Field of the invention;
The invention relates to the manufacture of stator bars for turbo generators
in general, and to pressing clamps for overhang of 500MW THDF type
stator bars in particular.
Background and prior art;
Stator winding in Turbo Generator is made of stator bars. These stator bars
are made of copper, formed in required shape.
This formed bar is passed through following stages for insulation:
First of all, the formed bar is taped at CNC Insulation Taping Machine and
then sent for impregnation. In impregnation process, taped insulated stator
bars are dipped in Hot Resin-Hardener mixture (Liquid Organic Material) at
70±5 °C.
After this, stator bars are placed on pressing wagon and then cured at 140
°C.
6 Stator bars are cured at a time on baking wagon.
Cured stator bars are delivered to finishing section for smoothening of the
edges and calibration of surface, if required for achieving proper dimension.
They are then handed over the quality control section.
In the process of pressing, bars are laid down on the wagon & then pressed
in two steps.

1- In first step, the slot portion is pressed by hydraulic machine.
2- In second step, over-hang portion of bar is pressed manually and then
pressing clamps are tightened on the overhang portion.
The process flow diagram for insulation of the formed bars is shown in
Fig.lA.
Drawbacks of the prior art:
During the pressing on baking wagon, several problems were faced.
1-Working space on Baking wagon is low as per its design.
2-Pressing is to be done on heated wagon at the temperature of 60 °C.
3-Hot Resin-Hardener starts dropping from overhang portion during
pressing.
4-Since the overhang portion is above the surface of heated wagon, its
temperature drops rapidly. This drop in temperature increases the
viscosity of Resin-Hardener in impregnated bars. So, whole process
of pressing has to be finished within 5-6 hours. Out of this the clamps
must be tightened within 4 hours at the most.
5-Average number of clamps on each over hang is 16. Total number of
overhangs are 12 i.e. 12x16=192 clamps have to be tightened within
the limited time available.
Analysis:
Often clamps are mounted improperly because of typical assembly of
pressing clamps which have to be assembled in very limited time in
congested area. This causes the problem in profile of overhang of
stator bars.

The present invention seeks to overcome the above mentioned drawbacks of
the prior art.
Objects of the invention:
An object of the invention is to provide a simpler clamp assembly.
Another object of the invention is to provide easier working in the congested
working space of the wagon.
Yet another object of the invention is to reduce the man power requirement
for assembly and tightening of the clamps.
A further object is to reduce the time taken for executing the job.
A still further object is to achieve less variation from standard dimensions
for overhang portions of stator bars.
Yet another object of the invention is to save cost of production of 500 MW
turbo generator stator bars.
Brief Description of Accompanying Drawings:
Fig. 1 shows the stator bar on pressing wagon.
Fig.lA shows the flow diagram of insulation process of the stator bars.
Fig.2 shows the assembled clamp in prior art.
Fig.3 shows the top plate of clamp.
Fig.4 shows the front plate of clamp.

Fig.5 shows two separate bolts as in prior art clamp.
Fig.6 shows a straight steel strip for joining the heads of two bolts as per
Fig.7.
Fig.7 shows the two bolts connected with steel strip according to the
invention.
Fig.8 shows the assembled clamp after modification according to the
invention.
The invention will now be described in details in an exemplary embodiment,
which is non-limiting. There can be other embodiments of the same
invention, all of which are deemed covered by this description.
Description of the preferred embodiment:
The formed stator bars, after taping and impregnation by dipping in hot
resin-hardener mixture are pressed on pressing wagon (8). Fig.l shows a
stator bar placed on pressing wagon (8). Its slot portion (7) is pressed
through hydraulic pressing device and its overhang portion (6) is pressed
through pressing clamps.
As best seen in Fig.2, the assembled clamp which is used in the prior art has
eight components. These are:-
two bolts (1); two nuts(2); two top clamp plates (3) and two front clamp
plates (4).
Details of the top and front clamp plates are shown in Fig.3 and Fig.4
respectively.

It is not possible for a single workman to assemble such a clamp on the
processing wagon all by himself. One workman is required to hold the two
bolts in position while the other workman must fit the nuts on the bolts for
the assembly of the clamp.
The congested floor of pressing wagon (8) makes the work very difficult
because the workman do not have enough room for comfortable working.
This renders the process more time-consuming and also results is poor
assembly of the clamps, which in turn gives improper shape to the overhang
portion (6). This calls for further shaping process of the overhang.
To overcome these drawbacks, in accordance with the invention, the two
bolts(l) as shown in Fig.5 are formed into a single component as shown in
Fig.6 by welding (9) the heads of the two bolts (1) with the straight steel
strip (5). In this process following two conditions must be met.
1. The longitudinal axes of both the bolts (1) must be kept at right
angles with the plane of straight steel strip (5). The dimensions of
the strip (5) can be varied to have different clamp sizes.
2. The distance between the longitudinal axes of the bolts must be
equal to the distance between the centers of the holes in top clamp
plate (3), so that they can be assembled.

With this modification, the two loose bolts (1) of the prior art are formed
into an integral part as shown in Fig.7. This modification makes it possible
for one workman to assemble the clamp all by himself, while being
positioned in the congested pressing wagon (8).
The modified pressing clamp according to the invention offers the following
advantages.
Man-power saving: After modification only single workman can assemble
and tighten of whole clamp instead of two workmen as in earlier process.
It means this modified process saves 50% man-power in 192 nos. clamp
assembly process.
Time Saving: Before modification, whole process of pressing of bars took
approx. five hours, in which assembly of 192 clamps took approx. 4 hours.
Because of modification in clamps, it takes approx. 2.5 hours. It makes
saving of 1.5 hours i.e. 30% reduction of time in whole process.
Quality Control: Dimensions in overhang portion of stator bars have less
variation from standard value but with in tolerance limit.
Saving in cost: It has been evaluated that total saving in cost (in one set of
500MW having 96 stator bars) through saving in man-hours including the
cost of modification in clamps is approx. 2 lakhs. Recurring nature of this
saving in the most attractive feature of this saving.

WE CLAIM :
1. A modified pressing clamp for overhang of 500 MW THDF type
stator bars comprising of:
- two bolts (1);
- two nuts (2);
- two top clamp plates (3);
- two front clamp plates (4); and
- a straight steel strip (5)
characterized in that the steel strip (5) is welded (9) to the heads of
the two bolts (1) to form an integral part to enable assembly of the
clamp by a single workman.
2. A modified pressing clamp as claimed in claim 1, wherein the
dimension of the said steel strip can be varied to have different clamp
sizes.
3. A modified pressing clamp as claimed in claim 1, wherein the
longitudinal axes of the bolts (1) are at right angles with the plane of the
straight steel strip (5).

4.A modified pressing clamp as claimed in claim 1, wherein the distance
between the longitudinal axes of the bolts (1) is equal to the distance
between centers of holes in top clamp plate (3).

A modified pressing clamp for overhang of 500 MW THDF type stator bars
comprising of two bolts (1), two nuts (2), two top clamp plates (3), two front
clamp plates (4), and a straight steel strip (5) characterized in that the steel
strip (5) is welded (9) to the heads of the two bolts (1) to form an integral
part to enable assembly of the clamp by a single workman.