Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The invention relates to a rotary electric machine
especially to a high-power and high-speed synchronous
machine pro~ided with cylindrical rotor.
The direct cooling of the rotor winding supplied
with direct current of the rotary electric machines of
very high power (several-hundred megawatts) and high speed,
especially the two-pole synchronous machines provided
with cylindrical rotor (turbogenerators) is ensured by
gas cooling or liquid cooling.
With higher powers~ the gas cooling is generally
realized by the use of hydrogen. The advantages of hydrogen
(low specific weight, low gas frictional loss, relatively
high specific heat, good electric insulating capacity,
etc.) are well known.
The designers striving after the development
of machines of even higher unit power can have the choice
of two basic types of the direct conductor cooling, i.e.
of the liquid cooling and the gas cooling. The choice
is not at all simple. For the gas cooling it is to be
said that this solution has traditions of several decades
both with the manufacturers and the consumers, it is,
however, doubtful whether the intensity of gas cooling
can be increased to such an extent as required by the
increasing demands. For the other alternative it is to
be said that the liquid has a very high specific heat and
; thermal conductivity, in order to enforce these advantages,
however, numerous new strucural, engineering and operat-
ional safety problems shall be solved (increasing the
number of parallel liquid paths, sealing of the cooling
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system etc.) and the risk involved in the unsolvedness
of these problems shall be taken, respectively.
Nowadays when the increase from 500-1000 HW to
1000-2000 MW of the unit power of two-pole turbogenerators
is aimed at, the question again arises whether the relative
cooling technical tasks can be performed by further developing
the classical hydrogen cooling or the change-over to the
liquid cooling and the assumption of the accompanying
risks are inevitable.
When examining this question, it should be briefly
mentioned that the most intensive forms of the hydrogen
cooling used in the rotors of large turbogenerators can be
also divided into two groups. The division is based on
that where the gas, cooling the most part of the winding,
the part laying in the iron body~ enters the rotor. The
'I' .
cooling gas discharges namely in case of both groups in
the same manner~ radially~ on the mantle surface of the
rotor in the direction corresponding to the centrifugal
force.
With the first group, the cooling gas enters
the rotor axially on the endfaces of the rotor, then
it flows axially either in the channels developed in
the conductors themselves or in the iron body of the rotor
in the subslots developed beneath the coil slots, then
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it turns in radial direction and leaves the rotor on
contacting the coils. In this case~ the axial direction
is characteristic to the flow of the cooling gas~ -
therefore these systems will be called further on "axial"
systems.
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With the second group, in case of rotors of
so-called "gap pick up" system, the cooling gas enters
the rotor on the mantle surface and flows inwards in
radial direction, then flowing in axial or tangential
direction, or having such direction-components it contacts
the conductors to be cooled, finally turning again in
radial direction it leaves the rotor. With the system,
being callet further on "gap pick up" system, the radial
flow is characteristic.
The usefulness of hytrogen-cooled rotors de-
pends to a significant extent on the gas quantity to
be introduced into the rotor in unit time. In case of
large gas quantity the warming-up of the gas is namely
lower at a given loss (I2R) and the heat drop on the
cooled surfaces of conductors is lower, respectively,
thus after all the overheating of the coil as compared
,
to the temperature of the cold cooling gas is lower.
Pinally, this is the pivotal question of the development
of very-high-power machines.
The gas quantity to be carried in into the rotor
is - as experience shows - approximately proportional to
D in case of "axial" system and
(D.L) in case of "gap pick up" system
(D-diameter of the rotor, L - active iron length).
; Consequently, the rotor of "axial" system shall be made
with a short iron body and with a diameter as large as
possible, whereas in case of a "gap pick up" system,
the gas quantity to be mtroduced increases proportional
to the iron length. While thus the length of the rotor
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: ~ . . . . .
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of axial flow is limited (the flow losses increase together
with the increase of the length of flow channel, the intake
cross-section on the front side is relatively small), with
the 'gap pick up" system the relatively small cross-section
of the inlet and outlet ports developed generally in the
coil fastening keys, on the mantel surface of the rotor
limits the quantity of cooling gas to be passed through
the rotor.
