Note: Descriptions are shown in the official language in which they were submitted.
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METHODS AND APPARATUS FOR ASSEMBLING A
TRANSFORMER CORE
BACXGROUND OF T~E IN~ENTION
Transformer cores for large power transformers are
assembled by arranging a plurality of core steel laminations
in a core bottom yoke and core leg arrangement in the
horizontal plane. When the three phase core is to be
assembled, the three legs and the bottom yoke that inter-
connects the three legs are assembled in a stack of coresteel laminations that are bound together by any of
several means, for instance, by use of an epoxy impregnated
glass tape. The assembled core legs and bottom core yoke
are then raised to a vertical position for ease in assembling
the transformer windings around each of the core legs. Once
the transformer windings are in place, the transformer core
is completed by inserting the upper yoke core steel
laminations and fastening the laminations together by
means of a clamping structure. The placement of a
plurality of core steel laminations upon the partially
completed core assembly is a difficult and time consuming
task to be performed in the latter stages of transformer
manufacture. It is therefore, desirable to be able to limit
the amount of time required to assemble the core yoke
laminations at a time in the transformer manufacturing process
when the transformex is near completion. The purpose of
this invention is to provide a~method and means for assembling
the upper yoke as a single unitary assembly at a substantial
saving in assembly time and cost.
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SUMMAR~ OF THE INVENTION
A plurality of inserts are employed between the upper
yoke laminations and core leg laminations in a transformer
core assembly process. The inserts allow removal of the
upper core yoke as a single unit to facilitate the place-
ment of the transformer winding on the core legs. The coreyoke unit is reassembled and the inserts are reinserted to
complete the transformer core.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a front perspective view of a transformer
core containing a yoke assembly according to the invention;
Figure lA is a cross-sectional view of a portion of
the transformer core-leg interface depicted along the plane
2 - 2 of the transformer depicted in Figure l;
Figure 2 is a top perspective view of a single phase
transformer winding according to the invention;
Figure 3 is a top perspective view in isometric pro-
jection of the core and coil assembly utilized in the
transformer shown in Figure l;
Figure 4 is a front perspective view in isometric
projection of the inserts of the instant invention shown
subsequent to removal from a top yoke assembly according
to the instant invention;
Figure 5 is a front perspective view of the transformer
depicted in Figure 4 after installing the transformer
windings and the top transformer yoke unit;
Figure 6 is a cross-sectional view of an alternate
insert configuration according to the instant invention;
and
Figure 7 is a top perspective Yiew including a partial
cutaway section of a transformer top yoke containing inserts
shown in Figure 6 in isometric projection and depicting the
6-6 plane which includes the inserts depicted in Fi~ure 6.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Figure 1 contains a transformer core 10 containing a
plurality of core steel laminations 11 which can consist
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5D-5744
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of one or more sheets of core steel material in a three-
phase configuration containing three core legs 12 and top
and bottom yokes 13A, 13B. A pair of core windows 14 are
defined between core legs 12 and yokes 13A, 13B to provide
for the arrangement of three transformer windings. Within
the corners, defined by the plane 2-2 between legs 12 and
top yoke 13 A are inserted a plurality of inserts 16 shown in
Figure lA. A stack of laminations 11 are arranged such
that every other pair of laminations 11 in the stack contact
each other at a boundary 15. Insert 16 comprising a length
of core steel lamination material having a thickness equal
to an individual lamination 11 is provided between opposing
laminations 11 as indicated. Insert 16 can be readily
removed from the stack of laminations 11 after the stack
has been completed. Insert 16 provides two important functions
namely, providing for removal of top yoke 13A from core
legs 12 as well as preventing boundries 15 from directly
aligning above each lamination 11 in the stack. The non-
alignment of boundries 15 prevents the occurrence of eddy
losses between subjacent laminations 11 in the stack and
provides a path across the joint for the transfer of
magnetic flux between yokes 13 and legs 12. In the assembly
of core 10, depicted in Figure 1, a plurality of laminations
11 are arranged to form yoke 13B and legs 12. Core
laminations 11 are arranged wit their major dimensions in a
horizontal plane such that once core 10 is assembled it can
be raised into the vertical position shown in Figure 1.
Once legs 12 and bottom yoke 13B are assembled they are
physically and mechanically clamped or bonded by the
arrangement of a plurality of turns of glass tape 17
impregnated with a heat curable epoxy resin (Figure 4~ or by
means of a core clamp. Top yoke 13A containing a plurality
of inserts 16 is bonded or clamped only at its central
portion and does not contain any glass tape, for example,
near the interface between top yoke 13A and 13gs 12. Inserts
16 are now removed to allow top yoke 13A to be removed as
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a single integral unit. As described earlier, top yoke
13A according to the prior art, was not assembled at the
time that bottom yoke 13B and legs 12 were assembled in
order to provide for the arrangement of transformer winding
18 ( Figure 5~ around core leg 12. Laminations 11 used
to form top yoke 13A were then individually inserted after
the placement of transformer winding 18 to complete core
10 .
