GB2500435A

GB2500435A - Double-insulated isolation and distribution box for railway signalling allowing part shutdown for live working

Info

Publication number: GB2500435A
Application number: GB1205157.9A
Authority: GB
Inventors: Paul Legry; Darron Jones
Original assignee: Control Systems & Equipment Ltd
Current assignee: Control Systems & Equipment Ltd
Priority date: 2012-03-23
Filing date: 2012-03-23
Publication date: 2013-09-25
Also published as: GB201205157D0; GB201216299D0; GB2500739A

Abstract

A double-insulated electrical isolation and distribution enclosure 10 comprises a lower housing 12 for terminating upstream and/or downstream large diameter power cables, such as those used in railway signalling. An upper housing 14 carries a bank of control switches 70 and fuse carriers 72 and is hinged to the lower housing 12 so that it closed over the lower housing. The upper housing has an access lid 16, and a retainer means to secure the upper housing closed on to the lower housing. The lower housing 12 has electrically insulating interior and exterior surfaces and an insulating partitioning element 24 forming two cable-terminating compartments 30, 32. Two insulating access covers 34, 36 close each of these 30, 32, respectively, and are themselves covered when the upper housing 14 is closed. This arrangement can be used to allow selective isolation of only some upstream and/or downstream large diameter power cables in a railway signalling system, so that some cables can be repaired or replaced while others are still live and maintain the double insulation.

Description

I

Double-Insulated Electrical Isolation And Distribution Enclosure The present invention relates to a double-insulated electrical isolation and distribution enclosure, to a method of distributing power to a railway signalling system using such an enclosure, and to a method of using such an enclosure to selectivdy electrically isolate upstream and/or downstream large diameter power cables feeding electrical components of a railway signalling system.

It is a requirement, especially for railway signalling systems. to provide long lengths of power cable. To reduce voltage drop over long distances, the power cables which terminate at local distribution boxes have large diameters, typically in the order of 30 mm or more. The diameter of the local power cables from the distribution box to the signalling system is typically much smaller, in the order of 16 mm, due to the shorter distance.

However, cable theft, particularly of the large diameter long distance power cables, is an increasing problem. The conductor materials of the power cables are valuable, thereby leading to unauthorised and hazardous removal andlor damage by third parties.

This not only inconveniences the travelling public by disabling the associated signalling systems, but repair costs are significant and can be time consuming.

Presently, the long distance large diameter power cables require earthing facilities, and as such armoured three core cables are utilised. These are expensive and heavy, thus being cumbersome and difficult to install and replace.

It is therefore a requirement to be able to safely utilise unarmoured two core power cable which dispenses with the need for earthing. Although significantly more cost-effective and simpler to install and replace, any electrical system without earthing presents potential senous electncal hazards.

Furthermore, at present, when replacing a large diameter power cable at a distribution box, both an incoming feed and an outgoing feed must be electrically isolated. This inevitably results in the entire associated signalling system or other electrical system being supplied to be deenergised.

Additiona'ly, plastics distribution boxes cannot be utilised iii enclosed spaces, such as tunnels and underground railway systems. This is due possible toxic fumes and the release of other hazardous chemicals into the air should the distribution box be subjected to excessive heat or fire.

The present invention seeks to overcome these problems.

According to a first aspect of the invention, there is provided a double-insulated electrical isolation and distribution enclosure comprising a lower housing for terminating upstream andlor downstream large diameter power cables as herein defined, an upper housing which is hinged to the lower housing and which includes at least a bank of control switches and a bank of fuses, a retainer for releasably retaining the upper housing in a closed condition on the lower housing, and an access lid for preventing or limiting access to the upper housing, the or a further retainer retaining the access lid in a closed condition on the upper housing, the lower housing having electrically-insulative interior and exterior surfaces and an electrically-insulative IS partitioning element whereby two cable-terminating compartments are defined in the lower housing, and first and second electrically-insulative access covers which close the two cable-terminating compartments, respectively, the upper housing when closed overlying the first and second dectrically-insulative access covers.

Preferable and/or optional features of the first aspect of the invention are set forth in claims 2 to 13, inclusive.

