WO2019137940A1

WO2019137940A1 - Enclosure for an electrical component in a potentially hazardous environment

Info

Publication number: WO2019137940A1
Application number: PCT/EP2019/050405
Authority: WO
Inventors: David James MAZZIOTTA
Original assignee: Bartec Technor As
Priority date: 2018-01-10
Filing date: 2019-01-09
Publication date: 2019-07-18
Also published as: GB2571513A; GB201800386D0

Abstract

Enclosure for an electrical component in a potentially hazardous environment A portable enclosure(2)is provided for an electrical component for use in a potentially hazardous environment. The enclosure (2) is sealed and adapted to be pressurised so as to maintain a higher internal pressure than an external pressure without atop-up gas supply. The enclosure (2) comprises: a power supply for the electrical component; a diaphragm(38, 40) having two faces(48, 0), the first face(50)of the diaphragm being in contact with the interior of the enclosure and the second face(48)of the diaphragm being in contact with the external atmosphere, the diaphragm (38,40) being configured to snap from an engaged position into a disengaged position when the difference between the internal pressure and the external pressure falls below a first predetermined threshold; and an arrangement for isolating the power supply when the diaphragm(38, 40)snaps into the disengaged position.

Description

Enclosure for an electrical component in a potentially hazardous environment

Technical Field

The invention relates to enclosures for housing electrical components used in potentially hazardous environments such as for example on oil rigs or in other environments where inflammable or explosive gas may be present. There is a need to contain electrical components away from such environments to avoid sparks or heat from the electrical components igniting potentially hazardous gases in the environment and causing a fire and/or explosion.

Background

It is already known to provide overpressurised enclosures for containing electrical components such as computers or measuring instruments in a potentially hazardous environment. Some such enclosures rely on continuous flow or leakage compensation methods which use a permanently connected gas supply together with an external reference pressure to re-pressurise the enclosure if the internal pressure drops below the desired level. Usually the gas supply would comprise an inert gas or instrument air. As they require a connection to a gas supply, these systems are immobile or (even if they use a pressurised gas cylinder) heavy and so not easily portable. Further, the use of the gas supply carries a risk as failure of the gas supply would lead to a malfunction in the system with the risk of fire and/or an explosion.

WO 2005/036678 A1 discloses an electrical instrument for use in a hazardous atmosphere, comprising an enclosure sealed from the external atmosphere, an internal battery and a compressed gas cylinder for pressurising the enclosure. A pressure-operated switch, which may comprise a diaphragm, inside the enclosure is arranged to move to an off state in which the battery is isolated if the internal pressure of the enclosure falls below a predetermined threshold value. Thus, by isolating the battery when the internal pressure of the enclosure falls below the predetermined threshold value, WO 2005/036678 A1 provides a way of reducing the risk associated with a failure of the gas supply.

Although the instrument disclosed in WO 2005/036678 A1 is described as being portable, the enclosure includes a gas cylinder and so the instrument will be relatively heavy. It is unlikely that a portable enclosure for electrical instruments can be provided using such a design that can be carried by one person and is light enough to take on a helicopter for example. Summary

From a first aspect the invention provides a portable enclosure for an electrical component for use in a potentially hazardous environment, the enclosure being sealed and adapted to be pressurised so as to maintain a higher internal pressure than an external pressure without a top-up gas supply,

the enclosure comprising:

a power supply for the electrical component;

a diaphragm having two faces, the first face of the diaphragm being in contact with the interior of the enclosure and the second face of the diaphragm being in contact with the external atmosphere,

the diaphragm being configured to snap from an engaged position into a disengaged position when the difference between the internal pressure and the external pressure falls below a first predetermined threshold; and

an arrangement for isolating the power supply when the diaphragm snaps into the disengaged position.

By providing a diaphragm which snaps into a disengaged position when the difference between the internal pressure and the external pressure falls below the first predetermined threshold, the invention provides a means of detecting a change in pressure which might risk an insufficient overpressure being present and of isolating the power supply which is both faster and more accurate than the known mechanisms. The diaphragm may snap back to its disengaged position very rapidly such that the isolation of the power supply may occur substantially simultaneously with the pressure differential falling below the first predetermined threshold. This is advantageous as any delay in the power supply being isolated could risk a fire or explosion.

