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, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
An improved instrument transformer.
APPLICANT(S)
Crompton Greaves Limited, CG House, Dr. Annie Besant Road, Worli, Mumbai -400030, Maharashtra, India, an Indian Company
INVENTOR(S):
Upadhyay Pankaj, Kusale Sarang, Katti Sudarshan, Joshi Sachin; all of Crompton Greaves Limited, Industrial Design Centre (IDC), CG Global R&D, Bhaskara Building, Kanjur Marg (East), Mumbai - 400042, Maharashtra, India; all Indian Nationals.
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 current transformers and instrument transformers.
Particularly, this invention relates to an improved instrument transformer,
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 Faraday's 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.
Instrument transformer used for measuring the voltage and/or current in a circuit and are, typically, used in industries, in power stations, sub-stations and the like.
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.
PRIOR ART:
US8189323 discloses a gas-insulated switchgear apparatus including a cylindrical part that is mounted about a center conductor in a manner to surround it. It also discloses a tubular part in the cylindrical part.
US447I333 discloses a current transformer with a primary conductor as well as atubular part.
US4052685 discloses a current transformer, comprising U-shaped tubular conductor.

OBJECTS OF THE INVENTION:
An object of the invention is to eliminate multiple components from a transformer.
Another object of the invention is to eliminate leakage of oil from a transformer.
Yet another object of the invention is to reduce components in a transformer.
Still another object of the invention is to provide increased reliability in a transformer.
An additional object of the invention is to minimize weld joints in a transformer.
Yet an additional object of the invention is to eliminate gaskets from an assembly of a transformer.
SUMMARY OF THE INVENTION:
According to this invention, there is provided an improved instrument transformer comprising a transformer tank with secondary turns and a conducting assembly located within said tank and between said secondary turns, said improved instrument transformer comprises: i. a pair of elongate shafts with semi-circular cross section for its most part which further extends into a first laterally located rounded solid end, and the second laterally located end being of semi-circular cross section; ii. a pair of hollow tubular components, each of said pair of tubular components adapted to be ensconced over said pair of elongate shafts located over each other, said pair of elongate shafts and said pair of hollow tubular components forming a conducting assembly; and iii. insulating material adapted to fill in spaces between said conducting assembly.
Typically, each of said elongate shafts comprises a flat surface on one side and a rounded surface on the other side, said flat surfaces of said elongate shafts facing each other, in that, the second laterally located end of a first elongate shaft rests close to the first laterally located end of a

second elongate shaft and the first laterally located end of the first elongate shaft rests close to the second laterally located end of the first elongate shaft.
Typically, each of said elongate shafts comprises a flat surface on one side and a rounded surface on the other side, said flat surface of a first elongate shaft is spaced apart from the flat surface of a second elongate shaft.
Typically, the laterally located ends are rounded solid ends which jut out beyond the facing surfaces of the elongate shafts.
Typically, each of said pair of hollow tubular components comprises a first open end and a partially covered end, said first open end of the hollow tubular components being located medially with respect to said conducting assembly, said partially covered end being in proximity to said rounded solid ends of said elongate shafts.
Typically, each of said pair of hollow tubular components are spaced apart from each other as well as spaced apart from said elongate shafts to form said conducting assembly, in that, the partially covered end mates with the semi-circular end of said elongate shaft, in that, the semicircular end of the elongate shaft mates with the inner side of the partially covered end of the tubular component, where it is affixed.
Preferably, said insulation is epoxy based material or epoxy based resin.
Typically, said conducting assembly is welded, advantageously, to said transformer tank.
Typically, first primary turn is initiated by the first elongate shaft and second tubular component.
Typically, second primary turn is initiated by the second elongate shaft and first tubular component.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1 illustrates a primary turns' sub assembly fitted into an instrument transformer of the prior art; and
Figure 2 illustrates a current traversing path through various components of an instrument transformer of the prior art.
The invention will now be described in relation to the accompanying drawings, in which:
Figure 3 illustrates various components, discretely located, which form a part of the improved instrument transformer.
Figure 4a illustrates a pair of elongate shafts.
Figure 4b illustrates a pair of hollow tubular components ensconced over the pair of elongate shafts.
Figures 4c and Figure 5 illustrate cut-section views of the assembly formed in Figure 4b.
Figure 6 illustrates the assembly of Figure 4b fitted into a transformer tank, in a cut-sectionaf view.
Figure 7 illustrates the path for current loops after this assembly of Figure 4b is fitted into a transformer tank.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1 illustrates a primary turns' sub assembly fitted into an instrument transformer of the prior art.
Figure 2 illustrates a current traversing path through various components of an instrument transformer of the prior art.

