Capacitor with over pressures safety device comprising sensor and switching elements

Abstract

A capacitor (10) having an over pressure safety feature (12). The capacitor (10) includes a housing (20) with a retention element (50) located near the bottom (26). A safety device (50) having a bottom cap (60) is connected to the retention element. The bottom cap (60) including two sensor holders (62, 64). A beam-shaped ceramic sensor element (70) is connected to the sensor holders (62, 64). The beam-shaped ceramic sensor element (70), has two contacts (74, 76) with a conductive layer or circuit trace (72) therebetween. A force transfer element (80) on the capacitor housing (20) bottom (26) is moved as the bottom deflects upon an increase in an internal pressure in the housing (20) beyond a predetermined limit, such that the force transfer element (80) contacts and breaks the beam-shaped ceramic sensor element (70) with the conductive layer or the electrical circuit trace (72) to interrupt an electrical continuity between the contacts (74, 76). This allows the capacitor to be disconnected from its voltage source or other action to be taken as a safety measure.

Description

CAPACITOR WITH OVER PRESSURES SAFETY DEVICE COMPRISING SENSOR AND SWITCHING ELEMENTSTECHNICAL FIELD

[0001] The present disclosure relates to capacitors with a sensor system for an over pressure condition, and more particularly to DC-link capacitors used on traction applications, such as trains or other vehicles, industrial equipment, as well as other applications.BACKGROUND

[0002] Capacitors with protection devices that monitor for over-heating and overpressure are known.

[0003] DE 271 587 A1 discloses a capacitor protection device using strain gauges located on the capacitor housing to monitor the electrical and thermal conditions of the capacitor. The strain gauges can be attached various manners during the manufacture of the capacitor.

[0004] DE 10 2021 1 10 439 A1 also discloses a sensor system for a capacitor. In this reference, a plate-shaped switching device is mounted via screws to mounts on the bottom of the capacitor, and the switching device includes a substrate with an articulated tongue. An increase in pressure in the capacitor housing causes a bottom of the capacitor housing to deflect the tongue, which causes a conductor track on the substrate to separate, interrupting a detection circuit.

[0005] In either case, gas pressure building up inside the capacitor housing or can is detected and the capacitor can be disconnected from its voltage source. Further energy input and any further increase in pressure are therefore avoided as a safety measure.

[0006] It would be desirable to provide a capacitor sensor system which is simple, reliable, and can be easily installed on or retrofitted to a capacitor that is not initially supplied with such a sensor system, and that can be connected to and evaluated by external safety systems.SUMMARY

[0007] In one aspect, a capacitor is provided having a safety feature for over pressure according to one or more of the features disclosed herein. The capacitor includes ahousing including a top, a sidewall, and a bottom. At least one winding is located in the housing, which is of the known type including thin conductive layers, for example aluminum and / or zinc, that are separated by an insulator and wound to provide a compact capacitor element. First and second connection elements are electrically connected to the at least one winding and extend inside the housing to respective first and second terminals, with the terminals extending through the housing to an outside area where they can be connected to electrical or electronic components. There are at a minimum first and second terminals, while additional connection elements and / or terminals can be provided depending on the particular application. Electrical insulation is located between housing and the at least one winding. A retention element is located on the sidewall in proximity to the bottom and / or at the bottom of the housing. A safety device is provided having a bottom cap that is connected to the retention element, with the bottom cap including two sensor holders located on an inner surface thereof. A beam-shaped ceramic sensor element is connected to the two sensor holders. The beam-shaped ceramic sensor element, which may be a circuit board formed of a ceramic material, includes a conductive layer or electrical circuit trace extending from a first contact, located closer to a first end thereof, to a second contact, located at a second end. At least one force transfer element is either formed as a part of or connected to a center of the bottom and / or to the beam-shaped ceramic sensor element at a position between the first and second contacts. In use, upon an increase in an internal pressure in the housing beyond a predetermined limit, the bottom of the housing is adapted to deflect such that the at least one force transfer element contacts and breaks the beam-shaped ceramic sensor element with the conductive layer or the electrical circuit trace to interrupt an electrical continuity between the first and second contacts. This allows the capacitor to be disconnected from its voltage source or other action to be taken as a safety measure.

[0008] In one embodiment, the sidewall is cylindrical and the top can be integrally formed with the sidewall. This may be formed as a punched or deep-drawn “can” of a metallic material, such as aluminum, and the circular bottom is attached thereto after the internal components are inserted. The bottom can also be formed from aluminum.