Figure 2 shows a single-phase arrangement of a
transformer core 10 having two legs 12 and a top and bottom
yoke 13A, consisting of laminations 11 and defining core
window 14. Top yoke 13A and bottom yoke 13B can consist
of a single structure rather than the two-part assembly
of top and bottom core yokes 13A, 13B shown earlier in
Figure 1. Inserts 16 are provided between the ends o~ top
yoke 13A and core legs 12 in the same manner as shown for
Figure 1.
The assembly arrangement of core 10, shown in Figure
1, is shown in enlarged isometric projection in Figure 3.
2Q To distinquish between the finished core 10 shown in
Figure 1, the core assembly depicted in Figure 3 is
designated lC'. Since a plurality of laminations 11 are
employed within core assembly 10', the laminations comprising
the core legs are designated llL, the laminations comprising
the top yoke are designated llYT, and the laminations
comprising the bottom yoke are designated llYB. Inserts
16 are included within every layer as shown. Since the
top yoke 13A, of Figure 1, is to be removed~ inserts 16
are shown in Figure 3 only with top ~oke laminations llYT.
Inserts 16 can be included between bottom yoke laminations
llYL and leg laminations llL if removal of bottom yoke 13B
(Figure 1~ is desired. Inserts 16 are included at the
corner formed between a leg core lamination llL and an
adjacent top yoke core lamination llYT at both corners.
Once core assembly 10' is completed, a clamping structure
- or an epoxy impregnated glass tape 17 is used to
mechanically secure bottom yoke laminations llYB, yoke leg
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laminations llL, and top yoke laminations llYT. In addition,
epoxy resin may be applied to the edges of yoke laminations
llYT, llYB to prevent displacement. ~fter being mechanically
bonded, core assembly 10' becomes a completed transformer
core lQ and is raised to its vertical position as shown in
Figure 4. In order to remove top yoke 13A from trans~ormer
core 10 inserts 16 are removed and top yoke 13A is removed
from core 10 as a single unit. The epoxy impregnated glass
bonding tape 17 holds the remaining core legs 12 and bottom
yoke 13B fixedly attached. Transformer windings 18 are
then centered around legs 12 and top yoke 13 A is then
reassembled by bringing top yoke 13A into contact with
transformer legs 12 and reinserting inserts 16 which then
become a physical portion of core 10 and provide a magnetic
link between individual laminations 11.
A completed core 10 is shown in Figure 5 with winding
18 surrounding core legs 12 and with top and bottom yokes
13B firmly in place. Inserts 16 provide a useful function
in the event that windings 18 become damaged during the
operating life of the transformer and must be removed for
replacement and/or repair. Inserts 16 are then removed
and top yoke 13A is removed as a single unit without
damaging core 10.
Figure 6 contains an alternate arrangement for inserts
16 which are attached together to form an insert assembly
16'. As described earlier for the embodiment depicted in
Figure 2, adjacent pairs of laminations 11 meet at a joint
15 and insure that subjacent joints 15 do not directly
overlap to prevent eddy current loss. Insert assembly 16'
can provide a stepped core joint configuration wherein
successive layers o~ laminations 11 are offset by a fixed
increment to further reduce core loss. Providing insert
assembly 16' in the manner depicted in Figure 6, imparts
an accurate stepped lap configuration to core 10, by
providing a stop for each individual lamination 11
resulting in the configuration shown. Insert assembly 16'
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is inserted within transformer core in a manner similar to
that described earlier for the configuration depicted in
Figure 4 and is shown in a similar assembly arrangement
in Figure 7 . Insert assembly 16 ' is shown both in place
within transformer core 10 as well as prior to insertion
within core 10 to show the stepped relation between indlvid-
ual laminations 11.
The prior art assembly of top yoke 13A was deferred
until transformer windings 18 were installed on the core
10, at which time the assembly of core laminations 11 to
form top yoke 13 was performed at a later stage in the
transformer manufacturing process after a large amount of
time and expense had already accrued. From a manufacturing
cost standpoint, the provision of a plurality of inserts
16 allo~ing for the assembly of laminations 11 to form
upper core yoke 13A in the early stages of the transformer
manufacturing process is highly beneficial and desirable.
The reassembly of top yoke 13A, as a single unit in the
later stages of transformer manufacture, is a relatively
simple procedure that does not require a great deal of
manufacturing time.
