially if the phases are poorly balanced.

The installation tool may attach to the phase module in place of the fuse holder during installation, and similar wing knobs to those used on fuse holders may be used to activate the clamping contacts such that the installation process is familiar to personnel with less need for training.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic cross section of a first embodiment showing the fuseway, one phase module and the installation tool all separated;

Figure 2 is a schematic cross section of the fuseway with a phase module of the first embodiment installed and a fuse holder containing a fuse ready to be fitted;

Figure 3 is a projected view of the first embodiment showing a fuseway with a first phase module installed in the fuseway and a second phase module in alignment ready to be fitted;

Figure 4 is a schematic cutaway of the first embodiment showing the connector interface between phase modules in the process of being fitted, prior to connection;

Figure 5 is a schematic cutaway of the first embodiment showing the interface module and connector interface between the interface module and the phase module;

Figure 6 is an exploded view of the connector cover of the first embodiment;

Figure 7 is a schematic cross section of the first embodiment showing among other things the connections to the busbar conductor;

Figure 8 is a schematic projection of a second embodiment, illustrating the neutral connection;

Figure 9 is a schematic cutaway of the phase module of a third embodiment showing the sensing Rogowski coil and powering induction coil;

Figure 10 is a projection of the single assembly according to a fourth embodiment;

Figure 11 is a simplified circuit schematic showing the high voltage rectifiers and virtual neutral circuit for the three phase modules of the first embodiment;

- 18Figure 12 is a schematic cross section of a fifth embodiment, showing the shaped busbar used to make the current distribution stay similar under different connection conditions;

Figure 13 (a) to (h) show busbars with geometric features to direct, steer or distribute the current within the busbar; and

Figure 14 is a schematic projection of the busbar showing the magnetic coupling cancellation path of the signal line.

Referring to the drawings, and particularly referring to Figure 1, a first embodiment of the apparatus comprises a measurement apparatus phase module 1, which in use is installed into a fuseway 2 using an installation tool 3. The fuseway comprises a pair of blades 4 for each phase of the 3-phase electrical supply. The pair of blades on the fuseway are arranged to interface with a fuseholder in normal operation (i.e. were the measurement apparatus phase module 1 to not be installed). The phase module comprises a fuseway-side interface, replicating the interface on a fuseholder that would otherwise be connected to the fuseway blades, with two female terminals 5 arranged to as contacts that interface with the blades, the terminals having screw clamps 6 to attach to the blades.

The screw clamps are actuated via a pair of rods 7 located within the installation tool, and held captive within the installation tool by circlips 8 such that they are free to rotate about their axis but may not translate axially relative to the installation tool. The phase module is installed by pushing the installation tool containing the phase module into the fuseway, the phase module being guided into position by its outer casing 9 aligning with the casing of the fuseway 10. Once the phase module is pushed sufficiently far into the fuseway, the wing knobs 11 on the installation tool are turned by hand, which in turn turns the screw clamps via the rods to lock the phase module into place. The installation tool is then pulled by its handle 12 to detach it from the phase module, leaving the phase module in place.

With reference to Figure 2, the phase module 1 comprises a fuse-side interface with a pair of secondary blades 13 replicating the interface (i.e. the pair of blades 4) of the fuseway, such that a standard fuse 14 of the type that would normally be installed into the fuseway may be installed into phase module. This fuse would be

- 19installed in the industry standard way within a standard fuseholder 15, which is not required to be of a proprietary type to interface with the phase module.

With reference to Figures 3 and 4, a first phase module 16 is installed in the uppermost fuse holder interface 17 in the fuseway, and a second phase module 18 is in alignment ready to be installed in the fuseway in the fuse holder interface directly below the first phase module. The second phase module interfaces with the first phase module via a series of female connectors 19 on the lower of the first phase module, and a series of male connectors 20 on the upper of the second phase module. The connectors are suitable for the transfer of power and data. The connectors are arranged in such a male-female arrangement so that when the first phase module is installed and prior to the installation of the second phase module, there are no exposed live parts beyond those typically experience during a fuse installation. As the second phase module is installed, the male connectors 20 on the second phase module become live; however, at this point they are already sufficiently installed and interfaced with the female connectors 19 on the first phase module such that they cannot be accessed.

