Electrical machine with an axial fan

In gas-cooled electrical machine with an axial fan (9) at one shaft end and with a rotor (1) and a stator body surrounded by a machine housing (14), a gas-guide device (18) arranged coaxially to the rotor shaft is provided in the outflow space (17) of the axial fan (9), out of which gas-guide device the cooling gas conveyed by the axial fan is fed to the rotor and to the stator body and stator winding. Said gas-guide device (18) comprises a plurality of guide rings (19-25) in the form of a cone envelope and spaced radially from one another and a ring part (27) likewise in the form of a cone envelope, which rings and ring part are connected to one another and to the machine housing (14) directly, or indirectly by means of bars (28, 29) extending essentially radially and/or guide plates (36, 36'). Ring-shaped channels (K.sub.1, . . . , K.sub.8) widening continuously in the direction of flow of the cooling gas are formed between respective radially adjacent guide rings, and between the ring part (27) and its adjacent guide ring. The gas-guide device (18) brings about a pressure transition, and it reduces the outlet losses downstream of the latter in relation to the hitherto conventional axial outlet provided by the rotor configuration. Between 15% and 25% of the pressure losses in the machine can be saved in this way and consequently the cooling effect can be greatly increased.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to an electrical machine with an axial fan at one 
shaft end, with a rotor and a stator body which is surrounded by a machine 
housing and which is provided with a stator winding having winding heads 
on the two end faces of the stator-body, with an inflow space of the axial 
fan, formed essentially by the end wall of the machine housing and by a 
partition wall between the winding head and said end wall, and with an 
outflow space of the axial fan, out of which the cooling gas advanced by 
the axial fan is fed to the rotor and to the stator body and stator 
winding. 
The invention refers to a state of the art such as emerges, for example, 
from EP-A-0,279,064 and from U.S. Pat. No. 4,876,470 of identical content. 
2. Discussion of Background 
With an increasing mass of material to be cooled, the cooling demand in a 
rotating electrical machine increases appreciably. This applies 
particularly to gas-cooled turbogenerators and to an even more significant 
extent to turbogenerators with an indirectly cooled stator winding. In 
these machine types, the dissipative heat generated in the stator winding 
has to be diverted through the winding insulation into the cooled 
sheet-metal stator body. 
The generation of pressure in gas-cooled turbogenerators usually is 
accomplished by means of axial fans. For the purpose of an increase in 
pressure, multistage compressors are ruled out for reasons of space. Also, 
on account of the conditions of installation and assembly, the 
incorporation of upstream or downstream distributors has hitherto been 
avoided. 
SUMMARY OF THE INVENTION 
Accordingly, one object of the invention is to increase the cooling effect 
in a simple and economical way, without lowering the efficiency of the 
machine. 
This object is achieved, according to the invention, in that there is 
provided in the outflow space of the axial fan a gas-guide device which is 
arranged coaxially relative to the rotor shaft and which comprises a 
plurality of guide rings in the form of a cone envelope and radially 
spaced from one another and a ring part likewise in the form of a cone 
envelope, which are connected to one another and to the machine housing 
directly, or indirectly by means of bars or guide plates extending 
essentially radially, and in that ring-shaped channels widening 
continuously in the direction of flow of the cooling gas are formed 
between respective radially adjacent guide rings. 
The effect of this gas-guide device in the winding-head space can be 
compared with that of so-called outlet diffusors which consist of 
subdivided annular guide blades and which were used years ago in the 
region of the exit of large wind tunnels (see the book by Bruno Eck, 
"Technische Stromungslehre" ("Engineering Fluid Mechanics"), pub. 
Springer-Verlag, Berlin/Heidelberg/New York, 1966, pages 186 and 187, 
especially FIG. 176 on page 187. It brings about a marked increase in 
pressure in the winding-head space, the result of this being that more 
cooling gas per unit time flows through the cooling channels in the rotor 
and stator. 
Furthermore, the dynamic pressure at the outlet of the axial fan is 
reduced, that is to say the outlet loss decreases. With the fan being the 
same, between 15 and 25% of the pressure loss in the machine as a result 
of the pressure transitions can be avoided in this way.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawing, wherein like reference numerals designate 
identical or corresponding parts throughout the several views, in the 
simplified longitudinal section through the non-drive-side end part (NS 
side or exciting side) of a turbogenerator according to FIG. 1, the 
reference numeral 1 denotes a rotor, 2 its shaft, 3 the rotor cover and 4 
its cover plate. The stator winding, of which only the end yokes can be 
seen, has a lower bar 5 and an upper bar 6 which are connected 
electrically and mechanically by means of lugs ("ear members") 7. All the 
end yokes form in their entirety the winding head. 
