U.S. patent number 3,691,425 [Application Number 05/134,340] was granted by the patent office on 1972-09-12 for transformer with a fuse.
This patent grant is currently assigned to Certron Corporation. Invention is credited to Richard R. Bertrand, Edwin D. Karinski, Arthur G. Weyrich.
United States Patent |
3,691,425 |
Weyrich , et al. |
September 12, 1972 |
TRANSFORMER WITH A FUSE
Abstract
A plastic bobbin-like body for a fused coil, such as a primary
winding of a power transformer, is provided with end flanges. A
fuse-mounting groove is provided on the outside of a thickened
section of one flange. A fuse strip made of a metal having a
suitably low melting point is placed in the groove and is held in
position by barbed connecting lugs inserted into passages which run
parallel to the flange walls to the bottom of the groove. The coil
is connected in series with the fuse through the lugs. A large
cavity around the center of the groove allows liquid metal to
quickly fall away from the fuse when excessive current heats the
fuse to its melting temperature. Alternatively, the lugs may be
provided with tabs which project out of the thickened section. The
tabs are then rolled over the fuse mounted on the outside of the
thickened section.
Inventors: |
Weyrich; Arthur G. (Rolling
Meadows, IL), Bertrand; Richard R. (Skokie, IL),
Karinski; Edwin D. (Chicago, IL) |
Assignee: |
Certron Corporation (Anaheim,
CA)
|
Family
ID: |
22462905 |
Appl.
No.: |
05/134,340 |
Filed: |
April 15, 1971 |
Current U.S.
Class: |
361/41; 336/105;
336/198; 336/192; 361/104 |
Current CPC
Class: |
H01F
27/402 (20130101); H01H 37/761 (20130101) |
Current International
Class: |
H01F
27/00 (20060101); H01F 27/40 (20060101); H01H
37/00 (20060101); H01H 37/76 (20060101); H02h
007/04 () |
Field of
Search: |
;336/192,198,105
;317/15,157.6 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Goldberg; E. A.
Claims
What is claimed is:
1. A form for a fused coil comprising:
a body of electrical insulating material having a longitudinal axis
for carrying a coil wound around said longitudinal axis, said body
having an end section with a surface normal to said axis,
a pair of passages in said body running in a direction
substantially parallel to the surface of said end section,
a strip of metal having two ends, said strip of metal being
selected both as to composition and form to heat to a melting
temperature in response to current at a predetermined level
conducted from one end thereof to the other end,
a pair of connecting lugs, one lug inserted into one of said
passages, and the other lug inserted into the other of said
passages, each of said lugs being sufficiently long to have a
substantial portion protruding from said body, and
means for securing said metal strip in electrical contact with said
lugs, one lug at each end of said metal strip whereby one end of a
coil wound on said body may be connected directly to one tab
thereby placing said metal strips as a fuse in series between the
other end of said coil and the other tab, said means comprising a
groove formed in said end section through said end surface, wherein
each of said pair of passages in said body is in communication with
a different end of said groove at a level near the bottom of said
groove, said strip of metal being placed in said groove, and said
pair of connecting lugs being inserted sufficiently into said
passages to engage said metal strip and secure said metal strip in
said groove.
2. The combination of claim 2 including a cavity formed in said
body around the center of said groove, the depth of said cavity
being greater than the depth of said groove.
3. The combination of claim 3 wherein said groove intersects said
pair of passages and each of said lugs engages said metal strips by
abutting said metal strip in said groove, thereby holding said
metal strip in place by pressure of said abutting lugs.
4. The combination of claim 2 wherein said groove is behind said
pair of passages relative to said surface and in communication with
said passages and each of said lugs engages said metal strip by
overriding said metal strip in said groove.
5. The combination of claim 2 wherein said body includes two
flanges, a flange on each end.
6. The combination of claim 5 wherein said body is tubular, and one
of said flanges at one end of said body provides said section into
which said groove and cavity are formed.
7. The combination of claim 6 wherein said body includes a third
flange intermediate said end flanges and further includes,
first and second coils wound around said body to form a
transformer, each coil being separately wound between a separate
pair of flanges, said first coil being wound next to said flange
into which said groove is provided, one end of said first coil
being connected to one of said lugs, and
a transformer core passing through said tubular form and around
both of said coils on at least one side in a closed magnetic
circuit.
