Load-break fuse equipment

This load-break fuse equipment comprises two draw-out fuse assemblies, one of the load-break type and one of the non-load-break type, each removably mounted in its own individual receptacle. The load-break fuse assembly and its receptacle comprise a load-break switch and a fuse electrically connected in series with each other. The non-load-break fuse assembly comprises a fuse, and this fuse is electrically connected in parallel with the fuse of the load-break fuse assembly and in series with said load-break switch.

BACKGROUND 
This invention relates to load-break fuse equipment comprising a tubular 
receptacle and, removably mounted within the receptacle, a load-break 
drawout assembly that comprises a fuse and the movable contact of a 
load-break switch. 
Examples of load-break fuse equipment of this type are disclosed in U.S. 
Pat. Nos. 3,471,816--Giegerich; 3,628,092--Keto; and 4,059,816--Bonecutter 
et al. In certain applications of such load-break fuse equipment, the 
largest diameter single fuse that is receivable within the receptacle may 
not have sufficient current-carrying or current-interrupting capacity for 
the power circuit in which the equipment is to be connected. For such high 
current applications, it is conventional to provide two identical 
load-break fuse equipments of this type and to connect them electrically 
in parallel. 
While this approach can provided increased current-carrying and 
current-interrupting capacity while the two load-break drawout assemblies 
are in place within their receptacles, it is subject to the distinct 
disadvantage that the desired current-interrupting capacity is not present 
during certain intervals while the load-break drawout assemblies are being 
removed from or being inserted into their receptacles. More specifically, 
if one of the load-break drawout assemblies of such prior equipment is 
withdrawn, the fuse of the remaining assembly must alone provide current 
interrupting ability until the remaining assembly is withdrawn. This same 
condition is, of course, present if one of the load-break drawout 
assemblies is inserted before the other one. 
SUMMARY 
An object of this invention is to provide load-break fuse equipment of this 
general type that comprises fuses connected in parallel, which fuses 
remain connected in parallel both during removal and insertion of the 
load-break drawout assembly. 
Another object is to provide load-break fuse equipment comprising a tubular 
receptacle and a load-break drawout assembly removably mounted therein, 
which equipment is constructed in such a way that a separate fuse can 
readily be connected in parallel with the fuse of the drawout assembly and 
in series with the load-break switch within the receptacle, all without 
interfering with the easy removability of the drawout assembly and the 
ability of the load-break switch to interrupt load currents coincident 
with removal of drawout assembly. 
Another object is to achieve the immediately-preceding object without 
interfering with easy insertability of the drawout assembly and the 
ability of the load-break switch to close against currents coincident with 
such insertion, e.g., inrush currents. 
In carrying out the invention in one form, we provide two spaced-apart 
tubular receptacles mounted on a wall. Each receptacle comprises an 
outboard contact and an inboard contact at axially-spaced locations along 
the bore of the receptacle, first tubular insulating structure between 
said contacts, and second tubular insulating structure between the 
outboard contact and said wall. One of the receptacles further comprises a 
generally stationary load-break contact at its inner end and a third 
tubular insulating portion between said load-break contact and its inboard 
contact. 
Insertable as a unit into said one receptacle is a load-break drawout 
assembly comprising a fuse, two sliding contacts at opposite ends of the 
fuse, a movable load-break contact inboard of the fuse, and an insulating 
drawout rod outboard of the fuse. When this drawout assembly is fully 
inserted, the movable load-break contact engages the stationary load-break 
contact and the two sliding contacts respectively engage the inboard and 
outboard contacts of said one receptacle. Insertable as a unit into the 
other receptacle is a non-load-break drawout assembly comprising a fuse, 
two sliding contacts at opposite ends of the fuse, and an insulating 
drawout rod outboard of the fuse; said two sliding contacts respectively 
engaging the inboard and outboard contacts of said other receptacle when 
said non-load-break drawout assembly is fully inserted. 
