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EP0725993B1 - An overload protective system - Google Patents

An overload protective system Download PDF

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Publication number
EP0725993B1
EP0725993B1 EP93909127A EP93909127A EP0725993B1 EP 0725993 B1 EP0725993 B1 EP 0725993B1 EP 93909127 A EP93909127 A EP 93909127A EP 93909127 A EP93909127 A EP 93909127A EP 0725993 B1 EP0725993 B1 EP 0725993B1
Authority
EP
European Patent Office
Prior art keywords
electrodes
pressure
elastomeric
electrically conductive
abutment
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP93909127A
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German (de)
English (en)
French (fr)
Other versions
EP0725993A1 (en
Inventor
Per Olov KARLSTRÖM
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Individual
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Individual
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Publication of EP0725993A1 publication Critical patent/EP0725993A1/en
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Expired - Lifetime legal-status Critical Current

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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
    • H01C—RESISTORS
    • H01C10/00—Adjustable resistors
    • H01C10/10—Adjustable resistors adjustable by mechanical pressure or force
    • H01C10/106—Adjustable resistors adjustable by mechanical pressure or force on resistive material dispersed in an elastic material
    • 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

  • the present invention relates to a protective device for protecting against overcurrents in electric circuits, said device comprising at least one electrically conductive body and two electrodes which function to supply circuit current through said conductive body and which lie against the body at corresponding positions either directly or through the medium of an intermediate part, and further comprising pressure means for generating an abutment pressure.
  • the device is primarily intended for use in low voltage systems having an operating voltage of at most 1000 V.
  • short circuiting protectors are mainly comprised of fuses and circuit-breakers which most often possess current limiting properties.
  • the technique is known to the art and several standards, such as IEC 269 concerning fuses, and IEC 947-2 concerning circuit-breakers, have been instituted.
  • the short-circuiting protector is excited by the short circuiting currents flowing therethrough.
  • the shortcircuiting protector is excited in accordance with two main principles and is therefore divided here into the following groups 1 and 2:
  • Hybrids in which the two principles are used are disclosed in Patent Specification GB 1,472,412 and in the article "A New PTC Resistor for Power Applications" by R.S. Perkins, et al, published in the journal IEEE Transactions on Components, Hybrids and Manufacturing Technology, Vol. CHMT-5, No. 2, June 1982, pages 225-230 and publications U.S. 3,249,810 and DE 35 446 47, among others.
  • the arc is delayed on the electrical contacts in arc-based circuit-breakers, and consequently the arc voltage, important in achieving current limitation, will not reach the values at which the otherwise monotonously growing short circuit current is limited until a relatively long delay time (ms) has lapsed.
  • a very high contact pressure proportional to the square of the rated or nominal current of the apparatus, is required in order for the electrical contacts to be able to carry rated current under normal operating currents. This also prevents the electrical contacts from separating quickly, since the contact pressure is opposed to the electrodynamical repelling and separating forces.
  • short-circuiting protectors based on the principles disclosed in categories 1 and 2 above are less suited as short-circuiting protectors or current transient protectors for thyristors or electronic equipment, since they are sensitive to both high current derivatives and high short-circuiting currents can also occur in capacitive circuits or inductive motor circuits with high presumptive short-circuiting currents.
  • a conventional fuse With a rated current of 100 A, a conventional fuse will then allow a current peak of about 16 kA and ⁇ i 2 .dt ⁇ 20 kA 2 s to pass through, which greatly exceeds the permitted values of corresponding thyristors. Consequently, chokes are often included in thyristor circuits in order to reduce current derivatives, therewith enabling the aforedescribed short-circuiting protector to be used.
