Protective Relaying in Resistance Grounded systems can be devised in two ways, measuring either the voltage or the current in the grounding in the event of a ground fault. When a ground fault occurs, the voltage between the neutral point increases. This can be measured to identify the earth fault. Current based protection use the current flowing through the grounding resistor to identify the presence of a fault.
Relays using the voltage measurement principle are advantageous as they can function even when the Grounding Resistor is open.
