1. System Earthing : In this a part of substation is directly connected to grounding grid. Like:- LV neutral of star connected transformer, Earth switch, Surge Arrester connection to ground etc.
2. Structure/Equipment/Safety Earthing : In this metallic body of equipments/devices is connected to grounding grid to prevent electric shocks to any personnel touching that equipment or device. Like :- Transformer tank body earthing, Circuit breaker body earthing, Panel’s outer body earthing etc.
System earthing deal with earthing of the system neutrals 2 sure system security and protections while equipment earthing deal with earthing of non current carrying parts of the equipment to ensure safety of person and protection against lightning.
System earthing is done at substation on the neutral wire, structure earthing is done at home to the third lug so appliances are driving any leak straight to ground in case of neutral failure and so trigger the differential breaker, otherwise the leak will go through the user body.