According to a second aspect of the invention, there is provided a method of distributing power to a railway signalling system, the method comprising the steps of: a] laying unarmoured two-core large diameter power cable to a double-insulated electrical isolation and distribution enclosure in accordance with the first aspect of the invention; bj terminating the large diameter power cable in a said cable-terminating compartment of the lower housing of the enclosure; ci electrically connecting an internal smaller diameter power cable from the terminated large diameter power cable with a said control switch and/or fuse of the upper housing; dl electrically connecting an external smaller diameter power cable from said control switch andlor fuse to a railway signalling system exterior of the enclosure; and e] closing the caNe-terminating compartment by its said electrically-insulative access cover, and closing and securing the upper housing to the thwer housing, so that the upper housing overlies the said electrically-insulative access cover.

According to a third aspect of the invention, there is provided a method of using a double-insulated electrical isolation and distnbution enclosure in accordance with the first aspect of the invention to selectively electrically isolate upstream and/or downstream large diameter power cables feeding electrical components of a railway signalling system, the method comprising the steps of: a] electrically isolating a terminal for an upstream andlor downstream large diameter power cable in the respective cable-terminating compartment via its respective control switch; b] releasing and hinging the upper housing away from the thwer housing; c] removing the respective electrically-insulative access cover to access the required cable-terminating compartment; d] connecting a large diameter power cable to the said terminal; e] replacing the electrically-insulative access cover, and closing and securing the upper housing; and f] electrically reconnecting the said terminal to the railway signalling system by turning on the respective control switch, whereby another terminal in the other said cable-terminating compartment can remain live during steps a] to f] without there being an electrical shock hazard.

Preferable and/or optional features of the third aspect of the invention are set forth in any one of claims 17 to 19.

The invention will now be more particularly described, by way of example only. with reference to the accompanying drawings, in which: Figure 1 shows a side elevational view of one embodiment of a double-insulated electrical isolation and distribution enclosure, in accordance with the first aspect of the invention and shown with an upper housing hinged open relative to a lower housing.

and an access lid hinged open relative to the upper housing; Figure 2 shows a side elevational view which is similar to Figure 1, but with the upper housing and the access lid both hinged to closed positions; and Figure 3 shows a top pbn view of the doubIe-insuated electrical isolation and distribution enclosure, shown in Figure 1; Figure 4 is a top plan view, similar to Figure 3, but with the upper housing removed and two electrically-insulative access covers partially sectioned to show two cable-terminating compartments within the lower housing of the enclosure; and Figure 5 is a side elevational view from another side of the enclosure, and showing smafi-diameter power cable openings for feeding dectrical components of a railway signalling system.

Referring to the drawings, there is shown a double-insulated electrical isolation and distribufion enclosure 10 which comprises a lower housing 12, an upper housing 14, and an access lid 16. The enclosure 10 is preferably formed of metal plate, such as mild steel, overcoated on the interior and exterior surfaces with a durable plastics electrically-insulative coating 18, for example, PPA57I manufactured by Plascoat Systems Limited of Farnham Industrial Estate, Farnham, Surrey, GU9 9NY, UK.

PPA57 1 is suitable due to being devoid of Bisphenol A BPA, PVC, halogens. phthalates and heavy metals. Consequently, unlike traditional fully plastics enclosures, the enclosure 10 of the present invention meets requirements for location in covered or enclosed areas, such as tunnels and in underground or subway railway systems.

Traditional fully plastics enclosures, if subjected to excessive heat or fire, may release toxic or hazardous chemicals.

However, for above ground or open-air use, the enclosure of the present invention may utilise fully plastics electrically-insulative panels, instead of plastics-overcoated metal plates. Other electrically-insulative materials may also be considered.

The lower housing 12, as best seen in Figure 3, includes a unifomily solid base 20, four contiguous walls 22 upstanding from a perimeter of the base 20, and a partitioning element 24 which in this case bisects the lower housing 12, extends from a front said wall 26 to a rear said wall 28 and upstands from the base 20. The partitioning element 24 is also electrically-insulative being in this case a metal plate fully overcoated with the aforementioned plastics.

