ABB RELION REX640 Technical Manual page 674

Section 4
Protection functions
668
GUID-2FA7824D-3042-4CF4-AAC5-03E49E8E86B6 V1 EN
Figure 369: Connection of the current transformers of Type 2. The phase currents
and the neutral current have equal directions at an external earth-
fault situation. Phase earthing is outside and neutral earthing is inside
the area to be protected.
Internal and external faults
LREFPNDF does not respond to any faults outside the protected zone. An external
fault is detected by checking the phase angle difference of the neutral current and the
sum of the phase currents. When the difference is less than 90 degrees, the operation
is internally restrained or blocked. Hence the protection is not sensitive to an external
fault.
1MRS759142 C
REX640
Technical Manual