[0009] The terminals preferably extend through the top of the housing.

[0010] In one embodiment, the retention element comprises a crimp flange that connects the bottom to the sidewall. This crimp flange extends radially outwardly from the sidewall.

[0011] In one embodiment, the bottom cap is formed of an electrically insulating plastic material, and includes at least one retainer that engages the crimp flange on housing. The at least one retainer can include a plurality of radially inwardly directed projections, and at least one of the bottom cap or the radially inwardly directed projections are elastically deflectable to allow a snap-on engagement of the bottom cap onto the housing, with the radially inwardly directed projections engaging behind the crimp flange. In one preferred arrangement, the radially inwardly directed projections include a sloped surface at a leading end thereof in a direction of engagement with the housing.

[0012] With this arrangement, the circular bottom cap is rotatable about an axis of the housing which allows for positioning of sensor wires in any radial direction to suit a particular application or location.

[0013] In an alternative embodiment, the retention element may comprise at least one indentation in the sidewall of the capacitor housing at or in proximity to the bottom. Here, the bottom cap which is formed of an electrically insulating plastic material, includes at least one retainer that engages the at least one indentation.

[0014] In one embodiment, the at least one force transfer element comprises at least one of a rivet, screw, or protrusion connected to the center of the bottom. Alternatively, the bottom can be configured so that a center portion thereof acts as the force transfer element. The beam-shaped ceramic sensor element is held by the sensor holders so that a portion thereof between the first and second contacts crosses the center of the bottom of the housing in a position aligned with the force transfer element.

[0015] The sensor holders each comprise a post and at least one elastically deflectable engagement clip that extends a distance above the post, and the distance is approximately equal to a thickness of the beam-shaped ceramic sensor element. Preferably, the at least one engagement clip includes a tapered surface on a side opposite to the post and provides for easier snap-on engagement of the beam-shaped ceramic sensor element at the first and second ends into the sensor holders.

[0016] In another aspect, a safety device is provided for a capacitor that includes a housing including a top, a sidewall, and a bottom, with at least one winding located in the housing, and first and second connection elements electrically connected to the at least one winding and extending inside the housing to respective first and second terminals, with the terminals extending through the housing to an outside area. The safety device includes a bottom cap adapted for connection to a retention element at or proximate to the bottom of the housing. The bottom cap includes two sensor holders located on an inner surface thereof, and a beam-shaped ceramic sensor element is connected to the two sensor holders. The beam-shaped ceramic sensor element includes a conductive layer or electrical circuit trace extending from a first contact located closer to a first end and a second contact located at a second end thereof. At least one force transfer element is provided as a part of and / or connected to a center of the bottom and / or to the beam-shaped ceramic sensor element at a position between the first and second contacts, such that upon an increase in an internal pressure in the housing of the capacitor beyond a predetermined limit, the bottom of the housing is adapted to deflect causing the at least one force transfer element to contact and break the beam-shaped ceramic sensor element with the conductive layer or the electrical circuit trace to interrupt an electrical continuity between the first and second contacts.

[0017] This safety cap can be retrofitted to capacitors that are initially provided without any safety device to the extent that such capacitors have a retention element to allow the safety device to be connected.

[0018] In one aspect, the bottom cap is formed of an electrically insulating plastic material, and includes at least one retainer that is adapted to engage the retention element at the bottom of the capacitor housing. The at least one retainer can include a plurality of radially inwardly directed projections, and at least one of the bottom cap or the radially inwardly directed projections are elastically deflectable to allow a snap-on engagement of the bottom cap onto the capacitor housing, with the radially inwardly directed projections engaging with the retention element at the bottom of the housing. The radially inwardly directed projections may include a sloped surface at a leading end thereof in a direction of engagement with the housing. The elastically deflectableprojections allow for easy installation as well as removal of the bottom cap to or from a capacitor.

[0019] In one embodiment, the bottom cap is circular and is adapted to be rotatable about an axis of the capacitor housing which is cylindrical. This allows the sensor wires / external connection to be positioned in any radial direction to suit a particular application or location.

[0020] Additional aspects and embodiments are disclosed herein.BRIEF DESCRIPTION OF THE DRAWINGS

[0021] A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings, wherein like reference numerals in the figures indicate like elements, and wherein:

[0022] FIG. 1 is a view of a capacitor having a safety device according to an embodiment of the present disclosure.

