EP1895562A1 - A current limiter - Google Patents

A current limiter Download PDF

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Publication number
EP1895562A1
EP1895562A1 EP06018302A EP06018302A EP1895562A1 EP 1895562 A1 EP1895562 A1 EP 1895562A1 EP 06018302 A EP06018302 A EP 06018302A EP 06018302 A EP06018302 A EP 06018302A EP 1895562 A1 EP1895562 A1 EP 1895562A1
Authority
EP
European Patent Office
Prior art keywords
current
contact piece
current limiter
movable contact
bimetallic block
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.)
Withdrawn
Application number
EP06018302A
Other languages
German (de)
French (fr)
Inventor
Martin Pfeifer
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Siemens AG
Original Assignee
Siemens AG
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Siemens AG filed Critical Siemens AG
Priority to EP06018302A priority Critical patent/EP1895562A1/en
Priority to CNA2007101409222A priority patent/CN101136293A/en
Publication of EP1895562A1 publication Critical patent/EP1895562A1/en
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H81/00—Protective switches in which contacts are normally closed but are repeatedly opened and reclosed as long as a condition causing excess current persists, e.g. for current limiting
    • H01H81/04—Protective switches in which contacts are normally closed but are repeatedly opened and reclosed as long as a condition causing excess current persists, e.g. for current limiting electromagnetically operated
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H71/00—Details of the protective switches or relays covered by groups H01H73/00 - H01H83/00
    • H01H71/10—Operating or release mechanisms
    • H01H71/12—Automatic release mechanisms with or without manual release
    • H01H71/14—Electrothermal mechanisms
    • H01H71/16—Electrothermal mechanisms with bimetal element
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H71/00—Details of the protective switches or relays covered by groups H01H73/00 - H01H83/00
    • H01H71/10—Operating or release mechanisms
    • H01H71/12—Automatic release mechanisms with or without manual release
    • H01H71/40—Combined electrothermal and electromagnetic mechanisms
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H71/00—Details of the protective switches or relays covered by groups H01H73/00 - H01H83/00
    • H01H71/10—Operating or release mechanisms
    • H01H71/50—Manual reset mechanisms which may be also used for manual release
    • H01H71/501—Means for breaking welded contacts; Indicating contact welding or other malfunction of the circuit breaker

