Note: Descriptions are shown in the official language in which they were submitted.
121~3715
1 50,656
CELLULOSE-FREE TRANSFORMER
COIL STRUCTURE AND METHOD
' CRO'SS'-'REFERENCE'TO'RELATED' ~PPLI'C'ATI'ONS
This application is related to Canadian Appli-
cation Serial No. 402,669, filed ~ay 11, 1982 in the name
of R. D. Buckley, assigned to the same assignee as the
present application.
'B'ACKGR~ND'OF'THE'_N~E'NTION
'Fie'l'd o'f''th'e''In'ven't'i'on:
This application relates to a cellulose-free
transformer structure and, more particularly, it pertains
to multi-layered resinous insulation along edges of coil
windings.
'Description'of 'the'Prior''Art:
Although the concept of cellulose-free insulated
transformers has been known, it is currently the subject
of improvement. As part of the cellulose-free coil con-
cept, liquid resin is applied and cured in-situ during
coil winding. The concept was preliminarily introduced to
benefit the coil structure in the radial direction, that
is, reduced radial build of insulation, application of
thin films of resin between layers, and reiteration of
thin-film resin curing to build up the high-low spaces to
result in a ceIlulose-free structure.
~,
'7~5
2 50,656
SUMMARY OF THE INVENTION
It has been found in accordance with this inven-
tion that a more satisfactory transformer coil may be
provided which comprises a tubular structure having an
inner coating of resinous material, a plurality of first
layers of metal windings including an inner layer and
outer layer, a first coating of resinous material between
the first layer of metal windings, a second coating of
resinous material on the outer first layer of metal wind-
ings, a plurality of second layers of metal windings onthe second coating of resinous material, a third coating
of resinous material between each of the second layers of
metal windings, and each of the resinous material includ-
ing overlay portions extending over the opposite edges of
the metal windings and over the overlay portions of prior-
applied coatings of resinous material to provide a multi-
layered cover having high dielectric breakdown strength.
The invention also encompasses a method for
making a cellulose-free transformer coil comprising the
steps of:
(a) providing a winding mandrel for repeated
rotation past a resin applicator and a resin curing sta-
tion;
(b) applying at least one coating of resin onto
the mandrel;
~c) winding a number of layers o~ metal windings
spirally onto the coating of resin;
~d) applying a coating of resin onto each layer
of metal winding;
(e) applying at least one coating of resin onto
the outer layer of the metal winding applied at step (c);
(f) winding at least one layer of an elongated
conductor helically onto and across the coatings of resin
applied at step (e); and
(g) applying a coating of resin onto each turn
of each layer of the elongated conductor applied at step
(f) with each coating flowing over opposite edges of the
layers of prior-applied coatings.
3 50,656
The advantage of the device and method of this
invention is that a cellulose-free transformer coil struc-
ture is provided which results in dielectric puncture
stress, rather than dielectric creep along layer extension
surfaces when the transformer coil is operated. The
multiple coatings of resin on the edges of the coil layers
provide a higher dielectric breakdown strength than the
same thickness applied in one layer. Thus, the probabil-
ity of a fault transcending the insulation thickness is
minimized or rendered unlikely.
BRIEF-DESCRIPTION OF THE DRAWINGS
Figure 1 is a fragmentary sectional view showing
layers of conductor windings and coatings of resin there-
on; and
Fig. 2 is an isometric view schematically illus-
trating one manner of forming the coil structure of Fig.
1.
In accordance with this invention a method for
making a cellulose-free transformer coil comprises the
following steps:
- (a) providing a winding mandrel for repeated
rotation past a resin applicator and a resin-curing station;
(b) applying at least one coating of a cross-
linkable resin onto the mandrel;
(c) winding a number of layers of metal windings
spirally onto the mandrel;
(d) applying a coating of cross-linkable resin
onto each layer of metal winding;
(e) applying a number of coatings of said resin
onto the layers of metal windings;
(f) winding at least one layer of an elongated
conductor helically onto and across the coating of said
resin of step (f);
(g) applying at least one additional coating of
such resin onto the outer layer of the elongated con-
ductor; and
7~S
4 50,656
(h) causing each coating of such resin to flow
over the opposite edges of the layers of metal windings
and of prior-applied coatings of such resin to provide a
multi-layered cover on the edges of the coil structure.
