CA1291227C - Capacitor circuit interruption - Google Patents

Abstract

Capacitor Circuit Interruption Abstract of the Disclosure A capacitor in which the interruption mechanism includes an actuator that moves in response to a predetermined physical condition to cause electrical disconnection of the capcitive element, and in which the actuator has a range of motion through a limited number of stable positions and is mechanically pre-biased to move toward one of the stable positions when not already in one of the stable positions.
In another aspect the capacitor housing includes an integral rim around the terminals that is filled with dielectric resin to insulate the terminals from the space surrounding the capacitor housing.

Description

~ 7 Capacitor Circuit Interruption Backqround of the Invention This invention relates to circult interruption in electrical capacitors.
Deterioration of a capacitor typically generates gasses that increase the internal presure within the sealed capacitor case, eventually causing rupture and leakage of the liquid dielectric. Pressure sensitive interrupters are sometimes used within the . 10 capacitor case to prevent rupture by breaking the electrical connection to the capacitive element in response to the internal pressure, thus stopping the gas buildup.
Published European patent application 15 0-093-455-A2 shows an interrupter in which the capacitor has terminals a-ttached to a central disk that is part of the plastic can cover. The central dis~ is connected to the peripheral rim o the cover by an intPrmediate : deformable "annular wall portion or web of reduced wall thickness" that permits the central disk to move away ~rom the can in response to internal pressure. The . capacitive element is held down by a rim around the .-.~ inside of the plastic can so that as the central disX
.,. moves upwa~d it eventually breaks the metal conductors : 25 that connect the terminals to the capacitive element.
Sometimes, after a pressure sensitive interrupter has broken the electrical connections, the internal pressure drops and the cover and terminals settle back to their original positions where electrical . 30 reconnection or arcing may occur.
. Su~nary of the Invention .' A general feature of the invention is a capaci~or in which the interruption mechanism includes t'~ -5 ..~

_ ~2g~Z~t7 an actuator that moves in response to a predetermined ` physical condition within the capacitor to cause electrical disconnection, and in which the actuator has a range of motion through a limited number of stable positions and is mechanically pre-biased to move toward one of the stable positions when not already in one of the stable positions.
Preferred embodiments of the invention include the following features. The physical condition is ` 10 internal gas pressure within the capacitor, and the actuator moves in response to the pressure. The actuator comprises a portion of a wall (e.g., the lid) of the housing; the actuator is attached to the housing by a support having at least one rigid section connected to the wall portion and the housing by hinge regions.
The wall portion is a disk, the support is a rigid annular rim, and the hinge regions are flexible annular :, rings. In some embodiments, there is one rigid section, two hinqe regions, and two stable positions. In other embodiments, there are two rigid sections interconnected by a hinge region, and three stable positions. In other embodiments, there is an annular rim that is thinner . than the wall portion. The capacitor terminals are ;~ mounted on the actuator. The electrical connections ~ 25 include co~ductors between the terminals and the .. capacitive element and the interruption mechanism further comprises means for retaining each conductor in a fixed position relative to motion of the actuator.
The capacitive element includes a core that is ultrasonically welded to the inside of the housing. In other embodiments, a panel is interposed between the .~ capacitive element and the terminals. The housing is .' plastic and includes a lid on which the actuator is located. The actua~or is polypropylene. The capacitor .
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I Z9~ XZ7 ~ ~0~12-1643 element in~ludes a dielectric imprer~nant, (i.e., a blend of polyl~utene and polyethvlene) havinrJ a drop poirlt that is above the normal vperatin~ temPerat.ure of the capacitor, and is below d temperature that ~^rould ocGur following failure of the capacitor winding. In ot.her embodiment.s, t,here is a liquid dielectric impregnant !e.g. polybutene) that is compatible with the plastic of the hous.ing.
Another general feature of the invention is a capacitor in which the terminals are mounted on ancl proiect from the housinq and the housing incLudes a rlm that surrounds the terminals and is filled with a dielectric material that insulates the terminals.
The capacitive element is quickly and effectively disconnected when Pressure builds up. The actuator pops up to aid in the disconnection and stably remains in its popped up position to reduce the cl~ance of reconnection. The entire caPacitor is easily made. ~ounting the terminals on the actuator ass~res positive mot,ion of terminals awa~ from the capacitive ele~ent.
When the terminals are fully insulated, the capacitor can be used safely in tight yuarters.
In accordance with a broad aspect of the invention there is proviclecl a cap~citor comprisln~
a capacitive element, a housinq ~ rltainin~ said element.
a portion o~ a ~Jall o~ said housin~ capa~le of mov:Lng outwardly in respons~ to a buildup o~ internal pressure ~7ithin salcl capacitor, ~aid outward movement includin~ an abrupt outwarcl mov~ment in wh:l~h said wall po~lon moves rapidly bet~een two , - ~