Definitions

  • the invention relates to current limiters
  • Current limiters are devices that are used limit current in a current circuit in the low voltage range which usually is understood to cover voltages from 100 V up to 1000 V. Typically, current limiters are adapted to limit current in a current circuit carrying three-phase currents, but it is also possible that the current circuit is a one-phase current circuit only.
  • Limiting a current in a current circuit can be used to avoid adverse effects of an overload condition, for example.
  • Current limiter is an electromechanical switching device that typically comprises at least one electromagnetic drive unit, of which there may be provided one for each phase.
  • Such an electromagnetic drive unit follows the current in the at least one phase and is adapted to limit the current in the phase or phases upon detecting an excessive current.
  • a problem specific for current limiters is that, since there, in contrast to circuit breakers or overload relays, is no latching mechanism available that would prevent the movable contact piece or pieces from returning to the responsive stationary contact pieces after the current has been limited, the contact pieces may weld together, after which the current limiter cannot operate reliably any more.
  • the problem may occur in particular after a short circuit when the operator turns the circuit breaker or overload relay to a conducting state without removing the cause of the short circuit. Since the contacts of the current limiter tend to melt in contrast to those of an overload relay, for example, repeated short-circuit may weld the contacts and thus destroy the current limiter.
  • a current limiter comprising an electromagnetic drive unit adapted to limit the current carried by a current circuit by displacing at least one movable contact piece from a responsive stationary contact piece in response to at least one current phase carrying an excessive current
  • an electromagnetic drive unit adapted to limit the current carried by a current circuit by displacing at least one movable contact piece from a responsive stationary contact piece in response to at least one current phase carrying an excessive current
  • a bimetallic block adapted to undergo such a thermal expansion in response to at least one current phase carrying an excessive current that the bimetallic block after the expansion is adapted to prevent said at least one movable contact piece from returning to contact with the responsive stationary contact piece, since this gives time for the contact pieces to cool down or, if they are molt, to solidify.
  • the bimetallic block may adapted to have after the expansion such a geometry that it inhibits the at least one movable contact piece to return to contact with the responsive stationary contact piece, which may help to avoid the need to use of complex or expensivy components.
  • the bimetallic block may be adapted to in its expanded state to inhibit a plunger adapted to move the at least one movable contact piece from returning to a position in which it makes a contact with the responsive stationary contact piece. In this manner, it may be possible to avoid modifying the electromagnetic drive unit which saves effort since the dimensioning and design of the electromagnetic drive unit can be tedious.
  • the bimetallic block may be adapted in its expanded state to inhibit the electromagnetic drive unit from returning to a position it had before detecting that the at least one current phase carries an excessive current. This may be an advantageous solution if the structure of the electromagnetic drive unit enables it, since the plunger and the contact bridge may be left unmodified.
  • the bimetallic block may be adapted to undergo the thermal expansion before the electromagnetic drive unit is adapted to displace said at least one movable contact piece. This makes it easier to have the thermal expansion, since after the movable contact piece has been displaced, in the current limiter there may be too little current available for heating.
  • a current limiter further comprises a unit adapted to reduce phase current passed through said bimetallic block or voltage over the bimetallic block, such as by using a voltage or current divider, the bimetallic block can be made smaller and it does not need to cause that much heat dissipation.
  • the sole Figure shows a simplified current limiter 10.
  • the current limiter 10 comprises an input terminal A1 and an output terminal T1 for each phase.
  • a current limiter 10 comprises thus three input terminals A1, A2, A3 and three output terminals T1, T2, T3.
  • the components for the second and third phase have been omitted from the Figure.
  • the input terminal A1 receives an input current, passes it along the current rail 11 to a stationary contact piece 12. If the contact bridge 14 is appropriately positioned, the stationary contact piece 12 has an electrical contact with the movable contact piece 13, which in turn is in electrical connection with a second movable contact piece 15 over the contact bridge 14. The second movable contact piece 15, given that the contact bridge 14 is still appropriately positioned, is then in electrical contact with the second stationary contact piece 16.
  • the current limiter 10 comprises an electromagnetic drive unit 30 adapted to limit the current carried by a current circuit, i.e. between the input terminal A1 and the output terminal T1, by displacing the movable contact pieces 13, 15 from the responsive stationary contact pieces 12, 16 in response to at least one current phase carrying an excessive current.
  • the electromagnetic drive unit 30 comprises a yoke 22 and a coil 21 around the yoke 22.
  • the current entering via the input terminal A1 to the current rail 17 is led through a bimetallic block comprising a first leg 18 and a second leg, before it gets to the coil 21 through a metallic conductor 20. From the coil 21 the current continues through a metallic conductor 23 to a connection point 24 that is located before the output terminal T1.
  • the magnetic field caused by the coil 21 and the yoke 22 cause the armature 26A to move downwards and to push the plunger 26 to overcome the balancing force at the biasing spring 25 so that the contact bridge 26 is pushed downwards, moving the movable contact pieces 13, 15 away from the stationary contact pieces 12, 16 and thus opening the current circuit.
  • the bimetallic block in the example shown in the Figure, comprising the first leg 18 and the second leg 19, is preferably adapted to undergo such a thermal expansion in response to at least one current phase carrying an excessive current that the bimetallic block after the expansion is adapted to prevent the movable contact pieces 13, 15 from returning to contact with the responsive stationary contact pieces 12, 16.
  • the bimetallic block may be adapted after the expansion to have such a geometry that it inhibits the movable contact pieces 13, 15 to return to contact with the responsive stationary contact pieces 12, 16.
  • the bimetallic block may be adapted in its expanded state to inhibit the plunger 26 adapted to move the movable contact pieces 13, 15 from returning to the position in which the movable contact pieces 13, 15 make a contact with the responsive stationary contact pieces 12, 16.
  • the bimetallic block may be adapted in its expanded state to inhibit the electromagnetic drive unit 30 from returning to a position it had before detecting that the at least one current phase carries an excessive current.
  • the bimetallic block is adapted to undergo the thermal expansion before the electromagnetic drive unit 30 is adapted to displace the movable contact pieces 13, 15.
  • the bimetallic block can be placed between the coil 21 and the second movable contact piece 16.
  • the bimetallic block may be or comprise a snap strip or a snap disc.

