EP2421021B1

EP2421021B1 - Method of installing an electrical fuse device

Info

Publication number: EP2421021B1
Application number: EP20110178087
Authority: EP
Inventors: John Cunningham; Coiln McIlroy; Adrian Moore
Original assignee: Kelvatek Ltd
Current assignee: Kelvatek Ltd
Priority date: 2010-08-19
Filing date: 2011-08-19
Publication date: 2013-10-02
Anticipated expiration: 2031-08-19
Also published as: GB201013888D0; EP2421021A3; EP2421021A2

Description

Field of the Invention

The present invention relates to electrical fuse devices for an electricity supply systems.

Background to the Invention

Electricity supply systems normally include fuses for protecting parts of the system in the event of a fault. For example, a respective fuse may be provided at each end of a ring circuit of an electricity mains supply network. Instead of a single fuse, it is known to provide a fuse device having a primary fuse, which is normally in-circuit, a secondary fuse, which is normally out-of-circuit, and a switching device arranged to bring the secondary fuse in-circuit in the event of a fault.
The document US 2091135 A describes a method according to the preamble of claim 1.
During installation, a fuse may be placed in a fuse holder, the fuse holder then being inserted between two terminals of the respective electrical circuit. In some systems, for example systems commonly used in the United Kingdom and Ireland, once the fuse holder is in place, the mechanical connection between the fuse and the terminals may be tightened, e.g. by operating one or more fuse clamps. In other systems, the mechanical connection between the fuse and the terminals is made by other mechanical connectors, e.g. push-fit clips, that do not require tightening. In any event, a period may exist where the fuse is in-circuit, i.e. an electrical connection has been established, but is not fully mechanically connected to its terminals. In arriving at the present invention, it has been observed that, if a fuse is not tightly connected to its terminals before electrical current, especially fault current, passes through it, then a catastrophic failure of the fuse can occur, which may seriously injure a person installing the fuse.
It would be desirable to mitigate the above-identified problem.

Summary of the Invention

Accordingly, a first aspect of the invention provides a method of installing an electrical fuse device as claimed in claim 1.
Said establishing of a secure mechanical connection is typically required in embodiments in which the fuses are mechanically connectable to the respective fuse contacts by means of a mechanical connector that is configurable to engage or release the fuse. Typically, the mechanical connector comprises a clamping device that is operable to clamp or release the fuse, or a friction fit or interference fit connector. The clamping device may have any suitable configuration, e.g. jaws that are movable to grip the fuse and/or one or more removable pins and/or one or more screws. Before said establishing of a secure mechanical connection takes place, a mechanical connection may already exist between the fuse and the contacts, for example to the extent that an electrical connection is established. Typically, therefore, said establishing of a secure mechanical connection involves tightening the mechanical connection, said tightening typically involving operating a clamp or other tightenable device. After the fuse first engages with the mechanical connector, the mechanical connector is operated to tighten the mechanical connection with the fuse. In other embodiments, clamps or the like are not used to engage the fuses to the respective connectors and so no tightening is necessary. For example, mechanical connectors arranged to provide an interference or friction fit with the fuse, e.g. clips, may be used, which can also provide a secure mechanical connection.
In some cases, said first and second main contacts may already be connected to said first and second electrical terminals, in which case said connecting step may be omitted. In such cases, if said secondary fuse is not already connected between said first and second secondary fuse contacts, said secondary fuse is connected between, and if necessary tightened to, said first and second secondary fuse contacts with said switching means in a state where said second secondary fuse contact is electrically disconnected from said second main contact. In cases where said secondary fuse is connected between said first and second secondary fuse contacts but not tightly clamped thereto, then said secondary fuse is tightened to said first and second secondary fuse contacts with said switching means in a state where said second secondary fuse contact is electrically disconnected from said second main contact.
The fuse device is adapted to receive a removable fuse holder for said primary fuse. When the fuse holder holds the primary fuse and is installed in the fuse device, the ends of the primary fuse are connectable to a respective one of the primary fuse contacts. When the fuse holder is removed, at least one of the ends of the primary fuse is ot connectable to the respective primary fuse contact. The fuse device is arranged such that said switching means cannot be operated, or at least cannot be operated from a state where said second secondary fuse contact is electrically disconnected from said second main contact (the open state) to a state where said second secondary fuse contact is electrically connected to said second main contact (the closed state), unless the fuse holder is installed in the fuse device. For example, in one embodiment, said fuse holder includes means, e.g. a mechanical or electromechanical actuator, for actuating said switching means from its open state to its closed state and so that fuse holder must be installed in order to close the switch. Accordingly said method involves installing said fuse holder, without said primary fuse, prior to said operating said switching means to electrically connect said second secondary fuse contact to said second main contact. Typically, said fuse holder is installed prior to said connecting step. The fuse holder is removed after said operating step in order to allow said primary fuse to be installed.
Typically, at least one respective end of said primary and secondary fuses needs to be tightened to their respective fuse contacts during the installation procedure in order to create adequate mechanical contact between the fuse and the contact. To this end, the fuse device typically includes a respective clamping device associated with each fuse contact to which a fuse end needs to be tightened. The clamping devices are operable to clamp the respective fuse end to the respective fuse contact and may take any convenient form, e.g. a screw clamp. The clamping devices are preferably releasable so that the respective fuses can be removed.
Typically, said fuse device includes means for causing said switching means to connect said second secondary fuse contact to said second main contact in response to a detected failure of the primary fuse. The device typically also includes means for detecting a failure of said primary fuse, although in some embodiments this may be provided externally of the device and arranged to communicate a detected failure to the device.
Preferred features are recited in the dependent claims.
The invention is particularly suitable for use with fuse devices for installation into electrical supply systems, for example into an electrical supply line of a transmission network or a distribution network or a mains network.
Further advantageous aspects of the invention will be apparent to those skilled in the art upon review of the following description of a preferred embodiment and with reference to the accompanying drawings.

