ABB RELION 620 Series Technical Manual page 468

Section 4
Protection functions
462
GUID-4C9B4650-70D1-402E-8AF2-8392758D5B04-ANSI V1 EN
Figure 212: Connection of the current transformers of Type 1. The connected phase
currents and the neutral current have opposite directions at an external
ground-fault situation.
GUID-7D94D578-73E0-4A12-8450-7FB46DFA00F3-ANSI V1 EN
Figure 213: Connection of the current transformers of Type 2. The phase currents
and the neutral current have equal directions at an external ground-fault
situation.
Internal and external faults
87LOZREF 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.
1MAC504801-IB E
620 series ANSI
Technical Manual