75 YEARS - Hubbell Power Systems

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.
18 www.hubbellpowersystems.com
Photograph 4 —Whole LAuxiliary Tube
Photograph 6—40 Amp T Link
STRAIN WIRE BROKEN
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
Photograph 5—10 Amp T Link
Photograph 7—65 Amp T Link
These links were mechanically pulled apart at forces above 20 lbs.
STRAIN WIRE PULLED OUT
SOLDER MELTED
STRETCHED ELEMENT
ROUGH ELEMENT SURFACE
(Fuse was operated at 22 amps, 15 kV)
Photograph 8
Photograph 9
Photograph 10 —6 Amp K Link
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