  • a self-restoring short-circuiting protector is mainly comprised of so-called thermistors.
  • the expression PTC-element is an accepted designation of thermistors whose resistivity has a P ositive T emperature C oefficient.
  • PTC-elements One problem with PTC-elements is that when heated by the current flowing therethrough and the temperature is reached at which the PTC-elements become self-adjusting, the voltage is taken over by a fragment of the PTC-element and the fragment is subjected to very high stresses, which are liable to destroy the PTC-element.
  • PTC-embodiments in which this problem is eliminated are known, for instance, from European Patent EP 0,038,716.
  • PTC-elements for overload protectors are often constructed of a polymeric material, for instance high-pressure polyethylene, containing particles of an electrically conductive material, for instance lamp black or carbon black, and exhibit a resistivity with high positive temperature coefficient.
  • Ceramic thermistors which exhibit PTC-characteristics are known from Patent Publication GB-A-1,570,138. The most common ceramic thermistors are based on BaTiO 3 or V 2 O 3 .
  • the polymer-based thermistor in comparison with the ceramic thermistor is that its resistance increases monotonously with temperature. It is also relatively cheap to produce.
  • commercially available polymer-type thermistors are designed for relatively low rated or nominal voltages and cannot therefore be used readily in distribution networks for instance.
  • the configuration and electrode connections of the thermistors are normally such that the thermistors are subjected to large repulsion forces at high short-circuiting currents, as a result of antiparallel current paths, therewith tearing the electrodes apart.
  • sandwich-type, polymer-based PTC-elements do not return to the initial resistance after passing from a low resistive state to a high resistive state.
  • polymer-based thermistors have not hitherto been used to any appreciable extent in practice within electric power technology, but have mainly only been used to protect electronic equipment, although the thermal inertia limits the fields of possible application.
  • thermoistors will self-restore after a short-circuit, i.e. thermistors can be reused after a short-circuit, which also applies to circuit-breakers.
  • Elastomers are comprised of all polymers that exhibit elastic properties which are similar to those exhibited by natural rubber. Elastomers can be compressed or stretched within a relatively large permitted elastic area, and return to their original state when the load is removed.
  • Electrically conductive elastomers are a class of rubber and plastics which have been made electrically conductive, either by the addition of metal mixtures or by orientating metal fibres under the influence of electric fields, or by the addition of different carbon mixtures or ceramics, for instance V203-material dispersed in the manner described in the article "V203 Composite Thermistors" by D. Moffat, et al, published in Proceedings of the Sixth IEEE International Symposium on Applications of Ferroelectrics, 1986, pages 673-676.
  • carbon black for instance graphite, acetylene black, lampblack and furnace black with particle diameters ranging from 10-300 nm.
  • Examples of appropriate rubber materials which become electrically conductive after adding metal mixtures or carbon mixtures are butyl, natural, polychloroprene, neoprene, EPDM, and the most important silicone rubber.
  • Additives of metals and metal alloys in powder form suited as elastomer additives are silver, nickel, copper, silver-plated copper, silver-plated nickel, and silver-plated aluminium.
  • Electrically conductive elastomer are used as pressure transducers within transducer technology, see WO-A-90/13800 and US-A-2752558.
  • the electrical properties are changed when electrically conductive elastomers are deformed, for instance as a result of being subjected to pressure or tension, which manifests in a change in resistance.
  • carbon or metal-filled plastics are polyethylene and polypropylene. These are used at present for heating cables and for overload protectors, for instance the earlier mentioned polymer-based PTC-thermistors.
  • Electrically conductive elastomers can be given very low resistances, for instance resistances of 2 mOhmcm or lower, by admixing metal powder.
