Note: Descriptions are shown in the official language in which they were submitted.
~ ~ 2191933 95/179
TITLE OF THE INVENTION
METHOD FOR RENEWING SLIPRINGS
5 BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a method for renewing
sliprings of synchronous machines.
Discussion of Backqround
Sliprings of synchronous machines, for example
turbine-driven generators, normally consist of steel
rings arranged in pairs. They are either shrunk in an
insulated fashion onto a slipring bushing or in an
insulated fashion directly onto the rotor shaft
(compare Wiedemann/Kellenberger "Konstruktion
elektrischer Machinen" ["Design of electric machines"],
Springer-Verlag Berlin, Heidelberg, New York 1967,
pages 392, 393).
Sliprings of high-speed machines are
necessarily subjected to wear. It is comparatively
expensive to replace them.
SUMMARY OF THE INVENTION - -
Accordingly, one object of this invention is to
provide a novel method for renewing sliprings which, on
the one hand, is simple to carry out and, on the other
hand, increases the service life and the current
transfer properties of the sliprings.
This object is achieved according to the inven-
tion by means of the following method steps:
a) Machining both sliprings on the shaft without
removing the sliprings from the shaft, for the ~urpose
of producing a slipring bushing, specifically to a
radius which is preferably 30 to 40 mm smaller than the
nominal radius of the slipring;
2 1 9 1 933
- 2 - 95/179
b) Heating and subsequently shrinking the new
sliprings consisting of a high-strength Cu-Ni-Be alloy,
onto the shrink surfaces, prepared in accordance with
step a), of the slipring bushings from the non-drive
end of the machine;
c) Skimming the slipring surfaces of the newly
shrunk-on sliprings to the nominal radius.
The method according to the invention offers
the possibility of renewing sliprings economically, and
moreover increasing the service life of the (new) slip-
rings, because the latter also have better running
properties in addition to a larger current carrying
capacity. Moreover, the invention offers further advan-
tages:
- The current transfer losses are reduced, and the
brush life is lengthened.
- The loadability of the brushes is increased. The
necessary brush number per polarity can therefore be
reduced. This produces a further reduction in the brush
consumption. Furthermore, there is thereby an increase
in the slipring surface uncovered by carbon brushes.
The slipring is thereby more effectively cooled, and
the slipring temperature drops, and this in turn favors
the operating characteristics of the sliprings.
- When the sliprings are operated in a closed
cooling circuit, the reduced carbon consumption
produces smaller filter contaminations and thus longer
filter lives. Moreover, owing to the reduced overall
losses it is also the case that lower exhaust air
temperatures, and thus reduced recooling performances
are required.
- When refitting existing installations, the
possibly increased field current requirement can be
ensured by the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete appreciation of the invention
and many of the attendant advantages thereof will be
21 91 933
- 3 - 95/179
readily obtained às the same becomes better understood
by reference to the following detailed description when
considered in connection with the accompanying
drawings, wherein:
Figure 1 shows a longitudinal section through the non-
drive-end shaft end of a turbine-driven
generator with two sliprings made from steel;
Figure 2 shows a longitudinal section through the non-
drive-end shaft end of the turbine-driven
generator according to Figure 1 after the
steel sliprings have been turned down and the
novel sliprings shrunk on;
Figure 3 shows a modification of the embodiment accor-
ding to Figure. 2, with sliprings which
respectively comprise two individual rings;
Figure 4 shows a further modification of the
embodiment according to Figure 2, with
stepped shrink surfaces on a larger scale
than in Figure 2; and
Figure 5 shows a particularly preferred embodiment of
the invention, with sliprings which respec-
tively comprise two individual rings with
different shrink surfaces and are mounted on
shrink surfaces, stepped in a complementary
fashion thereto, on the steel rings.- ~-
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, wherein line
reference numerals designate identical or corresponding
parts through the several views, in Figure two
sliprings 1, 2 made from steel are mounted, for example
shrunk on, on the non-drive-end shaft end NS of a
turbine-driven generator, in an insulated fashion on
t.le shaft 5 with the interposition of insulating foils
3, 4. For reasons of simplification, the electrical
connection to the exciter terminal studs arranged in a
shaft bore has been omitted from the drawing; for the
rest, it corresponds to the prior art such as is to be
2 1 9 1 933
- 4 - 95/179
gathered, for example, from the book by
Wiedemann/Kellenberger mentioned at the beginning, loc.
cit. Because such sliprings are subjected to wear, they
have to be replaced at certain intervals. To date, the
sliprings l, 2 have, for this purpose, been heated to
several hundred degrees Celsius and then pulled off in
the direction of the non-drive-end shaft end. Before
shrinking on new sliprings, the insulating foil 3, 4,
damaged during pulling off, has been replaced.
