US3129308A

US3129308A - Vacuum circuit breaker having buffering means in relatively stationary electrode structure

Info

Publication number: US3129308A
Application number: US189398A
Authority: US
Inventors: Yokoyama Masami; Kagoshima Toshio
Original assignee: Nippon Electric Co Ltd
Current assignee: NEC Corp
Priority date: 1961-04-22
Filing date: 1962-04-23
Publication date: 1964-04-14
Anticipated expiration: 1981-04-14

Description

April 14, 1964 PRIOR ART v a r i g E MASAMI YOKOYAMA ETAL 3, VACUUM CIRCUIT BREAKER HAVING BUFFERING MEANS IN RELATIVELY STATIONARY ELECTRODE STRUCTURE Filed April 23, 1962 g P lVIII/I/IIII/IA IN VENTORS MASAMI YOKOYAMA BY TOSHIO KAGOSHIMA ATTORNEY United States Patent Q 3,129,308 VACUUM CIRCUKT BREAKER HAVING BUFFER- ING MEANS IN RELATIVELY STATIONARY ELECTRODE STRUCTURE Masarni Yokoyarna and Toshio Kagoshima, Tokyo, Japan, assignors to Nippon Electric Company, Limited, Tokyo, Japan, a corporation of Japan Filed Apr. 23, 1952, Ser. No. 189,398 Claims priority, application Japan Apr. 22, 1961 2 Claims. (Cl. 200144) This invention relates to a vacuum switch for use in electric power systems, and more particularly to such switches of the circuit breaker type.

Power Vacuum switches have, as those knowledgeable in the art are aware, found extensive application in switching a power line in a power substation and also in largescale power equipment. A conventional power vacuum switch comprises, as will later be described with reference to the drawing, a fixed and a movable electrode which are disposed in substantial alignment with each other wherein respectively closing and opening the switch contacts. In such conventional construction, when the switch is closed, the movable electrode strikes the fixed electrode and rebounds, causing oscillation of one electrode with respect to the other electrode. This produces arcing between the tips of the electrodes with consequent premature disintegration of the tips and also results in the production of abnormal voltage variations in the circuit. Additionally, when the electrodes are first separated on opening the switch, the arc persists for a substantial length of time until the movable electrode has traveled a sufficient distance so that the arc will become extinguished. This undesirable condition is prolonged when the switch is employed with direct current as distinguished from alternating the latter is moved toward or away from the former for I current, with the result that the service life of the switch when used with direct current is further shortened.

Accordingly, it is an object of this invention to provide a power vacuum switch of the type described wherein the electrodes do not oscillate relative to each other on closing the switch and wherein less arcing is produced than with similar prior art devices upon separating the two electrodes when the switch is opened.

All of the objects, features and advantages of the invention will be understood from a reading of the specification taken with the claims and with the drawing in which:

FIG. 1 shows an axial cross-section of a conventional power vacuum switch in the opened state,

FIG. 2 shows an axial cross-section of a switch constructed in accordance with the principles of the invention with the electrodes in the open position, and

FIG. 3 is a graph showing the operating characteristics of the power vacuum switch of FIG. 2.

Referring first to FIG. 1, a conventional power vacuum switch 10 is shown having a rod-shaped fixed electrode 11 and a similar rod-shaped electrode 12. The fixed electrode 11 has one end thereof soldered or otherwise attached to the center of a metal disc 13. The movable electrode 12 has one end attached to the center of one planar surface of a small metal disc 14 which has a di ameter somewhat larger than the electrodes.

this rod being preferably in alignment with the movable electrode 12. The disc 14 is also hermetically sealed to one end of a metal bellows 18 which is larger in inner diameter and shorter in length than the metal rod 16. The other end of the bellows 18 is hermetically sealed to a metal disc 20 having at the center thereof a bore or aperture through which the metal rod 16 can freely slidably pass. The metal disc 13 and the apertured disc 20 are sealed, respectively, to the sealing

members

21 and 22 The opposite planar surface of the disc 14 is secured to a metal rod 16,

3,129,308 Patented Apr. 14, 1964 so as to produce air-tight seals between each disc and its sealing member. The sealing

members

21 and 22 are sealed, also in air-tight manner, to the opposite ends of a tube 25 of glass, ceramic, or other refractory insulating material, so that the fixed electrode 11 and the movable electrode 12 are preferably in substantial alignment with each other and so that the opposing ends or tips of the electrodes may be spaced by a predetermined distance when the switch is open.

