US3441698A

US3441698A - Vacuum-type circuit interrupter

Info

Publication number: US3441698A
Application number: US583893A
Authority: US
Inventors: Joseph C Sofianek
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1966-10-03
Filing date: 1966-10-03
Publication date: 1969-04-29
Anticipated expiration: 1986-04-29
Also published as: DE1640257B2; CH465694A; JPS4529934B1; DE1640257A1; SE329203B; GB1161443A; FR1552927A

Description

April 29, 1969 J. c. SOFIANEK K f 3,441,698

VACUUM-TYPE CIRCUIT INTERRUPTER Filed Oct. 3, 1966 /IZ 5F/.1. 610 M fw# /4 SWE /NvE/vTo/: JOSEPH C. Sor/A NEN,

ATTORNEY United States Patent O 3,441,698 VACUUM-TYPE CIRCUIT INTERRUPTER Joseph C. Sofanek, Broomall, Pa., assignor `to General Electric Company, a corporation of New York Filed ct. 3, 1966, Ser. No. 583,893 Int. Cl. H01h 33/66, 9/30 U.S. Cl. 200-144 6 Claims This invention relates to a vacuum-type circuit interrupter and, more particularly, relates to improved shielding structure for protecting the insulation of such an interrupter from being impaired by the condensation thereon of arc-generated metallic vapors.

It is customary to protect the tubular insulating housing of a vacuum-type circuit interrupter from such vaporcondensation by providing some form of shielding, preferably of metal, located between the insulating housing and the arcing gap of the interrupter. This shielding is intended to intercept and condense arc-generated vapors before they can reach the insulating housing, thus preventing the vapors from condensing on and coating the insulation with metallic particles. The present invention is especially concerned with vapor-condensing shielding of the general type disclosed and claimed in U.S. Patent 2,892,912, Greenwood et a1., assigned to the assignee of the present invention. This shielding comprises (l) a main shield of tubular form surrounding the arcing gap and maintained at a potential intermediate that of the electrodes of the intermpter and (2) a pair of auxiliary shields of tubular form respectively surrounding the opposite ends of the main shield and electrically connected to the electrodes. The auxiliary shields act to intercept metal vapors that might otherwise bypass the main shield and also provide a desired distribution of the electric field at the ends of the interrupter.

When the above-described shielding is employed in interrupters that are used for extreme high currents it has been found that small amounts of metal have still reached the insulating envelope despite the shielding. The quantity of such metal is minute, but even this minute quantity seems to detrimentally affect the interrupting ability of the interrupter.

An object of the present invention is to improve the ability of the shielding to condense metal vapors that tend to bypass the main shield.

Another object is to force any sparkover between the main shield and adjacent structure to occur in a location where there is a reduced chance for coating the insulating envelope with metal particles generated by the spark.

Another object is to condense -a large portion of the arc-generated vapors projected toward the ends of the main shield in a region that is essentially free of electrical stress.

In carrying out the invention in one form, I provide a main vapor-condensing metal shield of tubular form surrounding the usual arcing gap of the interrupter. This main shield extends longitudinally of the tubular insulating casing of the interrupter for substantial distances on opposite sides of the arcing gap and is maintained at a potential intermediate that of the interrupters electrodes following interruption. A first pair of auxiliary metal shields of generally tubular form respectively surround the ends of the main shield and are spaced radially outward therefrom. These auxiliary shields are respectively connected to the electrodes of the interrupter. In combination with this shielding, I provide additional auxiliary metal shields of generally tubular form that are respectively surrounded by said main shield at its opposite ends. These additional auxiliary shields are spaced radially inwardly from said main shield and are electrically connected to said electrodes.

ICC

In a preferred form of the invention, the additional shields are so shaped that higher electrical stresses are present in the regions between these additional auxiliary shields and the main shield than are present between said first auxiliary shields and the main shield.

For a better understanding of the invention, reference may be had to the following description taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a side elevational view in section of a vacuumtype interrupter embodying one form of the present invention.

FIG. 2 is a plan view taken along the line 2-2 of FIG. 1.