The claimed enclosure reduces the risk of the electrical component inside the enclosure causing a fire or explosion before the power supply is isolated. A change in pressure which causes the diaphragm to snap could be due to an increase in external pressure and/or a decrease in the internal pressure (for example due to a leak in the enclosure).

In addition to the above, enclosures in accordance with the invention do not require a regular supply of pressurised gas and can thus provide an enclosure which is relatively light weight and hence portable. This is useful for electronic components which are used by maintenance personnel for example and so need to be moved around. As the enclosure of the invention does not require a regular supply of pressurised gas, it may also be more energy efficient and so better for the environment.

It will be understood that the portable enclosure is for one or more electrical components such that any suitable number of electrical components might be placed inside the enclosure.

The power supply could be provided externally of the enclosure and suitably sealed from the external environment. In preferred embodiments however, the power supply is provided within the enclosure. This has the advantage that the power supply can be connected to the electrical component within the enclosure in use such that no additional protection from the external environment may be required for the power supply or the means for connecting the power supply to the electrical component.

In one set of embodiments, the arrangement for isolating the power supply generates and sends a signal to a controller which controls the supply of power to the electrical component. This signal can be the mechanism by which the controller then isolates the power supply.

Various alternative arrangements for isolating the power supply could be envisaged. For example, these might include the use of capacitance, magnetic switches or optics. Preferably, however the arrangement for isolating the power supply comprises a mechanical arrangement acted on by the diaphragm configured to isolate the power supply when the diaphragm snaps back to its disengaged position. Such an arrangement could comprise a switch.

It will be appreciated that various types of switch could be used to cause the power supply to the enclosure to be disconnected. These could include but are not limited to an end switch or a micro switch. In one set of embodiments, the mechanical arrangement comprises a limit switch. This allows simple and yet instantaneous switching to occur when the diaphragm snaps back to its disengaged position.

In a set of embodiments, the arrangement for isolating the power supply is provided inside the enclosure. This has the advantage that the arrangement for isolating the power supply may be contained within the sealed pressurised environment of the enclosure and so may be protected against the risk of causing a fire or explosion. It will be appreciated however that the enclosure would ideally be made as small as possible whilst maximising the storage space inside the enclosure.

In alternative embodiments therefore, the arrangement for isolating the power supply extends externally of the enclosure and may be sealed from the external atmosphere. This allows the space available for the electrical instrument inside the enclosure to be maximised. It also has the advantage that the switch does not need to be protected against the possibility of damage by the electrical instrument being placed in and/or moving inside the enclosure.

In a set of embodiments, the arrangement for isolating the power supply is arranged to generate an additional signal or other indication. This will, for example, enable a signal to be sent to maintenance personnel to make them aware that the power supply has been isolated and that the enclosure requires replacing or re-pressurising before it can be used again. In a set of embodiments, this is achieved by a light or other visual indicator on the enclosure being switched on or off when the diaphragm snaps into the disengaged position.

Only a single diaphragm need be provided in the enclosure of the invention. In preferred embodiments however, the enclosure comprises two or more diaphragms, and the arrangement, or independent parallel arrangements, for isolating the power supply is/are activated when one or more of the diaphragms snap into the disengaged position. This has the advantage of introducing redundancy so that the power supply will still be isolated even if one of the diaphragms fails.

The diaphragm(s) could, for example, be mounted directly into an opening in the enclosure wall. Preferably however, the enclosure further comprises a support plate with the diaphragm(s) mounted thereon.

The enclosure could be configured such that all parts of the electrical component are contained therein. For some components however, it may be desirable to have cabling which extends out from the enclosure. In a set of embodiments therefore, the enclosure further comprises a sealed port for the passage of cables and /or conductors into the enclosure.

Preferably the diaphragm is configured to be pushed automatically into the engaged position when the difference between the internal pressure and the external pressure is greater than a second predetermined threshold and to snap into the disengaged position when the difference between the internal pressure and the external pressure falls below the first predetermined threshold. In some embodiments, the first and second predetermined thresholds could be the same. Preferably however, the second predetermined threshold is greater than the first predetermined threshold.