A short cylinder 26, preferably made of the same material as the tube 25, is fused to one end of the tube 25 to thereby prevent the formation of a conductive film on the inner surface of the tube 25 by deposition of the sputtered electrode material during arcing of the electrodes. Alternatively, the movable electrode 12 and the metal rod 16 may be formed of a single metal rod, to which a small metal disc having a bore at the center thereof may be soldered or otherwise hermetically sealed intermediate of the ends of the metal rod. Also, it will be understood that the metal parts may be fixed by welding or in any other suitable manner instead of by soldering. The inside of the vacuum envelope composed of the tube 25 and its associated parts is evacuated through an exhaust port, not shown, which port is then sealed off in accordance with well known techniques.

The power vacuum switch is connected by means of the metal disc 13 and the metal rod 16 to the power line with which it is to be used. The movable rod 16 is connected to a suitable conventional operating or actuating mechanism, not shown, for advancing and retracting the movable electrode to thereby close and open the switch. When the switch 10 is closed the tip of the movable electrode 12 impinges against the tip of the fixed electrode 11 and oscillates along the axis of the electrodes. On opening the switch 10, the tip of the movable electrode 12 is moved away from the tip of the fixed electrode 11.

Referring now to FIG. 2, a power switch 30 constructed n accordance with the teachings of the invention is shown in which like numenals indicate like parts shown in FIG. 1. The portion corresponding to the fixed electrode 11 of the switch 10, however, comprises a buffer electrode 31 and is movable in the direction of its longitudinal axis. Similar to the portion of the movable electrode 12, the buffer electrode 61 is soldered or otherwise fixed at one end to the center of one side of a small metal disc 33 which is somewhat larger in diameter than the buffer electrode 31. To the other side of the small metal disc 33 opposite that which is secured to the buffer electrode 31, I2). metal rod 35 is fixed, the rod 35 preferably having the same diameter as and being in substantial alignment with the buffer electrode 31. A metal bellows 37 which is larger in inner diameter and shorter in length than the metal rod 35 is hermetically sealed to the disc 33. An annular ring or member 39 is secured at a predetermined axial position on the rod 35 and a coil spring 41 is positioned around the metal rod 35 on the upper side of the disc 33. A metal disc 43, having at its center thereof an aperture which the metal rod can freely slide through, is

hermetically sealed to the upper end of the bellows 37. The spring 41 bears against both the annular ring 39 and the disc 43.

A further annular member 45 is secured to the upper end of the metal rod 35, this member serving as a stop member upon opening of the switch, as will later appear. To the outer surface of the metal disc 43, there is attached a stopper housing 47 which is preferably made of a strip of flexible material so that the buffer electrode 31 may move a predetermined distance against the pressure of the coil spring 41 and the bellows 37. The switch assembly 30 thus described is hermetically sealed, as in the case of the switch 10, to both ends of the tube 25, and

it is then evacuated through an exhaust port, not shown, to a vacuum of the order of millimeters of mercury. The port is then sealed off in accordance with known techniques as in the case of the switch 1t 7 Referring now particularly to the buffer electrode assembly, it will be seen that several forces cooperate to urge the buffer electrode inwardly and provide a buffering action when the movable electrode 12 impinges against the buffer electrode 31. These are the compressive force of the helical spring 41, this force providing the major portion of the buffering action, the pressure of the air within the chamber of the bellows 37, and the tendency of the bellows 37 to expand axially. The electrode 31 is shown in FIG. 2 in the full open position, its limit of travel to this point being determined by the engagement of the annular member 45 with the outer surface of the disc 43. The buffer electrode 31 is, of course, allowed to assume this full inward position only when the movable electrode 12 is urged to its open position by the electrode actuating mechanism, not shown, which is suitably connected to the rod 16.

As in the prior art switch 10' of this kind, the power vacuum switch 30 is connected in conventional manner to a power line by means of suitable cables, not shown, which may be connected from the power line to either the

metal rods

16 and 35, or if desired to the

metal discs

20 and 43. On closing the switch 30, which is shown in the open position in FIG. 2, the movable electrode 12 is moved by the switch operating means inwardly so that the tip of the movable electrode 12 approaches the tip of the buffer electrode 31. After the tip of the movable electrode 12 has come into contact with the tip of the buffer electrode 31, the buffer electrode 31 is moved in the outward direction against the buffering force of the buffer electrode assembly. As a result of the buffering action, the switch is closed without any relative oscillation of the movable and

bufier electrodes

12 and 31,

even though the movable electrode 12 be advanced by the electrode actuating means into impact with the buffer electrode 31. This is achieved by means of the progressively retarding action of the buffering arrangement comprising the spring 41, the bellows 37 and the air pres- -sure in the chamber of this bellows, on the buffered elec- Even if the stopper trode 31 as it advances outwardly. housing 47 is not made of an elastic material, oscillation will still not occur, because the buffering action becomes very large when the buffer electrode 31 reaches an outer position just prior to the point where the annular stop member 45 meets the stopper housing '47.

