US2892913A - Air blast switch with auxiliary point of interruption for shunt resistance - Google Patents

Description

June 30, 1959 H. THOMMEN AIR BLAST SWITCH WITH AUXILIARY POINT OF INTERRUPTION FOR SHUNT RESISTANCE Filed April 17, 1958 0v a M 3 7- I m 3 3 q e5 I. Z 3 3 W Z lo mm m 0 W v 1, H \w 38k Q 5 z umw m mm a/ v PNN j m f II 3 Z l 7 w HE. H \H\\\ \\H QM .b 8 A,

INVENTOR Ha r1 5 Thom m e n BY I Am, JAW & PM ATTORNEYS United States Patent G AIR BLAST SWITCH WI H OF INTERRUPTIQN FOR SHUNT RESISTANCE Hans Thornmen, Baden, Switzerland, assignor to Aktiengesellschaft Brown, Boveri 8: Cie, Baden, Switzerland, a company of Sweden,

Application April 17, 1958, Serial No..729,198, Claims priority, application Switzerland April23, 1957 Claims. (Cl'. 200148) This invention relates to electric circuit breakers for interrupting considerable high electrical power usually at considerably high voltage, and in particular to those of theso-called air blast type which include one or more seriesarra'nged sets of contacts, at least one contact of cachset being movable relative to the other in the direction of flow of the compressed gas, usually air, to separate the contacts, and at least one contact of each set being a. hollow contact, so that the compressed gas, by

flowing into the hollow contact, causes the arc formed initially upon separation of the contacts to be bathed on all sides thus facilitating its extinction and a rapid opening of the electrical circuit.

For, improving the circuit breaking characteristic by potential control and for preventing a rapid rise in the return voltage following an extinction of the are it has heenknown to connect an electrical resistance in shun i.e. inparallel with each set of contacts on the breaker. Each such resistance is not permanently so connected but rather remains connected only so long as the circuit breaker contacts with which it is associated are engaged, i.e. closed. If the resistances were left connected across the high voltage line after the contacts of the circuit breaker open it is most probable that they would become overloaded and hence possibly lead to a short circuit ofv the high voltage line. Consequently, various expedients involving an auxiliary point of interruption have been developed for disconnecting the resistances as soon as the circuit breaker contacts have been separated and the current interrupted. It has been known, for example, to utilize the pressure air provided principally for disengaging the one or more series connected sets of circuit breaker contacts, in an auxiliary manner for also effecting the disconnection of the auxiliary point of interruption for each resistance. The pressure air is supplied to.the auxiliary point of interruption only after the movable contact member of the main, power breaking contact set has completed its stroke in the opening direction, i.e. it must have completed movement through such a distance as will be required to interrupt the power current. Upon completing its opening stroke, an aperture. is uncovered leading from the chamber in which the main contact set is located through a conduit to the auxiliary point of interruption by which the paralleling resistance. is then disconnected. Such an arrangement suffers from the disadvantage that it is based upon a predetermined displacement of the movable contact member of the main contact set wherein it becomes possible, insome situations where extinction of the are at the main contact set becomes difficult, to actually disconnect the paralleling resistance before the arc has been completely extinguished. Actually the most favorable operating condition is obtained when the paralleling resistance remains in the circuit until arc extinction is complete. Otherwise, itis necessary to reduce the maximum breaking capacity of; the switch. Another disadvantage is that a delay period must elapse between release of the pressure air from 2,892,913 Patented June 30, 1.959

2 the main circuit breaker chamber and the time of its arrival at the auxiliary point of interruption. Hence, retardations of a few half cycles of the alternating power can arise which requires a stronger construction for the resistances.

It has also been suggested to arrange the auxiliary point of interruption (for the paralleling resistance) in the air exhaust duct from the main point of interruption at the main contacts. The pressure air after flowing past the disengaging main contacts then functions to disconmeet the paralleling resistance. In this manner, there is very little in the way of a delay factor between the respective openings of the main and auxiliary points of interruption. However, such an arrangement does exhibit a dynamic airpressure characteristic which may unfavorably affect the disconnecting power of the breaker. Also, such an arrangement limits the freedom of choice in locating the auxiliary point of interruption since the pressure air discharge passage may not be the rnost convenient place in which to locate the auxiliary point of interruption.