In the instrument transformer (2) of the prior art, an assembly of conducting and insulating prefabricated components are used to create primary turns (4). Typically, the conducting prefabricated component is aluminium based pre-fabricated component. Typically, the insulating pre-fabricated component is epoxy based pre-fabricated component.
The arrangement is such that the current inlet is on one side of the transformer (called PI Side) and outlet is on the other side (called P2 Side). Whilst travelling from PI side to P2 side, the current traverses through the body of the transformer and eventually loops around an internal secondary coil. The output signals generated by the secondary coil are measured and further actions based on the measurement can take place.
Figure 1, of the accompanying drawings, show a cross-section of the instrument transformer of the prior art. This instrument transformer assembly of the primary turn comprises two concentric conductors i.e. an inner conductor which is solid and an outer conductor which is hollow.
There is a gap between these conductors which is maintained using insulating components. In such a construction, the tank is a live component, i.e. it helps in forming primary turns around a secondary coil.
Figure 3 shows how the current traverses through the conducting primary turn assembly and forms a loop around the secondary coil using the body as a live part.
The inner rod (6) is connected to incoming cable at the PI side. Current flows into the solid rod and at the other end the current flows through the tank to complete the 1st turn. Towards the PI side, the hollow rod is welded to the tank. The flowing current then takes this path and completes the second turn around the secondary coil. At the P2 end, it is necessary to insulate the conductor tube with the body to form a proper loop of current around the secondary coil. Also, since oil is used inside the tank, it is necessary to make the design leak proof. For accomplishing this, the prior art method is to use a subassembly of insulation (epoxy), conductor (aluminum), and fiberglass components and tighten, typically, using O-Rings. Reference numeral 8 refers to outer pipe.
Thus, it can be seen that to complete the primary turns' sub-assembly, there are a multitude of components. These components have to be assembled together in a leak-free manner. This is

achieved by using O-Rings at necessary positions. Due to the increase in the number of components, the overall reliability of the product decreases. The positions where the assembly is fixed using O-Rings becomes prone to leakage over a period of time.
Having such multitude of components also increases the number of processes and steps in assembly, which in turn increases the assembly time and creates the need to have a more diverse inventory during manufacturing.
The assembly also increases the difficulties in inspection and repair of the tank and sub assembly.
The electrical isolations required between the inner rod and hollow tube creates the need for an assembly that increases the overall size of the product.
The insulation (epoxy) based components require investments and the need for separate dies and fixtures which need to be pre-fabricated which, in turn, adds to the inventory
The cost of the product goes up due to the number of components, processes, and the assembly time required.
According to this invention, there is provided an improved instrument transformer.
Figure 3 illustrates various components, discretely located, which form a part of the improved instrument transformer.
Figure 4a illustrates a pair of elongate shafts.
Figure 4b illustrates a pair of hollow tubular components ensconced over the pair of elongate shafts.
Figures 4c and Figure 5 illustrate cut-section views of the assembly formed in Figure 4b.
In accordance with an embodiment of this invention, there is provided a pair of elongate shafts (12a, 12b) with semi-circular cross section for its most part which further extends into a first

laterally located rounded solid end. The second laterally located end is of semi-circular cross section. The elongate shafts have a flat surface on one side and a rounded surface on the other side. During assembly, the flat surfaces of the elongate shafts face each other, in that, the second laterally located end of a first elongate shaft rests close to the first laterally located end of a second elongate shaft and the first laterally located end of the first elongate shaft rests close to the second laterally located end of the first elongate shaft. After the assembly, the flat surface of the first elongate shaft is spaced apart from the flat surface of the second elongate shaft. Also, after assembly, the laterally located ends are rounded solid ends which jut out beyond the facing surfaces of the elongate shafts.
In accordance with another embodiment of this invention, there is provided a pair of hollow tubular components (14a, 14b); each tubular component adapted to be ensconced over the pair of elongate shafts located over each other. Each of the pair of hollow tubular components comprise a first open end and a partially covered end. The first open end of the hollow tubular components is located medially with respect to the assembly. The partially covered end is in proximity to the rounded solid ends of the elongate shafts. Furthermore, the two hollow tubular components are spaced apart from each other as well as spaced apart from the elongate shafts. The partially covered end mates with the semi-circular end of the elongate shaft, in that, the semi-circular end of the elongate shaft mates with the inner side of the partially covered end of the tubular component, where it is affixed.
In accordance with yet another embodiment of this invention, there is provided an insulating material (16) adapted to fill in the spaces between the conductors, which conductors are formed by the pair of elongate shafts and the pair of hollow tubular components. Typically, the insulation is epoxy based material or epoxy based resin.
This material is poured or inserted in between the cavities of the assembly; this creates a leak proof joint as well as reliable insulation. The poured epoxy, when cured, bonds with the pair of elongate shafts and the pair of tubular components and forms a leak proof joint. Also, after curing, the epoxy maintains the gap between the conductor surfaces and acts as an insulating material. Thus, the epoxy based material fulfills two of functional requirements for the rigid primary sub assembly. The pair of hollow tubular components is designed such that it is used as a member for welding on to the body and forming a placeholder for epoxy insulation material.

