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 turn-and-twist type isolator with rack and pinion arrangement
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 turn-and-twist type isolator with rack and pinion arrangement.
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.
According to the prior art, turn-and-twist type isolators are known. The prior art turn-and-twist isolator is lever based. The operating rod of the isolator is basically a copper pipe which enters inside the span of a 'C'-shaped OR 'M'-shaped opening with a 'turn' action and after this with a 'twist' action, it makes contact with fixed 'C'-shaped OR 'M'-shaped contact by pushing the contact outwards, thereby pressing the spring. Since the twisting action of operating rod is required to press the contact spring, torque supplied by motor of moving mechanism has to overcome the contact spring resistance, apart from inertia of rotating masses.
This requirement was fulfilled by earlier mechanism by having twisting action leverage based, but as far as repetitiveness of the movement was concerned, the mechanism was susceptible to malfunctioning. Because of this, contact heating related issues were evident.
Therefore, there is a need for an improved turn-and-twist type isolator which shall resolve all slip issues and deliver positive movement and ensure required repeatability of operation. Also, it shall provide a relatively more refined turning and twisting operation.
OBJECTS OF THE INVENTION:
An object of the invention is to provide a turn-and-twist type isolator which is slip-resistant.

Another object of the invention is to provide a turn-and-twist type isolator which delivers positive movement.
Yet another object of the invention is to provide a turn-and-twist type isolator which ensures required repeatability of operation
Still another object of the invention is to provide a turn-and-twist type isolator with relatively more refined turning and twisting operation.
An additional object of the invention is to increase isolator life.
SUMMARY OF THE INVENTION:
According to this invention, there is provided a turn-and-twist type isolator
with rack and pinion arrangement, said isolator comprises:
base plate coaxial with a bushing on an isolator centre pole adapted to angularly displace said base plate in tandem with angular displacement of said isolator centre pole, said base plate comprising at least a rack assembly adapted to engage with at least a pinion assembly, said pinion assembly coupled with an operating rod of said isolator, said rack assembly and said pinion assembly provided such that angular displacement of said base plate provides turn movement of said turn-and-twist type isolator and pinion movement on said rack provides twist movement of said turn-and-twist type isolator.
Typically, said base plate is a disc shaped base plate.

Typically, said rack assembly comprises a pair of semicircular racks, with its end portions facing each other.
Typically, said rack assembly comprises a pair of semicircular racks, with its end portions facing each other, said semicircular racks being placed on an operative top portion of said base plate and along the circumferential edge of said base plate.
Typically, said rack assembly comprises a pair of semicircular racks, said semicircular racks being helical racks, in that, each of said racks rise from one end to another with respect to a horizontal plane of said base plate.
Typically, said rack assembly comprises a pair of semicircular racks, said semicircular racks'being helical racks, in that, each of said racks rise from one end to another with respect to a horizontal plane of said base plate, said rise being provisioned by placing a spring at one of the ends of each semicircular rack.
Typically, said rack assembly comprises a pair of semicircular racks, said semicircular racks being helical racks, in that, each of said racks rise from one end to another with respect to a horizontal plane of said base plate, said rise being provisioned by placing a spring at one of the ends of each semicircular rack, said springs being placed diagonally opposite each other with respect to the disc shaped base plate.
Typically, said rack assembly comprises a pair of semicircular racks, said semicircular racks being helical racks, in that, each of said racks rise from one

end to another with respect to a horizontal plane of said base plate, said rise being provisioned by placing a spring at one of the ends of each semicircular rack, each of said springs adapted to space apart one end of corresponding said semicircular rack from said base plate.
Typically, said pinion assembly comprises a pair of pinions, each pinion corresponding to a semicircular rack from a pair of semicircular racks of said rack assembly.
Typically, said pinion assembly comprises a pair of pinions, said pinions being placed such that they are diagonally opposite on said base plate.
Typically, the length of the teeth of each pinion of said pinion assembly is less than the length of the teeth of each corresponding rack of said rack assembly.
Typically, said pinion assembly comprises a pair of pinions being coupled to said operating rod by means of a pair of corresponding holding blocks, each said holding block being located adjacent to said pinion.
Typically, said base plate comprises a pair of curved slots, said curved slots being provisioned in said base plate.
Typically, said base plate comprises a pair of curved slots, said curved slots being provisioned in said base plate, further being located internal to said semicircular racks, and still further being in synchronism in placement to the rack.

