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
PROVISIONAL SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
An improved material for vacuum interrupter contacts
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTORS
Wakode Deelip, Rajhans Rupesh Subhashrao, Paulzagade Dinesh Jagannath, Crompton Greaves Limited, S6 & Power quality Division, D2-MIDC, Waluj, Aurangabad - 431 136, Maharashtra India, all Indian Nationals
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention:

Field of invention
The invention relates to an improved material for vacuum interrupter contacts, to a method for preparing the material and to the contact prepared using the material. The invention also relates to a vacuum interrupter comprising the contact.
Background
Vacuum interrupters are widely used for short circuit current interruption during electrical transmission and distribution. Vacuum interrupter comprises fix and movable contacts housed in an evacuated envelop, with contacts being closed in a current carrying configuration and separated or opened to interrupt the operational or fault current. The operational characteristics of the vacuum interrupter is significantly dependent on the materials used for preparing the contact. The contact materials are usually prepared by a method comprising firing, blending, compaction, sintering and machining of virgin copper and chromium powders. However, the materials so prepared usually have oxygen and nitrogen gas content in higher levels that is detrimental to the performance of the interrupter. Further the conventional contact materials have low density and are prone to deformation on impact. Moreover, the virgin copper and chromium powders are costly raw materials and therefore the cost for preparing the conventional contact material is high.


There is need for improved vacuum interrupter contact materials without the above mentioned draw backs.
Accordingly the invention provides an improved material for vacuum interrupter contacts.
In one embodiment the invention provides an improved material for vacuum interrupter contacts, the material comprising around 20-30% chromium and 70-80% copper, the material having an oxygen content of not more than 300-600ppm and a nitrogen content of not more than 5-15 ppm.
In another embodiment, the invention provides a method for preparing an improved material for vacuum interrupter contact, the method comprising compaction, sintering and machining of a copper-chromium solid blend having density in the range of 8.0 to 8.15 g/cc, an oxygen content in the range of 500 to 1500 ppm and a nitrogen content in the range of 0 to 25 ppm.
In a further embodiment, the invention provides an improved contact for vacuum interrupter, the contact comprising around 20-30% chromium and 70-80% copper, the composition having an oxygen content of not more than 300-600ppm and a nitrogen content of not more than 5-15ppm.


In a still further embodiment of the invention, the invention provides a vacuum interrupter comprising a contact prepared from a material comprising around 20-30% chromium and 70-80% copper, the material having an oxygen content of not more than 300-600ppm and a nitrogen content of not more than 5-15ppm.
The contact materials of the invention are prepared from machining by products of copper chromium blends. The by products are subjected to compaction, sintering and machining to prepare the contact. The contact materials of the invention have high density and have low gas content. The hardness and electrical conductivity of the contact is also high.
The invention provides high purity contact materials having improved properties. The materials are prepared from machining by products that are usually discarded. Therefore, the invention provides high quality contact materials at relatively low cost. Further, due to the high density and hardness, the contact material of the invention resists deformation on impact. Moreover, the low gas content in the contact material would enable reduction in the arc extinction time thereby resisting the erosion of contacts