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 contact for isolators and an improved turn-and-twist isolator mechanism.
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTOR
Sathe Mahesh of Crompton Greaves Ltd, Industrial Design Centre, Global R&D, Crompton Greaves, Kanjurmarg (East), Mumbai- 400042 Maharashtra, 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 engineering. Particularly, this invention relates to the field of isolators or disconnectors. More particularly, this invention relates to turn and twist type isolators. Specifically, this invention relates to a contact for isolators.
BACKGROUND OF THE INVENTION:
Isolator switch is used to make sure that an electrical circuit can be completely de-
energized for service or maintenance. Such switches are often found in electrical
distribution and industrial applications where machinery must have its source of driving
power removed for adjustment or repair. High-voltage isolation switches are used in
electrical substations to allow isolation of apparatus such as circuit breakers and
transformers, and transmission lines, for maintenance.
In order to ground all the residual voltage, an earth switch with finger contacts is provided. This isolator finger contacts receive an operating rod, connected to ground (earth), which grounds the charge. Typically, there are provided a pair of finger contacts with face opposite to each other, and the operating rod is adapted to slide in between said two finger contacts. The contacts include a stopper element, in between its faces, in a position placed posterior to said contacts, in order to stop the operating rod motion from its operative resting position to its operative active position in between said faces of contacts so as to mate with the contact faces, for transfer of charge from said contact faces to operating rod.
Present Isolator Contact where flexibility to get proper face to face contact between operating rod and contact is provided by adjustment of contact gap and spring loading on moving contact do not offer perfect face to face contact and on line adjustment of contact is cumbersome and not accurate.

A continuous process of operating rod being inserted and withdrawn from said contacts, leads to the arms of the fixed contacts being spaced apart, thereby not providing the required contact.
There is a need to overcome the limitations of the prior art.
OBJECTS OF THE INVENTION:
An object of the invention is to provide an improved fixed contact assembly which
eliminates or reduces contact stress.
Another object of the invention is to provide a robust fixed contact assembly.
Yet another object of the invention is to reduce operating force of operating rod contact
with fixed contact assembly of isolator.
Still another object of the invention is to provide proper face contact in earthing
assemblies, for full earthing.
An additional object of the invention is to provide controlled operating rod slip in the
twist mechanism component.
Yet an additional object of the invention is to provide zero lateral forces on spring of
fixed contact, ensuring factory setting all the time.
SUMMARY OF THE INVENTION:
According to this invention, there is provided a contact for isolators and an improved
turn-and-twist isolator mechanism, thereby, said contact comprises;
a. a pair of opposing, spaced apart, co-axially aligned contacts (upper contact and lower contact), each contact having a first cylinder with a disc base and a central hollow portion there-through, said disc base being the mating face of said contact which receives an elliptical end section of an operating rod, with mating faces of spaced apart contacts adapted to face each other, said mating face being a recessed helical plane, in that, a horizontal seam from an edge of the disc base to the central hollow circumference forms a step adapted to provide a helical plane about said central hollow, starting from the raised portion of the step helically wrapping about the central hollow until the foot of the step; and

b. second cylinder ensconced co-axially within said first cylinder, said second cylinder being a helically grooved cylinder on its outer surface, which surface is in contact with the inner surface of said first cylinder, wherein said second cylinder is a ball bush cylinder such that there is operative movement of said second cylinder in a co-axial manner with respect to said first cylinder, in that, said ball bush configuration providing a frictionless play to said second cylinder and wherein, the provisioning of said helical grooves imparts rotary movement about bush axis apart from upward-downward movement along bush axis.
Typically, said contact includes said seam with a pre-defined length, the length of said seam being equal to the major axis of said elliptical end section of said operating rod. Typically, said contact includes a back-up compression spring provided to ensure required contact pressure on receivable said elliptical end section of said operating rod. Typically, said operating rod includes an elliptical end section with recessed operative mating surfaces to match said step of said disc base.
According to this invention, there is provided a method for making contact, for isolators,
and providing an improved turn-and-twist isolator mechanism, thereby, said method
comprises the steps of:
i. turning an operating rod with elliptical section at its two extreme ends, parallel to
an operative horizontal plane, in an operative horizontal plane by approximately
45 degrees around the central axis of a central bushing out of a set of three
bushings per phase, thereby allowing rod entry inside a fixed contact with helical
groove ball bush on two extreme bushings out of the three bushings per phase,
said fixed contact comprising: a pair of opposing, spaced apart, co-axially aligned
contacts, each contact having a first cylinder with a disc base with a central
hollow there-through, said disc base being the mating face of said contact which
receives said elliptical end section of said operating rod, with mating faces of
spaced apart contacts adapted to face each other, said mating face being a
recessed helical plane, in that, a horizontal seam from the edge to the central
hollow circumference forms a step adapted to provide a helical plane about the

