US2331162A - Electrical switch - Google Patents

Description

Oct. 5, 1943. M. c. BECKER ETAL I 2,331,162

ELECTRXCAL SWITCH Filed Jan. 20, 1940 WITNESSES:

. 1 INVENTORS Maxim 1/1027 6 Becker Patented Oct. 5, 1943 ELECTRICAL swrron Maximilian 0. Becker, East Orange, and Leslie N.

Crichton, Livingston, N. 'J., 'assignors to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application January 20, 194i), Serial No. 314,836

1 Claim. (Cl. 200-144) This invention relates to electrical switches, and it has particular relation to electrically operated circuit opening switches.

I many relay applications, it is desirable that a translating device, such as a circuit breaker trip coil, be actuated by an entirely self-con- .tained relay unit. For such an application it is possible to connect the trip coil across a current transformer employed for energizing the relay. Suitable control for the trip coil is provided by a circuit opening switch which is connected normally to by-pass the trip coil. When the relay operates in response to a predetermined condi tion of an electrical circuit to be protected, such as an overload condition, the circuit, opening switch is opened to permit actuation of the trip coil by the current transformer. The relay may be employed for various purposes. For example, it may be a time-delay relay set to permit other relays to operate first, or the relay may be a directional or an impedance relay.

Circuit opening switches of the type herein contemplated must operate under widely varying conditions. Because of the sensitive operation desired and the low energies available for actuation, the circuit opening switch must have a low contact pressure. Despite this low contact pressure, the switch must be capable of passing continuously currents of the order of 3% to 5 amperes without developing undue resistance. Should undue resistance be developed under these circumstances, an unnecessary and undesirable operation of the trip coil would result.

At the same time, the circuit opening switch must be capable of opening when carrying excessive currents without suffering appreciable damage. When a fault occurs on the circuit being protected, currents of the order of 50 amperes, and occasionally up to 200 amperes, maypass through the contacts of the circuit opening switch. Unless properly designed, a switch will be severely damaged by currents of this magnitude.

Moreover, the frequency of operation of such circuit opening switches depends on the. type of service to which the switch is to be subjected. In some applications, the switch may remain closed without a single operation for a period of several years. For other applications, an actuation of the switch may be expected several times an hour. Because of this wide variation in service conditions, the circuit opening switch is subjected to unusually severe duty. I

In accordance with our invention, a switch is providedhaving contacts formed from a noble metal, such as silver. These contacts are in the form of substantially parallel spaced plates. The only conductive contact between these plates occurs between a small button or protuberance associated with one of the plates and 2. corresponding small area on the other plate. Because of .the large area provided by the plates, an adequate cooling is assured for the contacts under operating conditions. Preferably, the circuit connections for the switch are so disposed that any are formed between the contacts is urged away from the button or protuberance and away from any supporting elements towards the edges or the contact plates. Consequently, any arcing occurring between the plates can damage only the edges thereof, and does not affect the current-carrying characteristics of the contacts.

' According to a further aspect of our invention, a barrier member is provided for partially bridging the contact plates. This barrier member not only may protect the supporting elements for the movable plates, but, in addition, provides with the plates a channel for directing gases formed by an electrical discharge between the plates towards predetermined edges of the plates. Consequently, the gases assist in carrying the electrical discharge towards these edges.

It is, therefore, an object of our invention to provide an electrical circuit opening switch capable of reliable and durable performance.

It is another object of our invention to provide a switch having all current-carrying portions formed of a noble metal.

It is a further object of our invention to provide a circuit opening switch with means for forcing an are formed between the contacts of the switch away from the normal current-carrying areas of the switch.

It is a further object of our invention to provide a circuit opening switch having contacts provided with relatively small current-carrying portions with connections so disposed that an arc forming between the portions is urged rapidly towards the edges of the contacts.

: It is a still further object of our invention to provide a circuit opening switch with a barrier partially bridging the contacts thereof for properly directing gases formed by an electrical discharge taking place between the contacts.

Other objects of our invention will be apparent from the following description taken in conjunction with the accompanying drawing, in which:

Figure 1 is a diagrammatic view, with parts in cross-section of a switch embodying our invention; and v Operation of energizing winding 24 which may be connected for energization to any suitable control circuit by means of conductors 25 and 28. s For operating the circuit opening switch .I 1, a solenoid mechanism is providedwhich includes a magnetic plunger 29 which is reciprocated by magnetic flux produced by the winding 24. A magnetic circuit is provided for this flux which includes a magnetic frame member 36 having ends terminating adjacent'the plunger 29, and having an adjustable magnetic core 3| which may be in threaded engagement with the frame member 36. By adjusting the core 3i relative to the frame member as and looking it in place by means of a lock nut 32, the calibration for the circuit opening switch may be adjusted as desired. Preferably, a non-magnetic spacer 33, such as brass or bronze, is afiixed to the core 31 in order to prevent direct contact of the core with the plunger 29. In addition, the core 3! may carry a non-magnetic sleeve 34 for guiding the plunger 29. The entire solenoid may be attached to a suitable insulating supporting base 35 by means of suitable screws 35.

The contact if: is associated for movement with the plunger 29 by providing the contact'fii with a pair of electroconductive supporting strips 3.! which are clamped at one end between clamping plates 38 and 39 formed of electroconductive material. These clamping plates may be secured and clamped to the base 35 by means of machine screws lii, which pass through the base 35 and are threaded into a retaining member 4!, One of the screws may serve as a terminal for the conductor IS.

