US3014111A - Pneumatic operating means for circuit breakers - Google Patents

Pneumatic operating means for circuit breakers Download PDF

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US3014111A
US3014111A US854182A US85418259A US3014111A US 3014111 A US3014111 A US 3014111A US 854182 A US854182 A US 854182A US 85418259 A US85418259 A US 85418259A US 3014111 A US3014111 A US 3014111A
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contacts
contact
movable contact
pressure
auxiliary
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US854182A
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Forwald Haakon
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ABB Norden Holding AB
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ASEA AB
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H33/00—High-tension or heavy-current switches with arc-extinguishing or arc-preventing means
    • H01H33/02—Details
    • H01H33/28—Power arrangements internal to the switch for operating the driving mechanism
    • H01H33/30—Power arrangements internal to the switch for operating the driving mechanism using fluid actuator
    • H01H33/302—Power arrangements internal to the switch for operating the driving mechanism using fluid actuator for fluid insulated switchgear, wherein the insulating fluid is also the working fluid

Definitions

  • This invention relates to circuit breakers which may be of the air blast type, and more specifically relates to a pneumatic operating structure for a circuit breaker wherein the main interrupting contacts operate as a pneumatic valve for controlling the operation of auxiliary contacts associated with the main interrupting contacts.
  • Circuit breakers of the air blast type which utilize more than one pair of contacts are well known in the art wherein the contacts may be series connected interrupter contacts, or parallel connected contacts where one of the parallel connected contacts is connected in series with a resistor, or, in the case of oil circuit breakers, where there is a pressure generating set of contacts in series with the main interrupting contacts.
  • the contacts operate in a predetermined sequence. Since the contacts are pneumatically actuated, this requires the use of a valve for delaying the operation of the last set of contacts to be operated.
  • the principle of the present invention is to utilize the first operated interrupter contacts as a pneumatic valve for delivering operating pressure to the subsequently operated contacts associated with the main interrupter contacts.
  • a specific embodiment of the invention is directed to the type of pneumatic circuit breaker wherein a resistor is connected in parallel with the main interrupter contacts. Included in the parallel resistor circuit there is an auxiliary pair of contacts adapted to be disengaged after the main interrupter contacts extinguish the arc during the opening of the circuit breaker.
  • the main interrupter contacts themselves are used as the valve to cause subsequent operation of the auxiliary contacts.
  • the invention further provides a time delay between the operation of the auxiliary contacts and the main interrupting contacts by controlling the size of an orifice in the pressure control structure of the auxiliary contacts Which controls the auxiliary operating pressure.
  • a primary object of this invention is to provide a novel plural contact pneumatically operated circuit breaker.
  • Another object of this invention is to eliminate the valve required for time delay operation of a second pair of contacts in a pneumatically operated circuit interrupter.
  • a further object of this invention is to provide a novel multi-contact interrupter which is pneumatically operated wherein the main interrupter. contacts act as a control valve for initiating subsequent operation of auxiliary contacts.
  • a metallic container 1 is carried from a support by the pillar insulator 2 which is partially shown.
  • Container 1 is filled with a gas under pressure such as compressed air, and carries both a main interrupting pair of contacts and an auxiliary pair of interrupting contacts which are, as will be seen hereinafter, connected in series with a resistor where the series combination of the auixiliary contacts and resistor are connected in parallel with the main interrupter contacts.
  • the main interrupter contacts are comprised of a stationary contact 3 and a movable contact 4.
  • the stationary contact 3 is generally formed of a hollow cylinder to be described more fully hereinafter, and is carried at the end of terminal bushing 5 which extends outwardly of the interrupter chamber 1 to serve as one terminal of the circuit interrupter.
  • Movable contact 4 is constructed in a standard manner of a hollow cylinder having spring biased contact fingers, such as contact finger 6, biased toward engagement with protruding stationary contacting portion 7 of stationary contact 3.
  • the right-hand end of the cylinder forming movable contact 4 is then electrically connected to casing 8 which is connected to container 1 in an airtight manner, and is electrically connected to movable contact 4 by a brush-type connection, including brushes such as brush 10.
  • the housing 1 is electrically connected to the movable contact 4, and can form the opposite terminal of the circuit interrupter.
  • connection between movable contact 4 and housing portion 8 is also an airtight connection, as by providing gasketing by circular gasket 9 which is arranged in any standard manner so that contact 4 can move with respect to housing portion 8, and yet form a pressure-tight seal between the two members.
  • movable contact 4 is provided with an outwardly flanged annular portion 11 which seats against a ring-shaped seating member 12, which is preferably of flexible material, whereby an airtight connection is formed between flange 11 and ring 12 to isolate the high pressure gas in container 1 from the centre of the hollow movable contact 4.
