Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H77/00—Protective overload circuit-breaking switches operated by excess current and requiring separate action for resetting
  • H01H77/02—Protective overload circuit-breaking switches operated by excess current and requiring separate action for resetting in which the excess current itself provides the energy for opening the contacts, and having a separate reset mechanism
  • H01H77/10—Protective overload circuit-breaking switches operated by excess current and requiring separate action for resetting in which the excess current itself provides the energy for opening the contacts, and having a separate reset mechanism with electrodynamic opening
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H1/00—Contacts
  • H01H1/02—Contacts characterised by the material thereof
  • H01H1/021—Composite material
  • H01H1/029—Composite material comprising conducting material dispersed in an elastic support or binding material

Definitions

• This invention relates to a device which is intended to prevent overcurrents in electrical circuits, comprising at least one electrically conductive elastomeric body and two electrodes which are intended to supply circuit current through said body, and constructed to repel one another under the influence of short circuit currents, where each electrode is in abutment with the elastomeric body at corresponding positions, either directly or through the intermediary of an intermediate part, and in which abutment pressure is obtained through the medium of a pressure device, so that in the abscence of pressure the elastomeric body is deformed by the pressure device at respective abutment sites.
• electrically conductive elastomeric bodies with electrodes can be used to protect against overcurrents in electrical circuits. In this respect reference can be made to Swedish Patent Applications No. 9201223-6 and No. 9203234-1.
• One other aim of the invention is to provide a device giving protection against overcurrents in electrical circuits as mentioned in the introductory paragraph, which device makes it possible to eliminate or greatly reduce the aforementioned current peak. This eliminates the aforementioned problem in connection with known devices of this type.
• the aim of the invention is therefore to ensure that the device will become more tolerant and be far less affected by overcurrents and so function satisfactory for a very long time.
• Fig. 1 shows a side view of a cross-section of a type of current limiting device based on the invention.
• Fig. 2 shows the same view as in Fig 1. but with a larger scale section which shows how the current striction is obtained.
• Fig. 3 and Fig. 4 show in two sections two embodiments of the current limiting device according to the invention, whereby current striction is obtained.
• Fig. 5 shows a diagram of current/time for a known current limiting device and for the current limiting device according to the invention.
• Fig. 6 shows a side view of a cross-section of another embodiment of the new current limiting device.
• Fig. 7 shows a side view of a cross-section of yet another variant of the new device where certain components of the arrangement are illustrated on a larger scale.
• Fig. 8 shows a side view of a cross-section of a further embodiment of the device described in the invention.
• Fig. 9 and Fig. 10 show a further variant of the device where Fig. 9 shows a side view of a cross-section and Fig. 10 shows a longitudinal side view of the device.
• Fig. 11 shows a modification of the current limiting device shown in Fig. 9 and Fig. 10.
• Fig. 12 shows a side view of a cross section of the current limiting device, which arrangement comprises several current limitmg devices stacked one on top of the other.
• Fig. 13 shows the current limiting device shown in Fig. 12 connected to an electrical circuit.
• Fig. 14. is a diagram illustrating voltage distribution of the different current limiting devices in the arrangement shown in Fig. 13 and
• Fig. 15 shows a cross-section of a special preferred embodiment of the current limiting device according to the invention.
• the main components are a centrally arranged electrically conductive elastomeric body together with two electrodes 12 and 14, one on each side.
• the device When the device is connected to a circuit there is a current supply between electrodes 12 and 14 through the elastomeric body 10.
• the Fig. does not show in detail the pressure device creating an abutment force between the respective electrodes 12 and 14 and the elastomeric body 10: this is illustrated by the F arrow.
• the electrodes 12 and 14 are always arranged in this way so that during a short circuit they repel each other.
• the directly applied abutment pressure F through electrode 12 normally ensures that there is a good contact between the consecutive parts 10, 12 and 14, whereby it is possible for the circuit current to pass through the device since it is connected to an external electrical circuit.
• the nets 20, 22 partly sink into the elastomeric body 10 due to the influence of pressure force F contributing to said contact effect between the respective electrodes 12 and 14 and the electrically conductive particles (not shown here) of the elastomeric body 10.
• the pressure will causethe nets 20, 22 to sink deeper into the elastomeric body and so create new contact with intact electrically conductive particles therein. In this way the device reverts to the initial state, when the current has passed and the circuit has re-opened.
• Fig. 5 illustrates the current/time curve for a device which does not include the net described above - continuous line.
• the aforementioned current peak is clearly evident but is missing completely in the curve - dotted line - which in the same Fig. relates to the version of the invention comprising a net.
• One possible explanation of the increased sensitivity which is achieved by using the net can be the interaction which arises through current striction in connection with the said net. This relationship is shown with desirable clarity in Fig. 2 where current lines are compressed in electrically conductive mesh threads 24, which are included in nets 20 and 22, respectively.