Fastened on a shaft collar 8 of the rotor shaft 2 is an axial fan 9. Its 
hub is designated by 10 and its moving blades by 11. Its inflow space 12 
is formed by the end face 13 of the machine housing 14 and a partition 
wall 15 made from glass-fiber-reinforced plastic or another material. This 
partition wall 15 (fan casing) is releasably fastened to the machine 
housing 14 on its (wall 15's) radially outward part, and extends radially 
inward, then bends in the axial direction and reaches axially behind the 
axial fan 9. The inflow space 12 is sealed off relative to the outside 
world by means of an axially pointing annular projection 16 having a 
rounded edge, on the fan hub 10. The design of the end part of the 
electrical machine corresponds thus far to the state of the art. 
According to the invention, to increase pressure, there is provided in the 
outflow space 17 (winding-head space) of the axial fan 9 a gas-guide 
device which is designated as a whole by the reference numeral 18. It is 
arranged coaxially relative to the rotor shaft and has a plurality of, in 
the example seven guide rings 19 to 25 in the form of a cone envelope and 
spaced radially from one another, the middle guide ring 22 being 
cylindrical (=borderline case of conical). With an even number of guide 
rings and the geometry of FIG. 1, the two middle guide rings would both be 
in the form of a cone envelope. The hub end 26 of the fan hub 10 also 
comprises part of the guide device, said hub end 26 narrowing conically 
towards the machine center; and a ring part 27 in the form of a cone 
envelope which virtually seamlessly adjoins the inner end 15a of the 
partition wall 15 further comprises part of the guide device. The outlet 
region of the axial fan 9 is thereby divided into a plurality of 
ring-shaped channels K.sub.1, . . . , K.sub.8 widening continuously in the 
direction of flow of the cooling gas and having an aperture angle alpha 
(.alpha.) of preferably .alpha..ltoreq.12.degree., which each 
independently form a diffuser and in their entirety a "multi-diffuser". In 
order to obtain approximately identical channel lengths, the axial lengths 
or, more precisely, the lengths of the generatrices of the guide rings 19 
to 25 in the form of a cone envelope are selected so that their inner ends 
form a torus surface segment T. The generatrix of this torus is a circle, 
of which the center point M.sub.T lies on a circle which is coaxial to the 
rotor shaft 2 and which passes approximately through the radial center of 
the moving blades 11. If the conditions of installation do not allow this 
torus configuration, the ends of the guide rings 19, . . . , 25 located on 
the winding-head side can alternatively terminate in a radial plane E 
(represented by broken lines in FIG. 1). 
The individual guide rings 19-25 and the ring part 27 are connected to one 
another by means of bars 28 and 29 which extend essentially radially and 
have a circular or oval cross section and which pass through the guide 
rings 19-25 and also the ring part 27. The uniform distribution of the 
bars in the circumferential direction can be seen from the top view 
according to FIG. 2. The guide rings 19-25 and also the ring part 27 as 
well as the bars 28 and 29 consist of non-magnetic material, preferably or 
an aluminum alloy. The connection of individual parts to one another in 
that case is preferably by welding. The guide rings 19-25 as well as the 
bars 28, 29 can also consist of glass-fiber-reinforced plastic. In that 
case, adhesive bonding preferably comes under consideration as a 
connecting technique. 
Alternatively or additionally to this, the guide rings 19-25 may be spaced 
and/or interconnected by guide plates 36 which extend over part or the 
entire length of the ring-shaped channels K1-K8. To avoid cluttering the 
drawing, only one guide plate 36 is illustrated in FIG. 1, namely in 
ring-shaped channel K1. 
The profile of the guide plates may be, e.g., circular (see plate 36 in 
FIG. 5) or twisted (see plate 36' in FIG. 5). The number of guide plates 
(36, 36') is freely optional, depending on their effects, i.e. their 
configuration; this number may be greater or less than the number of fan 
blades 11 on the fan hub 10. The guide plates (36, 36') enable improvement 
in the pressure conversion in the gas-guide device 18. 
The gas-guide device 18 is held by an annular plate 30 which, with filler 
pieces 31 interposed, is fastened to the partition wall 15 by means of 
screw bolts 32. At the same time, the axially outer bars 28 and/or the 
guide plates (36, 36') are welded to the annular plate 30. Furthermore, 
for stiffening purposes, triangular plates 33 are welded in between the 
annular plate 30 and the ring part 27. If the conditions of installation 
permit, the gas-guide device 18 can be mounted to a separate structure as 
well, for example a seris of radially inward-pointing struts S 
(represented by broken lines in FIG. 1) which extend from the wall of the 
housing 14 as far as the annular plate 30. 