- ~291Z2~7 3a 60412-16~3 positions in response to an increase in internal pressure.
means for retardin~ movement of said capacitive element in the direc.tion of said outward movement ~uring said pressure huildup at le~st one terminal on said housing for making said electrical connection to said capacitive element, sai.d terminal heing supported on said wall portion, a wire with a Preweak.ened region electrically connecting said càpacitive element to said terminal, said abrupt outward movement bein~ sufficient to break the preweakened region in said wire and separate the broken end~c Of said wire to prevent reconnection.
In accordance with another broad aspect of the invention there ls provide~ a capacit.or comprising a capacitive element.
a housing cont.aining said element, a first portion of a wall of said housing capable of moving outwar~.lly in response to a bul].dup of internal pressure wlthin said capacitor, at least one terminal on said housiny for making said electrical connectioll to said capacltive element! sald terminal heing supported on said first ~all portionr said capaci~ive element bein~ held down and prevente~ from moving ln sald out~1ard dlrection durlng said pressure buildup by a corlnection of said ca~cl~ive element to a second wall portion of sald houslny located on the other side of said housing from said ~lr~t wall portioll.
~,., ~L29~227 3b In accordance with another broad aspect of the invention there is provided a polymer lid for closing the open end of a housing for an electrical component, said lid comprising:
an outer ring for connection to the rim of said open end of said housing;
a normally-recessed inner portion, said inner portion recessed below said outer ring toward the interior of said housing in a first stable position;
a flexible, annular connecting portion connecting said inner portion to said outer ring, said connecting portion and said inner portion and outer ring being configured so that a predetermined pressure on the bottom surface of said inner portion will cause sa~d connecting portion to bend and said inner portion to displace to and remain in a second s~able position with said inner portion above said outer ring in a direction outward from said housing.
Other advantages and features will become apparent from the following description of the preferrad embodiment and from the claims.
De~criPtion of the ~referred Embodiment ~e first briefly describe the drawings.
Drawinqs Figure 1 ls a perspective vlew of a capacitor.
Figure 2 is a diagrammatic sectional side view at 2-2 of the capacitor of Figure 1.
Figure 3 is an enlarged sectional side view, broken away, along 2-2 of the capacltor of Figure 1.

.~. j j 1~912Z7 ; Fig. 4 is a sectional side view of a fragment near the bottom of the capacitor case of Fig. l.
Fig. 5 is a partial top view of the floor of the capacitor case of Fig. l.
Figs. 6, 7 are sectional side view and plan view respectively of the capactive element core of Fig.
3.
Fig. 8 is a view like Fig. 3 after disconnection - 10 Figs. 9A, 9B, 9C are a sequence of sectional side views of a fragment of the capacitor lid of Fig. l, showing three discrete positions of a lid using an alternative hinge arrangement.
Fig. lO is a sectional side view of one-half of an alternative embodiment to Fig. 3.
Fig. ll is a sectional side view of a portion of an alternative capacitor cover.
; Fig. 12 is a sectional side view of a portion of an alternative capacitive element core.
Figs. 13, 14 are isometric and sectional side views of an alternative capacitor cover.
Structure Referring to Fig. l, a capacitor 10 includes a capacitor roll 12 inside an injection molded round ~5 polypropyl-ene plastic case 14 having an injection molded polypropylene cover 16 (made, e.g., from polypropylene - ~ product no. PP-402 available from Monmouth Plastics, or Polyflam RPP 1058 available from A~ Schulman) in which two terminals 18, 20 are mounted. Case 14 has a segmented outer rim at the top end for mounting the capacitor.
Referring to Fig. 2, terminal 20 is electrically connected (in a conventional manner) to the top of capacitor roll 12 via an uninsulated tinned ~ro~le~n~

