Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H85/00—Protective devices in which the current flows through a part of fusible material and this current is interrupted by displacement of the fusible material when this current becomes excessive
  • H01H85/02—Details
  • H01H85/04—Fuses, i.e. expendable parts of the protective device, e.g. cartridges
  • H01H85/05—Component parts thereof
  • H01H85/055—Fusible members

Definitions

• the invention relates to electric fuses and in particular to fuses to be used under marginal conditions both in respect of the steady state operating current and of the operating voltage and in particular to fuses with an extremely fast action and current limiting operation.
• Such operating conditions are generally associated with fuses used for the protection of semiconductor devices.
• the invention is generally limited to enclosed fuses with fuse conductors embedded in a porous filler, and where the fuse conductor consists of successive parts of different metals in the direction of current flow.
• Such bi-metallic fuses are known to the trade and used because they allow advantages of an economic nature without necessarily being associated with any inferior performance.
• Prior art includes fuses where the current successively passes part of the fuse conductor made of copper, then a part made of silver, and finally again a part of copper, the parts so arranged that the fuse element, namely the part intended to melt and open the circuit, is situated entirely in the silver part, while the parts that primarily serve to conduct electricity and, the heat created in the fuse element are made from the less expensive material copper. This results in a fuse that by and large behaves like a fuse with the entire fuse conductor made of silver.
• the invention explores prior art in the light of this hitherto unnoticed advantage of copper by locating the thermally highly stressed fuse element in the part made of silver, while at the same time locating the part made of copper as close to the fuse element as compatible with an avoidance of the tendency to be subject to progressive oxidation.
• FIG. 1 is a plane view of a fuse conductor in one metal and according to prior art.
• FIG. 2 is a plane view of a fuse conductor in two metals demonstrating the difference between prior art and the invention.
• FIG. 3 is a plane view of a fuse conductor for use at a higher value of voltage.
• FIG. 4 is a plane view of a fuse conductor according to the invention but for different working conditions.
• FIG. 5 is a detail of FIG. 4.
• the fuse conductor of FIG. 1 consists of a thin plate of silver intended to carry the current in the direction coinciding with its largest dimension. Across this direction of current flow, fuse elements have been created by punching openings in the conductor. In FIG. 1 there are a number of holes in a row, namely four, thereby creating five instances of reduced cross-section forming five fuse elements at the locations indicated by (1), and this pattern of fuse elements is repeated five times along the lenght of the fuse, so that the fuse can be adapted to a voltage rating five times that of a single fuse element.
• the fuse conductor shown in FIG. 2 can be conceived as simply according to prior art as disclosed in US patent 2,781,434, but depending on the dimensions selected it can also be according to the present invention. For simplicity it only shows the fuse elements (1) formed by the punching of circular openings (2) in the part made of silver (3) located between the outer parts of the fuse conductor made of copper (4), but special attention should be directed to the location of the transitions (5) between silver and copper.
• the critical dimension defining the invention is the distance between the center of the fuse elements (1) and the transitions (5), because this distance shall be long enough to ensure that the temperature of any part of copper does not exceed the value of temperature that leads to harmful progressive oxidation, while on the other hand, the amount of silver located in between must burn away before the arc can be established between foot-points on copper.
• the invention centers on the means available to achieve the desirable but hitherto unnoticed effect resulting from an early transition of the arc from silver to copper.
• the object of design must be to achieve the reduction of cross-section in as short a distance as practical.
• An important means to that end is to increase the number of openings in a given width of conductor, i.e. to have many small openings in stead of a few large ones, and to locate the fuse elements essentially midway in between the transition lines (5). Further improvements can be achieved by proper deviations from the simple circular form in various ways generally known to the man skilled in the art.
• the degree to which this critical distance can be diminished also depends on the operating temperature of the fuse element.
• the most unfavorable case is that of the temperature of the fuse element being almost the melting point of silver.
• the fuse conductor shown on FIG. 3 is made according to the invention. It shows the use of a higher number of openings with intervening fuse elements across the width of the fuse conductor and also the use of several bands of fuse elements over the length, making it possible to design the fuse for any desired value of voltage.
• the fuse conductor shown on FIG. 4 is similar to that of FIG. 3 except that the length of silver is shown to be less than the diameter of the openings. A detail is shown enlarged on FIG. 5.
• aluminium In contrast to copper, aluminium will not be subject to harmful progressive oxidation because the first oxide film formed will be mechanically strong and impervious to oxygen and therefore protect against further oxidation. This implies that in case aluminium is used in place of silver and together with copper as explained, the fuse element can assume a temperature even above the melting point of aluminium, the molten aluminium being retained within the oxide film until it bursts. However, because of the lower temperature it can be used with less distance to the copper, and because aluminium at the temperature of the arc reacts with quartz, a frequently used component of the porous filler of the fuse, the burnback velocity in aluminium will be higher than for silver.
• the invention opens the possibility to exploit many more combinations of different metals, each with its particular advantages in the two parts of the bi-metallic fuse conductor. Such other combinations will occur to the man skilled in the art when the desired special properties of the fuse and its operating conditions are specified.

Landscapes

• Fuses (AREA)
• Fixed Capacitors And Capacitor Manufacturing Machines (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

Family

ID=8094268

Family Applications (1)

Country Status (11)

Cited By (1)

Families Citing this family (1)

Citations (9)

Family Cites Families (3)

• 1981
  • 1981-02-05 DK DK50081A patent/DK50081A/da not_active Application Discontinuation
• 1982
  • 1982-02-02 CA CA000395373A patent/CA1201470A/en not_active Expired
  • 1982-02-04 EP EP82100806A patent/EP0059334B1/en not_active Expired
  • 1982-02-04 DE DE8282100806T patent/DE3279223D1/de not_active Expired
  • 1982-02-04 GR GR67209A patent/GR78349B/el unknown
  • 1982-02-04 IE IE246/82A patent/IE54661B1/en unknown
  • 1982-02-05 JP JP57500574A patent/JPS58500148A/ja active Granted
  • 1982-02-05 FI FI820381A patent/FI820381L/fi not_active Application Discontinuation
  • 1982-02-05 BR BR8205980A patent/BR8205980A/pt unknown
  • 1982-02-05 WO PCT/DK1982/000011 patent/WO1982002795A1/en unknown
  • 1982-10-04 NO NO823332A patent/NO823332L/no unknown

Patent Citations (9)

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