  • One advantage afforded by elastomers is that they are very soft in comparison with carbon-filled polyethylene and polypropylene, even when containing large quantities of electrically conductive filler.
  • Such elastomers will have a typical Shore number of between 20-80, according American Standard ASTM D2240 (Q/C).
  • the object of the present invention is to provide a relatively simple and inexpensive overload protector which is able to limit the highest short-circuiting currents that occur in a low voltage network, even at very high current derivatives, and the release characteristic of which, i.e. its response sensitivity, can be adapted readily to the object to be protected.
  • This object is achieved in accordance with the invention with a protective device having the characteristic features set forth in the following Claim 1.
  • the device can replace both conventional fuses and so-called automatic circuit-breakers (MCB), and possesses the advantages afforded by both of these types of circuit-breaker without suffering their disadvantages, such as the limited length of life of the fuse and the limited circuit breaking ability of the automatic circuit-breaker on short-circuiting occurrences.
  • the device which functions as a current limiting element includes at least one electrically conductive elastomeric body and two electrodes.
  • the polymer composition of the elastomeric body may be of any known kind and forms no part of the present invention. Examples of suitable elastomers in this respect are particularly butyl, natural, polychlorpropene, neoprene, EPDM and silicone rubber.
  • the electroconductive powder material is preferably comprised of silver, nickel, cobalt, silver-plated copper, silver-plated nickel, silver-plated aluminium, lampblack, conductive soot or carbon black.
  • the powder material will suitably have a particle size of 0.01-10 micro-meters and the powder filler is suitably present in an amount corresponding to 40-90% of the combined weight of the powder filler and elastomeric material.
  • the resistivity of the electric elastomeric body will preferably lie within the range of 0.1 mohmcm-10 Ohmcm.
  • the bodies may be made of mutually the same or mutually different elastomers and then with mutually the same or mutually different fillers and resistivity.
  • the electrodes are of a conventional kind, for instance silver-plated copper. The electrodes are orientated so that repulsion forces will occur between the electrodes when high currents pass therethrough.
  • the pressure achieved on the electrodes deforms the convex abutment surface of the elastomeric body, when the device includes such an abutment surface.
  • This deformation will preferably reach at least 5%.
  • a deformation of 5-30% is particularly preferred, as defined with a starting point from the distance between the bodies that borders on a considered elastomeric body, i.e. if the distance when the pressure is 0 and bordering bodies lie in abutment with the elastomeric body is d and if the distance changes to 0.7 d after the pressure has been applied, the body will have been deformed by 30%.
  • Particularly preferred elastomeric bodies are those which have a hardness between 30-50 IRHD in accord with British Standard BS903/A26, although materials having both a lower and a higher hardness may conceivably be used.
  • the pressure device is provided with pressure exerting means which have spring properties.
  • a spring device of this preferred construction greatly facilitates separation and therewith reduction of the transition area between the convex abutment surface of the elastomer bodies, when such an abutment surface is included, and bordering body.
  • this elastomeric body when only one electrically conductive elastomeric body is included in the current limiting element this elastomeric body is inserted between a slotted electrically insulating plate.
  • the elastomeric body is placed in the slot and is enlarged so as to fill the slot when subjected to pressure. In this way, there is obtained an electric isolator which prevents electric flashover in the event of a short-circuit.
  • one elastomeric body is stacked on another elastomeric body in accordance with the invention, in the same pressure device.
  • the elastomeric body is cavitary and can be deformed by much more than 30%, the extent of deformation depending on the diameter of the cavity.
