US3599041A - Isolator switches provided with grounding switch blades and ground responsive signalling and protective means - Google Patents

Isolator switches provided with grounding switch blades and ground responsive signalling and protective means Download PDF

Info

Publication number
US3599041A
US3599041A US867744A US3599041DA US3599041A US 3599041 A US3599041 A US 3599041A US 867744 A US867744 A US 867744A US 3599041D A US3599041D A US 3599041DA US 3599041 A US3599041 A US 3599041A
Authority
US
United States
Prior art keywords
envelope
contacts
movable
switching
conductor
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
US867744A
Other languages
English (en)
Inventor
Rintje Harmelen
Gijsbert W Irik
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.)
COQ NV
Original Assignee
COQ NV
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 COQ NV filed Critical COQ NV
Application granted granted Critical
Publication of US3599041A publication Critical patent/US3599041A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02B—BOARDS, SUBSTATIONS OR SWITCHING ARRANGEMENTS FOR THE SUPPLY OR DISTRIBUTION OF ELECTRIC POWER
    • H02B13/00—Arrangement of switchgear in which switches are enclosed in, or structurally associated with, a casing, e.g. cubicle
    • H02B13/02—Arrangement of switchgear in which switches are enclosed in, or structurally associated with, a casing, e.g. cubicle with metal casing
    • H02B13/035—Gas-insulated switchgear
    • H02B13/075—Earthing arrangements
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B61—RAILWAYS
    • B61F—RAIL VEHICLE SUSPENSIONS, e.g. UNDERFRAMES, BOGIES OR ARRANGEMENTS OF WHEEL AXLES; RAIL VEHICLES FOR USE ON TRACKS OF DIFFERENT WIDTH; PREVENTING DERAILING OF RAIL VEHICLES; WHEEL GUARDS, OBSTRUCTION REMOVERS OR THE LIKE FOR RAIL VEHICLES
    • B61F9/00—Rail vehicles characterised by means for preventing derailing, e.g. by use of guide wheels
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H31/00—Air-break switches for high tension without arc-extinguishing or arc-preventing means
    • H01H31/02—Details
    • H01H31/04—Interlocking mechanisms
    • H01H31/10—Interlocking mechanisms for interlocking two or more switches
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H31/00—Air-break switches for high tension without arc-extinguishing or arc-preventing means
    • H01H31/14—Air-break switches for high tension without arc-extinguishing or arc-preventing means with bridging contact that is not electrically connected to either line contact in open position of switch
    • H01H31/24—Air-break switches for high tension without arc-extinguishing or arc-preventing means with bridging contact that is not electrically connected to either line contact in open position of switch with rectilinearly-movable bridging contact
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H9/00—Details of switching devices, not covered by groups H01H1/00 - H01H7/00
    • H01H9/0066—Auxiliary contact devices
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02B—BOARDS, SUBSTATIONS OR SWITCHING ARRANGEMENTS FOR THE SUPPLY OR DISTRIBUTION OF ELECTRIC POWER
    • H02B11/00—Switchgear having carriage withdrawable for isolation
    • H02B11/28—Earthing arrangements
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H31/00—Air-break switches for high tension without arc-extinguishing or arc-preventing means
    • H01H31/003—Earthing switches

