Winding of an electric machine

An improved electric machine wherein the machine comprises a slot for receiving a winding formed from a winding bar having an outer glow-discharge protection and wherein the improvement comprises a wrapping in the form of a strip of conductive material arranged in surrounding relationship to the bar so that the edge portions of the strip are situated adjacent a corner of the narrow side of the bar which faces the slot bottom. The improvement further includes cementing the edge portion of the strip lying beneath such narrow side to such side and a shim disposed adjacent the side of said bar along which the other edge portion resides.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an electric machine which includes slots each of 
which receives an individual winding bar provided with an outer 
glow-discharge protection and electrically conductive slot linings and 
electrically conductive shims which are inserted beside the winding bar 
for securing same in the slot. 
2. Description of the Prior Art 
Electric machines of the above type are described in the book "Die 
Isolierung grosser elektrischer Maschinen"--The Insulation of Large 
Electric Machines--by Hartmut Meyer, Springer-Verlag, 1962, on page 86. In 
such machines, care must be taken to ensure that the outer glow-discharge 
protection of the winding bar, which protection comprises coatings of 
conductive varnish in the region of the bar within the slot and 
semiconducting silicon carbide coating in the region thereof outside the 
slot, is neither damaged during the installation of the winding nor in the 
operation of the machine, as thereby the functioning of the outer 
glow-discharge protection would be jeopardized. 
It is, therefore, an object of the present invention to provide an improved 
electric machine of the above type wherein the design of the slot lining 
and arrangement of the shims is such as to substantially avoid any damage 
to the outer glow-discharge protection of the winding bar during the 
installation of same and the operation of the machine. 
SUMMARY OF THE INVENTION 
In accordance with the principles of the present invention the above and 
other objectives are accomplished in a machine of the above type by 
forming the slot lining as a wrapping having the form of a strip of 
material arranged in surrounding relationship to the winding bar. In 
particular, the strip has edge portions which lie adjacent a corner of the 
bar which borders a narrow side thereof facing the slot bottom and a 
further portion extending between the edge portions whose width 
corresponds to the extent of the circumference of the bar and whose length 
corresponds to the length of the slot. The machine is further provided 
with cement means for cementing the edge portion of the strip lying below 
the aforesaid narrow side of the bar to such side and with a shim arranged 
on the side of the bar which is adjacent the other edge portion of the 
strip. 
With the machine so configured, the winding bar and, thus, the coating 
serving as its outer glow-discharge protection, are surrounded entirely by 
a wrapping and are hence protected thereby. If applied appropriately 
early, this protective wrapping provides effective protection not only 
after insertion of the winding bar into the slot, but also during the 
storage and shipping of the winding bar prior to its installation. 
Since the winding bar, when surrounded by the wrapping, is still undersized 
with respect to the stator slot, to allow for the thickness of the shim 
that is to be later inserted in the slot, the bar can be installed in the 
slot relatively easily. Such installation is further simplified by the 
orientation of the winding bar such that the narrow side cemented to the 
one edge portion of the wrapping faces the bottom of the slot. This 
permits the shim to be inserted or driven-in only on that side of the bar 
which resides adjacent the free other edge portion of the wrapping. As a 
result, the latter edge portion is now pulled with certainty in the 
direction of its desired position (i.e., downward so its edge faces the 
slot bottom). Thus, neither the wrapping nor the outer glow-discharge 
protection is damaged during installation, and the winding bar is firmly 
anchored in the slot by the driven-in shim. The latter anchoring, in turn, 
prevents vibration of occurring the winding bar during the operation of 
the machine from affecting the outer glow-discharge protection, thereby 
preventing damage of same. 
For securing the winding bar axially, it is advisable to arrange conductive 
cement between the wrapping and the side wall of the bar opposite the wall 
located adjacent to the shim. Preferably, the cement should be applied to 
the subsections of the winding bar.

DETAILED DESCRIPTION 
The drawing shows a slot 2 in the stator lamination stack 1 of an electric 
machine with large output rating, e.g., a hydraulic generator, designed in 
accordance with the principles of the present invention. Situated in the 
slot 2 is the winding of the stator which includes a winding bar 3 formed 
of rectangularly arranged subconductors 4 which are insulated from each 
other and are enclosed overall in a high-voltage-resistant outer 
insulation 5. On the outer surface of the winding bar 3, an electrically 
conducting outer glow-discharge protection 6 is situated in the area of 
the slot 2, the latter protection being in the form of a varnish coating. 
The winding bar 3 and its glow-discharge protection are further surrounded 
by an electrically conductive wrapping 7 formed by a strip of conductive 
material such as, for example, graphite paper or conducting polyester 
fabric, whose width corresponds to the circumference of the winding bar 
and whose length to the length of the slot. The wrapping 7 is fastened to 
the winding bar 3 by a conductive adhesive 12 which is applied so as to 
cement the edge portion 8 of the wrapping 7, which edge portion lies 
adjacent the end or corner 9 of the narrow side 11 of the bar facing the 
bottom 10 of the slot, to such narrow side. The strip forming the wrapping 
7 is then wrapped around the winding bar 3 in such a manner that its other 
free edge portion 13 comes to lie again adjacent the corner 9 of the 
winding bar 3. The wrapping 7 thus totally encloses the winding bar 3 and 
thereby completely protects the outer glow-discharge protection 6. 
The wrapping 7 can be placed around the winding bar 3 as soon as possible 
after the outer glow-discharge protection 6 is applied thereto during the 
fabrication process. This ensures that the protection afforded by the 
wrapping is present during the storage of the winding bar before it is 
installed in the slots 2. 
The free edge portion 13 of the conductive wrapping 7, which is firmly 
pulled around the winding bar 3, is advantageously connected to the other 
edge portion 8 of the wrapping. This is accomplished by using individual, 
thin, self-sticking foil strips (not shown) to attach the edge portions. 
In order to substantially avoid any air gap between the winding bar 3 and 
the walls of the slot 2, a strip-shaped shim 14 of a hard, conductive 
material such as, for example, a conductive fiberglass-resin mat, is 
driven by blows and/or pressure into the slot on the side 13 of the 
winding bar 3 which is adjacent the free edge portion 13 of the wrapping 
7. This firmly secures the winding bar 3 in the slot 2 and prevents 
vibration of the winding bar 3 during the operation of the machine. It 
also prevents the ventilation slots of the stator lamination stack 1 
located on the side 15 of the bar 3 from engaging the bar. The outer 
glow-discharge protection 6 and the wrapping 7 are not damaged when the 
shim 14 is driven in, but the wrapping is rather pulled into its desired 
position by the shim 14. The edge portion 13 of the wrapping 7 thus comes 
to lie at the corner 9 of the winding bar 3 with certainty. 
Securing of the winding bar 3 in the axial direction can be further 
improved by arranging conductive cement 17 on the side wall 16 which lies 
opposite the side wall 15 of the winding bar, between the latter and the 
wrapping 7. This cement need not be applied along the entire length of the 
winding bar, but may be applied, preferably, to the winding bar 
subsections only.