After all, the utilizability of the rotor is
limited with the known solution of "axial" system and
of "gap pick up" system, since also the gas quantity
to be introtuced is limited. With the known methods, the
maximum unit capacity to be achieved at the two-pole
turbogenerator amounts to about 1000-1200 MW at the
largest rotor tiameter admissible with respect to the
strength (about 1250 mm).
With the "axial" system - as already mentionet -
the length of the iron body is limited, since an
advantageous "axial" cooling can be achieved with
proportions of at most L = 3~4 D. The diameter of the .
rotor, however, cannot be increased beyond a certain limit
for strength reasons, therefore the gas quantity to be
introduced can be increased only when increasing the length
of the iron body. The length of the iron body of the
machine of required very high power should be at least
L s 6r8 D, a rotor of such a length, however, cannot
be efficiently cooled with an "axial" cooling system.
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The basis of the "gap pick up" system consists in
that between the inlet and outlet ports developed on the
mantle surface of the rotor a constant differential
pressure occurs as a result of the rotation (dynamic pressure
and suction), rendering possible the introduction of the
cooling gas into the rotor. Since the centrifugal force
produces theoretically the same effect both in the inlet
and in the outlet channels, these two ef~ct~ should com-
pensate each other according to the principle of continuity.
In the practice~ however~ the gas entering the rotor is
considerably colder consequently of higher density than
the gas discharging from the rotor. Thus, a greater
centrifugal force is operative on the gas in the inlet
channel than in the outlet channel~ This phenomenon
impairs the intensity of cooling and to the greater extent,
the greater the difference between the temperature of the
; inlet gas and that of the outlet gas and the deeper the ;
coil slot is.
As it is to be seen, a proper cooling can be achieved
with the known "axial" and "gap pick up" systems only in case
of machines of specified dimension (power), with the former
system the length of the slot (iron body), with the latter
one the depth of the slot is limited.
The aim of the invention is the deve opment of a
~ gas cooling system for electric rotary machines~ especially
; for high-power and high-speed synchronous machines provided
with cylindrical rotor, by means of which machines of
larger dimensions (power) than those used up to now can
be effectively cooled and which renders unnecessary the
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change-over to the liquid cooling with machines of 1000-2000 MW power.
According to the invention there is provided in a high
power, high-speed rotary synchronous electric machine having an airgap,
in combination: a rotor including a metal body of predetermined length
and rotatable about an axis; a plurality of slots of predetermined
width defined in the body of said rotor, each slot extending
substantially along the length of said body, two sidewalls defining
the width of each of said slots, a plurality of subslots defined in
the body of said rotor, each of said subslots having a width smaller
than that of said slots, each subslot being associated with a respective
one of said slots and being arranged as a substantially symmetrical
and radially inward extension of the associated slot and communicating
with a part of said slot facing the axis along the length of said
body; said subslots terminating at opposite end faces of said rotor
and being open at said end faces; a rotor winding consisting of a
plurality of parts, each of said parts including a plurality of
winding turns, being arranged in a~respective one of said slots, and
being spaced from the two sitewalls of the corresponding slots, so
as to define first and second radial channels between the respective
sidewalls and the winding part, each part having a predetermined
length; a plurality of wedges in said rotor for closing said
slots, respectively, and for supporting respective of said winding
parts against centrifugal forces, said wedges defining a plurality
of groups of inlet and outlet ports for each of said slots, each
port communicating with said airgap, said inlet and outlet ports
in each of said groups being oppositely inclined relative to the
direction of rotation of the rotor, and being axially offset
relative to each other, each inlet port in a slot communicating
with the first, and each outlet port with the second of said
radial channels, said groups being substantially periodically
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arranged along the length of said body; each of said rotor winding
parts being disposed in a slot associated therewith and defining
a plurality of cooling channels arranged tangentially relative
to said axis, each cooling channel communicating with the first
and second radial channels in the slot, said cooling channels
being arranged at respective different radial levels corresponding
to the respective winding turns, substantially periodically along
the full length of a respective winding part; first insulating
means located between ad~acent turns of said winding parts in
each of said slots; and second insulating means located in each
of said slots between a radially inwardly facing portion of the
radially innermost winding part and a radially inwardly facing
portion of the slot, said second insulating means at least
partly closing the communication between a respective one
of the subslots and the associated slot; in each slot an inner
region of one of said winding parts and said first and second
insulating means defining a plurality of radial connecting channels,
each communlcating with sait subslot and at least some of the
cooling channels in said inner region, said radial connecting
channels being arranged substantially periodically along the
length of one of the winding parts.
