US2551830A - Fuse construction - Google Patents

Description

May 8, 1951 H. v. DRYER FUSE CONSTRUCTION Filed April 28, 1948 i 30 Z /lafff/rg- 0^/ A5/5 of 707,44 AAPC 5A/6TH 7. 6. 5. 4. 5. 2. QQQQQQQR l www Patented May 8, 1951 FUSE CONSTRUCTION Henry V. Dryer, 'Milwaukea Wis., assigner to .McGraw Electric Company, a corporation of Delaware Application Aprl`28, 1948, .Seria.l.No. 23,711

-Claims.

This invention relates toa fuse .construction and is particularly directed'to a current limiting cartridge type of fuse construction. Current limiting cartridge type fuses have frequentlybeen filled with sand or other granular material -to provide an extensive condensing-andrcocling surface, but these constructions Ahave :not always proven satisfactory. For example, Iin certain types of sand lled fuses it has been found that a fulgurite is Vfrequently formed under certain conditions which is conducting at very-high-temperatures and consequently interferes with the desired or correct action of the fuse. Also, certain types ci sand-filled fuses create an .excessively high voltage surge onthe -line When'the fuse Wire ruptures, which in some ycases has caused breakdown or flashover of ynearby insulation.

Objects of this invention are to provide aifuse construction in which sand or other granular refractory material is provided-at yopposite ends of the cartridge type Vfuse vto provide expansion zones for the gases generated by the blowingoi the fuse linie and to provide-extended -surfaces Which act as cooling and'condensing surfaces for the hot gases, and to provide intermediate the portions ci sand a material which, when acted upon by the arc, evolves a water vapor orother vapor which chills the arc and also quickly cools any fulgurite that may be formed in thesand and prevents it from reaching a temperature so high that it would'becomea conductor.

Further objects of this invention Vare to providea very simple type of construction Vin'which, though lthe vdevice is a closed cartridge type of fuse, nevertheless the pressure generated on blo-W- ing of the fuse even on heavy short-circuit 'currents never reaches an excessive or 2dangerous value.

A still further object of this invention .is to provide a current limiting vtype of fuse which does notdevelop an excessive `voltage surge when the fuse blows.

An embodiment Vof the invention is vshow-n Lin the accompanying drawings, .in which:

Figure l is a longitudinal, sectional view through the cartridge typefuse.

Figure 2 is a chart showing the effecto'fdifferent per cents of bauxite upon the ratio Vof the actual maximum current, .whenrupture occurs, to the maximum availablecurrent.

Figure 3 is a chart showing curvesillustrating the eii'ectiveness .of vlthe bauxite and :sand .-ar rangement in reducing Ivthe arc length-equivalent to length ci fuse Wire-required Lto rclear :in :an

2 ordinary sand-lilled fuse when both Vare operating under the same circuit conditions.

Any suitable type of cartridge type fuse can be employed. For instance, the cartridge fuse may be of the type disclosed in my ccpending application Serial No. 11,132, led February 26, i948, for Fuse Constructions, which has issued as Patent No. 2,490,950, dated 'December 13, 1949. This cartridge type of fuse is illustrated in 'Figure l and may comprise a Bakelite or'other outer tubular casing I provided with a clear acrylic transparent plug 2 screwed therein and with end conducting caps 3 and 5. VIt is understood that the indicator shown in Figure l is not essential to the proper operation of the fuse in clearing the circuit. The end conducting caps are in electrical connection with end iittings 5 and E between which a ribbed, ceramic supporting rod .'I is held. This ceramic supporting rod may be notched as indicated at 8 to position a portion of the fuse link 9 wrapped therearound immediately adjacent the inner end of the transparent plug. This construction, of course, can be varied as will be lseen as the description proceeds, but is merely detailed as one of the possible forms that the invention may take. .Sections of sand I!! and Ii are located adjacent opposite ends of theiinterior Vof the tubular casing I and 'a section of .bauxite I2 is located approximately centrally betweenthe two sand sections IB and II. Many othergranular or vgranulated refractory materials, as for example quartz, silica, alumina, or magnesia may be .used in place of the sand. A quartz or silica sand and bauxite are the most practical comb-ination of materials from the standpoint of `eiliciency of operation as Well as 10W cost. The ends of the fuse link 9 are attached in any suitable mannennot shown, to the ttings 5 and 6. Gbviously, other types of fuse constructions could be employed'. For example, with lower voltage fuse links it would not be necessary to use the ceramic supporting rod '1, but on high voltage fuse links of small diameter it is found more convenient to support the fuse link Von the ceramic rod 1. However, this invention is primarily concerned with the arrangement cf the bauxite and the sand, granular quartz, or other granular refractory material.

It has been Vfound that when the fuse link blows, thatit almost invariably ruptures initially in the region which is surrounded by bauxite. On very `high currents the initial rupture point vis not discernible since the fuse Wire melts almost instantaneously along its entire length. The sandsections AIl) and yI I provide expansion area-S tures.

and prevents it from reaching a temperature so high that it would become a conductor and thus support the arc and thus .causejfailure of the device.