With reference to Figures 5 and 6, a third phase module 21 is installed into the final fuse holder interface within the fuseway (e.g. relative to the second phase module 18 in the same manner as the second phase module 18 is installed relative to the first phase module 16), allowing measurement of all three phases of the electrical supply. In addition, a measurement apparatus interface (control) module 22 can then be installed onto the female connectors 19 of the third phase module 21 (as shown in Figure 5) and a cover 26 may be located over the male connectors 20 of the first phase module 16 (as shown in Figure 6). Covers may be installed during manufacture on all of the phase modules. These may then be removed by the installer from the second and third phase module during installation. In this way, the same phase modules may be used in any of the three positions within the fuseway.

The phase modules 16, 18, 21 are capable of identifying their relative locations by identifying which connectors are in use, e.g. owing to being informed their position during initialisation by the interface (control) module. Specifically, the top phase module will have only its female connectors being used, the middle phase module will have both its male and female connectors being used, while the bottom phase

-20module will have only its male connectors connected with another phase module (although, as shown in Figure 5, its female connectors may be used to connect to an interface module 22). Identification of whether the connectors are in use is achieved by measuring the presence of a signal voltage on a connector pin.

Communication between the phase modules 16, 18, 21 is achieved with a controller area network (CAN) bus, with optical isolation between the sensing circuit and the CAN bus to maintain isolation of the interface circuits such as ethernet outputs or Secure Digital (SD) ports.

The interface module 22 acts to control the phase modules 16, 18, 21 as well as record measurement data onto an SD card 23 and transfer data via radio signals or ethernet to an external service. The interface module 22 comprises a screen 24 and touch interface 25 on which a user can interrogate the data stored on the interface module 22.

With reference to Figure 11, there is provided through the connectors 19, 20 to each of the measurement apparatus modules 16, 18, 21 a line 51 that is used as a virtual neutral 51 for voltage and phase angle measurements. Each phase module has a connection from the phase (i.e. via the respective pair of blades 4) to the virtual neutral through a high value (1 megaohm), tight tolerance (±1% or better) resistor 52 such that when the three phases are connected there is a star of precision resistors, creating a virtual neutral at the mean voltage. This virtual neutral is then connected by a connection 53 as a reference for the voltage and phase measurements, using circuits with high input impedance to avoid pulling the virtual neutral away from its nominal value.

Two high voltage DC lines 54, 55 are also provided through the connectors 19, 20 to each of the three phase modules 16, 18, 21 and the interface module 22. Each of the phase modules contains a rectifying circuit with two series power diodes 56 supplying current to the high voltage DC positive line 55, and two series power diodes 57 accepting current from the high voltage DC negative line 54. Together all three phase modules form a standard six diode rectifier arrangement. The two series diodes in each line, and use of a clamping transient-voltage-suppression (TVS) varistor 58 and series resistor 59 adds resilience to surges, and a series fuse

-21 60 protects the system from downstream failure. Even if one phase supply is cut, the high voltage DC lines can be powered by the other phases.

As shown in Figure 5, the interface module 22 contains an isolating switch mode power supply 34, which is powered by the high voltage DC lines 54, 55, thus providing low voltage DC power to the logging and communications circuitry in the interface module, and via lines that pass through the connectors between modules to the measurement circuitry 50 in the phase module, where power is transferred by PCB trace inductors to transmit the power across an isolation gap, as described in WO 2017/158385.

In addition, a battery is provided within the interface module 22 with a charge circuit that keeps the battery charged when the switch mode power supply is on, and supplies 5V to the low voltage when the supply power is lost to cover short power outages both for logging the measured data at the time of fault and providing communications for interrogation. A real time clock circuit also has a coin cell for long term keeping ofthe real time (for example if the system is in storage).

With reference to Figure 7, the phase module 1 measures current via the principle of a shunt resistor. A conductor comprising a measured portion 27 of known resistance is disposed between the terminal 5 and the secondary blade 28 of the phase module 1. The resistance of the measured portion 27 of conductor is approximately 1.5 micro-ohms to give a typical in use voltage drop of up to 600 micro-volts when used within a 400A fuseway.