In Fig. 1 a transformer coil is generally indi-
cated at 3 and has a tubular member formed by applying
consecutive coatings of resin and metal windings for con-
ductor onto a rotating mandrel 5 about a center line 7.
As the mandrel turns (Fig. 2) in the direction of the
arrow 9 it rotates past function station including a resin
applicator 11, a winding station 13 for applying con-
ductors for winding such as a wire 15 onto the coil 3, and
a curing station 17 for curing the resin during rotation
of the mandrel through a 360-turn thereof as indicated by
the arrow 9. A particular method for making a coil 3 as
set forth herein may vary as required.
As shown more particularly in Fig. 1 the coil 3
comprises in the order of their application, the following
parts: a coating 19 of resinous material, a plurality of
layers 21 of metallic conductors or windings, a coating 23
of resin between each layer 21, a plurality of coatings 25
of resin, layers 27, 29, 31 of metal conductors for wind-
ings, coatings 33 of resin between layers 27, 29, coatings
35 of resin between layers 29, 31, and an outer coating 37
of resin. In addition, the transformer coil 3 comprises
laminated covers 39, 41 at opposite edges of the several
layers and coatings which comprise overlay portions of
each coating of resin as it is applied in place.
The coating 19 of resin (Fig. 1) is applied in
any suitable manner, such as by spraying, or by use of the
resin applicator 11, such as a paint roller. Practically,
the coating 19 comprises a plurality o applications
applied repetitively in order to cover any holes, voids,
or other undesirable contaminants that would reduce the
breakdown strength of the overall coating. For that
reason a plurality of thin coatings are applied, such as
from 5 to 30 coatings with each coating having a thickness
,12,.~t~
50,656
of about 2.0 mils. The coatings are applied spirally by
rotating the mandrel 4 with each coating being cured or
gelled in place at the curing station 17. The resin is
preferably high-temperature, cross-linkable resinous
material. For example, it may be a blend of acrylated
epoxies, acrylated epoxy novolacs, acrylated hydantoin
epoxies, and acrylated urethanes, all dissolved in acrylate
monomers which are susceptible to curing by ultraviolet
radiation. Each coating of resin may have a thickness of
10 from about 0.0005 to 0.0040 inch, i.e., 5 to 100 turns up
to 4 mils thickness per turn. The resin is applied and
gelled in one or multiple thin layers depending upon the
desired insulating strength.
; Where the layers 21 of windings include a pre-
''~' ~ o ~ q
insulated surface, the~coating~ ~3, 23 may be omitted.
The curing station 17 may comprise any suitable
radiation unit, such as infrared. An ultraviolet radia-
tion or electron beam unit has been found satisfactory for
this purpose. Ultraviolet radiation appears to be
practical.
After application of the coating ~4, the con-
- ductor windings or layers 21 are applied. The windings
preferably comprise a contiguous strip of metal, such as
copper or aluminum. The layers 21 may include an insulat-
ing coating, such as an enamel, on the outer surface in
which case consecutive turns of the layers may be applied
without intervening coatings 23 of resin. Generally, the
layers 21 comprise the low-voltage windings of the trans-
former coil 3.
After installation of the layers 21 of windings
is completed, a plurality of turns of coatings 25, such as
from about 5 to 100 turns of up to 4 mils thickness per
turn, are applied in a manner similar to the coating 19.