[0023] FIG. 2 is a cross-sectional view through the capacitor of Figure 1 showing the safety device prior to being installed on a bottom of the capacitor.

[0024] FIG. 3 is a view taken along line 3-3 in Figure 2 looking into the safety cap.

[0025] FIG. 4 is a side elevational view of the safety cap.

[0026] FIG. 5 is a view of a sensor holder taken along line 5-5 in Figure 3.

[0027] FIG. 6 is a perspective view looking into the safety cap with the beam-shaped ceramic sensor element removed.

[0028] FIG. 7 is a perspective view of the bottom of the safety cap.

[0029] FIG. 8 is a view looking into the safety cap with the beam-shaped sensor element installed.

[0030] FIG. 9 is a partial view showing a second embodiment of a capacitor with a safety device.

[0031] FIG. 10 is a partial view showing a third embodiment of a capacitor with a safety device

[0032] FIG. 11 is a side view of an alternate embodiment of the beam shaped ceramic sensor element which includes a force transfer element connected thereto.DETAILED DESCRIPTION

[0033] Examples of capacitor safety devices will be described more fully hereinafter with reference to the accompanying drawings. These examples are not mutually exclusive, and features found in one example can be combined with features found in one or more other examples to achieve additional implementations. Accordingly, it will be understood that the examples shown in the accompanying drawings are provided for illustrative purposes only and they are not intended to limit the disclosure in any way. Like numbers refer to like elements throughout.

[0034] It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present invention. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0035] It will be understood that when an element such as a layer, region or substrate is referred to as being "on" or extending "onto" another element, it can be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to as being "directly on" or extending "directly onto" another element, there are no intervening elements present. It will also be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements present. It will be understood that these terms are intended to encompass different orientations of the element in addition to any orientation depicted in the figures.

[0036] Relative terms such as "below" or "above" or "upper" or "lower" or "horizontal" or "vertical" may be used herein to describe a relationship of one element, layer or region to another element, layer or region as illustrated in the figures. It will be understood thatthese terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures.

[0037] The terms “generally” and “approximately” mean within about 10% of a specified value or a similar variance from a specified shape - i.e., a generally circular shape would allow for a curved shape in which a length of a radial line from the center point varies by 10% or less.

[0038] FIGS. 1 - 8 show a capacitor 10 having a safety device 12 in accordance with the present disclosure. The capacitor 10, shown in detail in Figures 1 and 2, includes a housing 20 having a top 22, a sidewall 24, and a bottom 26. In the illustrated embodiment, the sidewall 24 is generally cylindrical and the top 22 is integrally formed with the sidewall 24 providing a "can" in which the internal elements of the capacitor 10 can be inserted. At least one winding, and in the illustrated embodiment two windings 30, 32, are located in the housing 20. First and second connection elements 34, 36 are electrically connected to the at least one winding 30, 32, and extend inside the housing 20 to respective first and second terminals 38, 40. More than two of the terminals 38, 40 can be provided as well as additional connection elements, depending on the desired functionality of the capacitor 10. The terminals 38, 40 extend through openings 22a, 22b in the housing 20 to an outside area where they can be connected to an electrical or electronic circuit. In the illustrated embodiment, an insulating washer 13 is located between the terminals 38, 40 and the top 22 and rubber seals 14 extend through the openings 22a, 22b between the terminals 38, 40 and the top 22. A protective cover 15 can also be located over the top 22. Within the housing 20, the windings 30, 32 are wrapped in electrical insulation 16 and, as illustrated, may be separated from one another by an insulating layer 17. A distance cap 19 is located beneath the at least one winding 30, 32 to provide spacing from the bottom 26. This distance cap 19 allows for some expansion of the windings 30, 32.

[0039] Referring to Figure 2, a retention element 50 is located on the sidewall 24 in proximity to the bottom 26 and / or at the bottom 26 of the housing 20. The retention element 50 in the first embodiment is shown as a crimp flange 52 that connects the bottom 26 to the sidewall 24 and extends radially outwardly. Alternatively, as shown in Figure 9,the retention element 50' may comprise at least one indentation 53' in the sidewall 24' in proximity to the bottom 20'.

