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 tool, for regaining of bushing inner diameter, and an apparatus using said tool.
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTORS
Jadhav Rajendra and Patil Narendra; both of Crompton Greaves Ltd., Switchgear complex,S3 division, A3, MIDC, Ambad, Nashik-422010, India; both 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 circuit breakers.
Particularly, this invention relates to the field of arc assist circuit breakers.
More particularly, this invention relates to a tool, for regaining of bushing inner diameter, and an apparatus using said tool.
BACKGROUND OF THE INVENTION:
Circuit Breaker mechanisms are used in electrical equipment, as an adjunct mechanism, for preventing said electrical equipment from current / voltage aberrations such as overload, short circuit, or the like. Basically, it is designed to detect a fault condition, and operates to interrupt the working of the associated electrical equipment upon detection, thereby saving its health.
High-voltage circuit-breakers have greatly changed since they were first introduced about 40 years ago, and several interrupting principles have been developed that have contributed successively to a large reduction of the operating energy. These breakers are available for indoor or outdoor applications, the latter being in the form of breaker poles housed in ceramic insulators mounted on a structure.
Current interruption in a high-voltage circuit-breaker is obtained by separating two contacts in a medium, such as SF6, having excellent dielectric and arc quenching properties. After contact separation, current is

carried through an arc and is interrupted when this arc is cooled by a gas blast of sufficient intensity.
A piston, in a circuit breaker, is an essential component in order to open and close the circuit breaker. In one kind of SF6 circuit breakers, the relative movement of a piston and a cylinder linked to the moving part is used to generate the pressure rise necessary to blast the arc via a nozzle made of insulating material. In this technique, the pressure rise is obtained mainly by gas compression. The piston movement is directly proportion to breaker tripping time.
In the arc assist technology, a grooved piston is used, with an axial inner groove. A Teflon bushing is introduced in this axial inner groove in place of dry bearings (or DU bush). This bush, in the piston, is required to give smooth movement and support to piston rod (of moving contact assembly).
According to one exemplary embodiment, the dimension of groove in piston, typically, is 40mm +0.1 to +0.2; width is 5.5mm. Typically, the inner diameter of Teflon bushing is 35mm +0.1 to +0.2, and outer diameter of Teflon bushing is 40mm - 0.1 mm; with width being 5 mm.
The design requirement is Piston rod of diameter 35 mm so that it should move smoothly through these Teflon bushes.
After fitment of Teflon ring in Piston groove, the inner diameter of Teflon bushing ring gets compressed to 34.5mm to 34.8mm which prevents the entry of piston rod in the piston. To overcome this limitation and to 'regain'

the inner diameter of Teflon ring more than 35 mm, a filling process is used; which leads to uneven expansion of inner diameter and rough contact surface. This is a relatively crude filling process.
Further effect of this filling process is that, approximately, about 30% circuit breakers fail in final testing due to inability to achieve speed and timing as per rated specification.
There is a need to obviate the limitations of the prior art.
OBJECTS OF THE INVENTION:
An object of the invention is to provide a tool which aids in regaining bushing inner diameter after its fitment into a groove of a piston.
Another object of the invention is to provide a tool which aids in regaining bushing inner diameter after its fitment into a groove of a piston, in a smooth and efficient manner.
Yet another object of the invention is to provide a tool which aids in regaining bushing inner diameter after its fitment into a groove of a piston, without damage to the bush.
Still another object of the invention is to provide a tool which eliminates the crude filling process of the prior art.

An additional object of the invention is to provide a grasping fit between a piston rod and enveloping bushing fitted in a groove of a piston.
Yet an additional object of the invention is to provide even expansion of inner diameter of bushing after its fitment into a groove of a piston.
Still an additional object of the invention is to provide a smooth contact surface at the inner diameter of the bushing after its fitment into a groove of a piston.
Another additional object of the invention is to provide a smooth fit between a piston rod and enveloping bushing fitted in a groove of a piston.
Yet another additional object of the invention is to avoid manual skill and effort in order to provide a fit between a piston rod and enveloping bushing fitted in a groove of a piston.
Still another additional object of the invention is to provide accurate inner diameter of bushing after its fitment into groove of a piston.
SUMMARY OF THE INVENTION:
According to this invention, there is provided a tool, for regaining of bushing inner diameter, after fitment in piston groove, said tool being an elongate, substantially cylindrical, rod with pre-defined segments of body across its length in order to facilitate its smooth entry into the bushing and

further matching the tool outer diameter with said bushing inner diameter, said tool comprises:
a. a first operative bottom region such that it tapers from its operative
top to its operative bottom end with an operative top portion adapted
to match said inner diameter of said bushing, and with a tapered
region ensuring traverse of said tool through said bushing; and
b. a second operative middle region being a shaft member with its
diameter relatively lesser than said first operative bottom region, said
second operative middle region being a load transfer member of said
tool.
According to this invention, there is also provided an apparatus for regaining of bushing inner diameter, after fitment in piston groove, said apparatus comprises a tool, for regaining of bushing inner diameter, after fitment in piston groove, said tool being an elongate, substantially cylindrical, rod with pre-defined segments of body across its length in order to facilitate its smooth entry into the bushing and further matching the tool outer diameter with said bushing inner diameter, said tool comprises:
i. a first operative bottom region such that it tapers from its operative top to its operative bottom end with an operative top portion adapted to match said inner diameter of said bushing, and with a tapered region ensuring traverse of said tool through said bushing; and ii. a second operative middle region being a shaft member with its diameter relatively lesser than said first operative bottom region, said second operative middle region being a load transfer member of said tool;