In this embodiment, the conductor is not a separate element, but is a known section of the continuous busbar 29 running from the terminal to the secondary blade. As such, no additional conductor needs to be added, and the resistance of the phase module does not significantly differ from the resistance of a blade within a typical fuseway installation. The resistance ofthe conductor and temperature calibration value is measured and recorded within the sensing circuit 50 of the phase module during manufacture to account for variations in resistance owing to manufacturing variation.

-22In use, the voltage drop between two probe points 30, disposed approximately 22mm apart on either side of the known section of continuous busbar, is measured, as well as the temperature of the conductor via a temperature probe 31. (Note that a more accurate temperature measurement may be achieved if the temperature probe is attached closer to or on the measured portion, unlike the design shown in Figure 7.) From these measurements, an accurate measure of the current flowing is calculated by inferring the actual resistance of the measured portion at the temperature measured based on the calibration resistance and temperature, and then using Ohm’s law to infer the current. To connect with the probe points 30 in order to make these measurements, first and second contacts are provided, attached to the probe points by a high-temperature-stable conductive adhesive.

Figure 14 shows a busbar running from the terminal to the secondary blade in a phase module, in which a conductor for measuring the current is provided. There are provided a first signal line 63 and second signal line 65 to carry the signal from the first contact 69 and the second contact 64 on the conductor, respectively, into the sensing circuit. The first signal line 63 is insulated and then is attached to the conductor busbar to hold it in a path that brings it in close proximity with the second signal line 65 in a shape that cancels magnetic coupling with the current flowing in the conductor, using Kapton tape.

The shape of the path of the first signal line 63 follows three sides of a rectangle, passing downwards across the busbar in the wide direction (perpendicular to the direction of a line between the contacts 69, 64) for a length equal to the thickness 68 of the conductor (in this case 7mm), then along the busbar parallel to, and offset 67 by the 7mm thickness from, the line between the contacts until level with the second contact 64 along a line perpendicular to the line between the contacts, and then the 7mm back across to the conductor to the second contact, where the two signal lines are then twisted together 66 to minimise magnetic coupling over the length that passes to the sensing circuit board.

The phase voltage is measured within the phase module between the probe point and the virtual neutral provided by the interface module via the connectors.

-23The current and voltage readings are transferred to the interface module via the connectors to be recorded and transferred as required. In addition, the phase angle is calculated within the interface module and recorded and transferred as required.

With reference to Figure 8, a second embodiment of the apparatus that is similar to the first embodiment with the addition of an attachment of the interface module 22 to a neutral point 32 within the substation via a flying lead 33. This real neutral attaches to the virtual neutral provided by the star arrangement, tying this point to 0V. This change improves the accuracy of phase voltage measurement, by removing the error introduced by the difference in voltage between the virtual neutral and the real neutral, which occurs when the phase voltages are unbalanced.

Further advantageously, the power to power the power supply is provided not by connecting the power supply between the phase and real or virtual neutral, but is provided by connection of the power supply between two or more phases, by rectifying the connected phases into a positive and negative high voltage DC lines that are passed between the phase modules by the connectors, as described in the first embodiment. This means that the connection to the neutral point can be optionally connected, dependent upon whether the additional accuracy is required in the specific application. The resistors in the star arrangement are of high resistance, of the order of 1 megaohm, and thus the power absorbed through these resistors is not significant when clamped to real neutral.

With reference to Figure 9, a third embodiment of the apparatus that is similar to the first embodiment, except uses a Rogowski coil 35 around the busbar 29 to measure the current instead of using a shunt resistor as in the first embodiment; additionally, the measurement apparatus 1 is powered by an inductive coil 36 around the busbar. This advantageously enables the measurement apparatus to be powered independently of the connection of other measurement apparatuses, and so just a single phase can be measured if so desired, such as if a fault is suspected on a phase. Additionally, in the event of damage to one of the measurement apparatuses, the other measurement apparatuses can continue to function.

With particular reference to Figure 10, a fourth embodiment comprises a single assembly 37 incorporating all the features of three phase modules and the interface

-24module of the second embodiment. This advantageously reduces the number of components for installation. Additionally, the connectors are no longer required, with the connections between phases made internal to the assembly.

