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 INVENTION
Current Limiting Vacuum Interrupter
APPLICANTS
Name : CROMPTON GREAVES LIMITED
Nationality : Indian Company
Address : CG House, Dr Annie Besant Road, Worli Mumbai 400030, Maharashtra, India
INVENTORS:
Dr Raghavan Venkatesh and Rajhans Rupesh Subhashrao both Indian nationals and both of Crompton Greaves Ltd, Switchgear-6 & Power Quality Business Unit, D2, MIDC, Waluj, Aurangabad 431136, Maharashtra, India
PREAMBLE TO THE DESCRIPTION
The following specification describes the invention.

FIELD OF INVENTION
This invention relates to a current limiting Vacuum Interrupter.
Current limiting Vacuum Interrupters are used to switch inductive or capacitive loads in power distribution systems.
BACKGROUND OF INVENTION
A current limiting switching device used in a power distribution system generally comprises a main vacuum interrupter along with the auxiliary circuit connected to the external circuit or current carrying parts. The main vacuum interrupter comprises a fixed contact system and a movable contact system located in a vacuum sealed ceramic body. The auxiliary circuit comprises a switch with a insulating media such as SF6 or Oil or a conventional Vacuum Interrupter and a resistor connected in series. During switching operation, there will be initially a high inrush current flow in the system. This inrush current not only reduces the life of the Vacuum Interrupter and the auxiliary circuit but also generates stresses in the entire system. The sequence of operation of the main Vacuum Interrupter and the auxiliary circuit is controlled such that initially the auxiliary circuit will be closed to provide a high resistive path for the high inrush current. Following this, the main vacuum interrupter will be closed to provide a low resistive path and a continuous flow of current through the low resistive path. The time delay between the operations of the auxiliary circuit and the main vacuum interrupter is set for a few cycles such that when the current reduces and stabilizes, it will flow through the low resistive path provided by the main vacuum interrupter. The main vacuum interrupter and auxiliary circuit are external to each
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other and comprise a large number of components because of which the system is bulky and costly and thereby increasing the maintenance cost.
An object of the invention is to provide a current limiting Vacuum Interrupter with a single switching unit with a inbuilt current limiting device.
Another object of the invention is to provide a current limiting Vacuum Interrupter with a inbuilt time delay between main contacts and auxiliary contacts through special design and construction.
Another object of the invention is to provide a current limiting Vacuum Interrupter which eliminates a separate switch with a insulating media such as Sf6, oil or Vacuum.
DETAILED DESCRIPTION OF INVENTION
According to the invention there is provided a current limiting Vacuum Interrupter for switching an inductive or capacitive load in a power distribution system, the Vacuum Interrupter comprising a fixed contact system and a movable contact system located in a vacuum sealed ceramic body, the vacuum interrupter further comprising an auxiliary contact system comprising a contact ring fitted at the upper end of a compression spring disposed within the center shield around the fixed electrode of the fixed contact system in spaced apart relationship with the fixed electrode, center shield having a stopper arrangement fixed on the middle end plate of the auxiliary contact system, the lower end of the compression spring being fixed to the middle end plate of the auxiliary contact system and the upper end of the compression spring with
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the contact ring protruding out of the fixed contact, the contact ring being isolated from the fixed electrode and fixed contact and a wire wound resistor disposed around the fixed side ceramic tube spaced apart from the fixed electrode, the wire wound resistor being connected to the contact ring through the middle end plate and the outer end of the fixed electrode, the movable contact of the movable contact system being broader than the contact ring and adapted to close against the fixed contact prior to closing on the fixed contact.
