Fusible element for time-lag fuses having current-limiting actio

Details Fusible element for time-lag fuses having current-limiting actio Fusible element for time-lag fuses having current-limiting actio

1978-10-18

1980-08-26

Broome, Harold

Electricity: electrothermally or thermally actuated switches

Electrothermally actuated switches

Fusible element actuated

337163, 337295, H01H 0000

Patent

active

042197953

ABSTRACT:
A fusible element for electric fuses combining considerable time lag with current-limiting action. Time lag is achieved by providing the fuse with a combination of a plurality of means for achieving this end, such as folding the perforated center portion of the fusible element twice in a direction longitudinally thereof to achieve mutual heating of the folded portion, providing the center portion with end portions or heat dams of reduced cross-section which limit the flow of heat from the center portion to the terminals of the fuse, and are folded in transverse direction, and providing the fusible element with means capable of severing the fusible element by a metallurgical reaction, widely known as M-effect. The M-effect means increase time lag because of their mass and because they derate the fusible element. They cause severing of the center portion of the fusible element and are heated, in addition to i.sup.2 .multidot.r losses occurring in the center portion of the fusible element, by convection, conduction and radiation across a gap formed between the center portion of the fusible element and a section of one of the end portions of the fusible element.
In the interest of economy only the perforated center portion of the fusible element is of silver having a fusing i.sup.2 .multidot.t of 8.00.multidot.10.sup.8 (amp/cm.sup.2).sup.2 .multidot.sec., while the end portions are of a metal other than silver, such as copper, which has a fusing i.sup.2 .multidot.t of 11.72 (amp/cm.sup.2).sup.2 .multidot.sec.

REFERENCES:
patent: 3261950 (1966-07-01), Kozacka
patent: 3291943 (1966-12-01), Kozacka
patent: 3341674 (1967-09-01), Jacobs, Jr.
patent: 3935553 (1976-01-01), Kozacka et al.

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