US3614361A

US3614361A - Contact with low-cathode drop material insert

Info

Publication number: US3614361A
Application number: US864926A
Authority: US
Inventors: Donald E Weston
Original assignee: Allis Chalmers Corp
Current assignee: Allis Chalmers Corp
Priority date: 1969-09-10
Filing date: 1969-09-10
Publication date: 1971-10-19
Anticipated expiration: 1988-10-19
Also published as: CA926905A

Abstract

A circuit interrupter, such as a vacuum switch, comprises a pair of relatively movable contacts, at least one of which is a relatively flat disc made of high-cathode drop material, such as molybdenum and having one or more spiral slots extending inwardly from the periphery of the contact filled with solid low-cathode drop material, such as antimony to cause rotation of an arc between said contacts and to facilitate movement of the arc terminal as the arc rotates.

Description

States Patent 1 1 3,616,361

[72] inventor Donald E. Weston [56] References Cited Chicago, Ill. UNITED STATES PATENTS 5; m 3 6 I969 3,182,156 5/1965 Lee eta]. 200/166 c x f a i- 3,281,563 10/1966 Waterton 200/166 c Assignee Ams chalmers Manufacturing p y 3,327,081 6/1967 Pflanz 200/166 C X Milwauke Wi Primary Examiner-H. 01 Jones Att0rneys'l"homas F Kirby, Lee H. Kaiser and Robert B.

Benson [54] CONTACT WITH LOW'CATHODE DROP ABSTRACT: A circuit interrupter, such as a vacuum switch, MATER1ALlNSFRT comprises a pair of relatively movable contacts, at least one of 2Cla'mS6Dmwmg which is a relatively flat disc made of high-cathode drop [52] 10.5. C1 200/166 C material, h s olybdenum and having one or more spiral [51] Int. Cl 1-1101111 02, slots extending inwardly from the periphery of the contact HOlh 1/06 filled with solid low-cathode drop material, such as antimony [50] Field of Search 200/166 C, to cause rotation of an are between said contacts and to facilitate movement of the arc terminal as the arc rotates.

CONTACT WITH LOW-CATIIODE lDIIOlP MATERIAL INSERT SUMMARY OF THE. INVENTION This invention relates generally to means for extinguishing arcs generated between electric terminals or separable contacts. More specifically, it relates to electric terminals or separable contacts wherein an arc established therebetween is rotated to effect its extinguishment.

The arc interrupting capacity of a pair of relatively movable circuit breaker contacts, for example, can be increased substantially by rotating the arc terminals at high speed across the surfaces of the contact. U.S. Pat. No. 3,327,081, issued June 20, 1967 to H. M. Pflanz for Contact with High Resistance Material Insert" discloses contacts wherein such are terminal rotation is effected by means of one or more slots (filled with high-resistance material) extending inwardly from the periphery of a disc-shaped contact (made of low-resistance material). It is desirable to provide a contact on which the are or arcs tend to track along a predetermined path and to do so without damaging the path which it follows. In accordance with the present invention there is provided an electrical con tact which is made of high-cathode drop material, such as molybdenum or tungsten, and which has one or more spiral grooves in the face thereof filled with low-cathode drop material, such as antimony, bismuth, tin or zinc. An arc initiated at or near the center of the contact tends to track along that material which requires the least energy input to sustain itself. Consequently, the arc follows the path of the lowcathode drop material. In order to obtain the most uniform distribution of the thermal energy input of the contact, the arc should be driven at high velocity. Thus, a contact in accordance with the present invention performs very well at are currents near amperes or above, However, since the penetration depth of thermal energy into the contact for the lifetime of most normal arcs is relatively shallow, the depth of the low-cathode drop material need not necessarily be great. For example, in a contact having a diameter of about 3 inches the groove containing the low-cathode drop material need not exceed one-eighth inch. Smaller diameter contacts may be proportioned accordingly. A contact in accordance with the present invention is employed to particular advantage in polarized circuit interrupters wherein the present improved contact always serves as a cathode.