Definitions

  • ABSTRACT A metal-clad isolator switch for multiple interruption divided in two parts insulated from each other and comprising means for connecting the interconnected movable switching contacts of the isolator switch with earth and a selectively operating signalling and protecting system which selectively indicates, when and in which one of the isolator switch parts an unwanted earth-connection occurs.
  • the invention relates to a metal-clad isolator switch for high voltage and multiple interruption, comprising a metal envelope which is insulated from earth and connected with earth via a signalling and protecting circuit only, said envelope containing two spaced fixed contacts and two movable switching contacts mounted for cooperation with said fixed contacts in the space left between the latter, said fixed and said movable contacts being insulated from the envelope, said movable switching contacts being, at least in the closed condition of the isolator switch, electrically conductively interconnected and being supported by an insulator attached to the envelope and dividing the space within the envelope into two switching chambers which are separated by said insulator in a gastight manner and each contain a fixed contact and a movable switching contact, and a device for earthing the movable switching contacts, when the isolator switch is in its open condition
  • An isolator switch of this construction is the subject matter of copending application Ser. No. 867,745, filed Oct. 20, 1969.
  • the invention has the object to improve this formerly constructed switch in such a manner that, should an earthconnection occur, it will indicate in a simple way, in which one of the two switching chambers said earth-connection has occurred.
  • the invention consists in that the portion of the envelope which each surround a switching chamber are also insulated from one another and are each connected with earth by an individual conductor cooperating with the signalling and protecting circuit, the movable switching contacts being coupled with the signalling and protecting circuit in the open condition of the isolator switch and said circuit being arranged, in such a manner, that at the occurrence of an earth-connection in the isolator switch it is indica ed, in which one of the two switching chambers the earth-connection occurs.
  • the isolator switch may for obtaining the desired selective signalling and protection be constructed, in such a manner, that each movable switching contact cooperates with an individual earthing-switch and with an individual part of the signalling and protecting device, the movable switching contacts being interconnected by an auxiliary switch which is closed in the closed condition of the isolator switch and open in the open condition of the isolator switch. in this case two separate signalling and protecting circuits are used.
  • said switching rods may each be mounted in and electrically conductively connected with an individual metal tubular member which is contained in and supported by the insulator, said tubular members being spaced and insulated from one another and a slide contact may be provided in the tubular members which is operated by a switching rod, said slide contact constituting together with said tubular members the auxiliary switch and establishing, in the closed condition of the isolator switch, an electrically conductive connection between said tubular members and said switching rods, but keeping, in the open condition of the isolator switch, the switching rods electrically separated from one another.
  • the auxiliary switch is then automatically coupled, with the switching rods, so that a separate driving gear for said auxiliary switch can be dispensed with.
  • the isolator switch is provided with two movable switching contacts, which are permanently electrically conductively interconnected by a conductor extending through the insulator, and with an earthing-switch cooperating with both switching contacts and found in one of the two switching chambers only, the conductor extending between the two movable switching contacts, the conductor extending between earth and the portion of the envelope surrounding the switching chamber, in
  • the earthing-switch may each be coupled with an individual input-circuit reacting on the current, that flows through the relative conductor, and forming part of a composite control-circuit that is connected between said conductor and a signalling and protecting system, said control-circuit bringing said signalling and protecting system, at the event of an earthwonnection in one switching chamber, into one and, at the event of an earth-connection in the other switching chamber, into the other one of two operative conditions.
  • a reliable isolator switch having this selective signalling and protecting circuit is obtained, when said conductors are each coupled with said input-circuit of the control-circuit via a current transformer, said control-circuit comprising two summation transformers which are each provided with two primary windings and one secondary winding, the one primary windings of said summation transformers being connected in series and fed by the current transformer coupled with the conductor interconnecting the movable switching contacts, the other primary winding of one summation transformer being fed by the current transformer coupled with the conductor extending between earth and the envelope of the switching chamber, in which the earthing-switch is accommodated, and being coupled in counterconnection with the first mentioned primary winding of said summation transformer, the other primary winding of the other summation transformer being fed by the current transformer coupled with the conductor extending between earth and the envelope of the other switching chamber and being coupled in concurrent connection with the first mentioned primary winding of said other summation transformer and the secondary windings being connected in counterconnection to a double acting signalling and protecting device
  • FIG. 1 an axial sectional view of an isolator switch having a selective signalling and protecting circuit constructed in accordance with the invention
  • FIG. 2 a diagrammatical view of an other isolator switch provided with a selective signalling and protecting circuit
  • FIG. 3 a diagrammatical view of an isolator switch shown in FIG. 2 provided with a variant of the signalling and protecting circuit.
  • This insula tor supports two coaxial metal tubes 4, 5 which extend in the axis of the portions ll, 2 of the envelope.
  • the tubes 4, 5 are insulated from each other by a space 6 and they carry each an axially movable switching rod '7, 8.
  • These switching rods cooperate with fixed contacts 9, l0 and they are moved by means of screwed rods ll ll, M. which can be driven via the driving gear 113 by a driving shaft M.
  • the screwed rods ll, 12 cooperate with nuts l5 l6 insulatedly mounted in the switching rods 7, 8.
  • the tubes 4, 5 carry each a movable earthing-contact l7, 18 which, in the open condition of the isolator switch, are brought into cooperation with a fixed contact 19 26 respectively, which is electrically conductively connected with the envelope 1, 2 respectively.
  • the earthing-contacts l7, 18 are driven by the switching rods 7, 8 in such a manner, which is not described, that they are forced by said switching contacts, just before the switching contacts 7, 8 reach their open position, from the inactive position shown in complete lines into the active position shown in dotted lines and are swung from the active position into the inactive position, in which position they are locked, just after the switching rods 7, 8 have left their open position.