The following is a detailed description of the invention with reference to the accompanying drawings, in which Figs 1 and 2 show the general schematic arrangement with a switch or conventional Vacuum Interrupter and with current limiting Vacuum Interrupter of the invention, Figs 3, 4 and 5 show the current limiting Vacuum Interrupter of the invention according to an exemplary embodiment thereof in the fully open, auxiliary contact closed and fully closed positions. The current limiting Vacuum Interrupter as illustrated in Figs 3 to 5 of the accompanying drawings comprises a vacuum interrupter 1 comprising a fixed contact system 2 and a movable contact system 3 located in a vacuum sealed main ceramic body 4 and a fixed side ceramic body 5. The fixed electrode, fixed contact are marked as 6 and 7 respectively. The center shield and the stopper arrangement in the center shield are marked as 8 and 9 respectively. The center shield minimizes metal vapor deposition on the ceramic body due to arcing during the switching operation of the vacuum interrupter and the stopper arrangement provides a mechanical strength to the auxiliary contact required during opening operation to break the weld if any. The fixed seal cup and end plate are marked 10 and 11 respectively. The movable electrode, movable contact, bellows and bellows shield of the moving contact system
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are marked 12, 13, 14 and 15 respectively. The bellows shield protects the bellows from metallic vapours generated during switching operations of the vacuum interrupter. The stacking ring, movable seal cup and end plate, guide bush and arresting cap are marked 16, 17, 18, 19 and 20 respectively. The guide bush guides the axial movement of the movable electrode. The outer ends of the movable electrode and fixed electrode are provided with threaded holes 21 and 22 respectively for connecting them to the external circuit and current carrying parts. An auxiliary contact comprising a contact ring 23 is fitted at the upper end of a compression spring 24 disposed within the center shield around the fixed electrode of the fixed contact system in spaced apart relationship with the fixed electrode. The lower end of the compression spring 24 is fixed to the middle end plate 25. Main ceramic body 4 is connected to the middle end plate 25 through middle seal cup 26. Fixed side ceramic body 5 is connected to the other end of the middle end plate 25 through middle seal cup 27. The upper end of the compression spring with the a contact ring protruding out of the fixed contact. 28 is a support plate for the wire wound resistor fixed on the fixed side electrode 6. 29 is a wire wound resistor (cylindrical or spring type) disposed over the fixed side ceramic body 5 in spaced apart relationships with it and fixed between to the support plate 28 of the fixed electrode 6 and middle end plate 25. The contact ring 23 is isolated from the fixed electrode 6 and fixed contact 7 by the gap 30. The current limiting Vacuum Interrupter in the fully open position is as shown in Fig.3. During switching of the Vacuum Interrupter, the movable contact 13 moves towards the fixed contact and first closes against the contact ring 23 (Fig 4). The time delay between closing of the main contacts and moving and auxiliary contact is a function of the contact travel, spring characteristics and speed of operation. The design parameters are so controlled as to get a time delay of 1ms to 80 ms, this is
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controlled in both closing and opening operation of the Vacuum Interrupter. The contact ring and wire wound resistor provide the high resistive path for the inrush current. The arcing between the movable contact and the contact ring will be considerably reduced because of high resistive path offered by the contact ring and wire wound resistor. The movable contact continues to move forward under compression of the compression spring until it closes against the fixed contact. The inrush current reduces and stabilizes by this time and the movable and fixed contacts of the vacuum interrupter in their closed position ensure a low resistive path for the current to flow to the load (Fig 5). During opening operation, due to flow of electrical current, there can be a welding between the movable contact 13 and the contact ring 23, which will require a mechanical force to be generated between the movable contact and the contact ring, as the contact ring is fixed on the compression spring 24, which will not provide a rigid support due to its spring property, stopper 9 and contact ring 23 are designed in such a way that the stopper arrests contact ring after a definite travel of the movable contact and the contact ring and will provide mechanically rigid support to the contact ring to assist in breaking the weld.
Typically, the fixed and movable electrodes, and stacking ring are made of OFHC copper or equivalent material, fixed and movable contacts are made of any suitable alloy such as copper chromium alloy and auxiliary contact ring is made of any suitable material or alloy which exhibits good anti welding properties like Cr or W or Cu Cr alloy. Fixed and movable end plates, middle end plate, bellows, bellows shield, arresting cap, and center shield are made of stainless steel, fixed and movable side seal cups and middle seal cups are made of copper, stainless steel or copper nickel alloy or equivalent material, ceramic body is made of high alumina and
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bushing is made of nylon, support plate can be made of copper or stainless steel or any other suitable material, compression spring can be made of stainless steel, phosphor bronze, Cu Cr alloy or equivalent material with proper spring properties. Resistor is preferably wound type with a suitable material such as nichrome, stainless steel or any other suitable material. It is to be understood that the above examples of the materials of the components are only preferences and that the components can be made of other vacuum compatible materials. The value of resistance and wattage of wire wound resistor can be varied to suit the circuit parameters. Any other suitable type of resistor can be used by optimizing components. Compression spring can be made with any other suitable shape. The auxiliary circuit configuration and construction can vary. Such variations are to be construed and understood to be within the scope of the invention.
According to the invention, the auxiliary circuit comprising a SF6, Oil or vacuum switch or a conventional Vacuum Interrupter has been eliminated and the auxiliary circuit is built into the current limiting vacuum interrupter to provide both the high resistive path and low resistive path within the same current limiting Vacuum Interrupter. The number of components of the current limiting Vacuum Interrupter is reduced and it is rendered compact and cost effective thereby reducing maintenance cost.
Dated this 30th day of March 2007

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