Referring now to FIG. 1, there is shown a vacuumty-pe circuit interrupter comprising an envelope 10 evacuated to a pressure of 10-4 mm. of mercury or lower. The envelope comprises a tubular casing 11 of insulating material and metal end caps 12 and 13 joined to the tubular casing 11 at its opposite ends by suitable vacuumtight seals 14.

Located within the envelope 10 is a pair of relatively

movable contacts

17 and 18, shown by the solid lines of FIG. 1 in their disengaged or open position. The upper contact 17 is a stationary contact suitably attached to a conductive rod 17a, which at its upper end is united to the upper end cap 12. The lower contact 18 is a movable contact attached to a conductive operating rod 18a, which is suitably mounted for vertical movement. Upward movement of the contact 18 from its solid line position to its dotted line position engages the contacts and thus closes the interrupter, whereas return movement in a downward direction separates the contacts and opens the interrupter. l

The operating rod 18a projects freely through an opening in the lower end cap 13, and a flexible metallic bellows 20 provides a seal about rod 18a to allow for vertical movement of the rod without impairing the vacuum inside envelope 10. As shown in FIG. 1, the bellows is secured in sealed relationship at its respective opposite ends to the operating rod 18a and the lower end cap 13.

Although the present invention is applicable to interrupters having various types of contacts, I have illustrated it in connection with an interrupter having contacts of the type disclosed and claimed in my copending application Ser. No. 583,808, filed Oct. 3, 1966, and assigned to the assignee of the present invention. Accordingly, each of the illustrated

contacts

17 and 18 is of a disc-shape and has one major surface facing the other contact. Each contact comprises a centrally located contact-making button 25 suitably brazed to the remainder of the contact. Each of these contact-making buttons is provided with a centrally located recess 27 so that contact between the buttons occurs -on an annular contact-making area 30 when then contacts are in their dotted-line engaged position of FIG. l. These annular contact-making regions 30 are of such a diameter that current owing through the closed contacts follows a radially outwardly bowing loop-shaped path L, as is indicated by the dot-dash line of FIG. 1. The magnetic effect of current flowing through this loopshaped path L tends in a well-known manner to lengthen the loop. As a result, when the contacts are separated to form an arc between the areas 30, the magnetic effect of the current through the loop will impel the arc radially outward.

As the terminals of the arc move toward the outer periphery of the

discs

17 and 18, the arc is subjected to a circumferentially acting magnetic force that rotates the arc about the central axis of the discs. This circumferentially acting magnetic force is produced by a plurality of slots 32 provided in each of the discs and dividing the discs into a plurality of fingers 33 bounded by adjacent pairs of slots. The slots extend from the outer periphery I of the discs radially inward by paths that extend both circumferentially and radially of the discs, as is shown in FIG. 2. These slots 32 correspond to similarly designated slots in the U.S. Patent 2,949,520 Schneider and, thus, force the current iiowing to or from an arc terminal on the slotted portion of the contact to follow a path that has a component extending circumferentially of the disc in the 'vicinity of the arc. This circumferential component of the current path causes current owing through the loop L to develop a net circumferentially acting force component which tends to rotate the arc about the central axis of the disc.

This circumferentially acting force lcomponent is high enough to drive each terminal of the arc across slots 32, thus producing a continuous rotational movement of the arc on the contact surface. This continuous rotational movement of the arc enables higher currents to be interrupted, apparently because it reduces contact-erosion by the arc, thus reducing the quantity of metal vapors generated and thereby permitting more complete condensation of the metal vapors at current zero.

For condensing the metal vapors that are generated by the arc, I provide vapor-condensing

metal shielding

50, 54, 56 and 58. This shielding comprises a tubular main shield 50 surrounding the arcing gap 52 and located between the insulating casing 11 and the arcing gap. This main shield 50 extends longitudinally of casing 11 for substantial distances on opposite sides of the arcing gap 52. Preferably, the tubular main shield 50 has an enlarged diameter in the region around the

contacts

17 and 18, as compared to its diameter near its ends, so as to give added clearance between the shield and the

contacts

17, 18. The main shield 50 is suitably supported on the insulating casing 12 and is maintained at a voltage approximately midway that of the

contact

17 and 18 when the interrupter is opened. In the illustrated form of the invention, this midpotential relationship is provided by relying upon the substantially equal capacitances present between the shield and opposite ends of the interrupter.