Abstract

A current limiter (10) comprises an electromagnetic drive unit (30) adapted to limit the current carried by a current circuit by displacing at least one movable contact piece (13, 15) from a responsive stationary contact piece (12, 16) in response to at least one current phase carrying an excessive current. The current limiter (10) further comprises a bimetallic block (18, 19) adapted to undergo such a thermal expansion in response to at least one current phase carrying an excessive current that the bimetallic block (18, 19) after the expansion is adapted to prevent said at least one movable contact piece (13, 15) from returning to contact with the responsive stationary contact piece (12, 16).

Description

    Field of the invention
  • The invention relates to current limiters
    • Background
  • Current limiters are devices that are used limit current in a current circuit in the low voltage range which usually is understood to cover voltages from 100 V up to 1000 V. Typically, current limiters are adapted to limit current in a current circuit carrying three-phase currents, but it is also possible that the current circuit is a one-phase current circuit only.
  • Limiting a current in a current circuit can be used to avoid adverse effects of an overload condition, for example.
  • Current limiter is an electromechanical switching device that typically comprises at least one electromagnetic drive unit, of which there may be provided one for each phase. Such an electromagnetic drive unit follows the current in the at least one phase and is adapted to limit the current in the phase or phases upon detecting an excessive current.
  • A problem specific for current limiters is that, since there, in contrast to circuit breakers or overload relays, is no latching mechanism available that would prevent the movable contact piece or pieces from returning to the responsive stationary contact pieces after the current has been limited, the contact pieces may weld together, after which the current limiter cannot operate reliably any more.
  • The problem may occur in particular after a short circuit when the operator turns the circuit breaker or overload relay to a conducting state without removing the cause of the short circuit. Since the contacts of the current limiter tend to melt in contrast to those of an overload relay, for example, repeated short-circuit may weld the contacts and thus destroy the current limiter.
    • Summary of the invention
  • It is an object of the invention to improve a current limiter of a known kind to be less sensitive to contact welding. This object can be achieved with a current limiter as set out in claim 1.
  • The dependent claims describe various advantageous aspects of the invention.
    • Advantages of the invention
  • A current limiter comprising an electromagnetic drive unit adapted to limit the current carried by a current circuit by displacing at least one movable contact piece from a responsive stationary contact piece in response to at least one current phase carrying an excessive current can be improved by making it to further comprise a bimetallic block adapted to undergo such a thermal expansion in response to at least one current phase carrying an excessive current that the bimetallic block after the expansion is adapted to prevent said at least one movable contact piece from returning to contact with the responsive stationary contact piece, since this gives time for the contact pieces to cool down or, if they are molt, to solidify.
  • The bimetallic block may adapted to have after the expansion such a geometry that it inhibits the at least one movable contact piece to return to contact with the responsive stationary contact piece, which may help to avoid the need to use of complex or expensivy components.
  • The bimetallic block may be adapted to in its expanded state to inhibit a plunger adapted to move the at least one movable contact piece from returning to a position in which it makes a contact with the responsive stationary contact piece. In this manner, it may be possible to avoid modifying the electromagnetic drive unit which saves effort since the dimensioning and design of the electromagnetic drive unit can be tedious.
  • The bimetallic block may be adapted in its expanded state to inhibit the electromagnetic drive unit from returning to a position it had before detecting that the at least one current phase carries an excessive current. This may be an advantageous solution if the structure of the electromagnetic drive unit enables it, since the plunger and the contact bridge may be left unmodified.