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., ~29~L~27 copper or tinned copperweld wire 30; terminal 18 is electrically connected (also in a conventional manner) to the bottom of roll 12 via an insulated wire 32 which passes throu~h a hollow polypropylene capacitor core 34 or around the outside of the capacitive element.
Capacitor roll 1~ is surrounded by and embedded in a dielectric material 36.
~ eferring to Fig. 3, terminals 18, 20 are of eyelet design and include tubular portions 40 inserted .. 10 through access holes 42 in a rigid central disk section ; 44 of cover 16. The ends 46 of tubular portion 40 are bent back against the underside of disk 44 to hold terminals 18, 20 in place.
- Wire 30 is pulled taut and attached to terminal 20 by solder 50 and includes a carefully machined nick 51 by which the amount of tension (e.g., 15 lbs) needed to sever the wire can be carefully controlled.
Insulated wire 32 is stripped to expose an uninsulated tinned copper conductor (which may also be nicked) that is similarly pulled taut and attached to terminal 18 by solder 52, If wire 32 is not nicked, it ls not pulled taut, but is left with slack to allow cover 16 to move and break the nick in wire 30.
In addition to central disk 44, cover 16 includes a rigid L-shaped (in cross-sec-tion) peripheral .. portion 56 ul-trasonically welded to the inner wall of . case 14, A panel 54 on cover 16 forms an insulative barrier between terminals 18 and 20. A hinged portion 58 connects peripheral portion 56 and central disk 44.
Hinged portion 58 is ring-shaped, disposed at an angle of preferably 30-45 (a) ~ith respect to the ~ertical, ; and includes a rigid part 59.
~ ~xtending around the outer edge of rigid part ! 59 (where it joins peripheral portion 56) and around the ',;

, 129~;~2~

inner edge of part 59 (where it joins central disX 44) are inter-ior grooves 60, 62 and exterior grooves 66, 68.
Grooves 60, 62, 66, 68 are arranged in pairs with the interior groove and the exterior groove of each pair, e.g., 60, 66, vertically aligned, thus defining two flexible annular rings (hinge regions) 71, 73 which bend when the internal pressure in the can rises.
In one example, central disk 44 is 0.062" thick, part 59 is 0.044" thick, and grooves 60, 62, 66, 68 have typical radii of 0.031". The centers of radius oE grooves 60, 62, 66, 68 lie at the intersections of planes that extend from the upper and lower surfaces of part 59, central disk 44, and peripheral portion 56.
Referring to Fig. 4, capacitor 10 includes equally spac-ed vertical ribs 70 along inside wall 72 of case 14 and an ultra-sonic energy directing grid 74 molded into the bottom 76 of case 14.
Referring to Fig. 5, ribs 72 extend 0.02 inches into case 14 and are spaced 15 apart about the central axis of case 14. Grid 74 is 0.75 inches in diameter and is concentric with the bottom of case 14. Grid 74 includes upwardly extending peaks 80 and recessed rectangular regions 82.
Re~erring to Fig. 6, 7, the lower section of core 34 includes hexaganal bore 90 and circular bore 92. Energy directing flange 94 extends around the bottom of core 34, and, when placed ~n case 14, cQntacts the top oE peaks 80 of grid 74 at a limited 'ff=~

lX9~Z7 number of sharply defined contact points at which ultrasonic weld-ing can be accomplished.
Dielectric material 36 may be liquid pol~butene as des-cribed in U.S. patent No. 4,656,558, issued April 7, 1987 and assigned to the same assignee as this application. Polybutene has an advantage of not attacking the polypropylene material o~ case 14.
Alternatively, the capacitor may be formed as a "dry"
capacitor by substituting a waxlike blend for dielectric material 36. For example, the blend can be a mixture of polyethylene and polybutene chosen to be non-liquid at normal operating tempera-tures. As the capacitor begins to fail, the resulting temperature rise causes softening o~ the mixture, allowing gas to escape to the upper part of the interior o~ the capacitor case, to trigger operation o~ the disconnection ~echanism.
Assembly Terminals 18, 20 are mounted on cover 16 by inserting unbent tubular portions 40 through access holes 42 and bending ends 46 of portion8 40 back against the underside af disk 44.
Roll 12 and hollow core 34 are ~ixed inside case 14 by ultrasonically welcling the flange 94 of core 34 to the peaks 80 o~
grid 74~ The sharp lower edge of ~lange 9~ and the sharp upper edges o~ peaks 80 serve to direct the ultrasonic energy to the con-tact points between peaks 80 and flange 94, creating a strong weld.