Figure 2 shows the effect of variations in the per cent of bauxite on the current limiting ability of the fuse. The abscissa indicate the per cent of bauxite on the basis of the'per cent of the total arc length, that is to say, on length of arc in the bauxite area in Figure 1 to the total arc length between the fittings 5 and The ordinates represent the ratio of the actual value to which the current is limited by the fuse when rupture occurs to the maximum available current. The curve is typical of a fuse embodying the arrangement of materials shown in Figure l.

It will be seen that the greatest current limitation is obtained when approximately thirty per cent o1' less of bauxite is used.

It is possible to construct either an all-sand or an all-bauxite cartridge type of fuse that will operate satisfactorily under certain conditions. However, either material when used alone imposes certain limitations or undesirable fea- For example, an all-sand fuse creates very little internal pressure and is very effective in limiting the fault current, but frequently causesl an excessively high voltage surge at the time of rupture. On the other hand, an allbauxite fuse results in a relatively low and inconsequential voltage surge but is not as effective in limiting the fault current and at high currents produces rather high internal pressures at the time of rupture.

Thus by using a construction embodying the arrangement illustrated by Figure l, the designer, by varying the percentage of the materials involved, may construct a fuse having nearly any combination and degree of the above characteristics desired. For example, a fuse construction of this type containing approximately twenty per cent of bauxite is a practical compromise combining the most desirable features for general use in the industry.

Figure 3 shows a chart in which curves A and B show a typical relationship between the minimum arc length required to clear and the system voltage for sand as indicated by the curve A and for sand plus twenty per cent bauxite as indicated by the curve B. It will .be seen that the combination of sand with twenty per cent bauxite will clear in substantially half the minimum length as that required for sand alone.

It will also be seen from reference to Figure 2, that the fuse construction limits the short-circuit current to a value well belowthe maximum available current, particularly so where twentyfive to thirty per cent or less of bauxite is used.

The bauxite remains non-conducting even at high temperatures and serves the highly useful purpose of evolving a quantity of chilling water vapor as previously described. Preferably, the bauxite is a ne powdered material and the sand is a clean, ne grained quartz or silica sand.

It has been found that cartridge type fuses constructed in accordance with this invention do not allow the internal pressure to rise to a dangerous point even when blown under heavir short-circuit conditions. It has been found also that these cartridge type fuses, Whether constructed in the exact form shown in Figure l or in some other form, can be very cheaply manufactured provided the bauxite and sand are associated and used in the manner indicated. AThese relatively cheap cartridge type fuses are intended to be discarded after blowing and to be Areplaced with new cartridge type assemblies.

Although this invention has been described in considerable detail, it is to be understood that such description is intended as illustrative rather than limiting, as the invention may be variously i embodied and is to be interpreted as claimed.

I claim:

l. A fuse construction comprising a tubular outer casing, terminals adjacent opposite ends thereof, a fuse link extending through said casing and electrically connecting said terminals, bauxite within said casing adjacent an intermediate portion of said fuse link, and sand within said casing on opposite sides of said bauxite.

2. A fuse construction comprising a tubular outer casing having terminals adjacent opposite ends, a fuse link within said casing electrically connecting said terminals, bauxite within said casing and granular refractory material within said casing, said bauxite and granular refractory material being in contact with said fuse link and said granular refractory material arranged to provide extensive cooling and condensing surfaces for the gases and vapors incident to rupture of said fuse link.

3. A fuse construction comprising a tubular outer casing, terminals adjacent opposite ends thereof, a fuse link extending through said casing and electrically connecting said terminals, bauxite within said casing adjacent an intermediate portion of said fuse link, and sand Within said casing on opposite sides of said bauxite, said bauxite being not more than approximately thirty per cent of the total length of said sand and bauxite as measured along the active length of said fuse link.

4. A fuse construction comprising a tubular outer casing, terminals adjacent opposite ends thereof, a fuse link electrically connecting said terminals and extending through said casing, a cooling agent including bauxite located Within said casing adjacent an intermediate portion of said fuse link, and a granular refractory substance within said casing and located on opposite sides of said bauxite and arranged to provide extensive cooling and condensing surfaces for the gases and vapors incident to rupture of said fuse link.

5. A fuse construction comprising a tubular outer casing having terminals adjacent opposite ends, a fuse link within said casing electrically connecting said terminals, bauxite within said casing and sand within said casing, said bauxite and sand being in contact with said fuse link and said sand arranged to provide extensive cooling and condensing surfaces for the gases and vapors incident to rupture of said fuse link.

6. A fuse construction comprising a tubular outer casing having terminals adjacent opposite ends, a fuse link within said casing electrically connecting said terminals, powdered bauxite within lsaid casing and granular refractory material withinsaid casing, said powdered bauxite 5 and granular refractory material being in contact with said fuse link and said granular refractory material arranged to provide extensive cooling and condensing surfaces for the gases and vapors incident to rupture of said fuse link.

HENRY V. DRYER.

REFERENCES CITED NTED STATES PATENTS Number 1 The following references are of record in the 10 Number le of this patent:

Name Date Schattner Feb. 1, 1910 Banks May 26, 1914 Cole May 25, 1915 McMahon Aug. 26, 1941 Schuck Aug. 25, 1942 FOREIGN PATENTS Country Date Great Britain Jan. 22, 1936

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