To open the switch 30, the operating means connected to the movable electrode 12 moves this electrode outwardly, causing the buffer electrode 31 tofmove inwardly, initially with the movable electrode 12, with the switch still closed. However, as the'buffer electrode 31 advances inwardly, this electrode is abruptly arrested by reason of the stop member 45 engaging the outer surface of the disc 43 while the movable electrode 12 continues its outward movement, with the result that the switch is abruptly opened. I

Themovement of the

electrodes

12 and 31 during the opening action of the switch is graphically illustrated in FIG. 3 wherein the abscissa shows the distance x measured downwardly from the tip of the buffer electrode 31 at its outermost position and the ordinate shows its downward velocity v. The curve 50 represents the movement of the movable electrode 12 and the curve portions 51 representthe movement 'of the buffer electrode 31. As can be seen from FIG. 3, the velocity of the

electrodes

12 and 31 will gradually increase as the electrodes move downwardly together from the "full open switch position where 1 0. The buffer electrode 31, however, comes to an abrupt stop when it reaches the innermost position where x=x and actually attains a small reverse velocity -v due to the reaction produced by the collision of the outer [annular stop member 45 with the metal disc 43 if the opening movement velocity is great enough to produce such a reverse velocity. The relative velocity between the

electrodes

12 and 31, therefore, is larger than the velocity 1 when the electrodes are at the position x,. In contrast to the conventional switch 10 wherein the velocity of the electrodes 11 and 12 is zero when they first become separated from each other, the velocity of the

electrodes

12 and 31 of the switch 30 of the invention is at least equal to v even in the absence of any reaction as just described, and equals the sum of v and 'v where a reverse velocity is produced. As a result, the time required for extinguishment of the arc is veryshort and consequently the switch is capable of cutting off a large electric power within a short time interval. Since arcing is substantially reduced, the useful service life of both electrodes is considerably increased.

The spacing which is formed between the opposing tips of the

electrodes

12 and 31 when the switch 30 is open is determined in accordance with voltage with which the particular switch is to be used, "a figure of 1 millimeter generally made about half of the spacing which is formed between the tips of the

electrodes

12 and 31 when the switch 30 is open. It will be appreciated that adjustment of the buffering force can be effected by varying the elas ticity of the bellows 37 associated with the buffer electrode 31, or by varying the spring force of the coil spring '41, or by varying the air passages through which the air from inside the

bellows

18 and 37 passes to the atmosphere.

Although a preferred embodiment of the invention has been described above, it will be clear that various modifications can be made in the construction described. For example, the manner of attaching the metal parts, and the vacuum envelope can all be modified as in the case of'the conventional switch 10. Also, the means for buffering the contact of the electrode 12 with that of the electrode 31 and means for making the relative velocity between the electrodes a definite value other than zero on separation of the tips can suitably be modified. Additionally, the flexible stopper housing 47 may be made conductive and may be secured to the outermost end of the metal rod 35, in which case, the outer ring 45 could be dispensed with. With this modification, the buffer electrode 31 would be arrested during its inward movement by the inside surface of the stopper housing 47 engaging the outside surface of the metal disc 43 and would be arrested during its outward movement in the same manner as presently, when the stopper housing 47 has been elastically deformed to its outward limit. Also,

the power line can be connected to both the metal disc 43 and the metal rod 16 which is integral with the movable electrode 12 so that the major portion of the electric current may then flow through the flexible stopper housing 47. Such a modification is particularly advantageous for switching large currents.

Since many changes could be made in the above invention and many apparently widely different embodiments of this invention could be made without departing from the scope thereof it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as merely illustrative and not in a limiting sense.

We claim: a

1. A vacuum switch for electric power comprising a vacuum envelope, said envelope having opposed end members each provided with an aperture,

a movable electrode assembly provided at one end of said envelope and adapted for mechanical connection with an actuating mechanism for moving said assembly to thereby close and open said switch,

said assembly including a first electrode and a first conductive rod-like member substantially in axial alignment therewith, said rod-like member being slidably positioned in one of said apertures,

a buffer electrode assembly substantially in axial alignment with said movable electrode assembly and being disposed at the opposite end of said envelope from said movable assembly,

said buffer assembly including a second electrode and a second conductive rod-like member substantially in axial alignment therewith, said second rod-like member being slidably positioned in the other of said apertures,

a first bellows connected in an airtight manner between said movable electrode assembly and the end member associated therewith,

a second bellows connected in an airtight manner between said buffer electrode assembly and the end member associated therewith, a flexible stopping member disposed at said opposite end of said envelope in a position to be engaged by the end of said second rod-like member when said switch is closed,

a helical compression spring connected between said butter electrode assembly and the end member associated therewith for providing buffering action upon engagement of said first electrode with said second electrode when said switch is closed, and a stop means mounted on said buifer electrode assembly for abruptly arresting the movement of said buffer assembly as said electrodes are moved together when said switch is opened, the velocity of separation of said electrodes at the point of initial disengagement thereof being a value greater than zero.