  • The bimetallic block may be adapted to undergo the thermal expansion before the electromagnetic drive unit is adapted to displace said at least one movable contact piece. This makes it easier to have the thermal expansion, since after the movable contact piece has been displaced, in the current limiter there may be too little current available for heating.
  • If a current limiter further comprises a unit adapted to reduce phase current passed through said bimetallic block or voltage over the bimetallic block, such as by using a voltage or current divider, the bimetallic block can be made smaller and it does not need to cause that much heat dissipation.
    • Detailed description
  • The sole Figure shows a simplified current limiter 10. The current limiter 10 comprises an input terminal A1 and an output terminal T1 for each phase. Typically, a current limiter 10 comprises thus three input terminals A1, A2, A3 and three output terminals T1, T2, T3. For the sake of simplicity, the components for the second and third phase have been omitted from the Figure.
  • The input terminal A1 receives an input current, passes it along the current rail 11 to a stationary contact piece 12. If the contact bridge 14 is appropriately positioned, the stationary contact piece 12 has an electrical contact with the movable contact piece 13, which in turn is in electrical connection with a second movable contact piece 15 over the contact bridge 14. The second movable contact piece 15, given that the contact bridge 14 is still appropriately positioned, is then in electrical contact with the second stationary contact piece 16.
  • The current limiter 10 comprises an electromagnetic drive unit 30 adapted to limit the current carried by a current circuit, i.e. between the input terminal A1 and the output terminal T1, by displacing the movable contact pieces 13, 15 from the responsive stationary contact pieces 12, 16 in response to at least one current phase carrying an excessive current.
  • The electromagnetic drive unit 30 comprises a yoke 22 and a coil 21 around the yoke 22. The current entering via the input terminal A1 to the current rail 17 is led through a bimetallic block comprising a first leg 18 and a second leg, before it gets to the coil 21 through a metallic conductor 20. From the coil 21 the current continues through a metallic conductor 23 to a connection point 24 that is located before the output terminal T1.
  • If the current in the coil 21 is too high, indicating that the current circuit carries an excessive current, the magnetic field caused by the coil 21 and the yoke 22 cause the armature 26A to move downwards and to push the plunger 26 to overcome the balancing force at the biasing spring 25 so that the contact bridge 26 is pushed downwards, moving the movable contact pieces 13, 15 away from the stationary contact pieces 12, 16 and thus opening the current circuit.
  • The bimetallic block, in the example shown in the Figure, comprising the first leg 18 and the second leg 19, is preferably adapted to undergo such a thermal expansion in response to at least one current phase carrying an excessive current that the bimetallic block after the expansion is adapted to prevent the movable contact pieces 13, 15 from returning to contact with the responsive stationary contact pieces 12, 16.
  • The bimetallic block may be adapted after the expansion to have such a geometry that it inhibits the movable contact pieces 13, 15 to return to contact with the responsive stationary contact pieces 12, 16.
  • The bimetallic block may be adapted in its expanded state to inhibit the plunger 26 adapted to move the movable contact pieces 13, 15 from returning to the position in which the movable contact pieces 13, 15 make a contact with the responsive stationary contact pieces 12, 16.
  • The bimetallic block may be adapted in its expanded state to inhibit the electromagnetic drive unit 30 from returning to a position it had before detecting that the at least one current phase carries an excessive current.
  • Advantageously, the bimetallic block is adapted to undergo the thermal expansion before the electromagnetic drive unit 30 is adapted to displace the movable contact pieces 13, 15.
  • The bimetallic block can be placed between the coil 21 and the second movable contact piece 16.
  • Even though the invention was described by way of a nonlimiting example, the skilled person appreciates that the invention can be generalized within the scope of the annexed patent claims. For example, the bimetallic block may be or comprise a snap strip or a snap disc.

