Difference between safety grounding switch & high speed grounding switch in HV GIS. Also why CT is duly distributed on both sides of the CB.

The normal Grounding Switch is used to apply a safety ground to an isolated section of the GIS after it is isolated from the system. It also allows one to inject testing signals by the lifting of the external ground connection and connecting the testing device.

High Speed Grounding Switches are used on the incoming terminals of overhead lines or long cable runs to dissipate any retained charge or address capacitively induced voltages. They are spring loaded to quickly open or close the switch since a normal grounding switch's slow operation would lead to much errosion of the moving probe.

The Current Transformers are located on both sides of the breaker to provide various metering and protection schemes. As an example, a bus differential relay scheme will use the CT"s closest to the outgoing terminal while a transformer differentlal scheme would use CT's closest to the switchgear's main bus. This is also a more efficient use of space and limits the mechanical forces imposed from a much larger single CT housing.

Sanjeev,

In addition to what Allan has said, safety grounding switches are relatively slow acting and have absolutely no load-break/load-make capability and should be mechanically interlocked to prevent operation onto an energized circuit.

Alan