US2027836A - Vacuum switch - Google Patents

Description

Jan. 14, 1936- w. K. RANKIN El AL VACUUM SWITCH Filed Feb. 23, 1934 III ll Fig. I.

Inventors William KRanKhm Claude D. Hayward,

6. QMZM Then" Attorney.

Patent d Jan. 14, 1936 UNITED STATES PATENT OFFICE VACUUM swrrcn.

Application February 23, 1934; Serial No. 712,522

' 5Claims. (01. 200-144) Our invention relates to vacuum switches, more particularly to vacuum switches wherein a magnetic field is utilized to effect rapid interruption of a high tension power circuit.

The use of a coiled conductor for producing a magnetic field is accompanied by mechanical problems involving compression and bursting stresses where large currents necessarily traverse the coil. These stresses may be of such magnitude that mechanical failure of the coils results unless special provision is made for strengthening the coil structure. A vacuum switch having such coil structure for producing a magnetic field must be so constructed that the entire arrangement is simple and readily prepared for high vacuum operation, as by well known degassing methods wherein the switch parts are heated to drive off occluded gases.

The object of the present invention is the provision of an improved vacuum switch of the aforesaid type which shall be simple, mechanically strong and compact in construction, and reliable and eflicient in operation.

Our invention will be more fully set forth in the following description referring to the accompanying drawing, and the features of novelty which characterize our invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

Referring-to the drawing, Fig. 1 is an elevational view, partly in section, of a high tension vacuum switch embodying the present invention;

Fig. 2 is an enlarged sectional view of the switch contact and coil structure illustrated in Fig. 1, and Fig. 3 is a plan view of the upper contact shown in Fig. 2.

The vacuum switch shown in Fig. 1 comprises an evacuated casing l in which are disposed relatively movable contacts 2 and 3, the contact 2 being stationaryand connected to a lead-in conductor stud 4 and the contact 3 being mounted at the end of a pivoted operating rod 5 which is sealed,,as by a flexible metallic diaphragm 6, to a lateral extension l' of the switch casing. Operation of the switch is effected by suitable actuating means connected to the operating rod 5 exteriorly of the switch casing for moving the contact 3 into and out of engagement with the stationary contact 2. The operating rod 5 is of conducting material so as to constitute one terminal of the switch, the other terminal comprising the extension 4 of the lead-in conductor stud 4.

The conductor stud 4 is mounted and insulated with respect to the casing l by means of insulating cylinders 1 and 8 interposed between the upper wall of the casing and flanges 9 and ID at opposite ends of the conductor stud, respectively. The sealing means for the conductor stud comprises an insulating sleeve ll flexibly connected and sealed to the casing l and to a flange I 2 welded to the conductor stud by flexible metallic diaphragms l3 and M, respectively. A conelike shield I5 is connected to the lower end of the conductor stud for preventing formation of a short-circuiting deposition of metal particles on the insulator 1. The switch structure above described is mounted on a high voltage insulator l6.

For the purpose of providing a radial magnetic field for eiiecting rapid interruption of high tension power circuits upon separation of contacts 2 and 3, as described with more particularity and claimed in an application Serial No. 712,521 for Vacuum switches, filed concurrently herewith by W. K. Rankin, a coiled conductor ll'connected in series with the circuit to be interrupted is disposed between the conductor stud 4 and the stationary contact 2.

Referring more particularly to Fig. 2, the coiled conductor ll, which is in the form of a substantially fiat strip helically disposed, is electrically connected through its upper turn to the flange 9 which is in turn suitably connected as by screwthreaded engagement to the conductor stud 4 and through its lower turn to the stationary contact 2. As illustrated, the contact 2 comprises a circular or disk-like conducting member having a flared annular flange 2 and a central opening at l8. As illustrated by Fig. 3, which is a plan view looking upwards of the contact 2, the contact is slotted as at I9 for the'purpose of preventing circulation of currents and for minimizing heating due to the magnetic field of the coil I! and the flange 9 is similarly slotted at 29. It will be apparent that the contact 2 may be slotted at a plurality of points around the periphery thereof if desired.

The assembly of the coil with respect to the contact structure includes a conducting disk 2| which is secured with respect to the upper flange 9 as by bolts 22 which extend through the coiled conductor H and are insulated therefrom by an insulating sleeve 23 composed of glass or ceramic material which may be degassed without difliculty. The structure above described would be adequate in case of moderate currents traversing the coiled conductor I! but would in all probability fail in the case of heavy short circuits.

For the purpose of providing for heavy compression and bursting stresses imposed on the coil it adjacent turns of the coil at uniformintervals have recesses as hemispherical indentations at ll so as to receive balls 25 or the like composed of a strong insulating material, a ceramic material such as a glass having a low coefllcient of expansion known to the trade as Pyrex being a suitable example. In general, the insulating material used in the switch must be of such a nature that it will withstand temperatures between 300 and 700 C in vacuum without deterioration.