This hysteresis has the advantage that if the pressure differential falls to a level deemed to be unsafe the electrical component will remain isolated until there is a significant improvement (i.e. by re- pressurisation) rather than risking it being reconnected, possibly multiple times. The embodiments of the invention described above allow an electrical component to be contained in a potentially hazardous environment, thus reducing the risk of a fire or explosion being caused by heat or a spark from the electrical component by pressurising it, e.g. outside the environment, and then removing the gas or instrument air supply. This is novel and inventive in its own right and so, from a further aspect the invention provides a method of containing an electrical component in a potentially hazardous environment, the method comprising: placing an electrical component in a sealed portable chamber; connecting the sealed portable chamber to a gas supply; using the gas supply to pressurise the sealed portable chamber such that the internal pressure of the sealed portable chamber is greater than the external pressure; removing the gas supply; connecting the component to a power supply; and a snap action diaphragm attached to the sealed portable chamber causing the component to be isolated from the power supply by snapping from an engaged position into a disengaged position if a difference between the internal pressure and the external pressure falls below a first predetermined threshold.

Preferably, the gas supply comprises an inert gas or instrument air. Preferably movement of the diaphragm acts on a mechanical arrangement to isolate the electrical component from the power supply.

Preferably, the mechanical arrangement comprises a limit switch.

The method may further comprise generating and sending a signal to a controller when the difference between the internal pressure and the external pressure falls below the first

predetermined threshold.

Brief Description of the Drawings

Some preferred embodiments will now be described, by way of example only, and with reference to the accompanying drawings in which: Figure 1 is a front perspective view of an enclosure according to an embodiment of the invention;

Figure 2 is a rear perspective view of the enclosure of Figure 1;

Figure 3 is a top perspective view of a support plate for mounting on the enclosure;

Figure 4 is a bottom perspective view of the support plate of Figure 3;

Figure 5a is a side elevation view of the support plate of Figure 3 when inverted;

Figure 5b is a bottom plan view of the support plate of Figure 3

Figure 6 is a top plan view of a diaphragm according to an embodiment of the invention;

Figure 7 is a cross section through the diaphragm of Figure 6 along line J-J showing the diaphragm in its engaged position;

Figure 8 is a top plan view of a support plate according to an alternative embodiment of the invention;

Figure 9 is a bottom plan view of the support plate of Figure 8;

Figure 10 is a sectional view of the support plate of Figure 8;

Figure 11 is a section along line B-B of Figure 9; and

Figure 12 is a perspective view of the support plate of Figure 8 when assembled.

Description of the Preferred Embodiments

Figures 1 and 2 show a preferred embodiment of the invention comprising a portable sealed enclosure 2 for one or more electrical components (not shown) such as a PC or measuring instrument. The enclosure is formed of stainless steel although any other sufficiently strong and light material could be used. The enclosure 2 has a substantially square front panel 4 and a substantially square rear panel 6. Four side panels 8, 10, 12, 14 join the front and rear panels 4, 6 together to form the sealed, box shaped enclosure 2. A one way valve (not shown) is provided to allow gas to be supplied into the enclosure so as to pressurise the interior of the enclosure to a pressure above the external pressure (i.e. to overpressurise the enclosure). The gas supplied is preferably an inert gas (such as Nitrogen, N₂) or instrument air. The enclosure 2 can be filled with the gas in a safe area remote or shielded from the potentially hazardous environment so as to be overpressurised. The gas supply can be from a gas canister or from a fixed supply. The enclosure is sealed from the external environment such that the internal pressure should remain constant after the enclosure has been overpressurised. Thus the enclosure is a static overpressure enclosure. However, the pressure differential between the external environment and the interior of the enclosure may drop below a desired level if gas leaks from the enclosure, for example if there is a fault in the seal, or if the external pressure increases. For maintenance, the enclosure can therefore be refilled with gas at any time using the one-way valve.

The enclosure of the described embodiment is portable, making it practical for smaller electronic devices such as PCs or measuring instruments used by maintenance personnel. In one example, the enclosure can be used to house a 19" (48cm) screen and / or a PC. In this example, the weight of the enclosure containing the PC is less than 11.3kg (251 bs) which is within the Health and Safety

Executive (HSE) requirements for one person to lift alone.