said tool actuated by a hand press means in an operative vertical upward and downward manner.
Typically, said tool comprising a third operative top region (head) adapted to be a portion of said load transfer member.
Alternatively, said hand press means is a machine operated means.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
The invention will now be described in relation to the accompanying drawings, in which:
Figure la illustrates an isometric view of a bushing ring; Figure lb illustrates a top view of a bushing ring; Figure lc illustrates a side view of a bushing ring;
Figure 2 illustrates a piston which is a substantially cylindrical, axially grooved, plate. The groove, in this piston, is a through-hole; and
Figure 3 illustrates a piston with a bushing fitted into the groove channel of the piston.
Figure 4 illustrates the tool;
Figure 5a illustrates a tool fitted into a piston groove with a bushing
enveloping the tool; and

Figure 5b illustrates an apparatus incorporating the tool, which apparatus operated the tool by means of a hand press.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
According to this invention, there is provided a tool for regaining of bushing inner diameter, after fitment in piston groove.
Figure la illustrates an isometric view of a bushing ring (10). Figure lb illustrates a top view of a bushing ring (10). Figure lc illustrates a side view of a bushing ring (10). Typically, the bushing is a Teflon bushing. The bushing is an annular rim.
Figure 2 illustrates a piston (20) which is a substantially cylindrical, axially grooved, plate. The groove (22), in this piston, is a through-hole.
Figure 3 illustrates a piston (20) with a bushing (10) fitted into the groove channel (22) of the piston. After fitment, the bushing inner diameter gets compressed, and does not match the exact outer diameter of a piston rod which should enter the groove. This results in a bad fit, and crude filling, according to the prior art was carried out to enable a better fit.
Figure 4 illustrates the tool (100).
In accordance with an embodiment of this invention, the tool (100) is an elongate, substantially cylindrical, rod with pre-defmed segments of body across its length.

In accordance with another embodiment of this invention, there is provided a first operative bottom region (102) of the tool such that it tapers from the operative top to the operative bottom end. The operative top portion (102a) of the first operative bottom region is adapted to match the inner diameter of the bushing (10). The tapered region (102b), in general, ensures that the tool can smoothly guide through the bushing and is provided for initial engagement of the tool with the bushing.
In accordance with yet another embodiment of this invention, there is provided a second operative middle region (104) of the tool which is a shaft with its diameter relatively lesser than the operative bottom region. This shaft is the load transfer member of the tool.
In accordance with still another embodiment of this invention, there is provided a third operative top region (106) (head) of the tool which is also a portion of the load transfer member.
Figure 5a illustrates a tool (100) fitted into a piston (20) groove with a bushing enveloping the tool.
Figure 5b illustrates an apparatus (200) incorporating the tool, which apparatus operated the tool by means of a hand press, such that the following conditions are met:
1) Inner diameter surface finish should not be disturbed;
2) Inner diameter should be in accordance with pre-defined tolerance levels;
3) Circuit breaker should achieve required speed and timing.

In accordance with an additional embodiment of this invention, there is provided a hand press apparatus comprising the tool (100) and means to actuate the operation of the tool. The operation of the tool, typically, is in an operative vertical upward and downward manner.
The apparatus is used for load transfer of tool in an operative vertical motion using hand press for passing through the bushing inner diameter.The tool is designed in such a way that it will be easily engaged in compressed inner diameter of the bushing or the Teflon ring. The tool should be passed through in the piston support and piston. Exhaustive manual skill and manual effort is avoided for the operation of this tool.
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 tool, for regaining of bushing inner diameter, after fitment in piston groove, said tool being an elongate, substantially cylindrical, rod with pre-defined segments of body across its length in order to facilitate its smooth entry into the bushing and further matching the tool outer diameter with said bushing inner diameter, said tool comprising:
a. a first operative bottom region such that it tapers from its operative
top to its operative bottom end with an operative top portion adapted
to match said inner diameter of said bushing, and with a tapered
region ensuring traverse of said tool through said bushing; and
b. a second operative middle region being a shaft member with its
diameter relatively lesser than said first operative bottom region, said
second operative middle region being a load transfer member of said
tool.
2. A tool as claimed in claim 1 wherein, said tool comprising a third operative top region (head) adapted to be a portion of said load transfer member.
3. An apparatus for regaining of bushing inner diameter, after fitment in piston groove, said apparatus comprising a tool, for regaining of bushing inner diameter, after fitment in piston groove, said tool being an elongate, substantially cylindrical, rod with pre-defined segments of body across its length in order to facilitate its smooth entry into the bushing and further matching the tool outer diameter with said bushing inner diameter, said tool comprising:

i. a first operative bottom region such that it tapers from its operative top to its operative bottom end with an operative top portion adapted to match said inner diameter of said bushing, and with a tapered region ensuring traverse of said tool through said bushing; and ii. a second operative middle region being a shaft member with its diameter relatively lesser than said first operative bottom region, said second operative middle region being a load transfer member of said tool;
said tool actuated by a hand press means in an operative vertical upward
and downward manner.
4. An apparatus as claimed in claim 3 wherein, said tool comprising a third operative top region (head) adapted to be a portion of said load transfer member.
5. An apparatus as claimed in claim 3 wherein, said hand press means is a machine operated means.