FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003 As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION (See section 10 and rule 13)
TITLE OF THE INVENTION
A pressure exerting jack APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTORS
Chandrashekhar Kate and Siddarth Rakhra of Crompton Greaves Ltd, Power Transformer division (Tl), Kanjur Marg (East), Mumbai, Maharashtra, India, both Indian Nationals
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed:

FIELD OF THE INVENTION
This invention relates to a pressure exerting jack.
BACKGROUND OF THE INVENTION
Transformer windings are required to be compressed, as a part of the manufacturing process, to keep the transformers windings as tight as possible for removing moisture therefrom and to achieve a desired height of the transformer. The amount of compression force to be applied on the transformer windings depends upon the design of the transformer. For example, for a 315MVA/400kV transformer, around 240 tons of compression force is required to be exerted on the transformer windings. For compressing the transformer windings it is placed in a clamping stand comprising a base plate held on the ground and a plurality of spaced apart clamping studs projecting vertically from around the center of a base plate. The clamping studs remain disposed within the inner diameter of the transformer windings. A pressure exerting jack is placed atop the transformer windings. The jack comprises of a press plate and a jack plate held over the press plate in a spaced apart relationship by means of spacing studs. The press plate is placed atop the transformer windings. The hydraulic or pneumatic cylinders of the jack, whichever the case may be, are held within holes provided on the jack plate. Upon actuating the jack, piston from the cylinders from the jack exerts pressure on the press plate. Consequently, pressure is exerted on the transformer windings thereby compressing them. While the press plate is being exerted with pressure, reactive forces are exerted on the jack plate. In the event of excessive reactive forces, the jack plate is susceptible to bending. Thus the jack plate has to be sufficiently strong.

In the circumstances wherein high compression force is required to be exerted on the transformer windings, strength of the jack plate is also required to be adequately augmented. A simple method of increasing the strength of the jack plate is by increasing its thickness. However, an increase in thickness of the jack plate is always not feasible since it will lead to an increase in the weight of the jack plate and consequently the jack. Consequently, peripheral equipments required with the jack such as a crane required to lift the jack and place it on the transformer windings may also be required to be augmented appropriately or replaced altogether with a higher capacity. Such augmentation or replacement may be very costly. Therefore, there is a need to increase the strength the jack plate without a considerable increase in its weight.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention, there is provided a pressure exerting jack comprising a press plate, a jack plate held over the press plate in a spaced apart relationship therewith by means of spacer studs, a top surface of the jack plate comprising a plurality of spaced apart concentric endless stiffeners and a plurality of spaced apart radial stiffeners each extending from a center of the jack plate to an outer edge of the jack plate through the endless stiffeners and a cover plate smaller than the jack plate held over the jack plate and supported on the radial and circular stiffeners.
These and other aspects, features and advantages of the invention will be better understood with reference to the following detailed description, accompanying drawings and appended claims, in which,
Fig 1 is a perspective view of a pressure exerting jack.
Fig 2 is a schematic view of a pressure exerting jack placed on transformer
windings.

Fig 3 is an exploded view of Fig 2.
As shown in Figs 1-3, a pressure exerting jack comprises a circular press plate 1 and a circular jack plate 2 held concentrically over the press plate 1 in a spaced apart relationship with it by means of spacer studs (not shown). The top surface of the jack plate 2 comprises three spaced apart concentric circular stiffeners 3 placed around a center of the jack plate 2. Twelve radial stiffeners 4 are also provided on the top surface of the jack plate 2 each extending from the center of the jack plate 2 to an outer edge of the jack plate 2. The radial stiffeners 4 tapers along its length from the center of the jack plate 2. A cover plate 5, smaller in size as compared to the jack plate 2, is placed concentrically over the jack plate 2 and supported on the radial 4 and circular 3 stiffeners.
According to a preferred embodiment, the jack is hydraulic and comprises eighteen hydraulic cylinders (not shown) held within holes 6 on the top surface of the jack plate 2. The jack is designed to exert 500 tons of compression force on a 1200 kv transformer windings. The jack 2 and press plates 1 are of 3500 mm diameter and 50 mm thickness. At the center of the jack 2 and press 3 plates, a 200 mm diameter center hole is provided for easy maintenance and handling purposes. Each circular 3 and radial 4 stiffener and the cover plate 5 is of 25 mm thickness and made up of mild steel. The circular 3 and radial 4 stiffeners are welded on the top surface of the jack plate 2. The diameters of the three circular stiffeners 3 are 1300 mm (height - 110 mm), 2000 mm (height - 210 mm) and 2700 mm (height - 310 mm). It may be noted that the height of the circular stiffeners 3 may be same. The length of each radial stiffener 4 is 1550 mm and the height at its one end near the center of the jack plate 2 is 110 mm which goes on decreasing uniformly till 50 mm at its other end. The cover