Typically, said base plate comprises a pair of curved slots, said curved slots being provisioned in said base plate with ends of said semicircular racks being in synchronism with the ends of said curved slots.
Typically, said base plate comprises a pair of curved slots, said curved slots adapted to receive holding blocks by means of nuts attached to the underside of said holding block.
Typically, said base plate comprises a pair of curved slots, said curved slots adapted to receive holding blocks by means of nuts attached to the underside of said holding block, said nuts being placed such that they guide the movement of said operating rod in the curve.
Typically, said base plate comprises a pair of curved slots, said curved slots adapted to receive holding blocks by means of nuts attached to the underside of said holding block, said nuts being governed, in design, by a tightening coefficient such that there is a lower pre-determined threshold value to said nut and a higher pre-determined threshold value to said nut.
Typically, said isolator comprises guides to cover at least a portion of lateral edges of semicircular. racks of said rack assembly, starting from their end points.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1 illustrates an auxiliary view of an isolator, of the prior art, in its break condition;

Figure 2 illustrates a front view of an isolator, of the prior art, in its break condition;
Figure 3 illustrates a top view of an isolator, of the prior art, it its break condition;
Figure 4 illustrates an auxiliary view of an isolator, of the prior art, in its make condition;
Figure 5 illustrates a front view of an isolator, of the prior art, in its make condition; and
Figure 6 illustrates a top view of an isolator, of the prior art, in its make condition.
The invention will now be described in relation to the accompanying drawings, in which:
Figure 7 illustrates an auxiliary view of an isolator, of this invention, in its make condition;
Figure 8 illustrates a front view of an isolator, of this invention, in its make condition;
Figure 9 illustrates a top view of an isolator, of this invention it its make condition; and

Figure 10 illustrates a side view of an isolator, of this invention, in its make condition.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1 illustrates an auxiliary view of an isolator, of the prior art, in its break condition. Figure 2 illustrates a front view of an isolator, of the prior art, in its break condition. Figure 3 illustrates a top view of an isolator, of the prior art, it its break condition.
Figure 4 illustrates an auxiliary view of an isolator, of the prior art, in its make condition. Figure 5 illustrates a front view of an isolator, of the prior art, in its make condition. Figure 6 illustrates a top view of an isolator, of the prior art, in its make condition.
An isolator comprises bushings (10), a turn-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 (17) of the operating rod (12). The operating rod (12) swivels ('turn'

action) 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 (17) 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 turn-and-twist type isolator with rack and pinion arrangement.
Figure 7 illustrates an auxiliary view of an isolator, of this invention, in its make condition. Figure 8 illustrates a front view of an isolator, of this invention, in its make condition. Figure 9 illustrates a top view of an isolator, of this invention it its make condition. Figure 10 illustrates a side view of an isolator, of this invention, in its make condition.
In accordance with an embodiment of this invention, there is provided a disc shaped base plate (52) coaxial with a bushing (10) on the isolator first phase centre pole (13). The base plate angularly displaced itself in tandem with the angular displacement of the isolator first phase centre pole (13). The disc shaped base plate includes a pair of semicircular racks (54a, 54b), with its end portions facing each other. The semicircular racks are placed on the operative top portion of the base plate and along the circumferential edge of the base plate. Further, these semicircular racks are helical racks, in that, they rise from one end to another with respect to a horizontal plane. This rise is provisioned by placing a spring (56) at one of the ends of each semicircular rack. The springs are typically placed diagonally opposite with respect to the disc shaped base plate. The spring spaces apart one end of the semicircular rack from the base plate. The racks are raised so that extra inertia that is needed to overcome the height rise of the pinion on the rack during 'twist' movement causes extra

torque to be delivered to the pinions, thereby ensuring counter-pressure at the end sections (17) of the operating rod (12).
In accordance with another embodiment of this invention, there are provided pinions (58a, 58b) adapted to engage with said semicircular racks (54a, 54b). Typically, there is one pinion for each rack. The pinions are placed such that they are diagonally opposite on the base plate. The teeth of the pinions engage with the teeth of the rack. Preferably, the length of the teeth of the pinion is less than the length of the teeth of the rack. This takes care of lateral play of the pinion on the rack to avoid supping. TTfie pinions are coupied to an operating rod (12) which passes diametrically across the base plate. Each pinion is located adjacent a holding block (62a, 62b) which holds the operating rod in place. The pinion moves over the rack during the 'twist' movement of the isolator. This causes operating rod to twist by 90 degrees along its longitudinal axis.
In accordance with yet another embodiment of this invention, two curved slots (64a, 64b) are provisioned in the base plate (52). These slots are located internal to the semicircular racks and are in synchronism in placement to the rack. The ends of the semicircular racks are in synchronism with the ends of the curved slots. The slots receive the holding blocks by means of nuts attached to the underside of the holding block. The nuts are placed such that they guide the movement of the operating rod in the curved slot. The movement is the 'turn' movement of the isolator. The nuts are governed, in design, by a tightening coefficient such that there is a lower threshold value to the nut and a higher threshold value to the nut. The lower threshold value of the tightening coefficient of the nut ensures that the nut is just loose enough to

