FIELD OF THE INVENTION
The present invention generally relates to high capacity turbo-generators.
More particularly the invention relates to a device for constructing axial
holes on the exciter/rotor of large capacity turbo generators.
BACKGROUND OF THE INVENTION
In large size generators, magnetic field is created by electromagnets
which are fed by brushless exciters. The exciters are coupled on the same
rotor shaft and constitute small size generators. Electric direct current
from this brushless exciter to generator rotor coils travel through axial
male and female connection provided on coupling face of the exciter and
the generator shaft. For this transfer of power from the Exciter to the
generator rotator poles, an arrangement as shown in figure 1 is available:
1. Insulated core bar is fitted in the exciter shaft and generator shaft.
These core bars are made of copper and are in two equal halves in
cylindrical shape separated from each other with insulating sheet.
The whole core bar is covered with insulating glass tub assembly
throughout the length.
2. Exciter shaft and exciter end of the generator shaft have radial holes
for fitting current carrying bolts with core bars.
3. In the exciter shaft current carrying conductor are provided with
current carrying bolts and in the generator shaft the current carrying
bolts are connected to the rotor pole coils. End face of the core bar,
fitted in the exciter shaft, have two axial holes in each half for
inserting silver coated pint. End face of the core bar in the generator
shaft also has two matching holes in each half, fitted with rings made
of silver.
4. When the exciter shaft and generator shaft are bolted, the silver pins
in the exciter shaft fit tightly in the matching holes in the generator
shaft core bar.
Now to produce these axial holes in the core bars with perfect matching,
following procedure is adopted:
1) Axial holes in the core bars and coupling holes in the exciter shaft and
the coupling of generator shaft are produced with a drilling jig to
ensure proper matching of the holes.
2) The drilling jig is set on coupling face as per the 'X' axis and 'Y' axis
mark on the coupling face for drilling of axial holes in the core bar.
The jig is fixed in position with four pins tightly passing through the
holes of the jig and coupling holes in the shaft.
3) Holes from the jig are transferred in the core bar in steps. First, the
drilling with ? 26.5 is made followed by drilling of sizes ? 37,
? 47 mm and then the desired size in the required depth.
4) Before removing the drilling jig, a collar of ? 47.5 is produced up to
10 mm with the boring bar. This collar works as reference surface for
boring and reaming of holes to final size.
During manufacturing of Turbo-generator rotor, a peculiar problem in
encountered. There are 4 axial holes in the field lead core bar of the high
capacity turbo generator rotor of size dia 50.1 at a depth of 121mm (refer
Fig 1.2). In the rotors of lower capacity for example 250 MW, the hole
requirement is of only a depth of 95 mm (refer Fig. 1.1). The axial holes
are made by grooving and recessing by a boring bar of dia 30. This is
done in three steps where three rings are designed to be fitted. But in
case of high capacity TG rotors, the axial holes are done in four steps
with 4 provision for 4 rings (refer fig 1.2).
Due to larger depth hole, known boring bar can not be used for grooving
and recessing beyond 79 mm depth and three steps. Because after this
length, for the 4th step ring, grooving depth achieved is only 2 mm in
place of required 3mm.
As the rotor is a very sensitive part of the generator and has high bearing
on performance of the machine, it is essential to have the ideal groove
depth and recesses.
OBJECTS OF THE INVENTION
It is therefore and object of the invention to propose a device for
constructing axial holes on the exciter/rotor of large capacitor turbo
generators.
Another object of the invention is to propose a device for constructing
axial holes on the exciter/rotor of large capacity turbo generators, which is
enabled to configure higher depth of grooves and recesses necessary for
higher capacity generators.
A still another object of the invention is to propose a device for
constructing axial holes on the exciter/rotor of large capacity generators,
which eliminates the need of reworking on the initially constructed holes.
A further object of the invention is to propose a device for constructing
axial holes on the exciter/rotor of large capacity turbo generators, which
reduces the manufacturing cycle time and wastage of manpower and
material.
SUMMARY OF THE INVENTION
Accordingly, there is provided a device for constructing axial holes on the
exciter/rotor of large capacity turbo generators. The device essentially
consists of a shaft member having a diameter at first end matching with
that of a micro boring head of a horizontal boring machine for insertion, a
second end of the shaft member having to slots enabled to generate right
an angle in the axial holes being drilled, wherein the diameter of the first
end is increased to about 25% from an axial distance between 15 to 20%
of the total length of the shaft member from the first end all through the
second end.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - shows a schematic diagram of a rotor shaft of high capacity
turbo generators.