The plunger 29 is provided with a cylindrical connecting member 42 having an annular recess 63 for receiving the strips Bl. The member '42 may be attached to the plunger in any, suitable manner. It will be observed that reciprocation of the plunger 2s carries the movable contact .into and out of engagement with the fixed contact !6. Return of the movable .contact to the position illustrated in Fig. '1 after an actuation of the circuit closing switch may be effected by gravity, or the strips 3'! may be constructed of resilient material to bias the contact l against the contact IE5.

' The contact I6 may be supported from a depending portion of the base 35 by means of a bracket A integral with or connected to the contact l6 and attached to the .base 35 by means of suitable screws i5.

As shown in the drawing, the contacts .15 and h: are in theform of substantially parallel spaced plates. The contact it: may be constructed conveniently of two separate plates [Errand lib positioned on opposite sides of the stripsfi'l. Attaclnnent oi the plates to the strips may b'efby any suitable means, such as by frivets (not shown).

One of the contact plates, such as the contact 16, preferably is provided with a button or-protuberance H d which normally is in engagement with the contact i 5. This protuberance may be formed as an independent electroconducti-ve Moreover, because of the extended area of the contacts and .16, adequate cooling is provided therefor.

The operation of the apparatus thus far described may now be set forth. Under normal conditions, thecircuit opening switch I! remains closed. When the winding 24 is energized suitably the contacts I5and 16 separate. If the contacts carry substantial current at.the time of their separation, a heavy arc may be established therebetween. Because of the destructive ejfiects of such an arc, it is desirable'that the are be removed promptly from the contacts.

As illustrated in Fig. 1, the conductors for the contacts 15 and i6 represented by the conductor H and the strips 31 are positioned to provide a magnetic field which'assists in urging any arc formed between the contacts 15 and [*6 rapidly towards the left of the contacts, as viewed in Fig; 1, until the arc is at the left-hand edges of the contacts. During its movement, the arc travels so' rapidly that practically no damage is done to the surfaces of the contacts in the position shown by a dotted line A. Under these conditions, the "arc is substantially displaced from the protuberance 160;, which "normally establishes contact between the contacts t5 and iliB, and no damage can result thereto. The edges of the contacts may, of course, be slightly fused before the arc is extinguished, but since these edges do not normally carry current, the resulting fusion does not affect the performance of the contacts.

It should be noted that the edges which bear the brunt of the arc .disch'argepreferably are al- Ways separated. If these edges were in engagemenuas in the ordinary type of contact, the fus'hion produced by an electric discharge would tend .to fuse or weld the two contacts together, thereby rendering the circuit opening switch inoperative. Because of the separation which we provide, such fusion or welding cannot take place.

Although the "contacts 15 and [B may be cons'truc'ted :of various materials, Wei-have found that a the noble metals, such as gold, silver and platippm, are par'hcularly desirable for the reason that, when subjected to heating from an electric are, any compounds formed on their surfaces are reduced, leaving only the pure metal. The protuberance 16a couldbe 'offa dissimilar material, but preferably all surfaces in the neighborhood of the are are made of the same material, preferablysilver.

When an arc discharge occurs between two metallic surfaces, we have found that .a minute met-a1 sprayoften is produced thereby. If azdissimi lar metal or material were provided for the protuberance lfim the resulting spray would tend to contaminate :the material employed for the protuberance. By employing the 'sameimaterial throughout, such contamination is precluded.

It will be noted that the plates 1.50. and 1511 may *be substantially similar .50 that after one member affixed to the contact I6, but preferably plate lib has seen considerable service, thebon tact l5 may be reversed to present th contact lit: to the protuberance Ilia.

We have found that a further control of any electrical discharge occurring between the contacts may be effected by a flange or barrier 50 partially bridging the contacts l5 and I6. This barrier may be of any suitable material, but conveniently may be formed by bending the material of the plate lib substantially at right angles. If desired, a similar construction may be employed for the plate I5a to provide complete interchangeability, but normally the plate l5b will not require replacement.

Because of the barrier 50, a channel is provided between the contacts IS, IS and the barrier 50 which tends to direct gases formed by an electrical discharge between the plates towards the left, as viewed in Fig. 1. Consequently, the gases assist in blowing any electrical discharge between the contacts towards the left-hand edges thereof. In addition, the barrier 50 tends to protect the strips 31 from any flareback of an electrical discharge occurring between the contacts l5 and 16.

Although we have described our invention with reference to certain specific embodiments there- 7 of, numerous modifications thereof are possible.

Therefore, we do not wish our invention to be restricted except as required by the appended claim when interpreted in view of the prior art.

We claim as our invention:

In an electrical switch, a pair of substantially parallel contact plates formed of a nobl metal, means mounting said plates for movement from a first relationship wherein said plates are spaced from each other for increasing the spacing therebetween, a protuberance formed of said noble metal on a first one of said plates for engaging a predetermined portion of a second one of said plates to establish the only conductive path between said plates when said plates are in said first relationship, the contacting portions of said protuberance and said predetermined portion occupying small, centrally-disposed areas on said plates, and a barrier member formed from a portion of one of said plates and partly bridging said plates for directing gases formed by an electric are occurring between said plates towards predetermined edges thereof, said protuberance being positioned between said barrier and said edges.

MAXIMILIAN C. BECKER. LESLIE N. CRICHTON.

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