[0040] Referring to Figures 2-8, a bottom cap 60 is connected to the retention element 50 and the bottom cap 60 includes two sensor holders 62, 64 located on an inner surface 60a thereof. The bottom cap 60 is formed of an electrically insulating plastic material and includes at least one retainer 66a-66d that engages the crimp flange 52 on the housing 20. As shown in Figure 3, in one embodiment there are four of the retainers 66a-66d that are equally spaced about a periphery of the bottom cap 60. Each of these retainers 66a- 66d includes a radially inwardly directed projection 67, shown in Figures 2, 6 and 8 and at least one of the bottom cap 60 for the radially, inwardly directed projection 67 are elastically deflectable to allow a snap-on engagement of the bottom cap 60 onto the housing 20 with the radially, inwardly directed projection 67 engaging behind the crimp flange 52. In order to allow for easier engagement, the radially, inwardly directed projections 67 may include a sloped surface 68 at a leading end thereof in a direction of engagement with the housing 20. As shown most clearly in FIGS. 6 and 8, a stop 63 is formed below radially inwardly directed projection 67 so that the depth that the bottom cap 60 can be inserted onto the housing 20 is limited by the bottom of the crimp flange 52 contacting the stop 63.

[0041] Referring to Figure 9, in the alternate embodiment, the retention element 50' in the form of an indentation in the sidewall 24’ of the housing 20’ in proximity to the bottom 26’ that is engaged by the at least one retainer 66a-66d of the bottom cap 60. There can be a plurality of spaced apart indentations 53’ or a single continuous indentation 53’. Here, the at least one retainer 66a-66d is as discussed above in connection with the first embodiment.

[0042] Referring to Figure 10 a further alternate embodiment is shown, Here the retention element 50” is in the form of one or more protrusions 53” in the sidewall 24” of the housing 20” in proximity to the bottom 26”. The one or more protrusions 53” can be formed as a continuous annular ring-shaped protrusion or could be a plurality of spacedapart protrusions. The at least one retainer 66a-66d is as discussed above in connection with the first embodiment, and are spaced apart sufficiently to provide for a snap-on connection over the one or more protrusions 53”.

[0043] In each, with the generally cylindrical configuration of the sidewall 24 and bottom 26, the bottom cap 60 has a matching generally circular or cylindrical configuration such that it is adapted to snap-on to the housing 20. With this configuration it is possible to rotate the bottom cap about an axis A of the housing 20 in order to achieve a desired rotational position as discussed in further detail below.

[0044] As shown in Figures 2, 3, and 8, a beam-shaped ceramic sensor element 70 is connected to the two sensor holders 62, 64. The beam-shaped ceramic sensor element 70 includes a conductive layer or electrical trace 72 extending from a first contact 74 located closer to a first end 70a thereof to a second contact 76 located at a second end 70b thereof. The beam-shaped ceramic sensor element 70 is preferably in the form of a printed circuit board formed of a ceramic material that is relatively brittle such that it can act as the sensor element.

[0045] As shown in detail in Figures 3, 5, 6, and 8, eah sensor holder 62, 64 comprises a post 65 and at least one elastically deflectable engagement clip 68a, 68b that extends a distance X above the post 65. The distance X is approximately equal to a thickness T of a beam-shaped ceramic sensor 70. In the illustrated embodiment, there are two of the elastically deflectable engagement clips 68a, 68b. The engagement clips 68a, 68b include a tapered surface 69 on a side opposite to the post 65 and are elastically deflectable in order to provide for a snap-on engagement of the beam-shaped ceramic sensor element 70 at the first and second ends 70a, 70b, to the sensor holder 62, 64. The tapered surface 69 allows for easier insertion. Stops 65a may be provided on the posts that prevent sliding of the beam-shaped ceramic sensor 70.

[0046] The cap 60 with the sensor holders 62, 64, the stop 63, and the at least one retainer 66a-66d is preferably molded of a plastic material that is electrically insulating in one piece, as shown in FIGS. 6 and 7.

[0047] As shown in Figure 2, at least one force transfer element 80 is formed as a part of or connected to a center of the bottom 26 and / or to the beam-shaped ceramic sensor element 70 at a position between the first and second contact 74, 76. In the illustrated embodiment, the at least one force transfer element 80 comprises at least one of the rivet, screw, or protrusion that is connected to the center of the bottom 20. However, the bottom 26 could be configured such that the center portion expands outwardly first and to agreater extend than a remainder of the bottom 26 in an over-pressure condition and the center of the bottom 26 itself therefore acts as the force transfer element 80.

