Tips & News - September 2012

and stainless steel strain wires melted between connections, the remaining elements have smooth surfaces, and the connections are undisturbed. These are all signs of a normal fuse operation at low current. The 140 and 200 amp T links (see Photograph 8) have a solder connection at the buttonhead end. On low-level faults this connection will melt and pull out of the buttonhead. This type of operation is often mistakenly considered a “pull apart.” As long as buttonhead and element are well wetted with solder, this is a normal operation. T LINK PULL APART T links, 6 through 100 amps, which have been mechanically over stressed and pulled apart, will have a stretched tin element. The surface of the element will be rough and the element will be necked down where it pulled apart. The strain wire will either pull out of one of the crimps, recognized by the bend at that end of the wire, or will break off right at one of the crimps (Photograph 9). T links, 1 through 3 amps, have only stainless steel elements. If they pull apart, they will have elements which pull out or break off like the strain wires. The 140 and 200 amp T links are strong enough that a pull apart (pulling out of the crimp or solder connection) is unlikely. K LINK LOW-LEVEL OPERATION “K” links that have operated at low fault currents (Photograph 10) will have auxiliary tubes that have not ruptured. Like T links, the strain wire and element will melt somewhere between the connections, and the crimps will be undisturbed. The amount of element and strain wire consumed will be somewhat proportional to the ratio of fault current to the fuse rating, i.e., a fault of 15 times the fuse rating will consume more element than one which is only three times the rating.

Photograph4—WholeLAuxiliaryTube

Photograph5—10AmpTLink

Photograph6—40AmpTLink

Photograph7—65AmpTLink

SOLDERMELTED

Photograph8

STRAINWIREBROKEN

STRETCHEDELEMENT

Photograph9

Theselinksweremechanicallypulledapartatforcesabove20lbs.

STRAINWIREPULLEDOUT

ROUGHELEMENTSURFACE

Photograph10—6AmpKLink

(Fusewasoperatedat22amps,15kV)

K LINK PULL APART K links, 6 through 100 amps, which have been mechanically over stressed and pulled apart will have strain wires which pull out of the crimp and/or break off right at the crimp the same as T links. The element, being much stronger than tin, will not neck down much. Once the strain wire gives way, the total stress is placed on the element. The element will break at its weakest point anywhere along its length, not necessarily at the crimp. K links, 1 through 3 amps, have

only stainless steel elements. If they pull apart, they will have elements which pull out or break off like the strain wires shown at right (Photograph 11). The 140 and 200 amp K links are of such strength that a pull apart is unlikely.

SLO-FAST LINKS LOW-LEVEL OPERATION

Slo-Fast links have two sections that can operate at currents of 500 amps and below. The “fast” section is

www.hubbellpowersystems.com

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