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 INVENTION
A multi contact multi chamber vacuum interrupter for ring main unit
INVENTORS
Dr Raghavan Venkatesh, Rajhans Rupesh Subhashrao and Rajagopal Ratheesh, all Indian
nationals and all of Crompton Greaves Ltd, Switchgear-6 & Power Quality Business, D2,
MIDC, Waluj, Aurangabad 431136, Maharashtra, India
APPLICANTS
Name : CROMPTON GREAVES LIMITED
Nationality : Indian Company
Address : CG House, 6th Foor,
Dr Annie Besant Road, Worli, Mumbai - 400030, Maharashtra, India.
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 relates to a multi contact multi chamber vacuum interrupter (hereafter referred as switching unit) for ring main unit.
Ring main units are used to connect feeder lines from a power source to a ring power distribution network. A ring main unit comprises a switching unit and a control unit for controlling the operation of the switching unit.
BACKGROUND OF INVENTION
A generally used switching unit of ring main unit comprises a pair of knife type switches and a vacuum interrupter enclosed in a leak tight chamber filled with sulphur hexafluoride gas (SF6) or ring main unit uses oil as a insulating medium, wherein the main arcing contacts and the knife type switches are insulated with oil. The knife type switch assembly comprises large number of components and is complicated in construction. Byproducts formed during arcing in SF6 are not safe and environment friendly. The knife type switch assembly occupies large area due to its construction and required operating clearances. Both the knife type switches and leak tight chamber also increase the cost. During operation of the switching unit byproducts of SF6 are formed due to arcing, which reduce the dielectric performance and life of the switching unit and
are not desirable. In oil type ring main units, life of the main contacts is very limited and arcing in oil generates byproducts like carbon, reduces the dielectric performance of the oil, which calls for purification or replacement of oil periodically.
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Hitachi has described a vacuum-switching unit comprising a circuit breaker, disconnecting switch and pressure spring based earthing switch enclosed in a common chamber containing SF6 gas [Hitachi Review Vol 49 (2000) No2]. The movable electrode of the vacuum interrupter describes an arc motion and performs four functions, namely, circuit making, circuit breaking, circuit disconnecting and circuit earthing, all in the common chamber. In order to facilitate arc motion of the movable electrode, barrel shaped bellows is provided. Barrel shaped bellows is complicated in construction. Metallic vapours formed in the common chamber during switching operations of the vacuum interrupter reduce the dielectric performance and life of the switching unit. The bellows is subjected to undue stresses and strains during rotary motion of the movable contact. This also reduces the life of the bellows and switching unit. SF6 gas provided in the common chamber maintains electric insulation of the components in the chamber. Loss of vacuum in the common chamber during switching operations of the circuit
breaker renders the switching unit inactive. The switching unit described is of 24kV rating.
OBJECTS OF INVENTION
An object of the invention is to provide a switching unit for a ring main unit, which uses vacuum as a insulating media and eliminates arcing in SF6 gas and is compact and cost effective and also simple in construction.
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An object of the invention is to provide a switching unit for a ring main unit, which uses vacuum as a insulating media and eliminates arcing in oil and is compact and cost effective and also simple in construction.
Another object of the invention is to provide a switching unit of a ring main unit, which has improved bellows life and overall life.
Another object of the invention is to provide a switching unit of a ring main unit, which has improved dielectric performance and overall life.
DETAILED DESCRIPTION OF INVENTION
According to the invention there is provided a switching unit of a ring main unit, the switching unit comprising a main vacuum interrupter and a pair of auxiliary vacuum interrupters, the main vacuum interrupter being without the fixed side end plate, the fixed electrode and fixed side seal cup of the main vacuum interrupter being hermetically sealed to a common terminal block, the movable electrode of the main vacuum interrupter being adapted to be connected to the power circuit (not shown), which makes and breaks contacts under normal load and fault condition, the auxiliary vacuum interrupters each being without the fixed electrode and fixed side end plate, the fixed side seal cup, center shield and fixed contact of each of the auxiliary vacuum interrupters being hermetically sealed to the common terminal block, the movable electrodes of the auxiliary vacuum interrupters being adapted to be connected to an earth point (not shown) and to a connection and disconnection circuit (not shown) which makes and
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breaks contact under normal load condition or makes contact under fault condition, all the vacuum interrupters being encapsulated with an electric insulating material and being connected to the control unit of the ring main unit.
The following is a detailed description of the invention with reference to the accompanying drawings, in which:
Fig 1 is a schematic view of a typical distribution network with Ring main unit.
Fig 2 is a schematic view of the switching unit 1A of a ring main unit according to an exemplary embodiment of the invention; and
Fig 3 is a schematic view of the switching unit IB of a ring main unit according to another exemplary embodiment of the invention.
