US2885514A - Air-blast switch with auxiliary point of interruption for shunt resistances - Google Patents

Description

United States Patent AIR-BLAST SWITCH WITH AUXILIARY POINT OF INTERRUPTION FOR SHUNT RESISTANCES Hans Thommen, Baden, Switzerland, assignor to Aktiengesellschaft Brown, Boveri & Cie, Baden, Switzerland, a joint-stock company Application April 10, 1956, Serial No. 577,283

Claims priority, application Switzerland April 14, 1955 5 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 the so-called air blast type which include one or more series arranged sets of contacts, at least one contact of each set 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 are 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 been known to connect an electrical resistance in shunt, i.e. in parallel 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 of 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, in some situations where extinction of the are at the main contact set becomes difiicult, 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, it is 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 the main circuit breaker chamber and the time of its arrival 2,885,514 Patented May 5, 1959 ICC 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. I

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 disconnect the paralleling resistance. In this manner, there is very little in the way of a delay factor between the re spective openings of the main and auxiliary points of interruption. However, such an arrangement does exhibit a dynamic air pressure characteristic which may unfavorably affect the disconnecting power of the breaker, especially, its maximum disconnecting capacity when it appears necessary to use throttle elements. 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 most convenient place in which to locate the auxiliary point of interruption.

In accordance with the present invention, two advantages result. In the first place, it becomes impossible to disconnect the paralleling resistance at the auxiliary point of interruption until the current ceases to flow through the circuit breaker main contacts, and secondly the auxiliary point of interruption functions immediately upon termination of the current. That is, there is no delay period involved. The advantages stem from a new inventive concept, namely in the use of a magnetic action controlled directly by flow of the power current to the circuit breaker to be interrupted for operating the aux iliary point of interruption to disconnect the resistance. As long as current flows through the main contacts of the circuit breaker, the magnetic action derived from it prevents disconnection of the paralleling resistance. As soon as the magnetic action ceases, which occurs when the circuit breaker current ceases, the paralleling resistance becomes disconnected. Preferably, the pressure air available for actuating the main conatcts of the 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 etfective during current flow through the circuit breaker, acting as a block or lock to prevent the pressure air from being applied to the auxiliary point of interruption. One embodiment of the invention to be described comprises a simple iron circuit in the form of a ring placed around the conductor carrying the current to the circuit breaker main contacts. A portion of this iron ring is interrupted by an armature section, and the force exerted magnetically on this armature section during the time that current flows in the conductor is applied via lever action and an auxiliary spring-derived force to a blocking device at the auxiliary point of interruption which prevents a counterforce derived from the pressure air from disconnecting the paralleling resistance. A modified embodiment, also to be described, utilizes the magnetic force exerted on the armature section of the iron ring to maintain a release latch in position. When the current ceases to flow in the conductor leading to the circuit breaker, the magnetically derived force also ceases thus releasing the latch and permitting the force present in the pressure air to separate the contacts at the auxiliary point of interruption by overcoming a counteracting spring derived force.

Preferably, the arrangement according to the invention is such that it will be caused to function from a specific amplitude of load current since in the disconnection of small current potentials the shunt resistances are, in general, not required so that an opening of the auxiliary point of interruption is not allowed before the disconnection is completed. For example, the apparatus according to the invention can be adjusted to function at the minimum operating current. However, it can be made to operate at higher or lower values of such current, and the necessary adjustment can be efifected by Variation in the amount of spring-derived force utilized to supplement the force derived magnetically and/ or by adjustment in the position of the armature section of the magnetic unit itself.

In lieu of placing a magnetic, iron circuit about the conductor carrying current to the circuit breaker it is also possible to use a short-circuit loop of at least one turn placed about the conductor. This loop is constructed in such manner that it possesses movable webs which are spread apart by the action of the current, "the mechanical force derived by such spreading being utilized as a counterforce to prevent the pressure air derived force from opening the auxiliary point of interruption.

The foregoing objects and advantages inherent in the invention will become more apparent from the following description of exemplary embodiments and irom the appertaining drawings. In the latter, Fig. 1 is a view in vertical section through a typical form of gas blast circuit breaker having one set of main contacts, a paralleling resistance being situated in a housing located to the side of the housing containing the main circuit breaker contacts, and the magnetically derived force being established by lever action and a supplementing spring action which, so long as the lever action maintains, prevents the paralleling resistance from being disconnected.

Fig. 2 is a view similar to Fig. 1 but eliminating the circuit breaker itself for simplification, and illustrating an arrangement wherein the magnetically derived force working through lever action is used to maintain a release latch in its locked position.