OBJECTS OF THE INVENTION It is an object of the present invention to provide improved electric terminals or contacts of the type which apply the arc rotation principle to effect are extinguishment.

Another object is to provide electric terminals or contacts which employ the slotted disc principle to effect arc rotation but which overcome the problems of arch hangup or are jumping at the slot edges.

Another object is to provide electric terminals or contacts comprising slotted discs wherein the slots are filled with material which facilitates arc rotation.

Another object is to provide terminals or contacts of the aforesaid character wherein the material used to fill the slots has low-cathode drop characteristics and fills the slots so as to render the contact surfaces relatively smooth.

Another object is to provide terminals or contacts of the aforesaid character wherein the slots are filled with a material having lowwathode drop characteristics as compared to that of the material of which the contact body is made so as to effect preferential arcing on the contact body.

Another object is to provide terminals or contacts of the aforesaid character which are relatively easy to fabricate and are reliable in use.

Other objects and advantages of the invention will hereinafter appear.

DESCRIPTION OF THE DRAWINGS The accompanying drawing illustrates several preferred embodiments of the invention but it is to be understood that the embodiments illustrated are susceptible of modification with respect to details thereof without departing from the scope of the appended claims.

In the drawing:

FIG. 1 is a cross-sectional view of a vacuum interrupter employing one embodiment of a pair of contact incorporating the present invention;

FIG. 2 is an enlarged end view of one of the pair of contacts shown in FIG. ll;

FIG. 3 is a cross-sectional view of the contact taken along line III-III of FIG. 2;

FIG. 41 is a cross-sectional view of a portion of a contact similar to that shown in FIG. 3 but wherein the slot extends entirely through the thickness of the disc;

FIG. 5 is an end view of another contact embodying the invention; and

FIG. 6 is a cross-sectional view of the line VI-Vl of FIG. 5.

contact taken along DESCRIPTION OF THE INVENTION Referring to FIG. I, the numeral III designates a vacuumtype electric circuit interrupter or switch employing relatively movable contacts incorporating the present invention. It is to be understood, however, the contacts or terminals incorporating the present invention can be employed in other types of electrical apparatus beside circuit breakers, such as lightning arresters, for example.

Vacuum switch llh comprises a cylindrical envelope I2 which may be formed, for example, of a suitable vitreous material. One end of envelope I30 is provided with an annular rim M to which is rigidly secured in a vacuumtight connection one end of a ring or flange 116. A metallic cap 18 is sealed along its edge to the other end of flange I6. Cap 18 supports a stationary contact support 20 which extends along the longitu dinal axis of envelope I2 and is rigidly supported so as to be restricted against longitudinal or lateral movement. The opposite end of envelope I2 is provided with an annular rim 22 to which is rigidly secured in a vacuum tight connection one end ofa ring or flange 24. A retainer 26 is sealed along its rim in a vacuumtight connection to flange 24. A metallic cylindrically shaped flexible bellows 28 is rigidly secured in a vacuumtight connection at one end thereof to retainer 26. The other end of bellows 2d surrounds and is rigidly secured in a vacuumtight connection to a movable contact support 39 which is arranged to extend through retainer 26 into envelope I2 and is in cooperating relationship with contact support 20.

The relatively movable contact supports 20 and 3 may be made of a suitable electrically conductive material such as copper or the like. Contact support 30 is understood to be ar ranged for longitudinal movement along its axis for a limited predetermined distance by a suitable contact actuating mechanism (not shown).

The contact supports 20 and 30 support contacts 32 and 34-, respectively, hereinafter described. In order to control the dispersion of are products emitted upon separation of the con tacts 32 and 3d, a cylindrical cup-shaped tube or shield 36 is provided which is rigidly secured to contact support 24 and is arranged to extend beyond the adjacent ends of both

contact supports

20 and 30 so as to surround the

contacts

32 and 34 when the contacts are engaged and disengaged. Shield. as may be formed of glass or any suitable metallic or nonmetallic material.

