FIELD OF INVENTION
The present invention relates to a jig for drilling axial hole for core bar housing
inside turbo generator rotor/exciter rotor.
BACKGROUND OF THE INVENTION
Generally in brushless exciter, current from exciter to generator rotor coils flows
through axial male and female connection provided on coupling face of the
exciter and the generator shaft. A plurality of insulated core bar is fitted in the
exciter shaft and the generator shaft. These core bars are made of copper and
are in two equal halves separated from each other with insulating sheet and are
also covered with insulating glass tube assembly throughout.
The exciter shaft and the exciter end of a generator shaft have radial hole for
fitting current carrying bolts with core bars. In exciter shaft current carrying
+conductors are fitted with current carrying bolts and in generators shaft current
carrying bolts are connected with rotor pole coils.
The end face of the core bar is fitted in the exciter shaft have two axial holes in
each half for fitting of silver coated pins. The end face of a core bar in generator
shaft also has two matching holes in each half, fitted with signs made of silver.
When the exciter shaft generator shaft are fastened, silver pins in exciter shaft fit
tightly in machining holes in generator shaft core bar.
The problems arise from the experience are as follows:
1. Insulation resistance valve of exciter rotor and generator rotor after final
fitting of core bars was observed low.
2. The problem of low insulation resistance valve was experienced after
producing axial holes in core bar and silver plating holes.
These problems of low IR was being overcome in the following ways:
a) By removing core bar from exciter and generator rotors and heating.
b) Core bars halves are removed from insulating glass tube for proper
cleaning of copper filling dust and moisture. After re-assembly IR values
are recovered but in 35 to 45% cases, insulating glass tubes were getting
damaged at the time of removing core bar halves for cleaning.
Analysis of the problem
1. From rectification method explained at point (1) and (b) above it
was concluded that some gap exists between core bar halves and
insulating glass tube which allows cutting fluid, dust and tiny
copper particles ingress into the gap which results in low IR value.

2. Ingress of particles indicated at as above was due to cutting of part
of the end of the core bar producing outside generator and exciter
coupling faces.
3. Cutting of produced part of the core bar was necessary for proper
fitting and setting of drilling jig for drilling and reaming of pin holes
in core bars in assembled condition with respective shafts.
4. Hence it is concluded that the jig is designed to flush with the
coupling face for drilling of pin holes in the core bar. Protruded
portion of core bar was creating obstruction in proper fitting of jig
which necessitated cutting of core bar to flush it with the coupling
face. The cut portion of core bar was found responsible for ingress
of fluid, dust and thin copper particles in the space between core
bar and insulating cylinder.
Effects of the problem
1. Delay in final IR testing of generator rotor and exciter rotor up to 5-6
days.
2. Delay due to cutting of projected length of core bar. This led toloss of 24
machine hours on horizontal boring machine.
3. Rectification of core bars by way of heating and cleaning after removal of
core bar from cylinder takes about 3 days.
4. Replacement of damage insulating glass tube assembly takes about 32
hours.
5. Re-machining of replaced glass tube assembly takes about 16 hours.
From analysis of the problem, it reveals that two insulation resistance values was
due to cutting of the protruded portion of the field lead core bar.
The modification of existing jig was envisaged and developed a new modified jig
which will accommodate projected portion of the core bar and thus avoid cutting
of the projected portion.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose a jig for drilling axial
hole for core bar housing inside turbo generator rotor/exciter rotor which
eliminates the disadvantages of the existing state of art.
Another object of the present invention is to propose a jig for drilling axial hole
for core bar housing inside turbo generator rotor/exciter rotor which reduces
delay time in IR testing.
A further object of the present invention is to propose a jig for drilling axial hole
for core bar housing inside turbo generator rotor/exciter rotor which reduces the
damage of the glass covered.

A yet another object of the present invention is to propose a jig for drilling axial
hole for core bar housing inside turbo generator rotor/exciter rotor which
improves IR.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.1 - shows a schematic view of a plan of the new jig as per invention
Fig.2 - shows a schematic view how the core bar is fitted in exciter
Fig.3 - shows a side view of the new jig
Fig.4 - shows a photo view of exciter rotor face of the jig
Fig.5 - shows a photo view of turbine generator face of the jig
Fig.6 - shows a photo view of a rotor without core bar
Fig.7 - shows a photo view of a rotor with core bar of copper field inside
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
As shown in Fig. 2 and 3, the present invention relates to a new jig that
comprises a 'O' shaped steel thick plate with 14 peripheral holes for drilling holes
in the flange of the exciter rotor and the flange of the turbine generator rotor
and having four central holes co-axially matching with the peripheral holes to
drill holes in right position for insertion of core bar in exciter rotor and turbine
generator rotor shaft. One face (surface A in Fig.l) of the jig to be matched with
the face of coupling flange of generator rotor having two steps recesses at a
radius of 150 mm and 117.5 mm from the centre of the jig to accommodate
projected portion of the core bar and at the same time will provide proper
butting of the drilling jig with the coupling face of generator rotor. The opposite
face (surface B of Fig. 1) of the jig to be matched with the face of coupling flange
of exciter rotor shaft have protruded color and a recess of 235 mm up to the
depth of 4 mm has been produced to accommodate the projected portion of the
core bar from the exciter rotor.
Fig.6 shows a rotor without core bar wherein 14 threaded holes co-axially inside
the coupling holes on the coupling face of rotor.
Fig.7 shows a rotor with core bar fitted inside wherein jig fitted with threaded
bolts on the coupling face of rotor and two numbers of locating pins to locate the
jig circumferentially and also to arrest the circumferential movement of the jig
during working.

WE CLAIM
1. A jig for drilling axial holes for core bar housing turbo generator
rotor/exciter rotor comprising:
- one 'O' shaped thick steel plate with a plurality of peripheral holes
and a plurality of centre holes co-axially matching with the
peripheral holes;
- one face of the jig to be matched with flange of the coupling face
of generator rotor shaft have two step down recesses at a diameter
of 300 and 235 mm equi -axixed from centre of the jig;
- the opposite face of the jig to be matched with the flange of
coupling face of exciter rotor shaft, have one protruded color and a
recess of 235 mm up to the depth of 4 mm;
characterised in that the said jig assists in drilling a plurality of
peripheral holes and a plurality of centre holes co-axially matched
with the peripherals and recess faces on both sides accommodates
the protruded part of the core bar fitted with turbo generator rotor
and exciter rotor.

The present invention relates to a jig for drilling axial holes for core bar housing
turbo generator rotor/exciter rotor comprising one 'O' shaped thick steel plate with a plurality of peripheral holes and a plurality of centre holes co-axially matching with the peripheral holes and one face of the jig to be matched with flange of the coupling face of generator rotor shaft have two step down recesses
at a diameter of 300 and 235 mm equi-axixed from centre of the jig and the opposite face of the jig to be matched with the flange of coupling face of exciter rotor shaft, have one protruded color and a recess of 235 mm up to the depth of
4 mm characterised in that the said jig assists in drilling a plurality of peripheral holes and a plurality of centre holes co-axially matched with the peripherals and recess faces on both sides accommodates the protruded part of the core bar fitted with turbo generator rotor and exciter rotor.