central hollow starting from the raised portion of the step helically wrapping about the central hollow until the foot of the step, wherein, said step is a sloping surface; and second cylinder ensconced co-axially within said first cylinder, said second cylinder being a helically grooved cylinder on its outer surface, which surface is in contact with the inner surface of said first cylinder, wherein said second cylinder is a ball bush cylinder such that there is operative movement of said second cylinder in a co-axial manner with respect to said first cylinder, in that, said ball bush configuration providing a frictionless play to said second cylinder and wherein, the provisioning of said helical grooves imparts rotary movement about bush axis apart from upward-downward movement along bush axis; and ii. twisting said operating rod by 90 degrees about the rod axis without allowing any rotation of rod about central bushing axis, by traversing the slope of said seam such that a recessed portion in the operative lateral mating edge of said end section of said operating rod matches said step, thereby making elliptical section of operating rod at two ends with elliptical portion to rotate said second cylinder carrying helical contact resulting in upward lift for first cylinder of said upper contact and downward fall for first cylinder of said lower contact, thereby ensuring that at the time of closure of 90 degree twist movement, the bush contact helix open end makes a contact with the operating rod in the portion where the operating rod is cut.
According to this invention, there is provided a method for breaking contact, for isolators,
and providing an improved turn-and-twist isolator mechanism, thereby, said method
comprises the steps of:
I. twisting an operating rod by 90 degrees about the rod axis without allowing any
rotation of rod around central bushing axis, by traversing the slope of said seam,
thereby making elliptical section of operating rod at two ends with elliptical
portion to rotate said second cylinder carrying helical contact resulting in
downward for first cylinder of an upper contact and upward lift for first cylinder
of a lower contact, thereby ensuring that at the time of closure of 90 degree twist

movement, the bush contact helix open end breaks a contact with the operating rod in the portion where the operating rod is cut; and II. turning said operating rod with elliptical section at its two extreme ends, parallel to an operative horizontal plane, in an operative horizontal plane by approximately 45 degrees around the central axis of a central bushing out of a set of three bushings per phase, thereby allowing rod exit from fixed contact with helical groove ball bush on two extreme bushing out of the three bushings per phase, said fixed contact comprising: a pair of opposing, spaced apart, co-axially aligned contacts, each contact being a first cylinder with a disc base, said disc base being the mating face of said contact which receives an elliptical end section of an operating rod, with mating faces of spaced apart contacts adapted to face each other, said mating face being a recessed helical plane, in that, a horizontal seam from the edge to the central hollow circumference forms a step (54c) adapted to provide a helical plane about the central hollow starting from the raised portion of the step helically wrapping about the central hollow until the foot of the step; and second cylinder ensconced co-axially within said first cylinder, said second cylinder being a helically grooved cylinder on its outer surface, which surface is in contact with the inner surface of said first cylinder, wherein said second cylinder is a ball bush cylinder such that there is operative movement of said second cylinder in a co-axial manner with respect to said first cylinder, in that, said ball bush configuration providing a frictionless play to said second cylinder and wherein, the provisioning of said helical grooves imparts rotary movement about bush axis apart from upward-downward movement along bush axis.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1 illustrates an auxiliary view of an isolator break condition with a fixed contact assembly of the prior art;
Figure 2 illustrates a front view an auxiliary view of an isolator break condition with a fixed contact assembly of the prior art;