A schematic of a typical distribution network with ring main unit is shown in Figl. Ring main unit is used in the network as shown in Fig 1. The switching unit 1A as illustrated in Fig 2 of the accompanying drawings comprises a main vacuum interrupter 2 and a pair of auxiliary vacuum interrupters 3 and 4. The main vacuum interrupter 2 is without the fixed side end plate. The ceramic body and fixed side seal cup of the main vacuum interrupter are marked 5 and 6 respectively. The fixed electrode and fixed contact of the main vacuum interrupter are marked 7 and 8 respectively. The moving side end plate, seal cup and bushing of the main vacuum interrupter are marked 9, 10 and 11
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respectively. The movable electrode, movable contact and bellows of the main vacuum interrupter are marked 12,13 and 14 respectively. Bellows shield and center shield of the main vacuum interrupter are marked 15 and 16, respectively. 17 is the arc chamber of the main vacuum interrupter. The fixed electrode and fixed side seal cup of the main vacuum interrupter are hermetically sealed to the base 18a of a triangular shaped common terminal block 18 which is made of electrically conducting material such as copper or copper alloys. The auxiliary vacuum interrupters each are without the fixed electrode and fixed side endplate. The ceramic body, fixed side seal cup and fixed contact of auxiliary vacuum interrupter 3 are marked 19, 20 and 21 respectively. The movable electrode, movable contact and bellows of auxiliary vacuum interrupter 3 are marked 22, 23 and 24 respectively. The center shield and bellows shield of auxiliary vacuum interrupter 3 are marked 25 and 26 respectively. The bushing, end plate and seal cup at the moving side of vacuum interrupter 3 are marked 27, 28 and 29 respectively. The arc chamber of vacuum interrupter 3 is marked 30. The ceramic body, fixed side seal cup and fixed contact of auxiliary vacuum interrupter 4 are marked 31, 32 and 33 respectively. The movable electrode, movable contact and bellows of auxiliary vacuum interrupter 4 are marked 34, 35and 36 respectively. The center shield and bellows shield of auxiliary vacuum interrupter 4 are marked 37 and 38, respectively. The bushing, end plate and seal cup at the moving side of the vacuum interrupter 4 are marked 39, 40 and 41 respectively.
42 is the arc chamber of vacuum interrupter 4. The fixed contact, center shield and fixed side seal cup of the vacuum interrupters 3 and 4 are hermitically sealed to the sides 18b and 18c of the triangular shaped common terminal block 18. The movable electrode of main vacuum interrupter 2 is provided with a tapped hole 43 at the outer end thereof.
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Conducting flexible cable (not shown) from a ring power distribution network (not shown) is push or press fitted in the tapped hole 43. The movable electrodes of auxiliary vacuum interrupters 3 and 4 are also provided with tapped holes 44 and 45 at the outer ends thereof, respectively. Conducting flexible cables (not shown) from an earth point (not shown) or a connection and disconnection circuit (not shown) are press or push fitted in tapped holes 44 and 45, respectively. The triangular shaped common terminal block 18 is provided with a pair of tapped holes 46 and 47 at the vertex 18d thereof. The tapped holes 46 and 47 are provided at the vertex 18d for fixing of the switching unit.
The switching unit IB as illustrated in Fig 3 of the accompanying drawings comprises a square shaped common terminal block 48 whose sides are marked 48a, 48b, 48c and 48d. The tapped holes provided at the side 48d of the terminal block 48 are marked 49 and 50. The operations of the vacuum interrupters are controlled by a control unit (not shown) connected to the vacuum interrupters. Main vacuum interrupter 2 is operated to make and break the contacts under normal load condition and/or under fault condition. Auxiliary vacuum interrupters 3 and 4 are operated to earth the switching unit and / or make and break the contact under normal load condition and to make contact under fault condition, respectively. During making and breaking of the contacts, the movable electrode of the main vacuum interrupter moves axially. Similarly during the earthing and / or making and breaking of the contact under normal load condition and making under fault condition, the movable electrodes of the respective auxiliary vacuum interrupters move axially. Due to axial movement of the movable electrodes, stresses and strains on the bellows of the vacuum interrupters are reduced thereby improving the
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bellows life and overall life of the switching unit. Individual bellows are provided for the main vacuum interrupter and auxiliary vacuum interrupters, which helps in reducing no of operations of the individual vacuum interrupters, thereby increasing the life of the switching unit. Arcing occurs only in the arcing chamber of the main vacuum interrupter during the breaking and making of the contacts under normal load condition and / or under fault condition. Similarly the auxiliary vacuum interrupters 3 and 4 experience arcing only during the earthing and / or making and breaking of contacts under normal load condition and making of contact under fault condition, respectively. Therefore, generation of metallic vapours in the respective vacuum chambers is reduced thereby improving the dielectric performance and overall life of the switching unit. The switching unit of the invention eliminates SF6 gas and leak tight chamber and is compact and cost effective. As the main vacuum interrupter is without the fixed side end plate and the auxiliary vacuum interrupters are without the fixed electrode and end plates at the fixed sides thereof, cost of the switching unit is further reduced. The construction of the bellows has been simplified as the moving electrodes are designed for axial movement. The construction of the switching unit is simplified as the bellows construction has been simplified and SF6 gas and leak tight chamber have been eliminated. As SF6 gas has been eliminated generation of SF6 gas byproducts have been eliminated and dielectric performance and life of the switching unit are increased. The vacuum interrupters are encapsulated with electric insulating material such as polyurethane or Polycrete (polymer concrete). Encapsulation is not shown as encapsulation of vacuum interrupters is in general known.
