US2650971A - Electrical switch - Google Patents

Description

p 1953 A. J. DAWE 2,650,971

ELECTRICAL SWITCH Filed June 8, 1950 J INVENTOR.

l i} Q a 7 jt'larnay Patented Sept. 1, i953 ELECTRICAL SWITCH Albert J; Dawe, Milwaukee, Wis., assignor to Allen-Bradley Company, Milwaukee, Wis., a corporation of Wisconsin ApplicationJune 8, 1950, Serial No. 166,939

4 Claims.

This invention relates to electrical switches and resides in a novel switch arrangement in which auxiliary means in the form of a ring shaped ferro-magnetic body is related dimensionally and fixed positionally with respect to one of a pair of switch. contacts in such manner as to overcome arc displacing conditions prevailing upon interruption of current flow so as to avoid displacement of the are from the position in which it is initiated between the separated contacts until the arc becomes extinguished.

Circuit breakers for interrupting very heavy currents at large potentials depending upon air blast effects, de-ion plate effects, oil immersion and the like are large, bulky and expensive. For the interruption of smaller and medium alternating currents at moderate potentials, effective, economical and compact switches have heretofore been provided through the use of simple separating contacts of suitable alloys in multiple-break arrangement enclosed in insulating hoods or housings. In such switches much advantage has been gained by providing a sufficient number of breaks so that restriking potentials, not exceeding about 175 volts, are avoided. Because of the advantages of compactness and economy in such simple switches substantial and consistent effort has been made to extend the use thereof into higher ranges of current interrupting capacities. Heretofore the reliable current interrupting capacity of such simple switches has been sharply limited.

It is an object of this invention to extend the useful range of capacity of simple separating contact switches into a previously unattained operating range where alternating currents upwards from 500 amperes to 1,000 amperes and higher can be reliably interrupted.

This invention arises from my discovery that a ring of ferro-magnetic material, fixed in position surrounding one of a pair of axially separating contacts, with its outer rim substantially flush with the face of the surrounded contact, so as to not project at any time into the gap between the separated contacts, exerts an effect, as yet not fully explained, which neutralizes any lateral moving tendency of an alternating current are drawn on separation of the contacts.

This invention is herein described by reference to the accompanying drawing forming a part hereof in which there is set forth by way of illustration and not of limitation one form in which the apparatus of this invention may be embodied.

In the drawing,

Fig. l is a side view in elevation with parts 2 broken away and in section, viewed through the plane l-l shown in Fig. 2, of a. double break switch embodying the improvement of this invention;

Fig. 2 is a top plan view, partly in section, viewed through the broken plane 22 indicated in Fig. 1, of the switch there shown;

Fig. 3 is an end view in elevation and in section, of the switch shown in Fig. 1, viewed through the plane 33 there indicated, and

Fig. 4 is a detail, bottom plan view of one of the stationary contacts of the switch shown in Fig. 1.

The improvement of this invention as shown in the drawings forms a part of a so-called double-break switch having an insulating stationary contact mounting l and an insulating movable contact mounting 2. The stationary mounting I is in the form of a roughly rectangular arc hood which is open at the bottom and closed at the top by a horizontal wall 3.

Held in place in an opening 8 in the top wall 3 is a stationary contact assembly which includes contact stud 5to the lower face of which a silver composition contact disc 4 is attached. Stud 5 and contact disc 4 constitute a terminal composed of non-magnetic material. Bearing upon a shoulder formed by the head of the stud 5 is an insulating washer 6 between which and the wall 3 there is clamped a cup shaped ring 1 of mild steel or other ferro-magnetic material. The sides of the ring I extend downwardly surrounding but not touching the sides of the head of the stud 5 and by reason of the washer 6 the ring I is electrically insulated from the stud 5. The lower rim of ring 7 as shown terminates substantially flush with, or slightly above, the lowermost part of the contact disc 4 at the lower end of stud 5.

The upper end of stud 5 is formed as a threaded shank 9 which passes upwardly through a terminal lug I0 seated on the top wall 3. A lock washer I 2 and nut II which engages the shank 9 serve to securely unite the parts forming the stationary contact assembly and to hold the assembly rigidly in place in the mounting I.