not restrict 'twist' movement. The upper threshold value of the tightening coefficient of the nut ensures that the nut is just tight enough to cause 'turn' movement.
In accordance with still another embodiment of this invention, there are provided guides (66) to cover at least a portion of the lateral edges of the semicircular racks, starting from their end points.
The technical advance of the current invention lies in eliminating prior art components such as moving blade brackets and clamps mounted on operating rod. Sharp corner edges are eliminated thereby supporting creepage clearance requirements. The present invention provides improved repetitiveness of twisting of operating rod. Also, it avoids slippery components, thereby avoiding reduction in wear and tear due to friction between moving parts and reducing frictional loads, too. The present invention also reduces operating rod rotating movement based jerk issues present with prior art. Subsequently, isolator life increases. Further, since the rack and pinion arrangement provide defined segments or portions or quantum of travel with a calculated minimal resistance offered by the teeth, overtravel is also avoided.
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 turn-and-twist type isolator with rack and pinion arrangement, said
isolator comprising:
base plate coaxial with a bushing on an isolator centre pole adapted to angularly displace said base plate in tandem with angular displacement of said isolator centre pole, said base plate comprising at least a rack assembly adapted to engage with at least a pinion assembly, said pinion assembly coupled with an operating rod of said isolator, said rack assembly and said pinion assembly provided such that angular displacement of said base plate provides turn movement of said turn-and-twist type isolator and pinion movement on said rack provides twist movement of said turn-and-twist type isolator.
2. A turn-and-twist type isolator as claimed in claim 1 wherein, said base plate is a disc shaped base plate.
3. A turn-and-twist type isolator as claimed in claim 1 wherein, said rack assembly comprising a pair of semicircular racks, with its end portions facing each other.
4. A turn-and-twist type isolator as claimed in claim 1 wherein, said rack assembly comprising a pair of semicircular racks, with its end portions facing each other, said semicircular racks being placed on an operative top portion of said base plate and along the circumferential edge of said base plate.

5. A turn-and-twist type isolator as claimed in claim 1 wherein, said rack assembly comprising a pair of semicircular racks, said semicircular racks being helical racks, in that, each of said racks rise from one end to another with respect to a horizontal plane of said base plate.
6. A turn-and-twist type isolator as claimed in claim 1 wherein, said rack assembly comprising a pair of semicircular racks, said semicircular racks being helical racks, in that, each of said racks rise from one end to another with respect to a horizontal plane of said base plate, said rise being provisioned by placing a spring at one of the ends of each semicircular rack.
7. A turn-and-twist type isolator as claimed in claim 1 wherein, said rack assembly comprising a pair of semicircular racks, said semicircular racks being helical racks, in that, each of said racks rise from one end to another with respect to a horizontal plane of said base plate, said rise being provisioned by placing a spring at one of the ends of each semicircular rack, said springs being placed diagonally opposite each other with respect to the disc shaped base plate.
8. A turn-and-twist type isolator as claimed in claim 1 wherein, said rack assembly comprising a pair of semicircular racks, said semicircular racks being helical racks, in that, each of said racks rise from one end to another with respect to a horizontal plane of said base plate, said rise being provisioned by placing a spring at one of the ends of each

semicircular rack, each of said springs adapted to space apart one end of corresponding said semicircular rack from said base plate.
9. A turn-and-twist type isolator as claimed in claim 1 wherein, said pinion assembly comprising a pair of pinions, each pinion corresponding to a semicircular rack from a pair of semicircular racks of said rack assembly.
10. A turn-and-twist type isolator as claimed in claim 1 wherein, said pinion assembly comprising a pair of pinions, said pinions being placed such that they are diagonally opposite on said base plate.
11. A turn-and-twist type isolator as claimed in claim 1 wherein, the length of the teeth of each pinion of said pinion assembly is less than the length of the teeth of each corresponding rack of said rack assembly.
12. A turn-and-twist type isolator as claimed in claim 1 wherein, said pinion assembly comprising a pair of pinions being coupled to said operating rod by means of a pair of corresponding holding blocks, each said holding block being located adjacent to said pinion.
13. A turn-and-twist type isolator as claimed in claim 1 wherein, said base plate comprising a pair of curved slots, said curved slots being provisioned in said base plate.
14. A turn-and-twist type isolator as claimed in claim 1 wherein, said base plate comprising a pair of curved slots, said curved slots being

provisioned in said base plate, farther being located internal to said semicircular racks, and still further being in synchronism in placement to the rack.
15. A turn-and-twist type isolator as claimed in claim 1 wherein, said base plate comprising a pair of curved slots, said curved slots being provisioned in said base plate with ends of said semicircular racks being in synchronism with the ends of said curved slots.
16. A turn-and-twist type isolator as claimed in claim 1 wherein, said base plate comprising a pair of curved slots, said curved slots adapted to receive holding blocks by means of nuts attached to the underside of said holding block.
17. A turn-and-twist type isolator as claimed in claim 1 wherein, said base plate comprising a pair of curved slots, said curved slots adapted to receive holding blocks by means of nuts attached to the underside of said holding block, said nuts being placed such that they guide the movement of said operating rod in the curve.
18. A turn-and-twist type isolator as claimed in claim 1 wherein, said base plate comprising a pair of curved slots, said curved slots adapted to receive holding blocks by means of nuts attached to the underside of said holding block, said nuts being governed, in design, by a tightening coefficient such that there is a lower pre-determined threshold value to said nut and a higher pre-determined threshold value to said nut.

19. A turn-and-twist type isolator as claimed in claim 1 wherein, said isolator comprising guides to cover at least a portion of lateral edges of semicircular racks of said rack assembly, starting from their end points.