  • Movable contact 4 as indicated, has a hollow opening therein which communicates to atmospheric pressure, or to the pressure external of the interrupter chamber 1 through the centre of easing member 8, and thence through a check valve mechanism 13.
  • the check valve communicates with open air when the movable contact is in the closed position shown, and is closed when the movable contact is moved to a fully open position. Accordingly, in the closed contact position, the internal portion of the movable contact 4 is at external air pressure, since it communicates with external air through the centre of casing member 8 which is connected to check valve 13. V
  • the operating mechanism for movable contact 4 includes a piston 14 which is movable within cylinder 15. Piston 14 is connected to movable contact 4 by a connecting rod 16 and rod connecting head 17 which is connected to contact 4 by a spoke-type means which permits continued communication between the central portions of contact 4 and the central portions of member 8.
  • the movable contact 4 is biased-toward a contact engaged position by means of biasing spring 18 which biases piston 14 to its upper or left-hand position with respect to cylinder 15.
  • the stationary contact 3 has been described above as being comprised of a hollow cylinder, and internally carries a piston 20 which is connected to the movable auxiliary contact 21.
  • Movable auxiliary contact 21 is movable into and out of engagement with respect to stationary auxiliary contact 22 which is electrically connected to one end of resistor 23.
  • Resistor 23 is mounted in any desired manner with respect to container 1, and has its upper end electrically connected to extending casing portion 24, which in turn is electrically connected to container 1 in an airtight manner.
  • the lower portion of piston is normally exposed to the high pressure within casing 1 by means of orifice in contact 3, while the area above piston 20 communicates with the central portion of movable contact 4 through the orifice 26, it being noted that movable auxiliary contact 21 passes through the movable contact 3 in an airtight manner. Therefore, the portion above piston 20 is connected to the pressure external of the container 1 when the main interrupting contacts 3 and 4 are closed.
  • the auxiliary contacts 21 and 22 are biased to a disengaged position by the biasing spring 27 which is positioned within upper chamber 28.
  • Spring 27 is so dimensioned, however, that when the main interrupter contacts 3 and 4 are closed, and the pressure of chamber 28 is equal to the pressure external to container 1, the relatively high pressure in lower chamber 29, which is equal to the pressure within container 1, will force piston 20 upwardly and against the biasing force of spring 27.
  • compressed air or a high pressure medium
  • the conduit 19 to drive piston 14 downwardly and, thus, move contact 4 to the right and toward a disengaged position.
  • the compressed air or gas contained within container 1 will then flow through the centre of movable contact 4, since the valve formed between flange 11 and ring 12 is now released, and the are drawn between contacts 3 and 4 will be subjected to a strong gas blast. As previously discussed, this gas blast will pass through the hollow contact cylinder 4, chamber portion 8, and out through the open check valve 13.
  • orifice 26 of chamber 28 is exposed to the relatively high pressure within container 1. Accordingly, the pressure within chamber 28 will increase at a rate dependent upon the size of orifice 26 until a point is reached where the pressure on top of piston 20 due to spring 27 and the increasing pressure due to fluid passing through orifice 26, is equal to the pressure in container 29, at which point contacts 21 and 22 begin to seprote.
  • the air pressure on both sides of the cylinder 20 is equal, it will be clear that the movable contact 21 will be biased under the influence of spring 27 alone, the time delay for this opening operation being determined by orifice 26.
  • the movable contact 4 and stationary contact 3 operate as a control valve for initiating the operation of the auxiliary parallel contacts 21 and 22, and auxiliary valve means is not required.
  • conduit 19 is connected to low pressure, as by opening a valve which communicates between the conduit and the pressure external of container 1 whereby the spring 13 will drive piston 14 to the left to close movable contact 4.
  • the compressed air in conduit 30 may be exhausted through conduit 31 of check valve 13 whereby the check 4 valve is opened so that the area internal of movable contact 4 is connected to external pressure.
  • the structure presented herein provides a valve action for contacts 3 and 4 which is such that the main interrupter contacts will open, and after a predetermined time delay, the auxiliary contacts open to remove resistor 23 from the circuit.
  • the main interrupter contacts close, and after a predetermined time delay, the resistor 23 is connected in the circuit by the subsequent closing of auxiliary contacts 21 and 22.
  • Operating device for an auxiliary breaking gap in an air blast circuit breaker comprising a container permanently filled with compressed air, a main breaking gap enclosed in said container and having a stationary con tact and a movable contact, an outlet channel in said movable contact, means mounted on said stationary contact for closing said outlet channel in the closed position of the main breaking gap, an auxiliary breaking gap connected in parallel with the main breaking gap including a movable contact, a piston, the movable contact of said auxiliary breaking gap being connected to said piston, a cylinder in which the piston is slidable, means for connecting the space within the cylinder on one side of the piston, in the closed position of the main breaking gap, with the open air, said connecting means including a connecting channel arranged in the stationary contact of the main breaking gap and said outlet channel, said connecting means in the open position of the main breaking gap connecting said space with the container through said connecting channel.