At the right end of mounting l is a stationary contact assembly similar in all respects to the assembly at the left and it includes a contact disc l3 carried on a stud l4 whose shank I5 is engaged by a nut [6 which clamps the assembly together and secures the same in position in the mounting I. Surrounding the head of the Stud [4 and insulated therefrom is a ring I! of mild steel, similar in all respects to the ring I, the lower rim of which is nearly flush with the lowermost part of disc 89. Beneath the nut I6 is a lock washer 66 which bears upon and holds in place a terminal lug is similar to the lug Hi.

The movable mounting 2 is engaged by means not shown so as to be moved toward and away from the mounting I and bears a headed stem which loosely interlocks at its upper end with the mid-point of a conductive bridge bar 2| as shown.

t the left end of the bridge bar H is an upwardly facing movable contact disc 22, positioned to engage the disc Q as shown; while a similar movable contact disc 23, at the right, is positioned to engage the contact disc l3.

Disposed between the mounting Z and the bridge bar 2| is a telescoping capsule composed of interfitting members 26 and 25 which house an expansion spring 26. The spring 26 bearing upon the washer Z'i acts to urge the members '24 and 25 apart and thus to urge the bridge bar 2i against the head 28 of the stem 2!] when the switch is in open position and against the contacts 4 and 13 when in closed position as shown.

It has been found in operation, that a three phase switch constructed as above described, in which the double break contact discs were approximately 0.75 inch in diameter, normally rated to carry a continuous current of 100 amperes, that currents up to 900 'amperes would be reliably interrupted in a circuit where thevoltage was in the neighborhood of 550 volts. If the rings il and l were omitted from the switch and all other conditions otherwise were maintained the same the switch was found to fail at currents as low as 500 amperes by flashing-over of the arc to ground or other phase conductors. The result obtained as noted above has not as yet been explained by any manner of functioning which will withstand full analysis. Notwithstanding, a marked and surprising gain in capacity has been experienced. The outstanding character of the improved switch of this invention is the absence of any tendency for the arc to move transversely to its thread once the arc is established and the tendency for the arc, short though it may be, to become extinguished where restriking voltages are avoided.

While the improvement of this invention is effective with any suitable contact material its fullest advantages appear to be obtained where v a de-ionizing contact material such as a silver composition containing cadmium is employed.

The location of the ferro-magnetic ring has been found to be of major importance. The placement of the extreme rim of the ring substantially flush with the face of the surrounded contact or preferably slightly to the rear thereof is necessary in order that the improved result be obtained. If placed forward of this position while the contacts are separating the arc has a tendency to strike the ring with heavy currents and the beneficial efiect thereof is destroyed. If placed substantially back of the point of contact separation the tendency of the arc to move laterally is no longer restrained.

I claim:

1. In an electrical switch a pair of relatively movable separable metallic contacts having forward contacting faces, and a ferro-magnetic ring surrounding one of said contacts fixed with respect thereto and electrically insulated therefrom disposed with its forward rim substantially flush with the forward face of the contact which it surrounds.

2. In an electrical switch a first non-magnetic terminal having a shank and an enlarged head, a first non-magnetic contact mounted on said terminal head to expose a forward contact face, a hollow cylindrical steel ring having a forward rim and an inwardly turned rear rim closely surrounding said terminal head, an insulating member surrounding said terminal shank and engaging the rear of said terminal head disposed between said terminal head and the inwardly turned rim of said ring to interpose insulation between said first terminal and said ring, fastening means engaging said shank and ring to hold the same rigidly with respect to one another, the forward rim of said ring being substantially flush with but to the rear of said forward contact face, a second terminal, a second contact mounted on said second terminal, and actuating means engaging said contacts to move the same into and out of engagement with one another.

3. A switch in accordance with claim 2 in which the contacts are composed predominantly of silver.

4. A switch in accordance with claim 2 in which the contacts are composed of a silver composition containing cadmium.

ALBERT J. DAWE'.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,940,962 Matthias Dec. 26, 1933 2,032,926 Ford Mar. 3, 1936 2,151,905 Emmert Mar. 28, 1939 2,227,434 Bierenfeld Jan. '7, 1941 2,411,892 Peters Dec. 3, 1946 2,411,893 Peters Dec. 3, 1946

Images