For centering the gas-guide device 18 relative to the inner end 15a of the 
partition wall 15, the latter has on its terminal periphery a shoulder 15b 
which mates with a recess or groove 30a on the inner circumference of the 
annular plate 30. 
To enable the gas-guide device 18 to be installed in the machine--it cannot 
be slipped as a whole over the axial fan 9 for constructive and functional 
reasons--it is made multi-part, preferably, as in the example, two-part, 
the two halves being designated by 18a and 18b. The separating faces lie 
approximately in the horizontal plane of symmetry HM (FIG. 2) of the 
machine. The separating races pass through the two horizontally extending 
pairs of bars 28 and 29, of which only the pair of bars 29 can be seen in 
FIG. 2. The bars are divided there in the longitudinal direction of the 
bars, and the bar halves of semicircular cross-section are designated by 
28a, 28b, and 29a, 29b, respectively. All the guide rings 19-25, the ring 
part 27 and also the annular plate 30 are made correspondingly two-part, 
with separating faces along the horizontal plane of symmetry HM. In FIG. 
3, there can be seen only two adjacent guide rings 28, 29, the halves of 
which are designated by 23a, 23b, and 24a, 24b, respectively. These are 
welded to the bar halves 28a, 28b. Set pins 34, 35 which engage into the 
two bar halves 28a and 28b secure the mutual position of the two halves 
18a, 18b of the gas-guide device. Screw bolts 32 (FIG. 1) hold together 
the two halves 18a and 18b. Instead of using set pins, the two halves 18a 
and 18b can also be forcibly held together by screw connection of the bar 
halves 28a, 28b, and 29a, 29b. However, for reasons of space, this screw 
connection can take place only at the outer ends of the bar halves. 
As a result of the described two-part design of the gas-guide device 18, 
the latter can be assembled in a simple way: with the partition wall 15 
removed, the two halves 18a and 18b can be lowered behind the axial fan 9, 
secured temporarily there, and finally fastened permanently to the 
partition wall 15, the cooperation of the tapered mating shoulder 15b at 
the inner end 15a of the partition wall 15 with the recess or groove 30a 
of the annular plate 30 ensuring exact centering of the gas-guide device 
18. 
As a result of the pressure transition brought about by the gas-guide 
device 18 and the reduction of the outlet losses downstream of the latter 
in comparison to the hitherto conventional axial outlet provided by the 
rotor configuration, between 15% and 25% of the pressure losses in the 
machine can be saved and consequently the cooling effect can be greatly 
increased. 
The invention was illustrated in the foregoing with reference to a 
gas-cooled turbogenerator. However, it is not restricted to such machine 
types. It is suitable in all electrical machines with axial fans, insofar 
as the circumstances of construction and conditions of space allow 
installation of a gas-guide device of this type. The subsequent 
installation of such a gas-guide device, for example in a retrofit 
procedure, can also be considered under particular circumstances, since no 
modification of the basic structure of the machine is required. Changes 
are basically necessary only on the fan hub 10 and with regard to the 
design of the partition wall 15 (present in any case) as a carrier for the 
gas-guide device 18. 
Obviously, numerous modifications and variations of the present invention 
are possible in light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims the invention may 
be practiced otherwise than as specifically described herein. 
LIST OF DESIGNATIONS: 
1 Rotor 
2 Rotor shaft 
3 Rotor cover 
4 Cover plate 
5 Lower bar of stator winding 
6 Upper bar of stator winding 
7 Lugs ("ear members") 
8 Shaft collar on 2 
9 Axial fan 
10 Hub of 9 
11 Moving blades of 9 
12 Inflow space of 9 
13 End face of 14 
14 Machine housing 
15 Partition wall 
15a Inner end of 15 
15b Shoulder on 15a 
16 Annular projection having a rounded edge 
17 Outflow space of 9 (winding-head space) 
18 Gas-guide device 
18a,18b Halves of 18 
19-25 Guide rings in the form of a cone envelope 
23a,23b Halves of 23 
24a,24b Halves of 24 
26 Conical end of 10 
27 Ring part 
28,29 Bars 
30 Annular plate 
30a Recess or groove in 30 
31 Filler pieces 
32 Screw bolts 
33 Triangular reinforcing plates 
34,35 Set pins 
.alpha.Aperture angle of guide rings 
E Radial plane 
HM Horizontal plane of symmetry--separating plane of 18 
K.sub.1 -K.sub.8 Ring-shaped channels 
M.sub.T Center point of the generatrix of T 
S Struts 
T Torus surface segment