Means is provided for electrically connecting said two fuses in parallel 
with each other and in series with said load-break contacts comprising a 
first conductor interconnecting the outboard contacts of the two 
receptacles and a second conductor interconnecting the inboard contacts of 
the two receptacles.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
Referring now to FIG. 1, the illustrated load-break fuse equipment 
comprises a tubular receptacle 10 that is mounted on a wall 12 of 
electrical apparatus such as a pad-mounted distribution transformer. The 
wall 12, which may be of metal, contains an opening through which the 
tubular receptacle 10 extends, with the bore of the receptacle generally 
aligned with the opening. A flange 14 on the outer end of the receptacle 
10 is attached to the wall 12 by suitable fastening means (not shown). A 
suitable gasket (not shown) is disposed between the flange 14 and wall 12 
to provide a seal between these parts. 
In the usual electrical apparatus in which this load-break fuse equipment 
is used, wall 12 is a portion of a tank filled with a dielectric fluid, 
such as oil. The receptacle 10 constitutes a dry well projecting into this 
oil and having its interior sealed from the oil. 
The receptacle 10 is primarily formed as a cylindrical insulating tube 16 
of oil-resistant, glass-fiber reinforced epoxy material that is suitably 
jointed at its outboard end to flange 14. At the inboard end of insulating 
tube 16, there is a cup-shaped metal terminal member 18 suitably attached 
to tube 16. This metal terminal member 18 carries the stationary 
socket-type contact 19 of a conventional load-break switch 19, 48 soon to 
be described. Terminal member 18 also has an external stud 21 to which an 
external conductor 23 can be attached for electrically connecting terminal 
member 18 to an external source circuit (not shown). 
Receptacle 10 further comprises two conductive metal sleeves 20 and 22 
within the insulating tube 16 at axially-spaced locations along the bore 
of tube. As will soon appear more clearly, these sleeves 20 and 22 serve 
as tubular contacts for the load-break drawout assembly that is removably 
mounted in the receptacle. Sleeve 20 is referred to herein as an outboard 
contact, and sleeve 22 as an inboard contact. Electrically connected to 
sleeves 20 and 22 are terminal studs 24 and 26, each of which projects 
radially through the insulating tube 16 to its exterior. 
It will be apparent that receptacle 10 comprises a first tubular insulating 
portion 30 between the inboard and outboard contacts 20 and 22, a second 
tubular insulating portion 32 between outboard contact 20 and flange 14, 
and a third tubular insulating portion 34 between inboard contact 22 and 
metal terminal member 18 at its inner end that carries stationary 
load-break contact 19. When the load-break drawout assembly (soon to be 
described) is not in place within the receptacle, the first insulating 
portion 30 insulates contacts 20 and 22 from each other; the second 
insulating portion 32 insulates contact 20 from the metal wall 12; and the 
third insulating portion 34 insulates the inboard contact 22 from inner 
end terminal member 18. 
Removably mounted within receptacle 10 is a load-break drawout assembly 40. 
This drawout assembly comprises a current-limiting fuse 42, two sliding 
contacts 44 and 46 at opposite ends of the fuse, a load-break movable 
contact rod 48, 49 in a location inboard of the fuse, and a drawout rod 50 
of insulating material in a location outboard of the fuse. As will soon 
appear more clearly, these components 42-50 are all mechanically connected 
together so that the drawout assembly 40 is removable from receptacle 10 
as a unit and is insertable into receptacle 10 as a unit. When load-break 
drawout assembly 40 is fully inserted into its receptacle, as shown in 
FIG. 1, an electric circuit extends through the load-break fuse equipment 
from its outboard terminal 24 to the terminal member 18 at its inner end 
via a path that extends in series through the contacts 20 and 44, fuse 42, 
and load-break switch 48, 19. The outboard terminal 24 is connected to a 
load circuit, e.g., the high voltage winding (not shown) of the 
transformer, through a suitable conductor 51. The various components of 
the drawout assembly 40 will now be described in more detail. 
Current-limiting fuse 42 is of a conventional design, and, as such, 
comprises a casing 54 of insulating material, end caps at opposite ends of 
the casing having rod-type terminals 56 and 58, and fusible elements (not 
shown) disposed within casing 54 and electrically interconnecting 
terminals 56 and 58. Casing 54 contains an arc-extinguishing filler 
material, such as quartz sand, in which the fusible elements are embedded. 
