GIS earthing switch 1

[144x]

can anyone tell me what are the main reasons for using
high speed fault making earthing switches in GIS?
thanks

 

[jbartos]

Comments:
1. Land area for gas-insulated equipment is 10% for 800kV to 20% for 145kV of the space required for comparable air-insulated equipment.
2. The dielectric strength is greatly superior to that of air, and it is close to 100 times as effective as air in quenching an electric arc.
3. High speed is generic to any switch for this application to reduce a potential damage by the fault.
Reference: "Standard Handbook for Electrical Engineers" by Fink and Beaty, 14th Edition, 2000.

 

[peterb]

Earthing switches are an integral part of GIS design to provide safety earthing of the switchgear circuits. In this role, the switches must be capable of safely making full rated fault current, to allow for a case where they may be closed on to an energized external circuit. These switches would be 3-phase type.

Another reason for applying fault throwing switches is to put a solid single phase to earth fault on the system to ensure remote protection operation, where there is no local breaker to do the tripping.
This concept could be used, for example, where there is no communication path for sending a transfer trip signal to a remote station and it is desirable to trip the remote HV supply breaker for a transformer fault. The transformer protections (differential, restricted earth fault, sudden pressure etc.) are wired to trip a lockout relay, which in turn closes the high speed fault throwing switch - the resulting fault causes the remote high speed earth fault protection to trip the remote breaker and clear the transformer off line at a higher speed than waiting for the remote time-delayed overcurrent relays to operate. A switch of this type would be a single phase to ground design.