US3746811A

US3746811A - Vacuum circuit breaker

Info

Publication number: US3746811A
Application number: US00067874A
Authority: US
Inventors: O Saito
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1969-09-03
Filing date: 1970-08-28
Publication date: 1973-07-17
Anticipated expiration: 1990-07-17

Abstract

A vacuum circuit breaker in which a lid which hermetically and movably supports through a bellows a holder of a movable electrode disposed opposite to a fixed electrode is electrically connected with a terminal for said movable electrode in such a manner as to lead from said lid to said terminal through said connection a current which otherwise might flow in shunt with an arc, in metal shields through the electrode metal melted by the arcing heat during a breaking operation, said metal shields being provided for preventing the conduction of a vacuum cylinder made of insulating material to contain said electrodes, said current in shunt with an arc being thereby prevented from flowing through said bellows.

Description

United States Patent [1 1 Saito July 17, 1973 VACUUM CIRCUIT BREAKER [75] Inventor: Osamu Saito, Hitachi, Japan [73] Assignee: Hitachi, Ltd., Tokyo, Japan [22] Filed: Aug. 28, 1970 [211 App]. No.: 67,874

[30] Foreign Application Priority Data Sept. 3, i969 Japan 44/69349 [52] US. Cl. 200/144 B, 200/50 A [51] Int. Cl. H0lh 33/66 [58] Field of Search 200/144 B, 50 A [56] References Cited UNITED STATES PATENTS 3,555,223 1/1971 Robinson et a1. 200/144 B 3,123,698 3/1964 Waterton 200/144 B 3,189,715 6/1965 Jennings 200/144 B FOREIGN PATENTS OR APPLICATIONS 2/1965 France ZOO/144.2

Primary ExaminerRobert S. Macon AttorneyCraig, Antonelli and Hill [57] ABSTRACT A vacuum circuit breaker in which a lid which hermetically and movably supports through a bellows a holder of a movable electrode disposed opposite to a fixed electrode is electrically connected with a terminal for said movable electrode in such a manner as to lead from said lid to said terminal through said connection a current which otherwise might flow in shunt with an arc, in metal shields through the electrode metal melted by the arcing heat during a breaking operation, said metal shields being provided for preventing the conduction of a vacuum cylinder made of insulating material to contain said electrodes, said current in shunt with an are being thereby prevented from flowing through said bellows.

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SHEEI 2 UP 2 INVENTOR OSRMu smTo ATTORNEYS The present invention relates to a vacuum circuit breaker with an improved current path for a movable electrode.

With a fixed and a movable electrode each supported by an electrode holder in a highly vacuumized cylinder madeof an insulating material, a vacuum circuit breaker is so constructed that there is a bellows con necting between the holder of the movable electrode and an upper lid of the cylinder, which bellows maintains the highly vacuumized condition inside the cylinder, the movable electrode being movable by a certain distance with respect to the fixed electrode. In addition, a metal shield is provided around the electrodes to prevent a metal component of the electrodes melted by the are heat at the time of current breaking from being attached on the surface of the cylinder and thus contaminating the insulating material thereof. In the above construction, the vacuum circuit breaker proper is supported by a tank made of insulating material through a lower lid, an upper lid only supporting the movable electrode holder so as not to be deviated from the center position, so that the force required to contact the electrodes for conducting a large current and the force to detach them from each other is transmitted from an outside control device through the electrode holders and the electrodes to the lower lid which supports the fixed electrode, thereby preventing the me chanical force from being applied to the weak cylinder.

In breaking a large current, a hole or puncture sometimes develops in the bellows, impairing the function of the vacuum circuit breaker. Seeking the cause of such a hole or puncture, the inventor has found that at the time of breaking a large current a great quantity of metal vapor from the surface of the electrodes fills not only the space between the electrodes but also the neighborhood of the lids of the inner cylinder and around the bellows. Also, since the electric field is concentrated near around the ends of the metal shield, an electric discharge occurs between the lids and the metal shield, causing a part of the current to flow in parallel with the breaking current to the terminal for themovable electrodethrough the bellows.