The lower housing 12 is thus divided into two cable-terminating compartments 30, 32 by the partitioning element 24, and first and second electrically-insulative access covers 34, 36 are provided for closing each of the cable-terminating compartments As with the partitioning element 24, each access cover 34, 36 is preferably a uniformly solid metal plate overcoated with non-electrically conductive plastics. Each access covcr 34, 36 is dimcnsioncd to scat on an uppcr cdgc or shouldcr of thc rcspcctivc walls 22 and partitioning element 24 defining each cable-terminating compartment 30, 32.

Each cable-terminating compartment 30, 32 can thus be or substantially be electrically isolated from its surroundings and from the other cable-terminating compartment 30. 32.

Preferably, the partitioning element 24 includes an access aperture allowing cable passage from a first one of the cable-teiminating compartments. 30 to a second one of the cable-terminating compartments 32. Furthermore, the second access cover 36 of the second cable-terminating compartment 32 preferably includes a cable-access opening 40, in this case being a cut-out or recess in an edge. allowing cable passage between the upper housing 14 and the lower housing 12. The access aperture in the partitioning element 24 and the cable-access opening 40 in the second access cover 36 are preferably dimensioned to receive as a close fit or tight fit a small diameter power cable. Rubber or elastomeric glands may be utilised in the access aperture and/or the cable-access opening 40 to close the openings around the respective cables, thereby improving the electrical isolation.

The use of the phrases small diameter' and small power cable' used herein and throughout and in connection with a size of a power cable or its core is intended to mean power cables having an outside diameter in the range of 10 mm to 25 mm, and more preferably at least substantially 16 mm. The use of the phrases large diameter' and large power cable' used herein and throughout and in connection with a size of a power cable or its core is intended to mean power cables having an outside diameter in the range of 26 mm to 150 mm, and more preferably substantially 50 mm.

A right side wall 42 of the lower housing 12, in this case forming part of the second cable-terminating compartment 32 includes one or more, and in this case three, small cable access apertures 44 for receiving outgoing and incoming small power cables. Such small power cables, in this case, supply one or more railway signalling systems and/or their associated electrical components, such as transformers and points heating systems.

Beneficially, the small cable access apertures 44 are located in the right side wall 42 beneath the cable-access opening 40, thus providing a most direct route from the upper housing 14.

Preferably, further glands may be provided in the small cable access apertures 44 for sealing and further improving the electilcal isolation of the second cable-terminating compartment 32.

To provide access for upstream and downstream large power cables, each cable-terminating compartment 30, 32 includes a large cable access aperture 46. Even though the large power cables to be used with the enclosure 10 of the present invention are intended to be unarmoured two core cables, and therefore of somewhat smaller core diameter than the traditional armoured three core power cables, the unarmoured two core cables are still cumbersome, heavy and relatively resilient to bending.

Advantageously, therefore, the front wall 26 of the lower housing i2 can be at least in IS part temporarily dismantled. The front wall 26 includes a lowermost wall element 48 having first recesses 50 forming part of the large cable access apertures 46 in an upper edge thereof, and two upper wall elements 52 which are seatable on the upper edge of the lowermost wall element 48. The lowermost wall element 48 extends between the left and right side walls 42, 54 and thus across the two cable-terminating compartments 30, 32. It may not be removable. The removable two upper wall elements 52 each close a respective one of the first and second cable-terminating compartments 30, 32.

Each upper wall element 52 includes a second recess 56 in its lower edge. The ft-st and second recesses 50, 56 match to define the respective large cable access aperture 46.

Screw ports for screw-threaded fasteners 58 al-c provided in the two caNe-terminating compartments 30, 32. around the perimeter of the front wall 26, so that the upper wall elements 52 can be releasably fastened in place. The screw ports are electrically insulated to prevent a potential electncal shock hazard during removal and replacement.

However, other fastening means may be considered for retaining the upper wall elements 52 in place, such as channels for captively sliding the upper wall elements 52 therealong, or pivotable catches.

As before, each of the arge caNe access apertures 46 may include a gland for closing the aperture 46 around the large power caNe once located therein.

To electrically terminate an end of a large power cable in each caNe-terminating compartment 30, 32. first and second heavy-duty terminals 60 are provided fixed to the base 20. Electrically-insulative caps may also be provided which cover the terminals 60, thereby further shielding the terminals 60 during access.

Flange plates or brackets 62 may be provided on an exterior of the lower housing 12, in this case at or adjacent to an upper edge of the left and right side walls 42, 54. This enables secure mounting of the enclosure 10 at an installation site.