[0048] In the illustrated embodiment, the bottom 26 is formed of aluminum sheet, for example having a thickness of about 0.5 mm - 0.7 mm, and a central opening is provided in the bottom 26, shown in FIG. 2, in order to allow the capacitor housing 20 to be filled with an inert gas, oil, or resin after assembly. The rivet or screw in the illustrated embodiment is preferably used to seal the opening and also provides a protruding surface which acts as the at least one force transfer element 80. As an alternative, the beamshaped ceramic sensor element 70 can include a protruding portion 80’, shown in Fig. 11 , at a center thereof that extends upwardly toward the bottom 26. This can be adhered in position.

[0049] With this arrangement, upon an increase in the internal pressure in the housing 20 of the capacitor beyond a predetermined limit, the bottom 26 of the housing 20 is adapted to deflect, indicated in broken lines at 26’ in FIG. 2, such that the at least one force transfer element 80 contacts and breaks the beam-shaped ceramic sensor element 70 with the conductive layer or the electrical circuit trace 72 in order to interrupt an electrical continuity between the first and second contacts 74, 76. This interruption can be detected by a circuit connected to sensor wires 77 that extend from the first and second contact 74, 76 such that an appropriate safety measure can be taken, such as disconnecting the capacitor 10 from its voltage source. The wires 77 may extend to a plug connected to a plug opening 78 in the bottom cap 60

[0050] With the present arrangement, the safety device 12 with the bottom cap 60 can be easily snapped on to the bottom of the capacitor housing 20 or may be removed therefrom. This allows capacitors 10 that include the retention element, which can be in the form of the crimp flange 52, to be easily retrofitted with a safety device 12 including the bottom cap 60 having the beam-shaped ceramic sensor element 70 therein.

[0051] In another aspect, a safety device 12 for the capacitor 10 can be provided as a separate item for later installation. The safety device 12 can be used with the capacitor not initially fitted with such a device, and includes the bottom cap 60 as discussed above that is adapted for connection to a retention element 50, 50' at or in proximity to the bottom 26 of the capacitor housing 20. The bottom cap 60 is as discussed above and is providedwith the beam-shaped ceramic sensor element 70 that is connected to the two sensor holders 62, 64 preferably integrally formed with the bottom cap 60. The beam-shaped ceramic sensor element 70 is as discussed above and, with at least one forced transfer element 80 connected to a center of the bottom 26 and / or to the beam-shaped ceramic sensor element 70 at a position between the first and second contact 72, 74, upon an increase in an internal pressure in the housing 20 of the capacitor beyond the predetermined limit, the bottom 26 of the housing 20 is adapted to deflect as shown in broken lines at 26’ in FIG. 2, causing the at least one force transfer element 80 to contact and break the beam-shaped ceramic sensor element 70 with the conductive layer or the electrical circuit trace to interrupt an electrical continuity between the first and second contact 74, 76 in the same manner as discussed above.

[0052] The features and aspects disclosed herein can be implemented for various capacitor designs, and one skilled in the art would also recognize that the disclosure may be applicable to other applications or domains as well.

[0053] It will be appreciated that the foregoing is presented by way of illustration only and not by way of any limitation. It is contemplated that various alternatives and modifications may be made to the described embodiments without departing from the spirit and scope of the invention. Having thus described the present invention in detail, it is to be appreciated and will be apparent to those skilled in the art that many physical changes, only a few of which are exemplified in the detailed description of the invention, could be made without altering the inventive concepts and principles embodied therein. It is also to be appreciated that numerous embodiments incorporating only part of the preferred embodiment are possible which do not alter, with respect to those parts, the inventive concepts and principles embodied therein. The present embodiment and optional configurations are therefore to be considered in all respects as exemplary and / or illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all alternate embodiments and changes to this embodiment which come within the meaning and range of equivalency of said claims are therefore to be embraced therein.

Claims

CLAIMSWhat is claimed is:1 . A capacitor, comprising: a housing including a top, a sidewall, and a bottom; at least one winding located in the housing; first and second connection elements electrically connected to the at least one winding and extending inside the housing to respective first and second terminals, the terminals extending through the housing to an outside area; a retention element located on the sidewall in proximity to the bottom and / or the bottom of the housing; a safety device including a bottom cap connected to the retention element, the bottom cap including two sensor holders located on an inner surface thereof, a beam-shaped ceramic sensor element connected to the two sensor holders, the beam-shaped ceramic sensor element including a conductive layer or electrical circuit trace extending from a first contact located closer to a first end to a second contact located at a second end, and at least one force transfer element formed as a part of or connected to a center of the bottom and / or to the beam-shaped ceramic sensor element at a position between the first and second contacts; and wherein upon an increase in an internal pressure in the housing beyond a predetermined limit, the bottom of the housing is adapted to deflect such that the at least one force transfer element contacts and breaks the beam-shaped ceramic sensor element with the conductive layer or the electrical circuit trace to interrupt an electrical continuity between the first and second contacts.