  • One conceivable reason for the result achieved by the present invention may be as follows: With the normal passage of current, a low transition resistance is maintained between those elements which are in contact with one another through the transition surface which is formed when the body having a convex abutment surface or the bodies, when more than one such body is included, are deformed by an external pressure device. When high short-circuiting currents occur, the electrodes will separate as a result of current forces. Furthermore, so-called striction forces occur in the transition between the convex abutment surface of the elastomer bodies, when one such abutment surface is included, and bordering bodies, due to the configuration of the preferred abutment surface.
  • FIG 6 illustrates a current limiting element in accordance with an arrangement analogous with the arrangement illustrated in Figure 1b.
  • the current limiting element includes a centrally mounted body (10) in the form of a homogenous cylinder having a diameter of 3 mm and length of 10 mm and being made of a deformable electrically conductive elastomer material, for instance comprising 80 percent by weight silver powder and 20 percent by weight silicone plastic, and two mutually parallel electrodes (11, 12) which are tangential to the body (10) on opposite sides thereof.
  • the elastomeric body (10) has a Shore number of 40 according to BS 903/A26.
  • the electrodes (11, 12) are comprised of angled, silver-coated copper plates having a thickness of 0.7 mm.
  • the electrodes are held in abutment with the body (10) with the aid of a spring device (14) which exerts pressure on the electrodes (11, 12) in a known manner and therewith deform the abutment surfaces (10', 10") of the body against respective electrodes, this deformation being about 30%.
  • the sensitivity or response of the arrangement can be enhanced by including a repulsion device (13) of the kind described, for instance, in GB 1,519,559 or GB 1,489,010, or the electrodes may be constructed so that they themselves will give rise to repelling electrodynamic current forces.
  • the repulsion device (13) may be a self-activating magnetic circuit of the kind earlier described in U.S. 4,513,270, which is intended to act solely on one electrode and which is directed so that the electrodes will separate from one another under the action magnetic forces or electrodynamic current forces.
  • the resistance across the device is 2 mOhm.
  • the device is subjected to high short-circuiting currents, preferably currents above 50 A, and more particularly above 500 A, the current density will increase in the deformed abutment surfaces (10', 10"), wherewith the resistance in the element will increase to 100 mOhm or more. This is sufficient to limit short-circuiting currents in low voltage systems, which through the agency of the preferred arrangement in Figure 6 and the circuit illustrated in Figure 3 limits the short-circuiting currents and produces the current-time diagram shown in Figure 4.
  • Figures 1c and 7 illustrate a current limiting element which is similar to the element illustrated in Figure 6 with the exception that the elastomeric body (20) is not an homogenous body.
  • the body of the Figure 7 embodiment includes a cavity (9) which enables deformation of the elastomeric body to be increased to 30% or more, depending on the dimensions of the cavity. This enables a material of relatively high Shore number to be used, for instance a Shore number of 80.
  • the body (20) is preferably deformable so that the resultant convex abutment surface (9') will be in physical contact with the abutment surface (9").
  • Figure 8 illustrates an embodiment of the invention in which two electrically conductive elastomeric bodies (10a, 10b) have been stacked one upon the other, whereas the electrically conductive elastomeric bodies (10a, 10b) of the Figure 9 embodiment have been placed side-by-side.
  • Figures 10a-b illustrate an inventive device in which an electrically conductive elastomeric body (10) according to Figure 7 is placed between two electrodes (11, 12) which extend longitudinally parallel with the body (10).
  • the pressure applied to the electrodes and the elastomeric body abutment surfaces (10', 10") is obtained through the agency of the earlier described resilient pressure device.
  • Figure 11 illustrates an inventive device in which an electrically conductive elastomeric body (10) is placed between two electrodes (11, 12) according to Figures 10a-b.