The main advantage of the solution according to
the invention consists in that the cooling of "gap pick up"
system of the conductors being farther from the shaft is effected
at a relatively low counterpressure and the gas quantity necessary
for the cooling according to the "axial" system of the conductors
being nearer to the shaft can be introduced without difficulty
on the front side of the rotor.
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~049080
The invention will be now described with reference
to the exemplified embodiments shown in the enclosed drawings,
where
Figure 1 is the section taken in a plane vertical
to the shaft, of the rotor of a synchronous machine provided with
cylindrical rotor, using cooling channels of tangential direction,
Figure 2 shows the gradual section II-II of the rotor
according to Figure 1,
Figure 3 is the section taken in a plane vertical to
the shaft, of the rotor of a synchronous machine provided with
cylindrical rotor, using cooling channels of axial direction,
Figure 4 shows the gradual section IV-IV of the rotor
according to Figure 3.
In case of the embodiment according to Figures 1 and 2,
coil slots 2 are developed in the iron body 1 of the rotor of the
synchronous machine provided with
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cylindrical rotor. ~eneath the coil slots 2 subslots 3
connected therewith are provided for, running in axial direction
through the rotor and being open towards the front sides thereof.
In the coil slots 2 winding consisting of outer 8 and
inner 9 conductors is arranged. The conductors 8~ 9 are
arranged in the coil slots 2 parallelly to each other in
axial direction. One pair of conductors each constitutes
one turn each. The turns are separated from each other by
means of interturn insulations 17. At the bottom and top
of the coil slots 2 insulations 5 and 6~ along their side
walls an insulation each 7 are arranged. In the insulations
7 channels 10, 11 of radial direction are developed which
are in communicating connection with the tangential cooling
channels 14~ 15 developed in the conductors 8~ 9. Through
the inner conductors 9~ in the symmetry plane of the coil
slot 2~ inlet channels 16 (marked with dashed line in
Figure 2) are provided interconnecting the subslot 3 with
the cooling channels 15. The mouth of the coil slot 2 is
closed by a key 4 in which inlet 12 ports and outlet ports
13 are provided for. The ports 12, 13 are inclined as compared to
the radial direction~ in such a manner that the inlet ports
12 are slanted in the rotation sense, whereas the outlet
ports 13 opposite to the rotation sense.
The flow direction of cooling gas is indicated
by arrows in Figures 1 and 2. Accordingly, the cooling
gas enters the coil slot 2 through the subslot 3 and the
inlet ports 12. From the inlet ports 12 the cooling gas flows into
the channels 10 along one wall of the coil slot then into
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the tangential cooling channels 14, thereafter into the
channel 11 along the other wall of the coil slot and finally
flows out from the rotor through the outlet ports 13 in-
to the airgap of the synchronous machine. From the sub-
slot 3 the cooling gas flows through the inlet channels
16 into the tangential cooling channels 15, therefrom
directly, and through the channels 10 along one side wall
of the coil slot as well as through the tangential cooling
channels 14~ respectively into the channels 11 along the
other wall of the coil slot, finally through the outlet
ports 13 into the airgap of the synchronous machine.
It is to be seen from those said above, that
the cooling of the outer conductors 8 is performed accord-
ing to the "gap pick up" system~ that of the inner conduc-
tors 9 according to the ~'axial~' system.
In case of an embodiment according to Figures
I and 2~ a special advantage is ensured by that the
cross-section of the channels 10~ 11 of radial direction
- the coil slot 2 being trapezoidall- increases to the
same extent as the gas quantity passing it.
