FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
BUSHING FOR TRANSFORMERS;
RAYCHEM RPG PRIVATE LIMITED, A COMPANY INCORPORATED UNDER THE COMPANIES ACT, 1956, WHOSE ADDRESS IS RPG HOUSE, 463, DR. ANNIE BESANT ROAD, WORLI, MUMBAI -400030, MAHARASHTRA, INDIA
THE FOLLOWING SPECIFICATION
PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

FIELD OF THE INVENTION
The present invention relates to a bushing for electrical distribution transformers. BACKGROUND OF THE INVENTION
Electrical bushings find applications in electrical devices or apparatuses like
transformers, circuit breakers or gas insulated switchgears. Electrical bushings are very
essential and critical components to facilitate or establish electrical connectivity between outside
supply and internal parts of electrical apparatuses or devices and to avoid electrical break down
with the enclosures of the apparatuses or devices. Bushings for electrical distribution
transformers with mineral oil insulation or air insulation with air clearance have for some time
now been fitted on the cover or on the side walls of transformers immersed in oil or air, for
example distribution transformers, to obtain the outputs of the electrical terminations.
Traditionally known type bushings for high voltage (10) and low voltage transformers (20) comprise around 59 parts as shown in Figures 1A and 1B respectively and generally include single ceramic body in case of high voltage and two ceramic bodies (12) in case of low voltage which, once assembled, are held together and fixed to the transformer wall by means of a threaded conducting rod (14) which passes through them longitudinally, and appropriate washers and tightening nuts (16).
One of the two ceramic bodies is on the outer side of the wall that separates the inside of the transformer from the outside and the other ceramic body is located on the inner side of the wall. The two ceramic bodies are held together by means of a conducting rod which passes through the two bodies, and tightly packed by means of tightening nuts. During operation, inner

side ceramic body is immersed in the cooling oil of the transformer or cooled with Air in case of the air cooled transformer.
Due to the number of parts involved in the bushings, there are around 9 leakage points including a leakage point between the connection between the inner and outer ceramic body. Therefore more gaskets are required which involves skilled operations in case of oil cooled transformer.
Further, said gaskets are generally tightly packed between the ceramic bodies and the transformer wall, or between the ceramic body and any washers, nuts or other elements compacted together by means of a central conducting rod in order to form the assembled bushing. As a result of the compacting compression, said gaskets expand towards the outside where, they deteriorate fairly rapidly, losing their elasticity, undergoing permanent plastic deformation, becoming thin, cracking and no longer guaranteeing a good seat. This increases more maintenance.
Further, transformers are fixed at different heights and hence it makes difficult to replace the parts of the bushings at that height.
Furthermore, the presently available bushings are bulky, brittle and heavy as they are made of ceramics. Moreover, the ceramic parts break during the assembly or transportations and damage of the parts may hurt and not safe. They also require special storage arrangement which includes maintenance cost.
The objective of the present invention is to provide bushings for electrical transformers of known type to overcome atieast one of the above mentioned problems.

SUMMARY OF THE INVENTION
Accordingly, the present invention in one aspect provides a single piece bushings for
electrical transformers. The bushing comprises a conducting rod and an insulating body integrally formed on the conducting rod. The insulating body comprises a flange provided on the conducting rod with a cylindrical portion extending from both sides of the flange.
According to the present invention, the flange is provided at centre of the conducting rod for securing the bushing with the transformer.
In another aspect the present invention provides method for manufacturing single piece bushing, the method comprising the steps of: forming a liquefied mixture by mixing epoxy with hardener, plasticizer, accelerator and filler and moiding the liquefied mixture with a conductor rod or strip at a predetermined temperature and pressure to form the single piece bushing.
BRIEF DESCRIPTION OF THE DRAWINGS
Reference will be made to embodiments of the invention, examples of which may be
illustrated in the accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in the context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.
Figure 1 A, 1B shows a bushing of prior art.
Figure 2A, 2B show a bushing in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a single piece bushing for electrical transformers and a
method for manufacturing the same. The single piece bushing comprises a conducting rod and an insulating body integrally formed on the conducting rod. The insulating body comprises a flange and a cylindrical portion extending from both sides of the flange. Advantageously, the flange provided at the center for securing the bushing with the transformer. Alternatively, flange can be provided off center as per the requirements.
Reference will now be made to Figure 2A and 2B where a single piece bushing is explained in detail, where Figure 2A shows a bushing (100) according to the present invention for high voitage transformer and Figure 2B shows a bushing (200) according to the present invention for low voltage transformer.
As shown in Figure 2A and 2B, the bushing (100, 200) comprises a 'L'-shaped conducting rod or strip (110, 210) and an insulating body (120, 220).
According to the present invention, the conducting rod or strip (110, 210) is 'L' shaped and has means for electric connections provided at two ends of the rod (110, 210). The conducting rod (110, 210) illustrated in Fig 2A, 2B though has an 'L' shape the use of other shapes is also possible, and obvious to one skilled in the art. According to the present invention, the conducting rod (110, 210) is preferably made of material having 99.9% conductivity such as copper.
According to the present invention, a middle surface of the conducting rod or strip (110, 210) is roughened for adhering to the insulating body.
According to the present invention, the insulating body (120, 220) is integrally formed with the conducting rod. The insulating body includes a flange (122, 222) and a cylindrical

