GB1569186A

GB1569186A - Electrical roll capacitor with contact-breaking device

Info

Publication number: GB1569186A
Application number: GB4697776A
Authority: GB
Original assignee: International Standard Electric Corp
Current assignee: International Standard Electric Corp
Priority date: 1976-02-17
Filing date: 1976-11-11
Publication date: 1980-06-11
Also published as: DE2606175A1; DE2606175C2

Description

(54) ELECTRICAL ROLL CAPACITOR WITH CONTACT-BREAKING DEVICE (71) We, INTERNATIONAL STANDARD ELECTRIC CORPORATION, a Corporation organised and existing under the Laws of the State of Delaware, United States of America, of 320 Park Avenue, New York 22, State of New York, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to electrical roll capacitors.

It is known that electrical roll capacitors are likely to be deformed when loaded excessively, or in the case of faulty rolls. Such a deformation can be used for actuating a contact-breaking device for preventing such a capacitor roll from remaining connected to a current source.

Thus from the German Offenlegungsschrift (DTS) 2 350 271 there is known an electrical capacitor housed in a casing in which there are arranged a capacitor element and a contactbreaking device which is responsive to overpressure, causing an electrical conductor to be interrupted in the event of an overpressure. In this conventional arrangement, the contactbreaking device is actuated by a deformation of the capacitor element caused by an internal overpressure in the capacitor element.

In the conventional arrangement, gas is formed in the capacitor roll, causing the cylindrical roll to bulge on the jacketing side. This convexity is utilised for actuating a contactbreaking device which, for example, may consist of an electrical conductor attached to a strip of plastic material, which is caused to break when the roll jacket bulges.

Considering that the bulging of the roll jacket only occurs at a rather high gas pressure inside the roll, there exists the danger that the capacitor roll may burst before actuating the safety device, and thus be likely to cause subsequent damage which cannot be prevented by the safety device.

Moreover, it is known that some dielectric materials of roll capacitors, especially certain foils of plastics material, have the property of shrinking when heated. Such dielectric foils may have been provided with this property when being manufactured, but they may also have been subjected to a separate stretching treatment by which the foil is given such properties. The shrinking of such dielectric foils can also be utilised, in the case of an excessive heating of the capacitor roll, to break an electric lead wire.

Thus from the German Auslegeschrift (DT (DT-AS) 1 806 924, there is known a roll capacitor housed in a casing whose foil has the property of shrinking in the axial direction when the capacitor roll is heated. This capacitor roll is anchored at one point inside the casing while an electric lead wire is anchored at a second point inside the casing. If the roll be excessively heated it shrinks in the axial direction, thus causing the contact between the roll and the connecting point to break.

Such a contact-breaking device, however, can only be used with capacitor rolls housed in a casing.

Moreover, from the German Offenlegungsschrift (DT-OS) 2 060 907, there is known an electrical roll capacitor with a contact-breaking device not requiring a casing. This type of roll capacitor is likewise provided with a dielectric capable of shrinking in the axial direction of the roll, and has surface contact layers. By shrinking of the roll in the axial direction when heated, the electrical contact is interrupted either within the surface contact layer or between the surface contact layer and a lead wire. This arrangement utilises the phenomenon that the roll shrinks in the axial direction, but a core tube arranged inside the roll however, will maintain its original length.

Considering that roll capacitors contain a very long, but relatively narrow dielectric tape, the absolute value of the shrinking in the width of the tape is relatively low, so that there exists the danger that the interruption of the lead wire is either incomplete or not effective at all. Relative thereto, it still has to be taken into consideration that the surface contact layers to be interrupted consist of a relatively low-melting metal, or of a metal alloy and, moreover, have a porous structure, so that they are capable of following a slight displacement or expansion without causing the layer to be entirely interrupted (broken).

According to the present invention there is provided an electrical roll capacitor with a capacitor roll which is subjected to deformation when heated and thus actuates a contact breaking device, wherein the capacitor roll, being wound without a core tube and containing at least one dielectric tape capable of shrinking in longitudinal direction bulges in the axial direction of the roll when overheated, and wherein a contact breaking device is arranged at one end of the roll where it is actuated by the bulging of the roll.

By using a dielectric tape shrinking in the longitudinal direction, the shrinking path of the long tape becomes relatively long, so that there will result a rather high radial pressure inside the roll, causing the dielectric tape to be pushed out in the centre of the roll at the ends.