With reference now to Fig. 1 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 member 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 desiredto separate the main contacts, pressure air is introduced into the hollow column 1 flowing upwardly and exerting pressure against the underside of fiange 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 flow through the opening around all sides of the nose of pin contact member 2 and upwardly through the sleeves7 and 8 and member 6 to the exterior. As the 'airflows through opening 10 it bathes the are, 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 14. A contact pin 19, 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 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 also of electrically conductive material 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 .32 is biased in the downward position, that is in the direction of contact pin 19, by a helical loading spring 25 located within cylinder 23 the spring 25 being under compression, having one end bearing against plate 22 and the opposite end bearing against the top end closure wall of cylinder 23. Working within the spring 25 and bearing against plate 22 is a depending shaft portion 26 of a lever 27 connected pivotally at 28 at one end to the upper end closure wall of cylinder 23. The opposite, free end of lever 27 is connected to an armature element 29 in the form of a bar of magnetic material which extends across but spaced from the ends of the legs of a U-shaped laminated assembly 30 of magnetic material surrounding the conductor. So long as current flows through conductor 12, a magnetic field is set up in the magnetic assembly which tends to pull the armature section 29 inward toward conductor 12 and hence shorten the length of the rectangular magnetic path around the assembly which includes armature 29 and the air gaps between the latter and the ends of the legs of the U- shaped component 30. So long as this condition exists, the corresponding downward pull on the free end of lever 27 supplemented by the biasing force of spring 25 is snflicient to hold piston plate 22 engaged with pin contact 19 against the counterforce exerted upwardly at the underside of plate 22 by the pressure air which is admitted into casing 14 at the bottom of the latter from the interior of the main column 1 of the circuit breaker through a connecting conduit 31 which connects with the interior of sleeve 20, the air flowing upward through sleeve 20 and through one or more apertures 18a in plate 18 located adjacent pin contact 19. As soon as the arc has been extinguished at the main contacts, current flow ceases in conductor 12, the magnetic force acting inward on armature section 29 ceases, the force exerted by lever 27 ceases and the spring 25 is then no longer able to counteract the opposing force on piston plate 22 from the pressure of the air applied to the underside of plate 22 with the consequence that plate 22 is lifted and separated from pin contact 19 and resistance 13 is disconnected from its previous parallel association with the main contacts of the circuit breaker since the only path of connection from the upper terminal end of resistance 13 to conductor 12 is through plate 18, pin contact 19, plate piston 22 and cylinder 23. When the circuit breaker operation is completed and pressure air removed from the interior of the column 1, the main contacts close and the paralleling resistance 13 is reconnected because of the downward movement of plate 22 by the restoring force established in spring 25 by its compression.

In the embodiment of the invention illustrated in Fig. 2, the arrangement of casing 14, resistance winding 13, plate 18, contact pin 19, piston plate 22, cylinder 23, and biasing spring 25, are similar in arrangement and function to corresponding elements in Fig. 1 and hence have been assigned reference numerals but with primes added to the former for purposes of distinction. This embodiment differs from that of Fig. l in that the lever 27 is replaced by a latch pin 32 which protrudes laterally through a side wall of cylinder 23' at a level substantially equal to the top surface of plate piston 22 so as to prevent the latter from raising so long as the pin 32 occupies the position shown in the drawing. Pin 32 is loaded by a compression spring 33 surrounding the same in such direction as to cause its withdrawal from the interior of cylinder 23 thus releasing the plate piston 22' for movement in the upper direction, but the pin 32 is prevented from moving outwardly from the cylinder 23' by means of one arm 34 of a lever pivotally mounted at 35 on the cylinder 23', the arm 34 bearing against the head of pin 32 by reason of a connection of the other arm 36 of this lever to one end of another lever 37 pivotally mounted at its opposite end at 38 on the conductor 12', the armature section 29 of the magnetic ring being attached to the lever 37 at a point intermediate the ends thereof. So long as current flows through conductor 12, the magnetic force in the ring assembly 30 functions to draw the armature section 29' downwardly and hence also move the lever 37 downwardly thus rocking the lever arm 34 clockwise so as to press the pin 32 inwardly to the position shown in Fig. 2. When current ceases to flow in conductor 12 the magnetic action likewise ceases and hence also the downward pull on lever 37 with the result that the biasing spring 33 is then able to shift pin 32 to the right by such a distance as will withdraw the end of the pin within the wall of cylinder 23'. The pressure air flowing through casing 14 and being applied against the underside of plate 22' is then able to move plate 22' in the upward direction overcoming the biasing force of the spring 25' and hence causing separation of plate 22' from contact pin 19', thereby to disconnect the resistance 13' from its parallel association with the main contacts of the circuit breaker.

In conclusion it is to be understood that the embodiments of the invention above described are to be considered typical rather than exhaustive of all the constructions possible and hence various changes may be made in the construction and arrangement of parts without departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. In a gas blast circuit breaker, the combination comprising a hollow insulating column containing a set of normally closed main contacts and which are actuated to open position by application of pressure gas thereto, a conductor connected to one of said main contacts and adapted to carry the load current controlled by the circuit breaker, a casing of insulating material disposed adjacent said column, a resistance element and a set of normally closed auxiliary contacts actuatable to open position by pressure gas arranged in series and located within said casing, said series connected resistance element and set of auxiliary contacts being arranged in parallel to said set of main contacts, said set of auxiliary contacts when closed preventing any flow of pressure gas through said casing, means for introducing pressure gas into said column and casing and means deriving a force from the current flowing in said conductor and applying the same to maintain said set of auxiliary contacts closed and in counteraction to an opening force applied thereto by said pressure gas until after said main contacts have been opened by said pressure gas.

2. A gas blast circuit breaker as defined in claim 1 wherein one of said auxiliary contacts is constituted by a plate member slidable in a cylinder and loaded into engagement with the other auxiliary contact by a spring, said plate member being actuatable by the pressure gas and serving also as a valve to permit flow of pressure gas through said casing upon separation of said auxiliary contacts, and said force derived from the current flowing in said conductor is applied to said plate member to prevent any movement thereof in a direction away from the other auxiliary contact.

3. A gas blast circuit breaker as defined in claim 2 wherein said means deriving said force from the current flowing in said conductor is constituted by a magnetizable iron circuit surrounding said conductor, said iron circuit including an air gap and an armature movable in said air gap, and means transmitting said force through said armature to said plate member.

4. A gas blast circuit breaker as defined in claim 3 wherein said means transmitting said force through said armature to said plate member is constituted by a pivotally mounted lever applying pressure directly to said plate member.

5. A gas blast circuit breaker as defined in claim 3 wherein said means transmitting said force through said armature to said plate member is constituted by a latch member adapted to engage and be disengaged from said plate member.

References Cited in the file of this patent UNITED STATES PATENTS Stone Feb. 24, 1920 Thommen Nov. 9, 1948

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