The upper housing 14 comprises a base 64 and four contiguous walls 66 which upstand from a perimeter of the base 64. The walls 66 of the upper housing 14 are preferably lower than those of the lower housing 12, providing a slimmer upper container.

As with the lower housing 12, all panels are electrically-insulative at least on the interior and preferably also on the exterior surfaces. Metal plate overcoated with non-electrically conductive plastics is preferred, thereby enabling use in covered areas, but again the panels may be fully plastics if only to be used in open and uncovered installation sites.

The upper housing 14 is hinged at a lower edge of its right side wall 42 to an upper edge of the right side wall 42 of the lower housing 12, as best seen in Figure 5 and understood from Figure 1. The hinges 68 used may be plastics, for example, polyamide, or metal. Again, this is beneficial as it enables the most direct route for small power cables to run between the upper and lower housings 12, 14, without requiring significant extension or slack to be availaNe when pivoting open the upper housing 14.

A footprint of the upper housing 14 is dimensioned to match or substantially match that of the lower housing 12, so that in a closed condition the upper housing 14 overlies the lower housing 12. In such a closed condition, the upper housing 14 therefore sits over the first and second access covers 34, 36.

The upper housing 14 is adapted to house at east a bank of control switches 70 and a bank of fuse carriers 72 for fuses, along with preferably an electrical surge protection device and a bus bar. First and second control switches 74. 76 provide for electrical isolation of the terminals 60 in the first and second cable-terminating compartments 30, 32, and the remaining control switches 78 provide for electrical isolation of electrical componcnts bcing fcd by thc small powcr cables exiting thc lowcr housing 12 via thc small cable access apertures 44.

The control switches 70 may be lockable in an ON andior OFF condition. For example, each grip portion of the switch 70 may include an aperture, and a base portion may include one or more spaced apart apertures. Once the grip portion is moved to a certain position, the apertures align thereby allowing a lock, such as a padlock, to be inserted.

This is beneficial in that it prevents or limits the possibility of the switch being inadvertently operated whilst the lower and/or upper housings are being accessed.

The control switches 70 and preferably also the fuses on the fuse carriers 72 are IS accessible from the top of the upper housing 14 and through openings 80, 82 in the aforementioned access lid 16.

The access lid 16, as with the lower and upper housings 12, 14, is electrically insulated and preferably formed of metal plate overcoated with the previously mentioned suitable plastics. The access lid 16 is preferably hinged on an opposite side to the hinging of the upper housing 14. However, hinging on another side is feasible.

A switch opening 80 and a fuse opening 82 are formed in the access lid 16, and these openings 80, 82 are dimensioned to closely fit around the bank of control switches 70 and the bank of fuse carriers 72, respectively. The access lid 16 therefore closes off unhindered access to the other elements, such as the associated terminals and the bus bar, if included.

The access lid 16 is preferably lockable to prevent or limit unauthorised opening. In this case, the access lid 16 is lockable to the upper housing 14 by an independent locking device 84. Although a locking device is suggested, any suitable retainer can be utilised whereby the access lid 16 is releasably securaNe in its closed condition. For example, the retainer cou'd be a swing plate operable by a screwdriver or a detent.

Additiona'ly, the upper housing 14 is lockable to the lower housing 12, again to prevent or limit unauthorised opening. This further locking device is preferably accessible through an opening 86 in the access lid 16, thereby dispensing with the need to first open the access lid 16 in order to access the cable-terminating compartments 30, 32.

The further locking device of the upper housing 12 is preferably separate of the locking device of the access lid 16 for the safety reasons already mentioned. Although again a locking device is suggested, any suitable retainer can be utilised whereby the upper housing 14 is releasably securable in its closed condition to the lower housing 12. For example, the retainer could be a swing plate operable by a screwdriver or a detent.

The two retainers mentioned may be independent of each other, or may be combined together to simultaneously lock or secure the access lid and upper housing.

To install the douNe-insulated electrical isolation and distribution enclosure 10, the lower housing 12 is fixedly mounted at the installation site via the flange plates or brackets 62. With the upper housing 14 open and the access covers 34, 36 removed, upstream and downstream large power cables are inserted into respective cable-terminating compartments 30, 32 via the large cable access apertures 46. This process is simplified by the removal of the multi-part front wall 26, if necessary. The upstream and downstream power cables may be an incoming and an outgoing power cable, or two incoming power cables.