Figure 3 illustrates a top view an auxiliary view of an isolator break condition with a
fixed contact assembly of the prior art;
Figure 4 illustrates an auxiliary view of an isolator make condition with a fixed contact
assembly of the prior art;
Figure 5 illustrates a front view an auxiliary view of an isolator make condition with a
fixed contact assembly of the prior art; and
Figure 6 illustrates a top view an auxiliary view of an isolator make condition with a
fixed contact assembly of the prior art.
The invention will now be described in relation to the accompanying drawings, in which:
Figure 7 illustrates an auxiliary view of an isolator break condition with a fixed contact
assembiy in accordance with this invention;
Figure 8 illustrates a front view an auxiliary view of an isolator break condition with a
fixed contact assembly in accordance with this invention;
Figure 9 illustrates a top view an auxiliary view of an isolator break condition with a
fixed contact assembly in accordance with this invention;
Figure 10 illustrates an auxiliary view of an isolator make condition with a fixed contact
assembly in accordance with this invention;
Figure 11 illustrates a front view an auxiliary view of an isolator make condition with a
fixed contact assembly in accordance with this invention;
Figure 12 illustrates a top view an auxiliary view of an isolator make condition with a
fixed contact assembly in accordance with this invention;
Figure 13 illustrates a front view of the finger contacts, according to this invention,
during the make condition;
Figure 14 illustrates a top view of the finger contacts of Figure 13;
Figure 15 illustrates a cut section view of the finger contacts of Figure 13;
Figure 16 illustrates a front view of the finger contacts, according to this invention,
during the break condition;
Figure 17 illustrates a top view of the finger contacts of Figure 16;
Figure 18 illustrates a cut section view of the finger contacts of Figure 16;

Figure 19 illustrates a start position of the contact making operation of the finger contacts
of Figure 16;
Figure 20 illustrates a completed position of the contact making operation of the finger
contacts of Figure 16;
Figure 21 illustrates an isometric view of a finger contact; and
Figure 22 illustrates an end section of the operating rod.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1 illustrates an auxiliary view of an isolator break condition with a fixed contact assembly of the prior art. Figure 2 illustrates a front view an auxiliary view of an isolator break condition with a fixed contact assembly of the prior art. Figure 3 illustrates a top view an auxiliary view of an isolator break condition with a fixed contact assembly of the prior art.
Figure 4 illustrates an auxiliary view of an isolator make condition with a fixed contact assembly of the prior art. Figure 5 illustrates a front view an auxiliary view of an isolator make condition with a fixed contact assembly of the prior art. Figure 6 illustrates a top view an auxiliary view of an isolator make condition with a fixed contact assembly of the prior art.
An isolator comprises bushings (10), a tum-and-twist mechanism with an operating rod (12), and a turn-and-twist mechanism stopper (14), The bushings include an isolator first phase input pole (11), an isolator first phase centre pole (13), and an isolator first phase output pole (15) linearly aligned one beside another. At the extreme ends of the isolator i.e. on the isolator first phase input pole (11) and on the isolator first phase output pole (15), a contact assembly is installed. It comprises isolator fixed finger contact assembly (16) and a terminal pad (18) for isolator contacts. The isolator finger contacts are adapted to receive, in the spaced apart region between its fingers, the ends of the operating rod (12) such that it mates with the spaced apart contacts. Typically, the spaced apart measurement is equal to the major axis dimensions of the end section of the operating rod. The operating rod swivels along with a holding bracket (19) , about the isolator centre pole (15), said bracket being located atop the isolator centre pole (15), said

swiveling is in an operative horizontal plane with an axis which is collinear with respect
to the isolator centre pole (15).
Typically, this is a triple pole isolator. Only the first phase poles are shown. The second
pole and the third pole components are parallely lined to the component shown in Figure
1 of the accompanying drawings.
Isolator fixed contact assembly (16) include finger contacts (21) which are made,
typically, of copper with either a 'C' or an 'M' shaped cross-section and with spring
back-up. These finger contacts (21) are compression spring-loaded 'C'-shape or 'M'-
shape fork type contact, typically made of copper with silver plating on inner mating
faces. Operating rod (12) of isolator is basically a Copper pipe which enters inside the
span of'C' OR 'M' opening with a turn action and after this, with a twist action, it makes
contact with fixed 'C' OR 'M: profiled contact pushing contact outward, thus depressing
the spring. The moving contact i.e. operating rod is made from hard drawn copper pipe
with pressed end in elliptical shape and may be tin or silver plated.
Thus, this type of rod and fixed contact engagement relies on parameters such as contact
cross-section, bend and thickness based spring back action for ensuring positive contact
make.
To achieve high contact pressure combined with easy operation and self cleaning of
contacts, a turn and twist mechanism is provided on the centre rotating insulator. Spring
loaded linkages retain the end section of operating rod in one position where it can centre
freely as it twists to the close condition. As the operating rod is restricted by fix contact,
it starts to turn around its own axis. The spring loaded linkages causes the operating rod
and its end sections to rotate on its axis so that the contact gets pressurized. Similarly
when isolator has to be open contact, pressure restricts the operating rod end section to
swing around central bushing (13) axis. The spring loaded linkages causes the operating
rod end section to turn in reverse direction around operating rod turning axis and
resulting the release of contact pressure.
In its operative configuration, the operating rod (12), with elliptical end cross-sections
(17) at the two extreme ends of the operating rod (12) which is parallel to an operative
horizontal plane, 'turns' in the operative horizontal plane with a motor gear box
arrangement around a central operative vertical axis of central bushing (13). This angular

