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, 2005
PROVISIONAL SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
Axial Magnetic Field Vacuum Interrupter
INVENTOR
Saravanan Selvaraj of Analytical laboratory, CG Global R&D Centre, Crompton Greaves Ltd , Kanjur (E), Mumbai 400042, Maharashtra, India, an Indian National
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention :

FIELD OF INVENTION
This invention relates to axial magnetic field Vacuum Interrupter.
This invention also relates to a field coil system for axial magnetic filed Vacuum Interrupter.
PRIOR ART
In most of the prior art field coils such as the coils disclosed in U.S. Patent No. 4260864, include radial current carrying arms connecting the central electrode to arcuate coil elements. These radial arms generate non-axial fields. These non axial fields lessen the homogeneity of the axial field and hence delay the arc extinction. Besides, these non axial fields also create eddy current in the contacts which create fields opposing the main magnetic field.
In the Axial field vacuum interrupter design as disclosed in the patent U.S. Patent No. 5804788, the radial arms are eliminated by using cylindrical coil. But the axial field generated by the cylindrical coils is Gradient in nature i.e. the radial distribution of axial field is not homogeneous. Since the Arc tends to concentrate in the contact area with maximum flux density, there will be uneven temperature distribution in the contact surface.


Therefore, there is a need to design a field coil system that generates axial field having high homogeneity that lessens eddy current density.
OBJECTS OF INVENTION
An object of the invention is to design a field coil system that generates axial field having
high homogeneity that lessens eddy current density.
Another object of the invention is to provide an axial field with homogeneity in the range
of65to70%.
Another object of the invention is to reduce the eddy current density of the system as the eddy current density is only 2.4% of source current density.
DETAILED DESCRIPTION OF THE INVENTION
A vacuum interrupter comprises a movable contact assembly and a fixed contact assembly located within a vacuum envelope. During interruption of short current i.e. opening of the contacts in a fault condition heavy arcing occurs between the contacts. Arcing erodes and reduces the life of the contacts. In order to prevent constriction of the arc and to distribute the arc uniformly across the contacts and thus increase the life of the contacts, a magnetic field is generated in the space between the contacts. This magnetic field may be a radial magnetic field generated by using spiral petal shaped coils or it may


be an axial magnetic field generated by a circular shaped coils. In both the cases, the coils are fixed to movable and fixed contacts.
In Axial magnetic field (AMF) vacuum interrupter, the magnetic field generated by the coils fixed to either contacts. These coils generates magnetic field which is parallel to the arc drawn between the contacts. This axial magnetic field tries to distribute the arc throughout the contact surface.
According to the invention there is provided a Vacuum interrupter with a main coil system consists of two C shaped coils displaced vertically by approximately 1 to 1.5 times the mean radius. This coil generating a -Z gradient field.
Also the invention is provided with an auxiliary coil system consists of two C Shaped coils Displaced vertically by 0.5 times the mean radius. This coil is generating a +Z gradient field.
The two coil systems are connected in such a way that the gradient fields are getting cancelled in the region of interest and hence it generates uniform axial magnetic field. Also the fixed and moving coils are displaced by 90° to get homogeneity in X and Y directions.
Due to absence of radial arms, there is a substantial decrease of eddy current in the
system.


According to the invention there is provided a vacuum interrupter comprising an axial magnetic field generating coil assembly comprising two fixed coils fitted at the rear side of the fixed contact of the fixed contact assembly and two movable coil fixed at the rear side of the movable contact of the movable contact assembly; the fixed and as well as moving coil assembly consists of a main coil system and an auxiliary coil system made of copper.
In accordance to the present invention, each of the main coil system and auxiliary coil system consists of two C- shaped coils arranged with their axis parallel; in both fixed and moving coil assembly, the main C-shaped coils and auxiliary C-shaped coils are electrically connected in series and are positioned between the electrode and contact; both fixed and moving coil assembly are positioned in such a way, that the fixed main coil system and moving main coil system are displaced vertically by a certain distance, that the fixed auxiliary coil system and moving auxiliary coil system are displaced vertically by a certain distance.
In accordance to the present invention, the main coil system in the contact gap, generates -Z gradient field and auxiliary coil system generating +Z gradient field; thus the gradient fields are getting cancelled and therefore generates uniform axial magnetic field in the contact gap.


In accordance to the present invention, the fixed and moving coil systems are arranged with their slits offset by 90°, to generate homogeneous field in both X and Y direction.
The present invention provides highly homogeneous axial magnetic flux in the contact gap, leading to uniform temperature distribution in the contacts and also, reduces the eddy currents flowing in the contacts.