With particular reference to Figure 12, a fifth embodiment is provided that is similar to the first embodiment, but where the section of busbar comprising the measured portion of conductor comprises geometric features to achieve repeatable distribution of the current regardless of the relative quality of connection of different parts of the contact where the fuse holder or where the fuseway interfaces with the busbar. For this embodiment the geometric feature chosen is to shape the busbar such that the measured section of the busbar is parallel but offset from the line between the fuseway contact and the fuse-holder contact. By providing a kink 61 in the shape of the busbar to offset the measured portion from the line between the contacts, the current is pulled towards the edge 62 closest to the line between the contacts of the original of the measured portion wherever the majority of the current flows in the contacts. This means that the current distribution in use will better match the current distribution during calibration, even after the unit has be reinstalled and the fuse holder has been replaced. The busbar form is stamped, with minimum wastage owing to partial tessellation.

Figure 13 shows alternative geometric forms (61) to direct, steer or distribute the current in the conductor including narrowing (b,c), thinning (h), notching (g), serpentining (f), perforating (d,e) or shaping (a) of the conductor before during or after the measured portion (i.e. between the probe points 30).

Claims

1. A measurement apparatus for performing electrical measurements of an electrical fuseway, wherein the apparatus comprises:

a low resistivity conducting busbar for an electrical fuseway;

a pair of contacts arranged a distance apart on the conducting busbar and defining a measured portion therebetween; and a measurement circuit arranged to measure or determine a voltage drop across or a current flow through the measured portion of the conducting busbar;

2. The measurement apparatus as claimed in claim 1, wherein the voltage across the measured portion is sensed by the measurement circuit and a current passing through the measured portion is determined based on the particular resistance of the measured portion and, e.g., the temperature of the measured portion.

3. The measurement apparatus as claimed in claim 1 or 2, wherein the conducting busbar forms a contact of a fuseway for receiving a fuse or fuse holder.

4. The measurement apparatus as claimed in claim 1 or 2, wherein the conducting busbar forms a contact for connecting to a contact of a fuseway.

5. The measurement apparatus as claimed in claim 4, wherein the conducting busbar forms a contact for connecting to a contact of a fuse or fuseholder.

6. The measurement apparatus as claimed in any one of the preceding claims, wherein the resistance of the measured portion of the conducting busbar is less than 20 micro-ohms.

7. The measurement apparatus as claimed in any one of the preceding claims, wherein at least one of the signal lines of the measurement circuit that connect to the pair of contacts is arranged to follow a particular return path that is arranged to cancel the magnetic coupling of the signal lines to the conducting busbar.

8. The measurement apparatus as claimed in claim 7, wherein the return path comprises a rectangular path disposed on the surface of the conducting busbar, wherein a dimension of the rectangle comprises a cancellation distance arranged to cancel the magnetic coupling between the conducting busbar and the at least one signal line.

9. An apparatus for performing electrical measurements of an electrical fuseway, wherein the apparatus comprises:

a fuseway-side interface for connecting to a fuseholder interface of a fuseway;

10. The apparatus as claimed in claim 9, wherein the apparatus further comprises a fuseholder interface for connecting to a fuseholder and a pair of contacts for electrically connecting to a pair of contacts of the fuseholder.

11. The apparatus as claimed in claim 10, wherein the fuse-side interface and the fuse-side contacts are complementary to the fuseway-side interface and the fuseway-side contacts.

12. The apparatus as claimed in claim 9 or 10, wherein the apparatus further comprises a conducting element extending from the fuseway-side interface to the fuseholder interface, wherein the conducting element comprises one of the pair of contacts for electrically connecting to the pair of contacts of the fuseway and one of the pair of contacts for electrically connecting to the pair of contacts of the fuseholder, wherein the measurement circuit is arranged to perform electrical measurements of the fuseway via the conducting element.

13. The apparatus as claimed in claim 12, wherein the measurement circuit is arranged to measure a voltage drop across a portion of the conducting element to determine a current flowing through the portion of the conducting element.

14. The apparatus as claimed in claim 13, wherein the portion of the conducting element has a resistance of less than 20 micro-ohms.

15. The apparatus as claimed in claim 13 or 14, wherein the portion of the conducting element comprises substantially the same material as the rest of the conducting element.