US 3809836 A
A high current vacuum interrupter (rated to interrupt currents greater than 16,000 amperes r.m.s.) comprises (1) a pair of large disc-shaped contacts slotted to provide an arc-revolving action and (2) a tubular metal shield closely surrounding the contacts. Localized melting of the shield by an inter-contact arc is reduced by angularly displacing the contacts with respect to each other so that the starting points of slots in the contacts are angularly offset by substantially the maximum possible amount.
Claims available in
Description (OCR text may contain errors)
United States Patent [191 Crouch May 7, 1974 VACUUM-TYPE ELECTRIC CIRCUIT 3,522,399 7/1970 Crouch 200 144 B [NTERRUPTER 3,622,724 11/1971 Sofianek 200/144 B [75 Inventor: Donald W. Crouch, Newtown Square, Pa.
[7 3] Assignee: General Electric Company,
 Filed: Dec. 21, 1972 v 211 App]. No.2 317,222'
52 us. Cl. 200/144 B  Int. Cl. H0lh 33/66  Field of Search 200/144 B  References Cited UNITED STATES PATENTS 3,462,572 8/1969 Sofianek..... 2994154 e h Primary Examiner-Robert S. Macon Attorney, Agent, or Firm-J. Wesley Haubner,
[5 7] ABSTRACT A high current vacuum interrupter (rated to interrupt 7 Claims, 3 l)r ayving Figures BACKGROUND This invention relates to a vacuum-type electric circuit interrupter and, more particularly, relates to a high-current vacuum interrupter of the type comprising slotted disc-shaped contacts for revolving the are formed during interruption.
Contact structure of this general type is disclosed and claimed in U.'S. Pat. No. 2,949,520-Schneider, assigned to the assignee of the present invention. Each of the contacts of the Schneider patent comprises a discshaped member having a plurality of slots therein extending both radially and circumferantially of the disc member. These slots are used to produce an arcrevolving effect that forces arcs having a terminal located on the slotted portion of the disc' member to revolve about the central axis of the disc member. Centrally of the disc member there is a contact-making annular button where arcs are initiated during circuitinterrupting operations. Such an arc is magnetically driven radially outward off of the contact-making button; and as it approaches the outer periphery of the disc member, it is revolved by the arc-revolving action produced by the slots in the disc member.
An improved form of the Schneider contact structure is disclosed and claimed in US. Pat.'No. 3,522,399-- Crouch, assignedto the assignee of the present invention. In the contact structure of the Crouch patent, four slots are provided in each disc-shaped contact. Each slot has a configuration such that it extends from a starting point at the outer periphery of the contact into the contact body via a path approximately tangential to the outer periphery of the contact-making button. At its innermost end, the slot has a portion extending transversely of the tangential portion of the slot to a point spaced radially inward of the button periphery.
While generally very effective in producing the desired arc-revolution, there is one particular vacuum interrupter application where the contact structure of the Crouch patent appears to be not as effective as might be desired in this respect. This application is in a highcurrent vacuum interrupter (i.e., an interrupter rated at greater than 16,000 amperes r.m.s. interrupting current with any factor of asymmetry up to a maximum of 1.3) where the usual tubular metal shield surrounding the contact is separated by only a small distance from the contacts. In such an application, the high current are seems to have an undue tendency to melt and burn the adjacent shield. The probable cause of this undue tendency, my studies indicate, is that there are regions on the contact periphery where the magnetic force component urging an arc in this region radially-outward is high compared to the magnetic force component urging the arc circumferentially. This high radiallyoutward-acting force component blows the arc against the inner surface of the shield, increasing the heating and erosion of the shield wall at this location. As the pressure due to evaporating shield material builds up, the circumferential motion of the arc is impeded, thus increasing the rate of heat input to this localized region of the shield surface. This slows the arc even more, which further increases the erosion of the shield in this localized region, thus producing a pyramiding heating effect at a localized region of the shield.
