FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
AND
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2005
COMPLETE SPECIFICATION (See section 10 and rule 13)
TITLE OF THE INVENTION
A liquid nitrogen cooled pancake wound core and cast resin type transformer
using said core, thereof.
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTOR
Nair Sharath of Crompton Greaves Ltd., Transformer (T2) Division, Plot No. Tl & T2, MPAKVN Industrial Area, Malanapur, Distt. Bhind, Madhaya Pradesh, India; an Indian National.
PREAMBLE TO THE DESCRIPTION :
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

FIELD OF THE INVENTION:
This invention relates to the field of electrical and electronics engineering.
Particularly, this invention relates to the field of transformers.
More particularly, this invention relates to transformer windings.
Specifically, this invention relates to a liquid nitrogen cooled pancake wound core and cast resin type transformer using said core, thereof
BACKGROUND OF THE INVENTION:
A Transformer is an electrical device that transfers energy from one circuit to another by magnetic coupling without any moving parts. It works on the Principle of Faradays Law of Electromagnetic Induction together with other laws of electricity. When a magnetic flux linked with an electric circuit varies, an electro motive force (voltage) is generated in the electric circuit, proportional to the rate of variation of flux with time.
The basic functional components of the transformer are a core made of magnetic material, a primary winding, and a secondary winding. The primary winding is connected to a source of an alternating current and the secondary winding is connected to the output. As the alternating current flows through the primary winding, the change in current in the primary windings creates a time-varying magnetic flux in the core, which induces a voltage in the secondary windings.
There is insulation medium between the windings and the windings and core of the transformer which forms the core coil assembly of the transformer. This insulation

may be gas insulation, the gas being sulfur hexafluoride gas (SF6).
Transformers rated up to a few KVA can be adequately cooled by natural convective air-cooling, sometimes assisted by fans. Some transformers are immersed in specialized transformer oil that acts both as a cooling and insulatingmedium, thereby extending the lifetime of the insulation transformer. The transformers get heated due to iron and copper losses occurring in them. It is necessary to dissipate this heat so that the temperature of the winding is kept below the value at which the insulation begins to deteriorate. For efficient working of the transformer, it is required to maintain the temperature of the oil, which in turn maintains the temperature of the components of the transformer.
OBJECTS OF THE INVENTION:
According to the prior art cores are typically rectangular shaped. This results in relatively more short circuit forces.
An object of the invention is to use inter layer / inter coil cooling tubes with liquid nitrogen (LN2) in between foil wound pancake.
Another object of the invention is to provide windings which are possible to be worked at higher current densities.
Yet another object of the invention is to provide lower stray losses of windings.
Still another object of the invention is to provide space factor improvements over disc winding.

An additional object of the invention is to provide better Ampere-Turn balancing over layer winding.
SUMMARY OF THE INVENTION:
According to this invention, there is provided a liquid nitrogen cooled pancake wound core, said core comprises:
a. winding assembly comprising a plurality of annular rim shaped foil layers,
each pair of adjacent foil layers being interspersed with an annular rim
shaped insulation layer, said inner layer rim being spaced apart from said
outer layer rim by interlayer ducts; and
b. cooling tubes inserted between said interlayer ducts.
According to this invention, there is also provided a cast resin transformer comprising liquid nitrogen cooled pancake wound core, said core comprises: i. winding assembly comprising a plurality of annular rim shaped foil layers, each pair of adjacent foil layers being interspersed with an annular rim shaped insulation layer, said inner layer rim being spaced apart from said outer layer rim by interlayer ducts; and ii. cooling tubes inserted between said interlayer ducts.
Typically, said interlayer ducts are positioned at only one side of said winding, thereby rendering it an obround structure.
Typically, said first set of annular layers and foil layers are stacked to form an inner layer rim.

Typically, said second set of such annular layers and foil layers are stacked to form an outer layer rim.
Typically, said cooling tubes include gaps through which liquid nitrogen (LN2) comes in contact with said winding assembly.
According to this invention, there is still further provided a fixture for winding a winding assembly to obtain a wound core, said fixture comprises:
first rotating axle being placed above a second rotating axle which further being placed above a third rotating axle, said third rotating axle being motor driven, said first rotating axle and said second rotating axle being driven, secondarily in turn, by the drive of said third rotating axle, said first rotating axle containing a plurality of pancake shaped insulating sheets, said second rotating axle containing a plurality of pancake shaped conductor foils, said third rotating axle containing adjustable supports which receive said conductor coils and said insulating sheets in synchronism such that there is an overlap of said conductor foils with said insulating sheets to achieve winding assemblies.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
The invention will now be described in relation to the accompanying drawings, in which:
Figure 1 illustrates a top schematic view of the coils;
Figure 2 illustrates another cut-section view of the coils; and