Brief Description of the Drawings

An embodiments of the invention are now described by way of example and with reference to the accompanying drawings in which:

Figure 1 is circuit diagram of a fuse device suitable for use with the present invention, the fuse device being shown in a first state;
Figure 2 is a circuit diagram showing the fuse device of Figure 1 in a second state;
Figure 3 is a circuit diagram showing the fuse device of Figure 1 in a third state; and
Figure 4 is a circuit diagram showing the fuse device of Figure 1 in a fourth state.

Detailed Description of the Drawings

Referring now to the drawings, there is shown, generally indicated as 10, a circuit diagram representing an electrical fuse device. The fuse device 10 comprises first and second main contacts 12, 14 for connection to corresponding terminals 16, 18 of an electrical circuit (not shown) that it is desired to protect. Typically, the terminals 16, 18 are terminals of an electrical supply line in a transmission network or a distribution network or a mains network.
The fuse device 10 includes means for receiving a primary fuse 24, typically in the form of first and second fuse-receiving contacts 20, 22. The contacts 20, 22 are electrically connected to main contacts 12, 14 respectively. In typical embodiments, the primary fuse 24 is normally in-circuit during normal operation of the fuse device, e.g. prior to the occurrence of a fault. In preferred embodiments, the fuse device 10 is adapted to removably receive a fuse holder 26 for the primary fuse 24. To install the primary fuse, the fuse holder 26 is removed from the fuse device 10 and the primary fuse 24 placed in the fuse holder 26. The fuse holder 26 is then inserted into the fuse device 10 such that the primary fuse 24 is capable of being electrically connected to the contacts 20, 22. Typically, once the fuse holder 26 is inserted, a respective clamping device (not shown), or other mechanical connecting device, is operated (e.g. tightened) to clamp or otherwise mechanically secure the respective ends 28, 30 of the primary fuse 24 to the respective terminal 20, 22. The fuse holder 26 may be completely removable (i.e. completely separable) from the fuse device 10, or may be removable in the sense that the primary fuse is removed from the circuit of the fuse device such that it can be manually removed and replaced. For example, the fuse holder 26 may be movably, e.g. pivotably or slidably, mounted on the fuse device 10. Typically, the fuse holder 26 is capable of being removed and installed manually, e.g. it is susceptible of being grasped by a user's hand and/or includes a handle for this purpose. When the primary fuse is in place and in-circuit, it is electrically connected across main contacts 12, 14 and so carries current.
The fuse device 10 further includes means for receiving a secondary fuse 32, typically comprising first and second fuse-receiving contacts 34, 36. Optionally, the fuse device 10 is adapted to removably receive a fuse holder (not shown) for the secondary fuse 32 such that, when the fuse holder is inserted into the fuse device 10 the secondary fuse 32 is capable of being electrically connected to the respective contacts 34, 36 of the device. The fuse holder may be completely removable (i.e. completely separable) from the fuse device 10, or may be removable in the sense that the secondary fuse 32 is removed from the circuit of the fuse device such that it can be manually removed and replaced. For example, the fuse holder may be movably, e.g. pivotably or slidably, mounted on the fuse device 10. Typically, the secondary fuse holder is capable of being removed and installed manually, e.g. it is susceptible of being grasped by a user's hand and/or includes a handle for this purpose. Alternatively, the fuse device 10 includes a station for receiving the secondary fuse 32 such that, when the secondary fuse 32 is inserted into the station, its respective terminal ends are capable of being electrically connected to the respective contacts 34, 36 of the device 10. Typically, a respective clamping device (not shown), or other mechanical connecting device, is operated (e.g. tightened) to clamp or otherwise secure the respective ends of the secondary fuse to the respective contact 34, 36.
Contact 34 is electrically connected to contact 12 of the device 10. The other terminal 36 for the secondary fuse 32 is selectably connectable to the other contact 14 of the device by means of a switching device 40. The switching device 40 is operable between an open state, in which terminal 36 is electrically isolated from contact 14, and a closed state, in which terminal 36 is electrically connected to contact 14. Hence, when the switch 40 is closed, the secondary fuse is in-circuit, i.e. it carries current flowing between main contacts 12, 14, and when the switch 40 is open, the secondary fuse 32 is out-of-circuit and can carry no current.