In my co-pending application Serial No. 577,283, filed April 10, 1956, an improved arrangement is disclosed for opening the auxiliary point of interruption thereby to disconnect the paralleling resistance, such arrangement making it impossible to disconnect the paralleling resistance until current ceases to flow through the circuit breaker main contacts. Furthermore, such arrangement assures a disconnection of the paralleling resistance immediately upon termination of the current flow, i. e. there is no delay period. In that application, control over the auxiliary point of interruption is effected by means of a magnetic action controlled directly by flow of the power current through the circuit breaker. As long as current flows through the main contacts of the circuit breaker, the magnetic action or force derived from such current effectively prevents disconnection of the paralleling resistance. As soon as the magnetic action or force is no longer present, which occurs when the current through the main contacts of the circuit breaker ceases, the paralleling resistance becomes disconnected. The pressure-air available for actuating the main contacts of the circuit breaker is also utilized in a secondary manner for disconnecting the paralleling resistance at the auxiliary point of interruption, the magnetic action while it is effective during current flow through the circuit breaker, acting as a block or lock to prevent the pressure air from actuating the auxiliary point of interruption.

In accordance with the present invention, essentially the same result is effected but in a somewhat dilferent manner. More specifically, disconnection of the paralleling resistance at the auxiliary point of interruption is made dependent upon current flow through the paralleling resistance itself. As explained previously, the paralleling resistance is connected in parallel with the main contacts of the circuit breaker. When the main contacts are closed, no significant current flow through the paralleling resistance takes place because the closed main contacts establish a very low resistance path in parallel with the resistance. Since current flow through two parallel circuits divides inversely as the ratio of the impedances of such paths, practically all of the current will flow through the closed main contacts. When the main contacts open cutting off the main current and the impedance across the contacts rises, appreciable current will then begin to flow through the paralleling resistance and it is this current which is then used to effect opening of the auxiliary point of interruption and thus disconnect the paralleling resistance at a time subsequent to opening of the main circuit breaker contacts. The advantage of the present arrangement, using current flow through the paralleling resistance as the criterion for opening the auxiliary point of interruption rather than the decrease of the load current in the line in which the main contacts of the circuit breaker are connected is that smaller currents are involved and hence the operating components related to such currents can be made correspondingly smaller, simpler and at less expense.

The foregoing objects and advantages of the invention will become more apparent from the following detailed description of a typical embodiment thereof when considered with the accompanying drawing in which the single figure presented is a vertical longitudinal section through a typical form of gas blast circuit breaker having one set of main contacts, a paralleling resistance being enclosed in a housing located to one side of the housing contain ing the main circuit breaker contacts.

With reference now to the drawing, it will be seen that the circuit breaker unit is of generally conventional construction, including a hollow column 1 of insulating material within which is located a fixed pin contact mernher 2 upstanding centrally within the column, being supported by webs 3 of electrically conductive material connected to an annular plate member 4 also of electrically conductive material and to which plate is connected one of the main conductors 5, the current flow through which is controlled by the circuit breaker assembly. The hollow contact element of the circuit breaker consists of an assembly which includes a stationary annular member 6 of electrically conductive material supported upon insulating column 1, a stationary electrically conductive sleeve 7 depending centrally from tubular member 6 into the interior of column 1, a movable electrically conductive sleeve 8 arranged telescopically upon sleeve 7, the sleeve 8 including also a peripheral flange portion 9 making a sliding fit with the wall of hollow column 1, and a central aperture 10 into which extends the nose end 2a of pin contact member 2. A helical spring 11 surrounding the telescoped sleeves 7 and 8 and bearing downwardly against the flange 9 loads the hollow contact assembly into engagement with the nose of pin contact member 2. This view shows the hollow contact assembly engaged with the pin contact member and hence represents the positions of the components when current is flowing through the circuit breaker contacts from line conductor to line conductor 12 connected to the tubular member 6. When it is desired to separate the main contacts, pressure air is introduced into the hollow column 1 flowing upwardly and exerting pressure against the underside of flange 9 acting as a piston, causing the latter to rise and separate the movable contact assembly from the nose of the fixed pin contact member 2. The pressure air is now able to ilow through the opening around all sides of the nose of pin contact member 2 and upwardly through the sleeves 7 and 8 and member 6 to the exterior. As the air flows through opening 10 it bathes the arc, formed between the contacts upon separation, on all sides helping to extinguish the same.