  • the portions 1, 2 of the envelope and also the fixed earthing contacts 19, 20 are each connected to earth via a conductor 21, 22.
  • the conductors 21, 22 are each coupled via a current transformer 23, 24 with an individual signalling and protecting device 25, 26.
  • the insulating space 6 is bridged by a slide contact 27, which is secured to a movable block 28 contained in the tube 5.
  • This block is forced by a spring 29 in the shown position, in which the slide-contact 27 interconnects the tubes 4 and 5, and the switching rods 7 and 8 electrically conductively with each other. If the isolator switch is opened, the switching rods 7, 8 are moved towards each other and the block 28 provided with the slide-contact 27 is forced against the driving mechanism 13, so that the electrically conductive connection between the tubes 4 and is broken.
  • the switching chambers which are spatially and electrically separated from each other by the insulator 3 are then each separately grounded.
  • the movable switching contacts 30, 31 are permanently electrically conductively interconnected by a conductor 32.
  • the switching contacts 30, 31 cooperate with fixed contacts 33, 34 and in the open condition of the isolator switch only the switching contact 30 is brought into contact with a fixed earthing-contact 35.
  • the portions 1 and 2 of the envelope which are insulated from each other by the insulator 3 are each connected to earth via a conductor 21, 22 forming part of the current transformer 23, 24.
  • the conductor 32 is surrounded by the secondary winding 36 of a third current transformer.
  • the circuit for the selective signalling and protection shown in FIG. 2 comprises two summation transformers 37, 38 which are each provided with two primary windings 39, 40 and 41, 42 andone secondary winding 43, 44.
  • the primary winding 39, 41 is connected to the current transformer 23, 24 respectively.
  • the primary windings 40 and 42 are connected in series and fed by the current transformer 36.
  • the windings 39 and 40 are coupled concurrently and the windings 41 and 42 are coupled in counterconnection in respect of the summation transformers 37, 38.
  • the secondary windings 43, 44 of the summation transformers 37, 38 feed together a double acting relay 45 which is provided with two oppositely operating coils 46, 47.
  • This relay is adapted to close by means of a contact 48 the circuit of a signalling and protecting device 49, when the coil 46 is fed by the transformer winding 43, and adapted to close by means of a contact 50 the circuit of a signalling and protecting device 51, when the coil 47 is fed by the transformer winding 44.
  • This device operates as follows:
  • the conductor 32 is able to lead current, so that via the current transformer 36 a current can flow through the primary transformer windings 40, 42. Both coils 46, 47 of the relay 45 are then excited, so that the relay is held in the condition of rest and the devices 49, 51 remain inactive.
  • the envelope 1 is grounded via the conductor 21 whereas the switching contacts 30, 31 the conductor 32 and the envelope 2 are grounded via the conductor 22. Should an earth-connection occur between the fixed contact 34 and the envelope 1, the earth-current will flow through the conductor 21 and only the coil 46 of the relay 45 will be fed by the transformer 37, so that the contact 48 is closed and the signalling and protecting device 49 is set in action.
  • the relay 52 is fed by the current transformer 23, the relay 53 is flow by the current transformer 36 and the relay 54 is fed by the current transfonner to If the relay 52 is brought into operation the contact 55 is closed. If the relay 53 is fed the contact 56 is-opened and the contact 57 is closed and if the relay 54 becomes operative the contacts 58 and 59 are closed.
  • This device operates as follows:
  • the contact 56 is then opened. If the earth-connection or the rupture should occur in the switching chamber surrounded by the envelope 2, the earth-current will only flow through the conductor 22, so that only the relay 54 will be excited and the circuit of the signalling and protecting device 51 will be closed by the contact 53. The device 49 remains inactive, since the contacts 55 and 57 then remain open. If the isolator switch is closed and the service current flows through the conductor 32, only the relay 53 is fed by the current transformer 36, so that the contact 56 is opened and the contact 57 is closed. The relays 52 and 54 then remain in their position of rest, so that the contacts 55, 58 and 59 remain open and no one of the two signalling and protecting devices 49 and 51 will be set in action.
  • a metal-clad isolator switch for high voltage and multiple interruption comprising a metal envelope which is insulated from earth, a selectively operating signalling and protecting system connected between said envelope and earth, two'.
  • a metal-clad isolator switch for high voltage and multiple interruption comprising a metal envelope which is insulated from earth, a selectively operating signalling and protecting system connected between said envelope and earth, two spaced fixed contacts, two movable switching contacts mounted for cooperation with said fixed contacts in the space left between the latter and being, at least in the closed condition of the isolator switch, electrically conductively interconnected, said fixed contacts and said movable contacts being insulated from the envelope, an insulator attached to the envelope and supporting said movable switching contacts, said insulator dividing the space inside the envelope into two switching chambers, which are separated in a gastight manner by said insulator and each contain a fixed contact and a movable switching contact, means for connecting the movable switching contacts with the envelope, when the isolator switch is in its open condition, the envelope portion surrounding one switching chamber being insulated from the envelope portion surrounding the other switching chamber, a conductor extending between one envelope portion and earth and a conductor extending between the other envelope and earth said conductors
  • a double interruption isolator switch and fault indicating means for high voltage electrical systems comprising, in combination;
  • metal envelope means having portions electrically insulated from each other and defining separate first and second compartments
  • a pair of movable contacts and first conductor means electrically connecting said movable contacts one of said movable contacts being movable between a normal position engaging said one fixed contact and an interrupting position eiectrically connected to that portion of the envelope means defining said first compartment, the other of said movable contacts being movable between a normal position engaging the other of said fixed contacts and an interrupting position in which it is electrically connected only to said one movable contact through said first conductor means;
  • a double interruption isolator switch and fault indicating means for high voltage electrical systems comprising, in combination;
  • metal envelope means having portions electrically insulated from each other and defining separate first and second compartments
  • third conductor means connecting that portion of the envelope means defining said second compartment to ground;
  • first current-responsive means having an output in response to current flowing through said first conductor means
  • second current-responsive means having an output in response to current flowing through said second conductor means
  • third current-responsive means having an output in response to current fhowing through said third conductor means