The large power cables are connected to the terminals 60, and the optional insulative caps are fitted to the terminals 60. A small power cable is run from the terminal 60 in the first cable-terminating compartment 30, 32, through the partitioning element 24 and together with a small power cable from the terminal 60 in the second cable-terminating compartment 30, 32 through the cable-access opening 40 in the second access cover 34, 36. The small power cables are fed into the upper housing 14. Further small power cables from the upper housing 14, through the cable-access opening 40 and out through the small cable access apertures 44 provide power to the associated railway signalling systems or other electrical components external of the enclosure 10.

The access covers 34, 36, once in place and dosing their respective caNe-terminating compartments 30, 32, are secured by having the upper housing 14 hinged down to seat thereon and then locked.

In the case when the enclosure 10 is at the end of a power cable run, only one of the cable-terminating compartments 30, 32 may be utilised. Therefore, blanking plates may be utilised to close any access apertures in the walls 66 of the lower housing 12 not being used.

In the event of a problem with one, other or both upstream and downstream large power cables, for example, due to unauthorised tampering, removal, damage or vandalism, the respective terminal 60 can be selectively isolated via its control switch 74, 76. The upper housing 14 is unlocked and hinged open, and the relevant access cover 34, 36 removed to open the cable-terminating compartment 30, 32. Due to the electrically-insulative and isolating structures of the two cable-terminating compartments 30, 32 and the use of the electrically-insulative access covers 34, 36, in the event of only one large IS power cable requiring repair or replacement, the other large power cable can remain live and thus the associated external electrical systems operational.

The respective terminal 60 can thus be uncapped, the existing large power cable removed, and a new large power cable inserted and connected. The access cover 34, 36 is then replaced, and the upper housing 14 hinged closed and locked to securely shut the lower housing 12. The respective control switch 74, 76 is then turned on to reenergise the terminal 60 and associated external electrical components.

Although the double-insulated electrical isolation and distribution enclosure described above is ideally suited for railway signalling systems, it may also be used in other environments for supp'ying power to electrical components.

It is thus possible to provide a double-insulated electrical isolation and distribution enclosure which meets Class I and Class II requirements. The enclosure provides selective isolation of upstream and downstream electrical supplies, thereby dispensing with the need to electrically deenergise all electrically connected external systems and components during maintenance and repair procedures and thus minimising disruption ii to associated signalling equipment or other electrical components. It is also possible to provide an unearthed enclosure which meets or exceeds requirements for safe installation and usage at underground or covered sites. Furthermore, it is possible to provide a double-insulated electrical isolation and distribution enclosure which can preferably operate at up to 690 volts or more, whereby large diameter core power cables can be terminated and smaller diameter core power cables or spurs can feed ocal electrical equipment via dedicated isolation control switches. By providing a double-insulated segregated enclosure, less expensive large diameter unarmoured two core power cable can be utilised during initial installation or as a replacement for large diameter armoured three-core power cable.

Claims

Claims 1. A double-insulated electrical isolation and distribution enclosure comprising a lower housing for terminating upstream and/or downstream arge diameter power cables as herein defined, an upper housing which is hinged to the lower housing and which includes at least a bank of control switches and a bank of fuses, a retainer for releasably retaining the upper housing in a closed condition on the lower housing. and an access Ud for preventing or limiting access to the upper housing, the or a further retainer retaining the access lid in a closed condition on the upper housing, the lower housing having electrically-insulative interior and exterior surfaces and an electrically-insulative partitioning element whereby two cable-terminating compartments are defined in the lower housing, and first and second electrically-insulative access covers which close the two cable-terminating compartments, respectively, the upper housing when closed overlying the first and second electrically-insuative access covers.

