Note: Descriptions are shown in the official language in which they were submitted.
case 2582
This invention relates to an improved slot closure
for a dynamoelectric machine, and in particular it relates to an
improved slot closure which uses a transverse spring to provide
a spring action to hold conductors firmly in a slot.
In larger dynamoelectric machines there are slots
formed in a laminated stack of iron sheets to receive winding
conductors. The conductors are installed in these slots and
they must be held firmly in place against mechanical and elec-
tromagnetic forces which tend to cause movement. The slots are
usually formed with a dove-tail adjacent the slot mouth or slot
opening and a key of mating configuration with the dove-tail
is pressed into the dove-tail to close the slot. Shims are
frequently used between the key and the conductors to wedge
the conductors in place and thereby prevent movement of the
conductors.
Conductors used in larger dynamoelectric machines
usually have a jacket formed of a thermosetting resinous ma-
terial impregnating a porous material and this is cured to a
hard state forming the insulating jacket around the conductor.
In addition there may be portions oE the jacket coated with a
partially conducting elastomer to reduce the possibility of voids
developing between the conductors and the slot walls which might
cause corona problems. When these conductors are first installed
they are very firmly wedged into their slots and are satisfac-
torily restrained against movement. However, with time thepossibility of decreasing restraining forces has been a problem.
Repeated thermal cycling may permit some flowing of the jacket
surrounding the conductors or there may be some shrinkage. The
present machines may carry considerable currents in the conduc-
tors and the electromagnetic forces can be quite large. Thismay aid in decreasing the restraining forces by causin~ large
;
. . . : .
- :-
Case 2582
stresses. To reduce the possibility of restraining forces
decreasing with time, it is known to use spring forces be~ween
the key and the conductors.
various forms and arrangements o~ springs have
been devised ~or providing a spring action or spring ~orce
between a slot key and the conductors in the slot. One prior
art arrangement is shown, for example, in Canadian Patent No.
980 398 to Robert S. Brown and Robert Hawley, issued December 23,
1975. This patent describes two wedge members with opposite
tapers extending longitudinally of the wedge members. The two
wedge members are pressed into a slot so that they exert a
pressure or cause a wedging action between the conductors in that
slot and the slot key. A cooperating spring is also installed in
the slot to ensure a firm pressure by its spring action even i~
there is a slight decrease in the wedging pressure. The spring
member is in the form of an extended rectangle with transversely
extending ripples or deformations to give it the spring action.
Another prior art arrangement is shown in United
States Patent No. 3 976 901 to Gabor Liptak and Roland Schuler,
issued August 24, 1976. This patent describes a plurality of
ring-shaped disc springs, each in the form of a truncated cone
- with a diameter substantially equal to the width of the slot.
These disc springs are inserted between the conductors and the
key prior to the installation of the key and they provide a
spring action between the conductors and the key.
The prior art spring arrangements tend to provide,
along the length of the slot, a discontinuous force or loading.
The present invention is directed to a spring arrangement which
provides a substcmtially continuous line loading along the length
of the slot, and this substantially continuous loading is believed
to be preferable~
. :
Case 2582
It is thereEore a feature of the present invention
to provide an improved slot closure for a dynamoelectric machine
that makes use of a -transverse sprlng providing spring action
with continuous line contact along the length of the slot.
According to the invention there is provided in a
dynamoelectric machine having a stack of laminations in which
slots are provided extending substantially longitudinally of
said machine for holding conductors, each slot having a dove-
tail configuration adjacent the entrance thereto and a plur-
ality of slot keys for closing the slots, the slot keys having
complementary surfaces to said dove-tail configuration for
engagement with the surfaces of said dove-tail configuration to
retain the keys in position closing the slots, the improvement
comprising a spring in said slot between the key and the
conductor adjacent the slot entrance, said spring having a
width slightly less than the width of said slot and a length
extending longitudinally of said slot for at least several
times the width, and a curvature in said spring extending
transversely to provide a spring force between said key and
said conductor extending substantially continuously along the
length of said slot to maintain the winding conductors in
position with a compressive force.
The invention will be described with reference to
the drawings, in which
Figure 1 is a cross-sectional view taken across
a slot of a dynamoelectric machine showing conductors in the
slot and a slot c:losing key,
Figure 2 is a cross-sectional view taken along
line 2 - 2 of Fis~ure 1, and
Figure 3 is an isometric view of the transverse
spring according to the invention.