Description

Dec. 19, 1961 H. FORWALD 3,014,111
PNEUMATIC OPERATING MEANS FOR CIRCUIT BREAKERS Filed Nov. 19, 1959 Patented Dec. 19, 1961 3,014,111 PNEUMATIC OPERATING MEANS FOR CIRCUIT BREAKERS Haakon Forwald, Luclvika, Sweden, assignor to Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden, a
corporation of Sweden Filed Nov. 19, 1959, Ser. No. 854,182 Claims priority, application Sweden Nov. 24, 1958 3 Claims. (Cl. 200-148) This invention relates to circuit breakers which may be of the air blast type, and more specifically relates to a pneumatic operating structure for a circuit breaker wherein the main interrupting contacts operate as a pneumatic valve for controlling the operation of auxiliary contacts associated with the main interrupting contacts.
Circuit breakers of the air blast type which utilize more than one pair of contacts are well known in the art wherein the contacts may be series connected interrupter contacts, or parallel connected contacts where one of the parallel connected contacts is connected in series with a resistor, or, in the case of oil circuit breakers, where there is a pressure generating set of contacts in series with the main interrupting contacts. Generally in these plural contact devices, the contacts operate in a predetermined sequence. Since the contacts are pneumatically actuated, this requires the use of a valve for delaying the operation of the last set of contacts to be operated.
The principle of the present invention is to utilize the first operated interrupter contacts as a pneumatic valve for delivering operating pressure to the subsequently operated contacts associated with the main interrupter contacts.
A specific embodiment of the invention is directed to the type of pneumatic circuit breaker wherein a resistor is connected in parallel with the main interrupter contacts. Included in the parallel resistor circuit there is an auxiliary pair of contacts adapted to be disengaged after the main interrupter contacts extinguish the arc during the opening of the circuit breaker.
In the past, operation of the auxiliary contacts after main arc interruption was initiated by a valve mechanism which, after a predetermined delay, introduced operating pressures to the auxiliary contacts.
In accordance with the present invention, the main interrupter contacts themselves are used as the valve to cause subsequent operation of the auxiliary contacts. The invention further provides a time delay between the operation of the auxiliary contacts and the main interrupting contacts by controlling the size of an orifice in the pressure control structure of the auxiliary contacts Which controls the auxiliary operating pressure.
Accordingly, a primary object of this invention is to provide a novel plural contact pneumatically operated circuit breaker.
Another object of this invention is to eliminate the valve required for time delay operation of a second pair of contacts in a pneumatically operated circuit interrupter.
A further object of this invention is to provide a novel multi-contact interrupter which is pneumatically operated wherein the main interrupter. contacts act as a control valve for initiating subsequent operation of auxiliary contacts.
These and other objects of the invention will become more apparent when taken in conjunction with the description of the drawing which shows a cross-sectional view of a typical interrupting chamber of a pneumatically operated circuit breaker adapted in accordance with the present invention.
Referring to the drawing, a metallic container 1 is carried from a support by the pillar insulator 2 which is partially shown. Container 1 is filled with a gas under pressure such as compressed air, and carries both a main interrupting pair of contacts and an auxiliary pair of interrupting contacts which are, as will be seen hereinafter, connected in series with a resistor where the series combination of the auixiliary contacts and resistor are connected in parallel with the main interrupter contacts.
The main interrupter contacts are comprised of a stationary contact 3 and a movable contact 4. The stationary contact 3 is generally formed of a hollow cylinder to be described more fully hereinafter, and is carried at the end of terminal bushing 5 which extends outwardly of the interrupter chamber 1 to serve as one terminal of the circuit interrupter.
Movable contact 4 is constructed in a standard manner of a hollow cylinder having spring biased contact fingers, such as contact finger 6, biased toward engagement with protruding stationary contacting portion 7 of stationary contact 3. The right-hand end of the cylinder forming movable contact 4 is then electrically connected to casing 8 which is connected to container 1 in an airtight manner, and is electrically connected to movable contact 4 by a brush-type connection, including brushes such as brush 10. Accordingly, the housing 1 is electrically connected to the movable contact 4, and can form the opposite terminal of the circuit interrupter.
