US2156058A - Electric protective device - Google Patents

Description

April 25, 1939. A, ofl usg 2,156,058

ELECTRIC PROTECTIVE DEVICE Filed April 4, 1938 IIIIIIIIII 4, ,1 I'll f IIIIIIItifllllllllllllllflldlll IllllllIIIIIIIIIIIIIII'IIIII'IIIIIIIIIIII'llld1 W v IE4 Inventor: Karl A. Lohausen,

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Patented Apr. 25, 1939 UNITED STATES ELECTRIC PROTECTIVE DEVICE Karl A. Lohausen, Berlin-Oberschoneweide, Germany, assignor to General Electric Company, a corporation of New York Application April 4, 1938, Serial No. 199,948 In Germany April 10, 1937 10 Claims.

The present invention relates to electric protective devices, more particularly of the type which operate on the expulsion principle, and has for a principal object the provision of improvements in expulsion protective devices whereby such devices may be designed for higher capacity ratings than heretofore considered practical while at the same time making it possible to maintain the dimensions of such de- 10 vices within reasonable and practical limits.

In the design of expulsion protective devices, it has been found that, for interruption of currents of large magnitude, there is required a strong enclosing casing in order to withstand the high 15 pressures developed, and, also, a certain minimum and comparatively large cross-section of expulsion bore in order to prevent rise of the pressures beyond safe limits. n the other hand, it is required for satisfactory interruption m of currents of small magnitude, that the crosssection of the expulsion bore be as small as possible in order that suiilcient pressure may be developed for proper arc extinction.

The last two contradictory requirements, men- 25 tioned in the preceding paragraph, have presented a considerable problem in the design of expulsion protective devices and have constituted a major reason for the present comparatively re stricted scope of application of such devices, both 30 as regards pressure limits and current interrupting ability. Numerous proposals have been advanced for the solution of this diflicult problem, among which has been that of providing, in expulsion fuse devices employing a single conductor enclosed in an expulsion bore of relatively large cross-section, an inner expulsion tube in surrounding relation to the conductor, which inner tube has a relatively small bore and the walls of which are adapted to yield or rupture upon 40 development of high pressures incident to interruption of large currents. However, in the practice of these proposals, limitations as to current interrupting capacity, pressure limits and other factors have been encountered and, with 45 particular reference to the specific example mentioned, there are presented certain important disadvantages which will be referred to hereinafter.

An important object of the present invention 50 is therefore the provision of an improved expulsion safety device having increased pressure limits and capacity for interruption of currents of large magnitude, which at the same time is capable satisfactorily of interrupting currents of ll small magnitude.

Other objects and the details of that which I believe to be novel and my present invention will become apparent from the following description and the claims appended thereto, taken in conjunction with the accompanying drawing in 5 which are illustrated exemplary embodiments of the invention as applied to expulsion protective devices of the fused type. In the drawing, Figs.

1 and 2 show respectively longitudinal and transverse sections of one form of expulsion fuse v device, and Figs. 3 and 4 show respectively longitudinal and transverse sections of a second form of expulsion fuse device, embodying. the invention.

Each of the fuse devices illustrated has an insulating enclosing casing l0 provided with terminal elements II and I2, disposed respectively at opposite ends of the casing, between which are connected electrically in parallel a plurality of fusible conductors l3 disposed within the casing. These conductors extend respectively through a plurality of tube-like expulsion chambers, one of which, designated M, is centrally located, and the others of which, designated l5, are arranged in a circle around the central chamber. The partition walls of the chambers are so dimensioned that, upon occurrence of an excess current of large magnitude, such as due to shortcircuit or heavy overload, one, several, or all of the partitions open or burst so as to provide communication between adjacent chambers. As a result of this, the arc gases, corresponding roughly in quantity developed to the current strength, can expand in a space which is greater than that of a single chamber and, in an extreme case, can fill out a space corresponding to that of the aggregate of all of the chambers, so that rise in pressure within the casing beyond a safe limit is avoided. Thus the several chambers in effect combine with each other on heavy current inter- 4o ruption, due to yielding of the separating walls or partitions, so that there is produced a common are which is quenched by the expulsion of the gases, unhindered due to the effective enlargement of the expulsion bore, and at the same time the developed gas pressures are maintained within controllable limits.