SUMMARY An object of my invention is to provide a contact arrangement capable of causing high current arcs to revolve about the contact periphery at high speed without undue stalling despite the fact that slots of the general configuration shown in the Crouch patent are are used and also despite there being only a small clearance between the outer periphery of the contacts-and the surrounding tubular shield.
Anotherobject is to utilize contacts of the general configuration shown in the Crouch patent in such a way as to effect during high-current interruption a more even distribution around the entire shield circumference of the arcing energy into the shield, thus avoiding excessive melting and burning of the shield.
In carrying out my invention in one form, I provide a high-current vacuum interrupter comprising two discshaped contacts, each having a diameter of atleast 2% inches and each having four arc-revolving slots therein of a configuration similar to those shown in the aforesaid Crouch patent. Closely surrounding the contacts, but spaced therefrom, is a tubular metal shield that is normally electrically isolated from the contacts. The peripheries of the contacts are substantially aligned but are circumferentially displaced relative to each other so that the starting points of the slots on the periphery of one contact are displaced by 35 to 55 from the starting points of the slots on the periphery of the other contact.
BRIEF DESCRIPTION OF DRAWINGS For a better understanding of the invention, reference may be had tothe following description taken in conjunction with the accompanying drawings, wherein:
DETAILED DESCRIPTION- OF PREFERRED EMBODIMENT Referring now to FIG. -l,-there is shown a vacuumtype circuit interrupter comprising a sealed envelope l0 evacuated to a pressure of 10" torr or lower. This envelope comprises a tubular casing 11 of insulating material and a pair of end caps 12 and 13 joined to opposite ends of the casing 11 by suitable vacuum-tight 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.
The operating rod 18a projects freely through an opening in the lower end cap 13, and a flexible metallic bellows 20 provides a sea] 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.
Each of the contacts 17 and 18 is of a substantially circular disc-shape and has one major surface facing the other contact. Each contact comprises a centrally located contact-making button suitably brazed to the remainder of the contact. Each of the contactmaking buttons is provided with a centrally-located recess 27 so that contact between the buttons occurs on an annular contact-making area 30 when the contacts are in their dotted-line engaged position of FIG. 1. These annular contact-making regions 30 are of such a' diameter that current flowing through the closed contacts follows a radially-outwardly bowing loopshaped path L, as is indicated by the dot-dash line of FIG. 1. The magnetic effect of current flowing through this loop-shaped path L tends ina 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. To make the loop in the loop-shaped path sufficiently pronounced so as to provide the desired high radially-outwardly acting force, the outer diameter of the contact-making button 25 is made greater than half that of the disc-shaped contact.
As the terminals of the arc move toward the outer pe- I riphery of the discs 17 and 18, the arc is subjected to a circumferentially-acting magnetic force that rotates the are about the central axis of the discs. This circumferentially-acting magnetic force is produced by four slots 32 provided in each of the discs and dividing each disc into four fingers 33. Each slot 32 extends into the contact body from astarting point at the outer periphery of its disc 17 or 18 via a path wherein the center line 37 of the slot is substantially tangent to the outer periphery. of the contact-making button 25. The slot continues generally tangentially of the button 25 for a substantial distance past the point 34 at which the center line 37 first touches the button periphery. At the innermost end of the tangentially-extending portion of the slot, there is a radially-inwardly extending portion 35 that extends transversely of the tangentiallyextending portion. This inwardly-extending slot portion 35 extends from the outer. periphery of button 25 to a point 36 spaced radially inward from the outer periphery of the button. As seen in FIG. 2, the button extends across, or bridges, the inwardly-extending slot portion 35. a
These slots 32 force the current flowing to or from an arc terminal on a finger 33- to follow a path through the finger that extends circumferentially of the disc in the vicinity of the arc. For example, if the arc terminalis at a position 40 in FIG. 2, the effective path of'the current flowing through the finger 33' to the arcwill be shown at'4l, extending circumferentially of the disc. This circumferential component of the current path causes the current flowing through the loop L to develop a net circumferentially-acting force component which revolves the arc about the central axis of the disc.