Landscapes

  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Gas-Insulated Switchgears (AREA)
  • Arc-Extinguishing Devices That Are Switches (AREA)
US867744A 1969-08-04 1969-10-20 Isolator switches provided with grounding switch blades and ground responsive signalling and protective means Expired - Lifetime US3599041A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
NL6911833A NL6911833A (ru) 1969-08-04 1969-08-04

Publications (1)

Publication Number Publication Date
US3599041A true US3599041A (en) 1971-08-10

Family

ID=19807598

Family Applications (1)

Application Number Title Priority Date Filing Date
US867744A Expired - Lifetime US3599041A (en) 1969-08-04 1969-10-20 Isolator switches provided with grounding switch blades and ground responsive signalling and protective means

Country Status (8)

Country Link
US (1) US3599041A (ru)
AT (1) AT298601B (ru)
BE (1) BE749661A (ru)
DE (1) DE1965504C3 (ru)
FR (1) FR2057639A5 (ru)
GB (1) GB1256054A (ru)
NL (2) NL6911833A (ru)
SE (1) SE369253B (ru)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3806682A (en) * 1972-10-03 1974-04-23 Bbc Brown Boveri & Cie High-voltage gas-insulated switchgear with capacitive voltage divider for indicating contact position
US4104689A (en) * 1976-09-29 1978-08-01 Electric Machinery Manufacturing Company Vacuum contactor protector
US5828025A (en) * 1996-08-13 1998-10-27 Abb Patent Gmbh Disconnecting/grounding switch for metal-encapsulated, gas-insulated high-voltage switchgear
US6242708B1 (en) * 2000-01-03 2001-06-05 Eaton Corporation Isolator switch
US6362445B1 (en) * 2000-01-03 2002-03-26 Eaton Corporation Modular, miniaturized switchgear
CN103022925A (zh) * 2012-12-05 2013-04-03 广东天富电气集团有限公司 一种带加强绝缘的高原型开关设备
CN103151212A (zh) * 2013-02-25 2013-06-12 贵州中泉电气集团有限公司 一种回路自锁负荷开关
CN115565829A (zh) * 2022-09-08 2023-01-03 正泰电气股份有限公司 驱动结构及具有其的断路器

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2548173C3 (de) * 1975-10-24 1979-01-18 Siemens Ag, 1000 Berlin Und 8000 Muenchen Einrichtung zur Erfassung eines Hochspannungspotentials in metallgekapselten Hochspannungsschaltanlagen und -geräten
DE3020408A1 (de) * 1980-04-17 1981-10-22 BBC AG Brown, Boveri & Cie., 5401 Baden, Aargau Hochspannungsschaltanlage
DE4314822A1 (de) * 1993-04-30 1994-11-03 Siemens Ag Meßwandler
JP5546338B2 (ja) * 2010-04-30 2014-07-09 三菱電機株式会社 ガス絶縁計器用変圧器

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2542838A (en) * 1947-12-27 1951-02-20 Westinghouse Electric Corp Ground protective system
DE966204C (de) * 1939-01-17 1957-07-18 Siemens Ag Elektrische Unterbrechungseinrichtung, insbesondere fuer schlagwettergefaehrdete Betreibe
US3233151A (en) * 1962-12-31 1966-02-01 Gen Electric Electrical protective systems
FR1371871A (fr) * 1963-07-11 1966-03-04 Alsthom Cgee Poste électrique à haute tension du type blindé
US3323018A (en) * 1963-08-14 1967-05-30 Sprecher & Schuh Ag Metal-enclosed electrical protective systems
US3356798A (en) * 1965-12-13 1967-12-05 Westinghouse Electric Corp Disconnect switch
US3485971A (en) * 1967-06-19 1969-12-23 Cod Nv Fully enclosed switching devices for high voltages