Typically, each fuse 24, 32 has respective ends that are adapted for connection to the respective contact 20, 22, 34, 36. When the fuses are first installed, at least one and typically both their ends make relatively loose mechanical contact with the respect contacts and so tightening is required. To this end the preferred fuse device 10 includes a respective clamping device (not shown) for clamping the respective fuse end to the respective contact. The clamping devices are typically manually operable by the user, e.g. comprising a mechanical, or electromechanical, clamping device operable by a screw or other mechanical, or electromechanical, operating device.
The fuse device 10 typically also includes, or is co-operable with, a controller 42 (shown in Figure 1 only) arranged to monitor current and/or voltage in the device 10, and in particular in relation to the primary fuse 24. In normal operation, the primary fuse is in-circuit and the switch 40 is open. In the event of a fault causing fault (typically high) current to rupture the primary fuse 24, the controller 42 detects the failure of the primary fuse 24 (typically by detecting an increase in the voltage across contacts 20, 22 to the supply line voltage) and causes the switch 40 to close, thereby bringing the secondary fuse 32 in circuit.
In preferred embodiments, the fuse device 10 includes means (not shown) for manually operating the switch 40. Preferably, the switch operating means allow a user at least to open the switch or optionally to both open and close the switch. The switch operating device may take any suitable form, including mechanical, electrical or electro-mechanical devices.
In a preferred embodiment, the means for opening the switch 40 is manually operable, comprising for example a mechanical device, such as a lever or slide, that is movable by the user. Preferably, this manually operable device is configured such that it cannot be used to close the switch 40. In such embodiments, the means for closing the switch 40 may be separate from the switch opening device. Advantageously, the closing means comprises a power-operated actuator (not shown). The actuator may be powered by any suitable means, e.g. mechanical, electrical, pneumatic, hydraulic means, but is most conveniently powered by one or more springs, or other mechanical actuating means. The actuator is operable to close the switch 40 under the control of the controller 42, e.g. in the event of a fault being detected. Preferably, the actuator is also operable by a user, e.g. to close the switch during the installation procedure as is described in more detail below. In some embodiments, the actuator is carried by the primary fuse holder 26 and, accordingly, is only capable of acting on the switch 40 when the primary fuse holder 26 is installed.
A preferred installation method for the fuse device 10 is now described. Optionally, the fuse device 10 is permanently fitted to the terminals 16, 18, in which case there may be a permanent connection between main contacts 12, 14 and terminals 16, 18 respectively. Typically, however, the fuse device 10 is removable from the terminals 16, 18. Accordingly, to install the fuse device 10, the user connects the main contacts 12, 14 to the terminals 16, 18 respectively. The connection is typically a direct mechanical connection between the respective terminals, which are formed from an electrically conductive material so as to also provide an electrical connection. A respective clamping mechanism (not shown), e.g. a screw clamp, or other mechanical connecting device, may be provided at each terminal to hold the respective terminals together. Advantageously, this process of connecting the main contacts 12, 14 and 16, 18 is performed with the primary fuse 24 removed from the device 10, i.e. not in-circuit, and preferably also with the switch 40 in its open state, as shown in Figure 1. In this condition, no current flows through the device 10 as a result of any voltage present across the terminals 16, 18. As such, the user may safely connect the respective main contacts 12, 14 and 16, 18, and, if required, secure the respective mechanical connections, e.g. tighten the respective clamps, without being exposed to electrical current or the possibility of catastrophic failure of a non-tightened fuse.