The connection between movable contact 4 and housing portion 8 is also an airtight connection, as by providing gasketing by circular gasket 9 which is arranged in any standard manner so that contact 4 can move with respect to housing portion 8, and yet form a pressure-tight seal between the two members.
The left-hand end of movable contact 4 is provided with an outwardly flanged annular portion 11 which seats against a ring-shaped seating member 12, which is preferably of flexible material, whereby an airtight connection is formed between flange 11 and ring 12 to isolate the high pressure gas in container 1 from the centre of the hollow movable contact 4. Movable contact 4 as indicated, has a hollow opening therein which communicates to atmospheric pressure, or to the pressure external of the interrupter chamber 1 through the centre of easing member 8, and thence through a check valve mechanism 13.
The check valve communicates with open air when the movable contact is in the closed position shown, and is closed when the movable contact is moved to a fully open position. Accordingly, in the closed contact position, the internal portion of the movable contact 4 is at external air pressure, since it communicates with external air through the centre of casing member 8 which is connected to check valve 13. V
The operating mechanism for movable contact 4 includes a piston 14 which is movable within cylinder 15. Piston 14 is connected to movable contact 4 by a connecting rod 16 and rod connecting head 17 which is connected to contact 4 by a spoke-type means which permits continued communication between the central portions of contact 4 and the central portions of member 8. The movable contact 4 is biased-toward a contact engaged position by means of biasing spring 18 which biases piston 14 to its upper or left-hand position with respect to cylinder 15.
In order to operate movable contact 4 to a disengaged position against the biasing force of spring 18, compressed air is introduced above the top of piston 14 through the conduit 19 which is controllably connected to any conventional source of high pressure medium.
The stationary contact 3 has been described above as being comprised of a hollow cylinder, and internally carries a piston 20 which is connected to the movable auxiliary contact 21. Movable auxiliary contact 21 is movable into and out of engagement with respect to stationary auxiliary contact 22 which is electrically connected to one end of resistor 23. Resistor 23 is mounted in any desired manner with respect to container 1, and has its upper end electrically connected to extending casing portion 24, which in turn is electrically connected to container 1 in an airtight manner.
The lower portion of piston is normally exposed to the high pressure within casing 1 by means of orifice in contact 3, while the area above piston 20 communicates with the central portion of movable contact 4 through the orifice 26, it being noted that movable auxiliary contact 21 passes through the movable contact 3 in an airtight manner. Therefore, the portion above piston 20 is connected to the pressure external of the container 1 when the main interrupting contacts 3 and 4 are closed.
The auxiliary contacts 21 and 22 are biased to a disengaged position by the biasing spring 27 which is positioned within upper chamber 28. Spring 27 is so dimensioned, however, that when the main interrupter contacts 3 and 4 are closed, and the pressure of chamber 28 is equal to the pressure external to container 1, the relatively high pressure in lower chamber 29, which is equal to the pressure within container 1, will force piston 20 upwardly and against the biasing force of spring 27.
In operation, in order to open the circuit breaker, compressed air, or a high pressure medium, is connected to the top of piston 14 through the conduit 19 to drive piston 14 downwardly and, thus, move contact 4 to the right and toward a disengaged position. The compressed air or gas contained within container 1 will then flow through the centre of movable contact 4, since the valve formed between flange 11 and ring 12 is now released, and the are drawn between contacts 3 and 4 will be subjected to a strong gas blast. As previously discussed, this gas blast will pass through the hollow contact cylinder 4, chamber portion 8, and out through the open check valve 13. When the movable contact 4 finally reaches a fully disengaged position, and the top of piston 14 passes channel of check valve 13, the check valve will close to prevent further loss of compressed air or gas from container 1, and at this point the main are between contacts 3 and 4 is extinguished. It is to be noted that when piston 14 passes orifice 30, the compressed air from channel 19 is placed in communication with the orifice and thereby closes the valve.
