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 vacuum interrupter
INVENTORS
Phase Shantanu, Rajhans Rupesh, Joshi Narendra, Dusane Vijay, Kulkarni Laxmikant and Wakode Deelip, all of Crompton Greaves Limited, S6 Division, D-2 MIDC Waluj, Aurangabad 431 136, Maharashtra, India, all Indian nationals
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Prabhadevi,
Mumbai 400030, Maharashtra, India, an Indian Company
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 a vacuum interrupter.
BACKGROUND OF THE INVENTION
A vacuum interrupter (VI) is a switching device used for interruption of fault current in power supply systems. A vacuum interrupter generally comprises a fixed side subassembly and a moving side subassembly vacuum tight brazed at the opposite ends of a ceramic body which may be single or double ceramic. The fixed side subassembly generally comprises a fixed side electrode extending into the ceramic body through a fixed side end plate located at one end of the ceramic body and brazed to the fixed side electrode. The fixed side end plate is brazed to a fixed side seal cup which in turn is brazed to the said one end of the ceramic body. A fixed side contact is brazed to the inner end of the fixed side electrode. The moving side subassembly comprises a moving side electrode extending into the ceramic body through a moving side end plate located at the other end of the ceramic body and brazed to the moving side electrode. A bellows is disposed over the moving side electrode with its one end brazed to the moving side electrode and the other end brazed to the moving side end plate. A bellows shield is disposed over the bellows with its one end brazed to the said one end of the bellows. A stacking ring is located over the moving side electrode and brazed to the said one end of the bellows shield. The moving side subassembly also includes a moving side contact brazed to the inner end of the moving side electrode. The vacuum interrupter also comprises a centre shield. In the case of a single ceramic vacuum interrupter, the centre shield may be fixed type and may be located around the fixed side electrode and brazed to the fixed side end plate. Alternatively, the centre shield may be floating type and may be fixed to the ceramic body. In the case of a double ceramic vacuum interrupter the centre shield may be held between the ceramic portions and may be floating type centre shield. In such a vacuum interrupter, the end convolutes of the bellows are brazed to the moving side end plate and to a collar on the moving side electrode. Therefore, the vacuum joints formed at the ends of the bellows are very large and require considerable amount of braze material for the brazing and also considerable energy for the brazing. This increases the cost of the vacuum interrupter. Due to the vacuum joints being large, there are possibilities of micro channels or cracks being


formed at the joints. This may lead to leakage of vacuum thereby reducing the reliability and life of the vacuum interrupter. Besides the large vacuum joints are not mechanically very strong and will give in or break over a period of time due to stresses and strains introduced at the joints as a result of contraction and expansion of the bellows during opening and closing of the vacuum interrupter. This will also lead to leakage of vacuum and reduce the reliability and life of the vacuum interrupter.
OBJECTS OF THE INVENTION
An object of the invention is to provide a vacuum interrupter which is cost effective.
Another object of the invention is to provide a vacuum interrupter which has increased reliability and life.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention there is provided a vacuum interrupter comprising a fixed side subassembly and a moving side subassembly vacuum tight brazed at the opposite ends of a ceramic body, wherein the bellows of the moving side subassembly comprises an axial lip projecting from each end thereof, the axial lip at one end of the bellows being brazed to a collar on the moving side electrode and the axial lip at the other end of the bellows being fixed to the moving side end plate, the bellows being supported at each end thereof with spring means brazed to the respective end.
The following is a detailed description of the invention with reference to the accompanying drawings, in which :
Fig 1 is a crosssectional view of a vacuum interrupter according to an embodiment of the invention; and
Fig 2 is a crosssectional view of a vacuum interrupter according to another embodiment of the invention.


The vacuum interrupter 1 as illustrated in Fig 1 of the accompanying drawings comprises a fixed side subassembly 2 and a moving side subassembly 3 vacuum tight brazed at the opposite ends of a vacuum sealed single ceramic body 4. The fixed side subassembly comprises a fixed side electrode 5 extending into the ceramic body through a fixed side end plate 6 which is brazed to the fixed side electrode and to a fixed side seal cup 7 which in turn is brazed to one end of the ceramic body. 8 is a fixed side contact brazed to the inner end of the fixed side electrode. The moving side subassembly comprises a moving side electrode 9 extending into the ceramic body through a moving side end plate 10 which is brazed to a moving side seal cup 11 which in turn is brazed to the other end of the ceramic body. The moving side subassembly also comprises a bellows 12 disposed over the moving side electrode and provided with an axial lip 13 projecting from each end thereof. The axial lip at one end of the bellows is brazed to a flange 14 on the moving side electrode and the axial lip at the other end of the bellows is brazed to the moving side end plate. The bellows is further supported at each end thereof by a cup shaped leaf spring 15. One leaf spring is brazed to one end convolute of the bellows and to the collar and the other leaf spring is brazed to the other end convolute of the bellows and to the moving side end plate. The moving side subassembly also comprises a bellow shield 16 disposed over the bellows with its one end brazed to the collar. 17 is a moving side contact brazed to the inner end of the moving side electrode. 18 is a centre shield located around the fixed side electrode and brazed to the fixed side end plate. The vacuum interrupter 19 as illustrated in Fig 2 of the accompanying drawings comprises a double ceramic body formed of ceramic portions 20a, 20b. 21 is a floating centre shield supported between the ceramic portions.
According to the invention the vacuum joints of the bellows at the ends thereof as provided by the axial lips are knife joints and are considerably reduced in size. Therefore the braze material required for forming the joints and energy consumption for brazing are correspondingly reduced and the vacuum interrupter is cost effective. Due to the vacuum joints of the bellows being reduced in size, possibility of microchannels or cracks being formed in the joints are reduced correspondingly reducing leakage of vacuum through the joints. As the bellows are reinforced and supported at the ends by the leaf springs, stresses and strains developed in the bellows due to contraction and expansion of the bellow during closing and opening


of the vacuum interrupter are absorbed and cushioned by the leaf springs. Therefore, such strains and stresses are only partly transmitted to the vacuum joints of the bellows. As a result of all this, the reliability and life of the vacuum interrupter are improved. Instead of cup shaped leaf spring other spring, means can be used to support the bellows at the ends thereof. Such a variation is obvious to those skilled in the art and the scope of the invention should be construed and understood accordingly.


We claim :
1) A vacuum interrupter comprising a fixed side subassembly and a moving side subassembly vacuum tight brazed at the opposite ends of a ceramic body, wherein the bellows of the moving side subassembly comprises an axial lip projecting from each end thereof, the axial lip at one end of the bellows being brazed to a collar on the moving side electrode and the axial lip at the other end of the bellows being fixed to the moving side end plate, the bellows being supported at each end thereof with spring means brazed to the respective end.
2) The vacuum interrupter as claimed in claim 1, wherein the spring means comprises a cup shaped leaf spring.


Abstract
A vacuum interrupter (1) comprising a fixed side subassembly (2) and a moving side subassembly (3) vacuum tight brazed at the opposite ends of a ceramic bottle (4). The bellows (12) of the moving side subassembly comprises an axial lip (13) projecting from each end thereof.. The axial lip at one end of the bellows is brazed to a collar (14) on the moving side electrode and the axial lip at the other end of the bellows is fixed to the moving side end plate (10). The bellows is supported at each end thereof with spring means (15) brazed to the respective end (Fig 1).