Figure 3 illustrates a method of making the coils.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
According to this invention, there is provided a liquid nitrogen cooled pancake wound core and cast resin type transformer using said core, thereof.
Figure 1 illustrates a top schematic view of the coils.
Figure 2 illustrates another cut-section view of the coils.
Figure 3 illustrates a method of making the coils.
In accordance with an embodiment of this invention, there is provided a winding assembly comprising a plurality of annular rim shaped foil layers (22), each pair of adjacent foil layers being interspersed with an annular rim shaped insulation layer (24). A first set of such annular layers and foil layers are stacked to form an inner layer rim (12). A second set of such annular layers and foil layers are stacked to form an outer layer rim (14). The inner layer rim (12) is spaced apart from the outer layer rim (14) by interlayer ducts (16).
These ducts are positioned at only one side of the winding, thereby rendering it an obround structure.
In accordance with another embodiment of this invention, cooling tubes (18) are inserted between said interlayer ducts (16). These tubes have gaps through with liquid nitrogen (LN2) comes in contact with the winding assembly and thus

controls its temperature to the desired range. This allows the foil wound coil to be designed to work at higher current densities and thus save on the cost.
According to this invention, there is also provided a cast resin transformer using the winding assembly of this invention. Cast resin transformers are designed with cooling gaps between the casted part which allows air to circulate in between the gaps and hence cools the windings.
According to this invention, there is further provided a method of winding said winding assembly. These winding assemblies are formed using pancakes of foils. A first rotating axle (32) is placed above a second rotating axle (34) which is placed above a third rotating axle (36). The third rotating axle is motor (38) driven. The first rotating axle and the second rotating axle are not motor driven, but are driven by the drive of the third rotating axle which is effected on to the first rotating axle and the second rotating axle. The first rotating axle contains a plurality of pancake shaped insulating sheets (24). The second rotating axle contains a plurality of pancake shaped conductor foils (22). The third rotating axle contains adjustable supports (40) which receive the conductor coils (24) and the insulating sheets (24) in synchronism such that there is an overlap of conductor foils with insulating sheets to achieve winding assemblies.
The advantages of the invention include:
1. Cost reduction;
2. Lower stray losses;
3. Better mechanical strength due to inherent properties of foil current distribution;
4. Lower partial discharge value; and

5. Longer life.
While this detailed description has disclosed certain specific embodiments of the present invention for illustrative purposes, various modifications will be apparent to those skilled in the art which do not constitute departures from the spirit and scope of the invention as defined in the following claims, and it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

We claim,
1. A liquid nitrogen cooled pancake wound core, said core comprising:
a. winding assembly comprising a plurality of annular rim shaped foil
layers, each pair of adjacent foil layers being interspersed with an
annular rim shaped insulation layer, said inner layer rim being spaced
apart from said outer layer rim by interlayer ducts; and
b. cooling tubes inserted between said interlayer ducts,
2. A core as claimed in claim 1 wherein, said interlayer ducts are positioned at only one side of said winding, thereby rendering it an obround structure.
3. A core as claimed in claim 1 wherein, said first set of annular layers and foil layers are stacked to form an inner layer rim.
4. A core as claimed in claim 1 wherein, said second set of such annular layers and foil layers are stacked to form an outer layer rim.
5. A core as claimed in claim 1 wherein, said cooling tubes include gaps through which liquid nitrogen (LN2) comes in contact with said winding assembly.
6. A cast resin transformer comprising liquid nitrogen cooled pancake wound core, said core comprising:
i. winding assembly comprising a plurality of annular rim shaped foil layers, each pair of adjacent foil layers being interspersed with an

annular rim shaped insulation layer, said inner layer rim being spaced apart from said outer layer rim by interlayer ducts; and ii. cooling tubes inserted between said interlayer ducts.
7. A core as claimed in claim 1 wherein, said interlayer ducts are positioned at only one side of said winding, thereby rendering it an obround structure.
8. A core as claimed in claim 1 wherein, said first set of annular layers and foil layers are stacked to form an inner layer rim.
9. A core as claimed in claim 1 wherein, said second set of such annular layers and foil layers are stacked to form an outer layer rim.
10. A core as claimed in claim 1 wherein, said cooling tubes include gaps through which liquid nitrogen (LN2) comes in contact with said winding assembly.
11. A fixture for winding a winding assembly to obtain a wound core, said fixture comprising:
first rotating axle being placed above a second rotating axle which further being placed above a third rotating axle, said third rotating axle being motor driven, said first rotating axle and said second rotating axle being driven, secondarily in turn, by the drive of said third rotating axle, said first rotating axle containing a plurality of pancake shaped insulating sheets, said second rotating axle containing a plurality of pancake shaped conductor foils, said third rotating axle containing adjustable supports which receive said conductor coils and said

insulating sheets in synchronism such that there is an overlap of said conductor foils with said insulating sheets to achieve winding assemblies.