2. The capacitor of claim 1 , wherein the sidewall is cylindrical.

3. The capacitor of claim 2, wherein the top is integrally formed with the sidewall.

4. The capacitor of claim 3, wherein the terminals extend through the top of the housing.

5. The capacitor of claim 2, wherein the bottom is circular, and the retention element comprise a crimp flange that connects the bottom to the sidewall.

6. The capacitor of claim 5, wherein the bottom cap is formed of an electrically insulating plastic material, and includes at least one retainer that engages the crimp flange on housing.

7. The capacitor of claim 6, wherein the at least one retainer includes a plurality of radially inwardly directed projections, and at least one of the bottom cap or the radially inwardly directed projections are elastically deflectable to allow a snap-on engagement of the bottom cap onto the housing with the radially inwardly directed projections engaging behind the crimp flange.

8. The capacitor of claim 7, wherein the radially inwardly directed projections include a sloped surface at a leading end thereof in a direction of engagement with the housing.

9. The capacitor of claim 6, wherein the bottom cap is rotatable about an axis of the housing.

10. The capacitor of claim 2, wherein the bottom is circular, and the retention element comprises at least one indentation in the sidewall in proximity to the bottom.11 . The capacitor of claim 10, wherein the bottom cap is formed of an electrically insulating plastic material, and includes at least one retainer that engages the at least one indentation.

12. The capacitor of claim 1 , further comprising insulation between housing and the at least one winding.

13. The capacitor of claim 1 , wherein the at least one force transfer element comprises at least one of a rivet, screw, or protrusion connected to or formed on the center of the bottom.

14. The capacitor of claim 1 , wherein the sensor holders each comprise a post and at least one elastically deflectable engagement clip that extends a distance above the post, and the distance is approximately equal to a thickness of the beam-shaped ceramic sensor element.

15. The capacitor of claim 14, wherein the at least one engagement clip includes a tapered surface on a side opposite to the post and provides for a snap-on engagement of the beam-shaped ceramic sensor element at the first and second ends.

16. A safety device for a capacitor that includes a housing including a top, a sidewall, and a bottom, with at least one winding located in the housing, and first and second connection elements electrically connected to the at least one winding and extending inside the housing to respective first and second terminals, the terminals extending through the housing to an outside area, the safety device comprising: a bottom cap adapted for connection to a retention element at or proximate to the bottom of the housing, the bottom cap including two sensor holders located on an inner surface thereof; a beam-shaped ceramic sensor element formed as a part of or connected to the two sensor holders, the beam-shaped ceramic sensor element including a conductive layer or electrical circuit trace extending from a first contact located closer to a first end and a second contact located at a second end; and at least one force transfer element connected to a center of the bottom and / or to the beam-shaped ceramic sensor element at a position between the first and second contacts, such that upon an increase in an internal pressure in the housing beyond apredetermined limit, the bottom of the housing is adapted to deflect causing the at least one force transfer element to contact and break the beam-shaped ceramic sensor element with the conductive layer or the electrical circuit trace to interrupt an electrical continuity between the first and second contacts.

17. The safety device of claim 16, wherein the bottom cap is formed of an electrically insulating plastic material, and includes at least one retainer that is adapted to engage the retention element at the bottom of the housing.

18. The capacitor of claim 17, wherein the at least one retainer includes a plurality of radially inwardly directed projections, and at least one of the bottom cap or the radially inwardly directed projections are elastically deflectable to allow a snap-on engagement of the bottom cap onto the housing with the radially inwardly directed projections engaging with the retention element at the bottom of the housing.

19. The capacitor of claim 18, wherein the radially inwardly directed projections include a sloped surface at a leading end thereof in a direction of engagement with the housing.

20. The capacitor of claim 16, wherein the bottom cap is circular and is adapted to be rotatable about an axis of the housing of the capacitor which is cylindrical.

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