After the requisite number of coatings 25 are
35 applied, the windings 27, 29, 31 are applied. The windings
preferably comprise a continuous conductor, such as copper
or aluminum, and preferably include an insulating coating,
B~7~5
6 50,656
such as enamel. As the mandrel 4 is rotated -the turns of
the layer 27 are applied from a strand 15 of wire. The
strand advances along and over the outer surface of the
insulating coating 25 until it reaches the broken-line
position 15a (Fig. 2). As the wire layer 27 is wound in
place, the roller 11 for applying the resin advances with
the strand to apply a coating 33 of resin onto each turn.
Continued rotation of the assembly causes the first coating
33 to cure as it passes the curing station 17. As the
subsequent turn of the winding layer 27 is applied, it is
likewise coated with a coating 33 of resin and the previous
coating 33 is also covered with the subsequent resinous
coatings. Ultimately, the number of resinous coatings 33
equal the number of turns of the winding so that a wedge-
shaped insulator is evolved which consists of a pluralityof separately cured coatings 33.
The winding layer 29 is then applied by continu-
ing to rotate the mandrel and advance the strand of wire
15 in the direction opposite that applied for the first
layer 27. Likewise, the roller advances from the broken-
line position 15a with each turn of the wire to apply
individual resinous coatings 35 with each coating being
cured and subsequently covered with multiple coatings of
resin until the strand 15 reaches the left end of the coil
as shown in Fig. 1. At this point a wedge-shaped insu-
lator comprising a plurality of resinous coatings 35 is
completed.
Thereafter, the process similar to that for
applying the layer 27 is followed for applying the winding
layer 31. Where the layer 31 is the last layer to be
applied, an outer coating 37 is applied by the applicator
11. This is accomplished by first applying all turns 31
and then rotating the mandrel 4 ~ith the resin applicator
11 covering all turns to apply resinous coatings 37.
As shown in Fig. 1 the wedge-shaped insulator or
coating 33 is tapered with the thicker end being on the
left and the thin edge being on the right. Conversely,
73~5
7 50,656
the insulator or resinous coating 35 is oppositely disposed
with the thick edge at the right and the thin edge at the
left. Inasmuch as the winding layers 27, 29, 31 are
high-voltage windings the wedge-shaped coatings 33, 35 are
preferred. It is noted, however, that the structure and
method of this invention is applicable to coil windings
where an intermediate winding layer, such as the layer 29,
is not inclined at an angle as shown in Fig. 1, but rather
is parallel to the inner and outer layers 27, 31.
In accordance with this invention each time a
resinous coating is applied an overlay portion which
extends beyond the end of the winding layers flows over
the end of the prior-applied core parts. For example,
when the winding layer 21 adjacent the resinous coating 19
is applied the resinous coating 23 is applied so that
overlay portion at opposite ends of the layer flow over
the opposite edges of the layer 21 and onto the resinous
coating 19. The next winding layer 21 is similarly coated
with another resinous coating 23 with overlay portions
likewise flowing downwardly over the opposite end of the
winding layer 21 as well as over the previously applied
overlay portion of the resin 23.
Similarly, as each resinous coating 25 is ap-
plied overlay portions extend over opposite edges of the
winding layers and prior-applied coatings of resin 23 to
cover the same. As each resinous coating 33 is applied,
an overlay portion extends downwardly over prior-applied
winding layers 27 as well as overlay portion of the coat-
ings 23, 25, as shown by the laminated cover 41. Likewise,
as each resinous coating 35 is applied an overlay portion
extends downwardly over the end of the coil 3 to cover all
prior-applied overlay portions of resinous coatings 23,
25. Finally, the resinous coatings 37 include overlay
portions which extend downwardly on both sides as part of
the laminated covers 39, 41.
Accordingly, the cellulose-free transformer coil
of this invention provides multiple layers of resinous
8t7~5
8 50,656
material at the edges of the coil where higher dielectric
breakdown strength is required than is provided by the
same thickness of resin applied in one layer. The ad-
vantage of multiple layers is that the probability of
fault transcending the insulation thickness is minimized
or, in fact, nullified. Finally, the multiple layer of
resin results in dielectric puncture stress rather than
dielectric creep along layer extension surfaces when the
transformer coil is operated.