8. A form for a fused coil comprising
a body of electrical insulating material having a longitudinal axis
for carrying a coil wound around said longitudinal axis, said body
having an end section with a surface normal to said axis,
a pair of passages in said body in a direction substantially
parallel to the surface of said end section,
a strip of metal having two ends, said strip of metal being
selected both as to composition and form to heat to a melting
temperature in response to current at a predetermined level
conducted from one end thereof to the other end,
a pair of connecting lugs, one lug inserted into one of said
passages, and the other lug inserted into the other of said
passages, each of said lugs being sufficiently long to have a
substantial portion protruding from said body, and
means for securing said metal strip in electrical contact with said
lugs, one lug at each end of said metal strip whereby one end of a
coil wound on said body may be connected directly to one tab
thereby placing said metal strips as a fuse in series between the
other end of said coil and the other tab, said means comprising
slots opening said passages to said surface of said end section,
and a tab protruding from each of said lugs, each tab being tight
around said metal strip laying against said surface of said end
section, whereby said tabs hold said metal strip secure against
said end surface and provide electrical connection from one lug to
the other through said metal strip.
9. The combination of claim 8 wherein said body includes two
flanges, a flange on each end, and one of said flanges at one end
of said body provides said thickened section into which said lug
passages are formed.
Description
BACKGROUND OF THE INVENTION
This invention relates to fused coils wound on a bobbin-like body,
and more particularly to such a body having an integral means for
holding a fuse and for connecting a coil wound on the form in
series with the fuse.
In the past fused coils, such as in power transformers, have been
wound on a form and connected to a fuse on a separate connector
board. That fuse-connector board then had to be accommodated in
packaging the wound coil. It would be desirable to provide fused
coils without a separate connector board.
SUMMARY OF THE INVENTION
In accordance with the present invention, a coil is wound on a body
of electrical insulating material having an axis around which the
coil is wound. The form has a thickened section with a surface
normal to that axis and with sufficient area to accommodate a
groove into which a fuse of the metal-strip type is placed. The
fuse is secured in place by a pair of barbed connecting lugs
inserted into passages running through the body in a direction
parallel to the aforesaid surface area and leading to the ends of
the groove at a level near the bottom of the groove to make contact
with the fuse wire by butting the end of the terminal against the
fuse wire, or by overriding the fuse wire. Alternatively, the lugs
may be provided with tabs which project out of the thickened
section. The tabs are then rolled over the fuse mounted on the
outside of the thickened section. The lug passages are sufficiently
narrow to engage the barbs of the connecting lugs, and the lugs are
sufficiently long to leave a substantial portion protruding in
order to connect one end of the coil to one end of the fuse, and an
external connecting lead to the other end of the fuse.
For a fused transformer, the body is tubular and has a flange at
each end, one providing the surface area for the fuse or a fuse
groove. Each coil wound directly on the same body is separated from
any other coil wound on the same body by an additional flange. A
transformer core is inserted through the center of the tubular body
and around all of the coils on at least one side to form a closed
magnetic loop. In a fused power transformer of the type having the
coils covered on all sides by metal adapted to be connected to
earth, the leads of the fused coil pass through an aperture in the
cover. Leads from other coils in the transformer are adapted to be
connected to external circuits by conventional means.
The novel features that are considered characteristic of this
invention are set forth with particularity in the appended claims.
The invention will best be understood from the following
description when read in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is an isometric view of a bobbin-like body for winding coils
of a fused transformer in accordance with the present
invention.
FIG. 2 is a schematic diagram of a fused transformer to be provided
on the body of FIG. 1.
FIG. 3 is a sectional view of the body of FIG. 1 taken along the
line 3--3 with the two transformer coils wound in place.
FIG. 4 is a sectional view of FIG. 3 taken along a line 4--4 in
FIG. 3.
FIG. 5 is a sectional view taken along a line 5--5 of FIG. 4.
FIG. 6 illustrates a prior art technique for providing coils of a
fused transformer on a form.
FIG. 7 shows an exploded isometric view of a complete transformer
fused in accordance with the present invention.
FIG. 8 is a sectional view corresponding to FIG. 4 of an
alternative embodiment of the present invention.
FIG. 9 is an end view of a bobbin-like body with a fused coil in
accordance with an alternative embodiment of the present
invention.
FIG. 10 is a side view of FIG. 9.
FIG. 11 is a sectional view of FIG. 9 along a line 11--11 before a
fuse of the metal-strip type is added to the assembly.