As can be seen in Figure 2, an opening in the rear face 6 of the enclosure 2 is covered by a housing 15 which extends outwardly from the rear face 6 and is fixed thereto by welded studs 17. A support plate 16 (as shown in Figure 3 to 6) is provided within the housing 15. The support plate 16 extends over the opening and is fixed to the rear face 6 by welded studs (not shown). The support plate 16 is made from stainless steel and has a thickness of 1.5mm. The support plate 16 is elongate in form with rounded ends 18, 20. In one example, the length of the support plate is 160mm and the width is 60mm. The support plate 16 comprises three circular apertures 22, 24, 26 extending therethrough. The apertures are centred on the longitudinal axis 28 of the support plate 16 and are spaced from one another in the longitudinal direction such that the distance between the centres of adjacent apertures is e.g. 50mm.

In the example described herein, the first aperture 22, adjacent a first end 18 of the support plate 16, has a diameter of 39.6mm. A stainless steel bushing 30 extends therethrough and is supported by a stainless steel annular collar 32 welded to the underside of the support plate 16. The collar 32 has an internal diameter of 39.6mm and an external diameter of 46mm. A nickel shim washer 64 is provided to engage between the annular collar 32 and an annular rib on the outer wall of the bushing 30. The bushing 30 extends upwardly from the support plate 16 such that when the support plate 16 is in situ in the enclosure 2, the bushing 30 extends outwardly from the enclosure 2 from the rear face 6 thereof. The first aperture 22 and bushing 30 are provided for cables and / or conductors to pass into the enclosure 2. Moulded silicone or other suitable means (not shown) for sealing the first aperture 22 are provided such that the passage of the cables and / or conductors is achieved while the enclosure interior is sealed from the external atmosphere. The second aperture 24 extends through the support plate 16 approximately at the centre thereof. The third aperture 26 is located between the second aperture 24 and the second end 20 of the support plate 16. The second and third apertures have a diameter of 29.4mm. Second and third annular stainless steel collars 34, 36 are welded to the underside of the support plate 16 extending around and centred on the second and third apertures 24, 26 respectively. The second and third annular stainless steel collars 34, 36 for example have an inner diameter of 29.4mm, an outer diameter of 39.5mm and a height of 4mm. Second and third annular nickel shim washers 66, 68 are provided over the second and third stainless steel collars 34, 36 respectively. First and second circular snap action diaphragms 38, 40 are provided to extend over the respective second and third shim washers 66, 68.

The first and second diaphragms 38, 40 are formed from beryllium copper. In alternative embodiments, the diaphragms could be made of Inconel X750. They are electron beam welded onto the respective stainless steel collars 34, 36.

Each diaphragm 38, 40 is formed from a continuous sheet of material. An example diaphragm 38 is shown in greater detail in Figures 6 and 7. As seen, it comprises a thin annular flange 41 adapted to rest on and correspond in shape with one of the stainless steel collars 34, 36. The radially outer edge 37 of the thin annular flange 41 forms the outermost part of the diaphragm. The diaphragm extends from the radially inner edge 39 of the thin annular flange 41 substantially perpendicular thereto to form an annular wall 42. The diaphragm further comprises a circular body 43, the perimeter of which joins the annular wall 42 at the edge thereof which is removed from the thin annular flange 41. The circular body 43 comprises an external face 48 and an internal face 50, the external face being in contact with the external environment and the internal face 50 being in contact with the interior of the enclosure when the diaphragm is in situ. The circular body 43 comprises an outer ring 44 and an inner portion 45. The inner portion 45 is joined to the outer ring 44 by a "bellows" type portion 46 and extends substantially parallel to the support plate 16 and spaced from the outer ring 44 in a direction toward the interior of the enclosure when in situ. The outer ring 44 and inner portion 45 are adapted to extend substantially parallel to the support plate 16 when the difference between the external pressure and the internal pressure is for example 8 kPa ( the engage pressure) or more.

The diaphragms are adapted such that the whole circular body 43has a natural resting or memory state level (i.e. in a disengaged position) when the pressure differential between the external 48 and internal 50 faces thereof is less than for example 5 kPa (the disengage pressure). In this position, the outer ring 44 is adapted to extend inwardly towards the interior of the enclosure when in situ such that the centre of the circular body 43 (i.e. the centre of the inner portion 45) is located further towards the interior of the enclosure than the perimeter thereof. Thus, at any radial section through the outer ring 44, the outer ring 44 extends at an angle to the support plate in viewed in cross section in a plane perpendicular to the support plate 16 when in the first natural or resting position.