The resistance element arranged for parallel connection with the main contact members of the circuit breaker is represented by an annular winding 13 of resistance material arranged within a casing 14 of insulating material that is supported in part at the side of column 1 by means of a laterally extending bracket 15. The lower end of resistance winding 13 is connected electrically to conductor 5 by means illustrated schematically as a lead wire 16 and the upper end of winding 13 is connected electrically by lead wire 17 to a transverse plate 18 of electrically conductive material located in the upper end of casing M. A contact pin located centrally on plate 18 and in general. alignment with the longitudinal axis of casing 14 and the opening through a central sleeve 20 on which winding 13 is placed, extends vertically upward through a nozzle opening 21 in the top wall of casing 14 and is adapted to bear against the central portion of a plate 22 of conductive material disposed as a piston in a cylinder 23 arranged atop casing 14, the plate 22 when in contact with pin 19 also being virtually in contact with the upper face of the top wall of casing 14. The pin 19 and plate 22 constitute a set of auxiliary contacts by which the resistance winding 13 is connected or disconnected from its parallel relationship with the set of main contacts 2, 8. Cylinder 23 includes one or more outlet ports 24 for the escape of pressure air as the piston plate 22 is raised. Piston plate 22 is biased in the downward position, that is in the direction of contact pin 19, by helical loading springs 25 located within cylinder 23, the springs 25 being under compression, each spring having one end bearing against plate 22 and the opposite end bearing against a transverse stop 26 projecting inwardly from the inner wall of cylinder 23. The cylinder 23 is constituted by upper and lower sections 23a, 23b of electrically conductive material separated by an intermediate section 230 of electrically insulating material. Also located within cylinder 23 is a solenoid comprising a vertical helical coil 28 having a core or armature 29 slidable therein. The lower end of armature 29 is secured to piston plate 22 and the upper end of armature 29 terminates in a piston 30 slidable within a cylinder 31 arranged atop the end closure wall of cylinder 23.

The upper end of solenoid coil 28 is electrically connected to line conductor 12 and the latter is electrically connected with the member 6 through the upper electrically conductive portion 23a of cylinder 23. The lower end of solenoid coil 28 is electrically connected to piston plate 22 via the electrically conductive cylinder wall portion 23b. Consequently, with the ports occupying the positions indicated in the drawing, is. with the main contacts 2, 8 of the circuit breaker closed, the auxiliary resistance 13 will be connected in parallel with the main contacts. The connecting circuit can be traced from main line conductor 5, through connection 16, auxiliary resistance 13, connection 17, pin contact 19, piston plate 22, and solenoid coil 28 to the other main line conductor 12. However, as previously explained so long as the main contacts 2, 8 are closed there is virtually no current flowing through the auxiliary resistance and solenoid coil 28 and hence there is no upward pull exerted on the solenoid armature 29. So long as this condition exists, the downward force exerted by the loading springs 25 against piston plate 22 is suflicient to hold plate 22 engaged with pin contact 19 against a counter force exerted upwardly at the underside of plate 22 by the pressure air admitted to casing 14 at the bottom of the latter from the interior of the main column 1 of the circuit breaker through a conduit 32 which communicates with sleeve 20, the air flowing upward through sleeve 20 and through one or more apertures 18a in plate 18. The pressure air when introduced in the main column 1 of the circuit breaker initiates separation of the main contacts 2, 8. As soon as contacts 2, 8 separate, the shunt path around resistance 13 is broken and current will now begin to flow through resistance 13 and solenoid coil 28. This causes an upward force to be exerted on armature 29 and plate 22 counter to the force exerted by the loading springs 25, and hence the latter are no longer able to counteract the opposing force on plate 22 from the pressure air applied to the underside of plate 22 with the result that plate 22 is lifted and separated from pin contact 19, and resistance 13 will then be disconnected from its previous parallel association with the main contacts 2, 8. When the circuit breaker operation is completed and pressure air removed from the interior of column 1, the main contacts 2, 8 reclose and the paralleling resistance 13 is reconnected because of the downward movement of plate 22 by the restoring force established in springs 25 by their compression.