The drawout rod 50 has a cup-shaped metal end fitting 62 at its inboard end 
that snugly receives the fuse terminal 56. A plurality of set screws 63 
extend radially through end fitting 62 and clamp the end fitting and fuse 
terminal 56 together. The sliding contact 44 is attached to the end 
fitting 62 by suitable means providing a good electrical connection 
therebetween. In the illustrated embodiment, this sliding contact 42 is a 
disc of highly conductive metal having at its outer periphery 
circumferentially-spaced fingers of U-shaped cross section that press 
radially outward against the sleeve contact 20. Other suitable forms of 
sliding contact may, of course, be used in this location. When the 
terminal stud 24 is connected to an external circuit, current can flow 
from terminal stud 24 to the fuse terminal 56 via a path that extends in 
series through sleeve contact 20, sliding contact 44, and end fitting 62. 
The contact rod 48, 49 at the inboard end of fuse 42 has an end fitting 70 
that receives fuse terminal 58 and is clamped thereto by set screws in the 
same way as parts 62 and 56 are clamped together at the outboard end of 
the fuse. The sliding contact 46 at the inboard end of the fuse is of 
essentially the same construction as previously-described sliding contact 
44 and is suitably attached to end fitting 70. When terminal stud 26 is 
connected to an external circuit, current can flow between stud 26 and 
contact rod 48, 49 via a path extending through the following parts in 
series: 26, 22, 46, 70, and 48, 49. 
Contact rod 48, 49 is slidably received within the bore of tulip-type 
stationary contact structure 19, which comprises circumferentially-spaced 
fingers biased radially inward by suitable means (not shown) to provide 
increased contact pressure between contact 19 and 48. Contacts 19 and 48 
may be thought of as load-break contacts since they are usually separated 
while load current is flowing through them when the drawout assembly 40 is 
withdrawn. 
Current interruption at the load-break contacts is effected in a 
conventional manner. More specifically, an arc is drawn between contacts 
19 and 48 when rod 48 is withdrawn from contact 19, and this arc reacts 
with gas-evolving material in this region to produce an arc-extinguishing 
gas that acts to quickly extinguish the arc. Such gas-evolving material is 
present in the form of a stationary snuffer tube 76 surrounding rod 46 and 
a follower 76 attached to contact rod 48. 
The drawout assembly 40 further includes a flange 80 at its outboard end 
that seats against the flange 14 of receptacle 10 when the drawout 
assembly is fully inserted, as shown in FIG. 1. Flange 80 can be moved to 
the left by applying force to an eye bolt 82 secured to the flange. Such 
force is applied through a conventional hot-stick attached by an operator 
to eye bolt 80. 
When eye bolt 80 is thus pulled to the left, the entire load-break drawout 
assembly 40 is moved to the left and is eventually withdrawn from 
receptacle 10. Such withdrawal results, first of all, in the circuit 
through the device being interrupted at the load-break contacts 19 and 48, 
as above described. The sliding contacts 44 snd 46 are then still in 
engagement with their associated contact sleeves 20 and 22 so that there 
is no arcing at these contacts. When the drawout assembly 40 has been 
withdrawn sufficiently to complete the load-break operation and disconnect 
the circuit, the sliding contacts 44 and 46 separate from their associated 
contacts 20 and 22, and the drawout assembly is then completely withdrawn. 
When the drawout assembly 40 is in its fully inserted position of FIG. 1, 
the current-limiting fuse 42 functions in a conventional manner to protect 
the transformer against short-circuit and other abnormal currents flowing 
through the load-break fuse equipment. More specifically, if current 
through the fuse exceeds a predetermined value, portions of the fusible 
elements therein rapidly vaporize, creating arcs that are rapidly 
extinguished and prevented from reigniting by the interaction of the arc 
and the filler material within the fuse. Such operation of the fuse acts 
in a conventional manner to limit the current therethrough to a value far 
below the maximum available current of the circuit. 