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE966204C (de) * 1939-01-17 1957-07-18 Siemens Ag Elektrische Unterbrechungseinrichtung, insbesondere fuer schlagwettergefaehrdete Betreibe
US2542838A (en) * 1947-12-27 1951-02-20 Westinghouse Electric Corp Ground protective system
US3233151A (en) * 1962-12-31 1966-02-01 Gen Electric Electrical protective systems
FR1371871A (fr) * 1963-07-11 1966-03-04 Alsthom Cgee Poste électrique à haute tension du type blindé
US3323018A (en) * 1963-08-14 1967-05-30 Sprecher & Schuh Ag Metal-enclosed electrical protective systems
US3356798A (en) * 1965-12-13 1967-12-05 Westinghouse Electric Corp Disconnect switch
US3485971A (en) * 1967-06-19 1969-12-23 Cod Nv Fully enclosed switching devices for high voltages

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3806682A (en) * 1972-10-03 1974-04-23 Bbc Brown Boveri & Cie High-voltage gas-insulated switchgear with capacitive voltage divider for indicating contact position
US4104689A (en) * 1976-09-29 1978-08-01 Electric Machinery Manufacturing Company Vacuum contactor protector
US5828025A (en) * 1996-08-13 1998-10-27 Abb Patent Gmbh Disconnecting/grounding switch for metal-encapsulated, gas-insulated high-voltage switchgear
US6242708B1 (en) * 2000-01-03 2001-06-05 Eaton Corporation Isolator switch
US6362445B1 (en) * 2000-01-03 2002-03-26 Eaton Corporation Modular, miniaturized switchgear
CN103022925A (zh) * 2012-12-05 2013-04-03 广东天富电气集团有限公司 一种带加强绝缘的高原型开关设备
CN103151212A (zh) * 2013-02-25 2013-06-12 贵州中泉电气集团有限公司 一种回路自锁负荷开关
CN115565829A (zh) * 2022-09-08 2023-01-03 正泰电气股份有限公司 驱动结构及具有其的断路器
CN115565829B (zh) * 2022-09-08 2023-11-24 正泰电气股份有限公司 驱动结构及具有其的断路器

Also Published As

Publication number Publication date
DE1965504B2 (de) 1973-03-22
GB1256054A (en) 1971-12-08
AT298601B (de) 1972-04-15
DE1965504C3 (de) 1975-03-20
NL6911833A (ru) 1971-02-08
BE749661A (nl) 1970-10-01
SE369253B (ru) 1974-08-12
FR2057639A5 (ru) 1971-05-21
DE1965504A1 (de) 1971-02-25
NL133619C (ru)

Similar Documents

Publication Publication Date Title
US3599041A (en) Isolator switches provided with grounding switch blades and ground responsive signalling and protective means
US3660721A (en) Protective equipment for an alternating current power distribution system
US5206616A (en) Switching device for the interruption of fault currents
US3546535A (en) Transformers and composite tap changers associated therewith
US4107496A (en) Vacuum switching apparatus with double interruption and including an interposed barrier
US1783279A (en) Circuit interrupter
US3777218A (en) Metal-clad high-voltage switching system
US3708638A (en) Vacuum type electric circuit breaker
US3358104A (en) Heating means for compressed-gas circuit interrupters
US3114815A (en) Fluid-blast circuit interrupter with improved current-transformer housing means
EP2282322B1 (en) A disconnector for electric power equipment filled with dielectic liquid
US3323018A (en) Metal-enclosed electrical protective systems
US2458792A (en) Electric circuit breaker
GB398889A (en) Improvements in or relating to metal-clad electric switchgear
US3509267A (en) Multipurpose insulating column
US2218554A (en) Electric switchgear
US1694223A (en) Electric switch
US4172270A (en) Compressed gas filled circuit breaker
US2288117A (en) Fuse construction
DE1665637B2 (de) Druckgasisolierte hochspannungsschaltanlage
GB1057190A (en) Improvements in electric protective equipment
GB483784A (en) Improvements in or relating to multi-break electric circuit breakers
US4239948A (en) Grounded support tank type gas circuit breaker
US1930333A (en) Protective arrangement
US3543089A (en) Signaling system for transmitting information between points of different potential