2. A vacuum switch for electrical power comprising a vacuum envelope, said envelope including an enclosure having ends each provided with an aperture,

a first electrode within said envelope and adapted for electrical connection to the outside thereof,

a second electrode also within said envelope and adapted for electrical connection to the outside thereof,

a first extension member from said first electrode being slidably received in one of said apertures and a second extension member from said second electrode being slidably received in the other of said apertures,

expandible means connected between each of said extension members and the end of said envelope with which each extension member is associated to thereby allow movement of said electrodes while maintaining the vacuum within said envelope,

said first electrode being connected through said first extension member to an actuating mechanism for moving one end of said first electrode into and out of engagement with one end of said second electrode,

means for buffering the impact of said first electrode when it is advanced by said actuating mechanism into engagement with said second electrode,

said bufiering means including spring means associated with said second electrode for urging said latter electrode opposite to the direction of movement of said first electrode when the electrodes are engaging one another,

flexible stopping means disposed at one end of said envelope in a position to be engaged by said second extension member when said actuating mechanism causes said first electrode to engage said second electrode,

and means for abruptly separating said electrodes upon disengagement thereof, the velocity of separation at the point of initial disengagement being a value greater than zero.

References Cited in the file of this patent UNITED STATES PATENTS

Claims

1. A VACUUM SWITCH FOR ELECTRIC POWER COMPRISING A VACUUM ENVELOPE, SAID ENVELOPE HAVING OPPOSED END MEMBERS EACH PROVIDED WITH AN APERTURE, A MOVABLE ELECTRODE ASSEMBLY PROVIDED AT ONE END OF SAID ENVELOPE AND ADAPTED FOR MECHANICAL CONNECTION WITH AN ACTUATING MECHANISM FOR MOVING SAID ASSEMBLY TO THEREBY CLOSE AND OPEN SAID SWITCH, SAID ASSEMBLY INCLUDING A FIRST ELECTRODE AND A FIRST CONDUCTIVE ROD-LIKE MEMBER SUBSTANTIALLY IN AXIAL ALIGNMENT THEREWITH, SAID ROD-LIKE MEMBER BEING SLIDABLY POSITIONED IN ONE OF SAID APERTURES, A BUFFER ELECTRODE ASSEMBLY SUBSTANTIALLY IN AXIAL ALIGNMENT WITH SAID MOVABLE ELECTRODE ASSEMBLY AND BEING DISPOSED AT THE OPPOSITE END OF SAID ENVELOPE FROM SAID MOVABLE ASSEMBLY, SAID BUFFER ASSEMBLY INCLUDING A SECOND ELECTRODE AND A SECOND CONDUCTIVE ROD-LIKE MEMBER SUBSTANTIALLY IN AXIAL ALIGNMENT THEREWITH, SAID SECOND ROD-LIKE MEMBER BEING SLIDABLY POSITIONED IN THE OTHER OF SAID APERTURES, A FIRST BELLOWS CONNECTED IN AN AIRTIGHT MANNER BETWEEN SAID MOVABLE ELECTRODE ASSEMBLY AND THE END MEMBER ASSOCIATED THEREWITH, A SECOND BELLOWS CONNECTED IN AN AIRTIGHT MANNER BETWEEN SAID BUFFER ELECTRODE ASSEMBLY AND THE END MEMBER ASSOCIATED THEREWITH, A FLEXIBLE STOPPING MEMBER DISPOSED AT SAID OPPOSITE END OF SAID ENVELOPE IN A POSITION TO BE ENGAGED BY THE END OF SAID SECOND ROD-LIKE MEMBER WHEN SAID SWITCH IS CLOSED, A HELICAL COMPRESSION SPRING CONNECTED BETWEEN SAID BUFFER ELECTRODE ASSEMBLY AND THE END MEMBER ASSOCIATED THEREWITH FOR PROVIDING BUFFERING ACTION UPON ENGAGEMENT OF SAID FIRST ELECTRODE WITH SAID SECOND ELECTRODE WHEN SAID SWITCH IS CLOSED, AND A STOP MEANS MOUNTED ON SAID BUFFER ELECTRODE ASSEMBLY FOR ABRUPTLY ARRESTING THE MOVEMENT OF SAID BUFFER ASSEMBLY AS SAID ELECTRODES ARE MOVED TOGETHER WHEN SAID SWITCH IS OPENED, THE VELOCITY OF SEPARATION OF SAID ELECTRODES AT THE POINT OF INITIAL DISENGAGEMENT THEREOF BEING A VALUE GREATER THAN ZERO.