After an experiment, the inventor found that when a current of 25 KA (7.2 KV) is broken the branch current flowing through the bellows -reaches as high as several thousands ampere and stays at that level for about one-fourth of a cycle. The bellows wall is usually as thick as 0.1 mm to maintain the high vacuum inside and it is supposed that the branch current flowing through the bellows causes the wall to be heated, melting a part of it to develop a hole.

An object of the present invention is to provide an improved vacuum circuit breaker in which said branch current is prevented from flowing through the bellows.

Another object of the present invention is to provide a reliable vacuum circuit breaker with a long useful life, equipped with a strong bellows which'are not damaged by the branch current.

A third object of the present invention is to provide a vacuum circuit breaker in which no current flows from the holder for the movable electrode to the terminal thereof, the sole function of the holder of the movable electrode being to guide the same.

Still another object of the present invention is to provide a smaller vacuum circuit breaker which has a high resistance against a creeping discharge along the cylinder and is adapted to be used for a high'voltage circuit.

Still another object of the present invention is to provide a high-voltage vacuum circuit breaker with greater safety to an operator.

The feature of the present invention is that the upper lid of the movable electrode is electrically connected with the terminal of the movable electrode, to which is led the branch current which flows through the metal vapor diffused from the electrodes and the metal shields at the time of the current breaking, thereby to reduce to almost zero the current in the bellows.

The above and other objects, features and advantages will be made apparent by the detailed description taken in conjunction with the accompanying drawings, in which:

FIG. I shows a cross-sectional view of the vacuum circuit breaker according to the present invention;

FIG. 2 shows a cross-sectional view of an embodiment of the present invention.

Referring to FIG. 1, the reference numeral 1 shows the whole structure of the vacuum circuit breaker. The vacuum chamber 7 consists of a cylinder 2 made of an insulating material such as ceramics and an upper metal lid 5 and a lower metal lid 6 which are fastened on both ends of said cylinder by means of the

fasteners

3 and 4. In the vacuum chamber are the movable electrode 8 and the fixed electrode 11, the former being mounted for movement through the upper lid 5 by means of the holder 9 and the bellows 10 and the latter being fixed on the lower lid 6 through the holder 12.

The vacuum chamber 7 is vacuumized to the extent of 10 mmHg or less at the time of current breaking the electrodes 8 and 11 are detached from each other by moving the holder 9 in the direction shown by the arrow, thereby causing an are between the electrodes which is extinguished by the high capability of the vacuum for insulation and are extinguishing.

While the arc is generated, the surface of the electrodes is melted by the arcing heat and the metal vapor is diffused in the vacuum, attaching itself on the inside surface of the cylinder 2 with the result that said inside surface of the cylinder 2 is less insulated. To prevent this, the metal shield 13 disposed on the cylinder 2 surrounds the electrodes 8 and 11 with the additional metal shields l4 and 15 being placed on the upper and lower lids. The shields serve as a barrier between the cylinder 2 and the electrodes gap in order to prevent the metal vapor from advancing directly towards the wall of the cylinder 2. On the lower lid 6 is a stud 16 which, together with the supporting plate 17, fastens the vacuum circuit breaker proper to the flange 18a of the tank 18. The holder 12 for the fixed electrode 11 is mounted on the outside terminal plate 19 from which a current flows to the fixed electrode 11. The stud 20 on the upper lid 5 is elastically held by the guide 22 for the holder 9 through the spring 21, the guide 22 being fixed on the flange 18b of the tank 18 through the supporting plate 24 and the foot 23. The guide 22, the foot 23 and the supporting plate 24 are made of a metal and integrated with each other, the guide 22 being electrically connected with the upper lid 5 through the lead wire 25. The holder 9 of the movable electrode is provided with a collector 26 which together with an upper outside terminal plate 27 is fixed on the supporting plate 24 by means of an appropriate fastening means including a bolt, etc., thereby electrically connecting the holder 9 with the upper outside terminal plate 27. To prevent a short-circuit between the holder 9 and the guide 22., the insulating material 29 is inserted therebetween.