Surrounding the main shield 50 at its respective opposite ends are auxiliary shields 54 of the general type shown in the aforesaid Greenwood et al. patent. These auxiliary shields 54 are electrically connected to the end caps 12 and 13, respectively, and therefore are at the same potential as the contacts I17 and 18, respectively. Each of these auxiliary shields 54 is of a generally tubular form and surrounds the end of the |main shield 50` in radially-spaced relationship. These auxiliary shields 54 serve to intercept and condense metal vapors that might bypass the primary shield 50 at its ends. The auxiliary shields 54 also serve to relieve the seals 14 of voltage stresses.

Located radially inwardly of the main shield 50 at its opposite ends are additional auxiliary shields 56. These additional shields 56 ane also of a generally tubular form and are electrically connected to end caps 12 and 13, respectively. Thus, the upper auxiliary shield 56 is at the same potential as upper contact 17, and the lower shield at the same potential as lower contact 18.

Each of the auxiliary shields 56 surrounds a space 60 that has one end open, i.e., the end facing the contacts, and its other end closed oi by an end wall of the interrupter.` At each end of the interrupter, the

auxiliary shields

54 and 56 are both spaced from the main shield.

An additional shield 58 of cup-shaped form is provided about the bellows 20 to protect the bellows from the arc-generated products.

When an arc is formed across lthe gap 52 during interruption, most of the metallic vapors generated by the arc are projected radially outward from the arcing gap and are condensed on the inner surface of the main shield 50. In the illustrated interrupter, however, a relatively large quantity of metal vapors is also projected lfrom gap 52 through the slots 32 in directions longitudinal of insulating casing 12. A high percentage of these longitudinally directed vapors are trapped within the spaces surrounded by the two auxiliary shields 56. In the case of the upwardly directed vapors, most of these trapped vapors are intercepted and condensed either by the inner surface of the upper auxiliary shield 56 or by the lower surface of end cap 12. This trapping and condensation precludes these vapors from finding a path around the upperl end of main shield 50, thus preventing them from reaching insulating casing 12. In the case of the downwardly directed vapors, the vapors trapped within lower space 60 are condensed either on the inner surface of. lower auxiliary shield 56, the upper surface of end cap 13, or the outer surface of the shield 58 for the bellows. This condensation prevents these vapors form nding a path around the lower end of main shield 50.

It is to be noted that each of the spaces 60 is a region of very low, virtually zero, electric stress since it is bounded on substantially all sides, except the open side facing the contacts, by metal parts at the same potential. Even on the open side of space 60, the rcontact thereadjacent is at the same potential as the auxiliary shield 56, thereby precluding the entry into space -60 of a significant electric field. This very low electric stress greatly reduces the tendency for a sparkover to develop between the surface of the metal condensate on the walls of space k60 and an `adjacent part `such as main shield 50. Such sparkovers, even `though they are usually self-extinguishing, seem to detra-ct from the interrupting ability of the interrupter. Without the auxiliary shields 56, there is a significant chance for such a sparkover since the condensate has a rather rough surface that is conducive to lthe initiation of sparkover.

If a sparkover does occur between the main shield 50 and an adjacent part, it is most desirable that it be located -within the space bounded by the main shield 50 rather than outside this space. This is the case because the sparkover, even though it usually quickly extinguishes itself, generates some metallic vapors which are more likely to reach the casing 11 if the spark is outside the main shield 50. To encourage any sparkover involving main shield 50 to be located inside the main shield 50, I shape each of the inner auxiliary ,shields 56 so that the maximum electric stress between the main shield 50 and inner auxiliary shields 56 is greater than that between main shield 50 and the outer auxiliary shields 54. To this end, I provide each auxiliary shield 56 with a ared portion 56a at its free end that forms a region thereadjacent where the electrical stress is higher than in any region located between .shields 50 and 54. The relatively small diameter of the auxiliary shield 56 compared to that of auxiliary shield 54 also contributes to the higher stress adjacent portion 56a Of the inner shield 54.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects; and I, therefore, intend in the appended claims to A cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A vacuum-type circuit interrupter comprising:

(a) a highly evacuated envelope comprising a tubular casing primarily of insulating material,