Typically, the secondary fuse 32 is installed in the fuse device 10 before the device 10 is connected to the terminals 16, 18. In some embodiments, it may be possible to tighten, or otherwise secure, the secondary fuse 32 to its contacts 34, 36 prior to the device 10 being connected to the terminals 16, 18. More typically, one or both of the ends of the secondary fuse 32 (in particular the end that is connected to the terminal 34) cannot be tightened, or otherwise secured, to the respective terminal until after the device 10 has been connected to the terminals 16, 18 (this is because the, or each, respective connection may involve making a mechanical connection between the respective end of the secondary fuse 32 and the respective terminal 16, 18). Alternatively, however, the user may install the secondary fuse 32 into the device 10 after the device 10 has been connected to the terminals 16, 18 and tighten/secure the secondary fuse 32 to its contacts 34, 36 (with primary fuse 24 removed and switch 40 open). This may for example occur when the device 10 has been pre-installed (either permanently or removably) and the secondary fuse 32 is being replaced, or installed for the first time.
Subsequently, the user closes switch 40 (e.g. using a lever or other operating means) to bring the secondary fuse 32 in-circuit (Figure 2). Because the secondary fuse 32 has been fully clamped to its contacts 34, 36 before the switch 40 is closed, the user is not exposed to the possibility of a catastrophic failure of the secondary fuse.
In the preferred embodiment, the fuse device 10 is arranged such that the switch 40 cannot be operated by the user (at least not from the open state to the closed state) when the primary fuse holder 26 is not installed in the device 10, e.g. because the actuator for closing the switch 40 is carried by the fuse holder 26 . Therefore, prior to operating the switch 40, the primary fuse holder 26 must be installed, but without the primary fuse. This is because, when the fuse holder 26 is installed with the primary fuse 24, there would initially be a loose connection between the primary fuse and the contacts 20, 22, which could expose the user to a catastrophic failure of the primary fuse in the event that a fault condition is present. Typically the primary fuse holder is installed before the device 10 is connected to the terminals 16, 18, although it may alternatively be installed after this.
When the switch 40 is closed, the secondary fuse 32 is in-circuit. If a fault exists, the secondary fuse will fail, but the user is not exposed to dangerous conditions described above since the secondary fuse has previously been properly secured to its contacts 34, 36.
Assuming that the secondary fuse 32 does not fail upon closing the switch 40, the next step is the installation of the primary fuse 24 between contacts 20, 22 while the switch 40 remains closed. In the preferred embodiment, this is achieved by placing the primary fuse 24 in its fuse holder 26 (which may first have to be removed from the device 10 in embodiments where the fuse holder 26 must be installed to allow the switch 40 to be closed) and then installing the fuse holder 26 such that the primary fuse 24 is brought in-circuit. At this stage, the primary and secondary fuses 24, 32 are both in-circuit and in parallel with one another (see Figure 3). The user is able to tighten, or otherwise secure, the primary fuse 24 to the contacts 20, 22 without being exposed to the possibility of a catastrophic failure of the primary fuse.
Once the primary fuse 24 has been tightened, i.e. fully clamped or otherwise secured, to contacts 20, 22, the user may open the switch 40 to remove the secondary fuse 32 from the circuit. This leaves the fuse device 10 in its normal operating state with the primary fuse 24 in circuit and the secondary fuse 32 out-of-circuit, the installation having been completed without exposing the user to risks of catastrophic fuse failure.
It will be seen that the invention has particular application to the installation of a removable fuse device, or the installation of the primary and secondary fuses of a pre-installed fuse device. Parts of the method described herein may be used when it is desired to replace one or both of the primary and secondary fuses, as will be apparent to a skilled person. In particular, before installing or replacing the secondary fuse, the switch 40 is opened and the primary fuse is either removed, or present but failed. Before installing or replacing the primary fuse, the secondary fuse is installed and the switch 40 is closed.
The invention is not limited to the embodiments described herein, which may be modified or varied without departing from the scope of the appended claims.