In the embodiment of Figs. 1 and 2, one end of each of the fusible conductors I3 is connected to terminal element H by solder, as indicated at It, or other suitable means, while the other ends of the conductors are connected in a similar manner, as indicated at IT, to a relatively thin and light conductive plate l8 which is releasably secured by a small body of solder or other suitable means, as indicated at l9, so as to be readily expellable upon fuse operation. Adjacent ones of the chambers ii are separated from each other by radially inwardly projecting partitions or fins 20 which are integral with casing III. Casing l0 preferably is constructed of insulating material adapted for extrusion in the form illustrated, but may be constructed by any other suitable process if desired. Chamber I4 is formed by an insulating tube 2| disposed centrally of fins 20 and the walls of which abut the inner extremities of the fins. Although illustrated as being a separate element, tube 2| may by suitable extrusion process be formed integrally with casing l0 and the fins or partition walls 20. Preferably the central chamber has a slightly smaller effective cross-section than that of the chambers I5, and the walls of tube 2| are slightly thinner than partitions 20. As a result of this expedient, upon large excess currents, a higher pressure initially is developed within chamber l4 so that the walls of tube 2| burst, either in whole or in part, to place the central chamber in communication with one or more of the chambers IS, The radially extending, relatively thick partition walls 20 then extend into the gases to assist in the interruption process by provision of an increased cooling effect. Preferably also partitions 20 are made of a fibrous or other suitable insulating material which, under the action of the arc, does not become electrically conductive, but produces arc quenching gases for aid in the arc extinction process, As an alternative, any suitable and well known material having these properties may be applied as a coating to the partition walls.

In the modification of Figs. 3 and 4, the fusible conductors iii are connected at one end to terminal element I I in the same manner, as indicated at l6, as that employed in the embodiment of Fig. 1, while the flexible braided extensions 25 of the other ends of the conductors are secured directly to the inner wall of terminal I! by solder, as indicated at 26, or other suitable means. The conductors are surrounded respectively by a plurality of relatively thin walled insulating tubes 21 disposed within thick walled casing Ill and arranged, as best shown in Fig. 4, so as to provide a relation of chambers similar to that of the embodiment of Figs. 1 and 2. As in the previously described embodiment, one or more of the individual chambers may be made to have a slightly smaller cross-section than that of the other chambers and the walls of such smaller chamber or chambers may be made relatively thinner so that bursting takes place initially with respect to the walls of the smaller chamber or chambers. Also, tubes 21 may be constructed of fibrous or other suitable insulating material which does not become electrically conductive upon being subjected to the heat of an arc and which is capable of developing arc quenching gases, or a material having these desirable characteristics may be applied as a coating to the inner walls of the tubes. Upon occurrence of large excess currents, such as due to short-circuit or heavy overload, the operation is substantially the same as that of the embodiment previously described, in that one, several, or all of the tubes burst so as to provide intercommunication between the individual chambers and the space within casing Ill, thereby affording an effective enlargement of the expulsion bore for the expansion of the developed gases therein so that dangerously exces- "characteristics of the different conductors, one

of them first attains fusing temperature and ruptures. The remaining parallel connected conductors then take over the whole current until a second one of the conductors attains fusing temperature and ruptures. This operation continues progressively until the one of the conductors finally remaining carries the whole current. At this time the interrupting process actually begins and is facilitated by the fact that the finally remaining conductor, though of small cross-section, has imposed thereon the heavy duty of carrying the whole current so that upon rupture thereof a gap is opened very rapidly. After the resultant arc burns the ruptured ends of this final conductor back a certain distance, the arc transfers to one of the shorter gaps between the ends of one of the previously ruptured conductors and burns back these latter ends. Thereupon the arc transfers to the gap of still another one of the previously ruptured conductors and this transfer of the are from chamber to chamber continues until all of the fusible conductors have been burned back sufliciently to effect total interruption of the current flow. Due to the small bores of the individual tubes and the progressive fusion of the individual conductors, the described devices are capable very effectively and satisfactorily of interrupting extremely low currents.