Upon actuations of movable contact support 363! in axial contact engaging or contact disengaging direction, bellow 28 deflects, allowing restricted longitudinal movement of contact 1%. Tile required range of movement of contact 3% is very small. For example, with only three-sixteenths of an inch separation between engaging surfaces of contacts 32 and a current of several thousand amperes at a voltage of l8,(l0'd can be safely interrupted in the vacuum within the envelope. The contacts when engaged can continuously conduct current of several hundred amperes.

Referring to FIG. 1,

contacts

32 and 34 are shown as substantially identical to each other and a description of contact 34 will suffice for contact 32 as well. However, it is to be understood that the invention can be embodied in a circuit interrupter or other are extinguishing electrical device wherein only one contact or terminal is constructed in accordance with the present invention. FIGS. 1, 2 and 3 show that contact 34 is in the shape of a disc and has its arcing surface facing contact 32. Thus, when

contacts

32 and 34 are closed, the arc surfaces abut and current flows through the contacts. Upon contact separation an arc is initiated between

contacts

32 and 34 which has its terminals on the arcing surfaces of the contacts.

Referring to FIGS. 2 and 3, contact 34 comprises a first portion or body portion which is fabricated of high-cathode drop material such as molybdenum of tungsten. Body portion 37 of contact 34 is provided with a single spiral groove or slot 38 on the arcing surface thereof which is filled with solid lowcathode drop material 40 such as antimony, bismuth, tin or zinc. The slot 38 of contact 34 extends radially outward from near the center of body portion 36 to the edge or periphery thereof and traverses more than 360 of angular distance.

FIG. 4 shows a portion of a contact 42 which is to be understood as similar to contact 34 except that it has a spiral groove or slot 44 which extends all the way through the first portion or body portion 46 of the contact. The slot 44 in contact 42 is completely filled with low-cathode drop material 47.

Referring to FIGS. and 6, there is shown a contact 48 which is to be understood as similar to contact 34 except that is has a plurality of

spiral grooves

50, 52 and 53 which are filled with low-cathode drop material. FIG. 6 shows that the

grooves

50, 52 and 53 extend only a limited distance inward from the face of the contact but the

grooves

50, 52 and 53 could extend all the way through the first portion or body portion 54 of contact 48, as FIG. 4 shows in regard to contact 42.

Furthermore, more than three slots could be employed in contact 48.

In operation, an arc terminal initiated at or near the center of a contact, such as the

contacts

34, 42 or 48, tends to track along the material which requires the least energy input to sustain itself and, consequently, teaches along the lowcathode drop material. The are should be driven at high velocity to obtain the most uniform distribution of thermal energy throughout the contact. However, the penetration depth of the thermal energy into the contact is relatively shallow, if arc life is short, and the depth of the low-cathode drop material need not be great in such cases.

As is well known, magnetic forces causing rotation of the are are generated by the current flow path from the support rod 30 and radially outward through the contact body to the particular location of an arc terminal.

Other metal or alloy combinations may be employed to carry out the present invention provided the materials employed are selected according to the preceding principles.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In an electrical contact on which an electric arc terminal is to be established, an electrically conductive body comprising molybdenum and having at least one slot extending outwardly from near the center thereof in a curved path, and solid antimony disposed within said slot.

2. In an electrical apparatus, in combination, a pair of terminals between which an electric arc is established and is to be extinguished, at least one of said terminals comprising an electrically conductive disc comprising molybdenum and having a plurality of slots therein extending inwardly from the periphery thereof and solid conductive antimony disposed within said slots, said material filling said slots so as to be flush with the surface of said disc, whereby an arc terminal initiated near the central portion of the surface of the disc is rotated around said surface and toward the periphery thereof.