Claims

An installation method for an electrical fuse device (10) that is connectable first and second electrical terminals (16, 18) of an electrical circuit, the fuse device comprising first and second main electrical contacts (12, 14) between which a primary fuse (24) is electrically connectable via respective first and second primary fuse contacts (20, 22); means for receiving a secondary fuse (32), said means including a first secondary fuse contact (34) for electrically connecting one end of said secondary fuse to said first main contact and a second secondary fuse contact (36); and switching means (40) for selectably connecting said second secondary fuse contact to said second main contact, said fuse device being, wherein said method comprises:
with said switching means in a state where said second secondary fuse contact is electrically disconnected from said second main contact, and with said primary fuse not connected between said first and second primary fuse contacts,

connecting, if not already connected, said first and second main electrical contacts to said first and second electrical terminals respectively;

establishing, if not already established, a respective secure mechanical connection between one or both ends of said secondary fuse and a respective one of said first and second secondary fuse contacts;

operating said switching means to electrically connect said second secondary fuse contact to said second main contact;

installing said primary fuse between said first and second primary fuse contacts by installing said fuse holder, with said primary fuse, to said device such that both ends of said primary fuse are electrically connected to said primary fuse contacts; and

operating said switching means to electrically disconnect said second secondary fuse contact from said second main contact,

characterised in that said electrical fuse device is arranged such that said switching means cannot be operated from a state where said second secondary fuse contact is electrically disconnected from said second main contact to a state where said second secondary fuse contact is electrically connected to said second main contact unless the fuse holder is installed in the fuse device, and wherein said method includes installing said fuse holder, without said primary fuse, prior to said operating of said switching means to electrically connect said second secondary fuse contact to said second main contact.
A method as claimed in claim 1, including establishing a respective secure mechanical connection between one or both ends (28, 30) of said primary fuse (24) and a respective one of said first and second primary fuse contacts (20, 22).
A method as claimed in claim 1 or 2, wherein said establishing a respective secure mechanical connection involves tightening a mechanical connector, preferably a clamping device.
A method as claimed in any preceding claim, including, with said first and second main contacts (12, 14) connected to said first and second electrical terminals (16, 18) and said secondary fuse (32) not connected between said first and second secondary fuse contacts (34, 36), causing said switching means (40) to adopt a state where said second secondary fuse contact is electrically disconnected from said second main contact, before connecting said secondary fuse between said first and second secondary fuse contacts.
A method as claimed in any one of claims I to 3, with said first and second main contacts (12, 14) not connected to said first and second electrical terminals (16, 18) and said secondary fuse (32) connected between said first and second secondary fuse contacts (34, 36), causing said switching means (40) to adopt a state where said second secondary fuse contact is electrically disconnected from said second main contact, before connecting said first and second main contacts to said first and second electrical terminals.
A method as claimed in any preceding claim, wherein installing said primary fuse (24) involves directly or indirectly connecting both ends of said primary fuse to a respective one of said primary fuse contacts (20, 22).
A method as claimed in claim 1, wherein said fuse holder (26) is installed, without said primary fuse (24), prior to said connecting of said first and second main electrical contacts (12, 14) to said first and second electrical terminals (16, 18).
A method as claimed in claim 1 or 7, further including removing said fuse holder (26) after said operating of said switching means (40) to electrically connect said second secondary fuse contact (36) to said second main contact (14) and fitting said primary fuse (24) to said fuse holder prior to said installing said primary fuse between said first and second primary fuse contacts (20, 22).