In certain applications, any single fuse (42) which will properly fit 
within the receptacle 10 may not have sufficient current-carrying capacity 
and/or sufficient current-interrupting capacity to adequately protect the 
transformer. To provide adequate protection for such applications, we 
connect a separate fuse 142 in parallel with the above-described fuse 42 
and in series with the contacts 48, 19 of the load-break switch. 
This separate fuse 142 is part of a non-load-break drawout assembly 140 
mounted in a receptacle 110 located adjacent receptacle 10. Receptacle 110 
is in many respects similar in construction to receptacle 10, and most of 
its parts have therefore been assigned the same reference numerals as 
corresponding parts of receptacle 10 except for the addition of the prefix 
"1." Similarly, drawout assembly 140 is similar in many respects to 
drawout assembly 40, and most of its parts have been assigned the same 
reference numerals as corresponding parts of drawout assembly 40 except 
for the addition of the prefix "1." To avoid repetition, only the 
differences in the two side-by-side assemblies will be described. 
The non-load-break drawout assembly 140 differs from the load-break drawout 
assembly 40 in that it terminates at the end fitting (170) that receives 
the inboard fuse terminal (158). Thus, there is no load-break switch at 
the inboard end of the drawout assembly 140. 
The receptacle 110 differs from receptacle 10 in that it terminates at its 
inboard end just past the inboard fuse terminal 158. An end cap 118 is 
suitably attached to insulating tube 116 to provide a leak-proof end 
construction for the receptacle. 
For electrically connecting the two fuses 42 and 142 in parallel with each 
other and in series with the load-break switch 19, 48, a pair of flexible 
conductors 200 and 202 are provided. Conductor 200 is connected between 
terminals 24 and 124 of the two receptacles, and conductor 202 is 
electrically connected between terminals 26 and 126 of the two 
receptacles. This parallel connection of the fuses enables the fuses to 
share the continuous current-carrying duty and also the 
current-interrupting duty, thus enabling the protective equipment to 
handle higher continuous and available short-circuit currents. 
When it is desired to disconnect the transformer winding from the incoming 
conductor 23, the load-break drawout assembly 40 is withdrawn from its 
receptacle 10, thus breaking the load current at the load-break switch 19, 
48 and isolating the load side lead 51 from incoming (or source) lead 23. 
Because the load-break switch 19, 48 is in series with both fuses 42 and 
142, it is to be noted that the fuses remain in parallel during the 
load-breaking operation, and thus both are available during this interval 
to share in interrupting possible short-circuit or other abnormal 
currents. Similarly, if the load-break drawout assembly 40 is inserted 
while the fuse assembly 140 is in place within its receptacle, the 
parallel combination of fuses is available to share the interrupting duty 
from the instant that the load-break switch 19, 48 reestablishes the power 
circuit. 
The above operation is in distinct contrast to that present when two 
load-break fuse assemblies are provided and are connected completely in 
parallel, as in the prior art. When the drawout assembly of one of these 
fuse assemblies is removed, the remaining one carries all the current and 
its fuse may be called upon to interrupt possible short-currents alone and 
without assistance from the first fuse should a fault occur during this 
interval. Similarly, should one of these drawout assemblies be inserted 
prior to insertion of the other one, the first-inserted one may be called 
upon to handle possible short-circuit, or other abnormal, currents 
unassisted until the other one is inserted. 
The load-break fuse assembly 10, 40 is structurally quite similar to a 
prior load-break fuse assembly manufactured by the assignee of the present 
invention and can therefore be manufactured using most of the same parts 
as with the prior load-break fuse assembly and without drastically 
changing the manufacturing process. But, there is at least one important 
structural difference between the load-break fuse assembly 10, 40 and the 
prior load-break fuse assembly, and that resides in the presence of the 
inboard sliding contact 46 and the inboard sleeve contact 22 and terminal 
26 at the inboard end of the fuse, which components are not present in the 
prior load-break fuse assembly. 
