FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
A gas circuit breaker
APPLICANT
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTORS
Rao Sudhendra Nagesh and Chandalia Sandeep Kumar of Crompton Greaves Ltd, A-3 MIDC, Ambad, Nasik, Maharashtra, 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 INVENTION
This invention relates to a gas circuit breaker and more particularly to a gas circuit breaker having a scissor arrangement for a double movement of contacts therein.
BACKGROUND OF THE INVENTION
Circuit breakers usually comprises of at least two sets of contacts, which make or break the circuit. Such contacts when electrically connected or disconnected with each other makes or break the circuit. Such circuit breakers usually comprise of one stationary and a moving contact each or both moving contacts. In a circuit breaker with two moving contacts, both contacts are connected to each other in a way that they move towards or away from each other when one of the moving contacts is driven by a drive mechanism for making or breaking the circuit. Such circuit breakers are used when a high break capacity is required for a faster separation of the contacts. Conventionally, the design of such circuit breakers exhibiting a double motion of the contacts is complicated and uses complex mechanical systems like gears and levers. Such circuit breakers are also bulky in size and difficult to manufacture. Moreover, owing to a complicated design, such circuit breakers are not reliable and consume a large amount of energy for moving the contacts.
OBJECTS OF THE INVENTION
An object of the invention is to provide a gas circuit breaker exhibiting a double motion of contacts which has a simple design, light weight, easy to manufacture and service

Another object of the invention is to provide a gas circuit breaker having a reduced and controlled linear motion of the contacts.
Another object of the invention is to provide a gas circuit breaker which is energy efficient and wherein a faster relative movement of the contacts is achieved with a relatively lesser amount of energy.
DETAILED DESCRIPTION OF THE INVENTION
In order to achieve the aforesaid and other objectives, according to the invention, a gas circuit breaker is provided comprising a pair of movable contact assemblies, each assembly being electrically coupled to a fixed tube 3 & 4, the fixed tubes being disposed coaxially in a gas filled tubular chamber in a spaced apart relationship and fitted to the tubular chamber, one movable contact assembly comprising a drive rod axially extending through the respective fixed tube, the inner end of the drive rod comprising a nozzle and the outer end of the drive rod being connectable to a drive mechanism, the inner end of the drive rod further comprising a first arcing contact located within the nozzle and a first slidable contact member disposed over the nozzle and in electrical contact with the respective fixed tube, an inner end of the first slidable contact member being formed with a first slidable movable contact and the other movable assembly comprising a second slidable contact member in electrical contact with the respective fixed tube, the inner end of the second slidable contact member comprising a second movable contact protruding out of the respective fixed tube, the nozzle and the outer end of the second slidable contact member being coupled together by at least one set of scissor linkages hinged to the respective fixed tube, the slidable contacts being adapted to make and break electrical

contacts with each other, the other movable contact assembly further comprising a second arcing contact fitted therein and extending axially inwardly adapted to make and break contact with the first arcing contact.
These and other aspects, features and advantages of the invention will be better understood with reference to the following detailed description, accompanying drawings and appended claims, in which,
Fig la illustrates a gas circuit breaker in open condition according to one embodiment of the invention.
Fig lb illustrates a gas circuit breaker in closed condition according to one embodiment of the invention.
Fig la illustrates a gas circuit breaker in open condition according to one embodiment of the invention. The gas circuit breaker comprises of a pair of movable contact assemblies 1 & 2. The moving contact assembly 1 is located slidingly over the fixed tube 3 while the moving contact assembly 2 is located slidingly within the fixed tube 4. The fixed tubes 3 & 4 are disposed coaxially in a gas filled tubular chamber 5 in a spaced apart relationship and fitted to the tubular chamber 5. One movable contact assembly 1 comprises of a drive rod 6 axially extending through the respective fixed tube 3. An inner end of the drive rod 6 comprises of a nozzle 7 and an outer end of the drive rod 6 is connected to a drive mechanism (not shown in the fig). The inner end of the drive rod 6 further comprises of a first arcing contact 8 located within the nozzle 7 and a first slidable contact member 9 disposed over the nozzle 7. The nozzle 7 is provided with a support disc 10. The first slidable contact member 9 is a tubular body partially slidably located within the respective fixed tube 3 in electrical contact therewith. An inner end of