In case of the embodiment according to Figures
3 and 4~ no cooling chasnel is made along the side walls
of the coil slot 2 and the cooling channels 14, 15 between
the conductors 8~ 9 are not of tangential but of axial
direction. The cooling channels 14~ 15 run axially through
the conductors 8~ 9. The interconnection between the
subslot 3 and the inner conductors 9 is ensured by inlet
-- channels 16~ like with the former example, of which~
however~ only every second one lead directly into the
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~049080
subslot 3, the others reach only up to the innermost
cooling channel 15 and are connected through that with
the subslot 3. The connection between the cooling channels
14 of the outer conductors 8 and the airgap of the synchron-
ous machine, respectively, the inlet 12 and outlet 13
ports is ensured by channels 18, 19 developed similarly
to the channels 16 and laying in line therewith. They are
alternate~y ~ connected with the ports 12 and 13, namely
in such a manner that the channel 19 connected to the
port 13 i9 also directly connected to the channel 16
developed in line therewith, while the channel 18 connected
to the port 12 is separated from the channel 16 laying in
line therewith at the point "A".
The flow direction of the cooling gas is indicated
by arrows also in Figures 3 and 4. The cooling gas flows
from the subslot 3 into the channels 16 open at the bottom
then through the cooling channels 15 towards the adjacent
radial channels 16. These latters are interconnected with
the channels 19, through which the cooling gas flows into the
outlet ports 13 and therefrom into the airgap. The cooling
gas entering through the inlet ports 12 flows into the
channels 18, then - through the cooling channels 14 - into
the adjacent channels 19 and therefrom, through the outlet
ports 13 again into the airgap. The cooling of the outer conductors
8 takes place according to the "gap pick up" system, that of
the inner conductors 9 according to the "axial system ".
Since the channels 16 and 18 are separated from each other,
the cooling system of the outer conductors 8 and that of
the inner conductors 9 are practically fuIly independent of
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each other and the cooling gases flowing in the two systems
are mixed with each other only at the discharge.
The structural separation of the two systems is
not absolutely necessary. If in point "A" a breakthrough is
made, the separation develops in a natural manner but the
dividing line of the two systems shall~ be not by all means
at the middle conductor but - dependin8 on the prevailing
pressure ratio - above or beneath it.
The above described two embodiments are only examples
aiming at the better understanding of the invention. According to
those said above further embodiments may be produced without
deviating from the inventive idea.
The essence of the invention is the common use
(combination) of the "gap pick up" and "axial" systemæ
becoming poæsible thereby that the cooling channelæ 14,
15 run along the potential surfaceæ (concentric cylinders)
of the centrifugal field developing during the rotation
of the rotor.
How many of the conductors laying in the slot
are connected in the "gap pick up" cooling system and how
many in the "axial" cooling system, depend always on the
given special conditionæ. If a half-and-half ratio is
taken, it is obvious that the cooling of "gap pick up"
system will be conæiderably more intenæive aæ compared
to the case when all conductoræ would be cooled in the
"gap pick up" æyætem, since the available cooling gas
quantity is practically constant, the heat to be taken away
reduces to the half. Accordingly, the warming up of the
cooling gas and the density difference of the inlet and outlet
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cooling gas are also reduced to the half. Due to the reduction
to the half of the density difference as well as of the
thickness of layer to be cooled the counterpressure impeding
the flow of cooling gas is reduced as well.
If the "axial" cooling is applied only on the
lower 1/3 - 1/4 part of the complete coil height, the gas
quantity flowing from the part of ~'axial" system to the
common output channel will be even in this case advantage-
ous, reducing also the above mentioned density difference.
Moreover, with the embodiment according to Figures 1 and
2 a less quantity of hot cooling gas flows from the part
of "axial" system into the inlet channel of the part of
"gap pick up" system~ than in the case when the complete
coil slot is coded according to the "gap pick up" system.
The combined cooling system according to the
invention - the cooling gas being hydrogen - allows a
current density of 15-20 A/sq.mm at an overpressure of
about 5 at- in the coil turns, thus with its use, turbo-
generators of unit capacity even above 1000 MW can be
produced.
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