US2695350A - Contact means - Google Patents

Description

NOV. 23, 1954 a SCHULTZ 2,695,350

CONTACT MEANS Filed Dec. 26, 1951 2 Sheets-Sheet l INVENTOR.

.Blaine H 80h ll W2 HZlor'ne y B. H. SCHULTZ 2,695,350

CONTACT MEANS Nov. 23, 1954 2 Sheets-Sheet 2 Filed Dec. 26 1951 INVENTOR.

United States Patent Ofitice CONTACT MEANS vBlaine H. Schultz, South Milwaukee, Wis., assignor to McGraw Electric Company, Milwaukee, Wis., a corporation of Delaware This invention relates to an improvement in a contact spring on a heavy duty fuse cutout.

Fault interrupting tests on 7500 v. 200 amp. fuse cutouts reveal burning on both upper and lower contacts. When burning becomes extensive, corrosion results which injures the contact and causes increased electrical resistance between the relatively movable parts of the fuse cutout. For safetys sake it is very essential that every improvement be made to assure the smooth flow of electrical current.

One of the features of fuse cutouts made by the same assignee as the assignee of this invention is the releasable upper contact on a fuse tube. When the fuse link melts as a result of an overload or a moderate short circuit the fuse link separates and is instantly snapped out of the fuse tube by the flip-out device. Simultaneously, the downward pressure of the upper spring contact and the outward pressure of the lower spring contact forces the double hinge to collapse and permit the entire fuse tube to drop outward 90.

However, during fiow of short circuit current, the contact should be firm. If the contact is not firm, severe contact burning takes place with the subsequent destruction of the silver plated contact surface. On transmission lines and heavy distribution lines that carry high voltage ratings of the order of 7500 to 46,000 volts and thus require high interrupting capacities, it is very important that the contacts on fuse cutouts be strong.

It is the object of this invention to provide a contact spring for a fuse cutout that will acquire added contact pressure when current is flowing through it.

Another object of this invention is to provide a contact spring that utilizes the magnetic forces of an electrical current to increase the pressure contact.

And a further object of this invention is to provide a means of controlling the direction of electrical current through the contact spring.

Other objects will appear from time to time in the course of the specification and claims.

Like reference figures represent like parts in the accompanying drawing in which Fig. 1 is an elevation of a high voltage fuse cutout incorporating my inventive idea.

Fig. 2 is an enlarged fragmentary perspective view, partly in section, of my improved spring contact.

Fig. 3 is a side elevation of the spring contact with the electrical current flow and magnetic forces of repulsion shown diagrammatically.

Fig. 4 is a top view of the spring contact with the insulation broken away and diagrammatically showing the electrical current flow and the magnetic forces of attrac tion.

The essential construction of this fuse cutout is covered in Patent No. 2,176,227 issued to William O. Schultz et a1. and assigned to the same assignee as this application. Broadly it consists of a fuse tube 1 carried by an upper terminal 2 and a lower terminal 3, which terminals are supported by suitable insulators 4 from a base member 5. The fuse tube 1 is provided with an upper contact 6 and a lower contact or fuse strip receiving member 7. The upper contact 6 has outwardly projecting members 8 on opposite sides thereof which serve as pressure contact means between a spring contact 10 and the upper contact 6. An eyeleted portion 9 formed integrally with the upper contact 6 is adapted to be engaged by a switch stick.

Patented Nov. 23, 1954 The upper stationary terminal 2 has outwardly proecting members 15 on opposite sides thereof which serve as pressure contact means between the upper terminal 2 and the spring contact 10. It is to this spring contact 10 that my inventive idea is applied.

Referring to Figs. 2 and 4, it can be seen that the spring contact 10 is formed from one piece of metal rod bent at its middle section 11 and pivotally supported thereto by the stationary member 12 of the upper terminal 2. The spring contact 10 is provided with downwardly depressed portions 13 and with outwardly slanting guiding portions 14. Normally the projections 8 of the terminal 6 of the fuse tube 1 are latched behind the downwardly depressed portions 13 of the spring contact 10 and form tliie pressure contact which is improved by my inventive 1 ea.