When an arc is generated during a breaking opera tion, the electric field is concentrated between the metal shields l3 and 14 and between the

metal shields

13 and 15. The dielectric strength at the abovementioned portions markedly drops due to the diffusion of melted metal caused by the arcing heat especially when a large current is cut off, so that electricity is discharged between the metal shields l3 and 14 and between the

metal shields

13 and 15 through the metal vapor or between the fixed electrode 11 and the metal shield 13. As a result, a part of the current flows through the above-mentioned branch circuit in shunt with the are between the electrodes. Since the resistance of the bellows is far greater than that of the lead wire 25, this undesirable branch current flow to the outside terminal plate 27 not through the bellows 10 but through the lead wire 25. After that, according as the arc current is reduced near zero, the metal is melted at a lower rate and the density in the vacuum chamber 7 is reduced as the diffused metal is deposited on the surface of the

metal shields

13, 14 and 15, resulting in less branch current. The insulation between the electrodes 8 and 11 is thus restored as a result of the disappearance of the are between the electrodes.

FIG. 2 illustrates the vacuum circuit breaker according to the present invention installed on a carrier in order to incorporate it into an enclosed switchboard. A floor plate 30 is closely attached on the bottom of the tank 18, which is also provided with

hermetical bushings

31 and 32. An insulating material such as silicon oil or SF gas is contained in the space between the cylinder 2 and the tank 18 to improve the creeping resistance of the outer surface of the cylinder 2. The heat generated at the collector portions or junction points by the Joule effect is absorbed by the insulating material and is carried away by convection through the material. Thus, the insulating material contributes to, the prevention of an excessiverise in the temperature at such collector portions or junction points. The tank 18 and the

bushings

31 and 32 are covered with a grounded metal film on their outer surfaces to protect an operator from an electric shock the metal film being arranged so as not to contact the portions of the circuit breaker having a potential applied thereto in the manner known in the art.

The floor plate is directly or indirectly fixed on the carrier 33 which is movable in the horizontal direction by means of the wheels 34a and 34b, whereby the

bushings

31 and 32 is connected with or disconnected from bus bars, etc. (not shown in the drawing) located opposite to each other. The holder 9 for the movable electrode is operated by the operating mechanism in the carrier 33 through the link mechanism partially shown by the numeral 35.

As can be seen from above, the vacuum circuit breaker of the present invention has such an advantage that the current to be cut off does not flow through the bellows during the breaking operation, so that Joule heat generated by the current does not damage the be]- lows. Consequently, the reliability of the vacuum circuit breaker is improved and the useful life thereof is lengthened.

Instead of the connection of the upper lid 5 and the guide 22 through the lead wire 25 as employed in the above-mentioned embodiment, a connection of, say, the holder 9 or the collector 26 and the upper lid 5 can achieve the sameeffect.

What is claimed is:

l. A vacuum circuit breaker comprising at least a pair of electrodes relatively detachable from each other disposed in a vacuum chamber made airtight by a surrounding cylinder of insulating material and an upper and lower metal lid attached on both ends thereof, said vacuum chamber being vacuumized to the extent of 10 mmHg or less; a bellows which movably supports one of said electrodes and maintain said vacuum, and metal shields which surround said electrodes, said one of the electrodes which is movable being guided and centered by a guide means, holding means for fixedly mounting the other electrode to said lower lid, and said upper lid always being electrically connected with an upper outside terminal plate irrespective of the position of the movable electrode, a holder for said movable electrode, said guide means having a conductive portion integral with said upper outside terminal for said movable electrode and electrically connected with said upper lid and an insulating portion for centering said movable electrode, the resistance between said holder of said movable electrode and said terminal for said movable electrode through said guide means being much greater than the resistance through said bellows and said movable electrode.