When the difference between the external pressure and the internal pressure is for example 8 kPa (the engage pressure) or more, the diaphragms 38, 40 are adapted such that the outer ring 44 is pushed into the engaged position as described above. In the engaged position, at any radial section through the outer ring 44, the outer ring 44 extends substantially parallel to the support plate 16 in cross section in a plane perpendicular to the support plate 16 when in the engaged position. The diaphragms can also be moved manually into the engaged position.

The circular body 43 of the diaphragms will snap (move suddenly) back to the disengaged position when the pressure differential falls to or below the disengage pressure. The diaphragms have a snap distance of 3mm. (Where the snap distance is the distance the centre of the inner ring 45 moves through in a plane perpendicular to the thin annular flange 41 when moving from the engaged position to the disengaged position). It will be appreciated that the difference between the engage and disengage pressures of the diaphragm is due to hysteresis and that these values can be altered by varying the material used, and or the dimensions of the diaphragm. In the preferred embodiment, the diaphragms are designed to have a tolerance of about 50Pa in the engage and disengage pressures. In this embodiment, the diameter of each diaphragm to the outer edge of the thin annular flange 41 may be 39.40mm. The diameter of the circular body 43 may be 37mm.

In the embodiment of Figures 3 and 4, a bracket 52 is mounted to the upper surface of the support plate 16. The bracket 1 has a substantially rectangular portion 54 which extends parallel to the longitudinal axis 28 of the support plate 16 and extends upwardly so as to extend outwardly from the enclosure when the support plate 16 is in situ. The rectangular portion 54 is attached to the support plate 16 adjacent the second and third apertures 24, 26. First and second limit switches 56, 58 are mounted on the rectangular portion 54 so as to extend over the respective inner rings 45 of the diaphragms 38, 40 and to contact and be pushed upwardly by the external faces 48 thereof when the enclosure is pressurised such that the inner parts 42 are in their engaged position. Thus, with the enclosure pressurised so that it exceeds the external pressure by at least the engage pressure, the limit switches 56, 58 cause the power supply to the electrical component(s) in the enclosure to be maintained. When the pressure differential between the interior of the enclosure and the external atmosphere drops below the disengage pressure, the inner rings 45 snap back to their disengaged position. Thus, the limit switches are no longer pushed upwardly and so the switches cause the power supply to be interrupted.

The required function of isolating the power supply when the pressure inside the enclosure drops below a required threshold could be provided using only a single aperture in the enclosure and a single snap action diaphragm. By providing two snap action diaphragms, a safety mechanism or redundancy is built into the design of the enclosure as movement of either of the two diaphragms will cause the power supply to be isolated. Thus, failure of one of the diaphragms will not cause the mechanism to malfunction with the potential outcome of a fire or explosion as a result.

An alternative embodiment of the support plate 116 is shown in figures 8 to 12. Unless stated otherwise, all features and dimensions are the same as for the previously described embodiment. In this embodiment, the support plate is substantially rectangular in shape with a curved edge 170 being provided at each corner thereof. For example, the length of the support plate is 210mm, the width is 100mm and the thickness is 5mm.

As shown in Figure 11, the annular stainless steel collars 134, 136 have an outer diameter of 40mm and an inner diameter which varies over the thickness thereof. Thus, the collars 134, 136 are formed with a chamfered or angled surface 172 on the inner face thereof and the inner diameter is less at the edge adjacent the support plate 116 than the edge remote therefrom.

It will be appreciated that in the embodiments described, the bracket and limit switches are provided externally of the enclosure 2. For these to be safe, they must be sealed against the external environment, for example, by the housing 15 shown in Figure 2. As shown in Figure 12, a secondary housing 174 is provided on the support plate 116 extending outwardly from the rear face 6 of the enclosure 2 so as to enclose the bracket, limit switches and associated electrical components.

Apertures 180 are provided in the walls of the secondary housing 174. The housing is box shaped having one open face which is arranged over the support plate. Flanges 182 extend outwardly from the housing side walls at either end thereof so as to be parallel and adjacent to the upper surface of the support plate when the housing is in situ. A first aperture 178 is formed in the support plate 116 between the first 32 and second 34 apertures and a second aperture 179 is formed in the support plate 116 between the third aperture 36 and the edge of the support plate 116.