Claims (10)

  1. A current limiter (10) comprising an electromagnetic drive unit (30) adapted to limit the current carried by a current circuit by displacing at least one movable contact piece (13, 15) from a responsive stationary contact piece (12, 16) in response to at least one current phase carrying an excessive current, characterized in that: said current limiter (10) further comprises a bimetallic block (18, 19) adapted to undergo such a thermal expansion in response to at least one current phase carrying an excessive current that the bimetallic block (18, 19) after the expansion is adapted to prevent said at least one movable contact piece (13, 15) from returning to contact with the responsive stationary contact piece (12, 16).
  2. A current limiter (10) according to claim 1, wherein: the bimetallic block (18, 19) is adapted after the expansion to have such a geometry that it inhibits the at least one movable contact piece (13, 15) to return to contact with the responsive stationary contact piece (12, 16).
  3. A current limiter (10) according to claim 1 or 2, wherein: the bimetallic block (18, 19) is adapted in its expanded state to inhibit a plunger (26) adapted to move said at least one movable contact piece (13, 15) from returning to a position in which said at least one movable contact piece (13, 15) makes a contact with the responsive stationary contact piece (12, 16).
  4. A current limiter (10) according to any one of the preceding claims, wherein: the bimetallic block (18, 19) is adapted in its expanded state to inhibit the electromagnetic drive unit (30) from returning to a position it had before detecting that the at least one current phase carries an excessive current
  5. A current limiter (10) according to any one of the preceding claims, wherein: the bimetallic block (18, 19) is adapted to undergo the thermal expansion before the electromagnetic drive unit (30) is adapted to displace said at least one movable contact piece (13, 15).
  6. A current limiter (10) according to any one of the preceding claims, wherein: said bimetallic block (18, 19) is between a coil (21) of the electromagnetic drive unit (30) and said at least one movable contact piece (16).
  7. A current limiter (10) according to any one of the preceding claims, further comprising: a means (17) adapted to reduce phase current passed through said bimetallic block (18, 19).
  8. A current limiter (10) according to any one of the preceding claims, further comprising: a means (20, 17) adapted to reduce voltage over said bimetallic block (18, 19).
  9. A current limiter (10) according to any one of the preceding claims, wherein: the bimetallic block (18, 19) comprises a snap strip.
  10. A current limiter (10) according to any one of the preceding claims, wherein: bimetallic block (18, 19) comprises a snap disc.
EP06018302A 2006-09-01 2006-09-01 A current limiter Withdrawn EP1895562A1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
EP06018302A EP1895562A1 (en) 2006-09-01 2006-09-01 A current limiter
CNA2007101409222A CN101136293A (en) 2006-09-01 2007-08-10 A current limiter

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP06018302A EP1895562A1 (en) 2006-09-01 2006-09-01 A current limiter

Publications (1)

Publication Number Publication Date
EP1895562A1 true EP1895562A1 (en) 2008-03-05

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP06018302A Withdrawn EP1895562A1 (en) 2006-09-01 2006-09-01 A current limiter

Country Status (2)

Country Link
EP (1) EP1895562A1 (en)
CN (1) CN101136293A (en)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102347174A (en) * 2011-09-19 2012-02-08 广东天富电气集团有限公司 Shunting method of circuit breaker
CN105070615A (en) * 2015-07-11 2015-11-18 合肥正浩机械科技有限公司 Electronic breaker double-breakpoint mechanism
CN110364402B (en) * 2019-08-15 2021-05-18 红光电气集团有限公司 Quick response type direct current fuse

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE471947C (en) * 1929-02-18 Hugo Krieger Fa Switching contact that locks itself in the switch-off position, especially for current limiters
US2262344A (en) * 1940-03-05 1941-11-11 Penn Electric Switch Co Circuit cutout
EP0974997A2 (en) * 1998-07-21 2000-01-26 Eaton Corporation Fault current tolerable contactor
US20060066426A1 (en) * 2004-09-30 2006-03-30 Benard David J Method and apparatus for soft-fault tolerant circuit interruption

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE471947C (en) * 1929-02-18 Hugo Krieger Fa Switching contact that locks itself in the switch-off position, especially for current limiters
US2262344A (en) * 1940-03-05 1941-11-11 Penn Electric Switch Co Circuit cutout
EP0974997A2 (en) * 1998-07-21 2000-01-26 Eaton Corporation Fault current tolerable contactor
US20060066426A1 (en) * 2004-09-30 2006-03-30 Benard David J Method and apparatus for soft-fault tolerant circuit interruption

Also Published As

Publication number Publication date
CN101136293A (en) 2008-03-05

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