2. A vacuum circuit breaker comprising at least a pair of electrodes relatively detachable from each other disposed in a vacuum chamber made airtight by a surrounding cylinder of insulating material and an upper and lower metal lid attached on both ends thereof, said vacuum chamber being vacuumized to the extent of 10 mmHg or less, a bellows which movably supports one of said electrodes and maintaining said vacuum; and metal shields which surround said electrodes, said one of the electrodes which is movable being guided and centered by a guide means, holding means for fixedly mounting the other electrode to said lower lid, and said upper lid always being electrically connected with an upper outside terminal plate irrespective of the position of the movable electrode, said vacuum circuit breaker being contained in an airtight tank made of an insulating material, said tank being filled with an insulating medium, the outer surface of said tank ofinsulating material is covered with a metal film, said metal film being grounded, the outer surface of said tank having said metal film thereon being spaced from portions of said circuit breaker having an electric potential ap plied thereto.

3. A vacuum circuit breaker comprising a vacuum chamber formed by a cylinder of insulating material having an upper metal lid and a lower metal lid closing the ends thereof, at least a pair of electrode means relatively detachable from each other disposed in said chamber, metal shields surrounding said electrodes means, one of said electrode means being fixedly mounted to said lower lid, said other electrode means being movable, a bellows arranged on said upper lid for permitting movement of said movable electrode means and for maintaining the vacuum within said chamber, means for guiding and centering said movable electrode means, a terminal spaced from said upper lid and electrically connected with said movable electrode 3,746,81 1 5 6 means, and means for always electrically connecting lows being much greater than the resistance of said said upper lid of said vacuum chamber to said terminal irrespective of the position of said movable electrode a means, said bellows being electrically connected to said vacuum chamber to sand termmal' movable electrode means and the resistance of said bel- 5 means electrically connecting said upper lid of said

Claims

1. A vacuum circuit breaker comprising at least a pair of electrodes relatively detachable from each other disposed in a vacuum chamber made airtight by a surrounding cylinder of insulating material and an upper and lower metal lid attached on both ends thereof, said vacuum chamber being vacuumized to the extent of 10 4 mmHg or less; a bellows which movably supports one of said electrodes and maintain said vacuum, and metal shields which surround said electrodes, said one of the electrodes which is movable being guided and centered by a guide means, holding means for fixedly mounting the other electrode to said lower lid, and said upper lid always being electrically connected with an upper outside terminal plate irrespective of the position of the movable electrode, a holder for said movable electrode, said guide means having a conductive portion integral with said upper outside terminal for said movable electrode and electrically connected with said upper lid and an insulating portion for centering said movable electrode, the resistance between said holder of said movable electrode and said terminal for said movable electrode through said guide means being much greater than the resistance through said bellows and said movable electrode.

2. A vacuum circuit breaker comprising at least a pair of electrodes relatively detachable from each other disposed in a vacuum chamber made airtight by a surrounding cylinder of insulating material and an upper and lower metal lid attached on both ends thereof, said vacuum chamber being vacuumized to the extent of 10 4 mmHg or less, a bellows which movably supports one of said electrodes and maintaining said vacuum; and metal shields which surround said electrodes, said one of the electrodes which is movable being guided and centered by a guide means, holding means for fixedly mounting the other electrode to said lower lid, and said upper lid always being electrically connected with an upper outside terminal plate irrespective of the position of the movable electrode, said vacuum circuit breaker being contained in an airtight tank made of an insulating material, said tank being filled with an insulating medium, the outer surface of said tank of insulating material is covered with a metal film, said metal film being grounded, the outer surface of said tank having said metal film thereon being spaced from portions of said circuit breaker having an electric potential applied thereto.

3. A vacuum circuit breaker comprising a vacuum chamber formed by a cylinder of insulating material having an upper metal lid and a lower metal lid closing the ends thereof, at least a pair of electrode means relatively detachable from each other disposed in said chamber, metal shields surrounding said electrodes means, one of said electrode means being fixedly mounted to said lower lid, said other electrode means being movable, a bellows arranged on said upper lid for permitting movement of said movable electrode means and for maintaining the vacuum within said chamber, means for guiding and centering said movable electrode means, a terminal spaced from said upper lid and electrically connected with said movable electrode means, and means for always electrically connecting said upper lid of said vacuum chamber to said terminal irrespective of the position of said movable electrode means, said bellows being electrically connected to said movable electrode means and the resistance of said bellows being much greater than the resistance of said means electrically connecting said upper lid of said vacuum chamber to said terminal.