The secondary housing 174 is secured to the support plate 116 by welded studs 176 passing through the flanges 182 and the apertures 178, 179.

In an alternative embodiment, the limit switches and their associated electronics could be adapted to extend internally into the enclosure. In other alternative embodiments, a system could be provided for sending a signal to a controller when the pressure drops below the required threshold rather than isolating the power supply directly.

The arrangement of the snap action diaphragm and the limit switch described enables the power supply to be isolated at the instant that the pressure differential drops below the required threshold level. It also provides a relatively simple arrangement where there are not many components which can fail to function in the required manner. This therefore provides a safer pressurised enclosure as there is minimal delay in the power supply being disconnected when the pressure drops below the required threshold value. Although the embodiments described above include a support plate, annular rings and shim washers for mounting the diaphragms, it will be appreciated that one or more diaphragms could be mounted to the enclosure in various other ways in order to function as required. In one possible embodiment, a diaphragm could be mounted directly to an aperture in a wall of the enclosure 2.

It will be appreciated by those skilled in the art that many variations and modifications to the embodiments described above may be made within the scope of the various aspects of the invention set out herein.

Claims

1. A portable enclosure for an electrical component for use in a potentially hazardous

environment,

the enclosure being sealed and adapted to be pressurised so as to maintain a higher internal pressure than an external pressure without a top-up gas supply,

the enclosure comprising:

a power supply for the electrical component;

2. A portable enclosure as claimed in claim 1, wherein the power supply is provided within the enclosure.

3. A portable enclosure as claimed in claim 1 or 2, wherein the arrangement for isolating the power supply generates and sends a signal to a controller which controls the supply of power to the electrical component.

4. A portable enclosure as claimed in claim 1, 2 or 3, wherein the arrangement for isolating the power supply comprises a mechanical arrangement acted on by the diaphragm configured to isolate the power supply when the diaphragm snaps back to its disengaged position.

5. A portable enclosure as claimed in claim 4, wherein the mechanical arrangement comprises a switch, preferably a limit switch.

6. A portable enclosure as claimed in any preceding claim, wherein the arrangement for

isolating the power supply is provided inside the enclosure.

7. A portable enclosure as claimed in any or claims 1 to 5, wherein the arrangement for

isolating the power supply extends externally of the enclosure and is sealed from the external atmosphere.

8. A portable enclosure as claimed in any preceding claim, wherein the enclosure comprises two or more diaphragms, and the arrangement for isolating the power supply is activated when one or more of the diaphragms snap into the disengaged position.

9. A portable enclosure as claimed in claim 8, wherein the enclosure comprises two or more independent parallel arrangements for isolating the power supply, each independent parallel arrangement being adapted to be activated when a respective one of the diaphragms snap into the disengaged position.

10. A portable enclosure as claimed in any preceding claim, wherein the enclosure further

comprises a support plate with the diaphragm(s) mounted thereon.

11. A portable enclosure as claimed in any preceding claim, wherein the enclosure further

comprises a sealed port for the passage of cables and /or conductors into the enclosure.

12. A portable enclosure as claimed in any preceding claim, wherein the second predetermined threshold is greater than the first predetermined threshold.

13. A method of containing an electrical component in a potentially hazardous environment, the method comprising:

placing an electrical component in a sealed portable chamber;

connecting the sealed portable chamber to a gas supply;

using the gas supply to pressurise the sealed portable chamber such that the internal pressure of the sealed portable chamber is greater than the external pressure;

removing the gas supply;

connecting the component to a power supply; and

a snap action diaphragm attached to the sealed portable chamber causing the component to be isolated from the power supply by snapping from an engaged position into a disengaged position if a difference between the internal pressure and the external pressure falls below a first predetermined threshold.

14. A method as claimed in claim 13, wherein movement of the diaphragm acts on a mechanical arrangement to isolate the electrical component from the power supply.

15. A method as claimed in claim 13 or 14, further comprising generating and sending a signal to a controller when the difference between the internal pressure and the external pressure falls below the first predetermined threshold.