it is quite possible that in switching off small currents, there will be insufficient current flow through solenoid I coil 28 to efiect the necessary upward lifting force on plate 22. To ensure disconnection of the paralleling resistance 13 under such circumstances, the lifting force of the cylinder-piston unit 34l31 is employed. As is evident from the drawing, air conduit 32 also extends to the lower end of cylinder 31 below piston 30 and communicates with cylinder 31 through a small orifice 33. After a predetermined time, depending upon the size of orifice 33, sufiicient pressure will build up at the underside of piston 30 to establish the necessary lifting force on piston plate 22 that will result in separation of the latter from the pin contact 19.

In conclusion it is desired to be understood that while the illustrated embodiment represents one practical construction the inventive concept may be incorporated in somewhat diflerent constructions without, however, departing from the spirit and scope of the invention as defined in the appended claims.

For example, instead of utilizing an auxiliary coil to serve as the solenoid winding for actuating the armature connected to the piston plate, the entire auxiliary resistance winding which parallels the main contacts may itself serve as the solenoid coil. Another possible arrangement for effecting disconnection of the auxiliary resistance in response to a flow of current through the latter would be a pawl release.

I claim:

1. In a circuit breaker of the gas blast type, the combination comprising a main point of interruption for the load current passing therethrough defined by a set of main contacts, a resistance element and an auxiliary point of interruption defined by a set of auxiliary contacts connected in series therewith and arranged in parallel with said set of main contacts, said main and auxiliary sets of contacts being normally closed, means for applying pressure gas to said set of main contacts for separating the same, means for applying pressure gas to one of said contacts in said set of auxiliary contacts for separating the same, said pressure gas alone being insuflicient to effect separation of said auxiliary contacts, and means responsive to a flow of current through said resistance element initiated upon separation of the contacts of said main set for producing a force augmenting the force produced by said pressure gas to the extent necessary to effect separation of said auxiliary contacts thereby to disconnect said resistance element.

2. A circuit breaker as defined in claim 1 wherein said means responsive to a flow of current through said resistance element for producing a force augmenting the force produced by said pressure gas is constituted by solenoid having its operating coil connected in series with said resistance element and its armature element connected to that one of said auxiliary contacts to which said pressure gas is applied.

3. A circuit breaker as defined in claim 1 wherein said means responsive to a flow of current through said resistance element for producing a force augmenting the force produced by said pressure gas is constituted by a solenoid, the operating coil of said solenoid being constituted by said resistance element and the armature element of said solenoid being connected to that one of said auxiliary contacts to which said pressure gas is applied.

4. A circuit breaker as defined in claim 1 and which further includes means for producing a second force aug menting the force produced by said pressure gas for separating said auxiliary contacts, said second force producing means being non-electric and having a slowly increasing force characteristic.

5. A circuit breaker as defined in claim 1 and which further includes an auxiliary piston and cylinder unit for producing a second force augmenting the force produced by said pressure gas for separating said auxiliary contacts, said cylinder being provided with a small aperture for admitting the pressure gas at a reduced rate and said piston being connected to that one of said auxiliary contacts to which said pressure gas is applied.

References Cited in the file of this patent UNITED STATES PATENTS 2,125,525 Thommen Aug. 2, 1938 2,581,822 Thommen et al Jan. 8, 1952 FOREIGN PATENTS 538,672 Great Britain Aug. 12, 1941

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