The difference between large current grounding system and small current grounding system from the literal meaning is large and small. They are all power system grounding by neutral point, and neutral point directly grounding system. When single-phase grounding fault occurs, the grounding current is generally larger, so it is called large current grounding system. Generally, the system above 110kV adopts high current grounding system.

Large grounding current system is also called effective grounding system. It includes direct neutral grounding and low impedance grounding system. When a phase to ground fault occurs, the grounding current has a large value, and the steady-state voltage of the non fault phase to ground does not exceed 80% of the line voltage.

Small current grounding system is also called non effective grounding system. Generally, small current grounding system is often used in the system below 66kV. It includes ungrounded neutral point, arc suppression coil grounding and high impedance grounding system. Small current grounding system, as the name implies, has a small grounding current in case of fault. The main feature is that when a phase to ground fault occurs, the grounding current is limited to a small value, and the steady-state voltage of the non fault phase to ground may reach the line voltage.

The small current grounding line selection device is designed to detect and remove the fault in the first time when the small current grounding system fails. The small loan counter current grounding line selection device can accurately determine the switch cabinet where the fault current is located, which is convenient for the staff to find and deal with the fault in time, solve the fault problem technically, and ensure the safe and stable operation of the power station.