Between the operations described for extremely high and extremely low current interruption, various combinations of these operations take place to greater or less extent for interruption of intermediate currents, thereby insuring satisfactory operation over a wide range of current magnitudes.

Expulsion devices of the present invention afford distinct and important advantages over the 1 types of expulsion device, previously referred to, employing a single fusible conductor and a single inner enclosing tube. The total heat developed in the case of a plurality of parallel connected fusible conductors is about the same as for a single fusible conductor designed to carry the same current, since the total metal to be vaporized is before interruption approximately the same in both cases. In the operation of the devices of the present invention, the total heat due to arcing is distributed among the several chambers, an arc remaining only temporarily in any one of the chambers. Thus the construction of the herein described devices has the pronounced advantage that it considerably reduces the danger of detrimental carbonization of the enclosing walls which is experienced with the single conductor and single inner tube arrangements.

Also with expulsion fuse devices of the type hereinbefore referred to as employing only a single conductor, the disadvantage is encountered that upon interruption of extremely large currents, portions of the ruptured conductor are ejected at very high speed and in such manner as to endanger the safety of any one who may be located in the path of the ejected portion. This disadvantage may be avoided effectively with expulsion fuse devices constructed in accordance with the present invention, in that a relatively large number of parallel connected small crosssection conductors may be employed, thereby greatly reducing the mass of any single conductor portion which may be ejected upon use operation.

A still further advantage or the herein described construction over a construction, such as previously referred to, providing only a single arcing path, is that the described construction, which provides a plurality of parallel arcing paths distributed among a plurality of expulsion chambers, permits the use of smaller bore tubes or enclosures for-the individual chambers. By this means more intimate contact of the arcs with the partition walls is secured, the interrupting time is shortened, low current interruption is made more positive, and materially improved overall operating characteristics are obtained.

As will be evident from the foregoing description my invention is not limited to particular details of construction of the exemplary embodiments illustrated, and I contemplate that various modifications will suggest themselves to one skilled in the art. It is my intention, therefore, that the appended claims shall cover such modifications and other embodiments as do not depart from the true spirit and scope of the present invention.

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

1. In an electric protective device of the expulsion type, a tubular casing of relatively strong construction having spaced terminals associated therewith, means providing in said casing a plurality of substantially parallel extending expulsion chambers having wall portions yieldable under high pressure, and means electrically in parallel arranged so as to produce arcs respectively in said chambers, said chambers being operative to interrupt therein arcs of relatively low current magnitude, and said yieldable wall portions being operative under pressures incident to arcs of relatively large current magnitude to ailord efiective enlargement of the arc gas expansion space.

2. In an electric protective device of the expulsion type, an enclosing expulsion casing of relatively strong construction having spaced terminals associated therewith, partitioning means in said casing defining a plurality of substantially parallel extending and relatively small bore expulsion chambers, and means electrically in parallel arranged so as to produce arcs respectively in said chambers, said chambers being operative to effect interruption therein of arcs incident to excess current of relatively small magnitude, and at least portions of said partition means being constructed to yield so as to afiord communication between said chambers and adjacent spaces within said casing under the influence of high pressures incident to arcs produced by currents of relatively large magnitude.