  • a ferromagnetic repulsion circuit (13) surrounds the longitudinally extending electrodes (11, 12) and the elastomeric body (10), and amplifies the repulsion effect of electrode (11) when overcurrents flow through the current limiting element.
  • Pressure is applied to the electrodes and the elastomeric body abutment surfaces (10', 10") by the aforedescribed resilient pressure device.
  • Figure 12 illustrates a device which is analogous with the device shown in Figures 10a-b with the exception that the electrically conductive elastomeric body (10) is semi-cylindrical in shape and may be firmly anchored to the electrode (12) by means of an electrically conductive adhesive, or may lie free.
  • the electrically conductive elastomeric body (10) is semi-cylindrical in shape and may be firmly anchored to the electrode (12) by means of an electrically conductive adhesive, or may lie free.
  • Figure 13 illustrates an inventive device in which two electrically conductive elastomeric bodies (10a, 10b) are placed between two electrodes (11, 12), between which a further two elastomeric bodies (10c) and (10d) respectively have been placed, these further bodies surrounding the electrodes (11, 12). Pressure is applied to the electrodes, and particularly to the elastomeric bodies provided with convex end-surfaces, by the aforesaid, known pressure device.
  • Figure 14 illustrates a further embodiment of the invention according to the Figure 12 and Figure 9 embodiments, in which the elastomeric bodies (10c, 16a) and (10e, 16b) respective surrounding electrodes (11, 12) are comprised respectively of electrically conductive elastomer material (10c, 10e) and electrically insulating elastomeric material (16a, 16b).
  • the respective elastomeric bodies (10c, 16a) and (10e, 16b) are advantageously moulded in a two-part mould, so that the elastomeric bodies will be mutually joined, and the electrodes are electrically insulated.
  • the electrical connections to the electrodes are not shown in the Figure.
  • Figure 15 illustrates an inventive device according to Figures 6 and 7, in which two electrically insulating, polyethylene bodies (15a, 15b) are disposed parallel with an electrically conductive elastomeric body (10).
  • the body (10) When the device is subjected to pressure, as symbolized by the force F acting on the electrodes (11, 12), the body (10) is deformed and will therewith lie against the defining surfaces (15a') and (15b') of the electrically insulating bodies. There is obtained in this way an electric insulation which prevents flashover in the event of a short-circuit, at the same time as the electrically conductive elastomeric body will not flow outwards, which is otherwise a common problem.
  • Figure 16 illustrates an inventive device in which the electrically conductive elastomeric body (10) includes several convex deformable abutment surfaces (10a', 10b', 10c', 10d'), comprising several integrated elastomeric bodies according to earlier Figures.
  • the elastomeric body (10) is coherent and homogeneous.
  • Figure 17 illustrates an inventive device in which the electrically conductive elastomeric body (10) has a convex deformable abutment surface in a "spline configuration", comprising several integrated elastomeric bodies according to earlier Figures.
  • the elastomeric body (10) is thus coherent and several convex surfaces can be activated, for instance by increasing the pressure with the aid of the pressure device (14).
  • Figures 18a-b illustrate an inventive device which is comprised of two electrically conductive elastomeric bodies (20a, 20b) having convex deformable abutment surfaces (20a', 20b'), and two electrodes (11, 12).
  • the electrodes are surrounded by concentrical, electrically conductive elastomeric bodies (20a, 20b) whose abutment surfaces (20a', 20b') are in physical abutment with one another.
  • the abutment surfaces (20a', 20b') are deformed by pressure exerted by a pressure device (14).
  • the electrodes (11, 12) are provided with electrical connecting means (31) and (32) respectively.
  • Figure 19 illustrates an inventive device in which the electrically conductive elastomeric bodies (10a1, 10a2, 10a3, 10a4) have convex-defining surfaces which are orientated perpendicularly to the convex-defining surfaces of the electrically conductive bodies (10b1, 10b2, 10b3, 10b4).
  • the device includes two electrodes (11, 12) for conducting current therethrough, electrodes on which a pressure device exerts pressure such as to deform the abutment surfaces (10a1...10b1).