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The common terminal block of the invention can be of any other shape. For instance the terminal block can be rectangular and all the vacuum interrupters can be fixed to the block at one side thereof longitudinally spaced. Triangular or square block is preferred as
it is compact. Instead of providing tapped holes at the outer ends of the movable electrodes of the vacuum interrupters, other provisions for connection may be made for
connecting the movable electrodes of the vacuum interrupters 2, 3 and 4 to the ring power distribution network, earth point and connection and disconnection circuit. Similarly instead of providing tapped holes at the vertex of the triangular shaped common terminal block or at the side 48d of the square shaped terminal block, other provision for connection may be made for fixing the switching unit. Such variations in construction of the invention are obvious to those skilled in the art and are to be construed and understood to be within the scope of the invention.
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WE CLAIM
1. A switching unit of a ring main unit, the switching unit comprising a main vacuum interrupter and a pair of auxiliary vacuum interrupters, the main vacuum interrupter being without the fixed side end plate, the fixed electrode and fixed side seal cup of the main vacuum interrupter being hermetically sealed to a common terminal block adapted to fix the switching unit, the auxiliary vacuum interrupters each being without the fixed electrode and fixed side end plate, the fixed side seal cup, center shield and fixed contact of each of the auxiliary vacuum interrupters being hermetically sealed to the common terminal block, the movable electrode of the main vacuum interrupter being adapted to be connected to the power circuit, the movable electrodes of the auxiliary vacuum interrupters being adapted to be connected to an earth point and to a connection and disconnection circuit which makes and breaks contact under normal load condition and makes contact under fault condition, all the vacuum interrupters being encapsulated with an electric insulating material and being connected to the control unit of the ring main unit.
2. A switching unit as claimed in claim 1, wherein the complete vacuum interrupter assembly is encapsulated with polyurethane or any other solid insulating material such as epoxy, polymer concrete etc.
3. A switching unit as claimed in claim 1 or 2, wherein the common terminal block is triangular shaped, the fixed electrode and fixed side seal cup of the main vacuum interrupter being hermetically sealed to the base of the triangular shaped common terminal block and the center shield, fixed side seal cup and fixed contact of each of the
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auxiliary vacuum interrupters being hermetically sealed to each of the sides of the triangular shaped common terminal block, the outer ends of the movable electrodes of the main vacuum interrupter and auxiliary vacuum interrupters being provided with tapped holes for cable connection to the power circuit, earth point and connection and disconnection circuit, and the vertex of the triangular shaped common terminal block being provided with tapped holes for fixing the switching unit.
4. A switching unit as claimed in claim 1 or 2, wherein the common terminal block is a square shaped, the center shield, fixed side seal cup and fixed contact of each of the auxiliary vacuum interrupters being hermetically sealed to each of a pair of opposite sides of the square shaped common terminal block, the fixed electrode and fixed side seal cup of the main vacuum interrupter being hermitically sealed to a third side of the common terminal block, the fourth side of the square shaped common terminal block being provided with tapped holes for fixing the switching unit and the outer ends of the movable electrodes of the main vacuum interrupter and auxiliary vacuum interrupters being provided with tapped holes for cable connection to the power circuit, earth point and connection and disconnection circuit.
5. A switching unit as claimed in claims 1 to 4, wherein the common terminal block is made of copper.
6. A switching unit as claimed in claims 1 to 4, wherein the common terminal block is made of copper chromium.
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7. A switching unit as claimed in claim 1, can be used with insulating medium such as air, SF6, oil or any other suitable insulating fluid.
8. Switching unit of all the three phases can be caste together with a solid encapsulation such as polymer concrete, epoxy etc.
Dated this 7th day of March 2007
(Prita Madan)
Agent for the Applicants
Of Khaitan & Co
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