At the time the contacts 3 and 4 disengage, orifice 26 of chamber 28 is exposed to the relatively high pressure within container 1. Accordingly, the pressure within chamber 28 will increase at a rate dependent upon the size of orifice 26 until a point is reached where the pressure on top of piston 20 due to spring 27 and the increasing pressure due to fluid passing through orifice 26, is equal to the pressure in container 29, at which point contacts 21 and 22 begin to sepaarte. When the air pressure on both sides of the cylinder 20 is equal, it will be clear that the movable contact 21 will be biased under the influence of spring 27 alone, the time delay for this opening operation being determined by orifice 26.
Accordingly, it is seen that the movable contact 4 and stationary contact 3 operate as a control valve for initiating the operation of the auxiliary parallel contacts 21 and 22, and auxiliary valve means is not required.
In order to close the circuit breaker after the above noted opening operation, the conduit 19 is connected to low pressure, as by opening a valve which communicates between the conduit and the pressure external of container 1 whereby the spring 13 will drive piston 14 to the left to close movable contact 4. At the same time, the compressed air in conduit 30 may be exhausted through conduit 31 of check valve 13 whereby the check 4 valve is opened so that the area internal of movable contact 4 is connected to external pressure.
Since the pressure within contact 4 is thereby reduced, the relatively high pressure of chamber 28 which carries auxiliary movable contact 21 is decreased at a rate again depending upon the size of orifice 26 until such time that the pressure within chamber 29 is sufiicient to drive the movable contact 21 toward its engaged position against the biasing force of spring 27 and the reduced pressure within chamber 28. Therefore, the novel valve action formed by contacts 3 and 4 for operation of auxiliary contacts 21 and 22 operates to close the contacts after a predetermined time delay.
Accordingly, it will be seen that the structure presented herein provides a valve action for contacts 3 and 4 which is such that the main interrupter contacts will open, and after a predetermined time delay, the auxiliary contacts open to remove resistor 23 from the circuit. During contact closing, the main interrupter contacts close, and after a predetermined time delay, the resistor 23 is connected in the circuit by the subsequent closing of auxiliary contacts 21 and 22.
Although this invention has been described with respect to its preferred embodiments it should be understood that many variations and modifications will now be obvious to those skilled in the art, and it is preferred, therefore, that the scope of this invention be limited not by the specific disclosure herein but only by the appended claims.
What is claimed is:
1. Operating device for an auxiliary breaking gap in an air blast circuit breaker comprising a container permanently filled with compressed air, a main breaking gap enclosed in said container and having a stationary con tact and a movable contact, an outlet channel in said movable contact, means mounted on said stationary contact for closing said outlet channel in the closed position of the main breaking gap, an auxiliary breaking gap connected in parallel with the main breaking gap including a movable contact, a piston, the movable contact of said auxiliary breaking gap being connected to said piston, a cylinder in which the piston is slidable, means for connecting the space within the cylinder on one side of the piston, in the closed position of the main breaking gap, with the open air, said connecting means including a connecting channel arranged in the stationary contact of the main breaking gap and said outlet channel, said connecting means in the open position of the main breaking gap connecting said space with the container through said connecting channel.
2. Operating device according to claim 1, in which the cylinder is positioned in the stationary contact of the main breaking gap.
3. Operating device according to claim 1, including variable throttling means in the connecting channel.
References Cited in the file of this patent UNITED STATES PATENTS 2,665,351 Forwald Jan. 5, 1954 2,748,226 MacNeill May 29, 1956 2,757,261 Lingal July 31, 1956 2,773,484 Peek Dec. 11, 1956 2,824,937 Strom Feb. 25, 1958 FOREIGN PATENTS 582,599 Great Britain Nov. 21, 1946 933,819 Germany Oct. 6, 1955 167,384 Australia Apr. 6, 1956 1,186,221 France June 6, 1957 1,042,715 Germany Nov. 6, 19 3
US854182A 1958-11-24 1959-11-19 Pneumatic operating means for circuit breakers Expired - Lifetime US3014111A (en)