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  • Chemical & Material Sciences (AREA)
  • Dispersion Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Fuses (AREA)
  • Thermistors And Varistors (AREA)
  • Adjustable Resistors (AREA)
  • Emergency Protection Circuit Devices (AREA)
  • Amplifiers (AREA)
  • Centrifugal Separators (AREA)
  • Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)
  • Crushing And Grinding (AREA)
  • Control Of Eletrric Generators (AREA)
  • Heat Treatment Of Steel (AREA)
  • Control Of Multiple Motors (AREA)
EP93909127A 1992-04-16 1993-04-14 An overload protective system Expired - Lifetime EP0725993B1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
SE9201223 1992-04-16
SE9201223A SE470118C (sv) 1992-04-16 1992-04-16 Anordning för skydd mot överström i elektriska kretsar
PCT/SE1993/000324 WO1993021677A1 (en) 1992-04-16 1993-04-14 An overload protective system

Publications (2)

Publication Number Publication Date
EP0725993A1 EP0725993A1 (en) 1996-08-14
EP0725993B1 true EP0725993B1 (en) 1997-10-15

Family

ID=20385990

Family Applications (1)

Application Number Title Priority Date Filing Date
EP93909127A Expired - Lifetime EP0725993B1 (en) 1992-04-16 1993-04-14 An overload protective system

Country Status (10)

Country Link
EP (1) EP0725993B1 (fi)
JP (1) JPH07505757A (fi)
AT (1) ATE159385T1 (fi)
CZ (1) CZ238694A3 (fi)
DE (1) DE69314671D1 (fi)
FI (1) FI944831L (fi)
HU (1) HUT73373A (fi)
NO (1) NO943817L (fi)
SE (1) SE470118C (fi)
WO (1) WO1993021677A1 (fi)

Families Citing this family (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE514775C2 (sv) * 1994-04-22 2001-04-23 Seldim I Vaesteraas Ab För skydd mot överström i elektriska kretsar avsedd anordning
US5929744A (en) * 1997-02-18 1999-07-27 General Electric Company Current limiting device with at least one flexible electrode
US6535103B1 (en) 1997-03-04 2003-03-18 General Electric Company Current limiting arrangement and method
US5977861A (en) * 1997-03-05 1999-11-02 General Electric Company Current limiting device with grooved electrode structure
SE509270C2 (sv) 1997-04-14 1998-12-21 Asea Brown Boveri Variabelt elektriskt motstånd samt förfarande för att öka respektive ändra resistansen hos ett elektriskt motstånd
US6191681B1 (en) 1997-07-21 2001-02-20 General Electric Company Current limiting device with electrically conductive composite and method of manufacturing the electrically conductive composite
US6373372B1 (en) 1997-11-24 2002-04-16 General Electric Company Current limiting device with conductive composite material and method of manufacturing the conductive composite material and the current limiting device
US6124780A (en) * 1998-05-20 2000-09-26 General Electric Company Current limiting device and materials for a current limiting device
US6290879B1 (en) 1998-05-20 2001-09-18 General Electric Company Current limiting device and materials for a current limiting device
US6133820A (en) * 1998-08-12 2000-10-17 General Electric Company Current limiting device having a web structure
US6323751B1 (en) 1999-11-19 2001-11-27 General Electric Company Current limiter device with an electrically conductive composite material and method of manufacturing
FR2996638B1 (fr) * 2012-10-08 2014-12-26 Univ Haute Alsace Capteur de pression flexible
WO2018008367A1 (ja) * 2016-07-06 2018-01-11 アルプス電気株式会社 検出装置

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2752558A (en) * 1953-04-22 1956-06-26 Ernest M Kane Electric transducer
US3509296A (en) * 1967-10-23 1970-04-28 Ncr Co Resilient variable-conductivity circuit controlling means
JPS5824921B2 (ja) * 1977-12-30 1983-05-24 信越ポリマ−株式会社 感圧抵抗素子
DE3638641A1 (de) * 1986-11-12 1988-05-26 Richter Dietrich H Druckmesselement
DE3914555A1 (de) * 1989-05-03 1989-11-23 Wellhausen Heinz Elektronischer tastsensor

Also Published As

Publication number Publication date
WO1993021677A1 (en) 1993-10-28
FI944831A0 (fi) 1994-10-14
SE9201223L (sv) 1993-10-17
JPH07505757A (ja) 1995-06-22
NO943817D0 (no) 1994-10-10
SE470118C (sv) 1998-02-23
CZ238694A3 (en) 1995-01-18
SE470118B (sv) 1993-11-08
ATE159385T1 (de) 1997-11-15
SE9201223D0 (sv) 1992-04-16
DE69314671D1 (de) 1997-11-20
HU9402967D0 (en) 1995-02-28
HUT73373A (en) 1996-07-29
EP0725993A1 (en) 1996-08-14
NO943817L (no) 1994-10-10
FI944831L (fi) 1994-12-14

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