This circumferentially-acting force component is high enough to drive each terminal of the arc across the slots 32 at the free end of fingers 33, thus producing a continuous revolving movement of the are on the contact surface. Such continuous revolving movement of the arc aids in interrupting higher currents by reducing-the quantity of metal vapors generated by the are, thus permitting more complete condensation of the metal vapors at current zero.
For condensing the metal vapors generatedby arcing, suitable vapor-condensing shields and 54 are provided. The main shield -50-is a tubular metal member surrounding the contacts'l7 and 18 and located between the insulating casing 11 and the arcing gap between the contacts. This shield 50 is electrically isolated from the contacts and is preferably maintained at a potential substantially midway between that of the two contacts when the interrupter is open. To this latter end, the shield is supported on casing 11 by means of a radially-extending flange 55 that is located between the upper and lower halves of casing 11 and extends in sealed relationship through casing 11. Auxiliary shields 54 of tubular form connected to the end caps 12 and 13, respectively, surround opposite ends of the main shield 50. These auxiliary shields serve,.among other things, to condense any vapors bypassing the main shield. t
For .the sake of compactness and economy, it is desirable that thetubular main shield 50 have as small a diameter as possible. At the same time, it is necessary for the contacts 17 and 18 to have a certain minimum diameter if they are to interrupt currents of a given magnitude. Fulfilling these two requirements results in an interrupter in which only a relatively small clearance space is present between the outer periphery of the contacts and the inner periphery of the tubular shield. For example, in an interrupter rated to interrupt 20,000 amperes r.m.s. with any factorof asymmetry up to 1.3, I utilize contacts having a diameter of 2% inches and a main shield having an insidediameter 'of 4 inches,
with a resultant clearance space of onlynine-sixteenths inch between the contacts and the'shield.
When such a small clearance space is present with contacts of the general configuration and size described hereinabove, I have found there is a rather strong tendency during high'current interruptions for the arc to produce excessive burning and melting of the shield in localized regions. As pointed out in the introductory portion of this application, my studies indicate that the probable reason for this localized heating andmelting is that there are regions at the contact periphery-where the magnetic force component urging an arc in this region radially outward is high compared to the force component urgingthe arc circumferentially. This high radially-outward-acting force component blows the are against the inner surface of the shield, increasing the heating and erosion of the shield wall at this location. As the pressure due to evaporating shield material builds up, the circumferential motion of the arc is impeded, thus increasing the rate of heat input to this localized region of the shield surface. This slows the are even more, which further increases the erosion of the shield in this localized region, thus producing apyramiding heating effect at this localized region of the tion at which the radially-outward-acting magnetic force on the arc is highest relative to the circumferentially-acting force is the region at the proximal end of each of the circumferentially-extending fingers 33. When an arc, such as 60, is located in this particular region, the net current path (62) through the contact to the arc is almost entirely radial with little or no circumferentially-extending component. As a result, the principal force on an arc in this region produced by the passage of current through path 62 is radial rather than circumferential, and this results in a strong ten-' dency for the arc in this region to be blown radially outward against the adjacent metal shield 50. As the arc terminal moves circumferentially of the contact out onto the finger 33, the circumferentially-acting force component on the arc becomes progressively larger relative to the radial force component, and there is a correspondingly reduced tendency for the arc to be blown radially toward against the shield.
To reduce the tendency of the arc to be blown against the shield 50 while in the region at the proximal end of any finger 33, l circumferentially displace the two contacts from each other in such a manner that the starting points of the slots 32 on one contact are angularly displaced about the contact periphery from the starting points of the slots on the other contact. Preferably, this angularly displacement is by the maximum possible extent, i.e., 45, but my invention in its broader aspects contemplates a displacement of between 35 and 55. A displacement of 45 is illustrated in FIG. 3, where the slots 32 in one contact are shown in solidline form and those in the other contact are shown in dotted-line form. 1
As a result of this displacement, when one of the arc terminals is in the weak circumferential-force zone at the proximal end of finger 33 on one contact, as shown at 70 in FIG. 3, the opposite arc terminal is at a point well out on the finger 33 of the other contact, thus enabling said other contact to produce a strong circumferentially-acting driving force on the arc. At all points about the circumference of the contacts, either one or the other of the contacts can provide a strong circumferentially acting force on the arc, thus eliminating any peripheral zone occupiable by the .arcwhere both contacts might be providing a weak circumferentially-acting force and a strong radially-outwardlyacting force.