displacement is by about 45 degrees. Due to this motion, the operating rod, particularly,
its elliptical end sections enter inside the fixed C OR 'M' cross section contact on two
extreme bushings (11, and 15) out of 3 bushings (11, 13, 15) per phase
Further, 'twisting' action takes place which twists the rod by about 90 degrees around the
rod axial axis without allowing any rotation of rod around central bushing vertical axis
making elliptical section of operating rod at two ends to push the fixed 'C' OR "M' cross
section contact forks to deflect outward and allowing accommodation of rod end elliptical
section inside the fixed contact forks.
This completes contact-make operation. For contact-break operation, the operation is
reversed with the 'twist' operation first followed by the 'turn' operation. The deflected
forks of 'C' or 'M' cross section contacts falls inward and operating rod comes back to its
original position.
According to this invention, there is provided a contact for isolators and an improved
turn-and-twist isolator mechanism, thereby.
Figure 7 illustrates an auxiliary view of an isolator break condition with a fixed contact
assembly in accordance with this invention, Figure 8 illustrates a front view an auxiliary
view of an isolator break condition with a fixed contact assembly in accordance with this
invention. Figure 9 illustrates a top view an auxiliary view of an isolator break condition
with a fixed contact assembly in accordance with this invention.
Figure 10 illustrates an auxiliary view of an isolator make condition with a fixed contact
assembly in accordance with this invention. Figure 11 illustrates a front view an auxiliary
view of an isolator make condition with a fixed contact assembly in accordance with this
invention. Figure 12 illustrates a top view an auxiliary view of an isolator make condition
with a fixed contact assembly in accordance with this invention.
The contact arrangement, in accordance with this invention, instead of relying on contact
cross section, bend and thickness based spring back action for ensuring positive contact
make, makes the contact design independent of aforesaid parameters giving more
freedom to designer.

Figure 13 illustrates a front view of the finger contacts, according to this invention, during the make condition. Figure 14 illustrates a top view of the finger contacts of Figure 13. Figure 15 illustrates a cut section view of the finger contacts of Figure 13. Figure 16 illustrates a front view of the finger contacts, according to this invention, during the break condition. Figure 17 illustrates a top view of the finger contacts of Figure 16. Figure 18 illustrates a cut section view of the finger contacts of Figure 16. Figure 19 illustrates a start position of the contact making operation of the finger contacts of Figure 16. Figure 20 illustrates a completed position of the contact making operation of the finger contacts of Figure 16. Figure 21 illustrates an isometric view of a finger contact.
In accordance with an embodiment of this invention, there is provided a pair of opposing contacts (50a, 50b), each contact having a first cylinder (52) with a disc base (54). The first cylinder (52) along with the disc base (54) includes a central hollow portion. The disc base (54) is the mating face of the contact which receives the elliptical end section (17) of the operating rod (12). The mating face of the contact is a recessed helical plane, in that, a horizontal seam from the edge to the central hollow circumference forms a step (54c) adapted to provide a helical plane about the central hollow starting from the raised portion of the step helically wrapping about the central hollow until the foot of the step (54c). The step (54c) which seams the first portion (54a) (relatively upper) to the second portion (54b) (relatively lower) of the mating surface is a sloping surface. Preferably, the contact is a copper contact.
In accordance with another embodiment of this invention, there is provided a second cylinder (60) ensconced co-axially within the first cylinder. The second cylinder is a helically grooved (62) cylinder on its outer surface which surface is in contact with the inner surface of the first cylinder. The second cylinder is a ball bush cylinder such that there is operative movement of the second cylinder in a co-axial manner with respect to the first cylinder, in that, the ball bush configuration provides a frictionless play to the second cylinder. Also, the provisioning of helical grooves provided imparts rotary movement about bush axis apart from upward-downward movement along bush axis. The ball bearings of the ball bush are referenced by numeral 63 in the accompanying drawings.