Figure 2 - shows a schematic diagram of a prior art hole-making device.
Figure 3 - shows a schematic diagram of the device according to the
invention.
Figure 4 - shows the axial holes constructed with the device of figure 3.
Figure 5 - shows a photographic view of the device of figure 3.
Figure 6 - shows an engineering drawing of the device of figure 3.
DETAIL DESCRIPTION OF THE INVENTION
As shown in figure 1, a high capacity generator having a rotor shaft with
radial holes in the rotor part, in which the electromagnets present. Exciter
shafts having axial holes, which constitute small-size generators are
coupled on the rotor shaft. Electric current from the exciters are fed to the
electromagnets to create magnetic field. In order to transfer of power
from the exciter shaft to the rotor shaft, an arrangement is provided
which interalia constitutes providing insulated core bars on the exciter as
well as rotor shafts, current carrying conductors with current carrying
bolts on the exciter shaft, and current carrying bofts of the rotor shaft
connectable with said rotor coils.
For high-capacity turbo generators, the exciter shafts and the rotor shaft
are bolted through axial coupling holes configured on each, which requires
exactly matching configuration of the holes through drilling.
For such precision-construction of the matching holes on the exciter and
rotor shaft, an improved device is provided according to the invention.
Figure 2 shows a prior art device for hole-construction which may be
, particularly suitable for lower-capacity turbo generators (TG), but exhibit a
disadvantage while adapting for high capacity TGs in terms of mis-
matched-depth and size of the holes leading to damage of the TGS.
Figures 3 and 4 show a device for constructing axial holes on the
exciter/rotor of high capacity TGS including the precisely-matched holes
constructed by the new device.
Figure 5 shows a photographic view of the inventive device in an
operational mode and fitted on a micro-boring head of a horizontal boring
machine.
ADVANTAGES OF THE INVENTION
1. One time saving of FOREX
Saving in cost of imported spare micro boring head in foreign
exchange = Rs. 37,00,000/-
(Purchase from W.Germany M. Head no. UP A 6/4215 - 019001)
2. Regular saving
A. Saving on account of reduction in axial hole operation rework time:
per rotor saving
= 32 hour * 4 person* 286 Rs/hour = Rs 36608 * 8 rotor = Rs.2,92,864/-
B. Time saving on account of machine hours = 106(before)
Now after implementation machining time = 48
106-48= 58 hours per rotor xRs.4586 M/C per hr.cost x 8 = Rs.2,65,988/-
C. Less-cost of developing tooling:
Manpower cost = 24 hours * 2 persons * 286 = Rs. 13,728/-
Machining cost = 4 Hrs * 1265 per hour = Rs.5,060/-
SAVING (A + B-C) = Rs.5,40,064/-
Yearly Saving = 8 (set manufacturing) * 5,40,064=43.20 lacs
VTL UTILITY/APPLICABILITY OF THE SUGGESTION
• Designed and developed device can be used for making axial hole in rotor or horizontal
boring machine in other components made of copper material and this is applicable for
manufacturing of 600/600 MW.
• The process time has reduced and more number of Rotor Shaft defect - free axial hole
are being produced at first time.
• Reduction in rework, manpower, machine time. Cycle time and material due to
development of this innovative process resulted in reduced production cost.
WE CLAIM:
1. A device for constructing axial holes on the exciter/rotor of large
capacity turbo generators, comprising a shaft member having a
diameter at first end matching with that of a micro boring head of a
horizontal boring machine for insertion, a second end of the shaft
member having two slots enabled to generate right angle in the axial
holes being drilled, wherein the diameter of the first end is increased
to about 25% from an axial distance between 15 to 20% of the total
length of the shaft member from the first end all through the second
end.
2. A device for constructing axial holes on the exciter/rotor of large
capacity turbo generators substantially as herein described and
illustrated with reference to the accompanying drawings.

ABSTRACT

The invention relates to a device for constructing axial holes on the exciter/rotor
of large capacity turbo generators, comprising a shaft member having a diameter at first end matching with that of a micro boring head of a horizontal boring machine for insertion, a second end of the shaft member having two slots
enabled to generate right angle in the axial holes being drilled, wherein the diameter of the first end is increased to about 25% from an axial distance between 15 to 20% of the total length of the shaft member from the first end all
through the second end.