As illustrated in Fig. 3, the insulating balls 26 and supporting bolts 22 are disposed around the -coil it in suitable manner, depending of course on the mechanical requirements of the structure. The balls 26 which are capable of withstanding high compression and shearing stresses not only serve to insulate the turns of the coil with respect to each other and to prevent short circuiting of the same due to high compression stresses but also to prevent bursting of the coil. In fact, increase of the strength of the :1. emetic field serves to wedge the balls 24! into such high pressure engagement with the adjacent turns of the coil that the structure is self-locking and more y braced during heavy currents. It will be apparent t the insulating bracing members between the turns of the coil it may assume the form of cylinders, wedges, or the like.

The bursting force acting on the coil i?! can be considered as ac in the same way as a spiral spring which been wound tight by torsion applied at its ends. The spring becomes smaller in diameter when wound up but increases in diam eter when released. Winding up the spring and soldering the turns together at a number of points parallel with vits axis would prevent unwinding but such an arrangement is obviously out of the question in a coil wherein each turn is to be electiically insulated with respect to ad jacent turns.

The insulating balls above described likewise serve as keys to prevent rotation oi the turns of the coil upon each other. In order that the coil turns may rotate with respect to each other, the insulating balls must either shear, enlarge the ball pockets by side thrusts or roll out of the pockets by spreading of the turns. The coil is preferably proportioned so that the force tending to compress the coil is large relative to the force per turn tending to enlarge the coil diameter and since these forces increase substantially as thes uare of the current there will always be suincient force to main the balls tightly seated in their pockets.

A central insulating cylinder 25 composed of a suitable cec material or the like is posiof the contact 2 which is composed of a suitable a conducting material as copper. v The movable contact 8 which likewise comprises a conducting disk-like membercomposed of cop- I to surface to which is connected a stud secured per and fiared as at 3' similarly to contact Z'is provided with a securing flange 2'11 at its inner to the operating rod 5. The contact 3, however, is not slotted and comprisesa continuous conducting path extending around the periphery of the contact. Accordingly, when the contacts 2 and t and cathode spot at the center of the contacts turns for resisting compression and bursting are separated the magnetic field produced by the coil ll induces eddy currents in the contact 3 which in turn set up a countermagnetic field opposing the main field of the coil it as illustrated by the directional lines F of the fields. 5

The resulting magnetic field between the contacts 2 and 3 is radial with respect to the contact surfaces so that the stream of ions and the cathode spot which are formed upon initial separation of high tension circuit terminals in a high vacuum are moved and rotated as presently described at very high speed around the peripheries of the contacts.

In order to prevent localizing of the ion stream where the magnetic field is the weakest, the coacting contact faces of the contacts 2 and 3 are cut away or dished as at 28 and 29, respectively, so that the actual contact separation occurs near the outer peripheries of the contacts. The recess 28 in the contact 2 has a diameter slightly greater than the mean diameter of the coil turns so that current flowing from the lower turn of the coil through the contact to the cathode spot must be in a radially outward direction. The action of the field resulting from this current is such that the ion stream is moved towards the-rim of the contact. The ion stream and cathode spot are, therefore, positively moved toward the con tact peripheries and rapidly rotated at the outer flared edges of the contacts with the result that the circuit is quickly-interrupted.

It should be understood that our invention is not limited to specific details of construction and arrangement thereof herein illustrated, and that changes and modifications may occur to one skilled in the art without departing from the spirit of our invention.

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

1. In a vacuum switch comprising an evacuated casing and relatively movable contacts disposed therein, a coiled substantially fiat conductor connected in series with said contacts for producing a magnetic field adjacent the coacting contactas surfaces thereof, and insulating locking members individually disposed between adjacent turns of 'said coiled conductor, each member positioned in recesses formed in opposing faces of adjacent forces acting on said coil.

2. In a vacuum switch comprising an evacuated casing and relatively movable contacts disposed therein, a coiled conductor connected in series with said contacts for producing a magnetic field adjacent the coacting contact surfaces thereof, the adjacent turns of said conductor having substantially fiat opposing faces, and means for bracing said coiled conductor with respect to com= 1 pression and bursting forces including a plurality of insulating balls disposed between said turns and positioned by pockets formed. in said conductor.

3. In a vacuum switch comprising an evacuated casing, relatively movable contact structure disposed therein comprising a disk-like contact, a coil connected in series with the circuit to be interrupted mounted within the saidcasing and secured with respect to said stationary contact; and a coa'cting disk-like contact forming a continuous circular conducting path related to said coil so that eddy currents for producing an op posing field are generated in said coacting con== tact, said contacts having peripheries dared my opposite directions and arranged to break the circuit adjacent said peripheries.

4. In a vacuum switch comprising an evacuated casing, relatively movable contact structure disposed therein comprising a stationary, diskripheries of said contacts and the electron stream is rapidly rotated by said radial field towards the outer flared peripheries of said contacts.

5. A coil structure for producing a magnetic field comprising a substantially fiat helical conductor the turns of which are closely spaced, and

insulating members composed of a strong ceramic material or the like individually disposed between adjacent turns of said coil and positioned in recesses in said conductor, said insulating members separately locked in position by compression stresses acting on said coil so as to maintain the turns of said coil spaced and insulated with respect to each other.

K. RANKIN. CLAUDE D. HAYWARD.

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