The end-bulging of the roll so produced, is substantially greater than the shrinkage in the case of an axial shrinking of the roll or the bulging caused by a gas overpressure inside the roll. In this way there is achieved a relatively long disconnecting path, and the roll is completely prevented in this way from bursting.

The bulging appearing in the axial direction of the roll at the ends, is utilised for actuating a contact breaking device. In order to make sure that such a bulge is reliably formed on the roll ends, the roll must not contain a core tube.

Likewise, the roll's cavity should be as small as possible so as to require little material for filling the roll's cavity in response to a radial roll pressure, and to make sure that the pressure is actually only used for causing the dielectric material to bulge at the end.

It is sufficient to provide one non- displaceable abutment for the contact-breaking device opposite the end of the roll. Accordingly, it is sufficient for the capacitor roll to be provided only on one side with a firm envelope leaving free cavity over the one end of the roll, in which the contact-breaking device is arranged.

The capacitor roll however, may also be arranged inside a casing, so that the contactbreaking device will be arranged between the end of the roll and a lid (cover) or the bottom of the casing, respectively.

In one preferred emblodiment of the contactbreaking device, this consists of two arched pressure members the ends of which are firmly connected to a tensioned lead wire.

The contact-breaking device, however, may also consist of any other type of switch responsive to pressure. In this device, the contact between two conductors may be interrupted, or an electrical conductor may be torn or otherwise interrupted, as is actually known per se in connection with contact-breaking devices for use with electrical capacitors. In the manner known per se, this conductor to be interrupted (torn) may also be provided with a preset breaking point.

Embodiments of the invention are described below with reference to the accompanying drawings, in which: Figures la and ib schematically show the deformation of a capacitor roll when heated; Figures 2a and 2b show a roll capacitor employing one form of contact-breaking device; and Figures 3a and 3b show a roll capacitor employing a second form of contact-breaking device the capacitor roll being housed in a casing.

Figure la schematically shows a sectional view of a capacitor roll containing a dielectric tape capable of shrinking in the longitudinal direction when heated, thus exerting a radial pressure upon the roll 1. To permit this radial pressure to take effect upon the dielectric material positioned inside the roll, the capacitor roll 1 is not wound on to a core tube, and also only has a relatively small cavity (hollow space) 2. Figure la shows the capacitor roll prior to being heated. After having been heated, the capacitor roll has a shape as shown in the sectional view of Figure Ib. The cavity 2 has completely disappeared, and the capacitor roll has at each end developed a bulge 3 which can be used to actuate a contact-breaking device.

Figure 2a shows an embodiment in which the capacitor roll is partly surrounded by an envelope 4 of insulating material, with a cavity having been left free at one end of the roll, in which a switch 7 is arranged. The lead-in conductors 5 and 6 of the switch 7 extend within the envelope of insulating material 4.

Figure 2a shows the arrangement before being heated, and Figure 2b shows the arrangement after having been heated. The heating has caused the dielectric tape of the capacitor roll 1 to shrink in the longitudinal direction and, in so doing, to produce a high radial pressure resulting in the bulges 3 at both ends of the capacitor roll. By this, the switch 7 has been opened which switch is arranged in the path of a lead-in conductor connected (connection not shown) to the capacitor roll 1, which has thus been disconnected from a current supply.

Figure 3a shows another embodiment.

The capacitor roll 1 is arranged inside a casing 8, and lead wires 5 and 6 are connected to cap solder terminals 10 and 11 mounted on or inside a lid (cap) 9. In the path of the lead wire 5, that is between the cap solder terminal 11 and the capacitor roll 1, there is arranged a contact-breaking device consisting of two arched pressure members 12 and 13, to the ends 15 and 16 of which a tensioned conductor 14 is connected. The two pressure members 12 and 13 bear on the end of the capacitor roll 1 and the adjacent inner end wall of the casing 8, respectively. Figure 3a shows the state prior to the heating, while Figure 3b shows the state after the capacitor roll has been subjected to excessively high heat.Because of the longitudinal shrinking of the dielectric tape of the capacitor roll 1, a bulge 3 has formed at each of the ends of the capacitor roll, one of which presses the two pressure members 12 and 13 together. This causes the conductor 14 tensioned therebetween to be torn and to interrupt the circuit. Conductor 14 may be provided, in known manner, with one or more predetermined rupture points.

