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
APPLICANTS
Crompton Greaves Limited, CG House, Dr. Annie Besant Road, Worli, Mumbai -400 030, Maharashtra, India, an Indian Company
INVENTORS
Yadav Pallavi Sitaram,Waghmare Vishal Virsen both of CMDRC, CG Global R&D Centre, Kanjurmarg (E), Mumbai - 400042, Maharashtra and Patii Ghanshyam Narottam, Kale Subodh Suresh both of S3, Switchgear Division, Crompton Greaves Limited, A-3, MIDC, Ambad, Nashik 422 010, Maharashtra, India, all 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, in general, relates to a gas circuit breaker and more particularly towards an insulating nozzle thereof. BACKGROUND OF THE INVENTION
In a gas circuit breaker, an insulating nozzle is provided for aiding the extinguishment of an arc generated while the contacts of the circuit breaker open. In a high voltage circuit breaker, the intensity of the arc is substantially high thereby causing ablation/consummation of the nozzle as well as the contacts thereof. Such an ablation/consummation results in faster wear and tear of the nozzle and the contacts thereby reducing the life of the circuit breaker. To counter such problems, nozzles with varying designs and shapes based on the analysis of gas flow have been proposed. For example, US patent 5274205 claims a nozzle construction having divergent and slanting surfaces for increasing the reflectivity of energy intensity of the arc generated therein. Owing to such a design of the nozzle, it is required to be impregnated with a comparatively reduced amount of filler material of boron nitride powder in an amount of not more than 15 voI% for restraining the amount of surface deformation of the nozzle by the arc. Another US Patent no. 4339641 discloses a nozzle having an upstream section, a throat section having an internal diameter approximately equal to that of the outside diameter of one of the contacts and downstream section including a bell-shaped section and a flow confining section exhibiting an outward taper between 0 and 5 degrees. Such a shape of the nozzle claims to greatly reduce the ablation products and blocking of the throat which interfere with successful fast arc, interruption in the nozzle.
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The nozzle disclosed in the above mentioned US patent'5274205 focuses on a particular shape of the nozzle and a limited amount of filler being impregnated therein for enhancing the internal arc resisting capacity of the nozzle for withstanding high voltages. Whereas the nozzle disclosed in US Patent no. 4339641 focuses on a bell shaped nozzle for a rapid elimination of the ablation material from the nozzle throat which interfere with successful and fast arc interruption in the nozzle. However, there is a need of nozzle which increases the velocity of the extinguishing gas entering therein and directs it towards the arc with an increased pressure for impinging thereupon for a successful interruption of the arc. OBJECTS OF THE INVENTION
An object of the invention is to provide a gas circuit breaker having an insulating nozzle for increasing the insulating pressure therein for a successful extinguishment of the arc therein.
Another object of the invention is to provide a gas circuit breaker having a nozzle which tops up the velocity of the extinguishing gas entering therein and further directs the gas towards an arc generated therein with an increased pressure and velocity. 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 an insulating nozzle for blowing an extinguishing gas to an arc generated between arcing contacts of the circuit breaker, wherein an inner surface of the insulating nozzle having a Molybdenum sulphide (MoS2) coating and comprising of a throat section, an upstream section and a downstream section such that the throat section is located between the upstream and downstream sections, the
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downstream section having a diameter larger than the upstream section and the throat section having a diameter less than the upstream section, the throat section further comprising of a substantially triangular depression/concavity elongating from the upstream section and into the lumen of the nozzle for creating a constriction, receiving the gas coming through the upstream section and deflecting thereof with an increased velocity and pressure towards a point of generation of the arc and a divergent section continuing from the depression/concavity extending along the length of the nozzle and tapering upwardly to merge with the downstream section for a faster discharge of the extinguishing gas through the downstream section.
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 1 is a cross section of the gas circuit breaker;
Fig 2 is an exploded cross sectional view of the nozzle in the gas circuit breaker;
Fig 1 is a cross section of the gas circuit breaker. The gas circuit breaker comprises of a coaxially located fixed contact 1 and a main contact 2. The fixed contact is enclosed within a cylindrical casing 3 connected to an upper flange 4. The fixed contact 1 encloses a rod shaped fixed arcing contact 5 connected to the cylindrical casing 3. The main contact 2 is a finger type cylindrical contact connected to a lower flange 6 through an end plate 7. The main contact 2 slidingly holds a puffer cylinder 8 storing the SF6 gas. The puffer cylinder 8 encloses a fixed piston 9 mounted on the end plate 7 at its one end for imparting a thrust to the extinguishing gas while the cylinder 8 is slid there over. The puffer cylinder 8 is slid/driven by a drive rod 10 connected at its one end
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thereof through the lower flange 6, end plate 7 and the piston 9. The inner end of the drive rod 10 is connected to a finger type moving arcing contact 11 adapted to be abutted with the fixed arcing contact 5. The other outer end of the cylinder is connected to a finger type moving contact 12 through a bracket 13. For opening/closing the circuit breaker, the finger type contact 12 is made to make or break a contact with the fixed contact 1, The inner end of the bracket 13 connected to the finger type moving contact 12 is connected to a nozzle 14 which encloses the moving arcing contact 11. The contacts 1, 12, and 2 carry the current when the circuit breaker is carrying normal load and in closed condition. The nozzle 14 serves to blow the extinguishing gas stored in the cylinder 8 towards the arc generated between the arcing contacts 5 and 11 when the breaker opens. The inner surface of the nozzle 14 is coated with 0.1% Molybdenum sulphide (MoS2).