I place an insulating material 16 around the lower connecting portion of the spring contact in such a manner that the insulation extends between the metal of the spring contact and the metal of the stationary terminal. This insulation prevents electrical contact with the lower portion of the spring contact thus directing the flow of current through the upper arm 17 of the spring contact.

By this means the flow of current is directed from the upper terminal 2 through the contacts made between the projections 15 and the upper arms 17 of the spring contact 10, and around the outwardly slanting guiding portions 14, the depressed section 13, to the pressure contact 18 between the spring contact and the projections 8. From contact 18 the current is carried through the upper contact 6 and the fuse tube 1 to the lower terminal 3. The precise construction of the lower terminal is incidental to my invention. My invention can be used on a stationary terminal or a spring tensioned outward thrusting terminal as illustrated in Fig. 1. A detailed description of this construction is given in various patent applications on cutout fuses.

My improved method of constructing spring contact utilizes the magnetic force that accompanies electric current. It is a well-known law of physics that parallel paths of electric current flowing in the same direction set up a magnetic attraction toward each other as shown diagrammatically in Fig. 4 and that parallel paths of electric current flowing in opposite directions set up a magnetic repulsion toward each other as shown diagrammatically in Fig. 3. By directing the current as described heretofore, it can be seen that magnetic repulsion is set up between the upper portions 17 and the lower portions 13 so that the two portions of the arms tend to move away from each other. This upward force of the upper portion 17 makes a firmer contact with the projection 15 and the downward force of the lower portion 13 makes a firmer contact at 18 with the projections 8. These firmer stronger contacts reduce the burning at the point of con tact.

Since parallel currents flowing in the same direction set up a magnetic attraction between them, additional strength exists at the contact because this magnetic attraction causes the two upper portions 17 of the arms of the spring contact 10 to pull closer together with the upper terminal between them. In like manner the two lower portions 13 of the arms of the spring contact 10 tend to pull towards each other thus making the contact with the projection 8 and the upper contact 15 firmer and stronger.

Short circuit tests have been made with the spring contact 10 insulated at the bottom so as to direct the current outward through the upper part of the arms and inward along the lower part of the arms and during the higher fault currents, viz. 25,000 amps. in every case, burning has been considerably reduced. In some cases, it has been eliminated altogether. Thus, it has been tested and proved that the magnetic forces accompanying electric current can be utilized to increase the contact pressure in various forms of electric apparatus. When the current flow is heaviest, the magnetic forces will be greatest, which in turn makes the contact pressure greatest when strong contacts are most necessary.

I claim:

In a fuse cutout comprising a base, two fixed insulated :said second terminal upon overload; a contact Lheadon saidfnse comprising :an. axial portion .and atatransverse portion, :a contact assembly on said second terminal for engagement with contact means Jan s-aid iluse, saidzcon- :tact' assembly comprising a spring member having a Uashaped bight supported by saidflrsecond terminal and insulated. therefrom, :two first :amns extending from :said .bight'on's'oppnsite sides ofsaidifuse well .beyond the fuse and being normally biased ;towa;rd each other into contact with the .axial portion :of the contact head 1011 thexfuse and beingialso normally "biased axially :towa-rd said-fuse into-contactwith the'transverse portion of the contact head, said :spriugtmember having .rearwamdly projecting iarms respectively extending from' the outer. endvof said first arms back toward said terminal and biased attheir 20 respective :free ends into contact against said terminal, said bias being in adirection to "assist axial movement of said fuse upon overload and to increase the contact pressure betweensaid first arms and said --trans-ver-se portion of the fuse contact head, said first spring arms being insulated from said second terminal between the bight portion and the point of contact with the fuse whereby current flows between said second terminal and the fuse only through said rearwardl'y projecting arms and the portion of said first arms which extends beyond the fuse, whereby the magnetic forces surrounding said currentbearingportious assist the .bias of said spring member on both-the transverse and the axial portions of sa'idfuse contact.

References Cited in the .file of this patent UNITED STATES PATENTS Number Name Date 1,958,159 Bresson May 8, 1934 2,129,270 Froland Sept. 6, 1938 2,417,683 Harlow Mar. 18,1947 2,458,742 Schultz Jan. 1:1,11949 2,555,158 Schultz May 29, 951

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