~L29 ~2Z7 - 7a - 60412-1643 Next, roll 12 and core 34 are encased in material 36.
Cover 16 is then placed into the top of case 14 and wires 30, 32, previously connected to roll 12, are fed up through tubular portions 40. Peripheral portion 56 is ultrasonically welded to case 14. Finally, wires 30, 32 are pulled taut and soldered into place.

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~29il227 Operation Referring to Fig. 3, when the internal pressure - inside case 14 increases, an outward force is exerted on central disk 44 (in the direction indicated by arrow 100.) Eventually the internal pressure becomes lar~e enough to cause central disk 44 to pop outward to occupy - a second stable position as shown in Fig. 8.
As disk 44 moves to its new position, it pulls on wire 30, causing it to break at nick 51. r~ire 32 may also break if taut and nicked. This halts the 1Ow of electric current through roll 12 and in turn the generation of gasses and the building of increased internal pressure. Rupture of case 14 is thus prevented.
The effect of the design is to provide an actuator that has two stable positions, and is pre-biased to move toward one or the other stable position when not already in one of the stable positions. Thus, as the central disk 44 rises under pressure it reaches a point in its travel where it pops up to its upper position thus aiding rapid and complete disconnect. Once in the upper position the central disk resists downward movement except under a ~orce that -~! exceeds the pre-bias force.
r .
.~ 2S Other Embodiments Other embodiments are within the following claims.
For example, referring to Fig. ~A, hinged : portion 200 could include three (or more) interior grooves 202, 204, 206 and three (or more) exterior grooves 208, 210, 212. Referring to Fig. 9B, as central disk 214 moves outward portion 200 may bend irst at grooves 204, 210, 206, 212 to form a V-shape. ~eferring to Fig. 9C, as disk 214 continues to move outward .

~l29~L227 additional force on portion 200 causes it to bend at grooves 202, 208. Eventually disk 21~ reaches the final position shown in Fig. 9C and portion 200 is once again fully extended.
Referring to Fig. 10, in other embodiments, terminal 318 may be electrically connected to capacitor roll 312 via tinned steel terminal rive-ts 330 spot welded to tinned copper tabs 332. Terminals 318 are ;~ mounted on cover 316 by inserting rivets 330 through cover 316 and welding terminals 318 to rivets 330 while applying a clamping force between rivet shoulders 338 and terminals 318. Rivet tips 340 are then inserted through holes 342 in panel 344. Tabs 332 (previously connected to capacitor rolls 312) are spot welded to tips 340. Panel 344 and cover 316 are ultrasonically welded to the inner wall of case 314. As central disk 336 moves outward terminals 318 and rivets 330 also move outward causinq an outward force to be e~erted on foil tabs 332 and on the welds connecting tabs 332 to rivet tips 343. Tabs 332 are drawn outward until they come in contact with interrup~er panel 344. As central disk 336 continues outward, the force exerted on the welds between tips 340 and tabs 332 causes tabs 332 to tear Jl away from tips 340. This brea~s the electrical connection between terminals 318 and capacitor roll 312. In the embodiment of ~ig. 10, it is not necessary to attach the capacitor roll to the bottom of the case since panel 344 will prevent roll 312 from rising.
The dimensions of the central disk 44 (actuator), part 59, and grooves ~0, 62, 68 can be ., varied to change the fle~ibility of the hinges and thus i control the dynamic characteristics of the interruption . mechanism.

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lZ9~L22~

- When the dielectric impregnant is liquid, other impregnants can be substituted for polybutene, e.g., dioctyl phthalate (DOP), caster oil, or mineral oil, provided that it is not a li~uid that will attac~ the capacitor case.
Other materials can be used for case 14 and core 34 provided that they are chosen from the same organic polymer family to permit ultrasonic welding.
More than two terminals could be used. ~he externally exposed parts of the terminal could be encased in an insulator.
Referring to Fig. 11, hinged portion 58 may simply be a thinned down region 400 without grooves defining separate hinge regions.
Referring to Fig. 12, the capacitive element core may be formed by countersinking 402 the end of the core.
; Referring to Figs. 13, 14, cover 16 may include an annular rim 404 that rises above the level of terminals 406. Wires 408 are attached to terminals 406, and passed through ports 410. Then the space within rim 404 is potted with a dielectric resin material 412, thus eliminating all exposed conductive elements. Such a capacitor is especially useful in close quarters to prevent unintentional contacts, e.g., in ~ID type lamp ballasts.
Other materials can be used for the cover provided that they have appropriate physical, thermal, and elect~ical properties to provide the required mechanical operating features and also to satisfy the requirements of the particular application.
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Claims (25)