FIG. 12 shows the structure of FIG. 11 after a fuse of the
metal-strip type is added to the assembly.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1, a bobbin-like body 10 for a fused
transformer is shown comprising an elongated tubular section 11
having end flanges 12 and 13, and a center flange 14. The coils of
the transformer are wound directly on the tubular section 11, each
coil being wound between a separate pair of flanges. A thickened
section or block 15 is provided on the outside of the flange 13
either as a separate piece cemented or fused on the flange or as a
unitary section of the flange, and is adapted to hold a fuse of the
metal-strip type in such a manner that, in accordance with the
present invention, the coil wound between the flanges 13 and 14 may
be connected in series with the fuse through connecting lugs 16 and
17. Once the coils have been wound and the fuse has been connected
in series through the lugs 16 and 17, a laminated core is inserted
in the tubular section 11 in a conventional manner to form the
circuit illustrated schematically in FIG. 2 consisting of coils 20
and 21, a core 22 and a fuse 23. In a fused power transformer, the
coil 20 connected to the fuse 23 is generally the primary winding
of the transformer. Accordingly, the free ends of the coil 20 and
the fuse 23 are adapted to be connected to a power source with
heavily insulated wires.
The manner in which the fuse 23 is held in the thickened section 15
for series connection with the coil 20 by connecting lugs 16 and 17
will now be described with reference to FIGS. 3 and 4. A groove 30
is provided in the block 15 to a depth substantially half the
thickness of the block 15 as shown in the sectional view of FIG. 4
taken along the line 5--5 in FIG. 3. Passages are provided from the
top of the block 15 to the groove 30 in a plane parallel to the
face of the block 15. When the lugs 16 and 17 are inserted into the
passages, the ends of the lugs abut the fuse 23 and hold it in
place in the groove 30. In that manner pressure from the lugs press
the fuse against a wall of the groove 30. Friction between the lugs
16 and 17 and the walls of the passages 31 and 32 is enhanced by
barbs on the lugs.
A cavity 33 is provided in the block 15 at the center of the groove
30, and to a greater depth, in order to allow liquid metal from the
fuse to flow away and thereby open the current path between the
lugs 16 and 17 quickly when excessive current is conducted through
the fuse. The center of the fuse will be the first to melt because
the lugs 16 and 17 connected to the ends will function as heat
sinks, thereby keeping the ends below melting temperature while the
center is being heated to the melting temperature.
The bobbin-like body 10 is cast from a suitable plastic material.
The block 15 is also formed out of the same plastic material,
preferably by casting as a unitary part or thickened section of the
flange. Still another possibility is to cast the flange 13 of
sufficient thickness to accommodate the slot 30 and the passages 31
and 32 for the fuse 23 and the lugs 16 and 17, respectively. The
block 15 would then appear only as a section of the flange 13
selected for the slot 30 and the passages 31 and 32. The plastic
material serves to electrically insulate the lugs 16 and 17 and the
fuse 23 as well as the coils 20 and 21, although the coils do not
require that the body 10 be cast from an insulating material
because the wire used for the coils is already insulated.
It should be noted that the body 10 has a tubular section 11 which
is rectangular rather than circular in cross section only for the
purpose of receiving a core which has a rectangular cross section.
If the fused coil is to be provided without a core such as a choke
coil, the section 11 may be solid rather than tubular, and may in
some instances be formed without any flanges. In that event, the
slot 30, and passages 31 and 32, would be provided directly on the
end of the solid section 11, rather than on a flange at the
end.
Referring now to FIG. 5, the present invention as applied to a
fused transformer is shown in a sectional view taken along a line
5--5 of FIG. 1 with the coils 20 and 21 in place, but without a
transformer core and without any enclosure or cover. The prior art
technique for accomplishing the same thing in forming a fused
transformer is shown in FIG. 6 with corresponding reference
numerals distinguished by a prime in order to facilitate comparison
of the prior art technique with the present invention.
The prior art technique consist of employing a tubular form 11' on
which layers of the coils are wound, one layer at a time for a
given coil, each layer being covered with paper to separate it from
the next layer. First one coil is wound and then the other. Here
the first coil 20' is connected to a fuse 23' through a tab 17'
riveted to a board 15' of insulating material, the rivet serving
not only to connect the lug 17' to the fuse 23' but also to secure
both to the board 15'. A lug 16' is similarly connected to the
other end of the fuse 23' by riveting to the board 15'. Still
another lug 18' is riveted to the board 15' to provide means for
connecting the other end of the coil 20' to an outside circuit. The
board 15' is laid over the paper covering the last layer of turns
of the coil 21' in the dotted line position.