Fig 2 is an exploded cross sectional view of the nozzle 14 in the gas circuit breaker. The inner surface of the nozzle is coated with filler 0.1% Molybdenum sulphide (MoS2). The arc generated by interruption of high current flow in the circuit breaker generates a large amount of heat causing ablation of the filler material therein. Such an ablation leads to a rise in the pressure in the nozzle 14. Further, the nozzle 14 comprises of an upstream section 15, a throat section 16 and a downstream section 17. The internal diameter of the downstream section 17 is more than that of the upstream section 15 whereas the internal diameter of the throat section 16 is the least. The throat section 16 is located between the upstream 15 and downstream sections 17. The SFe gas stored in the cylinder 8 enters the nozzle 14 through the upstream section 15 at a velocity and pressure depending upon the size of the cylinder 8 and thrust by the piston 9. The upstream section 15 is a substantially flat portion extending along the length of the nozzle 14. The throat
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section 16 emerges from the upstream section 15 and is located between the upstream 15 and downstream 17 sections. The throat section 16 is essentially a constriction of a specific shape and size extending inwardly into the lumen of the nozzle 14 for receiving the extinguishing gas, topping up the velocity of the received gas and deflecting the gas with the increased velocity and pressure towards the arc for a successful quenching thereof. The throat section 16 comprises of a triangular like depression/concavity and a divergent section. The depression is formed by means of a first 18 and second 19 slanting surface. The first slating surface 18 elongates slantingly from the upstream section 15 into the lumen of the nozzle 14 at an angle of 75 degrees Of with respect to the upstream section \ 5. The length of the first slanting surface elongating into the lumen of the nozzle 14 is 12mm according to an embodiment of the subject matter. The second slanting surface 19 originates from the point of termination of first slanting surface 18 at an angle of 75 degrees G2 and into the lumen of the nozzle 14 till a distance of 8.5mm thereby creating a triangular like depression/concavity for receiving the gas coming through the upstream section 15 and deflecting thereof with an increased velocity and pressure towards a point of generation of the arc in the vicinity of the throat section 16. The divergent section originates from the point of termination of the second slanting surface 19 and comprises of a horizontal portion 20 and a third slanting portion 21. The horizontal portion 20 extends axially horizontally from the point of termination of the second slanting surface 19 towards the downstream section 17 till a distance of 12 mm; thereafter slanting upwardly at angle of 20 degrees 63 with respect to the horizontal portion 20 to form the third slanting portion 21 and merge with the downstream section 17 for a faster discharge of the extinguishing gas through the downstream section 17.
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The values of the slanting angles may be range bound. The length of the slanting surfaces may vary depending upon various parameters of the circuit breaker.
According to the invention, the shape of the nozzle as described above with the filler material Molybdenum sulphide (MoS2) coated on the inner surface thereof greatly enhances the insulating gas pressure within the nozzle leading to a successful quenching of the arc therein. The triangular depression/concavity tops up the velocity with which the extinguishing gas impinges upon the arc for increasing the pressure in the nozzle.
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.
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We claim:
1. A gas circuit breaker comprising an insulating nozzle for blowing extinguishing gas towards an arc generated between arcing contacts of the circuit breaker, wherein an inner surface of the insulating nozzle having a Molybdenum sulphide (MoS2) coating and comprising of a throat section, an upstream section and a downstream section such that the throat section is located between the upstream and downstream sections, the downstream section having a diameter larger than the upstream section and the throat section having a diameter less than the upstream section, the throat section further comprising of
* a substantially triangular depression/concavity elongating from the
upstream section and into the lumen of the nozzle for creating a
constriction, receiving the gas coming through the upstream section and
deflecting thereof with an increased velocity and pressure towards a point
of generation of the arc; and
• a divergent section continuing from the depression/concavity extending
along the length of the nozzle and tapering upwardly to merge with the
downstream section for a faster discharge of the extinguishing gas through
the downstream section.
2. A gas circuit breaker as claimed in claim 1, wherein 0.1% of Molybdenum sulphide (MoS2) is coated on the inner surface of the insulating nozzle.
3. A gas circuit breaker as claimed in claim 1, wherein the triangular depression/concavity elongating from the upstream section slants into the lumen of the nozzle at an angle of 75 degrees with respect to the upstream section.
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4. A gas circuit breaker as claimed in claim 1, wherein the depth of the depression/concavity is 12 millimeters.
5. A gas circuit breaker as claimed in claim 1, wherein a portion of the divergent section extending along the length of the nozzle is flat
6. A gas circuit breaker as claimed in claim 1, wherein the divergent section tapers upwardly at an angle of 20 degrees to merge with the downstream section.