In accordance with yet another embodiment of this invention, a back-up compression
spring is provided to ensure required contact pressure on receivable end section (17) of
operating rod (12). To generate rotary movement of contact through operating rod twist
movement, the contact connected to helical groove ball bush carries semicircular helical
cross section.
The diameter of the contact i.e. the diameter of the disc base is lesser than the major axis
length of the elliptical end section of the operating rod.
Figure 22 illustrates an end section of the operating rod.
In accordance with another embodiment of this invention, there is provided a slit end
section of the operating rod. There may be a plurality of slits. The slits (recesses) (70) are
provisioned to match the step (54c) of the disc base (54).
With aforesaid construction of existing and new isolator, the contact make and break
shall take place in following manner:
1. Operating rod with elliptical section at the two extreme ends is parallel to an operative horizontal plane, and turns in operative horizontal plane with motor gear box arrangement by approximately 45 degrees around the central axis of central bushing out of the set of three bushings per phase, thereby allowing rod entry inside the fixed contact with helical groove ball bush on two extreme bushing out of the three bushings per phase.
2. Twisting of rod by 90 degrees takes place around the rod axis without allowing any rotation of rod around central bushing axis, making elliptical section of operating rod at two ends with elliptical portion to rotate the bush (second cylinder) carrying helical contact, wherein the twisting action results in traversing the slope seam, thereby exerting pressure on the first cylinders in axial direction, thereby resulting in upward lift for upper bush contact (50b) and downward fall for down bush contact (50a) and ensuring that at the time of closure of 90 degree twist movement, the bush contact helix open end makes a contact with the operating rod in the portion where the operating rod is cut.
This completes make operation. For break operation, operating procedure is reversed and displaced bush helical contacts shall rotate and fall inward and operating rod comes back to its original position.
Due to the equipment of this invention, following advantages are envisaged: Contact stress elimination/reduction;

- Operating force reduction;
- Controlled Operating rod slip in the twist mechanism component;
- Zero lateral forces on spring, ensuring factory setting all the time;
- Balancing load for arcing horn based load on operating rod with fulcrum at operating rod and moving contact, contact point;
- Pole clamp principle baseline with only change is that instead of manual screw and slit based clamping as in standard pole clamp, in the new design spring backed helical bush based clamping has been adopted.
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 contact for isolators and an improved turn-and-twist isolator mechanism, thereby, said contacts comprising:
a. a pair of opposing, spaced apart, co-axially aligned contacts (upper contact and
lower contact), each contact having a first cylinder with a disc base and a central
hollow portion there-through, said disc base being the mating face of said contact
which receives an elliptical end section of an operating rod, with mating faces of
spaced apart contacts adapted to face each other, said mating face being a
recessed helical plane, in that, a horizontal seam from an edge of the disc base to
the central hollow circumference forms a step adapted to provide a helical plane
about said central hollow, starting from the raised portion of the step helically
wrapping about the central hollow until the foot of the step; and
b. second cylinder ensconced co-axially within said first cylinder, said second
cylinder being a helically grooved cylinder on its outer surface, which surface is
in contact with the inner surface of said first cylinder, wherein said second
cylinder is a ball bush cylinder such that there is operative movement of said
second cylinder in a co-axial manner with respect to said first cylinder, in that,
said ball bush configuration providing a frictionless play to said second cylinder
and wherein, the provisioning of said helical grooves imparts rotary movement
about bush axis apart from upward-downward movement along bush axis.
2. A contact as claimed in claim 1 wherein, said contact includes said seam with a predefined length, the length of said seam being equal to the major axis of said elliptical end section of said operating rod.
3. A contact as claimed in claim 1 wherein, said contact includes a back-up compression spring provided to ensure required contact pressure on receivable said elliptical end section of said operating rod.
4. A contact as claimed in claim 1 wherein, said operating rod includes an elliptical end section with recessed operative mating surfaces to match said step of said disc base.

