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
An automatic high speed gas insulated earthing switch for a gas insulated switchgear
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030,
Maharashtra, India, an Indian Company
INVENTOR
Patil Kiran Shashikant, Design and Development, A3, Ambad MIDC, Nashik, Maharashtra, India, an Indian national
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to
be performed:

FIELD OF THE INVENTION
This invention relates to an automatic high speed gas insulated earthing switch for a gas insulated switchgear,
BACKGROUND OF THE INVENTION
Switchgears are protective electrical devices used in power systems to de-energize electrical equipments/devices to carry out repairs and maintenance thereof and also to clear fault currents under fault or abnormal conditions. Among the various types of switchgears, gas insulated switchgears are very effective, reliable and efficient and are preferred. Earthing switches are used with switchgears in order to discharge residual charges in high voltage lines when there is tripping of the switchgears: Among the various types of earthing switches, automatic high speed gas insulated earthing switches are effective, reliable and efficient and are preferred.
A commonly used automatic high speed gas insulated earthing switch comprises three stationery contacts and corresponding number of moving contacts mounted in an insulating material plate and enclosed within a pressurized insluating gas (SF6) chamber. It also comprises a drive mechanism for the moving contacts and located within a housing. Both the gas chamber and the housing are separated by a gas tight partition wall. The drive mechanism comprises a drive shaft having an insulating material part and a magnetic material part. The drive shaft is linearly back and forth movably held in a support which is mounted to the partition well. The insulating material part of the drive shaft is connected to the insulating material plate and the magnetic material part of the drive shaft is coupled to a reversible electric motor through a plurality of

linkages. The drive mechanism also comprises a compression spring disposed over the magnetic material part of the drive shaft adapted to be compressed and decompressed by the electric motor through the linkages. On rotating the motor shaft in one direction, the drive shaft moves forward so as to move the movable contacts forward and make contacts with the stationery contacts. During the forward stroke of the drive shaft, the spring gets compressed. On rotating the electric motor in the opposite direction, the drive shaft moves back to its original position along with the moving contacts so as to open the earthing switch. During the reverse stroke of the drive shaft, the sping expands to its original stage. As the drive mechanism comprises a large number of components, it is complicated in construction and is not very reliable and is expensive. Wear and tear is high and it requires periodic maintenance and servicing thereby increasing the maintenance cost.
OBJECTS OF THE INVENTION
An object of the invention is to provide an automatic high speed gas insulated earthing switch which comprises few components parts and is simple in construction and cost effective and is reliable.
Another object of the invention is to provide an automatic high speed gas insulated earthing switch which has reduced wear and tear and requires no maintenance and serving and is further cost effective.

DETAILED DESCRIPTION OF THE INVENTION
According to the invention there is provided an automatic high speed gas insulated earthing switch for a gas insulated switch gear, the earthing switch comprising three stationery contacts and corresponding number of moving contacts mounted in an insulating material plate and disposed in an insulating gas chamber containing a pressurized insulating gas and a drive mechanism for the movable contacts enclosed in a housing, the gas chamber and the housing being separated by a gas tight common partition wall, wherein the drive mechanism comprises a drive shaft having a insulating material part and a magnetic material part, the insulating material part of the shaft being connected to the insulating material plate and the magnetic material part of the drive shaft being linearly slidably held in a support mounted to the partition wall and a magnetic actuator for the drive shaft.
The following is a detailed description of the drawings with reference to the accompanying drawings, in which:
Fig 1 is a partial crossectional view of an automatic high speed gas insulated earthing switch according to an embodiment of the invention; and
Fig 2 is a crossection at AA in Fig 1.
The automatic high speed gas insulated earthing switch 1 as illustrated in Fig 2 of the accompanying drawings comprises three sationery contacts out of which only two stationery

contacts 2,3 can be seen in Fig 1 as the third stationery contact is directly behind one of the stationery contacts 2,3. The earthing switch also comprises corresponding number of movable contacts 4,5 6 mounted in a insulating material plate 7. The stationery contacts, movable contacts and insulating material plate are disposed in insulating gas chamber 8 filled with pressurized insulating gas like SF6. 9 is a drive mechanism for the movable contacts disposed in a housing 10. The gas chamber and housing are separated by a gas tight common partition wall 11. Earthing plate, air seal and damper of the earning switch are marked 12, 13 and 14 respectively. The drive mechanism comprises a drive shaft 15 having a insulating material part 16 and a magnetic material part 17. The drive shaft is linearly back and forth movably held in a support 18 which is mounted to the partition wall. The insulating material part of the drive shaft is connected to insulating material plate. An electromagnetic coil 19 is disposed over the magnetic material part of the shaft. The drive shaft is moved forward and backward by reversing the direction of current supplied into the electromagnetic coil. On reversing the flow of current in the electromagnetic coil, the electromagnetic coil assumes opposite polarities and move the shaft forward and backward. When the drive shaft is moved forward the moving contacts move forward and make contact with the stationery contacts. When the drive shaft is moved back, the moving contacts move back with the drive shaft and disconnect themselves from the stationery contacts. According to the invention the drive mechanism comprises only a drive shaft moving within the electromagnetic coil. The drive mechanism comprises a few component parts and is very simple in construction. Wear and tear to the component parts and maintenance and servicing expenses of the drive mechanism are reduced. As a result of all this, reliability of the earthing switch is improved and cost is further reduced. Besides the electromagnetic coil, the magnetic actuator for the drive shaft can be of some other configuration and construction. The

earthing switch may comprise only one moving contact and only one stationery contact. Such variations in the configuration and construction of the invention are obvious to a person skilled in the art and should be construed and understood to be within the scope of the invention.

We claim:
1. An automatic high speed gas insulated earthing switch for a gas insulated switch gear, the earthing switch comprising three stationery contacts and corresponding number of moving contacts mounted in an insulating material plate and disposed in an insulating gas chamber containing a pressurized insulating gas and a drive mechanism for the movable contacts enclosed in a housing, the gas chamber and the housing being separated by a gas tight common partition wall, wherein the drive mechanism comprises a drive shaft having a insulating material part and a magnetic material part, the insulating material part of the shaft being connected to the insulating material plate and the magnetic material part of the drive shaft being linearly slidably held in a support mounted to the partition wall and a magnetic actuator for the drive shaft.
2. The earthing switch as claimed in claim 1, wherein the magnetic actuator comprises an electromagnetic coil disposed over the magnetic material part of the drive shaft.