A comparison of FIGS. 5 and 6 shows that the structure of FIG. 1
which comprises a bobbin-like body with an integral fuse-holding
structure provides distinct assembly advantages. First, it is
easier to wind the coils separated by flanges than it is to wind
coils separated by layers of paper. Second, it is easier to install
a fuse and to connect the fuse in series with one of the coils. And
third, no further effort is required in regard to the
fused-connecting structure before a transformer core and enclosure
or cover is provided, except bending the lugs 16 and 17 over the
coil 20 to avoid contact with a metal cover.
FIG. 7 illustrates in an exploded isometric view the manner in
which a transformer core 40 is added to complete the assembly of a
fused transformer in accordance with the present invention. The
core 40 consists of a first part 41 made of laminated iron sheets
in the form of an E and a second part 42 made of laminated iron
sheets in the form of a letter I. The center leg of the E-part 41
is inserted into the tubular section on which the coils 20 and 21
are wound. The I-part 42 is then placed over the open ends of
E-part 41 to complete two magnetic circuit loops through the center
of the coils 21 and 22 and around both sides. The two parts of the
core are held together in a conventional manner, such as by welded
joints 43 and 44. Any other technique for securely holding the
I-part 42 against the E-part 41 will suffice, such as simply
bolting together transformer covers 45 and 46 with the parts 41 and
42 in place.
The covers 45 and 46 are normally made of metal so that when they
are provided they form an electromagnetic shield around the
transformer coils. However, it should be understood that either one
or both covers may be omitted in some applications.
Before the covers 45 and 46 are bolted together to complete the
assembly, the ends of the secondary winding (coil 21) are soldered
to connectors 47 and 48 (which pass through the cover 46) for
connections to external circuits. Both of the connectors 47 and 48
are electrically isolated from the metal cover 46 in a conventional
manner, such as by mounting the connectors in a panel 49 of
nonconductive material that is set into a large aperture in the
cover 46.
One end of the primary winding (coil 20) is connected to the lug
17. The other lug 16 at the other free end of the fuse is connected
to a heavily insulated conductor 50. The other free end of the
primary winding is connected to a second heavily insulated wire 51
at an insulated junction 52. Both of the wires 50 and 51 are passed
through an aperture 53 in the cover 45. A rubber grommet 54
prevents the insulation of the wires 50 and 51 from being frayed.
The lugs 16 and 17 may be bent over the coil 20, but not in contact
with any of the turns in the coil 20, to avoid possible contact
with the cover 45. To assure that the heavily insulated wires 50
and 51 are not pulled loose from their connection within the cover
45, some measure may be taken to keep all of the slack from being
pulled out of the cover 45, such as tying a knot in the leads 50
and 51 inside the cover.
An alternative embodiment of the present invention will now be
described with reference to FIG. 8. It is essentially the same as
the embodiment just described, but differs in a manner which can
best be appreciated by comparison of FIG. 8 with FIG. 4. To
facilitate comparison, the same reference numerals are employed,
except for the groove 30' distinguished by a prime over the
reference numeral.
The difference between this embodiment and that of FIG. 4 is that
the groove 30' is made to a depth sufficient for the fuse 23 to be
behind the passages, but in communication with the passages, such
as the passage 31. Once the fuse 23 is in place, the lugs are
inserted to a sufficient depth in their passages to allow them to
override the fuse 23, as shown for the lug 16. This arrangement
provides a more positive way of securing the fuse in place.
Still another embodiment will now be described with reference to
FIGS. 9 to 12, again using the same reference numerals for elements
common to the first embodiment. The difference between this
embodiment and previously described embodiments is that no groove
is provided for the fuse 23 in the thickened section or block 15.
Instead, slots 60 and 61 are provided through which tabs 62 and 63
from the lugs protrude, as shown for the lug 16 in FIG. 11. Once
the fuse 23 is placed in the position shown in FIG. 9, the tabs 62
and 63 are rolled over the fuse 23, as shown for the tab 62 in FIG.
12. FIG. 10 shows a side view of a bobbin with the fuse 23 secured
in place.
A third lug 65 shown in the end view of FIG. 9 may be similarly
mounted in a passage like the lugs 16 and 17, except without a
front slot. The third lug serves as terminal post for connecting a
lead 50 to one end of a coil while the lug 16 serves as a terminal
post for connecting a lead 50 to one end of a coil and the lug 16
serves as a terminal post for connecting the other lead 51 to the
fuse 23, which is in turn connected to the other end of the coil
through the lug 17.
Although particular embodiments have been illustrated and described
herein, it is recognized that modifications and variations may
readily occur to those skilled in the art. Consequently, it is
intended that the claims be interpreted to cover such modifications
and variations.
* * * * *