The contact-breaking device, however, may also be arranged between the other end of the capacitor roll and the lid (cap) 9 of the casing.

Moreover a contact-breaker such as shown in Figures 2a and 2b may also be used in a casing such as shown in Figures 3a and 3b and at either end thereof, while similarly a contactbreaker such as shown in Figures 3a and 3b may also be used in an envelope such as shown in Figures 2a and 2b.

WHAT WE CLAIM IS: 1. An electrical roll capacitor with a capacitor roll which is subjected to deformation when heated and thus actuates a contactbreaking device, wherein the capacitor roll, being wound without a core tube and containing at least one dielectric tape capable of shrinking in the longitudinal direction bulges in the axial direction of the roll when overheated, and wherein a contact-breaking device is arranged at one end of the roll where it is actuated by the bulging of the roll.

2. A capacitor according to Claim 1, wherein the capacitor roll is at least partly arranged inside a firm envelope, and the contactbreaking device is arranged in a cavity (hollow space) between the envelope wall and the adjacent end of the capacitor.

3. A capacitor according to Claim 2, wherein the capacitor roll is housed in a casing, and the contact-breaking device is arranged between an interior end wall of the casing, and the adjacent end of the roll.

4. A capacitor according to Claims 1, 2 or 3 wherein the contact-breaking device consists of a pressure-responsive switch.

5. A capacitor, according to Claims 1, 2 or 3, wherein the contact-breaking device consists of an electrical conductor capable of being ruptured when acted upon by pressure.

6. A capacitor according to Claim 5, wherein the contact-breaking device consists of two arched pressure members whose ends are connected to a conductor tensioned between said two pressure members.

7. A capacitor according to Claim 5 or 6, wherein the conductor which is intended to break in response to the action of pressure, is provided with a preset breaking point.

8. An electrical roll capacitor substantially as described with reference to Figures 2a and 2b or Figures 3a and 3b of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

12 and 13 bear on the end of the capacitor roll 1 and the adjacent inner end wall of the casing 8, respectively. Figure 3a shows the state prior to the heating, while Figure 3b shows the state after the capacitor roll has been subjected to excessively high heat. Because of the longitudinal shrinking of the dielectric tape of the capacitor roll 1, a bulge 3 has formed at each of the ends of the capacitor roll, one of which presses the two pressure members 12 and 13 together. This causes the conductor 14 tensioned therebetween to be torn and to interrupt the circuit. Conductor 14 may be provided, in known manner, with one or more predetermined rupture points.

The contact-breaking device, however, may also be arranged between the other end of the capacitor roll and the lid (cap) 9 of the casing.

Moreover a contact-breaker such as shown in Figures 2a and 2b may also be used in a casing such as shown in Figures 3a and 3b and at either end thereof, while similarly a contactbreaker such as shown in Figures 3a and 3b may also be used in an envelope such as shown in Figures 2a and 2b.

WHAT WE CLAIM IS: 1. An electrical roll capacitor with a capacitor roll which is subjected to deformation when heated and thus actuates a contactbreaking device, wherein the capacitor roll, being wound without a core tube and containing at least one dielectric tape capable of shrinking in the longitudinal direction bulges in the axial direction of the roll when overheated, and wherein a contact-breaking device is arranged at one end of the roll where it is actuated by the bulging of the roll.
2. A capacitor according to Claim 1, wherein the capacitor roll is at least partly arranged inside a firm envelope, and the contactbreaking device is arranged in a cavity (hollow space) between the envelope wall and the adjacent end of the capacitor.
3. A capacitor according to Claim 2, wherein the capacitor roll is housed in a casing, and the contact-breaking device is arranged between an interior end wall of the casing, and the adjacent end of the roll.
4. A capacitor according to Claims 1, 2 or 3 wherein the contact-breaking device consists of a pressure-responsive switch.
5. A capacitor, according to Claims 1, 2 or 3, wherein the contact-breaking device consists of an electrical conductor capable of being ruptured when acted upon by pressure.
6. A capacitor according to Claim 5, wherein the contact-breaking device consists of two arched pressure members whose ends are connected to a conductor tensioned between said two pressure members.
7. A capacitor according to Claim 5 or 6, wherein the conductor which is intended to break in response to the action of pressure, is provided with a preset breaking point.
8. An electrical roll capacitor substantially as described with reference to Figures 2a and 2b or Figures 3a and 3b of the accompanying drawings.