The welding of the hollow tubular component alleviates the need for any O-Rings or other
mechanical fastening components for prevention of oil leakage in between the component
interface. The welded joint creates a leak proof joint which is much more reliable than using 0-
Rings.
Reference numeral 22 refers to secondary turns.
Reference numeral 24 refers to oil in transformer tank (26).
On either side of the assembly, the interface between the pair of tubular components and the transformer tank is welded. This makes a reliable leak proof joint and removes any requirement of an O-Ring and fasteners.
The assembly of the pair of elongate shafts and the pair of hollow tubular components is welded (18) to the transformer assembly, advantageously.
Figure 6 illustrates the assembly of Figure 4b fitted into a transformer tank, in a cut-sectional view.
Figure 7 illustrates the path for current loops after this assembly of Figure 4b is fitted into a transformer tank.
The first primary turn is illustrated by reference numeral 'PI side'. This is initiated by the first elongate shaft (12a) and second tubular component (14b).
The second primary turn is illustrated by reference numeral 'P2 side'. This is initiated by the second elongate shaft (12b) and first tubular component (14a).
It can be seen that the path for the current loops around a secondary coil by traversing through the CT tank and a leak proof arrangement is achieved by using molded epoxy and welded joints at both ends. This fulfills the functional requirement of the transformer rigid primary turns sub assembly.
The TECHNICAL ADVANCEMENT of this invention lies in providing a low cost, reliable, and fool-proof primary turn sub assembly for use in current transformers. This construction is such

that it is leak proof and reduces the number of components. The assembly which fits in to the transformer tank assembly comprises essentially four components; viz, a pair of elongate shafts, and a pair of tubular components. The disparity of inventory is drastically reduced. This furthermore drastically reduces the cost of manufacturing, assembly time, and errors. Also, since the subassembly is much smaller in volume, it is easier to transport and store. The assembly removes any requirement of prefabricated epoxy components and thus reduces the die investment costs.
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. An improved instrument transformer comprising a transformer tank with secondary turns
and a conducting assembly located within said tank and between said secondary turns, said
improved instrument transformer comprising:
i. a pair of elongate shafts with semi-circular cross section for its most part which further extends into a first laterally located rounded solid end, and the second laterally located end being of semi-circular cross section;
ii. a pair of hollow tubular components, each of said pair of tubular components adapted to be ensconced over said pair of elongate shafts located over each other, said pair of elongate shafts and said pair of hollow tubular components forming a conducting assembly; and
iii. insulating material adapted to fill in spaces between said conducting assembly.
2. The improved instrument transformer as claimed in claim 1 wherein, each of said elongate shafts comprising a flat surface on one side and a rounded surface on the other side, said flat surfaces of said elongate shafts facing each other, in that, the second laterally located end of a first elongate shaft rests close to the first laterally located end of a second elongate shaft and the first laterally located end of the first elongate shaft rests close to the second laterally located end of the first elongate shaft.
3. The improved instrument transformer as claimed in claim 1 wherein, each of said elongate shafts comprising a flat surface on one side and a rounded surface on the other side, said flat surface of a first elongate shaft is spaced apart from the flat surface of a second elongate shaft.
4. The improved instrument transformer as claimed in claim 1 wherein, the laterally located ends are rounded solid ends which jut out beyond the facing surfaces of the elongate shafts.
5. The improved instrument transformer as claimed in claim 1 wherein, each of said pair of hollow tubular components comprises a first open end and a partially covered end, said first open end of the hollow tubular components being located medially with respect to said

conducting assembly, said partially covered end being in proximity to said rounded solid ends of said elongate shafts.
6. The improved instrument transformer as claimed in claim 1 wherein, each of said pair of hollow tubular components are spaced apart from each other as well as spaced apart from said elongate shafts to form said conducting assembly, in that, the partially covered end mates with the semi-circular end of said elongate shaft, in that, the semi-circular end of the elongate shaft mates with the inner side of the partially covered end of the tubular component, where it is affixed.
7. The improved instrument transformer as claimed in claim 1 wherein, said insulation is epoxy based material or epoxy based resin.
8. The improved instrument transformer as claimed in claim 1 wherein, said conducting assembly being welded, advantageously, to said transformer tank.
9. The improved instrument transformer as claimed in claim 1 wherein, first primary turn is initiated by the first elongate shaft and second tubular component.
10. The improved instrument transformer as claimed in claim 1 wherein, second primary turn is initiated by the second elongate shaft and first tubular component.