plate 5 is of 1500 mm diameter and welded concentrically over the jack plate 2 on the on the top edges of the radial 4 and circular 3 stiffeners.
The transformer windings 7 is placed on a clamping stand comprising a base 8 held on the ground and twelve upstanding studs 9 projecting from the base 8- six at 1000 mm PCD of the base 8 of the clamping stand and six at 3300mm PCD of the base 8. The studs 9 at 1000 mm extends through the inner diameter of the transformer windings 7 and are received within corresponding holes in the press plate 1, jack plate 2 and cover plate 5 and fastened on the cover plate 5. The studs at 3300 mm are received within corresponding holes on the press plate 1 and jack plate 2 and fastened on the jack plate 2.
The jack is lifted by means of a crane and placed atop the transformer windings 7 such that the press plate 1 remains in contact with the transformer windings 7. Upon actuation of the jack, pistons from the cylinders of the jack emerge out and exert pressure on the press plate 1. Since the press plate 1 is placed on the transformer windings 7, the windings of the transformer are compressed. During the above compression, reactive forces are exerted on the jack plate 2.
In the aforementioned described embodiment, the weight of the jack plate 2 is 6.9 tons. Whereas, if the same jack plate was to be augmented to withstand 500T without the above mentioned reinforcements i.e. circular 3 and radial 4 stiffeners and cover plate 5, the thickness of the jack plate 2 had to be increased to 282 mm (appox) from 50 mm which would have lead to an increase in the weight of the jack plate 2 to 21 tons.
It will be obvious to a person skilled in the art that the above described dimensions are specific only to a specific embodiment and may vary as per

requirement. The press plate, jack plate, cover plate and circular stiffeners may not necessarily be circular.
According to the invention, the aforementioned reinforcements provided to increase the strength of the jack plate results in only a marginal increase in the weight of the jack plate as compared to a conventional method of increasing the strength of the jack plate by increasing its thickness. Limiting the weight of the jack plate in increasing its strength provides cost effectiveness and ease of handling the jack.
Although the invention has been described with reference to a specific embodiment, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiment, as well as alternate embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that such modifications can be made without departing from the scope of the invention as defined in the appended claims.

We claim:
1. A pressure exerting jack comprising a press plate, a jack plate held over the press plate in a spaced apart relationship therewith by means of spacer studs, a top surface of the jack plate comprising a plurality of spaced apart concentric endless stiffeners and a plurality of spaced apart radial stiffeners each extending from a center of the jack plate to an outer edge of the jack plate through the endless stiffeners and a cover plate smaller than the jack plate held over the jack plate and supported on the radial and circular stiffeners.
2. The jack as claimed in claim 1 is a hydraulic jack comprising hydraulic cylinders held in holes provided in the jack plate such that upon actuation of the jack, pistons from the hydraulic cylinders exerts pressure on the press plate.
3. The jack as claimed in claim 1, wherein the jack plate, press plate and the cover plate being circular and are held concentrically over each other.
4. The jack as claimed in claim 1, wherein the radial stiffeners being tapered along the length thereof towards the outer edges of the jack plate.
5. The jack as claimed in claim 1 is placed atop a transformer windings for exerting pressure thereupon.