FIELD OF THE INVENTION:
The present invention is related to an improved Stator Core Pressing Plate adaptable to hydrogenerator to ensure proper pressure distribution in Stator Core.
BACKGROUND OF THE INVENTION:
BHEL is a pioneer in manufacturing and commissioning large number of Hydro Generators. Variety of changes have been made in the design philosophy of stator core pressing plate based on manufacturing and operating experience of machines to reduce errors, time cycle and cost. BHEL adopted pressing plate design as shown in fig. 1 in most of stator core design since 1970.
Working principle of pressing plate is to transfer the required pressure on stator core at tooth as well as back of core portion by fingers which is welded to a plate as per design requirement.

In this arrangement first fingers are directly welded to machined surface of bottom plate of stator frame after making a layout of stator punching to ensure correct location of fingers beneath tooth portion. Then, complete welding of fingers is carried out and checked further for any cracks by NDT. Grinding is done on top of fingers to achieve a levelled surface for sitting of stator punching.
Then, the punchings are stacked to the required height and core thus formed is pressed with the help of top pressing plate with fingers.
For top pressing plate, fingers are welded to a pre-machined plate at the same angle in which slots are made in stator punching. Then, machining of each pressing plate with fingers is carried out as per design requirement.
In this process the pressing plates have to pass through different operations like fabrication of plates, machining of plates, welding of fingers on machined plates, NDT check of welds and machining of the complete assembly as per design requirement including drilling and tapping of different holes. Thus it has to be routed through fabrication and machine shop number of times which increases the product time cycle, as number of movement of job is more. Refer fig. 2A, 2B. Also, design margins are kept in all stages to ensure error

free pressing plate, viz. extra thickness in pre-machined plate and fingers. Lots of problems were faced during manufacturing of these pressing plates even after using templates and fixtures. Each time a modification had to be carried out to suit core punching tooth and core studs.
Hydro Generator is a tailor made product, thus, every time for a new design, a new pressing plate with fingers is designed.
Over the year manufacturing of pressing plate along with fingers has gone through modification and improvement.
Then, a second arrangement was tried to reduce errors and manufacturing cycle time. In this arrangement an independent finger plate for top and bottom side of the core was made separately. The finger plate was first assembled to bottom side of machined surface of the stator frame and stacking of core is carried out to the required height. Then, the core is pressed by top finger plate which is being pressed and held by a separate machined pressing plate. Both top and bottom finger plates are screwed to top pressing plate and bottom plate of stator frame respectively. Refer fig. 3.

This method improved over the first method and thus, reduced error and time cycle.
However, for each design time consumed to manufacture accurate pressing plates was of higher order. Figure 3A shows arrangement of pressing plate.
A third arrangement was also tried to reduce error and time cycles. In this method complete fully finished cast pressing plate with fingers was manufactured independently and directly deployed to build the core. In this arrangement finger plates were assembled at the bottom and top of core. Bottom finger plate is independent of stator frame. After completing the core building the core is pressed with the help of core studs and jacking screws. Refer fig. 4 & 4A. This process was error free, but cost of manufacturing cast pressing plate was the main factor to re-think for a new alternation and modification.
OBJECTS OF THE INVENTION:
It is therefore, an object of the present invention is to propose an improved stator core pressing plate which eliminates the disadvantages of the existing state of art.

Another object of the present invention is to propose an improved stator core pressing plate which reduces the movement of job through different manufacturing departments.
A further object of the present invention is to propose an improved stator core pressing plate which reduces the cost of manufacturing as it is made from a single piece.
A still further object of the present invention is to propose an improved stator core pressing plate which eliminates NDT testing.
An yet further object of the present invention is to propose an improved stator core pressing plate which achieves accurate pitch of fingers as the job is checked directly with 1:1 templates.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Fig. 1: Arrangement of fingers and pressing plate (Prior Art).
Fig. 2A: Pressing plate and finger (Prior Art).
Fig. 2B: Pressing plate assy (Prior Art).
Fig. 3: Arrangement of finger plate and pressing plate (Prior Art).
Fig. 3A: Pressing and finger plate (Prior Art).
Fig. 4: Arrangement of casted finger cum pressing plate (Prior Art).
Fig. 4A: Pressing plate cast finished (Prior Art).

Fig. 5: Arrangement of fabricated finger cum pressing plate (Prior
Art). Fig. 5A: Pressing plate fabricated as per new invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION:
The present invention is provided with an integrated construction wherein the finger parts (2) and stator core plate (1) are made from a single metallic body. The improved stator core plate (1) having a plurality of identical finger parts (2) configured at a distal end of the plate (1) through a machining process. Each finger (2) having a half round shaped contour (3) at the peak and a half round shaped contour (4) at the valley between the two fingers. Fingers (2) are identical in shape and size and having a width (5) and a height (6) and a plurality gap provided in between the fingers and the width of the gap same as that of width of the finger.
The right edge and the left edge of the plate having identical contour w.r.t to the centre line of the plate which comprises one outward

taper line followed by an inward taper line from the bottom edge. The top edge is a straight line. The proximate end of the plate consists of a plurality of holes (6) for lifting with crane, a set of holes (7) for fastening core stud, and a number of holes (8) for Jacking Screw. The stator core plate is prepared from a (50 to 63) flat plate as required from stress design calculation and the plate is ultrasonically tested. One template of top pressing plate with fingers are placed on flat sheet (1). Marking according to the contour of the template was made on the flat plate. Machining the plate by using CNC machine according to marking point of the steel plate. Thereafter smooth surface is prepared by grinding around the finger (2) portion. Two holes (6) are drilled for lifting the material by crane. A plurality of holes (7) is made for fastening core studs. A plurality of holes (8) is made for fastening jacking screws.

WE CLAIM:
1. An improved Stator Core Pressing Plate adaptable to
hydrogenerator in a Stator Core comprising:
- a pressing plate having a plurality of finger parts configured at a distal end through machining process;
- the fingers each provided with a half round shaped contour a peak and valley;
- a plurality of holes provided along the proximate end of the Pressing Plate for lifting, fastening core stud and Jacking Screw;
characterized in that, the Pressing Plate constitutes a single piece, in that the plurality of fingers are identical in respect of shape and size and in that a plurality of identical gaps corresponding to the width of the fingers between the fingers to ensure an optimum distribution of the pressure when affixed to the Stator Core.
2. A process of manufacturing of improved Stator Core Pressing
Plate as claimed in claim 1, comprising the steps of:
- selecting a pressed flat steel plate having ultrasonically
tested;

- placing the template (1:1) on the flat steel plate;
- marking the steel plate matching with the contour of template;
- machining the steel plate according to marking point;
- grinding the fingers of core pressing plate for smooth surface finish;
- drilling a plurality of holes for lifting;
- drilling a plurality of holes for fastening core studs;
- drilling a plurality of holes for fastening;
3. An improved Stator Core Pressing Plate as claimed in claim 1 wherein the required thickness of steel plate is of 50 to 63 mm as per stress design calculation.

The present invention is provided with an improved Stator Core Pressing Plate adaptable to hydrogenerator in a Stator Core comprising a pressing plate having a plurality of finger parts configured at a distal end through machining process; the fingers each provided with a half round shaped contour a peak and valley; a plurality of holes provided along the proximate end of the Pressing Plate for lifting, fastening core stud and Jacking Screw; characterized in that, the Pressing Plate constitutes a single piece, in that the plurality of fingers are identical in respect of shape and size and in that a plurality of identical gaps corresponding to the width of the fingers between the fingers to ensure an optimum distribution of the pressure when affixed to the Stator Core.