• a current striction can be achieved to a greater extent by using the current limiting device shown in Fig. 3 where the passage through which the current is devised to pass in the device, is reduced at at least one contact position 13 between the net 20 and the electrode 12 and the elastomeric body 10, respectively.
• the outer parts of the electrode 12 facing the elastomeric body 10 is covered by insulation 11.
• the contact device 20 is placed centrally in respect of the adjoining electrode 12 and the elastomeric body 10. In this way the increased current density in the elastomeric body 10 is obtained. Since the electrode 12 and the net 20 have very good thermal conductivity and great thermal mass the temperature increase under normal conditions is negligible. There will be no increase in resistance at normal momentary overloads, for example when starting an engine, etc.
• the net 20 should preferably comprise a material with considerably higher resistivity than the resistivity of the electrically conductive filling material of the elastomeric body 10.
• the material of the net 20 can be stainless steel, for example, while the filling material can be silver or similar low resistive material.
• Fig. 6 shows that the current protection device has a current limiting element, which comprises three separate elastomeric bodies 10a, 10b and 10c where the two outer elastomeric bodies 10a and 10c are surrounded by separate electrical conducting meshes 20a and 22a, respectively.
• the circuit may be completed with an external resistor, represented by the dotted lines, which prevents over-voltages and guarantees current through the device even after the occurrence of current limiting.
• an arc-limiting material 26 for which Al(OH) 3 in powder form can be used advantageously, is placed between the nets 20 and 22 and the mesh threads 24. The aim of this arrangement is to prevent arcing, which in turn leads to a reduction in the combustion of the material when the device is subjected to overcurrents.
• Fig. 8 refers to an arrangement of the invention, where the nets 20 and 22, of the type discussed above are also used as integrated electrodes in the current limiting device.
• Each electrode making up the nets 20 and 22 is, in this case, placed in a rigid circular frame 28 which can be similar to the fastening of strings in a tennis racket. In this way two integrated functions are achieved.
• the device shown in Fig.9 and 10 is arranged in cylindrical symmetry, one outer net 30 here being one of the electrodes.
• the other electrode 32 is arranged centrally arranged.
• the arrangement offers technical production advantages since it can later on be produced and handled as "metre goods”.
• Fig. 11 shows the device with one electrode 34 which in this case uses a "net equivalent".
• the thread-like electrode 34 has been wound on an elastomeric core 10 which surrounds a central electrode 36.
• the optimal resistance is high, preferably more than 10 mOhm.
• the diagram in Fig. 14 shows the voltage U p as a function of the consecutive current limiting elements j.
• the voltage division in Fig. 14 shows a case where the majority of the elastomeric bodies in Fig. 13 are in a state of high resistivity. In this illustration, for example, the elastomeric body 3 is still in a state of low resistivity.
• An external voltage source E is used, a current then passing through the device.
• both the electrically conductive elastomeric body 10, the electrodes 12 and 14, the contact arrangement (indicated by the electrically conductive nets 20 and 22), the pressure device (indicated by arrow F) and any additional components of the arrangement, are arranged in a preferably hermetic container 42.
• the direction of current circuit flow through electrodes 12 and 14 is also marked.
• the container 42 which is made of non-electrically conductive material (for example ceramic or plastic) contains a liquid 44, entrapped in such a way that the environment for the contact areas between the elastomeric body 10 and the electrodes 12 and 14 always is provided by said liquid 44, unaffected by the current limiting device's position in the room.
• a liquid 44 entrapped in such a way that the environment for the contact areas between the elastomeric body 10 and the electrodes 12 and 14 always is provided by said liquid 44, unaffected by the current limiting device's position in the room.
• the liquid 44 which can be water or water with added glycerine, should have such properties that it dissolves any residue between the various components so that a low contact resistance is achieved and to a great extent retained between the electrodes 12, 14 and the elastomeric body 10.
• the contact devices can also be made of an electrically conductive layer, being conductive essentially only perpendicular to the layer plane.
• the layer can be made of directionally arranged threads and of an electrically insulting material arranged therebetween and made of silicon rubber, for example.
• the contact device can also be produced, for example, through etching, plasma thermal coating etc. on the surface of the electrode.
• the contact device can comprise two separate nets arranged against each other where the size of the mesh in one of the nets differs from the mesh size of the other.

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Emergency Protection Circuit Devices (AREA)
• Electrotherapy Devices (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

Family

ID=20393750

Family Applications (1)

Country Status (4)

Cited By (9)

Citations (4)

• 1994
  • 1994-04-22 SE SE9401379A patent/SE514775C2/sv not_active IP Right Cessation
• 1995
  • 1995-06-15 WO PCT/SE1995/000731 patent/WO1995034931A1/en active IP Right Grant
  • 1995-06-15 EP EP95922857A patent/EP0767981B1/en not_active Expired - Lifetime
  • 1995-06-15 DE DE69509774T patent/DE69509774T2/de not_active Expired - Fee Related

Patent Citations (4)

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