,
Case 25~2
Referring primarily to Figures 1 and 2, there is
shown a conductor slot 10 in laminations l:L of a dynamoelectric
machine. The conductor slot 10 is one of a series or plurality
of slots formed by punching the laminations. The laminations
are stacked adjacent to one another to form the slot which
extends substantially longitudinal]y of the dynamoelectric
machine. A conductor bar 12 is shown having several conductors
14 surrounded by an insulating jacket 15. ~acket 15 may be
formed for example, by wrapping conductors 14 with a porous
material such as a fiberglass cloth and impregnating the material
with a thermosetting resin. Depending on the design requirements
there may be two or more conductor bars in each slot. Figure 1
shows slot 10 with one complete conductor bar illustrated and
with a portion of the jacket of an adjacent bar.
A top filler strip 16 is in engagement with the
surface of jacket 15 nearest the opening of slot 10. A key 17
is mounted in the slot opening to close it. The key 17 has
sloping edges 18 that mate with sloping sides 20 of the walls of
slot 10 adjacent the slot opening. There is a groove 21 on
the inside of key 17. Groove 21 has a rectangular cross-section
and the wide surface has a taper or slope extending in the
longitudinal direction. A wedge 22-is positioned in groove 21.
Wedge 22 has a longitudinally extending taper on one side
which is substantially the same slope as onthe groove. The
engaging tapered surfaces of groove 21 and wedge 22 are oppo-
sitely directed or mating to provide an adjustable wedging
action.
The key 17 is made in relatively short lengths,
for example of the order of perhaps 3 or 4 inches to 8 inches
in length for slot widths of the order of 3/4 to 1~ inches.
The length dimensions may be greater or less than those
-- 4
.~ .
: ~ .
..
Case 2582
3~
indicated as required by the size of the slot and other design
considerations. There are, of course, a sufficient number of
keys 17 to close slot 10 along its entire length. The wedges
22 are shorter in length than the key 17 to permit some adjust-
ment without the wedge extending beyond the respective key.
Between the wedge 22 and the filler strip 16 is a
transverse spring 23. Spring 23 is perhaps best seen in Figure
3 and is a lonyitudinally extending spring with a curve extending
transversely of slot 10 to provide a spring action. Spring 23
has a width substantially the same as the width of slot lO
(its width is slightly less than that of slot ]0 to provide
some clearance) and its length is preferably several times the
length of a key and at least is several times the width of the
spring.
The spring 23 may be made of any spring material
but a preferred material is several layers of glass cloth im-
pregnated with a thermosetting resinous material, for example,
four or five layers of woven glass cloth impregnated with a heat
resistant, thermosetting, polyester type, laminating resin and
cured in a mould under the influence of heat and pressure.
It is desirable that the set or relaxation of the spring as
it ages be kept to a minimum to maintain as high a spring
pressure as possible.
; The following relationship may be used as a guide
when designing and making a transverse spring
= E~t
2R
where ~ = bending stress
E = Young~s Modulus
t a thickness
R = radius of curvature of spring.
'',', -,' : ' '' . ~
Case 2582
~A,~S~
When a particular material is selected for the
spring, and the selected mat~rial should have a low set, then
E and ~ are known. Thickness and radius of curvature must
then be chosen to fulfill, at least approximately, the equation
while remaining within the practical limits for a suitable
spring. For example, ~or most springs the radius o~ curvature
will-be within the range of 1.5 to 3 times slot width, and it
will be apparent that too small a thickness will result in a
spring so flexible it cannot apply an adequate force within
the slot and too great a thickness will result in a spring
that is difficult to deform or flex at all.
When a dynamoelectric machine is being assembled,
; after the conductor bars are pressed into the slot, the top
filler strip 16 is placed on the exposed surface of the jacket
15 of the top conductor bar 12. The transverse spring 23 is
put in position and the keys 17 are slid into position one at
a time. When a key 17 is in position its associated wedge 22
is tapped into place beneath it to give a desired wedging
force. A small amount of adhesive is normally used between
key 17 and the associated wedge 22 so that it will not shift
once it is installed. When one key and wedge are completed
the next adjacent key is slid into position and the associated
wedge tapped into place. This is continued until the slot is
filled.
By way of example, a transverse spring was made
for a machine having a slot width of one inch of five layers of
cloth impregnated with a thermosetting polyester resin and
having a thickness of 0.045 inches. The spring was made with a
radius of curvature of 2.1 inches and with a length of 36 inches
and a width of approximately one inch.
It is believed that the line force provided by
. .
- 6 -
Case 2582
the transverse spring of this invention is desirable as the
restraining force is applied continuously along the slot.
It is, of cours~, possible to use different
wedging methods, such as are provided for example by two
oppositely tapered wedges beneath a key.