portion (124, 224) extending from both sides of the flange (122, 222). According to the present invention, the flange {122, 222) is provided at the centre of the conducting rod (120, 220). The flange (122, 222) is provided for securing the bushing (100, 200) with the transformer. In this regard, the bushing (100, 200) has means for securing (For e.g. holes) the bushing (100, 200) with the transformer and is fitted with the transformer through a single gasket. Advantageously, as the bushing (100, 200) of the present invention requires only single gasket for fitting over the transformer, it reduces potential for leakage.
The cylindrical portion (124) shown in bushing (100) of figure 2A for low voltage transformers has a non-planar surface, and the cylindrical portion (224) shown in bushing (200) of figure 2B for high voltage transformers has a planar surface.
In an embodiment of the invention, the insulating body (120, 220) is made of epoxy
material i.e. the flange (122, 222) and the cylindrical portion (124, 224) extending both side from
the flange (122, 222) are made from epoxy material.
According to the present invention the bushing (100, 200) is preferably adapted from outside of the transformer. Alternatively, the bushing (100, 200) of the present invention can be
adapted from the inside of transformer.
The present invention also provides a method for manufacturing the bushing according to the present invention, the method comprising steps of forming a liquefied mixture by mixing epoxy with hardener, plasticizer, accelerator and filler and molding the liquefied mixture with the conductor rod or strip at predetermined temperature and pressure to form a bushing.
According to the present invention, the step of forming the mixture includes heating the epoxy and mixing with hardener, plasticizer, accelerator and filler. Also, a pigment can be mixed

with the mixture as per requirement. In an embodiment of the invention, the hardener and accelerator is added to the mixture after stirring the heated mixture of epoxy, plasticizer, pigment and filler for a pre-determined time period, preferably thirty minutes. Once this mixture is formed, the mixture should be utilized within four hours.
According to the present invention, the step of step molding includes providing a conductor rod or strip in a mould and heating the mould at a predetermined molding temperature and adding the liquefied mixture to heated mould and curing to form the single piece bushing
According to the present invention, the curing is carried for 8 to 10 hours. After curing, the bushing may be machined if required and then inspected for visual and dimensional acceptability.
According to the present invention, the molding temperature is about 130-140°C.
According to the present invention, the molding pressure is 1.5 Kg/sq. cm.
The bushing of the present invention are interchangeable with existing Bushings and is a single piece as compare to the existing bushings and requires only four components for connecting including the bushing. As it requires only single gasket for fitting over the transformer, it reduced potential for leakage. Further, the bushing being molded there is component perfection in dimensions of the bushing and light in weight. Further, the shelf life is good as it does not contain breakable items like ceramics and no special storage means are required. Further, the bushing reduces electricity loss. The time require to manufacture the bushing is very less as compare to the existing bushings. Copper parts having 99.9% conductivity can be used in the present invention for manufacturing the bushing. As the bushing

of the present invention is a single piece, it gives more short circuit withstand capability and is very easy to install than the existing connectors and requires less time for installment.
Furthermore, the present invention allows using a copper strip as a conducting means which increases simplicity in mechanical fittings of the bushing on transformers.

We Claim:
1. A single piece bushing for electrical transformers, the bushing comprising:
a conducting rod; and
an insulating body integrally formed on the conducting rod, the insulating body having a flange provided on the conducting rod with a cylindrical portion extending from both sides of the flange, the flange provided for securing the bushing with the transformer.
2. The bushing as claimed in claim 1, wherein the flange is provided at the centre of the conducting rod.
3. The bushing as claimed in claim 1, wherein the insulating body is made from epoxy.
4. The bushing as claimed in claim 1, wherein the conducting rod is L-shaped.
5. The bushing as claimed in claim 1, wherein the cylindrical portion of the insulating body is a planar surface.
6. The bushing as claimed in claim 1, wherein the cylindrical portion of the insulating body is a non-planar surface.
7. A method for manufacturing single piece bushing, the method comprising the steps of:
forming a liquefied mixture by mixing epoxy with hardener, plasticizer, accelerator and filler; and

molding the liquefied mixture with a conductor rod or strip at predetermined temperature and pressure to form the single piece bushing.
8. The method as claimed in claim 6, wherein the step of forming the liquified mixture includes heating the epoxy and mixing with hardener, piasticizer, accelerator and filler.
9. The method as claimed in claim 7, wherein the step of molding includes providing the conductor rod or strip in a mould and heating the mould at a predetermined molding temperature and adding the liquefied mixture to the heated mould and curing to form the single piece bushing
10. The method as claimed in claim 7, wherein the mixture is formed under vacuum.
11. The method as claimed in claim 7 or 9, wherein the molding is carried out at a temperature between 130 to 140°C.
12. The method as claimed in claim 7, wherein the molding pressure is 1.5 kg/sq-cm.

13. The method as claimed in claim 7, wherein the method for manufacturing single piece bushing further comprises the step of curing the bushing.