IS
2. A double-insulated electrical isolation and distribution enclosure as claimed in claim 1, wherein a retaining mechanism for releasably securing the upper housing to the lower housing is accessible through the closed access lid.
3. A double-insulated electrical isolation and distribution enclosure as claimed in claim 1 or claim 2, wherein the access lid is hinged to the upper housing.
4. A double-insulated electrical isolation and distribution enclosure as claimed in claim 3, wherein the access lid is hinged on an opposite side to the hinging of the upper housing.
5. A double-insulated electrical isolation and distribution endosure as claimed in any one of claim 1 to 4, wherein a side wall of the lower housing at each cable-terminating compartment indudes a caNe-access opening for an incoming andlor outgoing large diameter power cable.
6. A double-insulated electrical isolation and distribution endosure as claimed in claim 5, wherein the cable-access opening includes a cable gland.
7. A double-insulated electrical isolation and distribution enclosure as claimed in claim 5 or daim 6, wherein the side wall includes a removaHe panel for enabling location of the large diameter power cable in at least part of the cable-access opening.
8. A double-insulated electrical isolation and distribution enclosure as claimed in any one of claims I to 7, wherein each cable-terminating compartment includes a terminal block for electrically connecting an incoming or outgoing arge diameter power cable, the terminal block being secured to an interior surface of its respective cable-terminating compartment.
9. A double-insulated electrical isolation and distribution enclosure as claimed in claim 8, wherein each terminal block includes a removable electrically-insulative cap.
10. A double-insulated electrical isolation and distribution enclosure as claimed in any one of claims 1 to 9, wherein at least one of the first and second electrically- insulative access covers includes a smaller-diameter cable opening for electrical-cable communication between the upper housing and the cable-terminating compartments.
11. A double-insulated electrical isolation and distribution enclosure as claimed in any one of claims 1 to 10, wherein the electrically-insulative partitioning element includes a further smaller-diameter cable opening for electrical-cable communication between the two cable-terminating compartments.
12. A double-insulated electrical isolation and distribution enclosure as claimed in any one of claims I to 11, wherein a side wall of the lower housing indudes a further cable-access opening for an incoming and/or outgoing small diameter power cable iii dectrical communication with at east one said control switch andlor said fuse of the upper housing.
13. A double-insulated electrical isolation and distribution enclosure as claimed in any one of claims 1 to 12, wherein the lower housing, upper housing and lid are formed of metal plate coated with an electrically-insulative plastics coating.
14. A double-insulated electrical isolation and distribution endosure substantially as hereinbefore described with reference to the accompanying drawings.
15. A method of distributing power to a railway signalling system, the method comprising the steps of: a] laying two core unarmoured large diameter power cable to a double-insulated electrical isolation and distribution enclosure as claimed in any one of the preceding claims; b] terminating the large diameter power cable in a said cable-terminating compartment of the lower housing of the enclosure; ci electrically connecting an internal smaller diameter power cable from the terminated large diameter power cable with a said control switch and/or fuse of the upper housing; d] electrically connecting an externa' smaller diameter power cable from said control switch and/or fuse to a railway signalling system exterior of the enclosure; and e] closing the cable-terminating compartment by its said electrically-insulative access cover, and closing and securing the upper housing to the lower housing, so that the upper housing overlies the said electrically-insulative access cover.
16. A method of using a double-insulated electrical isolation and distribution enclosure as claimed in any one of claims 1 to 14 to selectively electrically isolate upstream and/or downstream large diameter power cables feeding electrical components of a railway signalling system, the method comprising the steps of: a] electrically isolating a terminal for an incoming andJor outgoing large diameter power cable in the respective cable-terminating compartment via its respective control switch; hi releasing and hinging the upper housing away from the lower housing; ci removing the respective electrically-insulative access cover to access the required caHe-terminating compartment; d] connecting a large diameter power cable to the said terminal; ci replacing the electrically-insulative access cover, and closing and securing the upper housing; and f] electrically reconnecting the said terminal to the railway signalling system by turning on the respective control switch, whereby another terminal in the other said cable-terminating compartment can remain live during steps a] to fi without there being an electrical shock hazard.
17. A method as claimed in claim 16, wherein, subsequent to step a], the large diameter power caNe is damaged or at least in part removed.
18. A method as claimed in claim 16 or claim 17, wherein, in step d], an existing large diameter power cable is disconnected from the terminal and a new large diameter power cable is connected to the terminal.
19. A method as claimed in any one of claims 16 to 18, wherein, in step d], the large diameter cable is unarmoured and two core.