Although the fuse 142 is connected in parallel with fuse 42 and in series 
with load-break switch 19, 48, it is to be noted that the load-break 
drawout assembly can be removed and reinserted without interference from 
the extra fuse 142 and in generally the same straightforward manner as 
previously. 
It is important, however, that the two drawout fuse assemblies be withdrawn 
in the proper sequence and also reinserted in the proper sequence. More 
specifically, it is important that the load-break drawout assembly 40 be 
withdrawn before the non-load-break drawout assembly 140 and be reinserted 
after the non-load-break assembly 140. Unless this sequence is followed, 
there will be an interval during each of these operations when only one 
fuse will be connected in the circuit and will be available to interrupt 
possible short-circuit currents. To assure that the correct sequence is 
followed in these operations, an interlock arrangement such as shown in 
FIGS. 2 and 3 is provided. 
This interlock arrangement comprises a barrier 210 that is mounted on the 
outside of wall 12 and is guided for movement in a vertical path only by 
suitable pin and slot connections, one of which is shown at 215, 216. When 
the drawout assemblies are both in their fully-inserted position of FIG. 
1, the barrier 210 is in a position to block drawout motion of the lower, 
or non-load-break, drawout assembly 140. If an attempt is made to lift the 
barrier 210 to unblock the lower drawout assembly, such lifting of the 
barrier is blocked by the flange 80 of the upper drawout assembly 40, 
which is in the path of a projection 220 on the barrier. Thus, the lower 
drawout assembly is prevented from being withdrawn before the upper 
drawout assembly is withdrawn. 
When the upper drawout assembly is withdrawn, upward movement of the 
barrier 210 is no longer blocked by flange 80, and the barrier 210 can 
therefore be lifted to unblock the lower drawout assembly, thus permitting 
its withdrawal. 
When barrier 210 is thus lifted into an unblocking position with respect to 
the lower drawout assembly 140, it is latched in its elevated position by 
a latch 225 cooperating with a projection 227 on the barrier 210. This 
latch 225 is pivotally mounted on a stationary pivot 230 and is biased 
counterclockwise by a spring 232 against a generally stationary, but 
slightly yieldable, stop 235. When the barrier 210 is lifted, the latch is 
temporarily brushed aside by projection 227 but is pivoted 
counterclockwise into place underneath the projection 227 when the 
projection moves above the latch. 
When the lower drawout assembly is withdrawn, the flange 180 will pivot 
latch 225 clockwise a short distance against yieldable stop 235 but not 
enough to release latch 225 from projection 227. Thus, the barrier 210 
remains in its elevated position of FIG. 3 when both drawout assemblies 
are withdrawn. When barrier 210 is in this position, it blocks insertion 
of the upper drawout assembly. It is necessary to first insert the lower 
drawout assembly. During such insertion, the outer periphery of flange 180 
of the lower drawout assembly trips latch 225, allowing barrier 210 to 
fall into place behind flange 180 on the lower drawout assembly. When 
flange 180 nears its fully-seated position, the latch 225 is free to reset 
by pivoting counterclockwise into its position of FIG. 2. 
It is to be understood that our invention in its boarder aspects is not 
limited to any particular form of interlock. But it is highly desirable 
that some means be provided for providing reasonable assurance that the 
desired sequence of operations will be followed both during withdrawal and 
during reinsertion of the drawout fuse assemblies. 
While I have shown only a single phase form of the invention, it is to be 
understood that the invention is readily usable for polyphase apparatus. 
In such apparatus, an assembly corresponding to that shown in FIG. 1 is 
provided for each phase; and, preferably, a suitable interlock is provided 
which assures that all of the load-break drawout assemblies will be 
withdrawn before any of the non-load-break assemblies are withdrawn and 
also assures that all of the non-load-break assemblies will be inserted 
before any of the load break assemblies are inserted. 
While we have shown and described particular embodiments of our invention, 
it will be obvious to those skilled in the art that various changes and 
modifications may be made without departing from our invention in its 
broader aspects; and we, therefore, intend herein to cover all such 
changes and modifications as fall within the true spirit and scope of our 
invention.