3. In an electric protective device of the expulsion type, a relatively strong enclosing expulsion casing having spaced terminals associated therewith, a plurality of conducting means, each including a fusible section, extending in said casing and connected electrically in parallel between said terminals, and partition means defining a plurality of substantially parallel extending expulsion chambers respectively individual to said conducting means, said chambers being operative to interrupt therein arcs incident to relatively low current rupture of said fusible sections, and at least portions of said partition means being constructed to yield so as to aiford communication between adjacent spaces within said casing upon development of high pressures in said chambers incident to rupture of said fusible sections by current of relatively large magnitude.

4. In an electric protective device of the expulsion type, a relatively strong enclosing casing having spaced terminals, partition means in said casing defining a plurality of substantally parallel expulsion chambers operative to interrupt therein arcs of relatively low current magnitude and having wall portions constructed to yield under high pressures incident to arcs of relatively high current magnitude, and means electrically in parallel arranged so as to produce arcs respectively in said chambers, at least portions of the said partiiton means which form the walls of certain of said chambers being of relatively weaker construction than other of the said partition means which form walls of other of said chambers.

5. In an electric protective device of the expulsion type, a relatively strong enclosing casing having spaced terminals, partition means in said casing defining a plurality of substantially parallel extending expulsion chambers operative to interrupt therein arcs of relatively low current magnitude and having wall portions constructed to yield under high pressures incident to arcs of relatively high current magnitude, and means electrically in parallel arranged so as to produce arcs respectively in said chambers, certain of said chambers having relatively smaller cross-section than other of said chambers.

6. In an electric protective device of the expulsion type, a relatively strong enclosing casing defining a plurality of substantially parallel extending expulsion chambers operative to interrupt therein arcs of relatively low current magnitude and having wall portions constructed to yield under high pressures incident to arcs of relatively high current magnitude, and means electrically in parallel arranged to produce arcs respectively in said chambers, at least one of said chambers having a relatively smaller cross-section than other of said chambers and at least a portion of the said partition means which form the walls of said one chamber being of relatively weaker construction than other of the said partition means which form walls of said other of the chambers.

7. In an electric protective device of the expulsion type, a relatively strong expulsion casing having spaced terminals, a plurality of tubes disposed in substantially parallel extending relationship in said casing and arranged to provide expulsion chambers operative to interrupt therein arcs of relatively low current magnitude, and means electrically in parallel arranged so as to produce arcs respectively in said chambers, at least portions of the walls of said tubes being constructed to yield so as to afiord communication between said chambers and adjacent spaces with said casing upon development of high pres sures in the chambers incident to arcs of relatively high current magnitude.

8. In an electric protective device of the expulsion type, a relatively strong enclosing casing having spaced terminals, partition means in said casing defining a plurality of substantially parallel extending expulsion bores operative to interrupt therein arcs of relatively low current magnitude, at least one of said bores being located substantially centrally of said casing and others of said bores being located around said central bore, and means electrically in parallel arranged so as to produce arcs respectively in said bores, at least a portion of said partition means being constructed to yield so as to afford eflective enlargement of the gas expansion space upon subjection of said yieldable portion to high pressure incident to arcs of relatively larger current magnitude. v

9. In an electric protective device of the expulsion type, a relatively strong tubular expulsion casing having spaced terminals, means providing pressure of predetermined magnitude so as to allord communication between said chambers.

10. A housing for an electric protective device ,of the expulsion type, comprising a tubular expulsion casing of relatively strong construction, wall means defining an expulsion chamber extending substantially longitudinally and centrally of said casing, and means including a plurality of-partitions, extending substantially longitudinally of the casing and projecting inwardly from the inner wall of the owing in spaced relationship, cooperative with said first mentioned means to form a plurality of expulsion chambers arranged around said flrst mentioned chamber, at least a portion of the walls separating said central chamber from the said chambers therearound being relatively weaker than said partitions and being yieldable under pressure of predetermined magnitude so as to afford communication between said chambers.

KARL A. LOHAUSEN.

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