5. A method for making contact, for isolators, and providing an improved turn-and-twist
isolator mechanism, thereby, said method comprising the steps of:
i. turning an operating rod with elliptical section at its two extreme ends, parallel to
an operative horizontal plane, in an operative horizontal plane by approximately
45 degrees around the central axis of a central bushing out of a set of three
bushings per phase, thereby allowing rod entry inside a fixed contact with helical
groove ball bush on two extreme bushings out of the three bushings per phase,
said fixed contact comprising: a pair of opposing, spaced apart, co-axialily aligned
contacts, each contact having a first cylinder with a disc base with a central
hollow there-through, said disc base being the mating face of said contact which
receives said elliptical end section of said operating rod, with mating faces of
spaced apart contacts adapted to face each other, said mating face being a
recessed helical plane, in that, a horizontal seam from the edge to the central
hollow circumference forms a step adapted to provide a helical plane about the
central hollow starting from the raised portion of the step helically wrapping
about the central hollow until the foot of the step, wherein, said step is a sloping
surface; and second cylinder ensconced co-axially within said first cylinder, said
second cylinder being a helically grooved cylinder on its outer surface, which
surface is in contact with the inner surface of said first cylinder, wherein said
second cylinder is a ball bush cylinder such that there is operative movement of
said second cylinder in a co-axial manner with respect to said first cylinder, in
that, said ball bush configuration providing a frictionless play to said second
cylinder and wherein, the provisioning of said helical grooves imparts rotary
movement about bush axis apart from upward-downward movement along bush
axis; and
ii. twisting said operating rod by 90 degrees about the rod axis without allowing any rotation of rod about central bushing axis, by traversing the slope of said seam such that a recessed portion in the operative lateral mating edge of said end section of said operating rod matches said step, thereby making elliptical section of operating rod at two ends with elliptical portion to rotate said second cylinder

carrying helical contact resulting in upward lift for first cylinder of said upper contact and downward fall for first cylinder of said lower contact, thereby ensuring that at the time of closure of 90 degree twist movement, the bush contact helix open end makes a contact with the operating rod in the portion where the operating rod is cut.
6. A method for breaking contact, for isolators, and providing an improved turn-and-twist isolator mechanism, thereby, said method comprising the steps of: I. twisting an operating rod by 90 degrees about the rod axis without allowing any rotation of rod around central bushing axis, by traversing the slope of said seam, thereby making elliptical section of operating rod at two ends with elliptical portion to rotate said second cylinder carrying helical contact resulting in downward for first cylinder of an upper contact and upward lift for first cylinder of a lower contact, thereby ensuring that at the time of closure of 90 degree twist movement, the bush contact helix open end breaks a contact with the operating rod in the portion where the operating rod is cut; and II. turning said operating rod with elliptical section at its two extreme ends, parallel to an operative horizontal plane, in an operative horizontal plane by approximately 45 degrees around the central axis of a central bushing out of a set of three bushings per phase, thereby allowing rod exit from fixed contact with helical groove ball bush on two extreme bushing out of the three bushings per phase, said fixed contact comprising: a pair of opposing, spaced apart, co-axially aligned contacts, each contact being a first cylinder with a disc base, said disc base being the mating face of said contact which receives an elliptical end section of an operating rod, with mating faces of spaced apart contacts adapted to face each other, said mating face being a recessed helical plane, in that, a horizontal seam from the edge to the central hollow circumference forms a step (54c) adapted to provide a helical plane about the central hollow starting from the raised portion of the step helically wrapping about the central hollow until the foot of the step; and second cylinder ensconced co-axiaily within said first cylinder, said second cylinder being a helically grooved cylinder on its outer surface, which

surface is in contact with the inner surface of said first cylinder, wherein said second cylinder is a ball bush cylinder such that there is operative movement of said second cylinder in a co-axial manner with respect to said first cylinder, in that, said ball bush configuration providing a frictionless play to said second cylinder and wherein, the provisioning of said helical grooves imparts rotary movement about bush axis apart from upward-downward movement along bush axis.