For Earth Fault Protection there is the neutral displacement guard, the "Open Delta" guard and the generator stator guard.
The neutral displacement guard measure the voltage level between the neutral point and PE. And on any phase fault the neutral displacement is detected, and unit will trip the power.
The Open Delta guard is similar but measure the neutral displacement via a step-down open delta transformer.
The generator stator protection uses 2 sets of current transformers in a Merz-Price configuration. This unit protects against phase-earth and windings faults within the generator stator area.