The net effect of the above-described angular, or circumferential, displacement of the contacts is to eliminate regions where the arc has an undue tendency to stall as it moves about the peripheral region of the contacts. As a result, the arc moves more smoothly around the contact periphery, thus distributing arcing energy into the shield more uniformly and reducing the tendency for overheating and excess vaporization of the shield in any localized regions.
It is to be noted that my invention is limited to a high current interrupter (i.e., an interrupter rated to interrupt currents greater than 16,000 amperes r.m.s. with any factor of asymmetry up to 1.3 and requiring a contact disc diameter of at least 2% inches). In lower current interrupters such as disclosed in my aforesaid U.S. Pat. No. 3,522,399, with the shield-to-contact clearances typically used, no significant reduction in localized shield-melting is produced by angularly displacing the starting points of the slots in the two contacts. Commercial forms of the interrupter disclosed in my aforesaid patent have a contact disc diameter of only about 1% inches, a shield-to-contact clearance of about thirteen-thirty-seconds inch, and an inthe current flowing through the finger to an arc terminal thereon in a more nearly circumferentially-directed path, thus strengthening the circumferentially-acting component of the magnetic force developed by current flowing through said path. Along these lines, the average slot width is preferably greater than one-third of the. average finger width, considered in the region where the fingers extend parallel to the circumference of the disc, said widths being measured as viewed in FIG. 2 from the other contact. 7
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 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: y
1. A vacuum-type interrupter for interrupting currents greater than 16,000 amperes r.m.s. with any factor of asymmetry up to 1.3 comprising:
a. an envelope evacuated to a pressure of 10 torr or lower,
b. a pair of relatively movable disc-shaped contacts within said envelope, each having a generally circular'outer periphery, a diameter greater than 2% inches, and a contact-making face confronting the other contact that is engageable with said other contact, Y
a contact-making button having a substantially circular outer periphery substantially concentric with the outer periphery of said disc-shaped contact, the diameter of said button being greater than half the diameter of said disc-shaped contact,
d. each contact having four circumferentially-spaced slots therein, each slot having a tangential portion extending into the body of said contact from a starting point at the outer periphery. of said contact via a path wherein the center-line region of the slot is generally tangent to the outer periphery of said button, thereby providing circumferentiallyextending finger portions between said tangential slot portions and the outer periphery of said contact,
. each slot having a portion at the innermost end of said tangential portion extending transversely of said tangential portion and radially inwardly of said contact body to a point spaced radially inward from the outer peri-phery of said button,
f. a tubular metal shield surrounding said disc-shaped contacts and electrically isolated therefrom when said interrupter is open,
g. the inner periphery of said shield being separated by a small annular clearance space from the outer periphery of said disc-shaped contacts,
. each contact comprising at its contact-making face h. the starting points of the slots in each contact being spaced substantially equally about the outer ery of said shield, is no greater than five-eighths inch..
' 3. The interrupter of claim 1 in which said discshaped contacts have substantially the same diameter and have their generally circular peripheries substantially aligned radially.
4. The interrupter of claim 1 in which each contact at its outer periphery at the proximal ends of said circumferentially-extending finger portions has regions occupiable by an arc terminal to which current can flow from the central portion of said contact via a path that is substantially entirely radial with substantially no tangential component, thus causing current in passing through said path to develop a predominantly radiallyoutwardly acting force on an are having its terminal in one of said regions.
5. The interrupter of claim 4 in which said regions at the proximal ends of said finger portions in one contact are angularly displaced by 35to 55 from said regions in said other contact.
6. The vacuum type circuit interrupter of claim 1 in which the displacement referred to in (i) is about 45.
width greater than one-third the average width of the finger portion immediately adjacent said slot, said widths in each contact being measured as viewed from the other contact.