the first slidable contact member 9 is formed with a step and comprising of a first slidable movable contact 11. The other movable contact assembly 2 comprises of a second slidable contact member 12 having a tubular body with a closed outer end 13 and slidably located within the respective fixed tube 4 and in electrical contact therewith. The inner end of the second slidable contact member 12 is formed with a second movable contact 14 protruding out of the respective fixed tube 4 and bent inwardly so as to adapted to abut against the respective step at the first movable contact 11. The support disc 10 and the outer end 13 of the second slidable contact member 12 are coupled together by a pair of scissors linkages 15 (only one scissor linkage shown in the fig) on the periphery of the tubular body of the contact member 12. Both the scissor linkages 15 are hinged to the respective periphery of fixed tube 4 such that the hinge points 16 (only one hinge point shown in the fig) face each other. The other movable contact assembly 2 further comprises of a second arcing contact in the form of a rod 17 fitted to the closed outer end 13 therein and extending axially inwardly. The arcing contacts 8 & 17 are adapted to make and break contact with each other.
To close the circuit breaker, the drive mechanism drives the drive rod 6 connected to the movable contact assembly 1 towards the other movable contact assembly 2. The support disc 10 to which one end of the scissor linkages 15 are attached is pushed towards the right hand side of the circuit breaker. Since the scissor linkages 15 are hinged to the fixed tube 4, a push to one end of the scissor linkages 15 causes the other end to move towards the end being pushed, thereby, moving the respective contacts 11 & 14 of each contact member 9 & 12 towards each other. Consequently, the circuit breaker in

closed in a fashion as illustrated in Fig lb. Simultaneously, the arcing contact 8 & 17 of each moving contact assembly 1 & 2 makes a contact with each other.
To open the circuit breaker, the drive mechanism drives the rod 6 connected to the movable contact assembly 1 away from the other movable contact assembly 2. The support disc 10 to which one end of the scissor linkages 15 are attached is pulled away towards the left hand side of the circuit breaker. Since the scissor linkages 15 are hinged to the fixed tube 4, a pull force being applied to one end of the scissor linkages 15 causes the other end to be pulled away from the other end being pulled, thereby, pulling the respective contacts 11 & 14 of each contact member 9 & 12 away from each other. Consequently, the circuit breaker in opened in a fashion as iJJustrated in Fig Ja. Simultaneously, the arcing contact 8 & 17 of each moving contact assembly 1 & 2 breaks contact with each other.
The amount of relative movement being achieved between the moving contact assemblies after applying a push or a pull force depends upon the length of linkages and the position at which the scissor linkage is hinged onto the fixed tube. Instead of a pair of scissor linkages, a single assembly of scissor linkages can be used on either periphery of the fixed tube.
According to the invention, a double motion of the contacts is achieved by driving only a single contact of the circuit breaker. Further, the weight of the circuit breaker is substantially reduced owing to a simple design and use of simple linkages. The unique design of the gas circuit breaker enables a controlled linear motion of the contacts. Further, vis-a-vis a conventional gas circuit breaker, same amount relative speed of the contacts is achieved with a reduced amount of mechanical energy.

Although the invention has been described with reference to a specific embodiment, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiment, as well as alternate embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that such modifications can be made without departing from the spirit or scope of the invention as defined.

A gas circuit breaker comprising a pair of movable contact assemblies, each assembly being electrically coupled to a fixed tube, the fixed tubes being disposed coaxially in a gas filled tubular chamber in a spaced apart relationship and fitted to the tubular chamber, one movable contact assembly comprising a drive rod axially extending through the respective fixed tube , the inner end of the drive rod comprising a nozzle and the outer end of the drive rod being connectable to a drive mechanism, the inner end of the drive rod further comprising a first arcing contact located within the nozzle and a first slidable contact member disposed over the nozzle and in electrical contact with the respective fixed tube , inner end of the first slidable contact member being formed with a first slidable movable contact and the other movable assembly comprising a second slidable contact member in electrical contact with the respective fixed tube, the inner end of the second slidable contact member comprising a second movable contact protruding out of the respective fixed tube, the nozzle and the outer end of the second slidable contact member being coupled together by at least one set of scissor linkages hinged to the respective fixed tube, the slidable contacts being adapted to make and break electrical contacts with each other, the other movable contact assembly further comprising a second arcing contact fitted therein and extending axially inwardly adapted to make and break contact with the first arcing contact.
The circuit breaker as claimed in claim 1, wherein the first slidable contact member is a tubular body in sliding contact with the respective fixed tube and in

electrical contact therewith, the inner end of the first tubular body comprising the first movable contact and formed with a step and the second movable contact member comprising a second tubular body with a closed outer end, the second tubular body in sliding contact with the respective fixed tube and in electrical contact therewith, the inner end of the second tubular body comprising the second movable contact, the second contact protruding out of the respective fixed tube and bent inwardly adapted to abut against the respective step at the first movable contact, the nozzle is provided with a support disc and the scissor linkages are fixed to the support disc at their one ends, to the closed outer end of the second tubular body at their other ends and hinged to the fixed tube. 3. The circuit breaker as claimed in claim 1, wherein a ratio of relative distance being traveled by each moving contact upon a push/pull to one of the said moving contact assembly can be varied by changing the length of links and/or position of said hinge.
Dated this 24th day of December 2008