(b) a pair of electrodes within .said casing deiining an arcing gap therebetween across which arcs are established during a circuit-interrupting operation,

(c) a main vapor-condensing metal shield of tubular form surrounding said arcing gap and extending longitudinally of said tubular casing for substantial distances on opposite sides of said gap,

(d) means for maintaining said main shield at a potential intermediate that of said electrodes following interruption,

(e) a rst pair of auxiliary metal shields ol' generally tubular form respectively surrounding the ends of said main shield and space-d radially outward therefrom,

(f) means for respectively electrically connecting said auxiliary shields to said electrodes,

(g) a pair of additional auxiliary metal shields of generally tubular form respectively surrounded by said main shield at its opposite ends,

(h) said additional auxiliary shields beinglspaced radially inward from .said main shield andbein'g yelectrically connected to said electrodes.

2. A vacuum-type circuit interrupter as defined in claim 1 in which each of said electrodes has openings therein through which metallicvapors are expelled from said arcing gap longitudinally vof said tubular casing during an interrupting operation.

3. The circuit interrupter of claim 1 in which the space bounded by each of said additional auxiliary shields has one end facing said electrodes that is open and another end remote from said electrodes that is substantiallyclosed oli by metallic structure extending thereacross.

4. A vacuum-type circuit interrupter as defined in claim 3 in which each of said electrodes has openings therein through which .metallic vapors are expelled from said arcing gap longitudinally of said tubular casing dur ing an interrupting operation.

S. A vacuum-type circuit interrupter as defined in claim 1 in which said auxiliary shields are so shaped that when said interrupter is open, higher electrical stresses are present in the regions between said main shield and said additional auxiliary shields than in any region between said main shield and said first pair of auxiliary shields.

6. The vacuum type circuit interrupter of claim 5 in which at least one of said additional auxiliary shields has a flared portion at its free end surrounded by said main shield, where the highest electric stress is present Vbetween said main shield and said one additional auxiliary shield.

References Cited UNITED STATES PATENTS 2,892,912 6/1959 Greenwood et al. 3,185,800 5/1965 Titus. 3,189,715 v6/1965 Jennings. 3,283,100 1v1/1966 Frink. 3,372,258 3/1968 POIteI'.

ROBERT s. MACON, Primary Examiner.

U.S. Cl. X.R. ZOO-168

Claims

1. A VACUUM-TYPE CIRCUIT INTERRUPTER COMPRISING: (A) A HIGHLY EVACUATED ENVELOPE COMPRISING A TUBULAR CASING PRIMARILY OF INSULATING MATERIAL, (B) A PAIR OF ELECTRODES WITHIN SAID CASING DEFINING AN ARCING GAP THEREBETWEEN ACROSS WHICH ARCS ARE ESTABLISHED DURING A CIRCUIT-INTERRUPTING OPERATION, (C) A MAIN VAPOR-CONDENSING METAL SHIELD OF TUBULAR FORM SURROUNDING SAID ARCING GAP AND EXTENDING LONGITUDINALLLY OF SAID TUBULAR CASING FOR SUBSTANTIAL DISTANCES ON OPPOSITE SIDES OF SAID GAP, (D) MEANS FOR MAINTAINING SAID MAIN SHIELD AT A POTENTIAL INTERMEDIATE THAT OF SAID ELECTRODES FOLLOWING INTERRUPTION, (E) A FIRST PAIR OF AUXILIARY METAL SHIELDS OF GENERALLY TUBULAR FORM RESPECTIVELY SURROUNDING THE ENDS OF SAID MAIN SHIELD AND SPACED RADIALLY OUTWARD THEREFROM, (F) MEANS FOR RESPECTIVELY ELECTRICALLY CONNECTING SAID AUXILIARY SHIELDS TO SAID ELECTRODES, (G) A PAIR OF ADDITIONAL AUXILIARY METAL SHIELDS OF GENERALLY TUBULAR FORM RESPECTIVELY SURROUNDED BY SAID MAIN SHIELD AT ITS OPPOSITE ENDS, (H) SAID ADDITIONAL AUXILIARY SHIELDS BEING SPACED RADIALLY INWARD FROM SAID MAIN SHIELD AND BEING ELECTRICALLY CONNECTED TO SAID ELECTRODES.