1. A capacitor comprising a capacitive element, a housing containing said element, a portion of a wall of said housing capable of moving outwardly in response to a buildup of internal pressure within said capacitor, said outward movement including an abrupt outward movement in which said wall portion moves rapidly between two positions in response to an increase in internal pressure, means for retarding movement of said capacitive element in the direction of said outward movement during said pressure buildup, at least one terminal on said housing for making said electrical connection to said capacitive element, said terminal being supported on said wall portion, a wire with a preweakened region electrically connecting said capacitive element to said terminal, said abrupt outward movement being sufficient to break the preweakened region in said wire and separate the broken ends of said wire to prevent reconnection.

2. The capacitor of claim 1 wherein said housing and wall portion are made of a polymer, and said wall portion is connected to adjoining portions of said housing by hinge portions integrally formed in said polymer.

3. The capacitor of claim 1 wherein said wall portion has a range of motion through a limited number of stable positions and is pre-biased to move toward one of said stable positions when not already in one of said stable positions.

4. The capacitor of claim 1 wherein said wall portion is attached to said housing by a support.

5. The capacitor of claim 4 wherein said support comprises at least one rigid section connected to said wall portion and said housing by a hinge region.

6. The capacitor of claim 5 wherein said wall portion comprises a disk, said support comprises a rigid annular rim, and said hinge region comprises one or more flexible annular rings.

7. The capacitor of claim 5 wherein there are two said rigid sections and two said hinge regions, one said hinge region connecting two of said rigid sections, and the other said hinge regions connecting the inner of said rigid sections to said inner portion.

8. The capacitor of claim 2 wherein said capacitive element includes a polymer core that is ultrasonically welded to the inside of said housing.

9. The capacitor of claim 1 wherein said means for retarding movement comprises a panel interposed between said terminals and said capacitive element.

10. The capacitor of claim 1 wherein said housing is a polymer and said wall portion is on a lid of said housing.

11. The capacitor of claim 2 or 10 wherein said polymer is polypropylene.

12. The capacitor of claim 2 wherein said capacitor is impregnated with a dielectric impregnant having a softening point above the normal operating temperature of said capacitor, and below a temperature that would occur following failure of the capacitor winding.

13. The capacitor of claim 12 wherein said impregnant comprises a blend of at least two components one of which is polybutene.

14. The capacitor of claim 13 wherein a second of said component comprises polyethylene.

15. The capacitor of claim 2 wherein said capacitor comprises a liquid dielectric impregnant that is compatible with said polymer.

16. The capacitor of claim 15 wherein said impregnant is polybutene.

17. A capacitor comprising a capacitive element, a housing containing said element, a first portion of a wall of said housing capable of moving outwardly in response to a buildup of internal pressure within said capacitor, at leastone terminal on said housing for making said electrical connection to said capacitive element, said terminal being supported on said first wall portion, said capacitive element being held down and prevented from moving in said outward direction during said pressure buildup by a connection of said capacitive element to a second wall portion of said housing located on the other side of said housing from said first wall portion.

18. The capacitor of claim 17 wherein said housing and first and second wall portions and said core are made of one or more polymers.

19. The capacitor of claim 18 wherein the connection of said core to said second wall portion is by ultrasonic welding.

20. A polymer lid for closing the open end of a housing for an electrical component, said lid comprising:
an outer ring for connection to the rim of said open end of said housing;
a normally-recessed inner portion, said inner portion recessed below said outer ring toward the interior of said housing in a first stable position;
a flexible, annular connecting portion connecting said inner portion to said outer ring, said connecting portion and said inner portion and outer ring being configured so that a pre-determined pressure on the bottom surface of said inner portion will cause said connecting portion to bend and said inner portion to displace to and remain in a second stable position with said inner portion above said outer ring in a direction outward from said housing.

21. The lid of claim 20 wherein said outer ring comprises means for being sealed to said housing to seal said open end.

22. The lid of claim 20 wherein said connection and inner portions and said outer ring are all integral portions of the same polymer body.

23. The lid of claim 22 wherein said connecting portion includes portions thinner than said inner portion and outer ring.

24. The lid of claim 23 wherein said connecting portions includes recessed regions at its junctions with said inner portion and outer ring.

25. The lid of claim 20, 22, or 23 wherein said lid is formed of a thermoplastic or thermoset polymer.