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CH (1) CH373445A (en)
DE (1) DE1088581B (en)
FR (1) FR1241059A (en)
GB (1) GB890535A (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3433913A (en) * 1965-07-28 1969-03-18 Westinghouse Electric Corp Gas-blast circuit interrupter

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH386530A (en) * 1960-09-07 1965-01-15 Asea Ab Compressed air switch with a container which is arranged at high voltage potential and is constantly filled with compressed air
DE1261930B (en) * 1961-03-23 1968-02-29 Liebknecht Transformat High-voltage gas switch
DE1212189B (en) * 1962-11-09 1966-03-10 Bbc Brown Boveri & Cie Pulse-like switching device for compressed gas switch
GB1052905A (en) * 1963-04-10

Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB582599A (en) * 1944-07-07 1946-11-21 English Electric Co Ltd Improvements in electric circuit breakers
US2665351A (en) * 1951-02-09 1954-01-05 Asea Ab Arrangement in air blast circuit breaker provided with damping resistance
DE933819C (en) * 1953-10-23 1955-10-06 Liebknecht Transformat Arrangement for switching off the protective resistors of high-voltage switches with compressed gas drive
US2748226A (en) * 1953-02-26 1956-05-29 Westinghouse Electric Corp Compressed-gas circuit interrupter
US2757261A (en) * 1951-07-19 1956-07-31 Westinghouse Electric Corp Circuit interrupters
US2773484A (en) * 1952-12-27 1956-12-11 Allis Chalmers Mfg Co Pneumatically operated circuit breaker with closing valve cutoff switch
US2824937A (en) * 1954-12-30 1958-02-25 Westinghouse Electric Corp Circuit interrupters
DE1042715B (en) * 1957-06-07 1958-11-06 Bbc Brown Boveri & Cie Compressed air switch with circuit breakers and voltage disconnection points
FR1186221A (en) * 1956-06-07 1959-08-18 Westinghouse Electric Corp Pneumatic switch

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB582599A (en) * 1944-07-07 1946-11-21 English Electric Co Ltd Improvements in electric circuit breakers
US2665351A (en) * 1951-02-09 1954-01-05 Asea Ab Arrangement in air blast circuit breaker provided with damping resistance
US2757261A (en) * 1951-07-19 1956-07-31 Westinghouse Electric Corp Circuit interrupters
US2773484A (en) * 1952-12-27 1956-12-11 Allis Chalmers Mfg Co Pneumatically operated circuit breaker with closing valve cutoff switch
US2748226A (en) * 1953-02-26 1956-05-29 Westinghouse Electric Corp Compressed-gas circuit interrupter
DE933819C (en) * 1953-10-23 1955-10-06 Liebknecht Transformat Arrangement for switching off the protective resistors of high-voltage switches with compressed gas drive
US2824937A (en) * 1954-12-30 1958-02-25 Westinghouse Electric Corp Circuit interrupters
FR1186221A (en) * 1956-06-07 1959-08-18 Westinghouse Electric Corp Pneumatic switch
DE1042715B (en) * 1957-06-07 1958-11-06 Bbc Brown Boveri & Cie Compressed air switch with circuit breakers and voltage disconnection points

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3433913A (en) * 1965-07-28 1969-03-18 Westinghouse Electric Corp Gas-blast circuit interrupter

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CH373445A (en) 1963-11-30
GB890535A (en) 1962-03-07
FR1241059A (en) 1960-09-09
DE1088581B (en) 1960-09-08

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