By contrast, the invention adopts a different
approach:
The existing sliprings 1, 2 are not removed,
but they are turned down to a radius r which is smaller
by the thickness d (typically 30 mm) of the slipring 6
or 7 to be shrunk on anew than the nominal outside
radius rN of the slipring. The previous sliprings now
form, as it were, slipring bushings 8, 9 for the
sliprings 6, 7 to be shrunk on anew.
The sliprings to be shrunk on anew consist
according to the invention of a hardenable copper alloy
with alloying additions of Ni or Be. An alloy which is
available commercially under the designation of HOVADUR
CuNiBe from the Schmelzmetall AG Company, CH-6482
Gurtnellen/Uri (data sheet HOVADUR CuNiBe, undated) has
proved to be particularly advantageous in this Acase.
This copper alloy has alloying additions of
approximately 1.8% Ni and approximately 0.4~ Be. In the
hardened "normal state", it already has a high hardness
and thermostability in conjunction with good electrical
and thermal conductivity. In addition, this alloy can
also be delivered in heat-treated form and in a so-
called "special state". In this form of supply, this
alloy achieves strength values which correspond to
those of ste_l. Its electrical and thermal
conductivity, by contrast, correspond to those of
copper.
The new sliprings 6, 7 are heated to approxi-
mately 200C and shrunk onto the slipring bushings 8
~ 21 91933
- 5 - 95/179
and g, respectively (compare Figure 2). Because of the
high modulus of elasticity and the high yield point of
the copper alloy, an optimum shrink fit results upon
cooling and withstands all the operating stresses. The
newly shrunk-on sliprings 6, 7 are subsequently skimmed
to nominal radius rN.
In order to facilitate slipping the inner
slipring 7 on over the slipring bushing 8 of the outer
slipring 6, it is expedient to skim the outer slipring
1 to a radius which is smaller by the measure ~ and,
consequently, to increase the thickness of the to be
shrunk on slipring 6 anew by this difference ~ (compare
Figure 2). A difference ~ of between 1 and 2 mm
suffices in this case.
Sliprings of medium and large turbine-driven
generators have an axial width of the order of
magnitude of 200 to 400 mm. Narrow rings made from said
copper alloy - they are normally produced from a blank
by forging - are more economical to produce than wide
rings; it is also easier to manipulate them during
installation. For this reason, it is expedient to form
the (new) slipring from a plurality of mutually
identical individual rings 6a, 6b or 7a, 7b, as is
represented in Figure 3 for a slipring comprising two
individual rings. - ~-
It is expedient, here, as well, to make theradius r of the outer slipring bushing 8 smaller by the
measure ~ than the inner slipring bushing 9, and conse-
quently to increase the thickness of the two partial
rings 6a, 6b by ~.
In the embodiment represented in Figure 4, the
shrink surfaces on the two slipring bushings 8, 9 and,
consequently, also the associated shrink surfaces on
the inner circumference of th~ sliprings 6 and 7 are
stepped. The respective radii are denoted by rl, r2, r3
and r4, it being the case that rl ~ r2 > r3 > r4 holds,
in order to be able to slip the inner slipring 7 over
the outer slipring bushing 8. This step additionally
2 1 9 1 933
- 6 - 95/17g
secures the sliprings 6, 7 in the axial direction and
also renders installation easier, because an axial stop
is available during the shrinking on owing to the step.
The embodiment according to Figure 4 can also
be carried over to individual rings 6a, 6b or 7a, 7b as
illustrated in Figure 5. There, the individual rings
6a, 6b or 7a, 7b are respectively seated on stepped
shrink surfaces with the radii r1, r2, r3 and r4, it
being the case, again, that r1 > r2 > r3 > r4 holds.
The invention is not, of course, restricted to
renewing sliprings shrunk directly onto the rotor
shaft. It can, of course, also be applied in the case
of slipring arrangements in which the steel sliprings
are shrunk onto a slipring bushing or onto a preshrunk
ring, as is represented, for example, in Figure 386 and
Figure 388 on page 392 in the book by
Wiedemann/Kellenberger mentioned at the beginning.
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.
